Abstract: The aims of this work turn towards the valorization of the underutilized Raw Sugar Beet Pulp by-product to produce white Cellulose Microfibers (CMFs), and its potential effect as a reinforcement for the development of High-Density Polyethylene (HDPE) composites. Pure CMFs were first obtained by subjecting raw SBP to alkali and bleaching treatments. Several characterization techniques were performed to confirm the successful removal of the amorphous compounds from the surface of individual fibers, including SEM, XRD, TGA, and FT-IR analysis. Various CMF loadings (5–10 wt%) were incorporated as bio-fillers into HDPE polymer to evaluate their reinforcing ability in comparison to raw and alkali-treated SBP using twin-screw extrusion followed by injection molding. Styrene–(Ethylene–Butene)–Styrene Three-Block Co-Polymer Grafted with Maleic Anhydride was used as a compatibilizer to improve the interfacial adhesion between fibers and the matrix. Thermal, mechanical, and rheological properties of the produced composite samples were investigated. It was found that the Young’s modulus were gradually increased with increasing of fibers loadings, with a maximum increase of 30% and 26% observed for composite containing 10 wt% of CMFs and raw SBP, respectively, over neat HDPE. While, the use of coupling agent enhances the ductile behavior of the composites. It was also found that all fiber improves the hardness and toughness behavior of all reinforced composites as well as the complex modulus particularly at 10 wt%. The thermal stability slightly increases with the addition of fibers. This study demonstrates a new route for the valorization of SBP by-products. These fibers can be considered as a valuable bio-fillers candidate for the development of composite materials with enhanced properties.

Key words: Sugar beet pulp , · By-product , · Cellulose , · HDPE , · Coupling agent , · Composite , · Mechanical and rheological properties