Transforming heterogeneous fibreboard waste into form-pressed bio-polyester composites

Abstract

Abstract Efficient recycling of fibreboard production residues is hindered by their chemical heterogeneity, fine particle size and low bulk density, which limit transport and reprocessing in conventional processing routes. This study investigates the transformation of heterogeneous fibreboard waste streams into bio‑based particulate composites using an in situ-formed citric acid-sorbitol polyester matrix, with a focus on identifying structure-property relationships governing mechanical performance and moisture response. Composite formulations based on three industrial fibreboard dust types were systematically explored using two mixture designs that varied dust composition and resin content. The results show that resin content is the dominant factor controlling specific compressive strength, reflecting improved interparticle bonding rather than an increase in density alone. Fibreboard dust chemistry affected water-vapour sorption and water‑induced thickness swelling, with dusts containing fire-retardant salts exhibiting distinct moisture responses. X‑ray density profiling revealed pronounced density gradients in cured composites, which were identified as a key limitation to failure behaviour under compression. Based on the identified composition-property relationships, formability at the decimetre scale was demonstrated using a manual form press, illustrating the effects of scaling‑induced density gradients and geometric imperfections rather than intrinsic material strength. Overall, the study demonstrates a robust route for converting diverse fibreboard waste into bio‑polyester composites and provides transferable insights into the roles of binder content, fibre chemistry and density distribution in compacted particulate materials.