A combined differential scanning calorimetry-dynamic mechanical thermal analysis approach for the estimation of constrained phases in thermoplastic polymer nanocomposites

Poly(butylene terephthalate) (PBT) nanocomposites reinforced with different weight fractions of montmorillonite (MMT), and nanoprecipitated calcium carbonate (NPCC) were prepared by a two-step melt compounding method. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses were employed to explore the effect of nanofiller inclusion on the crystalline structure of PBT nanocomposites. The mobile amorphous fraction (MAF) and the rigid amorphous fraction (RAF) were first measured using the specific heat capacity (C-p) and melting enthalpy data. However, the contributors to total RAF, including interfacial RAF (RAF(int)) and crystalline RAF (RAF(c)), could not be discerned using only DSC. A novel and simple method was hence developed by employing a combined DSC-dynamic mechanical thermal analysis (DMTA) approach (CDDA) to disentangle the RAF components and determine the fractions of constrained volume constituents. To validate the results, the MAF calculated by CDDA were compared to those of DSC. The values obtained using CDDA were relatively higher, owing to the more significant sensitivity of this approach to polymer chain mobility.