Friction stir welding of PP and HDPE/TiO 2 nanocomposite to improve tensile and impact properties

Friction stir welding (FSW) of dissimilar polymers, particularly polypropylene (PP) and high-density polyethylene (HDPE), remains challenging due to their incompatible thermal properties. This study addresses this challenge by incorporating 3 wt% TiO 2 nanoparticles into HDPE via fused filament fabrication (FFF) 3D printing, which increases its melting temperature from 137.1°C to 139.4°C and crystallinity from 47.3% to 52.6%, as confirmed by differential scanning calorimetry (DSC). The modified HDPE/TiO 2 nanocomposite was subsequently joined to PP using FSW. Tensile and impact tests, along with SEM and DSC analyses, were used to characterize the nanocomposites and the welded interfaces. The Response Surface Methodology (RSM) was employed to model the effect of rotation speed, feed rate, and axial force on the tensile and impact strength of the welded specimens. The results show that increasing rotating speed to 1300 rpm and reducing feed rate to 10 mm/min minimizes microstructural defects, enhancing mechanical performance. Simultaneous optimization of both properties was achieved at a rotating speed of 1315 rpm, feed rate of 15 mm/min, and axial force of 5 kN, yielding a tensile strength of 33.4 MPa and impact strength of 11.1 kJ/m 2 . Confirmation experiments validated the regression models with relative errors below 5.5%. This work demonstrates that TiO 2 nanoparticle reinforcement, combined with statistical process optimization, enables high-performance dissimilar polymer joints for lightweight structural applications.