Properties controlling the impact of styrenic block copolymer based pressure-sensitive adhesives on paper recycling

A model was developed for predicting the removal of hot-melt pressure-sensitive adhesives (PSAs) from paper recycling operations via screening using standard adhesive response data. A series of hot-melt PSAs consisting of a styrene-isoprene-styrene/styrene-isoprene linear triblock, diblock copolymer blend, tackifying resin, and naphthenic process oil were blended in combinations to produce a range of properties. The PSAs were formulated with two types of tackifiers, a pentaerythritol ester of rosin and a C-5 petroleum hydrocarbon, to provide variation in the formulation composition. The measured removal efficiency versus temperature curves for these PSAs possess a sigmoidal shape, with removal decreasing from 100 to 0% between transitions for the rubbery and polystyrene domains marking significant changes in the mechanical properties. An exponential-based sigmoidal function containing two fitting parameters, inflection temperature and a factor that determines the width of the sigmoid, provided an excellent fit of experimental data. It was found that inflection temperatures and the width factor could be predicted using shear adhesion failure temperatures and the thermal width of the plateau region extracted from dynamic mechanical spectroscopy thermal scans, respectively. Application of the developed model to two commercial hot-melt PSAs formulated with different base polymers and additives provided an excellent fit of experimental removal efficiency data. Results of this study indicate that properties of hot-melt PSAs can be controlled to produce formulations that minimize the negative impact on paper recycling.