The Use of Whole Hawaiian Macroalgae to Engineer Bioplastics and Adhesives for Wood-Particleboards

Abstract

Production of novel materials from sustainable biological matter (biomatter) can contribute to the development of a global, circular bioeconomy. Among potential feedstocks, macroalgae stand out due to their fast growth rates and richly diverse biochemical composition. However, very few studies demonstrate the direct conversion of whole macroalgal biomatter into bulk materials and also perform comprehensive biochemical characterization. Here, we present a detailed, species-resolved compositional and macromolecular analysis of four native Hawaiian macroalgae, including carbohydrate speciation, protein molecular weight distributions, lipid profiles, and inorganic content. Each macroalgal species was then processed directly, without chemical pretreatment or fractionation, into two structurally distinct bioproduct classes: self-bonded bioplastics and algae-bonded wood particleboards. We characterized the mechanical properties and micromorphology of all bioproducts, as well as the flame resistance and seawater-biodegradation of selected materials, to establish structure–property relationships across species and material classes. The Hawaiian macroalgae exhibited carbohydrate, protein, lipid, and organic sulfate contents of 58 - 69 wt.%, 5 - 12 wt.%, 2 - 10 wt.%, and 1 - 39 wt.%, respectively, and species-specific sulfated polysaccharides were identified. Green macroalgae displayed broader protein molecular weight distributions (15-75 kDa) than red macroalgae (15-20 kDa). Bioplastics made from the red macroalgae exhibited higher flexural strength (46-70 MPa) and flexural modulus (8-9 GPa) compared to the green macroalgae (29-32 MPa, flexural strength; 5 GPa, flexural modulus). Differences in the bioplastic mechanical properties were correlated with differences in the macroalgal powder particle size distributions and protein characteristics. In wood particleboards bonded by macroalgal biomatter, the addition of 40% algae by weight improved the flexural strength and flexural modulus by 180 - 500% and 62.5 - 112.5%, respectively. All of the macroalgae-bonded wood particleboards also impressively self extinguished in approximately 10 seconds, compared to the wood control which was completely consumed by flames. Overall, this work demonstrates that whole, minimally processed macroalgal biomatter can be directly transformed into multiple mechanically relevant material classes while retaining performance-relevant chemical complexity. Beyond the demonstrated bioplastics and particleboards, the comprehensive compositional dataset reported here provides a reference for the broader valorization of native macroalgal biomatter through diverse material and chemical pathways.