# Alternative Fiber-Based Paperboard Adhesion Evaluation with T- and Y-Peel Testing
## 1 Introduction  
The significance of adhesive joints in packaging extends throughout various stages of the packaging lifecycle, encompassing conversion, transportation, storage, shelf exposure, and end-of-life operations. In this dynamic cycle, adhesive joints endure persistent loads stemming from environmental factors such as external forces from adjacent packaging units, dynamic stresses from machinery, and climatic fluctuations including temperature and relative humidity variations. The principal determinant of effective adhesive bonding for fiber-based packaging products is consistently the attainment of complete fiber tear upon separation of the adhesive joint. Traditionally, the assessment of mechanical strength in the converting industry involves visual inspection of fracture surfaces subsequent to manual peeling. An adhesive joint is acceptable if over half of the affected fibers remain attached to the fractured adhesive surface. Failure to achieve fiber tear along the adhesive joint signifies a deficiencyin packaging conversion success. However, this technique relies heavily on subjectivity, relying on individual expertise and experience [1]. According to [PERSON] [2], this method can lead to misinterpretation of adhesive bond performance in scenarios where (a) the fiber structure's strength falls short of application demands; (b) failure does not involve fiber tear, yet the strength exceeds application requirements; (c) the bond's long-term response to stress differs from its short-term behavior, such as the occurrence of creep effects. Adhesive bonding can succumb to three distinct failure mechanisms: adhesive failure, cohesive failure, or substrate failure. Adhesive failure primarily arises from inadequate adhesive penetration into the surface, while substrate failure pertains to the internal bonding of the substrate (in the case of paper packaging, the interlocking of fibers and/or additives/coatings). Cohesive failure relates to inadequate cohesive forces within the adhesive or coating layer itself. The process of adhesive bonding in paper-based materials can be divided into three phases [3]. The initial phase involves pressure-regulated adhesive penetration into the paper structure, influenced by factors such as surface pore structure, liquid rheology, and other material properties. In the subsequent phase, the applied adhesive layer undergoes dewatering (affected mostly by paper surface sizing), and in the final phase, the adhesive solidifies and sets through processes involving penetration, evaporation, and/or curing reactions. In a recent investigation by [PERSON] and [PERSON] [4], diverse paper properties affecting the adhesive strength of starch bonding were explored through measurements of surface roughness, wettability, and glue penetration. Their findings indicated that macro-scale roughness had limited influence, with the primary parameters affecting the adhesive strength being fiber wetting and glue penetration into the fibers. This aligns with the research conducted by [PERSON] et al. [5], who examined adhesive joints in decor papers. The adhesive exhibited minimal impact on the mechanical properties of the paper, whereas significant variations were noted based on the raw paper's basis weight (grammage). Additional paper attributes such as porosity and surface energy were found to influence adhesive penetration [6]. All these studies were performed using commercially available softwood or hardwood pulp papers, while no previous studies were conducted on alternative fiber papers. Alternative fiber papers have been in focus throughout the research and industry community due to the predicted over-use of tree-based papers (even with the high recycling rates). In addition to lowering the demand for wood-type cellulose, which takes several years to grow, the use of alternative fibers (derived from non-woody biomass) helps carbon sequestration strategies due to their quick renewing. An overview of the non-wood fibers for papermaking can be found in the research of [PERSON] et al. [7].