Green bionanocomposites based on polyhydroxybutyrate and filled with cellulose nanocrystals: melting processing and characterization

Abstract This article contributes to the understanding of biobased and biodegradable polyhydroxybutyrate (PHB) bionanocomposites reinforced by weight contents of 1 wt% and 3 wt% of cellulose nanocrystals (CNC), which are derived from waste streams of the paper industry. Samples were melt processed by pre-industrial methods such as extrusion and injection molding. Thereby, already existing ultrasonic treatment was used for dispersing the CNC. Subsequently, the CNC dispersion analysis was completed by transmission electron microscopy. Their thermal properties and their crystallization behavior were studied by thermogravimetric analysis, differential scanning analysis, X-ray diffraction and polarized optical microscopy. Investigations on the bending properties were carried out in conjunction with the analysis of their dynamic mechanical behavior. Scanning electron microscopy was used to characterize the fracture surface. All these analyses give a deep insight into their structure-property relationship. The applicability of the processed bionanocomposites in the packaging industry was investigated by analysing their moisture absorption measurements and their gas barrier properties, which provided an insight into their behavior under environmental conditions. PHB bionanocomposites with a low content of 1 wt% CNC were found to have the best dispersion quality, which had a positive effect on almost all mechanical and thermal properties. The incorporation of crystalline nanocellulose leads to a significant increase in crystallinity, which contributes to an improvement in mechanical properties. In addition, the bionanocomposites show a slightly lower tendency to absorb moisture and better barrier properties to oxygen and water vapor. The findings show that these bionanocomposites are suitable for use in the packaging industry.