What Is a Polyurethane Elastomer?
Polyurethane elastomer, a synthetic rubber, is known for its excellent elasticity and rigidity. This polymer, characterized by urethane bonds, stands out for its superior mechanical strength and abrasion resistance, allowing for long-term usage. The properties of polyurethane elastomers vary significantly based on material composition and bonding methods.
There are two main types: polyester urethane rubbers (AU), which have ester bonds in the main chain, and polyether urethane rubbers (EU), with ether bonds. AU is known for its excellent oil resistance and mechanical strength but is susceptible to hydrolysis. Conversely, EU offers better resistance to hydrolysis and superior water resistance but has lower oil resistance and mechanical strength compared to AU.
Uses of Polyurethane Elastomers
Polyurethane elastomers are versatile, and used in applications like rolls, tires, conveyor belts, and sports shoe soles. Their abrasion resistance makes them ideal for belts in factories. However, caution is advised in acid or high-humidity environments due to potential deterioration. The material’s high elasticity is particularly beneficial in sports shoes, highlighting the wide range of applications achievable by varying the material composition and manufacturing process.
Causes and Countermeasures for Polyurethane Elastomer Degradation
Factors such as light, heat, oxygen, water, and microorganisms contribute to the degradation of polyurethane elastomers in natural environments. Light and heat can cause oxidative decomposition, breaking urethane bonds and degrading physical properties. Countermeasures include adding UV absorbers or antioxidants. Water-induced degradation, especially in polyester urethane rubbers, involves hydrolysis of urethane bonds. This can be mitigated by incorporating carbodimide compounds. Microbial degradation, often due to fungi, is more pronounced in polyurethane than other polymers. Polyester urethane rubber, in particular, is vulnerable, with degradation mechanisms often involving hydrolysis by microorganism-produced esterases.
Types and Manufacturing Methods of Polyurethane Elastomers
Polyurethane elastomers’ properties vary based on their types and manufacturing methods. The synthesis typically involves a polyaddition reaction between polyol, like glycol, and diisocyanate. The primary manufacturing methods are as follows:
Miracle Type
This common method involves forming a dough from raw materials, and then pouring and pressing it into molds. It’s straightforward and efficient but has drawbacks such as susceptibility to hydrolysis and variable material properties.
Thermoplastic Type
Also known as the injection method, this approach uses resin processing techniques. Polyurethane elastomer pellets are heated, melted, and injected into molds for molding. It’s cost-effective but requires expensive equipment, making it suitable for mass production.
Castable Urethane Type
In this method, liquid polyurethane elastomer is mixed with a curing agent and vulcanized in the mold. The resulting cross-linked polyurethane molecules provide high elasticity. This method is favored for its inexpensive setup and ability to process complex shapes, though it has lower manufacturing efficiency due to longer production times.