Peroxide induced cross-linking by reactive melt processing of two biopolyesters: Poly(3-hydroxybutyrate) and poly(l -lactic acid) to improve their melting processability

Abstract

Poly(3-hydroxybutyrate) (PHB) and poly(l-lactic acid) (PLLA) were individually cross-linked with dicumyl peroxide (DCP) (0.25-1 wt %) by reactive melt processing. The cross-linked structures of the polymer gel were investigated by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies. The size of the polymer crystal spherulites, glass transition temperature (Tg), melting transition temperature (Tm), and crystallinity were all decreased as a result of cross-linking. Cross-linking density (νe) was shown to increase with DCP concentration. Based on parallel plate rheological study (dynamic and steady shear), elastic and viscous modulus (G and G), complex viscosity (η∗) and steady shear viscosity (η) were all shown to increase with cross-linking. Cross-linked PHB and PLLA showed broader molar mass distribution and formation of long chain branching (LCB) as estimated by RheoMWD. Improvements in melt strength offer bioplastic processors improved material properties and processing options, such as foaming and thermoforming, for new applications.