UV-Initiated Crosslinking Reaction Mechanism and Electrical Breakdown Performance of Crosslinked Polyethylene

Abstract

The ultraviolet (UV) irradiation crosslinking reactions of polyethylene and the electronic properties of photo-initiators and reaction products are theoretically investigated by the first-principles calculations. The crosslinked polyethylene (XLPE) materials are prepared in experiments that employ the UV-initiated crosslinking technique with different photon-initiation systems. Infrared spectrum and the alternating current dielectric breakdown strength of UV-initiated XLPE are tested to explore the effect of reaction products on the breakdown characteristics in combination with the electron structure calculations. The theoretical calculations indicate that the 4-hydroxybenzophenone laurate, which is compatible with polyethylene, can effectively initiate crosslinking reactions of polyethylene molecules under UV photon excitation and will produce reaction by-products from carbonyl radicals; as a macromolecular auxiliary crosslinker, the monomer or homopolymer of dioleyl-2,2′,4,4′-tetraallyl isocyanurate can form chemical connections with multiple polyethylene molecules acting as a crosslinking node in a photon-initiated reaction process. The carbonyl, hydroxyl, or ester groups of reaction by-products are capable of capturing hot electrons to prevent polyethylene molecules from impact ionization, and thus will increase the breakdown electric field. The macromolecular auxiliary crosslinker and the macromolecular photon initiator as well as its reaction by-product can convert the energy of their captured high-energy electrons into heat, which can act as a voltage stabilizer. The molecule characterization of infrared spectra demonstrates that the characteristic absorption peaks of the carbonyl in the macromolecular photon initiator and the allyl in the macromolecular auxiliary crosslinking agent are gradually decreasing in intensity as the crosslinking reaction proceeds, which is consistent with the conclusion from theoretical calculations. Compared with the small molecular photon-initiation system generally used in the photon-initiated crosslinking process, the higher dielectric breakdown field of XLPE being prepared by utilizing a macromolecular photon-initiation system is in good agreement with the calculation results of electronic affinity and ionization potential. The consistent results of the experiments and first-principles calculations elucidate the fundamental mechanism of the UV-initiation crosslinking technique and suggest a prospective routine to improve the insulation strength for developing high-voltage XLPE insulating materials.

Design of Electrochemically Effective Double-Layered Cation Exchange Membranes for Saline Water Electrolysis

“…After AA-DVB C layer formation, the peak is weakened owing to the limited penetration depth of FT-IR beam [ 21 ]. The NR212/AA-DVB_2 spectra has characteristic peaks assigned to C=C stretch in the aromatic rings of DVB, and –CH stretch in the main chain of AA-DVB layer [ 15 , 22 ]. NR212/AA-DVB_2 also exhibits a strong C=O vibration peak at around 1700 cm −1 .…”

“…For this, each membrane coupon (dimension = 5 × 5 cm 2 ) was dried under vacuum at 60 °C for one day, and fully hydrated in deionized water at 30 °C for one day. The ohmic resistance of the SWE membranes ( R , membrane coupon size = 1 × 4 cm 2 ) was measured in liquid water in the temperature range from 30 to 90 °C via four-point probe alternating current (a.c.) impedance spectroscopy using a VMP3 impedance spectrometer (Biologic, Seyssinet-Pariset, France) [ 15 ]. The Na + ion conductivity ( σ , S cm −1 ) was obtained using an equation of σ = l /( R × S ).…”

Full-life-cycle eco-friendly polymeric insulating materials: research progress and future prospects

“…(2) Photo-crosslinked power cable In addition to photocurable insulators, photo-crosslinked power cables have also been widely studied and applied. Fu et al [71] studied the UV light-initiated crosslinking reaction mechanism and the electrical breakdown performance of XLPE. Figure 13(a) shows the representative UV-initiated crosslinking reactions of polyethylene molecules by using photon initiator and auxiliary crosslinking agent, which indicates that the auxiliary crosslinking agent in the form of monomers or homopolymers represents higher ability in the participation of forming polyethylene crosslinking nodes, and improving the photon-initiated crosslinking efficiency.…”

Chondrogenic Differentiation of Adipose-Derived Stromal Cells Induced by Decellularized Cartilage Matrix/Silk Fibroin Secondary Crosslinking Hydrogel Scaffolds with a Three-Dimensional Microstructure

“…In addition, the crosslinking method of the hydrogel is crucial to the mechanical properties of the biomaterials. At present, the traditional chemical, physical, and energy excitation crosslinking methods used to prepare hydrogels have their limitations, thus it is difficult to effectively regulate the mechanical properties, pore connectivity, and degradation time [17][18][19][20].…”