Wood extractives entering the paper mill along with mechanical pulp are well known to cause various problems, such as deposition issues, reduced paper machine efficiency and decreased paper quality. In the case of kraft pulping many of these problems can be expected to occur to a considerably lesser extent due to efficient washing of the extractives dissolved during cooking. However, it has been previously shown that the strength of softwood kraft pulp hand sheets is very sensitive to the extractive content, i.e. almost 50% decrease in tensile index has been observed with the addition of wood extractives. Softwood kraft pulp is added to provide strength to the fiber based packaging materials. Thus, the wood extractive induced strength decrease of this pulp potentially disturbs the desired shift towards stronger and lighter packaging papers and boards. In order to better understand the effect of extractives on packaging papers and boards strength the objective of our work was as following: 1. Investigate which softwood extractive compounds, i.e. fatty acids, resin acids, sterols and other unsaponifiables, are efficiently carried over with kraft pulp to paper mill. This was done by separating the carry-over pitch through acetone extraction and analysing it by 2D GC-MS. 2. Study the harmfulness of these extractive compounds carried over to paper mill on packaging paper and board strength. This was done through papermaking simulations in the laboratory with extractive model compounds, softwood kraft pulp and functional/process chemicals. Through these investigations we identified the softwood extractive compounds which are most problematic for packaging paper and board strength. This enables us to develop strategies to overcome the harmful effect of extractives, and thus contribute to the development of high-performance renewable packaging materials.

Towards lighter and stronger fiber based packaging materials: Influence of wood extractives on paper strength

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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