Abstract:
The invention relates to a process for producing a water-absorbing resin by polymerization of a reaction mixture comprising at least one hydrophilic monomer and, if appropriate, at least one crosslinker in a reactor, which comprises admixing the reaction mixture with at least one first portion of a particulate additive before the reaction mixture has reached a residence time of 40% of the overall residence time in the reactor and with at least one second portion of a particulate additive when the reaction mixture has reached a residence time of 45% or more of the overall residence time in the reactor, the additive being selected from water-absorbing resin powders, fillers and mixtures thereof, the total solids content of monomer and additive being in the range from 30% to 60% by weight, the amount of additive being in the range from 5% to 50% by weight, based on the monomers, and the weight ratio of the first portion to the second portion of the additive being in the range from 10:1 to 1:5. The resin powder is recycled fine-sized material for example. Not only the residual monomer content, specifically the residual crosslinker content, but also the level of extractables in the water-absorbing resin are reduced by the method of addition described. A high fraction of additives can be incorporated without the properties of the water-absorbing resin obtained being adversely affected. The additives enter a sufficiently firm bond with the resin, so that no excessive dusting occurs on exposure to mechanical stress.
Abstract:
What is described is a process for producing water-absorbing resins, in which a) acrylic acid is prepared at an acrylic acid production site, b) the acrylic acid prepared is dissolved in water at the acrylic acid production site to obtain an aqueous acrylic acid solution, c) the aqueous acrylic acid solution is fed into a pipeline at the acrylic acid production site and passed through the pipeline to an acrylic acid processing site and d) the aqueous acrylic acid solution is subjected to a free-radical polymerization at the acrylic acid processing site. The process ensures safe transport of the highly reactive acrylic acid. Endangerment as a result of premature polymerization, as in the case of glacial acrylic acid, is ruled out, since the acrylic acid is “diluted” by the aqueous solvent and the specific heat capacity and the evaporation enthalpy of the water limit the maximum temperature rise. The amount of polymerization inhibitors used be reduced or it is possible to entirely dispense with polymerization inhibitors. Temperature control of vessels and pipelines within which the aqueous acrylic acid solution is conducted can be dispensed with because the solidification point of the aqueous acrylic acid solution is lower than that of anhydrous acrylic acid.
Abstract:
The invention relates to the production of superabsorbent polymers comprising conveying a polymer gel having acid groups on an oscillating conveyor belt to a continuous through-circulation belt dryer, wherein the belt speed of the conveyor belt is at least 0.4 m/s.
Abstract:
A process for producing water-absorbing polymer particles by polymerizing droplets of a monomer solution in a gas phase surrounding the droplets and postcrosslinking the polymer particles, wherein the postcrosslinked polymer particles are at least partly coated.
Abstract:
The invention relates to the production of superabsorbent polymers on a continuous belt reactor, wherein the continuous belt rests at least partly upon at least one support belt and the at least one continuous support belt is a metallic belt with a basis weight of at least 1 kg/m2.
Abstract:
Water-absorbing composites comprising at least two particulate water-absorbing polymers having different pH values and at least one fibrous material are produced without premixing the water-absorbing polymers and are used in hygiene articles.
Abstract:
A process for preparing postcrosslinked water-absorbing polymer beads with high absorption by polymerizing droplets of a monomer solution in a gas phase surrounding the droplets, wherein the solids content of the monomer solution is at least 35% by weight and the polymer beads have a mean diameter of at least 150 μm.
Abstract:
A process for the reduction of the residual monomer content and enhancement of the wet strength of articles formed from water absorbent crosslinked polymer foams containing units derived from monoethylenically unsaturated acids, which comprises treating the formed articles with at least 0.5% by weight of a polymer containing primary and/or secondary amino groups and having a molar mass of at least 300, the formed foam articles thus obtainable and use of the wet strength enhanced formed foam articles in hygiene articles.
Abstract:
The invention contains a process for the surface postcrosslinking of water-absorbing polymers in which the polymers are treated with a surface postcrosslinking solution and during or after the treatment are postcrosslinked by means of an increase in temperature and are dried, wherein the crossiinker comprises a bis-2-oxazolidinone or a poly-2-oxazolidinone comprising structural units of the formula in which R1 is branched or unbranched C1-C18-alkylene, branched or unbranched C2-C18-alkenylene, C5-C18-cycloalkylene, phenylene, naphthylene, anthracenylene, hydrocarbon-substituted phenylene, naphthylene or anthracenylene or another substituted or unsubstituted C6-C18-arylene radical, R2 is branched or unbranched C1-C18-alkylene and n is an integer from 1 to 50 or a mixture of bis-2-oxazolidinones and poly-2-oxazolidinones dissolved in an inert solvent.