Mechanical and Rheological Behavior of High-Density Polyethylene under the Reversible Crosslinking Method and Comparison to a Conventional Method

This study investigates a Reversible Crosslinking (RXR) technique that enables the melt-state crosslinking of High-Density Polyethylene (HDPE). Reactive extrusion was carried out using a Brabender mixer, after which the RXR-crosslinked HDPE was ground in the solid state and subsequently reprocessed by compression molding. Dynamic Rheological Analysis (DRA) was employed to evaluate the crosslinking efficiency and viscosity variation through torque time curves. The Melt Flow Index (MFI) and gel content measurements were correlated with the DRA results after the second processing cycle. Differential Scanning Calorimetry (DSC), Wide-Angle X-ray Scattering (WAXS), Fourier-Transform Infrared Spectroscopy (FTIR), and mechanical measurements were conducted after the second compression molding. The RXR methodology provided a tunable rheological response, offering clear advantages in processing versatility and industrial optimization. FTIR confirmed the formation of new interchain C–S bonds, demonstrating effective bridging between HDPE main chains. WAXS and DSC revealed a slight reduction in crystallinity, whereas Thermogravimetric Analysis (TGA) indicated enhanced thermal stability in the early stages of decomposition. Mechanical tests showed a strong correlation between the crosslinking degree and crystallinity with both Young’s modulus and impact strength, suggesting that higher structural organization improves stiffness and impact resistance.