In prison cubicle at Seoul, lost some rayon base (9)

I believe the answer is:

cellulose

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(Other definitions for cellulose that I've seen before include "O cull eels for what causes the pitted look" , "Polysaccharide" , "dietary fibre" , "film-makers use it" , "Substance in plants -- so cull eel (anag)" .)

I've seen this clue in the Sydney Morning Herald.

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