Influence of the processing parameters on the degradation of poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and modification of their molecular weight using chain extenders

Abstract

Poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) exhibit valuable mechanical properties like high stiffness and tensile strength but are sensitive to processing parameters. The influence of these parameters was evaluated by measuring the variation of melt viscosity during processing. For all experiments, in the absence of chain extenders, the decrease in melt viscosity clearly showed the degradation of polymers during processing. This is more pronounced for PHBV than PLA. In order to compensate for the degradation and, if possible, improve the melt strength of these bio-based polymers, two chain extenders have been evaluated: dicumyl peroxide (DCP) and a polymeric epoxy acrylate chain extender (Joncryl^® ADR 4400). DCP reacts quickly with PLA and PHBV, while the epoxy-acrylate chain extender shows slower kinetics. For the PLA, with both investigated chain extenders, an increase in the molecular weight as compared with the virgin polymer and eventually the apparition of an insoluble fraction due to branching and crosslinking are observed. In the case of PHBV, the degradation is compensated by using DCP, requiring short processing times. No significant increase in molecular weight was observed when using the polymeric epoxy acrylate chain extender, requiring longer residence times, although the apparition of a gel fraction suggests the presence of branching and crosslinking.

Keywords:

• Biopolymers
• rheology
• biodegradable polymers
• chain extenders

SUBJECT CLASSIFICATION CODES:

• Aging and Degradation
• Polymer Bulk Characterization
• Polymeric-Based Materials
• Structure-Property-Processing Relationship

Author contributions

F. Cordenier: conceptualization (formulation of overarching research goals and aims), methodology (design of the applied methods), investigation (sample preparations, viscosity analyses, data interpretation). A. Boborodea: investigation (analyses of GPC, data interpretation), writing the original draft, writing the final version of the manuscript, corresponding author. C. Lemenu, L. Panarisi, P. Le Maître, S. Denis: investigation (sample preparations, performing analyses, interpretation of data). Ph. De Groote: conceptualization (evolution of overarching research goals and aims), writing the original draft, supervision of the project.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

These results were obtained with the financial support of the European Regional Development Fund (ERDF) for the MACOBIO project.