New Type Of Stonewool (Ht Fibres) With A High Dissolution Rate At Ph=4.5

HT-3 fibre (a new type of stonewool), characterised by a relatively high content of alumina and a relatively low content of silica, has recently been tested and found to have a low biopersistence after intratracheal instillation in rat lungs. Several advantages of this fibre were found. The HT fibres have a relativley low in-vitro dissolution rate at pH=7.5, similar to that of normal stonewool fibres, but a high in-vitro dissolution rate at pH-4.5. The explanation of in-vitro properties of the HT-3 fibre is based on the recent investigations of the ability of alveolar macrophages to dissolve certain fibres, coupled with the observation of the high dissolution rate of the HT fibres at the pH value of 4.5-5 prevailing inside the macrophages.