Rubber compounding requires a precise balance between processing safety and curing efficiency. Two chemicals that are often discussed—but frequently misunderstood—are PVI and DPG. Although both influence the vulcanization process, they perform very different roles. Selecting the wrong one, or using the right one incorrectly, can result in premature scorch, poor flow, under-cure, or inconsistent physical properties.
This guide explains the difference between PVI and DPG in rubber compounding, how each works chemically, where they should be used, and how to choose the right option based on compound type, accelerator system, and processing conditions. The focus is on scorch safety, cure control, and practical selection, with clear tables and application guidance.
Understanding the Basics: What Are PVI and DPG?
Before comparing them, it’s important to understand what each material is designed to do.
- PVI (Pre-Vulcanization Inhibitor) is a retarder.
Its primary role is to delay the onset of vulcanization, improving scorch safety during mixing, extrusion, calendaring, and handling. - DPG (Diphenyl Guanidine) is a secondary accelerator.
Its role is to activate or boost primary accelerators, improving cure efficiency and final mechanical properties.
Although both affect cure behavior, PVI slows vulcanization, while DPG promotes it.
Chemical Identity and Classification
| Parameter | PVI | DPG |
|---|---|---|
| Full Name | N-Cyclohexylthiophthalimide | Diphenyl Guanidine |
| Chemical Class | Cure retarder | Guanidine accelerator |
| Primary Function | Scorch prevention | Cure activation |
| Role in Cure System | Delays cure onset | Enhances accelerator activity |
| Typical Use Level | Very low | Moderate |
Role of PVI in Rubber Compounding
PVI is used mainly to prevent premature vulcanization (scorch) during processing. In modern tyre and industrial rubber manufacturing, compounds often experience high temperatures during mixing and shaping. Without proper scorch protection, rubber can begin to cure too early, leading to processing failures.
Key Functions of PVI
- Delays onset of sulfur crosslinking
- Improves processing window
- Prevents scorch in high-temperature mixing
- Enhances safety for complex shaping operations
- Works best with sulfenamide accelerators (CBS, TBBS)
PVI does not increase cure speed or final crosslink density. Its role ends once the curing temperature is reached.
Role of DPG in Rubber Compounding
DPG is a secondary accelerator used to support primary accelerators such as MBT and MBTS. It improves accelerator efficiency and helps develop better physical properties in the cured rubber.
Key Functions of DPG
- Activates thiazole accelerators
- Improves cure rate and modulus
- Enhances crosslink formation
- Improves hardness and tensile strength
- Widely used in mechanical rubber goods
DPG does not provide scorch protection. In fact, excessive DPG can reduce scorch safety if not balanced properly.
PVI vs DPG: Functional Comparison
| Aspect | PVI | DPG |
|---|---|---|
| Scorch Safety | Excellent | Poor |
| Cure Activation | None | Strong |
| Cure Speed | Delays onset only | Increases cure efficiency |
| Processing Safety | Very high | Limited |
| Influence on Final Properties | Minimal | Significant |
| Typical Use Case | Tyres, high-temp processing | Mechanical rubber goods |
Interaction with Common Accelerators
| Accelerator System | Effect of PVI | Effect of DPG |
|---|---|---|
| CBS / TBBS | Improves scorch delay | Limited interaction |
| MBT | Minor effect | Strong activation |
| MBTS | Minor effect | Strong activation |
| TMTD | Reduces scorch risk | Can accelerate too much |
| ZDEC / ZDBC | Rarely used | Limited benefit |
Typical Dosage Levels
| Chemical | Typical Dosage (phr) | Notes |
|---|---|---|
| PVI | 0.05 – 0.30 | Excess may delay cure excessively |
| DPG | 0.2 – 1.5 | High levels reduce scorch safety |
Application-Wise Selection Guide
Tyre Compounds
- Prefer PVI for improved scorch safety
- Especially important for tread and carcass compounds
- Used with CBS or TBBS systems
Industrial & Mechanical Rubber Goods
- Prefer DPG for improved cure efficiency
- Used with MBT or MBTS
- Common in hoses, belts, gaskets, seals
High-Temperature Processing
- PVI is essential
- Prevents premature cure during extrusion or calendaring
Fast-Cure Requirements
- DPG is preferred
- Helps shorten cure cycle time
Common Problems and Practical Solutions
Problem: Premature Scorch During Mixing
- Cause: High processing temperature, fast accelerator system
- Solution: Add PVI at low dosage
Problem: Slow or Incomplete Cure
- Cause: Weak accelerator activation
- Solution: Add DPG with MBT or MBTS
Problem: Poor Tensile Strength
- Cause: Low crosslink density
- Solution: Use DPG to improve cure efficiency
Problem: Excessive Cure Delay
- Cause: Overuse of PVI
- Solution: Reduce PVI dosage or balance accelerator system
Can PVI and DPG Be Used Together?
Yes, but with caution.
- PVI controls scorch
- DPG promotes cure
When balanced correctly, both can coexist in complex formulations, especially in tyre compounds where scorch safety and cure efficiency must be tightly controlled.
Key Selection Summary
| If Your Priority Is… | Choose |
|---|---|
| Scorch safety | PVI |
| Cure activation | DPG |
| High-temperature processing | PVI |
| Faster cure & higher modulus | DPG |
| Tyre manufacturing | PVI |
| Mechanical rubber goods | DPG |
Practical Difference Between PVI and DPG
The difference between PVI and DPG in rubber compounding is fundamental.
PVI is a protector, ensuring processing safety.
DPG is a promoter, improving cure efficiency and physical properties.
They are not interchangeable, and confusing their roles can lead to serious production issues. Selecting the right one—or the right balance—depends on compound design, processing conditions, and performance targets.
Optional Technical Support from ARPL
For manufacturers seeking consistent performance from PVI, DPG, and complete rubber accelerator systems, Arihant Reclamation Pvt. Ltd. (ARPL) supplies quality-controlled rubber chemicals including PVI, DPG, MBT, MBTS, CBS, TBBS, TMTD, ZDEC, ZDBC, ZMBT, TMQ, TDQ, and Zinc Oxide, with Pan-India supply and technical assistance.
📞 +91-8860732624
📧 arihantreclamation@gmail.com
🌐 https://arihantreclamationpvtltd.com/