Encapsulation of biobased fatty acid amides for phase change material applications

Abstract

A novel technique was used to produce macrocapsules containing a new type of biobased phase change material (fatty acid amides or FAAms) using a UV-curable polyester resin as the shell material. The production of capsules with varying phase change material (PCM) loading was achieved by generating core/shell droplets using a coaxial nozzle and subsequently curing them with a broad-spectrum light. All the capsules produced were approximately 3 mm in diameter independently of the process parameters used during generation. Also, the addition of rheology additives to the shell resin was proven successful in improving the capsules' final shape and the stability of the production process. The PCM loading of the capsules ranged from 40 to 54 vol. % with latent heats of fusion going from 36 to 51 J/g, respectively. The encapsulated FAAms showed higher melting points than the bulk FAAms in differential scanning calorimetry analysis as a result of the low thermal conductivity of the shell material. Results from thermogravimetric analysis showed that the capsules are thermally stable under 190 °C. The effect of core content on the mechanical properties of the capsules was also studied. The general trend observed from compression test results was the decrease in 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. Results from thermal cycling experiments showed that the thermal properties of the capsules remained unchanged after 50 cycles. Also, 95% of the capsules subjected to thermal cycling were able to withstand the PCM's volumetric changes without cracking or rupturing. Findings 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.