Biodeinking of mixed ONP and OMG waste papers with cellulase

Development of qualitative properties and surface modification of mixed recycled 70% old newspaper and 30% old magazine pulp after enzymatic treatment with commercial cellulase was evaluated. The results of the present research demonstrated that the quality of the pulp and paper obtained from cellulase deinking process was comparable or even better than that from the chemical deinking. Under mild conditions of cellulase deinking (charge of 0.025–0.1% and duration time of 20 min, the paper with similar opacity as well as the increased brightness and whiteness values were obtained in comparison with non treated pulp or chemical one. Increasing reaction time to 30 min (at higher levels than 0.25% cellulase) and also enhancing the charge of cellulase to more than 0.1% (at different reaction times) were not advisable due to weak optical features of paper produced. The highest deinking efficiencies of 11.77 and 10.04% were obtained in enzymatic runs with cellulase (C₂T₂ and C₁T₃, respectively) but it was 9.3% for chemical deinking process (run of Cc). Increase in duration from 10 to 30 min at the maximum cellulase charge (0.2%) has been negatively influenced tensile index, breaking length, stretch and stiffness. In general, the best strength properties were obtained at middle charges of cellulase (0.025–0.05%) and duration times of 10–20 min. All strength characteristics were severely declined for run C₄T₃ (charge 0.2% and reaction time of 30 min). Run of C₃T₂ (charge 0.1% and reaction time of 20 min) was resulted in the higher tensile index (by 22%), stretch (by 9%) and stiffness (by 42%) compared to chemically deinked pulp. Cellulose crystallinity obtained by FTIR and XRD spectra was remarkably increased up to 0.2% cellulase but reduced severely at higher charges than 0.2% cellulase which implied declining the strength properties. In addition, FESEM micrographs of recycled fibers treated at different cellulase charge and duration times revealed surface modification and morphological changes like external fibrillation, peeling, fine production as well as rougher fiber surface due to cellulase act on the fiber surface. With increasing enzyme charge and duration time to some extent, fiber fibrillation have been developed and appearing much fibrils may result in the increased hydrogen bonding, number and contact area between fibers and consequently paper strength properties. However in harsh conditions particularly higher cellulase charges, the fiber structure is degraded, more fines appeared on fiber surface and strength properties are declined (especially tear resistance) due to a possible reduction in average fiber length.