Improving the barrier properties of thermoplastic corn starch-based films containing bacterial cellulose nanowhiskers by means of PHA electrospun coatings of interest in food packaging

Abstract

In the present study, property enhanced thermoplastic corn starch (TPCS) nanobiocomposites containing bacterial cellulose nanowhiskers (BCNW) prepared by melt mixing were characterized in terms of morphology, mechanical, optical and barrier properties. Improved barrier to water vapour and oxygen at high relative humidity (80%) was noticed, reaching the best performance at 15 wt% BCNW loading with a maximum drop of 46% and 95% for water and oxygen permeability, respectively. In a second approach, the optimized nanobiocomposites (containing 15 wt% BCNW) were successfully hydrophobized by coating them with electrospun poly(3-hydroxybutyrate) (PHB) or electrospun PHB-BCNW fibres. To this end, hybrid electrospun PHB fibres reinforced with highly dispersed crystalline BCNW in solutions concentrations up to 15 wt% were directly electrospun onto both sides of TPCS nanobiocomposites containing 15 wt% BCNW. Similar coated structures prepared without BCNW were developed and characterized for comparative purposes. The methodology used resulted in good adhesion between the layers, also leading to enhanced barrier performance. Interestingly, the incorporation of BCNW in one of the layers led to a decrease on the oxygen permeability values showing no significant differences between multilayer films incorporating BCNW whatever the layer where the BCNW were located. However, when comparing amongst the different multilayer samples containing BCNW, the greatest reduction in the water vapour permeability values was seen for multilayer structures incorporating BCNW in both, the TPCS inner layer and the PHB coating. This study has demonstrated the potential of the combination of both technologies (nanocomposites and multilayered design) in the development of food packaging materials based on corn starch with improved barrier properties.