No abstract

Layered double hydroxide‐poly(methylmethacrylate) (LDH‐PMMA) graft copolymers were prepared via activators regenerated by electron transfer for atom transfer radical polymerization. The results showed that the hydrophobicity of LDH‐PMMA was improved by the incorporation of hydrophilic groups. Moreover, poly(lactic acid) (PLA)/LDH‐PMMA nanocomposites were prepared by melt blending to enhance the performances of PLA. The crystallization and mechanical properties of the PLA/LDH‐PMMA nanocomposites were studied by differential scanning calorimetry, tensile testing, and polarized optical microscopy, respectively. Results of mechanical testing showed that the tensile strength, elongation at break, and impact strength of PLA/LDH‐PMMA nanocomposites were increased by 5.64%, 37.95%, and 49.70%, respectively, compared with PLA. The differential scanning calorimetry results indicated that LDH‐PMMA eliminated the cold crystallization of PLA matrix and improved the crystallinity of PLA by 37.26%. The polarized optical microscopy of PLA/LDH‐PMMA nanocomposites demonstrated that LDH‐PMMA increased the crystallization rate of PLA. It was also found that the rheological behaviors of the PLA nanocomposites were significantly enhanced. Based on these results, a new choice for modified LDHs was provided and used as a nucleating agent to improve the properties of PLA.

Poly(D-lactic acid) (PDLA) was prepared from D-lactic acid under optimized polymerization conditions of 1 wt% stannous octoate, at 170°C for 12 hr. Poly(L-lactic acid) (PLLA) and its optical isomer, PDLA, were blended to improve the thermal and mechanical properties. Mechanical testing showed an increase in the impact strength of the PLLA/PDLA (0.3 wt%) by 27.6%. SEM showed more shear zones and fibrillation on the composite surfaces, compared withthe PLLA, suggesting high toughness and shock strength. TGA showed the enhanced thermal stability of PLLA composites. The DSC results indicated that the crystallinity of PLLA/PDLA (0.3 wt%) was increased by 54.31%, compared with pure PLLA. Non-isothermal crystallization kinetics suggested the formation of crystal nucleus and the growth rate of PLLA/PDLA (0.3 wt%) increased gradually. Half crystallization time showed a decreasing trend, which could provide a large number of heterogeneous nucleation sites and improved the crystallization rate of PLLA. K E Y W O R D S crystallization kinetics, poly(D-lactic acid), poly(L-lactic acid), toughness

The chain-extended poly(D-lactide) (PDLA) was prepared from D-lactide under optimum polymerization conditions of 1 wt% stannous octoate, at 170 o C, 10 rpm for 15 min or 10 min with the addition of chain extender (4,4'diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI)) by reactive extrusion process. The molecular weight of PDLA-MDI and PDLA-HDI was 45376 and 47238 g/mol, respectively, which had been significantly improved compared with PDLA (M w =20730 g/mol). Furthermore, differential scanning calorimetry (DSC) results showed that the crystallinity of PDLA-MDI and PDLA-HDI was increased by 66.04 and 78.60%, respectively, compared with PDLA. Moreover, the rheological results and thermal decomposition kinetics results showed that the MDI and HDI had restricted the mobility of PDLA chains and enhanced the apparent activation energy (E a) of thermal degradation of PDLA.

No abstract