Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE Table 3: Base oil effects on PUGT grease conversion.
Within the proper dosage range the choice of base oil is essential to give higher thickening efficiencies and thus higher yield. For instance, at 20% PUGT dosage (see Table 3), AN and AB fluids and PAG give excellent thickening effect with good milling characteristics (usually 2 x milling is enough). Insufficient process conditions and improper PUGT dosage in the first stage would require many times more milling and/ or lead to low grease yield. The alternative 1-stage conversion is not recommended due to extended process time and lower grease yield.
Table 4 compares the structural (mechanical) and high temperature stability of the commercial PUG made via the in-situ method with the PUG made via the two-stage method via PUGT. PUG made via the two-stage method (PUG-1) clearly outperforms one of the commercial greases (PUG-A) and is on par with the other two commercial candidates (PUG-B and C). The ease in the use of PUGT allows PUG to be easily made in the lab, pilot plant, and well as any commercial plant.
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from 25 to 150 C, Figure 6), OBCSG grease shows substantial softening (G’, the storage modulus, dropped nearly 70%) for OBCSG Grease whereas polyurea Grease PUG-1 had a minimum reduction in G’, a clear sign of far superior temperature stability.
Figure 6: Rheological grease data under thermal stress.
Table 5: Boosted Load Carrying Performance.
Performance additives such as extreme pressure, anti-wear, friction modifier, and rust preventive can be added in the second step during the PUGT conversion. In Table 5, via the addition of commonly used EP additives, polyurea grease made with PUGT easily matches up and exceeds lithium complex grease made with preform thickener.
Table 4: Mechanical/HT stability comparison of PUG via PUGT powder or via in-situ method.
When compared to OBCSG grease, via rheological testing under thermal stress (a temperature sweep
22 LUBE MAGAZINE NO.158 AUGUST 2020
Work is in progress within Novitas to develop alternative PUGT options in addition to PUGT powder to further simplify and streamline the conversion process. For instance, the noodle formed after the first step would be difficult to go beyond more than 30% PUGT content with the typical batch processing equipment. It is now easily manageable via continuous mixer such as Twin-Screw Extruder that produces the PUGM masterbatch in noodle or extrudate forms.
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