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Mineral wool products, composed of stone wool fibers and organic binder, are used in many construction applications. Among all their beneficial properties, the most important requirement is safety for human health, such as when fibers are inhaled. For determining long-term toxicity, biosolubility and biopersistence studies in vitro and in vivo are essential. In vitro fiber dissolution rate, which depends on the medium, fiber composition, and the surface available for dissolution, is a key parameter in determining biopersistence of the material in vivo. We investigated how organic binder (phenol-ureaformaldehyde), which can partially shield fiber surfaces from the solution, influences fiber dissolution kinetics in synthetic lung fluid (modified Gamble's solution) at pH 4.5 and temperature 37 °C, in vitro. Dissolution experiments were made in batch and continuous flow using stone wool fibers with typical insulation product binder amounts (0−6 wt %), applied by the standard industrial process. Dissolution rates were determined from element concentrations in the reacted solution, and changes in fiber surface composition and morphology were monitored. Stone wool fiber dissolution was close to stoichiometric and was similar, whether or not the material contained binder. The high dissolution rate (508 ng of fiber/cm 2 /h) is explained by Al and Fe complexing agents, that is, citrate and tartrate, in the synthetic lung fluid. The organic binder mainly forms micrometersized discrete droplets on the fiber surfaces rather than a homogeneous thick coating. During in vitro tests, fibers with organic binder preferentially dissolved in the areas free of binder, forming cavities, whereas the untreated fibers dissolved homogeneously. Propagation of cavities undermined the binder droplets, leading to complete fiber dissolution. Thus, presence of organic binder on stone wool fibers, produced by the standard industrial process, had no measurable effect on dissolution rate in synthetic lung fluid containing Al and Fe complexing agents.

The ability of bulk glass and fibers to react in aqueous solution, with organic polymers and coupling agents, depends on the surface charge, reactivity, and adsorption properties of the glass surface, i.e. the character and density of surface −OH groups, whereas glass and fiber chemical stability and biosolubility depend on the resistance to dissolution. If glass dissolution products are accumulated in a media, they can change the surface properties by specific adsorption. We determined the −OH surface concentration, reactivity, adsorption, and dissolution properties of aluminosilicate glasses containing various modifiers and compared the results with the behavior of complex mineral wool fibers. Using proton consumption and element release from batch surface titration experiments, over the range 5 < pH < 10, surface −OH adsorption properties were modeled with the FITEQL program. During titration, network modifiers in the glass subsurface are preferentially replaced by protons, resulting in cation accumulation in the solution and formation of a leached layer enriched with Si on the solid. The behavior of Al was different. At 5 < pH < 9, only very small amounts of Al were found in the leachates, which can be explained by almost complete Al adsorption as stable surface complexes, i.e. >XOAl­(OH)2 (where X = Si or Al and > represents the surface). At pH > 9, divalent cations adsorbed specifically, as >XOMe+ complexes (Me = Ca or Mg). This deeper understanding of the surface behavior of glasses and fibers is important for the design of composite materials, for applications in biology and medicine and in materials production in general, as well as for understanding natural processes, such as global uptake estimates of CO2 during rock weathering.

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