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

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