Polymers have become an indispensable part of everyday life as they are widely used in many different applications. Natural rubber, silk, and amber are natural polymers that have played an important role in human history. Unique physical properties such as viscoelasticity, toughness, self-lubrication and many others can be achieved by optimizing the fabrication process of the synthetic polymers.
Importance of Wear and Friction of Polymers
Polymers are often used for tribological applications, such as conveyor belts, tires and bearings. Different wear mechanisms take place based on the contact conditions, the mechanical properties of the polymer, and the properties of the debris or transfer film that is formed during the wear process. Reliable and measurable tribological evaluation is required to ensure that the polymers have adequate wear resistance under the service conditions. This ensures that the wear behaviors of different polymers are quantitatively compared in a controlled and monitored manner and that the best candidate for the target application is selected.
The Nanovea Tribometer provides repeatable wear and friction testing using ASTM and ISO compliant linear and rotative modes, with optional high temperature wear and lubrication modules available in a single pre-integrated system. This unprecedented range enables users to replicate a different work environment of the polymers such as high temperature, concentrated stress, wear and so on.
In this application, it is shown that the Nanovea Tribometer is a perfect tool for comparing the wear and friction resistance of a variety of polymers in a quantitative and well-controlled way.
Figure 1. Setup of the polymer wear test.
The Nanovea Tribometer was used to evaluate the coefficient of friction (COF) and the wear resistance of various common polymers. An Al2O3 ball served as the counter material. The Nanovea 3D non-contact profilometer was first used to measure the wear tracks on the polymer samples and then optical microscope was used after the tests. Table 1 summarizes the test parameters. Using the formula K=V/(Fxs), the wear rate, K, was evaluated where V is the worn volume, s is the sliding distance, and F is the normal load.
It should be noted that the Al2O3 ball as a counter material was employed as an example in this study. The performance of different material coupling under true application conditions, such as in lubricant or liquid, can be simulated by applying any solid material.
Table 1. Test parameters of the wear measurements.
|Duration of test
|Wear track radius
||24 °C (room)
Results and Discussion
Wear rate is a critical factor for establishing the materials’ service lifetime, whereas the friction plays a vital role during the tribological applications. In Figure 2, the evolution of the COF for different polymers is compared against the Al2O3 ball during the wear tests. COF acts as an indicator when there are failures and the wear process enters a new stage. Among the polymers tested, HDPE was found to retain the lowest constant COF of ~0.15 all through the wear test. The smooth COF suggests the formation of a stable tribo-contact.
Figure 2. Evolution of COF during the wear tests.
Figures 3 and 4 compare the wear tracks of the polymer samples following the tests determined by the optical microscope and Nanovea non-contact optical profilometer, respectively. The 3D morphology of the wear track on the CPVC sample is shown as an example in Figure 5. The results of the wear track analysis are summarized in Table 2. The wear volume of the polymer samples is precisely determined by the Nanovea 3D profilometer. This allows the wear rates to be accurately calculated and compared. It can be seen that Polypropylene, HDPE, and Nylon 66 samples exhibit small wear scars following the wear tests and have similar wear rates of 0.0032, 0.0029, and 0.0020 m3/Nm, respectively. On the other hand, the CPVC sample displays the highest wear rate of 0.1121 m3/Nm. The wear track of CPVC has deep parallel wear scars.
Figure 3. Wear scars on the polymer samples after the tests.
Figure 4. Profiles of the wear track cross section.
Figure 5. 3D morphology of the wear track on the CPVC sample.
Table 2. Wear track depth and wear rate analysis of the polymers.
The wear resistance of polymers plays an important role in their service performance. In this analysis, it was demonstrated that the Nanovea Tribometer assesses the coefficient of wear rate and friction of a variety of polymers in a quantitative and well-controlled manner. Among the tested polymers, HDPE was found to have the lowest COF of ~0.15. Polypropylene, HDPE, and Nylon 66 samples have low wear rates of 0.0032, 0.0029 and 0.0020 m3/Nm, respectively. The combination of great wear resistance and low friction makes HDPE an excellent candidate for polymer tribological applications. The Nanovea 3D non-contact profilometer allows precise wear volume measurement and serves as a tool to study the complex morphology of the wear tracks, thus affording a better insight into the fundamental understanding of wear mechanism.
This information has been sourced, reviewed and adapted from materials provided by Nanovea.
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