Enzymatically modified starch for paper surface sizing: Enzymes with different action modes and sites

Enzymatically modified starch is frequently applied as a kind of superior surface sizing agent to improve paper quality, but the available options for various enzyme types, except for α-amylases, are limited. Herein, starch was modified using various commercial enzymes with different action modes and sites, namely, α-amylase (CSTWA), β-amylase (CSTWB), pullulanase (CSTWP), glucoamylase (CSTWG), and compound enzyme (α-/β-amylase, CSTWAB), for sizing paper. The performance of the paper and the properties of the sizing agents were comprehensively determined. Moreover, the molecules of the modified starch were characterized to explore the enzymolysis mechanism. Results showed that enzymatic hydrolysis should be performed ahead of gelatinization. Compared with CSTWA, CSTWB and CSTWP endowed the paper with higher strength owing to their apposite viscosity and molecular mass distribution. CSTWG and CSTWAB contained excess low-molecular-mass molecules, making them weakly effective as surface-sizing agents. Therefore, pullulanase and β-amylase have better application prospects as surface-sizing agents than α-amylase.