Polyurethane (PU), also known as polyurethane, is a polymer material with excellent mechanical properties formed by the polycondensation reaction of polyols and polyisocyanates.Its synthesis can be traced back to 1937, when Professor Byaer first synthesized a linear polyurethane resin using 1,6-hexamethylene diisocyanate and 1,4-butanediol as raw materials.The main types of polyurethane include polyether, polyester, polyimide, polyurea, etc. They can be made into polyurethane plastics (mainly foam plastics), polyurethane fibers (called spandex in China), polyurethane rubber and elastomers. And other materials.
After nearly eight decades of technological development, this material has been widely used, involving products such as coatings, adhesives, fabric finishing agents, leather modifiers, polyurethane soft/rigid foams, elastomers, etc., and is used in the fields of textiles, construction, aviation, shipping, transportation, medicine, electronics, etc. Soft polyurethane is mainly a thermoplastic linear structure. It has better stability, chemical resistance, resilience and mechanical properties than PVC foam materials, and has smaller compression deformation. It has good thermal insulation, sound insulation, earthquake resistance and anti-toxic properties. Therefore, it is used as packaging, sound insulation and filtration materials. Rigid polyurethane plastic is light in weight, has excellent sound insulation and thermal insulation properties, is resistant to chemicals, has good electrical properties, is easy to process, and has low water absorption. It is mainly used in construction, automobiles, aviation industry, and thermal insulation structural materials. The performance of polyurethane elastomers is between that of plastics and rubbers. It is oil-resistant, wear-resistant, low-temperature-resistant, aging-resistant, high in hardness and elastic. It is mainly used in the footwear industry and the medical industry. Polyurethane can also be used to make adhesives, coatings, synthetic leather, etc.
Physical and chemical properties
Physical properties
Physical properties: The physical properties of polyurethane vary depending on its type. Generally speaking, the density of polyurethane is between 1.2 and 1.3 g/cm³. It has the characteristics of high density, high strength, high toughness, and high wear resistance. Polyurethane has a yellow or brownish-yellow viscous liquid appearance. It is insoluble in water, but soluble in organic solvents such as styrene and xylene. Its melting point, relative density, solubility and other physical and chemical properties vary depending on the specific type.
Chemical properties
Physical properties: The physical properties of polyurethane vary depending on its type. Generally speaking, the density of polyurethane is between 1.2 and 1.3 g/cm³. It has the characteristics of high density, high strength, high toughness, and high wear resistance. Polyurethane has a yellow or brownish-yellow viscous liquid appearance. It is insoluble in water, but soluble in organic solvents such as styrene and xylene. Its melting point, relative density, solubility and other physical and chemical properties vary depending on the specific type.
Computational chemistry data
Molecular weight: 302.37 g/mol
Exact mass: 302.18417193
Isotope mass: 302.18417193
Complexity: 230
Number of rotatable chemical bonds: 11
Number of hydrogen bond donors: 3
Hydrogen bond acceptor count: 7
Topological surface area: 120
Number of heavy atoms: 21
Number of atomic stereocenters determined: 0
Number of uncertain atomic stereocenters: 0
Determine the number of chemical bonding stereocenters: 0
Number of uncertain chemical bonding stereocenters: 0
Isotope Atom Count: 0
Number of covalent bond units: 2
Development Overview
Polyurethane (PU) was first developed by German scientists in the 1930s. German scientists polycondensed liquid isocyanate and liquid polyether or diol polyester to produce a new material. The physical performance parameters of this material were different from those of polyolefin materials at the time. Scientists named it polyurethane. With the end of World War II, the chemical manufacturing industry in the United States flourished, and polyurethane soft foam plastics were synthesized in the 1950s. This was a milestone research in the chemical industry at the time and provided a solid technical foundation for the future development of the polyurethane industry.
Overview of the main raw material market
The main raw materials for polyurethane include diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), and polypropylene glycol (PPG), which have now become international commodities. The production technology and equipment for these raw materials are very complex, and product competition is quite fierce. As a result of long-term development, production has been relatively concentrated.
Isocyanate is a general term for various esters of isocyanic acid. If classified by the number of -NCO groups, it includes monoisocyanate R-N=C=O, diisocyanate O=C=N-R-N=C=O and polyisocyanate, etc. It can also be divided into aliphatic isocyanate and aromatic isocyanate. Currently, aromatic isocyanate is the most widely used, such as toluene diisocyanate TDI and diphenylmethane diisocyanate MDI.
(1) Toluene diisocyanate TDI (relative molecular weight 174.16)
TDI is a light yellow or colorless transparent liquid with a pungent odor. It has the advantages of good economy, storage, and convenient transportation, but it is not resistant to yellowing. It has high reactivity, mainly due to the electron-withdrawing effect of the benzene ring in its structure. The reaction temperature needs to be controlled during synthesis.
It is mainly divided into 2 isomers: 2,4-TDI and 2,6-TDI.1. There are 3 main types in industry: (1) TDI-100 contains 100% 2,4-TDI; (2) TDI-80 contains 80% 2,4-TDI and 20% 2,6-TDI; (3) TDI-65 contains 65% 2,4-TDI and 35% 2,6-TDI, among which TDI-80 is the most common.
(2) MDI diphenylmethane diisocyanate (relative molecular weight 250.26)
MDI mainly includes pure MDI, polymerized MDI, liquefied MDI, crude MDI, etc. Pure MDI is a white or light yellow solid, toxic, unstable at room temperature, easy to self-polymerize, and needs to be stored below 5°C. Polymerized MDI is a brown transparent liquid and can be stored at room temperature. Crude MDI is a mixture of polymerized MDI and pure MDI, also known as PAPI. MDI has good molecular regularity, hardness, solvent resistance, and water resistance, but is not resistant to yellowing. It is mainly used as raw materials for plastic tracks, soft and hard foams, etc.
In actual industrial production, TDI and MDI are substitutes. The foam density produced by the TDI system is relatively large, while the polyurethane produced by MDI has better moldability.
The production technology and equipment requirements for MDI are relatively complex, and the production technology is controlled by several giant companies around the world. More than 95% of the world’s MDI production companies are concentrated in Asia and Europe. Compared with the two, the growth rate of the European market is not as fast as that of Asia, but its MDI industry started earlier and the market is more mature.
After the signing of the China-South Korea Free Trade Agreement on June 1, 2015, the tax rate on polyurethane raw materials changed. The export tax rate of Chinese poly MDI fell faster than the import tax rate. With the increase in domestic polyMDI market capacity and output, the import dependence decreased and the export dependence increased.
(3) Polyoxypropylene glycol PPG
The ether bonds of polyether polyols are easy to rotate, and can be used to prepare water-based polyurethanes with good flexibility. The ether bonds are resistant to hydrolysis, and the polyurethane has good hydrolysis resistance. However, its carbon atoms are easily oxidized, so the thermal stability of the material is poor. PPG is one of the main raw materials for the production of polyurethane products. Its usage in polyurethane foam plastics can reach more than 90%, accounting for the largest proportion of usage. Due to the large scale of polyether polyol production facilities, production capacity is mainly concentrated in several large multinational companies such as BASF, Bayer, Dow Chemical, and Shell. China’s polyether polyol manufacturers have only formed a certain scale through technology introduction and independent research and development. In recent years, with the expansion of large manufacturers, the varieties and specifications of polyether polyols are basically complete, and product quality and stability have also been greatly improved.
Classification
Classification by appearance
According to the appearance of polyurethane (dispersion form and particle size), it can be classified into: polyurethane aqueous solution, polyurethane dispersion, and polyurethane emulsion (Table 1).
| Name | Polyurethane aqueous solution | Polyurethane emulsion | Polyurethane dispersion |
|---|---|---|---|
| state | Colloidal dispersion | dispersion | dispersion |
| Appearance | transparent | White turbidity | Milky white translucent |
| Particle size/nm | Less than 10 | 10～100 | Greater than 100 |
| Relative molecular weight | 100～1000 | More than 5000 | 1000～200,000 |
Classification by hydrophilic group
According to the different types of ionic groups and charges, they are classified as anionic, cationic, and non-ionic. (Table 2).
| Name | Features |
|---|---|
| Anionic | Anionic groups are attached to the main chain or side chain, mainly sulfonic acid type and hydroxy acid type. Ions are introduced through chain extenders and anionic polyurethane is formed after emulsification. |
| Cationic | A tertiary amine group is introduced into the main chain or side chain, and after quaternization treatment, it contains ammonium ions or sulfonium ions (mostly quaternary ammonium ions). |
| Non-ionic | The molecule does not contain ionic groups, and the emulsifier and polyurethane are emulsified by a shearing machine or non-ionic hydrophilic groups are used as raw materials for emulsification. |
Classification by usage
According to the form of use, it can be divided into two categories: single component and two-component. (Table 3).
| Name | Features |
|---|---|
| Single component | The required waterborne polyurethane can be obtained without adding crosslinking agent and can be used directly |
| Two-component | A crosslinking agent must be added, and it cannot be used alone. Alternatively, a crosslinking agent can be added to a single-component waterborne polyurethane to increase adhesion, so that the polyurethane raw material and the crosslinking agent form a two-component |
Current status of research on polyurethane modification
There are many types of waterborne polyurethane (WPU), which have the advantages of strong functionality, low volatility, low odor, and good wear resistance, and are widely used in various industries. However, poor water resistance and poor heat resistance have limited the development of waterborne polyurethane to a certain extent, which can be treated by modification.
Generally, it is modified by acrylic acid, organic fluorine, organic silicon, nanomaterials, epoxy resin, bio-based materials, and cross-linking. In addition, modification of other materials by polyurethane is also a research hotspot.
Acrylic acid modification
Acrylic acid has good light stability, weather resistance, acid and alkali resistance, water resistance, and is not easy to yellow. It is also inexpensive. Currently, acrylic acid modification mainly adopts methods such as block, grafting, and core-shell emulsion polymerization. Through acrylic acid modification, the adhesion, weather resistance, and solid content of polyurethane can be improved. The low-cost polyurethane prepared by this method has broad application prospects and is currently widely used in many fields.For example, a super-hydrophobic layer was prepared using acrylic polyurethane and a hydrophobic ZnO bactericidal suspension , using reactive emulsifiers instead of traditional emulsifiers to prepare waterborne polyurethane with small particle size, narrow particle distribution and high solid content, or by using hexafluorobutyl acrylate (FA) to improve the thermal stability and tensile strength of the film.
Organic fluorine modification
The fluorine atom in organic fluorine has a high C-F bond energy and a short bond length, and has good water resistance, chemical solvent resistance, heat resistance, biological resistance, wear resistance, and insulation.Introducing organic fluorine into polyurethane is one of the common modification methods. The heat resistance and water resistance of the modified polyurethane film are improved.
Silicone modification
The main chain of silicone contains Si-O-Si bonds, and the side groups are formed by organic groups connected to silicon atoms. It has the advantages of thermal stability, water resistance, weather resistance, corrosion resistance, non-toxicity, tastelessness and biocompatibility. The use of silicone to modify polyurethane can improve the mechanical properties of the film and give polyurethane properties such as water resistance, weather resistance and low surface energy. Currently, there are five main methods: (1) silanol modification method; (2) aminoalkyl polysiloxane modification method; (3) hydroxyalkyl polysiloxane modification method; (4) alkoxysilane cross-linking modification method; (5) cage-type silsesquioxane (POSS) modification method. After modification, the material properties are effectively improved.
Nanomaterial modification
Nanomaterial modification can improve the mechanical properties of the film, give it functions such as heat insulation, hydrophobicity, and conductivity, and can also form an open-pore structure. Currently, metal nanomaterials and carbon nanomaterials are the main materials, among which TiO 2, graphene, and carbon nanotubes are widely studied. Modified polyurethane is mainly used in medicine, aerospace, electronics, etc.
Epoxy resin modification
Epoxy resin has epoxy groups, ether bonds, hydroxyl groups, etc. It has good stability, mechanical strength, adhesion, small curing shrinkage and low price. The modification method is mainly to introduce epoxy groups into polyurethane through ring opening, and the water resistance and solvent resistance of the modified polyurethane emulsion are improved. However, after modification, it is brittle and lacks toughness, which limits its application in high-end fields. It is mainly used in electronics, aerospace, transportation and other fields.
Cross-linking modification
Cross-linking modification refers to the cross-linking between polyurethane molecules and introduced molecules. Cross-linking modification is divided into internal cross-linking, external cross-linking and self-cross-linking. Generally, internal cross-linking modified polyurethane belongs to single-component polyurethane, external cross-linking modified polyurethane belongs to two-component polyurethane, and self-cross-linking modification refers to the introduction or blending of cross-linking groups. After modification, the water resistance, heat resistance, solvent resistance and mechanical properties of the polyurethane film are significantly improved.
Modification of bio-based materials
Bio-based materials are mainly environmentally friendly materials used to modify polyurethane. For example, chitosan, lignin, cellulose, etc. have the advantages of being renewable and green.
Product Classification
Polyurethane products mainly include the following: foam plastics, elastomers, fiber plastics, fibers, leather and shoe resins, coatings, adhesives and sealants, among which foam plastics account for the largest proportion.
Polyurethane foam
Polyurethane foam is divided into two types: hard foam and soft foam. It has excellent elasticity, elongation, compression strength and softness, as well as good chemical stability. In addition, polyurethane foam has excellent processing, adhesion, thermal insulation and other properties, and is a high-performance cushioning material.
Polyurethane elastomer
Since polyurethane elastomers have two segments, one soft and one hard, in their structure, they can be given excellent properties such as high strength, good toughness, wear resistance, and oil resistance through the design of the molecular chain. Polyurethane, known as “wear-resistant rubber”, has both the high elasticity of rubber and the rigidity of plastic.
Polyurethane fiber plastic
Polyurethane fiber plastic has high tensile strength and toughness, making it a preferred material in many applications. It has good wear resistance and excellent oil resistance, making it suitable for applications that require anti-wear performance, such as ropes, sports shoe materials, etc., and can maintain stable performance in environments where some oils and chemicals are present. Polyurethane fibers show high elasticity and resilience, making them widely used in applications with high elasticity requirements, such as elastic fabrics, springs, etc.
Polyurethane coating
Application Status
With the continuous improvement of the material living standards of the general public, polyurethane coatings have entered a new stage of rapid development with their outstanding performance advantages. According to statistical data, from 1980 to 2004, the use of polyurethane coatings in various industries has shown a very rapid development trend. The total use of polyurethane coatings has achieved a breakthrough development from 1,700 to 200,000 tons. The output of polyurethane coatings is second only to alkyd resin paint, acrylic resin paint and phenolic resin paint, becoming the fourth largest variety in the coating field. This development trend continues to this day, and its output and scope of use still maintain a very rapid development trend.
From the perspective of the research, development and application of polyurethane coatings, the most mainstream is still two-component polyurethane coatings, and its application scope in the fields of wood furniture coating is constantly expanding and improving. In addition, single-component polyurethane coatings still have very strong application advantages in the fields of automobile processing and basement waterproofing. This type of coating uses polyurethane as the main material and has very good application value in the production of various types of paints and varnishes. The newly developed acrylic polyurethane paint uses biuret as a curing agent, and its application value in automobile repair paint is quite reliable. Especially for light vehicles, large buses and vans, the coating function in vehicle processing is very worthy of recognition, and the market prospects are quite considerable. The various new types of polyurethane coatings developed on the basis of acrylic polyurethane coatings can also play an application value in other manufacturing and processing fields to meet the processing quality requirements of processed objects such as home appliances and trains.
In addition, special polyurethane coatings that can be used in floor coatings, machine tool coatings, aerospace equipment surface coatings and other fields are in the process of accelerated development and research. The relevant reports reviewed and analyzed the classification, characteristics and application fields of current polyurethane coatings.
Research and Development
(1) Waterborne polyurethane coating
In 1942, P. Schlack of Germany synthesized water-based polyurethane emulsion for the first time, and the development of polyurethane entered a new era. In 1967, the United States took the lead in achieving industrialization. In 1972, Dieterich of Bayer Company in Germany successfully prepared waterborne polyurethane coatings using diisocyanate and diol as raw materials. Compared with the synthesis of P. Schlack, the particle size is smaller (0.03-100.00 μm).
At present, the annual output of waterborne polyurethane resin in the world is about 50,000 to 60,000 tons. Waterborne polyurethane coatings use water as the coating dispersion medium. There are fewer organic solvents in the entire polyurethane coating structure system, which meets the energy-saving and emission-reduction requirements of the current environmental protection in the coating field. Therefore, the application and development of waterborne polyurethane coatings in related fields are increasingly concerned and valued by industry insiders. Up to now, although the application proportion of polyurethane coatings in the entire coating field in China is only about 4%, the engineering application of waterborne polyurethane coatings has maintained a growth rate of nearly 10% in recent years. Generally speaking, waterborne polyurethane coatings do not require additional dispersants or emulsifiers, and the molecular size and molecular structure can be appropriately adjusted according to the situation. In view of this feature, compared with the traditionally widely used latex coatings, waterborne polyurethane coatings can have better low-temperature film-forming properties, without the need to add plasticizers and film-forming aids in appropriate proportions. Compared with other coatings, waterborne polyurethane coatings not only have a good appearance, but also have a short drying time, showing a unique advantage in the field of wood coatings. Traditional solvent-based acrylic leather coatings are gradually being replaced by water-based polyurethane leather coatings. With their advantages in chemical resistance and low temperature resistance, they have attracted much attention and attention from leather coating professionals. In addition, this type of material also has very specific application value in related fields such as plastics, vehicles, industry, and anti-corrosion, and has a very broad development space.
The performance of waterborne polyurethane coatings still has certain limitations, and insufficient water resistance is one of the most important factors affecting the application of waterborne polyurethane coatings in practice. In addition, there are certain problems with the application of waterborne polyurethane coatings during engineering construction. For example, for two-component waterborne polyurethane coatings, the drying speed is relatively slow after being added to the construction raw materials, and it takes a long time to maintain. The carbon dioxide bubbles generated during the reaction between waterborne polyurethane coatings and water may remain in the coating film in large quantities, affecting its performance. In addition, high costs have also become one of the main factors affecting the industrial application of waterborne polyurethane coatings. More importantly, in waterborne polyurethane coatings, the large amount of waterborne coatings added may affect the iron substrate in engineering construction, leading to flash corrosion problems, and even affecting the wettability and appearance performance of the surface coating. In view of the above problems, in order to promote the further development of waterborne polyurethane coatings, composite modified water-dispersible polyurethane coatings should be taken as the development direction and research focus in the future, and attempts should be made to introduce some molecular structures with special functions, such as silicon-containing polymer chains and fluorine-containing polymer chains, into the polyurethane chain to improve the comprehensive performance of the coating film and give full play to its advantages in high temperature resistance, water resistance and weather resistance. Low VOC and high-performance two-component waterborne polyurethane coatings can also be taken as the focus of research and development, while reducing the cost of polyurethane coatings and improving the use efficiency.
(2) Modified polyurethane coating
For the relatively single polyurethane coating, its appearance, glossiness, water resistance and hardness still have certain limitations in the process of industrial production and application. Therefore, it is possible to try to improve its performance level by developing modified polyurethane coatings. Under the current technical level, there are two types of modification methods that can be applied to polyurethane materials: the first is to intervene by chemical methods so that polyurethane coatings can have two or more characteristics; the second is to intervene by physical methods to mix two or more resin materials with complementary characteristics so that polyurethane coatings can have diversified properties. Among them, for silicone materials, this material has a series of characteristics and advantages such as non-corrosive, non-toxic, flame retardant, ozone resistant, weather aging resistant, and electrical insulation, and has very good application value in the modification and processing of polyurethane coatings. Bayer took the lead in the basic research and development of polyurethane powder coatings and successfully developed a closed isocyanate cross-linking system. The commonly used one is the caprolactam-blocked IPDI curing system, and its curing temperature is above 170 ℃. This high-temperature curing is conducive to the high leveling of the coating film and is a variety without volatile by-products. Previous reports have also pointed out that attempts to combine silicone materials with polyurethane coatings and apply appropriate methods for modification and processing can significantly overcome the performance defects of polyurethane materials, which is of great value in expanding the application field of polyurethane materials. At the same time, the chemical structure of polysiloxane is relatively special, showing excellent stability, biocompatibility, electrical insulation, and high and low temperature resistance. Since the 1940s, it has been widely used in industrial production practices. In the process of research and development of modified polyurethane materials, it is possible to try to use polysiloxane as the soft segment to synthesize polysiloxane-polyurethane block copolymers to highlight the advantages of both polyurethane and polysiloxane, and highlight the outstanding advantages of the modified polyurethane coating in terms of surface enrichment, dielectric properties and biocompatibility. It has a very large application space and development potential.
(3) Environmentally friendly polyurethane coatings
Influenced by environmental protection requirements and the requirements for sustainable development of the entire coatings industry, relevant personnel in the industry must actively explore and develop polyurethane coating products with environmental benefits, such as light-curing polyurethane coatings, high-solid content low-viscosity polyurethane materials, and powdered polyurethane materials. Polyurethane coatings presented in the form of powders can have good physical and mechanical properties and chemical resistance, while also showing good appearance. Waterborne polyurethane dispersion resin materials have a lot of advantages over polymer materials with other structures, and are in line with environmental protection requirements. They can be dispersed in water, have no free isocyanate, are non-toxic, and have good adhesion to the substrate. Waterborne two-component polyurethane coatings are composed of waterborne polyols containing -OH groups and low-viscosity polyisocyanate curing agents containing -NCO groups. The coating film performance is mainly determined by the composition and structure of the hydroxyl resin.
One-component waterborne polyurethane coatings are a type of coating that uses waterborne polyurethane resin as a base material and water as a dispersion medium. Waterborne polyurethane coatings modified by cross-linking have good storage stability, film mechanical properties, water resistance, solvent resistance and aging resistance, and are similar to the performance of traditional solvent-based polyurethane coatings. They should be regarded as one of the most important development directions for environmentally friendly polyurethane coatings. From the perspective of future development trends, polyurethane powder coatings have become one of the most mainstream development directions in the entire coatings field, and their proportion in various types of powder coatings and even polyurethane coatings is constantly increasing. For example, in the automotive coatings processing market, polyurethane powder coatings should be the best choice and development direction in the process of coatings product development. At the same time, through technological innovation and research and development, a new generation of polyurethane powder coatings with good adaptability to low temperature environments and no volatile by-products are developed. This new type of powder coating has good similarity in performance with two-component solvent-based polyurethane coatings and can be applied to the manufacturing and processing of coatings for the new generation of automobile production lines. While ensuring the performance of the coatings, it also reflects good environmental benefits and has very considerable comprehensive benefits.
Polyurethane Adhesive
The synthesis of polyurethane adhesives is based on the unique chemical properties of isocyanates. Isocyanates are compounds containing isocyanate groups (-NCO) in their molecules. This group has a highly unsaturated bond structure with overlapping double bonds and can react with various compounds containing active hydrogen. In the field of polyurethane adhesives, isocyanates containing two or more -NCO characteristic groups are mainly used. Polyurethane adhesives are divided into general-purpose isocyanate polyurethane adhesives and yellowing-resistant isocyanate polyurethane adhesives based on whether the product turns yellow under light.
General PU adhesive
Universal isocyanates, i.e. aromatic isocyanates, are the most widely used isocyanates in the polyurethane industry. The methylene group connected to the benzene ring in the structure is easily oxidized to form quinone-type chromophores, which causes the material to turn yellow. Common universal isocyanates include TDI, MDI, and polymethyl polyphenylene isocyanate (PAPI). TDI is liquid at room temperature and is easy to use. It is the earliest isocyanate used in the polyurethane industry.
Yellowing resistant PU adhesive
In order to improve the yellowing phenomenon of polyurethane materials caused by general-purpose isocyanates, in addition to using relevant additives, the generation of benzene ring conjugated quinone structure chromophores should be avoided. For this purpose, researchers have developed many yellowing-resistant isocyanates: such as xylene diisocyanate (XDI), hexamethylene diisocyanate (HDI), isophorone isocyanate (IPDI), etc.
Polyurethane Adhesive Modification
Although polyurethane adhesives have excellent properties, they are easily affected by external environments such as light, heat, oxygen, and water, which reduces their use value. With the development of society, the single performance of polyurethane adhesives can no longer meet application requirements. Research on the modification of polyurethane adhesives has become a hot topic, among which physical modification and chemical modification are the main modification methods.
(1) Physical modification
Physical modification is a method of improving the performance of polyurethane adhesives by doping some fillers and additives under certain conditions during the preparation of polyurethane adhesives. Quartz powder has good compatibility with polyurethane adhesive systems and has a significant effect on improving the tensile strength, elongation at break and tear strength of polyurethane adhesive products. Nano boron nitride (BN) is ultrasonically dispersed in polyols and then reacted with MDI to prepare polyurethane adhesive films for food packaging. Compared with the adhesive without nano BN, the water vapor permeability of the film was reduced by 50%, the bonding strength was increased by 37%, and the peel strength was increased by 7.14%. When SiO2 nanofibers were added to the polyurethane matrix, it was found that the hydroxyl groups on the surface of the SiO2 nanofibers formed a tight cross-linked structure with the polyurethane, which improved the adhesion of the adhesive, the hardness of the film, and the tensile strength, but also increased the viscosity of the colloid.
(2) Chemical modification
Chemical modification is a modification method that changes the type of atoms or atomic groups on the molecular chain and their bonding mode through polymer chemical reactions. Block and grafting are several commonly used chemical modification methods for polyurethane adhesives. Among them, high-performance epoxy resin-modified polyurethane adhesives, acrylate-modified polyurethane adhesives, and silicone resin-modified polyurethane adhesives are the targets of competitive development in the industry. Epoxy resin has many advantages such as good adhesion, corrosion resistance, and high strength, but its toughness is poor. Introducing epoxy groups into the polyurethane system can produce products with better performance. Silane-modified polyurethane adhesives can not only improve flexibility but also avoid the shortcomings of traditional polyurethane adhesives, such as easy blistering during curing and poor adhesion to smooth substrates.
Product application areas
Furniture Industry
In the furniture industry, imitation wood materials are one of the main applications of polyurethane rigid foam. Imitation wood materials are lightweight and have density and strength comparable to wood. Using this material to make furniture will not only prevent cracks after molding, but also reduce the cost of production and manufacturing. As the public’s awareness of environmental protection continues to increase, imitation wood materials will be used more and more in the furniture industry, replacing the position of natural wood in furniture.
Construction Industry
Polyurethane rigid foam is the preferred material for building insulation. It has a simple structure, long product life, high construction efficiency, high fire resistance and low overall cost. As China’s energy conservation and environmental protection policies continue to be implemented, the construction industry will face more stringent tests during the “13th Five-Year Plan” period, and polyurethane rigid foam will be widely used in the field of building insulation. In addition, polyurethane is widely used as a waterproof coating in building roofs, exterior walls, ceilings, basements, kitchens and bathrooms, roads and bridges, etc. With the continuous development of China’s rail transit and high-speed railway industry, polyurethane waterproof coatings will also be widely used in the field of railway construction, there is still a lot of room for development.
Shoemaking and leather industry
China is the world’s largest exporter and production base of footwear products, with footwear production accounting for 60% of the world’s total. Polyurethane (PU) material is a type of polyurethane. In addition, slurry is mainly used to manufacture artificial leather, synthetic leather and other related products. With the continuous improvement of China’s industrial production technology, the manufacturing cost of polyurethane slurry will continue to decrease, and its development potential is unquestionable.
Transportation Industry
Polyurethane is also present in the transportation industry. It mainly includes soft, hard and semi-hard foam plastics, as well as polyurethane elastomers, polyurethane glues, polyurethane sealants and polyurethane coatings. The total amount of polyurethane required for a finished car is about 30 kg. The amount of high-quality polyurethane products used in cars is also one of the factors to measure the grade of cars. China is a major automobile country, ranking first in the world in terms of both automobile manufacturing volume and car ownership. According to relevant statistics, China consumes nearly 400,000 tons of polyurethane in the automotive industry each year. With the continuous introduction of new energy vehicle models, the consumption of polyurethane in the automotive industry will have a broader room for growth.
In addition to the automotive industry, China’s cold chain transportation industry is another area of polyurethane development. As the living standards of the Chinese people continue to improve, more and more people have a sharp increase in demand for flowers and aquatic products from all over the country, which has driven the development of China’s cold chain transportation industry. Transport vehicles in the cold chain transportation industry usually use polyurethane rigid foam sandwich panels as insulation materials. At the same time, a large amount of polyurethane insulation materials are also required during the construction of cold storage, which is also a major benefit to China’s polyurethane industry.
Home appliance industry
Refrigerators and freezers mainly use polyurethane rigid foam as the insulation material for home appliances. Under the same volume conditions, this material can effectively increase the internal volume of refrigerators and freezers and reduce the total amount of external shell materials. It can not only reduce production costs, but also reduce the weight of the refrigerator and improve the insulation performance. In China, the weight of polyurethane rigid foam required to manufacture a standard volume refrigerator is about 6-8kg, while a freezer requires about 11kg of rigid foam plastic. China is a major refrigerator manufacturing country and has gradually become the world’s integrated refrigerator research and development, production and transportation base; the total amount of polyurethane rigid foam used in China’s refrigerator manufacturing industry is about 800,000 tons per year. With the continuous implementation of China’s “energy conservation and emission reduction” policy for home appliances, the total amount of polyurethane used in refrigerators will show a downward trend, and various manufacturing companies will move towards a “green and environmentally friendly” development path.
In addition, the insulation material of solar water heaters is also polyurethane rigid foam. China’s solar energy industry is an emerging industry. With the continuous optimization of the energy structure, the solar energy industry will be further developed and polyurethane industrial products will also be more popular.
Sports Industry
Polyurethane paving materials are widely used in the construction of plastic tracks, indoor basketball courts, and volleyball courts in sports stadiums and public sports venues. In the past few years, the “toxic track” incident continued to ferment, resulting in the entire industry being in a low-end and fiercely competitive state, and many unlicensed small businesses were seeking huge profits; with the continuous improvement of the quality of China’s polyurethane industrial products, the quality of polyurethane paving materials has been greatly improved, and companies are constantly moving towards environmentally friendly paving products
Other
Polyurethane can also be used to package fragile goods, especially in the transportation packaging of some precision instruments, handicrafts, fragile goods, etc.; such products can also be used in the fields of aviation, aerospace, automobile manufacturing, liquefied natural gas transport vehicle (ship) manufacturing, etc.
Safety Matters
Health Hazard Data
Acute toxicity data:
(1) Test type: TCLo – Lowest Published Toxic Concentration
Exposure routes: Inhalation
Species observed: Human
Dose/Duration: 12 mg/m^3/11W-C
Toxic Effects: Sense Organs and Special Senses (Eyes) – Changes in Visual Field
(2) Test type: TDLo – lowest published toxic dose
Exposure route: trachea
Species Observed: Rodents – Rat
Dose/Duration: 225 mg/kg
Toxic Effects: Tumorigenicity – Equivocal tumorigenicity according to RTECS criteria Lung, thoracic or respiratory – Emphysema Lung, thoracic or respiratory – Fibrosis (interstitial)
(3) Test type: TDLo – lowest published toxic dose
Exposure route: Implantation
Species Observed: Rodents – Rat
Dose/Duration: 293 mg/kg
Toxic Effects: Tumorigenicity – Equivocal tumorigenicity by RTECS criteria Liver – Tumors Hematology – Lymphomas, including Hodgkin’s disease
(4) Test type: TD – toxic dose (except the lowest dose)
Exposure route: Implantation
Species Observed: Rodents – Rat
Dose/Duration: 10g/kg
Toxic effects: Tumorigenicity – equivocal tumorigenicity according to RTECS criteria Immunology including hypersensitivity – increase in cellular immune response.
General description of human hazards
1. Respiratory tract irritation: During the production and processing of polyurethane, some toxic substances, such as isocyanate, may be produced. When people inhale these toxic substances, they will irritate the respiratory tract and cause symptoms such as coughing, wheezing, and asthma. In severe cases, it may also cause difficulty breathing or even suffocation.
2. Skin contact allergy: Direct contact with polyurethane may cause skin contact allergy. This allergic reaction manifests as skin redness, itching, rash and other symptoms. If not treated in time, these symptoms may further develop into dermatitis or eczema. Therefore, when contacting polyurethane products, it is recommended to wear gloves and other protective equipment to avoid direct contact with the skin.
3. Chronic toxic effects: Long-term exposure to an environment containing polyurethane may produce chronic toxic effects on the human body. For example, such long-term exposure may cause damage to the nervous system, liver damage, etc., thus posing a potential threat to physical health.
In order to reduce contact with polyurethane and its related chemicals, especially in the production and processing environment, necessary protective measures should be taken, such as wearing masks and gloves, to ensure personal safety. If any discomfort occurs, seek medical attention in time.
