This work is devoted to evaluating the effectiveness of the recovery of carbon fibers from end-of-life wind turbine blades in the pyrolysis process, and the use of those fibers in the production of flat composite panels. The recovery of carbon fibers from wind turbine blades uses a pyrolysis process at 500–600 °C in a non-oxidizing atmosphere, in such a way that makes it possible to preserve the shape and dimensions of the fibers. Using recycled carbon fibers, flat CFRP sheets with epoxy resin matrix were produced by pressing. Seven different series of samples were tested, which differed in fiber length, fiber orientation, and pressure holding time. The results obtained on the recycled fibers were compared to the original carbon fibers, cut to corresponding lengths. Additionally, one of the series was reinforced with a biaxial fabric. The most favorable pressing parameters are empirically found to be pre-pressing 2 MPa (10 min), and further pressing at a pressure of 7 MPa until the resin completely cross-linked (about 120 min). A number of tests were carried out to demonstrate the usefulness of pyrolytic fibers, including tensile strength of carbon fibers, bending strength, SEM observations, FT-IR, and Raman spectroscopy. The tests carried out on the carbon fibers show that the pyrolysis process used leaves about 2% of the matrix on the surface of the fiber, and the tensile strength of the fibers drops by about 20% compared to the new carbon fibers. The research results show that the use of the recycled carbon fibers in the production of flat composite plates is reliable, and their mechanical properties do not differ significantly from plates made of corresponding original carbon fibers. Composite panels with the pyrolytic fibers (274 MPa) show up to a 35% higher flexural strength than similarly produced panels with the original new carbon fibers (203 MPa), which means that the panels can be used in the production of elements for footbridges, bridges, pipelines, or structural elements of buildings and roofing.

Degradation of polymer composites is a significant problem in many engineering aspects. Due to the interaction of various degradation factors during the exploitation of composites, a synergistic effect of destruction is observed. The article describes the phenomena occurring in glass fiber reinforced polyester laminates under the influence of ultraviolet radiation (UV) in an aquatic environment. The laminates were exposed to UV-A, UV-B and UV-C radiation for 1000 h in free-air and underwater conditions. During the test, the materials were immersed at stable depth of 1 mm and 10 mm, respectively. The three-point bending tests performed on the samples after being exposed to UV showed an increase in the flexural strength of the composites. Simultaneously, degradation of the outer surface layer was observed. The degradation removed the thin resin film from the surface which resulted in a direct exposure of the reinforcing fibers to the environment. The transformations taking place in the deeper layers of the composite increased the mechanical strength due to the additional cross-linking reactions excited by the energy arising from the radiation. Moreover, the formation of polymer structures from free styrene remaining after the technological process and the occurrence of free radical reactions as a result of the cage effect was also observed.

In this work, epoxy composites filled with flake graphite of various size (less than 10 μm and less than 45 μm) were produced. The aim of the research was to develop a self-lubricating material with favorable tribological properties, i.e., reduced friction coefficient compared to unfilled epoxy resin and limited abrasive wear. The research material was produced using technical epoxy resins based on bisphenol A. The detailed process of composite production was described, and typical technological problems were considered. The addition of graphite led to an increase in dynamic viscosity, which positively limits the phenomenon of sedimentation, but an increase in the filler content also led to an increase in the porosity of the material. A series of tests have shown that the addition of graphite above 5% by weight allows for a reduction in the friction coefficient from 0.6 to 0.4 and significantly reduces the material’s tendency to abrasive wear.

The paper presents an attempt to use milled waste of carbon fiber reinforced polymer (rCFRP) laminates as fillers for polyester resin. The obtained polyester-rCFRP composites were tested for technological, mechanical and frictional properties. It was found that the viscosity increased for the compositions containing rCFRP particles in comparison to the neat resin. Flexural strength improved in comparison to the neat resin, but only for the composites filled with a fraction containing particles below 0.2 mm in diameter and a mixed-diameter particles fraction. For composites containing the above-mentioned fractions, a significant reduction in the dynamic friction coefficient and a reduction in wear (the weight loss after friction test) were found. The obtained results indicate the advisability of further research and optimization of this new type of composites in terms of frictional applications.

In this study, a novel lightweight epoxy polymer concrete (PC) was developed with lightweight ceramic aggregates based on waste materials, which can be applied in construction materials. For the purposes of this study, lightweight ceramic aggregates based on waste materials were produced and used as fillers in the production of epoxy polymer concretes. Two aggregate fractions were used in the study: 4–8 mm and 8–16 mm. The physical properties of non-infiltrated and infiltrated granules were compared, which clearly demonstrated that infiltration is beneficial, as the penetration of liquid resin into deep pores increases the interfacial surface area. Next, using the infiltrated granules, a series of polymer concretes were prepared and tested for compressive strength, flexural strength, open porosity, water absorption, apparent density, and thermal diffusivity. The highest mechanical properties were achieved for samples containing only a fine fraction with aggregates with a diameter of 4–8 mm, 99.68 MPa compression, and 18.71 MPa flexural strength. Thermal diffusivity measurements were obtained for heat transfer comparison between the developed polymer concrete and traditional concrete. The results showed that the thermal diffusivity value for the polymer concrete was equal to 2.33 ×10^-7 m²/s, which was nearly half of traditional concrete. The investigated material was considered to be frost-resistant because of its low water absorption (0.36%). It was proven that the utilization of lightweight ceramic aggregates based on waste materials was reasonable and increased the mechanical properties of the polymer concrete alongside the overloading environment by processing wastes that are difficult to reuse.