The effects of four agro wastes viz. corncob, rice hull, walnut shell and flax shive fibers on the thermal, mechanical and rheological behavior of high density polyethylene biocomposites was investigated. It was discovered that the fibers showed two and three mass loss steps due to moisture evaporation and decomposition of hemicelluloses, cellulose and lignin. The flax shive was thermally more stable and showed a decrease in activation energy with increase in conversion rate, while the other three fibers showed increased activation energy with conversion rate. The apparent activation energy values of the fibers was 161±11.06 to 200±4.69 kJ/mol. Particle size distribution of 60-100 mesh of the fibers was 0.295 mm to ‹ 0.125 mm. Mechanical analyses of the composites showed remarkable increases in flexural modulus and un-notched Izod impact strength and a decrease in flexural strength compared with the neat HDPE. The rice hull composites showed superior flexural strength of 22.5 MPa. The flax shive composite gave superior flexural modulus of 3.3 GPa and the walnut shell composites gave superior un-notched Izod impact strength of 52.5 J/m. Rheological analyses showed that the complex viscosities of the composites decreased with increase in frequency. The corncob composite showed higher complex viscosity of 3,600,000 Pas. The walnut shell composite exhibited higher storage modulus of 800,000 GPa at low frequency but decreased with increase in frequency. Corncob composite showed superior loss modulus of 200,000 GPa. The damping factor of the composites decreased with increasing frequency with walnut shell composites showing superior damping factor. The study has shown that the properties of the composites varied substantially based upon the type of fiber utilized.
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