Crystallization behaviour of PHBV/WS2 inorganic nanotube nanocomposites

aTyler Silverman, aMohammed Naffakh, bCarlos Marco and bGary Ellis

aETSI Industriales, UPM ([email protected]) bInstituto de Ciencia y Tecnología de Polímeros (ICTP-CSIC)

cooling (10ºC/min) GO 5 Abstract C60 (5 wt.%) 26 SWCNT (5 wt.%) 4 Using disulphide inorganic nanotubes (INT-WS ) in organic- MWCNT (0.08 wt.%) 12 2 INT-WS2 21 PLLA inorganic hybrid composite materials provide the potential for improving BN 25 Talc (5 wt.%) 21 thermal, mechanical, and tribological properties of conventional Tb2O3 10 La2o3 10 composites [1]. Recent results have raised new expectations, since it has CNF 1 HNT (3 wt.%) 1 been observed that well-dispersed INT-WS2 exhibit a much more MWCNT 21 PHBV prominent nucleation activity, improving the overall crystallization process INT-WS2 24 BN 32 Thyamine 28 of poly(L-lactic acid) (PLLA) and poly(3-hydroxybutyrate) (PHB) than specific α-CD 18 Melamine 16 nucleating agents or other reported nano-sized fillers, such as carbon Lignine 12 nanotubes and graphene [2,3]. Similarly, good dispersion and interfacial Talc 10 MWCNT 6 PHB GO 9 adhesion of INT-WS2 in a poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) INT-WS2 36 matrix significantly influence the crystallizability of PHBV. These features 0 5 10 15 20 25 30 35 40 D º may be advantageous for the enhancement of the mechanical properties Tp ( C) and processability of this new class of WS2-based composite materials. Figure 2. Increment in the ΔTp of PHB and PHBV systems containing different kinds of fillers. Results and discussion The major issue in expanding commercial opportunities for PLLA, PHB and related materials (PHBV) is their crystallization behavior.

Incorporating well-dispersed like INT-WS2 into biopolymer G=1/ can modify the crystallization behavior. Therefore, it is of great interest to 0.5 σ (erg cm-2)  : Time e 0.5 = investigate the nucleation, crystallization, and structural development of required to the matrix in INT-reinforced biopolymer materials. In this regard, the non- 74.9 reach 50% 56.6 isothermal melt-crystallization of neat PHBV and its nanocomposites crystallinity 70.5 obtained with different INTs loadings, using a simple solution blending 58.1 method, was investigated by DSC using a Perkin Elmer DSC7/Pyris differential scanning calorimeter. The results of revealed that the incorporation of INT-WS2 in small weight percents (1.0 wt.%) dramatically accelerated the crystallization rate compared to the pure biopolymer Figure 3. Variation of the rate of crystallization of PHBV/INT-WS (Figure 1). Nevertheless, for the same nanofiller loading, the improvements 2 nanocomposites as a function of the crystallization temperature (Tc). in crystallization temperature peak (Tp) for the PHBV(PLLA)-based samples are lower than those observed for the corresponding binary PHB-INT In the same way, the isothermal crystallization behaviours and kinetics of neat PHBV and its nanocomposites were intensively studied. It was found nanocomposites (Figure 2). In particular, incorporating 1.0 wt.% INT-WS2 that the overall crystallization rates were reduced with an increase in the effectively increased the Tp of PHBV to a value comparable to that of BN, and greater than all other NAs. BN is currently estimated to be more crystallization temperatures for both neat PHBV and PHBV/INT-WS2 nanocomposites. Moreover, at a given crystallization temperature (T ), the expensive than INT-WS2 and, like talc, is not a filler, also c possibly leading to deficient mechanical reinforcement qualities that are overall crystallization rates were faster in the nanocomposites than in neat observed with other nano-sized filler materials. PHBV and increased further with an increase in the INT-WS2 loading (Figure 3). The addition of INT-WS2 remarkably influences the energetics and 20 PHB kinetics of nucleation and growth of PHBV, reducing the fold surface free 0 0.1 wt.% INT-WS2 energy (σe) by up to 25.4 %. 0.5 wt.% INT-WS2 -20 1.0 wt.% INT-WS2 -40 Conclusions PHBV -60 1 wt.% INT SEM The results obtained from the DSC crystallization experiments, along with 0.1 wt.% INT-WS -80 2 the good materials processability, economic and sustainability benefits,

dQ/dT (a.u.) dQ/dT Endo Tp 0.5 wt.% INT-WS2 -100 encourage further investigations in order to evaluate the full potential of 1.0 wt.% INT-WS 2 these new bionanocomposites for their potential use in eco-friendly and -120 cooling (10ºC/min) medical applications. -140 40 60 80 100 120 140 160 T (ºC) Acknowlegments 150 This work was supported by the Spanish Ministry Economy and Competitivity (MINECO), Project MAT2013-41021-P. MN would also like to 130 acknowledge the MINECO for a ‘Ramón y Cajal’ Senior Research Fellowship. 110

(ºC) References

p PHB T 90 0.1 wt.% INT-WS2 1. M. Naffakh, A. M. Díez-Pascual, Thermoplastic polymer nanocomposites based 0.5 wt.% INT-WS2 1.0 wt.% INT-WS2 on inorganic -like nanoparticles and inorganic nanotubes. Inorganics 70 PHBV 0.1 wt.% INT-WS2 2014, 2, 291-312. 0.5 wt.% INT-WS2 2. M. Naffakh, C. Marco, G. Ellis. Inorganic WS Nanotubes that improve the 50 1.0 wt.% INT-WS2 2 0 5 10 15 20 25 crystallization behavior of poly(3-hydroxybutyrate). CrystEngComm 2014, 16, f (ºC/min) 1126-1135. 3. M. Naffakh, C. Marco, G. Ellis. Development of novel melt-processable Figure 1. DSC data of the dynamic crystallization of biopolymer/INT-WS2 nanocomposites. biopolymer nanocomposites based on poly(L-lactic acid) and WS2 inorganic nanotubes. CrystEngComm 2014, 16, 5062-5072.