Molecular structure and physical properties of E‐beam crosslinked low‐density polyethylene for wire and cable insulation applications

Crosslinking of homemade low‐density polyethylene (LDPE) was performed by electron‐beam (EB) irradiation. The gel content of the EB‐exposed LDPE was determined by the solvent‐extraction method. The degree of crosslinking was also evaluated by a hot set measuring test. The results obtained from both the gel–sol and the hot set methods showed that the degree of crosslinking was dependent on the deposited energy in LDPE samples. Increasing the absorbed dose increased the degree of network formation. The LDPE with higher molecular weight yielded higher efficiency of crosslinking at the same irradiation dose. The effect of irradiation dose on the molecular weight between crosslinks (M_c), glass‐transition temperature, and free volume were calculated. Mechanical test results showed that the tensile strength of the samples increased with increase in the irradiation dose up to 150 kGy and then slightly decreased with further increasing the deposited energy. The elongation at break decreased with increasing the absorbed dose. The results obtained from differential scanning calorimetry exhibited a small reduction in the melting point and the degree of crystallinity of the EB‐exposed LDPE samples compared to those of the untreated samples. The effect of crosslinking on the electrical properties of the irradiated samples was insignificant. The dielectric constant of the treated samples remained nearly constant within the irradiation dose range, although the dissipation factor increased slightly with increasing the absorbed dose. The results obtained from characterizing the EB‐induced crosslinking of homemade polyethylene, including LH0030 and LH0075, showed the higher molecular weight polyethylene (LH0030) as a preferred option for wire and cable insulation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1959–1969, 2002     

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     

Crosslinking of low‐density polyethylene by diisocyanates for superior barrier properties

The chemical modification of low‐density polyethylene (LDPE) resins with hexamethylene diisocyanate and toluene diisocyanate was achieved. The reaction of LDPE with diisocyanate was monitored by Fourier transform infrared spectroscopy, wherein the appearance of new peaks at 3326, 1620, and 1572 cm^?1 corresponding to ? N? H stretching, ? (C?O)? NH₂ stretching, and ? N? H bending in an amide moiety, respectively, was observed. Modified films of excellent clarity and uniform thickness were obtained by the solution casting of crosslinked polyethylene. The oxygen transmission rate (OTR), water vapor transmission rate (WVTR), grease resistance, and thermal properties of the modified films were studied. The results clearly indicate that the OTR was improved by 35% and that grease resistance was improved by 90–125% in the crosslinked LDPE films with little change in their strengths. The heat seal characteristics, however, showed that relatively higher temperatures were needed to achieve efficient sealing in these films. Differential scanning calorimetry showed a decrease in the melting temperature from 104°C for LDPE to 101°C for both of the crosslinked LDPE films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1193–1199, 2005     

The conductivity behavior of multi‐component epoxy,metal particle,carbon black,carbon fibril composites

Following the previous studies of epoxy/silver conductive composites, a detailed investigation of the influence of ethylene glycol on the resulting resistivity of various composites was carried out. Ethylene glycol was found to have a catalytic effect on the curing process of the epoxy resin, verified by differential scanning calorimetry studies. The accelerated curing process diminishes settling of the metal particles and therefore results in better and more uniform conductivities. High temperature curing of the composites was found to have a similar effect on the conductivity. The conductivity behavior of some other composites, such as epoxy/nickel, epoxy/nickel/carbon fibrils, and epoxy/carbon black/carbon fibrils, were also studied. The structure–property relations were better understood through scanning electron microscopy observations. Silver and nickel particles were found to perform differently in the cured epoxy, showing different percolation concentrations and conductivity levels. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1706–1713, 2002     

Study on electrical conductivity of 2‐vinylpyridine‐methyl methacrylate copolymer in presence of cobalt acetate

2‐Vinyl pyridine (2VP)‐methyl methacrylate (MMA) copolymers with different molar ratios were prepared. Their electrical properties were studied in the presence of Co(CH₃COO)₂. It was found that the electrical properties of the copolymer were changed by altering the molar ratio of 2VP : MMA and by varying the concentration of Co(CH₃COO)₂. The highest electrical conductivity was found when the 2VP : MMA molar ratio was 1 : 1. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2145–2153, 2001     

Blend of high‐density polyethylene and a linear low‐density polyethylene with compositional‐invariant mechanical properties

This article presents the tensile properties and morphological characteristics of binary blends of the high‐density polyethylene (HDPE) and a linear low‐density polyethylene (LLDPE). Two constituents were melt blended in a single‐screw extruder. Injection‐molded specimens were evaluated for their mechanical properties by employing a Universal tensile tester and the morphological characteristics evaluated by using a differential scanning calorimeter and X‐ray diffractometer. It is interesting to observe that the mechanical properties remained invariant in the 10–90% LLDPE content. More specifically, the yield and breaking stresses of these blends are around 80% of the corresponding values of HDPE. The yield elongation and elongation‐at‐break are around 65% to corresponding values of HDPE and the modulus is 50% away. Furthermore, the melting endotherms and the crystallization exotherms of these blends are singlet in nature. They cluster around the corresponding thermal traces of HDPE. This singlet characteristic in thermal traces entails cocrystallization between these two constituting components. The clustering of thermal traces of blends near HDPE meant HDPE‐type of crystallites were formed. Being nearly similar crystallites of blends to that of HDPE indicates nearness in mechanical properties are observed. The X‐ray diffraction data also corroborate these observations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2604–2608, 2002     

Phase dispersion–crosslinking synergism in binary blends of poly(vinyl chloride) with low‐density polyethylene: Entrapping phenomenon in PVC/LDPE/DCP blend

The co‐crosslinked products and the entrapping phenomenon that may exist in a poly(vinyl chloride)/low density polyethylene/dicumyl peroxide (PVC/LDPE/DCP) blend were investigated. The results of selective extraction show that unextracted PVC was due to not being co‐crosslinked with LDPE but being entrapped by the networks formed by the LDPE phase. SBR, as a solid‐phase dispersant, can promote the perfection of networks of the LDPE phase when it is added to the PVC/LDPE blends together with DCP, which leads to more PVC unextracted and improvement of the mechanical properties of PVC/LDPE blends. Meanwhile, the improvement of the tensile properties is dependent mainly on the properties of the LDPE networks. Finally, the mechanism of phase dispersion–crosslinking synergism is presented. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1296–1303, 2003     

Use of zinc‐neutralized ethylene/methacrylic acid copolymer ionomers as blend compatibilizers for nylon 6 and low‐density polyethylene

The effect of the composition on the morphologies and properties of uncompatibilized and compatibilized blends of nylon 6 and low‐density polyethylene were studied over a wide range of weight fractions. The uncompatibilized blends had substantially reduced mechanical properties after mixing, and this was almost certainly due to poor interfacial adhesion between the two polymers. The addition of a zinc‐neutralized poly(ethylene‐co‐methacrylic acid) ionomer (Surlyn® 9020) as a compatibilizer improved the mechanical properties in comparison with those of the material blended without the compatibilizer. The clearest evidence of this improvement came from dynamic mechanical studies; for selected blends with high polyethylene contents, the drop in the modulus corresponding to the transition of a solid to a melt occurred at higher temperatures with the added compatibilizer. This improvement in the properties was accompanied by a reduction in the dispersed‐phase size due to the interaction between the ionic part of the ionomer and the amide groups of nylon 6, especially when nylon 6 was the dispersed phase of the blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 620–629, 2003     

Combining Designer Cells and Click Chemistry for a One‐Pot Four‐Step Preparation of Enantiopure β‐Hydroxytriazoles

The multistep catalytic process using designer cells, either added as freshly prepared suspensions or as stable lyophilized powder, and click reaction can be performed in one pot. The sequence of four reactions allows the production of both enantiomers of β‐hydroxytriazoles with high enantiomeric excess.     

Mechanical and thermal properties of blends of low‐density polyethylene and ethylene vinyl acetate crosslinked by both dicumyl peroxide and ionizing radiation for wire and cable applications

Formulations of chemically crosslinked and radiation‐crosslinked low‐density polyethylene (LDPE) containing an intumescent flame retardant such as ammonium polyphosphate were prepared. The influence of blending LDPE with a poly(ethylene vinyl acetate) copolymer (EVA) and the effects of various coadditives, including polyethylene grafted with maleic anhydride (PEgMA), vinyl silane with boric acid, and talc, on the mechanical and thermal properties were investigated. Chemical crosslinking by dicumyl peroxide and crosslinking by ionizing radiation from an electron‐beam accelerator were both used and compared. Improved mechanical properties were observed by the partial replacement of LDPE with EVA. Similar mechanical or thermal properties were observed with coadditives such as PEgMA and vinyl silane with boric acid. The addition of a small amount of talc improved the tensile strength of the formulations. All crosslinked formulations showed good thermal stability on the basis of the retention of mechanical properties after thermal aging for 168 h at 135°C and a hot‐set test. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Study of using aluminum hypophosphite as a flame retardant for low‐density polyethylene

Aluminum hypophosphite (AHP) was first used to improve the flame retardance of low‐density polyethylene (LDPE). The flame‐retardant properties of LDPE composites were investigated by the limiting oxygen index, vertical burning test (UL‐94), microscale combustion calorimetry, and cone calorimeter tests. The results showed that the incorporation of AHP could improve the flame retardancy of LDPE dramatically, the limiting oxygen index of LDPE containing 50 phr AHP reached 27.5%, and the UL‐94 could pass V‐0 rating. The cone calorimeter test results indicated that PP/AHP composite exhibited superior performance, and the heat release rate and the total heat release of composites were significantly reduced. In addition, the strength of the char was improved with the load of AHP increased. The structure of the char was researched by Fourier transform infrared spectrometry (FTIR) and scanning electron microscope‐energy dispersive spectrometer, and the results revealed that AHP promoted the formation of compact char layer. The TG‐FTIR analyses proved that AHP could react with LDPE to reduce the production of olefin in gas phase. Moreover, the structure of P–O–C was found, and the effective mechanism of AHP in LDPE composites was also hypothesized in this work.     

Evaluation of the shrinking‐core model for examining the kinetics of film formation in a reactive latex blend

We prepared reactive latex blends from two copolymer latices comprised of n‐butyl methacrylate (n‐BMA) with acetoacetoxyethyl methacrylate and n‐BMA/dimethylaminoethyl methacrylate to study the kinetics of film formation. We generated thin films by blending equal weights of the two latices. The films were then cured at temperatures ranging from 50 to 90°C. The extent of the crosslinking reaction was calculated from the crosslink density, which was determined from swelling measurements of the films in toluene. The shrinking‐core model, a diffusion/reaction model, which was originally derived for combustion reactions of coal particles, was adopted to calculate the diffusion coefficient (D_e) and reaction rate constants from the extent of the reaction with time data. This model system exhibited a diffusion‐controlled regime above 70°C and a reaction‐controlled regime at temperatures below 70°C. In the reaction‐controlled regime, the shrinking‐core model predicted D_e for the system, which was in agreement with literature values for n‐BMA. In the diffusion‐controlled regime, the model predicted a lower apparent value for D_e but with an activation energy that was close to that obtained for n‐BMA. The model was also used to examine the kinetics of the crosslinking reaction. The kinetic rate constants for the crosslinking reaction were also determined. The activation energy for the crosslinking reaction was 18.8 kcal/mol, which compared reasonably with the activation energy of 22.8 kcal/mol determined for the reaction between the functional monomers as small molecules. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3659–3665, 2006     

Synthesis of alkyne‐terminated xanthate RAFT agents and their uses for the controlled radical polymerization of N‐vinylpyrrolidone and the synthesis of its block copolymer using click chemistry

Two new alkyne‐terminated xanthate reversible addition‐fragmentation chain‐transfer (RAFT) agents: (S)‐2‐(Propynyl propionate)‐(O‐ethyl xanthate) (X₃) and (S)‐2‐(Propynyl isobutyrate)‐(O‐ethyl xanthate) (X₄) were synthesized and characterized and used for the controlled radical polymerization of N‐vinylpyrrolidone (NVP). X₃ showed better chain transfer ability in the polymerization at 60°C. Molecular weight of the resulted polymer increased linearly with the increase in monomer loading. Kinetics study with X₃ showed the pseudo‐first order kinetics up to 67% monomer conversion. Molecular weight (M_n) of the resulting polymer increased linearly with the increase in the monomer conversion up to around 67%. With the increase in the monomer conversion, polydispersity of the corresponding poly(NVP)s initially decreased from 1.34 to 1.32 and then increased gradually to 1.58. Chain‐end analysis of the resulting polymer by ¹H‐NMR and FTIR showed clearly that polymerization started with radical forming out of xanthate RAFT agent. Living nature of the polymerization was also confirmed from the successful homo‐chain extension experiment and the hetero‐chain extension experiment involving synthesis of poly(NVP)‐b‐polystyrene amphiphilic diblock copolymer. Formed alkyne‐terminated poly(NVP) also allowed easy conjugation to azide‐terminated polystyrene by click chemistry to prepare well‐defined poly(NVP)‐b‐polystyrene block copolymers. Resulting polymers were characterized by GPC, ¹H‐NMR, FTIR, and thermal study. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Investigation of charge transport properties in conducting copolymers of aniline with 3‐aminobenzenesulfonic acid for their applications as antistatic encapsulation materials blended with low‐density polyethylene

The electrostatic charge dissipative (ESD) properties of conducting self‐doped and PTSA-doped copolymers of aniline (AA), o‐methoxyaniline (methoxy AA) and o‐ethoxyaniline (ethoxy AA) with 3‐aminobenzenesulfonic acid (3‐ABSA) blended with low‐density polyethylene (LDPE) were investigated in the presence of external dopant p‐toluenesulfonic acid (PTSA). Blending of copolymers with LDPE was carried out in a twin‐screw extruder by melt blending by loading 1.0 and 2.0 wt% of conducting copolymer in the LDPE matrix. The conductivity of the blown polymers blended with LDPE was in the range 10^?12–10^?6 S cm^?1, showing their potential use as antistatic materials for the encapsulation of electronic equipment. The DC conductivity of all self‐doped homopolymers and PTSA‐doped copolymers was measured in the range 100–373 K. The room temperature conductivity (S cm^?1) of self‐doped copolymers was: poly(3‐ABSA‐co‐AA), 7.73 × 10^?4; poly(3‐ABSA‐co‐methoxy AA), 3.06 × 10^?6; poly(3‐ABSA‐co‐ethoxy AA), 2.99 × 10^?7; and of PTSA‐doped copolymers was: poly(3‐ABSA‐co‐AA), 4.34 × 10^?2; poly(3‐ABSA‐co‐methoxy AA), 9.90 × 10^?5; poly(3‐ABSA‐co‐ethoxy AA), 1.10 × 10^?5. The observed conduction mechanism for all the samples could be explained in terms of Mott's variable range hopping model; however, ESD properties are dependent upon the electrical conductivity. The antistatic decay time is least for the PTSA‐doped poly(3‐ABSA‐co‐AA), which has maximum conductivity among all the samples. © 2013 Society of Chemical Industry     

Research on the related properties of EVM/Al(OH)3/SiO2 composites applied for halogen‐free flame retardant cable insulation and jacket

The halogen‐free flame retardant (HFFR) ethylene‐vinyl acetate copolymer (EVM)/ATH/SiO₂ composites have been prepared by melting compounding method, and the flame retardant, thermal stability, rheological, electrical, and mechanical properties have been investigated by cone calorimeter, LOI, UL‐94, TG, FE‐SEM, rotational rheometer, dielectric breakdown, and ultimate tensile. The results indicate that the flame retardant of EVM vulcanizates is improved and the fire jeopardizing is dramatically reduced due to the addition of ATH. It is necessary that sufficient loading of ATH (≥120 phr) is needed to reach essential level (LOI > 30; V‐0 rating) of flame retardant for HFFR EVM/ATH/SiO₂ composites used as cable in industry. The rheological characteristics show that at all the measurement frequencies, the storage and loss modulus of the composites increase monotonously as the concentration of ATH filler increases, while the complex viscosity and tan delta present reverse trend. And also, it has been found that the HFFR composites at high filler concentrations still keep good mechanical and electrical properties, which is very important for practical applications as cable. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Studies on curing kinetics and total thermal degradation of the modified epoxy copolymer with penta‐coordinated phosphate as a tribranched junction

Curing kinetics and thermal degradation of phosphate‐modified thiodiphenol‐containing epoxy copolymer (P3‐ETP) were conducted. The kinetic study reveals that P3‐ETP resin has better curing properties than unmodified epoxy resin (ETP). The activation energy, in kJ/mol, was 61.5 for P3‐ETP, 89.1 for ETP, 109.9 for Epon 1001, and 124.7 for Epon 828, respectively. The low activation energy of P3‐ETP may indicate that the penta‐coordinated phosphate moieties facilitated the self‐crosslinking process by providing the needed flexibility of the epoxy backbone. Thermal degradation study reveals that the char yield at 850°C was 33.0% for P3‐ETP, 24.8% for P3‐EBPA, and 8.9% for E‐1001 under nitrogen atmosphere. The thermal transformation of the phosphate moiety in P3‐ETP into phosphate salt was confirmed by the presence of P and S elements in the char residue by scanning electronic microscope/energy dispersive X‐ray and by the observation on the delaying emission of the thermal degradative volatiles in the Direct pyrolysis–gas chromatography/mass spectrometric analysis. The flame retardancy of the phosphate moieties with thiodiphenol (TDP) as a whole was found effective, judging from the char yield. This may imply that sulfur atom in TDP also providing additional thermal stability for the P3‐ETP epoxy copolymer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 719–732, 2000     

Development of novel functional conducting elastomer blends containing butyl rubber and low‐density polyethylene for current switching,temperature sensor,and EMI shielding effectiveness applications

A new class of functional conductive butyl rubber (IIR) with different loadings of low‐density polyethylene (PE) was prepared by roll mixing in a milling at a rotor speed of 24 rpm. To understand the filler dispersion and filler/matrix interaction, the network structure of the specimens was examined by evaluating of the crosslinking density, volume fraction of elastomer, interparticle distance among conductive phases, interfacial area per unit volume, torque rheometer, hardness, tensile strength, elongation at break, X‐ray, glass transition temperature, thermal gravemetry, differential scanning calorimetry, degree of crystallinity, and SEM microanalysis. Static conductivity, mobility carrier's concentration, number of charge carriers, and thermoelectric power as a function of PE content were investigated. The temperature dependence of the electrical conductivity as well as the conduction mechanism of IIR–PE blends were also analyzed. The isothermal resistance stability test was examined by displaying the resistance–time curve at certain temperatures. The relationship between current and DC applied voltage was measured for all samples. The self‐electrical heater with PE content of 10 wt % exhibited the highest nonlinearity. The thermal stability was tested by means of temperature–time curve at certain applied power, on and off, for two cycles. Dielectric constant and relative loss factor of the blends are reported. The applicability of the rubber system for switching current, temperature sensor, and electromagnetic shielding effectiveness (EMI) was examined. The experimental results of EMI were compared with theoretical predictions. The results of the present study indicate that these blends are suitable for switching current, temperature‐sensitive sensor, and EMI shielding effectiveness applications with good thermal stability for consumer products. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1125–1138, 2005     

Treatment of carbon cloth anodes for improving power generation in a dual‐chamber microbial fuel cell

BACKGROUND: For a microbial fuel cell (MFC), the anode material plays a crucial role in power output. RESULTS: A dual‐chamber MFC was constructed using carbon cloth (CC) anodes treated by concentrated nitric acid (CC‐A) and heated in a muffle furnace (CC‐H), respectively. The experiment results showed that the stable maximum voltages were 0.42–0.46 V for CC, 0.52–0.58 V for CC‐A and 0.80 V for CC‐H under the condition of a 1000 Ω external resistance, which were much higher than those reported in the literature so far. Moreover, the maximum power density of the CC‐H anode (687 mW m^?2) was larger than for the CC‐A anode (480 mW m^?2) and the CC anode (333 mW m^?2). Electrochemical impedance spectroscopy (EIS) results revealed that the internal resistance was 251 Ω for CC anode, 202 Ω for CC‐A anode and 162 Ω for CC‐H anode. Scanning electron microscopy (SEM) results indicated that the increase of power generation was attributed to the increase of bacteria counts attached to anodes. The power output of the MFC increased along with the increase of the N1s/C1s ratio, which was proved by X‐ray photoelectron spectroscopy (XPS) analysis. CONCLUSIONS: Carbon cloth anodes treated by concentrated nitric acid and high temperature resulted in improved power generation by a microbiol fuel cell. © 2012 Society of Chemical Industry