Co-production of cellulose and lignin by Taguchi-optimized one-pot deep eutectic solvent-assisted ball milling pretreatment of raw oil palm leaves.

This study explores an eco-friendly delignification technique for raw oil palm leaves (OPL), highlighting the optimized conditions of choline chloride-lactic acid deep eutectic solvent (DES)-mediated ball milling pretreatment to maximize the co-production yields of highly crystalline cellulose and lignin. Our five-level-four-factor Taguchi design identified the optimal reaction settings for cellulose production (85.83 % yield, 47.28 % crystallinity) as 90-minute milling, 1500 rpm, mill-ball size ratio of 30:10, ball-to-sample mass ratio of 20:1, DES-to-sample mass ratio of 3:1. Conversely, the maximal lignin extraction yield (35.23 %) occurred optimally at 120-minute milling, 600 rpm, mill-ball size ratio of 25:5, ball-to-sample mass ratio of 20:1 and DES-to-sample mass ratio of 9:1. Statistical results showed that milling frequency (p -value ≤ 0.0001) was highly significant in improving cellulose crystallinity and yield, while DES-to-sample mass ratio (p -value ≤ 0.0001) was the most impacting on lignin yield. The thermogravimetric method affirmed the elevated cellulose thermal stability, corroborating the enhanced cellulose content (40.14 % to 73.67 %) alongside elevated crystallinity and crystallite size (3.31 to 4.72 nm) shown by X-ray diffractograms. The increased surface roughness seen in micrographs mirrored the above-said post-treatment changes. In short, our optimized one-pot dual-action pretreatment effectively delignified the raw OPL to produce cellulose-rich material with enhanced crystallinity and lignin solidity. [Display omitted] • Effective DES-assisted ball milling pretreatment in biomass delignification • A single-step co-production of cellulose and lignin under optimized condition • Pretreated OPL enhanced the isolated cellulose crystallinity from 19.09 % to 47.28 %. • A 2-hour milling (600 rpm) at 1:9 sample-to-DES ratio maximized lignin yield (35.2 %). • Cellulose yield and crystallinity were maximized at 1500 rpm milling frequency. [ABSTRACT FROM AUTHOR]