Introduction to methods to improve the heat resistance of polyurethane materials

Polyurethane is a high-quality polyurethane mainly made of diisocyanate, chain extender and oligomer polyol as basic raw materials. Molecular material with the combined properties of rubber and plastic. It has excellent mechanical properties, wear resistance, oil resistance, tear resistance, chemical corrosion resistance, radiation resistance, and good adhesion. But its use temperature Generally it does not exceed80℃. Materials above 100℃ will soften and deform, and their mechanical properties will be significantly weakened. The short-term use temperature does not exceed 120℃, which seriously limits its application in high temperature fields.

Today, the editor starts with oligomer polyols, isocyanates, chain extenders, catalysts, polymerization process conditions, introduction of intramolecular groups, and addition of fillers , composite with nanomaterials and other aspects, the influencing factors of elastomer heat resistance are reviewed.

1. Effect of raw materials on the heat resistance of polyurethane elastomer

Polyurethane elastomer is composed of soft segments( Oligomer polyols are mainly divided into polyester type, polyether type and polyolefin type polyols, etc.) and hard segments (diisocyanate and chain extender). The relative molecular weight of oligomer polyols is polydisperse, while polyisocyanates are often a mixture of multiple isomers. The presence of isomers will destroy the regularity of the hard segments and reduce the heat resistance of the elastomer. Strictly controlling the purity of raw materials and reducing the mole fraction of groups with poor thermal stability such as biuret and allophanate can improve the heat resistance of elastomers.

1 , oligomer polyol

The thermal decomposition temperatures of urethanes produced by reacting oligomer polyols with different structures and the same isocyanate are quite different, with primary alcohols being the highest and tertiary alcohols being the lowest. This is because bonds close to tertiary carbon atoms and quaternary carbon atoms are most likely to break. 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 polyester polyurethane is better than that of polyether polyurethane. Polyurethane prepared from polyester, the different polyester types have little impact on the thermal properties.

For polyether polyurethane, the type of polyether is very important Its heat resistance has a certain impact, such as toluene diisocyanate(TDI), 3,3′-dichloro-4,4′-diphenylmethanediamine ( After aging for 7 days at 121°C, there is a significant difference in the tensile strength of polyurethane prepared from MOCA) and polyoxypropylene glycol and polytetrahydrofuran ether glycol (PTMG). The tensile strength retention rate of the former at room temperature is is 44%, while the latter retention rate is 60%. The relative molecular weight or molecular chain length of oligomer polyols has no obvious effect on the characteristic decomposition temperature of thermal degradation of polyurethane. Liu Liangbing studied the degradation mechanism of polyester and polyether polyurethane and analyzed the factors that affect its heat resistance. , and concluded that the heat resistance of polyester-type polyurethane elastomer is better than that of polyether-type.

2 , Isocyanate

<p style="margin-top:0;margin-right:0; margin-bottom:0;margiThe polyimide produced by the reaction of anhydride and diisocyanate is insoluble and high temperature resistant. The introduction of polyimide rings into PU can improve the heat resistance and mechanical stability of polyurethane elastomers. The oxazolidinone compound produced by the reaction of epoxy and isocyanate in the presence of a catalyst has good thermal stability, with a thermal decomposition temperature exceeding 300°C and a glass transition temperature of over 150°C, which is significantly higher than the glass transition temperature of ordinary polyurethane elastomers. .

3 , Effect of compounding with nanoparticles and fillers on the heat resistance of elastomers

Nanomaterials are“the most promising materials in the 21st century”, polymers A nanocomposite material is one in which the size of the dispersed phase is in the nanoscale range in at least one dimension. Due to their unique properties, nanoparticles are combined with polyurethane elastomers to significantly improve their mechanical properties, and can increase the elastomer’s functional properties such as heat resistance and anti-aging. The composite of nanoparticles and elastomers is a new composite material system worthy of research and development.

By polyurethane-montmorillonite nanocomposite X-ray diffraction results show that montmorillonite is widely dispersed in the polyurethane matrix with an average interlayer spacing of not less than 415nm. The silicate in montmorillonite plays a thermal insulation role. It can effectively improve the heat resistance of composite materials. Utilizing polyurethane elastomer and inorganic particles – nano-SiO₂Excellent comprehensive properties, prepared by sol-gel methodSiO₂Polyurethane elastomer nanocomposites. Experimental results show that nanoSiO₂ can significantly improve the mechanical properties of the polyurethane elastomer matrix and also improve its heat resistance to a certain extent.

Calcium carbonate, carbon black, quartz stone, carbon fiber, Fillers such as glass fiber, nylon, and cured resin particles can also improve the heat deformation resistance of polyurethane elastomers. Du Hui and others studied the effects of different inorganic fillers on the mechanical properties and heat resistance of polyurethane elastomers. The results showed that the mechanical properties and heat resistance of polyurethane elastomers modified with micron-sized inorganic fillers were significantly better than ordinary polyurethane elastomers. .

Four. Formula design and application

There are many methods to improve the heat deformation resistance of polyurethane elastomers. In practical applications, reasonable selection must be made based on product performance indicators and process requirements to determine feasible process routes. Although improving the heat resistance of polyurethane elastomers has always been a very active topic in the field of polyurethane elastomers, and a lot of research has been conducted, there are still few polyurethane elastomers with superior comprehensive properties such as heat resistance and mechanical properties, and the overall level is still low. It is in the laboratory development stage. Developing new modification systems and strengthening the industrialization of results are still major recent research topics in the field of polyurethane.

Good heat resistance,PPDI, NDI, TODI and CHDI, if they are to be made into prepolymers, NDI activity is too high, which is currently unrealistic (it is said that Burley Bayer’s Prepolymer Research Institute has successfully synthesized storage stability Good NDI prepolymer), the rest is okay. Generally speaking, if thermal stability and yellowing properties are required, CHDI is better, while PPDI, which requires heat resistance and dynamic mechanical properties, is better. If TODI uses amine chain extension, its performance is very close to that of NDI.

However, there are still few polyurethane elastomers with superior comprehensive properties such as heat resistance and mechanical properties, and the overall level is still in the laboratory development stage. Developing new modification systems and strengthening the industrialization of results are still major recent research topics in the field of polyurethane.

Good heat resistance,PPDI, NDI, TODI and CHDI, if they are to be made into prepolymers, NDI activity is too high, which is currently unrealistic (it is said that Burley Bayer’s Prepolymer Research Institute has successfully synthesized storage stability Good NDI prepolymer), the rest is okay. Generally speaking, if thermal stability and yellowing properties are required, CHDI is better, while PPDI, which requires heat resistance and dynamic mechanical properties, is better. If TODI uses amine chain extension, its performance is very close to that of NDI.