Discussion on the influence mechanism of PVC microplastics on the performance and adsorption behavior of composite inorganic corrosion inhibitors

• Microplastics can affect the adsorption process of inorganic corrosion inhibitors. • Microplastics participate in the protective film-forming process on metal surface. • PVC microplastics adsorb polyphosphate ions in the anodic region. • Microplastics show most significant impact to inhibitors in the initial immersion The issue of microplastic adsorption in solution has emerged as a crucial research focus within the field of interfacial science. However, no studies have systematically explored the mutual interactions between microplastics and inorganic corrosion inhibitors. This study investigates the influence of polyvinyl chloride (PVC) microplastics on the corrosion inhibition performance of a combined inorganic inhibitor system comprising zinc sulfate (ZnSO 4 ) and sodium polyphosphate (SP). Multiple testing methodologies were employed to elucidate the underlying mechanisms. Experimental results reveal that the addition of the composite inhibitors significantly inhibit the metal corrosion, achieving an inhibition efficiency of 94.2 % based on corrosion current density ( i corr ), when added at concentrations of 100 mg/L and 10 mg/L, respectively. The introduction of PVC microplastics markedly alters the inhibition effectiveness of the corrosion inhibitor. Specifically, as the microplastic content increases, the performance of the composite inhibitors initially enhances before declining. At a microplastic concentration of 100 mg/L, the i corr of carbon steel is reduced by 37 %. Multifaceted characterization analyses suggest that microplastics exert a more pronounced influence on polyphosphate ions in solution, indicating their effect on anodic reaction processes. Microplastics can enrich corrosion inhibitors as porous carriers, affecting their diffusion and adsorption processes, thereby altering their adsorption behavior on metal surfaces. Conversely, the adherence of microplastics to carbon steel influences the formation of inhibitive films, thereby altering their barrier properties against permeation. This study comprehensively analyzes the mechanisms underlying the influence of microplastics on inorganic corrosion inhibitors, offering valuable guidance and insights for the application of corrosion inhibitors in solution enriched with microplastics.