Biocomposites of rice straw paper with chitosan: hydrophobicity and mechanical properties

Rice straw is an agricultural by-product that is considered to have the potential to be processed into pulp and various kinds of its derivative products. Pulping condition is an essential prior step to isolate cellulose from fibers. In this study, atmospheric hot soda pulping (AHSP) and soda pulping (SP) methods were successfully used to manufacture pulp and paper from rice straw residues. Pulp modification using water-soluble chitosan was performed aimed at increasing the hydrophobicity of the pulp and paper. X-ray diffraction analysis (XRD) results revealed an increased degree of crystallinity of pulp after both treatments compared to native rice straw. The significant effect of pulping process and chitosan concentration on paper hydrophobicity and its mechanical properties were conducted by performing ANOVA and Duncan tests. According to the statistical results, pulping types, chitosan concentration, and their interaction significantly affected the hydrophobicity but not the mechanical properties of paper (p < 0.05). The best hydrophobicity properties were obtained from AHSP 2% chitosan paper (water absorption of 24.23 ± 1.32% and contact angle (θe) 122.852 ± 0.268) while the best tensile properties of paper were obtained from SP 2% chitosan (tensile strength (S) 1401 N/m). However, the thermal stability was not affected by chitosan concentration. According to the micrographs by Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM–EDS) images, chitosan addition in the paper created changes in surface characteristics compared to the unmodified pulp possibly due to fiber–fiber and fine-fiber flocculation phenomenon Besides, the presence of chitosan can be seen in the N element of the EDS result.