1,720,974 research outputs found
Dielectric properties of modified epoxy resin systems: A novel approach for developing materials for new generation technologies
No full textEpoxy resins are thermosetting polymers that features attractive electrical, thermal and mechanical properties, which made them widely used as a primary insulating material in many electrical applications. Over the past decade, the increase in the energy demands led to increase in the size and change in the operation conditions of the electrical equipments, where their insulating materials are expected to withstand the continuous shift in the operation conditions. Consequently, polymer nanocomposite materials were introduced as a potential solution for producing high-performance insulators, and tailor the properties that effect field distribution in epoxy based materials. Later on, it was reported that some of the fillers are suggested to cause deterred properties, for example, some nano-fillers were difficult to disperse in the host material, which limited the advantages of these nanocomposites. An alternative and/or complementary approach is to use liquid functional network modifiers FNM. These FNM contains epoxide groups within their chemical structure which allows the FNM to contribute to the curing process, thus, the FNM modifier become incorporated in the cured network structure of the modified systems and influence the final properties of the system.This research was set out to provide insights into the effect of functional network modifiers on the properties of epoxy resin systems with the hope of engineering novel epoxy based insulating material for the future. While using liquid functional network modifiers FNM approach has previously been used as a means for altering the mechanical properties of epoxy resins. This research investigated this approach in depth, and also the first study that explores this approach as means of integrating different functional groups into a thermosetting polymers, in order to effectively customise its properties. The research started by providing a background for epoxy curing mechanisms and the method used for modifying the properties of epoxy resin systems reported in the literature. In addition to review of studies investigated the concept of voltage stabilisers that is based on which an explanation or interpretation was provided for the body of knowledge about FNM behaviour. Prior to investigating the effect of any FNM on the properties of the modified systems, the effect of the of the FNM on the stoichiometric ratio of epoxy resins was established by running a series of experiments (FTIR, DSC, dielectric properties and AC breakdown strength of the modified systems). These experiments were carried out on a simple amine-cured epoxy resin system by using compensated and uncompensated systems. In the compensated systems, the FNM was added by precisely calculating the number of the epoxide groups being supplied by the FNM, where the equivalent number of epoxide groups provided by the resin are removed, ensuring the same number of epoxide groups present in the system after the addition of the FNM. While, in the uncompensated systems the FNM was added without changing the stoichiometry of the system. By comparing the variation in the properties of the compensated and uncompensated systems, it was concluded that the stoichiometric ratio of the FNM plays a vital role in determining the properties of the final material. In addition, the effect of the FNM on the Tg, dielectric spectroscopy and the breakdown strength is found to be attributed to several factors. In these experiments, the most dominant factor was the structure of the functional groups of the FNM. By investigating the effect of the chemical structure of the FNM on the FTIR, DSC, dielectric properties, AC breakdown strength and DC conductivity of epoxy resin systems modified by the inclusion of varied concentrations of different FNM modifiers, it was found that the properties of the modified systems are influenced by both the chemical structure of the functional groups and the concentration of the FNM in the system. For example, the use of liquid epoxy resin and low concentration FNM (4%) suggested to produce FNM modified epoxy resins with improved properties compared to that of the neat epoxy, which is suggested to offer a new means of engineering novel materials to meet current and future needs in an adaptable way. This research also investigated the effect of the curing mechanisms on the behaviour of the modified systems. It was found that the presence of the functional network modifier influenced the chemical, thermal and electrical properties of the amine and anhydride cured systems. This was followed by a a detailed analysis study of the molecular origin and the activation energy of each relaxation process. This analysis was needed because of the lack detailed analysis of the dielectric behaviour of anhydride cured resins in literature. Also, the presence of the FNM made prediction of the behaviour more challenging. The study analysed the temperature dependent dielectric properties along with Havriliak-Negami deconvoluted peaks, as well as the Arrhenius plots and the associated activation energies of the different molecular relaxations. It was concluded that the type of the functional group of the FNM plays a vital role in determining the network topology and the dielectric molecular dynamics of the final material.The work reported in this research proves that functional network modifiers constitute a complementary and alternative approach for nanotechnology for designing materials with controlled dielectric properties. The systems researched, combined with the applied research method and the described experimental setup provides a complete guide for future studies to replicate the results and experiment with different FNM combinations
Effect of seawater diffusion on the dielectric properties of silicone elastomer
No full textThis study investigates the diffusion kinetics of seawater into silicone dielectric elastomers and examines their detrimental effects on electromechanical performance in energy harvesting applications. Encapsulated dielectric elastomer samples are prepared and immersed in water to correlate DC resistivity changes with water content diffusing through the membrane. Results demonstrate that water ingress induces significant conduction losses, which appear similar in both seawater and deionized water. When considering the use of these materials for ocean energy harvesting, conduction losses reduce transducer efficiency. Therefore, the dielectric properties of water-saturated samples are analyzed under typical electro-mechanical harvesting schemes, highlighting severe limitations at low stretch amplitudes. Furthermore, water-saturated samples exhibit a 22% reduction in dielectric breakdown strength, substantially diminishing the achievable energy density of submerged generators such as wave energy converters
Functional design of epoxy-based networks: tailoring advanced dielectrics for next-generation energy systems
No full textEpoxy resins are widely used as the primary insulation material in many demanding energy-related applications. As such, the ability specifically to tailor the electrical performance of such systems to meet increasingly demanding insulation situations has considerable utility. This paper describes a new approach to this problem, which is based upon the controlled introduction of specific functional groups into the cured resin's network architecture. Here, two additives are considered, termed functional network modifiers (FNM), namely glycidyl hexadecyl ether and glycidyl 4-nonylphenyl ether; in all the investigated systems, the ideal stoichiometric ratio of epoxide groups to amine hydrogens is retained. In the case of both FNM, their inclusion resulted in a progressive reduction in the glass transition temperature Tg of the system, a reduction in the real part of the permittivity and reduced dielectric losses wihin the accessible frequency range, increased DC conductivity and increased AC breakdown strength. The magnitude of the observed effects are found to be dependent upon the choice of functional modifier, which suggests that such changes are not related merely to the inclusion of an additive within the system, but are also influenced by the chemistry of the additive itself. Explanations for these effects are proposed. It is concluded that the use of such FNM at low concentrations (~4% in the work reported here) offers a novel alternative means of engineering advanced materials to meet the current and future needs in an adaptable and easily implemented manner
The nature of the gamma dielectric relaxation in diglycidyl ether Bisphenol-A (DGEBA) based epoxies
No full textA γ relaxation dielectric loss peak has been measured in the temperature range 113–163 K for a series of epoxy resins based on diglycidyl ether bisphenol-A (DGEBA). The network architecture of the examined systems were systematically altered using varied types of functional network modifiers featuring different functional groups. Analysis of the temperature dependence of the loss peak frequency leads to a radically new interpretation of the fundamental processes that are associated with the γ relaxation. The analysis has shown that the relaxation process can best be described in terms of a thermally assisted tunnelling displacement of a proton, termed activated tunnelling. The parameters derived not only fit the experimental data well, but have a clear physical origin that is shown to be consistent with the network topology as expressed through the glass transition temperature. The maximum temperature for which such behavior is observable has been determined and shown to be consistent with the measurements. The approach proposed here provides a new method for understanding γ relaxations in these and similar systems
Investigation of dielectric and thermal properties of iPP/MA-PP/TPU blends
No full textIsotactic polypropylene (iPP)-based blends have been widely investigated for their potential as next-generation insulating materials for high voltage cables. Pure iPP is too brittle; hence, blends with various elastomers have been developed. In the present work, maleic anhydride grafted polypropylene (MA-PP) is used as a compatibilizer, enhancing its compatibility with thermoplastic polyurethane (TPU) elastomer in an attempt to prepare and characterize iPP/MA-PP/TPU blends. This study investigates the thermal properties, molecular structure, and dielectric performance of these blends using differential scanningcalorimetry (DSC), Fourier-Transform Infrared (FTIR) spectroscopy, and dielectric spectroscopy (DS). The results reveal that the introduction of maleic anhydride (MA) into the blends results in the formation of imide structures, through crosslinking with the TPU, that do not affect the crystallinity and melting pointof iPP. The iPP/MA-PP/TPU blends display increased dielectric permittivity and losses in the low frequency domain; characteristics that are dependent on the concentration of MA
Investigation of the functional network modifier loading on the stoichiometric ratio of epoxy resins and their dielectric properties
No full textReactive molecular additives have often been employed to tailor the mechanical properties of epoxy resins. In addition, several studies have reported improved electrical properties in such systems, where the network architecture and included function groups have been modified through the use of so-called functional network modifier (FNM) molecules. The study reported here set out to investigate the effect of a glycidyl polyhedral oligomeric silsesquioxane (GPOSS) FNM on the cross-linking reactions, glass transition, breakdown strength and dielectric properties of an amine-cured epoxy resin system. Since many previous studies have considered POSS to act as an inorganic filler, a key aim was to consider the impact of GPOSS addition on the stoichiometry of curing. Fourier transform infrared spectroscopy revealed significant changes in the cross-linking reactions that occur if appropriate stoichiometric compensation is not made for the additional epoxide groups present on the GPOSS. These changes, in concert with the direct effect of the GPOSS itself, influence the glass transition temperature, dielectric breakdown behaviour and dielectric response of the system. Specifically, the work shows that the inclusion of GPOSS can result in beneficial changes in electrical properties, but that these gains are easily lost if consequential changes in the matrix polymer are not appropriately counteracted. Nevertheless, if the system is appropriately optimized, materials with pronounced improvements in technologically important characteristics can be designed.</p
Data set in support of the doctoral thesis: 'Ultra-high molecular weight polyethylene nanocomposites for enhanced dielectric, thermal and mechanical performance in polypropylene ‒ advancing towards a more sustainable high voltage power grid'
No full textThis is the raw data in Excel file format of all the results presented in the thesis.
This dataset contains: 5 Excel files containing datasets produced in the thesis of each chapter (Chapter 4 to Chapter 8).
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Effect of mechanical loading history on the electrical breakdown strength of dielectric elastomers
No full textOptimizing energy density in dielectric elastomer generators: a reliability-dependent metric
No full textDielectric elastomer generators (DEGs) are soft transducers capable of converting mechanical energy into electrostatic energy. Increasing the mechanical stretch amplitude and the electric field imposed to the DEG leads to higher energy conversion at the cost of a reduced lifetime. Here, mechanical fatigue and electrical degradation were assessed on a silicone-based DEG, and the outcome was used to build an electro-mechanical reliability model. A novel metric, termed levelized energy density, has been introduced to carefully balance the conflicting objectives of high energy output and long-term reliability. Through a multi-dimensional anaylsis of this index, the optimal operating parameters (stretch amplitude and electric field) that maximize energy conversion can be derived. Energy densities reported in literature are generally obtained after pushing the DEG close to their intrinsic limits for a limited number of cycles. In our approach, more realistic values in the endurance domain are presented, which typically leads to a 9-fold decrease in energy density for a design life of 1 million cycles. This article not only addresses the challenge of optimizing DEG performance but also emphasizes the importance of considering realistic operational conditions to enhance reliability, ultimately contributing to the practical and sustainable deployment of these soft transducers in various applications.</p
Influence of layer height on the dielectric and tensile properties of 3D printed polypropylene-based copolymer
No full textThis study examines the effect of layer height on the dielectric and mechanical properties of 3D printed polypropylenebased polymer using fused deposition modelling (FDM). Samples with 0.1 mm and 0.15 mm layer heights were evaluated for real permittivity, loss tangent, DC conductivity, and tensile properties. The 0.1 mm layer height resulted in higher permittivity, lower dielectric losses, and better mechanical performance due to reduced porosity. While its DC conductivity was slightly higher, both samples remained highly insulating. Tensile tests confirmed greater strength and elongation for the 0.1 mm layer. These findings highlight the importance of layer height in 3D printed insulation components to ensure reliable dielectric and mechanical performance
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