Use of Raman spectroscopy in the characterisation of the acid-base reaction in glass-ionomer cements

Raman spectra of various combinations of glass-ionomer cement components ha ve been compared with those of the reactants and the salts of polyacrylic a nd tartaric acids. The components consisted of a fast-setting acid-degradab le dental glass (containing, inter alia, oxides of Si, Al, Ca, Ba and Na), polyacrylic acid (PAA) and/or tartaric acid (TA). On the addition of water to the glass and tartaric acid, Raman spectroscopy indicated loss of acid a nd production of tartrate salts within seconds of mixing. Mixtures containi ng the glass, PAA and water in mass ratios 2:1:(0.1-4) reacted to form poly acrylate salts. The maximum fraction of unreacted PAA was found to decrease linearly with initial water/PAA mass ratio to a minimum of approximately 2 0% when this ratio exceeds 1.5. The data are consistent with 5.6 moles of w ater being required when each mole of acidic groups is nentralised. In newl y prepared cements containing glass, water, polyacrylic and tartaric acids, polyacrylic acid and its salts, in both ionised and solid state form, can be detected. After about 1 h, however, Raman peaks associated with ionised species disappear. (C) 2000 Elsevier Science Ltd. All rights reserved.