The most common and most likely answer to this crossword clue is the 11 letter word POLYMERISED
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The straight part
We know that "changed into something like PVC" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case changed into something like pvc = polymerised.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does POLYMERISED mean?
POLYMERISED verb- To convert a monomer to a polymer by polymerization.
- To undergo polymerization.