Investigation of the physical, mechanical and thermal properties of waste coffee powder filled polypropylene biocomposites

Petroleum-based polymers cause intense carbon emissions during production and degrade in nature for a long time after use. The use of biocomposites as an alternative to petroleum-based composites increases with the use of waste materials. While the use of waste materials in biocomposites ensures waste assessment, environmental pollution is reduced and resource efficiency is ensured. In recent years, studies on the use of wasted coffee powder (KKT) as an alternative reinforcement element in the production of biocomposites, which has increased as a result of intense consumption, have increased. Coffee waste consists of the shells, fibers, skin and fat residues that arise during the processing of coffee beans and is generally considered waste. However, coffee waste becomes a valuable material when used in the production of biocomposites. The high amount of cellulose and lignin in coffee waste is important for the production of biocomposites. The coffee powder (KKT) used in this thesis study was produced of polypropylene (PP) biocomposite material (PPKKT). The use of maleic anhydrite (MAPP) in the production of biocomposites is aimed at improving the interface between the natural reinforcement and the matrix. MAPP has been added to PPKKT biocomposites sample containing 10%, 20% and 30% KKT by weight. After being supplied from a coffee chain, the KKTs are mixed in determined proportions by removing moisture until a homogeneous mixture is obtained in the mechanical mixer. The PP and PPKKT groups were granulated after being processed in the double screw extruder. Granular biocomposites are obtained by hydraulic press processing plates. Standard samples for mechanical tests and thermal analysis were cut by laser cutting machine. The effects on the physical, mechanical, thermal and morphological properties associated with the variable weight ratio of KKT were studied with experiments with samples. Test results were compared with PP samples produced for control purposes. The physical properties of PPKKT biocomposites; density, water absorption, thickness swelling with mechanical values with tensile and bending test and thermal properties have been studied with differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), fouirer transform infrared spectroscopy (FTIR), heat deflection temperature (HDT), thermal conductivity analysis. The density of the biocomposite decreased with the increase of coffee filler in the produced biocomposite groups. As a result of the periodic measurements, the highest increase in water absorption and thickness swelling was observed in the PPKKT30 group. In the group containing 30% KKT, there was a 22.4% increase in water absorption and a corresponding 2.5% increase in thickness swelling. When the mechanical results were examined, the tensile-bending strength decreased and the tensile-bending modulus increased proportionally with the increasing filling ratio. As a result of the DSC analysis, there was no significant change in the crystallization temperature (Tc) due to the increased KKT filling, while the crystallinity degrees (Xc) decreased. As a result of the FTIR analysis, the peak at 3300 cm-1 and the O-H stretching vibration in hemicellulose and/or cellulose were determined. When the TGA curves were examined, it did not change significantly with the addition of KKT, and the degradation temperatures showed small decreases according to the increasing KKT filling ratio. The thermal conductivity coefficient and heat deflection temperature values decreased with the addition of KKT to the biocomposites. As a result, coffee waste is a valuable source of material for the production of biocomposites. Biocomposites from coffee waste are a sustainable source of materials and low costs encourage the use of natural materials in composite.