Types of Rubber Vulcanization Systems
Created on 07.23
Vulcanization is a critical process that transforms raw rubber froma soft, plastic material into a tough, elastic one by forming cross-linksbetween polymer chains. The choice of vulcanization system directly impactsrubber performance (e.g., elasticity, heat resistance, durability) andproperties like odor or chemical stability. Below are the main types of rubbervulcanization systems, categorized by their core cross-linking agents:
#### 1. SulfurVulcanization System
The most traditional and widely used system, relying on sulfur (orsulfur donors) to form cross-links between rubber polymer chains.
- **Workingprinciple**: Sulfur atoms reactwith unsaturated bonds in rubber (e.g., natural rubber, styrene-butadienerubber, EPDM with diene monomers) to form polysulfide cross-links (-Sₓ-), connecting adjacent polymer chains.
- **Keycomponents**:
- **Sulfur**: The primarycross-linking agent; particle size and purity affect reaction efficiency.
- **Accelerators**:Compounds (e.g., thiazoles, thiurams, sulfenamides) that speed up vulcanizationand reduce sulfur dosage, preventing brittleness.
- **Activators**: Typicallyzinc oxide (ZnO) and stearic acid, which enhance accelerator activity andpromote cross-link formation.
- **Advantages**: Low cost, easy operation, and versatile for most unsaturatedrubbers (e.g., NR, SBR, EPDM).
- **Disadvantages**: May leave residual sulfur or volatile by-products (e.g.,mercaptans), causing mild odors. Cross-links (polysulfides) are lessheat-resistant than other systems.
#### 2. PeroxideVulcanization System
Uses organic peroxides as cross-linking agents, suitable for bothsaturated and unsaturated rubbers (e.g., EPDM, silicone rubber,polyethylene).
- **Workingprinciple**: Peroxides decomposeat high temperatures to generate free radicals, which abstract hydrogen frompolymer chains, triggering cross-linking via carbon-carbon (C-C) bonds.
- **Commonperoxides**: Dicumyl peroxide(DCP), benzoyl peroxide (BPO), and di-tert-butyl peroxide (DTBP), chosen basedon rubber type and processing temperature.
-**Advantages**:
- Forms stable C-Ccross-links, improving heat resistance, chemical resistance, and compressionset.
- Minimal odor (fewervolatile by-products) and lower risk of harmful residues, making it ideal forfood-contact, medical, or odor-sensitive applications.
- **Disadvantages**: Higher cost than sulfur systems; may reduce rubber elasticity ifoverused.
#### 3. MetalOxide Vulcanization System
Primarily used for rubbers with high halogen content (e.g.,chloroprene rubber, chlorinated polyethylene).
- **Workingprinciple**: Metal oxides (e.g.,magnesium oxide, zinc oxide) react with halogen groups (-Cl, -Br) in the rubberto form ionic cross-links.
- **Keyapplications**: Neoprene (CR) andother halogenated rubbers, where oxides also act as acid acceptors toneutralize corrosive by-products.
- **Advantages**: Enhances flame resistance and oil resistance, critical forindustrial seals and adhesives.
- **Disadvantages**: Limited to halogenated rubbers; may require higher temperaturesfor effective cross-linking.
#### 4. QuinoneDioxime Vulcanization System
A specialized system often used for butyl rubber (IIR) and EPDM,relying on quinone dioximes (e.g., p-quinone dioxime) as cross-linkers.
- **Workingprinciple**: Reacts with activehydrogen in polymer chains to form stable cross-links, often with metal oxides(e.g., Pb₃O₄) as activators.
- **Advantages**: Produces rubber with excellent heat resistance and lowpermeability, suitable for tire inner tubes and chemical seals.
- **Disadvantages**: Higher cost and potential toxicity from heavy metal activators(e.g., lead compounds), limiting use in food/medical applications.
#### 5. UrethaneVulcanization System
A newer technology using isocyanates or urethane prepolymers toform cross-links, primarily for specialty rubbers (e.g., polyurethane rubber,nitrile rubber).
- **Workingprinciple**: Reacts with hydroxylor amino groups in polymers to form urethane linkages, offering precise controlover cross-link density.
- **Advantages**: Produces rubber with high tensile strength, abrasion resistance,and customization options for hardness/elasticity.
- **Disadvantages**: High cost and sensitivity to moisture, requiring strict processingconditions.
### Summary
The choice of vulcanization system depends on rubber type,application requirements (e.g., heat resistance, odor), and cost. Sulfursystems dominate general-purpose uses, while peroxide systems are preferred forodor-sensitive or high-performance scenarios. Understanding these systems helpsin selecting rubber products tailored to specific needs.