Preparation And Properties Of Wood Flour Reinforced Lignin/Epoxy Resin Composite

First, the curing kinetics of different matrix systems including lignin/epoxy, epoxy/polyamine and lignin/epoxy/polyamine were studied. Their transformation trend of activation energy was calculated in order to illustrate their curing course and to analyze the function of lignin in the curing course. It was divided as two obvious stages in the curing progress of the epoxy/polyamine system. The reaction at low temperature area (below 200℃) mainly was the ring-opening reaction between the epoxy group and the amino. The activation energy was 62.1-86.2 kJ/mol, the average value was 69.0 kJ/mol (0.2<a<0.8);the reaction at high temperature area (above 200℃) mainly was polymerization or etherification, the activation energy was above 169.1 kJ/mol (a< 0.8).The curing reaction between lignin and epoxy is a multistep reaction. In the initial stage the hydroxyl groups (phenolic hydroxyl and alcoholic hydroxyl) within lignin open epoxy ring at low temperature, the activation energy was about 92.0-110.0 kJ/mol; then the polymerization or etherification takes place at high temperature, finally cured, the activation energy was about 110.0-121.0 kJ/mol.For the ternary lignin/epoxy/polyamine matrix system, lignin mainly provides phenolic hydroxyl groups to accelerate the reaction of the amine with the epoxy group and acts as a catalyst to reduce the activation energy of the LEP system in the initial stage, the average activation energy was 65.4 kJ/mol (0.2< a< 0.8). which was reduced 3.6 kJ/mol compared with epoxy/polyamine system.the polymerization was more easy to take place in the presence of lignin. There was not only physical mix but also formed chemical bond when lignin as composited with epoxy resin.In this paper, wood flour was used to reinforce lignin-epoxy resin composite to improve the mechanical properties, creep and creep recovery properties, thermal properties, water absorption and. It was found that more of the wood flour gathered together as the wood flour content increased, but no obvious aggregation was found. Good interface bonding was formed among the wood flour,epoxy resin and lignin. The initial modulus, bending strength and impact strength of the composite increased with the increasing content of the wood flour. Meanwhile, the glass transition temperature decreased. And the thermal stability first decreased and then increased slightly. The water absorption of the composite was increased with the increasing content of the wood flour.The particle size of the wood fiber also has an impact on these properties of the composite. As the particle size of the wood flour decreased, the wood flour was well distributed in the epoxy resin matrix, and no obvious interphase was observed, which explained the good interfacial combination among each component. The fracture surfaces of the composite reinforced with different particle size wood flour indicated that these composites had similar break-form. With the decrease in the wood flour’s particle size, the initial modulus, bending strength and impact strength of the composite increased at first, and then decreased slightly. The Tg increased, and the thermal stability first decreased, then increased slightly. But the water absorption was decreased.The creep resistances of the composite were significantly improved after the addition of the wood flour. The composite’s creep resistance was improved with increase of the wood flour content. A moderate aggregate size (40 to 60 mesh) wood flour reinforced composite had a better creep resistance.