Branching-Density Dependent Chain Relaxation and Orientated Crystallization Behavior of the Stretched Polylactic Acid Melt

作者：Ye Ma, Deyu Niu, Jiale Liu, Bo Liu, Pengwu Xu, Xingchen Jiao, Weijun Yang, Tianxi Liu, Piming Ma · 发表于：Macromolecules · 年份：2025 · DOI：10.1021/acs.macromol.5c00347 · 被引用次数：16 · 研究领域：biodegradable polymer synthesis and properties、Polymer crystallization and properties、Polymer Foaming and Composites

The branching density of long-chain branched polymers is crucial for polymer crystallization and orientation during melt processing, but there are few reports on related quantitative research. In this work, poly(lactic acid) (PLA) was used as an example, and long-chain branched PLA (LCB-PLA) with different branching densities (φ) was constructed by melt blending with epoxy copolymers. The influence of branching density on the chain relaxation, orientation, and crystallization of stretched PLA melt was quantitatively studied. The long-chain branched structure effectively inhibited the chain relaxation of PLA melt, promoting the orientation and crystallization of PLA. The orientated crystallization behavior of LCB-PLA is closely related to the branching density, and there are two critical branching densities. When φ ≤ 2.57 mol/10 4 mol C, an effective strong molecular chain network that inhibits the chain relaxation of PLA has not yet been formed, and the orientation and crystal structure are hardly formed. When φ is in the intermediate stage (2.57 mol/10 4 mol C < φ < 6.47 mol / 10 4 mol C), a local strong chain network is formed, which is able to inhibit the relaxation of the oriented chains to some extent. At a higher φ (≥6.47 mol/10 4 mol C), chain slip and chain mobility are enormously reduced due to the complex topological constraints of adjacent chains, forming a strong global chain network that effectively restricted the relaxation of oriented chains during melt stretch...