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Poly(lactic acid) (PLA) is a well-known sustainable plastic but with an inherent brittleness, slow crystallization rate, and poor heat resistance, which significantly limits its application. In thi...

Non-isothermal and isothermal crystallization of polylactic acid/poly(D-lactic) acid blends with various molecular weights have been investigated. Formation of polylactic acid stereocomplex crystal between L-lactic acid segments and D-lactic acid segments in the blends was confirmed by the differential scanning calorimetry and X-ray diffraction. The non-isothermal crystallization kinetics of polylactic acid and the blends was studied and analyzed by Kissinger equation. The crystallization temperature was found to depend on the content and molecular weight of poly(D-lactic) acid. Higher content and lower molecular weight of poly(D-lactic) acid have a more pronounced effect on improving crystallization temperature of the blends and effectively reduce the crystallization activation energy of the blends. Isothermal crystallization kinetics of polylactic acid and the blends was also investigated at various temperatures and analyzed by Avrami equation.

Crystallization behavior and morphology of PLA blended with 0.05–1.00 wt % loadings of poly(D-lactic acid) (PDLA) forming stereocomplex crystallites as in-situ nucleating agents, were studied using wideangle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and polarizing-light optical microscopy (POM). Blending PLA with small amount of PDLA does lead to formation of PLA stereocomplex (SC), although the PLA is a random copolymer. The in-situ formed SC crystal acted as nucleation sites in blends and accelerated the crystallization of PLA by decreasing the half-time (t1/2). The nucleation efficiency of PDLA obviously increased and the crystallization induction time decreased while the content of PDLA reached up to 0.20 wt %. While the content of PDLA is 0.2 wt %, the nucleation efficiency of PDLA is up to 43.8%, and the induction time decreased from 430 to 88 s. In addition, compared with pure PLA, t1/2 decreases from 15.1 to 3.5 min at Tc = 127.5°C while the amount PDLA is 1.0 wt %. The equilibrium melting temperature of PLA decreased from 187.2 to 181.2°C with the increase of PDLA content.

Poly(butylene succinate-co-butylene dimerized fatty acid) (P(BS-co-BDFA)) copolyesters were synthesized from succinic acid (SA) and dimerized fatty acid (DFA) with 1,4-butanediol (BDO) through a two-step process of esterification and polycondensation. The polyester compositions and physical properties of copolyesters were investigated by GPC, 1H NMR and 13C NMR, DSC, WAXD, DMA, TGA, tensile and rheology test. The melting temperature (T m), and crystallization temperature (T c) decreased gradually as the content of DFA monomer increased. P(BS-co-BDFA) copolyesters showed the same crystal structure as the PBS homopolyester. Besides, TGA results indicated that P(BS-co-BDFA)s were of higher thermal stabilities. Moreover, it was found that the synthesized P(BS-co-BDFA)s showed the maximum elongation at break (591%) as the DFA contents were 10 mol%. Rheology analysis indicated that the viscoelastic behavior of the polyesters greatly depended on the molecular weight of polyesters.

The poly(lactic acid) (PLA)/montmorillonite (MMT) composites were prepared by melt blending in an internal mixer. The effect of MMT and organically modified MMT (OMMT) addition on crystallization and mechanical preferences has been studied. The DSC results show that the crystallization ability of PLA is improved by MMT or OMMT. The addition of MMT and OMMT increase the crystallinity of PLA from 27.3 to 32.8%, and the cold crystallization temperature (TCC) of PLA decreases from 93.1 to 88.9°C with the MMT. However, the nucleating effect of MMT is better than that of OMMT due to the velvety surface resulted from the organic modification. The average size of the spherulites in PLA/MMT is smaller than that in PLA/OMMT. The addition of MMT or OMMT increases the tensile strength of PLA from 29.6 to 34.7 MPa and decrease the elongation at break of PLA. The modulus of PLA composites is enhanced rapidly from 338 to 660 MPa by the addition of MMT.

To improve the crystallization ability of poly(lactic acid) (PLA), a novel nucleating agent with a benzoyl hydrazine compound was used in this study. The crystallization behaviors of PLA/talc and PLA/bibenzoylhydrazinepropane (BBP) with or without poly(ethylene glycol) (PEG) were investigated with differential scanning calorimetry (DSC) and polarized optical microscopy. The DSC curves showed that the crystallization temperature and crystallinity of PLA/BBP (PBBP) was higher than that of PLA/talc. With the addition of PEG, a synergistic effect was found. According to the results of nonisothermal crystallization kinetics, the values of F(T) of PBBP0.5PEG5 were usually smaller than those of PTa3PEG5, so the nucleation efficiency of BBP was much better than that of talc. From a polarized optical microscopy photo, it was easy to determine that the nucleation density of BBP was higher than that of PTa3PEG5, and the spherulitic diameter increased linearly with the crystallization time no matter the impingements. The spherulitic growth rate of PBBP0.5PEG5 was faster than that of PTa3PEG5, and the induction time of PBBP0.5PEG5 was the shortest among all of the samples. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41367.