*3.1.3 Analysis of tribological properties*

Tribological properties were evaluated with the help of a four ball tester equipment [25]. Coefficient of friction (COF) and wear scar diameter (WSD) are the parameters used to evaluate tribological properties. From **Figure 6**, it is noted that with the addition of nanoparticles, the WSD is reduced [26–29]. The WSD is found to be decreased by 18.31% with the blending of 0.85% weight percentage of SiO2. The small size of SiO2 makes improvement in the tribological properties by reducing friction and wear by rolling, mending, and protective film formation [30].

From **Figure 7**, it is noted that with the addition of nanoparticles, the COF is increasing for PO blends with SiO2. However, in comparison with SAE20W40, the COF value of PO blends is considerably low.
