Alkyd resins (e.g., glyptal) applications: which of the following is NOT a common use of alkyd resins?

Introduction / Context:
Alkyd resins are polyester-based coating binders derived from polyols (e.g., glycerol), dibasic acids/anhydrides (e.g., phthalic anhydride), and fatty acids or oils. They dominate many architectural and industrial coatings due to good film formation, durability, and compatibility with pigments and additives.

Given Data / Assumptions:

• Alkyds are used as primary binders in paints/varnishes.
• They can act as film-forming materials in coatings.
• Modified alkyds may contribute plasticising effects in certain formulations.
• Continuous synthetic fibre production typically requires polymers with melt or solution-spinning suitability and precise molecular architecture (e.g., PET, nylon).

Concept / Approach:
Coatings require a binder that forms a coherent film after application and drying/curing. Alkyds excel here. Fibre manufacture, in contrast, needs polymers that can be spun into filaments and drawn to achieve strength and orientation; alkyd resins are not used as fibre-forming polymers.

Step-by-Step Solution:
Identify core alkyd applications: coatings, varnishes, enamels—film formation and adhesion.Recognise that 'fibres' implies melt- or solution-spun filament production (PET, nylon, acrylics), not alkyds.Therefore, 'Fibres' is the excluded application.

Verification / Alternative check:
Market usage data consistently list architectural coatings, industrial enamels, and air-drying alkyds; no commercial fibre segment exists for alkyds.

Why Other Options Are Wrong:
Paints/varnishes and film-formers are primary alkyd domains.Plasticiser: alkyd components and modifiers can impart plasticising/flexibility in coating films, though dedicated plasticisers are separate chemicals.

Common Pitfalls:
Assuming any polymer can be spun into fibres; conflating plasticiser function with true plasticiser molecules (e.g., phthalates) even though alkyds contribute film flexibility.

Final Answer:
Fibres