The effect of different enzymatic pretreatment processes on the production of nanocellulose from wheat straw

Purpose: The purpose of this study is to investigate the changes in the chemical, morphological, thermal and rheological properties of nanocellulose (CNF) obtained after different enzymatic pretreatments applied to soda-NaBH4 bleached pulp fibers of wheat straw and homogenization process as shown in Figure A.Theory and Methods: Soda-NaBH4 method was used for pulping of wheat straws and then bleaching process were carried out. Fiber production was carried out in the reactor and chlorite bleaching process was applied to the soda-NaBH4 pulp fibers obtained after the pulping stage. Viscosity and kappa numbers of the fibers were determined before and after the bleaching process. Chemical analyzes (HPLC) of the fibers were also carried out before and after the bleaching process. Afterwards, the fibers obtained by using Pulpzyme HC 2500 and Celluclast 1.5 L commercial enzymes were pretreated. The processes of reducing the fibers obtained after enzymatic treatment to micro and nano size were carried out using a high pressure homogenizer. Chemical (HPLC, FTIR, 13C-CP/MAS NMR), morphological (SEM), thermal (TGA, DSC) and rheological properties of all were determined. Results: HPLC analyzes recorded after enzymatic pretreatment showed that Pulpzyme HC 2500 enzyme was very effective on xylose and Celluclast 1.5 L enzyme was very effective on glucose and more carbohydrates were removed from the structure with increasing enzyme concentrations. In FTIR analysis, a slight decrease in the permeability intensities of the peaks was observed in general, depending on the change in the physical structure of the fibers and the decrease in the surface area dimensions. 13C-NMR analyzes revealed that the crystal/amorphous structure changed. Rheology analyzes revealed that as a result of the applied treatments, the tension between the fibers decreased, the viscosity values decreased, and therefore the samples showed shear thinning behavior. On the other hand, SEM images revealed that the fibers were homogeneously (fully) reduced to nano size as a result of the homogenization. Thermal analyzes revealed that the decomposition temperature of the samples obtained decreased due to the decrease in the crystalline ratio in the polymer structure as a result of the glucose units being affected.Conclusion: In this study, Pulpzyme HC 2500 and Celluclast 1.5 L commercial enzymes used in CNF production and showed comparable results with traditionally used enzymes. It has been observed that higher quality CMF/CNF products can be produced, especially with the use of Celluclast 1.5 L enzyme.