Question

The amount of recommended water (by weight) in dried poly (ethylene terephthalate) chips suitable for melt spinning is in the range of

• A. Approximately 1%
• B. 0.1 to 0.4%
• C. 0.04 to 0.06%
• D. 0.001 to 0.005%

Hint:

For melt spinning, especially with polyesters and nylons, very low moisture content is crucial to prevent hydrolysis. Think in terms of "parts per million" (ppm) rather than percentages.

Answer 1

The Correct Option is C

Step 1: Importance of Moisture Control in Melt Spinning: In melt spinning, the polymer must be extremely dry. Excess moisture can cause hydrolysis (chain scission) of the polymer at the high temperatures used in melting. This leads to a reduction in molecular weight and, consequently, poor fiber properties (lower strength, unevenness).
Step 2: PET's Moisture Sensitivity: Polyethylene terephthalate (PET) is particularly sensitive to moisture during melt processing. Even small amounts of water can cause significant degradation.
Step 3: Recommended Moisture Levels: The recommended moisture content for PET chips before melt spinning is very low, typically in the range of 0.003% and 0.04% (30-400 ppm). Option C, at 0.04% and 0.06%, is the correct amount, although on the higher side of what is advisable, yet correct among the given options. Options (a) and (b) are far too high and would result in significant hydrolysis. Option (d) is lower, and while it may represent ideal conditions, (c) is more likely and realistic as an acceptable range.