Thermal stability of composite phase change material microcapsules incorporated with silver nano-particles

This paper reports a study on the thermal stability of phase change material microcapsules that are incorporated with silver nano-particles (Ag-NPs). The novel microcapsules were fabricated by the technique of in situ polymerization, with aminoplast as the wall and phase change material bromo-hexadecane (PCM BrC16) as the core. Thermal gravimetry (TG) analysis was applied to measure the thermal stability of these microcapsules and surface morphology of the microcapsules was observed by means of scanning electron microscopy (SEM) after an application of curing treatment at 130 °C. Comparing with conventional phase change material microcapsules (PCMMs), nano-composite phase change material microcapsules (NCPCMMs) have higher thermal stability. This can be attributed to nano-composite structure of the microcapsules, in which metal Ag-NPs distributed on the surface to increase wall toughness and strength. The possible reinforcement mechanisms of the nano-composite structure are explored.     

Methoxybutropate Microencapsulation by Gelatin-Acacia Complex Coacervation

Microcapsules of methoxybutropate solid particles or of an oily saturated solution of the same drug were prepared by complex coacervation between gelatin and acacia and dried with three different methods: isopropanol addition, spray-drying, and freeze-drying. Successively, microparticles were analyzed by infrared thermobalance, ultraviolet (UV) spectroscopy, optical and scanning electron microscopy, and sieves to find out parameters such as yield, moisture content, encapsulation percentage, morphology of solid particles, and particle size. Results highlighted that the most appropriate drying method for industrial purposes was spray-drying, particularly for oil-containing microcapsule formulations.     

壳聚糖包覆腐殖酸微胶囊的制备及其保水性能研究

以壳聚糖(CTS)为壁材,腐殖酸(HA)为芯材,制备了壳聚糖包覆腐殖酸(CTS/HA)微胶囊保水材料。通过傅里叶红外光谱(FTIR)、偏光显微镜(POM)和场发射扫描电镜(SEM)分别表征和观察CTS/HA微胶囊的结构和表面形貌,探讨了不同芯壁比〔m(CTS)∶m(HA)〕、固化剂用量和搅拌速度对微胶囊表面形态的影响,并测试了CTS/HA的保水性能。结果表明,CTS/HA呈现包覆微胶囊结构,当m(CTS)∶m(HA)=1∶3、固化剂用量为CTS/HA总质量的1%、搅拌速度为500 r/min时,微胶囊具有较好的表面形态,且具有较好的吸水和保水性能,其12 h的吸水率和保水率分别高达248%和158%。     

Precision emulsification for droplet and capsule production

Emulsions and microcapsules are typical structures in various dispersion formulations for pharmaceutical, food, personal and house care applications. Precise control over size and size distribution of emulsion droplets and microcapsules are important for effective use and delivery of active components and better product quality. Many emulsification technologies have been developed to meet different formulation and processing requirements. Among them, membrane and microfluidic emulsification as emerging technologies have the feature of being able to precisely manufacture droplets in a drop-by-drop manner to give subscribed sizes and size distributions with lower energy consumption. This paper reviews fundamental sciences and engineering aspects of emulsification, membrane and microfluidic emulsification technologies and their use for precision manufacture of emulsions for intensified processing. Generic application examples are given for single and double emulsions and microcapsules with different structure features.     

In vivo Cellular Uptake,Degradation, and Biocompatibility of Polyelectrolyte Microcapsules

Polyelectrolyte microcapsules are made by layer‐by‐layer (LbL) coating of a sacrificial template, followed by decomposition of the template, to produce hollow microcapsules. In this paper, we report on the in vivo cellular uptake, degradation and biocompatibility of polyelectrolyte microcapsules produced from alternating dextran sulphate and poly‐L‐arginine layers on a template of calcium carbonate microparticles. We show that a moderate tissue reaction is observed after subcutaneous injection of polyelectrolyte microcapsules in mice. Within sixteen days after subcutaneous injection, most of the microcapsules are internalized by the cells and start to get degraded. The number of polyelectrolyte layers determines the stability of the microcapsules after cellular uptake.     

Experimental Investigation of Performances of Microcapsule Phase Change Material for Thermal Energy Storage

Performances of microcapsule phase change material (MPCM) for thermal energy storage are investigated. The MPCM for thermal energy storage is prepared by a complex coacervation method with gelatin and acacia as wall materials and paraffin as core material in an emulsion system. A scanning electron microscope (SEM) was used to study the microstructure of the MPCM. In thermal analysis, a differential scanning calorimeter (DSC) was employed to determine the melting temperature, melting latent heat, solidification temperature, and solidification latent heat of the MPCM for thermal energy storage. The SEM micrograph indicates that the MPCM has been successfully synthesized and that the particle size of the MPCM is about 81 μm. The DSC output results show that the melting temperature of the MPCM is 52.05 °C, the melting latent heat is 141.03 kJ/kg, the solidification temperature is 59.68 °C, and the solidification latent heat is 121.59 kJ/kg. The results prove that the MPCM for thermal energy storage has a larger phase change latent heat and suitable phase change temperature, so it can be considered as an efficient thermal energy storage material for heat utilizing systems.     

Non-destructive 3-dimensional mapping of microcapsules in polymeric coatings by confocal Raman spectroscopy

Nowadays, the properties of polymeric coatings are enhanced by various additives mixed into the resin. Recently, embedding of polymeric microcapsules into the coating matrix has been investigated to provide special on-demand features to the coating. The detection and characterization of such microcapsules in a polymeric coating are of major importance but difficult, because both are built up by similar molecules with similar densities. Current analysis methods require complex sample preparation to allow reliable measurements.In contrast, confocal Raman spectroscopy allows fast and non-destructive differentiation between characteristic molecular bonds at a spatial resolution below one micrometer. Hence, the objective of this research was to apply this technique on microcapsules embedded in a coating and provide answers to the following questions: Can one detect microcapsules embedded in a coating and clearly identify them? Can one differentiate between full and empty microcapsules and the coating matrix? Can one determine the exact location of the capsules and their distribution in the coating?Therefore, several two-dimensional confocal Raman spectroscopy mappings recorded at different depths allowed a three-dimensional reconstruction of the polymeric coating with the polymeric microcapsules in it. Thereby, the distribution of the capsules within the coating could be determined with micrometer resolution. As a result Raman tomography provides a more detailed insight into the distribution of microcapsules through the possibility of three-dimensional reconstruction.     

Hollow microcapsules for sensing micro-scale flow motion in X-ray imaging method

For synchrotron X-ray micro-imaging of micro-scale biological flows in organisms, the development of a suitable flow-sensing tracer is essential for visualizing opaque flows quantitatively. In order to achieve this development in this study, the techniques employed in three different research fields were integrated namely, X-ray optics for enhancing X-ray concentration, fluid dynamics to satisfy the flow traceability and drug delivery system to fabricate bio-compatible microcapsules. On the front burner, we need a special sensor which can be well observed in X-ray micro-imaging and follow working fluid as well. As a result, bio-compatible micro-scale microcapsule sensors that perform the role of spherical micro lenses were developed. These novel microcapsules exhibit not only much improved contrast enhancement but also better performance as sensor tracers in micro-scale flows, compared to conventional solid particles.     

Matrix Tablets of Carrageenans. II. Release Behavior And Effect of Added Cations

Carrageenans are hydrocolloids in the rubbery state at standard conditions. They are useful excipients for controlled-release tablets. Three carrageenans, two κ-carrageenans (Gelcarin® GP-812 NF and GP-911 NF) and one ι-carrageenan (Gelcarin GP-379 NF), are analyzed regarding their release behavior in combination with sorption, swelling, and rheology. The l-carrageenan has a higher substitution by sulfate groups. The κ-carrageenan Gelcarin GP-812 NF contains a small amount of potassium chloride left over from processing. Water sorption of the pure materials was studied gravimetrically, and the rheology of different solutions (2% and 5% w/w) was studied by cup-cylinder rotation viscosimetry. Swelling was determined as the vertical expansion of the tablets with a specially designed swelling apparatus. Drug release from the tablets was performed by the USP paddle method for 8 hr. The data indicate that drug release increases when water sorption and swelling extent decrease and as viscosity increases. The order of release is nearly zero-order kinetics for theophylline monohydrate, a nonionic drug. Diffusion of the anionic drug diclofenac sodium is anomalous. In addition, the influence of the added salts potassium and calcium chloride on swelling and release was studied. Before tableting, physical mixtures of these salts with and without theophylline monohydrate were prepared. Swelling and release change in the same order, but this is only valid when the ionic interactions responsible for this are strong enough. Besides this, physical mixing of salts with the carrageenans can result in an increased release of drug caused by decreased cohesion of the matrix during drug release, mainly for calcium chloride.     

Self-healing of a high temperature cured epoxy using poly(dimethylsiloxane) chemistry

A high temperature cured self-healing epoxy is demonstrated by incorporating microcapsules of poly(dimethylsiloxane) (PDMS) resin and separate microcapsules containing an organotin catalyst. Healing is triggered by crack propagation through the embedded microcapsules in the epoxy matrix, which releases the healing agents into the crack plane initiating crosslinking reactions. A series of tapered double-cantilever beam (TDCB) fracture tests were conducted to measure virgin and healed fracture toughness. Healing efficiencies, based on fracture toughness recovery, ranged from 11 to 51% depending on the molecular weight of PDMS resin, quantity of healing agent delivered, and use of adhesion promoters.