Absorbent articles made from carboxylic polyelectrolyte solutions containing bis-oxazoline crosslinker and methods for their preparation

#This invention relates to water swellable absorbent articles made from crosslinked polyelectrolytes, methods for their preparation, and to an aqueous solution consisting of polyelectrolytes containing free carboxylic groups which is useful to make absorbent articles.

#It is known from U.S. Pat. Nos. 3,669,103 and 3,670,731 that cross-linked polymeric sorbents can be sandwiched between flexible supports to achieve disposable diapers or dressings.

#It is further known from U.S. Pat. Nos. 2,988,539; 3,393,168; 3,514,419 and 3,557,067 that water swellable cross-linked carboxylic copolymers can be prepared. However, these prior art copolymers are all crosslinked during copolymerization or crosslinked after polymerization with subsequent neutralization of the carboxylic acid groups to form water swellable polyelectrolytes and hence these prior art polyelectrolytes cannot be crosslinked in situ as a coating on a substrate or as a flexible film thereof.

#The following examples are presented solely to illustrate but not limit the invention.

#A latex of ethyl acrylate (85 parts) and methacrylic acid (15 parts) was dissolved in 50 mole percent aqueous sodium hydroxide and then treated with 2 mole percent acetic acid to form an acidified polyelectrolyte solution which was 25% solids (pH about 6). Oxyethylene-bis-(2-oxazoline), (1.5% by weight of the polymer) was dissolved in the polyelectrolyte solution and a 25 mil film was drawn on a chrome plate. After air drying, the film was cured in a 150.degree. oven for 16 hours. One gram of cured film was swollen in excess 0.27 N NaCl solution and filtered to give 51 grams of firm gel (absorbency 51 g/g.

#An acrylic polyelectrolyte solution was prepared as in Example 1 except that 10 mole percent of acetic acid was used. Portions of this acidic polyelectrolyte solution were then mixed with various amounts of curing agents and cast as films on mirror-finish chrome sheet. After air drying, the films were stripped from the sheet and cured in an oven set at 150.degree.C for the times indicated below. Cure times in excess of one hour have no further effect on the polymer but were done for convenience. Absorbency was measured in the usual way by swelling the tared film in excess 0.27 n NaCl solution, draining, and weighing gel.