Enhancing the Melt Strength of Poly(Lactic Acid) via Micro-Crosslinking and Blending with Poly(Butylene Adipate-co-Butylene Terephthalate)for the Preparation of Foams

Abstract

The melt strength of poly(lactic acid) (PLA) is an important factor in preparing foams and blowing films. Aiming to endow PLA with a suitable melt strength via a slight crosslink, a superficial micro-crosslinking method was introduced in which the PLA feed was mixed with benzoyl peroxide (BPO) and crosslinked in a 100 °C oven for 1 h. Additionally, poly(butyleneadipate-co-terephthalate) (PBAT) was blended with the crosslinked PLA (C-PLA) to further improve melt strength and viscosity. The blend foams were prepared using a single-screw extruder and azodicarbonamide as a foaming agent. The properties were characterized by gel fraction, melt flow rate (MFR), rheometry, DSC and SEM. The rheological results showed that the complex viscosity and storage modulus of C-PLA and C-PLA/PBAT blends increased, attributed to the micro-crosslinking and addition of PBAT and indicating an improvement in melt strength. Furthermore, the crystallization of modified PLA was also enhanced. Compared with pure PLA foams, the C-PLA/PBAT blend foams showed larger cells with more uniform shapes and homogenous distribution. This approach to improve the melt strength of polymers with micro-crosslinking and blending with PBAT represents an attractive method for preparing foams with regular cells.