Preparation of macro-capsules containing shape-stabilized phase change materials and description of permeation kinetics of its wall

Through in situ polymerization, a kind of macro-capsule was prepared by using silica gel as the shell material and shape-stabilized phase change materials (SSPCM) containing 50 wt% of n-octadecane (OD) of high density polyethylene (HDPE) as the core. The surface and its construction of capsules, the permeability of the capsule wall and the release kinetics parameters of the OD in the system of petroleum ether were experimental investigated by a scanning electron microscope (SEM), thermal cycles and the extraction release kinetics. The results showed that the wall thickness of the macro-capsules was about 20–50 μm under the experimental conditions. The SSPCM surface, modified with chromic acid, is rough, and there are many tiny holes about 3 μm in diameter in it. For these reasons, either the hydrophilicity of the SSPCM surface or the cohesion between the core and the wall have been greatly improved, and then, the weight loss percentage (WLP) of the macro-capsules is decreased by about 1.5 and 2.5 times relative to that of un-modified and modified SSPCM, respectively. Additionally, after the macro-capsules were re-sprayed by using a calcium chloride solution, its wall was more compact. From the fitting parameters of the power exponent, there were two different release mechanisms, quasi-Fickian diffusion and anomalous transport for the un-encapsulated SSPCM and the macro-capsules, respectively.