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.