The current study discusses the preparation and long-term performance of polymer composites used for various purposes under different ageing conditions. The first part deals with the preparation and characterization of polymer nanocomposites based on poly(ethylene-co-butyl acrylate) (EBA–13 and EBA–28 with 13 and 28 wt % butyl acrylate, respectively) and 2–12 wt % (0.5–3 vol %) of aluminum oxide nanoparticles (two types with different specific surface areas and different hydroxyl-group concentrations; uncoated and coated with, respectively, octyltriethoxysilane and aminopropyltriethoxysilane). The nanocomposite with EBA–13 showed better overall nanoparticle dispersion while EBA–28 resulted in poor dispersion, probably due to insufficiently high shear forces acting during extrusion mixing which were unable to break down nanoparticle agglomerates. The activity of hindered phenolic antioxidant (0.2 wt%) in all EBA nanocomposites was assessed by determining the oxidation induction time using DSC. The composites containing uncoated aluminium oxide nanoparticles showed a much shorter initial OIT than the pristine polymer with the same initial concentration of antioxidant, indicating adsorption of antioxidant onto the nanoparticle surfaces. Composites containing coated nanoparticles showed a significantly smaller decrease in the initial OIT, suggesting the replacement of hydroxyl groups with organic silane tails, decreasing the concentration of available adsorption sites on the nanoparticle surfaces. The decrease in OIT with increasing ageing time in dry air at 90 °C of the nanocomposites was slower than that of the unfilled pristine polymer, suggesting a slow release of antioxidant from adsorption sites. The EBA nanocomposites exposed to liquid water at 90°C showed faster decrease of OIT than samples exposed to dry or humid air. The migration rate of antioxidant was controlled by the boundary conditions in the case of ageing in humid air and liquid water. The antioxidant diffusivity was lower for the composites containing uncoated ND than for the composites containing ND coated with octyltriethoxysilane or aminopropyltriethoxysilane. The migration and chemical consumption of deltamethrin DM, (synthetic pyrethroid) and synergist piperonyl butoxide from molded polyethylene sheets was also studied. Deltamethrin and piperonyl butoxide are often used for food  storage and insect control purposes. DM showed no signs of crystallization and remained in a liquid state after being cooled to room temperature. Exposure of polyethylene compound sheets to liquid water (at 80 &amp; 95 °C), caused degradation and hydrolysis of the ester bond in the DM, present in the prepared material, and generated species containing hydroxyl groups. Liquid chromatography and infrared spectroscopy showed a significant migration of the active species in liquid water, whereas in air at 80 °C (60 and 80 %RH) the loss of DM and PBO was negligible over 30 days. The long-term performance of medium-density polyethylene stabilized with six different phenolic antioxidants (0.1 wt%) in aqueous chlorinated media at 70 °C was studied. The results were compared with data for previously studied solutions of antioxidants in squalane (a liquid, low molar mass analogue of polyethylene). A linear relationship was established between the time to reach antioxidant depletion in polyethylene tape samples and the time in squalane samples. Infrared spectroscopy and scanning electron microscopy of drawn samples revealed the onset of surface oxidation and surface embrittlement in tape samples exposed beyond the time for antioxidant depletion. / <p>QC 20121109</p> / Cable insulation materials / Loss of deltamethrin and pipronyl butoxide from polyethylene / long-term performance of polyethylene in chlorine dioxide water

In this work the electrical insulating properties of the nanocomposite materials based on poly(ethylene-co-butyl acrylate) filled with alumina nanoparticles are studied. The dielectric properties chosen for the evaluation are the dielectric permittivity and loss as well as the breakdown strength and the pre-breakdown currents. The reason for choosing these particular properties is partly due to the importance of these for the general electrical applications and partly due to the uncertainties involved for these particular properties of the nanocomposite materials. The importance of moisture absorption for the dielectric properties is outlined in this work. All measurements were performed in both dry conditions and after conditioning of the materials in humid environment until saturation. The data for moisture absorption was taken from the water absorption study performed at the Department of Fibre and Polymer Technology, KTH. The dielectric spectroscopy in frequency domain was employed for measuring dielectric permittivity and loss. Havriliak-Negami approximation was used for characterization of the measurement data and at the same time ensuring the fulfillment of the Kramers-Kronig relations. Results from the dielectric spectroscopy study in dry conditions suggest that dielectric spectroscopy can be used for evaluating nanoparticle dispersion in the host matrix, based on correlation between the morphology data obtained from SEM investigation and the scatter in the dielectric loss. The dielectric spectroscopy study performed on the nanocomposites after conditioning in humid environment showed that absorbed moisture has a distinct impact on the dielectric loss. Especially pronounced is its’ influence on the frequency behavior, when the dielectric loss peaks are shifted towards higher frequencies with increased moisture content. The nanocomposite materials characterized by higher specific surface area generally exhibit higher dielectric losses. Surface functionalization of the nanoparticles does not seem to have much influence on the dielectric loss in dry conditions. After conditioning in humid environment, however, the surface modification was shown to have a significant impact. Temperature is another significant factor for the frequency behavior of the dielectric loss: it was found that the studied nanocomposites can be characterized by Arrhenius activation. The breakdown strength and pre-breakdown currents study outlined the influence of moisture as well. The study indicated that surface treatment of the nanoparticles can enhance properties of the nanocomposite materials, namely aminopropyltriethoxy silane was an especially successful choice: • The highest breakdown strength was determined by the study for NDA6 material formulation in dry conditions. • After conditioning in humid environment the NDA6 material continued showing the best breakdown strength among the nanocomposite mate rials, as well as this value was close to the breakdown strength of the reference unfilled material. This study confirms the existence of the optimal nanofiller content or rather optimal specific surface area of the dispersed nanoparticles in the host matrix. The latter is supported by the comparison between the nanocomposites based on nanoparticles with two different specific surface areas, which shows that the dielectric properties worsen, i.e. the dielectric losses increase and the influence of absorbed moisture on the breakdown strength becomes more pronounced, for nanomaterials with larger specific surface area. The pre-breakdown currents were found to follow space-charge limited conduction mechanism reasonably well. The following conduction regimes were identified: constant region (likely due to measurement difficulties at low field strengths), Ohm’s regime, trap-filled-limit regime and trapfree dielectric regime. The breakdown usually occurred either during the trap-filled-limit regime, when the current increased dramatically for the small change in electric field, or during the trapfree dielectric regime. The threshold values between different conduction regimes seem to correlate well with the oxidation induction times (OIT), which in turn depend on the total specific surface area. The pre-breakdown currents tend to be highest for the materials filled with the untreated nanoparticles. Increased absorbed moisture content causes higher pre-breakdown currents for the nanocomposite materials, while for the reference unfilled material the pre-breakdown currents do not show such tendency. Generally it can be said that the repeatability in the measured data is higher for the nanocomposite materials in comparison to the unfilled host material, as was demonstrated by both dielectric spectroscopy and breakdown studies. / <p>QC 20130207</p>

Polymer nanocomposites are promising materials for dielectrical use in high voltage applications and insulations. This work presents a study of nanocomposites based on poly(ethylene-co-butyl acrylate) with two different comonomer compositions and two different aluminium oxide nanoparticles. The nanoparticles were either untreated, or surface-treated with two different silanes, aminopropyl triethoxy silane and octyltriethoxy silane. The best level of dispersion was found for the polymer with 13 wt. % of butyl acrylate (EBA-13) whereas the low melt viscosity of the polymer with 28 wt. % of butyl acrylate (EBA-28) resulted in insufficient mixing with uneven dispersion as a result. Octyltriethoxy silane-treated particles were best dispersed in the polymer. The nanoparticles acted as nucleation agents in EBA-28, increasing the crystallization temperature by several degrees. Studies of the water uptake in the nanocomposite materials showed the effect of the enormous interfacial surfaces and great number of polar groups present on the nanoparticle surfaces. For the well-dispersed nanomaterials, the water sorption data could be modeled by a single Fickian equation, whereas materials that contained a sizeable fraction of large nanoparticle agglomerates showed a two stage sorption process, first a fast process associated with the saturation of the polymer phase and second, a slow diffusion process due to water sorption of large particle agglomerates. The long-term performance and interaction between the nanoparticles and the phenolic antioxidant (Irganox 1010) was investigated by differential scanning calorimetry in order to assess the oxidation induction time (OIT); the latter being proportional to the concentration of efficient antioxidant. It was found that the stabilizer was adsorbed to the untreated Al2O3 nanoparticles, resulting in a significant reduction in OIT. However, silanization of the nanoparticles resulted in an increase in OIT, compared to the materials containing untreated particles. Furthermore, it was shown that the stabilizer was not irreversibly adsorbed to the particles, allowing a gradual release of stabilizer with ageing time. / Polymera nanokompositer är lovande material för användning som dielektriskt material inom högspänningsområdet. I detta arbete studeras nanokompositer framställda av två olika sampolymerer av eten och butylakrylat (EBA-13 med 13 vikt% butylakrylat samt EBA-28 med 28 vikt% och två olika typer av nanopartiklar av Al2O3. Nanopartiklarna användes antingen som obehandlade eller efter silanisering med aminopropyltrietoxysilan- eller oktyltrietoxysilan. Den bästa partikeldispergeringen observerades för de material som baserats på EBA-13 medan den låga smältviskositeten hos EBA-28 resulterade i låga skjuvkrafter under kompounderingen och en observerat ojämn dispergering och förekomst av mikrometerstora agglomerat. Partiklar som silaniserats med oktyltrietoxysilan var lättast att dispergera. Nanopartiklarna fungerade som kärnbildare i EBA-28 vilket medförde en höjning av kristallisationstemperaturen. Vattensorptionsstudier demonstrerade dels effekten av den stora specifika gränsytan mellan partikel och matris och dels av förekomst av polära grupper lokaliserade till nämnda gränsyta. Kompositer med väldispergerade partiklar uppvisade en enkel Ficksk sorptionsprocess medan de material som innehöll en betydande mängd stora agglomerat påvisade en tvådelad process. Den första processen var kopplad till mättningen av polymermatrisen och den andra kunde länkas till vattenupptaget i de stora agglomeraten. Vidare undersöktes långtidsegenskaperna hos nanokompositerna, samt om det fanns någon växelverkan mellan nanopartiklar och en fenolbaserade antioxidant (Irganox 1010). DSC användes för att bestämma induktionstiden för oxidation (OIT) vilket är ett mått på koncentrationen av aktiv fenolisk antioxidant. Det framgick det att Irganox 1010 adsorberades på nanopartiklarna, vilket ledde till en minskning av OIT. Det framgick även att de material som innehöll silaniserade nanopartiklar hade högre OIT jämfört material med obehandlade partiklar. Antioxidanten var däremot inte irreversibelt bunden till nanopartiklarna, utan frigjordes från deras ytor och blev aktiv under åldringen. / QC 20110128

In this work dielectric properties of the poly(ethylene-co-butyl acrylate)filled with alumina nanoparticles are evaluated. These nanocomposite materialswere manufactured at the department of Fibre and Polymer Technology,KTH.This study is limited to the properties of general importance for the AC applications.The dielectric permittivity of the nanocomposite materials wasstudied as a function of filler size, filler content, coating, temperature and airhumidity used for conditioning of the samples. The ultimate goal with thisproject is to describe the influence of material composition, temperature andair humidity on the dielectric properties and model these dependencies.In this thesis the experimental setup for voltage endurance testing of thenanocomposites, namely studying applied voltage frequency dependence ofpartial discharges in electrical trees, with a possibility of following electricaltreeing optically, was developed and described.The dielectric spectroscopy measurements were performed on thoroughly driednanocomposites - so-called dry DS study. It was shown that the experimentaldata can be fitted with Havriliak-Negami approximation, which justifiesthe correctness of the measurement results. It has been shown that addingnanoparticles to the EBA matrix changes the low frequency dispersion significantlyfor the dried samples. It was also indicated that the particle coatingused has very low impact on the resulting permittivity of the thoroughly driedsamples. From the dry DS studies it was suggested that the main cause ofthe scattering in data between the dry samples is most likely the influenceof the material inhomogeneity and possibly the moisture absorption. Thisleads to a possibility of using dielectric spectroscopy as a tool for probing thedispersion of nanoparticles in the polymer matrix.The dielectric spectroscopy measurements were also carried out on the nanocompositesconditioned in the environments with different humidity levels of air inorder to study the influence of absorbed water on the dielectric permittivity- so-called wet DS study. From the wet study it was shown that for the wetsamples the amplitude of the loss peak is defined by the filler size, filler contentand coating used; while its position in frequency domain is determinedby the coating and the humidity level used for conditioning. / QC 20110315