Fibre spinning routes: in wet spinning, a polymer solution is extruded through spinnerettes into a coagulation bath to form filaments. Wet spinning is NOT used for which of the following fibre types?

Introduction / Context:
Spinning processes depend on whether the polymer is handled as a melt or a solution. Wet spinning precipitates the polymer from solution in a coagulation bath; it is appropriate for polymers that cannot be melt-spun due to decomposition before melting or because of very high melt viscosities. Saturated polyesters such as PET are melt-spun, not wet-spun.

Given Data / Assumptions:

• Viscose rayon and cupro rayon are regenerated celluloses made by wet spinning.
• Many acrylics (PAN-based) are wet- or dry-spun from solutions.
• Saturated polyester (PET) cleanly melts and is melt-spun.

Concept / Approach:
Check each polymer’s standard spinning route: regenerated celluloses (viscose, cupro) and many PAN acrylics use wet spinning; PVAc derivatives can be wet-spun in some specialty contexts. PET is produced in massive volumes by melt spinning with subsequent drawing and heat setting. Thus, among the options, the fibre not associated with wet spinning is saturated polyester.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturing references describe PET melt-spinning lines; wet spinning lines are associated with viscose and acrylic fibre plants.

Why Other Options Are Wrong:

• Viscose/cupro: canonical wet-spun fibres.
• Acrylic: widely wet-/dry-spun due to PAN thermal behavior.
• PVAc: specialty wet-spun derivatised systems exist; exam context accepts as wet-spinnable vs. PET.

Common Pitfalls:
Conflating dry spinning (evaporation) with wet spinning (coagulation); both are solution processes but distinct mechanisms.

Final Answer:
Saturated polyester