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Synthesis, Characterization and Encapsulation of Phase Change Materials and Their Incorporation in Asphalt Pavements
thesisposted on 29.04.2021, 22:56 by Daniela Betancourt Jimenez
This document summarizes the research conducted on organic phase change materials, from the synthesis, characterization, and encapsulation of biobased FAAms for PCM applications to the incorporation of commercially available PCM microcapsules in asphalt pavement to regulate its temperature and potentially prevent or mitigate rutting and the urban heat island (UHI) effect.
The first chapter presents the synthesis of bio-based fatty acid amides for PCM applications. Fatty acid amides (FAAms) were successfully synthesized from commercial vegetable oils and primary alkyl amines. The chemical structures of the samples were characterized through FTIR, 1H-NMR and 13C-NMR while their thermal properties were studied using DSC and TGA. Results show the potential of FAAms synthesized from corn and sunflower oils to be used as phase change materials, which exhibited single transitions over narrow temperature ranges upon cooling/heating even when no fractionation or separation of the material was carried out. The melting temperature of the FAAms increased with the length of the precursor amine and a similar trend was observed for latent heat except for FAAms from hexadecylamine. Latent heats of the synthesized materials were as high as 141 kJ/kg, and all the FAAms were thermally stable under 200 °C.
The second chapter focuses on the encapsulation of biobased FAAms in core-shell UV curable polyester capsules fabricated using a coaxial needle. Capsules were dripped from the needle tip into a collection bath where they were exposed to UV light to cure the polyester shell. The addition of rheology additives to the shell resin was proven successful in improving the capsules’ shape and the stability of the generating process. Capsule production parameters such as core and shell flow rates were varied and their effect on the process stability and the capsules’ size and core content were studied. Thermal properties were also assessed with results indicating that the FAAms retain their PCM potential after encapsulation. Furthermore, the capsules were determined to be thermally stable under 190 °C. The general trend observed from compression test results was the decrease of the capsules’ mechanical performance when the core content was increased; however, it was also discovered that their failure response is highly dependent on the uniformity of the capsule’s shell. It was concluded that the thermal properties of the capsules can be improved by adding fillers with high thermal conductivities to the shell; similarly, the failure behavior can be enhanced by reducing the level of core off centeredness with changes in the shell formulation or addition of higher density particles to the FAAms. Results from this investigation are expected to lay the groundwork for the commercial use of biobased FAAms and potential replacement of petroleum derived PCMs currently in the market.
The third and last chapter of this document presents efforts made to incorporate commercially available PCM microcapsules in asphalt pavements in order to prevent them from reaching high temperatures that can promote rutting and the UHI effect. First, the thermal properties and stability of the capsules were characterized using DSC and TGA analysis. They exhibited high latent heats (200 J/g) and were thermally stable under 400 °C. Next, the ability of the capsules to withstand compression forces and high temperatures typical of asphalt processing was assessed by milling them at a high temperature (<145 °C) for 20 minutes. Results from visual inspection indicate that approximately 90% of the capsules endured the experiment. Microcapsules were then added to asphalt mixtures in 10 and 20 vol% and thermal cycling experiments were conducted to study the effect of the PCMs on the temperature of the samples. As the specimens were heated and they approached the melting point of the PCM, the temperature of those containing 10 vol% and 20 vol% PCM were 5 °C and 10 °C lower than that of the control specimen, respectively. Similarly, when the mixtures were cooled down from 62 °C to room temperature, specimens with 10 and 20 vol.% PCM were 2.9 and 5.4 °C hotter than the control when their temperatures were just below the melting point of the PCM. However, the dynamic modulus of control and PCM containing mixtures was also studied and results indicate that the addition of the microcapsules resulted in a reduction of this property which could decrease the pavement’s rutting resistance.