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(12) United States Patent (io) Patent No.: US 9,428,647 B2 Li et al. (45) Date of Patent: Aug. 30, 2016
(54) SELF-HEALING COMPOSITE OF 26/26 (2013.01); C04B 28/02 (2013.01); C08G THERMOSET POLYMER AND 18/4238 (2013.01); C08G 18/664 (2013.01); PROGRAMMED SUPER CONTRACTION C08G 18/7671 (2013.01); DOIF 6/70 FIBERS (2013.01); C04B 210310065 (2013.01); C04B 2111100612 (2013.01); C04B 2111172 (71) Applicants:Guogiang Li, Baton Rouge, LA (US); (2013.01); C08G 210110025 (2013.01); C08G Harper Meng, Baton Rouge, LA (US) 2280100 (2013.01); C08G 2350100 (2013.01) (58) Field of Classification Search (72) Inventors: Guoqiang Li, Baton Rouge, LA (US); CPC ...... C08L 75/04; C04B 26/26; C04B 26/16; Harper Meng, Baton Rouge, LA (US) B29C 73/18; C08G 18/664; C08G 18/7671; C08G 18/4238; DO1F 6/70 (73) Assignee: Board of Supervisors of Louisiana See application file for complete search history. State University And Agricultural and Mechanical College, Baton Rouge, LA (56) References Cited (US) PUBLICATIONS (*) Notice: Subject to any disclaimer, the term of this Li et al. Healable thermoset polymer composite embedded with patent is extended or adjusted under 35 stimuli-responsive fibres. J. R. SOc. Interface (2012)9, 3279-3287. U.S.C. 154(b) by 0 days. Aug. 15, 2012.* (Continued) (21) Appl. No.: 14/248,711 Primary Examiner John Uselding (22) Filed: Apr. 9, 2014 (74) Attorney, Agent, or Firm Timothy J. Lithgow; John H. Runnels (65) Prior Publication Data US 2014/0303287 Al Oct. 9, 2014 (57) ABSTRACT A composition comprising thermoset polymer, shape Related U.S. Application Data memory polymer to facilitate macro scale damage closure, (60) Provisional application No. 61/810,015, filed on Apr. and a thermoplastic polymer for molecular scale healing is 9, 2013. disclosed; the composition has the ability to resolve struc- tural defects by a bio-mimetic close-then heal process. In (51) Int. Cl. use, the shape memory polymer serves to bring surfaces of a structural defect into approximation, whereafter use of the C08L 75/04 (2006.01) thermoplastic polymer for molecular scale healing allowed B29C 73/18 (2006.01) for movement of the thermoplastic polymer into the defect C04B 26/16 (2006.01) and thus obtain molecular scale healing. The thermoplastic C08G 18/66 (2006.01) can be fibers, particles or spheres which are used by heating C08G 18/76 (2006.01) to a level at or above the thermoplastic's melting point, then C08G 18/42 (2006.01) cooling ofthe composition below the melting temperature of (Continued) the thermoplastic. Compositions of the invention have the ability to not only close macroscopic defects, but also to do (52) U.S. Cl. so repeatedly even if another wound/damage occurs in a CPC ...... C08L 75/04 (2013.01); B29C 73/18 previously healed/repaired area. (2013.01); C04B 20/1037 (2013.01); C04B 26/04 (2013.01); C04B 26/16 (2013.01); C04B 8 Claims, 64 Drawing Sheets
Healed configuration
Molecule entanglement at crack interface7V US 9,428,647 B2 Page 2
(51) Int. C1. (56) References Cited DOIF 6/70 (2006.01) C04B 26/04 (2006.01) PUBLICATIONS C04B 26/26 (2006.01) C04B 28/02 (2006.01) Li et al. Effect of strain hardening of shape memory polymer fibers C04B 20/10 (2006.01) on healing efficiency of thermosetting polymer composites. Poly- 008G 101/00 (2006.01) mer 54 (2012) 920-928. Dec. 22, 2012.* C04B 103/00 (2006.01) C04B 111/00 (2006.01) C04B 111/72 (2006.01) * cited by examiner Fig. 16
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0.86 Soo 1000 1500 2000 2600 3000 3500 4000 Wav um r( Fig. 5 Fi Am sating ,ocess Heating J Melting rack TPs process Closure Cooling process Solidification of molten TPs IWO:go ffitedwew of, i# Qracklaterfac crack. Fig. 6C U.S. Patent Aug. 30, 2016 Sheet 8 of 64 US 9,428,647 B2 ~ y L V c c 0 ® L. Q U V CL e 1 LL Soft segment Hard segment C wawi 'tnV ZS Lt,9`8Zt,`6 Sfl b9 3O 6 JaNS 910Z `0£ Jualled -S-fl b Melting transition ~ E of the hard segment E n w 0N .Q Mass transition ; -°0 of the soft segment 1 -20E o 20 40 60 80 100120140160180200220 ~ Temperature (oC) `O N 00 Fig. 9 N 1735cm-1: -MDI ,«««««««»SRF Free(C=0) v BDO PBA 0.14 !• 1730cm-1: Free(C=O) A 0.09 3320cm 1: Hydrogen 1700cm-1: Hydrogen bonded (NH) v .-_-----banded (C=0)v 0.04 _ PBA 3:f34 ...... :...... MDI 1800 1.760 1.720 1.680 16-40 1600 13600 5 34(0 3~ Wave number(cm -1) Wave number(cm -1) IMM ml i 0.2 fk~ 3500 3000 2500 2000 1500 1000 1 Wavenumber (cm- Fig. 11 U.S. Patent Aug. 30, 2016 Sheet 13 of 64 US 9,428,647 B2 a 2400 cn 1600 0.35 0.75 1.15 1.55 1.95 True Strain Fig. 12A 300 ``'` co $k ~a U.S. Patent Aug. 30, 2016 Sheet 14 of 64 US 9,428,647 B2 00 fir! s~ \ s+L/ m Q w f 077i►►w...... VJM 0 ~l i V PC 9 U.S. Patent Aug. 30, 2016 Sheet 15 of 64 US 9,428,647 B2 100 80 40 Am= 4- c 20 U 0 20 50 80 110 140 170 Temperature (°C) cn 1.5 a) L ~ 1 0 0.5 a)U 3IZ 0 40 80 120 160 200 Temperature (°C) IMM 40 80 120 160 200 Temperature (°C) U.S. Patent Aug. 30, 2016 Sheet 16 of 64 US 9,428,647 B2 SRF (Stimuli-responsive Fiber) ® Thermoplastic particles (TPs) Epoxy matrix 0 Macroscopic crack happens in the composite •. oc Sample is cooled down to Troom (room temperature) to recover yiii f ►~iiEy~ ~wlr►.►~ u►ow; strength I.R.I,'I,'►AI~M.MARiRirA►AI.IA►. w,1►.wA►A►A - glass transitionrange of - T2 = The bonding temperature of the TPI Fig. 15 U.S. Patent Aug. 30, 2016 Sheet 17 of 64 US 9,428,647 B2 Original sample First healing cycle 50 ® Second healing cycle Third healing cycle 40 ...... Fourth healing cycle r D z 30 0 ®' 20 II 10 . 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 Extension (mm) Fig. 16A m 20 10 0 NP Aw ` c " Fig. 16 U.S. Patent Aug. 30, 2016 Sheet 18 of 64 US 9,428,647 B2 SMP fiber strand l Av l I Fig. 17A A SMPF bundle hooked to a pin before stretch ~1 Pin a Pin ------l I Stretch at room temperature The SMPF bundle The SMPF bundle before stretch after stretch Pin - ►Stretch direction Pin l l AMM 80 100% Pre- tr r: ~ o C /50% Pre-strained 20 % Pre-strained 0 0 50 100 Strain(% N Fig. 18 00 J N 21.5 167.9°C 21.0 E 20.5 A c 20.0 0 _0 0 19.5 0 -cu 19.0 m im 0 50 100 150 200 gom M 5 0 72 62 52 cu E h 0 42 -1 32 _2 _3 22 0 10 20 30 40 50 Time (min) Fig. 20 Control 30 25 20 cu a. 100% Pre-strain 15 wuwuu, cn 10 -- 50%® Pre-strain 5 .w ^ 0% Pre-strain t 0- 0 0.25 0.5 0.75 1 1.25 1.5 Strain (%) Fig. 21 U.S. Patent Aug. 30, 2016 Sheet 23 of 64 US 9,428,647 B2 I~ ~ fL'6s°ji3'tc-sbni» "~ fSi,'PFo£'z~.•ar~ie S 14 1:4 TSZ C ~.~. ~ /'y' M $ Pt»~s::sir 3f3 r ~ ~+Y $51'£'a f•'.iL-SSSRin 2 2 ;«. " first cycle f'~' Si d cycle .r...... «...... t a i ff 'C------r------v------r------r------r------a Fig, 22A Fig. 228 s~C` 3s3iF°i: Y:tt~is;R '.~ kiX3;b ?!\tiiff'dJ1 Fm 3'r.4x£i:itr< :.r3 St;'~a f';t•sisRin •' ..~ 0 ______z___------T ------s ------T------______z >1 u.75 as ft,}5 [ €•2`i O'Gs 1,15 0 015 03's € Fig. 22C Fig. 22D 1 113 ltk3?c Psc r ass l:lt!? Pt ~ArriR 14 .. +~x'~t4';~J.~tG•J,K2055 t fi ,°;fs`P"/o« £+.i•3•.`~'SAliii' ~., ,.""' •.~~'`4 ~ ~ ~~ " `,,,•w...-~" •.~ aria & if~- , Xi`'. ~YR222`JSR lam£ cycle /z Shift cycle . ...~...... i...... i...... y...... y...... Y. 0 015 st"its j Fig. 22E Fig. 22F 1Fz 14' ,.."..., .4 V7 seventh cycle 0,75 Strad E4~J Fig. 22G IMIP • ♦ ) I' 500 i a~. m 400 .Q a.. 0 _ 300 •U.0• c Gy =130PMa ~ of Fiber bundle before GDP 0 i 10 401 611 Engineering stretch ratio(%) Fig. 23 i ij a 70 i vi 60 ~3 .Lw 50 C ~L 40 w 30 NEI W Cis 0 20 40 60 80 100 Engineering stretching ratio(%) Fig. 25 Shape fixity(%) 0 0 0 0 0 0 12 0 P e N e 'tnV ZS Lt,9`8Zt,`6 Sfl b9 3O LZ JaauS 910Z `0£ Jualled -S-fl OM After 5t" loading cycle After 4t" loading cycle 8.65 After 3rd loading cycle After 2nd loading cycle After 1St loading cycle 8.45 Un-cold-drawn PU fibers O C W 8.25 8.05 O 4- 7.85 Ri O 7.65 -70 -30 10 50 90 130 170 quo Temperature (°C) Fig. 27 0.15 0.14 0.12 0.12 W 0.10 (0 0.08 (00.06 Q 0.04 i 0.02 0.00 0.00 4000 3500 3000 2500 2000 1500 1000 500 1600 1400 1200 1000 800 600 Wavenumbers(cm -1) Wavenumbers(cm -1) Fig. 28A Fig. 28B ...... 0.015 i. 0.045 CDP Fibers before 2040cm-1 2340cm 1 2010cm-1 0.037 0.013 2190cm-1 O 1955cn O v v c 0.029 cc Q 0.011 O 0 Y) 0.021 .Q Q 0.009 Q 0.013 Fibers after CDP 0.007 4 , v p 1 1 1 1 1 g `_ --, 0.005 2700 2500 2300 2100 1900 1700 3700 3500 3300 3100 2900 2700 Wavenumbers(cm -1) Wavenumbers(cm -1) Fig. 28C Fig. 28D Recovered Stress(MPa) s ® C) w 40 N m Ul 8 Recovered Stress(MPa) O N ¢a O3 CO O N $a 0 0w 0 0 0 W 0 000 0 N 0 0 'tnv ZS Lt,9`8Zt,`6 S11 b9 3O Of iaags 9ioz `o£ Jualled -S-fl Remained stress(MPa) s w w 4 'tnv ZS Lt,9`8Zt,`6 S11 b9 3O if taNs 9i0Z `0£ Jualled -S-fl i a 1 0.0001 0.001 0.01 0.1 1 10 100 1000 10000 Days 9.E-12 9.E-12 10E-16 8.E-12 8.E-12 7.E-12 7.E-12 i Y 6.E-12 6.E-12 5E-16 5.E-12 rn w 4.E-12 a ® 3.E-12 s r_ W W ul 0E+00 2.E-12 2.E-12 1.E-12 1.E-12 0.E+00 -1.E-12 -SE-16 1000 2000 3000 4000 5000 0.000001 0.001 1 1000 0.000001 0.0001 0.01 1 Amm Fig. 32C Fiber stress(MPa) co 0 0 0 0 0 0 0 0 0 E-1 Is i m 1 CQ co W ~J 'tnv ZS Lt,9`8Zt,`6 S11 b9 3O b£ JaauS 9i0Z `0£ Jualled -S-fl r rra lOrflm Ni 2 m I i rn 4 'k r.,€ f Fig. 34 Temperature • Crack closed by • Diffusion of CAPA into programmed PU fibers fractured Epon matrix Polymer matrix • CAPA polyester Short SMPU fibers • Y, Crack damaged by Crack healed by CAPA three-point bending polyester 25°C WTI Fig. 35 In INU i 60 40 FM N 10 15. 20 25 30 mm Fig. 36 9N M 0- i 2 'a (D CD CO 2) Q) r+ U) 15 60' "CD 6 CD 0 o. 0 d U " CD Of ru; Temperature, 51Clmin EE Stress recovery behavior of coated SMPU fiber Stress recovery behavior of un-coated SMPU fiber 0 41] 0 0.5 1 1.5 3 Time (hour) Fig. 37 i m Recovery .strain Am i 230 3w 3w C 11 130 130 39D 5313 5313 £'i'F4petatute, £'i'F4petatute, Fig. Fig. `s `s !PO !PO 2C.5 -24D -24D fitj fitj .: .: x'.15 235 235 M M 103*C V V ;gat ;gat 193 193 145 145 39C 39C 39A 85 85 em"rAvre em"rAvre ^ T Fig. Fig. 35 35 Fig. Fig. 75 75 1.51.5 030 . 4 4 fiber 3.143 3.143 3,16 3,32 ;5.zu fez fez 396 396 SM.Po £i3tt3 £i3tt3 F F fE3 fE3 Fig. Fig. nVr-aL2'.mod nVr-aL2'.mod 5 4 -is -is 44 44 210 1 1 1 F~.AS G v.• Tc.rnperat rc (0 NJ NJ NO rIJ ho Lo. -n -a Q Vi 'tnv ZS Lt,9`8Zt,`6 S11 b9 3O it, iaags 9i0Z `0£ Jualled -S-fl 2.50 i 10.0 pm N Dii-Pplacc-ment (mm) gm U.S. Patent Aug. 30, 2016 Sheet 43 of 64 US 9,428,647 B2 MW o tl t :R iP F = U.S. Patent Aug. 30, 2016 Sheet 44 of 64 US 9,428,647 B2 x m co U- Z m mff PPO I )l P -d U.S. Patent Aug. 30, 2016 Sheet 45 of 64 US 9,428,647 B2 U.S. Patent Aug. 30, 2016 Sheet 46 of 64 US 9,428,647 B2 U.S. Patent Aug. 30, 2016 Sheet 47 of 64 US 9,428,647 B2 250 t 2-5,000 f s i ~e !A ------~ ------MI First cyclew ~ t Second cycle~ f i ' I 150 j t a ) }t r S 50 i ' 20"C 0 -50 i ~...._..- ...-_..._ ...... :..._ .._ .._...... -60*C 0 20 40 60 $0 100 120 140 Time (minutes) •I ~ Tttt'I orlized feat Floe' mW/mg) P, 0 t•.: 6 ,6 'tnV ZS Lt,98Zt 6 S11 b9 3O 6b JaauS 910Z `0£ Jualled -S-fl Q „ Qtd 2 Step Step Step 1 Step 2 80 70 60 tep 3 -C5 50 ,all ~ 4C 3C cn 'r Step 5 Step 4 Normalized Heat Flow(mW/mg) 0 0 aUl -n CQe ~ ~P M Y w Ul 'tnv ZS Lt,9`8Zt,`6 S11 b9 3O Z9 iaags 9loZ `o£ Jualled -Sell U.S. Patent Aug. 30, 2016 Sheet 53 of 64 US 9,428,647 B2 M~N Q s ~ a mot' E M 00 N :y C N cn CL N !/) •+°• MN N d W V- r (8dW) SSBJ}S U.S. Patent Aug. 30, 2016 Sheet 54 of 64 US 9,428,647 B2 '•~®~®.s•®®®•rf-x rrrr`i a.r■rnrrrr e:•:~~ ■ . El T N M Cl to (fl co 11 r e r E AMA K-1 CV T O 09 QO h CO to ICp co 04 T C7 T T T (edW)SSOJ1S U.S. Patent Aug. 30, 2016 Sheet 55 of 64 US 9,428,647 B2 M Step 2 f; cc a. 40 Fig. 50A Step 3 20 Step 4 ❑I 0 1 2 24 26 28 30 32 34 36 38 Time (h) 80 70 60 ca 50 o. Step 2 Step 1 n 40 Fig. 50B Y 30 Step 3 s t 20 Step 4 a i j' 10 t Step 5 f 0 Y 0 10 20 30 40 50 60 70 80 90 100 110 Strain (%) Me wol i 1 kwo 6101 0 0 50 100 150 200 250 300 Engineering strain (%) Fig. 51 7 EM Mol A U a 4 L 250 L L Q. tI im N 411 D 0 5000 10000 15000 20000 25000 30000 35000 Time (s) Peak Stress 6.58±0.19 IA Peak Stress 5.87±0.21 Final Stress Final Stress 4.73±0.23 4.13±0.29 Sample #2 Sample #3 AMM U.S. Patent Aug. 30, 2016 Sheet 59 of 64 US 9,428,647 B2 0.40 0.35 0.30 50°C 1 0.25 0.20 N 0.15 75°C 0.10 25°C 0.05 100°C 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Frequency(Hz) Fig. 53A 0.40 0.35 0.30 0.25- . (10 50°C r- 0.20 ca N 0.15- 250C 0.10- 750C 0.05- 1000C 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Frequency(Hz) Fig. 53B U.S. Patent Aug. 30, 2016 Sheet 60 of 64 US 9,428,647 B2 0.40 0.35 0.30 69061 0.25 W 0.20 0.15 75°C 0.10 250C 0.05 00°C I 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Frequency(Hz) Fig. 53C U.S. Patent Aug. 30, 2016 Sheet 61 of 64 US 9,428,647 B2 0.30 0.28 0.26 0.24 0.22 0.20 Sample#1 10 0.18 Sample#2 0.16 I Sample#3 0.14 0.12 0.10 0.08 0.06 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Frequency (Hz) 0.4C 0.3E 0.3E 0.34 0.32 0.3C W 0.2E t6 ~ 0.2E 0.24 0.22 0.2C 0.1E 0.1E U L 4 0 0 "IU -IL 14 10 78 LU LL L4 L0 L6 Frequency (Hz) U.S. Patent Aug. 30, 2016 Sheet 62 of 64 US 9,428,647 B2 0.30 0.28 0.26 0.24 0.22 0.20 Sample#1 Sample#2 Sample#3 W 0.18 0.16 0.14 0.12 0.10 0.08 0.06 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Frequency (Hz) 0.24- 0.22 0.20- 0.18- 0.16- 0.14 Imm 0.12 Sample#1 0.10 Sample#2 nu.. Sample#3 A I I 0.02 0.00 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Frequency (Hz) U.S. Patent Aug. 30, 2016 Sheet 63 of 64 US 9,428,647 B2 I v vt 3 LO LO s ~•+ atr tMb li ff U.S. Patent Aug. 30, 2016 Sheet 64 of 64 US 9,428,647 B2 25 50 75 100 Temperature (-C) US 9,428,647 B2 N SELF-HEALING COMPOSITE OF typically organic polymers of high molecular mass, but they THERMOSET POLYMER AND often contain other substances. There are two types of PROGRAMMED SUPER CONTRACTION plastics: thermoplastic polymers and thermosetting poly- FIBERS mers. 5 Thermoplastics are the plastics that do not undergo CROSS-REFERENCE TO RELATED chemical change in their composition when heated and can APPLICATIONS be molded again and again. Examples include polyethylene, polypropylene, polystyrene, polyvinyl chloride, and poly- This application claims priority from U.S. Provisional tetrafluoroethylene (PTFE). Common thermoplastics range Application Ser. No. 61/810,015, filed 9 Apr. 2013, entitled io from 20,000 to 500,000 amu. "Self-Healing Composite of Thermoset Polymer and Pro- In contrast, thermosets are assumed to have large molecu- grammed Super-Contraction Fibers". This application is lar weight. These chains are made up of many repeating related to U.S. Provisional Application Ser. No. 61/483,196, molecular units, known as repeat units, derived from mono- filed 6 May 2011 which is entitled `Biomimetic Self- mers; each polymer chain will have several thousand repeat- Healing Composite'; co-pending application U.S. Ser. No. 15 ing units. Thermosets can take shape once; after they have 13/464,461, filed 4 May 2012, entitled "Compression Pro- solidified, they stay solid. In the thermosetting process, a gramming of Shape Memory Polymers Below the Glass chemical reaction occurs that is irreversible. According to an Transition Temperature"; co-pending U.S. Ser. No. 13/464, IUPAC-recommended definition, a thermosetting polymer is 062, filed 4 May 2012, entitled "Thermosetting Shape a prepolymer in a soft solid or viscous state that changes Memory Polymers with Ability to Perform Repeated 20 irreversibly into an infusible, insoluble polymer network by Molecular Scale Healing"; U.S. Provisional Ser. No. 61/723, curing. The cure may be done through heat (generally above 844, filed 8 Nov. 2012; co-pending PCT application number 200° C. (392° F.)), through a chemical reaction (two-part PCT/US2013/068895, filed 7 Nov. 2013 entitled "Sandwich epoxy, for example), or irradiation such as electron beam Panel with a ductile Hybrid Core Comprising Tubular Rein- processing. A cured thermosetting polymer is often called a forcements'; and to U.S. Provisional Application Ser. No. 25 thermoset. 61/897,437, filed 30 Oct. 2013 which is entitled "Liquid Thermoset materials are usually liquid or malleable prior Sealant with Thermally Adaptive Properties". The contents to curing and designed to be molded into their final form, or of each of the foregoing are fully incorporated by reference used as adhesives. Others are solids like that of the molding herein. compound used in semiconductors and integrated circuits All documents, including patents or published applica- 30 (IC). In contrast to thermoplastic polymers, once hardened a tions, whether cited or referenced for relatedness in this thermoset resin cannot be reheated and melted back to a application are fully incorporated by reference herein. liquid form. The curing process transforms the thermosetting resin into STATEMENT REGARDING FEDERALLY a plastic or rubber by a cross-linking process. Energy and/or SPONSORED RESEARCH OR DEVELOPMENT 35 catalysts are added that cause the molecular chains to react at chemically active sites (unsaturated or epoxy sites, for This invention was made with government support under example), linking into a rigid, 3-D structure. The cross- grant number CMMI 0900064 awarded by the National linking process forms a molecule with a larger molecular Science Foundation, grant number NNXIIAM17A awarded weight, resulting in a material with a heightened melting by NASA, and grant number CMMI 1333997 awarded by 40 point. During the curing reaction, the molecular weight has the National Science Foundation. The Government has increased to a point so that the melting point is higher than certain rights in the invention. the surrounding ambient temperature, the material forms into a solid material. BACKGROUND OF THE INVENTION However, uncontrolled heating of the material results in 45 reaching the decomposition temperature before the melting 1. Field of the Invention point is obtained. Thermosets never melt! Therefore, a This invention relates to polymeric materials, more par- thermoset material cannot be melted and re-shaped after it is ticularly it relates to compositions with three aspects: ther- cured. A consequence of this is that thermosets generally moset polymer, shape memory polymer (SMP) capable of cannot be recycled, except as filler material. shrinking at temperatures above the SMP's glass transition 50 Thermoset materials are generally stronger than thermo- temperature, and thermoplastic polymer or other means for plastic materials due to their three dimensional network of healing at a molecular level; which compositions generally bonds (cross-linking). Thermosets are also better suited to have repeatable, self-healing properties without the need for high-temperature applications (up to their decomposition external shape confinement. temperature). However, they are more brittle. Because of 2. Description of Related Art 55 their brittleness, thermoset is vulnerable to high strain rate Polymers are large molecules (macromolecules) com- loading such as impact damage. Since a lot of lightweight posed of repeating structural units. These sub-units are structures use fiber reinforced thermoset polymer compos- typically connected by covalent chemical bonds. The term ites, impact damage, if not healed properly and timely, may polymer encompasses a large class of compounds compris- lead to catastrophic structural failure. ing both natural and synthetic materials with a wide variety 60 A thermoplastic material, also known as a thermosoften- of properties. Because of the extraordinary range of prop- ing plastic, is a polymer that turns to a viscous liquid when erties of polymeric materials, they play essential and ubiq- heated and freezes to a rigid state when cooled sufficiently. uitous roles in everyday life. These roles range from familiar Most thermoplastics are high-molecular-weight polymers synthetic plastics and elastomers to natural biopolymers whose chains associate through weak Van der Waals forces such as nucleic acids and proteins that are essential for life. 65 (polyethylene); stronger dipole-dipole interactions and A plastic material is any of a wide range of synthetic or hydrogen bonding (nylon); or even stacking of aromatic semi-synthetic organic solids that are moldable. Plastics are rings (polystyrene). As noted herein, thermoplastic polymers US 9,428,647 B2 3 4 differ from thermosetting polymers (e.g. phenolics, epoxies) [Wool R P, O'Connor K M. JAppl Phys 1981; 52:5953- in that they can be remelted and remolded. 5963] suggested a five-stage model to explain the crack Thermoplastics can go through melting/freezing cycles healing process in terms of surface rearrangement, surface repeatedly and the fact that they can be reshaped upon approaching, wetting, diffusion and randomization. Kim and reheating gives them their name. However, this very char- 5 Wool[Kim Y H, Wool R P. Macromolecules 1983; 16:1115- acteristic of reshapability also limits the applicability of 1120] also presented a microscopic theory for the diffusion thermoplastics for many industrial applications, because a and randomization stages. In another study [Kausch H H, thermoplastic material will begin to change shape upon 7ud K. Rubber Process Appl 1982; 2:265-268], it was being heated above its Tg and Tm. observed that the development of the mechanical strength Initiation of cracks and other types of damage on a io during the crack healing process of polymers is related to microscopic level has been shown to change thermal, elec- interdiffusion of the molecular chains and subsequent for- trical, and acoustical properties, and eventually lead to mation of molecular entanglements. Other reported healing whole scale failure of the material. From a macromolecular mechanisms in thermoplastic polymers include photo perspective, stress induced damage at the molecular level induced healing, recombination of chain ends, self healing leads to larger scale damage called microcracks. A microc- 15 via reversible bond formation, and with nanoparticles[Wu D rack is formed where neighboring polymer chains have been Y, Meure S, Solomon D.Prog Polym Sci 2008; 33:479-522]. damaged in close proximity, ultimately leading to the weak- In thermoset polymers, self-healing mechanisms by the ening of the polymer as a whole. In view of the diverse use incorporation of external healing agents such as liquid of polymers in industry, it is self-evident that failure of healing agent (monomer) encased in hollow fibers [Kirkby safety-critical polymer components such as brittle thermoset 20 E L, Michaud V 7, Manson 7 A E, Sottos N R, White S R. polymers is a serious problem; failure of these materials can Polymer 2009; 50: 5533-5538; Blaiszik B 7, Caruso M M, lead to serious even catastrophic accidents. McIlroy D A, Moore 7 S, White S R, Sottos N R. Polymer For thermoset polymers that have developed cracks, 2009; 50: 990-997], micro-capsules [Brown E N, White S R, unfortunately there are only two fundamental choices, Sottos N R. Compos Sci Technol 2005; 65:2474-2480; attempt to repair the crack or entirely remove and replace the 25 Brown E N, White S R, Sottos N R. 7 Mater Sci 2006; component that contains the damaged material. Usually, 41:6266-6273], and solid healing agent (thermoplastic par- cracks are mended by hand, which is difficult because cracks ticles) dispersed in the thermoset matrix [Wu D Y, Meure S, are often hard to detect. A polymeric material that can Solomon D. Prog Polym Sci 2008; 33:479-522; Zako M, intrinsically correct damage caused by normal usage could Takano N. 7 Intell Mater Syst Struct 1999; 10:836-841], lower production costs through longer part lifetime, reduc- 3o have; been proposed and tested. However, the different tion of inefficiency over time caused by degradation of the physical and behavioral characteristics of thermoset SMPs part, as well as prevent costs incurred by material failure. relative to standard thermosets make the applicability or In an attempt to heal damage, restore mechanical prop- suitability of a component on one type of the thermosets of erties and extend the service life of polymers, the concept of uncertain relevance to the any. For example, with regular crack healing in polymeric materials has been widely inves- 35 thermosets suitability of an additional component depends tigated [7ud K, Kausch H H. Polymer Bulletin 1979; 1:697- on the chemical compatibility, viscosity of the molten ther- 707; Keller M W, White S R, Sottos N R.Polymer 2008; 49: moplastic, and the concentration gradient, whereas for ther- 3136-3145; Prager S, Tirrell M. J Chem Phys 1981; moset SMPs, suitability of an additional component also 75:5194-8; De Gennes P G. J Chem Phys 1971; 55:572-9; depends on the diffusion under the recovery force. Doi M, Edwards S F. J Chem Soc: Faradays Trans 2 1978; 40 Self-healing of polymer components has been a much- 74:1789-1801; Kim Y H, Wool R P. Macromolecules 1983; explored but essentially unmet need. Some polymers by 16:1115-1120; Kausch H H, 7ud K. Rubber Process Appl themselves possess the self-healing capability such as ther- 1982; 2:265-268; Wool P R, O'Connor K M.Polym Eng Sci mally reversible crosslinked polymers [Chen X, Wudl F, 1981; 21:970-977; McGarel O 7, Wool R P. JPolym Sci Part Mal AK,Shen H, Nutt S R. Macromolecules 2003; 36:1802- B Polym Phys 1987; 25: 2541-2560; Yang F, Pitchumani R. 45 1807] and ionomers [Varley R 7, Shen S, van der Zwaag S. Macromolecules 2002; 35:3213-3224; Chung C M,RohY S, Polymer 2010; 51: 679-686]. Although these systems are Cho S Y, Kim 7 G. Chem Mater 2004; 16:3982-3984; Yuan very successful in healing micro-length scale damage, they Y C, Rong M Z, Zhang M Q, Yang G C. Polymer 2009; face tremendous challenge when they are used to repair 50:5771-5781; Takeda K, Tanahashi M, Unno H. Sci Tech large, macroscopic, structural-length scale damage, which Adv Mater 2003; 4:435-444; Kalista S 7, Ward T C. JR Soc 5o are visible by the naked eye [Li G and Nettles D. Polymer Interface 2007; 4:405-411; Chipara M, Wooley K. Mater 2010; 51:755-762; Li G and Uppu N. Comp Sci Tech 2010; Res Soc Symp 2005; 851:127-132]. 70: 1419-1427; Nji 7 and Li G. Smart Mater Struct 2010; 19: In thermoplastic polymers, the most widely studied and paper No. 035007]. Prior to the present invention, the reported mechanism for self healing is the molecular inter- state-of-the-art for self-repair ofthermosetting polymers and diffusion mechanism. It has been reported [7ud K, Kausch H 55 their composites includes: (1) use of hollow fibers/micro- H. Polymer Bulletin 1979; 1:697-707] that when two pieces capsules to release polymeric resin when ruptured, and heal of the same polymer are brought into contact at a tempera- the crack through in-situ polymerization triggered by the ture above its glass transition temperature(T g), the interface catalyst contained in the polymer matrix; (2) use of ther- gradually disappears and the mechanical strength at the moplastic particles to flow into the crack when heated up and polymer-polymer interface increases as the crack heals due 60 glue the crack when cooled down; and (3) use of thermo- to molecular diffusion across the interface. To better explain reversible covalent bonds via the retro Diels-Alder (DA) the process of crack healing by this mechanism, various reaction. Despite the significant advancements made using a models have been proposed [Keller M W, White S R, Sottos bio-mimetic approach, there is still a long way to go before N R. Polymer 2008; 49: 3136-3145; Prager S, Tirrell M. J even the simplest biological healing mechanism can be Chem Phys 1981; 75:5194-8; De Gennes P G. J Chem Phys 65 replicated within these synthetic materials. One immediate 1971; 55:572-9; Wool R P, O'Connor K M. JAppl Phys difference between biological and these synthetic healing 1981; 52:5953-5963]. In particular, Wool and O'Connor mechanisms is that biological systems involve multiple-step US 9,428,647 B2 5 6 healing solutions. For example, mammalian healing pro- In the context of thermoset SMPs, the different physical cesses rely on fast forming patches to seal and protect and behavioral characteristics of thermoset SMPs relative to damaged skin before the slow regeneration ofthe final repair standard thermosets make the applicability or suitability of tissue. a component of one type of the thermosets of uncertain Several self-healing schemes have been reported in the 5 relevance to the any. For example, with regular thermosets literature primarily for healing microcracks, including incor- suitability of an additional component depends on the poration of external healing agents such as liquid healing chemical compatibility, viscosity of the molten thermoplas- agent in microcapsules, hollow fibers, and microvascular tic, and the concentration gradient, whereas for thermoset networks, and solid healing agent such as embedded ther- SMPs, suitability of an additional component also depends io on the ability for diffusion under the recovery force. moplastic particles. Some polymers by themselves possess Previously, it was shown that the stress-controlled pro- self-healing capabilities, including ionomers, which consist gramming and confined shape recovery of a SNIP based of over 15% of ionic groups, and a highly cross-linked syntactic foam was able to close impact damage repeatedly, polymer, which is synthesized via the Diels-Alder (DA) efficiently, and almost autonomously (the only human inter- cycloaddition of furan and maleimide moieties, and the 15 vention was by heating) [Li G and John M. Composites thermal reversibility of the chemical bonds is accomplished Science and Technology 2008; 68: 3337-3343]. In this via the retro-DA reaction. A combination of microcapsule previous study two key aspects were found with compres- and shape memory alloy(SMA) wire has also been studied. sion programmed shape memory effect to self-close an area Because damage is usually in structural-length scale, the of damage: 1) reduction of structure volume during pro- challenge is how to heal macrocracks. However, the existing 20 gramming and 2) the external confinement of the structure systems are unable to very effectively heal macroscopic during shape recovery. damage. For instance, in order to heal macrocracks, a large These two aspects were found to be important in order to amount of healing agent is needed. However, incorporation repair damage created in the programmed structure that had of a large amount of healing agent will significantly alter the a reduced volume due to its shape memory functionality. In physical/mechanical properties of the host structure. Also, 25 order to achieve repair, expansion in volume must be large capsules/thick hollow fibers themselves may become resisted by external confinement, whereupon the material potential defects when the encased healing agent is released. will be pushed towards internal open space such as crack, Therefore, the grand challenge facing the self-healing com- achieving the self-closing purposes. In these earlier munity is how to heal structural-length scale damage such as schemes, therefore, compression programming was impact damage autonomously,repeatedly, efficiently, timely, 3o required. and at the molecular-length scale. It is noted that, while it seems that tension programming One further problem with the existing self-healing sys- can also repair internal cracks during free shape recovery tems is the presence of voids after the healing process. For (the specimen becomes shorter and thus closes the crack), example, a polymeric material will contain microcapsules of the free recovery changes the geometry of the structure or monomer throughout, and similarly an initiator/catalyst 35 compromises the dimensional stability as the structure would be uniformly present throughout the material. When recovers to its original shape. If confined recovery is used a crack occurs, the monomer-bearing capsules at the site of after tension programming (i.e., if the dimensional stability the crack would rupture, disgorge monomer and polymer- is maintained), the internal crack cannot be closed because ization would result because of the presence of the initiator. the material is not allowed to be pushed towards the internal Prior to polymerization, the capillary forces at the crack face 40 open space (i.e., the crack). Therefore, compression pro- would encourage even flow of monomer, resulting in an gramming is a better choice, as tension programming may evenly-healed crack. However, after the crack has healed the not work. Although tension programming "drawing" of material now has voids where the monomer capsules used to SMPs was also known, tension programming was at odds be. These voids can have an adverse effect upon the mate- with the earlier SMP-based healing approaches because any rial's mechanical properties. Moreover, this self-healing 45 shrinkage of SNIP material would exacerbate wounds/dam- process is available for only one time in the area of the age rather than serving to close any defect, particularly healed crack. where there was external confinement. It was noted that the Recently, shape memory polymer(SMP) has emerged as repeatability in self-closing (up to 7 cycles) comes from the new type of smart material. Various types of applications fact that each round of confined shape recovery served dual have been studied, particularly in lightweight structure 50 purposes: one to self-close internal cracks and the other to applications. Tey et. al [Tey S J, Huang W M and Sokolwski complete a new round of compression programming [Li G W M 2001. Influence of long term storage in cold hiberna- and John M. Composites Science and Technology 2008; 68: tion on strain recovery and recovery stress of polyurethane 3337-3343] shape memory polymer foam. Smart Materials and Struc- This combination of closing and reprogramming in Li and tures, 10(2): 321-25] studied the shape memory functional- 55 John is achieved because the confined shape recovery came ity of a polyurethane (PU) based SNIP foam by performing about by heating the foam above the Tg, applying a certain the conventional thermomechanical programming cycle and compressive stress to the foam due to confinement, and recommended those PU based foams be used in foldable cooling down below Tg while maintaining the prestrain, space vehicles and quick molding devices. On the other which is typical for strain-controlled programming. In other hand, Huang et. al [Huang W M,Lee C W and Teo H P 2006. 60 words, strain-controlled compression programming was Thermomechanical behavior of a polyurethane shape coupled with confined shape recovery. Therefore, although memory polymer foam. Journal of Intelligent Material Sys- it may seem as if only one programming was conducted at tems and Structure, 17: 753-60] studied the influence of cold the very beginning of the repeated impact/closing cycles, hibernation on the shape memory properties of PU based each shape recovery actually had one prior programming to SNIP foams. They concluded that the cold hibernation pro- 65 supply the energy. The only difference was that the subse- cess did not affect the shape memory properties in spite of quent programmings were automatically performed by keeping them in a compacted state for a prolonged period. being coupled with each confined shape recovery. Therefore, US 9,428,647 B2 7 8 in this disclosure of confined shape recovery, one "nominal' In addition, ropes and cables made of metal or synthetic programming led to several cycles of shape recovery. [Li G fibers have been used as safety ropes (e.g., for mountain and John M. Composites Science and Technology 2008; 68: climbing, high risk construction, high risk repairs, window 3337-3343] Of note, the method of Li and John although washing); such cables are also used as support in cable- referred to as "healing" was, as discussed in greater detail s stayed bridges. Unfortunately, the current ropes/cables made below, only a closing of the polymer defect; no molecular of polymeric fibers are poor at damping vibration; further- scale healing was achieved. The approach of Li and John had more, steel wires are used in cable stayed bridge are very disadvantages, it lacked the ability to regain a substantial heavy. amount of the original integrity as the two sides of a crack Although FRPs are typically lighter than metals, owing to the lightweight they are very easily excited (e.g., are subject were brought back into contact with each other, but were not to to vibrations). Without sufficient damping this leads to reconnected in a "healing" manner one to the other. resonance and structural failure at loads well below ideal Although applying external confinement can be a challenge, design levels. Vibration-induced structural failure is not it may be coupled with architectural design of the composite uncommon. For example, collapse of buildings and bridges structures such as 3-D woven fabric reinforced composites during earthquake or hurricane is typical examples of vibra- [Nji J and Li G. Smart Mater Struct 2010; 19: paper No. 15 tion-induced catastrophic structural failure. 035007] or grid stiffened composites [M. John and G. Li. For the majority of structural polymers such as epoxy, Self-Healing of Sandwich Structures with Grid Stiffened they are very brittle with very low damping properties. Shape Memory Polymer Syntactic Foam Core. Smart Mate- Viscoelastic materials have been widely used for vibration rials and Structures, Vol. 19, No. 7, paper number 075013 damping. Although adding viscoelastic materials such as (12 pages), (July, 2010)], where the important external 20 rubber particles may improve damping, unfortunately a confinement inherently is applied by the structural cells. consequence is that the viscoelastic particles serve as stress However,the unmet need and ongoing challenge is that most concentration centers and result in reduced structural of the polymer composite structures used today are conven- strength and impaired usefulness. Active materials such as tional thermosetting polymers, which do not have shape shape memory alloy (SMA) have also been used to control memory capability. Therefore, prior to the present invention 25 vibration. Although SMA is very effective in damping a challenge has been how to imbue such "non-smart" vibration, it is generally both heavy and expensive, and its load-bearing polymers with self-healing capability. More- stiffness does not match that of polymer matrix, and they over, such existing thermoset composites generally do not tend not to be compatible with polymers, limiting SMA application in vibration control. utilize particular structural elements that imbue them with Moreover, there has been concern over the use and safety "external confinement" properties. 30 of composite structures, such as laminated or sandwich Thus, not merely the healing of polymers, but the ability composites, if they become damaged, e.g., if subjected to to self-heal structural damage has been a tremendous interest impact forces. The root cause for these types of damage is in the scientific community. With polymer repair, an unmet the brittleness of polymer matrix and synthetic fibers such as need exists to effectively repair the internal damage autono- glass fiber or carbon fiber. Even a low velocity impact on mously, repeatedly, efficiently, and at molecular-length 35 laminated or sandwich composites can cause various types scale, such as is possible with biological repair processes. of damage such as delamination, face sheet/core debonding, Thus, prior to the disclosure of the present invention, a need fiber breakage, matrix cracking, and fiber-matrix interfacial in the art has existed for a self-closing mechanism that not debonding. These types of damage are very dangerous only closes macroscopic defects, but which also allows for because they often cannot be detected visually and may lead molecular-scale healing of defects without the need for 40 to structural failure at loads well below original design external shape confinement; in particular there is a need for levels. Low velocity impact is not uncommon. For example, such healing that can be performed on a repeated basis at or a drop of a tool during routine maintenance or inspection near the site of prior damage. characterizes a low velocity impact event. Fiber reinforced polymer(FRP) composite materials have Generally, in fiber reinforced polymer composites, fiber is been widely used in various engineering sectors and com- 45 responsible for carrying the applied load, while polymer mercial goods. These include, communication devices, matrix is responsible for bonding fiber together, transferring energy storage and transportation, and in commercial goods load to the fiber, and protecting the fiber from damage. Consequently, in traditional fiber reinforced polymer com- such as bicycles, sport equipment, etc. These uses derive posites if fiber is fractured, the load carrying capacity of the primarily due to their high specific strength/stiffness and composite will be significantly reduced or lost. Unfortu- corrosion resistance of such composites. 50 nately, fiber fracture is a common failure mode in fiber For example, fiber reinforced polymer (FRP) composite reinforced polymer composite materials when they are sub- materials have been widely used, including in communica- jected to impact. tion devices (satellites, gyroscopes, etc), energy storage and Previously, several ways have been explored to enhance transportation (such as pipelines, pressure vessels, offshore the impact tolerance of composites, such as grid stiffened oil drilling platforms,); and in transportation vehicles (such 55 composites and 3-D woven fabric reinforced composites. as aircraft, boats, ships, trains, automobiles, bicycles, etc.); However, the fundamental reason for fiber fracture has not infrastructure (such as in bridges/overpasses in deck panels, been overcome and remains an unmet need: the reason is concrete bridge columns, girders, and as repair panels); that almost all synthetic fibers such as glass fiber and carbon buildings (e.g., cladding for roofs and walls, decks and fiber have high strength but low toughness. As a result, these railings, air flow duct work and ventilation equipment, water 60 fibers are good in carrying static load, but inferior in impact handling systems, subterranean uses, seawalls); harbor tolerance as they can decompensate or rupture when equipment (e.g., pilings, piers, seawalls and floats); military impacted. equipment(such as tanks, military vehicles, armor, etc.); and commercial goods such as safety helmets (sports and trans- BRIEF SUMMARY OF THE INVENTION portation), etc. These uses come about primarily due to the 65 high specific strength/stiffness and corrosion resistance of Disclosed herein is a polymeric composition which can composites. achieve a two-step healing process which mimics the bio- US 9,428,647 B2 9 10 logical healing process of human skin, e.g., an initial closing invention is not based on new polymerization, such as of a wound by bleeding and clotting (or by suturing) after occurs when monomers are released from fractured or which a step of healing where new tissue cells gradually melted containers within a matrix. It is a physical process. grow and heal a wound. This healing approach is referred to In a two-step close-then-heal(CTH) process of the inven- as a close-then-heal (CTH) process; in such a two-step 5 tion, a shape memory polymer that possesses the ability to process (closing and healing) in accordance with the inven- impose a shape recovery force by shrinking is a key aspect. tion, the shape recovery ability of pre-embedded shape In certain embodiments, programming or training to memory polymer fibers ("SMPFs" or "SMP fibers") is used increase the length of the shape memory polymer (SMP) to narrow and/or close the macroscopic crack (Step 1), and fiber is used. Such programming may occur by the tradi- then pre-embedded molten thermoplastic particles are used io tional method of tension programming upon use of applied to heal on a molecular scale (Step 2). In accordance with the thermal energy or isothermal programming which takes present invention the SNIPE in a composition were subject place without the need to raise the SMP's temperature above to tension programming, and in certain embodiments the its Tg. In the literature, programming a shape for SMPs tension programming was by cold drawing. required an initial heating above the glass transition tem- Disclosed herein is a SNIP fiber based self-healing system 15 perature (Tg), applying prestress or prestrain, subsequent whereby shrinkage of tension-programmed SMP fibers can cooling below Tg while holding the stress or strain constant, close damage such as cracks (or substantially narrow cracks and removal of the applied load. This process is a very or other damage, e.g., macroscopic closure) in a conven- time-consuming, low-efficiency, and cost-ineffective pro- tional thermosetting polymer matrix and then embedded cess. thermoplastic particles melt for molecular scale healing. In 20 In certain embodiments the invention comprises a com- preferred embodiments: (1) strain hardening/programming position which comprises a thermoset material, a shape of SMP fibers by cold-drawing programming is used; (2) memory polymer capable of shrinking upon exposure to programming is to a level such that there is sufficient additional energy, and, means for self healing dispersed recovery force in the SMP fibers to close cracks in conven- throughout said composition. The self-healing may be tional thermosetting polymer matrix; (3) certain chemical 25 termed autologous or integral self-healing ability, in that compatibility between the SMP fibers and conventional such healing is obtainable without additional materials, and thermosetting polymer matrix and between thermoplastic only thermal energy need be added to accomplish the particles and conventional thermosetting polymer matrix; in healing. It is to be understood that the energy supplied need essence this compatibility is that these materials do not repel not be thermal energy, so long as a change elicited by such one another and that they are able to be in close physical 30 energy is a thermal one, e.g. without limitation, microwave proximity one with the other. or sonic energy may be used. The means for self-healing can Embodiments of methods and compositions in accor- comprise thermoplastic polymer; in addition to thermoplas- dance with the invention rely upon a characteristic of shape tic particles, milled thermoplastic fibers can also be used; memory polymers in which their length is initially increased such thermoplastic fibers may serve two purposes (1)further through tension programming or training, e.g., either the 35 reinforcing the composition and (2) provide molecular heal- more traditional heat-based or cold drawing. Following ing per CTH process. Preferably, the melting temperature of programming, when subsequently stimulated by heating the thermoplastic polymer is lower than the decomposition above its glass transition temperature, the programmed SMP temperature of the thermoset matrix. The shape memory fiber remembers its original shape and shortens when polymer can be programmed to a certain length such that, heated, bringing the fractured polymer matrix to closure. 40 when it shrinks upon heating, it is able to close a wide- Additional heating to a level above the melting point of the opened crack. The tension programming can be by either thermoplastic particles allows the molten thermoplastic mol- cold drawing at a temperature below the glass transition ecules to be sucked by capillary forces into the now nar- temperature of the SMP fiber, or programmed at a tempera- rowed/closed defect; these molten molecules are also driven ture above the glass transition temperature of the shape into the fractured conventional thermosetting polymer 45 memory polymer fiber. The shape memory polymer can be, matrix by concentration gradient diffusion and the shape e.g., a polyurethane. In certain embodiments, the thermo- memory-based recovery force. Upon cooling, the thermo- plastic polymer is less than 40%, 25% or less, 20% or less, plastic hardens thereby "gluing" the crack at a molecular 15% or less, 10% or less, 9% or less, 8% or less, 7% or less, scale (step 2, the healing step). This sequence completes one 6% or less, 5% or less, 4% or less, 3% or less, or, 2% or less autonomous and molecular damage-healing cycle. 50 of the volume of the composition. In certain embodiments, Moreover, because the tension programming of SMPs the fiber volume fraction is determined in accordance with allows for substantial stretching of the material, relatively the Examples herein, e.g., in accordance with Li et al "Effect large damage areas or wound can be repaired; moreover of Strain Hardening of Shape Memory Polymer Fibers on where the damage is not so large and there is residual energy Healing Efficiency of Thermosetting Polymer Composites" retained in the tension-programmed material multiple 55 Polymer 54 (2013) 920-928. rounds of injury then healing can occur, Together with the In certain embodiments, a method for closing and healing fact that the thermoplastic particles can also be repeatedly a damage/defect//crack/wound in a composite of the inven- melted and hardened, the damage-then-healing cycle is tion, comprises use of a composite comprising a shape repeatable. In addition, because the amount of thermoplastic memory polymer capable of shrinking and thereby imposing particles used is very small (e.g., 3%), and each particle just 6o a shape recovery force, said method comprising steps of: spreads in the vicinity during melting and healing, there is a) heating an area comprising the damage or wound to a no cavity/void left behind as those did by microcapsules or temperature above the glass transition temperature of the hollow fiber schemes. shape memory polymer(SMP) fiber, whereby the SMP fiber Therefore, structural-length scale damage was shown to contracts and achieves some closure of the wound; be healed repeatedly (both macroscopically and molecu- 65 b) heating an area comprising the damage/wound to a larly) by a small amount of SMP fibers and thermoplastic temperature above the melting temperature of the thermo- particles in a thermoset composition. Of note, the present plastic material, and further increasing to the "bonding US 9,428,647 B2 11 12 temperature" (approximately 10-20° C. higher than the as high strength and toughness. For instance a falling spider melting temperature), whereby molten thermoplastic mate- hanging with a single silk can stop immediately and exactly rial flows into the narrowed wound and the thermoplastic where it wants, indicative of superior damping capabilities molecules diffuse into the fractured conventional thermoset of spider silk. Spider silks are made of two-phase semi- polymer matrix and establish molecular entanglement; and, 5 crystalline proteins with hydrogen bonded crystalline mol- c) cooling the structure below the melting temperature of ecules as hard phase and amorphous molecules as soft phase. the thermoplastic, whereby the thermoplastic hardens and In accordance with the present invention, a semi-crystalline heals the wound at a molecular scale. The heating steps can polyurethane fiber uses polyols as the soft segment, and take place concurrently. Preferably heating is held below the diisocyantes and small molecular extenders as the hard decomposition temperature of the thermoset matrix. The io segment. Consistent with the similar molecular structure to heating may be above the bonding temperature of the spider silk, spun SMP fiber has remarkable strength, stiff- thermoplastic material. ness, and damping properties after programming. The pro- In Example 5, shape-memory polyurethane (SMPU) gramming is preferably cold-drawing programming fibers (also referred to herein as SMP fibers) were strain although other programming approaches such as hot pro- hardened by cold-drawing programming (CDP) process. 15 gramming can also be used. Structural relaxation, which determines shape memory capa- In accordance with the present invention, SMP-based bility of the SMP fibers, is quantified by conformational "spider silk like" fibers of the invention are used as fila- entropy change. Based on the entanglement tube theory and ments, fibers, ropes, cables, etc. for vibration damping; in reptation theory, the entropic force is derived as a "bridge" such embodiments the SMP need not be part of a composite to link the stress relaxation and structural relaxation, 20 but can be embodied as filaments, twine, yarn, cable or whereby structural relaxation can be evaluated by stress woven as fabric. Accordingly, with embodiments of the relaxation. It was found that the cold-drawn programmed invention used for vibration damping, the SMP fibers can be SMPU fibers would still have good crack-closing capability fabricated without a surrounding thermoset or other matrix after 13 years of hibernation in polymer matrix composite. such as generally used in composites. Advantageously how- In Example 6 a particulate composite dispersed with 25 ever, when these SMPs are used in polymer matrix-contain- thermoplastic particles and strain hardened short shape ing composites, such composites also have enhanced vibra- memory polymer fibers was prepared and evaluated for its tion damping characteristics (vibration damping fiber- ability to repeatedly heal wide-opened cracks per the two- reinforced polymers (FRPs.)) step close-then-heal(CTH) self -healing scheme. In addition, When embodied as composites, embodiments of the pres- a two-step fiber coating approach was used to enhance the 30 ent invention are used in lightweight structures such as shape fixity and workability of the cold-drawn programmed satellites, transportation vehicles, gyroscope, pipes, pressure short polyurethane fibers. The relationship between recov- vessels and commercial goods such as bike, bed, etc. Addi- ery-stress and recovery-strain was experimentally deter- tionally, compositions of the invention are used in structural mined by partially constrained shape recovery test. Notched materials such as beams, panels, reinforcements in build- beam specimens were prepared and fracture-healing was 35 ings, structures (e.g., bridge or overpasses) or in concrete. conducted up to five cycles. It is found that the composite When SMP fiber is added to art-accepted concrete, it also was able to heal the wide-opened crack repeatedly with provides healing and damping capability to concrete, which considerable healing efficiency. It is also found that the is a cement based composite. healing efficiency increased as the fiber length increased, but When compositions of the invention are used (compos- in a reducing rate of increase. The recovery stress-recovery 40 ites, or structures composed solely or largely of SMP)they strain of the strain hardened shape memory polymer fiber provide improved performance and survival during disasters behaves nonlinearly. The coated fiber is more effective than (such as war, terrorism, earthquakes and hurricanes). Also, the uncoated fiber in closing wide-opened cracks when the SMP fibers of the invention can be woven, braided, or recovery strain is within a certain range. knitted into textiles such as cables as safety belts or ropes for As shown herein, see e.g., Examples 3 and 7, the 45 construction workers or persons engaged in activities that mechanical and dynamic properties of shape memory poly- involve a high risk of falling (construction/repair of tall urethane fiber (SMPU) are reported and compared to those structures skyscrapers, water towers etc., tall building win- of spider dragline silk. Although the polymeric fiber has a dow washers, acrobats) and as cables in cable stayed lower strength compared to spider dragline silks (0.2-0.3 bridges. GPa versus 1.1 GPa), it possesses much higher toughness 50 The spider-silk like fibers, after cold-drawing program- (276-289 M7/m3 versus 160 M7/m3), due to its excellent ming, are lightweight, inexpensive, tough, strong, and are extensibility. Dynamic mechanical tests revealed that SMPU compatible with polymer matrices, in contrast to the situa- fiber has a high damping capacity (tan 6-0.10-0.35) which tion when heavy and stiff SMAs are used. Therefore, the is comparable to or even higher than that of spider silks (tan present invention provides an appealing and useful option 6-0.15). In addition, it is shown that different programming 55 for vibration control in high tech structures and a wide methods change the properties of the fiber in different ways spectrum of commercial and military goods. SMP-based and in certain embodiments cold-drawing programming is spider silk-like fibers, with their light weight and vibration appealing in structural applications. These results showed damping, can be used instead of or to replace such existing that the SMPU fiber has similar vibration damping and metal wires or polymeric fibers. mechanical properties as spider silk, and is used to great 60 In related aspects of the present invention, the combina- advantage in many lightweight engineering structures. tion of strength and toughness in SMPs, obtained through In accordance with the present invention (see e.g., controlled drawing programming, preferably cold drawing Example 7), vibration is controlled by the use of high- programming is utilized. Accordingly, SMP fiber reinforced toughness SMP fiber. The composition of such SMP fiber polymer composites of the invention have desired structural mimics the microstructure of spider silk, and thus shares 65 strength along with excellent impact tolerance. many of the physical properties of spider silk. For example, In accordance with the present invention, shape memory spider silks possess remarkable mechanical properties such polymer fiber (SMP fiber) replaces conventional synthetic US 9,428,647 B2 13 14 fibers in certain composites. In certain embodiments, as set controlled programming; if the strain maintains constant, it forth herein (see e.g., Examples 3 and 5) it was found that, is called strain controlled programming. after cold-drawing programming, SMP fibers have mechani- "Decomposition Temperature (TD)": As used herein the cal strength and stiffness similar to other high performance decomposition temperature can be defined as a temperature polymeric fibers such as polyethylene or polypropylene 5 at which chemical bonds are broken or violent oxidation fibers, due to the special "spider silk-like" molecular struc- occurs whereupon a material catches fire. ture of SMP fibers, (See. e.g., FIG. 8). Spider silks possess "Fixed strain" is the difference between the prestrain and remarkable mechanical properties such as high strength and the springback. At the end of programming, there is a toughness. This is why a spider net, although very delicate rebound or springback when the load is removed. in appearance, can catch flying prey (which occurrence 10 "Glass transition temperature (Tg)": describes the tem- constitutes an impact), and also as nests (which indicates perature at which amorphous polymers undergo a transition high strength). SMP fibers have extreme toughness, similar from a rubbery, viscous amorphous liquid (T>Tg), to a to or better than spider silks. Therefore, SMP fibers in brittle, glassy amorphous solid (T Fundamental difference between the previous approaches and the current invention Previous bio-mimetic scheme proposed by Li, G. and Uppu, N., Aspect for 2010. Composites Science and comparison Technology, 70, 1419-1427 The current study Matrix SMP. Conventional thermosetting polymer. Fiber No. Yes. Continuous SMP fiber. US 9,428,647 B2 25 26 TABLE 1-continued Fundamental difference between the previous approaches and the current invention Previous bio-mimetic scheme proposed by Li, G. and Uppu, N., Aspect for 2010. Composites Science and comparison Technology, 70, 1419-1427 The current study Programming Volume reduction by compression. Strain hardening by cold-tension. Mechanism for Confined shape recovery by resisting Constrained shape recovery by resisting free crack closing free expansion of the SMP matrix shrinking of SMP grid skeleton (does not (need external confinement). need external confinement). Cost High. Large volume fraction of SMP Low. Small volume fraction of SMP fibers as as the continuous phase. the dispersed phase. 15 In this Example, we experimentally investigate the strain embodiment of a composition or structure in accordance hardening of polyurethane fibers through cold-drawing pro- with the invention. In this Example, the present invention is gramming, in order to achieve the required recovery stress. demonstrated through experimental testing and finite ele- We also investigate the thermomechanical cycle (program- ment modeling. ming and shape recovery) ofthe strain-hardened SMP fibers. 20 It is found that the polyurethane thermoplastic fibers, Microstructure change and anisotropic behavior due to pro- upon strain hardening by cold-drawing programming, can gramming will be examined by Polarized Optical Micro- achieve the required recovery stress to close macroscopic scope (POM), Fourier Transform Infrared Spectroscopy cracks. Further, the microstructure changes due to the cold- (FTIR), Small Angle X-ray Scattering (SAXS), and drawing programming are characterized by instrumented Dynamic Mechanical Analysis (DMA). After that, a Repre- 25 microstructural analysis, which provides fundamental sentative Volume Element(RVE) is utilized to correlate the understanding and parameters for the constitutive modeling. microstructure of the SMP fiber to the macroscopic loading Due to the fact that the polyurethane SMP fibers are cat- conditions. The soft and hard segments are assumed to egorized in the class of the semicrystalline polymers, the follow respectively the amorphous and crystalline constitu- enhanced mechanical responses of the cold drawn fibers are tive relations. The well established micromechanics averag- 30 correlated to the stress induced crystallization process and ing techniques are then incorporated to average the micro- the morphological texture changes in the amorphous and stress and micro-strain fields in these sub-phases and the crystalline phases in this work. A micromechanical multi- macroscale mechanical response of the SMP fiber is then scale viscoplastic theory is developed to link the microscale estimated. This approach was proposed formerly by Eshelby mechanical responses of the amorphous and crystalline and later it has been developed to the Mori-Tanaka and 35 sub-phases to the macroscale mechanical behaviors of the self-consistent methods (Eshelby, J. D., 1957. The determi- SMP fibers including the cyclic hardening, and stress recov- nation of the elastic field of an ellipsoidal inclusion, and ery responses. The proposed theory takes into account the related problems. Proceedings of the Royal Society of stress induced crystallization process and the initial mor- London. Series A. Mathematical and Physical Sciences, 241, phological texture while the polymeric texture is updated 376-396; Nemat-Nasser, S. and Hori, M., 1993. Microme- 4o based on the applied stresses. The cyclic loading and the chanics: Overall properties of heterogeneous materials. then nomechanical responses of the SMP fibers are experi- Amsterdam, Elsevier). The local-global relations between mentally investigated in which the proposed theory is uti- the applied macroscale and the resulting microscale lized to capture these phenomena. The proposed viscoplastic mechanical fields can be established analytically when the theory together with the material characterizations of the medium behaves elastically. Once the non-linearity is intro- 45 SMP fibers allow designers to predict the strength, stress duced in one of the sub-phases a history dependent solution recovery and life of the self-healing structures made from algorithm should be enforced in order to update these the semicrystalline SMP fibers. The data of this Example relations. Shojaei and Li discussed in detail the solution open up new opportunities for the application of SMP fibers algorithm for such a multiscale analysis incrementally (A. in load-bearing and self-healing composite structures. In this Shojaei and G. Li. Viscoplasticity Analysis of Semicrystal- 5o Example, polyurethane was synthesized from poly(butylene line Polymers: A Multiscale Approach within Micromechan- adipate)-600 (Mn) (PBA), 4'4-diphenylmethane diisocya- ics Framework. International Journal of Plasticity, Vol. 42, nate (MDI) and 1,4-butanediol (BDO). On average, the pp. 31-49,(March 2013)). Additionally, in section 2 experi- molar ratio of(MDI+BDO):PBA=3:1. The average formula mental characterizations of the SMP fibers are discussed. In weight ratio of(MDI+BDO):PBA=1021:650. The hard seg- section 3 the constitutive relations for the amorphous and 55 ment, soft segment, and their contents were selected to crystalline phases together with the texture updates are prepare polyurethane with amorphous soft segment phase elaborated. Furthermore, the constitutive relations for the and crystalline hard segment phase. The polyurethane fiber stress recovery and the stress induced crystallization process was spun by melt spinning. The fiber passed three pairs of are proposed. In section 4 the kinematics of the finite rollers with the same rotation speed before being wound up. deformation together with the required numerical algorithms 60 In this work two types of single SMP fibers (filaments) are are elaborated. In section 5 simulation results are presented. characterized in which their microstructure changes upon Overview of Example 1, in this Example a bio-inspired cold drawing process are evaluated. "bio-mimetic" healing scheme is set forth through architec- Optical microscopy was used to visualize a single SMP tural design of a composite structure, which is constructed fiber with an initial diameter of 0.04 mm, which is called by SMP fiber z-pinned, continuous SMP fiber grid rein- 65 sample #1 hereinafter. In the non-stretched SMP fiber #1 the forced thermoset polymer embedded with thermoplastic microstructure of the fiber is almost random; when the fiber particles. It is to be noted that the z-pinned grid is but one is highly stretched, the microstructure aligns along the fiber US 9,428,647 B2 27 28 (loading) direction. Optical microscopy was also used to counterparts, and plateaus in a wide range of temperature, visualize an SNIP fiber with an initial diameter of 0.002 mm, suggesting significant increase in stiffness and thermal sta- which is denoted as sample #2 hereinafter. The oriented bility. microstructures along the fiber direction are obvious when In order to better understand the shape memory mecha- the sample #2 fiber was cold drawn. The samples #1 and #2 5 nism due to strain hardening by cold-drawing, the change in were cyclically stretched by cold drawing up to 350% and the microstructure of the SNIP fiber is further investigated. 200% level of strains, for sample #1 and sample #2 respec- Using TENSOR 27, the Fourier Transform Infrared Spec- tively. troscopy (FTIR) test is implemented on two samples to Using an NITS Alliance RT/5 machine, which is usually check the microstructural changes during cold stretching io process of SNIP fibers. FIG.5 shows the FTIR test results for used for fiber tension tests, the SNIP fiber #1 and fiber #2 are the sample #2 in which the blue line shows the non-stretched cyclically stretched and the results are shown in FIG. 2(a) SNIP fiber #2 and the red line represents the SNIP fiber #2 and FIG. 2(b), respectively. The elastic stiffness of the SNIP which is stretched up to 1 SO% strain level prior to the FTIR fiber is increased gradually while the strength of the fiber is test. The synchronized peaks confirm that the chemical increased significantly. Obviously, cyclic cold-drawing 15 compositions of the two fibers are the same and there are no leads to strain hardening of the SNIP fibers. The reason for new chemical bonds upon cold drawing. The change in the this is the alignment of the amorphous phase and crystalline intensity after strain hardening by cold-drawing program- phase along the loading direction up on cold-tension, as ming may indicate the change in density and molecular evidenced by microscopy. alignment. The fully constrained (zero strain) stress recovery 20 Using Small Angle X-ray Scattering (SAXS)facilities in response of these fibers with respect to time is depicted in the Center for Advanced Microstructures and Devices FIG. 3. In this process the programmed fiber is gripped by (CAMD)at Louisiana State University the microstructure of the fixture while the heating process is controlled by a digital the non-stretched and stretched SNIP fibers (sample #1) is furnace. An initial stretch within the elastic region, e.g., investigated. A SAXS image for the non-stretched fiber E-10% (epsilon=10%), is applied to ensure that the fibers 25 showed a non-oriented microstructure while in the case of remain zero strain before the shape recovery process starts, the stretched fiber, whereas the SAXS imaging showed which needs a temperature rising process and causes thermal orientational changes in the microstructure. expansion and thus looseness of the fiber between the grips. The crystallization process in polymers may occur during It is worthwhile to note that this pre-stretch is determined in the cooling down process from the melting point along the a trial-and-error process in which the stress recovery is set 3o direction ofthe largest temperature gradient or may occur by external loading which is called stress induced crystalliza- to start from almost zero stress. In fact both of these fibers tion (SIC). In many cases, the crystallization process does show a sudden stress relaxation before activation of the not develop fully and consequently the resulting microstruc- shape recovery process. In other words, the pre-tension is ture contains dispersed crystalline phases within an amor- fully consumed by the stress relaxation and thermal expan- 35 phous matrix, leading to a polymeric system that is called sion before the stress recovery starts. Therefore, the pre- "semicrystalline." stretch does not affect the stress recovery. In this study, the Based on the above test results and microstructural exami- heating rate is 0.35° C./sec and the final temperature is set nation, it is evident that both the soft segments and hard to be 90° C. in the digital furnace. From FIG. 3, the segments in the semicrystalline SNIP fiber align along the pre-tension stress is relaxed to zero at about 20 s. Because 40 loading direction after cyclic cold-drawing programming, the starting temperature of the fiber is about 23° C., the which also leads to considerable increase in stress recovery. temperature becomes 30° C. after 20 s of heating. As shown This suggests that the polyurethane fibers, after strain hard- in FIG. 4, this is the temperature when the glass transition ening through cold-drawing programming, may be used in starts. Therefore, as expected, the 10% pre-tension is fully load-bearing structural applications, particularly in the bio- used up by stress relaxation and thermal expansion of the 45 mimetic healing scheme proposed in FIG. 1. However, an fiber before stress recovery starts. The pre-stretch is a in-depth understanding ofthe then nomechanical behavior of technique to compensate for the inability for the machine to the semicrystalline polyurethane fiber needs constitutive measure the stress when the fiber is loose. From FIG. 3, the modeling. stabilized recovery stress is about 16 MPa. Based on closing Recoverable Stresses of the macroscopic crack due to shape recovery of the SNIP 50 One of the vital parameters in designing the bio-inspired grid skeleton through localized heating data, it was seen that Close-Then-Heal healing systems is the available amount of the fiber after cyclic cold-drawing programming was able to the crack closure force which is necessary to close the provide the required recovery stress (e.g., 10 MPa in the data macroscale cracks. As shown in FIG. 3, the SNIP fibers show generated) for close the macroscopic crack. We also tested considerable recovery stresses which are in general depen- the stress recovery of non-stretched (as received) SNIP fiber 55 dent on the amount of the induced strain hardening during using the same procedure. The stress recovery is almost the cold-drawing process. Basically upon the cold-drawing zero. process, the crystalline phase of the semicrystalline poly- FIG. 4 shows the DMA experiments (with heating rate of urethane SNIP fibers undergoes the stress induced crystalli- 5° C./min and frequency of 1 Hz) in which both the zation process, and it stores the applied deformations non-stretched and cold-drawn SNIP fibers #1 are tested to 60 through the entropy changes in the crystalline network. investigate the changes in their glass transition temperature, Once the temperature exceeds the glass transition tempera- Tg, upon work hardening process. From FIG. 4 (a), the ture of the semicrystalline polymer, the viscosity of the cold-drawn SNIP fiber shows a small shift in its Tg towards polymeric network drops and the frozen crystalline network higher temperature. The glass transition starts at about 30° is allowed to release the stored energy and achieve its C., which echoes the information in FIG. 3. From FIG. 4 (b), 65 minimum energy level. In other words upon heating, the it is clear that the storage modulus of the strain hardened stored energy in the crystalline phase is released and the SNIP fibers is much higher than that of the as received polymeric network returns to its minimum level of internal US 9,428,647 B2 29 30 energy. As shown in FIG. 3 after a few cold-drawing cycles during the cold drawing process and this stress recovery the amount of the recoverable stresses is considerably should saturates to a certain limit due to the limit in aggrandized. Then one may relate the amount of the recov- reversibility in these microstructural changes. In other words erable stresses to the loading history and stress induced certain amounts of the microstructural changes are revers- crystallization process. In this study, the recoverable stress is 5 ible in an SNIP fiber and after certain limit these microstruc- assumed to be a function of the stress induced crystallization tural changes may results in failure of the polymeric net- process and the accumulated inelastic strains in the amor- works and produce non-reversible defects. In this study, it is phous phase. Basically a portion of these induced inelastic assumed that the recovery stress saturates to a certain limit entropic and energetic changes in the SNIP molecular net- as a function of the microstructural changes through Eqs.(1) work is recoverable upon heating where the viscosity of the to and (3) and the physical parameter to control these changes frozen network drops and the recoverable inelastic strains is the accumulated inelastic strain and its rate. are restored. Then the proposed evolution law for the stress recovery takes into account the history of the loading, Example 2 including the inelastic strains in the sub-phases. The kine- matic and isotropic hardening relations in the classical 15 The following Example 2 is based on studies and data also continuum plasticity context provide a suitable governing set forth in: Amir Shojaei, Guoqiang Li, George Z. Voyiad- equation form to explain the stress recovery process (Chabo- jis; "Cyclic Viscoplastic-Viscodamage Analysis of Shape che, J. L., 1991. On some modifications of kinematic hard- Memory Polymers Fibres with Application to Self-Healing ening to improve the description of ratchetting effects. Smart Materials", Journal of Applied Mechanics (January International Journal of Plasticity, 7, 661-678; Shojaei, A., 20 2013), Vol. 80, 011014-1 through 011014-15; this document Eslami, M. and Mahbadi, H., 2010. Cyclic loading of beams is fully incorporated by reference herein. based on the chaboche model. International Journal of Cold-drawn programmed Shape Memory Polymer(SMP) Mechanics and Materials in Design, 6, 217-228; Voyiadjis, fibres show excellent stress recovery property, which pro- G. Z., Shojaei, A. and Li, G., 2012. A generalized coupled motes their application as mechanical actuators in smart viscoplastic-viscodamage-viscohealing theory for glassy 25 material systems. A full understanding of the thermome- polymers. International Journal of Plasticity, 28, 21-45). The chanical-damage responses of these fibres is useful in order stress recovery evolution relation is then proposed as fol- to minimize the trial-and-error manufacturing processes of lows: these material systems. In this Example, a multiscale vis- coplastic-viscodamage theory is developed to predict the - 1- cr'- R( exp(-E(T T,_,_))) (Eq. 1) 30 cyclic mechanical responses of SNIP fibres. The viscoplastic where rl is a material constant that controls the rate of theory set forth is based on the governing relations for each saturation of the recovery stress to its final value which is R, of the individual micro-constituents and establishes the and T and T_,_ are respectively elevated and room tem- microscale state of the stress and strain in each of the peratures. Parameter R takes into account the history of the sub-phases. These microscale fields are then averaged loading which includes the inelastic deformation, texture 35 through the micromechanics framework to demonstrate the updates and residual stresses due to the cyclic hardening. macroscale constitutive mechanical behaviour. The cyclic Taking time derivative of Eq. (1) results in the following loss in the functionality of the SNIP fibres is interpreted as incremental relation for the stress recovery computations: the damage process herein and this cyclic loss of stress recovery property is calibrated to identify the state of the aY i',Rqexp(-q(T-T _)) (Eq. 2) 4o damage. The Continuum Damage Mechanics (CDM) where T shows the rate of the heating process. As shown together with a thermodynamic consistent viscodamage in FIG. 3 the maximum stress recovery is achieved after theory is incorporated to simulate the damage process. reaching Tg and the rate of heating controls this peak time. The developed coupled viscoplastic-viscodamage theory The heating process is controlled by time integration of the provides an excellent correlation between the experimental heating rate as: T=fTdt+T_,_ and once the temperature 45 and simulation results. The cyclic loading-damage analysis reaches its final value during the simulation, the heating rate in this work relies on the underlying physical facts and is set to zero. The saturation limit, R,for the stress recovery accounts for the microstructural changes in each of the is related to the loading history and the amount of the plastic micro constituents. The established framework provides a strain by the following expression: well-structured method to capture the cyclic responses of the 50 SNIP fibres which is of utmost importance for designing the R=w(K-R)I cP I (Eq. 3) SNIP fibre based smart material systems. where w and K are two material parameters for control- The ability to close macroscopic crack through localized ling the saturation parameter, R, and heating has been demonstrated (see Example 1 herein; Guoqiang Li and Amir Shojaei, "A Viscoplastic Theory of 55 Shape Memory Polymer Fibres with Application to Self- Healing Materials", Proc. R. Soc. A(2012) 468, 2319-2346). 2 EP = EP(~) EP(~) In this work, instead of the SNIP fibre grid skeleton, we 3 envision that uniformly distributed short SNIP fibres, which are programmed through cold-drawn programming, may is the equivalent plastic strain rate. Then during each of the 6o have the same capability to close structural-length scale cyclic loadings the magnitude of R is updated incrementally crack in the thermosetting polymer matrix. As discussed in and its final value is introduced in Eq. (1) for the stress Example 1 (see also, Guoqiang Li and Amir Shojaei, "A recovery computation. Eq. (3) represents a monotonically Viscoplastic Theory of Shape Memory Polymer Fibres with increasing value for the parameter R up to a certain satura- Application to Self-Healing Materials", Proc. R. Soc. A tion limit which is enforced by K. The underlying physics 65 (2012) 468, 2319-2346) the key advantage of this newly for Eqs. (1) and (3) is that the recoverable stress in a SNIP proposed approach is (1) it closes macroscopic crack with a fiber is a function ofthe recoverable microstructural changes small amount of SNIP material; and (2) the SNIP fibres can US 9,428,647 B2 31 32 function repeatedly because each constrained recovery leads The performance of the proposed self-healing scheme is to a new round of tension programming (Li, G. and N. Uppu examined in FIG. 7. FIG. 7(a) shows Optical Microscopy (2010). "Shape memory polymer based self-healing syntac- (OM)image of an induced macroscale crack in a polymer tic foam: 3-D confined then nomechanical characterization." matrix composite system which is reinforced with continu- Composites Science and Technology 70(9): 1419-1427). 5 ous SNIP fibres. Upon heating the macroscale crack is FIG. 6 presents a schematic view of the proposed self- sealed, as shown in FIG. 7(b). The crack interface in FIG. healing scheme with distributed short SNIP fibres (also see 7(b) is magnified in FIG. 7(c) in which the SEM image of FIG. 15 and FIG. 35, and respective related text), where the interface is depicted. Upon further heating the molten short SNIP fibres are shown with rods and Thermoplastic TPs are diffused into the crack surfaces and provide a Particles (TPs) are shown as particles. FIG. 6(a) illustrates 10 molecular level of entanglement at the interface, as shown in a Representative Volume Element (RVE) of the material FIG. 7(d). Application of SNIP fibres as mechanical actuators in system with a macroscale crack. FIG. 6(b) shows the crack smart material systems is evaluated herein. A new bio- is closed due to the stress recovery process of these cold- inspired self-healing material system is set forth in which the drawn programmed fibres upon the heating process. In FIG. 15 stress recovery of the SNIP fibres provides the required crack 6(c) the TPs are molten due to further heating and they closure force. The present self-healing system can be con- diffuse into the cracked surfaces. In FIG. 6(d) the room stituted from thermosetting polymer matrix together with temperature configuration is shown in which the molten TPs dispersed short SNIP fibres and embedded thermoplastic solidifies and provides a microscale healed configuration. In particles. It is found that the polyurethane thermoplastic order to better design this self-healing system, understand- 20 fibres are strain hardened upon cold-drawing programming ing of the mechanical responses of SNIP fibres subjected to and they can achieve the required recovery stress to close cyclic loading condition is important because the healing macroscopic cracks (see e.g., Example 1; Guoqiang Li and process of the invention encompasses the possibility that the Amir Shojaei, "A Viscoplastic Theory of Shape Memory healing be achieved repeatedly. Polymer Fibres With Application To Self-Healing Materi- SNIP fibres are mainly manufactured from thermoplastic 25 als", Proc. R. Soc. A (2012) 468, 2319-2346). Furthermore, SMPs, particularly polyurethane (Meng and Hu 2008). In the strain hardened SNIP fibres show excellent mechanical polyurethane SNIP elastomers the hard segment can undergo properties in which a new application field is opened for phase separation and form distinguishable domains(Clough, these fibres to be deployed in SNIP fibre reinforced com- S. B. and N. S. Schneider (1968). "Structural studies on posite structures. urethane elastomers." Journal of Macromolecular Science, 30 The enhanced mechanical responses of the cold-drawn Part B 2(4): 553-566; Clough, S. B., N. S. Schneider and A. semicrystalline polyurethane SNIP fibres are correlated to O. King (1968). "Small-angle X-Ray scattering from poly- the stress induced crystallization process and the texture urethane elastomers." Journal of Macromolecular Science, updates in the amorphous and crystalline phases in Amir Part B 2(4): 641-648). Appearance of these distinctive Shojaei, and Guoqiang Li, George Z. Voyiadjis; "Cyclic micro-phase segregations depends on the degree of the 35 Viscoplastic-Viscodamage Analysis of Shape Memory Poly- compatibility between the soft segment molecular chains mers Fibres with Application to Self-Healing Smart Mate- and the hard segment blocks (Ferguson, J., D. J. Hourston, rials", Journal of Applied Mechanics (January 2013), Vol. R. Meredith and D. Patsavoudis (1972). "Mechanical relax- 80, 011014-1 through 011014-15. A micromechanical mul- ations in a series of polyurethanes with varying hard to soft tiscale viscoplastic theory is developed to link the segment ratio." European Polymer Journal 8(3): 369-383; 40 microscale mechanical responses of the amorphous and Ferguson, J. and D. Patsavoudis (1972). "Chemical struc- crystalline sub-phases to the macroscale mechanical behav- ture-physical property relationships in polyurethane elasto- ior of the SNIP fibres including cyclic hardening, and stress meric fibres; property variations in polymers containing high recovery responses. The cyclic loading and cyclic damage hard segment concentrations." European Polymer Journal responses of the SNIP fibres are experimentally investigated 8(3): 385-396). This segregated structure may motivate 45 in which the proposed theory is utilized to capture these designers to incorporate a micromechanical approach for phenomena. A new damage parameter is proposed based on characterization of the semicrystalline polymer-based mate- the loss offunctionality of SNIP fibres and a thermodynamic rial systems. We aim at developing a multiscale approach consistent viscodamage theory is developed to accurately because it provides correlation between micro-constituent predict the damage process. The proposed viscoplastic- governing behavior and macroscale mechanical responses. 50 viscodamage theory together with the SNIP fibres charac- In this work two well-established viscoplastic theories for terizations provide designers with the ability to predict the the amorphous and crystalline polymers are utilized. These cyclic strength, stress recovery and life of smart structures theories are based on certain physical description of the made from the semicrystalline SNIP fibers. viscoplastic deformation mechanisms in each of these sub- phases and the material constants are related to certain 55 Example 3 physical properties such as microstructural properties. These two constitutive relations are linked within the microme- The following Example 3 is based on studies and data also chanics framework to build the macroscale mechanical set forth in: Guoqiang Li, Harper Meng and Jinlian Hu, responses. The averaging micromechanics techniques are "Healable Thermoset Polymer Composite Embedded With utilized herein and certain numerical approaches are adopted 60 Stimuli-Responsive Fibres", J. R. Soc. Interface (2012) 9, to take care of non-linearity, e.g. plasticity and damage, in 3279-3287; this document is fully incorporated by reference each of the sub-phase (See, e.g., for citations to relevant art herein. techniques: Amir Shojaei, Guoqiang Li, George Z. Voyiad- In this Example, a thermal-responsive fiber (e.g., stimuli- jis; "Cyclic Viscoplastic-Viscodamage Analysis of Shape responsive fiber `SRF' or SNIP fiber) with outstanding Memory Polymers Fibres with Application to Self-Healing 65 mechanical properties and super contraction capability was Smart Materials", Journal of Applied Mechanics (January fabricated for the purpose of healing macroscopic damages 2013), Vol. 80, 011014-1 through 011014-15). in thermoset polymer compositions. The SNIP fibers and US 9,428,647 B2 33 0_! thermoplastic particles were incorporated into regular ther- Materials. Proceedings of the Royal Society A 2012, 468: mosetting epoxy for repeatedly healing macroscopic dam- 2319-2346.]). In developing these synthetic fibers, we analo- ages. The system works by mimicking self-healing of bio- gized from the natural biology. Spider silks possess humid- logical systems such as human skin, where a wound us first ity-responsive super-contraction, in addition to outstanding closed (e.g., by a stitch) thereafter the wound is healed. In 5 mechanical properties [Harmer A M T, Blackledge T A, the present context of thermoset polymer composites of the Madin J S, Herberstein M E. High-performance Spider invention, a damage is closed through the thermal-induced Webs: Integrating Biomechanics, Ecology and Behaviour. super-contraction of the SMP fibers, and bonding of the Journal of the Royal Society-Interface 2011; 8:457-471; closed crack through melting and diffusing of thermoplastic Eisoldt L, Smith A, Scheibel T. Decoding the Secrets of particles at the crack interface. The healing efficiency deter- io Spider Silk. Materials Today 2011; 14:80-86; Buehler M J, mined using tapered double-cantilever beam specimens was Keten S, Ackbarow T. Theoretical and Computational Hier- 94%. The self-healing process was reasonably repeatable. archical Nanomechanics of Protein Materials: Deformation Previously, a two-step self-healing approach CTH (close- and Fracture. Progress in Materials Science 2008; 53:1101- then-heal) for macroscopic damages using shape memory 1241; Wu X, Liu X Y, Du N, Xu G, Li B. Unraveled polymers [Li G, Uppu N. Shape Memory Polymer Based 15 Mechanism in Silk Engineering: Fast Reeling Induced Silk Self-healing Syntactic Foam: 3-D Confined Thermome- Toughening. Applied Physics Letters 2009; 95:093703]. chanical Characterization. Composites Science and Tech- Unfortunately, natural spider silks cannot be obtained in a nology 2010; 70:1419-1427; Li G, Xu W. Thennomechani- large scale because spiders cannot be farmed. Though much cal Behavior of Thermoset Shape Memory Polymer effort has been made to fabricate artificial spider silks, not Programmed by Cold-compression: Testing and Constitu- 20 much success has been achieved as a result of the extreme tive Modeling. Journal of the Mechanics and Physics of difficulty of replicating spider silk proteins and mimicking Solids 2011; 59:1231-1250] was set forth. In the first step, the exact spinning process of spider silks [Zhou G, Shao Z, the macro-cracks were closed as a result of the constrained Knight D P, Yan J, Chen X. Silk Fibers Extruded Artificially shape recovery of the shape memory polymer matrix. In the from Aqueous Solutions of Regenerated Bombyx Mori Silk second step, thermoplastic particles (TPs) which were pre- 25 Fibroin Are Tougher Than Their Natural Counterparts. embedded in the shape memory polymer matrix melted, Advanced Materials 2009; 21:366-370; Bosia F, Buehler M diffused, and bonded the closed cracks through molecular J, Pugno N M. Hierarchical Simulations for the Design of entanglement. However, as indicated in Example 1 (see, e.g., Supertough Nanofibers Inspired by Spider Silk. Physical Li G, Shojaei A. A Viscoplastic Theory of Shape Memory Review E 2010; 82:056103]. Polymer Fibers with Application to Self-Healing Materials, 30 In this Example, we set forth a spider-silk-like stimuli- Proceedings of the Royal Society A 2012, 468: 2319-2346), responsive fiber (SRF, or "SMP fiber") by synthesizing a this system required a shape memory polymer as the matrix. non-protein polymer with a similar molecular structure to However, in engineered structures, conventionally-used silk fibroin protein, and fabricating the fiber from the poly- thermosetting polymers do not have shape memory capa- mer using a conventional spinning process. The main dif- bility. In order to address this, regular thermosetting polymer 35 ference between the SMP fiber and natural spider silk is that composite structures which can be healed by embedding the SMP fiber is thermal-responsive (supercontraction when shape memory polymer fibers are set forth herein (also see heated) while spider silk is humidity-responsive (supercon- Li G, Shojaei A. A Viscoplastic Theory of Shape Memory traction when wetted) [Agnarsson I, Boutry C, Wong S C, Polymer Fibers with Application to Self-Healing Materials, Baji A, Dhinojwala A, Sensenig A T, et al. Supercontraction Proceedings of the Royal Society A 2012, 468: 2319-2346). 40 forces in spider dragline silk depend on hydration rate. It is noted that Kirkby et al [Kirkby E L, Rule J D, Zoology 2009; 112:325-331; Boutry C, Blackledge T. Evo- Michaud V J, Sottos N R, White S R, Manson J-AE. lution of Supercontraction in Spider Silk: Structure-function Embedded Shape-Memory Alloy Wires for Improved Per- Relationship from Tarantulas to Orb-weavers. Journal of formance of Self-Healing Polymers. Advanced Functional Experimental Biolgoy 2010; 213:3505-3514.]. In this Materials 2008; 18:2253-2260; Kirkby E L, Michaud V J, 45 Example, we will first evaluate the outstanding mechanical Mason J A E, Sottos N R, White S R. Performance of properties of the SMP fiber, then address the use of the SMP Self-healing Epoxy with Microencapsulated Healing Agent fibers and TPs to heal macro-cracks in regular thermosetting and Shape Memory Alloy Wires. Polymer 2009; 50: 5533- epoxy composite. 5538] embedded shape memory alloy wires in epoxy matrix Sample Preparation to narrow down cracks (about 150 µm)by taking advantage 50 The SMP fiber was prepared from a segmented polyure- of the shape recovery of the shape memory alloy wires. thane with relatively short polyols as the scarce soft seg- Limitations of the Kirkby system are:(1) because of the low ment, diisocyantes and small molecular extenders as the rich recoverable strain of shape memory alloy wires, which is hard segment. The novel polyurethane was synthesized below 8%, the capability for shape memory alloy wires to using poly(butylene adipate)(PBA) (Sigma -Aldrich, USA), close macro-cracks in polymer composites is limited; and, 55 4'4-diphenylmethane diisocyanate (MDI) (Sigma-Aldrich, (2) shape memory alloy wires do not mechanically match USA) and 1,4-butanediol (BDO) (Sigma-Aldrich, USA). the polymer matrix, particularly at the high recovery tem- Dibutyltin dilaurate was used as catalyst with a content of perature. At the high recovery temperature, the shape 0.02 wt %. The average formula weight ratio was (MDI+ memory alloy wire is very stiff while the polymer matrix BDO):PBA=1021:300. BDO was dehydrated with 4 A becomes soft, limiting the load transfer capability and crack 60 molecular sieves for one day in advance. All the chemicals closing efficiency. were de-moisturized prior to use in a vacuum oven. Molten Therefore, the stimuli-responsive shape changing poly- MDI was filtered to remove the precipitate dimmers and any meric fibers with outstanding mechanical properties set forth impurities before use. The reaction was conducted in a high herein are a viable alternative for the purpose of automati- speed mixer at room temperature. The obtained polyure- cally closing macro-cracks.(See, e.g., Example 1 and Li and 65 thane was further cured in a vacuum oven at 110° C. for 12 Shojaei [Li G, Shojaei A. A Viscoplastic Theory of Shape hours. Before spinning, the polymer was dried in a vacuum Memory Polymer Fibers with Application to Self-Healing oven at 80° C. for 6 hours. The SMP fibers with a diameter US 9,428,647 B2 35 36 of 50 µm were spun by melt spinning. A customer made -3.0° (20) at a scanning rate of 0.05° min'. The detector screw was used because of the high shear viscosity of the was a BrukerAXS HI-STAR position sensitive area detector. polymer. The laminar air temperature was 22° C. Extruder The SAXS was conducted for 1 hour on every sample. The head pressure was 5.00 MPa. The fiber passed three pairs of model and calculation equations used to calculate the rollers before being wound up. 5 domain structure can be seen in reference [Ji F. Study on the SMP fiber/TP/epoxy composites were fabricated accord- Shape Memory Mechanism of SMPUs and Development of ing to the following series for fabricating orthogrid SMP High-performance SMPUs. Kowloon: Hong Kong; 2009]. fiber grid skeleton/TP/epoxy composites:(a) First, pins were The orientation function of the SMP fiber amorphous phase nailed down on a plywood board along the perimeter. A and crystalline phase was determined by IR dchroism using polytetrafluoroethylene sheet was laid on the board for easy io a Perkin-Elmer microscopy (Perkin-Elmer Inc, USA) de-molding. (b) The SMP fiber was dry wound around the equipped with a diamond cryogenic Micro-ATR unit and an pins. No resin was applied to the fibers during the weaving IR polarizer [Siesler H W, Holland-Moritz K. Infrared and process.(c) TP/epoxy mixture was poured into the bay areas Raman Spectroscopy ofPolymers, Marcel Dekker Inc., New of the woven SMP fiber grid skeleton. The composite was York; 1980; Estes G M,Seymour R W, Cooper S L. Infrared degassed and cured. (d) The sample was de-molded. 15 Studies of Segmented Polyurethane Elastomers. II. Infrared Polycaprolactone was chosen as the thermoplastic healing Dichroism. Macromolecules 1971; 4:452-457]. The calcu- agent because it was reported that it could diffuse and rebond lation methods of the soft and hard segment orientation can cracked epoxy surfaces with a healing efficiency of about be found in references [Lee H S, Ko J H, Song K S, Choi K 100% [Rodriguez E D, Luo X, Mather P T. Linear/Network H. Segmental and Chain Orientational Behavior of Spandex Poly(e-caprolactone) Blends Exhibiting Shape Memory 20 Fibers. Journal of Polymer Science Part B: Polymer Physics Assisted Self-Healing (SMASH). ACS Applied Materials 1997; 35:1821-1832; Seymour R W, Jr. AEA, Cooper S L. and Interfaces 2011; 3:152-161; Luo X, On R, Eberly D E, Segmental Orientation Studies of Block Polymers. I. Hydro- Singhal A, Viratyaporn W, Mather P T. A Thermoplastic/ gen-Bonded Polyurethanes. Macromolecules 1973; 6:896- Thermoset Blend Exhibiting Thermal Mending and Revers- 902]. ible Adhesion. ACS Applied Materials and Interfaces 2009; 25 The tensile properties of the SMP fibers were tested using 1(3):612-620]. The polycaprolactone (Mn 45,000, Sigma- MTS (Alliance RT/5, MTS Inc, USA)equipped with a 250 Aldrich, USA) had a melting temperature at around 60° C. N load cell. Sample clamps specified for fibers were used. and density of 1.145 g/cm3. The composites were prepared The crosshead speed was 80 mm/min and the gage length by a dry weaving process per the pin-guided filament was 38.1 mm (1.5 inch). 10 specimens were tested. The winding process [Li G, Muthyala V.Impact Characterization 30 cross-section area of the SMP fiber was obtained using a of Sandwich Structures with an Integrated Orthogrid Stiff- Scanning Electron Microscope (SEM, JSM-6390, JEOL ened Syntactic Foam Core. Composite Science and Tech- Ltd, Japan). The fibers were coated with gold before obser- nology 2008; 68:2078-2084]. The spacing between the fiber vation. The damping property tests were conducted using the bundles (ribs) was 13 mm. Epoxy was prepared using same MTS (Alliance RT/5, MTS Inc, USA). One end of the bisphenol A diglycidyl ether (The Dow Chemical Company, 35 fiber was fixed in the upper clamps of the MTS. The other USA) and triethylenetetramine (The Dow Chemical Com- end ofthe fiber was hooked with a mass(222.2 g). The initial pany, USA). Bisphenol A diglycidyl ether was melt in force exerted by the mass was set to be zero. A 1-N force was advance and mixed with TPs by vigorous stirring for one applied to the fiber and then released to record the damping hour before triethylenetetramine was added. The volume properties of the fibers. The elastic fiber was an XLA fractions of the TPs and SMP fiber were 12% and 7%, 40 elastomeric fiber made of crosslinking polyolefin from respectively. The mixture was poured into the bay areas of Aquafil Group, Italy. The Supercontraction of the fiber was the SMP fiber woven grid skeleton. The composite mixture evaluated by measuring the shrinkage percentage of the free was degassed in a vacuum oven for 20 minutes and cured at fiber with increasing temperature. The Supercontraction ratio ambient temperature (22° C.) for 40 hours. The glass tran- of the SMP fiber was determined by the following equation: sition temperature of the epoxy matrix was around 75° C. 45 Supercontraction ratio=[(L-1)/L]x100%, where L is the 3. Materials Characterization original fiber length; 1 is the length after shrinkage. The 3.1 Characterization of SMP Supercontraction stress of the SMP fiber was tested using The molecular structure ofthe SMP fiber was investigated MTS (Qtest/150, MTS Inc, USA)equipment with a thermal using Fourier Transform Infrared Spectroscopy (FT-IR, Nic- chamber (10-162, Thermodynamic Engineering Inc. USA). holet 6700, Thermo Scientific, USA)equipped with a Smart 5o To determine the thermal-induced Supercontraction stress, iTR universal sample holder in the region of 700-4000 cm'- the fully restrained SMP fiber was heated up from the at room temperature. The thermal properties of the SMP ambient temperature (25° C.) to 170° C. at a heating rate of fibers were investigated using a Differential Scanning Calo- 5° C./min. The contraction stress of the SMP fiber was rimeter (PerkinElmer DSC 4000, USA). The sample was recorded. To improve the contraction stress, the second set cooled from room temperature to -50° C. at a speed of 10° 55 of samples was cold-drawn with a strain of 150%. The C./min. Then the sample was scanned from -50° C. to 240° samples were held for 30 minutes at the strain to partially fix C. at a heating rate of 10° C./min. The phase separation the deformation. Then the strain-hardened fibers were morphology of the polymer was investigated using an heated up to test the contraction stress. The experiments Atomic Force Microscope (AFM, SPA-300 HV, Seiko were repeated 5 times. Instruments Inc.) in the tapping-mode under an ambient 60 The cyclic thermomechanical behavior of the SMP fiber environment (22±2° C., 45±5% RH). In phase images, a under tension was determined by Instron MTS (Instron Inc, higher modulus material induces a higher phase offset and it USA). First, the SMP fiber was stretched to 50% elongation appears lighter as opposed to a softer phase which appears ratio at the ambient temperature at a drawing speed of 10 darker. SAXS (small angle x-ray scattering) tests of the fiber mm/min. Second, the strain was maintained for 15 minutes. were conducted on a Nanostar SAXS machine (Bruker, 65 Third, the upper clamp was returned and the SMP fiber was USA). The x-ray source was Cu Ka and the wavelength was heated up to 80° C. for contraction. Forth, the SMP fiber was about 0.154 mu. Samples were scanned in the range of 0.5° cooled down to ambient temperature. After the cycle was US 9,428,647 B2 37 38 completed, a second cycle began. To study the interface Abundant hydrogen bonding forms between amino group between the SNIP fiber and the polymer matrix, the prepared and carbonyl group in the crystalline hard phase. The composite was broken in liquid nitrogen to create fracture amorphous phase and crystalline phase are partially ori- surface. The interface between the SNIP fiber and the poly- ented. The segment assembling into crystalline rigid beta mer was observed using SEM (SEM, JSM-6390, JEOL Ltd, 5 sheet domains can be regarded as the hard segment. The Japan). The fracture surface was coated with gold before segment forming helical and beta turn amorphous phase can SEM observation. Shape memory alloy wires/TP/epoxy be regarded as the soft segment. The interplay between the composites were also prepared to study the compatibility in crystalline hard region and the soft amorphous region comparison with that of SNIP fiber/TP/epoxy composite. endows spider silks with the extraordinary toughness and 3.2 Characterization of the Self-Healing Composite io strength. The hydrogen bond in spider silks is one of the To demonstrate the self-closure of macro-cracks upon basic chemical bonds that play a vital role in the mechanical heating, specimens of 8xl5x80 mm' were cut from the properties of spider silk as demonstrated by Buehler's composite panel. A macro-crack was first created on the research [see, e.g., Qin Z, Buehler M J. Cooperative Defor- specimen using the NITS (Qtest 150, NITS Inc, USA) by mation of Hydrogen Bonds in Beta-strands and Beta-sheet tension. The crosshead speed was 10 mm/min. The specimen 15 Nanocrystals. Physical Review E 2010, 82:061906]. In the with the macro-crack was put on a hot plate (CORNG spider silk, the hard segment and soft segment are partially 6795-420D, USA) to trigger the supercontraction of the orientated. programmed SNIP fiber. A high resolution CCD camera As shown in FIG. 9, the SNIP fiber has an amorphous soft (Sony XCD-CR90, Sony Inc. Japan) with a resolution of phase and a crystalline hard phase. The broad glass transi- 3.7x3.7 µm/pixel was used to record the closure of the 20 tion of the soft phase locates around ambient temperature in macro-crack. TDCB (tapered double-cantilever beam speci- the range of 0-50° C., and melting transition of the crys- mens) were used to determine the healing efficiency and talline hard phase locates at around 120-190° C. Like spider repeatability of the healing. The healing efficiency was silk, the SRP undergoes microphase separation into crystal- evaluated by tensile test using a NITS Qtest150 machine line phase and amorphous phase as demonstrated by the (NITS Inc, USA) with lab-made sample holders. The pro- 25 DSC results in FIG. 9. This is because of the low compat- tocol for evaluating the self-healing efficiency using the ibility of the rich hard segment and the scarce soft segment. TDCB sample can be seen in reference [Rule J D, Sottos N The hard segment phase forms crystalline domains which R, White S R. Effect of Microcapsule Size on the Perfor- can act as reinforcing nanofillers, stiffening and strengthen- mance of Self-healing Polymers. Polymer 2007; 48:3520- ing the SNIP fiber [Ji F L, Hu J L, Li T C, Wong Y A W. 3529]. The self-healing of the TDCB sample was achieved 30 Morphology and Shape Memory Effect of Segmented Poly- simply by keeping the cracked TDCB samples in a preheated urethanes. Part I: With crystalline Reversible Phase. Poly- oven (Gruenberg Model L341-IV104 from Lunaire Limited, mer 2007; 48:5133-5145]. The phase separation structure of USA)for 15 minutes at 80° C.(>T g of the SNIP fibers and the polymer was observed using AFM.in which darker areas Tm ofthe TPs). The oven was power off after 15 minutes and are indicative of soft segment phase and lighter areas may the mechanical property tests on the healed samples were 35 represent hard segment phase [see, e.g., Garrett J T, conducted after 24 hours. The healing efficiency h was Siedlecki C A, Runt J. Microdomain Morphology of Poly calculated using the equation: (urethane urea) Multiblock Copolymers. Macromolecules 2001; 34:7066-7070]. The phase image indicated the phase hn[(F of 1Fo)x100%, separation of the polymer with lighter hard segment phase where F. is the maximum loading of the original sample; 4o regions and darker soft segment phase regions. The SAXS f is the maximum loading of the sample after the nth time of profile of the SNIP fiber with a scattering shoulder (data not self healing. shown) also indicated that the SNIP fiber is phase separated. 4. Results and Discussion The calculated interdomain spacing based on the Bragg's 4.1. Molecular Structure and Aggregate Structure of the law is 7.95 nm. SNIP Fiber 45 The abundant hydrogen bonding in the SNIP fiber was The molecular and aggregate structures of the SNIP fiber demonstrated by FTIR.(see FIG. 10). The FTIR spectrum of were studied using DSC,AFM, SAXS, and FTIR dichroism. the SNIP fiber and the raw chemicals is shown in the ranges The similarity between SNIP fiber and natural spider silks in of: FIG. 10 Panel (a)4000-3200 cm'- and FIG. 10 Panel(b) the primary and aggregate structure is shown in FIG. 8. 1800-1600 cm'. In FIG. 10 Panel (a), because of the hydro- Spider silk molecules are sequence of different long chain 50 gen bonding of N H... C O, the stretching vibration of amino acids mainly consisting of highly repetitive alanine (N H)shifts to 3320 cm-'.(free v(N H)locates at around and glycine blocks [Lee S M,Pippel E, G6sele U, Dresbach 3440 cm-1)[Sun H. Ab initio Characterizations of Molecu- C, Qin Y, Chandran C V, et al. Greatly Increased Toughness lar Structures, Conformation Energies, and Hydrogen-bond- of Infiltrated Spider Silk. Science 2009; 324:488-492; ing Properties for Polyurethane Hard Segments. Macromol- Gatesy J, Hayashi C, Motriuk D, Woods J, Lewis R. Extreme 55 ecules 1993; 26:5921-5936; Seymour R, Estes G, Cooper S. Diversity, Conservation, and Convergence of Spider Silk Infrared Studies of Segmented Polyurethane Elastomers. I. Fibroin Sequences. Science 2001; 291:2603-2605]. The Hydrogen bonding. Macromolecules 1970; 3:579-583; Yil- alanine mainly forms the crystalline domains with a dimen- g6r E, Yilg6r S, Yurtsever E. Hydrogen Bonding and Poly- sion of about 2x5x7 run. The Glycine with larger side groups urethane Morphology. I. Quantum Mechanical Calculations forms most of the amorphous phase [Gatesy J, Hayashi C, 60 of Hydrogen Bond Energies and Vibrational Spectroscopy Motriuk D, Woods J, Lewis R. Extreme Diversity, Conser- of Model Compounds. Polymer 2002; 43:6551-6559;] As vation, and Convergence of Spider Silk Fibroin Sequences. shown in FIG. 10 Panel (b), because of the hydrogen Science 2001; 291:2603-2605]. The crystalline domains are bonding N H... C O, most of the stretching vibration of embedded in the amorphous phase (see FIG. 8(c) which (C-0)shifts from 1730 cm-1 to 1700 cm-1. Both the shift shows the aggregate phase structure of SNIP fiber and spider 65 of the N H and C-0 stretching vibration to low wave silk). The soft segment and hard segment form the amor- numbers indicates significant hydrogen bonding in the SNIP phous soft phase and crystalline hard phase, respectively. fiber. Because of the complexity of the hydrogen bonding in US 9,428,647 B2 WE HE this SMP fiber, the hydrogen bonding degree was not Farmington Hills, Mich., 153. In; 1996. p. 627-628]), and calculated based on the FTIR spectra. steel bar (designated B) (standard tensile specimen, The shift of the stretching vibration of N H from high STFC18, cold rolled steel, USA). The tensile strength of the wave number to low wave number indicates the hydrogen SMP fiber is approaching though it is still lower than that of bonding between the N H... O C. The "bifurcated" C-0 5 the spider dragline silk. The tensile strength ofthe SMP fiber stretching vibration suggests that the C O groups are is 3 times of that of the recombinant fibers. Both the tensile mostly hydrogen bonded [Lin C K, Kuo J F, Chen C Y, Fang strength of the spider dragline silk and SMP fiber is much J J. Investigation of Bifurcated Hydrogen Bonds within the higher than that of steel bar. Thermotropic Liquid Crystalline Polyurethanes. Polymer Spider silk is the toughest fiber of all the silks and 2012; 53:254-258]. Both the shift of the N H and C-0 io synthetic fibers in existence. Kevlafrm fiber (aromatic fiber) stretching vibration to low wave numbers indicates abundant is the toughest synthetic fiber which has been widely used hydrogen bonding in the SMP fiber. for ballistic rated body armor fabric and ballistic compos- The soft segment and hard segment orientation of the ites. FIG. 12(b) shows the toughness of the SMP fiber in SMP fiber was determined using IR dichroism as shown in comparison with spider dragline silk, Kevlar fiber, recom- FIG. 11. The significant differences between the two profiles 15 binant dragline silk, other high performance fibers, and steel A,and Al suggest the orientation of the macromolecules in bar [Omenetto F G, Kaplan D L. New Opportunities for an the SMP fiber. The soft segment orientation function was Ancient Material. Science 2010; 329:528-531; Gosline J M, calculated to be 0.19; and the hard segment orientation Guerette P A, Ortlepp C S, Savage K N. The Mechanical function was calculated to be 0.56 according to the equations Design of Spider Silk: From Fiberoin Sequence to Mechani- from references [Siesler H W, Holland-Moritz K. Infrared 20 cal Function. The Journal of Experimental Biology 1999; and Raman Spectroscopy of Polymers, Marcel Dekker Inc., 202:3295-3303]. The SMP fiber has a toughness value of New York; 1980; Estes G M, Seymour R W, Cooper S L. 245 MJ/m3 which is much higher than natural spider dra- Infrared Studies of Segmented Polyurethane Elastomers. II. gline silk, and Kevlar fiber; it is 1.4 times of that spider Infrared Dichroism. Macromolecules 1971; 4:452-457]. dragline silk, 4 times of that ofthe recombinant fiber, 5 times 4.2. Mechanical Properties of the SMP Fiber 25 of that Kevlar fiber (Intermediate modulus, IM), 5 times of Spider silks in particular dragline silk, exhibit a unique that of Steel bar (Cold drawn Ferritic Steel 18#, STFC18), combination of high tensile strength and extensibility. This 6 times of that of Glass fiber (E-glass, E), 11 times of that enables the unbeatable toughness (area under a stress-strain of Carbon fiber (High strength, HS), and 30 times of that of curve) of spider dragline silks [Lee S M,Pippel E, G6sele U, Carbon fiber (High modulus, HM). Dresbach C, Qin Y, Chandran C V, et al. Greatly Increased 30 Experiments mimicking prey striking fibers were con- Toughness of Infiltrated Spider Silk. Science 2009; 324:488- ducted wherein a 5 pound mass was dropped from 0.7 m 492; Lazaris A, Arcidiacono S, Huang Y, Zhou J-F, Duguay height above the fibers to strike the SMP fibers and carbon F, Chretien N, et al. Spider Silk Fibers Spun from Soluble fibers. The mass was regarded as a prey to strike fibers. Recombinant Silk Produced in Mammalian Cells. Science A series of SMP fiber and carbon fiber bundles with 2002; 295:472-476]. However, because of the difficulty of 35 different numbers of fibers were tested. The total cross- replicating spider silk proteins and mimicking the exact section area of the fibers was obtained by multiplying the spinning process of spider silks, the research on fabricating cross-section area of a single fiber with the number of the artificial spider dragline silk is not very successful. One of fibers in the bundle. The cross-section area of the single the best achievements to fabricate artificial spider silk is to SMP fiber and carbon fiber was obtained from their SEM use recombinant spidroin-like protein to prepare fiber 40 images. The SMP fiber bundles with the total cross-section through wet spinning. Elices et al. [Elices M, Guinea G V, areas of 0.1 mm2, 0.2 mm2, 0.3 mm2, 0.4 mm2, and 0.5 mm2 Plaza G R, Karatzas C, C. Rickel, Agullo-Rueda F, et al. were tested. Carbon fiber bundles with the total cross- Bioinspired Fibers Follow the Track of Natural Spider Silk. section areas of 0.6 mm2, 1.2 mm2, 1.8 mm2, 2.4 mm2, and Macromolecules 2011; 44:1166-1176] prepared artificial 3.0 mm2 were tested. The experiments were repeated three spider silk recombinant spidroin-1 and spidroin-2 (dragline 45 times for consistency. spider silk) in the major ampullate gland of the spider It was found that with increasing the total cross-section Nephila clavipes. The maximum mechanical strength of the area, the SMP fiber bunches with the total cross-section recombinant spider dragline silks achieved was only '/5 of areas of 0.1 mm2 and 0.2 mm2 were broken; while the SMP natural spider dragline silk [Elices M, Guinea G V, Plaza G fiber bunches with the total cross-section areas of 0.3 mm2, R, Karatzas C, C. Rickel, Agullo-Rueda F, et al. Bioinspired 50 0.4 mm2, and 0.5 mm2 were not broken after the impact Fibers Follow the Track of Natural Spider Silk. Macromol- tests. For carbon fiber bundles, with increasing total cross- ecules 2011; 44:1166-1176; Plaza G R, Corsini P, Marsano section area, the carbon fiber bundles with the total cross- E, Perez-Rigueiro J, Biancotto L, Elices M, et al. Old Silks section areas of 0.6 mm2 and 1.2 mm2 were completely Endowed with New Properties. Macromolecules 2009; broken after the impact; while the carbon fiber bundles of 42:8977-8982.]. 55 1.8 mm2 total cross-section area was almost broken com- FIG. 12(a) shows the tensile properties of the SMP fiber pletely and the carbon fiber bundles with the 2.4 mm2, and (designated D) in comparison with natural spider dragline 3.0 mm2 total cross-section areas were not broken after the silk (designated B) [Omenetto & Kaplan, Science, 2010; impact. 329:528], recombinant dragline silk (collectively designated The carbon fiber bundle with a cross-sectional area of 1.8 D)) (Elices M, Guinea G V, Plaza G R, Karatzas C, C. 60 mm2 was severely damaged; while no damage was found on Rickel, Agullo-Rueda F, et al. Bioinspired Fibers Follow the the SMP fiber bundle with a cross-sectional area of0.3 mm2. Track of Natural Spider Silk. Macromolecules 2011; The results showed that the SMP fiber is much tougher than 44:1166-1176]), other high performance fibers (collectively carbon fiber. Thus, this data demonstrated the outstanding shown within oval at uppermost arrow and designated A) toughness of the SMP fiber. (ACI Committee 440,[440 AC.ACI Committee 440,"State - 65 In addition to the outstanding toughness, another crucial of-the-Art Report on Fiber Reinforced Plastic Reinforce- issue for spider dragline silk is damping properties which ment for Concrete Structures" American Concrete Institute, represent how the energy is absorbed if it is impacted. FIG. US 9,428,647 B2 !FI !, N 13 shows the remarkable damping properties of the SMP fiber will be deformed by stretching (similar to cold-drawing fiber as compared with spider dragline silk and elastomeric programming) Upon heating, the contraction of the SMP fiber. Visual observation showed the outstanding damping fibers closes cracks in the composite by recovering the strain property of SMP fiber as compared with elastomeric fiber. to 0. Furthermore, because the SMP fiber with the super- The oscillation amplitude of a mass attached to the SMP 5 contraction has a tendency to shrink further, the fiber may fibers reduced quickly with no obvious twisting and swing- exert a compressive force on the closed crack interfaces. The ing. The oscillation of the mass attached to the elastomeric cyclic thermo-mechanical cycles were repeatable; therefore, lasted a long time period with obvious twisting and swinging the capability ofthe SMP fiber to heal macroscopic damages of the string. (Also see Supplementary Video 1 to Guoqiang is repeatable. Li, Harper Meng and Jinlian Hu, "Healable Thermoset io 4.5. Thermal-Induced Self-Healing of the SMP Fiber Polymer Composite Embedded With Stimuli-Responsive Composite Fibres", J. R. Soc. Interface (2012) 9, 3279-3287) FIG. 13 It is expected that the SRFs with the outstanding mechani- compares the damping properties of the SMP fiber, spider cal properties and thermal-induced supercontraction can dragline silk ([440 AC. ACI Committee 440, "State-of-the- close macroscopic cracks if they are embedded in compos- Art Report on Fiber Reinforced Plastic Reinforcement for 15 ites. The SMP fiber and TPs were incorporated into a regular Concrete Structures" American Concrete Institute, Farming- epoxy for the self-healing of macroscopic damages. The ton Hills, Mich., 153. In; 1996. p. 627-628]), and elastic interface between the SMP fiber and polymer matrix was fiber. Similar to dragline silk, the SMP fiber has outstanding compared with that of shape memory alloy wire and the damping properties. The dragline silk and SMP fiber can polymer matrix. Microscopic data found that the interface become stabilized in a much shorter time. The decay speed 20 between the SMP fiber and the matrix is not clear; while the of the SMP fiber is even higher than that of dragline silk. interface between the shape memory alloy wire and the This suggests that the SMP fiber through molecular friction polymer matrix was clear indicating a lack of compatibility. can effectively transform the impact energy into heat thereby Consequently, the shape memory alloy wire is pulled out of dissipating the energy. Just like the dragline silk acts as a the matrix. In comparison with shape memory alloy wire, safety line, the SMP fiber can also stop the twisting and 25 the SMP fiber has better compatibility with the polymer swinging of an object hung at the end as a result of the good matrix. damping properties. FIG. 15(a) shows the schematic self-healing process of 4.3. Thermal-Responsive Supercontraction of the SMP the SMP fiber/TP/epoxy composite with a macro-crack (also Fiber see, FIG. 6 and FIG. 35, and respective related text). The A free spider dragline silk shrinks up to 50% in length 3o healing process consists of two-steps. In the first-step, the when wetted. The mechanism is the plasticizing effect of damaged sample is heated to a temperature (TJ above the water and disruption of hydrogen bonds in spider silk, glass transition temperature of the SMP fiber to trigger the leading to the formation of less organized silk protein thermal-induced supercontraction of the SMP fibers. The [Boutry C, Blackledge T A. Evolution of Supercontraction in supercontraction of the SMP fibers closes the macro-crack. Spider Silk: Structure-function Relationship from Tarantulas 35 In the second step, the composite is further heated up to the to Orb-weavers. The Journal of Experimental Biology 2010; bonding temperature(T 2)of the TPs. The molten TPs flows 213:3505-3514]. No obvious water-induced supercontrac- into the narrowed crack by capillary force, diffuses into the tion was observed on the SMP fiber because the SMP fiber fractured epoxy matrix by concentration gradient, and forms is not as hydrophilic as spider silk. The SMP fiber showed physical entanglement and solid wedge when the sample is thermal-induced supercontraction as a result of its special 40 cooled down. two-phase structure. During the spinning process, at a tem- Actual self-healing of the composite was performed. In perature above the melting temperature of the crystalline Step 1, the damaged sample was put on a hot plate. A hard segment phase, the fiber is extruded from spinneret. macro-crack(3 mm wide)closed within 2 minutes as a result Upon cooling to ambient temperature, the fiber is wound up. of the thermal-induced contraction of the SMP fiber (Also The molecules of SMP fiber are slightly oriented resulting 45 see Supplementary Video 2 to Guoqiang Li, Harper Meng from the spinning process. When the SMP fiber is heated up, and Jinlian Hu, "Healable Thermoset Polymer Composite the soft segments in the amorphous phase have enough Embedded With Stimuli-Responsive Fibres", J. R. Soc. mobility. The hydrogen bonded crystalline hard segment Interface (2012) 9, 3279-3287). Visual observation showed phase has a tendency to contract the fiber which leads to that heating the damaged sample triggered the thermal- shrinkage of the fiber. Cold-drawing leads to more align- 50 induced supercontraction of the SMP fibers to close the ment of the amorphous phase and thus more supercontrac- macro-crack. The damaged sample is put on a preheated hot tion. Further increasing the temperature leads to the melting plate. The crack is about 3 mm in width (rising ofthe sample of the hard segment phase, which results in the further was because of the uneven heating of hot plate). In Step 2, shrinkage of the SMP fiber. the composite with the closed/narrowed crack was main- FIG. 14(a) presents the thermal-induced free supercon- 55 tained in an oven preheated to 80° C. for 15 minutes. The traction ratios of the SMP fibers at different temperatures. molten TPs diffused into the cracked matrix and bridged the FIG. 14(b) shows the contraction stress curves of the crack plane. In addition to direct heating, in future research, restrained SMP fiber. The SMP fiber has a contraction stress conducting fillers or magnetic fillers may be filled into the of 1.8 MPa. The contraction stress of the SMP fibers can be composites so that the self-healing can be achieved by improved by strain-hardening through cold-drawing; as 60 electric field, alternating magnetic field, or infrared light shown in FIG. 14(c), after a one-time of 100% strain- [Jung Y C, Yoo H J, Kim Y A, Cho J W, Endo M. hardening by cold-drawing, the contraction stress of the Electroactive Shape Memory Performance of Polyurethane SMP fiber reaches 7.8 MPa. Composite Having Homogeneously Dispersed and Cova- 4.4. Cyclic Thermo-Mechanical Tensile Test lently Crosslinked Carbon Nanotubes. Carbon 2010; Cyclic then no-mechanical tensile testing curves of the 65 48:1598-1603; Liu Y, Lv H, Lan X, Leng J, Du S. Review SMP fiber were generated (data not shown). If a crack is of Electro-Active Shape-Memory Polymer Composite. created in a composite embedded with the SMP fibers, the Composites Science and Technology 2009; 69:2064-2068]. US 9,428,647 B2 43 44 The healing efficiency of the composite was investigated materials. Proceedings ofthe Royal Society A-Mathematical using TDCB (tapered double cantilever beam) specimens as Physical and Engineering Sciences 2012; 468:2319-2346; Li suggested by Rule J D, Sottos N R, White S R. Effect of G, Meng H, Hu J. Healable thermoset polymer composite Microcapsule Size on the Performance of Self-healing Poly- embedded with stimuli-responsive fibers. Journal of the mers. Polymer 2007, 48:3520-3529. FIG. 16(a) shows the 5 Royal Society Interface 2012; 9:3279-3287]. This mimics typical load-deflection curves of the original and healed the healing of human skin, i.e., for a wide or deep cut, the TDCB samples after different fracture/healing cycles; and skin needs to be first closed by stitch before new cells grow. FIG. 16(b)presents the maximum loading ofthe original and In this idea, SNIPE grid skeleton is embedded into conven- healed TDCB samples after different fracture/healing cycles. tional thermosetting polymer matrix as built-in suture to According to FIG. 16(b), after the first two-step healing io close crack; thermoplastic particles/structures are dispersed process, 94% of the strength of the sample was recovered. in the thermosetting polymer matrix and these function like After four rounds of cracking/healing cycles, the healing "new cells" to heal crack molecularly. For example, when a efficiency can reach 80%. The healing process is reasonably wide-opened crack is created, heating leads to constrained repeatable. "To conduct more precise healing efficiency shrinkage of the SMPFs, resulting in closure of the crack. evaluation, the healing efficiency can be further calculated 15 Further heating leads to melting of the embedded thermo- following energy based approach for proposed by Rule J D, plastic particles. The molten thermoplastic is sucked into the Brown E N, Sottos N R, White S R, Moore J S. Wax- narrowed crack through capillary force, diffused into the protected Catalyst Microspheres for Efficient Self-healing fractured thermosetting polymer matrix by concentration Materials. Advanced Materials 2005; 72:205-208. gradient, and glues the fractured surfaces molecularly when 5. Discussion 20 the thermoplastic wedge is solidified by cooling below the SNIP fibers with superior mechanical properties and ther- melting temperature of the thermoplastic particles. mal-responsive supercontraction were fabricated for the In accordance with the present invention, partial misci- purpose of healing macroscopic damages in composites. The bility between the SMPFs/matrix and thermoplastic par- SNIP fiber has superior toughness which is 1.4 times of ticles/matrix is called for. In addition, the following tem- spider dragline silk, 5 times ofthat Kevlar fiber(IM), 6 times 25 perature relationships are generally important: of that of Glass fiber (E), 11 times of that of Carbon fiber T, Tgsp (23.80±0.44° C.), phase de-mixing at TDMx 55 segments, while in Sample #3, both soft and hard segments (82.42±0.88° C.), hard phase disorder procedure around TM have been stretched during the programming procedure. (145.72±0.77° C.) and finally, phase mixing around Tmx Without being bound by theory it is believed that the (166.27±1.35° C.). difference in the mechanical properties between Sample#2 For Sample#2, according to the first DSC cycle of and Sample#3 is from the difference in the level of orien- Sample#1 in FIG. 48, the programming temperature (100° 60 tation in soft and hard segments. C.) is above the phase de-mixing temperature TD,,,, It has 3.2.2 Shape Memory Properties been proved in the literature that upon heat treatment, the Typical fully constrained stress recovery tests results are hydrogen bond between soft segments and hard segments shown in FIG. 52(a). Based on observation, during the fully decreases and the "purity" of soft phase increases. As a constrained stress recovery test, the overall stress recorded result, without the strong restriction of the hard segments, 65 is determined by three effects: 1) thermal expansion; 2) without being bound by theory it is understood that the soft releasing of the "stored stress"; and 3) stress relaxation. At segments could possess a greater mobility and their stiffness the beginning of the test, since the temperature is not high US 9,428,647 B2 81 82 enough to trigger the massive releasing of the "stored value of tan 6 means better damping properties. The tem- stress", the dominating effect is thermal expansion. As perature and frequency dependence of all these three param- temperature increases, two competitive mechanisms begin eters can be obtained by DMA. to dominate the total stress: On one hand, driven by the In FIG. 53, each plot represents the isothermal dynamic entropic force, the molecular chains tend to recoil and return 5 frequency sweep test of a certain sample. Tan 6 reaches its to the original configuration, i.e., shape recovery. Due to the maximum at T=50° C. and minimum at T=100° C. for all fully constrained boundary condition, the shape recovery is three samples. This is because 50° C. is the test temperature not allowed, leading to buildup of tensile stress (e.g., as if a that is closest to their corresponding glass transition tem- material had a negative thermal expansion coefficient), peratures (around 40° C., based on the DMA Tg tests [See, which is considered to be the releasing of the stored stress. io e.g., Example 1, Example 3, Example 6]), whereas T=100° This tensile stress increases as the recovery process pro- C. is farthest away from the corresponding Tg. The results ceeds. On the other hand, once the fibers are in tension, also indicate that the loss tangent of the material has an order molecules tend to align along the loading direction, leading of 0.1, and can be as high as 0. 35. to stress relaxation. Because the constrained stress recovery 3.3.2 Dependence of Damping Property on Frequency test has the same test configuration as conventional stress 15 In FIG. 54, the tan 6 vs. frequency curves were regrouped relaxation test, it helps understand why stress relaxation is for the convenience of investigation and comparison. Each one ofthe major components in stress recovery test. The two plot represents the results of all three samples at a certain mechanisms competed with each other until the microstruc- temperature. The plots indicate that the loss tangent is ture reaches an equilibrium state and by that time, the controlled by temperature, frequency and programming pro- recovery stress is stabilized. 20 cess simultaneously. However, the dependence of the loss The peak and final stresses for both the programmed tangent on frequency has similar trends for all three samples samples are reported in FIG. 52(b). The results revealed that at a certain temperature: at low temperature(T -25° C.), tan Sample#2 has a higher peak recovery stress, while 6 decreases monotonically with respect to frequencies; at Sample#3 has a higher stabilized recovery stress. The dif- intermediate temperature (T=50° C., 75° C.), tan 6 first ferences in the recovery behaviors of both samples can be 25 increases then flattens, and finally decreases; at high tem- explained by the difference in their microstructures we perature (T=100° C.), the curve is more flattened at lower hypothesized before. It is understood that Sample#2 has frequencies and is close to zero at higher frequencies. higher amount of oriented soft segments and the soft seg- This phenomenon can be explained by time-temperature ments have lower transition temperature, the recovery pro- equivalent principle, that is, higher frequency is equivalent cess of Sample#2 was thus triggered first. The slightly lower 30 to lower temperature and vice versa. According to the DMA recovery temperature, together with the slightly higher stiff- Tg tests, at T=25° C., the fiber is in glassy state or at the ness of Sample #2, makes it have a higher peak stress than beginning of the glass transition zone [See, e.g., Example 1, Sample#3 (see, e.g., FIG. 51). When comparing the stabi- Example 3, Example 6]. Increasing frequency is equivalent lized stress, for Sample#2, most of the stabilized stress is to decreasing temperature, which will result in lower loss sustained by the soft segments, while for Sample#3, some 35 tangent. Similarly, at the intermediate temperature, 50° C. hard segments taking part in the recovery process leadings and 75° C., the material is within the glass transition zone or to higher stabilized stress. In the bio-inspired self-healing at the end of the zone. Applying higher frequency load is applications, a sustained force is needed to close the mac- equivalent to bringing the material back from the rubber roscopic crack (see e.g., Example 4 and Example 5)In other elastic state to the glass transition zone, passing the glass words, the stabilized recovery stress plays a more important 40 transition region and finally entering the glassy state. Thus role in self-healing process. Therefore, Sample#3 is gener- an upward trend of the loss tangent curve appeared at the ally more desired in self-healing embodiments. beginning followed by a downward trend of loss tangent. At 3.3 Damping Properties even higher temperature T=100° C., the amorphous phase of 3.3.1 General Description of the Damping Property the polymer is in pure rubber elastic state. Loss tangent stays The ability for polymers to damp vibration persists in 45 close to zero within this region. their viscoelastic nature [Chung, D., Review: Materials for For a description on how to relate the frequency depen- vibration damping. Journal of Materials Science, 2001. dence and temperature dependence of loss tangent, see FIG. 36(24): p. 5733-5737; Ganeriwala, S. and H. Hartung, 55. In order to utilize FIG. 55 the following steps can be Fourier Transform Mechanical Analysis and Phenomeno- employed: (1) Start from a certain test temperature, 50° C., logical Representation of Viscoelastic Material Behavior. 50 for example. (2) Follow the direction of the arrow; this 1989] This damping capability is maximized within the direction represents the decrease in temperature, and also glass transition region. Within this region, when the material represents the increase in frequency according to the time- is forced to vibrate, some molecules exhibit viscous flow temperature equivalence principle. (3) Select the curve while others remain stiff. Internal molecular friction thus between 50° C. and a reasonable ending temperature, 25° C., increases, which results in heat buildup and dissipation of 55 for example, make an axial symmetry with respect to the the input energy [Couchman, P. and F. Karasz, A classical vertical dash line corresponding to 50° C.(4) A sketch ofthe thermodynamic discussion of the effect of composition on tan 6 vs. frequency is obtained; comparing with the experi- glass-transition temperatures. Macromolecules, 1978. 11(1): mental result in FIG. 53 [there was a typo here please verify p. 117-119]. The dynamic properties of polymers can be that 53 is now the correct Fig.], they have the same trend. characterized by storage modulus E', loss modulus E", and 60 Thus, by starting from the tan 6 vs. temperature sketch, loss tangent tan 6. Theoretically, to obtain the best damping following the above four steps with and corresponding steps property, it is desired to maximize E". However, there is a in the FIG. 55, a schematic tan 6 vs. frequency curve can be limit. Maximizing E" results in lower elastic response and, obtained. Accordingly, use of FIG. 55 in this way allows one therefore, poor physical and mechanical properties may to customize or design SNIP programming. result. Furthermore, both E' and E" are sensitive to geom- 65 Although all the samples obey similar patterns, different etry. Therefore, tan 6 was used here as a quantitative programming methods differentiate the loss tangent curves representation of material ability to dissipate energy: higher of the three samples from each other. As mentioned earlier, US 9,428,647 B2 83 84 the source of damping in a polymer is mainly from the TABLE 4 friction among molecular chains against relative motion [Bicerano, J. and J. K. Rieke, Internal friction in polymer Approximate mechanical properties for some structural materials systems. The Journal of the Acoustical Society of America, Strength Extensibility Toughness 1989. 86: p. S51; Hermida, E. B., F. Povolo and P. Porta, 5 Materials (GPa) N (MI/m3) Internal friction and loss tangent of nonlinear viscoelastic SMPU (Sample#1) 0.190 ± 0.013 264 ± 21 277 ± 25 materials: different concepts, different results. Journal of SMPU (Sample#2) 0.280 ± 0.014 187 ± 4 290 ± 17 alloys and compounds, 2000. 310(1): p. 280-283]. Higher SMPU (Sample#3) 0.250 ± 0.015 212 ± 9 284 ± 27 orientation can increase such resistance, while phase sepa- Spider dragline silk* 1.1 27 160 10 Nylon fiber* 0.95 18 80 ration caused by heat treatment can decrease the restriction. Kevlar 49 fiber* 3.6 2.7 50 At lower temperature (25° C.), Sample#1 has the lowest Glass fiber* 2.4 3 35 Carbon fiber* 3.9 1.5 22 value of tan 6, indicating that programming increases the High tensile steel* 1.5 0.8 6 damping capability of SMPU fibers, mostly due to higher orientation of the programmed samples. Meanwhile, since 15 Sample#2 has the lowest glass transition temperature, at 25° In Table 4, these data (*) are obtained from published literature; no standard deviation is available in the publica- C., Sample#2 is the closest to its glass transition region. tions. [Hsia, Y., E. Gnesa, F. Jeffery, S. Tang and C. Vierra, Therefore, Sample#2 has the highest value of tan 6. At intermediate temperature (50° C. and 75° C.), cold-drawn Spider silk composites and applications. Metal, ceramic and 20 polymeric composites for various uses. InTech, Rijeka, SMPU fiber (Sample#3) exhibits the highest damping capa- 2011; Li, G., H. Meng and J. Hu, Healable thermoset bility, followed by as-spun SMPU fiber (Sample#1), and the least by the hot-drawn SMPU fiber (Sample#2). This is polymer composite embedded with stimuli-responsive fibres. Journal of The Royal Society Interface, 2012. 9(77): because Sample#2 has been through the phase separation p. 3279-3287 Li, G., H. Meng and J. Hu, Healable thermoset process, while Sample#3 has higher molecular orientation. At higher temperature (100° C.), although all the samples 25 polymer composite embedded with stimuli-responsive fibres. Journal of The Royal Society Interface, 2012. 9(77): have entered the rubbery state, it is still clear that Sample#3 p. 3279-3287; Fu, S.-Y, B. Lauke, E. Mader, C.-Y. Yue and has slightly higher damping property. X. Hu, Tensile properties of short-glass-fiber- and short- According to the above analysis, the influence of the carbon-fiber-reinforced polypropylene composites. Com- programming procedures on damping properties were 30 posites Part A: Applied Science and Manufacturing, 2000. embedded in two aspects: first, decrease (Sample#2) or 31(10): p. 1117-1125] increase (Sample#3) the overall value of loss tangent; sec- 3.4.2 Super-Contraction Forces ond, shift the glass transition temperature to a lower In Section 3.2.3, fully constrained stress recovery tests (Sample#2) or higher (Sample#3) value. In FIG. 56, these were used to characterize the shape memory properties of two changes have been visualized in the tan 6 vs. tempera- 35 SMPU fibers. If the programmed fiber is kept at high ture curves, and the differences were explained schemati- temperature and allowed to deform freely, it will undergo cally. super-contraction and shrink to about half of its original 3.4 Comparison with Spider Silk length. Spider dragline silks also possess similar feature: As stated above, it is set forth that SMPU fiber of the 40 when the humidity is above 60%, unrestrained silk shrinks invention has similar properties to spider silk. In the fol- up to 50% of its original length while constrained fibers, lowing subsections, comparisons of SMPU fiber with spider such as in webs, generate substantial forces during super- silk in various aspects are set forth. contraction. In this invention, SNIP fibers are used in poly- 3.4.1 Mechanical Properties mer composite, i.e., here they are protected by polymer, so that water/moisture is not a problem. For the case of outdoor The mechanical properties of dragline silk of several 45 different species have been investigated in the literature. cables, One may simply add an art-accepted water-proof or Most spider silks have an outstanding combination of water-resistance coating so that the fibers are protected. strength and extensibility, which yields a very high tough- [Work, R. W., A comparative study of the supercontraction ness (the amount of energy absorbed per volume before of major ampullate silk fibers of orb-web-building spiders breakage) that exceeds most natural or man-made fibers. A 50 (Araneae). Journal of Arachnology, 1981: p. 299-308; comparison in mechanical properties, including strength, Guinea, G., M. Elices, J. Perez-Rigueiro and G. Plaza, extensibility and toughness of the SMPU fiber with spider Self-tightening of spider silk fibers induced by moisture. dragline silk and other common structural materials are Polymer, 2003. 44(19): p. 5785-5788]. Water absorbed given in Table 4 below during super-contraction is hypothesized to plasticize silk 55 fibers by disrupting hydrogen bonding between proteins, The strength of the SMPU fiber is close to, but still lower thus allowing an entropy-driven re-orientation and coiling of than that of the spider silk. However, due to its excellent silk molecules [Jelinski, L. W., A. Blye, O. Liivak, C. extensibility, SMPU fiber has the highest toughness among Michal, G. LaVerde, A. Seidel, N. Shah and Z. Yang, these materials. In other words, it can absorb the highest Orientation, structure, wet-spinning, and molecular basis for amount of energy before fracture. 60 supercontraction of spider dragline silk. International jour- One thing which should be mentioned is the incredibly nal of biological macromolecules, 1999. 24(2): p. 197-201; thin diameter of spider silk. The thickest silk fibers are only Agnarsson, L, C. Boutry, S.-C. Wong, A. Baji, A. Dhino- 5-10 µm in diameter and some can be as fine as 50 nm in jwala, A. T. Sensenig and T. A. Blackledge, Supercontrac- diameter [53]. As is well known, smaller diameter means tion forces in spider dragline silk depend on hydration rate. higher molecular orientation and less defects. Compared to 65 Zoology, 2009. 112(5): p. 325-331; Savage, K. N., P. A. our SMPU fiber, the small diameter of spider silk is thus one Guerette and J. M. Gosline, Supercontraction stress in spider of the reasons for its high strength and stiffness. webs. Biomacromolecules, 2004. 5(3): p. 675-679]. US 9,428,647 B2 85 86 Compared to SMPU fiber, spider dragline silk can gen- kinetically free oligopeptide chains rich in glycine, provides erate remarkably higher super-contraction stresses, ranging the fiber with outstanding extensibility. Also, the friction and from 10 MPa to 140 MPa. The variation in the reported resistance among the entangled molecular chains can dissi- super-contraction stresses depends on the type of spiders, pate the input energy efficiently and thus give the material an spinning conditions and environmental factors, such as, 5 extraordinary damping property. It is believed that water can hydration rate [in addition to citations immediately above, prevent the formation of the hydrogen bonds between the also see: Guinea, G., M. Elices, J. Perez-Rigueiro and G. molecular chains. Hence, the H-bond can be interpreted as Plaza, Self-tightening of spider silk fibers induced by mois- a switch that is responsible for the molecular mobility during ture. Polymer, 2003. 44(19): p. 5785-5788; Blackledge, T. the super contraction procedure. [see, e.g., Example 3; Li, to A., C. Boutry, S.-C. Wong,A. Baji, A. Dhinojwala, V. Sahni G., H. Meng and J. Hu, Healable thermoset polymer com- and I. Agnarsson, How super is supercontraction? Persistent posite embedded with stimuli-responsive fibres. Journal of versus cyclic responses to humidity in spider dragline silk. The Royal Society Interface, 2012. 9(77): p. 3279-3287; Journal of Experimental Biology, 2009. 212(13): p. 1981- Termonia, Y., Molecular modeling of spider silk elasticity. 1989]. 15 Macromolecules, 1994. 27(25): p. 7378-7381] 3.4.3 Damping Properties Table 5 provides a damping property comparison of Microstructure of SMPU fiber is similar to that of spider SMPU fiber with spider dragline silk, and some other silk [see e.g., FIG. 8 above and related text; Li, G., H. Meng representative materials. According to the data provided, and J. Hu, Healable thermoset polymer composite embedded SMPU fiber has a very high damping capability comparable with stimuli-responsive fibres. Journal of The Royal Society to or even higher than that of spider silks and at the same 20 Interface, 2012. 9(77): p. 3279-3287]. The hard phase of the time possesses a fairly high storage modulus. Moreover, as SMPU fiber ensures the high local stiffness and acts as the demonstrated above, the simple programming procedures net-points to retain the stable permanent shape; after pro- can not only change the glass transition temperature and the gramming, the soft phase mainly contains soft segments and mechanical properties, provide the material with shape short hard segments, gives its outstanding extensibility. The memory function, but also improve the damping capability. 25 restriction among entangled soft and hard segments and the All these features exemplify the utility and value of this highly oriented chains act as the source of damping. Heating material in commercial and academic applications. up can increase the molecular mobility of the oriented molecular chains and makes them recoil and finally bring the TABLE 5 30 fiber back to its original shape. Therefore, the fiber has the shape memory effect. Dynamic mechanical properties of materials 4. Conclusions Material tans Storage modulus (GPa) Based on this Example the following conclusions are Spider dragline silk* 0.15 10 made: SMPU fibers 0.1-0.35 2.5 35 Cement paste (plain)* 0.016 13.7 (1) Similar to spider silk, SMPU fiber of the invention Mortar with silica fume 0.021 13.11 possesses high damping ability, and at the same time has a (treated)* fairly high strength and toughness. In addition, the polymer Aluminum (pure)* 0.019 51 Zn At* 0.021 74 fiber has shape memory effect, and after tension program- Polycarbonate* 0.008-0.013 2-3 40 ming, has super-contraction upon heating, similar to mois- Neoprene rubber* 0.67 0.0075 ture triggered spider silk. These similarities between spider silk and SMPU fiber are determined by their commonalities In Table 5, data designated (*) are obtained from pub- in microstructure. lished literature [Blackledge, T. A., J. E. Swindeman and C. (2)Programming the SMPU fiber can alter its mechanical Y. Hayashi, Quasistatic and continuous dynamic character- 45 and thermal properties. After programming, stiffness and ization of the mechanical properties of silk from the cobweb strength can be increased while extensibility is decreased. of the black widow spider Latrodectus hesperus. Journal of Programming at high temperature (Sample#2) lowers glass Experimental Biology, 2005. 208(10): p. 1937-1949; Chung, transition temperature and the overall damping ability. On D., Review: Materials for vibration damping. Journal of the contrary, programming at low temperature (Sample#3) Materials Science, 2001.36(24): p. 5733-5737]. No standard 50 increases the glass transition temperature and increases deviation is available in the publications. damping ability. 3.4.4 Microstructure (3) The shape memory property is characterized by the The above data show features shared between SMPU fiber fully constrained recovery stress. Different programming and spider silk. These similarities between spider silk and procedures result in different recovery behaviors. The cold- SMPU fiber are determined by their resemblances in micro- 55 drawn fiber (Sample#3) can generate higher stabilized structure. stress, with is desirable in self-healing applications. As stated above, spider dragline silk is a semicrystalline material made of amorphous flexible chains reinforced by Considering the increased damping capability, which is strong and stiff crystals. In spider silk, the amorphous chains useful in controlling vibration, and the increased stabilized are also linked together through hydrogen bonds (see FIG. 60 recovery stress, which helps provide the sustained crack- 8 above and related text). The crystals, made of hydrophobic closure force in self-healing applications, together with its polyalanine sequences arranged into hydrogen-bonded beta- time and energy efficiency process, cold-drawing program- pleats, produce thin regions of locally high modulus, leading ming of the SMPU fibers is used to great effect in structural to the enormous stiffness of the overall material. Due to its applications. mechanical stability, the crystals also act as net-points to 65 All documents, including patents or published applica- keep the permanent shape during the super contraction tions, cited or relied on for priority in this application are procedure. The highly entangled amorphous phase, made of fully incorporated by reference herein. US 9,428,647 B2 87 88 The invention claimed is: 1. A composition comprising: a matrix of thermoset polymer; programmed fibrous shape memory polymer which com- prises the ability to contract when heated to above its 5 shape recovery temperature; and, means for healing at a molecular scale dispersed through- out said matrix. 2. The composite of claim 1, wherein the shape memory polymer is a polyurethane shape memory polymer. 10 3. The composition of claim 1 wherein the fibrous shape memory polymer fiber is coated by a fixing agent. 4. The composition of claim 3 wherein the fixing agent comprises an epoxy supportive coating, and a protective coating applied prior to the epoxy coating which protects the 15 shape memory polymer from chemicals used for the epoxy coating. 5. The composite of claim 1 wherein the fibrous shape memory polymer is in segments of at least the critical fiber length. 20 6. The composite of claim 1 wherein the fibrous shape memory polymer is woven or is formed as a cable. 7. The composition of claim 1 wherein the means for healing at a molecular scale is thermoplastic polymer. 8. The composition of claim 7 wherein the thermoplastic 25 polymer is 40% or less of the volume of the composition.