Modified Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) with Interesting Properties for Food Packaging Applications

Abstract

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) belongs to the family of biobased and biodegradable polyhydroxyalkanoates (PHA). Although the general properties of PHBHHx are very promising for packaging applications amongst other PHA, the crystallization rate is very slow. This research focuses on the modification of PHBHHx using nucleating agents and fillers to augment its applicability as potential food packaging material. PHBHHx is modified using talc, organomodified montmorillonite clay (OMMT), and unmodified and surface-modified zinc oxide (sZnO). The samples are compression molded and analyzed for their crystallization, thermal, dispersion, colorimetric, opacity, barrier and tensile properties. PHBHHx presents a moderate barrier for O2 (8 cm3 mm/m2 day atm) and CO2 (40 cm3 mm/m2 day atm) and a fairly low water vapor permeability (1.4 g mm/m2 day). The latter could be useful, e.g. to protect a moisture-sensitive inner oxygen barrier layer. Ultra-fine talc is identified as an efficient nucleating agent. The non-isothermal crystallization half-time reduces with 97% at 70°C by adding 2 wt% talc. The gas permeability coefficients of the talc-filled composites remain within the same range as virgin PHBHHx. The Young’s modulus increases with 13% at 2 wt% talc loading, whereas tensile strength and elongation at break remain fairly constant. Adding 10 wt% OMMT reduces the O2, CO2 and water vapor permeability coefficients by 47%, 42% and 37% respectively. Unfortunately, the nanocomposites are more brittle upon increasing OMMT concentrations, with a 44% reduction of the elongation at break at 10 wt%. Adding up to 5 wt% sZnO nanorods shows fine dispersions in PHBHHx, but does not significantly affect the gas permeability. The Young’s modulus increases with 7%, whereas the elongation at break reduces by 19%. Despite the opacity increases from 11.5 to 15.9% by adding 1 wt% sZnO, this modification provides UV shielding, which can be a valuable feature for food packaging. Additional research is necessary to further optimize and combine selected additives in PHBHHx.