Crosslinking of PVA and glutaraldehyde in water monitored by viscosity andpulse field gradient NMR: a comparative study

The crosslinking of poly(vinyl alcohol) (PVA) with glutaraldehyde at 80 deg rees C was characterized by viscosity and pulse field gradient (PFG) nuclea r magnetic resonance (NMR) techniques. NMR signified an initial dormant per iod of approximately 6 hr, in ruhich the self-diffusion coefficient of PVA was found to be constant and independent of time. During the next 7 hr (the "primary" gel period), this induction period was succeeded by a fast decay of the self-diffusion coefficient of rate (9.13 +/- 0.45) x 10(-5) sec(-1) followed by a slower decay rate of (3.22+/-0.30) x 10(-5) sec(-1) (the "se condary" gel period). The viscosity of the solution showed the same time behavior, i.e. an initia l dormant period (similar to 6 hrs), followed by a fast increase of the vis cosity for the next 7 -8 hr. During the "secondary" gel regime, the viscosi ty became too large to be reliably determined. However, within the time reg ime where both techniques produced reliable data, they gave identical infor mation regarding the kinetics of the gel process, suggesting that PFG NMR e nables in situ monitoring of gelation within porous materials (for instance sandstone). Copyright (C) 2000 John Wiley & Sons, Ltd.