Hindered phenol grafted carbon nanotubes for enhanced thermal oxidative stability of polyethylene

Thermal Aging Properties of 500 kV AC and DC XLPE Cable Insulation Materials

Despite similar material composition and insulation application, the alternating current (AC) cross-linked polyethylene (XLPE) and direct current (DC) XLPE materials cannot replace each other due to different voltage forms. Herein, this work presents a systematical investigation into the effects of thermal aging on the material composition and properties of 500 kV-level commercial AC XLPE and DC XLPE materials. A higher content of antioxidants in the AC XLPE than in the DC XLPE was experimentally demonstrated via thermal analysis technologies, such as oxidation-induced time and oxidation-induced temperature. Retarded thermal oxidation and suppression of space charge effects were observed in thermally aged AC XLPE samples. On the other hand, the carbonyl index of DC XLPE dramatically rose when thermal aging was up to 168 h. The newly generated oxygen-containing groups provided deep trapping sites (~0.95 eV) for space charges and caused severe electric field distortion (120%) under -50 kV/mm at room temperature in the aged DC XLPE samples. For the unaged XLPE materials, the positive space charge packets were attributed to the residue crosslinking byproducts, even after being treated in vacuum at 70 °C for 24 h. Thus, it was reasoned that the DC XLPE material had a lower crosslinking degree to guarantee fewer crosslinking byproducts. This work offers a simple but accurate method for evaluating thermal oxidation resistance and space charge properties crucial for developing high-performance HVDC cable insulation materials.

Enhancement of aging resistance of EPDM rubber by natural rubber‐g‐N (4‐phenylenediamine) maleimide as a grafted antioxidant

A new antioxidant was prepared by graft copolymerization of N (4‐phenylenediamine) maleimide (pPDAM) onto natural rubber (NR). Fourier transform infrared technique was used to confirm the grafting of (pPDAM) onto the NR backbone. The grafted copolymer (NR‐g‐pPDAM) was incorporated into the ethylene propylene diene monomer rubber (EPDM) rubber mix as an antioxidant. For comparison purposes, a widely used antioxidant N‐(1,3‐dimethylbutyl)‐N′‐phenyl‐p‐phenylenediamine (6PPD) was used in addition to a blank sample without antioxidant. The rheometric characteristics of EPDM vulcanizates were determined using an oscillating disc rheometer. Different mechanical properties of the EPDM vulcanizates were measured before and after exposure to thermal and ultraviolet/ozone (UV/O3) accelerated aging. The results revealed that the grafted antioxidant NR‐g‐pPDAM is more efficient, for EPDM rubber vulcanizates than the commercial antioxidant (6PPD). EPDM containing grafted (NR‐g‐pPDAM) antioxidant exhibited promising properties, such that it is expected to fulfill major requirements of industrial, automotive, and construction applications.

Aging retardation strategy of PVDF membranes: evaluation of free radical scavenging effect of nano-particles

ESR and spectrophotometry proved that nano-particles can effectively remove free radicals produced by NaClO, and analyzed the mechanism of delaying aging.

Effects of chain polarity of hindered phenol on the damping properties of polymer-based hybrid materials: insights into the molecular mechanism

For hindered phenol (HP)/polymer-based hybrid damping materials, the damping properties are greatly affected by the structure variation of HPs. However, the unclear relationship between them limits the exploitation of such promising materials. Therefore, three HPs with different chain polarity were synthesized to explore the relationship in this paper. The structures of the HPs were firstly confirmed by Nuclear Magnetic Resonance Spectrum, Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Diffraction (XRD). For further prepared HP/polyurethane hybrids, FT-IR and XRD were also adopted to confirm the hydrogen bonding interactions and micromorphologies. And, Molecular dynamics simulation was further used to characterize the effects of polarity variation on the hydrogen bonding interactions and chain packing of the hybrids in a quantitative manner. Then, combined with dynamic mechanical analysis, the relationship between the chain polarity variation of the hindered phenols and the damping properties was established.

Preparation of nano-SiO2 compound antioxidant and its antioxidant effect on polyphenylene sulfide

Polyphenylene sulfide (PPS) is easily oxidized at high temperature, which greatly limits its applications. In this study, a nano-SiO2 compound antioxidant (SiO2-g-AO) was prepared and incorporated into PPS by melt compounding to obtain PPS/SiO2-g-AO composites. SiO2-g-AO was prepared by reacting 3-(3,5-di-tert-butyl-4-hydroxyphenyl) (antioxidant AO) with an aminosilane coupling agent (KH792). Fourier transform infrared (FTIR) spectroscopy, energy dispersive spectroscopy (EDS) and thermogravimetric analysis (TGA) confirmed that the antioxidant AO was successfully immobilized on the surface of SiO2 and the thermal stability was improved. Scanning electron microscopy (SEM) images showed that SiO2-g-AO was uniformly dispersed in PPS. It has been found that the crystallinity and mechanical properties of PPS composites improved, and the dynamic oxidation induction temperature (OIT) increased in the range of 16.7°C–21.1°C. A synergistic anti-oxidation model of nanoparticles and antioxidants, namely a multi-stage antioxidant system, was established by comprehensive analysis of experimental results. The synergistic anti-oxidation model provides a new idea for the antioxidant modification of polymer composites.

Towards a Stable and High-Performance Hindered Phenol/Polymer-Based Damping Material Through Structure Optimization and Damping Mechanism Revelation

Although hindered phenol/polymer-based hybrid damping materials, with excellent damping performance, attract more and more attention, the poor stability of hindered phenol limits the application of such promising materials. To solve this problem, a linear hindered phenol with amorphous state and low polarity was synthesized and related polyurethane-based hybrid materials were prepared in this study. The structure and state of the hindered phenol were confirmed by nuclear magnetic resonance spectrum, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The existence of intermolecular hydrogen bonds (HBs) between hindered phenol and polyurethane was confirmed by FT-IR, and the amorphous state of the hybrids was confirmed by XRD. Moreover, by a combination of molecular dynamics simulation and dynamic mechanical analysis, the relationship between the structure optimization of the hindered phenol and the high damping performance of the hybrids was quantitatively revealed. By constructing the synthetic hindered phenol, the intramolecular HBs between hindered phenols were restricted, while the strength and concentration of the intermolecular HBs increased by increasing the amount of hindered phenol. Thus, intermolecular interactions were enhanced, which lead to the compact chain packing of polyurethane, extended chain packing of hindered phenol, and good dispersion of hindered phenol in polyurethane. Therefore, the stability of the hindered phenol and the damping properties of the hybrids were both improved. The experiment results are expected to provide some useful information for the design and fabrication of high-performance polymeric damping materials.

Sulfonated Poly(Arylene Ether Sulfone) and Perfluorosulfonic Acid Composite Membranes Containing Perfluoropolyether Grafted Graphene Oxide for Polymer Electrolyte Membrane Fuel Cell Applications

Sulfonated poly(arylene ether sulfone) (SPAES) and perfluorosulfonic acid (PFSA) composite membranes were prepared using perfluoropolyether grafted graphene oxide (PFPE-GO) as a reinforcing filler for polymer electrolyte membrane fuel cell (PEMFC) applications. PFPE-GO was obtained by grafting poly(hexafluoropropylene oxide) having a carboxylic acid end group onto the surface of GO via ring opening reaction between the carboxylic acid group in poly(hexafluoropropylene oxide) and the epoxide groups in GO, using 4-dimethylaminopyridine as a base catalyst. Both SPAES and PFSA composite membranes containing PFPE-GO showed much improved mechanical strength and dimensional stability, compared to each linear SPAES and PFSA membrane, respectively. The enhanced mechanical strength and dimensional stability of composite membranes can be ascribed to the homogeneous dispersion of rigid conjugated carbon units in GO through the increased interfacial interactions between PFPE-GO and SPAES/PFSA matrices.

Using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for the characterization of functionalized carbon nanotubes

RATIONALE

Functionalization of carbon nanotubes (CNTs) generates complex systems that require the development of suitable characterization protocols. New techniques have been explored, and existing analytical and spectroscopic methods to characterize functionalized CNTs have been adapted. Presently, chemical characterization of functionalized CNTs (f-CNTs) remains a difficult task.

METHODS

Matrix-assisted laser desorption/ionization (MALDI) analysis is performed on f-MWCNT samples prepared via grafting or absorption of anti-oxidant (AO) molecules on both MWCNT-COOH and MWCNT-OH. Covalently functionalized MWCNTs were subjected to thermal degradation and/or hydrolysis reaction before analysis, whereas MWCNTs with a physical adsorption of the functionalizing molecules were directly spotted in the target sample. Noteworthy, in our approach f-MWCNTs constitute at the same time analyte and MALDI matrix.

RESULTS

The identification of functionalizing AO molecules is ascertained after degradation or hydrolysis reactions in both MWCNT-COOH and MWCNT-OH grafted samples. Absorbed AO molecules, as well as organic impurities derived from grafting reactions, are also revealed by MALDI MS without any preliminary cleavage reaction.

CONCLUSIONS

A simple MALDI-TOF mass spectrometry method permits to obtain the unambiguous discrimination between grafted or adsorbed functionalized molecules onto the surface of MWCNTs.