Thermal stabilizers are one of the most important additives in the plastics and polymers industry, used to increase the resistance of polymers to heat and prevent thermal degradation. These materials play a very important role in maintaining the physical, mechanical and chemical properties of polymers in production processes and end applications.

Definition and importance of heat stabilizers

In the process of manufacturing and using polymers, increasing temperature can cause degradation of polymer chains, discoloration, loss of strength, and increased brittleness of the materials. For this reason, it is essential to use additives that can reduce or delay this degradation. These additives are known as thermal stabilizers.

Mechanism of action of thermal stabilizers

Thermal stabilizers prevent thermal degradation of polymers by several different mechanisms:

• Free radical inhibition: In the thermal degradation process, free radicals cause the polymer chains to break. Stabilizers neutralize these radicals.
• Neutralization of acids: In some polymers, thermal degradation leads to the production of acids that help accelerate degradation. Stabilizers neutralize these acids.
• Protection against oxidation: In the presence of oxygen and heat, polymers oxidize. Stabilizers prevent this reaction.
• Heat absorption or transfer: Some stabilizers reduce the local temperature of the polymer by absorbing excess heat.

Types of heat stabilizers

1. Metal stabilizers:
   • Zinc (Zn) compounds: Used to inhibit thermal degradation in PVC and some other polymers.
   • Cadmium and lead compounds: They were used in the past, but have been gradually eliminated due to their high toxicity.
   • Magnesium and calcium compounds: more compatible and non-toxic alternatives to traditional stabilizers.
2. Antioxidants:
   • Phenolic compounds: such as butylated hydroxytoluene (BHT), which scavenge free radicals.
   • Aromatic amines: for stabilizing engineered polymers.
   • Phosphites and phosphonates: as auxiliary compounds to inhibit oxidation.
3. Combined stabilizers:
   • A combination of antioxidants and metal stabilizers for better performance.

Applications of thermal stabilizers

• Plastics industry: Preventing thermal degradation of polymers in processes such as extrusion, injection, blow molding, and film making.
• PVC: Special protection against thermal and oxidative changes.
• Polyethylene and polypropylene: Increased thermal life and stability against light and heat.
• Elastomers and engineering polymers: maintaining mechanical and thermal properties at high temperatures.
• Paint and coating industries: Prevent discoloration and degradation of compounds.

Benefits and importance of using heat stabilizers

• Increase product life: Preventing damage and increasing the life of plastic parts and products.
• Maintaining mechanical properties: Preventing a decrease in the strength, flexibility, and toughness of materials.
• Reduce discoloration: Prevent products from yellowing or darkening at high temperatures.
• Improving the production process: Reducing problems caused by polymer degradation during production.
• Economic savings: Reduced waste and less need to replace parts and products.

Important points in choosing thermal stabilizers

• Compatibility with polymer type: Selecting a stabilizer that is appropriate for the type of base polymer.
• Application temperature: A stabilizer must be selected that is sufficiently effective at the temperature used.
• Resistance to environmental factors: If required, the stabilizer must be resistant to light, moisture, and chemicals.
• Environmental considerations: Choosing stabilizers that cause the least damage to the environment.

Conclusion

Thermal stabilizers play a vital role in maintaining the quality and durability of polymers. By preventing thermal and oxidative degradation, these additives extend the shelf life of plastic products, maintain their appearance and mechanical properties, and make the production process more efficient and economical. The selection of the appropriate thermal stabilizer is of great importance depending on the type of polymer, the process conditions, and the end use.