ARTICLE Flax nanofibrils production via supercritical carbon dioxide pre-treatment and enzymatic hydrolysis Hervé Nlandu 1,2 | Khaled Belkacemi 1† | Nasima Chorfa 1 | Said Elkoun 3 | Mathieu Robert 3 | Safia Hamoudi 1 1 Department of Soil Sciences and Agri-Food Engineering, Université Laval, Centre in Green Chemistry & Catalysis, Québec, Canada 2 Department of Chemical Engineering, Université Laval, Québec, Canada 3 Centre for Innovations in Technological Ecodesign, Université de Sherbrooke, Sherbrooke, Québec, Canada Correspondence Safia Hamoudi, Department of Soil Sciences and Agri-Food Engineering, Université Laval, Centre in Green Chemistry & Catalysis, Québec, G1V 0A6, Canada. Email: safia.hamoudi@fsaa.ulaval.ca Funding information Natural Sciences and Engineering Research Council of Canada Abstract Flax fibres are an agro-industrial waste available in large quantities in several coun- tries 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-CO 2 ) pre-treatment and enzymatic hydrolysis. Raw flax fibres (RFF) were submitted to a SC-CO 2 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- CO 2 pretreated flax fibres, and extracted lignocellulosic nanofibrils (LCNF) were characterized by Fourier transformed infrared spectroscopy (FTIR), x-ray diffrac- tion (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was shown that the effect of the SC-CO 2 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-CO 2 pre-treat- ment. The XRD characterization revealed that the crystallinity increased with the SC-CO 2 pre-treatment and LCNF extraction. SEM images showed holes, cracks, and erosion on the surface of the SC-CO 2 pretreated flax fibres (SC-CO 2 -PFF). TEM evidenced the production of nano/micro-sized fibril and fibril aggregates. KEYWORDS enzymatic hydrolysis, flax fibres, lignocellulosic nanofibrils, supercritical CO 2 explosion 1 | INTRODUCTION Due to environmental concerns, biopolymers derived from renewable resources are regarded as potential replacements for non-biodegradable and non-renewable petroleum-based polymers. Unfortunately, those biopolymers exhibit generally lower performances compared to synthetic polymers and, consequently, must be reinforced. Natural fibres (eg, flax, hemp, cotton, sisal, etc.) and their derivatives (eg, cellulose, lignin, etc.) prove to be effective for biopolymers reinforce- ment, while preserving their biodegradability. Lignocellulosic waste materials obtained from agricultural activities, energy crops, and wood industries represent the most abundant global source of renewable biomass. [1] Depending on the extraction method and surface treatment, cellulose micro- and † The late professor Khaled Belkacemi passed away in the terrorist attack perpetrated at Québec City on January 29th, 2017. Received: 25 January 2019 Revised: 8 March 2019 Accepted: 29 April 2019 DOI: 10.1002/cjce.23596 84 © 2019 Canadian Society for Chemical Engineering Can J Chem Eng. 2020;98:84–95. wileyonlinelibrary.com/journal/cjce