Modification of polylactide by reactive blending with polyhydroxybutyrate oligomers formed by thermal recycling through E1cB-elimination pathway

Abstract

This study aimed to thermally recycle polyhydroxybutyrate (PHB), a microbial polyester with low thermal stability and limited re-processability, into crotonate-ended oligomers through the E1cB-elimination pathway. The resulting products were used as a functional additive to improve the mechanical and rheological properties of polylactide (PLA), which has intrinsic brittleness and low melt stability. The PLA was modified through a reactive blending process in an internal mixer. The quantitative 1H NMR analysis confirmed the crotonate functionality of the oligomers and their consumption during the reactive blending process. Tensile testing revealed that reactive blending 20 wt% PHB oligomers with PLA improve tensile toughness 24 times over pure PLA while keeping the elastic modulus above 1 GPa. Oscillatory-shear rheometry confirmed the improved shear-thinning behavior of reactive blends, while extensional viscosity measurements revealed a significant strain hardening behavior. The increase in melt stability was attributed to the formation of high molecular weight structures as a result of possible chain extension and branching reactions. DSC traces showed that branching and grafting points acted as nucleation sites, accelerating PLA melt crystallization. It was also found that increasing the PLA crystallinity above 44% gives rise to crystallization-induced phase separation, despite initial miscibility.