couldn't be PVOH hardenable (at least in an alkaline medium) by using boric acid? Or perhaps using glutaraldehyde?
regarding its mechanical/optical properties, does it differ much from gelatine? were there any attempts for using PVOH in photo emulsions?
since there are also some PVA variants available functionalized with anionic (and cationic) groups, couldn't be that stuff hardenable by just adding an aluminium salt?