Full definition
Protective additive incorporated into rubber compounds (1-3 phr) to retard degradation caused by the combined attack of oxygen and heat (thermo-oxidation), which breaks polymer chains and cross-links, causing hardening, cracking, and loss of elasticity over time. Two major chemical families: (1) Amines — paraphenylenediamines (6PPD, IPPD) and diphenylamines (TMQ/polymerized TMQ); most effective protection, but cause staining and discoloration (restricted to black products). (2) Phenolics — hindered phenols (BHT, Irganox 1010/1076); non-staining, suitable for light-colored and food-grade products, but weaker protection than amines. Mechanism: scavenge free radicals that initiate oxidative chain reactions. Dosage and selection depend on expected service temperature, required color stability, and anticipated service life. Per ASTM D4817 for classification. Often combined with antiozonants for comprehensive protection. Critical for NR and SBR compounds; less needed for inherently stable EPDM and silicone.