Enhancing interfacial adhesion and electrical conductivity of steel/polymer composites via molecular adhesion for sustainable structural materials

Steel/Polymer Composites (SPCs) represent a promising class of materials that combine the strengths of steel and polymers, making them ideal candidates for various structural applications. Notably, they offer heat shielding properties, energy absorption, reduced noise, vibration, and harshness, high rigidity, as well as weight reduction benefits. Achieving robust interfacial adhesion between steel and polymer, while maintaining electrical conductivity for welding, presents a significant challenge in SPC development. Conventional SPCs relying on physical adhesion through polymer coating are susceptible to environmental factors, compromising durability. To address this, novel adhesion concepts are explored, leveraging molecular-level interactions. In this study, we investigate the adhesion between electro-galvanized iron steel treated with a phosphate conversion coating and four polymers: polyethylene (PE), acrylonitrile-butadiene-styrene (ABS), Nylon 6, and Polyketone. The primary amines are anchored on the steel surface using 3-aminopropyltriethoxysilane (APTES), while maleic anhydride (MA) is introduced onto the polymer chains. The adhesion strength of the SPCs dramatically increased from 0 to 11.5 MPa for PE, from 1.5 to 11.1 MPa for ABS, from 12.7 to 14.1 MPa for Nylon 6 and from 7.1 to 14.2 for Polyketone. In particular, the adhesion strength of Nylon 6 was maintained at 89.0% for 7 d aging despite moisture absorption being fatal to interfacial adhesion. The findings suggest two presumable interactions at the steel/polymer interface, including molecular adhesion. In order to enable spot welding of these SPCs, mechano-chemistry was employed to embed carbon-based graphitic materials within the plastic matrix, enhancing electrical conductivity. The selection of Polyketone as a core material facilitates the adsorption of conductive fillers, such as Carbon Nanotubes (CNT) and Graphite Platelets (GPs). Graphite Nanoplatelets-Polyketone, with smaller lateral dimensions (50 similar to 100 nm), exhibits the highest electrical conductivity of 207.5 S/cm. Scanning Electron Microscopy (SEM) confirms effective filler adsorption without pre-treatment. This comprehensive study enhances our understanding of SPC development, shedding light on innovative approaches to achieve robust adhesion, electrical conductivity, and suitability for spot welding applications.