Epoxy composites modified with ground walnut shell used as organic waste fillers were prepared and examined. Post-agricultural waste materials after grinding were characterized by evaluation of grain size distribution and structure observations realized using scanning electron microscope (SEM). The influence of filler addition on the mechanical properties of epoxy-based composites was determined by: static tensile test, Charpy impact test, and ball indentation hardness measurements. Composite samples containing 20, 30, 40, and 50 wt% of walnut shell were characterized by increased stiffness and hardness in comparison to the unmodified resins. Moreover, the incorporation of the filler resulted in a decrease of composite material tensile strength and impact resistance. Thermo-mechanical properties of the composites were investigated by dynamic mechanical thermal analysis (DMTA). Results obtained from DMTA tests showed a growth in the composites’ stiffness at elevated temperatures as a function of the increasing natural filler content. The material characterization was supplemented by thermal stability evaluation realized by thermogravimetric analysis (TGA). It was found that the incorporation of ground walnut shell led to an improved thermal stability of composite materials. The analysis of the change in composite material properties, caused by natural filler incorporation, was complemented by material microstructure observations.

The purpose of this work was to obtain environmentally friendly natural fibre composites (NFC) from high-density polyethylene (PE-HD) foil and either finely ground sunflower husk or pistachio shells, which both possess physico-mechanical characteristics similar to wood-polymer composite. The composites were prepared from waste materials without the use of additives. It was found that 66% of the sunflower husk grains were from 180 to 850 μm in size, and 88% of the pistachio shell particles were less than 63 μm in size. With the use of a rolling mixer, six mixtures were produced with filler shares amounting to 5, 15 and 30 wt.% of sunflower husk and 15, 35 and 55% of pistachio shell, from which dumbbell-shaped samples were formed via injection processing. The produced materials were analysed for their mechanical properties (impact strength, hardness, tensile strength, Young’s modulus and DMA). The morphologies and chemical composition of the filler as well as the morphological properties of the composites (SEM) were also investigated. The chemical constitution and shape of the filler particles affected the investigated properties of the obtained NFC, and the results were especially significant for the properties of impact strength, stiffness and tensile strength.

The influence of plant fillers on the flammability and smoke emission of natural composites was investigated. Epoxy composites with 15, 25, and 35 wt % of walnut and hazelnut shell, as well as sunflower husk, were prepared and examined. The ground organic components were characterized by grain size distribution, thermogravimetric analysis (TGA) and microstructure observations (SEM). The composite materials were subjected to dynamic mechanical analysis (DMA) and structural evaluation with scanning electron microscopy. Cone calorimeter tests and TGA determined the influence of plant waste filler addition on thermal stability and flammability. Moreover, the semi-volatile and volatile compounds that evolved during the thermal decomposition of selected samples were identified using a steady state tube furnace and a gas chromatograph with a mass spectrometer. The intensity of the degradation reduced as a function of increasing filler content, while the yield of residue corresponded to the amount of lignin that is contained in the tested plants. Moreover, the incorporation of agricultural waste materials resulted in the formation of a char layer, which inhibits the burning process. The yield of char depended on the amount and type of the filler. The composites containing ground hazelnut shell formed swollen char that was shaped in multicellular layers, similar to intumescent fire retardants.