Volume 62, Issue 1

Abstract: This paper was created within the EU Horizon project - RECICLARM - which conducted waste management research with the purpose of recycling up to 70% of Europe’s waste [1]. Our investigation focused on developing an algorithm capable of accurately classifying materials including plastic onces in categories of interest with the help of machine learning. Various types of materials and input variables have been documented and considered while prototyping and testing the intelligent classification algorithm, which resulted in a precise and efficient solution.

Abstract: Treating skin injuries remains challenging due to issues like wound infections. In this study, polyvinylidene fluoride (PVDF)/polyethylene oxide (PEO)/azithromycin (AZ) composite nanofibers were prepared using electrospinning to reduce bacterial infections in skin wounds. The surface morphology, chemical structure, and hydrophilicity of the nanofibers were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, and contact angle measurements, respectively. Antibacterial performance tests revealed that increasing the AZ dosage expanded the antibacterial zone, indicating improved effectiveness. Furthermore, experiments on rat skin infections showed that the PVDF/PEO/AZ membrane inhibited suppuration at S. aureus-infected wound sites. These findings demonstrate the potential of AZ-loaded PVDF/PEO nanofiber membranes as effective antibacterial dressing.

Abstract: Comparing and evaluating the fracture load of different posts and composite core of root canal-treated teeth is the aim of this study. Endodontically treated teeth were restored with zirconia (ZP), prefabricated glass fiber (GFP), and carbon (CP) post systems. Single root eighty maxillary 2nd premolars were chosen, and they received endodontic therapy. Depending on the kind of length used, the teeth were randomly assigned to four groups (n = 20), each of which was then divided into two subgroups: subgroup 1/2 removed the one-half sealing material, and subgroup 2/3 removed two-thirds of the sealing material. Prefabricated glass fiber posts were used in Group I, zirconia posts were used in Group II, carbon posts were used in Group III, and direct composite resin restoration without a post was used in Group IV (control). Samples were loaded into a universal testing machine, and statistical interpretations were made. Fracture resistance was noted. The results of the fracture one-way ANOVA were used to examine the load, and then multiple comparisons with the Bonferroni test with a threshold significant value (α=0.05). The prefabricated glass fiber post group, the carbon post, the zirconia post, and the control group all had lower fracture loads than the zirconia post.

Abstract: Due to their high energy dissipation properties, in recent years, composite materials based on natural resins and fibers have been increasingly used. The paper studies the vibration behavior of composite bars reinforced with chopped wheat straw and, respectively, chopped sunflower seed shells. As matrix, an epoxy resin and, respectively, a hybrid resin based on rosin were used. A mathematical model useful for the study of damped vibrations is presented. For each of the analyzed bars, the frequency and damping factor for the first natural vibration mode are experimentally determined. Based on the experimental data, a coefficient that characterizes the vibration damping capacity for each bar is determined.

Abstract: In this study, fan blades and thermosetting polyurethane foam were mechanically recycled, and glass fibers of different lengths and polyurethane powders of different particle sizes were separated by crushing and screening. The recycled materials with different particle sizes and mass fractions were selected and homogeneously mixed with the matrix thermoplastic polypropylene powder, and nine groups of different composite insulation boards were prepared using hot press molding method. The tensile strength, flexural strength and thermal conductivity of different insulation boards were analyzed. The results show that when the glass fiber mass fraction is 20%, the mechanical properties can reach the maximum value, and its tensile strength and bending strength are 7.196 MPa and 13.2 MPa, respectively. The thermal conductivity can reach the minimum value of 0.091 W/(m∙K) when the glass fiber mass fraction is 10%. In this study, polyurethane and glass fibers were recycled at the same time to obtain insulation boards with good mechanical strength and thermal insulation properties, which provides new possibilities for the development of insulation materials.

Abstract: Perishable food products, including fruits, vegetables, and seafood, require preservation techniques to extend their shelf life. In recent years, nanotechnology has emerged as a promising approach to enhance the properties of edible coatings. Nanocomposite coatings incorporating various materials and technologies have been developed to optimize coating performance. PSA, SEM, XRD, and FT-IR analyses were conducted to characterize the physical and morphological properties of these nanocomposite coatings. The findings indicated that the use of Ultra-Turrax (UT) technology in the preparation of the coating solution resulted in smaller particle sizes (458.9-1037.2 nm), improved visual appearance, and smoother films with uniformly distributed nanoparticles on the surface. XRD and FT-IR analyses confirmed the crystallinity and functional groups of ZnO and TiO₂ within the nanocomposite coatings. These newly developed coatings have significant potential as environmentally friendly packaging materials and preservation technologies to extend the shelf life of perishable food products.

Abstract: In order to solve the wall thickness error problem of filament-based extrusion additive manufacturing (MEAM) of thin-walled model and to improve the printing accuracy of MEAM thin-walled model. In this study, a square thin-walled model A was designed as the experimental specimen, and a wall thickness error correction method based on pre-experiment was proposed, by which the corrected extrusion flow rate R was calculated to be 92.8%. Model A was reprinted using the corrected extrusion flow rate (92.8%), and the wall thickness error of model A printed using the corrected extrusion flow rate was found to be significantly reduced by spiral micrometer measurement. When model A was observed through an industrial microscope, it can be seen from the sidewall surface detail diagram that the surface of model A printed with the corrected extrusion flow rate has no bumps, cracks and other structures, and the surface quality is better; moreover, it can be seen from the cross-sectional dimension diagram that the wall thickness (0.403 mm) of model A printed with the corrected extrusion flow rate (92.8%) is significantly reduced compared to the wall thickness (0.472 mm) of model A printed with the default extrusion flow rate (100%), and is close to the designed wall thickness (0.400 mm), which further verifies that the wall thickness error of the MEAM thin-walled model with the corrected extrusion flow rate has been significantly reduced.

Abstract: The paper presents part of the results of larger research aimed at evaluating the possibility of improving the characteristics of the FFF printed product by using hybrid heating sources. The results presented aim at the influence of the cooling rate on the characteristics of parts manufactured by 3D FFF printing from Polylactic acid (PLA), with a focus on the structural, thermal and mechanical properties, when the additional heat source is represented by a hot air jet. Microscopic analysis showed that rapid cooling generates a more irregular texture, poor interlayer adhesion and a rougher surface, while slow cooling ensures a uniform texture, improved interlayer adhesion and fewer defects. From a thermal point of view, the glass transition temperature (T_g) was slightly higher for the slowly cooled samples, due to the relaxation of internal stresses. The crystallization temperature (T_c) increased progressively with the reduction of the cooling rate, indicating a higher initial crystallinity, and the energy associated with the crystallization reaction decreased. The melting temperature (T_m) showed minimal variations, but the melting enthalpy was higher for the slowly cooled samples, reflecting better organized crystals. Mechanical properties revealed that the rapidly cooled parts have higher stiffness at low temperatures, due to internal stresses, but brittle behaviour. The slowly cooled parts showed higher stiffness at high temperatures and ductile behaviour, with progressive deformations before fracture, due to the relaxation of internal stresses and the formation of partial crystals. The results emphasize the importance of controlling the cooling rate in the FFF process to optimize the interlayer adhesion, mechanical properties and thermal stability of the printed parts, allowing to adapt their performance to specific application requirements.

Abstract: The manufacture of composite materials with hybrid matrix and reinforcements from agricultural waste, which have properties/structure corresponding to the field where they will to be used, is a challenge both in terms of environmental protection and low production costs. Based on this premise, in this article, composite materials reinforced with crushed sunflower seed shells or chopped wheat straw were fabricated, and a hybrid resin matrix based on rosin was used. The chemical structure was studied, along with the influence of the reinforcement addition on the morphology of the materials and their behaviour under various mechanical solicitations: tension and compression.