70 Basic Concepts of Polyurethane

Polyurethane foam is derived from a mixture comprising a crude isocyanate component and a polyol component which contains all or some of the following products in a homogeneous mixture: polyols, catalysts, surfactants, water, flame-retardants, expanding agents, fillers, colourings, and pigments, in which the expanding agents comprise a pentane component associated with a diethanolamide derived from substances of vegetable origin. Polyurethane (PU) is a polymer that is made of different organic molecules (polyols and polyisocynates) that are bonded by urethane linkages. It can be either thermoplastic polyurethane (TPU) or thermosetting polyurethane. Pentanes are mainly known as blowing agents for insulation materials. But they can do even more: the three isomers n-Pentane, Isopentane and Cyclopentane can each show their advantages in a wide variety of applications, either on their own or as a blend. In this article you can read about the differences between the three Pentane isomers and the applications in which they have proven to be particularly useful.

1. Hydroxyl value: the amount of hydroxyl (-oh) contained in 1g polymer polyol is equivalent to the milligram of KOH, in mgkoh/g.
2. Equivalent: the average molecular weight of a functional group.
3. Isocyanate content: isocyanate content in the molecule
4. Isocyanate index: indicates the degree of excess isocyanate in polyurethane formula, usually represented by the letter R.
5. Chain extender: refers to low molecular weight alcohols and amines that can extend, expand or form spatial network crosslinks.
6. Hard segment: the segment on the main chain of polyurethane molecule formed by the reaction of isocyanate, chain extender and crosslinker. These groups have large cohesive energy, large space volume and large rigidity.
7. Soft segment: carbon carbon main chain polymer polyol with good flexibility. It is a flexible segment in the polyurethane main chain.
8. One step method: it refers to the method that oligomer polyol, diisocyanate, chain extender and catalyst are mixed at the same time, and then directly injected into the mold, and cured at a certain temperature.
9. Prepolymer method: the oligomeric polyol and diisocyanate are prepolymerized to form NCO terminated polyurethane prepolymer, and then the prepolymer is reacted with chain extender during pouring to prepare polyurethane elastomer, which is called prepolymer method.
10. Semi prepolymer method: the difference between semi prepolymer method and prepolymer method is that some polyester polyols or polyether polyols, chain extenders and catalysts are added to the prepolymer in the form of mixtures.
11. Reaction injection molding: also known as reaction injection molding (RIM), it is a process in which oligomers with small molecular weight are measured in liquid form, mixed instantaneously and injected into the mold at the same time, which react rapidly in the mold cavity, the molecular weight of the material increases rapidly, and a brand-new polymer containing new characteristic group structure is generated at an extremely fast speed.
12. Foaming index: that is, the number of parts of water equivalent to 100 parts of polyether is defined as foaming index (if).
13. Foaming reaction: generally refers to the reaction in which water reacts with isocyanate to generate substituted urea and release CO2.
14. Gel reaction: generally refers to the formation reaction of carbamate.
15. Gel time: the time required for liquid substances to form gel under certain conditions.
16. Opacification time: at the end of zone I, opacification occurs in the liquid-phase polyurethane mixed materials. This time is called 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, the ratio of the molar number (equivalent number) of active hydrogen group to NCO.
18. Low unsaturation polyether: it is mainly developed for PTMG. The price of PPG is reduced to 0.05mol/kg, which is close to the performance of PTMG. DMC catalyst is used, mainly Bayer acclaim series products.
19. Urethane grade solvent: the solvent selected for the production of polyurethane should consider the solubility and volatilization rate, but the solvent used for the production of polyurethane should focus on the heavy nc0 group in polyurethane. Solvents such as alcohols, ethers and alcohols that react with NCO groups cannot be selected. The solvent shall not contain water, alcohol and other impurities, nor alkali substances, which will deteriorate the polyurethane.
Ester solvents are not allowed to contain water, free acids and alcohols, which will react with NCO groups. The ester solvent used for polyurethane shall be “urethane grade solvent” with high purity. That is, the solvent reacts with excess isocyanate, and then the amount of unreacted isocyanate is determined with dibutylamine to test whether it is suitable. The principle is that the one that consumes more isocyanates is not applicable, because it indicates that the water, alcohol and acid in the ester will consume the total value of isocyanates. If it is expressed in grams of solvent required to consume leqnco group, the higher the value, the better the stability.
Isocyanate equivalent less than 2500 shall not be used as polyurethane solvent.
The polarity of the solvent has a great influence on the reaction of the resin. The greater the polarity, the slower the reaction. For example, the difference between toluene and methyl ethyl ketone is 24 times. The polarity of this solvent molecule is large, and it can form hydrogen bond with the hydroxyl group of alcohol to slow the reaction.
Aromatic solvents are better for polychlorinated esters, and their reaction speed is faster than that of esters and ketones, such as xylene. The use of ester and ketone solvents can prolong the service life of the polyurethane In the production of coatings, the “urethane grade solvent” mentioned earlier in the film selection is beneficial to the stable parts stored.
Ester solvents have strong solubility, moderate volatilization rate, low toxicity and are used more. Cyclohexanone is also used more. Hydrocarbon solvents have low solid solubility and are rarely used alone. They are often used in combination with other solvents.
20. Physical foaming agent: physical foaming agent means that foam pores are formed through the change of physical form of a substance, that is, through the expansion of compressed gas, the volatilization of liquid or the dissolution of solid.
21. Chemical blowing agent: chemical blowing agent is a compound that can release carbon dioxide, nitrogen and other gases after heating and decomposition, and form fine pores in the polymer composition.
22. Physical crosslinking: there are some hard chains in the polymer soft chain, and the hard chain has the same physical properties as the vulcanized rubber after chemical crosslinking at the temperature below the softening point or melting point.
23. Chemical crosslinking: refers to the process in which macromolecular chains are connected by chemical bonds under the action of light, heat, high-energy radiation, mechanical force, ultrasound and crosslinking agent to form a network or body structure polymer.
24. Foaming index: the number of parts of water equivalent to 100 parts of polyether is defined as foaming index (if).
25. what are the commonly used isocyanates in terms of structure?
Answer: aliphatic: HDI, alicyclic: IPDI, htdi, hmdi, aromatic: TDI, MDI, Papi, PPDI, NDI.
26. what kinds of isocyanates are commonly used? Write the structure
Answer: toluene diisocyanate (TDI), diphenylmethane-4,4 ‘- diisocyanate (MDI), polyphenylmethane polyisocyanate (Papi), liquefied MDI, hexamethylene diisocyanate (HDI).
27. What are the meanings of tdi-100 and tdi-80?
Answer: tdi-100 refers to toluene diisocyanate with 2,4 structure; Tdi-80 refers to a mixture composed of 80% toluene diisocyanate with 2,4 structure and 20% 2,6 structure.
28. What are the characteristics of TDI and MDI in the synthesis of polyurethane materials?
A: for the reactivity of 2,4-TDI and 2,6-TDI. The reaction activity of 2,4-TDI is several times higher than that of 2,6-TDI, because the NCO at position 4 in 2,4-TDI is far away from the NCO at position 2 and methyl group, and there is almost no steric hindrance, while the NCO of 2,6-TDI is greatly affected by the steric hindrance effect of ortho methyl group, so the reaction activity is affected.
The two NCO groups of MDI are far away from each other, and there are no substituents around, so the activities of these two NCOs are large. Even if one NCO participates in the reaction, the activities of the remaining NCOs are reduced, and the overall activity is still large. Therefore, the reaction activity of MDI polyurethane prepolymer is greater than that of TDI prepolymer.
29. Which of HDI, IPDI, MDI, TDI and NDI has better yellowing resistance?
Answer: HDI (belonging to invariant yellow aliphatic diisocyanate) and IPDI (the polyurethane resin made has excellent optical stability and chemical resistance, and is generally used to manufacture high-grade non discolored polyurethane resin).
30. Purpose of MDI modification and common modification methods
A: Liquefied MDI: modification purpose: Liquefied pure MDI is a kind of MDI modified by liquefaction. It overcomes some defects of pure MDI (solid at room temperature, melting when used, and the performance is affected by repeated heating). It also provides a basis for large-scale modification to improve the performance of MDI based polyurethane materials.
method:
① Urethane modified liquefied MDI.
② Carbodiimide and uretonimine modified liquefied MDI.
31. what types of polymer polyols are commonly used?
Answer: polyester polyol, polyether polyol
32. how many industrial production methods are there for polyester polyols?
Answer: A. vacuum melting method B. carrier gas melting method C. azeotropic distillation method
33. what are the special structures on the molecular backbone of polyester and polyether polyols?
Answer: polyester polyol: a macromolecular alcohol compound containing ester group on the main chain and hydroxyl (-oh) on the end group. Polyether polyol: polymer or oligomer containing ether bond (-o-) and terminal group (-oh) or amino group (-nh2) in the molecular main chain structure.
34. according to the characteristics, polyether polyols are divided into several categories?
Answer: high activity polyether polyol, grafted polyether polyol, flame retardant polyether polyol, heterocyclic modified polyether polyol, polytetrahydrofuran polyol.
35. how many kinds of ordinary polyether are there according to the initiator?
Answer: polyoxypropylene glycol, polyoxypropylene triol, hard foam polyether polyol, low unsaturation polyether polyol.
36. what is the difference between hydroxyl terminated polyether and amino terminated polyether?
Amine terminated polyether is a polyoxypropylene ether whose hydroxyl end is substituted by amino group.
37. what types of polyurethane catalysts are commonly used? Which common varieties are included?
Answer: the common types of tertiary amine catalysts are: triethylenediamine, dimethyl ethanolamine, N-methyl morphorphine, N, N-dimethyl cyclohexylamine
Metal alkyl compounds, common varieties are: organotin catalysts, which can be divided into stannous octanoate, stannous oleate, dibutyltin dilaurate.
38. what are the commonly used polyurethane chain extenders or crosslinkers?
Answer: Polyols (1,4-butanediol), alicyclic alcohols, aromatic alcohols, diamines, alcohol amines (ethanolamine, diethanolamine)
39. reaction mechanism of isocyanate
Answer: the reaction between isocyanate and active hydrogen compound is caused by the nucleophilic center in the active hydrogen compound molecule attacking the carbon atom of NCO group. The reaction mechanism is as follows:
40. how does the isocyanate structure affect the reactivity of NCO groups?
Answer: electronegativity of A.R group: if R group is electron absorbing group, the electron cloud density of C atom in -nco group will be lower and more vulnerable to attack by nucleophiles, that is, it is easier to conduct nucleophilic reaction with alcohols, amines and other compounds. If R is an electron donor group, the electron cloud density of C atom in -nco group will increase through electron cloud transmission, making it less vulnerable to attack by nucleophiles, and its reaction ability with compounds containing active hydrogen will decrease. B. Induction effect: because the aromatic diisocyanate contains two NCO groups, when the first NCO gene participates in the reaction, due to the conjugation effect of the aromatic ring, the -nco group that does not participate in the reaction will play the role of electron withdrawing group and enhance the reaction activity of the first NCO group, which is the induction effect. C. Steric hindrance effect: in the aromatic diisocyanate molecule, if two -nco groups are on an aromatic ring at the same time, the influence of one NCO group on the reaction activity of the other NCO group is often significant. However, when two NCO groups are located on different aromatic rings in the same molecule, or they are separated by hydrocarbon chains or aromatic rings, the interaction between them is small, and decreases with the increase of the length of chain hydrocarbons or the number of aromatic rings.
41. types of active hydrogen compounds and NCO reactivity
Answer: aliphatic nh2> aromatic nh2> primary oh> water > secondary oh> phenolic oh> carboxyl group > substituted urea > amide > carbamate. (if the electron cloud density of nucleophilic center is higher, its electronegativity is stronger, and its reaction activity with isocyanate is higher, and the reaction speed is faster; otherwise, its activity is lower.)
42. effect of hydroxyl compounds on their reactivity with isocyanates
Answer: the reactivity of active hydrogen compounds (Roh or rnh2) is related to the properties of R. when R is an electron withdrawing group (with low electronegativity), it is difficult to transfer hydrogen atoms, and the reaction between active hydrogen compounds and NCO is more difficult; If R is an electron donor substituent, the reactivity of active hydrogen compounds with NCO can be improved.
43. what is the purpose of the reaction of isocyanate with water
Answer: it is one of the basic reactions for preparing polyurethane foam. The reaction between them first generates unstable carbamic acid, and then decomposes into CO2 and amine. If the isocyanate is excessive, the generated amine will react with the isocyanate to generate urea.
44. during the preparation of polyurethane elastomers, the water content of polymer polyols shall be strictly controlled
Answer: no bubbles are required in elastomers, coatings and fibers, so the water content in raw materials must be strictly controlled, usually less than 0.05%.
45. difference of catalytic effect of amine and tin catalysts on isocyanate reaction
Answer: tertiary amine catalysts have high catalytic efficiency for the reaction of isocyanate with water, while tin catalysts have high catalytic efficiency for the reaction of isocyanate with hydroxyl.
46. why can polyurethane resin be regarded as a block polymer? What are the characteristics of the chain segment structure?
Answer: the chain segment of polyurethane resin is composed of hard segment and soft segment. The hard segment refers to the chain segment formed by the reaction of isocyanate, chain extender and crosslinker on the main chain of polyurethane molecule. These groups have large cohesive energy, large space volume and large rigidity. The soft segment refers to the carbon carbon main chain polymer polyol, which has good flexibility and is a flexible segment in the polyurethane main chain.
47. what are the factors that affect the properties of polyurethane materials?
Answer: cohesive energy of group, hydrogen bond, crystallinity, crosslinking degree, molecular weight, hard segment and soft segment
48. what are the raw materials for the soft and hard segments of the main chain of polyurethane materials
Answer: the soft segment is composed of oligomer Polyols (polyester, polyether glycol, etc.), and the hard segment is composed of polyisocyanate or its small molecule chain extender.
49. how do the soft and hard segments affect the performance of polyurethane materials?
Answer: soft segment: (1) molecular weight of soft segment: assuming that the molecular weight of polyurethane is the same, if the soft segment is polyester, the strength of polyurethane will increase with the increase of molecular weight of polyester glycol; If the soft segment is polyether, the strength of polyurethane decreases with the increase of molecular weight of polyether glycol, but the elongation increases. (2) Crystallinity of soft segment: it contributes greatly to the crystallinity of linear polyurethane segment. Generally speaking, crystallinity is beneficial to improve the performance of polyurethane products, but sometimes crystallization will reduce the low-temperature flexibility of materials, and crystalline polymers are often opaque.
Hard segment: the hard segment usually affects the softening melting temperature and high temperature performance of the polymer. The polyurethane prepared by aromatic isocyanate has a rigid aromatic ring in its hard segment, so its hard segment cohesion strength increases. The material strength is generally greater than that of aliphatic isocyanate polyurethane, but its UV degradation resistance is poor and it is easy to yellowing. Aliphatic polyurethane will not turn yellow.
50. classification of polyurethane foam
Answer: (1) hard foam and soft foam; (2) high density and low density foam; (3) polyester and polyether foam; (4) TDI and MDI foam; (5) polyurethane foam and polyisocyanurate foam; (6) one-step and prepolymerization production; (7) continuous and intermittent production; and (8) block foam and molded foam.
51. basic reaction of foam preparation
Answer: it refers to the reaction between -nco and -oh, -nh2 and H2O. When it reacts with polyols, the “gel reaction” in the foaming process generally refers to the formation reaction of carbamate. Because the foam raw material uses multi-functional raw materials, the crosslinked network is obtained, which makes the foaming system quickly gel.
Foaming reaction occurs in the foaming system with water. The so-called “foaming reaction” generally refers to the reaction in which water reacts with isocyanate to generate substituted urea and release CO2.

52. nucleation mechanism of bubbles
The raw material reacts in the liquid or depends on the temperature of reaction production to produce gaseous substances and volatilize the gases. With the progress of the reaction and the large amount of reaction heat, the amount of gaseous substances and volatilization is increasing. When the gas concentration increases beyond the saturation concentration, the maintained bubbles begin to form in the solution phase and rise.
53. the role of foam stabilizer in the preparation of polyurethane foam
Answer: it has emulsification function, which enhances the mutual solubility of each component of foam material; After adding silicone surfactant, the surface tension of the liquid is greatly reduced γ ， The increased free energy required for gas dispersion is reduced, which makes the air dispersed in the raw material easier to nucleate in the mixing process, helps to produce small bubbles and improves the stability of foam.
54. stability mechanism of foam
Answer: the addition of appropriate surfactant is conducive to the formation of fine bubble dispersion.
55. formation mechanism of open cell foam and closed cell foam
Answer: formation mechanism of open cell foam: in most cases, 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 wall membrane tension caused by the increase of gas pressure. The bubble wall membrane is pulled and broken, and the gas escapes from the rupture to form open cell foam.
Formation mechanism of closed cell foam: for hard foam system, due to the reaction of polyether polyols with multi-functional and low molecular weight with polyisocyanate, the gel speed is relatively fast, and the gas in the cell can not break the cell wall, thus forming a closed cell foam.
56. foaming mechanism of physical foaming agent and chemical foaming agent
Answer: physical foaming agent: physical foaming agent means that foam pores are formed through the change of physical form of a substance, that is, through the expansion of compressed gas, the volatilization of liquid or the dissolution of solid.
Chemical blowing agent: chemical blowing agent is a compound that can release carbon dioxide, nitrogen and other gases after heating and decomposition, and form fine pores in the polymer composition.
57. preparation method of flexible polyurethane foam
Answer: one step and prepolymer method
Prepolymer method: the prepolymer containing free NCO group is prepared by the reaction of polyether polyol and excess TDI, and then mixed with water, catalyst, stabilizer, etc. to make foam.. One step method: various raw materials are directly mixed in the mixing head through calculation to produce foamed plastics in one step, which can be divided into continuous type and intermittent type.
58. characteristics of horizontal foaming and vertical foaming
Answer: characteristics of horizontal foaming: side film lifting method: this method adds an upward traction side paper device on the basis of the original horizontal foaming machine to make the edge and middle of foam rise and foam synchronously, so as to make a foam block close to the flat top. Balanced pressing plate method: it is characterized by the use of top paper and top cover plate. Overflow trough method: characterized by the use of overflow trough and conveyor belt landing plate.
Vertical foaming features: large cross-sectional area of foam blocks can be obtained with a small flow rate, while the horizontal foaming machine is usually used to obtain blocks with the same cross-section, and the horizontal flow rate is 3 ~ 5 times larger than the vertical foaming; Because the cross section of the foam block is large, there is no upper and lower skin, and the side skin is thin, so the cutting loss is greatly reduced; The equipment covers a small area, the plant height is about 12 ~ 13m, and the investment cost of plant and equipment is lower than that of horizontal foaming process; The cylindrical or rectangular foam body can be produced conveniently by changing the hopper and model, especially the round block foam blank for rotary cutting.
59. basic points of raw material selection for soft foam preparation
Answer: polyols: polyether polyols used for ordinary block foam, with a molecular weight of 3000 ~ 4000, mainly polyether triols. High resilience foam mostly uses polyether triol with molecular weight of 4500 ~ 6000. When the molecular weight increased, the tensile strength, elongation and resilience of foam increased; The reactivity of the same polyether decreased. When the functionality of polyether is increased, the reaction is relatively accelerated, the crosslinking degree of polyurethane is increased, the hardness of foam is increased, and the elongation is decreased. Isocyanate: toluene diisocyanate (tdi-80) is the main Isocyanate Raw Material of polyurethane soft block foam. Tdi-65 with relatively low activity is only used for polyester polyurethane foam or special polyether foam. Catalysts: the catalysts used for block soft foam foaming can be roughly divided into two categories: one is organometallic compounds, of which stannous octanoate is the most commonly used; The other is tertiary amine, commonly used as bis (dimethylaminoethyl) ether. Foam stabilizer: the polyester type polyurethane block foam is mainly composed of non silicon surfactants, and the polyether type block foam is mainly composed of silicone olefin oxide copolymers. Foaming agent: generally, when manufacturing polyurethane soft block foam with a density greater than 21 kg / m3, only water is used as foaming agent; Only low boiling point compounds such as methylene chloride (MC) are used as auxiliary blowing agents in low-density formulations.
60. influence of environmental conditions on physical properties of block foam
Answer: influence of temperature: the foaming reaction of polyurethane accelerates with the rise of material temperature, which will cause the risk of core burning and fire in sensitive formulas. Influence of air humidity: with the increase of humidity, the hardness of foam decreases and the elongation increases because the isocyanate group in foam reacts with the moisture in the air; The tensile strength of foam increased due to the increase of urea group. Effect of atmospheric pressure: for the same formula, when foaming at a higher altitude, the density decreases significantly.
61. main differences of raw material system between cold molded soft foam and hot molded foam
Answer: the raw materials used for cold curing molding have high reactivity. During curing, there is no need for external heating. Depending on the heat generated by the system, the curing reaction can be basically completed in a short time, and the raw materials can be demoulded within a few minutes after injection molding. The raw material reaction activity of heat curing molding foam is low. After the reaction mixture is foamed in the mold, it needs to be heated together with the mold. The foam products can be demoulded only after they are completely cured in the drying channel.
62. what are the characteristics of cold molded soft foam compared with hot molded foam
Answer: ① there is no need to provide external heat in the production process, which can save a lot of heat energy; ② High sag coefficient and good comfort; ③ High rebound rate; ④ Foam without flame retardant also has certain flame retardancy; ⑤ The production cycle is short, which can save the mold and cost.
63. characteristics and applications of soft foam and hard foam
Answer: characteristics of soft foam: the cell structure of polyurethane soft foam is mostly open cell. Generally, it has the properties of low density, good elastic recovery, sound absorption, ventilation, heat preservation, etc. Application: mainly used as furniture, cushion material, vehicle seat cushion material, various soft cushion laminated composite materials. In industry and civil use, soft foam is also used as filter material, sound insulation material, shockproof material, decorative material, packaging material, heat insulation material, etc.
Characteristics of rigid foam: polyurethane foam has light weight, high specific strength and good dimensional stability; Polyurethane rigid foam has superior thermal insulation performance; Strong adhesion; Good aging performance and long thermal insulation service life; The reaction mixture has good fluidity and can smoothly fill the mold cavity or space with complex shapes; The raw materials for the production of polyurethane rigid foam are highly reactive, which can realize rapid curing, and can realize high-efficiency and mass production in the factory.
Uses: used as insulation materials for refrigerators, freezers, refrigerated containers, cold storages, etc., insulation layers for oil transmission pipelines and hot water transmission pipelines, insulation layers for building walls and roofs, insulation sandwich panels, etc.
64. key points of hard foam formula design
Answer: polyols: polyether polyols used in hard foam formulation are generally polyoxypropylene polyols with high functionality and high hydroxyl value (low molecular weight); Isocyanate: at present, the isocyanate used for hard foam is mainly polymethylene polyphenyl polyisocyanate (commonly known as Papi), i.e. crude MDI and polymerized MDI; Blowing agent: (1) CFC blowing agent (2) HCFC and HFC blowing agent (3) pentane blowing agent (4) water; Foam stabilizer: the foam stabilizer used for polyurethane rigid foam formulation is generally a block polymer of polydimethylsiloxane and polyolefin. At present, most foam stabilizers are mainly Si-C type; Catalyst: the catalyst of hard foam formula is mainly tertiary amine, and organotin catalyst can be used in special occasions; Other additives: according to the requirements and needs of different uses of polyurethane rigid foam products, flame retardant, pore opening agent, smoke inhibitor, antioxidant, mildew inhibitor, toughening agent and other additives can also be added to the formula.
65. preparation principle of whole skin molded foam
Answer: integral skin foam (ISF), also known as self skinning foam, is a kind of foam that produces a dense skin during manufacturing.
66. characteristics and applications of polyurethane microporous elastomer
A: characteristics: polyurethane elastomer is a block polymer, which generally consists of oligomer polyol flexible long chain to form soft segment, diisocyanate and chain extender to form hard segment, and hard segment and soft segment are arranged alternately to form repeated structural units. In addition to containing urethane groups, polyurethane can form hydrogen bonds within and between molecules, and the soft and hard segments can form microphase regions and generate microphase 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, the required low hardness can be achieved without plasticizer, so there is no problem caused by plasticizer migration; 2. Under the same hardness, the bearing capacity is higher than that of other elastomers; 3. Excellent wear resistance, its wear resistance is 2 ~ 10 times that of natural rubber; 4. Excellent oil and chemical resistance; Aromatic polyurethane radiation resistance; Excellent oxygen resistance and ozone resistance; 5. High impact resistance, fatigue resistance and vibration resistance, suitable for high-frequency flexure applications; 6. Good low temperature flexibility; 7. Ordinary polyurethane can not be used above 100 ℃, but it can withstand 140 ℃ high temperature with special formula; 8. Molding and processing costs are relatively low.
68. polyurethane elastomers are classified according to polyols, isocyanates, manufacturing processes, etc
Answer: 1 According to the raw materials of oligomer polyols, polyurethane elastomers can be divided into polyester type, polyether type, polyolefin type, polycarbonate type, etc. the polyether type can be divided into polytetrahydrofuran type, polyoxypropylene type, etc. according to specific varieties; 2. according to different diisocyanates, they can be divided into aliphatic and aromatic elastomers, which can be subdivided into TDI, MDI, IPDI, NDI and other types; In terms of 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 properties of polyurethane elastomers?
Answer: from the perspective of molecular structure, polyurethane elastomer is a block polymer. Generally, the soft segment is composed of oligomer polyol flexible long chain, and the hard segment is composed of diisocyanate and chain extender. The hard segment and soft segment are arranged alternately to form repeated structural units. In addition to containing urethane groups, polyurethane can form hydrogen bonds within and between molecules, and the soft and hard segments can form microphase regions and generate microphase separation. These structural characteristics make polyurethane elastomer have excellent wear resistance and toughness, and it is known as “wear-resistant rubber”.
70. performance difference between ordinary polyester type and polytetrahydrofuran ether type 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.
The elastomer prepared from polyether polyol has good hydrolytic stability, weather resistance, low temperature flexibility and mold resistance.

Where do Pentanes come from?
Pentanes are all saturated hydrocarbons that have five carbon atoms. n-Pentane and iso-Pentane occur naturally in crude oil and as a by-product of natural gas production. Cyclopentane, a ring-shaped molecule much sought after by the industry, is found more in naphtha (crude petrol), which is obtained in refineries from so-called cracking processes.

Naphtha contains varying amounts of Pentanes, depending on the origin of the crude oil, the construction of the refinery and the management of the processes. They are the first hydrocarbons to be liquid at room temperature.

Isopentane has the lowest boiling point at 29 °C, followed by n (35 °C) and Cyclopentane (49 °C). Due to the low boiling points and the large interval between them, the three isomers of Pentane can be easily separated from each other.

Pentane production: What are the differences between n-Pentane, Isopentane and Cyclopentane?
Due to their property profile, Isopentane, n and Cyclopentane can show their advantages in a wide variety of applications. Moreover, the three isomers can be mixed with each other or with other chemical components. In this way, it is possible to create Pentane blends that fulfil the desired requirement profile in the best possible way.

Application area Isopentane
Isopentane is almost insoluble in water, but shows very good solubility or unlimited miscibility with many organic solvents such as paraffins, ethers, esters, aromatics or chlorinated hydrocarbons. Therefore, the product is suitable for a wide range of applications:

Personal care products such as shaving foam and shower gel
Working medium in geothermal plants
Non-polar solvent with very high volatility
Process medium for polyethylene (PE, LLDPE) and polypropylene (PP)