Title
Optimisation and enhancement of crystalline nanocellulose production by ultrasonication pretreatment of dissolving wood pulp fibres
Authors
MAGDI GIBRIL TAMRAT TESFAYE BRUCE SITHOLE PRABASHNI LEKHA and DERESH RAMJUGERNATH

Received August 10, 2017
Published Volume 52 Issue 9-10 October-December
Keywords ultrasonication, pretreatment, crystalline nanocellulose, optimisation, dissolving wood pulp

Abstract
Cellulose degradation with sulphuric acid is widely used for the preparation of nanocellulose from wood fibres. However, the low-yield, the high concentration of sulphuric acid used and the long reaction time are major challenges in commercial production of crystalline nanocellulose using this process. In this study, ultrasonication was used as a pretreatment step to induce cavitation of cellulose in suspension. The idea was to break down the non-crystalline regions in cellulose, thus destroy the interfibrillar bonds between cellulose molecule layers, causing ‘cracking’ or ‘erosion’ on the cellulose surface. This would enhance the accessibility of the acid to the cellulose during the hydrolysis process, thus minimising the consumption of acid, energy, as well decreasing the hydrolysis time. The effect of ultrasonication time on the morphology, structure and properties of cellulose was investigated using SEM, XRD and TGA. SEM analysis showed ‘cracks’ on the surface of fibres for short treatment time (<5 minutes). Beyond this time, the surface morphology of cellulose fibres was totally changed into nanofibrils. XRD analysis indicated a marginal increase in the crystallinity index. TGA analysis showed that the pretreatment did not influence the thermal properties of cellulose. The extraction process of crystalline nanocellulose was further optimised using Response Surface Methodology/Box-Behnken design, with three levels and three variables: temperature, acid concentration and reaction time as independent variables, and percentage yield and particle size of crystalline nanocellulose as dependent variables. Regression equations were obtained to analyse the dependent variables and the optimum process parameters identified. From the results, it is evident that the ultrasonication pretreatment of dissolving wood pulp fibres results in enhanced generation of crystalline nanocellulose from the fibres.