Efficient Isolation of Cellulosic Fibers from Coffee Parchment via Natural Acidic Deep Eutectic Solvent Pretreatment for Nanocellulose Production

The efficient pretreatment of lignocellulosic biomass is essential for cellulose valorization. This work investigated the fractionation efficiency of the pretreatment process based on natural acidic deep eutectic solvent (NADES) for isolating cellulose-rich materials (CRM) from coffee parchment (CP). The results showed that NADES, composed of choline chloride, oxalic acid, and water in a 2:2:1 molar ratio, was the most efficient solvent for CP fractionation. The sequential pretreatment using NADES under microwave heating (MW-NADES) at 130 °C for 15 min, followed by a two-step alkaline hydrogen peroxide (AHP) process, could maximize the removals of hemicellulose (99.6%) and lignin (97.7%) from CP, leading to production of the CRM with 86.1% cellulose content. This process generated a rough, fractured surface and promoted microfibril disassembly observed in the pretreated fibers. As a result, the CRM exhibited a highly crystalline structure and good thermal stability. Furthermore, the results also highlighted the successful transformation of the isolated CRM to nanofibril networks having a diameter of less than 10 nm and a length of several hundred nanometers. Overall, this work suggests that the sequential MW-NADES and AHP pretreatment could be considered an effective approach in isolating high-purity cellulose from CP, potentially a sustainable source for nanocellulose production.