Introduction to Polyurethane Classroom

Polyurethane, also known as polyurethane, is a general term for macromolecular compounds containing repeating amino ester groups on the main chain. It is formed by the addition of organic diisocyanates or polyisocyanates with dihydroxy or polyhydroxy compounds. In addition to carbamate, polyurethane macromolecules can also contain functional groups such as ether, ester, urea, biuret, and urea based formate. According to the different raw materials used, there can be products with different properties, generally divided into two categories: polyester type and polyether type. It can be used to manufacture plastic, rubber, fiber, rigid and soft foam plastics, adhesives and coatings. Polyurethane is an emerging organic polymer material, known as the “fifth largest plastic”. Due to its excellent performance, it is widely used in many fields such as construction, automotive, light industry, textile, petrochemical, metallurgy, electronics, national defense, medical, machinery, etc.
[Raw Materials]
TDI, MDI, AA and other products belong to polyurethane raw materials and cannot be called polyurethane products. Polyurethane raw materials mainly include isocyanates, polyester polyols (generated by the reaction of polyols and polyacids, commonly used polyacids include adipic acid, commonly used polyols include 1,2-butanediol, ethylene glycol, etc.), polyether polyols (commonly used PPG, POP, PTMEG, etc.), solvents (commonly used DMF, TOL, MEK, etc.), chain extenders (commonly used BDO), and various additives.
(Isocyanate is a general term for various esters of isocyanate. If classified by the number of – NCO groups, it includes monoisocyanates R-N=C=O and diisocyanates O=C=N-R-N=C=O, as well as polyisocyanates. Currently, the most widely used and produced are Toluene Diisocyanate, abbreviated as TDI, and Methylenediphenylmethane diisocyanate, abbreviated as MDI.)
[TDI]
Toluene diisocyanate, abbreviated as TDI, is mainly used in soft foam, coatings, elastomers, and adhesives. Among them, soft foam is the largest consumer sector, accounting for over 70%, and coatings account for over 15%. Soft polyurethane foam materials are widely used in the fields of furniture, construction and transportation. In addition, TDI can also be used to generate rigid polyurethane foam materials, adhesives, concrete sealants, nylon-6 crosslinkers, polyurethane coatings and polyurethane elastomer intermediates.
[MDI]
Diphenylmethane diisocyanate, abbreviated as MDI, can be divided into pure MDI, polymerized MDI, liquefied MDI, modified MDI, etc. Pure MDI is mainly used to generate slurries, shoe sole solutions, spandex, TPU, and polyurea spray coatings. Polymerized MDI is mainly used in the production of polyurethane rigid foam and CASE fields. Polyurethane hard foam is widely used in the insulation industry, such as refrigerators, freezers, solar water heaters, insulation pipes, etc. It can also be used to produce imitation wood furniture, PU panels, etc.
[Polymethylene polyphenyl polyisocyanate]
Polymethylene polyphenyl polyisocyanate, abbreviated as PAPI, or crude MDI. PAPI is actually a mixture of 50% MDI and 50% polyisocyanates with a functional degree greater than 2. When heated up, it can generate agglomeration. Soluble in chlorobenzene, o-dichlorobenzene, toluene, etc. PAPI has low activity and low vapor pressure, only one percent of TDI, so its toxicity is very low. Used for manufacturing polyurethane adhesives, it can also be directly added to rubber adhesives to improve the bonding performance between rubber and nylon or polyester threads.
[Other isocyanates (HDI), etc.]
For example, 1,6-hexanediisocyanate (HDI), benzylidene diisocyanate (XDI), naphthalene-1,5-diisocyanate (NDI), etc., the latter two products are currently not widely used in the domestic market. HDI, due to its good yellow resistance, will replace TDI in the paint industry and be widely used. Currently, the use of HDI in some high-end automotive paints is quite common.
(Polyester polyols are usually formed by condensation of organic dicarboxylic acids with polyols or polymerization of lactone feather polyols. Dicarboxylic acids include benzoic acid or phthalic anhydride or its esters, adipic acid, halogenated phthalic acid, etc. Polyols include ethylene glycol, propylene glycol, diethylene glycol, trimethylolmethane, pentaerythritol, etc.)
[Adipic acid]
Abbreviated as AA, in nylon 66 salt, it is mainly used to produce adiponitrile and then produce adipic diamine, and synthesized with adipic diamine to produce polyamide 66 (nylon 66). Polyamide 66 can be used as engineering plastics and nylon fibers. The most important use of adipic acid in the field of polyurethane is to produce polyurethane elastomers, which are the main raw materials for PU resin and shoe sole original solution factories. React with dicarboxylic acid to produce polyester polyols, which are used to produce slurries or shoe soles with pure MDI and other solvents. In addition, it can also be used for adhesives, plasticizers, polyester polyols, TPU, etc.
[1,4-butanediol]
Abbreviated as BDO, it is mainly used in the production of tetrahydrofuran (THF), g-butyrolactone (GBL), polybutylene terephthalate (PBT), and polyurethane. In the field of polyurethane, it can be used to produce slurries, shoe soles, TPU, spandex, etc. At present, there are four main industrial production process technologies for BDO worldwide: Reppe method, butadiene method, butane/maleic anhydride method, and epoxypropane/propylene alcohol method.
[Ethylene glycol (EG MEG), diethylene glycol (DEG), propylene glycol]
These products, like BDO, are mainly used as raw materials for polyester polyols in the spectrum industry, but compared to BDO, the proportion of these polyols used in the PU industry is very small.
(Polyether polyols, collectively known as PPG, are important derivatives of epoxy propane and one of the main raw materials for synthesizing polyurethane. Due to the different types of initiators, the produced polyethers can be divided into soft foam polyethers, hard foam polyethers, and elastic polyethers. The biggest use of polyether polyols is to produce polyurethane plastics, followed by surfactants such as soft foam stabilizers, defoamers for papermaking industry, crude oil demulsifiers, acid treatment wetting agents for oil wells, and high-efficiency low foam detergents. They are also used as lubricants, hydraulic fluids, heat exchange fluids, quenching agents, latex foaming agents, various cutting and stretching agent components, and special solvents.)
[Polytetramethylene ether glycol]
PTMEG, abbreviated as PTMEG, is a polymer of polyhydrofuran. Mainly used for producing polyurethane elastic fibers (i.e. spandex), polyurethane elastomers, synthetic leather, coating additives, adhesives, sealants, and polyamides.
(Additives)
[DMF]
The full name is dimethylamide, which is not only a widely used chemical raw material, but also an excellent solvent with a wide range of uses. DMF is mainly used for the synthesis of leather resins and the production and processing of PU leather, accounting for more than 90% of the total. It can also be used in other industries such as medicine, acrylic, pesticides, dyes, electronics, etc.
(Other)
[Epoxy propane PO]
It is the third largest propylene derivative besides polypropylene and acrylonitrile, and is an important basic organic chemical synthesis raw material mainly used for the production of polyethers, propylene glycol, etc. It is also the main raw material for fourth generation detergents, non-ionic surfactants, oilfield demulsifiers, pesticide emulsifiers, etc. The derivatives of epoxy propane are widely used in industries such as automobiles, construction, food, tobacco, pharmaceuticals, and cosmetics. Nearly a hundred downstream products have been produced, making them important raw materials for fine chemical products.
[Tetrahydrofuran THF]
It is a type of heterocyclic organic compound and one of the strongest polar ethers. It is used as a medium polarity solvent in chemical reactions and extraction, and is an important raw material for the production of polytetramethylene ether glycol PTMEG. It is also the main solvent in the pharmaceutical industry.
[A component material]
It refers to a composite material composed of a combination of polyols (polyethers or polyesters) and foaming agents, commonly known as white material, which is one of the main raw materials for forming polyurethane rigid foam.
[B component material]
It refers to raw materials mainly composed of isocyanates, commonly known as black materials, and is also one of the main raw materials for forming polyurethane rigid foam.

[Craft]
{Phosgene]
Phosgene is an important organic intermediate with many applications in pesticides, engineering plastics, polyurethane materials, and military applications. Isocyanate products produced from phosgene, such as TDI, MDI, and PAPI, are important raw materials for polyurethane hard foam, soft foam, elastomers, and synthetic leather; Some varieties of isocyanates are widely used in polyurethane coatings, while there are also special varieties used in adhesives, such as Lekner adhesive.
[Decomposition method]
The decomposition method is to decompose the residue of isocyanates with caustic soda to form corresponding aromatic amine compounds, and then distill and recover the amine compounds. Alternatively, the decomposition solution can be directly used as a crosslinking agent for polyurethane elastomers, waterproof materials, paving materials, etc. Alternatively, the alkaline solution can be further oxidized to propylene, and then polymerized to produce the corresponding aromatic amine propylene oxide polyether alcohol, which is used as the raw material for hard foam.
[Solution method]
It is a method to dissolve isocyanate residue in organic solvent to form an organic solvent containing NCO group, and then use it as coating, adhesive and foam plastic.
[Alcoholic hydrolysis]
It refers to the method of heating and decomposing polyurethane foam with alcohol compounds as decomposing agents to recover polyether polyols.
[Cracking method]
It refers to the method of recovering polyether and aromatic diamine with caustic soda as decomposition agent of waste polyurethane foam.
[One step foaming method]
It is a method that all raw materials are mixed at the same time and directly injected into the mold, and then solidified at a certain temperature to form foam plastics.
[Complete prepolymerization method]
It is the reaction of all polyester or polyether with isocyanate to form prepolymer, which will react with water under the action of catalyst to form foam plastic products.
[Semi prepolymer method]
It refers to the foamed plastic obtained by first reacting the excess isocyanate with polyester or polyether, and the content of free isocyanate in the obtained prepolymer ranges from 20% to 35%. When foaming, the prepolymer is mixed with polyester or polyether, foaming agent, foam stabilizer, catalyst, etc.
[Mechanical pouring foam]
It refers to using a foaming machine instead of manual operation to mix raw materials in proportion and inject them into the mold or cavity.
[Spray foaming molding]
It refers to the molding method of spraying the raw materials of hard disk polyurethane foam directly onto the surface of the object and foaming on this surface.
[Self skinning foam plastic]
Also known as whole skin molded foam plastic, it refers to the foam plastic products that use a special process to form a solid skin of PU components at one time.

[Application]
[Polyurethane soft foam]
Soft polyurethane foam, referred to as polyurethane soft foam for short, is a flexible polyurethane foam with certain elasticity. It is a polyurethane product with the largest amount of polyurethane products, mainly used as furniture cushion, mattress, vehicle seat cushion and other cushion materials. In industry and civil use, soft foam is also used as filter material, sound insulation material, shock proof material, decoration material, packaging material and thermal insulation material. According to the degree of softness and hardness, that is, the load resistance performance, polyurethane soft foam can be divided into ordinary soft foam, ultra soft foam, high load-bearing soft foam, high rebound soft foam, etc.
[Polyurethane rigid foam]
Rigid polyurethane foam, referred to as rigid polyurethane foam for short, is a rigid foam material with waterproof box, thermal insulation and other functions formed by the mixing reaction of component A and component B. Polyurethane rigid foam is mostly a closed cell structure, with excellent characteristics such as good insulation effect, light weight, high specific strength, and convenient construction. At the same time, it also has characteristics such as sound insulation, shock resistance, electrical insulation, heat resistance, cold resistance, and solvent resistance. It is widely used as insulation materials for refrigerators, freezers, refrigerated vehicles, buildings, storage tanks, and pipelines, and a small amount is used in non insulation situations such as imitation wood and packaging materials.
[Polyurethane semi-rigid polyurethane foam]
The physical and mechanical properties of polyurethane semi-rigid foam plastic are between soft and hard foam, so it can also be called “semi soft” foam plastic, which is used to prepare functional parts such as steering wheel, armrest, bumper and interior trim.
[Imitation wood]
High density (300-700kg/m3) polyurethane rigid foam or glass fiber reinforced rigid foam is a kind of structural PU foam, also known as wood imitation. It has the characteristics of high strength, good toughness, dense and tough crust, simple molding process, high production efficiency, etc. Its strength can be higher than that of natural wood, and its density can be lower than that of natural wood. It can replace wood imitation as a high-grade product.
[Polyurethane Elastomers]
(1) Cast polyurethane elastomer (referred to as CPU)
It is a type of polyurethane elastomer that is poured and reacted by liquid resin through pouring technology. It is the most widely used and largest product of polyurethane elastomers.
(2) Thermoplastic polyurethane elastomer (TPU)
It is a linear block copolymer composed of low polymer polyol soft segments and diisocyanate chain extender hard segments, which can be classified into polyester and polyether types, accounting for about 25% of the total amount of polyurethane elastomers.
(3) Mixed polyurethane elastomer (MPU)
It first synthesizes and stores stable solid rubber, and then processes it through a mixing machine to produce a thermosetting network molecular structure polyurethane elastomer, which accounts for about 10% of the total amount of polyurethane elastomers.
According to their different properties, polyurethane elastomers are widely used in sieve plates and shakers in the mining industry; Rubber rollers, tapes, and seals in the mechanical industry; Tires, sealing ring transmission belts, and shock absorber springs in the automotive industry; Components such as soles, heels, and insoles in the footwear industry; Medical materials such as tracheal cannula, prosthetics, and skull defect repair.
(4) Microporous elastomer
The most typical application is the sole stock solution for shoe making, which is actually a mixture of foam and elastomer. Generally speaking, polyurethane sole stock solution is a two-component (or three-component), and component A is a mixture of hydroxyl terminated polyester polyol, water, silicone oil, and possibly a binary alcohol chain extender; Component B is a pre aggregate with NCO at the end, while component C is a catalyst. Polyurethane soles have many advantages, such as low density, soft texture, comfortable and lightweight wearing, good dimensional stability, long storage life, excellent wear resistance, flexural resistance, excellent shock absorption, anti slip performance, good temperature resistance, good chemical resistance, etc. They are often used to manufacture high-end leather shoes, sports shoes, travel shoes, etc.
[Polyurethane slurry]
Divided into wet and dry methods, it is a polymer solution system with a transparent or slightly cloudy appearance, used as a coating to prepare polyurethane synthetic leather and artificial leather. During the application process of dry polyurethane slurry, the solvent in the slurry is evaporated by heating and evaporation. Most of the solvents are toluene and butanone, and the evaporated solvent cannot be recovered, which not only pollutes the environment but also causes unnecessary waste. Wet polyurethane slurry, due to the use of DMF extracted with water during the processing, is relatively environmentally friendly. Moreover, the synthetic leather produced has good moisture permeability and breathability, with a soft, plump, and lightweight feel, and is more rich in the style and appearance of natural leather. Therefore, its development speed is extremely astonishing.
{Synthetic leather]
A plastic product that simulates the composition and structure of natural leather and can be used as a substitute material, usually made of impregnated non-woven fabric as a mesh layer and microporous polyurethane layer as a grain surface layer. Its front and back sides are very similar to leather and have a certain degree of breathability, which is closer to natural leather than ordinary synthetic leather. Generally, synthetic leather refers to polyurethane synthetic leather.
Polyurethane coating
It refers to coatings with polyurethane resin as the main film material, divided into two-component polyurethane coatings and single component polyurethane coatings. The application fields of polyurethane coatings mainly include: vehicle coating, ship, wood, building coating, anti-corrosion coating, surface coating of aircraft, plastics, rubber, leather, etc. Among them, water-based polyurethane coatings mainly use water as the main medium, with low VOC content, low or no environmental pollution, and construction characteristics, and are one of the main substitutes for solvent based coatings.
Coatings with polyurethane resin as the main membrane material are divided into five categories based on their composition and film-forming mechanism: polyurethane modified oil coatings, moisture cured polyurethane coatings, closed polyurethane coatings, catalytic cured polyurethane coatings, and hydroxyl cured polyurethane coatings.
[Polyurethane adhesive]
It refers to adhesives that contain amino ester groups or isocyanate groups in their molecular chains. Polyurethane adhesives are divided into two categories: polyisocyanates and polyurethane. The polyisocyanate molecular chain contains isocyano and carbamate groups, so the polyurethane adhesive shows high activity and polarity, and has excellent chemical adhesion with the substrate containing active hydrogen, such as foam, plastic, wood, leather, fabric, paper, ceramics and other porous materials, as well as metal, glass, rubber, plastic and other materials with smooth surfaces.
Polyurethane adhesive is an important component of the rapidly developing polyurethane resin, which has excellent properties and has been widely used in many aspects. It is one of the important varieties in the synthesis of adhesives.
(1) Polyisocyanate adhesive
Polyisocyanate adhesive is an adhesive composed of polyisocyanate monomers or their low molecular weight derivatives. It is a reactive adhesive with good bonding ability and is particularly suitable for bonding metals to rubber, fibers, etc. There are three common types: triphenylmethane 4,4,4-diisocyanate adhesive (TTI), tris (4-isocyanate phenyl ester) hexaphosphate adhesive (TPTI), and tetraisocyanate adhesive.
(2) Universal polyurethane adhesive
Universal PU adhesive is the earliest synthesized PU solvent adhesive in China, with the representative product being PU 101 adhesive. Generally, hydroxyl terminated PU resin is prepared by reacting polyethylene adipate and TDI, which is dissolved in organic solvents as the main component; Using a solution of ethyl acetate obtained from the addition of trimethylolpropane and TDI as the curing agent; The proportion of curing agent can be mixed from multiple to at least one, which can effectively bond different materials such as metals, plastics, fabrics, etc. Especially in the composite of polyester film and porous materials in electrical insulation materials, and the composite of packaging and decorative materials.
(3) Polyurethane adhesive for food packaging
This type of polyurethane adhesive is generally two-component, with components A and B similar to the general type. But there are some special requirements for adhesives, such as heat resistance, cold resistance, oil resistance, acid resistance, drug resistance, gas resistance, transparency, and other properties. Especially for solvent based polyurethane composite film adhesives, water-based polyurethane composite film adhesives, and solvent-free polyurethane composite film adhesives that require resistance to boiling or steaming with minimal changes in peel strength.
(4) Polyurethane adhesive for shoes
This type of adhesive is a solvent based PU resin or a modified PU resin used in combination with a curing agent. This type of adhesive requires high initial adhesion, a soft adhesive layer, good solvent resistance, and can adapt to various materials such as PU, PVC, EVA, rubber, etc. There are solvent based polyurethane shoe adhesives, adhesive based TPU solid resin adhesives, and water-based polyurethane shoe adhesives.
(5) Polyurethane hot melt adhesive
Polyurethane hot melt adhesive is made from linear or slightly branched TPU resin with relevant additives. At room temperature, it is a solid material that is heated, melted, and coated during use. After being pressed and cooled, it can be bonded within seconds to minutes; Processed into powder, strip, film and other shapes, it is easy to store, transport, and use. It is coated with glue in conjunction with specialized hot melt machines and tools, with less waste and can be recycled and reused. It is commonly used in the fields of fabric composite, book binding, packaging, decorative parts, furniture manufacturing, etc., especially suitable for high-speed production lines.
(6) Reactive polyurethane hot melt adhesive
Reactive PU hot melt adhesive, also known as wet cured PUR hot melt adhesive, is a type of PU hot melt adhesive with superior performance. After hot melt bonding, the end NCO group in the adhesive can further react and solidify in the environment or on the surface of the substrate with wet vapor and active hydrogen. Its adhesive strength, temperature resistance, moisture resistance, medium resistance, creep resistance, and other properties are further improved, making it more suitable for high demand assembly lines.
(7) Polyurethane sealant
Polyurethane sealant has excellent performance, good elasticity, flexibility, and compensation for displacement. Its price is moderate, and its adhesive strength and cohesive strength are generally higher than those of organic silicon and polysulfide sealants. In recent years, it has developed rapidly and has been widely used in sealing and bonding of buildings, automobiles, ships, container containers, civil engineering, electronics, infrastructure, etc. This type of sealant mainly includes: single component moisture cured PU sealant box two-component PU sealant.
(8) Polyurethane pressure-sensitive adhesive
This type of adhesive is single component and does not use solvents during the preparation process, avoiding solvent contamination and recovery issues. This type of adhesive has excellent adhesion, retention, stability, and heat resistance, and can also be used for underwater bonding.
[Polyurethane fiber Spandex]
Polyurethane fiber is a synthetic fiber in which more than 85% of the chemical structure is formed by linear polymer substances in the polyurethane formic acid chain segment. It belongs to high elasticity fibers and is collectively referred to as Spandex internationally, while in China it is called spandex. Spandex has been widely used in textiles and is a new type of high value-added textile material. There are four main forms of use: bare silk, core-spun yarn, covered yarn, and twisted yarn, such as stockings, swimwear, dance clothes, silk covered silk, clothing, etc. In traditional textiles, less than 5% of spandex can be added to significantly improve the grade of traditional fabrics, displaying a soft, comfortable, beautiful, and elegant style.
[Polyurethane paving material]
There are many types of polyurethane paving materials, including paving materials, waterproof materials, and grouting materials. Among them, paving materials are used for laying sports fields and floors, waterproof materials are used for waterproofing and insulation of building roofs, and grouting materials are used for water blocking, waterproofing, reinforcement, reinforcement, and anti-corrosion in departments such as buildings, coal mines, railways, oil mining, water conservancy and electricity, and geological drilling.

[Extension]
[Waterborne Polyurethane]
Waterborne polyurethane is a new type of polyurethane system that uses water as a dispersant instead of organic solvents, also known as water dispersed polyurethane, water-based polyurethane, or water-based polyurethane. Waterborne polyurethane uses water as a solvent, which is pollution-free, safe and reliable, has excellent mechanical properties, good compatibility, and is easy to modify. It can be widely used in coatings, adhesives, fabric coatings and finishing agents, leather finishing agents, paper surface treatment agents, and fiber surface treatment agents.
[Spray polyurethane]
It is an elastic material generated by the reaction of isocyanate component (component A) and resin component (component R). Isocyanates can be both aromatic and aliphatic, with component A being monomers, polymers, derivatives of isocyanates, prepolymers, and semi prepolymers; Prepolymers and semi prepolymers are prepared by reacting hydroxyl terminated compounds with isocyanates. The R component must be composed of hydroxyl terminated resins (such as diols, ternary alcohols, multi hydroxyl polymer polyols, etc.) and hydroxyl terminated (aromatic or aliphatic) chain extenders. In hydroxyl terminated resins, catalysts must be included to enhance reaction activity.
[Biodegradable PU material]
Biodegradable plastics are currently a hot topic in global development, and there are basically two technological approaches to industrialization: one is to develop high molecular weight biodegradable materials, typical varieties such as polylactic acid (PLA), polybutylene succinate (PBS), polycarbonate (PPS), polyhydroxyfatty acids (PHA) and other biodegradable plastics. Although these biodegradable plastics have excellent biodegradability, they generally have mechanical properties, especially poor toughness and temperature resistance. The other is to develop low molecular weight biodegradable polyols, which can be extended by isocyanates to produce polyurethane biodegradable plastics with high molecular weight.
[Green Biomass Polyols]
The upstream raw materials of traditional polyols come from resources such as oil and natural gas. However, with the increasingly serious energy shortage and people’s increasing awareness of environmental protection, the development and utilization of renewable resources to produce biomass polyols have made green PU materials a new highlight. At present, the main raw materials for preparing biomass polyols include vegetable oil, plant cellulose, and lignin polyols. Biomass polyols can replace some polyether polyols and are used to manufacture various PU materials, including PU hard foam, adhesives, coatings, elastomers, and plastic runways. They have been applied in fields such as automotive and building external insulation boxes and refrigerators.

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