2.2 Measurement of coefficient of friction
The selected waxy materials were melted at 5 °C higher than their melting point and pool into a cylindrical mold (40 mm in diameter × 25 mm in height). The molten waxes were allowed to solidify under room temperature (23 °C) for 2 hours before removed from the mold. The wax disc was then taped on the platform of a Discovery Hybrid Rheometer (TA Instruments, New Castle, DE) equipped with tribo-rheometry accessories for measurement of coefficient of friction. The test was conducted following the procedures reported by Krasmik and Schlattmann (2015) [9] except that a three-ball on plate setup (Figure 1) was used. Normal load (FLoad), sliding velocity (υ) and temperature were varied to determine their influence on friction and wear behaviors of different waxes. The bottom surface of samples in contact with glass were tested. When testing the effect of normal load, normal load of 5, 10 and 15 N were used at a fixed sliding velocity of 5 rad/s under room temperature (25 °C). For evaluating the effect of sliding velocity, 1, 5 and 10 rad/s were used with fixed normal load of 5 N under room temperature. For evaluating the effect of temperature, environment temperature of 0, 25 and 50 °C were tested at fixed normal load (5 N) and sliding velocity (5 rad/s). Three samples were prepared for each test, and each sample was measured once.