Patent ES-8504648-A3 (ES)
Title: Method for manufacturing a material similar to fibre- reinforced cement
Filed: 1983-06-23
Abstract: The inventors have found that substrates which are similar to cement which have superior resistance to bending and impact and which do not have the abovementioned disadvantages can be manufactured by adding at least 2% by volume of special short poly(vinyl alcohol) fibres to the cement-containing material. These fibres must have an elongation at fracture of 4 to 8% and a modulus of more than 130 g/dtex. These poly(vinyl alcohol) fibres (PVA fibres) represent the so-called second generation of PVA fibres. They are prepared by the addition of e.g. boric acid to the spinning solution and are subjected to subsequent heat treatment. The fibres so obtained differ from first generation PVA fibres in their greater strength, their insolubility in water, their lower elasticity and their high initial modulus. The useful materials similar to cement according to this invention include materials which can contain an inorganic cement and/or an inorganic agglomerating material or adhesive which hardens by hydration. Particularly suitable agglomerating agents which harden by hydration include e.g. Portland cement, alumina cement, Portland cement containing iron, volcanic tufa cement, blast furnace cement and gypsum. First generation PVA fibres are polymers of general formula (-CH2-CH(OH)-)n with molecular weights of e.g. 13,000 to 100,000 and a density of e.g. 1.23 to 1.30, and are generally prepared by the saponification of poly(vinyl acetate) (see e.g. Rompps Chemie Lexikon, vol. 7, page 2776). Second generation PVA fibres are also known in the art and can be prepared e.g. in accordance with United States Patent no. 3,987,140. The PVA fibres according to this invention are added to the substrate similar to cement in a quantity which provides at least 2% by volume, preferably from 2 to 20% by volume of these fibres, in the resulting product. Mixtures with fibres below 2% do not provide a material similar to cement with the desired characteristics. Mixtures with fibres in excess of 20% by volume make preparation of the desired products very expensive without an appreciable increase in resistance to bending or impact. These fibres are preferably between 3 and 12 mm long. The length of the individual fibres may be uniform or variable. Ground fibres may also be used. The denier of the individual fibres may vary within a wide range, although deniers between around 1 and 5 dtex are preferable. These fibres can be distributed uniformly in the cement material. On the other hand they may be placed in high concentrations in shaped parts, in places which are particularly exposed to the action of mechanical forces. The fibres can also be added in the form of fibre fleeces, yarns, cords, gauzes, woven fabrics, etc. The transverse cross-section of the fibres may have a variety of shapes, especially resulting from physical and chemical variations in preparation processes. For example the material of the spinning solution, the precipitation bath and the spinnerets may vary. In this way the preparation of round fibres, multilobular fibres, hollow fibres, porous fibres, etc., can be brought about. The outer surface of the fibre may be roughened, divided or felted by subsequent physical treatment processes. The PVA fibres can be easily altered chemically as a result of their high chemical reactivity. Various functional groups such as carboxyl groups, amide groups, nitrile groups, phosphate groups, sulphate groups, etc., can be introduced by addition reactions or reactions with radicals. Brightening or adhesive agents may be introduced onto or within the fibres by purely physical means and can help bonding of the PVA fibres in the material similar to cement. Through the methods described above, inflammable, hydrophobic or crosslinked PVA fibres can be obtained. All PVA fibres modified in this way are suitable as fillers according to this invention. In accordance with the process according to this invention the poly(vinyl alcohol) fibres can be added alone to the material similar to cement. Nevertheless it is preferable to add asbestos, glass or other synthetic or natural fibres, alone or in combination. In addition to the reinforcing fibres coadjuvants such as cellulose residues, wood shavings, "fibrils" (e.g. polypropylene fibrils) and other fillers are frequently added to the reinforced material.