Super-absorbent polymer having improved absorbency properties

Claim 1

A process of preparing a super-absorbent polymer which comprises: (a) forming an aqueous solution of acrylic acid, a water soluble polysaccharide, and a multifunctional monomer, wherein said multifunctional monomer has at least two polymerizable ethylenically unsaturated double bonds per molecule, wherein said acrylic acid and said polysaccharide are present in the amount of about 90 to about 100 weight percent acrylic acid and about 0 to about 10 weight percent polysaccharide wherein said weight percents are based on the weight of the acrylic acid and the polysaccharide, wherein said multifunctional monomer is present in the amount of about 0.075 to about 1 mole percent based on the moles of acrylic acid, and wherein the acrylic acid and the polysaccharide are present in the aqueous solution in the amount of about 5 to about 30 weight percent wherein the weight percent is based on the weight of acrylic acid, polysaccharide and water; (b) adding to the aqueous solution at a temperature of about 5° to about 20° C., a redox catalyst system and a thermal free radical initiator wherein the reducing agent part of the redox catalyst is present in the amount of about 6×10 -5 to about 2.5×10 -3 mole percent based the moles of acrylic acid, wherein the oxidizing agent part of the redox catalyst is present in the amount of about 3.4×10 -3 to about 0.42 mole percent based on the moles of acrylic acid and wherein the thermal free radical initiator is present in the amount of about 0.1 to about 0.4 weight percent based on the weight of acrylic acid, (c) allowing the exothermic temperature to rise under adiabatic conditions to a peak temperature not to exceed 90° C., thereby forming a polymer gel (d) holding the temperature within 10° C. of the peak temperature for a time sufficient to reduce residual monomer content below 1000 ppm; (e) neutralizing about 50 to about 100 percent of the carboxylic acid groups in the polymer with an aqueous base; (f) adding a multifunctional compound having at least two groups capable of forming ionic or covalent bonds with carboxylic acid groups wherein said multifunctional compound is added in the amount of about 0.05 to about 15 mole percent based on the moles of acrylic acid; (g) heating at a temperature of about 20° C. to about 200° C. to dry the polymer to a moisture content below about 10 percent by weight; (h) and grinding the polymer to a particle size of about 20 to 400 mesh (U.S. Standard Sieve).