Preparation And Properties Of Heat - Resistant Polyurethane Elastomers

Polyurethane is a kind of materials, whose performance is between rubber and plastic. It has high strength, excellent wear resistance, solvent resistance, weather resistance and other characteristics. It could be used in metallurgy, construction, automotive and light industry. Heat resistance of traditional polyurethane elastomer is poor; it limits the application of the polyurethane at high temperature. Silica has a high heat resistance, high specific surface areas, and hydroxyl groups of surface, which could react with polyurethane matrix to form a cross-linked network structure in order to improve the heat resistance of the polyurethane. This paper aims to synthetize a heat-resistant polyurethane elastomer. The main contents and results are as follows.1. We synthesized MDI-based or NDI-based polyurethane elastomer with organic mixed chain extender of different molecular weight, pure inorganic chain extender, organic and inorganic mixed chain extender and isocynate index. We analyzed the structures, thermal properties, mechanical properties, dynamic performance and morphologies of these polyurethane elastomers to get a heat-resistant polyurethane elastomer.2. For MDI-based polyurethane elastomer, organic mixed chain extender of different molecular weight had little effect on its thermal properties.330N, as a tri-functional chain extender of a large molecular weight, was added to the polyurethane elastomeric which equivalent to introduce the second soft segment structure that destroyed the regularity and crystallinity of the urethane segment and affected the properties of polyurethane elastomer. With the content of 330N increasing, the degree of hydrogen bonding, tensile strength, stress at definite elongation, and hardness and storage modulus of rubbery plateau region decreased, while the elongation at break increased.3. For MDI-based polyurethane elastomer, we synthesized the polyurethane elastomeric by using silica for the inorganic chain extender by mechanical blending method. This method was very simple, and didn’t need to process the surface of silica, and it could improve the properties of the polyurethane significantly. The OH groups of silica could react with NCO group in the polyurethane pre-polymer and enter the polyurethane matrix. The heat resistance of silica was passed to poryurethane matrix, which improved the thermal decomposition temperature and glass transition temperature.4. For MDI-based polyurethane, we studied the properties of the polyurethane with different isocynate index. When the isocynate index was 1.05, the property of the polyurethane was the best. By comparing with MDI-based polyurethane elastomer with NDI-based polyurethane elastomer, we found that the degree of hydrogen bonding, heat resistance and modulus of NDI-based polyurethane elastomer were higher than MDI-based, while the loss factor was lower. This is because NDI had good regularity and symmetry.5. For MDI-based and NDI-based polyurethane elastomers, we could use organic and inorganic mixed chain extender to prepare them. We found that add small amount of silica could improve the degree of hydrogen bonding, glass transition temperature, tensile strength, hardness and storage modulus of rubbery plateau region. When the amount of silica was 4% and 2%, the properties of MDI-based and NDI-based polyurethane elastomers would in the best respectively.