Adhesion in thermomechanically processed seaweed-lignocellulosic composite materials

Abstract

The increasing concerns associated with petroleum-derived polymers motivate the development of sustainable, renewably sourced alternatives. In ubiquitous applications such as structural materials for infrastructure, the built environment as well as packaging, where natural materials such as wood are used, we rely on nonrenewable and nondegradable polymers to serve as adhesives. In wood panels, such as medium density fiberboards (MDFs), formaldehyde-based resins are predominantly used to bond wood fibers and to provide strength to the materials. To further mitigate the environmental impact of construction materials, more sustainable adhesives need to be investigated. In this article, we introduce Ulva seaweed as an adhesive to enable cohesion and strength in hot-pressed wood panels. Upon hot-pressing, powdered Ulva flows in between the wood particles, generating a matrix, which provides strong binding. We show that the flexural strength of Ulva-bonded wood biocomposites increases with increasing Ulva concentrations. At an Ulva concentration of 40 wt%, our composites reach an average elastic modulus of 6.1 GPa, and flexural strength of 38.2 MPa (compared to 4.7 GPa and 22.6 MPa, respectively, for pure wood compressed at the same pressing conditions). To highlight the bonding mechanisms, we performed infrared and x-ray photoelectron spectroscopy and identified indications of fatty acid mobility during hot-pressing. In addition, we demonstrate that the presence of Ulva improves other properties of the composites such as water resistance and flame retardancy. Ulva is also shown to behave as an excellent adhesive agent between two prepressed beams. Finally, we perform an in-depth analysis of the environmental impact of wood-Ulva biocomposites.

Impact statement

This research introduces a sustainable alternative to petroleum-derived adhesives used in wood-based panels, addressing a pressing environmental concern in our infrastructure and construction materials. Here, we discuss the use of Ulva, a green seaweed species, as a renewable and biodegradable solution for such adhesives. We demonstrate its efficacy as a bonding agent in hot-pressed wood panels, offering enhanced strength and durability. Moreover, the use of Ulva contributes to mitigating the environmental footprint associated with traditional materials, aligning with global efforts toward sustainability and circular economy principles. Through comprehensive spectroscopic analyses and mechanical testing, we provide insights into the underlying mechanisms of Ulva-based adhesion. Furthermore, we report the water resistance and improved flame retardancy of Ulva-bonded wood, which are essential for applications in infrastructure and construction. Finally, we discuss environmental and social advantages of Ulva-based composites.

Graphical abstract