Investigation of nanoindentation as a fast characterization tool for polymer degradation study

The aim of this study is to compare the mechanical properties of aged polymers measured at nano and macro scales in order to develop a fast characterization tools to predict polymer durability. Commercial thick PP/PE copolymer samples were aged under artificial aging conditions. The evolution of the mechanical properties with aging time was studied either at nano scale using a nanoindenter and at macro scale using a Dynamic Mechanical Analysis aparatus, nano and macro scale results were compared. Chemical degradation was monitored by infrared spectrometry and the surface topography was studied by Scanning Electron Microcopy. A Voigt model was used to calculate the Young's modulus of the bulk sample using the nano mechanical data and the results were compared to the measured macro Young's modulus. A good correlation was found between macro and nano scales as long as macroscopic defects such as cracks does not appeared. This work shows that nano indentation is a suitable technique to detect early stage degradation of polymers and therefore a powerful tool to predict durability of materials.