Regulation of Entanglement Networks under Different Shear Fields and Its Effect on the Properties of Poly(l-lactide)

Abstract

Entanglement will lead to a sharp increase in viscosity and a decrease in flowability of polymers and affect their crystallization behavior adversely. Thus, it seems that disentanglement becomes a feasible way to improve the flowability and crystallization ability of polymers without adding other substances. Poly(l-lactide) (PLLA), as a renewable polymer material, has attracted increasing attention in the past decades. Accelerating crystallization of PLLA is extremely important to improve its performance. The present study utilizes a self-designed polymer melt disentanglement machine (PMDM) with PLLA as the experimental material, which can effectively promote polymer disentanglement by applying a unique complex shear field (superposition of rotational and vibrational shear fields) to a polymer melt. The experimental results show that compared with the untreated material, the disentangled ones have a lower viscosity and a higher melt flow rate and can fill the mold cavity at a lower pressure and a lower melt or mold temperature during the injection molding process. Simultaneously, the crystallization kinetics of the disentangled materials is accelerated, the crystallinity is higher under the same secondary processing conditions, and the heat resistance and mechanical properties of prepared products are better. This study provides new ideas for resolving the conflict between mechanical properties and processing flowability, improving the heat resistance of PLLA, and expanding its application range.