Introduction
Vulcanization accelerators, or accelerators, are essential additives in rubber compounds. They enhance the reaction between rubber and vulcanizing agents, reducing sulfur usage, lowering curing temperatures, and improving the mechanical properties of vulcanized rubber. The choice of accelerator depends on the rubber type and desired curing characteristics.
Key Functions
Boost Efficiency: Accelerators shorten curing time and reduce energy consumption.
Improve Safety: They enhance scorch resistance, preventing premature curing during processing.
Enhance Quality: Accelerators ensure uniform curing, improving mechanical properties and aging resistance.
Optimize Appearance: Reduced sulfur and lower curing temperatures preserve product color.
Classification by Curing Speed
| Speed Level | Accelerator Types |
|---|---|
| Ultra-Ultra Fast | Dithiocarbamates, Xanthates |
| Ultra Fast | Thiurams |
| Semi-Ultra Fast | Thiazoles, Sulfenamides |
| Medium Fast | Guanidines |
| Slow | Aldehyde-amines, Thioureas |
Classification by Acidity/Basicity
Acidic: Thiazoles, Thiurams, Dithiocarbamates, Xanthates
Basic: Guanidines, Aldehyde-amines
Neutral: Sulfenamides, Thioureas
Key Accelerator Types & Features
| Accelerator Type | Common Examples | Features |
|---|---|---|
| Thiazoles | M, DM | High activity, good aging resistance. |
| Sulfenamides | CZ, NOBS | Delayed action, excellent mechanical properties. |
| Thiurams | TMTD, TETD | Ultra-fast, often used as secondary accelerators. |
| Dithiocarbamates | ZDC, BZ | Ultra-ultra-fast, low activation temperature. |
| Guanidines | DPG, DOTG | Medium curing speed, improves storage stability. |
| Thioureas | ETU, DETU | Primarily for chloroprene rubber, good mechanical properties. |
| Aldehyde-amines | H, 808 | Mild activity, good scorch resistance. |
| Xanthates | DIP, ZIX | Ultra-fast, limited curing flatness. |
Selection Criteria
- Rubber Type: Match accelerator to rubber for optimal performance.
- Scorch Resistance: Ensure sufficient scorch time for processing safety.
- Curing Flatness: Aim for a wide curing plateau to prevent over-curing.
- Mechanical Properties: Consider impact on tensile strength, elongation, etc.
- Dispersion: Ensure uniform distribution to avoid curing defects.
- Staining/Coloration: Avoid accelerators that may discolor light-colored products.
- Water Solubility: Prefer water-soluble accelerators for latex applications.
- Toxicity: Choose non-toxic accelerators for medical or food-contact products.
Synergistic Blending
Accelerators are often blended to achieve optimal performance:
AB Blends (Acid-Base): Combine acidic and basic accelerators for faster curing and improved mechanical properties.
AA Blends (Acid-Acid): Use two acidic accelerators to balance scorch resistance and curing speed.
NA Blends (Neutral-Acid): Activate neutral accelerators with acidic ones for enhanced curing.
NB Blends (Neutral-Basic): Combine neutral and basic accelerators for efficient curing with reduced accelerator usage.
