In polymer science, which of the following materials is generally not drawn into fibre form for textile or technical filaments (while the others commonly are)?

Introduction / Context:
Drawing is the process of orienting polymer chains by stretching a partially solidified filament to improve strength, modulus, and dimensional stability. Most fibre-forming polymers must be linear or lightly branched, with adequate molecular weight and chain flexibility so that they can be melt- or solution-spun and then drawn. This question compares several common polymer families and asks which one is generally not used for fibre drawing.

Given Data / Assumptions:

• Polyamide (nylon), saturated polyester (PET), and polyacrylonitrile (PAN) are classical fibre-forming polymers.
• Unsaturated polyesters are typically crosslinked thermosetting resins used with fillers/fibres (e.g., glass) to make composites.
• Drawing requires extensibility and chain mobility prior to final orientation and crystallization; extensive crosslinking prevents this.

Concept / Approach:
Fibre formation normally uses thermoplastic, linear polymers that can be extruded as filaments and subsequently drawn to align chains. Unsaturated polyester resins are designed to cure into a network (crosslinked) structure through styrenic or similar reactive diluents. After curing, they cannot be softened or stretched to produce oriented fibres. By contrast, nylon, PET, and PAN are archetypal fibre polymers used in apparel, tire cord, and carbon-fibre precursors respectively.

Step-by-Step Solution:
Identify which listed polymers are linear thermoplastics suitable for fibre spinning.Recognize that unsaturated polyesters cure to a crosslinked network (thermoset).Conclude that unsaturated polyesters are generally not drawn into fibres.

Verification / Alternative check:
Industrial practice uses PET, nylon, and PAN for fibres at massive scale. Unsaturated polyesters are used as matrices in fibre-reinforced plastics, not as the fibre itself.

Why Other Options Are Wrong:
Polyamide: classic fibre polymer.Saturated polyester (PET): classic fibre polymer (terylene/dacron).Polyacrylonitrile: key precursor for high-performance carbon fibres.Cellulose acetate: used for cigarette filters and specialty fibres.

Common Pitfalls:
Confusing “polyester” generally with “unsaturated polyesters”; PET (a saturated polyester) is fibre-forming, whereas unsaturated polyesters are thermoset matrices.

Final Answer:
Unsaturated polyesters (thermoset resins)