What is Polyurethane ?
Polyurethanes are named after the urethane group, which forms when the isocyanate group reacts with the hydroxyl group of the alcohol.Polyurethane elastomers are exceptionally versatile, durable, flexible, adaptable, and resilient.Formed by a synthesis of poly-isocyanate and polyol, polyurethane holds mechanical properties that give it the strength of rigid plastic and the elasticity of rubber.
Forming of urethane group.
Polyurethane elastomers are built up of long, soft segments and short, hard segments.The soft segments are formed by the reactions between polyesterdiol or polyetherdiol with hydroxyl group ends.The hard segments are formed by the reactions between isocyanates and chain extenders.The polyurethane elastomers can be divided into polyesterurethane elastomer and polyetherurethane elastomer according to the polyol used.
Typical polyols used in polyurethanes
Polyester
Polyether
Typical diisocyanates that are used in polyurethanes.
MDI (diphenylmethane 4,4'-diisocyanate)
NDI (naphthalene 1,5-diisocyanate)
TDI (toluene diisocyanate) HDI (hexamethylene diisocyanate)
The properties of polyurethane elastomers depend on the structure of their chains. The physical properties of polyesterurethane elastomers are usually better than polyetherurethanes elastomers. Polyetherurethane elastomers have better chemical resistance and better low temperature flexibility.
Polyurethane elastomers can be compounded in a wide range of hardness from 20A to 85D thus they can be as soft as a rubber band or as hard as plastic.
Advantages of Polyurethane elastomers
1. Superior abrasion, cut, and tear resistance
Superior abrasion resistance of Polyurethane elastomers when compared to other materials, such as PVC and rubbers.
2. Good tensile strength
Most rubber materials have high elongation but low tensile strength.Most plastics have high tensile strength properties but low elongation. Polyurethane elastomers have both high tensile stress and high elongation properties.
3. Higher load-bearing capacity and improved compression set
Polyurethane elastomers have a greater load bearing capacity when compared to conventional elastomers of equal hardness.
4. Good Flexibility
Polyurethane elastomers perform very well when used in high flex fatigue applications. Flexural properties can be isolated allowing for very good elongation and recovery properties. Good flexibility over a wide temperature range
5. High tolerance to greases, oils, water, oxygen, and ozone
Polyurethane elastomers are resistant to oil, water, most weather conditions, as well as ozone and oxidation. Some formulations are even resistant to radiation, fungus and bacteria.
6. Other Benefits of Polyurethane elastomers
- Excellent low-temperature and impact strength
- High Vibration and damping characteristics
- Good electrical insulating properties.
- Robust weather and high-energy radiation resistance
- longer life, especially in outdoor or extreme environments
Compared to conventional materials
