In a substantial breakthrough for industries dependent on composite materials, scientists at Nanyang Technological University, Singapore and the Agency for Science and Technology and Research (A*STARR) have achieved notable advancements in adhesive bonding and debonding. Adhesive bonding is a pervasive technology utilised to join composite components across various sectors, encompassing aerospace, automotive, construction, and wind turbine production. However, the enduring nature of adhesive bonding has precipitated environmental and economic apprehensions, particularly when a component requires disassembly for repair or remanufacturing.
Recent research, spearheaded by a group of scientists, concentrated on the challenge of securely and proficiently separating components joined by adhesive bonding without inflicting damage on the costly adherents. Their discoveries illuminated the potential for the reuse, repair, and recycling of composite materials, thereby endorsing sustainability and environmentally conscious design.
A crucial aspect of the study which was conducted, involved examining various debonding techniques applicable to metals and composites. Procedures such as cryogenic cooling, laser shock, and the application of externally activated particle-modified adhesives were scrutinized. Nevertheless, the research indicated that debonding methods remain in their developmental stages and are yet to be fully actualised.
A critical analysis of Thermally Expanded Particles (TEPs)
The necessity of identifying an effective debonding method was underscored by a past incident in which insufficient disassembly precipitated the destruction of a seaplane and tragically culminated in the loss of two lives. Acknowledging the gravity of this issue, the researchers investigated the influence of thermally expanded particles (TEPs) on the behaviour of joints bonded adhesively with glass fiber-reinforced polymer (GFRP).
Through a sequence of experimental studies, the team scrutinised the chemical composition of TEPs and epoxy adhesive, evaluated the thermomechanical properties of the modified adhesive, and examined the surface roughness as well as the contact angle analysis of GFRP adherends. Additionally, they conducted lap shear strength investigations. The team further performed failure analysis of adhesive joints, both prior to and subsequent to heat treatment, employing scanning electron microscopy.
The findings disclosed that the introduction of TEPs to the adhesive exerted a marginal effect on the glass transition temperature (Tg) of the adhesive. Thermomechanical analysis indicated that TEPs underwent a loss of permanent expansion above the maximum expansion temperature, attributable to gas eruption or diffusion through the thin shell. The researchers also ascertained that the discrepancy in the coefficient of thermal expansion (CTE) escalated with a higher TEP content, resulting in more pronounced dimensional alterations in the epoxy adhesive.
Furthermore, the study delved into the repercussions of surface modification techniques on debonding behaviour. Sandblasting was compared with plasma surface treatments, with the latter demonstrating greater effectiveness by offering enhanced bond strength and forestalling fibre-tearing during the debonding process. This surface modification method facilitated the reuse of GFRP samples following debonding at elevated temperatures (e.g., 145°C), in line with sustainable waste management practices.
The research team underscored the criticality of averting mechanical and thermal damage to composite parts during the debonding process. Their findings illustrated the feasibility of debonding GFRP joints without inflicting damage on the adherends, heralding new opportunities for the reuse and recycling of costly composite materials.
A game-changer for composite industries
This pioneering development in adhesive bonding and debonding methods carries substantial potential for numerous industries that rely on composite components. By facilitating the secure separation of adhesively bonded structures, companies can minimise costs, advocate sustainable practices, and contribute to a more environmentally friendly future.
The implications of the study transcend the boundaries of the scientific community, stressing the necessity for sophisticated techniques that enable the reuse and repair of composite materials. Looking ahead, additional research and development in this domain will be pivotal in the establishment of efficient and environmentally considerate debonding methods.
As industries persistently pursue innovative solutions for sustainability, this research represents a substantial stride forward in advocating circular economy principles and diminishing the environmental impact emanating from composite component manufacturing.
Caglar, H., Sridhar, I., Sharma, M., & Chian, K. S. (2023). Debonding of bonded composite joints with TEP modified epoxy adhesives. The Journal of Adhesion, 99(10), 1626-1649. https://doi.org/10.1038/s42003-022-04382-w