Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Patent
1984-10-16
1987-03-03
Van Balen, William J.
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
162 70, 162 71, 162 72, 162 79, 162158, 428703, D02G 300, B32B 1302, D21C 300
Patent
active
046475052
DESCRIPTION:
BRIEF SUMMARY
This invention relates to cellulose fibres suitable for cement reinforcement, and is concerned with a process for making cellulose fibres more suitable for that purpose and with fibre-reinforced cement products incorporating such fibres.
Substantial activity is being directed to developing reinforcing fibres for cement which replace the asbestos fibres formerly used. Cellulose fibres are being used for this purpose because of their capacity for dispersing in cement slurries to form webs in the manufacture of fibre-reinforced cement products. However, cellulose fibres are susceptible to swelling and degradation in the alkaline cement medium and this tends to reduce their performance as a reinforcement.
According to this invention, a process for making cellulose fibres more suitable for cement reinforcement is characterised by dispersing the fibres in an aqueous medium which swells the fibres, impregnating the swollen fibres with a titanium chelate compound and/or a zirconium chelate compound in solution, drying the fibres, and then effecting reaction between the chelate compound(s) and the hydroxyl groups on the cellulose fibres to link titanium and/or zirconium radicals to residues of said groups.
Preferably the aforesaid chelate compound(s) react with the hydroxyl groups on the cellulose fibres to form cross-links between residues of hydroxyl groups.
The cellulose fibres are preferably wood pulp fibrs, but other natural or regenerated cellulose fibres, for example viscose fibres, may also benefit from treatment by the process of the invention.
The invention includes cellulose fibres having an improved suitability for cement reinforcement after treatment by the process of the invention.
Cellulose fibres treated by the process of the invention have an enhanced stability against swelling, particularly if cross-linked as described. Moreover, the stabilising effect is apparent not just on the surface of the fibres but throughout the body of the fibres. This is the result of dispersing the fibres in an aqueous medium and allowing them to separate and to swell so that the chelate compound(s) can throughly impregnate the fibres.
The chelate compound(s) may be added to the same aqueous medium used to disperse and swell the cellulose fibres and may be added at the same time as the fibres or later, after they have been dispersed. Preferably the chelate compound(s) are already in solution before being added to the aqueous dispersion medium.
The use of the chelated form of compound makes it possible to use an aqueous medium to disperse and swell the cellulose fibres and to act as a vehicle for impregnation because, unlike other titanates or zirconates, the chelated compounds resist hydrolysis by water at ambient temperatures. Thus, it is possible to control the conditions during impregnation and the subsequent drying step so that there is minimal hydrolysis of the chelate compound(s) by the water, and subsequently to treat the dried fibres to effect the desired reaction with the hydroxyl groups of the cellulose fibres when there is little or no water present to effect preferential hydrolysis.
Conditions which minimise hydrolysis during impregnation are the maintenance of the aqueous impregnation medium at ambient temperature and preferably at a low solution pH. If alkaline conditions are to be used to enhance the swelling of the cellulose fibres, then it is preferable to inhibit water hydrolysis of the chelate compound(s) by incorporation, for example, of a polyhydroxy compound such as sorbitol in the aqueous medium.
The aqueous medium may be mechanically extracted from the impregnated fibres, suitably to a solids concentration of 20 to 50, preferably 30 to 35, percent by weight, prior to final drying. The usual equipment for hydroextraction may be used including porous screens, squeeze rollers and rotary extractors. The hydroextracted fibres may be dried as a fixed or fluidised bed of fibres using a current of warm air as the drying medium. Hydrolysis of the impregnant chelate compound(s) by residual water is minimis
REFERENCES:
patent: 3243447 (1966-03-01), Rinse
patent: 3625934 (1971-12-01), Rinse
patent: 4423112 (1983-12-01), Luthringshauser et al.
Chemical Abstracts, vol. 95, No. 12, 1981, p. 264, Abstract No. 102047Z, Coutta, Robert, "The Chemistry of Titanium Coupling Agents".
Composites, vol. 10, No. 4 (Oct. 1979), IPC Business Press Limited, Sussex G. B., pp. 228-232.
Blackie Merrick S.
Poynton David J.
Courtaulds PLC
Van Balen William J.
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