effect of onp recycled fibers use on the properties of mixed hardwoods virgin kraft pulp

this study has been conducted in order to investigate the effect of using onp recycled fibers on the mechanical and optical properties of local mixed hardwoods kraft pulp at iran wood and paper industry (chooka). onp and virgin kraft pulp have been prepared from chooka’s waste paper storage and pulping digester, respectively. onp has been repulped in the common method as used by paper recycling industry. after determination of the initial freeness of each pulp, they have been separately refined to reach the appropriate freeness value required to produce kraft paper. the pulps, then, have been mixed at 90.10, 80.20, 70.30, 50.50 and 30.70 percentage rates of recycled fibers and virgin kraft pulp, respectively. according to the related standard test method, handsheets were made from each treatment and their mechanical and optical properties have been measured. the results were compared with those of control sample (100% virgin kraft) using anova technique and classification of the means was done by duncan test. finally, to determine the best treatment, normalization equation was calculated. the results show that the values of tensile, tear, and burst indices, folding endurance and density of the combined papers have been increased compared with those of control sample, but the values of bulk, thickness, brightness and opacity of the combined samples have been decreased. the scores of the treatments indicate that 50 percent of recycled fibers can be used in the furnish to produce paper with suitable mechanical and optical properties.