Indian Journal of Fibre & Textile Research Vol. 27, September 2002, pp. 290-306 Review Articles Aramid fibres - An overview M Jass:tI " & S Ghosh Department of Textil e Techno logy, Indian In st itute o f Tcchnology, New Delhi 11 0016, In dia Received 16 lilly 2001; accepted 24 Septelllber 2001 The hi story, preparati on and structure of aramids in ge neral and of Nomex and Kevlar aramid fi bres in particul ar arc discussed. T he structure-property correlation and th e applicati on areas of these fibres arc reviewed. Aramid fibres arc characteri zed by their superior thermal propert ies, resistance to chemi cals and out standing mechani cal propert ies. Keywords: Aramid fibre, Aromati c polyami dcs, Kevlar, Liquid crystalline spinning, Nomex, Technora 1 Introduction aramid fibres, giving emphas is on th eir structure­ The first organic fibre with hi gh enough tensil e property correlations and th eir di fferent outstandin g modulus and strength to be used as reinforcement in applications. adva nced compos ites was an aromati c polyamide The hi story of development of aramid fibres is fibre or aramid fibre. As aramids have 5-10% hi gher given in Tabl e I. It took a long time to fi gure out how mechani cal properti es th an oth er syntheti c fibres, to make an ything useful out of arami d fibres becau se these are di spl ac ing metal wires and inorganic fibres it would not di ssolve in anythin g. Therefo re, fro m the market of hi gh performance uses like vari ous processing it as a soluti on was not poss ibl e. It struc tural compos ites fo r applicati on in aircraft, wouldn ' t melt below - 500°C, so melting it down was marine and automobil e, ropes for offs hore oil rigs, out too. The development of aromati c polyamides and bullet proof ves ts. The fibres not onl y have much changed dramati cally in direction wi th the di scovery 5 better mechanical properti es th an steel and glass of lyotropic liquid crystalline aramid s. Kwo lek , a fibres on an eq ual we ight basis , but also maintain DuPont Research Scienti st, prepared the first high th ese properti es at hi gh temperatures as aramid molecul ar weight lyotropi c aramid . He synthes ized polymers are excell ent heat and flame resistant. So, the ri gid chain poly (p-benza mide) in high mo lecu lar they also have wide applicati ons in areas like we ight and with limited crys tallinity to promote the protecti ve cl othing in hostil e environment where heat, di sso lution of thi s seemingly intrac tabl e polymer in chemi cal and radi ati on are present, furni shin g in amide sa lt solve nts. This di scovery all owed the public pl aces as fl ame resistant, industri al filters and development of a novel fibre spin nin g process fo r 6 hollow fibres for desalin ati on by reverse osmosis. The ani sotro pi c solution by Bl ades , res ulting In word 'Aramid' is a generi c term for a manu factured commerci ali zation of Kevl ar. The synthes is of fibre in whi ch the fibre formin g substance is a lon g - numerous aromati c polyamide compos itions and the chain sy ntheti c pol yamide, in which at \east 85% of development of a number of com mercial aramid amide linkages are attached directl y to two aromati c fibres foll owed thi s. In addition to aromati c n ngs, as defin ed by the U.S. Federal Trade pol yamides, aromatic heterocycli c polymers like poly Commission. Therefore, by definiti on, the aramid (p-phenylene benzobi sthi azole) (PB ZT) and poly (p­ famil y will cover Kev lar, Nomex, Techn ora , phenyl ene benzobisoxazole) (PB ZO) also have hi ghl y Teijinconex, Twaron, etc. fibres. In thi s revi ew, an ordered structures in solid 7. 8. DuPont is world 's attempt has been made to present a brief overview of leading producer of aramid fibres, controlling about two-thirds of the market. Teijin Ltd , Japan, is the second largest producer.Others include Rh one­ a To whom all the correspondence should be addressed. Phone: 659 1426; Fax: 009 1-0 11-6858 11 2; Poul ene, France; Toray Indu stri es In c. , Japan; 9 E-mai l: manj eetj assal@holmail. co m Acordi s ; Akzo Nobel NY, Netherl ands. JASSAL& GHOSH: ARAMlD FIBRES 291 Tablc I- Hi story of devclopmcnt of aramid fibre Yc ar Evc nt Produccr Basc polymer 1938 Commcrcializa tion of Nylon 1962 Introduction of Nomcx fibrc DuPont Co., USA MPD-I 1965 Discovcry of ani sotropic polymcr by P.F. Flor/ 1970 Di scovcry of air-gap spinning 197 1 Introduct ion or ribrc-B DuPont Co. , USA (i)PBA (ii )PPD-T 1972 Introducti on of Tcijincorcx Tcijin Ltd, Japan & DuPont Co., USA MPD-I Comm crciali sa ti on of Kev lar Akzo Chcmicals BF, Ncthcrlands PPD-T Introducti on of Twaron Rhonc-Poulenc, Francc PPD-T Introduction of Kcrmcl 2 USSR MPD-I Introduction of Fenilon' MPD-I 1976 Int rod uction of SYM fibrc (formcrl y Yniivlon)3 USS R Polyhctero arylcne 1978 Dcvelopment of arcnka aramid fibrc 1987 Int roduc ti on of HMO-50 (Tcchnora) aramid fibrc Tcijin Ltd, Japan 1988 Commcrcia li sation of Twaron (formcrly Arneka) Toyobo, Japan Introducti on of PBO-HM Toyobo. Japan 1996 Introdu ction of Trevar (discontinucd latcr) Hocchst. Gc rman y 1997 Kcv lar 49 HS by ncw fib rc tcchnology (NFT) DuPont Co., USA 1998 Introduction or Armos4 Russia p-a romatic hydrocyc li c copolya midc MPD-I-Poly(m-p henylcne iso phthalam idc); PBA-Poly(p-bcnzamidc);and PPD-T - Poly(p-phenylcne tcrcphthalamidc) 2 Preparation of Aramid Fibres condensation and solution polycondensation, the 2.1 Synthesis second process is preferred, because in interfacial Ri gid molecul es in solution behave differently polymerization the molecular weight distribution is from fl exible mol ecules. Flexible molecules, in going broad, which is not suitable for preparation of fibres. from dilute to higher concentrations, pack together by In solution polycondensation , the polymerization bending and entanglin g, forming random coils. But medium is an inert solvent for at least one of th e rigid molecules, in going from dilute to higher reactant and solvent or swelling agent for th e pol ymer concentrations, cannot form random coils because (preferably a solvent). The preferred solvents are their movement is restricted. Therefore, at a critical dimethyl acetamide (DMAc), N-methyl-2-pyrrolidone concentration, th ey have transition to a liquid (NMP), hexamethyl phosphoric triamide (HMPA) and crystalline state. In this state, th e molecules are tetramethyl urea (TMU). But no organi c solvent i.. ali gned parallel to each oth er in randomly oriented sufficiently powerful fo r aral11ids to keep the pol ymer domains or aggregates of the rod-like polymer in solution as its mol ecular weight builds up. mo!ecules. Therefore, th e usual methods for the However, by addition of lithium or calcium chloride preparation of aliphatic polyamides are unsuited to the the solvating power of many organic solvents is preparation of hi gh mol ecul ar weight aromatic greatly increased. Typical polymeri zation condi tion s polyamides. Howevcr, two methods are ava ilable for for some commerciall y attractive aramids are given in the preparation of medium to hi gh mol ecular weight Table 2 .The chain confor:nation of different arami ds polymer: is shown in Fi g. I whi Ie the chemical reactions (i) Low-temperature polycondensation (preferably occurring during the sy nthesis are shown in Fig. 2. below SO DC to avoid degradation, side reaction and The Nomex ™ (meta aramid) polymer was crosslinking), and produced using l1l-phenylenediamine and dichloride (ii ) Direct polycondensation in solution using of III-i sophthalic acid . Amorphous heat-resistant phosphites (in presence of metal sa lts). polyamides (copolymers of meta and para aram ids) Among th e two low-temperature polycondensation have been prepared by solution polymeri zation in ,­ methods available, namely interfacial poI- meth yl pyrrolidone (NMP) fro m eq uimol ar amoun ts 292 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2002 Table 2- Polymeri zalion condilions for ccrlain aramids SI.No. Monomer Solvcnl Polymcr llinh p-Phcnylencdiamine HMPA/NMP 95/5 Copoly (p-phenylene lerephlhalamicIc/i sophlhalamide) 4.48 Terephlhaloyl chloridc Isophlhaloyl chl ori de 2 Isophlhaloyl chloridc HMPA/NMP 5/95 Copol y(p-phcny Icnc isophlhalamidcllcrcphlhalamicIe) 3.9 p-Phcnylcncdiaminc Tcrcplllhaloyl chloridc 3 p -Phcny lenediamine HMPA/NMP 90/1 0 Copoly (p-phcnylcnc-p-phcnylcnc diisocyano Icrcphlhalamid c) 1. 83 p-Phcnylcnc dii socyanalc LiCI Tcrcphlhaloyl chloridc HMPA/NMP 95/5 Copolymcr 2.87 LiCI HMPA/NMP 80/20 Copoly mcr 2. 82 LiCI 4 p-Phcnylenediamine HMPA/NMP Copoly (p-phcnylenc)/2, 5-bis - (p -amin ophcnyl)- I, 3, 4- o x~ d iazo 4.48 2, 5-Bis(p-aminophenyl)- LiCI Icrcphthalamidc 1,3,4-oxadiazolc Tcrcphlhaloyl chloridc 5 fl-Phcny Icncdiami nc DMAC/LizCO, 50/50 Copoly (p-phcnylcnc/2-chloro-p -phcnylcnc Icrcphthalamicle) 3.85 2-Chl oro-p­ phenylcncdiaminc Tcrcphlhaloyl chloride HMPA - Hexamclhyl phosphoric lri amidc. DMAC- Dimelhyl acelamidc. NMP- N- mClhyl-2-pyrrolicIonc. The preparation of AB polyamides rpoly (p ­ benzamide)] using acid chloride and amine condensation requires protection of amine group with a labile group, which is removed as th e poly­ meri zation proceeds.