Improving the sustainable utilization of cotton stalks through the synergistic effect of complex enzyme pretreatment in biorefining processes

Cotton stalks (CS), an abundant byproduct of cotton production, remain underutilized, resulting in inefficient biomass resource utilization. This study investigated a sustainable biorefining approach utilizing a synergistic laccase pectinase enzyme complex for pretreatment. Compared with single enzyme treatments, the complex enzymes exhibited superior efficiency, achieving maximal reducing sugar yields (increases of 37 % and 252 %, respectively) and significant removal of pectin and lignin, as confirmed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses. At an optimal dosage of 100 U/g (pectinase:laccase ratio of 1:3), the crystallinity increased to 43.4 %, whereas the SEM results revealed increased surface porosity, facilitating subsequent chemical penetration. Hand sheets from complex enzyme-pretreated CS displayed markedly improved mechanical properties, with a tensile strength, tearing index, and bursting index of 65.29 N·m/g, 5.49 mN·m 2 /g, and 3.16 kPa·m 2 /g, respectively. At a 1:9 CS-to-wood pulp ratio, pulp molding exhibited optimal performance, with the tensile and burst indices increasing by 51.3 % and 33.1 %, respectively, compared with those of pure wood pulp. This improvement was attributed to short CS fibers filling voids and strengthening the fiber network. Compared with that of the pure wood pulp group, the hydrophobicity was slightly lower; however, the water contact angle remained as high as 104.7°, which was greater than that of the other ratios. This synergistic enzymatic strategy offers an efficient, sustainable pathway for valorizing cotton stalk biomass. • Pectinase/laccase synergy improved the permeability of cotton stalks. • Pectinase/laccase pretreatment removed lignin and pectin, exposing cellulose more. • Hand-sheets treated with pectinase/laccase showed higher mechanical properties. • The synergistic mechanism underlying pectinase/laccase pretreatment was investigated. • Pulp molding blended with 10 % cotton stalk fibers resulted in optimized properties.