Additives are important raw materials in rubber industry. Although the amount is small, the effect is very large. Polyurethane elastomers cannot be separated from additives from synthesis to processing and application.According to the different role, can be divided into synthetic system, modification and operation system, vulcanization system and protection system four kinds of auxiliaries.
Synthetic aid
01 Catalyst and inhibitor
In the synthesis of polyurethane elastomers, in order to accelerate the speed of the main reaction, often need to add catalysts, commonly used catalysts are tertiary amine and organotin two categories, tertiary amines are triethylenediamine, triethylenediamine, trimethylbenzylamine, dimethylethanolamine, morphine and so on, among which triethylene diamine is the most important; Organotin includes stannous caprylate, dibutyl tin dilaurate and so on. In addition, there are organic mercury, copper, lead and iron, with organic lead and mercury being the most important, such as lead caprylate and phenylmercuric acetate. Organic dibasic acids such as adipic acid and azelaic acid can be used as catalysts for pouring rubber of polyether polyurethane.
02 Chain extender and chain extender crosslinking agent
In the synthesis of polyurethane elastomers, chain extender refers to diols and binary amines which are essential for chain growth reaction. Chain extension crosslinking agent refers to the compound that participates in chain growth reaction and can form crosslinking points between chain nodes, such as three alcohols and four alcohols, allyl ether diol, etc. In addition to allyl ether diol is not suitable for casting polyurethane elastomers, other chain extension or chain extension crosslinking agents can be used, thermoplastic polyurethane elastomers only use diol; Mixed polyurethane elastomers can use either diols or allyl ether diols.
Modifier handling agent
Some of these additives can improve the performance and appearance of the product, and some can improve the operation process, such as plasticizer, wear reducer, lubricant, filler, colorant and release agent.
01 Plasticizer
Plasticizer is mainly used in polyurethane compound. The purpose of use is to increase the plasticity of the compound, improve the processing property and the low temperature property of vulcanized rubber, and reduce the hardness and elongation 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 selection of polar plasticizer. Phthalates, phosphate esters, aliphatic alkyds and other resins, such as dimethoxy-glycol phthalate, tritoluene phosphate, dipropylene glycol phthalate, triethylene glycol dinononate, Kumaron-indene resin, etc. The experimental results show that when dioctyl sebacate is used, the spouting phenomenon occurs after vulcanization. When using Gumaron resin, the tensile strength is higher, the permanent deformation is small, but the hardness is reduced obviously; When tricresol phosphite is used, the tensile strength is inferior to that of Coumaron resin, but the hardness is reduced obviously.
02 Wear reducer
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 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, used as bearings, bushing and other parts, has great economic significance.
03 Lubricant
The lubricant used in polyurethane elastomer is mainly used in the processing of thermoplastic and mixed elastomer. Stearic acid and its salts, paraffin and stearamide are commonly used.
04 Release agent
Release agent is an indispensable operating agent in the production of three types of polyurethane elastomer products. Polyurethane is a strong polar polymer material. It has a strong bonding force with metal and polar polymer materials. Without releasing agent, the products are difficult to come out from the mold. The commonly used release agents are silicone rubber, silicone ester, silicone oil, soap and paraffin, etc. Non-polar polymer materials such as polytetrafluoroethylene, silicone rubber, polystyrene, polyethylene and other materials can also be used to make molds, in order to remove rubbing or spraying release agent process.
05 Filler
Fillers are added to reduce product costs and improve heat resistance, reduce shrinkage and coefficient of thermal expansion and other properties. In the mixing type polyurethane rubber is often added to 20-30 copies of carbon black, its purpose is not to strengthen, but to keep the physical and mechanical properties of rubber basic unchanged under the premise of reducing the cost of products. With the increase of the amount of carbon black, the tensile strength and elongation of the rubber gradually decreased, the hardness rose straight, different specifications of carbon black on the strength and other properties are different, with easy to mix 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.
06 Colorant
Polyurethane elastomer products are colorful, beautiful and generous appearance depends on colorant. There are two kinds of colorants, organic dyes and inorganic pigments, organic dyes are mostly used in thermoplastic polyurethane products, decorative and beautifying injection parts and extrusion parts. The coloring of elastomer products generally have two ways: one is the pigment additives and oligomer polyol grinding into the mother liquor, and then the appropriate amount of the mother liquor and oligomer polyol mixed evenly, and then after heating vacuum dehydration and isocyanate component reaction products, such as thermoplastic polyurethane color particle and color paving materials; Another method is the pigment and other additives and oligomer polyols or plasticizer grinding into color paste or color paste, after heating vacuum dehydration, packaging reserve. When used, add a little color paste to the prepolymer, stir evenly and then reaction with chain extension crosslinking agent pouring products. This method is mainly used for MOCA vulcanization system. The pigment content in the color paste accounts for about 10%-30%. The additive amount of the color paste in the products is generally less than 0.1%.
Vulcanizing agent mainly refers to the vulcanizing agent and accelerator, only used in mixed polyurethane elastomers. The vulcanizing agent includes isocyanate, peroxide and sulfur. Isocyanate esters are commonly used in TDI and its dimer, MDI dimer and PAPI, etc., the crosslinking bond generated is ureyl formate bond, because of the volatility of diisocyanate, easy to react with water, and toxic, so it is necessary to pay attention to safety and prevent water into the compound.
The advantages of using isocyanate as vulcanizing agent are good wear resistance, high strength and hardness. Peroxide vulcanizing agent to diisopropylbenzene peroxide (DCP) is the most common, other varieties have tert-butyl isopropylbenzene peroxide, dibenzoyl peroxide and other dialkyl, alkyl, aryl and aryl alkyl peroxides, vulcanization temperature to 140-150℃ is appropriate.
With peroxide vulcanizing agent and isocyanate as vulcanizing agent compared to the compound, the former can greatly reduce the early vulcanization, prolong the storage time of the compound, the vulcanizing rubber has good dynamic performance, compression permanent deformation small, slightly lower hardness, moderate strength, elasticity and aging resistance are good, the disadvantage is that can not use steam directly vulcanizing, tearing strength and temperature resistance is poor, Have a smell; When the structure of polyurethane compound contains unsaturated chain segments, sulfur vulcanization can be used.
Stabilizing system agent
In order to prevent the aging of polyurethane rubber, prolong the service life of the product, can be used to add heat stabilizer, light stabilizer, hydrolysis stabilizer, anti-agent and flame retardant and other compounds.
01 Heat stabilizer
General polyurethane rubber heat resistant oxidation performance is not very good, easy oxidation and discoloration under heat, affecting the appearance and performance of products, so antioxidants in polyurethane raw materials intermediate and product production is commonly used as additives, 2, 6-tert-butyl-4-methyl phenol (antioxidant -264), four (4-hydroxy-3, Pentaerythritol (5-di-tert-butylphenylpropionate) (antioxidant -1010), octadecyl 3, 5-di-tert-butyl-4-hydroxyphenylpropionate (antioxidant -1076), triphenyl phosphite (TPP), trinonylphenyl phosphite (TNP), etc.
02 Light stabilizer
Also known as ultraviolet absorbent, it can significantly improve the photostability of aromatic isocyanate polyurethane. Commonly used light stabilizers include benzophenone, benzotriazole and piperidine, such as 2-hydroxy-4-methoxybenzophenone (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 humid environment, especially in hot water, hydrolysis stabilizer must be added. The hydrolysis stabilizer widely used in industry is carbonized diimide compounds. Produced by Germany Rhein Chemical plant carbonized diimide (PCD) has two grades: Stabaxol-1 (single carbonized diimide) and Stabaxol-P (polycarbonized diimide), the former molecular mass is low, melting range 40-50℃, mainly used in the molten state of polyester liquid polymer, such as pouring type polyurethane, polyurethane coatings; The latter has higher molecular weight and is used in thermoplastic and mixed polyurethane elastomers.
04 Anti-mold agent
Polyether polyurethane elastomer has strong anti-mold ability, 0-1 level, basically free from microbial erosion, will not grow mold; The polyester type and polyε-caprolactone type polyurethane rubber are susceptible to microbial erosion and mildew in hot and humid and dark environment, especially the polyε-caprolactone type polyurethane rubber mildew is more serious, so it is necessary to add mildew prevention agent. The commonly used antimildew agents are 8-hydroxyquinoline, 8-hydroxyquinolone, pentachlorophenol, sodium pentachlorophenol, tetrachloro4 – (methyl sulfonyl) pyridine, salicylidene aniline, double (tri-n-butyl tin) oxide, phenylmercuric acetate, etc. The addition score is 0.1%-1%. The selection of mildew inhibitor should take into account the mildew effect and low toxicity to the human body and environmental pollution and other factors, with 8-hydroxyquinolone as an example, add 0.2%, mildew grade for 1-2, no obvious effect on the physical and mechanical properties of products, strong bactericidal power and low toxicity to human body (LD50=500-16000mg/kg), but there is coloration.
05 Flame retardant
The flame retardant grade of materials is usually measured by oxygen index: oxygen index >38 for primary flame retardant materials and >25 for secondary flame retardant materials. The oxygen index of common polyurethane elastic material is 19-20, which belongs to combustible material. When polyurethane is used in furniture, construction, automobiles, paving materials, it must meet the flame retardant standards above Class II. Therefore, flame retardant is widely used in polyurethane products, and it is the largest dosage of the complex, accounting for about 1/3 of the total amount of polyurethane compounds. Flame retardant is divided into inorganic and organic two categories, inorganic flame retardant often contains aluminum, boron, zinc, antimony and other elements, such as aluminum hydroxide, alumina hydrate, borate, zinc oxide, antimony trioxide and so on, its advantages are good flame retardant effect, cheap, does not produce smoke, the disadvantage is solid, high density, to the measurement, transportation, mixing equipment put forward higher requirements, use is not very convenient.
Various chemical auxilaries play an important role in the field of fine chemicals. Although the amount is not large, there are many varieties, wide uses and high added value. Many companies at home and abroad are committed to developing new auxilaries, especially functional auxilaries. Polyurethane is an emerging sunrise industry, comprehensive performance is excellent, the scope of application is expanding.
Qingdao Yinhepley New Materials is committed to the development and production of professional polymer additives, such as antioxidants, UV absorbent, light stabilizer, flame retardant, a wide range of English engineering plastics.
Welcome to inquire： yihoo@yihoopolymer.com
Post time: Apr-12-2023