Types and functions of rubber compounding agents Unvulc […]
Types and functions of rubber compounding agents
Unvulcanized raw rubber, there is no coach between the molecules, and rubber products cannot be made. The raw rubber must be added with a compounding agent to make the raw rubber vulcanization coach into a vulcanized rubber with certain physical and mechanical properties. Compounding agents are multiple chemicals. There are many types of compounding agents. According to the main role of these chemicals in raw rubber, they are divided into vulcanizing agents, vulcanization accelerators, anti-scorching agents, anti-aging agents, fillers, plasticizers, softeners or special compounding agents Big category.
1. Vulcanizing agent
Under certain conditions, the material that can make the rubber vulcanization coach is called vulcanizing agent. The type of vulcanizing agent can be divided into elements such as sulfur, selenium and tellurium according to the chemical structure, sulfur-containing compounds, organic peroxides, metal oxides, amine compounds and synthetic resins. Among them, sulfur is used as the main vulcanizing agent for vulcanization of natural rubber and styrene-butadiene rubber. In addition to sulfur in the production of rubber abrasives, a certain amount of accelerators, active agents, etc. need to be added. Therefore, the aging process of rubber abrasives is the sum of many bimolecular reactions in parallel and in sequence in a multi-component system. The sulfur and vulcanization process is a refitting structure where the sulfur molecules are 8 yards under normal conditions. In the raw rubber, sulfur undergoes ring opening at the vulcanization temperature and the molecular energy of about 30J / mol, resulting in a chain-like double group Sexual sulfur. According to different conditions, free radicals or ionic dibasic sulfur can be generated after the sulfur ring is broken. When the dibasic sulfur reacts with the rubber macromolecule at the double bond or α-carbon atom, a “molecular compound” can be formed on one molecular chain, or “intermolecular compound” can be formed between two molecular chains The "compound" is cross-linked. As the amount of sulfur increases, the amount of combined sulfur also increases. The strength, hardness, and heat resistance of the vulcanized rubber increase, the elasticity decreases, the solvent resistance and water resistance increase, the rubber becomes brittle, and the impact strength decreases. Therefore, the amount of sulfur is not unlimited. A maximum limit, that is, the maximum bright yellow content (g) of 100g raw rubber, becomes the vulcanization coefficient (%). The vulcanization coefficient of natural rubber is 47%, and the vulcanization coefficient of styrene-butadiene rubber is 44.5%.
2. Vulcanization accelerator
All substances that can promote the vulcanization reaction are called vulcanization accelerators, or accelerators for short. Accelerators can improve and improve the physical and mechanical properties of vulcanized rubber, reduce the amount of vulcanizing agent, shorten the vulcanization time, increase productivity, can promote the appropriate temperature of vulcanization, ensure that the rubber has a considerable drying time, and ensure the mixing and calendering And safe operation during the extrusion process. Commonly used are thiazoles, 2-mercaptobenzothiazole (trade name: accelerator M), disulfonated dibenzothiazole (accelerator DM), guanidines (diphenylguanidine).
3. Active agent
It can increase the activity of accelerators, exert the vulcanization efficiency of accelerators, reduce the dosage of accelerators and shorten the curing time. Vulcanization active agent is divided into organic active agent and inorganic active agent. Stearic acid is commonly used for organic active agents, and zinc oxide is commonly used for inorganic active agents.
4. Filler and reinforcing agent
In the production of rubber, the product volume is increased, the raw rubber is saved, and the filler that improves the process performance of the raw rubber becomes an inactive filler, referred to as filler. In rubber production, fillers that can significantly improve the impact resistance, elongation, tear resistance and other wear resistance of vulcanized rubber are called active agents or reinforcing fillers, referred to as reinforcing agents. Both are fillers. According to the chemical composition and shape of the filler, it can be divided into three categories: granular filler, resin filler and fiber filler. Granular fillers are most widely used in the rubber industry, mainly carbon black, white carbon black and other Guangwu. Among the resin fillers are modified phenolic resin and polystyrene resin, which are mainly used for reinforcement. Fiber fillers mainly include asbestos, glass fibers, organic short fibers, etc., which can be used for reinforcement. Rubber abrasives are also commonly used in the early filler carbon black, zinc oxide, magnesium oxide, iron oxide, calcium oxide, clay, phenolic resin and so on. Soft abrasive tools such as flexible polishing wheels mainly use carbon black and zinc oxide. Hard abrasive tools mainly use MgO, ZnO, Fe2O3, CaO, phenolic resin, rubber powder.
Before the rubber is mixed, calendered, or extruded, it must be plasticized. Add some additives to increase the plastic flow of the compound, easy to process, and improve some properties of the product. Plasticizers are divided into chemical plasticizers and physical plasticizers. When chemical plasticizer is added to raw rubber, it can cut the rubber molecular chain, reduce the molecular weight of raw rubber, thus reduce the elasticity of rubber and improve the plasticity. It can be called rubber plasticizer. The physical plasticizer also becomes a softener. After the raw rubber is added, the raw rubber swells, increases the distance between the raw rubber molecules, and reduces the interaction force between the raw rubber molecules, thereby lowering the elasticity Ian and improving the plasticity. Commonly used chemical plasticizers are thiophenol, benzoyl peroxide, sulfurized benzoic acid and so on. Physical plasticizers include: petroleum softeners, such as mechanical oil, spindle oil, heavy oil, asphalt, paraffin, etc .; pine oil softeners, such as pine tar, rosin, etc.
6. Anti-aging agent
During the use and storage of rubber products, they often become hard, brittle or soften and sticky, lose their elasticity and cannot be used, which becomes an aging phenomenon. The main cause of aging is oxidation. To prevent aging, anti-aging additives are often added to the raw rubber. There are physical antioxidants and chemical antioxidants. The manufacture of soft elastic abrasives uses chemical anti-aging agent A (anti-aging agent A) and anti-aging agent D (anti-aging agent D). Physical anti-aging agent is to add paraffin and other substances to the raw rubber, which can form a film on the surface of rubber products to protect the rubber products from oxidation.