One-step poly vinyl alcohol-based hydrogel preparation using subcritical water/CO2 process

In the present work, a novel preparation method of poly vinyl alcohol (PVA)-based hydrogel using subcritical water/CO2 medium in presence of citric acid (CA) as crosslinker is reported. This method is a single step procedure, it is less time consuming and thus industrially viable. In contrast, PVA hydrogel preparations typically consists of two steps—preparation of PVA solution and curing of the same. PVA powder, loaded into aqueous solution of CA is taken into subcritical state by using CO2. Water acts as plasticizer and reduces melting temperature of PVA. Further, subcritical water acts as catalyst and reduces the crosslinking reaction time. Additionally, at 100 bar constant pressure, CO2 produces carbonic acid in subcritical water which also acts as mild acid catalyst for crosslinking reaction. In subcritical medium, PVA powder gets melted, fused and cross-linked in a single step process to develop hydrogel. Effect of process time, process temperature and amount of crosslinker on the properties of prepared PVA hydrogels were studied. PVA hydrogels were characterized in terms of gel content, thermal characterizations, chemical properties, morphology, swelling behaviour, rheology and dye absorption study. Successful dye absorption, high swelling property and high storage modulus establish the potential for application of prepared hydrogels in several areas such as biomedical, textile effluent, water purification, etc.