disbound ☜☞ desencuadernado(a)

If used as the English translation of the word desglosada it is very imprecise. Disbound may simply refer to any text block (i.e., all the printed pages) of a book removed from its binding. 
To say “removed from a nonce volume” is also ambiguous. It may have been removed from a factitious volume, in which case it probably started as a suelta, lost its companions, and went back to being a singleton.

See also: bindings, desglosada, nonce volume, factitious volume