Hot Set Test Research Articles

Improving the DC Dielectric Properties of XLPE with Appropriate Content of Dicumyl Peroxide for HVDC Cables Insulation

In this research, crosslinked polyethylene (XLPE) is developed with selective content of dicumyl peroxide (DCP), and the influence of microstructural properties and chemical composition on the mechanical and direct current (DC) dielectric properties are investigated. The measurements for the microstructural analysis are taken by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), gel content test and Fourier transform infrared (FTIR). The mechanical properties of XLPE are evaluated by hot-set test. The results of microstructural and chemical composition show that the increase in DCP content increases the crosslinking degree from 74.3% to 81.6%, reduces the crystallinity/lamella thickness from 36.8% to 35.5%/7.6–7.1 nm, reduces the average molecular weight between two crosslinks by 0.01 kg/mol and reduces the oxidation level/carbonyl index. The increase in DCP in XLPE samples decreases the permanent elongation from 2.2% to 0% and elongation rate from 300% to 80% of the cable insulation. The rise in DCP content increases the crosslinking degree due to which the DC resistivity and activation energy is increased. The DC breakdown strength at 30–90 °C is increased due to the increase in crosslinking degree and reduction in carbonyl index/oxidation level. The space charge accumulation is measured at 30 °C under 20–60 kV/mm, resulting in less homo-charges and hetero-charges with the increase in DCP. It is proven that the role of appropriate DCP content is vital in increasing the DC dielectric performance, internal material characteristics and mechanical performance of XLPE.

Temperature Stability of DC Conductivity and Breakdown of Crosslinked LLDPE

In this paper, a way to improve the temperature stability of DC conductivity and breakdown characteristics of polyethylene (PE) is proposed using a crosslinked linear low density polyethylene (LLDPE). The ratio of DC conductivity, as well as breakdown strength values under 90 to 30°C is used to determine the temperature stability of DC properties. The closer it is to 1, the better the performance of temperature stability. The results show that when using crosslinked-LLDPE material, the ratio of DC conductivity under 90 to 30°C is 10.5, while it is 461.6 for crosslinked-LDPE samples with the same DCP content. And the ratio of DC breakdown strength is 0.97 for crosslinked-LLDPE, while it is 0.32 for crosslinked-LDPE. The gel permeation chromatography (GPC) method, hot-set test, differential scanning calorimetry (DSC) analysis and scanning electron microscopy (SEM) images show that the fine arrangement and smaller molecular weight between crosslinks of molecular and morphology structure that LLDPE owns contribute to the improvement in comparison with LDPE. The findings may contribute a solution to the development of HVDC power cable insulation materials.

Examining impact of vapor-induced crosslinking duration on dynamic mechanical and static mechanical characteristics of silane-water crosslinked polyethylene compound

Silane-crosslinked polyethylene (Si-XLPE) compounds are widely used cable insulation materials, cured by water as the crosslinking inducer. Herein, an attempt was made to evaluate the alterations of dynamic mechanical and static mechanical properties of Si-XLPE by increasing the water vapor-triggered crosslinking duration. The criterion for determining the progress of crosslinking was based on an industrially-used method (hot set test), and results indicated 16 h of vapor exposure as an appropriate duration for approaching maximum attainable crosslinking extent. Progress in crosslinking during this period was confirmed by FTIR spectroscopy. DMA was employed to assess the variations of dynamic mechanical behavior. Extending the crosslinking duration affected the storage modulus noticeably, and decreased it due to adverse effect of crosslinking on crystallinity. DSC confirmed the diminishment of crystallinity owing to the extended crosslinking time. Furthermore, prolonged vapor exposure period impacted β and γ transitions due to the influence of formed crosslinks on the mobility of chains. Tensile testing was carried out to ascertain the static mechanical characteristics of crosslinked samples. Findings demonstrated that tensile strength at yield increased below 5%, and tensile stress at break grew around 17%. Besides, elongation and Young's modulus experienced nonmonotonic changes due to the lengthened crosslinking period.

Determination of WUBHS speed range for electron beam irradiation of wire and cable

The electron beam machine was installed in 1991 at Nuclear Malaysia Agency. There are about one million meters of wire and cable irradiated in the facility every year. Electron beam irradiation introduces to crosslink the polymer material for high-performance wire and cable for the automobile industry. ALURTRON is facing few challenges while of irradiating wire and cable to determine the speed and to comply with the product quality (QC) test. The uncertainty of Wire Under Beam Handling System (WUBHS) speeds while irradiating wire and cable due to different situations. In this study, Polyethylene (PE) and Polyvinylchloride (PVC) wire and cable irradiated with electron beam irradiation at suitable speed based on the material, size and calculation etc. The sample analyse with hot set and gel content test. The speed decided at range 220-232, 180-196 and 180-194 m/min for 6.4 mm tube, 9.5 mm tube and PVC wire respectively.

Effect of electron beam irradiation on the properties of EVA/EPDM blends

Effect of electron beam (EB) irradiation on the properties of ethylene vinyl acetate (EVA)/ethylene–propylene–diene monomer (EPDM) (50/50) blends was studied. The blends were firstly melt-compounded at 130°C followed with being irradiated using 4.0 MeV EB energy at doses ranging from 0 kGy to 200 kGy. It is found that the dosage of irradiation plays a key role in the properties of the blends. With the increasing dosage of irradiation, tensile strength and thermal stability were enhanced. The irradiation exerts a cross-linking effect on the blends, and the increase in density is responsible for the enhanced properties. Dynamic mechanical and thermal analyses and morphology indicate that irradiation does not play any negative role in the compatibility between EVA and EPDM. Hot set test reveals that irradiation could improve the heat deformation property of blends. Thus, it is reasonable and interesting to modify EVA/EPDM blends using EB irradiation to further increase its properties.

A new approach for silane curing polyolefin elastomer/linear low density polyethylene blends by Monosil and Sioplas processes

Silane cross-linking of metallocene-based polyethylene-octene elastomer (POE)/linear low density polyethylene (LLDPE) blend was carried out using the single-step Monosil process and two-step Sioplas process in an industrial scale twin-screw extruder. The study revealed that benzoyl peroxide (BPO) is a better initiator than dicumyl peroxide (DCP) for grafting reaction of vinyl trimethoxysilane (VTMS). The optimum values of compression set, gel content and tear strength which were, respectively, found to be 40.4%, 79% and 22.6% obtained at 0.2 w% of BPO. Addition of 0.3 w% antioxidant cause the curing time decreased from 14 to 16 h to 8 h. Oit of the sample was increased linearly with increasing the antioxidant content up to 0.5 w%. The effect of dibutyltin dilaurate (DBTDL) as catalyst on the melt flow index (MFI) of the silane grafted compounds, with the aim of selecting an appropriate silane grafting process, was investigated. The results showed a MFI= 6.4 g/10 min for the silane grafted compound obtained from the Sioplas process, but, MFI= 1.9 g/10 min which was due to the presence of the catalyst in the Monosil process indicated that this method is not a promising process for silane grafting.HighlightsSilane crosslinking POE/LLDPE blend was carried out using the Monosil and Sioplas processes in a twin-screw extruder.BPO is better initiator for grafting reaction of VTMS than DCP.The curing time required for confirming hot set test was decreased from 14 to 16 h to 8 h by addition of 0.3 wt% antioxidant, Irganox 1010.OIT time increased linearly with increasing the antioxidant concentration.Sioplas process caused lower crosslinking degree as well as minimum pre-crosslinking, which prevented the formation of gell spots and rough surface.

Improvement in volume resistivity and morphology of a blend of polyolefin elastomer with linear low-density polyethylene

A silane moisture-cured polyolefin elastomer/linear low-density polyethylene (LLDPE) blend was prepared through a two-step silane-grafting method (Sioplas Process) in an industrial scale twin-screw extruder. The silane-grafted compound was used to make wire and cable coatings. In this work, the effect of some interactive parameters on quality of the products prepared by the above method has been studied, while so far, there have been less experimental investigations. The volume resistivity of cross-linked compound was changed from 2.96 × 1014 to 7.41 × 1014 Ω cm with increasing LLDPE component by maximum 10 wt%. Surface morphology of the product was corrected with reduction in benzoyl peroxide (BPO) concentration from 0.2 wt% to 0.13 wt%. BPO at this level acted as an initiator in grafting reaction of vinyl trimethoxysilane. The curing condition and specimen preparation method by injection molding and/or extrusion were factors which influenced the hot-set test results at 200 °C. The results of tensile and elongation studies showed a maximum value of 9 MPa and 397% for the tests, after 6 h curing. With increases in curing time at a specified temperature, the gel content of the cross-linked compound was increased and reached its maximum value. The maximum gel content values were found to be approximately 60%, 80%, and 82% at temperatures of 25, 60, and 85 °C, respectively. The hardness, density, and tear strength of the samples did not vary significantly with the curing temperature.

Temperature Dependence of Mechanical, Electrical Properties and Crystal Structure of Polyethylene Blends for Cable Insulation.

There is a long-standing puzzle concerning whether polyethylene blends are a suitable substitution for cable-insulation-used crosslinking polyethylene (XLPE) especially at elevated temperatures. In this paper, we investigate temperature dependence of mechanical, electrical properties of blends with 70 wt % linear low density polyethylene (LLDPE) and 30 wt % high density polyethylene (HDPE) (abbreviated as 70 L-30 H). Our results show that the dielectric loss of 70 L-30 H is about an order of magnitude lower than XLPE, and the AC breakdown strength is 22% higher than XLPE at 90 °C. Moreover, the dynamic mechanical thermal analysis (DMA) measurement and hot set tests suggest that the blends shows optimal mechanical properties especially at high temperature with considerable temperature stability. Further scanning electron microscope (SEM) observation and X-ray diffraction (XRD) analysis uncover the reason for the excellent high temperature performance and temperature stability, which can be ascribed to the uniform fine-spherulite structure in 70 L-30 H blends with high crystallinity sustaining at high temperature. Therefore, our findings may enable the potential application of the blends as cable insulation material with higher thermal-endurance ability.

Enhancement effect of trimethylopropane trimethacrylate on electron beam irradiated acrylonitrile butadiene styrene (ABS)

This paper reports the effect of electron beam irradiation on physico-mechanical properties of trimethylopropane trimethacrylate (TMPTMA) added acrylonitrile–butadiene–styrene (ABS) blends. The increasing of TMPTMA amount has gradually induced the gel content of all ABS samples. This is because incorporation of TMPTMA promotes formation of crosslinking networks in ABS matrix through releasing of monomer free radicals when irradiated. The results of hot set test also revealed that higher irradiation dosage required ≥ 6 phr TMPTMA to promote higher degree of crosslinking networks. The addition of TMPTMA also gradually improved the tensile strength and elongation at break of all ABS blends due to the existing of crosslinked chains. However, higher electron beam irradiation (≥ 200 kGy) has significantly reduced the tensile strength and elongation at break of all ABS samples due to chain-scissioning effect. The formation of crosslinking networks has induced the extendability of ABS matrix as evidenced in SEM observation. The crystallite size of deflection peak (110) also found to increase with low irradiation dosages.

Influence of Fuzzy Parameters on the Modeling Quality of XLPE Insulation Properties under Thermal Aging

In this work, we have used the fuzzy logic approach to predict mechanical properties (hot set test) of cross-linked polyethylene (XLPE) used as insulation in high voltage cables. The studied property presents non linear variations according to the aging time under high temperatures. So it is very difficult to find a theoretical or experimental model of the properties evolution under thermal aging. For that reason, several factors have been considered such as aging time and applied temperature. The obtained results are very encouraging and pointed out that the fuzzy logic is a powerful tool to predict the insulation proprieties. In other words, the obtained results are in good accordance with the experimental results with an acceptable error margin.

Hot Set Characterization of Electron Beam Irradiated-Copper (II) Oxide Added LDPE Composites under Acidic Aging

In this research study, the effect of aging duration time and electron beam irradiation dosages on the hot set results of copper (II) oxide added LDPE composites have been investigated. The addition of copper (II) oxide particles in LDPE matrix has significantly reduced the formation of crosslinking networks in LDPE matrix by blocking the mobility of free radicals generated by electron beam irradiation. At lower irradiation dosages (< 100 kGy), all the copper (II) oxide added LDPE composites were immediately failed the hot set test when subjected to static load of 20 N/cm2 under high temperature. Besides, the occurrence of copper (II) oxide particles in LDPE matrix also reduced the matrix continuities of copper (II) oxide added LDPE composites and caused the matrix resistance ability of LDPE matrix to be decreased. The increasing of irradiation dosages has significantly delayed the failing time of all LDPE composites when under static load at high temperature. This is because the increasing of electron beam irradiation could further induce the generation of free radicals to form higher degree of crosslinking networks in LDPE matrix. At higher irradiation dosage up to 250 kGy, the pristine LDPE was observed able to withstand the applied static load under high temperature more than 15 minutes. This is due to higher degree of crosslinking networks formed in LDPE matrix could effectively restrict the mobility of LDPE chains under static load and thus delay the failing of sampels. When the aging duration time increased from 4 days to 14 days, the resistance ability of all LDPE has been significantly weakened due to the occurrence of chain scissioning process in LDPE matrix by delaying the failing time of samples.

Electron-Beam Irradiation of Halogen Free Flame Retardant Polymers for Wire and Cable Applications

Effect of addition different polymers and fillers with electron beam irradiation on changes of physical, electrical and flammability properties of low density polyethylene (LDPE) / trimethylol propane trimethylacrylate (TMPTMA) / Irganox/ zinc borate (ZB) have been investigated. Results of measured gel content (GC), tensile strength (TS), elongation at break (EL), hot set (HS) tests, melt index (MFI), dielectric strength (DS), volume resistivity (VR), flammability and limiting oxygen index (LOI) have confirmed positive effects of adding maleic anhydride grafted LDPE (LDPEgMAH), ethylene vinyl acetate (EVA) and CS whereas effect of ATH to blends drastically had negative effects on improvement of physical properties of blends. Meanwhile, presence of TMPTMA and enhancing irradiation could improve properties seriously. Keywords Halogen free; polymers; irradiation; wires and cables

Electron-beam irradiation of low density polyethylene/ethylene vinyl acetate blends

Abstract In this work, the properties of electron-beam irradiated low density polyethylene (LDPE), ethylene vinyl acetate (EVA) and blends were investigated. EVA addition had an enhancement effect on crosslinking of irradiated LDPE/EVA blends. The measured gel content increase of the blends and the improvement of thermal elongation, tensile strength, elongation at break, thermal aging and heat deformation, have confirmed the positive effects of electron-beam irradiation on the blend properties. The crystallinity of the blends decreased with irradiation. The gel content and hot set tests showed that the degree of crosslinking in the amorphous regions was dependent on the dose and blend composition. Increasing the EVA content resulted in tighter network structures. A significant improvement in the tensile strength of the neat EVA samples was obtained upon electron-beam irradiation up to 210 kGy. The irradiated LDPE/EVA blends showed improved tensile strength and elongation at break, when compared to LDPE. The enhanced irradiation crosslinking of the LDPE/EVA blends was proportional to the good compatibility and the increasing degree of the amorphous region’s content of the LDPE/EVA blends. The possible degradation mechanism of LDPE/EVA blends was discussed quantitatively with a novel method step analysis process of irradiated LDPE/EVA blends in the thermal gravimetric analysis (TGA) technique. It was found, with measuring thermal conductivity (k) and specific heat capacity (Cp) of the blends, that the k values of the LDPE samples at a prescribed temperature range decreased with increasing irradiation. An increase in the crystallinity led to an increase in the k values and a decrease in the Cp values of the LDPE samples. Irradiation below 150 kGy decreased the Cp (at 40°C) and k in average values, whereas increasing the EVA made enhanced the Cp and k values of LDPE/EVA blends at each irradiation. The surface resistance and volume resistivity (VR) of the blends reached a maximum at a 170 kGy irradiation and 30 wt% of EVA. Increasing the amount of EVA contents resulted in enhancement of the dielectric loss factor for the irradiated blends.

Mechanical, electrical, and thermal properties of irradiated low-density polyethylene by electron beam

The effect of electron-beam (EB) irradiation on the mechanical, electrical, and thermal properties of low-density polyethylene (LDPE) was studied The LDPE was irradiated by using 3 MeV EB machine at doses ranging from 25 to 250 kGy in air at room temperature and analyzed for mechanical, thermal, and electrical properties. It was revealed by differential scanning calorimetry analysis that the crystallinity of the EB-radiated LDPE decreased slightly as verified by a marginal reduction in the densities, enthalpy, and melting points. Thermogravimetric analysis test showed that the thermal degradation of LDPE improved by increasing irradiation. The results obtained from both gel content and hot set tests, indicating whether the applicable LDPE has been properly cross-linked or not, showed that under the EB irradiation conditions employed, the cross-linking of the LDPE samples occur mainly in the amorphous region, and the cross-linking density at each irradiation dose depends almost on the amorphous portions of the LDPE. A significant improvement in the tensile strength of the neat LDPE samples was obtained upon EB up to 250 kGy with a concomitant decline in elongation at break. The results on the electrical properties revealed that the surface resistance, volume resistivity, and dielectric strength of the LDPE increase with irradiation dose and reaches a maximum at a 250 kGy irradiation dose. No considerable change of breakdown voltage, dielectric constant, and dielectric loss factor were observed with increasing irradiation dose. The enhancement in the heat deformation, hardness, and thermal aging properties of LDPE upon EB irradiation, suggests that irradiated LDPE is more thermally and mechanically stable than virgin LDPE.

Effect of EVA copolymer on properties of different polyethylenes in silane crosslinking process

The effect of molecular structure of polyethylene (PE) [low density PE (LDPE), linear LDPE and high density PE] and silane/peroxide concentration on the grafting level and gel content in silane crosslinking process has been studied. The effect of incorporation of ethylene vinyl acetate (EVA) copolymer on the rate of crosslinking and thermal properties of PEs has been reported. The order of gel content was LDPE>linear LDPE>high density PE. With the incorporation of EVA, the rate of crosslinking increased. The degree of crystallinity did not change with crosslinking significantly. However, the shape of melting and crystallisation peaks changed, and two regions due to gel and sol parts were formed. In EVA/PE blends, two melting points were observed for both crosslinked and uncrosslinked samples. The SEM images showed the droplet matrix morphology with the EVA as the dispersed phase, especially for EVA/LDPE blend. The EVA/PE blends failed in hot set test, while the origin of PEs passed the hot set test successfully.

Mechanical, Thermal and Electrical Properties of Ethylene Vinyl Acetate Irradiated by an Electron-Beam

The effects of electron beam irradiation of (ethylene vinyl acetate) EVA containing 18% vinyl acetate was studied. The EVA sample was then irradiated by using 3 MeV electron beam machine at doses ranging from 120 to 360 kGy in air at room temperature and analyzed for mechanical, thermal and electrical properties. It was revealed by DSC analysis that the crystallinity of the electron-beam radiated EVA decreased slightly as verified by a marginal reduction in the densities and heats of melting. Thermal degradation of EVA occurred through two steps as shown by the thermogravimetric curve with maximum rates of 350 and 450°C, respectively. The results obtained from both gel content and hot set tests showed that under the irradiation conditions employed, the EVA sample cross-linked by the electron beam irradiation, and the degree of cross-linking in the amorphous regions was dependent on the irradiation dose. A significant improvement in the tensile strength of the neat EVA samples was obtained upon electron-beam radiation up to 210 kGy with a concomitant decline in elongation of break. Various electrical properties of EVA such as surface and volume resistance, breakdown voltage and dielectric constant were studied as a function of radiation dose. It was revealed that the surface resistance and volume resistivity of the EVA reaches a maximum at a 190 kGy dose of radiation. No considerable change of breakdown voltage and dielectric constant was observed with increasing irradiation dose. These studies suggest that radiation-cured EVA is more thermally and mechanically stable than pure EVA. Similarly, the results from the electrical properties revealed that surface and volume resistance are higher than pure EVA.

Crosslinking of binary blends of ethylene/vinyl acetate copolymer and low density polyethylene or metallocene polyolefin elastomer as heat-shrinkable materials

The results of investigation of selected properties of peroxide crosslinked binary blends of ethylene/vinyl acetate copolymer and low density polyethylene or metallocene polyolefin elastomer as candidates for production of heat-shrinkable materials were presented. Analytical methods used ¯ i.e. gel content, hot set test and rheometric investigations - as the measures of crosslinking degree, oxidation induction time and tensile properties measurements, before and after accelerated degradation, proved that the tested recipes were good starting points for further technological work. Some aspects of analytical determination of crosslinking degree are discussed.

The investigation of using magnesium hydroxide as a flame retardant in the cable insulation material by cross-linked polyethylene

The use of magnesium hydroxide was investigated as a flame retardant in the cable insulation material that has low density polyethylene cross-linked by silane grafting method. The different insulation samples with low density polyethylene filled magnesium hydroxide were prepared and physical and mechanical properties of these samples were measured such as tensile strength, elongation at break, impact, bending, oxygen index, smoke density, flammability, ageing test, hot set test, ozone resistant, according to standard test methods. The test results were analyzed to determine suitable magnesium hydroxide ratio for the cable insulation material. The magnesium hydroxide ratios were found to give good material properties which will meet insulation standard.

Electron beam crosslinking of poly(ethylene-co-vinyl acetate)/clay nanocomposites

Effect of electron beam irradiation on the thermal and mechanical properties of poly(ethylene-co-vinyl acetate) (EVA)/clay nanocomposites prepared by melt blending method has been investigated. The hot set test results show that elongation at high temperature under static load decreased with the increase of irradiation dose. The tensile modulus increased continuously with increasing dose. While the tensile strength increased up to 100 kGy, it decreased with further increase in dose. The elongation at break decreased continuously with increasing dose. Thermogravimetric analysis showed that thermal stability of the EVA/clay nanocomposites improved with increasing dose. The improvement in the mechanical and thermal properties is attributed to the formation of radiation-induced crosslinking as evidenced by the gel content results.

Effect of peroxide crosslinking on thermal and mechanical properties of poly(ε‐caprolactone)

AbstractPoly(ε‐caprolactone) (PCL), a saturated polyester, derived from ring‐opening polymerization of ε‐caprolactone, was chemically crosslinked with various amounts of benzoyl peroxide (BPO) by a two‐step method by first evenly dispersing the BPO into the PCL matrix and then crosslinking at elevated temperature. The gel fraction increased with an increase in BPO content. The modified Charlesby–Pinner equation was used to calculate the ratio of chain scission and crosslinking. The results showed that both scission and crosslinking occurred, and that crosslinking predominated over scission. The number‐average molecular weight between the crosslinks determined by the rubber elasticity theory using the hot set test showed a decrease with increasing BPO content. The melting temperature and crystallinity decreased with an increase in BPO content, and the crystallization temperature increased after crosslinking. Dynamic mechanical analysis results showed a decrease in the glass transition temperature as a result of chemical crosslinking of PCL. This was explained by the observed reduction in crystallinity and the increase in free volume due to restrictions in chain packing. Moreover, Young's modulus and elongation at break generally decreased with an increase in BPO content, but the tensile strength first increased with BPO content up to 1.0 wt%, reached a maximum, and then decreased. Copyright © 2007 Society of Chemical Industry