Effect of Delignification Process on the Properties of Barley-Straw Pulp and Paper

Barley straw represents an underutilized agricultural residue with potential as a supplementary source of papermaking fibers. This study compared nitrate-alkaline, soda, and peracetic-acid delignification processes for the preparation of pulp from barley straw and evaluated the resulting laboratory paper sheets. The raw material was characterized by a cellulose content of 35.84%, an acid-insoluble lignin content of 18.79%, and ash content of 7.65%. Seven pulping variants were assessed in terms of total yield, reject content, Schöpper-Riegler degree, and Kappa number, while the paper sheets were tested for tear index, burst index, ISO brightness, Cobb₆₀ water absorptiveness, and surface structure using optical microscopy. Total pulp yield ranged from 31.57% to 55.68%, and Kappa numbers varied from 13.50 to 47.86. Soda pulps had the highest Kappa numbers and the lowest brightness. Nitrate-alkaline treatments produced lower Kappa numbers than soda pulping but were generally accompanied by lower yields. Under the tested conditions, peracetic-acid delignification produced a pulp with a yield of 55.68%, a Kappa number of 13.50, an ISO brightness of 76.77%, a tear index of 6.26 mN·m²·g^-1, and a burst index of 0.67 kPa·m²·g^-1. Qualitative optical microscopy suggested a comparatively uniform fiber network. Among the evaluated variants, peracetic-acid delignification provided the most favorable combination of pulp yield, Kappa number, mechanical properties, and brightness; however, this finding is restricted to the specific treatment conditions applied in this study.