Surface properties of vitreous fibers

The surface properties of various vitreous fibers, suspected to be toxic to humans and animals, were investigated by means of paramagnetic labels cova lently linked to the surface. Computer-aided analysis of the electron param agnetic resonance (EPR) spectra provided structural and dynamic information on the label and its environment. Calorimetric measurements provided infor mation on the hydration mechanism. The results were analyzed in terms of (a ) different polarity and interaction abilities of surface regions, (b) pres ence of ions at the surface, (c) silica contents, (d) vicinity of the inter acting sites, (e) fiber dimension and morphology of the surfaces, and (f) w ater hydration. The mobility of the labels decreased due to interaction of the fibers with ions or ionic and polar groups at the surface, Close intera cting sites were identified on the basis of spin-spin effects and were dist inguished and quantified in strongly and weakly interacting sites. The spin -labeling technique indicated decreased ability of the surface to interact with decreased silicon concentration and in the presence of contaminants at the surface. The interaction with water revealed in all cases a substantia l heterogeneity in hydrophilicity of surface sites. The labels were not eas ily hydrated. Vitreous fibers of various compositions adsorbed much more wa ter than crystalline or amorphous silica; water coordinated to surface cati ons played a major role in the overall adsorption. The surface reaction mec hanisms were the same on fibers of different compositions, but the surface composition affected the extent of adsorption. Glass wool exhibited a much higher adsorption capacity than rock wool under the same experimental condi tions. In conclusion, the combination of EPR and calorimetric measurements provided insight into the surface properties of silica-based fibers. (C) 20 00 Academic Press.