Abstract
The research started from the fact that the coacervation process represents the process of formation of macromolecular aggregates after separation from the phase that takes place in a homogeneous polymer solution as a result of the addition of a non-solvent. This process is very complex, and takes place in several stages of emulsification technology. The first step of the research created a sample through an encapsulation process of complex coacervation, followed by the creation of three different samples with specific emulsification technologies. Each resulting sample and step of emulsification went through rheological analysis, including the development of evolutions of the complex viscosity, loss module and respective storage module. When we analyzed the rheological properties of each sample at different emulsification stages, we reached the conclusion that, at the moment when the polymerization reaction develops the methyl methacrylate (MMA), the loss modules of the samples were stronger than the storage modules. In this context, the emulsification technology strongly influenced the process of forming the polymethyl methacrylate (PMMA) layer over the butyl stearate particles. In addition, in order to obtain the corresponding microcapsules, it was preferable for the butyl stearate particles covered with MMA to be vigorously stirred in a short period of time, under 250 s, because after that the polymerization process of the MMA on the surface of the particles begins. When producing microcapsules, it is very important that the whole process of emulsification be accompanied by rigorous stirring.
Highlights
The variables that affect the performance of thermal energy storage systems can be divided into the following categories: variables related to Phase change materials (PCM) and storage tank geometry; variables related to the flow of the transfer fluid; variables associated
After rheological testing of Sample B for the EM1_b step 1 emulsifier, with an angular speed ω = 1 rad/s, see Figure 5, it was observed that the sample was almost devoid of elasticity because the storage module was much smaller than the loss module, it was concluded that after this step of emulsification the viscosity of the obtained substance was larger and had values between 0.8 Pa and
Following the rheological testing of emulsions obtained in the intermediary steps of a microencapsulation process using the complex coacervation of butyl stearate in polymethyl methacrylate membranes, the following conclusions were made:
Summary
Phase change materials (PCM) are increasingly used in thermal energy storage systems and temperature control systems due to the advantages they offer, namely high capacity storage in a reduced volume and the possibility of maintaining a near constant temperature in an enclosure [1,2,3].The variables that affect the performance of thermal energy storage systems can be divided into the following categories: variables related to PCMs and storage tank geometry (shape and size of the PCM capsule, length and diameter of the storage tank, capsule geometry and tank geometry storage); variables related to the flow of the transfer fluid (debit, speeds, fluid properties); variables associatedEnergies 2019, 12, 917; doi:10.3390/en12050917 www.mdpi.com/journal/energiesEnergies 2019, 12, 917 with the storage system response (initial state, entrance temperature, PCM physical and thermal properties, convection thermal transfer coefficient) [4,5,6,7,8].The use of PCMs is limited by the relatively low thermal conductivity of these materials, and by the possibility of leakage occurring during the time the material is in the liquid phase.Micro-encapsulation creates conditions for incorporating PCMs into conventional building materials, and such materials have the advantages of easy application, good heat transfer, and no need of protection against destruction. Phase change materials (PCM) are increasingly used in thermal energy storage systems and temperature control systems due to the advantages they offer, namely high capacity storage in a reduced volume and the possibility of maintaining a near constant temperature in an enclosure [1,2,3]. The use of PCMs is limited by the relatively low thermal conductivity of these materials, and by the possibility of leakage occurring during the time the material is in the liquid phase. A possible solution for obtaining a PCM with superior characteristics would be to embed the phase change material into a polymeric mass and close the PCM in a polymeric membrane to create a material which avoids leakage (PCM). The most commonly used methods for the preparation of microcapsules are chemical methods, including in situ polymerization, interfacial polymerization, separation of internal phases and solvent evaporation techniques [9,10,11]
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