Adhesives and Sealants in Packaging: Functional Roles and System-Level Classification (Part I)

Adhesives and sealants are critical components in modern packaging, governing bond integrity, barrier continuity, and mechanical reliability across rigid, semi-rigid, and flexible formats. Beyond simple bonding or closure, they enable multilayer architectures, high-speed converting, and functional integration across food, beverage, pharmaceutical, cosmetic, and technical applications. Despite the extensive literature on adhesive chemistries and sealing technologies, comprehensive analyses integrating adhesives and sealants within the architecture of packaging systems remain limited. This review takes a materials- and system-level approach, linking adhesive and sealant families — natural, synthetic, hot-melt, pressure-sensitive, and tie layers — to processing routes, functional performance, regulatory constraints, and circularity requirements. Sealant materials including polyolefins, barrier polymers, and biodegradable alternatives are also covered. Special attention is given to the functional distinction between bonding and sealing roles, and to hybrid systems operating at their intersection within multilayer packaging architectures. Structure–property–function relationships are analysed with respect to bond and seal strength, seal initiation temperature, hot-tack behaviour, resistance to thermal and mechanical stresses, and end-of-life compatibility. By offering a unified framework connecting materials selection, interfacial performance, regulatory compliance, and sustainability considerations, this Part I lays the classification and functional groundwork for Part II, which addresses advanced materials, quantitative performance data, and emerging technologies.