In the rubber industry, vulcanization is a crucial process that determines the final performance and application scope of rubber products. This article will delve into the definition, process, influencing factors, and applications of rubber vulcanization in various fields.
I. Definition of Sulfurization
Sulfurization is the cross-linking process of rubber where the rubber macromolecules change from a linear structure to a network structure under certain conditions. During this process, the rubber molecular chains form stable cross-links through chemical reactions, thereby endowing the rubber material with excellent physical and mechanical properties, heat resistance, solvent resistance, and corrosion resistance.
II. The Three Stages of the Vulcanization Process
The sulfurization process can be divided into three stages: the induction stage, the cross-linking reaction stage, and the network formation stage.
Induction stage: During this stage, sulfur molecules react with the accelerator system to form more active intermediate compounds. These compounds further trigger the rubber molecular chains, generating crosslinkable free radicals or ions. The duration of this stage depends on the rubber compound formula and processing conditions, and is mainly influenced by the accelerator.
2. Crosslinking reaction stage: The freely reactive radicals or ions interact with the rubber molecular chains, initiating a chain reaction that forms crosslink bonds. During this stage, the elasticity and tensile strength of the rubber increase sharply, which is the core part of the vulcanization process.
3. Network formation stage: In the early stage of this process, the crosslinking reaction has basically been completed. The generated crosslinking bonds undergo rearrangement and degradation reactions, ultimately resulting in a stable vulcanized rubber with a grid structure. During this stage, the rearrangement and thermal degradation reactions of the crosslinking bonds play a dominant role, and the mechanical properties of the rubber material tend to stabilize.
III. Sulfurization Process Diagram and Sulfur Detection Parameters
The vulcanization process diagram characterizes the vulcanization process by the relationship between the change of a certain property of the rubber and the vulcanization time. The common parameters in the diagram include:
1. ML (Minimum Torque): This indicates the creep property of the rubber compound. The lower the ML value, the better the creep resistance.
2. MH (Maximum Torque): This parameter represents the shear modulus, hardness, elongation at break, and crosslinking density of the rubber compound. The higher the MH value, the higher the hardness.
3. TS2 (Remaining Curing Time): This indicates the time during which the rubber compound can flow in the mold cavity. It is of great significance for processing and formulation design.
4. TC90: This parameter assesses the one-time vulcanization conditions during the molding production process. A longer TC90 value indicates a slower vulcanization rate, which will result in lower product hardness and lower production efficiency.
IV. Selection of Sulfurization Conditions
1. Vulcanization temperature: The vulcanization temperature directly affects the vulcanization speed and product quality. Increasing the vulcanization temperature can accelerate the vulcanization process, but excessively high temperatures will cause the rubber molecular chains to break down and lead to reversion of vulcanization, thereby reducing the mechanical properties of the rubber compound.
2. Vulcanization pressure: Vulcanization pressure is used to prevent bubbles from forming in the rubber compound, and to enhance the density of the compound and the adhesion between different layers. The selection of pressure should be determined based on factors such as product type, formulation, and plasticity.
V. Vulcanization Method
The main sulfurization methods include direct sulfurization, indirect sulfurization and mixed gas sulfurization.
Direct vulcanization: Place the product directly into a hot water or steam medium for vulcanization.
2. Indirect vulcanization: The product is vulcanized in hot air. This method is suitable for products with strict appearance requirements.
3. Blended sulfurization: First, air sulfurization is employed, followed by direct steam sulfurization. This approach combines the advantages of both methods.
VI. Application Areas of Rubber Vulcanizing Agents
Rubber vulcanizing agents are widely used in various fields, including the automotive industry, electrical and electronic industry, construction industry, and aerospace industry, etc.
Automotive industry: Used for manufacturing components such as tires, seals, and shock absorbers, to enhance wear resistance, tear resistance, and aging resistance.
2. Electrical and Electronic Industry: Produces wires and cables, insulating materials, sealing gaskets, etc., to ensure the safe and reliable operation of electrical and electronic equipment.
3. Construction Industry: Produces waterproof materials, sealing materials, flooring materials, etc., to enhance weather resistance, water resistance and chemical corrosion resistance.
4. Aerospace industry: Produces critical components such as seals, shock absorbers, and transmission belts to ensure the safe and reliable operation of aerospace vehicles.
VII. Summary
Rubber vulcanization is the final crucial process in the production of rubber products. Through complex chemical reactions, it transforms rubber from a linear structure to a network structure, thereby achieving excellent physical and mechanical properties as well as chemical stability. Understanding the process, conditions and applications of vulcanization is of great significance for improving the quality of rubber products and expanding their application fields.