Read the basic concepts related to polyurethane
1、Hydroxyl value: The amount of hydroxyl group (-OH) contained in 1 gram of polymer polyol is equivalent to the milligram of KOH, unit 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 polyurethane formulation, usually expressed by the letter R.
5、Chain extender: It refers to the low molecular weight alcohols and amines that can make the molecular chain extend, expand or form spatial network cross-link.
6、Hard segment: The chain segment formed by the reaction of isocyanate, chain extender and cross-linker on the main chain of polyurethane molecule, these groups have higher internal aggregation energy, larger space volume and higher rigidity.
7、Soft segment: Carbon-carbon main chain polymer polyol with better flexibility, which is a flexible segment in the main chain of polyurethane.
8、One-step method: It refers to the method of mixing oligomeric polyol, diisocyanate, chain extender and catalyst at the same time and then injecting them directly into the mold and curing and molding at a certain temperature.
9、Prepolymer method: Firstly, the oligomeric polyol is prepolymerized with diisocyanate to produce polyurethane prepolymer with terminal NCO group, and then the prepolymer is reacted with chain extender to prepare polyurethane elastomer during casting, which is called prepolymer method.
10、Semi-prepolymer method: The difference between semi-prepolymer method and prepolymer method is that part of polyester polyol or polyether polyol is added to the prepolymer in the form of mixture with chain extender and catalyst.
11, reaction injection molding: also known as reaction injection molding RIM (Reaction Injection Moulding), is measured by the molecular weight of the zwitterionic material in liquid form, instantaneous mixing while injected into the mold, and rapid reaction in the mold cavity, the material molecular weight increased rapidly to generate a new polymer containing a new structure of characteristic groups at a very fast rate of the process.
12、Foaming index：That is, the number of parts of water used in 100 parts of polyether is defined as the foaming index (IF).
13、Foaming reaction: Generally, it refers to the reaction of water and isocyanate to generate substituted urea and release CO2.
14, gel reaction: generally refers to the formation of carbamate reaction.
15, gel time: under certain conditions, the time required to form a gel of liquid material.
16、Milk time: When the I zone is about to end, the milky phenomenon appears in the liquid-phase polyurethane mixture. The time in the generation of polyurethane foam is called the cream time (cream time).
17、Chain expansion factor: It is the ratio of the amount of amino and hydroxyl groups (unit: mo1) in the chain expander component (including mixed chain expander) and the amount of NCO in the prepolymer, which is the ratio of the molarity (equivalent number) of active hydrogen groups to NCO.
18、Low unsaturation polyether: mainly developed for PTMG, the price of PPG, unsaturation is reduced to 0.05mol/kg, close to the performance of PTMG, using DMC catalyst, the main varieties of Bayer Acclaim series.
19、Urethane grade solvent: The solvent chosen for the production of polyurethane should consider the solvency power and evaporation speed, but the solvent used for the production of polyurethane should focus on the heavy NC0 group in polyurethane. Can not use the alcohol, ether alcohol Lou and other solvents that react with NCO base. The solvent also cannot contain impurities such as water and alcohol, and cannot contain alkali substances, which will make the polyurethane deteriorate.
Ester solvents are not allowed to contain water, and must not contain free acids and alcohols, which will react with the NCO group. The ester solvent used in polyurethane should be “urethane solvent” with high purity. That is, the solvent and excess isocyanate reaction, and then use dibutylamine to determine the amount of unreacted isocyanate, to test whether it is suitable. The principle is that the one who consumes more isocyanate is not applicable, because it shows the total value of isocyanate consumed by water, alcohol and acid contained in the ester, and if the grams of solvent needed to consume leqNCO group are used, the value is large and stable.
Isocyanate equivalents below 2500 are not used as polyurethane solvents.
The polarity of the solvent has a great influence on the reaction of the generated resin. The greater the polarity, the slower the reaction, such as the difference between toluene and methyl ethyl ketone 24 times, the polarity of this solvent molecule is large and can form hydrogen bond with the hydroxyl group of alcohol and make the reaction slow.
Polychlorinated ester solvent is better to use aromatic hydrocarbon solvent, and their reaction speed is faster than esters and ketones, such as xylene. In the construction of double new cent polyurethane, the use of ester and ketone solvents can extend its service life. In the production of coatings, the “urethane-grade solvent” mentioned earlier in the selection sheet is beneficial to the storage of stable parts.
Ester solvents have strong solvency power, moderate evaporation speed, low toxicity and more use, cyclohexanone is also used, hydrocarbon solvents have low solvency power, less used alone, more used with other solvents.
20, physical blowing agent: physical blowing agent is the foam pore is formed by a change in the physical form of a substance, that is, through the expansion of compressed gas, liquid volatilization or dissolution of solids.
21、Chemical blowing agent: Chemical blowing agents are those compounds that can release gases such as carbon dioxide and nitrogen after decomposition by heating, and form fine pores in the composition of the polymer.
22, physical cross-linking: In the polymer soft chain has part of the hard chain, hard chain in the softening point or melting point below the temperature with the same physical properties of chemical cross-linking of vulcanized rubber phenomenon.
23、Chemical cross-linking: refers to the process of forming a net or body-shaped structure polymer by chemical bonding between macromolecular chains under the action of light, heat, high-energy radiation, mechanical force, ultrasonic waves and cross-linking agents, etc.
24. Foaming index: The number of parts of water equivalent to that used in 100 parts of polyether is defined as the foaming index (IF).
25. What are the commonly used isocyanates from the structural point of view?
A: Aliphatic: HDI, alicyclic: IPDI, HTDI, HMDI, aromatic: TDI, MDI, PAPI, PPDI, NDI.
26. What are the commonly used isocyanates? Write down the structural formula
A: Toluene diisocyanate (TDI), diphenylmethane-4,4′-diisocyanate (MDI), polyphenylmethane polyisocyanate (PAPI), liquefied MDI, hexamethylene diisocyanate (HDI).
27. What do TDI-100 and TDI-80 mean?
A: TDI-100 means that it is composed entirely of 2,4 structured toluene diisocyanate; TDI-80 means a mixture of 80% of 2,4 structured toluene diisocyanate and 20% of 2,6 structured.
28. What are the characteristics of each of TDI and MDI in the synthesis of polyurethane materials?
A: For the reactivity of 2,4-TDI and 2,6-TDI, the reactivity of 2,4-TDI is several times higher than that of 2,6-TDI because, the 4-position NCO in 2,4-TDI is far away from the 2-position NCO and methyl group and has almost no site resistance, while the 2,6-TDI NCO is subjected to a larger site-blocking effect by the neighboring methyl group, and the reactivity is affected.
The two NCO groups of MDI are far away from each other and there is no substituent around, so the activity of both NCOs is larger. Even if one of the NCOs participates in the reaction, so that the activity of the remaining NCO decreases, the overall activity is still larger, so the reaction activity of MDI-type polyurethane prepolymer is larger than that of TDI prepolymer.
29. Which of HDI, IPDI, MDI, TDI and NDI is better in yellowing resistance?
A: HDI (belongs to non-yellowing aliphatic diisocyanate), IPDI (the polyurethane resin made has excellent optical stability and chemical resistance, and is generally used to make high-grade non-discolored polyurethane resin).
30. The purpose of modification of MDI and the common modification methods.
A: Liquefied MDI: Purpose of modification: Liquefied pure MDI is the MDI modified by liquefaction, which overcomes some defects of pure MDI (solid at room temperature, melting when used, and affecting performance by repeated heating), and also provides the basis for the improvement and enhancement of the performance of MDI-based polyurethane materials for a wide range of modification.
Methods:
①Liquefied MDI modified by carbamate (urethane ).
②carbodiimide and uretonimine type modified liquefied MDI.
31. What are the common types of polymer polyols?
A: Polyester polyol, polyether polyol
32. What are the main industrial production methods of polyester polyol?
A: A, vacuum melting method B, carrier gas melting method C, azeotropic distillation method
33. polyester, polyether polyol molecules on the main chain of what special structure?
A: polyester polyol: in the main chain of the molecule contains ester groups, in the end group has a hydroxyl (-OH) of large molecules of alcohol compounds. Polyether polyols: polymers or zwitterions that contain ether bonds (-O-), end groups with (-OH) or amine groups (-NH2) in the main chain structure of the molecule.
34. How many types of polyether polyols are there according to their properties?
A: Highly reactive polyether polyol, graft polyether polyol, flame retardant polyether polyol, heterocyclic modified polyether polyol, polytetrahydrofuran polyol.
35. How many kinds of common polyethers are there according to the starting agent?
A: Poly(propylene oxide diol), poly(propylene oxide triol), hard foam polyether polyol, low unsaturated polyether polyol.
36. What is the difference between terminal hydroxyl polyether and terminal amine polyether?
Terminal amine-based polyethers are poly(propylene oxide) ethers in which the terminal hydroxyl group is replaced by an amine group.
37. What are the common types of polyurethane catalysts? What are the common varieties of each?
A: Tertiary amine catalysts, commonly used varieties include: triethylenediamine, dimethylethanolamine, N-methylmorpholine, N,N-dimethylcyclohexaneamine
Metal alkyl compounds, commonly used varieties include: organotin catalysts, which can be divided into stannous octanoate, stannous oleate, dibutyltin dilaurate.
38. What are the commonly used polyurethane chain extenders or cross-linking agents?
A: Polyols (1,4-butanediol), alicyclic alcohols, aromatic alcohols, diamines, alcohols and amines (ethanolamine, diethanolamine)
39. Reaction mechanism of isocyanate
A: The reaction of isocyanate with active hydrogen compounds is caused by the nucleophilic center of the active hydrogen compound molecule attacking the carbon atom of the NCO group. The reaction mechanism is as follows:
40. How does the structure of isocyanate affect the reactivity of the NCO group?
A. Electronegativity of R group: If R group is electron-absorbing group, the electron cloud density of C atom in -NCO group is more reduced and more easily attacked by nucleophilic reagents, i.e. more easily nucleophilic reaction with alcohols, amines and other compounds. If R is an electron donor group, through electron cloud transfer, it will increase the electron cloud density of C atoms in the -NCO group, making it less susceptible to attack by nucleophilic reagents, and its ability to react with compounds containing active hydrogen decreases. b. Induced effect: Since aromatic diisocyanates contain two NCO groups, when the first -NCO group will play the role of electron-absorbing group when the first -NCO group participates in the reaction due to the conjugation effect of the aromatic ring, so that the first NCO group reactivity is enhanced, this effect is the induction effect. c. Spatial site blocking effect: in the aromatic diisocyanate molecule, if two -NCO groups are in a Aromatic ring, then one of the NCO group on the other NCO group reactivity effect is often relatively significant. But when the two NCO groups are in the same molecule on different aromatic rings, or they are separated by hydrocarbon chains or aromatic rings, so that the interaction between them is not significant, and with the increase in the length of the chain hydrocarbon or the number of aromatic rings to reduce.
41. Reactivity of active hydrogen compound species with NCO
A: Aliphatic NH2＞Aromatic NH2＞Po drunken OH＞Water＞Secondary OH＞Phenol OH＞Carboxyl＞Substituted urea＞Amide＞Carbamate. (If the electron cloud density of the nucleophilic center is greater, the stronger its electronegativity, the higher its reaction activity with isocyanate and the faster the reaction speed; vice versa, the activity is low.)
42. Effect of hydroxyl compounds on their reactivity with isocyanates
A: The reactivity of active hydrogen compounds (ROH or RNH2) is related to the nature of R. When R is an electron-absorbing group (low electronegativity), it is difficult to transfer out the hydrogen atom, and the reaction of active hydrogen compounds with NCO is more difficult; if R is an electron-donating substituent, it can improve the reactivity of active hydrogen compounds with NCO.
43. What is the use of the reaction of isocyanate with water
A: It is one of the basic reactions for the preparation of polyurethane foam. The reaction between them first produces unstable carbamic acid and then decomposes into CO2 and amine. If there is an excess of isocyanate, the resulting amine will react with isocyanate to form urea.
44. In the preparation of polyurethane elastomer, the water content of polymer polyol should be strictly controlled
A: For elastomers, coatings, fibers require that there should be no air bubbles, so the water content in raw materials must be strictly controlled, usually requiring less than 0.05%.
45. The difference of catalytic effect of amine and tin catalysts on isocyanate reaction
A: The catalytic efficiency of tertiary amine catalyst for the reaction between isocyanate and water is large, while the catalytic efficiency of tin catalyst for the reaction between isocyanate and hydroxyl group is large.
46. Why can polyurethane resin be regarded as a kind of block polymer and what are the characteristics of chain segment structure?
A: Because the chain segments of polyurethane resins are composed of hard and soft segments. Hard segments are those formed by the reaction of isocyanate, chain extender and cross-linker on the main chain of polyurethane molecule, and these groups have higher internal aggregation energy, larger space volume and higher rigidity. And the soft segment refers to the carbon-carbon main chain polymer polyol, which is more flexible and is a flexible segment in the main chain of polyurethane.
47. What are the factors that affect the performance of polyurethane materials?
A: cohesion energy of groups, hydrogen bonding, crystallinity, cross-linking, molecular weight, hard segment, soft segment.
48. Which raw materials are the soft and hard segments in the main chain of polyurethane material?
A: The soft segment is composed of oligomeric polyol (polyester, polyether glycol, etc.), while the hard segment is composed of polyisocyanate or its chain extender with small molecules.
49. How do the soft and hard segments affect the performance of polyurethane materials?
A: Soft segment: (1) Molecular weight of soft segment: assuming the same molecular weight of polyurethane, if the soft segment is polyester, the strength of polyurethane increases with the increase of molecular weight of polyester diol; if the soft segment is polyether, the strength of polyurethane decreases with the increase of molecular weight of polyether diol, but the elongation increases. (2) Crystallinity of soft segment: It has a greater contribution to the crystallinity of linear polyurethane chain segment. In general, crystallinity is beneficial to improve the performance of polyurethane products, but sometimes crystallization reduces the low temperature flexibility of the material and crystalline polymers are often opaque.
Hard segments: Hard chain segments usually affect the softening melt temperature and high temperature properties of the polymer. Polyurethanes prepared from aromatic isocyanates contain rigid aromatic rings in the hard segment, which increases the cohesive strength of the hard segment and generally makes the material stronger than aliphatic isocyanate polyurethanes, but they are less resistant to UV degradation and are prone to yellowing. Aliphatic polyurethanes do not yellow.
50. Classification of polyurethane foam
A: (1) Rigid and soft 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 pre-polymerization production, (7) continuous and intermittent production, (8) block foam and molded foam.
51. The basic reaction of foam preparation
A: It refers to the reaction of -NCO with -OH, -NH2 and H2O, and the reaction with polyol, and the “gel reaction” in the foaming process generally refers to the formation of carbamate. Because the foam is made of polyfunctional raw materials, a cross-linked network is obtained, which makes the foaming system gel rapidly. The reaction formula of the group is as follows:
In a foaming system where water is present, a foaming reaction is generated. The so-called “foaming reaction” generally refers to the reaction of water with isocyanate to form substituted urea and release CO2.
52. The nucleation mechanism of bubbles
The reaction of the raw material in the liquid or the temperature of the reaction production produces gaseous substances and makes the gas volatilize. As the reaction proceeds and a large amount of reaction heat is generated, the amount of gaseous substances occurring and volatilized increases. After the gas concentration increases beyond the saturation concentration, a dimensional bubble begins to form and rise in the solution phase.
53. The role of foam stabilizers in the preparation of polyurethane foam
Answer:It has emulsifying effect, which makes the mutual solubility between the components of foam materials enhanced; after adding silicone surfactant, because it greatly reduces the surface tension of liquid γ , the free energy required to increase when the gas is dispersed is reduced, so that the air dispersed in the raw material is easier to nucleate in the mixing process of stirring, which helps the generation of fine bubbles and improves the stability of foam.
54. Stabilization mechanism of foam
A: The addition of appropriate surfactants helps to generate fine bubble dispersions.
55. Formation mechanism of open cell foam and closed cell foam
A: The formation mechanism of open cell foam: Most of the time, when the maximum pressure is generated in the bubble, the strength of the bubble wall formed by the gel reaction is not high, and it cannot withstand the stretching of the wall film caused by the increase of gas pressure, so the bubble wall film is pulled, and the gas escapes from the rupture, forming open cell foam.
Closed cell foam formation mechanism: For hard foam system, due to the use of multifunctional, low molecular weight polyether polyol and polyisocyanate reaction, the gelation speed is relatively fast, the gas in the bubble pore can not squeeze through the bubble wall, so as to form a closed cell foam.
56. Physical foaming agent and chemical foaming agent foaming mechanism
A: physical blowing agent: physical blowing agent is the foam pore is formed by a change in the physical form of a substance, that is, through the expansion of compressed gas, liquid volatilization or dissolution of solids.
Chemical blowing agents: Chemical blowing agents are those compounds that can release gases such as carbon dioxide and nitrogen after decomposition by heating and form fine pores in the composition of the polymer.
57. Preparation methods of flexible polyurethane foam
A: One-step method and prepolymer method
Prepolymer method: That is, the prepolymer containing free NCO group is made by the reaction of polyether polyol and excess TDI first, and then mixed with water, catalyst, stabilizer, etc. to make foam. One-step method: Various raw materials are mixed directly into the mixing head through calculation to make foam in one step, which can be divided into continuous type and intermittent type.
58. The characteristics of horizontal foaming and vertical foaming
A: Horizontal foaming characteristics: Side film lifting method: This method adds upward traction side paper device on the basis of the original horizontal foaming machine, so that the foam edge and the middle rise synchronously foaming, so as to make a foam block close to the flat top. Balanced platen method: characterized by the use of top paper and top cover. Overflow trough method: characterized by the use of overflow trough and conveyor landing plate.
Vertical foaming characteristics: can use a smaller flow rate to get a large cross-sectional area of foam blocks, while usually with the horizontal foaming machine to get the same cross-sectional blocks, the flow level is 3 to 5 times larger than vertical foaming; because of the large cross-sectional foam blocks, there is no up and down
