Optimization and Comparative Evaluation of Fungal Laccase-Based Biobleaching of Pineapple Leaf Pulp: Toward Sustainable Non-Wood Pulp Processing

The conventional chemical bleaching of pulp generates substantial environmental burdens due to toxic effluents and high chemical consumption. This study explores a sustainable alternative through the enzymatic biobleaching of pineapple leaf fibre (PALF) pulp using crude laccase extracted from Marasmiellus palmivorus , a white-rot fungus. The effects of enzyme dosage (1–10 U g⁻¹ pulp) and reaction time (2–10 h) on pulp quality were systematically optimized using Response Surface Methodology (RSM). Key pulp properties, including Kappa number, brightness, and intrinsic viscosity, were evaluated and compared to chemical bleaching using hydrogen peroxide (H₂O₂). Results showed that laccase treatment reduced the Kappa number by up to 57% (to 3.91) and enhanced brightness by 29.5% ISO, achieving comparable delignification to H₂O₂ treatment (Kappa = 4.07). Although the effect of dosage and time on brightness and viscosity was not statistically significant (p > 0.05), enzyme dosage had a pronounced influence on lignin removal (p < 0.05). Enzymatic bleaching preserved cellulose integrity with only 22.5% viscosity loss, markedly lower than the 34% loss observed under chemical bleaching. Optimization predicted optimal conditions at 9.8 U g⁻¹ pulp and 2.1 h, balancing high delignification and minimal cellulose degradation. These findings demonstrate the potential of M. palmivorus laccase as an eco-friendly and efficient biocatalyst for partial or total replacement of chemicals in non-wood pulp bleaching, supporting the transition toward greener pulp industries.