Role of lignin removal on the properties of crude pulp fibers from corn stover via high-temperature formic acid pulping.

An effective removal of lignin could reduce the chromogenic groups of lignin in pulp. Herein, corn stover was pulped via the formic acid to investigate the effects of cooking time and temperature on the crude pulp properties. The strong hydrogen ion action of formic acid helped inhibiting both the re-polymerization of degraded lignin molecules and the subsequent adsorption on fiber. The brightness of the crude pulp could reach 51.5 %ISO with the increased lightness and decreased yellowness. The effective lignin removal reduced the residual lignocellulosic bundles in the crude pulp with the increased cooking temperature and time. The lowest lignin content of 3.5 %, α-cellulose content of 94.0 %, and Kappa number of 9.3 were obtained. Meanwhile, the lignin and monosaccharide content in the black liquor could reach 13.3 % and 28.5 %, respectively. The number-average molecular weight of lignin was as low as 818 g/mol. These were helpful to form the hydrogen bonds between fibers, thus enhancing the tensile and burst index of paper sheets. The tensile, burst and tearing indices of the corresponding crude pulp were 47.5 N·m/g, 1.42 kPa·m/g and 6.53 mN·m/g, respectively. This work provided valuable practical significance for studying the performance of straw pulp by high temperature formic acid cooking.