Scientists have developed a method of manufacturing composites to create bearings that do not require lubrication.

Scientists have developed a method of manufacturing composites to create bearings that do not require lubrication.

Photo of an oriented tape of ultra-high molecular weight polyethylene with an adhesive on a metal cylinder. An example of the formation of a trunnion of a sliding bearing. Source: Tarek Dayyub

Scientists have achieved better adhesion between the layers of polymer and metal materials by treating them with the first acids and “sewing” cellulose molecules to them. This approach will make it possible to create composite materials for various products: from endoprostheses to moving elements of metal structures, for example, car bearings. The results of the study, supported by a grant from the Presidential Program of the Russian Science Foundation (RNF), were published in the Journal of Composites Science.

Ultra-high molecular weight polyethylene is increasingly used in various composite materials, i.e., materials consisting of several components. It is called the “polymer of the future” for its unique mechanical and functional properties: biocompatibility, low coefficient of dry friction, high wear resistance and chemical inertness, that is, the inability to react with other substances. Due to this set of properties, it is used in medicine for the production of implants and inserts of endoprostheses, in industry – for the creation of sliding bearings, lining of metallurgical ladles, as well as in many other areas. In addition, composites based on such a polymer make it possible to abandon environmentally polluting lubricants.

Previously, scientists from Sicheniv University (Moscow) and National Technical University “MISIS” (Moscow) developed a technology for obtaining high-strength and wear-resistant ultra-high molecular weight polyethylene from commercially available components using an orientation hood. This process makes it possible to achieve the rearrangement of both the molecular chains of the polymer and the supramolecular structures. As studies have shown, the hood plays a role in improving the sliding of the polymer. However, it will not be possible to use polyethylene tapes obtained in this way to form a sliding surface on their own — for this, they must be attached to a substrate made of other materials, including metals.

“The main method for joining ultrahigh molecular weight polyethylene with metals is thermopressing, that is compression at high temperatures. However, heating the polymer above 100°C leads to the loss of its unique structure and, accordingly, all its properties. Therefore, the best solution for bonding polymer tapes to a metal surface will be gluing with the help of adhesives – substances that provide surface adhesion – without the influence of high temperatures,” says project manager Tarek Dayyub, candidate of physical and mathematical sciences, senior researcher at Secheniv University, assistant Department of Physical Chemistry of NITU MRS.

Now researchers have developed a way to modify the surface of ultrahigh molecular weight polyethylene tapes, which improves the ability of the material to bond with the surface of metals. The process includes two stages. The first surface of the tapes is pre-treated with a mixture of acids. On the second, cellulose grafting is carried out using ultraviolet radiation.

Mechanical tests showed that the peel strength of polymer tapes treated in this way with a metal substrate increased three times compared to untreated tapes. Also, studies have shown that the tensile strength of the material has decreased by only 6%, and the susceptibility to abrasion and wear has practically not increased.

“The proposed method of surface modification of ultra-high molecular weight polyethylene allows to increase its adhesive properties by three times, while the mechanical properties of the material decrease slightly. In addition, the grafting of cellulose using ultraviolet radiation is promising due to the low cost of the process and its high efficiency,” said Oleksiy Maksymkin, candidate of physical and mathematical sciences, head of the controlled bionic systems laboratory of the Secheniv University, a participant in the project supported by a grant from the Russian Academy of Sciences, co-author of the article.

The developed tapes of ultra-high molecular weight polyethylene have a low coefficient of friction, high wear resistance and strength. On the basis of such tapes, you can easily form a slippery friction surface, for example, for moving metal structures. And the application of such polymer tapes on the trunnion of sliding bearings will make it possible to design bearings that work in dry friction conditions and under high loads.

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