Investigation of some mechanical and thermalproperties of hemp HURD/PLA biocomposite materialmanufactured by fused deposition modeling

Global warming is a phenomenon caused by human activities such as the use of fossil fuels and the emission of greenhouse gases. It refers to the overall increase in average temperatures worldwide. As a result of global warming, polar ice caps melt, leading to rising sea levels. Changes in weather conditions also cause ecosystems to alter, resulting in the displacement of certain species and the endangerment of various forms of life. The significant rise in global temperatures is primarily attributed to human activities. Global initiatives have been launched to mitigate greenhouse gas emissions. There has been a shift towards bioplastics derived from renewable sources as an alternative to materials that contribute to greenhouse gas emissions. The production of bioplastics results in fewer toxic gases compared to fossil-based plastics. The recycling potential and biodegradability of the bioplastics allow for faster decomposition in the natural environment when these products become waste, thereby reducing environmental impacts. The aim of this study is to enhance the brittle nature of PLA material and explore the utilization of hemp stalk waste by making a biocomposite filament with PLA and hemp. A separate experimental group was established where maleic anhydride was added to improve the compatibility between hemp and PLA. Glycerol was added to another group. The filament produced using pure PLA served as the control group. The study aimed to observe whether the addition of hemp had a statistically significant effect on the mechanical and thermal properties of the PLA. PLA and hemp flour were mixed in predetermined ratios. In the case of the PLA/hemp flour/maleic anhydride mixture, the hemp flour was treated with maleic anhydride before being mixed with PLA and kept in an oven for a certain period. Oven-dry materials were initially passed through a twin-screw extruder to obtain irregular filaments. As for the PLA/hemp flour/maleic anhydride/glycerol mixture, glycerol was added before feeding it into the extruder. The irregular filaments obtained were pelletized and fed into a single-screw extruder to obtain regular filaments suitable for 3D printing. The obtained filaments were used to print tensile and flexural samples using a 3D printer, and tensile and flexural tests were conducted to analyze their mechanical properties. TGA analysis was performed on samples before and after the printing process for degradation temperatures. DSC analysis was carried out to investigate the thermal properties of the biocomposites, while FTIR analysis was conducted to examine the functional groups within the biocomposite. When comparing the TGA curves of hemp-filled filaments to pure PLA, it was observed that the degradation temperatures decreased at 5%, 10%, and 90% of weight loss with the addition of hemp, maleic anhydride, and glycerol. The lowest degradation temperature was observed in the glycerol-added biocomposite. Among the bioplastic and biocomposite filament sample groups, the only group with an increased crystallinity ratio compared to PLA was the PLA+K03+MA+G sample group. Adding hemp to PLA bioplastic was observed to reduce PLA brittleness, and adding glycerol resulted in a more flexible structure, as observed in SEM images. In PLA and PLA+K03 biocomposites, there was an excellent interfacial connection between the layers. However, in PLA+K03+MA and PLA+K03+MA+G biocomposites, the interfacial cohesion was not strong, and fiber delamination was observed during the breakage process. According to the three-point bending test results, the flexural strength of the materials increased by adding hemp, maleic anhydride, and glycerol, respectively. However, the groups have no statistically significant difference in flexural strength. Those of modulus of elasticity showed the same pattern, but adding the glycerol decreased its modulus of elasticity. According to the results of the tensile test, the changes in biocomposite content do not have a statistically significant effect on the tensile strength of the material. As can be seen from , the PLA+K03+MA group has the highest modulus of elasticity, while PLA has the lowest value. Statistically, there is a significant difference between PLA and the other three groups. Consequently, it was observed that material properties were increased quantitatively by adding hemp hurd as a lignocellulosic material to PLA. Test results would be beneficial to produce semi- and final-product by using these materials for R&D applications.