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Abstract
The aim of this work was the investigation of the elastic behavior and the internal stress of two different polyvinyl alcohols (PVAs) and how their swelling behavior and drug release are influenced through internal stress. We used thermal mechanical analysis (TMA 202/1/F Netzsch-Germany) to make a qualitative evaluation of the internal stress and the elastic behavior of PVA 55/12 and 55/03. These two PVAs have the same molecular weight and different acetyl contents. The tablets were compressed with an instrumented eccentric tablet machine. Tablets from different PVAs showed different elastic behavior. The measured internal stress of PVA 55/12 was higher than that of PVA 55/03. By increasing the compaction force, the internal stress increased. The internal stress decreased as the humidity increased for both kinds of PVA. The expansion behavior in the diametrical and axial direction was significantly different due to the predominant orientation of the PVA crystals. PVA tablets that were thermal analyzed showed different swelling behavior from those that were not thermal analyzed. This can be caused by the released internal stress of thermal-analyzed tablets. The compaction behaviors of both PVAs were also investigated using different methods. PVA 55/03 had better compactibility and compressibility behavior. The drug release behavior was also investigated and showed that the drug release rate of PVA 55/12 was higher than that of PVA 55/03. This can be due to the different solubilities and elastic behaviors of the PVAs. TMA can be used to predict and evaluate elastic behavior and internal stress. Humidity can influence the internal stress of the tablet. The measured swelling of PVA was a combination of real swelling and the released internal stress. TMA also allowed prediction of the binding mechanism in tablets.