Effect of D-Lactide Content and Molecular Weight of PLA on Interfacial Compatibilization with PBAT and the Resultant Morphological, Thermal, and Mechanical Properties

Interfacial compatibilization is essential to generate compatible blend structures with synergistically enhanced properties. However, the effect of molecular structure on the reactivity of compatibilizers is not properly known. This study investigates the compatibilization effect of multifunctional, epoxy-based Joncryl chain extender in blends of polylactide (PLA) and polybutylene adipate-co-terephthalate (PBAT) using PLA with varying D-lactide contents and molecular weights. These PLAs were high molecular weight amorphous PLA (aPLA) with D-content of 12 mol% and semi-crystalline PLA (scPLA) grades with D-contents below 1.5 mol% at both high (h) and low (l) molecular weights. The reactivity of Joncryl was assessed with each individual neat polymer, and its compatibilization effect was examined in blends at a weight ratio of 75 wt/25 wt using small amplitude oscillatory shear (SAOS) rheological analysis. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile and impact tests, as well as scanning electron microscopy (SEM) observations, were conducted to characterize the blends. The addition of Joncryl resulted in remarkable improvements rheological behavior of all neat polymers and noticeably refined PBAT droplets in all blends, particularly in aPLA/PBAT and scPLA(l)/PBAT. The ductility, toughness and impact strength of these blends were significantly enhanced, while their tensile strength and modulus also showed slight improvements. Although the addition of Joncryl retarded the crystallization of the scPLA samples, the scPLA(h)/PBAT blend with Joncryl exhibited the highest thermomechanical performance over a wide temperature range. This was attributed to the higher crystallinity of scPLA(h), which, even in the presence of Joncryl, provided high thermal stability.