Study on the mechanism of hydrogen bond to construct PP/ETFE Co-crystalline supramolecules and its space charge characteristics

As a new-generation cable insulation material, polypropylene (PP) has received much attention and replaced crosslinked polyethylene. However, the space charge accumulation under high fields still needs to be improved to ensure the safe operation of high-voltage direct current (HVDC) cables. Here, PP was chemically grafted with propenoxy-2-hydroxybenzophenone (AHB) to form PP-g-AHB, and ethylene tetrafluoroethylene copolymer (ETFE) was chemically grafted with glycerol (GL) to obtain ETFE-g-GL. Then PP/ETFE co-crystalline supramolecules were prepared via melt blending. The effect of hydrogen bonds on the space charge inhibition of PP/ETFE co-crystalline supramolecules was investigated using molecular dynamics simulation of differential charge density, energy band, and trap energy level combined with microstructure characterization. Simulations and experiments show that PP-g-AHB and ETFE-g-GL can form PP/ETFE co-crystalline supramolecules very well, owing to the existence of hydrogen bonds. When the mass fraction of PP-g-AHB is 80 %, the cocrystallization size of PP/ETFE supramolecules maximizes to 390 ± 10 μm. Under the action of direct current source, the carrier mobility of PP/ETFE co-crystalline supramolecules is as low as 7.94 × 10⁻¹³m²/(V.s), and the space charge is dominated by heteropolarity, when the average charge density minimizes to 0.08 C/m³. So far, the charge transport characteristics of PP/ETFE co-crystalline supramoleculars have been significantly improved using hydrogen bonds as a bridge. This study lays a foundation for the application of PP in HVDC cable insulation.