Preparation, characterization and permeation kinetics description of calcium alginate macro-capsules containing shape-stabilize phase change materials

Macro-capsules containing shape-stabilize phase change materials (SSPCM) which have 50 wt% of n-octadecane (OD) and 50 wt% of high-density polyethylene (HDPE) were prepared by using a traditional coating pan with calcium alginate (CA) as the shell material. The surface morphologies and construction, wall permeability and the kinetic release parameters of OD in a solvent of petroleum ether along with the thermal properties of the materials were investigated using a scanning electron microscope (SEM), thermal cycles, the extraction release kinetics, and differential scanning calorimeters (DSC), respectively. The results show the wall thickness of the macro-capsules was about 30–50 μm under the experimental conditions. The surface of the SSPCM after the application of chromic acid is rough and littered with numerous, microscopic holes measuring about 3 μm in diameter. From this one may conclude that either the hydrophilicity of the SSPCM surface or the permeability of the prepared macro-capsules was altered during the process and thus differed from the unmodified samples. In addition to this, the weight loss percentage (WLP) of the macro-capsules was approximately 1.5 times in the unmodified capsules, and 3 times in the modified SSPCM. The addition of the plasticizer glycerin into the wall significantly decreased the impermeability of the macro-capsules. From the parameters of the Power exponent, there are two different release mechanisms, Fickian/quasi-Fickian diffusion and anomalous transport for modified and unmodified SSPCM.