Thermoprocessable Bio-waste-Based Composites from Animal Glue and Lignocellulosic Waste Fibers

Abstract

This study exploited the use of byproducts from food production and other bio-waste to develop new thermoprocessable polymers and composites. In particular, the thermoprocessability of animal glue, a biopolymer extracted from the bones and skin of animals taken from the waste of meatpacking and tanning industries, was investigated. As animal glue alone does not exhibit thermoplasticity, its plasticization was explored using water as a temporary plasticizer and glycerol as a permanent plasticizer. Optimization showed that at least 30 wt % water was necessary to allow processing of the material, while excessive brittleness was suppressed with 10 wt % glycerol. As a result, the optimized composition provided a bio-based polymer material with Young's modulus of 2.43 GPa, which was thermoprocessable through compression molding at temperatures as low as 50 °C. Its use as a composite matrix was explored using different lignocellulosic waste fibers. In particular, wood flour and bark fibers from the forestry industry, cotton fibers from recycled blue jeans, and seagrass were used. Composites with differently pretreated fibers with sieving sizes ≤0.25 mm, ≤1 mm, and ≤4 mm, as well as fiber contents of 5 to 30 wt %, were prepared, which showed that the fiber size does not significantly affect either mechanical properties or volume shrinkage, yet it drastically affects the viscosity, which increases with the fiber sieving size; therefore a fiber size of ≤0.25 mm was kept for further investigations. Higher fiber content brought a 76% reduction in shrinkage as well as an increase in stiffness by 38% compared to the unfilled matrix. Lastly, melt extrusion 3D printing was utilized as a processing method for the composites with 5 wt % bark or cotton fibers, demonstrating the feasibility of processing these composites on a larger scale and through different thermoprocessing methods.