Documents disponibles écrits par cet auteur

Synthesis and characterization of paraffin wax microcapsules with acrylic - based polymer shells / Luz Sanchez-Silva in Industrial & engineering chemistry research, Vol. 49 N° 23 (Décembre 2010) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 49 N° 23 (Décembre 2010) . - pp. 12204–12211 Titre : Synthesis and characterization of paraffin wax microcapsules with acrylic - based polymer shells Type de document : texte imprimé Auteurs : Luz Sanchez-Silva, Auteur ; John Tsavalas, Auteur ; Donald Sundberg, Auteur Année de publication : 2011 Article en page(s) : pp. 12204–12211 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Microcapsules  Polymer Résumé : Microencapsulation of PRS paraffin wax was carried out by means of suspension-like homopolymerization of methyl methacrylate (MMA) and by the copolymerization of this monomer with methyl acrylate (MA) and methacrylic acid (MAA). The influence of the type of monomers and their proportion as shell materials, the mass ratio of polyvinylpyrrolidone to monomers (PVP/monomers), and the mass ratio of PRS paraffin wax to monomers (PRS/monomers) on the properties of phase change material (PCM) microcapsules has been studied. The analytical techniques used for the characterization of the particles were differential scanning calorimetry (DSC) and modulated DSC, dynamic light scattering, environmental scanning electron microscopy (ESEM) and gel permeation chromatography (GPC). The chemical property differences between the encapsulating “shell” material, acrylic polymer in this case, compared to the “core” material (PRS paraffin wax), such as polarity and interfacial tensions, largely determine the thermodynamically favored morphology of the microcapsules. While the equilibrium morphology was a core/shell structure, kinetic factors relating to the competition between the fast acrylic polymerization rate and the diffusion limited rate of phase separation were found to constrain the ability of the system to approach that equilibrium structure. For both homopolymerization of methyl methacrylate (PMMA) and copolymerizations of methyl methacrylate with methyl acrylate (P(MMA-co-MA)), “pomegranate” microspheres were observed with a thin acrylic shell surrounding an inner composite structure constituted by a paraffin matrix with a dense assortment of PMMA spherical domains. Ter-polymerizations incorporating methacrylic acid (P(MMA-co-MA-co-MAA) had a remarkable effect on the morphology and average particle size, resulting again in “pomegranate” microparticles but where the internal PMMA spheroids were more densely populated closer to the outer portion of the capsule; approaching a core/shell structure. As the amount of polyvinylpyrrolidone stabilizer in the aqueous medium was increased and the PRS/monomers proportion was decreased, the mean particle size of the microcapsules decreased. However, higher PVP/monomer and PRS/monomer ratios led to less efficient encapsulation of the PRS paraffin wax. Near perfect encapsulation efficiency was obtained for two pairings of these ratios via P(MMA-co-MA-co-MAA) polymerization, but only up to an equal mass ratio of PRS to acrylic polymer. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie101727b [article] Synthesis and characterization of paraffin wax microcapsules with acrylic - based polymer shells [texte imprimé] / Luz Sanchez-Silva, Auteur ; John Tsavalas, Auteur ; Donald Sundberg, Auteur . - 2011 . - pp. 12204–12211. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 49 N° 23 (Décembre 2010) . - pp. 12204–12211 Mots-clés : Microcapsules  Polymer Résumé : Microencapsulation of PRS paraffin wax was carried out by means of suspension-like homopolymerization of methyl methacrylate (MMA) and by the copolymerization of this monomer with methyl acrylate (MA) and methacrylic acid (MAA). The influence of the type of monomers and their proportion as shell materials, the mass ratio of polyvinylpyrrolidone to monomers (PVP/monomers), and the mass ratio of PRS paraffin wax to monomers (PRS/monomers) on the properties of phase change material (PCM) microcapsules has been studied. The analytical techniques used for the characterization of the particles were differential scanning calorimetry (DSC) and modulated DSC, dynamic light scattering, environmental scanning electron microscopy (ESEM) and gel permeation chromatography (GPC). The chemical property differences between the encapsulating “shell” material, acrylic polymer in this case, compared to the “core” material (PRS paraffin wax), such as polarity and interfacial tensions, largely determine the thermodynamically favored morphology of the microcapsules. While the equilibrium morphology was a core/shell structure, kinetic factors relating to the competition between the fast acrylic polymerization rate and the diffusion limited rate of phase separation were found to constrain the ability of the system to approach that equilibrium structure. For both homopolymerization of methyl methacrylate (PMMA) and copolymerizations of methyl methacrylate with methyl acrylate (P(MMA-co-MA)), “pomegranate” microspheres were observed with a thin acrylic shell surrounding an inner composite structure constituted by a paraffin matrix with a dense assortment of PMMA spherical domains. Ter-polymerizations incorporating methacrylic acid (P(MMA-co-MA-co-MAA) had a remarkable effect on the morphology and average particle size, resulting again in “pomegranate” microparticles but where the internal PMMA spheroids were more densely populated closer to the outer portion of the capsule; approaching a core/shell structure. As the amount of polyvinylpyrrolidone stabilizer in the aqueous medium was increased and the PRS/monomers proportion was decreased, the mean particle size of the microcapsules decreased. However, higher PVP/monomer and PRS/monomer ratios led to less efficient encapsulation of the PRS paraffin wax. Near perfect encapsulation efficiency was obtained for two pairings of these ratios via P(MMA-co-MA-co-MAA) polymerization, but only up to an equal mass ratio of PRS to acrylic polymer. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie101727b