Characterization and rheological properties of hybrid fillers filled high density polyethylene bio-composite

As the world tries to minimise possible harmful destruction of our environment and move towards GO GREEN Agenda, hybrid fillers have been widely used as alternative reinforcing filler for thermoplastic polymer composite. One of the most characteristic features of hybrid composite lies in its balanced performance of strength, as well as other properties, which include manufacturing cost. In this research, different fillers were used to obtain optimal hybrid composite composition from kenaf, rice husk (RH) and calcium carbonate (CaCO₃). Different varying compositions up to 30 wt% of mixed kenaf and rice husk with CaCO₃ were compounded with 40-70 wt% of high density polyethylene (HDPE) using twin screw extruded at 50rpm, to produce two different hybrid composites, HDPE/kenaf/CaCO₃ and HDPE/rice husk/CaCO₃. Properties of hybrid composites were compared between particulate CaCO3/kenaf fibrous form and CaCO₃/rice husk particulate form. Hybrid composites were tested for physical, mechanical, thermal, burning rate and rheological behaviour. From test results, addition of filler had decreased melt flow index (MFI) up to 72% and increased density of hybrid composites up to 19%. In general, addition of both natural fibres, either kenaf or rice husk with CaCO₃ decreased the tensile strength, elongation, and impact. However, addition of 20 wt% rice husk in fixed 30 wt% CaCO₃ showed an increment of about 10% in its impact strength. Increment of filler subsequently increased flexural strength, flexural modulus and Young Modulus properties of both hybrid composite systems. Water absorption properties were increased with addition of filler, while kenaf hybrid composite system exhibited higher water uptake, which is 6.47% in 80 days. For thermal properties, hybrid composite showed good thermal stability with addition of kenaf, rice husk and CaCO₃ fillers. HDPE/kenaf/CaCO₃ exhibited lower burning rate compared to similar filler loading of HDPE/rice husk/CaCO₃ hybrid composite. Viscosity of hybrid composites was increased due to addition of fillers. Rice husk/CaCO3 particulate had lower viscosity compared to kenaf fibrous/CaCO₃ particulate hybrid composite system. From observations of Rule of Mixture (ROM) and Rule of Hybrid Mixture (RoHM), it was found that, there were lower and upper bound of hybrid composites which depended on compositions of their fillers. Meanwhile, observations from field emission scanning electron microscope (FESEM) revealed bonding between filler and matrix from impact fracture.