Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
values to the best synthetic oil, PAO10. Meanwhile, Group III observed the greatest drop in COF over time, but the highest COF range from 0.14 to 0.19 during the first 40 minutes. The increase in COF of Group III is attributed to the abrasive and adhesive interactions between the ball and the significant amount iron oxide debris on the disc, implying Group III’s inefficient surface protection.
Furthermore, each base stock’s wear scar volumes from the ball-on-disc tribo-test were also examined with HQLs exhibiting a 43% reduction in wear compared to Group III. Both Group III and PAO4 were unable to protect their surfaces and produced large wear scars, which were results of high degrees of carbon branching that limited intermolecular forces within alkane chains and incapability of forming a protective layer with small molecules, respectively. However, PAO10 and all HQLs exhibited the lowest wear scars due to their extremely low carbon branching that encouraged methylene interactions in between alkane chains to maintain a protective film. The COF and wear scar volume results highlight HQLs’ comparable tribological property of surface protection to that of industrial grade synthetic oils and both their superior performance over standard mineral oil.
No.156 page 5
Figure 2. COF Changes at 300°C for Group III, PAO4, LLDPE, Bubble Wrap, PAO10, and HDPE[10]
Since HDPEs and PAO10 performed exceptionally well with similar COF results, synergistic interactions between the two were examined. 0, 10, 20, 30, 50, 70, 90, and 100 percent weight of HDPE-derived HQL was added to PAO10 before undergoing friction and wear tests at 25°
C and 100°C. Before the synergy,
virgin HQL presented lower wear scar volume due to its high viscosity and increasing COF from the formation of an iron oxide tribolayer on the test disc at 25°C (Figures 3 and 4). However, virgin HQL obtained much lower COF with increased fluidity and wettability that prevented iron oxide accumulation at 100°C (Figure 5). After the various trials, an optimal 20-30% HQL in PAO10 at 25°C and 100°C demonstrated the most decrease in friction and wear of around 9% and 30%, respectively. The COF and wear scar volume at that concentration are even lower than that achieved by virgin PAO10 due to the addition of linear polymer chains in HQL enhancing the fluidity and polydispersity of bulky PAO10 molecules, creating a finer friction reduction.
Figure 3: Wear Scar Volumes of PAO10 and HQL Concentrations [10]
Figure 2: COF Changes at 300o PAO10, and HDPE [10]
C for Group III, PAO4, LLDPE, Bubble Wrap,
In the end, the performance of HQLs supersedes that of mineral oil and is on par with synthetic oil
LUBE MAGAZINE NO.185 FEBRUARY 2025 35
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