Thermoformed PBS films exhibiting two glass transitions (Tg). The first Tg at ca. -39°C is the same for all samples, whereas the second transition at 44.8°C for unmodified PBS is shifted towards lower temperatures (38.3 -39.5°C) for the composites. This phenomenon indicates that the presence of the filler in the matrix restricted the polymer chain interaction, and a weaker interaction between the polymer matrix and the filler was formed.