Non-isothermal crystallization kinetics of polypropylene and hyperbranched polyester blends

Composites made of Ginkgo biloba fibers and polylactic acid exhibit non-isothermal crystallization kinetics

Polymer crystallization affects material microstructure and the final product quality, and the crystallization kinetics that govern this process are critical. In this study, alkali-treated Ginkgo biloba fibers (GFs) were melt blended with polylactic acid (PLA) to obtain GF/PLA blends. The non-isothermal crystallization kinetics of the GF/PLA composites were subsequently investigated using the Avrami, Jeziorny, Ozawa, and Liu-Mo methods, and the crystallization activation energies of the systems were calculated by Kissinger and Friedman models. The results showed that the GFs significantly promoted PLA crystallization, accelerated the crystallization rate, and shortened the crystallization time. The Avrami method showed some deviation from the linear relationship due to the effect of secondary crystallization, while the numeric value obtained by the Jeziorny method increased with the cooling rate. The Ozawa method could only be used in a very narrow range of temperatures, while the Liu-Mo method showed a more desirable fit. Crystallization activation energy calculations showed that the GFs promoted an increase in the crystallization capacity of the blend and a decrease in the effective potential barrier. This resulted in more selective biocomposites than pure PLA, offering greater applicability in domains including tissue engineering and 3D printing.

Non-isothermal crystallization kinetics of graphene/PA10T composites

Crystallization kinetics is the key factor in controlling the polymer crystallization process and affecting crystallinity and crystalline morphology, which determine the polymer's main properties. In this work, the non-isothermal crystallization kinetics of graphene/PA10T composites are investigated by the Jeziorny method and Mo method, and the crystallization activation energy is calculated by the Kissinger method. It is found that the addition of an appropriate amount of graphene to PA10T can significantly promote the crystallization of PA10T and accelerate its crystallization rate. The Jeziorny equation does not have a linear relationship across the whole crystallization range, while the Mo equation does a good linear fitting. In addition, the crystallization activation energy decreases when the graphene content is below 1 wt.%. TGA results indicate that the addition of graphene improves the thermal stability of PA10T.

Non-Isothermal Crystallization Behavior and Thermal Properties of Polyethylene Tuned by Polypropylene and Reinforced with Reduced Graphene Oxide

This research work is the first to report thermal stability, heat deformation resistance, and crystallization behavior of a Polyethylene (PE)-based biphasic polyolefin system reinforced with Reduced Graphene Oxide (RGO), which was obtained through Graphene Oxide (GO) chemical reduction. Polypropylene (PP) represented the polymeric dispersed phase. A strategic PE/PP/RGO manufacturing procedure was employed to thermodynamically localize RGO at the PE/PP interface, as confirmed by Transmission Electron Microscopy (TEM), bringing a uniform micro phase dispersion into the macro phase. In addition, studies of PE non-isothermal crystallization kinetics indicated that the morphology tunable micro phase and the nanolayered RGO promoted a nucleation-controlled PE crystallization, which was supported by Polarized Light Optical Microscopy (PLOM). This, together with fine morphology, justified the remarkable enhancement registered for the ternary system’s thermal stability and heat deformation resistance. Different filler loads were employed, with weight fractions of 2% and 4%. It was observed that the former, being better exfoliated and more homogeneously distributed at the PE/PP interface than the latter, led to a more improved PE crystallization, alongside a greater ternary system’s thermal properties. Moreover, the thermal stability of PE/PP reinforced with 2% of RGO was even higher than that of virgin PP, while their heat deformation resistance values were found to be similar. Therefore, this unique outcome provides industries, such as the energy and automotive sectors, with the opportunity to substitute PP-rich products with those mostly comprised of a cheaper, more abundant, yet performant PE.

Morphology and Isothermal Crystallization Kinetics of Polypropylene/Poly(ethylene-co-vinyl alcohol) Blends

Polypropylene (PP)/poly(ethylene-co-vinyl alcohol) (EVOH) blends were prepared by melt blending using PP-g-MAH as a compatabilizer. The microstructure and rheological behavior of PP/EVOH blends were studied. The results showed the that EVOH particles were uniformly dispersed in the PP matrix and inhibited the mobility of PP chains. The isothermal crystallization kinetics and morphology development of PP/EVOH blends were compared with that of pure PP. It was found that the EVOH essentially acted as an effective nucleating agent for PP, which could significantly increase the nucleation rate because the EVOH molecules in PP/EVOH blends aggregated together to form interface. Therefore, the introduction of EVOH increased the overall rate of isothermal crystallization compared with pure PP, although the PP molecular chains would be hindered seriously if excessive amounts of EVOH were added. X-ray diffraction showed that pure PP and PP/EVOH blends exhibited an identical crystal structure, and the crystallinity of the PP phase in the blends was not significantly different from that of pure PP.