Melia dubia Valorization at 4, 5- and 6-year Age for Pulp and Paper Production

Melia dubia, a fast-growing hardwood tree, has been identified as a potential pulpwood species which can be cultivated under agroforestry scheme in diverse climatic and geographical conditions. This study explores 4, 5- and 6-year harvests of M. dubia for pulp and paper production with an aim to choose the most suitable harvesting age. All the three harvests of M. dubia were subjected to physicochemical analysis, fiber characterization, kraft pulping and OD0EopD1 bleaching (O = oxygen delignification, D = chlorine dioxide, Eop = extraction fortified with peroxide and oxygen). The unbleached and bleached pulps were evaluated for chemical characteristics and physical strength properties. The black liquor properties, heavy metal contents in pulp and SEM characteristics of pulps as well as hand sheets were also analyzed. The basic densities of M. dubia trees were found in the range of 433 490 kg/m3. The 5-year-old harvest exhibited the lowest ash (0.65 %) and alcohol benzene extractives (1.75 %) while the highest holocellulose (82.55 %) and pentosans (16.60 %). Fiber length (1152.8 m) and fiber diameter (24.34 m) of the 6-year-old harvest was the highest among all. Kraft pulping of M. dubia harvests resulted in 51 51.66 % screened yield with kappa number, intrinsic viscosity and brightness of unbleached pulps in ranges 14.5 15.6, 658.19 785 cm3/g and 31.96 32.67 % ISO respectively. Their OD0EopD1 bleaching produced pulps with brightness 85.07 90.40 % ISO, intrinsic viscosity 440.56 455.50 cm3/g, tensile index 43.19 68.43 Nm/g, tear index 3.23 4.14 mNm2/g, burst index 2.47 4.15 kPam2/g etc. This study confirmed the papermaking suitability of all the three harvests of M. dubia; however, the five years was rated as the best age at which M. dubia should be harvested for pulp and paper.