Determination of opening force of hot-melt adhesive joints in flexible packaging.

Introduction. Numerical modeling of the strength of hot-melt adhesive joints in flexible packaging materials allows for predicting the peel force values to achieve consumer-friendly packaging joint strength. Materials and methods. For experimental tensile strength testing, three types of packaging materials were used: offset paper, cardboard, and polyethylene, which were subsequently bonded with a hot-melt adhesive. The hot-melt adhesive is based on EVA (ethylene-vinyl acetate). Numerical modeling was conducted to analyze the failure of the hot-melt adhesive joint, aiming to predict the initiation and propagation of failure under static loads. Results and discussion. A mathematical model is proposed that allows experimentally determined resistance values to be used to calculate the maximum failure force. A numerical determination of the contact zone strength was performed, which enables the calculation of the failure force. The dependencies of the force at the edges of samples made from the three packaging materials on displacement for both experimental values and those obtained from numerical modeling were found. It was shown that plasticity zones arise on the interface surface when maximum stress is reached, leading to unloading in the local zone of the sample material. As the joint continues to fail, the breaking forces gradually decrease. The dependencies of forces at the edges of samples made from paper, cardboard, and polyethylene on the displacement of the sample edges during stretching were obtained. The appearance of the experimental curves of the dependence of the applied forces on the displacement corresponds to the model of nonlinear elastic-plastic failure of the adhesive zone. It was found that under the considered bonding conditions, the total peel force for paper materials is 0.1 N/mm, for cardboard materials -- 0.22 N/mm, and for polyethylene materials -- 0.75 N/mm. The highest force value among the bonded samples was observed for polyethylene. This can be explained by the fact that, during bonding with hot-melt adhesive, some films undergo welding rather than just bonding. Conclusions. The considered model and methodology of numerical modeling of the strength of hot-melt adhesive joints provide the ability to predict the necessary and sufficient values of their strength. [ABSTRACT FROM AUTHOR]