Abstract: Provided are polyvinyl alcohol-based synthetic fiber having excellent performances as a fiber for FRC that is prepared by autoclave curing and its very effective production processes. One of the processes comprises having a monoaldehyde or a dialdehyde or its acetalization product penetrate into the central region of a polyvinyl alcohol-based synthetic fiber at a first stage and then, at a second stage, effecting crosslinking reaction with a mixed solution containing a monoaldehyde and an acid. The other process comprises conducting acetalization with a bath containing 100 to 250 g/l of formaldehyde and 30 to 80 g/l of sulfuric acid at a temperature of 70.degree. to 100.degree. C. The processes can give a polyvinyl alcohol-based synthetic fiber having a strength of at least 11 g/d, a gel elasticity of at least 6.0.times.10.sup.-3 g/cm.multidot.d and a dissolution ratio of not more than 40% and being able to withstand an autoclave curing at 140.degree. C.

Abstract: Provided is a process for producing molded articles having excellent flexural strength, flexibility and dimensional stability, which comprises autoclave-curing at not lower than 100.degree. C. an aqueous composition comprising a hydraulic material (A) and a polyvinyl alcohol (B) powder, said polyvinyl alcohol (B) powder being contained in an amount of 0.1 to 20% by weight based on the weight of said hydraulic material (A).Also provided are molded articles comprising a hydraulic material (A) and a polyvinyl alcohol (B), said polyvinyl alcohol (B) being contained in an amount of 0.1 to 20% by weight based on the weight of said hydraulic material (A), said molded article having a structure comprising said polyvinyl alcohol (B) having once dissolved and then solidified being dispersed therein in the form of islands. These molded articles have excellent flexural strength, flexibility and dimensional stability.

Abstract: Provided is a high-performance PVA fiber and its production.Each filament of the PVA fiber of the present invention having a structure comprising an aggregate of substantially innumerable fibrils, the fiber has high strength, elastic modulus, and resistances to fatigue, hot water and chemicals and can be pulpified while keeping its excellent features such as high strength. The PVA fiber of the present invention cannot, even drawn to a high ratio, be readily whitened by virtue of its fibril-aggregate structure, and can hence be made still higher in performances. The PVA fiber can be obtained by adding to a PVA solution a relatively large amount of surface active agent, and wet or dry-jet-wet spinning the thus prepared dope solution into an aqueous alkaline coagulating bath.

Abstract: A synthetic fiber suited for use as a reinforcement for cement mortar or concrete as derived from monofilaments having a tensile strength of not less than 80 kg/mm.sup.2, Young's modulus of not less than 2,300 kg/mm.sup.2, a flat cross section in which the minor axis-to-major axis ratio is 1:2 to 1:10, and a fineness of 1,000-9,000 denier, and being cut to a fiber length such that the aspect ratio (the value obtained by dividing the fiber length by the diameter of a circle equivalent in area to the cross section of the fiber) amounts to 20-150, in particular a polyvinyl alcohol fiber having the above-mentioned characteristic features, shows good dispersibility in cement mortar and produces very good reinforcing effect. Materials of construction which are excellent in workability and postcure strength can be obtained by incorporating the above-mentioned fiber to cement and the like.

Abstract: A fine-denier, high-tenacity, water-resistant polyvinyl alcohol fiber is produced by dissolving a polyvinyl alcohol having an average degree of polymerization between 1,200 and 3,000, boric acid or a salt thereof in a proportion of 0.5 to 5 weight percent relative to said polyvinyl alcohol and an acid for adjusting a final spinning solution to pH 5 or less in water to prepare an aqueous solution containing 8 to 14 weight percent of said polyvinyl alcohol, discharging said aqueous solution as said spinning dope from a spinneret nozzle having an average orifice diameter of 0.02 to 0.04 millimeters into a bath comprising an aqueous solution containing alkali and dehydrating salt at a bath draft within a range of 10 to -60 percent, and finally stretching the resulting tow at least 10-fold. The fine-denier fiber thus obtained has a marked reinforcing effect on various materials, particularly inorganic hydraulic materials such as cement.

Abstract: In a process for producing fiber-reinforced hydraulically setting extruding materials, the process which comprises, not adding the reinforcing fiber in the form of single fibers to the starting materials, but employing it as collected yarns by collecting the single fibers with a collecting agent, uniformly dispersing them in the starting materials, then releasing the collected condition of said dispersed collected yarns and splitting into single fibers by swelling and dissolution of the collecting agent and by the shear force by a screw etc., thereby the dispersion is improved.The single fibers having a great aspect ratio which have been released from the collected condtion are uniformly dispersed in the extruding material, and a remarkable reinforcing effect is obtained.

Abstract: Polyvinyl alcohol synthetic fibers are used as reinforcing materials for hydraulically setting materials, and by selecting the aspect ratio of the polyvinyl alcohol fiber and the dispersing agent for said fiber, adequate dispersion is made possible even with the fiber of 2 denier or less, thereby a higher reinforcing effect may be achieved.The polyvinyl alcohol fiber is obtained by depositing 0.1-3.0% by weight based on the fiber of an oxidized polyethylene having an acid value of 5-150, and has a single yarn fineness of 0.5-2 denier, a length of 3-8 mm and an aspect ratio of 200-800, and the hydraulically setting material contains 0.1-4% by weight of said fiber.

Abstract: A water-soluble polyvinyl alcohol fiber is obtained by subjecting to the conventional dry or wet spinning process, a solution prepared by adding to a polyvinyl alcohol aqueous solution, an adduct composed of a polyamide condensation product and 1-halogen-2,3-epoxy propane or ethylene glycol diglycidyl ether in the range from 5 to 50 percent by weight based upon the polyvinyl alcohol-after the solution's pH has been adjusted to 2 to 7. The resulting fiber, which has not been subjected to any heat treatment at a temperature above 120.degree. C. is blended with a fibrous material to make a fibrous sheet such as paper or non-woven fabric. By virtue of a subsequent heat-treatment, said polyvinyl alcohol fiber becomes boiling water-resistant; as a result, the wet strength of the fibrous sheet is significantly increased.

Abstract: Disclosed is a method for preparing polyvinyl alcohol fibers which comprises spinning an aqueous solution of polyvinyl alcohol containing boric acid or a borate and from about 0.01-5 weight per cent based on said polyvinyl alcohol of an additive comprising an amino acid, an amine, salicylic acid and derivatives thereof or a derivative of pyridine into an alkaline coagulation bath, and subsequently treating the resultant spun fiber by roller drawing, neutralizing with acid, wet hot drawing, washing with water, drying and dry hot drawing.