Overcoming the drying-induced pore closure of APMP poplar fibers in old newsprint by surfactant treatment to promote enzymatic hydrolysis of the cellulose

Abstract This study analyzed the hornification properties of the old newsprint fiber and its effects on the enzymatic hydrolysis and investigated the strategy for improving the hydrolysis efficiency. The results showed both of heating and vacuum can dry the fibers and cause hornification, which resulted in a significant decrease in the pore volume and the enzymatic saccharification efficiencies. A good linear relationship was presented between the enzymatic digestibility and the pore volume of the drying-induced hornified fibers from the two drying methods. The high content of lignin in this kind of hornified fiber aggravated the inhibition of hornification on the enzymatic saccharification of cellulose through physical barriers blocking cellulase to contact the partial surface of hornified cellulose. Moreover, the strategy of using surfactants to enhance enzymatic hydrolysis was preliminarily explored. The results showed that enzymatic saccharification of the hornified lignin-containing fiber was significantly improved after the addition of surfactants. The increase in glucose yield reached the maximum value of 7.15 g/L after adding PEG 8000. Anionic surfactants exhibited the similar effects but weaker than the non-ionic ones. And the most effective time of the surfactants applied to hornified fibers was postponed from 6 to 12 h as the fiber hornification degree increased. This study provides a meaningful complement for the research work of enzymatic hydrolysis of recycled fiber. Graphical abstract