# Alternative Fiber-Based Paperboard Adhesion Evaluation with T- and Y-Peel Testing
## 1 Introduction
One of the under-utilized cellulose sources, also for packaging papers, are the so-called invasive plants. Invasive plants are non-native in an ecosystem, where their spreading can cause economic and environmental harm to the local environments. Furthermore, an important factor with invasive plants is the preservation of the local biodiversity, as these invasive plants tend to eradicate the local species. Based on the data obtained from the European Environmental Agency (EEA) there are around 10,000 alien species which endanger biodiversity in the EU (European Union). In the agency's report on the impact of these species in the EU, Japanese knotweed is classified as a negative species due to inhibiting the growth of woody seedlings and shading out other plants, which results in a delayed succession. Furthermore, direct economic impacts were reported in the EEA report, as they may profoundly change ecosystem functioning by altering species composition, physical habitat components, nutrient cycling, primary production, and by damaging the flood defense structures. In Slovenia, Japanese knotweed can be found in all kinds of habitats, with very dense structures along riverbeds. There is no exact data on the surfaces covered in the whole of the EU but, for example, based on the data in the UK, 70% of land had some trace of Japanese knotweed, and the socio-economic cost is around GBP 165.6 million per annum in the UK alone [8]. Its quick replenishment and spreading can be made useful if appropriate utilization can be organized, and recently alternative papers made from invasive plants have been found to be good materials for packaging [9; 10] as well as for printing [11; 12; 13; 14]. While there are several ISO and ASTM standards regarding the measurement of peel adhesion on materials, a specific standard for folding boxes made of fiber-based materials is non-existent. Some studies report the use of experimental methods where the intrinsic strength of an adhesive joint between solids can be determined and are based on experiment--the theory of contact mechanics [15]. The research of [PERSON] and [PERSON] [16] discussed assumed elastic deformation of the substrate material forming the interface, and this type of problem was subsequently studied in more detail by other authors. [PERSON] and [PERSON] [17] reported that the energy expended in the substrate when it undergoes plastic deformation can make a major contribution to the total measured peel force. They observed that the extent of such plastic energy was governed by the adhesion strength relative to the thickness and yield stress of the substrate. These forces and deformations in the adhesive joints are applied through the measurement of the peel strengths of joints. A recent comprehensive overview of the different peel tests has been published by [PERSON] et al. [18]. The modified methods of so-called T-peel (ISO 11339 [19] and ASTM D1876 [20]) are used instead. There are some specially developed methods, such as the Y-peel presented in the works by [PERSON] et al. [1], which give an objective result from the force-elongation curve. This method was specifically developed for cardboard packaging which deals with bonding two semi-rigid materials. The Y-peel test is a redesign of the constrained T-peel test. A non-standardized method for packaging adhesive joint testing is the angle peel method [21]. The peel angle always affects the peel forces. Most measurements are performed at a peel angle of 90 or 180 degrees. All peel adhesion curves have broadly three regions: the initial increase, the transitional decline, and the steady-state propagation regions. This test also enables the peak forces to be derived, as the force required to initiate the peeling. The objective of the presented research is to test the influence of the material properties of three different papers produced from the alien invasive plants Japanese knotreed and black locust, and from sawdust residual paperboard combinations on the adhesive joint strengths.