Based on this question and answer about a human sized creature that lives completely on textiles, how feasible is it for a creature to consume nylon and polyester to derive fats/lipids useful for building cell walls? Whether the creature performs the transformation itself or special gut bacteria perform the transform is irrelevant to the question.
Assume an approximately human sized creature that requires between 1500 and 2000 calories per day. We have established that this creature can synthesize its own amino acids and vitamins, so it doesn't need to consume those from the textiles. Mineral consumption has been handwaved a bit because there just isn't much mineral content in the dyes and fabric of textiles.
Remember, this is a hard-science so equations, journal entries, or official sources are required in the answer.