30 basic concepts about polyurethane

2. Equivalent: the average molecular weight of a functional group.

3, isocyanate content: the content of isocyanate in the molecule

4. Isocyanate index: indicates the degree of excess of isocyanate in the polyurethane formulation, usually indicated by the letter R.

5. Chain extender: refers to low molecular weight alcohols and amine compounds that can extend, expand or form spatial network crosslinks.

6. Hard segment: the segment formed by the reaction of isocyanate, chain extender and crosslinker on the main chain of polyurethane. These groups have larger cohesive energy, larger space and greater rigidity.

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

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

9. Prepolymer method: Firstly, the oligomer polyol and the diisocyanate are prepolymerized to form a NCO-based polyurethane prepolymer, and the prepolymer is reacted with a chain extender to prepare a polyurethane elastomer. The method is called the prepolymer method.

10. Semi-prepolymer method: The difference between the semi-prepolymer method and the prepolymer method is that a part of the polyester polyol or the polyether polyol is added to the prepolymer as a mixture with a chain extender, a catalyst or the like.

11. Reaction injection molding: also known as reaction injection molding RIM, which is measured by liquid molecular form of oligomers with a small molecular weight, which is injected into the mold while mixing instantaneously, and reacts rapidly in the cavity, and the molecular weight of the material increases sharply. Extremely fast process to create a new polymer with a new characteristic group structure.

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

13. Foaming reaction: generally refers to a reaction in which water reacts with isocyanate to form a substituted urea and emits 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: At the end of the I zone, the milky white phenomenon appears in the liquid phase polyurethane mixture. This time is referred to as cream time in the formation of polyurethane foam.

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

18, low unsaturation polyether: mainly for PTMG development, PPG price, unsaturation reduced to 0.05mol / kg, close to the performance of PTMG, using DMC catalyst, the main variety Bayer Acclaim series products.

19. Urethane ester solvent: The solvent used for the production of polyurethane should consider the solvent and volatilization speed. However, the solvent used in the production of polyurethane should focus on the weight of the NC0 base in the polyurethane. A solvent such as an alcohol or an ether oxime which reacts with the NCO group cannot be used. The solvent can not contain impurities such as water and alcohol, and cannot contain alkali substances, which will deteriorate the polyurethane.

Ester solvents are not allowed to contain moisture, nor contain free acids and alcohols, which react with NCO groups. For the ester solvent used in polyurethane, a "urethane ester solvent" having a high purity should be used. That is, the solvent was reacted with an excess of isocyanate, and the amount of unreacted isocyanate was measured by dibutylamine to check whether it was used in combination. The principle is that the consumption of isocyanate is not suitable because it indicates that the total value of the isocyanate is consumed by the water, alcohol and acid in the ester. If the number of grams of solvent required to consume the leqNCO group is expressed, the numerical value is good. .

An isocyanate equivalent of less than 2,500 or less is not used as a urethane solvent.

The polarity of the solvent has a great influence on the reaction of the resulting resin. The higher the polarity, the slower the reaction, such as the difference between toluene and methyl ethyl ketone by 24 times. The solvent molecule has a large polarity and can form a hydrogen bond with the hydroxyl group of the alcohol to make the reaction slow.

Polyurethane solvents are preferably selected from aromatic hydrocarbon solvents, and their reaction speed is faster than esters and ketones, such as xylene. In the double-bond polyurethane construction, the ester and ketone solvents can be used to extend the service life. In the production of coatings, the "urethane-grade solvent" mentioned above is advantageous for the storage of the stabilizer.

20. Physical foaming agent: The physical foaming agent is a foaming pore formed by the physical form of a certain substance, that is, by the expansion of a compressed gas, the volatilization of a liquid or the dissolution of a solid.

21. Chemical foaming agents: Chemical foaming agents are those which release carbon dioxide and nitrogen gas after being decomposed by heating and form pores in the polymer composition.

22. Physical crosslinking: There are some hard chains in the high polymer soft chain, and the hard chain has the same physical properties as the chemically crosslinked vulcanized rubber at a temperature below the softening point or below the melting point.

23. Chemical cross-linking: refers to the process of forming macro-molecular chains through chemical bonds under the action of light, heat, high-energy radiation, mechanical force, ultrasonic waves and cross-linking agents to form a network of mesh or body structures.

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

25. What types of commonly used isocyanates are structurally considered?

A: Aliphatic: HDI, alicyclic: IPDI, HTDI, HMDI, aromatic: TDI, MDI, PAPI, PPDI, NDI.

26. What kinds of commonly used isocyanates? Write out the structure

A: Toluene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI), polyphenylmethane polyisocyanate (PAPI), liquefied MDI, hexamethylene diisocyanate (HDI).

27. What does TDI-100 and TDI-80 mean?

A: TDI-100 means that it is composed entirely of toluene diisocyanate of 2,4 structure; TDI-80 means a mixture of 80% of toluene diisocyanate of 2,4 structure and 20% of 2,6 structure.

28. What are the characteristics of TDI and MDI in the synthesis of polyurethane materials?

A: Reactivity for 2,4-TDI and 2,6-TDI. The reactivity of 2,4-TDI is several times higher than that of 2,6-TDI. This is because the 4 NCO in 2,4-TDI is far from the 2 NCO and methyl, almost no steric hindrance, and 2,6 The NCO of -TDI is more affected by the steric hindrance of the ortho-methyl group, and the reactivity is affected.

The two NCO groups of MDI are far apart and have no substituents around them, so the activity of these two NCOs is relatively large, even if one of the NCOs participates in the reaction, the remaining NCO activity is reduced, in general The activity is still large, so the reactivity of the MDI-type polyurethane prepolymer is larger than that of the TDI prepolymer.

29. What are the commonly used polyurethane chain extenders or crosslinkers?

A: Polyols (1,4-butanediol), alicyclic alcohols, aromatic alcohols, diamines, alcohol amines (ethanolamine, diethanolamine)

30. What are the factors that affect the performance of polyurethane materials?

A: The cohesive energy of the group, hydrogen bonding, crystallinity, degree of crosslinking, molecular weight, hard segment, soft segment.