Flax nanofibrils production via supercritical carbon dioxide pre-treatment and enzymatic hydrolysis

Flax fibres are an agro-industrial waste available in large quantities in several countries around the world. This resource can be properly used. The goal of this work was to extract lignocellulosic nanosized flax fibres using an environmentally friendly process based on a combination of supercritical carbon dioxide (SC-CO₂) pre-treatment and enzymatic hydrolysis. Raw flax fibres (RFF) were submitted to a SC-CO₂ pre-treatment at various temperatures (ie, 70°C and 80°C) and pressures (ie, 20 and 37.7 MPa) for 60 minutes. The enzymatic hydrolysis was performed at 40°C for 24 hours in a pH 4.0 buffer. Cellulase, xylanase, pectinase, and viscozyme were used as hydrolytic enzymes. The as-received raw flax fibres, SC-CO₂ pretreated flax fibres, and extracted lignocellulosic nanofibrils (LCNF) were characterized by Fourier transformed infrared spectroscopy (FTIR), x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was shown that the effect of the SC-CO₂ pre-treatment of flax fibres was two-fold. It helped to disorganize biomass without changing its chemical composition and it increased access to enzymes to extract LCNF. The FTIR analysis showed no changes in the functional groups after SC-CO₂ pre-treatment. The XRD characterization revealed that the crystallinity increased with the SC-CO₂ pre-treatment and LCNF extraction. SEM images showed holes, cracks, and erosion on the surface of the SC-CO₂ pretreated flax fibres (SC-CO₂-PFF). TEM evidenced the production of nano/micro-sized fibril and fibril aggregates.