The impact of boron nitride on the barrier and thermal properties of bionanocomposites

The preferred packaging material is very important in order to keep the food from external influences without losing nutritional value. Besides the good properties of the packaging material, the packaging raw materials and waste after the use of the packaging should not cause environmental pollution. However, conventional fossil-based synthetic polymers can not decay into the soil as waste for too long and cause the environmental pollution. Moreover, the fact that these synthetic polymers obtained from petroleum are derived from a depleting source also requires alternative search for the packaging industry. As a result of these searches, nowadays the most studied subject is the use of biopolymers as packaging material. These biopolymers, obtained from renewable carbon sources or biologically derived raw materials, can break down CO2, water and biomass when appropriate conditions are met, without harming the environment. However, although biopolymers have great advantages for the environment, they do not carry the necessary properties for industrial use. Biopolymers are supported by various filling materials to prepare bionanocomposites and made suitable for industrial use. In this work, poly (3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, copolymer, which is a biobased and biodegradable, environmentally friendly thermoplastic biopolyester was used as food packaging material. Bionanocomposites have been developed using nano hexagonal boron nitride (h-BN) which has superior properties such as high thermal stability, high mechanical strength and high thermal conductivity to improve the gas barrier, mechanical and thermal properties of PHBV. Before preparation of the composite, h-BN was exfoliated by various methods and surface modification studies were performed using octyl (triethoxy) silane (OTES). The h-BN exfoliation was examined by SEM, Nano-S and Particle Size Distribution analyzes and the optimal conditions were determined. The modified h-BN was then characterized by XRD, FTIR, TGA, DSC and combined with PHBV using the melt blending method with different loading percentages of BN. The prepared nanocomposites were characterized by XRD, SEM, FTIR, TGA, DSC analyzes, oxygen permeability and mechanical properties were measured. Oxygen permeability, diffusivity and solubility were determined for PHBV/BN nanocomposites with 0.05 wt% to 1 wt% filler loading. An increase in the gas barrier property was observed by adding BN nanoparticles into polymeric systems up to 0.5% BN loading. The nanocomposites prepared with silane treated BN were found to be higher gas barrier property improvement than non-silanized samples. The best barrier properties are obtained for the nanocomposite sample containing 0.5 wt% the silanized BN for which a reduction of oxygen permeability (OP) up to 27.4% was observed in comparison to the neat PHBV. It was shown that mechanical and thermal properties of the composites were also improved by addition of the BN to biopolymer. Thermogravimetric analysis (TGA) showed that the thermal stability of the composites was higher than that of neat PHBV. The Young's modulus of the composite was increased by 12.7%, at 0.5 wt% in the presence of silanized BN. At higher loading, BN agglomeration takes place within the PHBV matrix and the lack of proper adhesion between the matrix and the BN results in insufficient stress transfer. The Halpin–Tsai and Hui-Shia models were used to evaluate the effect of reinforcement by BN particles on the elastic modulus of the composites. Micromechanical models for initial composite stiffness showed good correlation with experimental values. Keywords: The biopolymer, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), hexagonal boron nitride (h-BN), oxygen permeability