Enabling Wet strength agent-reductions through CMC-addition; A case study investigating the possibilities to lower PAE in packaging board with CMC.

Sammanfattning: In 2015, the United Nations adopted 17 different sustainability development goals. These goals were set for the global community to be guided by – but also to follow thus slowingdown climate change, prevent inequality, end poverty and make sure that by 2030 all people enjoy peace and prosperity. One step needed to support these goals is for the packaging community to increase the reusability and recyclability-rates of produced fiber-based packages. By doing so, new or alternative ways of designing the packaging material is needed – circularity must be implemented in an early stage of the design phase, so when the package reaches its end-of life state, reusability through recyclability is enabled. Wet strengthened papers and packages are highly necessary, given wet environments and complex transportation-chains, where both high humidity and the risk of wetting is high. Polyamideamine-epichlorohydrin resins (PAE) are by far the most common Wet Strength additive (WSA) when manufacturing wet strengthened papers. There is however a major drawback when using PAE; Fiber-based products and packages produced with PAEadditives cannot be fully recycled or reused.Laine et al. (2000, 2001, 2003) made a series of studies investigating the benefits of using carboxymethyl cellulose (CMC) as an additive to modify the surface charge of a cellulosic fiber. These studies showed that it is possible to increase the negative charge of the fiber, i.e modify the surface charge of the fiber with CMC. Based on Laine et al.’s series of studies (2000, 2001, 2003), Aarne et al. (2013) later showed that it is possible to build multilayered structures of additives if using CMC as a start and intermediate player. The purpose of this Master Thesis was to investigate the possibilities of reducing the usage of PAE by supporting the process system with CMC, without compromising the wet physical properties of the board. The methodology used is mainly through a full-scale board machine trial. Based on the results given from the study, positive indications were PAE can be reduced is seen. The results indicate that CMC is affecting and modifying the surface charge of a bleached sulphate pulp fiber, while showing that the amount of CMC correlates well to the Zpotential level. The results also indicate that the addition of PAE can be lowered if CMC is added to the system, given the maintained relative wet tear strength of the board. The package performance when wet were also maintained in trial points where CMC and PAE where added. These are also indications of an increased retention of PAE enabled with CMC.According to the PTS (PapierTechnischeStiftung)-results (a test assessing the recyclability rate of a packaging material), reject rates were corresponding well to the decreased PAE-dosages. When lowering PAE, the reject rate was also lowered. One interesting observation made from the PTS-evaluation was the trial points indicating an increased retention of PAE through CMC, where the wet board properties where maintained. The increased PAE-retention did not affect the PTS-rate negatively. This means that it is possible to further build on the concept of CMC and PAE, using CMC as an aid to keep the wet physical properties of the board while making it slightly more recyclable.