Regenerated cellulose fibre reinforced casein films: Effect of plasticizer and fibres on the film properties

Abstract

The idea of using man-made cellulosic fibres as reinforcement for casein films in this study was inspired by their well defined fibre diameter and availability in large quantity, eventually leading to a homogeneous high quality composite at low cost. The casein biofilms were fabricated by solution casting from an aqueous alkaline solution of the bovine milk protein casein in the presence of glycerol as a plasticizer, and the fibre-reinforced biocomposites were prepared by the addition of regenerated cellulose fibre to the casein casting solution with various amounts of glycerol. The effects of glycerol content and cellulose fibre reinforcements on the mechanical, thermal and physiological properties were characterized. The results showed that increasing glycerol content decreased the film strength, Young’s modulus and thermal stability with a gradual increase in the elongation. However, the tensile properties were noticeably improved when reinforced with cellulose fibre. The composite with 20 wt% glycerol and 20 wt% cellulose fibre showed the maximum tensile strength of 23.5 MPa and Young’s modulus of 1.5 GPa. The corresponding values for the composite with 30 wt% glycerol and the same fibre content were 15.1 MPa and 0.9 GPa, which were 2.3- and 3.2-fold higher compared to 30 wt% glycerol plasticized film. The thermal analysis revealed that the glass transition temperature and the thermal stability were decreased when the glycerol content was increased. Addition of cellulose fibres increased the glass transition temperature as well as the thermal stability. The gel electrophoresis (SDS-PAGE) analysis indicated that there was no significant decrease in the molecular weight of the casein protein during sample preparation. Scanning electron microscopy showed that the obtained composites with low glycerol content had adequate interfacial bonding, and Fourier transform IR spectroscopy confirmed the formation of molecular interactions between the cellulose fibres and the casein.