Scratch Resistance Assessments of Polymeric Systems – Using Instrumented Indentation Testing and Laser Scanning Confocal Microscopy
Date Issued
2010
Date
2010
Author(s)
Huang, Yu-Hsin
Abstract
In this thesis, a combination of instrumented indentation technique (IIT) and laser scanning confocal microscopy (LSCM) was used to assess the scratch resistance of polymer systems. The effect of glass transition temperatures Tg and nanoparticle additive polarities on the surface mechanical properties and scratch resistance of polymers were investigated. By the continuous stiffness measurement (CSM) method, the elastic modulus and hardness of polymer systems were measured using IIT. The scratch resistance assessment was based on measuring the damage deformation and analyzing the scratch data, such as the scratch depths, scratch width, recovery, and friction coefficient as a qualitative method to evaluate the durability of the polymer system. Two types of scratch test methods were used: the progressive force and constant force scratch tests. The onset force at which scratch damage changed from elastic (total recover, invisible) to plastic (visible) deformation was approximately estimated from the progressive force scratch test. From an array of constant force scratch test, the onset force was determined more accurately. The onset force of elastic-plastic deformation can be used as an indicator to rank scratch resistance of a polymer system. The scratch morphology including scratch depths, scratch width, pile-up height were measured using LSCM. The scratch morphological data were analyzed and also used to assess the scratch resistance of the system.
Two polymer systems were studied in this thesis: 1. Crosslinked epoxy (EP) systems with different glass transition temperatures; 2. Polyurethane (PU) thin films containing 2 % nanosilica (SiO2) with dispersant/additive of different polarities. In the first case study, the effect of glass transition temperature on the scratch behavior was evident. The higher glass transition temperature, the higher scratch resistance. In the second case study, two series of the PU-SiO2 films were used due to different preparation conditions. Series 1 is thinner and has a higher glass transition temperature (~ 90 oC), and series 2 is thicker and has a lower glass transition temperature (~ 55 oC). In series 1, the control sample and reference group had similar mechanical data and scratch morphology so that the final ranking of scratch resistance is not clear. On the other hand, the control sample in the series 2 has the weakest scratch resistance and worst damage right after scratched. However, after 16 hours, the scratch damage of control sample (in series 2) recovered faster than that of the reference group. The scratch morphology of control sample (in series 2) became wider and shallower and less visible. Overall, the scratch damages were found to be more severe in the series with the lower glass transition temperature. Therefore, the testing results in both case studies indicated that the higher glass transition temperature had a stronger scratch resistance.
Subjects
Instrumented indentation technique
Laser scanning confocal microscopy
Nanoparticle silica
Glass transition temperature
Elastic modulus
Hardness
Scratch resistance
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