Deep Eutectic Solvents for Bast Fibre Degumming: A Cross-Crop Review of Systems and Mechanisms

This review places deep eutectic solvent (DES) degumming of the five bast fibre crops—ramie, hemp, kenaf, flax and Apocynum venetum—on a common basis, covering systems, conditions, outcomes, mechanisms and reuse records. It draws on eighteen research studies and one dedicated review, prioritising quantified works indexed in the Science Citation Index. The field has converged on a narrow solvent family, with choline chloride the near-universal hydrogen bond acceptor and choline chloride–urea best on ramie and kenaf and most balanced on hemp. Processes run at 100–175 °C with microwave assistance shortening treatment time; residual gum falls to 3.15% on ramie and 9.42% on kenaf, with reuse demonstrated over three to five cycles. Bond-level mechanistic evidence, however, covers only hemp and kenaf, leaving the consensus mechanism inferred for most crops. No solvent mass balance has been reported, leaving the energy and water demand of regeneration, and hence the claimed environmental advantage, unquantified. Degumming performance is judged by multiple indicators, and without weighting schemes or standardised protocols the reported optimal conditions are not directly comparable. DES degumming of bast fibres is therefore technically verified but industrially unvalidated; process scaling and long-term solvent recycling are priorities for deployment.