Production of Glucose from PEG-Based Pretreated Green Coconut Fiber and Synthesis of Lignin Nanoparticles for Stabilization of O/W Pickering Emulsion

Solvolysis processes or organosolv pretreatments alone have been widely used as a way to obtain glycolated lignins, a type of lignin with thermoplastic properties. Despite this interest, there are still many gaps regarding the byproducts generated and other potential destinations for glycolated lignins, which must be addressed for the process to reach a commercial level. In the present study, the authors investigated the enzymatic digestion of green coconut fiber pretreated with polyethylene glycol (PEG) 400 and sulfuric acid, as well as the performance of glycolated lignin as a stabilizer of o/w Pickering emulsions, a notable application for lignins. The PEG-based organosolv pretreatment promoted extensive delignification (reduction of Klason lignin from 35.7 to 29.7%) and enabled greater cellulose enrichment than pretreatment with sulfuric acid alone (33.4 vs 44.8%). In terms of enzymatic digestibility, glucose release from the organosolv-pretreated sample was 4.3- and 2.8-fold higher than that from the untreated and acid-pretreated samples, respectively. Glycolation in green coconut fiber lignin was confirmed by FTIR and thermogravimetry analyses. Glycolated lignin nanoparticles were successfully prepared and exhibited a rounded shape and size in the range of 30-50 nm. Regardless of the o/w system (including toluene/water, soybean oil/water, and <i>n</i>-octanol/water), glycolated lignin nanoparticles led to higher emulsification index (up to ∼80% after 14 days) and better stability than lignin nanoparticles isolated from acid pretreatment. This study confirms the versatility of PEG pretreatment and demonstrates that it can serve as the basis for an alternative biorefinery for lignocellulosic biomass.