Microencapsulation using poly(DL-lactic acid) IV: Effect of storage on the microcapsule characteristics

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Abstract
Poly (dl-lactic acid) [dl-PLA] microcapsules containing phenobarbitone were prepared using a W/O emulsion method. Microcapsules of nominal C: P ratio, 1:2 and 1:3 using three different molecular weight polymers, 20500, 13300 and 5200 were investigated to study the effect of storage conditions on the microcapsule properties. All microcapsules were stored under desiccated condition at temperatures of 4°, 20° and 37°C for six months. Storage temperatures of 4° and 20°C did not cause appreciable changes in the release rate after storage. Microcapsules stored at 37°C showed an annealing effect, causing shrinkage of microcapsules, and lowering of the release rate after storage for six months. The microcapsules prepared from low molecular weight dl-PLA fused completely whilst stored at 37°C and the other two high molecular dl-PLA also showed some aggregation. There were insignificant variations in the mean microcapsule diameter during storage. The phenobarbitone content of the microcapsules was also unchanged.