Hydrophobically Modified Cationic Starches for Surface Treatment, 2000 Coating Conference Proceedings

L. Jarnstrom, C. Brossmer, P. Nilsson, P. Hansson, K. Wiklander--This study is addressed to hydrophobically modified starch ethers possessing an Upper Critical Solution Temperature (UCST). This special feature has here been used in order to improve surface treated products. Starches used today do not give sufficient water resistance to the paper, due to the very hydrophilic nature of conventional paper grade starches. Conventional surface sizing starches have to be mixed with hydrophobic synthetic polymers for the paper to achieve the desired water repellence, Cobb value and interactions with water-borne printing inks. The novel starches investigated here, show a reversible phase transition that originates from interactions between hydrophobic substituents. This transition was found to be reversible and the onset of phase transition was possible to control chemically. Compared to the state-of-the-art technology (i.e. mixtures of starch and hydrophobic synthetic polymers) the novel starches alone give impaired water resistance, measured as Cobb value and long-time contact angle. With respect to print properties and mechanical properties, no substantial differences have been found.