70 basic concepts of polyurethane to help you understand it thoroughly!

1. Hydroxyl value: The amount of hydroxyl (-OH) contained in 1 gram of polymer polyol is equivalent to the number of milligrams of KOH in mgKOH/g.

2. Equivalent: The average molecular weight occupied by a functional group.

3. Isocyanate content: The content of isocyanate in the molecule

4. Isocyanate index: Indicates the degree of excess isocyanate in the polyurethane formula, usually represented by the letter R.

5. Chain extender: refers to low molecular weight alcohols and amine compounds that can extend and expand molecular chains or form spatial network cross-linking.

6. Hard segment: The segment on the main chain of the polyurethane molecule formed by the reaction of isocyanate, chain extender and cross-linking agent. These groups have larger cohesion energy, larger space volume and greater rigidity.

7. Soft segment: Carbon-carbon main chain polymer polyol has good flexibility and is a flexible segment in the polyurethane main chain.

8. One-step method: refers to a method in which oligomer polyol, diisocyanate, chain extender and catalyst are mixed at the same time and directly injected into the mold, and solidified at a certain temperature.

9. Prepolymer method: First, the oligomer polyol and diisocyanate are prepolymerized to generate a polyurethane prepolymer with terminal NCO groups. During casting, the prepolymer is reacted with a chain extender to prepare polyurethane. The elastomer method is called the prepolymer method.

10. Semi-prepolymer method: The difference between the semi-prepolymer method and the prepolymer method is that part of the polyester polyol or polyether polyol, chain extender, catalyst, etc. are added to the prepolymer in the form of a mixture. among things.

11. Reaction injection molding: Also known as RIM (Reaction Injection Molding), oligomers with small molecular weight are measured in liquid form, mixed instantly and injected into the mold at the same time, and rapidly in the mold cavity. A process in which the molecular weight of a material increases rapidly through a reaction, creating a new polymer containing a new characteristic group structure at an extremely fast rate.

12. Foaming index: The proportion of water equivalent to 100 parts of polyether is defined as the foaming index (IF).

13. Foaming reaction: Generally refers to the reaction in which water reacts with isocyanate to form substituted urea and releases CO2.

14. Gel reaction: Generally refers to the formation reaction of carbamate.

15. Gel time: The time required for a liquid substance to form a gel under certain conditions.

16. Milky white time: When zone I is about to end, milky white phenomenon will appear in the liquid polyurethane mixture material. This time is called cream time in polyurethane foam production.

17. Chain extension coefficient: refers to the ratio of the amount of amino and hydroxyl groups (unit: mo1) in the chain extender component (including mixed chain extender) to the amount of NCO in the prepolymer, that is, the active hydrogen group Ratio of moles (equivalents) of groups and NCO.

18. Low unsaturation polyether: Mainly developed for PTMG. The price of PPG and the degree of unsaturation are reduced to 0.05mol/kg, which is close to the performance of PTMG. It uses DMC catalyst and the main variety is Bayer’s Acclaim series products.

19. Urethane grade solvent: When selecting a solvent for the production of polyurethane, the solubility and evaporation speed must be considered. However, the solvent used for the production of polyurethane should focus on the heavy NC0 group in the polyurethane. Solvents such as alcohols and ether alcohols that react with NCO groups cannot be used. The solvent must not contain water, alcohol and other impurities, and it must not contain alkali substances, which will cause the polyurethane to deteriorate.

Ester solvents are not allowed to contain moisture, nor free acids and alcohols, as they will react with NCO groups. The ester solvent used for polyurethane should be a high purity “urethane grade solvent”. That is, react the solvent with excess isocyanate, and then use dibutylamine to measure the unreacted amount.��Polymers generally consist of long flexible chains of oligomer polyols as soft segments, and diisocyanates and chain extenders as hard segments. The hard segments and soft segments are alternately arranged to form repeating structural units. In addition to containing urethane groups, hydrogen bonds can be formed within and between polyurethane molecules, and soft and hard segments can form microphase regions and produce microscopic phase separation.

67. What are the main performance characteristics of polyurethane elastomer

Answer: Performance characteristics: 1. High strength and elasticity, which can maintain high elasticity in a wide hardness range (Shore A10 ~ Shore D75); generally no plasticizer is needed to achieve the required Low hardness, so there is no problem caused by plasticizer migration; 2. Higher load-bearing capacity than other elastomers at the same hardness; 3. Excellent wear resistance, its wear resistance is 2 to 10 times that of natural rubber; 4. Excellent resistance to grease and chemicals; aromatic polyurethane is resistant to radiation; has excellent oxygen resistance and ozone resistance; 5. High impact resistance, fatigue resistance and vibration resistance, suitable for high-frequency flexing applications; 6. Good low-temperature flexibility; 7. Ordinary polyurethane cannot be used above 100 ℃, but a special formula can withstand high temperatures of 140 ℃; 8. Molding and processing costs are relatively low.

68. Polyurethane elastomers are classified according to polyol, isocyanate, manufacturing process, etc.

Answer: 1. According to the raw materials of oligomer polyol, polyurethane elastomer can be divided into polyester type, polyether type, polyolefin type, polycarbonate type, etc. Polyether type can be divided into different types according to specific varieties. Polytetrahydrofuran type, polyoxypropylene type, etc.; 2. According to the difference of diisocyanate, it can be divided into aliphatic and aromatic elastomers, and further subdivided into TDI type, MDI type, IPDI type, NDI type and other types; from the manufacturing process Polyurethane elastomers are traditionally divided into three categories: casting type (CPU), thermoplastic type (TPU), and mixing type (MPU).

69. From the perspective of molecular structure, what are the factors that affect the performance of polyurethane elastomer?

Answer: From the molecular structure point of view, polyurethane elastomer is a block polymer. Generally, the soft segment is composed of long flexible chains of oligomer polyol, and the hard segment is composed of diisocyanate and chain extender. The hard segment and The soft segments are arranged alternately to form repeating structural units. In addition to containing urethane groups, hydrogen bonds can be formed within and between polyurethane molecules, and soft and hard segments can form microphase regions and produce microscopic phase separation. These structural characteristics make polyurethane elastomers have excellent wear resistance and toughness, and are known as “wear-resistant rubber”.

70. Performance differences between ordinary polyester and polytetrahydrofuran ether elastomers

Answer: Polyester molecules contain more polar ester groups (-COO-), which can form strong intramolecular hydrogen bonds. Therefore, polyester polyurethane has high strength, wear resistance and oil resistance.