The most complete summary! TPU additives in one article
Additives are important raw materials for the rubber industry, although the amount is small, but the role is very large, polyurethane elastomers from synthesis to processing applications are inseparable from the additives, according to the role of different, can be divided into synthetic system, modification and operation system, vulcanization system and protection system four types of additives.
Synthetic additives
01
Catalysts and polymerization inhibitors
Polyurethane elastomer synthesis, in order to accelerate the speed of the main reaction, often need to add catalysts, commonly used catalysts are tertiary amines and organic tin two categories, tertiary amines are triethylenediamine, triethylamine, trimethylbenzylamine, dimethylethanolamine, morpholine, etc., of which triethylenediamine is the most important; organic tin class of stannous octanoate, dibutyltin laurate, etc.. In addition, there are organic mercury, copper, lead and iron, with organic lead and mercury being the most important, such as lead octanoate and phenylmercury acetate. Organic dibasic acids, such as adipic acid and azelaic acid, can be used as catalysts for polyether-based polyurethane cast rubber.
Amine catalysts are mostly used for foam-forming reactions in foam formulations, and in polyether systems, amine and tin catalysts are used to obtain the best bubble structure.
Organotin catalysts usually catalyze the HO and NCO reaction process, avoiding the side reaction of OH. In addition to increasing the overall reaction rate, this type of catalyst can make the reactivity of high molecular mass polyol and low molecular mass polyol converge, resulting in a prepolymer with narrow molecular mass distribution and low viscosity.
The use of catalysts has an adverse effect on the performance of the final product of elastomers, mainly affecting high temperature performance and hydrolysis resistance.
Polymerization inhibitors are used more often in acids and chlorides. The most used acids are hydrogen chloride gas, and the chlorides are benzoyl chloride and adipoyl chloride.
02
Chain extender and chain extender crosslinker
In the synthesis of polyurethane elastomers, chain extenders are diols and diamines that are essential for chain growth reactions, while chain extender crosslinkers are compounds that participate in chain growth reactions and form crosslinking points between chain links, such as tertiary alcohols and quaternary alcohols, allyl ether diols, etc. Cast polyurethane elastomers can use all chain-expanding or chain-expanding cross-linking agents except allyl ether diols, and thermoplastic polyurethane elastomers use only diols; blended polyurethane elastomers can use both diols and allyl ether diols. The aliphatic diols are ethylene glycol, butylene glycol and hexylene glycol, the most important of which is 1,4-butanediol (BDO), which is most used in the preparation of thermoplastic polyurethane. Among the aromatic diols, the more important one is hydroquinone dihydroxyethyl ether (HQEE), which can improve the rigidity and thermal stability of polyurethane elastomers; another aromatic diol is resorcinol dihydroxyethyl ether (HER), which can maximize the durability, elasticity and plasticity of elastomers while limiting the shrinkage to a minimum. advantages and does not pollute the environment, but when the use of a slight drop in temperature, HQEE has a tendency to rapidly crystallize, thus limiting its application, if the HER and HQEE mixed use, can solve the problem of crystallization, but also improve the mechanical properties of the product.
Generally used binary amine chain extenders are aromatic, the most commonly used is 3,3′-dichloro-4,4′- diphenylmethane diamine (MOCA) The chlorine atom substituent on the benzene ring reduces the reaction rate of amino and isocyanate, thus extending the life of the kettle, which is extremely important for hand-cast polyurethane elastomer products s. Some other diamines, such as 3,3′-dichloro-poly(dichlorodiamino), 4,4′-diphenylmethane diamine, biphenyldiamine and triazine diamine can also be used as chain extenders in the synthesis of polyurethane elastomers, etc. The chain-expanding cross-linking agents are triols, tetrahydric alcohols and allyl ether diols. The commonly used triols and tetrahydric alcohols are propanetriol, trimethylolpropane, 1,2,6-hexanetriol and pentaerythritol, etc., which react with isocyanate to produce carbamate cross-linking; the commonly used allyl ether diols are: α-allyl glycerol ether (α-Age), trimethylolpropane allyl ether and allyl glycidyl ether, the former The first two compounds can be added in the synthesis of polyesters to introduce allyl into the polyester main chain; also can be added in the synthesis of raw rubber, allyl into the raw rubber main chain. All three compounds can be used in the production of polyethers.
Modifier operating additives
Some of these additives can improve the performance and appearance of the product, and some can improve the operation process, such as plasticizers, abrasion reducers, lubricants, fillers, colorants and mold release agents.
a
01
Plasticizers
Plasticizer is mainly used in polyurethane compounding rubber, the purpose is to increase the plasticity of the compounding rubber, improve the processing performance and low temperature performance of vulcanized rubber, reduce the hardness and tensile strength of vulcanized rubber. The amount of plasticizer should not be too large, otherwise it will reduce the wear resistance of vulcanized rubber. Polyurethane rubber has strong polarity, so the general choice of polar plasticizers. Benzenedicarboxylic acid esters, phosphate esters, aliphatic alkyd and other resins, such as benzodicarboxylic acid dimethoxy glycol ester, trimethylene phosphate ester, benzodicarboxylic acid dipropylene glycol ester, triethylene glycol dinonanoate, gummaron-indene resin, etc.. The test results show that: when using dioctyl sebacate, there is the phenomenon of ejection after vulcanization; when using Gummaron resin, the tensile strength is higher and the permanent deformation is small, but the hardness is reduced significantly; when using tricresyl phosphite, the tensile strength is second to Gummaron resin, but the hardness is reduced more significantly.
02
Wear reducing agent
In some special occasions, in order to reduce the friction coefficient of polyurethane elastomer and further improve wear resistance, it is necessary to add wear reducing agents in polyurethane elastomer, such as silicone oil, molybdenum disulfide, titanium disulfide, graphite and tetrafluoroethylene, etc. This modified material has self-lubricating properties and is used as bearings, bushings and other parts, which has great economic significance.
03
Lubricant
The lubricants used in polyurethane elastomers are mainly used in the processing of thermoplastic and blended elastomers, commonly used stearic acid and its salts, paraffin waxes, stearamide.
04
Release agents
Mold release agents are indispensable operating aids for the production of all three types of polyurethane elastomer products. Polyurethane is a strong polar polymer material, which has a strong bond with metal and polar polymer material, so it is difficult to release the product from the mold without the release agent. Commonly used mold release agents are silicone rubber, silicone ester, silicone oil, soap and paraffin, etc. You can also choose non-polar polymer materials such as PTFE, silicone rubber, polystyrene, polyethylene and other materials to make molds to avoid rubbing or spraying mold release agent process. Traditional mold release agent are used organic solvent formulation, in recent years at home and abroad are developing water-based release agent, some varieties such as domestic PRW-105 has been put into the market, it has non-toxic, tasteless, non-combustible, non-polluting environment and other characteristics, there is a brush can do more than one product quality mold release agent.
05
Filling agent
Filler is added to reduce the cost of products and improve heat resistance, reduce shrinkage and thermal expansion coefficient and other certain properties. In the blended polyurethane rubber, 20-30 parts of carbon black are often added, the purpose of which is not to strengthen, but to reduce the cost of products while keeping the physical and mechanical properties of rubber basically unchanged. As the amount of carbon black added increases, the tensile strength and elongation of rubber gradually decreases, while the hardness rises linearly. Different specifications of carbon black have different effects on the strength and other properties, with easy to mix slot black as the best, followed by wear-resistant carbon black, semi-reinforced carbon black is poor. Other fillers such as clay, white carbon black, calcium carbonate, barium sulfate, etc. can also be used. In cast polyurethane rubber, the commonly used prepolymer MOCA batching system generally does not add filler, because the system viscosity is large, gel fast, it is difficult to operate. In other ingredient systems such as prepolymer / polyol system for the production of paving materials, waterproof materials, sealants, repair adhesives, potting adhesives and low hardness rollers and other products, often adding calcium carbonate, quartz powder, titanium dioxide, clay, barite, talc, coal powder, glass beads and glass fiber, the viscosity of such systems is small, easy to add and can improve the processing properties, certain physical properties, and reduce costs. In the reaction injection molding (RIM) products in order to improve the rigidity and modulus of the product, reduce the coefficient of thermal expansion and product cost, often add glass fiber as a filler, and sometimes also add mica flakes, wollastonite, carbon fiber, polyarylamide and other fillers.
06
Coloring agent
Polyurethane elastomer products colorful, beautiful and generous appearance relies on coloring agents. There are two kinds of colorants, organic dyes and inorganic pigments. Organic dyes are mostly used in thermoplastic polyurethane products to decorate and beautify injected and extruded parts. There are generally two ways to color elastomeric products: one is to grind pigments and other additives and oligomeric polyol into color paste master batch, then mix the appropriate amount of color paste master batch with oligomeric polyol, and then react with isocyanate components after heating and vacuum dehydration to produce products, such as thermoplastic polyurethane color granules and colored paving materials; the other method is to grind pigments and other additives and oligomeric polyol or plasticizer into color paste or color paste, and then produce products after heating and vacuum dehydration, such as thermoplastic polyurethane color granules and colored paving materials. Another method is to grind pigments and other additives and oligomeric polyol or plasticizer into color paste or color paste, dehydrate it by heating and vacuum, and seal it for use. When using, a small amount of color paste is added to the pre-polymer, stirred well and then reacted with chain-expanding cross-linking agent to cast into products. This method is mainly used in MOCA vulcanization system, the pigment content in the color paste is about 10%-30%, and the amount of color paste added in the products is generally below 0.1%.
