Document Type : Pulp and Paper
Authors
1 M.Sc. Dept. of Biorefinery Eng, Shahid Beheshti University, Tehran, Iran
2 Associate Prof., Dept. of Biorefinery Eng, Shahid Beheshti University, Tehran, Iran
Abstract
Background and Objective: The accessibility and shortage to virgin pulps and recycled pulps with lower reusing cycles in recent years has led to adverse effects on the quality of recycled paper products which are used for packaging. The use of chemical additives is considered as an effective strategy to improve properties of the pulp and the recycled papers. In the meantime, the use of biomass-based materials such as nanocellulose and multifunctional materials such as cationic poly diallyldimethylammonium chloride (p-DADMAC) is growing and attracting attention from various technical and environmental aspects. Therefore, in order to improve the properties of the product and the production process, the effect of nanocellulose and p-DADMAC as polymers with the aforementioned potential was studied on a laboratory scale.
Material and Methodology: Recycled brown pulp was prepared from an OCC domestic mill without any additives and with a Canadian standard freeness (CSF) of 350 ml. Medium molecular weight cationic polydiallyldimethylammonium chloride (poly DADMAC) from Sigma Aldrich and cellulose nanofibers with an average diameter of 35 nm from Nano Novin Polymer Co. were purchased. The addition of chemicals to the pulp slurry was studied at four levels: 0, 0.1, 0.15, and 0.2 based on oven dry (O.D) mass of pulp. Effects of the polymer additions, individually and in combination, on pulp properties including CSF, total retention, and material loss in the DDJ analyzer, as well as on the properties of laboratory handsheets including density, tensile, bursting, and tearing strength indices, were investigated according to TAPPI standards procedures.
Results: The individual addition of cationic p-DADMAC (patching system) resulted in an increment of total retention of the recycled pulp ingredients, but increasing the amount of addition did not significantly change the total retention. It also reduced the amount of material loss through passing the DDJ screen and increased the pulp CSF from 350 ml in the control sample without any additives to 430 ml at the lowest level of p-DADMAC usage (0.1%). It also significantly improved the apparent density, but higher levels of p-DADMAC did not have a significant effect on this structural property of the recycled paper. Regarding the tensile and bursting strengths of the recycled paper, the single application of p-DADMAC and increasing its dosage caused some changes, mainly increasing but relatively limited. Cellulose nanofibers, when used alone, also resulted in an increase in the total retention and density, tensile and bursting indices of the paper; and a decrease in tear index, CSF, and material loss from the pulp in the DDJ analyzer. The anionic nature, high specific surface area, and hydrogen bonding potential were reported to be the reasons for such results. The use of cellulose nanofibers after p-DADMAC to the pulp as a complex system in the wet end of papermaking has increased the total retention of the pulp ingredients on the wire of the laboratory handsheet maker, which can be reported in the form of reduced material loss. It also often has a significant and severe adverse effect on CSF and has made drainage slower and longer. The use of nanocellulose after p-DADMAC has also had different effects, mainly increasing, on the tensile, bursting, and tearing resistance of the produced recycled packaging paper, depending on the percentage of each of the additives.
Conclusion: It was shown that, except for the undesirable reducing effect of the single application of nanocellulose on the tear index and CSF freeness, in other single and complex addition treatments of chemical additives of nanocellulose and poly-DADMAC, an increase in all strength properties and paper density, improvement of drainage ease of recycled pulp, increase in pulp retention during paper formation, and reduction of material loss can be achieved compared to the control treatment. However, the single application of the cationic polymer showed better results in pulp in terms of retention and drainage than the single application of nanocellulose and their combination. The trend of changes in strength properties also depended on the percentages of combined application of two different chemicals.
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