The article discusses the influence of the post-process on the mechanical properties of elements produced with the use of the mask stereolithography (mSLA) method. Printed samples were subjected to the following post-process steps: Washing and post-curing, at various times. Then, static tensile and static bending tests were carried out, as well as Shore D hardness measurements for the inner and surface part of the sample, as well as profilographometric analysis of the surface. The post-curing time has been found to strongly affect the tensile and bending strength of printouts, and to improve their surface quality. Washing has an ambiguous effect on the strength of the printouts, but, in the end, it was found that extended washing slightly reduces the strength. Washing significantly affects the quality of the printout surface. A washing time that is too short results in a surface that strongly resembles the printing process, with high roughness. Increasing the washing time to 10 min lowers the roughness by one order of magnitude. Post-curing has also been shown to be beneficial for the cured sample with the application of shielding water. This approach results in an improvement in the flexural strength of the printouts. In general, the obtained research results indicate that, for printouts with cross-sectional dimensions of several mm, the optimal washing time is no more than 10 min and the post-curing time is at least 30 min.

Low-density polyethylene (LDPE) composites reinforced with finely powdered waste glass were identified as a potential material for 3D printed structures for use in low-duty frictional applications. A recently published 3D printing model was used to calculate the limits in the filament feed rate and printing speed. Tribological tests (pin-on-disc method) of the printed composites were performed for different print-path directions. Differential scanning calorimetry (DSC) was performed on the samples and the composites showed a higher crystallinity compared with LDPE, which partially explains the higher elastic modulus of the composites determined during static tensile tests. Using a fine glass powder as reinforcement improved the wear resistance of LDPE by 50% due to the formation of a sliding film on the sample’s surface. An evident effect of friction direction vs. the printed path direction on wear was found; which was likely related to differences in the removal of friction products from the friction area for different print-path directions. The LDPE composites with fine waste glass particles are promising materials for low-duty frictional applications and should be the subject of further research.

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.

In this paper, we investigated theimpact of glassy carbon (GC) reinforcement oncrystal structure and the mechanical performance of high-density polyethylene (HDPE). We made composite samples by mixing HDPE granules with powder in ethanol followed bymelt mixing in a laboratory extruder. Along with the investigated composite, we also prepared samples with carbon nanotubes (CNT), graphene (GNP) and graphite (Gr) to compare GC impact with already used carbon fillers. To evaluate crystal structure and crystallinity, we used X-ray diffraction (XRD) and differential scanning calorimetry (DSC). We supported the XRD results with a residual stress analysis (RSA) according to the EN15305 standard. Analysis showed that reinforcing with GC leads to significant crystallite size reduction and low residual stress values. We evaluated the mechanical properties of composites with hardness and tensile testing. The addition of glassy carbon results inincreased mechanical strength incomposites with CNT and GNP.

Natural fiber-reinforced composites have drawn attention of the research community mainly because of their economical and environmental attractiveness. So far, the shortened natural fibers were mainly used as the reinforcement, but textile products like yarn and fabrics can improve mechanical properties of composite in a significant way. The objective of the investigation is to develop a textile material suitable for composite reinforcement based on flax fibers. Pure flax fabric as well as hybrid fabrics containing flax fibers and chemical fibers: Kevlar, glass fibers, and poliimid have been developed in order to meet requirements related to mechanical properties of composites. The results of the mechanical tests confirmed suitability of the flax fabrics as a composite reinforcement. Due to strongly hydrophilic properties of pure flax, composites reinforced by the hybrid fabrics with polyaramide or glass fibers showed evidently better mechanical properties (even by about 80%). Chemical modification of flax fabric results in the improvement in adhesion between fibers and matrix. The results obtained within the work show that chemically treated flax fiber can serve as a valuable reinforcement for polymer matrix composite material ensuring mechanical properties comparable to glass fibers.