Cold Crystallization Of PLA Research Articles

Fabrication of high-expansion microcellular PLA foams based on pre-isothermal cold crystallization and supercritical CO2 foaming

Poly(lactic acid) (PLA) is a kind of bio-based and biodegradable polymers. PLA foams with high expansion ratio have great application potential in heat insulation, adsorption and other areas. However, due to its low melt strength and slow crystallization rate, linear PLA has poor foaming ability, so it is hard to prepare PLA foams with high expansion ratio. Although chain branching, blending, and other methods have been utilized to improve PLA's melt strength and foaming ability, they easily destroy PLA's biodegradability, cause chemical pollution, and raise production costs. In this study, a new supercritical fluid foaming process, based on pre-isothermal cold crystallization, was proposed to prepare PLA foams with high expansion ratio. To improve PLA's melt strength and foaming ability, a pre-isothermal treatment was applied to induce sufficient cold crystallization. According to the SEM results, the cold crystallization of PLA becomes more sufficient and the crystal morphology becomes more perfect with the pre-isothermal treating. The DSC and WAXD results confirm that, the pre-isothermal treatment remarkably promotes the PLA's cold crystallization, and endows the PLA sample higher crystallinity and more perfect crystalline structure. Moreover, the high-pressure rheology testing results indicate that the pre-isothermal treatment improves the PLA's melt viscoelasticity significantly. Finally, the foaming results show that the pre-isothermal treatment significantly enhances the PLA's foaming ability. With the pre-isothermal treatment, the PLA's maximum expansion ratio increases from 6.40-fold to 17.7-fold, and the uniformity of cellular structure is also improved obviously. The new process provides a green, flexible, and low-cost way to prepare fully biodegradable PLA foams with high expansion ratio.

Valorisation of macroalgae industrial by-product as filler in thermoplastic polymer composites

Poly(lactic acid) composites filled with algae industrial by-product were prepared using melt-mixing process at filler weight fractions of 20, 30 and 40wt%. Algae by-products were after the extraction of alginate (AW) and mixed with diatomaceous earth (DE). The composition and morphology of both fillers were analysed. Composites’ mechanical properties and thermal degradation were investigated as a function of filler type and content. The addition of DE-filler at 40wt% resulted in the increase of Young’s modulus by 20% compared to the neat PLA. The presence of small DE particles improved stress distribution and led to stronger composites as compared with AW-filled. Cold crystallization of PLA was induced by small algae particles. Thermal degradation of all composites started at lower temperatures compared with neat PLA. A glow-wire test was carried out to evaluate the effect of inorganic matter on the ignition of the material.

Crystallization of poly(ε-caprolactone) in its immiscible blend with polylactide: insight into the role of annealing histories

Cold crystallization of PLA can improve its affinity to PCL in their blends, and crystallized PLA domains have better nucleation effect to PCL crystallization relative to amorphous PLA ones.

Effect of Chain-Extenders on the Properties and Hydrolytic Degradation Behavior of the Poly(lactide)/ Poly(butylene adipate-co-terephthalate) Blends

Biodegradable poly(lactide)/poly(butylene adipate-co-terephthalate) (PLA/PBAT) blends were prepared by reactive blending in the presence of chain-extenders. Two chain-extenders with multi-epoxy groups were studied. The effect of chain-extenders on the morphology, mechanical properties, thermal behavior, and hydrolytic degradation of the blends was investigated. The compatibility between the PLA and PBAT was significantly improved by in situ formation of PLA-co-PBAT copolymers in the presence of the chain-extenders, results in an enhanced ductility of the blends, e.g., the elongation at break was increased to 500% without any decrease in the tensile strength. The differential scanning calorimeter (DSC) results reveal that cold crystallization of PLA was enhanced due to heterogeneous nucleation effect of the in situ compatibilized PBAT domains. As known before, PLA is sensitive to hydrolysis and in the presence of PBAT and the chain-extenders, the hydrolytic degradation of the blend was evident. A three-stage hydrolysis mechanism for the system is proposed based on a study of weight loss and molecular weight reduction of the samples and the pH variation of the degradation medium.

Crystallization and biodegradation of polylactide/carbon nanotube composites

AbstractThe crystallization behavior of polylactide/carbon nanotube composites was studied using differential scanning calorimeter and polarized optical microscope. The nucleation mechanisms and the crystallization kinetics were explored. The results show that the presence of nanotubes has nucleating effect on both the melt crystallization and the cold crystallization of PLA. However, the nanotubes also play the role of physical barrier, impeding the crystal growth dynamically. In the experimental range of temperatures, the presence of nanotubes accelerates the melt crystallization, while retards the overall kinetics of the cold crystallization. The biodegradability of the samples with various crystallization histories was then further examined. The results show that the presence of nanotubes reduces the biodegradation rate of PLA, and the amorphous sample shows the highest degradation levels. Moreover, a lower degradation level is observed both on the surface and inside the sample with melt crystallization history in contrast to the one with cold crystallization history. POLYM. ENG. SCI., 50:1721–1733, 2010. © 2010 Society of Plastics Engineers

Influence of thermal history on the nonisothermal crystallization of poly(L‐lactide)

AbstractThe effect of thermal history on the nonisothermal crystallization of poly(L‐lactide) (PLA) was studied. The cold crystallization of PLA by heating from the glassy state was dominated by the heating rate. However, the temperature to which PLA was cooled before crystallization markedly affected the crystallization kinetics. The lower the temperature was to which PLA was cooled, the lower the nonisothermal crystallization peak temperature was and the larger the crystallization enthalpy was, which indicated enhanced nucleation of spherulites. Fast heating from the glassy state reduced the time available for the growth of spherulites and also suppressed the number of nuclei stable at elevated temperatures by limiting the recrystallization of nuclei formed at low temperatures and their overgrowth by thicker and more perfect crystals. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 282–290, 2007