Potential of converting coffee husk waste into regenerated cellulose as a strength additive in the papermaking industry

In this study, coffee husk waste, a lignocellulosic by-product, was used to prepare regenerated cellulose (RC) by dissolving holocellulose (HC) in NaOH/Urea/Thiourea/Water solutions through freeze-thawing. The RC had a crystallinity index of 42.2%, indicating greater amorphousness and hydroxyl group content than HC. Fiber length in RC decreased by 49.27%, while fibres width increased by 24.31%. RC fibers were less kinked (15.2%) and had a lower curl index (3.8%) compared to HC (32.1% kinked fibers, 11.2% curl index). RC also had a higher fines content (95.26%) than HC (58.31%). Paper made from areca leaf sheath pulp and reinforced with coffee husk RC fibers showed enhanced mechanical properties. With 15% RC, the tensile index improved by 8.79%, while the burst and tear indices increased by 29.30% and 21.77%, respectively, with 5% RC addition. The study reports significant improvement by adding RC to areca pulp (8.79%), but “slightly higher” than hardwood pulp, but the tensile strength results of areca paper are 50% higher than hardwood. The final paper met IS 1848:2007 standards for writing and printing paper and exhibited better mechanical strength than hardwood pulp-based paper.