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, It can be divided into four types of additives: synthesis system, modification and operation system, vulcanization system and protection system.
Synthetic auxiliaries
01 Catalyst and polymerization inhibitor
In the synthesis of polyurethane elastomers, 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, and trimethylamine. Benzylamine, dimethylethanolamine, morpholine, etc., among which triethylenediamine is the most important; organic tins 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.
02Chain extender and chain extender cross-linking agent
In the synthesis of polyurethane elastomers, chain extenders refer to diols and diamine compounds that are essential for chain growth reactions; chain extender cross-linking agents refer to compounds that both participate in chain growth reactions and Compounds that can form cross-linking points between chain segments, such as triols and tetrahydric alcohols, allyl ether diols, etc. Except for allyl ether glycol, which is not suitable for cast polyurethane elastomers, other chain extenders or chain extender cross-linking agents can be used. Thermoplastic polyurethane elastomers only use glycols; mixing polyurethane elastomers can use both glycols. Allyl ether glycols can also be used.
Modifier operating aid
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 and the permanent deformation is small, but the hardness is significantly reduced; when using tricresyl phosphite , the tensile strength is inferior to that of Gumaron 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-friction 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 used as bearings, bushings and other components, which has great economic significance.
03 Lubricant
Lubricants used in polyurethane elastomers are mainly used in the processing of thermoplastic and kneaded 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. It has strong adhesion to metals and polar polymer materials. It is difficult for products to come out of the mold without a release agent.
��Brands: Stabaxol-1 (monocarbodiimide) and Stabaxol-P (polycarbodiimide). The former has a lower molecular weight and a melting range of 40-50°C. It is mainly used in the molten state for polyester liquid polymerization. Materials, such as cast polyurethane and polyurethane coatings; the latter has a higher molecular weight and is used in thermoplastic and compounded 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 and humidity. In dark and dark environments, it is easy to be corroded by microorganisms and cause mold growth, especially poly-epsilon-caprolactone polyurethane rubber.
Commonly used antifungal agents include 8-hydroxyquinoline, 8-hydroxyquinolinone, pentachlorophenol, sodium pentachlorophenol, tetrachloro4-(methylsulfonyl)pyridine, salicylanilide, bis- (Tri-n-butyltin) oxide, phenylmercuric acetate, etc. The added fraction is 0.1%-1%.
When choosing an antifungal agent, you must take into account factors such as its antifungal effect, low toxicity to the human body, and no pollution to the environment. Taking 8-hydroxyquinolinone as an example, add 0.2%, and the antifungal grade is 1-2 Grade, has no significant impact on the physical and mechanical properties of the product, has strong bactericidal power and low toxicity to the human body (LD50=500-16000mg/kg), but 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 compounding agent 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.
Summary
Various 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 ones. Types of additives, especially functional additives. Polyurethane is an emerging sunrise industry with excellent comprehensive properties and expanding application scope.
However, in the trial production and production process of polyurethane elastic materials, domestic manufacturers currently do not widely use functional additives, and the requirements for improving product performance by adding additives are not very urgent, which shows that there is still a lack of understanding. If there is a gap, scientific research and trial production units should take the first step and use more cheap and high-quality new varieties of additives in polyurethane elastomers to contribute to accelerating the development of polyurethane elastic materials in my country.
