Veronika Melcova
Brno University of Technology, Czech Republic
Title: Unexplained effect of commercial stabilizers on poly(3-hydroxybutyrate) during processing
Biography
Biography: Veronika Melcova
Abstract
Poly(3-hydroxybutyrate) (PHB) is a promising polymer from the group of biodegradable polyesters. It is generally known, that it degrades markedly upon heating to temperatures between 170 and 200 °C, which are the typical processing temperatures for PHB. As a result, molecular weight and viscosity of the system drops. As generally accepted by science community, molecular weight is lowered by random scission through cis-elimination mechanism. This reaction leads to the formation of two sub-molecules one with unsaturated crotonate end group and the other with carboxylate end group. This susceptibility to degradation complicates the processing and possible after-use handling of PHB. The effect of stabilizers and antioxidants traditionally used for commercial plastics is not clearly stated in the literature. The purpose of this work is to study the effect of selected commercial stabilizers based on phenolic stabilizer (Irganox 1010) or phosphites (Irgafos 168) on melt properties of PHB. Moreover, oligomeric carbodiimide with commercial name Raschig 9000 was used as a positive control which is proven to react with PHB. Stabilized samples and unstabilized reference material were subjected to the total of five extrusion cycles. The effect of processing on melt properties was studied by means of melt volume rate. The results clearly show that these stabilizers do not prevent thermal degradation of polyhydroxybutyrate. Moreover, after the third extrusion cycle, the effect of selected additives seems to be rather probe grading.