Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
performance exceeding that of standard products: 1. Waste plastic-derived synthetic lubricants [10]
In 2021, Hackler et al. attempted to produce synthetic lubricants from upcycled polyolefin waste plastics and compare their tribological characteristics to industrial standard mineral and synthetic oils. According to Hackler et al., more than 410 million metric tons of plastic are produced annually. Nonetheless, around 300 million metric tons of plastic are discarded each year with 58% found in landfills, 24% incinerated for heat and power, and 18% recycled. As shown in Figure 1, most plastics undergo mechanical recycling, a process of converting waste plastic into secondary raw materials for new products, but this method yields unfavorable downcycled products with lower quality than their primary source. On the other hand, chemical recycling proves to be a potentially more cost-effective strategy that upcycles waste plastics into high-value products through plastic polymer conversions to alkanes, alkenes, alkynes, and aromatics. A energy-efficient chemical recycling process known as catalytic hydrogenolysis, a process that severs carbon-carbon bonds by a catalyst and H2
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to produce alkanes, has been experimented with a platinum on strontium titanate nano cuboid catalyst (Pt/STO) on high-density polyethylenes (HDPEs). Through this process, HDPEs were successfully transformed into high-quality liquids (HQLs) with potential applications as a base oil component in commercial automobile lubricants. Since total plastic production consists of 29% polyethylene and 17% polypropylene, the two most common polyolefins, hydrogenolysis was performed on various waste plastics with HDPEs, linear low-density polyethylene (LLDPEs), and bubble wrap. The tribological performance of the HQLs created from those polyethylene sources was compared to industrial standard mineral oil (Group III) and synthetic oils (PAO4 and PAO10).
These lubricant base stocks were subjected to an hour-long engine stimulation test with a ball-on-disc tribo-test machine at 100°C to analyse their changes in coefficient of friction (COF), represented graphically as seen in Figure 2. LLDPE-derived HQL displayed the lowest average COF of 0.08, followed closely by HDPE and bubble wrap-derived HQLs, which both had a 0.15. In fact, all HQLs revealed comparable COF
Figure 1: Chemical recycling methods: downcycling and upcycling [10]
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LUBE MAGAZINE NO.185 FEBRUARY 2025
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