Joncryl Chain Extender Reactivity with Polylactide: Effect of PLA Molecular Weight and the Resultant Rheological and Crystallization Behaviors

This study investigates the effect of polylactide (PLA) molecular weight on the reactivity of multifunctional epoxy-based chain extender, Joncryl. PLA samples with low (L-PLA), medium (M-PLA), and high (H-PLA) molecular weights, each with D-lactic acid contents below 1.5 mol%, were melt-processed with 0.5 and 1.0 wt% Joncryl ADR 4468. The melt rheological behavior, molecular weight, and crystallization kinetics of the processed samples were evaluated using a rheometer, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC), respectively. Small-amplitude oscillatory shear rheology and GPC analyses showed that Joncryl reactions with higher molecular weight PLA resulted in more dramatic enhancements. This enhanced long-chain branching in turn provided stronger improvements to the melt rheological properties and to final molecular weight. Non-isothermal DSC analysis demonstrated that Joncryl modification suppressed crystallization more noticeably in high-molecular weight PLAs. Isothermal DSC analysis further revealed that long-chain branching nearly doubled the crystallization time while significantly reducing the final crystallinity.