Authors: Bárbara Gonçalves Prates1, Homero Ribeiro Neto, Alvaro Vianna Novaes de Carvalho Teixeira,
O PAPEL vol. 82, N.o 11, pp. 84 - 89 - NOV 2021
ABSTRACT
Cellulose nanocrystals (CNC) are the highly-ordered
crystalline domains of lignocellulosic materials very abundant
in nature, with high crystallinity, purity and mechanical and
multifunctional properties favorable for various applications.
They are commonly isolated by acid hydrolysis in the form
of stable aqueous suspensions in low concentrations. One of the
critical points for obtaining an individualized and dried form
is the drying step, due to the aggregation of the nanocrystals.
The consequence is that the recovering of rehydrated and
isolated CNC is low. After dehydration of the material in
considerably-high temperatures, the aggregation is promoted by
hydrogen bonds between the surfaces of the CNC nanocrystals,
promoting a loss of the nanometric dimension. Thus, in order
to minimize CNC agglomeration, the effects of some conditions
were studied: (a) whether or not to perform dialysis in CNC
suspensions, and (b) addition of anti-binder agents (glycerin
or dodecyltrimethylammonium bromide - DTAB). To study
the drying alternatives, some of the CNC suspensions of 1%
w/v extracted from cotton fibers were subjected to drying by
evaporation in an oven with forced air circulation. Firstly, the pH
of the stock suspensions, with and without dialysis, was adjusted
to ~7. Each test was sonicated, and each anti-binder agent (0.8%
w/v) was added separately to the suspension. The dried CNCs
were redispersed, sonicated and centrifuged. More-satisfactory
results were obtained from the dialyzed sample with a recovery
efficiency of 35.2%. The same, without dialysis, was 15.6%. The
addition of glycerin and DTAB showed a recovery efficiency
of 30.6% and 49.6%, respectively. The dynamic light scattering
technique was used to determine the average equivalent CNC
diameter and zeta potential for all tests. The values found are
within ranges equivalent to those normally found in literature
(100-300 nm and -50 to -25 mv, respectively). None of the
samples showed significant differences in morphology and
dimension between the recovered CNC and the reference ones.
Keywords: Cellulose nanocrystals, evaporative drying, glycerin,
dodecyltrimethylammonium bromide, recovery efficiency.