Fabrication and characterization of rice husk pyrolyzed biochar reinforced polypropylene composite

Abstract

Growing polymer consumption, depletion of metallic resources, and rising environmental concerns have resulted in an increased interest in bio-derived environment friendly polymeric composite materials. The utilization of biochar as a reinforcement in polymers can be viewed as a sustainable attempt that incorporates pyrolyzed biomass based value-added material and simultaneously aids environmental management through effective utilization of bio-wastes. On the other hand, polypropylene (PP), a semi-crystalline thermoplastic polymer has favorable properties like low cost, good mechanical strength, lightweight, easy processing, excellent chemical resistance, etc. However, some other properties such as inferior mechanical properties at alleviated temperatures, poor UV resistance, and poor surface adhesion, etc. limit its application. To overcome the limitations exhibited by polymeric composites, biochar reinforced polymer composites have attracted the attention of researchers all over the world because of their low cost, renewability, and improved thermochemical properties. In this thesis work, rice husk biochar (RHB) reinforcement polypropylene (PP) composite has been fabricated and characterized to evaluate its performance. Biochar was prepared from rice husk via slow pyrolysis at four different temperatures (400, 550, 700, and 8500C). Characterization of the RHB samples revealed high carbon, ash, and silicon contents. The RHB samples exhibited porous structure and their thermal stability increased with increasing pyrolysis temperatures. The biochar samples were then hand ground and applied as particle reinforcement material for PP composite fabrication with two different loadings of 10 and 15 wt%. RHB was blended with PP by melt mixing technique followed by the hot press molding process. Pyrolysis temperature and wt% of RHB were found to be crucial factors affecting the compatibility, thermo-mechanical and electrical properties of the resulted composites. The tensile strength of the fabricated composites was found to be lower when compared with neat PP, but the flexural strength and hardness (shore D) were improved, where composite containing 15 wt% of RHB prepared at higher temperatures (700 and 8500C) exhibited better results. According to SEM results, the biochar particles were firmly embedded in the PP matrix due to their porous structure and the molten PP has penetrated a large number of pores of the biochar particles creating a mechanically interlocked system, which consequently improved the mechanical properties. Moreover, the incorporation of thermally stable biochar was found to have a positive impact on the thermal stability of the composites, where increasing the RHB pyrolysis temperature and higher RHB loading helped the fabricated composite to sustain higher thermal decomposition temperatures. However, the RHB incorporation into the PP matrix had a negligible effect on the melting temperature (Tm) of the developed composites. Finally, the increased loading of high-temperature RHB has potentially reduced the resistance and the impedance of the fabricated composites. Thus, the improvements of the composite properties were found to increase when the RHB content was increased and the incorporated RHB had been pyrolyzed at higher temperatures.