Innovative composites based on agro-industrial by-products and bio-based resins : production of particleboards for industrial use

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This thesis explores the valorization of almond and walnut shells, abundant lignocellulosic by-products, into sustainable precursors for bio-based adhesive formulations. Initially, their chemical composition was analyzed to assess their suitability for cellulose and lignin extraction. Advanced, energy-efficient extraction methods, including ultrasound (US), pulsed electric fields (PEF), and high-voltage electrical discharges (HVED), were optimized and compared with conventional alkaline treatments. These physical pretreatments significantly improved extraction efficiency, cellulose crystallinity, and lignin recovery. Further chemical modifications were conducted to enhance the functional properties of the biopolymers: cellulose was phosphorylated using diammonium phosphate (DAP) and urea, while lignin was modified via phosphorylation (using orthophosphoric acid (OPA) and DAP) and phenolation to increase its reactivity and flame-retardant potential. Structural, thermal, and morphological analyses (FTIR, XRD, NMR, TGA/DTG, DSC, SEM) confirmed successful modification and improved performance characteristics. Finally, the extracted cellulose was incorporated into formaldehyde-free cornstarch–mimosa tannin (CM) adhesives, yielding composites with superior mechanical strength, water resistance, and thermal stability. The study demonstrates the potential of almond and walnut shells as renewable resources for producing high-performance, eco-friendly adhesives and functional biopolymers, contributing to sustainable material innovation and circular bioeconomy development.

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