The straw ammonium sulfite pulp is completely free from chlorine-based bleaching agents

Rice straw is a low-cost material (with a purchase price of less than 100 yuan per ton) and belongs to the annual monocotyledonous grass family Poaceae. It grows in clusters, reaching heights of approximately 1 meter; its stems are erect and cylindrical, hollow with nodes. The leaves are narrow and elongated with pointed tips, featuring parallel veins and petioles that encase the stem in a sheath-like structure measuring 30–60 cm in length. The inflorescences are sparse panicles, either erect or distinctly pendulous; the spikelets are yellow-green, with or without awns. For paper production, both stems and leaves are commonly utilized. Rice straw has a loose tissue structure and low lignin content (approximately 11.93%), making it easily processed into pulp through cooking. Its fibers are fine and short, averaging 0.92 mm in length and 8 μm in width. The cellulose content is low (35.2%), while hemicellulose constitutes 18.06%. The cell composition includes up to 54% heterocytes, primarily composed of parenchyma cells (rod-shaped, rectangular, or oval), epidermal cells (saw-toothed or toothed with variable spacing), vessels (spiral, annular, or lenticular), stone cells, and reticulate cells, along with spherical, pillow-shaped, and polyhedral heterocytes.