Dissolution behaviour of biosoluble HT stone wool fibres

The dissolution behaviour of two types of fibres, the biosoluble HT and the traditional MMVF21 stone wool fibres, in synthetic simulated lung fluid (G amble's solution) at pH 4.5 was investigated in order to clarify the mechan isms, and the effect of the various constituents in the liquid. The Gamble's solution contains various organic acids and salts. The study s howed that organic acids which are able to form complexes with aluminium (e .g. citric and tartaric acid) caused both fibres to dissolve at a high rate at pH 4.5. Organic acids without the ability to form complexes with alumin ium (e.g. acetic, maleic, lactic and pyruvatic acid) have no (or minor) imp act on the dissolution rate at pH 4.5. The presence of sodium chloride lowers the dissolution rate, especially tha t of MMVF21. The silica that remains when the silica network has been deple ted of aluminium ions (due to citric and tartaric acid) behaves differently in the two fibres. In HT fibres the silica dissolves at a high rate, proba bly as a diluted sol. Thus the HT fibre has a high dissolution rate in Gamb le's solution at pH 4.5. For the MMVF21 fibre, condensation of the silica n etwork as a el results in a lower dissolution rate. It is assumed that the different Al/(Al+Si) ratios for HT and MMVF21 fibres explain why the fibres behave differently.