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Application of different sulfur forms in rubber
Release time:
2020-04-10
1. Application of ordinary sulfur and insoluble sulfur in rubber
As the most common and important vulcanizing agent for natural rubber and synthetic rubber, sulfur is an indispensable product in industrial rubber and is widely used. However, there are obvious differences in the purpose and use points of the two.
In terms of types, sulfur can be divided into ordinary sulfur and insoluble sulfur.
(1) Application of ordinary sulfur in rubber
The solubility of sulfur in rubber increases with the increase of temperature, while the solubility of ordinary sulfur in rubber is 1%. When the temperature decreases, the compounding amount of sulfur in the rubber compound exceeds its solubility and reaches supersaturation. The inside of the rubber material is precipitated on the surface, forming a layer of white frost, which is called frost spray. Or when the amount of ordinary sulfur exceeds its solubility, it will spray out the surface after the rubber compound is cooled, that is, spray frost.
Adverse effects of frosting:
1. Destroy the uniformity of sulfur dispersion in the rubber compound;
2. Decrease the adhesiveness of the rubber surface and bring difficulties to the processing.
Actions to be taken to avoid frost spray:
1. Sulfur should be added at the lowest possible temperature;
2. Use insoluble sulfur;
3. Use a reasonable feeding sequence;
4. Reduce the amount of sulfur and increase the amount of accelerator.
(2) Application of insoluble sulfur in rubber
Insoluble sulfur is a polymer of sulfur, insoluble in carbon disulfide and water, unstable in nature, and easily converted into insoluble sulfur. The higher the temperature, the faster the conversion rate. In order to prevent the transformation, a small amount of chlorine, bromine, iodine-sulfur chloride and diene hydrocarbons can be added. The α-sulfur is heated to a high temperature (close to the boiling point), and when it becomes a dark brown viscous liquid, it is rapidly cooled to polymerize into insoluble sulfur. It can also be prepared by spraying superheated sulfur steam in cold water and rapidly cooling it to below 90 degrees.
Insoluble sulfur is often used as a vulcanizing agent for special rubber products. Compared with ordinary sulfur, it has the following advantages:
1. Insoluble sulfur exists in a dispersed state in the rubber, so that the rubber does not bloom, has good viscosity, and can ensure the appearance quality of light-colored products.
2. The insoluble sulfur is evenly dispersed in the rubber compound, which can effectively resist the aggregation of sulfur and reduce the tendency of scorch during the storage process of the rubber compound.
3. The insoluble sulfur prevents the rubber from blooming during the storage period and maintains the uniform performance of the rubber components. Prevent the pollution of products and molds, and remove the slurry coating process added to overcome frost, providing conditions for production linkage.
4. The insoluble sulphur keeps the rubber from migrating in the adjacent rubber layer. Especially in the rubber compound of smooth rubber and butyl butyl rubber, the migration speed of ordinary sulfur is very high, which can be avoided by adding insoluble sulfur.
5. It can maintain the viscosity between semi-finished parts, which is beneficial to the molding operation, and ensures the uniformity of product vulcanization and product quality.
Insoluble sulfur can be used to manufacture tires, tapes, hoses, rubber shoes, industrial products and latex products, etc., and has been widely used in the bonding of rubber and steel wire. When used as a vulcanizing agent, insoluble sulfur can be directly added to the rubber compound during mixing. Common sulfur should be added on the cold roll of the open mill, preferably after other compounding agents have been added. Insoluble sulfur can be added on the mixer, but it should be added at a temperature lower than 90 degrees before degumming. When used for soft rubber, the general dosage is 0.2-5.0 parts by mass, and when used for hard rubber, the dosage can be as high as 25-40 parts by mass.
2. Application of Microcapsules Coated Sulfur Natural Rubber
Sulfur is widely used in the rubber industry as a vulcanization system for rubber. However, the solubility of ordinary sulfur in rubber fluctuates with the change of temperature. During the aging process of rubber processing, the sulfur that has been uniformly dispersed in the early stage will be precipitated from the rubber due to the decrease in temperature, resulting in frequent spraying during rubber processing. Frost phenomenon, which essentially produces or aggravates the uneven dispersion of sulfur in the rubber matrix, which affects the normal use of rubber. In addition, due to the different polarities of sulfur and rubber, the sulfur is easy to agglomerate in the rubber matrix, and it is difficult to achieve uniformity and distribution, which leads to the inhomogeneity of the internal structure of the rubber after vulcanization. This will seriously affect the mechanical properties of rubber, and seriously reduce the qualified rate of products in the production of rubber products, resulting in huge waste of energy, material resources, and manpower. In addition, ordinary sulfur has certain toxicity, especially the sulfur vapor produced after being heated and the sulfur dioxide produced by oxidation, which will have a huge toxic effect on the human body.
Based on the above problems in actual production, at present, by adopting a new technology, the above-mentioned problems of using ordinary sulfur are overcome by the method of coating ordinary sulfur. After coating the sulfur, it can not only effectively solve the above problems such as the uneven mechanical properties of the vulcanizate caused by frost spraying and uneven sulfur dispersion, and make the sulfur more stable and safe, but also can adjust the molecular structure of the coating material. Controlling the release of sulfur, on the one hand, can improve the effective utilization of sulfur and rubber, and at the same time, it can appropriately prolong the scorch time, which is beneficial to the processing and molding of rubber.
At present, the commonly used coating materials include a series of low molecular weight polyvinyl alcohol with different molecular weights, vinyl alcohol vinyl triethoxysilane copolymer, polyvinyl alcohol modified with methyl hydrogen-containing dichlorosilane, polystyrene, etc. A series of coated sulfurs were prepared by different coating methods.
Welcome friends who are interested in the improvement of sulfur technology to inquire and communicate!
Sulphur Technology Exchange Contact: Cen Zhongru
Tel: 13907711145
Email: cenzhongru1145@126.com
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