Effects of cellulose fiber content on physical properties of polyurethane based composites

For the sake of environmental protection and public health, the utilization of natural fibers in industrial application composites provides challenges for researcher to develop suitable techniques to produce good quality fibers for use as reinforcement for polymer composites. This is the backdrop to the issue of elaboration and study of the use of cellulose fibers extracted from Alfa stems as reinforcement of polyurethane (PU) based composites. Several characterization techniques were used to study the physical properties of the composite when the thermoplastic matrix is filled with cellulose fibers up to 30% by weight. The thermal and mechanical properties of the composite show a slight and gradual change, when it exists, based on the content of the embedded fibers. However, the cellulose concentration-dependence of the electrical properties of the composites, especially conductivity and capacitance, show a surprising percolation behavior beyond a critical concentration of 10% of cellulose fibers. These features are correlated with the cellulose concentration-dependence of charging effect of the composite under electronic beam irradiation in a scanning electron microscope. Poor dispersion of the fibers and their agglomeration when their concentration exceeds a threshold of 10% and their consequences on dipole concentration may explain such cellulose concentration-dependence.