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ABSTRACT The microencapsulation of linoleic (LinA), oleic, erucic, and palmitic acids (PAs) from styrene and divinylbenzene were studied by using the suspension-like polymerization technique. All materials exhibited a spherical shape, with a particle size between 166 and 416 μm. The phase change material (PCM) content decreased with the presence of double bonds in the fatty acid molecule. The thermal energy storage (TES) capacity of the microcapsules (MC) containing saturated PA was the highest (123.30 J g−1). Whereas, the lowest TES capacity was observed for the LinA. TES capacity values from unsaturated fatty acid materials and the high particle yield indicated that these kinds of acids played two different roles, as PCM and also as monomers, in the radical polymerization processes. At high initiator concentrations, the unsaturated fatty acids were observed to react. This was confirmed by Fourier transform infrared where the peak assigned to the CC bond disappears in the spectrum of MC. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45970. [ABSTRACT FROM AUTHOR]

Mercury is one of the most toxic pollutants, with high capacity of accumulation in living organism, causing important human health problems. Therefore, the mercury removal from water is an important research goal. In a previous work, an extractant agent [di(2-ethylhexyl)phosphoric acid] was microencapsulated in poly(styrene-co-divinylbenzene) by means of suspension polymerisation using toluene as diluent. In this study, this recipe has been modified changing the toluene by heptane and extended to four additional extractants (trioctylamine, trioctylmethylammonium chloride [TOMAC], tributyl phosphate and trioctylphosphine oxide). The polluting potential of the waste liquid from the process was measured by total organic carbon and chemical oxygen demand analyses. The morphology, particle size and distribution were studied by scanning electron microscopy and low angle laser light scattering. The amount of extractant agent into the microcapsules and the microencapsulation efficiency were determined by thermogravimetric analysis and the mercury removal capacity by equilibrium studies. Microcapsules containing TOMAC demonstrated to be the best material for the mercury removal and retention. [ABSTRACT FROM PUBLISHER]

Rigid polyurethane (RPU) foams were synthesized incorporating up to 18 wt % of two different kinds of thermo-regulating microcapsules having a different shell material consisting of polystyrene or poly(methyl methacrylate), named as mSP-(PS-RT27) and Micronal®DS 5001X, respectively. The type of microcapsules and their content affected the final foam height, which decreased with the content and particle size. However, the foam rising curve shape was not dependent on the microcapsules type or content and was successfully predicted by means of a model of reaction curve of four tanks in series. Thermal energy storage (TES) capacity of PU foams was improved by incorporating both, mSP-(PS-RT27) or Micronal®DS 5001X, with the values close to those reported in the literature (16 J/g) for the highest content. Nevertheless, the highest particle size of the microcapsules from PS and the agglomeration of the microcapsules from poly(methyl methacrylate), promoted by their additive SiO2, led to the strut rupture, damaging the final mechanical properties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Catalyst Tegoamin 33 has been used for the synthesis of rigid polyurethane (RPU) foams containing microencapsulated Rubitherm RT27 and having a high mechanical resistance. These materials could be employed in buildings for thermal insulation and thermal energy storage (TES). The fillers content influence on the foaming process and also the foam properties was evaluated. It was observed that a foam containing up to a 18 wt% of microcapsules can be manufactured, improving the TES capacity while maintaining the mechanical properties of the neat foam. Besides, it was observed that the mechanical resistance of foams synthesized using catalyst Tegoamin 33 are higher than those obtained when catalyst Tegoamin BDE was employed, with the mechanical resistance of the foam containing 21 wt% being higher than those of foams synthesized with catalyst BDE containing only 11 wt% of fillers while maintaining the advantages of an improvement in TES capacity. A general model of reaction curve of n tank-in-series of a same time constant was used to fit the rising curves. This model allowed to predict the final volume of the synthesized foam. Finally, TES capacities and mechanical properties of the synthesized foams were in the range of those reported in literature. Moreover, foam densities satisfied the restriction established by the Spanish regulation for building applications. [ABSTRACT FROM AUTHOR]

Microcapsules of polystyrene with a high level of encapsulated paraffin wax and a narrow size distribution were prepared by a suspension-like polymerization process. The scale-up of this microencapsulation process was carried out by designing a pilot plant that was geometrically proportional to that used on the laboratory scale with the aim of preparing microcapsules with a similar particle size and with the same phase change material (PCM) content as those obtained in the laboratory. In order to verify the effectiveness of the scale-up procedure, a number of experiments on the pilot plant were carried out using the optimal formulation found on the laboratory scale. Only slight differences in mean particle size and encapsulated paraffin content were observed between the two scales at higher stirring rates. The experimental values were fitted to the theoretical expression for the average dissipation rate as a function of the mean particle size. This showed that the classical nonintermittent Kolmogoroff theory is applicable on the laboratory scale, whereas in the pilot plant a large intermittence took place, thus limiting the scale-up to higher stirring rates at which an equal average dissipation rate in both scales led to the same mean particle size. The final results indicated that the assumptions made during the scale-up process were correct. [ABSTRACT FROM AUTHOR]

The morphology and encapsulation efficiency of thermoregulating microcapsules based on a spreading coefficient theory and polar surface energy component were evaluated. For this purpose the microencapsulation of phase change materials (PCMs) with different copolymer shells and using different suspending agents by the suspension-like polymerization technique has been carried out. Contact angles and interfacial tensions were measured, and results were discussed with respect to the internal structure as well as encapsulation efficiency of the microcapsules. A core/shell structure was expected as the equilibrium morphology, whereas the experimental structure exhibited a matrix morphology. A core-shell structure was favored by increasing the polarity of the polymer and decreasing the solubility between the core and shell. The type and amount of suspending agent do not have a significant influence on the final characteristic of the microcapsules. Shells with various polarities were synthesized from styrene (S), divinylbenzene (DVB) and hexa(methacryloylethylenedioxy)cyclotriphosphazene (PNC-HEMA), and it was found that a core-shell structure was only obtained for microcapsules with a high polar surface energy component. [ABSTRACT FROM AUTHOR]

Abstract: A new sulfonated material from styrene–divinylbenzene copolymer, P(St–DVB), containing di(2-ethylhexyl)phosphoric acid (DEHPA) that combines the advantages and capabilities of the ion exchange and the solvent extraction technologies has been developed. Microcapsules with a DEHPA content of 34.86wt.%, an average particle size of 340.83μm and an equivalent thickness shell of 22.4μm were prepared by suspension-like polymerization technique and further sulfonated. The influence of the chemical nature and properties of the suspending agent on the microcapsules characteristics were studied. The polluting potential of the wastewater generated in the encapsulation process with the different suspending agents was also evaluated. Arabic gum:PVA showed to be the best combination of suspending agent for the process. The incorporation of sulfonic groups to the polymeric network turn the hydrophobic nature of the particle into another with hydrophilic character. The increase of the sulfonation time from 10 to 30min promoted the cracking of the microcapsules (from 24.49 to 75.36wt.%). A total ion exchange capacity of 3.56meqg−1 was achieved. The large ion exchange rate and capacity observed confirm that the sulfonation of the shell makes easier the mobility of the metallic ions from the liquid phase to the extractant agent phase through the shell. It was also observed that the presence of DEHPA into the microcapsules makes them more selective than a conventional ion exchange material. [Copyright &y& Elsevier]

Geopolymer concrete (GPC) containing microencapsulated phase change materials (MPCM) were fabricated in order to achieve a high thermal energy storage capacity of an environmental friendly concrete. Different kinds of MPCM were utilized to investigate the influence of the hygroscopic nature, latent heat, and size of microcapsules on the microstructure and thermal properties of GPC. A combination of polar functional groups on the polymer shell and microcapsules with a small size was found to improve the interface bonds between microcapsules and the GPC matrix, how well the MPCM is dispersed in the GPC, and the thermal insulation properties of the GPC. The energy storage capacity of GPC increases at higher concentrations of MPCM and with a higher latent heat of the MPCM. To determine the thermal impact of buildings utilizing GPC containing MPCM, a numerical model was utilized. The model is based on the implicit finite differences method using an energy balance approach and the heat capacity method. In order to improve the model, a new equation was successfully utilized to fit the specific heat capacity of GPC containing MPCM as function of temperature. The numerical model was verified by experimental measurements of the thermal performance of the GPC. The simulated numerical values obtained for GPC containing MPCM were in good agreement with the experimental data. Higher amounts of MPCM and thicker concrete walls reduce the power consumption needed to maintain an indoor temperature of 23 °C. A power reduction of nearly 35% was achieved when utilizing a 75 mm concrete wall containing 5.2 wt.% MPCM. These building materials are therefore promising for improving human comfort and for reducing the energy consumption of buildings. [ABSTRACT FROM AUTHOR]

Microencapsulated phase change materials (MPCM) were added to geopolymer concrete (GPC) for utilization as a thermal energy storage concrete for passive building applications. Three different MPCM were compared to examine the influence of the hygroscopic nature of the MPCM shell, the PCM core/polymer shell ratio, and the MPCM size on the microstructure, thermal properties and compressive strength of GPC. The combination of a hygroscopic nature of the polymer shell, a high core/shell ratio, and a small MPCM size were found to improve the interface bonds between microcapsules and the GPC matrix, increase the energy storage capacity of GPC, and results in a good dispersion of MPCM in the GPC matrix. After adding 5.2 wt% MPCM to GPC, the power consumption for stabilizing the indoor temperature at 23 °C may be reduced by up to 18.5 ± 0.3% for GPC containing PS-DVB/RT27 (paraffin Rubitherm®RT27 core and a shell of polystyrene cross-linked with divinylbenzene), 20.1 ± 0.7% for GPC containing PMMA/PCM26 (paraffin mixture core with a crosslinked polymethyl methacrylate shell) and 25.9 ± 0.3% for GPC containing MF/PCM24 (paraffin mixture core with a melamine–formaldehyde polymer shell). Adding MPCM to GPC induces a higher amount of air pockets, which weaken the compressive strength. Unfortunately, the same parameters that are advantageous for reducing the energy consumption also results in a greater decline of the compressive strength. The compressive strength is further reduced when the microcapsule core is in its liquid state. However, the compressive strength still satisfies the mechanical European regulation (EN 206-1, compressive strength class C20/25) for concrete applications, except for GPC containing 5.2 wt% of MF/PCM24. [ABSTRACT FROM AUTHOR]

Concretes with a high thermal energy storage capacity were fabricated by mixing microencapsulated phase change materials (MPCM) into Portland cement concrete (PCC) and geopolymer concrete (GPC). The effect of MPCM on thermal performance and compressive strength of PCC and GPC were investigated. It was found that the replacement of sand by MPCM resulted in lower thermal conductivity and higher thermal energy storage, while the specific heat capacity of concrete remained practically stable when the phase change material (PCM) was in the liquid or solid phase. Furthermore, the thermal conductivity of GPC as function of MPCM concentration was reduced at a higher rate than that of PCC. The power consumption needed to stabilize a simulated indoor temperature of 23 °C was reduced after the addition of MPCM. GPC exhibited better energy saving properties than PCC at the same conditions. A significant loss in compressive strength was observed due to the addition of MPCM to concrete. However, the compressive strength still satisfies the mechanical European regulation (EN 206-1, compressive strength class C20/25) for concrete applications. Finally, MPCM-concrete provided a good thermal stability after subjecting the samples to 100 thermal cycles at high heating/cooling rates. [ABSTRACT FROM AUTHOR]

The optimisation process for the synthesis of microcapsules containing trioctylmethylammonium chloride (TOMAC), a selective extractant agent for the removal of mercury from wastewaters, by the suspension copolymerisation of styrene (St) and divinylbenzene (DVB) was studied. The influence of the diluent, mass ratio of the suspending agents (arabic gum –AG– and polivinylalcohol –PVA–), TOMAC:diluent volume ratio and weight percentage of DVB respect to the monomers mixture (% DVB) on the encapsulation process and the physical properties of the resulting microcapsules were investigated. It was found that using heptane as diluent led to non-spherical microcapsules with poor reaction yield and conversion of the monomers. Nevertheless, when toluene was used these properties were improved. Furthermore, for a TOMAC:toluene ratio of 1:3 spherical beads were obtained. The combined use of the suspending agents was more appropriate than using them separately, due to the latex product and the low conversion of the monomers for AG and PVA, respectively. The increase of the % DVB from 18.8 to 50% enhanced the mechanical resistance of the polymeric shell, increasing the reaction yield up to an 84.7% and maintaining the TOMAC encapsulation (36.0%) and the sphericity of the microcapsules. The obtained particle size (40 μm) indicated that the main application of this material will be in fluidised beds or in perfectly mixed reactors. On the basis of the experimental results, a AG:PVA mass ratio of 1:1, a TOMAC:toluene volume ratio of 1:3 and 50% DVB were established as the best conditions to produce this kind of microcapsules, enabling its reproduction on a pilot scale plant. In addition, the high values of the distribution coefficient for mercury removal confirm the success of this optimisation process. [ABSTRACT FROM AUTHOR]

A new class of particulate material for the selective removal of mercury from polluted aqueous streams has been developed. The material consists in core–shell microcapsules containing a highly selective extractant agent for mercury. For this purpose, trioctylmethylammonium chloride (TOMAC) has been encapsulated within a poly(styrene-co-divinylbenzene) – P(St-DVB) – shell by suspension-like polymerisation technique. This process gave rise to a high product yield with an encapsulation efficiency of 95%. Microcapsules presented an average particle size lower than 40 μm and a TOMAC content of 37.70 wt.%. Different equilibrium experiments for mercury uptake were conducted at pH = 1 and natural pH, using synthetic solutions and natural waters from the mining district of Almadén (Spain). A mathematical model that takes into account the dissociation of mercuric chloride in solution was proposed and the solid equilibrium parameters were obtained. A good fitting between the experimental data and the model was achieved, obtaining a maximum useful capacity of 1.009 ± 0.018 eq kg −1 with a value of equilibrium constant of the monovalent specie ( HgCl 3 - ) two orders of magnitude smaller than those of the divalent HgCl 4 2 - . The mercury uptake was favoured at acid pH and low chloride concentration. Finally, it was demonstrated that using this material is possible to remove more than 92% and 99% of the metal content from the natural waters containing mercury in ng L −1 levels at natural and acid pH, respectively. The use of this new type of extractive microcapsules allows to get mercury removal levels in surface polluted waters that satisfy the mercury standard for aquatic life proposed by the USEPA (12 ng L −1 ) without additional pretreatments for the adjustment of the pH value. [ABSTRACT FROM AUTHOR]

Abstract: The microencapsulation of phase change materials (PCMs) by a suspension copolymerisation of styrene (St) and methyl methacrylate (MMA) has been studied. The influence of the monomers/paraffin and the MMA/St mass ratio on the encapsulation process and the physical properties of the resulting microcapsules has been studied. The thermal properties, morphology, chemical composition and particle size distribution of the microcapsules were characterised by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), environmental scanning electron microscopy (ESEM), optical microscopy (OM), Fourier transform infrared spectroscopy (FT-IR) and low angle laser light scattering (LALLS). It was found that the MMA/St mass ratio has a marked influence on the polymerisation rate, affecting the conversion and the time at which the identity point is reached. As the amount of MMA is increased, the reaction time and the mean particle size decrease. On the other hand, paraffin was not encapsulated when the monomers/paraffin mass ratio was lower than 3.0 due to the shortage of copolymer. On the basis of the experimental results, an MMA/St mass ratio of 4.0 and monomers/paraffin ratio of 3.0 were established as the best conditions to produce this kind of microcapsule. The higher reactivity and solubility of the methyl methacrylate in water, when compared to styrene, favours paraffin microencapsulation – as shown by the average storage energy capacity of the microcapsules obtained using this copolymer. Furthermore, TGA analysis shows that the thermal stabilities of both the virgin copolymer and the microcapsules containing PCMs are similar when P(St-co-MMA) is used as the shell material. [Copyright &y& Elsevier]