Surface engineering and coating strategies for biaxially oriented polypropylene (BOPP) films: performance, processability, and environmental trade-offs

Biaxially oriented polypropylene (BOPP) films are widely used in packaging for their transparency, low cost, and strong mechanical properties, but they suffer from a notable drawback: poor gas barrier performance, especially to oxygen. To address this limitation, a range of coating strategies has been pursued, from traditional inorganic layers to more sustainable solutions such as renewable-source coatings, barrier varnishes, functional adhesives, and nanocoatings, aimed at improving protection against oxidation and moisture loss in food applications. Surface treatments (plasma, flame, corona) and adhesion promoters are commonly employed to enhance coating bonding and thereby lower oxygen transmission rate (OTR) and water vapor transmission rate (WVTR). Coating effectiveness is governed by key factors including thickness and uniformity, adhesion strength, relative humidity sensitivity, and processing conditions, underscoring the ongoing need for optimized high-barrier multilayer films. This review critically examines these coating technologies and surface treatments, evaluates the principal performance determinants and characterization methods, and outlines challenges and future research directions, with emphasis on food-safety compliance, regulatory considerations, and sustainable, circular economy aligned solutions, to guide development of optimized high-barrier BOPP multilayer systems.