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  • 1.
    Shetty, Pramod
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Study on Supramolecular Gel Lubricants2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Most of the rolling element bearings are lubricated with Grease lubricant. Generally, the grease is expected to serve for life. The major causes of the bearing failure are due to the failure of the lubrication. The grease will experience creeping, oil permeation, oil separation etc. The separated oil will be lost permanently from the bearing. The widely used grease for general application is the lithium grease. The thickener of the grease consists covalent bond. When the grease is sheared, the breakage of the covalent bond will be permanent, resulting in the permanent loss of the rheological properties.

    The gels have unique properties such as thermal reversibility, viscoelasticity and thixotropy. They become mobile under shear stress and solidify again when the shear stress is removed. This property can be harnessed to avoid the base oil creeping, oil permeation, leakage in gears and bearings. Due to the presence of the polar group in the gels, they form a good tribo film and prevent the wear.  Under the shear stress, weak supramolecular interactions will be distorted, and this leads to the release of the oil and they re-form the structure after a certain period of rest. When the gel is in the solid-state, it will avoid creeping and evaporation. Many classes of gels are either derived from natural sources or from environmentally friendly materials. Thus, the lubricant formed out of gel would effectively solve both environmental as well as lubrication problems.

    In this work, supramolecular gel lubricants were prepared out of fully green, cellulose derivatives and starch hydrolysates. The non-ionic hydroxyethyl cellulose (HEC) and anionic sodium carboxymethyl cellulose (NaCMC) were chosen to understand the effect of ionic and non-ionic gelators on the rheological and the tribological parameters. Traditionally fat was used as a lubricant, now, in food industry various fat replacers are being used. To study whether the fat replacers can act as a thickener, Dextrin and maltodextrins were chosen.  Dextrin and maltodextrin with the different DE values were selected to understand the influence of molecular weight on gelation and tribological performance.  Inspired by the recent developments and advantages of aqueous lubrication, mixer of water and poly(ethylene glycol) 200 (PEG 200) is chosen as the base fluid. It was found that a very small amount of gelator can increase the viscosity of the PEG/water to several orders. The thermal stability of the gels was studied using thermogravimetric analysis (TGA) and found that gels can increase the thermal stability of the base fluid. FTIR results showed the formation of a non-covalent bond between the PEG molecules and water. It is shown that anionic gelator will result in producing low friction and wear in comparison to non-ionic gelator. The possible tribo-film formation due to the negative charge in the NaCMC molecules is attributed to these results. The very low friction and low wear was exhibited by the dextrin and maltodextrin gels. It is proposed that this could be due to the microspherical particles of gels which can act as nano bearings. It was found that choosing the optimum concentration of the gelator is important to reduce friction and wear. The higher gelator concentration will form the hard gel, which cannot flow and replenish the sliding contact, resulting in the starved lubrication. This will cause high wear and friction. These gel lubricants can be used in food, pharmaceutical and biomedical industries.

  • 2.
    Shetty, Pramod
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Mu, Liwen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Fat mimicking compounds as grease thickeners in Poly(ethylene glycol)/water: Adopting the solution from history2020In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 578, p. 619-628Article in journal (Refereed)
    Abstract [en]

    Water-based lubricants are thought to be the next generation green lubricants, however, there are very few developments of aqueous grease lubricants. Here, water-based grease lubricants were developed using the food fat replacers. The concept of using fat replacers was inspired by the historical usage of fat as a lubricant. Dextrins were chosen as the fat replacers and mixture of water and PEG as the base fluid. Dextrins with different molecular weights were selected to study its effect on the rheological, tribological and thermal behavior of the gels. It was found that only higher molecular weight dextrins will form the colloidal gels, whereas low molecular weight dextrins will form the colloidal solution. The SEM images of the dried samples showed the agglomerated micro-spherical network with the void to hold the base fluid. It was found that, at an optimum concentration, the fat replacers showed 35–58% lower friction and 29–41% lower wear than the pure PEG200/water solution regardless of their molecular weight. The spherical shaped colloidal particles will form the film over the metal surface by nano-filling and these particles will act as nano-bearings which will reduce the wear and friction. These gel lubricants can be used where the highly biodegradable and bio-compatible green lubricant is needed.

  • 3.
    Shetty, Pramod
    et al.
    Luleå University of Technology.
    Mu, Liwen
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Polyelectrolyte Cellulose Gel with PEG/Water: Toward Fully Green Lubricating Grease2020In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 230, article id 115670Article in journal (Refereed)
    Abstract [en]

    Developing a fully green lubricant is an urgent need due to the growing consciousness of environmental protection and dwindling resources. In this work, fully green gel lubricants were developed out of cellulose derivatives as gelator and mixture of water and poly(ethylene glycol) 200 (PEG 200) as the base fluid. The non-ionic hydroxyethyl cellulose (HEC) and anionic sodium carboxymethyl cellulose (NaCMC) were chosen to understand the effect of ionic and non-ionic gelators on the thermal, rheological and the tribological properties of the gel lubricant. HEC or NaCMC is demonstrated as effective additive to reduce wear, stabilize friction coefficient and enhance the thermal stability of developed lubricants. It is shown that anionic gelator will result in producing lower friction and wear in comparison to non-ionic gelator, which may be attributed to the possible tribo-film formation due to the negative charge in the NaCMC molecules and its larger molecular weight.

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