Cellulose microfibrils consist of numerous cellulose
nanofibrils which are tightly hooked to one another by
multiple hydrogen bonds. Thus, it is difficult to split cellulose
nanofibrils only by mechanical treatments. Many
researchers [17, 18] reported that the matrix substances can
be removed using chemical methods before the fibrillation
process. As a result, the narrow cellulose nanofibrils can be
obtained by the combination of chemical treatment and
ultrasonication. More interestingly, a class of aerogels can
be prepared from the aqueous or alcohol dispersion of cellulose
nanofibrils using freeze-drying technique.