An investigation on the friction stir welding of PP/TiO2 nanocomposites for improving the tensile strength and hardness of the weld joint

In the present work, the fused filament fabrication method was applied to fabricate polypropylene nanocomposite sheets reinforced with TiO 2 nanoparticles. The friction stir welding was also applied to join the polypropylene/TiO 2 nanocomposite sheets. The response surface methodology was used to examine the effect of the parameters of rotational speed, welding speed, and TiO 2 content on the mechanical properties of the obtained welds. The mechanical properties of weld samples were examined by tensile and hardness tests, while their thermal properties were studied by thermogravimetric analysis, differential scanning calorimetry, and scanning electron microscopy. The results revealed that the addition of TiO 2 nanoparticles increased the melting point and crystallinity percentage of the polypropylene nanocomposite up to 170.2 °C and 57.7%, respectively, due to good interfacial interaction between TiO 2 nanoparticles and PP matrix. The weld strength enhanced (about 21%) when rotational speed increased from 500 to 1000 rpm, while the hardness deteriorated (about 20.5%). The increase of welding speed from 20 to 40 mm/min resulted in an improvement of hardness by 13.5% and a decline of tensile strength by 9%. The highest hardness of the weld joint (12.5 HV) was obtained at 4 wt% TiO 2 , whereas the tensile strength of the weld joint maximized (43 MPa) at 2 wt% TiO 2 . Finally, the concurrent enhancement of hardness and tensile strength was achieved by a rotational speed of 833 rpm, welding speed of 20 mm/min, and TiO 2 content of 3.5 wt%. At the optimal conditions, the tensile strength and hardness improved up to 43.87 MPa and 12.45 HV, respectively. Graphical Abstract