Starch-based fixative with proper substitution degree for controlling dissolved and colloidal substances in a bleached chemithermomechanical pulp.

Starch-based fixatives (SBF), specifically low molecular weight, highly-cationic starches (LHCS), have been reported to efficiently control dissolved and colloidal substances (DCS) in pulp suspensions, and to enhance paper strengths. However, as their degree of substitution (DS) was as high as 0.65, their preparation cost was very high. In this study, two products with lower DSs of just 0.08 (LHCS 0.08) and 0.22 (LHCS 0.22) were prepared and compared to a traditional polyamine (PA) fixative. It was found that the novel LHCSs interacted more readily with the anionic pulp fibers while the PA interacted more readily with the anionic DCS. Consequently, both LHCS 0.08 and LHCS 0.22 increased the paper strength more than the PA. Moreover, it was found that the LHCS 0.22 was most efficient in fixing the colloidal substances onto fibers, while the PA was most efficient in neutralizing the dissolved substances. We conclude that LHCS with DS as low as 0.22 can be used as a good fixative, however, starch with DS of only 0.08 is not efficient enough. [ABSTRACT FROM AUTHOR]