Alkyl Ketene Dimer (AKD) Sizing of Recycled-Virgin Cardboard with Engineered Heterogeneous Layers under Neutral and Alkaline Condition

Background and objectives: Resistance to liquid sorption is important in various paper and board applications which would be contributed by chemicals as hydrophobizers of the structures. The hydrophobization process is called; Sizing, that could be done as internal and surface treatment with prevalence happening on internal sizing. Necessity and inspirations of recycled fiber together with bringing of required properties in the product, predominate engineering layering of paper and board production to supply and compromise requirements. The aim of this study focused on internal sizing effect of alkyl ketene dimer in multilayered cardboard constructed by heterogeneous and diverse fiber in its different layers.
Materials and methods: Multi-layer cardboard (330 g/m2) patterned on engineered heterogeneous layering of recycled and virgin pulp were internally sized by Alkyl Ketene Dimer (AKD) as 1% based on the pulp O.D. in two papermaking conditions; neutral and alkaline. Then, effects of the considered conditions on the recycled-virgin board properties were evaluated such as top and back layers Cobb test, bulk, gloss, surface roughness and strengths criteria.
Results: The cellulose reactive nature of cationic alkyl ketene dimer led to improvements in strength and water sorption of sized board compared to the unsized one. Resisting to water sorption in the fibrous network have been occurred after the fiber bonding and have not been as an effective obstacle in fiber bonding. At alkaline condition, all of addressed properties, especially water sorption and strengths of the board, improved considerably compared to the neutral. At alkaline condition, regarding to more ionization of fiber surface carboxylic groups, more and better bonding are occurred between fiber and AKD, as a cationic sizing agent, resulted in reduction in water sorption and provided more bonding ability among pulp ingredients. On the other hand, higher swelling of the ingredients together with higher cationic demand of fiber at alkaline situation, enhanced fines retention and fiber bonding which is resulted in the board surface smoother.
Conclusion: The sizing treatment of multi-layer cardboard by AKD reduced its water sorption in top and back layers and its surface roughness. Increment of bulk and strength properties of the cardboard include tensile, bending stiffness and ply bond were observed as a sizing results, with no effect on the duplex cardboard gloss. The noted improvements were attributed to the bonding enhancement among fibers and also the board layers via AKD, followed by sizing agent curing at drying section lead to hydrophobic creation in the board structure and lower water sorption.