| Abstrakt: |
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. [ABSTRACT FROM AUTHOR] |
