Investigating the tribological performance of different polymer and polymer nanocomposites using nanoscratch and wear techniques

Abstract

The objective of this research project is to gain an in depth understanding on the tribological behavior for a number of polymeric systems. These includes: (1) alumina-filled polypropylene (PP) nanocomposite; (2) rubber filled poly(ethylene terephthalate) (PET) nanocomposite; and (3) PET subjected to different heat treatment durations. The maximum loading of the alumina particles and rubber particles added to the matrix are 5 and 10wt% respectively. Nowadays, polymers and polymer composites are used as coatings, food packaging and automotive applications due to their adequate strength, lightness, ease of processing and low cost. However, they are susceptible to surface damage which may affect their appearance and weaken their strength. So, there is a strong need to know the scratch behavior of polymers. In this work, a number of tests have been conducted. They included the tensile test, polarized light microscopy, differential scanning calorimetry, nanoindentation test, nanoscratch test and wear test. According to the tensile test, the general results for the three kinds of specimens were different. The modulus of sample was enhanced with the addition of hard alumina particles or increasing crystallinity with annealing, while adverse results were obtained as rubber particles were incorporated. The tensile properties can be correlated to the results obtained from the nanoscratch test. From the nanoindentation and nanoscratch test, similar trend was observed for both the alumina-filled PP and annealed PET. Both systems showed increase nanohardness and scratch resistance significantly. The plastic depth was greatly reduced in the nanoscratch test. In contrast, the performance of the rubber-filled PET was totally different. Reductions in nanohardness and scratch resistance was found in the rubber filled PET. Two testing parameters were studied in the scratch test, i.e. the effects of maximum terminal load and the scratch rate. Both parameters have obvious influences on the scratch behavior. It was found that the scratch penetration increased by employing higher maximum terminal load or reduction in the scratch velocity.