Melt grafting of sepiolite nanoclay onto poly(3-hydroxybutyrate-co-4-hydroxybutyrate) by reactive extrusion with multi-functional epoxy-based styrene-acrylic oligomer

Abstract

This paper deals with grafting of sepiolite nanoclay onto poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P(3HB-co-4HB)) biopolymer by melt compounding. Reactive extrusion was performed in a twin-screw extruder in the presence of an epoxy-based styrene-acrylic oligomer (ESAO). The chemical interaction of sepiolite with P(3HB-co-4HB) were investigated using Fourier transform infrared (FTIR) spectroscopy. A novel grafting mechanism was proposed based on the multiple epoxy groups present in the reactive coupling agent. Epoxy ring-opening generated, on the one hand, the formation of alkoxy silanes bonds with the silanol groups exposed on the external surface of pristine sepiolite. On the other hand, ester bonds were produced with the terminal acid groups of the biopolymer chains. The newly formed sepiolite-grafted P(3HB-co-4HB) (sepiolite-g-P(3HB-co-4HB)) nanocomposite showed higher thermal, thermomechanical, and mechanical performance than the equivalent ungrafted nanocomposite. Melt grafting of sepiolite at different weight contents (1, 3, and 5 wt.-%) interestingly increased the thermal stability and stiffness of P(3HB-co-4HB) without impairing its ductility and toughness.