Basic Concept Q&A on Polyurethane(Part Six)

1. What factors influence the performance of polyurethane materials?  

Answer: Factors include cohesive energy of the group, hydrogen bonds, crystallinity, degree of cross-linking, molecular weight, hard segments, and soft segments.

2. What raw materials contribute to the soft and hard segments on the main chain of polyurethane molecules?  

Answer: Soft segments consist of oligomeric polyols (such as polyester, polyether glycols, etc.), while hard segments consist of polyisocyanates or their combinations with small molecule chain extenders.

3. How do soft and hard segments affect the performance of polyurethane materials?  

Answer: Soft segments: (1) Molecular weight of soft segments: Assuming the molecular weight of polyurethane is the same, if the soft segment is a polyester, the strength of polyurethane increases with the increase of the molecular weight of the polyester glycol; if the soft segment is a polyether, the strength of polyurethane decreases with the increase of the molecular weight of the polyether glycol, although the elongation at break increases. (2) Crystallinity of soft segments: It contributes significantly to the crystallinity of linear polyurethane segments. Generally, crystallinity is beneficial for improving the performance of polyurethane products, but sometimes crystallization may reduce the low-temperature flexibility of the material, and crystalline polymers are often opaque.

Hard segments: Hard segments typically affect the softening melting temperature and high-temperature performance of polymers. Polyurethanes prepared from aromatic isocyanates have increased intramolecular cohesive strength due to the presence of rigid aromatic rings in the hard segments, resulting in generally higher material strength compared to aliphatic isocyanate-type polyurethanes, but they have poor resistance to UV degradation and are prone to yellowing. Aliphatic polyurethanes, on the other hand, do not yellow.

4. Classification of polyurethane foam  

Answer: (1) Rigid foam and flexible foam, (2) High density and low-density foam, (3) Polyester type and polyether type foam, (4) TDI type and MDI type foam, (5) Polyurethane foam and polyisocyanurate foam, (6) One-step and prepolymer method production, (7) Continuous and batch production, (8) Block foam and molded foam.

5. Basic reactions involved in foam preparation  

Answer: The basic reaction refers to the interaction of -NCO with -OH, -NH2, and H2O. During the foaming process, the "gel reaction" typically denotes the formation of urethane when reacting with polyols. The use of multifunctional raw materials results in a cross-linked network, facilitating rapid gelation of the foam system.

In foaming systems containing water, foaming reactions occur. The term "foaming reaction" generally describes the reaction where water reacts with isocyanates to form substituted ureas, releasing CO2.refers to the formation of urethane. Because the foam raw materials use multi-functional.