Tyre reinforcement cords: Which of the following fibres is generally not used as cord material for synthetic-rubber tyre casing? (Assume historical and modern practice in automotive tyres.)

Introduction / Context:
Tyre casings require strong, fatigue-resistant cords to reinforce the rubber matrix. Materials selection evolved from rayon to nylon and polyester. Understanding which fibres are or have been used is essential for materials engineers working in automotive components and composites.

Given Data / Assumptions:

• The question spans historical and current industrial practice.
• Dacron denotes polyester (e.g., PET fibre); Nylon denotes polyamide; Cellulose reflects rayon cord.
• We consider typical passenger and truck tyre constructions.

Concept / Approach:
Rayon (cellulose), nylon, and polyester have all been used as tyre cords. Rayon was common in early radial tyres; nylon is used for cap plies and some carcasses; polyester (Dacron) is widely used in passenger tyre body plies. Since all listed fibres have been used as cord materials, the correct response is that none are excluded.

Step-by-Step Solution:

Verification / Alternative check:
Tyre construction references list rayon, nylon, and polyester as common reinforcement fibres; steel cords are used in belts for many modern radials, but textile cords remain essential in carcasses and cap plies.

Why Other Options Are Wrong:

• Dacron (polyester): Actively used; not excluded.
• Nylon (polyamide): Actively used; not excluded.
• Cellulose (rayon): Historically and selectively used; not excluded.

Common Pitfalls:
Assuming only steel belts are used today; textile cords are still critical. Also, confusing brand names with generic polymers can lead to incorrect exclusions.

Final Answer:
None of these