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Diffusion of low molecular weight siloxane from bulk to surface[outdoor insulators]
Abstract
Silicone-based materials for outdoor insulators have the advantage that low molecular weight (LMW) components migrate through the material and coat the surface, thereby restoring hydrophobicity over a period of hours. By measuring the infrared (IR) absorption of siloxane migrating to the silicone surface through a thin carbon coating, the aspect of the LMW siloxane migration was observed as a real time plot and the time constant of the migration was calculated. According to the time dependence of IR-absorbance, the migration mostly saturated within only 12 hours after the carbon coating was applied. Also, the time constant showed a dependence on the concentration of added filler in the silicone samples
... In Figure 2a, two parameters are presented: mass rise after the swelling process, which is proportional to the number of bonds created between different macromolecules, and mass loss during the swelling process, which is proportional to the amount of low molecular weight particles washed out in the swollen state [52]. Thus, it may be concluded that δ-TF and QU did not affect cross-linking density in a significant way as the samples are swollen similarly to the reference ENR/PLA blend. ...
... Furthermore, analyzing the data concerning the mass loss during the swelling process, it is visible that different amounts of low-molecular weight substances were washed out during the swelling of ENR/PLA. The reason for the observed differences could be the varied rate in the migration of the applied compounds to the surface of the polymer blend [52], e.g., the mass loss of the CM-loaded sample is the lowest, while for δ-TF addition the highest rinsing effect is detected. ...
... The specimen which was expected to have cross-linked the most and exhibited the lowest swelling degree, namely, ENR/PLA + β-CT, was revealed to have the lowest tensile strength and Furthermore, analyzing the data concerning the mass loss during the swelling process, it is visible that different amounts of low-molecular weight substances were washed out during the swelling of ENR/PLA. The reason for the observed differences could be the varied rate in the migration of the applied compounds to the surface of the polymer blend [52], e.g., the mass loss of the CM-loaded sample is the lowest, while for δ-TF addition the highest rinsing effect is detected. ...
The aim of this study is to present the possible influence of natural substances on the aging properties of epoxidized natural rubber (ENR) and poly(lactic acid) (PLA) eco-friendly elastic blends. Therefore, the ENR/PLA blends were filled with natural pro-health substances of potentially antioxidative behavior, namely, δ-tocopherol (vitamin E), curcumin, β-carotene and quercetin. In this way, the material biodeterioration potential was maintained and the material’s lifespan was prolonged while subjected to increased temperatures or high-energy UVA irradiation (340 nm). The investigation of the samples’ properties indicated that curcumin and quercetin are the most promising natural additives that may contribute to the delay of ENR/PLA degradation under the above-mentioned conditions. The efficiency of the proposed new natural anti-aging additives was proven with static mechanical analysis, color change investigation, as well as mass loss during a certain aging. The aging coefficient, which compares the mechanical properties before and after the aging process, indicated that the ENR/PLA performance after 200 h of accelerated aging might decrease only by approximately 30% with the blend loaded with quercetin. This finding paves new opportunities for bio-based and green anti-aging systems employed in polymer technology.
... Moving forward, the mass loss detected during the swelling process might be attributed to some low molecular weight additives rinsed when the sample was put in the solvent environment. This could be explained by the fact that low molecular weight additives usually migrate to the surface of the polymeric material [42]. Therefore, washing out of some part of the applied additives is, in most cases, inevitable. ...
The study aimed to prepare sustainable and degradable elastic blends of epoxidized natural rubber (ENR) with poly(lactic acid) (PLA) that were reinforced with flax fiber (FF) and montmorillonite (MMT), simultaneously filling the gap in the literature regarding the PLA-containing polymer blends filled with natural additives. The performed study reveals that FF incorporation into ENR/PLA blend may cause a significant improvement in tensile strength from (10 ± 1) MPa for the reference material to (19 ± 2) MPa for the fibers-filled blend. Additionally, it was found that MMT employment in the role of the filler might contribute to ENR/PLA plasticization and considerably promote the blend elongation up to 600%. This proves the successful creation of the unique and eco-friendly PLA-containing polymer blend exhibiting high elasticity. Moreover, thanks to the performed accelerated thermo-oxidative and ultraviolet (UV) aging, it was established that MMT incorporation may delay the degradation of ENR/PLA blends under the abovementioned conditions. Additionally, mold tests revealed that plant-derived fiber addition might highly enhance the ENR/PLA blend’s biodeterioration potential enabling faster and more efficient growth of microorganisms. Therefore, materials presented in this research may become competitive and eco-friendly alternatives to commonly utilized petro-based polymeric products.
Silicone rubber micro nanocomposite specimens were aged in acidic (acid rain and HNO3) and saline (NaCl) solutions at 90˚C for 24 h and subsequently placed in the open air at room temperature to monitor its recovery characteristics. The specimens aged in acidic and saline solutions with high conductivity have shown better performance than the samples aged in acidic and saline solutions with normal conductivity. Lesser reduction in hydrophobicity and surface roughness after ageing and marginally faster recovery of hydrophobicity and surface roughness were observed for the silicone rubber specimens aged in NaCl solution followed by HNO3 and acid rain solutions. The micro nanocomposites have reflected the least water intake and lesser surface degradation along with better hydrophobicity compared to pure silicone rubber specimens. Surface morphological changes in aged silicone rubber specimens were analysed in detail at various decomposition levels, by employing wavelet transform to surface profile signal obtained through Atomic Force Microscopy (AFM). The fractal dimension and lacunarity parameters evaluated for the surface profile data of aged silicone rubber composites were found to increase marginally, indicating marginal increment in the complexity and the fractal surface density.
Silicone rubber and EPDM compounds are widely used to build outdoor insulators such as cable terminations and line insulators. These materials undergo the simultaneous effects of electrical stresses (corona, arcing) and climatic environmental stresses (UV, pollution, rain). It is important to test the performances of these materials and predict their long term behavior. Three specific properties are selected as important features of these outdoor insulating materials: (i) The resistance to erosion and tracking when submitted to dry band arcing. (ii) The time before losing hydrophobicity when submitted to a wet environment (fog, rain). (iii) The speed of the hydrophobicity transfer to a pollution layer. Three specific tests are developed to independently measure these three characteristics. They are respectively based on: (i) Measurement of the eroded volume of material submitted to controlled dry band arcing. (ii) Surface conductivity measurement after submission to rain for lengthy periods. (iii) Contact angle monitoring of the pollution layer hydrophobicity. This paper describes the tests and presents some results conducted on silicone rubber materials. This work yields physical criteria which allows us to classify different formulations with regards to their application as outdoor housings
Room temperature vulcanized (RTV) silicone rubber coatings are used increasingly on outdoor high voltage (HV) insulators subjected to heavy pollution. An important property of the RTV coatings is the ability to restore the surface hydrophobicity after a pollutant layer has built up on the surface, which can suppress the development of leakage currents, dry band arcing and flashover. The present study analyzes the hydrophobicity and the hydrophobicity transfer of RTV coatings and the factors that affected the hydrophobicity. A modification of absorption and cohesion theory was used to analyze the hydrophobicity transfer mechanisms and the influences of temperature, polydimethylsiloxane (PDMS) molecular weight, degree of cross-linking, extent of soluble and non-soluble components, and the pollutant properties. The hydrophobicity transfer of RTV coatings was also investigated with various conditions of contaminations and various factors, which affect the hydrophobicity transfer, including the composition of RTV coatings and the outside conditions. Results show that the hydrophobicity transfer of RTV coatings is not only dependent on compositions but also on factors of circumstance. The analysis also explains the obvious difference between the hydrophobicity transfer of RTV coatings to kieselguhr and kaolin based on a particle and surface analysis using the Brunauer, Emmett and Teller (BET) method, which explains the relationship between a BET surface area and the hydrophobicity transfer of the RTV coatings
There are many instances in polymer research and problem solving wherein GC/MS can be useful. The isolation and identification of compounds that relate to or are the cause of a problem or failure can be accomplished readily provided that they are sufficiently volatile to pass through a GC column. The apparatus described herein, Direct Dynamic Headspace Accessory, has been found advantageous as a means of releasing volatiles from samples directly in the GC injection port. Chromatograms of good resolution were obtained, enhancing the chances of making identification by MS. The temperature limit for devolatilization is that of the GC injection port, ca. 350°C in this case. In many instances the method is the best and most direct way of proving if an unusual or unacceptable condition developed from an external service condition or is related to the composition as manufactured.
Results of a study performed to obtain a better understanding of
the material characteristics responsible for hydrophobicity recovery
leading to a high wet surface resistance in silicone rubbers used for
outdoor HV insulation, are reported. The samples were obtained from new
and artificially aged HV insulators using HTV silicone rubbers (3
different formulations) as weathershed and RTV silicone rubbers (2
different formulations) as a protective coating. The main experimental
facilities employed consist of a salt fog chamber for artificially aging
the insulators, and a scanning electron microscope (SEM) for material
studies. New results of practical significance that have emerged from
this study are: (1) hydrophobicity recovery, predominantly due to
diffusion of low molecular weight (LMW) silicone polymer chains, occurs
with only a fraction (<20%) of the total LMW polymer content
initially available in an unaged material surface, (2) LMW chain
regeneration and hence surface hydrophobicity recovery occurs even after
the initial supply of LMW polymer is depleted, and (3) hydrophobicity
recovery is significantly affected by ambient temperature. The results
show the same pattern for different formulations of HTV and RTV rubber
materials studied. The X-ray Mapping feature in the SEM provides a
visual indication of the diffusion process which is a noteworthy
contribution
The results of a study on silicone rubber and ethylene propylene
diene monomer (EPDM) polymers are presented. The study was done to
understand the mechanisms involved in the loss and subsequent recovery
of surface hydrophobicity due to dry-band arcing and to investigate
various experimental techniques which could be used for characterizing
surface hydrophobicity. The materials are subjected to dry-band arcing
in a log chamber. Several techniques such as measurement of contact
angle, determining surface composition using electron spectroscopy for
chemical analysis (ESCA), and measuring crossover voltage (COV) using a
scanning electron microscope are examined. The experimental results and
theoretical calculations demonstrate that the mobile species in the
polymer are responsible for the surface hydrophobicity. In terms of
repeatability and simplicity of measurement, the COV determination
appears to be the most suitable technique for hydrophobicity studies
The results of a study on the suppression of leakage current on
room temperature vulcanizing (RTV) silicone rubber coated porcelain
suspension insulators in a salt-fog chamber are reported. A comparative
study of the performance of coatings on different parts of suspension
insulators with RTV is reported. The results of attenuated total
reflection (ATR) Fourier transform infrared (FTIR) spectroscopy are
reported. On the basis of these results, a suppression mechanism for
leakage current is suggested. A mechanism for the suppression of leakage
current on RTV coated porcelain and silicone rubber insulators dealing
with the temporary loss of hydrophobicity and its return is suggested
The wettability of aged surfaces and of the bulk of naturally aged
silicone and EPDM (ethylene-propylene diener monomer) insulator housings
and silicone elastomer insulator coatings was studied. The samples were
taken either directly from the insulators or treated by exposing them to
corona discharges and/or to saline pollution. The results show that the
contact angles of the silicone rubber insulator surfaces are larger than
the contact angles of the RTV (room-temperature vulcanizing) silicone
rubber coating and of the EPDM rubber insulator surfaces, especially
when the surfaces are aged. When the insulators were exposed to corona
discharges, the contact angles of the silicone rubber insulators are
reduced but after exposure recover with time. The contact angles of the
EPDM rubber insulators, however, continue to reduce after the exposure.
When exposed to artificial saline pollution, the silicone rubber
insulators show a limited recovery of their contact angles with time,
while when exposed to corona discharge after saline pollution, they show
a recovery of the contact angle after the exposure. The recovery time is
dependent on the exposure time to the corona discharges. The EPDM
samples do not show any recovery of their contact angles, either when
left to rest after the salt deposition or, when after the salt
deposition, they undergo a subsequent exposure to corona discharges.
Furthermore, such an exposure may be deleterious for the EPDM polymer
and the insulator surface may become completely hydrophylic