Extraction and production of cellulose nanofibers

A VAZQUEZ; MARIA LAURA FORESTI; JUAN I MORÁN; VIVIANA CYRAS

Handbook of Polymer Nanocomposites: Processing, Performance and Applications

Springer-Verlag GmbH

Lugar: Berlín; Año: 2015; p. 81 - 118

The chapterwill content the review of different methodologies used for obtainingnanofibers of cellulose from lignocellulosic materials and bacterial cellulose.The first part of the chapter will deal with the extraction of cellulose. Theclassic methodology implies alkaline and acid treatment, but new ones includemilder chemical conditions as well as chemo-enzymatic protocols. The secondpart deals with production of nanofibers from cellulose. Extraction ofcellulose nanoparticles from lignocellulose materials has different routes:acid hydrolysis, mechanical  and enzymatictreatment.  Strong acid hydrolysispromotes transversal cleavage of non-crystalline fractions of cellulosemicrofibrils, leading to the so-called cellulose nanocrystals or whiskers.Nanocrystals are characterized by high crystallinity and their aqueoussuspensions display a colloidal behavior. On the other hand, strong mechanicaltreatment that imposes high shear forces to cellulose fibers, allows theextraction of microfibrils and microfibril aggregates with high aspect ratiowhich form highly entangled networks. This kind of nanocellulose is calledmicrofibrillated cellulose (MFC). Although widely used the mechanical processdeveloped for the production of MFC has an important drawback which is the highenergy input involved (several passes through high pressure homogenizers whichget blocked frequently). In the last years, enzymatic and chemicalpretreatments have been proposed to reduce the energy input of the process.Moreover, microbially produced cellulose pellicles appear also as an attractiveroute of cellulose nanofibers, which will also be described in the chapter.