Production of microfibrillated cellulose by steam explosion

This doctoral thesis was prepared at the Université Grenoble Alpes under the supervision of Professor Evelyne Mauret (Grenoble INP-Pagora / LGP2) and of the Nicolas Brosse (Université de Lorraine / LERMAB)

Saad Nader presented the results of his research entitled NanoSteamEx: production of microfibrillated cellulose by steam explosion.

Micro and nanofibrillated cellulose (MNFC) exhibits remarkable properties with high added value applications in various fields. In recent years, there has been a growing interest in lignin-containing micro and nanofibrillated cellulose (L-MNFC) produced from different lignocellulosic materials. However, current L-MNFC production processes are energy-intensive, which limits their use.

Steam explosion (SteamEx) is an efficient lignocellulose pretreatment process, accessible on an industrial scale. The objective of this study is to propose an energy-efficient and environmentally friendly process, involving pre-treatment by SteamEx, in order to manufacture L-MNFC from beech wood and Eucalyptus globulus bark, then used for the production of nanopapers and the reinforcement of wood adhesives.

The originality of this study is twofold:

• L-MNFC with different lignin contents are produced from beech wood and eucalyptus bark (two understudied biomasses for MNFC production, in particular eucalyptus bark).
• The cooking step of the raw material (pulping) was carried out in a SteamEx apparatus combining the effects of alkaline delignification and explosive defibration. Pulping was followed by a refining and a grinding step. The chemical composition, morphology and mechanical properties of the produced L-MNFC gels and nanopapers have been studied.

The results demonstrated the possibility of producing L-MNFC by SteamEx. They have a quality comparable to that of L-MNFC produced by conventional processes (involving chemical and/or enzymatic treatments) while benefiting from a shorter reaction time. SteamEx promotes the detachment of lignin from the fibers by forming spherical nanoparticles dispersed in the L-MNFC gels.

• The L-MNFC produced from eucalyptus bark are formed of nanofibrils with diameters between 5 and 100 nm and coarser elements. With quality indices of ≈ 60, they are used as reinforcements in Urea-Formaldehyde adhesives to improve the mechanical properties of particleboard.
• The L-MNFC produced from beech wood presents quality index between 60 and 80. They are used to produce nanopapers with Young's moduli of 8 - 9 GPa.