Green Tribology: New Insights toward a Sustainable World

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (30 November 2021) | Viewed by 18284

Special Issue Editors

Department of Civil and Industrial Engineering, University of Pisa, Largo Lucio Lazzarino 2, 56126 Pisa, Italy
Interests: biotribology; computational biomechanics; motion analysis; vibration analysis
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In this particular period we are living in due to the COVID-19 pandemic, ecological issues assume more and more importance in the framework of a sustainable environment. In this framework, green tribology, defined as “the science and technology of the tribological aspects of ecological balance and environmental and biological impacts”, represents a modern and interesting direction in scientific research, aimed to explore the role of tribological investigation regarding saving energy and, in general, the ecological environment. Green tribology is an emerging and actual area of tribological science. It can be viewed as an interdisciplinary topic, which includes mainly classical tribology, chemical engineering, materials science, energy, green lubrication, and environmental sciences, with the purpose to improve the efficiency in processes (cleaner production) and machine components, by minimizing friction, wear, and, in general, dangerous pollution, in order to protect the environment and to improve the quality of life. Therefore, the main goals of green tribology are the minimization of friction and wear, and the reduction in or complete elimination of lubrication, including self-lubrication (natural and biodegradable lubrication). Green tribology is also devoted to the study of biomimetics, sustainable chemistry, surface texturing, environmental implications of coatings, real-time monitoring, design for degradation, and sustainable energy applications. Recent investigations report that “…by applying for advances in Green Tribology in terms of new surfaces, materials and lubrication technologies, the total global energy loss in tribological systems could be decreased by 18% in the next 8 years and up to 40% in the next 15 years. An additional advantage of environmentally friendly Green Tribology is a significant reduction in carbon dioxide emissions and economic costs”.

This research topic aims to collect manuscripts within, but not limited to, the following research areas:

  • Contact mechanics;
  • Modeling and minimization of friction and wear;
  • Tribology of biodegradable materials;
  • Environmentally friendly lubrication;
  • Superlubricity;
  • Sustainable chemistry and green engineering principles;
  • Biomimetic and self-lubricating materials;
  • Surface texturing, coatings, and their environmental implications;
  • Real-time monitoring, analysis, and control of tribological systems;
  • Tribology of renewable and/or sustainable sources of energy;
  • Design for degradation.

Prof. Dr. Alessandro Ruggiero
Dr. Lorenza Mattei
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • friction
  • wear
  • lubrication
  • biodegradable
  • green lubricants
  • superlubricity
  • biomimetic
  • surface texturing
  • coatings
  • real-time monitoring

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Published Papers (6 papers)

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14 pages, 9496 KiB  
Article
Tribological Evaluation of Lead-Free MoS2-Based Solid Film Lubricants as Environmentally Friendly Replacements for Aerospace Applications
Lubricants 2022, 10(1), 7; https://doi.org/10.3390/lubricants10010007 - 06 Jan 2022
Cited by 10 | Viewed by 3226
Abstract
Solid lubricants, such as MoS2 have been widely used in the aerospace industry with the primary purpose of reducing the friction and wear of tribological interfaces. MoS2 based solid film lubricants are generally doped with other compounds, which can help overcome [...] Read more.
Solid lubricants, such as MoS2 have been widely used in the aerospace industry with the primary purpose of reducing the friction and wear of tribological interfaces. MoS2 based solid film lubricants are generally doped with other compounds, which can help overcome some of their limitations related to environmental conditions. For instance, compounds like Sb2O3 and Pb have been traditionally used to improve the endurance life of these lubricants. However, with the recent zest in transferring to eco-friendly lubricants, there is a strong push to eliminate Pb based compounds. The main purpose of this work is to better understand the influence of Pb based compounds on the tribological behavior of MoS2 based solid film lubricants as well as to critically evaluate the performance of Pb free lubrication strategies. More specifically, the baseline ‘non-green’ lubricant was doped with Pb compound and Sb2O3 and the Pb compound in the ‘Green’ alternative lubricant was replaced by more Sb2O3. The wear test was done using a ball-on-disk tribometer for specific loads and for 5000 cycles. Ex-situ analysis was conducted using Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), and micro-Raman to capture the interfacial processes of these lubricants at different loads. Overall, the non-green lubricant performed better in terms of the tribological behavior (i.e., lower friction and wear), which was attributed to the formation of a dense MoS2-based tribo-/transfer-film with the basal planes oriented in the parallel direction to the sliding. The finding on the interfacial phenomena provided critical insights into the development of novel green alternatives that may have the ability to replace Pb based compounds in the future for a sustainable environment. Full article
(This article belongs to the Special Issue Green Tribology: New Insights toward a Sustainable World)
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12 pages, 1929 KiB  
Article
Low-Temperature Rheology and Thermoanalytical Investigation of Lubricating Oils: Comparison of Phase Transition, Viscosity, and Pour Point
Lubricants 2021, 9(10), 99; https://doi.org/10.3390/lubricants9100099 - 06 Oct 2021
Cited by 6 | Viewed by 3251
Abstract
According to the ASTM D97, the pour point is the temperature below which petroleum products cease to flow. To evaluate the relevance of pour point measurements for synthetic lubricating oils, we investigated the crystallization, melting temperature and low-temperature flow behavior of one mineral [...] Read more.
According to the ASTM D97, the pour point is the temperature below which petroleum products cease to flow. To evaluate the relevance of pour point measurements for synthetic lubricating oils, we investigated the crystallization, melting temperature and low-temperature flow behavior of one mineral and five synthetic lubricating oils. The classification of three groups emerged from this process. The formation of paraffin crystals in mineral oils (I) below the crystallization temperature causes shear-thinning behavior and a yield point. The crystallization temperature determined in the thermal analysis and rheology correlates well with the pour point. Synthetic lubricating oils, which solidify glass-like (II), exhibit a steady viscosity increase with falling temperature. The temperature at which viscosity reaches 1000 Pas corresponds well to the pour point. Synthetic oils, especially esters, with complex crystallization behavior (III), exhibit supercooling depending on the shear rate and cooling conditions. For these lubricating oils, the pour point provides no information for low-temperature applicability. Full article
(This article belongs to the Special Issue Green Tribology: New Insights toward a Sustainable World)
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20 pages, 5097 KiB  
Article
Synthesis of a Lubricant to Mimic the Biorheological Behavior of Osteoarthritic and Revision Synovial Fluid
Lubricants 2021, 9(9), 87; https://doi.org/10.3390/lubricants9090087 - 01 Sep 2021
Cited by 2 | Viewed by 2724
Abstract
The rheological properties of synovial fluid (SF) are essential for the friction behavior and wear performance of total joint replacements. Standardized in vitro wear tests for endoprosthesis recommend diluted calf serum, which exhibits substantial different rheological properties compared to SF. Therefore, the in [...] Read more.
The rheological properties of synovial fluid (SF) are essential for the friction behavior and wear performance of total joint replacements. Standardized in vitro wear tests for endoprosthesis recommend diluted calf serum, which exhibits substantial different rheological properties compared to SF. Therefore, the in vitro test conditions do not mimic the in vivo conditions. SF samples from osteoarthritis knee patients and patients undergoing knee endoprosthesis revision surgery were compared biochemically and rheologically. The flow properties of SF samples were compared to synthetic fluid constituents, such as bovine serum albumin (BSA) and hyaluronic acid (HA). Interestingly, HA was identified as a significant contributor to shear-thinning. Using the acquired data and mathematical modelling, the flow behavior of human SF was modelled reliably by an adapted adjustment of biorelevant fluid components. Friction tests in a hard/soft bearing (ceramic/UHMWPE) demonstrated that, in contrast to serum, the synthetic model fluids generate a more realistic friction condition. The developed model for an SF mimicking lubricant is recommended for in vitro wear tests of endoprostheses. Furthermore, the results highlight that simulator tests should be performed with a modified lubricant considering an addition of HA for clinically relevant lubrication conditions. Full article
(This article belongs to the Special Issue Green Tribology: New Insights toward a Sustainable World)
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20 pages, 14679 KiB  
Article
The Influence of Mechanical Deformations on Surface Force Measurements
Lubricants 2021, 9(7), 69; https://doi.org/10.3390/lubricants9070069 - 13 Jul 2021
Cited by 1 | Viewed by 2259
Abstract
Surface Force Balance (SFB) experiments have been performed in a dry atmosphere and across an ionic liquid, combining the analysis of surface interactions and deformations, and illustrate that the mechanical deformations of the surfaces have important consequences for the force measurements. First, we [...] Read more.
Surface Force Balance (SFB) experiments have been performed in a dry atmosphere and across an ionic liquid, combining the analysis of surface interactions and deformations, and illustrate that the mechanical deformations of the surfaces have important consequences for the force measurements. First, we find that the variation of the contact radius with the force across the ionic liquid is well described only by the Derjaguin–Muller–Toporov (DMT) model, in contrast with the usual consideration that SFB experiments are always in the Johnson–Kendall–Roberts (JKR) regime. Secondly, we observe that mica does not only bend but can also experience a compression, of order 1nm with 7μm mica. We present a modified procedure to calibrate the mica thickness in a dry atmosphere, and we show that the structural forces measured across the ionic liquid cannot be described by the usual exponentially decaying harmonic oscillation, but should be considered as a convolution of the surface forces across the liquid and the mechanical response of the confining solids. The measured structural force profile is fitted with a heuristic formulation supposing that mica compression is dominant over liquid compression, and a scaling criterion is proposed to distinguish situations where the solid deformation is negligible or dominant. Full article
(This article belongs to the Special Issue Green Tribology: New Insights toward a Sustainable World)
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11 pages, 3101 KiB  
Article
Moringa and Graphite as Additives to Conventional Petroleum-Based Lubricants
Lubricants 2021, 9(7), 65; https://doi.org/10.3390/lubricants9070065 - 22 Jun 2021
Viewed by 2554
Abstract
Many researches are focused on the tribological performances of pure vegetable oil in order to replace the conventional mineral engine oils. This work investigates the influence of local moringa oil (noted VO) on the performances of lubricants formed from a blend of dodecane [...] Read more.
Many researches are focused on the tribological performances of pure vegetable oil in order to replace the conventional mineral engine oils. This work investigates the influence of local moringa oil (noted VO) on the performances of lubricants formed from a blend of dodecane and graphite particles at ambient temperature. In a first part, a reduction of about 50% of friction properties of dodecane is observed when adding small amounts of moringa oil (VO), which is intended to be used as a bio-base performance additive in lubricant formulations. The friction properties of their blends with graphite, generally employed as solid lubricant additive, showed an adsorption effect of fatty acid molecules. The more promising results were obtained for the blend containing 2 w% of VO. Physicochemical characterizations of the tribofilms evidence the good antiwear properties of the lubricant. Full article
(This article belongs to the Special Issue Green Tribology: New Insights toward a Sustainable World)
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8 pages, 890 KiB  
Perspective
The Effects of Energy Efficiency and Resource Consumption on Environmental Sustainability
Lubricants 2021, 9(12), 117; https://doi.org/10.3390/lubricants9120117 - 03 Dec 2021
Cited by 7 | Viewed by 2503
Abstract
Primary energy has become a vital part of society—from mobility, heating, and cooling to refrigeration to preserve food as well as for simple communication methods, such as texting. As such, pollution and environmental concerns regarding the impact of human activities have become mainstream [...] Read more.
Primary energy has become a vital part of society—from mobility, heating, and cooling to refrigeration to preserve food as well as for simple communication methods, such as texting. As such, pollution and environmental concerns regarding the impact of human activities have become mainstream and efforts have been made to reduce solid wastes as well as CO2 and greenhouse gas emissions. Renewable energy is almost synonymous with environmentally friendly. While energy conversion from fossil fuels and natural gases is responsible for most of the pollution (CO2, NOx, SO2, particulate matter (PM), etc.) in modern society, these processes also generated 86% of global primary energy in 2019. Furthermore, as humans become more dependent on energy, power demands will only increase with time. Material hunger represents another little perceived dependency of human prosperity. The longevity of products and goods is crucial to limit CO2eq emissions associated with material streams. This paper will focus on two relationships: that of CO2 and friction, and that of sustainability and wear protection. Full article
(This article belongs to the Special Issue Green Tribology: New Insights toward a Sustainable World)
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