Grafted Starch | Starch Graft Polymers in Paper Coating and Adhesives

Starch is often used to bind pigments in paper coating and can improve water retention. Adding 1,3-butadiene and styrene to starch can create a paper with high gloss and smoothness while maintaining ink receptivity. To do this, the starch must be lightly oxidized and enzyme-converted. The reaction takes place under pressure and is carried out using a blend of styrene and 1,3-butadiene monomers, with ratios of 6:10 to 8:10. Surfactants may also be used. Films of the starch graft polymers have improved coating properties, consisting of a water-soluble polymer phase reinforced with non-coalesced, submicron-sized latex particles that provide toughness and mechanical strength. The improved compositions can be spray dried and redispersed to yield coatings with good performance. The starch graft copolymers with 1,3-butadiene styrene and optionally acrylonitrile and acrylic acid require the use of a modified or unmodified dextrin. The use of cationic and/or hydrophobically modified dextrins has also been evaluated. Finally, hydrogen peroxide-oxidized or enzyme-degraded potato starch can be used in moisture-barrier coatings for paper, and paper sacks made with these starch graft polymers have improved repulpability.

Enzyme-thinned starch that has been grafted with vinyl acetate is a good replacement for soy protein or casein in board coatings, providing enhanced strength and glueability. Adhesives can be made by combining starch and polymer dispersions such as hydroxypropylstarch and poly(vinyl acetate). Non-formaldehyde, self-crosslinking binders for nonwovens have also been developed using starch. Starch grafts can be mixed with granular starch derivatives and crosslinked with a cyclic urea-glyoxal condensate to create high surface tension latexes that prevent wicking or rewetting and improve emulsion stability.

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