Preparation and characterization of long-chain branched HDPE by UV-induced reactive extrusion at mild temperature

To improve the processability of HDPE, we reported an ultraviolet (UV)-induced reactive extrusion process for preparing long-chain branched high-density polyethylene (LCB-HDPE) at mild temperature. UV lamps were used to irradiate the extruded HDPE filaments near the crystallization temperature, enabling continuous production of the modified resin while enhancing reaction efficiency. The effect of photoinitiator 2-isopropyl thioxanthone (ITX) and chain extender trimethylolpropane triacrylate (TMPTA) on the molecular structure of HDPE was investigated by triple-detector GPC and shear rheology, and two possible reaction mechanisms were discussed. HDPE formed a star-shaped LCB structure under the synergistic effect of ITX and TMPTA, but no gel was produced. Various rheological curves such as the VGP curve, relaxation time spectrum, and Cole-Cole diagram demonstrated the existence of LCB topology in modified HDPE. The LCB structure in modified HDPE not only reduced crystallinity but also increased the nucleation rate during isothermal crystallization, resulting in the development of a large number of tiny and dense spherical crystals. In addition, the mechanical properties of the modified HDPE were enhanced, and the impact strength of PE-I1-T1 reached 5.02 kJ/m2, which was about 17% higher than that of virgin HDPE.