Mitsubishi Escalator: Polyurethane elastomer is a polymer material polymerized from diisocyanate and oligomeric polyol as basic materials. It has good mechanical properties, abrasion resistance, oil resistance, tear resistance, chemical resistance, radiation resistance, and adhesion. Excellent performance, but its use temperature generally does not exceed 80 ℃, materials above 100 ℃ will soften and deform, mechanical properties will obviously weaken, short-term use temperature does not exceed 120 ℃, which severely limits its wide application. Therefore, many research institutions and scholars have researched the heat-resistant deformation properties of polyurethane elastomers, and prepared many materials with excellent heat-resistant properties, which make them have better mechanical properties at higher temperatures. However, the complexity of the polyurethane elastomer structure has many factors that affect its heat-resistant deformation. 1. Influence of raw materials on the heat resistance of elastomers
1) Oligomeric polyols: The urethanes formed by the reaction of oligomeric polyols of different structures with the same isocyanate have very different thermal decomposition temperatures, with primary alcohols being the most. High, the lowest tertiary alcohol. Since the thermal stability of the ester group is relatively good, and the hydrogen on the carbon atom of the ether group is easily oxidized, the heat resistance of the polyester polyurethane is better than that of the polyether polyurethane. Polyurethanes made from polyesters have different types of polyesters that have little effect on thermal properties.
2) Isocyanate: The hard segment is the main structural factor that affects the heat resistance of polyurethane elastomers. In general, the higher the isocyanate purity, the less isomers, the higher the regularity and symmetry of the polyurethane elastomer produced, and the better the heat resistance. The structured isocyanate hard segments are easily aggregated, which improves the degree of microphase separation. The polar groups between the hard segments generate hydrogen bonds to form the crystalline regions of the hard segment phase, which makes the entire structure have a higher melting point. In addition, the addition of a trimerization catalyst or post-vulcanization process measures under the premise of excess isocyanate can form stable isocyanate crosslinks in the elastomer, thereby improving the heat resistance of the elastomer.
3) Catalyst: The cycloaliphatic isocyanate has relatively low reactivity, and a catalyst must be added to the reaction system to promote the reaction to proceed in the expected direction and speed. The most practical catalysts are organometallic compounds. High-molecular organic carboxylic acids and tertiary amine compounds can also promote the chemical reaction of isocyanates.
4) Cross-linking agent: The excellent characteristics of polyurethane elastomers are closely related to its physical cross-linking and chemical cross-linking structure. Some experimental results show that by adding the cross-linking agent triol N3010, the polyurethane elastomer is cross-linked between the hard segments, and the light transmittance, thermal stability and mechanical properties are significantly improved compared with the polyurethane elastomer without the cross-linking agent. .
5) Chain extender: The effect of chain extender on heat resistance is related to its rigidity. In general, the higher the rigid segment content, the better the heat resistance of the elastomer. In addition, the chain extender hydroquinone dihydroxyethyl ether (HQEE) is a new type of non-toxic chain extender that can replace MOCA. It has many advantages and is widely used in polyurethane elastomers to improve the heat resistance and tear resistance of polyurethane. Crack strength and rubber storage stability.