Improvements in the melt and solid-state properties of poly(lactic acid), poly-3-hydroxyoctanoate and their blends through reactive modification

- We implement radical mediated grafting of a multi-functional coagent in the melt.
- The viscosity of PHO is increased substantially by reactive modification.
- Blends of PLA with PHO have improved impact strength.
- PLA and PLA/PHO blends with enhanced melt strength and crystallinity are produced.
- Reactively modified PLA/PHO blends have finer morphologies.

Poly(3-hydroxyoctanoate) (PHO), poly(lactic acid) (PLA) and PHO/PLA blends were reactively modified in the melt state, using dicumyl peroxide (DCP) and triallyl trimesate (TAM) trifunctional coagent. The viscosity and elasticity of PHO and PLA increased substantially following reactive modification. The processability of the partially cross-linked PHO was improved, whereas coagent-modified PLA displayed strain hardening and enhanced crystallization. Reactive compounding of PLA and PHO in the presence of DCP and TAM resulted in blends with enhanced strain hardening, indicative of high melt strength, and improved crystallinity compared to the unreacted blend. Furthermore these blends had a finer morphology, which was attributed to a compatibilizing effect possibly arising from copolymer formation at the interface. The elongation at break and impact properties of the blends were improved compared to the neat PLA, while the heat deflection temperature remained unaffected.