Fracture Behaviour of adhesive Joints in carton board

A carton-board package is often sealed and closed with an adhesive. Package requirements vary depending on how the package is to be used. A package that is only supposed to protect the product during transport differs from one that is supposed to attract consumers and facilitate the use of the product by consumers. Fracture of the adhesive joint may occur in several different ways, e.g. cohesive fracture in the adhesive, interfacial fracture between the adhesive and one of the carton-board surfaces, and cohesive fracture in the carton board. The traditional way of testing the adhesive joint is to subjectively evaluate the fibre tear after manually tearing the joint apart. The adhesives used in carton-board packages are either hot-melt adhesives (adhesives that are applied in a molten state on the carton board) or dispersion adhesives (adhesives that are applied as water-based dispersions). The primary interest of this study has been to find an objective method that can characterise the adhesive joint, i.e. the strength and joint characteristics. The work has principally concentrated on physical experiments where the Y-peel method is evaluated and further developed, including construction of a laboratory adhesive applicator. Adhesive joint failure is analysed and correlated to the force-elongation curve in order to explore various mechanisms of adhesive-joint failure. The force versus elongation curves are transformed into a force versus inelastic deformation curve for the adhesive joint. The inelastic deformation of the adhesive joint is defined as the inelastic opening of the adhesive joint perpendicular to the carton-board surface. The dissipative descending energy has been used to evaluate the adhesive joint. High descending dissipative energy resulted in high resistance against final failure of the joint. This correlates very well with the manual fibre-tear test. Characteristic force-elongation curves in Y-peel testing, i.e. the shape of the curve, have been analysed and found to have four main failure modes. Using both the newly designed adhesive applicator and the Y-peel test method revealed a large discrepancy, about three orders of magnitude, between the theoretical thermodynamic analysis and the experimental test result. The new objective method can be used to design the interaction between the adhesive and the carton-board surface for a specific application. This can be achieved by modifying the carton board, the adhesive or the process parameters