Sustainable design and life cycle engineering of adhesive joints for polymeric products: assessment of surface activation technologies

The adoption of lightweight materials in engineering applications has become more popular over recent years, with adhesives replacing traditional joining methods such as bolts and rivets. Adhesion science and related technologies are arising as cleaner options for sustainable production in modern industry, with adhesive-bonded joints increasingly being used as design solutions in complex products and assemblies. However, the use of structural adhesives has several significant drawbacks, most of which are related to environmental impact, linked to the nature of the adhesive substance, as well as product disassembly/disposal deriving from the fact that adhesive joints are usually irreversible. Within this context, the goal of this paper is to study adhesive joints in mechanical assemblies from a life cycle perspective, offering more comprehensive analysis tools and assembly solutions suitable for industries such as automotive, aerospace, and assembly/packaging machinery. A methodological framework for the comprehensive characterization of bonded joints using effective surface activation techniques has been created and tested. The first phase encompasses the production of samples for mechanical testing under static and fatigue loading conditions. The second includes the characterization of inputs/outputs (life cycle inventory—LCI) for life cycle assessment (LCA) of mechanical assemblies employing adhesive joints and innovative surface activation techniques. The final phase provides a set of eco-design actions based on a critical analysis of the obtained results. The outcomes demonstrate how it is possible to achieve optimal adhesive-bonded joint properties under specific working conditions (e.g., static or fatigue loading) while maintaining a low environmental load using novel surface pre-treatments such as laser and plasma technologies. These outcomes are supported by a case-study in which adhesive joints are applied to the mechanical assembly of a bottle gripper for a food packaging machine. The adoption of eco-design rules in adhesive joint applications will help designers in the development of suitable solutions for lightweight applications from a complete life cycle perspective.