Particle reinforced polypropylene biocomposites based on lignocellulosic biomass from organic wastes

Abstract

The aim of this study was to examine the effects of lignocellulosic biomass on the properties of polypropylene (PP) biocomposites. The biomass used in this experiment was apricot kernel shell (AKS), hazelnut shell (HS), walnut shell (WS), and corn cob (CC). In the first section of the thesis, the characterization of biomasses was analyzed. For the characterization of each biomass, chemical analysis was done chemically and thermally. FTIR analysis was applied to determine the spectral analysis of biomasses. Lignin has more hydrophobic, higher available sites and more reactive groups that can bind from the surface. From the results of chemical analysis, AKS showed that it had the highest lignin content among all. Biomass selection was critical for mass production. The biomass was selected based on its use by secondary consumers. Nut shells and corncobs could be harvested before the second consumer. In Arçelik's previous study, used coffee waste was collected after the second consumer. Coffee waste could not be cleaned or separated after collection. In some cases, undesirable substances were seen. If the unwanted external materials are not cleaned, they may damage the mold during the previous processes. AKS, HS, WS and CC wastes can be used easily in mass production. The hydroxyl bonds of the material were determined. After titration with anhydrite and pyridine mixture, the amount of OH and the OH equation were measured. According to the results, it was seen that the OH amount was highest in WS and CC. The reason for the excess of these two is that the amount of free OH in the cellulose is high, and it is predicted that their amount is excessive. It was observed that the amount of hydroxyl bonds coming from the cellulose parts was excessive because the OH amounts in the lignin were not reached due to the structure requirement. WS and CC are more hydrophilic biomass due to their cellulose content. When looking at the TGA analysis of biomass, the decomposition temperature of AKS and HS started later. The reason for this is that the amount of complex structured lignin is higher, and its thermal resistance is higher than other HS and CC biomass. Lignin decomposition is slower than hemicellulose and cellulose. In addition, according to the result obtained from the TGA graph, the most mass loss was seen in AKS. According to the literature research, the high amount of heavy metal in the ACS was associated with this high mass loss.Two different PPs were used in the biocomposite process. Since the mechanical results with the two were different from each other, FTIR analysis was performed and the differences between them were examined. The isotactic ratio was determined as a result of the FTIR analysis. The ratio of isotacticity ratios to the percentage of crystallization was examined. As a result, Borealis PP was more atactic, while Sumitomo PP was more isotactic. With the mechanical tests, the bending modulus and elastic modulus of Sumitomo PP were higher, while the impact value was lower compared to Borealis PP. The percentage of crystallization according to the difference in isotactic ratios confirmed the results. While the crystallization percentage of Sumitomo PP increased to 36%, the crystallization of Borealis PP increased to 15%. After obtaining biocomposite with AKS, isotacticity ratios were determined according to the percentage of ACS. In PP/AKS biocomposites made with Borealis, isotacticity increased as the percentage increased. The most atactic PP/10AKS was found in PP/AKS biocomposites made with Sumitomo. On the other hand, isotacticity increased with the increase of biomass ratio in biocomposites after 10%. It was revealed that the biomass surfaces exhibit impurities and irregularities, which could degrade the biocomposite properties after compounding, because it would be harder to mechanically interlock of the biomass and PP matrix. For the removal of those impurities from the biomass surface, AKS was washed with ethanol, and it was exposed to an esterification reaction to modify its surface properties. Modification is then analyzed with FTIR spectra. The requirement for the surface modification came from the inherent hydrophilic nature of the biomass, which caused poor interfacial adhesion and incompatibility with the PP matrix. The esterification reaction reduced the hydroxyl sites of the AKS. For the modification of AKS, six different cases were experimented by changing the time, temperature, and content of the stearic acid (SA) modifier. From the characterization of modified AKS, it was revealed that just by changing the temperature from room temperature to 50 C, the modification became prominent. The biomass was compounded with PP matrix to obtain a biocomposite form of the material. The compounding process involved melt mixing by twin screw extrusion and then injection molding. The mechanical and thermal properties of biocomposites were investigated. The effect of biomass content, type and the interfacial compatibility were examined.For AKS, increasing biomass content resulted in agglomeration of the biomass particles according to the SEM images. This occurrence caused the matrix compatibilization to break and AKS particles detached leading to the fiber pull-out. The general trend for all type of biocomposites was an increase in proportion resulted in decreased the elongation at break and impact strength while increasing the moduli in general. TGA analysis revealed that, in the first 25% of the curve, neat PP had a higher thermal stability compared to biocomposites. Yet, in the last quartile of the graph the biocomposites had a higher decomposition temperature in comparison with the neat PP. This is an indication of in high temperature applications it would be better to use biomass-filled biocomposites. The first heating cycle of the biocomposites was studied with DSC analysis. As the biomass content increased, it was expected to have a high degree of crystallization, yet the crystallization increased up to 10% AKS biomass and then decreased afterward. This could be attributed to the fact that at higher biomass contents, the agglomeration deteriorated the crystallization behavior. The hydrophilic nature of biomass was inconsistent with the PP matrix which could result in poor interfacial compatibility. Therefore, to improve the properties of biocomposites, maleic anhydride- grafted PP (MAPP) was added as a compatibilizer. The impact of MAPP on biocomposites was tested to see if the effect of the compatibilizer xxiii enhanced the mechanical and thermal properties of the material. The improved properties of the biocomposite with the addition of 2 wt% MAPP were also confirmed with the SEM imaging, which decreased the surface roughness and provided a uniform distribution of the biomass particles inside the PP matrix. DSC curve revealed that the degree of crystallization was highest in the MAPPcompatible biocomposite. TGA results that the thermal stability of biocomposites was also improved with the addition of MAPP. Without compatibilizer, low molecular weight compounds were thermally decomposed earlier, and MAPP addition holds these compounds and inhibits the detachment from the PP matrix. Finally, the rheological behavior of the biocomposites was studied with a capillary rheometer. The materials exhibited pseudoplastic fluid behavior, in which shear thinning occurs when the shear rate is applied. As the biomass content increased, the power law index decreased, and the inverse proportionality of the power law index and shear thinning behavior showed that shear thinning was more distinct at high biomass contents. The viscosity of biocomposites decreased as the shear rate increased. There was no discernible difference in behavior between the viscosities of various biomass content biocomposites.