Extraction and Production of Cellulose Nanofibers

Abstract

The chapter will content the review of different methodologies used for obtaining nanofibers of cellulose from lignocellulosic materials and bacterial cellulose. The first part of the chapter will deal with the extraction of cellulose. The classic methodology implies alkaline and acid treatment, but new ones include milder chemical conditions as well as chemo-enzymatic protocols. The second part deals with production of nanofibers from cellulose. Extraction of cellulose nanoparticles from lignocellulose materials has different routes: acid hydrolysis, mechanical, and enzymatic treatments. Strong acid hydrolysis promotes transversal cleavage of non-crystalline fractions of cellulose microfibrils, leading to the so-called cellulose nanocrystals or whiskers. Nanocrystals are characterized by high crystallinity and their aqueous suspensions display a colloidal behavior. On the other hand, strong mechanical treatment that imposes high shear forces to cellulose fibers allows the extraction of microfibrils and microfibril aggregates with high aspect ratio which form highly entangled networks. This kind of nanocellulose is called microfibrillated cellulose (MFC). Although widely used the mechanical process developed for the production of MFC has an important drawback which is the high energy input involved (several passes through high-pressure homogenizers which get blocked frequently). In the last years, enzymatic and chemical pretreatments have been proposed to reduce the energy input of the process. Moreover, microbially produced cellulose pellicles appear also as an attractive route of cellulose nanofibers, which will also be described in the chapter.