Preparation And Properties Of Typical Biomass-Polyethylene Composites

Biomass/thermoplastic composites is a new type of environmental protection material. It is prepared by extrusion molding or other processes based on the mixture of a certain proportion of biopolymer fiber, thermoplastic resin, and processing aids. The application of biomass/thermoplastic composites is more and more extensive because of its excellent processability, waterproof, fire resistance, environmental protection and other good characteristics. The development and application of biomass/thermoplastic composites can not only promote the resource utilization of agricultural and forestry solid wastes and waste plastics, reduce environmental pollution but also alleviate the pressure of the increasing tension of forest resources. This project prepared biomass-polyethylene composites with HDPE as matrix resin and studied the effects of biomass content and species, fillers and additives content, temperature and other factors on the rheological properties, mechanical properties, static viscoelasticity and pyrolysis characteristics of the composites.(1) The equilibrium torque of melting system decreasing firstly and increasing later with increasing temperature. The most suitable extrusion temperature is 175℃. Excessive biomass content affects the melt fluidity. The rotor is subjected to a much smaller shearing force and slipped in the process of rotor rotation. The equilibrium torque get smaller. The melt fluidity properties of composites prepared by using poplar wood powder and rice hull powder are better than that of corn stalk and cotton stalk. The lubricant could effectively improve the melt flow properties. A small amount of calcium carbonate has little influence on the flow properties of composites. However, when the amount of calcium carbonate is over 20 parts the rotor torque is increased obviously and the melt fluidity properties become worse due to agglomeration. Coupling agent has little effect on the flow properties of the composite melt system.(2) Biomass increases the strength but reduces the elastic modulus of the composites. The mechanical properties of composites with corn stalk are the best. Calcium carbonate particles can be better filled composites to improve the density of the composites and can toughening composites. The lubricant can improve the processing performance but reduce the mechanical properties of the composites. The appropriate amount of coupling agent is about 8 parts. The orthogonal experimental results show that the main effects on the tensile, flexural and impact strength of composites are the content of the lubricant, calcium carbonate and biomass, calcium carbonate and lubricants interactive. Calcium carbonate and lubricants have an interaction effects on the mechanical properties.(3) The critical stress and strain values of linear viscoelastic region of composites are 0.8MPa and 0.03% respectively. Creep compliance of composites is increasing as the increase of temperature. The creep compliance increased with the biomass content increasing and decreased with the calcium carbonate content increasing at the same temperature. The creep compliance of composites prepared by rice husk is greater than other kings of biomass. The stress relaxation modulus of composites decreases and the stress relaxation rate increases with increasing temperature. The stress relaxation modulus increased with the biomass content and the calcium carbonate content increasing at the same temperature. The stress relaxation modulus of composites prepared by corn stalk is greater than other kings of biomass.(4) There are two main stages in pyrolysis of the composites, pyrolysis of biomass and HDPE. Increasing the biomass content can improve thermal stability of composites. Biomass and HDPE have a certain synergistic reaction in the second pyrolysis stage. The final pyrolysis mass loss of the composites increased with the increase of the biomass content. The composite prepared by poplar wood powder has better thermal stability. The increase of the calcium carbonate content increases the temperature of the first phase and improves the thermal stability of the composites.