Role of diphenylamine in rubber compounding: what is the primary purpose of adding diphenylamine to rubber formulations?

Introduction / Context:
Antioxidants are critical additives in rubber to inhibit degradation that leads to cracking, hardening, or loss of elasticity. Aromatic amines, including diphenylamine and its derivatives, are classic antidegradants in many diene rubbers.

Given Data / Assumptions:

• We consider the function of diphenylamine within typical rubber recipes.
• We separate antioxidant roles from curing chemistry.

Concept / Approach:
Diphenylamine acts as a stabiliser that scavenges radicals and inhibits oxidative chain reactions, thereby protecting rubber during service and processing. Vulcanisation is driven by sulphur/accelerator systems, not by diphenylamine. Flame retardancy requires other additives (e.g., halogenated systems, ATH), and thermosetting arises from crosslinking via curing agents, not antioxidants.

Step-by-Step Solution:
Identify diphenylamine class → antioxidant/antidegradant.Associate with protection against oxygen, heat, and ozone effects.Exclude vulcanisation, flame retardancy, and curing roles.

Verification / Alternative check:
Compounding guides list aromatic amines/phenolics as antioxidants improving heat-aging resistance.

Why Other Options Are Wrong:
(a) Vulcanisation requires sulphur/accelerators.(c) Non-inflammability needs dedicated FR systems.(d) Antioxidants do not crosslink rubber.

Common Pitfalls:
Assuming any additive that improves durability must be a curing agent; functions are distinct.

Final Answer:
To protect against oxidative deterioration during air/heat exposure