PREPARATION AND APPLICATION OF STARCH GRAFT POLY(VINYL) COPOLYMERS AS PAPER COATING ADHESIVES

A series of starch graft copolymers were prepared from commercial cornstarch products and vinyl monomers and were evaluated as adhesives in pigmented paper coatings. Hypochlorite oxidized (HO), acid modified (AM), and hydroxyethlated acid modified (HEAM) starches were reacted separately with acrylamide (AAm), acrylic acid (AAc), and acrilonitrile (AN) using ceric ammonium nitrate as the polymerization initiator to yield copolymers containing 2-45% synthetic polymer. Pigmented coating mixtures with 6-14 parts copolymer/100 parts clay and 40-50% total solids were prepared and applied on one side of the paper stock using a hand-drawn doctor blade. Viscosities, adhesive strength, and wet-rub resistance of the coating adhesives and mixtures were determined. Adhesive strength of starch graft polyacrylamide (S-g-PAAm) copolymers containing as little as 12% PAAm was considerably superior to the commercial starches as paper coating adhesives. Adhesive strength of S-g-PAAc copolymers was similar to that of the HO and HEAM commercial starches, whereas adhesive strength of the S-g-PAN copolymers was poor. Copolymers that were prepared from the HO starch were slightly superior to those prepared from the AM and HEAM starches. Wet-rub resistance of the pigmented copolymer coatings was not improved over that of the coatings containing the commercial starches.