Optimization of atmospheric pressure plasma treatment for enhanced adhesion performance of microporous EVA

Atmospheric pressure plasma treatment (APPT) is a versatile technique for modifying polymer surface properties and improving adhesion in industrial applications. This study investigates a specific and industrially relevant system: microporous ethylene-vinyl acetate (EVA) bonded to leather using a hot-melt polyurethane reactive (HMPUR) adhesive. The novelty lies in the statistical optimization of APPT parameters under application-relevant conditions by evaluating the effects and interactions of treatment speed, nozzle distance, and plasma gas composition on EVA/leather adhesive performance. A design of experiments approach combined with multifactorial analysis of variance was used to determine the significance of process parameters and their interactions on T-peel strength, selected as the optimization response. Gas composition was the only statistically significant main effect, while nozzle distance × gas composition was the only significant two-factor interaction. The statistical optimization model identified air plasma, an 8 mm nozzle distance, and a treatment speed of 0.10 m/s as optimal conditions, which were experimentally validated. Surface modifications were characterized using XPS, SEM, surface roughness, contact angle, and adhesion tests. Optimized APPT conditions improved bonding performance, enabling EVA/leather joints to exceed footwear adhesion requirements and demonstrating APPT potential for industrial footwear bonding applications.