Water-absorbent adhesive compositions and associated methods of manufacture and use

A method for improving the adhesion of a water-insoluble, water-absorbent adhesive composition, by combining, under conditions effective to form a substantially homogeneous admixture:

• (a) a film-forming, hydrophilic polymer (FFHP) containing a plurality of recurring polar groups, the FFHP selected from the group consisting of poly(dialkyl aminoalkyl acrylates), poly(dialkylaminoalkyl methacrylates), poly(N,N-dialkyl acrylamides), polyvinyl amine), poly(alkylene imine), poly(N-vinyl acrylamide), poly(N-vinyl alkylacrylamides), poly(trimethylammonioethyl methacrylate), poly(N-vinyl lactams), chitosan, copolymers thereof, and combinations of any of the foregoing;
• (b) a complementary multifunctional polymer (CMP) containing a plurality of recurring functional groups, the CMP selected from the group consisting of poly(acrylic acid), poly(methacrylic acid), poly(maleic acid), poly(sulfonic acid), poly(vinyl alcohol), poly(vinyl phenol), poly(ethylene oxide), poly(hydroxyalkyl methacrylates), cellulose derivatives, alginic acid, copolymers thereof, and combinations of any of the foregoing;
• wherein the CMP has a molecular weight lower than the molecular weight of the FFHP, and the FFHP and the CMP are selected such that functional groups contained in the CMP are capable of non-covalently binding to recurring polar groups in the FFHP, and where at least one of the FFHP and the CMP possesses ionogenic groups,
• (c) a plasticizer capable of plasticizing the FFHP, the plasticizer selected from the group consisting of dialkyl phthalates, dicycloalkyl phthalates, diaryl phthalates, mixed alkyl-aryl phthalates, alkyl phosphates, aryl phosphates, alkyl citrates, citrate esters, alkyl adipates, dialkyl tartrates, dialkyl sebacates, dialkyl succinates, alkyl glycolates, alkyl glycerolates, glycol esters, glycerol esters, and mixtures thereof,
• (d) a solvent in an amount effective to provide a solution,
• the improvement comprising:
• (i) choosing a weight fraction amount of the FFHP that is greater than the weight fraction amount of either the CMP or the plasticizer,
• (ii) adding to the solution, or to the FFHP or CMP prior to the choosing step, an ionizing agent in an amount effective to ionize from about 5% to about 10% of the ionogenic groups in the solution or in the FFHP and/or CMP respectively,
• (iii) casting the resulting solution from (d) onto a substrate, and
• (iv) heating the solution-coated substrate to volatilize the solvent;
• wherein the resulting adhesive composition from (iv) displays an adhesion that is enhanced over the adhesion for the same composition absent the ionizing agent.