The Role of Interchain Force and/or Chain Entanglement in the Melt Strength and Ductility of PLA-Based Materials

As an eco-friendly material, PLA was a desirable alternative to polyethylene and polypropylene films due to its biodegradability. The preferable melt strength of PLA-based materials was a key factor in ensuring its processing using extrusion blow. This paper focuses on the influence of interchain force and/or chain entanglement on the melt strength and ductility of PLA-based materials in recent years. In addition, the preparation of PLA-based materials via physical blending or reactive processing was also summarized. The blending of PLA with a flexible heteropolymer, driven by the interchain force and/or chain entanglements, were characterized as a practicable method for toughening PLA-based materials. Also, the restructuring of PLA chains, by branching based on chain entanglement, was suitable for increasing chain entanglements in PLA matrix, yielding satisfactory melt strength and ductility. This review aims to elucidate the relationship between interchain forces and/or entanglement with the melt strength and ductility of PLA-based materials. An essential and systematic understanding of the tailoring melt strength and rheological properties of PLA by interchain forces and/or entanglement was apt to improve and perfect the processing technology of the extrusion blow, and consequently improve the tensile strength and toughness of PLA films.

PEG-Grafted Graphene/PLLA Nanocomposites: Effect of PEG Chain Length on Crystallization Kinetics of PLLA

Poly-l-lactic acid (PLLA) nanocomposites containing graphene oxide (GO), modified with different chain lengths of poly(ethylene glycol) (PEG) (400, 2000, and 10 000 g/mol), were prepared by solution casting. The effect of the PEG chain length and nanoparticle content (0.5, 1, and 1.5 wt %) on the nucleation, crystal growth rate, and overall crystallization rate, under isothermal conditions, was then evaluated. The results showed that, in samples containing GO modified with 400 g/mol of PEG, the nucleation density increased as a function of a modified nanoparticle concentration. In the case of the samples containing GO modified with PEG of a molar mass of either 2000 or 10 000 g/mol, the nucleation density exhibited a maximum at a concentration of 1 wt %. Furthermore, the addition of graphene oxide modified with poly(ethylene glycol) of a molar mass of 2000 g/mol resulted in the largest nucleation, fastest crystal growth, and highest overall crystallization rate, for all concentrations. The results were explained in light of the steric hindrance between the modified nanoparticles.

Recent progress of preparation of branched poly(lactic acid) and its application in the modification of polylactic acid materials

Poly (lactic acid) (PLA) with branched structure has abundant terminal groups, high melt strength, good rheological properties, and excellent processability; it is a new research and application direction of PLA materials. This study mainly summarizes the molecular structure design, preparation methods, basic properties of branched PLA, and its application in modified PLA materials. The structure and properties of branched PLA prepared by ring-opening polymerization of monomer, functional group polycondensation, and chain extender in the processing process were introduced. The research progress of in situ formation of branched PLA by initiators, multifunctional monomers/additives through dynamic vulcanization, and irradiation induction was described. The effect of branched PLA on the structure and properties of linear PLA materials was analyzed. The role of branched PLA in improving the crystallization behavior, phase morphology, foaming properties, and mechanical properties of linear PLA materials was discussed. At the same time, its research progress in biomedicine and tissue engineering was analyzed. Branched PLA has excellent compatibility with PLA, which has important research value in regulating the structure and properties of PLA materials.

Isothermal Crystallization Kinetics of Poly(ethylene oxide)/Poly(ethylene glycol)-g-silica Nanocomposites

In this work, the crystallization kinetics of poly(ethylene oxide) (PEO) matrix included with poly(ethylene glycol) (PEG) grafted silica (PEG-g-SiO2) nanoparticles and bare SiO2 were systematically investigated by differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM) method. PEG-g-SiO2 can significantly increase the crystallinity and crystallization temperature of PEO matrix under the non-isothermal crystallization process. Pronounced effects of PEG-g-SiO2 on the crystalline morphology and crystallization rate of PEO were further characterized by employing spherulitic morphological observation and isothermal crystallization kinetics analysis. In contrast to the bare SiO2, PEG-g-SiO2 can be well dispersed in PEO matrix at low P/N (P: Molecular weight of matrix chains, N: Molecular weight of grafted chains), which is a key factor to enhance the primary nucleation rate. In particular, we found that the addition of PEG-g-SiO2 slows the spherulitic growth fronts compared to the neat PEO. It is speculated that the interfacial structure of the grafted PEG plays a key role in the formation of nuclei sites, thus ultimately determines the crystallization behavior of PEO PNCs and enhances the overall crystallization rate of the PEO nanocomposites.

Correlation between molecular weight and confined crystallization behavior of polymers grafted onto a zero-dimensional filler

In this work, polymer chains of different molecular weights are grafted onto a zero-dimensional filler.