Rubber protection: antioxidants are added to guard against light, heat, and ozone degradation. Which compound class is a widely used rubber antioxidant?

Introduction / Context:
Unsaturated elastomers degrade via oxidative chain scission, crosslink modification, and surface cracking (e.g., ozone cracking). Antioxidants and antiozonants protect rubber articles such as tyres, belts, and seals, improving service life and appearance.

Given Data / Assumptions:

• The question targets chemical classes that function as antioxidants.
• Light, heat, and ozone are cited as stressors.
• We assume typical NR, SBR, and related elastomer systems.

Concept / Approach:
Alkylated diphenyl amines (and related p-phenylenediamines) are effective antioxidants/antiozonants that scavenge free radicals and intercept oxidative pathways, thereby delaying embrittlement and surface cracking. Carbon (elemental), magnesium (metal), and “Thiokol” (polysulfide rubber) are not used as antioxidants in standard compounding practice.

Step-by-Step Solution:
Recall common antioxidant families: amine-based and phenolic types.Match “alkylated diphenyl amine” with proven antioxidant function in rubber.Select it as the correct answer.

Verification / Alternative check:
Tyre compound data sheets list amine antioxidants/antiozonants (e.g., 6PPD) as standard ingredients.

Why Other Options Are Wrong:
Carbon and magnesium: not antioxidants in rubber compounding.Thiokol: itself an elastomer, not an antioxidant additive.

Common Pitfalls:
Confusing carbon black's reinforcement with antioxidant function; mixing base elastomers with additives.

Final Answer:
Alkylated diphenyl amine