With the development of 3D printing technology, there is a need to produce printable materials with improved properties, e.g., sliding properties. In this paper, the authors present the possibilities of producing composites based on biodegradable PLA with the addition of graphite. The team created composites with the following graphite weight contents: 1%, 2.5%, 5%, 7.5%, and 10%. Neat material was also subjected to testing. Tribological, mechanical, and chemical properties of the mentioned materials were examined. Measurements were also made after keeping the samples in ageing and climatic ovens. Furthermore, SEM observations of samples before and after friction tests were carried out. It was demonstrated that increasing graphite content caused a significant decrease in wear (PLA + 10% graphite had a wear rate three times lower than for a neat material). The addition of graphite did not adversely affect most of the other properties, but it ought to be noted that mechanical properties changed significantly. After conditioning in a climatic oven PLA + 10% graphite has (in comparison with neat material) 11% lower fracture stress, 47% lower impact strength, and 21% higher Young’s modulus. It can be certainly stated that the addition of graphite to PLA is a step towards obtaining a material that is low-cost and suitable for printing sliding spare parts.

Nowadays, the replacement of a hip joint is a standard surgical procedure. However, researchers have continuingly been trying to upgrade endoprostheses and make them more similar to natural joints. The use of 3D printing could be helpful in such cases, since 3D-printed elements could mimic the natural lubrication mechanism of the meniscus. In this paper, we propose a method to deposit plastics directly on titanium alloy using 3D printing (FDM). This procedure allows one to obtain endoprostheses that are more similar to natural joints, easier to manufacture and have fewer components. During the research, biocompatible polymers suitable for 3D FDM printing were used, namely polylactide (PLA) and polyamide (PA). The research included tensile and shear tests of metal–polymer bonds, friction coefficient measurements and microscopic observations. The friction coefficient measurements revealed that only PA was promising for endoprostheses (the friction coefficient for PLA was too high). The strength tests and microscopic observations showed that PLA and PA deposition by 3D FDM printing directly on Ti6Al4V titanium alloy is possible; however, the achieved bonding strength and repeatability of the process were unsatisfactory. Nevertheless, the benefits arising from application of this method mean that it is worthwhile to continue working on this issue.

MoS₂ is an additive used to improve the tribological properties of plastics. In this work, it was decided to verify the use of MoS₂ as a modifier of the properties of PLA filaments used in the additive FDM/FFF technique. For this purpose, MoS₂ was introduced into the PLA matrix at concentrations of 0.025–1.0% by weight. Through extrusion, a fibre with a diameter of 1.75 mm was obtained. 3D printed samples with three different filling patterns were subjected to comprehensive thermal (TG, DSC and HDT), mechanical (impact, bending and strength tests), tribological and physicochemical characteristics. The mechanical properties were determined for two different types of fillings, and samples with the third type of filling were used for tribological tests. Tensile strength has been significantly increased for all samples with longitudinal filling with improvement up to 49%. In terms of tribological properties, higher values of the addition (0.5%) caused a significant increase of up to 457% of the wear indicator. A significant improvement in processing properties in terms of rheology was obtained (416% compared to pure PLA with the addition of 1.0%), which translated into more efficient processing, increased interlayer adhesion and mechanical strength. As a result, the quality of printed objects has been improved. Microscopic analysis was also carried out, which confirmed the good dispersion of the modifier in the polymer matrix (SEM-EDS). Microscopic techniques (MO, SEM) allowed for the characterization of the effect of the additive on changes in the printing process (improvement of interlayer remelting) and to assess impact fractures. In the tribological area, the introduced modification did not bring spectacular effects.

3D printing is becoming widely used and printed parts very often replace extruded parts. Plastics, due to their ability to work with steel without lubrication, are commonly used for sliding components and are therefore exposed to various types of wear, including abrasive wear. In this paper, abrasive wear resistance tests were carried out to compare extruded and 3D-printed samples. Moreover, microhardness tests, surface topography and microscopic observations of the surface of the samples before and after friction were also conducted. Samples were made from eight materials that are most commonly used in 3D FDM printing: PLA, PET-G, ABS, PA, PP, PC, PMMA and HIPS. For six out of the eight materials tested, samples made by extrusion proved to be more resistant to abrasive wear (between 10% and 24%) than those printed ones. Fabrication by 3D printing can lead to different object properties and thus different abrasion resistance. The abrasion resistance of extruded samples depends on factors reported in the literature such as hardness, density and surface roughness. In the case of 3D printed samples, no such relationship was found. For this reason, the researchers believe that the reduced abrasion wear resistance of printed samples is due to their specific internal structure.

Polymer materials are increasingly being used for sliding machine elements due to their numerous advantages. They are used even where they are deformed and in such a state that they interact frictionally, e.g., in machine hydraulics or lip seals. Few publications deal with the influence of deformation, which is the effect of, e.g., assembly on tribological properties of polymeric material. This deformation can reach up to ε ≈ 20% and is achieved without increasing the temperature of the polymer material. The paper presents the results of investigations in which high-density polyethylene (PE-HD) was maintained in deformation by means of a special grip (holder). The wear of the sample was significantly higher than that of the undeformed sample. This effect persisted even after partial relaxation of the stress in the sample after 24 h. Additional investigations were carried out to explain the obtained results. There were the microscopic observations of the surface after friction, measurements of microhardness, and surface free energy. Changes in the value of surface free energy and a significant decrease in microhardness with deformation under tension were observed. Deformed materials have a different surface appearance after friction and a different size and form of wear products. It was indicated that it is probable that the cohesion of the material will decrease and that the character of the wear process will change as a result of tension. Deformation under tension without heating of polymeric material (PE-HD), e.g., as a result of assembly, has been qualified as a threat to be taken into account when designing and analysing polymeric sliding elements.

Plastics are widely used due to their numerous advantages. Unfortunately, most of their types do not decomposequickly in the natural environment, causing environmental pollution. In order to counteract the problem ofwaste, there is a growing interest in plastics that degrade under the influence of the natural environment.The authors of this article are trying to use biodegradable plastic for sliding elements. Polylactide (PLA)is a biodegradable, environmentally friendly polymer; however, it has a high wear and friction coefficientwhen working with steel. It was decided to check whether the addition of 10% graphite (a commonly used,environmentally friendly modifier) would improve the tribological properties of PLA. Using a pin-on-discstation, the coefficient of friction, wear and temperature of the sample were determined depending on thespeed of cooperation and pressure. The addition of graphite significantly reduced the linear wear of thecomposite in a wide range of parameters (sliding speed and pressure), slightly decreased the coefficient offriction and slightly increased the temperature of the composite.