From vapour to gas: optimising cellulose degradation with gaseous HCl†
A cellulose degradation technique utilizing a pressurized HCl gas (up to 100 kPa) device is introduced. High pressure HCl quickly degraded cellulose in purified cotton linters, reaching the so-called levelling-off degree of polymerisation (LODP) in less than 1.5 h. LODP marks the point where the disordered portions of cellulose microfibrils have been degraded and only the crystalline portions remain, generally signalling the end of cellulose degradation unless remarkably high concentrations are used. In the present high pressure system, however, continued hydrolysis following the LODP was detected by incremental release of sugars from the hydrolysate after its exposure to water, supposedly caused by erosion from the cellulose crystallite ends. With minimal water consumption and the ease of recycling the gaseous acid, the technique could be a potential candidate for pre-treatment considering the future production of cellulose nanomaterials, particularly cellulose nanocrystals.