Polyurethane, the versatile material found in everything from furniture foam to car seats, is a marvel of modern engineering. But did you know that its incredible properties are often enhanced by a secret ingredient: additives? These tiny but mighty compounds play a crucial role in shaping the performance and durability of polyurethane, making it the go-to material for a wide range of applications.
Beyond the Basics:
Polyurethane itself is a remarkable material, but additives are the secret sauce that unlocks its full potential. These carefully chosen compounds, added in small but precise amounts, can dramatically alter the properties of polyurethane, tailoring it to specific needs.
A Symphony of Additives:
Additives can be broadly classified into five categories, each playing a unique role in the polyurethane symphony:
- Synthetic System Additives: These additives, like catalysts, chain extenders, and crosslinkers, are essential for the initial synthesis of polyurethane. They control the chemical reactions that create the polymer, influencing its structure and properties.
- Modifiers and Operation Aids: These additives, including plasticizers, anti-wear agents, lubricants, demolding agents, fillers, and colorants, enhance the performance and processing of polyurethane. They can improve its flexibility, reduce friction, and add color or texture.
- Curing Agents: These additives, like sulfurizing agents and promotion agents, are crucial for the curing process, which transforms the liquid polyurethane into a solid, durable material. They control the crosslinking reactions that create the final structure of the polyurethane.
- Stabilizing System Additives: These additives, including heat stabilizers, light stabilizers, hydrolysis stabilizers, antifungal agents, and flame retardants, protect polyurethane from degradation and damage. They ensure that the material retains its properties over time, even in harsh environments.
- Special Additives: These additives, such as toughening agents, reinforcement agents, and conductive agents, provide specific functionalities to polyurethane. They can enhance its strength, durability, and conductivity, making it suitable for a wider range of applications.
The Future of Additives:
The research and development of new and improved additives for polyurethane is an ongoing process. Scientists are constantly exploring new ways to enhance the performance, durability, and sustainability of polyurethane, pushing the boundaries of this versatile material.
Additives are the unsung heroes of polyurethane, playing a crucial role in shaping its properties and unlocking its full potential. They are the key to creating high-performance, durable, and versatile polyurethane materials that meet the demands of a wide range of applications. As research continues, we can expect to see even more innovative additives emerge, further expanding the possibilities of this remarkable material.
Auxiliary is an important raw material in the rubber industry. Although the dosage is small, the effect is huge. Polyurethane elastomers are inseparable from synthesis to processing and application. According to their different functions, they can be divided into synthesis system, modification and operation system, Four types of additives for vulcanization system and protection system.
Synthetic auxiliaries
01 Catalysts and polymerization inhibitors
In the synthesis of polyurethane elastomer, in order to speed up the main reaction, it is often necessary to add a catalyst. Commonly used catalysts include tertiary amines and organotin. Tertiary amines include triethylenediamine, triethylamine, trimethylbenzylamine, Dimethylethanolamine, morpholine, etc., among which triethylenediamine is the most important; organotins include stannous octoate, dibutyltin dilaurate, etc. In addition, there are organic mercury, copper, lead and iron, with organic lead and mercury being the most important, such as lead octoate and phenylmercuric acetate. Organic dibasic acids, such as adipic acid and azelaic acid, can be used as catalysts for polyether polyurethane casting rubber.
02 Chain extenders and chain extender cross-linkers
Modifier operating aids
Some of these additives can improve the performance and appearance of the product, and some can improve the operating process, such as plasticizers, anti-wear agents, lubricants, fillers, colorants and release agents.
01 Plasticizer
Plasticizers are mainly used in polyurethane rubber compounds. The purpose of their use is to increase the plasticity of the rubber compound, improve the processing performance and low-temperature properties of the vulcanized rubber, and reduce the hardness and elongation strength of the vulcanized rubber. The amount of plasticizer should not be too large, otherwise it will reduce the wear resistance of the vulcanized rubber. Polyurethane rubber is highly polar, so polar plasticizers are generally used. Phthalates, phosphates, aliphatic alkyds and other resins, such as dimethoxyethylene glycol phthalate, tricresyl phosphate, dipropylene glycol phthalate, triethylene glycol dinon acid ester, coumaron-indene resin, etc. Relevant test results show that: when using dioctyl sebacate, there will be a spurting phenomenon after vulcanization; when using coumaron resin, the tensile strength is higher, the permanent deformation is small, but the hardness is significantly reduced; when using tricresyl phosphite , the tensile strength is inferior to that of Comaron resin, but the hardness is significantly reduced.
02 Anti-wear agent
In some special occasions, in order to reduce the friction coefficient of polyurethane elastomer and further improve the wear resistance, it is necessary to add anti-wear agents to polyurethane elastomer, such as silicone oil, molybdenum disulfide, titanium disulfide, graphite and tetrafluoroethylene. etc. This modified material has self-lubricating properties and is of great economic significance when used as bearings, bushings and other components.
03 Lubricant
Lubricants used in polyurethane elastomers are mainly used in the processing of thermoplastic and mixed elastomers. Commonly used lubricants include stearic acid and its salts, paraffin waxes, and stearamides.
04 Release agent
Release agent is an indispensable operating aid in the production of three types of polyurethane elastomer products. Polyurethane is a highly polar polymer material with strong adhesion to metals and polar polymer materials. It is difficult for products to come out of the mold without a release agent. Commonly used release agents include silicone rubber, silicone ester, silicone oil, soap and paraffin, etc. You can also use non-polar polymer materials such as polytetrafluoroethylene, silicone rubber, polystyrene, polyethylene and other materials to make molds to avoid Go to the rubbing or spraying release agent process.
05 Filler
Fillers are added to reduce product costs, improve heat resistance, reduce shrinkage, thermal expansion coefficient and other properties. 20-30 parts of carbon black are often added to mixed polyurethane rubber. The purpose is not for reinforcement, but to reduce the cost of the product while keeping the physical and mechanical properties of the rubber basically unchanged. As the amount of carbon black added increases, the tensile strength and elongation of the glue gradually decreases, while the hardness rises linearly. Different specifications of carbon black have different effects on strength and other properties. Easy-to-mix tank black is the best. Followed by wear-resistant carbon black, semi-reinforced carbon black is worse. Other fillers such as clay, white carbon black, calcium carbonate, barium sulfate, etc. can also be used.
06 Colorants
Polyurethane elastomer products are colorful, and their beautiful appearance relies on colorants. There are two types of colorants, organic dyes and inorganic pigments. Organic dyes are mostly used in thermoplastic polyurethane products to decorate and beautify injection parts and extrusion parts. There are generally two ways to color elastomer products: one is to grind pigments and other additives and oligomer polyols into color paste mother liquor, then stir and mix an appropriate amount of color paste mother liquor and oligomer polyols evenly, and then heat them. After vacuum dehydration and different The cyanate ester component reacts to produce products, such as thermoplastic polyurethane color granules and colored paving materials; another method is to grind pigments and other additives and oligomer polyols or plasticizers into color paste or color paste, and then Heat and vacuum dehydrate, package and set aside. When using, add a little color paste to the prepolymer, stir evenly, and then react with the chain extension cross-linking agent to cast the product. This method is mainly used in MOCA vulcanization systems. The pigment content in the color paste accounts for about 10%-30%. The amount of color paste added to the product is generally less than 0.1%.
Vulcanization aid
Vulcanization aids mainly refer to vulcanizing agents and accelerators , which are only used in mixing polyurethane elastomers. Vulcanizing agents include isocyanates, peroxides and sulfur. Commonly used isocyanates include TDI and its dimer, MDI dimer and PAPI, etc. The cross-linked bonds generated are allophanate bonds. Due to the high volatility of diisocyanate, it easily reacts with water and is toxic. , so pay attention to safety during use and prevent moisture from entering the mixed rubber.
The advantages of using isocyanate as a vulcanizing agent are good wear resistance, high strength and hardness; among peroxide vulcanizing agents, dicumyl peroxide (DCP) is the most commonly used, and other varieties include tert-butyl isopropyl peroxide. For benzene, dibenzoyl peroxide and other dialkyl, alkyl, aralkyl and diaralkyl peroxides, the vulcanization temperature is preferably 140-150°C.
Compared with the rubber compound using peroxide vulcanizing agent and using isocyanate as the vulcanizing agent, the former can greatly reduce the early vulcanization and extend the storage time of the rubber compound. The vulcanized rubber has good dynamic properties, small compression permanent deformation and slightly hardness. Low, moderate strength, good elasticity and aging resistance. The disadvantage is that it cannot be vulcanized directly with steam, has poor tear strength and temperature resistance, and has an odor; when the polyurethane compound structure contains unsaturated segments, it can Vulcanized with sulfur.
Stabilizing system additives
In order to prevent the aging of polyurethane rubber and extend the service life of the product, compounding agents such as heat stabilizers, light stabilizers, hydrolysis stabilizers, anti-virus agents and flame retardants can be added.
01 Heat stabilizer
The thermal oxidation resistance of general polyurethane rubber is not very good. It is easily oxidized and discolored when heated, which affects the appearance and performance of the product. Therefore, antioxidants are commonly used additives in the production of polyurethane raw material intermediates and products. The most commonly used ones are 2 ,6-tert-butyl-4-methylphenol (antioxidant-264) , Tetrakis (4-hydroxy-3,5-di-tert-butylphenylpropionate) pentaerythritol ester (antioxidant-1010), 3,5-di-tert-butyl-4-hydroxyphenylpropionate stearyl ester (antioxidant Oxygen-1076), triphenyl phosphite (TPP), trinonylphenyl phosphite (TNP), etc.
02 Light stabilizer
Also known as ultraviolet absorber, it can significantly improve the light stability of aromatic isocyanate polyurethane. Commonly used light stabilizers include benzophenones, benzotriazoles and piperidines, such as 2-hydroxy-4-methoxy benzophenone (UV-9), 2,2′- Dihydroxy-4-methoxybenzophenone (UV-24), 2(2-hydroxy-3′,5′-di-tert-butylphenyl)-5-chlorobenzotriazole (UV-328 ), bis(2,2,6,6-tetramethylpiperidine) sebacate, etc.
03 Hydrolysis stabilizer
When polyester polyurethane rubber is used in a humid environment, especially in hot water, a hydrolysis stabilizer must be added. The hydrolysis stabilizer widely used in industry is carbodiimide compounds. Carbodiimide (PCD) produced by Rheinland Chemical Plant in Germany has two brands: Stabaxol-1 (monocarbodiimide) and Stabaxol-P (polycarbodiimide). The former has a lower molecular weight and a melting range of 40 -50℃, mainly used in the molten state of polyester liquid polymers, such as cast polyurethane and polyurethane coatings; the latter has a higher molecular weight and is used in thermoplastic and mixing polyurethane elastomers.
04 Antifungal agent
Polyether polyurethane elastomer has a strong anti-fungal ability, which is level 0-1. It is basically not corroded by microorganisms and will not grow mold; while polyester and polyε-caprolactone polyurethane rubber are resistant to heat, humidity and darkness. It is easy to be corroded by microorganisms and grow mold in the environment, especially poly-epsilon-caprolactone polyurethane rubber. The mold growth is more serious. For this reason, anti-fungal agents must be added. Commonly used antifungal agents include 8-hydroxyquinoline, 8-hydroxyquinolinone, pentachlorophenol, sodium pentachlorophenol, tetrachloro4-(methylsulfonyl)pyridine, salicylanilide, bis(trichlorophenol) Butyltin) oxide, phenylmercuric acetate, etc. The added fraction is 0.1%-1%. When selecting an antifungal agent, factors such as its antifungal effect, low toxicity to the human body, and no pollution to the environment must be taken into consideration. Taking 8-hydroxyquinolinone as an example, adding 0.2%, the antifungal grade is 1-2. There is no obvious impact on the physical and mechanical properties of the product. It has strong bactericidal power and low toxicity to the human body (LD50=500-16000mg/kg), but it has coloring properties.
05 Flame retardant
The flame retardant grade of materials is usually measured by the oxygen index: the oxygen index of first-level flame-retardant materials is >38, and the oxygen index of second-level flame-retardant materials is >25. The oxygen index of ordinary polyurethane elastic materials is 19-20, which is a flammable substance. When polyurethane is used in furniture, construction, automobiles, and paving materials, it must meet secondary or higher flame retardant standards. Therefore, the application of flame retardants in polyurethane products is quite common, and it is the largest amount of compounding agent, accounting for about 1/3 of the total amount of compounding agents added to polyurethane. Flame retardants are divided into two categories: inorganic and organic. Inorganic flame retardants often contain aluminum, boron, zinc, antimony and other elements, such as aluminum hydroxide, hydrated alumina, borate, zinc oxide, antimony trioxide, etc. Their advantages It has good flame retardant effect, is cheap and does not produce smoke. The disadvantage is that it is solid and has high density, which puts higher requirements on metering, conveying and mixing equipment and is not convenient to use.
Various types of chemical additives occupy an important position in the field of fine chemicals. Although their dosage is not large, there are many varieties, wide uses, and high added value. Many companies at home and abroad are working hard to develop new additive varieties. , especially functional additives. Polyurethane is an emerging sunrise industry with excellent comprehensive properties and expanding application scope.