Asphaltenes as Tackifiers for Hot-Melt Adhesives Based on Polyamide-12

The potential of petroleum asphaltenes as novel, low-concentration tackifying agents in polyamide-12-based hot-melt adhesives was systematically investigated. The structural, rheological, thermophysical, mechanical, and adhesive properties of polyamide blends containing 5 to 20 wt% asphaltenes were comprehensively evaluated. A maximum twofold increase in lap-shear adhesion to steel was achieved at an optimal loading of 5 wt%, with the bond strength rising from 3.2 MPa to 6.9 MPa. This enhancement is attributed to the surfactant-like nature of asphaltenes. The peripheral aliphatic moieties of asphaltenes enable their partial dissolution within the polyamide matrix, enhancing interfacial affinity with the steel substrate without requiring the high loadings typical of conventional resin tackifiers. Mechanically, the tensile strength of the blends remained comparable to neat polyamide up to 10 wt%, whereas at 20 wt%, undissolved asphaltene aggregates acted as stress concentrators, reducing the cohesive strength from 42 MPa to 27 MPa. Rheologically, while the zero-shear viscosity increased only moderately (by a factor of 1.1–1.5), the absence of yield stress and a pronounced viscosity decrease at high shear stresses indicated excellent processability. Furthermore, the incorporation of asphaltenes caused no systematic changes in melting or crystallization temperatures, with the relative degree of crystallinity decreasing by only 0.3–6.4%. Ultimately, this work demonstrates that asphaltenes serve as highly efficient, sustainable tackifiers for polyamide hot-melts, offering a novel pathway for the valorization of heavy crude oil by-products.