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The main goal of this study is to evaluate the potential of waste stone powders as filler in composite materials with a matrix of unsaturated polyester. These wastes are generated in the form of stone fragments and stone‐cutting sludge. Ground marble wastes are thoroughly characterized with the aim to use them as fillers: Mineralogical and chemical composition, particle size distribution, and morphology of these waste stone powders are investigated. Unsaturated polyester resin composites with the different stone powder fillers are prepared. The influence of powder type on the composites’ mechanical properties (tensile, bending, impact, and hardness characteristics), water resistance, thermal stability as well as surface fracture morphology of composites are studied. The moduli of the composites increase by 100%, the hardness of the composites may be improved by 80% upon loading with the “waste” filler, leading to an economical material and helping to reduce waste.

7Due to the global demand for fibrous light-weight materials, research on composites 8 reinforced with plant materials has increased. Natural fiber reinforced composites offer 9 several advantages: light weight, competitive specific mechanical properties, easy 10 processing, large volume availability, low cost, and low environmental footprint. 11Especially, using agricultural wastes such as rice husk, saw dust etc. as fillers/fibres in 12 composites provides the chance to improve material properties while improving their 13 sustainability. In the present work, rice husk and saw dust were chosen as fillers for their 14 differing morphology, aspect ratios, and difference of structure. As matrices, polyethy-15 lene (PE) and polypropylene (PP) were studied, either neat or modified with maleic 16 anhydride grafted PP/PE as coupling agent or compatibilizer between hydrophobic 17 matrices and hydrophilic bio-fillers. The bending modulus is improved due to filler 18 addition. In presence of compatibilizer, the improved interfacial interaction leads to 19 improved bending and tensile strength as well as toughness. Furthermore, the influence 20 of the filler and compatibilizer on composite properties such as hardness, dynamic 21 mechanical behaviour, thermal expansion, thermal degradation, melting and crystalli-22 sation behaviour are presented.23