Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Patent
1998-08-20
2000-12-05
Group, Karl
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
501 36, 501 70, 65469, 65470, 65520, C03C 1306, C03B 3704
Patent
active
061566837
DESCRIPTION:
BRIEF SUMMARY
This invention relates to man-made vitreous fibres (MMVF) which are durable in use but which can be shown to be biologically advantageous.
MMV fibres are made from vitreous melt, such as of rock, slag, glass or other mineral melts. The melt is formed by melting in a furnace a mineral composition having the desired analysis. This composition is generally formed by blending rocks or minerals to give the desired analysis. The mineral composition often has an analysis, as oxides, which includes at least 32% SiO.sub.2, below 30% Al.sub.2 O.sub.3 and at least 10% CaO. The elemental analyses in the specification are by weight and calculated as oxides. The iron oxide may be a mixture of FeO and Fe.sub.2 O.sub.3 but is quoted herein as FeO.
Efficient and cost-effective formation of the melt in the furnace and of the fibres from the melt requires that the composition should have a suitable liquidus temperature and should have a suitable viscosity during the fibre-forming process. These requirements impose constraints on the selection of the composition that is to be melted.
Although there is no scientific evidence establishing that there is a health risk associated with the manufacture and use of MMV fibres, commercial interests have led manufacturers to provide MMV fibres that retain the required physical properties of MMV fibres (e.g., durability at elevated temperatures and under humid conditions) but which can also be alleged to be of improved biological safety.
This allegation of improved safety is usually made on the basis of in-vivo tests. Biopersistence or durability in the lung is regarded as an important parameter for the possible health effect of man-made vitreous fibres. Often used methods for evaluating the biopersistence of fibres are the observation of the clearance of fibres (which could be all fibres, WHO-fibres, fibres longer than 20.mu.) after instillation or inhalation in rats. A typical result of such tests is the halftime of this clearance.
Based on in vivo research, some mechanisms have been recognised. For instance Oberdbrster in VDI Berichte 853, 1991, pages 17 to 37 showed that, in addition to mechanical clearance, the mechanisms could involve dissolution in the near-neutral lung fluid (around pH 7.5) and dissolution in the acidic environment (maintained at pH 4.5 to 5) created around fibres surrounded by macrophages in the lung. It is believed macrophages promote removal of the fibres from the lung by promoting local dissolution of the surrounded fibre area leading to weakening and breaking of the fibres so as to reduce the average fibre length, thereby enabling macrophages to engulf and transport the shorter fibres out of the lung. This mechanism is illustrated in the article by Morimoto et al in Occup. Environ. Med 1994, 51, 62-67 and especially FIGS. 3 and 7 and articles by Luoto et al in Environmental Research 66 (1994) 198-207 and Staub-Reinhaltung der Luft 52 (1992) 419-423. Other relevant references are Bellmann et al "Investigation on the durability of man-made vitreous fibers in rat lungs", Environ Health Perspect; 1994, 185-89; Bernstein D. et al "Evaluation of soluble fibers using the inhalation biopersistence model, a nin-fiber comparison", Inhalation Toxicology, 1996, 8, p.345-85, and Carr I. "The Macrophage--A Review of Ultrastructure and Function" New York: Academic Press, 1973.
Traditional glass fibres and many of the MMV fibres claimed to have increased solubility in lung fluid (at pH 7.5) have a worse solubility at pH 4.5 than at pH 7.5 and so presumably attack by macrophages would not contribute significantly to the shortening and final removal of the fibres from the lung.
The two different dissolution processes described above are simulated by in-vitro measurements. The in-vitro tests measures the dissolution rate or degradability of the fibres in a liquid which is intended to simulate the lung liquid, such as the Gamble's solution at a pH of 7.4-7.8 or the environment within the macrophages using a modified Gamble's solution, adjusted to the pH of 4.5-5 found inside th
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Chemical Abstracts, vol. 121, No. 24, Dec. 12, 1994, Columbus, OH, Abstract No. 285294.
Christensen Vermund Rust
Grove-Rasmussen Svend
Guldberg Marianne
Jensen Soren Lund
Group Karl
Rockwool International A/S
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