Effect of ethylene ionomers on the properties of crosslinked polyethylene

Most premature failure of underground crosslinked polyethylene (XLPE) cables in service, a matter of great concern, is due to aging induced by water treeing. To improve the water‐tree resistance, sodium‐neutralized poly (ethylene‐co‐acrylic acid) (EAA–Na) ionomers were blended with XLPE; the EAA–Na ionomers were prepared through the neutralization of sodium hydroxide and poly(ethylene‐co‐acrylic acid). A series of XLPE/EAA–Na ionomer blends were investigated through the measurement of the water absorption ratio, water treeing, and mechanical and dielectric testing; the results strongly suggested that EAA–Na ionomers could improve the water‐tree resistance of XLPE, and the XLPE/EAA–Na blends retained excellent mechanical properties and dielectric properties. Moreover, through the characterization of XLPE/EAA–Na blends with Fourier transform infrared spectrometry, dynamic mechanical analysis, and scanning electron microscopy, it was found that the neutralization reaction could be achieved completely; the XLPE and EAA–Na ionomers were partially compatible, so the EAA–Na ionomers could be dispersed well in the matrix with the process examined in this study. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3483–3490, 2007     

Synthesis and characterization of novel odd–even nylons based on eicosanedioic acid

A series of novel odd–even nylons based on eicosanedioic acid, including nylons 11/20, 9/20, 7/20, 5/20, and 3/20, were prepared through step‐heating melting polycondensation with various diamines, and the products were comprehensively characterized. The results of FTIR, Raman spectra, NMR, and elemental analysis confirmed that the synthesized polyamides had the expected chemical structures. The viscosity‐average molecular weights of the obtained polyamides were in the range of 6.0 × 10³–1.4 × 10⁴. The melting points of the nylons, determined by differential scanning calorimetry, changed from 167 to 194°C. Thermogravimetric analysis gave the decomposition temperatures of the obtained nylons at about 460°C, except for nylon 3/20. Furthermore, dynamic mechanical analysis (DMA) was applied to nylons 11/20, 9/20, 7/20, and 5/20. The glass‐transition temperatures, measured by DMA, ranged from 29 to 52°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2066–2071, 2004     

Modification of a two‐component system by introducing an epoxy‐reactive diluent: Construction of a time–temperature–transformation (TTT) diagram

Curing reactions of a three‐component system consisting of an epoxy resin diglycidyl ether of bisphenol A (DGEBA n = 0), 1,2‐diaminecyclohexane as curing agent, and vinylcyclohexene dioxide as a reactive diluent were studied to calculate a time–temperature–transformation isothermal cure diagram for this system. Differential scanning calorimetry (DSC) was used to calculate the vitrification times. DSC data show a one‐to‐one relationship between T_g and fractional conversion α, independent of cure temperature. As a consequence, T_g can be used as a measure of conversion. The activation energy for the polymerization overall reaction was calculated from the gel times obtained using the solubility test (58.5 ± 1.3 kJ/mol). This value was similar to the results obtained for other similar epoxy systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1190–1198, 2004     

Comparison of oxidation induction time measurements with values derived from oxidation induction temperature measurements for EPDM and XLPE polymers

Oxidative stability and retained operational utility of polymers used as insulation for electrical cables, such as ethylene propylene diene monomer (EPDM) and crosslinked polyethylene (XLPE), may be assessed by oxidation induction time (OIT) analysis. OIT is measured directly with a differential scanning calorimeter. Using a simplified kinetics model, Gimzewski demonstrated that it is possible to calculate the OIT from measured values of oxidation induction temperature and the activation energy for petroleum lubricants. In the present research, directly measured OITs are compared with OITs calculated from measured oxidation induction temperatures and activation energies for EPDM and XLPE cable insulation. Good agreement between the two methods was demonstrated for these materials.     

Mechanical and electrical properties of poly(vinylidene fluoride–tetrafluoroethylene–propylene)/Super‐S carbon black swelled in liquid solvent as an electrode binder for lithium‐ion batteries

The mechanical and electrical properties of poly(vinylidene fluoride–tetrafluoroethylene–propylene) (PVDF–TFE–P) and carbon black–filled PVDF–TFE–P composites were investigated. The carbon black was used for its electrolyte absorption properties in addition to boosting the conductivity. This elastomeric binder system may have application to tin‐ or silicon‐based electrode materials for Li‐ion batteries, which undergo huge volumetric changes during charge/discharge cycling. The mechanical and electrical properties were measured while film samples were immersed in a liquid solvent (ethylene carbonate : diethyl carbonate 1 : 2) commonly used in the battery electrolyte. Uncrosslinked PVDF–TFE–P uptakes about 140% solvent by mass and swells significantly. The amount of solvent absorbed can be reduced and the mechanical properties improved by crosslinking the polymer. Two crosslinking recipes, based on bisphenol and triethylenetetramine (TETA), were investigated carefully. Compared to the bisphenol‐based crosslinking recipe, the proposed TETA‐based crosslinking recipe gave films with a higher degree of crosslinking and better mechanical properties. The TETA‐crosslinked composites had very good mechanical and electrical reversibility even during cyclic deformation to 100% strain. The cycling results of amorphous Si_0.64Sn_0.36 electrodes show that the capacity retention of the electrodes can be significantly improved by using the proposed elastomeric binder. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2958–2965, 2004     

Influence of Ethylene Ionomers on the Electrical Properties of Crosslinked Polyethylene

Summary: Water treeing is a deterioration mechanism observed in the polymeric insulation of extruded cables, which can affect the service life of the transmission and distribution XLPE power cables. To improve the water‐tree resistance of XLPE, it was blended with sodium‐neutralized EAA‐Na ionomers which were formed by neutralization of EAA with NaOH. A series of XLPE/EAA‐Na ionomer blends were investigated for their electrical properties, such as water treeing, electrical breakdown strength, dielectric constant, and dissipation factor. The results strongly suggest that EAA‐Na ionomers can improve the water‐tree resistance of XLPE, and the XLPE/EAA‐Na blends retain excellent dielectric properties. Characterization of XLPE/EAA‐Na blends by using FTIR indicates that the neutralization reaction is effectively achieved. In addition, it can be found that XLPE/EAA‐Na blends are partially compatible from observing morphology observations made by SEM and, therefore, EAA‐Na ionomers can be well dispersed in the matrix.

Water tree length of the XLPE/EAA‐0.5Na blends.     

Reaction kinetics,thermal properties of tetramethyl biphenyl epoxy resin cured with aromatic diamine

Epoxy resins, 4, 4′‐diglycidyl (3, 3′, 5, 5′‐tetramethylbiphenyl) epoxy resin (TMBP) containing rigid rod structure as a class of high performance polymers has been researched. The investigation of cure kinetics of TMBP and diglycidyl ether of bisphenol‐A epoxy resin (DGEBA) cured with p‐phenylenediamine (PDA) was performed by differential scanning calorimeter using an isoconversional method with dynamic conditions. The effect of the molar ratios of TMBP to PDA on the cure reaction kinetics was studied. The results showed that the curing of epoxy resins contains different stages. The activation energy was dependent of the degree of conversion. At the early of curing stages, the activation energy showed the activation energy took as maximum value. The effects of rigid rod groups and molar ratios of TMBP to PDA for the thermal properties were investigated by the DSC, DMA and TGA. The cured 2/1 TMBP/PDA system with rigid rod groups and high crosslink density had shown highest T_g and thermal degradation temperature. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Modeling the curing kinetics for a modified bismaleimide resin using isothermal DSC

The kinetics of curing for a modified bismaleimide (BMI) resin was investigated to ascertain a suitable cure model for the material. The resin system used in this study was composed of 4,4′‐bismaleimidodiphenylmethane (BMIM) and 0,0′‐diallyl bisphenol A (DABPA, DABA). The BMIM was the base monomer and the DABPA was the modified agent. A series of isothermal DSC runs provided information about the kinetics of cure in the temperature range 170–220°C. Regardless of the different temperatures, the shape of the conversion curves was similar, and this modified BMI resin system underwent an nth‐order cure reaction. Kinetic parameters of this BMI resin system, including the reaction model, activation energy, and frequency factor, were calculated. From the experimental data, it was found that the cure kinetics of this resin system can be characterized by a first‐order kinetic model. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3338–3342, 2004     

Effect of styrene–ethylene–butadiene–styrene and its synergetic effect with ethylene vinyl acetate on the mechanical,thermal, dielectric,and water‐treeing behaviors of crosslinked polyethylene

In this study, we investigated the effect of an aromatic polymer, styrene–ethylene–butadiene–styrene (SEBS), on the water‐tree resistance of crosslinked polyethylene (XLPE), and the synergetic effect of SEBS and ethylene vinyl acetate (EVA) was also investigated. The XLPE/SEBS and XLPE/SEBS/EVA samples were characterized by means of differential scanning calorimetry, scanning electron microscopy, mechanical measurements, and an accelerated water‐treeing experiment, and the obtained results clearly show the relevant influence of SEBS and EVA, and as expected, the addition of SEBS and EVA was found to synergistically influence the water‐tree resistance of XLPE more positively in comparison with that without the addition of EVA. In addition, it also indicated that the blends possessed excellent dielectric behaviors, such as the dielectric constant and dissipation factor. The crystallization of the blends decreased with increasing SEBS content and addition of EVA. However, the melting temperature of the blends increased with the addition of SEBS and EVA, but the melting temperature of the blends decreased with increasing SEBS content. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of silane‐grafting on water tree resistance of XLPE cable insulation

Water treeing is one of the main deterioration phenomena observed in the polymeric insulation of extruded crosslinked polyethylene (XLPE) cables, which can affect the service life of power cables. In this work, we investigated the effect of grafting of a silane (vinyl trimethoxysilane, VTMS) on the resistance of XLPE to water treeing. A series of water‐treeing tests, the mechanical and dielectric measurements indicated that the silane‐grafting could significantly improve the water tree resistance of the conventional XLPE cable insulation with little influences on its dielectric properties, e.g., the dielectric breakdown strength, dielectric constant and loss tangent, and its mechanical performance. It was found that there exists an optimum value of VTMS concentration (about 0.6 phr) corresponding to the minimum water tree length. The water tree resistance mechanism of silane‐grafted XLPE was proposed on the basis of the process of silane hydrolysis and crosslinking. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Morphological and structural development of recycled crosslinked polyethylene during solid‐state mechanochemical milling

Waste crosslinked polyethylene (XLPE) was partially decrosslinked to obtain a thermoplastic recycled material through solid‐state mechanochemical milling with pan‐mill equipment at ambient temperature. The gel fraction and size exclusion chromatography measurements showed that the gel content of XLPE decreased remarkably with increasing cycles of mechanochemical milling, whereas the molecular weight of the sol fraction was not significantly reduced; this indicated the realization of partial decrosslinking during mechanochemical milling. Differential scanning calorimetry and X‐ray diffraction analysis showed that the melting temperature of decrosslinked polyethylene increased by 3.5°C because the bigger crystallites size resulting from the higher mobility of the chain segment. The improved thermoplastic characteristic of XLPE after mechanochemical milling were confirmed by scanning electron microscopy and rheological measurement. The mechanical properties of recycled XLPE also achieved significant improvement after mechanochemical milling. Solid‐state mechanochemical milling is a cost‐effective, reliable, and environmentally friendly method for recycling XLPE at ambient temperature without any additional materials or chemicals. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal stability of modified end‐capped poly(lactic acid)

The influence of functional end groups on the thermal stability of poly(lactic acid) (PLA) in nitrogen‐ and oxygen‐enriched atmospheres has been investigated in this article using differential scanning calorimetry, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Functional end groups of PLA were modified by succinic anhydride and l ‐cysteine by the addition–elimination reaction. PLA was synthesized by azeotropic condensation of l ‐lactic acid in xylene and characterized by nuclear magnetic resonance. The values of the activation energies determined by TGA in nitrogen and oxygen atmospheres revealed that the character of functional end groups has remarkable influence on the thermal stability of PLA. Moreover, DMA confirmed the strong influence of functional end groups of PLA on polymer chains motion. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41105.     

Influence of the synthesis conditions on the curing behavior of phenol–urea–formaldehyde resol resins

The curing behavior of synthesized phenol–urea–formaldehyde (PUF) resol resins with various formaldehyde/urea/phenol ratios was studied with differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The results indicated that the synthesis parameters, including the urea content, formaldehyde/phenol ratio, and pH value, had a combined effect on the curing behavior. The pH value played an important role in affecting the shape of the DSC curing curves, the activation energy, and the reaction rate constant. Depending on the pH value, one or two peaks could appear in the DSC curve. The activation energy was lower when pH was below 11. The reaction rate constant increased with an increase in the pH value at both low and high temperatures. The urea content and formaldehyde/phenol ratio had no significant influence on the activation energy and rate constant. DMA showed that both the gel point and tan δ peak temperature (T_tanδ) had the lowest values in the mid‐pH range for the PUF resins. A different trend was observed for the phenol–formaldehyde resin without the urea component. Instead, the gel point and T_tanδ decreased monotonically with an increase in the pH value. For the PUF resins, a high urea content or a low formaldehyde/phenol ratio resulted in a high gel point. The effect of the urea content on T_tanδ was bigger than that on the gel point because of the reversible reaction associated with the urea component. Too much formaldehyde could lead to more reversible reactions and a higher T_tanδ value. The effects of the synthesis conditions on the rigidity of the cured network were complex for the PUF resins. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1368–1375, 2005     

Compatibilizing Effect of SEBS for Electrical Properties of LDPE/PS Blends

Summary: In the previous study, we observed compatibilizing effects of low density polyethylene (LDPE)/polystyrene (PS) with polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene (SEBS), a triblock copolymer. Blends consisting of 70 wt.‐% LDPE and 30 wt.‐% PS were prepared with a SEBS concentration of up to 10 wt.‐%. This study examined the electrical properties such as the electrical breakdown, water tree length, permittivity and tan δ in the blends. The possibility of using these blends as insulating material substitutes for LDPE was investigated. The electrical breakdown strength reached a maximum of 66.67 kV/mm, which is superior to 50.27 kV/mm of the LDPE used as electrical insulators for cables. In addition, the water tree length decreased with increasing SEBS concentration. The water tree lengths of the blends containing SEBS were shorter than that of the LDPE. The permittivity of the blends was 2.28–2.48 F/m, and decreased with increasing SEBS concentration with the exception of S‐0. Tan δ of the blends increased smoothly with increasing SEBS content.

Breakdown strength , water tree length, permittivity and tan δ of the LDPE/PS/SEBS blends and raw materials.     

Use of isoconversional methods to analyze the cure kinetics of isocyanate‐ended quasi‐prepolymers with water

The curing of an isocyanate (NCO)‐ended quasi‐prepolymer by reaction with water in stoichiometric ratio was monitored by using differential scanning calorimetry both under isothermal and non‐isothermal conditions. A quasi‐prepolymer containing 16 wt % free NCO prepared by reacting trifunctional polypropylene glycol (PPG) with polymeric MDI was used in this study. The variation of the effective activation energy with the extent of the curing reaction was calculated by means of model‐free differential and integral isoconversional methods. Both isoconversional methods provided similar results showingthat the activation energy depends on the extent of thereaction of the quasi‐prepolymer with water. The dependence of the effective activation energy proved to be different under isothermal and non‐isothermal curing conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1049–1057, 2007     

Enhancement of Service Life and Electrical Insulation Properties of Polymeric Cables With the Optimum Content of Aromatic Voltage Stabilizer

This article presents the possibility of extending the service life of XLPE insulation based on high voltage cables by blending the optimum concentration of the aromatic voltage stabilizer. The insulation performance of XLPE is analyzed by adding the 0.5, 1, and 3 wt% of 3-aminobenzoic acid voltage stabilizer. The investigated insulation properties include the DC step-by-step breakdown to estimate the life exponent, space charge, DC conductivity, surface potential decay, dielectric loss, and dielectric constant measurements. The results illustrate that the 1 wt% voltage stabilizer addition increases the life exponent from 10 up to 15, which is highly suitable for the high voltage cables. Moreover, it exhibits the negligible space charge accumulation and the least electrical field distortion inside the insulation bulk. It also exhibits the lower DC conductivity by one order of magnitude comparing to the pure XLPE. The highest bandgap value of 1 wt% addition further supports its better insulating properties. Furthermore, the dielectric measurements show that the XLPE with 1 wt% voltage stabilizer exhibits the least dielectric constant and dielectric loss. The differential scanning calorimetry and thermogravimetric analysis results show that the thermal properties are significantly improved after the voltage stabilizer addition. POLYM. ENG. SCI., 60:717–731, 2020. © 2020 Society of Plastics Engineers     

The conduction characteristics of electrical trees in XLPE cable insulation

Depending on the morphology of the material and applied voltage frequency, three kinds of electrical trees can exist in cross‐linked polyethylene (XLPE) cable insulation, which are conducting, non‐conducting, and mixed trees with different growth mechanisms. It is suggested that when the needle is inserted into large spherulites, conducting trees will form in those spherulites; when it is inserted among spherulites, non‐conducting trees will appear along the boundaries of spherulites. Frequency will accelerate the growth of non‐conducting trees but have little influence on the initiation and growth processes of conducting trees. If the initiation process of non‐conducting trees is too difficult, they will grow into mixed trees. Finally, it is concluded that the space charge limited tiny breakdown around the tips of electrical trees is responsible for the propagation process of conducting trees; on the other hand, fast expansion occurs due to local high temperature and pressure along the boundaries, partial discharge in electrical tree paths and charge recombination, etc., which are the main reason for the growth of non‐conducting trees. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study of the miscibility and crystallization behavior of poly(ethylene oxide)/poly(vinyl alcohol) blends

The miscibility and crystallization behavior of poly(ethylene oxide)/poly(vinyl alcohol) (PEO/PVA) blends were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and polarizing optical microscopy. Because the glass‐transition temperature of PVA was near the melting point of PEO crystalline, an uncommon DSC procedure was used to determine the glass‐transition temperature of the PVA‐rich phase. From the DSC and DMA results, two glass‐transition temperatures, which corresponded to the PEO‐rich phase and the PVA‐rich phase, were observed. It was an important criterion to indicate that a blend was immiscible. It was also found that the preparation method of samples influenced the morphology and crystallization behaviors of PEO/PVA blends. The domain size of the disperse phase (PVA‐rich) for the solution‐cast blends was much larger than that for the coprecipitated blends. The crystallinity, spherulitic morphology, and isothermal crystallization behavior of PEO in the solution‐cast blends were similar to those of the neat PEO. On the contrary, these properties in the coprecipitated blends were different from those of the neat PEO. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1562–1568, 2004     

Synthesis and properties of novel aromatic poly(ester–amide)s derived from 1,5‐bis(3‐aminobenzoyloxy)naphthalene and aromatic dicarboxylic acids

A new naphthalene‐ring‐containing bis(ester–amine), 1,5‐bis(3‐aminobenzoyloxy)naphthalene, was prepared from the condensation of 1,5‐dihydroxynaphthalene with 3‐nitrobenzoyl chloride followed by catalytic hydrogenation. A series of novel naphthalene‐containing poly(ester–amide)s was synthesized by direct phosphorylation polyamidation from this bis(ester–amine) with various aromatic dicarboxylic acids. The polymers were produced in high yields and had moderate inherent viscosities of 0.47–0.81 dL g^?1. The poly(ester–amide) derived from terephthalic acid was semicrystalline and showed less solubility. Other polymers derived from less rigid and symmetrical diacids were amorphous and readily soluble in most polar organic solvents and could be solution‐cast into transparent, flexible and tough films with good mechanical properties. The amorphous poly(ester–amide)s displayed well‐defined glass transition temperatures of between 179 and 225 °C from differential scanning calorimetry and softening temperatures of between 178 and 211 °C from thermomechanical analysis. These poly(ester–amide)s did not show significant decomposition below 400 °C in nitrogen or air. Copyright © 2004 Society of Chemical Industry     

Curing behavior of epoxy resin/tung oil anhydride exfoliated nanocomposite by differential scanning calorimetry

The nanocomposite of epoxy resin/tung oil anhydride/organic montmorillonite was prepared by casting and curing. The distance of the clay gallery rose and the exfoliated nanocomposite was formed. The exfoliation behaviors of the nanocomposite had been investigated by X‐ray diffraction (XRD). The curing mechanism and kinetics of epoxy resin with the different amounts of organic montmorillonite were studied using isothermal and dynamic methods by differential scanning calorimetry (DSC). Some parameters, the activation energy and reaction orders, were calculated by the modified Avrami equation in analysis of the isothermal experiment. The total curing mechanism and kinetics of curing reaction were also analyzed by the Flynn–Wall–Ozawa method. It was noted that the instantaneous activity energy during the curing process could be obtained by the Flynn–Wall–Ozawa method and the trend of the results was in agreement with those obtained from the modified Avrami equation. These results show that the activity energy decreases with the addition of organic montmorillonite. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3822–3829, 2004