Tuning the Adhesive Strength of Functionalized Polyolefin-Based Hot Melt Adhesives: Unexpected Results Leading to New Opportunities

The development of lightweight, often multicomponent products requires adaptable and robust bonding solutions. Hot melt adhesives increasingly attract industrial interest as they combine good adhesive strength, facile processability, and cost-efficiency. Recently, our group has reported on the remarkable adhesive performance of hydroxyl-functionalized propylene-based copolymers in bonding both polar and nonpolar surfaces. The obtained adhesive strength proved to be too high for applications such as single-use packaging, which requires low to moderate adhesion for easy opening. Tuning the adhesive strength by manufacturing numerous functionalized polyolefin grades with varying contents of hydroxyl-functional groups is challenging in view of industrial-scale production. Herein, we elucidate an alternative approach to tune the adhesive performance by blending the functionalized propylene copolymers with nonfunctionalized congeners. To understand the structure-property relationship of the investigated diluted blends, a thorough characterization of morphology, physical properties, crystallization, and viscoelastic behavior was performed. It appeared that the crystallinity of the nonfunctionalized polyolefin and its miscibility with the functionalized polyolefin play a crucial role on the adhesive strength of the blends. Either a gradual decrease in adhesive strength with dilution was noticed or─surprisingly─no loss of adhesive strength was observed at all, not even after diluting 100 times! Molecular dynamics simulations revealed an intrinsic tendency of the hydroxyl-functionalized polyolefin to migrate to and interact with the aluminum oxide surface.