A study on the gelation of poly(vinyl alcohol)/dimethylsulfoxide system using differential scanning calorimetry - Effects of molecular weight and degree of saponification of poly(vinyl alcohol) on gelation

Poly(vinyl alcohol) (PVA)/dimethyl sulfoxide(DMSO) gels were prepared by repeating the freezing(-20 degrees C)-thawing (30 degrees C) cycles. Differential scanning calorimetry was employed to investigate the gelation hehavior of PVA/DMSO solutions. The optimized concentration for gelation of PVA/DMSO solution was 15wt%. From the melting behavior of PVA/DMSO gels prepared From PVA with different molecular weights and degrees of saponification (DS), it was found that the effect of the DS of PVA on gelatian was more important than the molecular weight of PVA. In PVA gel with a lower DS, the increase of the gel melting temperature (T-m) and enthalpy (Delta H-m) was not remarkable though the freezing-thawing cycle was repeated up to 20 times. This result indicated that the formation of microcrystallites through intermolecular hydrogen bonding was hindered by residual acetyl groups in PVA chains. However, the increase of the gel melting temperature and enthalpy, in PVA gel with a higher DS, was remarkable as the number of freezing-thawing cycles was increased. This observation indicated that the size and number of microcrystallites increased by repeated freezing-thawing cy:les because of the easier formation of intermolecular hydrogen bonding.