Physicochemical characterization of different treatment sequences on kenaf bast fiber

Abstract

Three different processing sequences for pulping kenaf ( Hibiscus cannabinus L.) bast fibers were investigated, and the chemical composition (cellulose, hemicellulose and lignin content) and physical properties (viscosity, degree of polymerization and crystallinity index) of the extracted pulp were determined. Three processing steps were employed: treatment with (a) ammonium oxalate, (b) sodium hydroxide, and (c) acidic chlorite. Variations in the order, conditions and duration of their application resulted in three different pulping methods. The kenaf fiber treated sequentially with acidified sodium chlorite, 0.5% ammonium oxalate and 1% sodium hydroxide (AC–AO–SH 1) generated the greatest yield and highest kappa number; whereas the sample treated sequentially with 0.5% ammonium oxalate, 15% sodium hydroxide and acidic chlorite (AO–SH 15–AC) developed the highest viscosity. No significant difference in hemicellulose content was observed between pulping methods. While Fourier Transform Infra Red spectra (FT-IR) and X-ray diffractometry of all extracted pulp samples revealed the same chain conformation, mean hydrogen bonding, and crystallinity index were apparent. X-ray diffractograms indicated the presence of residual oxidized lignin between the ( 1 1 ¯ 0 ) planes of the fibers subjected to AC–AO–SH 1 processing sequence that were absent from fibers processed differently. From CP/MAS 13C NMR spectra of extracted pulp, weak shoulder peaks at 57 and 110 ppm were observed in sample treated by AC–AO–SH 1 sequence that confirm the presence of oxidized lignin. Lignin content may adversely affect the viscosity of treated kenaf bast fiber.