Silane Cross-linked Polyethylene Research Articles

Cross-linking tendency and photo-oxidation degradation in Silane-grafted LDPE insulation under accelerated cyclic weathering aging

Si-g-LDPE (Silane-grafted LDPE) is the based material of silane-crosslinked polyethylene (Si-XLPE) nominated to be used in renewable energy (photovoltaic) structures for the reason of its good behavior under weathering circumstances. The present study has an attempt to follow up the cross-linking process of Si-g-LDPE under cyclic accelerated weathering aging and to track its photo and thermo-oxidative degradation at both microscopic and macroscopic scales. The realized experiments consist to carry out cyclic accelerated weathering aging of 1152 hours, using QUV chamber, on films of Si-g-LDPE. The process of cross-linking is checked by using Hot-Set-Test measurements and Fourier Transform Infrared (FTIR) spectroscopy. Evolution of mechanical properties and carbonyl index are used as relevant precursors of photo and thermo-oxidation degradation. Additional information on the microstructural changes (crystallinity) and on the optical properties is gained by using X-ray difractometry and UV-visible measurements. Our findings lead to a result that Si-g-LDPE has a big ability to crosslink under cyclic weathering aging. The elastic behavior of the material was enhanced gradually with increasing aging time. The elastic behavior enhancement is a consequence of crosslink network density increase. FTIR results support perfectly the Hot-Set-Test results by the increase of single or multi-siloxane linkages absorption bands. These linkages modify the digital fingerprint of the material. Our results ascertained also that we can relate the elongation at break and tensile strength changes to the changes in the carbonyl index. Both characteristics are related to the photo and thermo-oxidation degradation. Photo-oxidation degradation leads to the decrease of mechanical properties and to the increase of carbonyl index. An abrupt and sharp increase at the beginning of aging in the crystallinity of the material followed by a level-off state was observed. Finally, the optical properties (band gaps, Urbach energy and dielectric constant) are greatly affected by the weathering aging process.

Preparation and properties of silane cross-linked polyethylene nanocomposite foams: The effect of silane and nanoclay type and content

In this study, silane grafted and moisture cross-linked low density polyethylene nanocomposite foams were prepared by melt mixing and batch foaming process and the effects of silane content, nanoclay content, foaming agent concentration and clay type (clay modified with vinyltriethoxysilane (VTES) and amino-propyltriethoxysilane on foaming efficiency and foam properties were investigated. The morphology and the efficiency of silane modification of modified clay were characterized by series of tests, including X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA). The results of Fourier transform infrared and thermogravimetric analysis showed that the silane modifiers were bonded to the surface of nanoclay through both physical and chemical bonds. According to XRD, these modifiers caused characteristic peak of clay to shift to lower angles, and make an increase in basal spacing. Gel content, density, scanning electron microscopy, compression, creep and rheological tests were used to determine the effect of different parameters on properties of cross-linked polyethylene foams. Results indicated that silane content has the significant effect on stress-strain behavior in compression mode. Compression set and creep deformation were affected by cell size and gel content. Furthermore, the rheological properties including complex viscosity, storage and loss modulus of unformed samples increased with the addition of silane and nanoclay content.

Study on mode I, mode II and mixed mode I/II fracture behavior of hot mix asphalt containing silane crosslinkable polyethylene waste

Polymeric bitumen modification is widely employed to improve the performance of asphalt mixtures against some distresses such as fatigue damage, rutting and stripping. Silane-crosslinked polyethylene (Si-XLPE) waste, with better thermal, elasticity and mechanical properties than conventional polyethylene, is usually incinerated or landfilled due to some challenges in recycling such crosslinked wastes. This study investigated the fracture behavior of hot mix asphalt (HMA) containing 0 %, 0.5 %, 1 % and 1.5 % Si-XLPE under pure mode I, pure mode II, and mixed mode I/II at 25 °C, 0 °C and −20 °C through semi-circular bending (SCB) test. Results indicated that with increasing Si-XLPE content up to 1.5 %, fracture toughness of the modified HMA in the mixed mode I/II of loading, which was mainly the most critical loading mode, increased by 26.5 % and 16.9 % at 0 °C and −20 °C SCB testing, respectively. Incorporating Si-XLPE into the base bitumen altered the fracture behavior of HMA at low-temperature testing (-20 °C) from brittle-ductile to ductile, leading to an unpredictable reduction of fracture energy with a temperature decrease from 0 °C to −20 °C. FESEM analysis exhibited a uniform dispersion of 1.5 % Si-XLPE in the bitumen matrix, which was not achieved by adding 0.5 % and 1 % Si-XLPE.

Consequences of Radiothermal Ageing on the Crystalline Morphology of Additive-Free Silane-Crosslinked Polyethylene.

The radiothermal ageing of silane-crosslinked low-density PE (Si-XLPE) films was studied in the air under three different dose rates (8.5, 77.8, and 400 Gy·h−1) at a low temperature close to ambient (47, 47, and 21 °C, respectively). Changes in crystalline morphology were investigated using a multi-technique approach based on differential scanning calorimetry (DSC), wide- (WAXS) and small-angle X-ray scattering (SAXS), and density measurements. In particular, the changes in four structural variables were accurately monitored during radiothermal ageing: crystallinity ratio (), crystalline lamellae thickness (), long period (), and interlamellar spacing (). Concerning the changes in , a perfect agreement was found between DSC and WAXS experiments. Successive sequences of self-nucleation and annealing (SSA) were also performed on aged Si-XLPE samples in the DSC chamber in order to assess the thickness distribution of crystalline lamellae. This method allowed the thermally splitting of the melting domain of Si-XLPE into a series of elementary melting peaks, with each one characterised by a distinct thickness of crystalline lamellae. DSC (used with the SSA method) showed a slight increase in during the oxidation of Si-XLPE, while SAXS confirmed a catastrophic decrease in . The critical value of the interlamellar spacing characterising the ductile/brittle transition of Si-XLPE was found to be of the same order of magnitude as that for linear polyethylene ( nm). This structural end-of-life criterion can now be used for predicting the lifetime of Si-XLPE in a nuclear environment.

A New Kinetic Modeling Approach for Predicting the Lifetime of ATH-Filled Silane Cross-Linked Polyethylene in a Nuclear Environment.

This study focuses on the degradation of a silane cross-linked polyethylene (Si-XLPE) matrix filled with three different contents of aluminum tri-hydrate (ATH): 0, 25, and 50 phr. These three materials were subjected to radiochemical ageing at three different dose rates (8.5, 77.8, and 400 Gy·h−1) in air at low temperatures close to ambient (47, 47, and 21 °C, respectively). Changes due to radio-thermal ageing were investigated according to both a multi-scale and a multi-technique approach. In particular, the changes in the chemical composition, the macromolecular network structure, and the crystallinity of the Si-XLPE matrix were monitored by FTIR spectroscopy, swelling measurements in xylene, differential scanning calorimetry, and density measurements. A more pronounced degradation of the Si-XLPE matrix located in the immediate vicinity of the ATH fillers was clearly highlighted by the swelling measurements. A very fast radiolytic decomposition of the covalent bonds initially formed at the ATH/Si-XLPE interface was proposed to explain the higher concentration of chain scissions. If, as expected, the changes in the elastic properties of the three materials under study are mainly driven by the crystallinity of the Si-XLPE matrix, in contrast, the changes in their fracture properties are also significantly impacted by the degradation of the interfacial region. As an example, the lifetime was found to be approximately halved for the two composite materials compared to the unfilled Si-XLPE matrix under the harshest ageing conditions (i.e., under 400 Gy·h−1 at 21 °C). The radio-thermal oxidation kinetic model previously developed for the unfilled Si-XLPE matrix was extended to the two composite materials by taking into account both the diluting effect of the ATH fillers (i.e., the ATH content) and the interfacial degradation.

Towards a Kinetic Modeling of the Changes in the Electrical Properties of Cable Insulation during Radio-Thermal Ageing in Nuclear Power Plants. Application to Silane-Crosslinked Polyethylene.

The radio-thermal ageing of silane-crosslinked polyethylene (Si-XLPE) was studied in air under different dose rates (6.0, 8.5, 77.8, and 400 Gy·h−1) at different temperatures (21, 47, and 86 °C). The changes in the physico-chemical and electrical properties of Si-XLPE throughout its exposure were determined using Fourier transform infrared spectroscopy coupled with chemical gas derivatization, hydrostatic weighing, differential scanning calorimetry, dielectric spectroscopy and current measurements under an applied electric field. From a careful analysis of the oxidation products, it was confirmed that ketones are the main oxidation products in Si-XLPE. The analytical kinetic model for radio-thermal oxidation was thus completed with relatively simple structure–property relationships in order to additionally predict the increase in density induced by oxidation, and the adverse changes in two electrical properties of Si-XLPE: the dielectric constant and volume resistivity R. After having shown the reliability of these new kinetic developments, the lifetime of Si-XLPE was determined using a dielectric end-of-life criterion deduced from a literature compilation on the changes in R with for common polymers. The corresponding lifetime was found to be at least two times longer than the lifetime previously determined with the conventional end-of-life criterion, i.e., the mechanical type, thus confirming the previous literature studies that had shown that fracture properties degrade faster than electrical properties.

The preparation of cross-linkable polyethylene via coordination copolymerization of ethylene with alkene-derived chlorosilane

A facile and controllable way to prepared silane-crosslinked polyethylene by coordination polymerization was proposed in this article. Four alkene-derived chlorosilanes, trichloro(oct-7-en-1-yl)silane (Oct-TriSi), dichloro(methyl)(oct-7-en-1-yl)silane (Oct-DiSi), chlorodimethyl(oct-7-en-1-yl)silane (Oct-MoSi) and (2-(bicyclo[2.2.1]hept-5-en-2-yl)ethyl)dichloro(methyl)silane (Nor-DiSi) were first synthesized by hydrosilylation and copolymerized with ethylene to prepare cross-linkable polyethylene. The copolymerization results of ethylene/octenyl-silanes indicated monochloro-substituted silane showed lowest crosslinking ability while trichloro-substituted silane showed the lowest copolymerization ability, therefore, their ability to prepare cross-linkable polyethylene was: Oct-DiSi > Oct-TriSi > Oct-MoSi, moreover, Nor-DiSi outcompeted Oct-DiSi as comonomer to obtain higher copolymerization activity, comonomer proportion in copolymer, comonomer conversion and gel content. The crosslinking process was simply finished via alcoholysis with methanol and subsequent hydrolysis catalyzed with DBTDL. Even with a slight addition of Nor-DiSi, the polyethylene was able to be crosslinked, with the gel content ranging from 42.0 to 98.0%. The TGA and DMA tests demonstrated the crosslinked copolymers showed better thermal stability and heat deformation resistance than polyethylene. After crosslinking, the copolymers with an appropriate gel content would have higher yield stress, tensile modulus and tensile stress.

Thermal ageing of a silane-crosslinked polyethylene stabilised with an excess of Irganox 1076Ⓡ

This work focuses on the thermal ageing in air of a silane-crosslinked polyethylene stabilised with an excess of phenolic antioxidant (Irganox 1076®) in the temperature range between 87°C and 130°C. In such case, it was shown in previous works that the antioxidant is present in two physical states: dissolved in the polymer matrix and exuded at the sample surface under the form of crystals. The purpose was, in particular, to investigate the role of an antioxidant excess in the stabilisation process of the polymer. On this purpose, the pure antioxidant crystals (i.e. the commercial powder) and a polymer sample stabilised with only dissolved antioxidants (i.e. in a concentration lower than the solubility threshold) were investigated at 130°C to isolate and elucidate the thermal ageing behaviour of each antioxidant phase. For all the three studied samples, quinone methide and cinnamate species were formed through the chemical consumption of antioxidants. For both stabilised samples (with an excess, or not, of antioxidants), similar behaviours were observed in term of antioxidant depletion. In particular, it was shown that although some chemical consumption was also detected, the initial antioxidant depletion was essentially due to its physical loss through evaporation. In addition, in both cases, the polymer oxidation was observed after the almost total depletion of antioxidants and without any additional oxidation induction period. The comparison of the oxidation induction periods obtained at 130°C for these two samples showed that the antioxidant excess efficiently participates to polymer stabilisation during thermal ageing, which could be due to a further solubilisation of antioxidants during thermal exposure.

Silane crosslinkable polyethylene waste as bitumen modifier: A new fortunate destiny by in time recycling of thermoplastic waste before conversion to thermoset end-of-life unrecyclable polymer

Polymer modification of bitumen is a popular method to enhance its performance. Over the years, researchers have suggested and developed various polymeric bitumen modifiers, and this trend in research is in progress to introduce new polymers with higher modification efficacies. Silane crosslinkable polyethylene is a widely used polymer as cable insulation, and its waste was used as bitumen modifier in this study. After shaping this polymer around the metal conductors and providing the crosslinking condition, silane-crosslinked polyethylene (Si-XLPE) insulation is obtained. When compared to ordinary polyethylene, Si-XLPE exhibits superlative performance, such as enhanced thermal, mechanical, elasticity, and stress cracking properties. Herein, the cable production wastes of this polymer were utilized for bitumen modification before crosslinking. Comprehensive analyses were carried out for characterizing the fabricated samples, including conventional physical (softening point, penetration, and storage stability), morphological (optical and fluorescence microscopies), chemical (FTIR), thermal (DSC), and performance grade (PG) assessments. For PG determination, rolling thin film oven (RTFO) and pressure aging vessel (PAV) tests, along with rotational viscometer (RV), dynamic shear rheometer (DSR), and bending-beam rheometer (BBR) tools were employed. Findings indicated the formation of a polymeric phase network in the bitumen matrix with altering shapes depending on the polymer content. This was identified to be the origin of appeared structural enhancements in the Si-XLPE modified bitumen samples. Moreover, it was revealed that Si-XLPE contents in 2% and more led to phase separations in the unaged or aged states due to high swelling ratio of Si-XLPE. Strikingly, it was seen that only 1% of Si-XLPE could change the PG 58-22 of base bitumen to PG 70-22, which confirmed promising efficiency of recycled Si-XLPE in low contents for significant improvements in the bitumen's high temperature performance without adverse effects on its low temperature performance. Eventually, recycled silane crosslinkable polyethylene can be an advantageous potential bitumen-modifier that is favorable from technical, environmental, and economical perspectives.

A new analytical model for predicting the radio-thermal oxidation kinetics and the lifetime of electric cable insulation in nuclear power plants. application to silane cross-linked polyethylene

The radio-thermal oxidation of silane cross-linked polyethylene (Si-XLPE) was studied in air under different γ dose rates (6.0, 8.5, 77.8, and 400 Gy.h−1) at different temperatures (21, 47, and 86°C). The changes in the physico-chemical and mechanical properties of Si-XLPE throughout its exposure were determined by FTIR spectroscopy, differential scanning calorimetry (DSC), swelling measurements, rheometry in rubbery (DMTA) and in molten states, and uniaxial tensile testing. It was found that oxidation leads to the build-up of a wide variety of carbonyl and hydroxyl products (mostly carboxylic acids and hydroperoxides) and an efficient chain scission process that catastrophically reduces the concentration in elastically active chains and the elongation at break from the early periods of exposure. A new analytical model was derived from the current radio-thermal mechanistic scheme without making the usual assumption of thermal stability of hydroperoxides. After an initial period where the oxidation kinetics occurs with a constant rate, this model allows also predicting the auto-acceleration of the oxidation kinetics when the hydroperoxide concentration reaches a critical value of about 1.6 × 10−1 mol.L−1. Choosing this critical value as a structural end-of-life criterion allows a more direct assessment of the lifetime of Si-XLPE in the various radio-thermal environments under study, except at the highest temperature (i.e. 86°C) where the kinetic model can still be noticeably improved.

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.

Comparison of radical processes in non-aged and radiation-aged polyethylene unprotected or protected by antioxidants

Silane cross-linked polyethylene was examined by electron paramagnetic resonance (EPR) spectroscopy before and after gamma-irradiation at a dose rate of 77.7 Gy/h to a dose of 374 kGy, which corresponds to approximately 40 years of radiation aging in nuclear power plants (NPP). Radicals generated after post-aging by gamma radiation at 77 K (10 kGy, 2.2 kGy/h) were identified in a polymer unprotected, doped with phenolic antioxidant, thioether antioxidant or both. The radical processes in non-aged and long-term aged polyethylene differed significantly. In the second case, peroxyl radicals dominated at lowest temperatures, while the content of secondary alkyl radicals increased gradually during thermal annealing to 220 K, whereas above ambient temperature tertiary or primary alkyl radicals appeared. The stability of alkyl radicals was related to the rapid consumption of oxygen and, consequently, its depletion in earlier stages of radical processes. Phenolic antioxidant suppressed the above effects and protected the cross-linked structure of the polymer matrix.

Thermal ageing of a silane-crosslinked polyethylene stabilised with a thiodipropionate antioxidant

The thermal ageing of a silane-crosslinked polyethylene stabilised with 1 wt% of distearyl thiodipropionate (Irganox PS802) was studied in air at three different temperatures: 87 °C, 110 °C, and 130 °C. FTIR spectroscopy and DSC under O2 were used in a complementary way to monitor the antioxidant (AO) depletion during thermal ageing, but also to detect the polymer oxidation. In particular, at the three ageing temperatures under study, it was observed that the physical loss of AO is the main ageing mechanism and is controlled by AO evaporation. However, the contribution of the AO chemical consumption in the overall kinetics of AO depletion was also estimated. In addition, the temperature dependences of the evaporation constant and the rate constant of the chemical consumption of AO were approximated with the usual Arrhenius law in the temperature range under investigation. Although the corresponding activation energies must be considered with caution, due to the limited amount of data acquired in this study, they were found to be in good agreement with the few results available in the literature.

Selective Decomposition Process and Mechanism of Si–O–Si Cross-Linking Bonds in Silane Cross-Linked Polyethylene by Solid-State Shear Milling

Material recycling of silane cross-linked polyethylene (Si-XLPE) by the solid-state shear milling (S3M) technology could produce thermoplastic polyethylene. To take advantage of thermoplastic polyethylene from Si-XLPE, the de-cross-linked mechanism of Si-XLPE in S3M must be evaluated. The products prepared by the S3M technology were characterized using gel content, molecular weight measurement (GPC), Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (29Si-NMR), and re-cross-linking test to obtain insight into the selective de-cross-linking effect of the S3M technology. The results had confirmed that a cross-linking element consisting of Si–O–Si chemical bonds was destroyed during S3M, which was responsible for the destruction of cross-linked structures of Si-XLPE materials, and the molecular structures of the resulting products were close to that of silane-grafted polyethylene. The mechanical properties of Si-XLPE materials prepared by the S3M technology before and after water-cross-linking treatment were compared. It was found that the products obtained by the S3M technology could still undergo the cross-linking reaction and form more silane-grafted polyethylene with the increase of milling cycles. Based on the results of this study, we expected that practical applications of de-cross-linking of Si-XLPE materials could be successfully achieved. In this study, favorable conditions were established for the direct recovery of thermoplastic polyethylene from Si-XLPE by the selective de-cross-linking reaction in S3M and an idea about the recycling of Si-XLPE materials was developed.

Tethering vapor-phase deposited GLYMO coupling molecules to silane-crosslinked polyethylene surface via plasma grafting approaches

Herein, an attempt was made to deposit and graft GLYMO (3-glycidyloxypropyltrimethoxysilane) self-assembled layers on silane-crosslinked polyethylene (Si-XLPE). The principal objective was to create an anchoring layer on the pristine surface of Si-XLPE to modify its poor surface bonding properties. Since attachment of the GLYMO self-assembled layers to the partially non-polar surface of Si-XLPE seemed challenging, plasma post-irradiation and syn-irradiation grafting methods were utilized separately for activating the substrate and the deposited GLYMO molecules to provide the necessary condition for grafting and fabrication of uniform self-assembled layers. According to surface chemistry analyses, plasma grafting methods appeared to be beneficial tools for enhancing grafting of GLYMO molecules and reducing the self-condensed GLYMO aggregates and its self-assembled multilayer structures. Morphology investigations confirmed the positive role of plasma grafting in decreasing the self-condensed aggregated GLYMO structures on the surface. Moreover, GLYMO plasma grafting flattened the surface owing to the special orientation of the deposited molecules during the grafting and plasma etching. Surface wettability studies, along with chemistry outcomes, demonstrated the tendency of GLYMO molecules to tether to the surface with their trimethoxysilane groups, while their closed epoxide rings aligned to the out of surface. Overall, the plasma post-irradiation grafting approach exhibited higher grafting density.

Physico-chemical characterization of the blooming of Irganox 1076® antioxidant onto the surface of a silane-crosslinked polyethylene

This study aims at investigating the blooming of Irganox 1076® onto the surface of a silane-crosslinked polyethylene. Preliminary studies on the commercial Irganox 1076® powder enabled to identify its crystalline structure and determine its main physico-chemical properties (characteristic IR absorption bands, melting properties, etc.). Then, the behaviour of Irganox 1076® in silane-grafted polyethylene was studied. Several films containing a concentration of Irganox 1076® ranged between 0.1 wt% and 2.1 wt% were characterized with FTIR spectroscopy and DSC. A peculiar attention was paid to the phase separation within the polymer bulk and the blooming of the antioxidant onto the polymer film surface. Then, this methodology was transposed to an industrial silane-crosslinked polyethylene containing at least 1 wt% of Irganox 1076® as in-service protective antioxidant. For this latter, optical microscopy was of great help for monitoring the blooming of Irganox 1076® onto the polymer film surface. In addition, the polymorphism phenomenon of Irganox 1076® was revealed by FTIR spectroscopy and DSC after thermal treatment at 70 °C under vacuum.

Surface characterization of an organosilane-grafted moisture-crosslinked polyethylene compound treated by air atmospheric pressure non-equilibrium gliding arc plasma

In this study, surface modification of a silane-crosslinked polyethylene (Si-XLPE) compound was carried out by gliding arc atmospheric plasma. Samples were exposed to the plasma for different durations and the plasma-induced alterations of the surfaces were comprehensively assessed. Surface chemistry was evaluated initially via Fourier transform infrared spectroscopy (ATR-FTIR) and energy-dispersive X-ray (EDX) analysis. Surface morphology was investigated by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). For calculating surface free energy (SFE), contact angle measurement (CAM) was performed. In order to have accurate details on the surface chemistry and morphology, X-ray photoelectron spectroscopy (XPS) and Grazing Incidence X-ray Diffraction (GIXRD) analysis were conducted, respectively. Results revealed that this modification method doubled the amount of atomic oxygen and nitrogen on the surface, indicating the formation of polar chemical components on the surface. Moreover, plasma could change the surface morphology considerably by selective etching and impacting on roughness. Furthermore, it was observed that the modification improved the surface crystallinity to some extent and also increased SFE drastically. Surface modification of Si-XLPE by gliding arc plasma has then proved to be an effective technique during which noticeable improvement in wettability has occurred.

Heat of Combustion as the Key Fire Characteristics of Electrical Cables

Abstract This scientific study deals with investigation of the heat of combustion and effective heat of combustion of selected electrical cables. Two different electrical cables for rated voltage of 0.6/1 kV were investigated. Both cables were power three-core with cross-section area of each core of 1.5 mm2. The cores of both cables were made of a bar cooper wire. Insulations of conductors of both cables were made of silane cross-linked polyethylene without any inorganic filler, while the bedding and outer sheath were made of polyethylene-based copolymer (the beddings were filled with two fillers - aluminium hydroxide and calcium carbonate, while the outer sheath were filled only with aluminium hydroxide). Reaction to fire class of both cables was B2ca, s1, d0, a1. The main difference in the investigated cables was that the core of one of them was wrapped in a glass mica tape (this cable showed circuit integrity maintenance under fire conditions during 180 minutes). The heat of combustion and effective heat of combustion were determined by the oxygen bomb calorimeter according to the ISO 1716:2018 standard. The highest effective heat of combustion showed the insulation of wires (for both cables 42.47 ± 0.03 MJ/kg), lower value showed outer sheath (interval form13.61 to 15.26 MJ/kg) and the lowest value was determined for bedding (interval from 4.69 to 6.39 MJ/kg). The effective heath of combustion per unit of length of both investigated cables lies in the interval from 1.37 to 1.38 MJ/m. Therefore, there is no significant difference in effective heats of combustion of the electrical cables investigated.

Enhanced through-plane thermal conductive properties of Ag/rGO nanocomposite

ABSTRACTHigh thermal conductivity of nanocomposite-based polymer matrix is one of the most important keys in developing many heat exchanger instruments. Here, we report a novel nanocomposite system based on silver-coated reduced graphene oxide (Ag/rGO) in silane cross-linked low-density polyethylene (XLPE) matrix with unprecedented through-plane thermal conductivity. Compared to the virgin rGO, Ag/rGO nanocomposite showed 67% higher thermal conductivity due to the Ag nanoparticles (NPs) decoration. The Ag NPs within the nanocomposites are believed to act as a thermal conductor among rGO nanosheets and eventually enhance the heat conduction in 3D manner.

Decrosslinking reaction kinetics of silane-crosslinked polyethylene in sub- and supercritical fluids

Supercritical methanol is a popular fluid as a supercritical medium for decrosslinking reaction of crosslinked polyethylene. However, due to its toxicity, a safe alternative medium is much to be desired. In this work, various sub- and supercritical fluids with different polarity characters were investigated to find a safe alternative medium for continuous decrosslinking of silane-crosslinked polyethylene (S-XLPE). Like methanol, all examined fluids, including ethanol, propanol, and water, exhibited first-order reaction kinetics regarding the gel content in the continuous decrosslinking process. The reaction rate constant values were observed as 2.806, 2.569, 2.383, and 2.130 min−1 in supercritical methanol, supercritical ethanol, supercritical 2-propanol, and subcritical water at 380 °C, respectively. As a non-toxic fluid with reaction kinetics very comparable to that of methanol, ethanol was found to be the best alternative medium for the continuous decrosslinking reaction of S-XLPE.