Integrated Valorization of Oil Palm Empty Fruit Bunch (OPEFB) by Deep Eutectic Solvent Pretreatment: Glucose Production Enhancement and Lignin-CMC Composite for Sustainable Packaging

Abstract

Oil palm empty fruit bunch (OPEFB) is an abundant lignocellulosic residue with potential for integrated biorefinery applications, but its recalcitrant structure limits direct enzymatic conversion and lignin utilization. This study investigated the integrated valorization of OPEFB through deep eutectic solvent (DES) pretreatment using choline chloride–lactic acid (ChCl:LA) and choline chloride–glycerol–FeCl₃ (ChCl:Gly:FeCl₃) systems for glucose production, lignin recovery, and CMC–lignin composite film development. Modified severity descriptors, namely combined delignification factor (CDF) and combined hydrolysis factor (CHF), were applied to describe severity-dependent lignin removal and xylan hydrolysis. The CDF and CHF models successfully described the severity-dependent fractionation behavior of OPEFB during DES pretreatment. ChCl:LA promoted stronger lignin solubilization and higher lignin recovery,while ChCl:Gly:FeCl₃ enhanced hemicellulose removal and enzymatic digestibility through Lewis acid-assisted deconstruction. The highest enzymatic hydrolysis yields reached 75.8% for ChCl:LA and 93.8% for ChCl:Gly:FeCl₃. On a 100 g raw OPEFB basis, ChCl:LA pretreatment at 140 °C for 6 h produced 21.6 g glucose and 24.7 g recovered lignin, whereas ChCl:Gly:FeCl₃ pretreatment at 140 °C for 3 h produced 21.7 g glucose and 23.1 g recovered lignin. The recovered DES lignins showed high purity and were successfully incorporated into CMC-based films. ChCl:LA lignin improved water resistance and reduced WVTR, while ChCl:Gly:FeCl₃ lignin provided stronger antioxidant activity and tensile reinforcement. These findings demonstrate that DES pretreatment enables the dual valorization of OPEFB into fermentable glucose and functional lignin-derived packaging materials, supporting a multiproduct biorefinery pathway for sustainable biomass utilization.

Keywords: Oil palm empty fruit bunch, deep eutectic solvent, fractionation, enzymatic hydrolysis, CMC-Lignin film, modified severity factor