Toughness evaluation of poly(butylene terephthalate) nanocomposites

Abstract

This research investigates the toughness of poly(butylene terephthalate) (PBT) nanocomposites, based on mechanical characterizations and subsequent microstructural observations. Montmorillonite (MMT) and nano-precipitated calcium carbonate (NPCC) were selected as nano-reinforcing phases. Notched Izod impact test, tensile test as a quasi-static loading, and mode-I fracture toughness test, were conducted to evaluate the toughness. The corresponding fracture surfaces were analyzed using scanning electron microscopy (SEM). Tensile test results were linked with the morphologies of corresponding tensile-fractured surfaces. The results indicated that massive fibrillation in PBT/MMT nanocomposites dissipated lower energy relative to the large plastic deformation that was induced in the fracture surface of pure PBT. For PBT/NPCC samples, however, surface roughening mechanism was observed to increase the toughness in the tensile test, as compared to plain PBT. The fracture morphology of compact tension (CT) specimens exhibited a low extent of plastic deformation for pure PBT. However, the crack initiation zone of both nanocomposites showed a fibrillated morphology, leading to the increase of stress intensity factor up to 57% and 45% with the application of MMT and NPCC, respectively, as compared to pure PBT. The crack propagation region was, however, associated with shallow fibrils for MMT and local polymer yielding for NPCC.