“…On the other hand, the pure-organic compounds commonly act as cross-linkers in PVA chains. These include (1) hexamethylene diisocyanate; the crosslinking ranged from 1.7 up to 74 mol% of reacted OH groups [23]; (2) The maleic acid addition causes an increase of the T g (i.e., for the pure PVA and the maleic acid treated PVA was 90 and 1208C, respectively), indicates the presence of flexible interlinks between two PVA chains [24]; (3) The BHES (bis b-hydroxyethyl sulfone), when the BHES concentration increases, the T m of the heat-treated films shifted to the lower temperature, in addition to existence of the crystalline phase for PVA with high water resistance [25]; (4) The glutaraldehyde, where the cross-link density increase up to 34%, corresponding to reduction of free volume in polymer backbone, yielded reduction in PVA properties (e.g., swelling, water uptake, and conductivity) with lower oxygen diffusivity across films [26]. Finally the chemical linking adverse effects can be avoided by using the physical cross linking process such electron beam or radiation techniques [27].…”