Residual stress behavior and physical properties of transparent polyimide/surface-modified CaCO₃ nanocomposite films

A series of polyimide (PI) nanocomposite films with various surface-modified colloidal calcium carbonate (SCaCO₃) contents were prepared and their physical properties were investigated to understand their possible use as polymer substrates. The morphology, thermal stability, residual stress behavior, moisture barrier and optical properties of nanocomposite films were investigated as a function of the SCaCO₃ content and were found to be strongly dependent upon the chemical and morphological structures. With the addition of up to 0.5 wt% SCaCO₃ in the PI matrix, resultant nanocomposite films exhibit not only enhanced thermal properties, but also minimized residual stress and excellent optical properties, simultaneously. With increasing SCaCO₃ content, the water vapor transmission rate (WVTR) is greatly decreased from 630.76 to 484.22 g/m²/day. The residual stress was in the range of 26.0 to 12.1 MPa and is highly dependent on both temperature variation and SCaCO₃ content. Although the residual stress becomes lower at 0.5 wt% SCaCO₃ content, it increases at relatively high SCaCO₃ loadings due to inadequate dispersion of the SCaCO₃ and low interfacial interactions between the polymer and filler surfaces. Therefore, further studies are needed to maximize the performance of nanocomposite films by enhancing the compatibility of the polymer matrix and fillers.