Studies on the thermal and mechanical behaviour of PLA-PET blends

Abstract

The increasing use of bio-sourced and biodegradable polymers such as PLA in bottle packaging presents an increasing challenge to the PET recycling process. Despite advanced separation technologies to remove PLA from PET recyclate, PLA may still be found in rPET process streams. This study explores the effects of PLA on the mechanical properties and crystallisation behaviour of blends of PET containing 0.5% to 20% PLA produced by injection moulding. SEM indicates an immiscible blend of the two polymers and TGA confirms the independent behaviour of the two polymers under thermal degradation conditions. Temperature-modulated DSC studies indicate that adding PLA to PET increases the rigid amorphous fraction of the PET moiety. Critical amounts of PLA induce stress oscillation behaviour during mechanical testing. The mechanical behaviour of the samples is explained by antagonistic interaction between increased rigid amorphous fraction and decreased fracture strength arising from an increased population of PLA microparticles.