Rheological and tribological approaches as a tool for the development of sustainable lubricating greases based on nano-m
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Rheological and tribological approaches as a tool for the development of sustainable lubricating greases based on nano-montmorillonite and castor oil José Enrique MARTÍN-ALFONSO1,*, María José MARTÍN-ALFONSO1, Concepción VALENCIA1, María Teresa CUBERES2 1
Department of Chemical Engineering and Materials Science, Campus de “El Carmen”, University of Huelva, Chemical Product and Process Technology Research Center (Pro2TecS), Huelva 21071, Spain
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Department of Applied Mechanics and Project Engineering, University of Castilla-La Mancha, Almadén 13400, Spain
Received: 11 April 2020 / Revised: 14 May 2020 / Accepted: 21 May 2020
© The author(s) 2020. Abstract: This study investigates the development of novel montmorillonite/castor oil blends to formulate sustainable lubricating greases to promote the replacement of petrochemicals industry-derived materials by substances obtained from renewable sources. Specifically, the effect of the thickener concentration on the rheological, chemical, thermal, tribological properties, and atomic force microscopy (AFM) microstructure of these systems were studied. The results showed that the C20A nanoclay content could be used to modulate the viscosity values, the linear viscoelastic functions, and tribological properties of these montmorillonite dispersions. In general, these gel-like dispersions exhibited remarkable lubricant properties; the samples showed values of the friction coefficient and wear scars similar or lower than those obtained with model bentonite grease. Keywords: lubricating greases; nanoclay; vegetable oil; rheology; tribology
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Introduction
During the last few years, the depletion of fossil fuels and the general raising of global concern over environmental risks and climate change have aroused a global widespread alarm. For this point, currently, the development of biodegradable materials and products with appropriate properties is a challenging research subject for the material scientists and technologists worldwide. In this sense, there is a huge need of producing “green” products suitable to be used as lubricants with the aim of decreasing the impact that fossil fuels-based materials yield in the nature [1, 2]. Lubricating greases are soft matter multiphase systems that consist of fluid lubricant, traditionally a mineral or synthetic oil, as continuous
phase that is physically or chemically entrapped in a network formed by a solid (thickener agent), generally a metal soap. The adequate rheological and tribological behaviour of lubricating greases depends on their formulation and the morphology achieved during their manufacture. With regard to majority components of lubricating greases, it is worthy to note that they are non-renewable materials, there is currently an enormous demand for promoting change in these constituents by substances obtained from renewable sources. One possible approach for improving this point is developing lubricating greases with other constituents, such as clays and vegetable oils
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