Method for forming high strength composites

Claim 1

A method for preparing high strength composites comprising (a) mixing an aqueous slurry of a negatively charged, water-insoluble natural or synthetic fiber or a blend of such fibers with a latex containing a cationic water insoluble copolymer as particles having pH independent bound charges at or near the particle surface in an amount from about 0.07 milliequivalent to about 0.6 milliequivalent per gram of copolymer and a co-additive which is a water-soluble anionic polymer having a degree of polymerization above about 3000, having an available charge of from about 0.3 milliequivalent to about 8 milliequivalents per gram of polymer, having an acyclic carbon-carbon chain backbone and having the capability of retaining its solubility in the presence of polyvalent metal ions at a pH from about 4 to about 7 to form an aqueous suspension of components; the amount of said latex being more than the amount required to cause charge reversal on the fiber but less than the amount which would exceed the capacity of the fiber to hold a wet mat together during processing; and the amount of said co-additive being greater than that required to cause essentially complete retention of the latex on the fiber but less than the amount which would be effective to start redispersion of the components of the aqueous suspension; (b) removing water from the aqueous suspension to form a wet mat; (c) drying the mat by heating; said copolymer particles of the latex being deformable at the temperature used in heating the mat.

Claim 2

A method for preparing high strength composites comprising (a) mixing an aqueous slurry of a negatively charged, water-insoluble natural or synthetic fiber or a blend of such fibers with a latex containing a cationic water insoluble copolymer as particles having pH independent bound charges at or near the particle surface in an amount from about 0.07 milliequivalent to about 0.6 milliequivalent per gram of copolymer and a co-additive which is a water-soluble anionic polymer having a degree of polymerization above about 3000, having an available charge of from about 0.3 milliequivalent to about 8 milliequivalents per gram of polymer, having an acyclic carbon-carbon chain backbone and having the capability of retaining its solubility in the presence of polyvalent metal ions at a pH from about 4 to about 7 to form an aqueous suspension of components; the amount of said latex being more than the amount required to cause charge reversal on the fiber but less than the amount which would exceed the capacity of the fiber to hold a wet mat together during processing; and the amount of said co-additive being greater than that required to cause essentially complete retention of the latex on the fiber but less than the amount which would be effective to start redispersion of the components of the aqueous suspension; (b) removing water from the aqueous suspension to form a wet mat; (c) drying the mat by heating; said copolymer particles of the latex being deformable at the temperature used in heating the mat.