High-energy consumption is the main factor limiting the production of cellulose nanofibrils on industrial scale. Therefore, the objective of this work was to verify the effect of alkaline pretreatments of cellulosic pulps from commercial bleached pulps of Eucalyptus sp. and Pinus sp. on the easiness of mechanical defibrillation and its energy consumption. NaOH in concentrations of 5% with 2 h of reaction and 10% with 1 and 2 h of reaction were evaluated. The nanofibrils were obtained by mechanical process using a grinder (Super Masscolloider) and the energy consumption during the defibrillation process of the cellulosic fibers for each pretreatment was evaluated. The results show that the hemicelluloses content of the fibers may influence on the occurrence of curls, mainly for Eucalyptus treated with NaOH 10%, whose this occurrence was more severe. NaOH pretreatments also caused decrease in the length and diameter of the fibers mainly in Eucalyptus pulps. The degree of defibrillation was also influenced by hemicelluloses removal, been less defibrillated when excessive removal occurred (hemicelluloses in the range of 2 to 6%). The pretreatment of the fibers with NaOH 5% 2 h demonstrated to increase water retention value (WRV) and was effective for easier obtention of cellulose nanofibrils with lower energy consumption. This treatment caused partial removal of hemicelluloses (maintaining them in the range of 9 to 12%) and led to nanofibrils with lower diameter. The results of XRD shows that the reaction time was determinant for the crystallinity of the samples, where a longer exposure time to the alkali promoted the increase of the crystallinity index (57% to 63% in Eucalyptus in both methods and 61% to 62% calculated by the Segal method and from 59% to 65% calculated by the Mercury software in Pinus. Additionally, the partial conversion of cellulose I to cellulose II in those treatments with NaOH 10% (1 and 2 h) may also prejudiced the defibrillation of the fibers. The NaOH 5% 2 h pretreatment also promoted energy savings of 23% and 25% for Eucalyptus and Pinus pulps respectively.

Relationship of hemicelluloses content on grinding process for obtaining cellulose micro/nanofibrils from Eucalyptus and Pinus fibers

2019 Spring National Meeting

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