Basic Concept Q&A on Polyurethane(Part Ten)

1. Characteristics and Applications of Polyurethane Microcellular Elastomers

Answer:

Characteristics: Polyurethane elastomers are block copolymers typically composed of flexible long-chain segments of oligomeric polyols forming the soft segments, and diisocyanates and chain extenders forming the hard segments. The hard and soft segments alternate to form repeating structural units. In addition to containing urethane groups, polyurethane molecules can form hydrogen bonds within and between molecules. The soft and hard segments can form microphase regions and exhibit microphase separation.

2. Key Performance Characteristics of Polyurethane Elastomers

Answer:

Performance Characteristics:

High strength and elasticity, maintaining high elasticity across a broad hardness range (Shore A10 to Shore D75); generally achieves the required low hardness without plasticizers, thus avoiding issues related to plasticizer migration.

Higher load-bearing capacity compared to other elastomers at the same hardness.

Excellent abrasion resistance, being 2 to 10 times more resistant than natural rubber.

Superior resistance to oils and chemicals; aromatic polyurethanes are radiation-resistant; excellent oxygen and ozone resistance.

High impact resistance, good fatigue resistance, and vibration damping, suitable for high-frequency flexing applications.

Good low-temperature flexibility.

Standard polyurethanes cannot be used above 100°C, but special formulations can withstand temperatures up to 140°C.

Relatively low molding and processing costs.

3. Classification of Polyurethane Elastomers Based on Polyols, Isocyanates, and Manufacturing Processes

Answer:

Based on oligomeric polyol raw materials, polyurethane elastomers can be categorized into polyester-type, polyether-type, polyolefin-type, polycarbonate-type, etc. Among polyether-types, there are subcategories like polytetramethylene ether (PTMEG) and polypropylene oxide (PPO).

Based on different diisocyanates, they can be classified into aliphatic and aromatic elastomers, further subdivided into TDI-type, MDI-type, IPDI-type, NDI-type, etc.

Based on manufacturing processes, traditionally polyurethane elastomers are divided into castable (CPU), thermoplastic (TPU), and millable (MPU) types.

4. Factors Affecting the Performance of Polyurethane Elastomers from a Molecular Structure Perspective

Answer:

From a molecular structure perspective, polyurethane elastomers are block copolymers typically composed of flexible long-chain segments of oligomeric polyols forming the soft segments, and diisocyanates and chain extenders forming the hard segments. The hard and soft segments alternate to form repeating structural units. In addition to containing urethane groups, polyurethane molecules can form hydrogen bonds within and between molecules. The soft and hard segments can form microphase regions and exhibit microphase separation. These structural characteristics give polyurethane elastomers their excellent abrasion resistance and toughness, earning them the nickname "abrasion-resistant rubber."

5. Performance Differences Between Conventional Polyester-Type and Polytetramethylene Ether Glycol (PTMEG)-Type Elastomers

Answer:

Polyester-type: Contains a higher number of polar ester groups (-COO-), which can form strong intramolecular hydrogen bonds. Therefore, polyester-type polyurethanes have higher strength, abrasion resistance, and oil resistance.

Polyether-type: The elastomers made from polyether polyols exhibit better hydrolysis stability, weather resistance, low-temperature flexibility, and resistance to mold.