Rubber processing — In industrial rubber technology, “mastication” of rubber refers specifically to what?

Introduction / Context:
Mastication is a foundational step in rubber compounding. Before additives can be uniformly mixed and before the rubber can be processed effectively, the raw gum rubber must be softened and its viscosity reduced. This is achieved by mastication.

Given Data / Assumptions:

• Mastication uses mechanical working (mills or internal mixers).
• Objective: reduce viscosity, improve processability and dispersion of fillers/chemicals.
• Not primarily a chemical antioxidant or curing operation.

Concept / Approach:
Mechanical shear and heat during mastication break long polymer chains (chain scission), lowering molecular weight and thus viscosity. This facilitates subsequent mixing of carbon black, zinc oxide, sulfur, accelerators, and other compounding ingredients.

Step-by-Step Solution:
Apply mechanical work in mixers → induce chain scission.Result: lower Mooney viscosity and improved flow.Outcome: easier dispersion of compounding agents and better downstream processing.

Verification / Alternative check:
Rheological measurements show reduced viscosity after mastication; micrographs evidence improved dispersion capability post-mastication.

Why Other Options Are Wrong:

• Antioxidant addition: protects from oxidation but is not mastication.
• Accelerators: affect curing kinetics, not the softening step.
• Plasticizers: can lower viscosity, but mastication specifically refers to mechanical softening.
• Raising Tg via fillers: inconsistent; fillers often raise modulus but do not define mastication.

Common Pitfalls:
Confusing mastication with plasticization or vulcanization; assuming it is primarily a chemical process.

Final Answer:
Softening of raw rubber by mechanical working to reduce molecular weight and viscosity