Light-weight fibers reinforced polymer (FRP) composite frames are essential parts of vehicles body in the aerospace and automotive industries. Composite frames are often designed in complex curved 3D geometry through the dry winding process. The winding process of homogeneously wound-up layers of fibers without overlapping and gaps is the main challenge in the fabrication of frames with consistent thickness and acceptable quality. In this study, an industrial robot and winding head are set with a novel optimum process to wind the dry fiber with the specified angles on the frame, to fabricate it with minimum overlapping and local commulation of fibers, yet without gaps. Mathematical models and algorithms are developed to determine the optimal number of simultaneously wounds rovings of fibers in a given layer. In addition, this study addresses the optimum dry winding of curved parts of frames that form a torus geometry. It is shown that the combination of layers of rovings wound successively on the frame at angles of 45°, 90° (i.e. the rovings are laid along with the frame), and −45°, is the most used variant of winding that provides the composite frame with higher strength. Results indicated that an optimal selection of the number and width of the rovings minimizes the overlap of the wound rovings, which saves up to 20% of the utilized fibers. The derived theory is verified on practical tests and experiments, which confirms the development of new suitable procedures to improve the fabrication of FRP composite frames.

This article is focused on the comparison of the reliability of the results obtained by image analysis (newly proposed evaluation method) with well-known methods of evaluation of long-term corrosion resistance of glass fibers in an alkaline environment (pH > 12). The developed method is based on the analysis of scanning electron microscopy images (diameter and structures on the fiber surface). An experiment (52 weeks) was performed to evaluate two types of glass fibers: anticorrosive glass fibers (ARGFs) and E-glass fibers (EGFs). Three media were used to treat the fibers (23 ± 2 °C): H₂O, Ca(OH)₂, and K₂SiO₃. The ARGFs’ tensile strength did not reduce; a decrease by 68% was observed for EGFs in H₂O. Tensile strength decreased by 32% and 85–95% in K₂SiO₃; by 50% and 64% in Ca(OH)₂ for the ARGF and EGF, respectively. Statistical analysis was performed to validate the reliability and plausibility of the developed method. ARGFs and EGFs did not show any relationship between the fiber diameter and weight in H₂O; however, the linear trends may predict this relationship in Ca(OH)₂ and K₂SiO₃. For the ARGF and EGF, the cubic trend was suitable for predicting the change in fiber weight and diameter over time in Ca(OH)₂ and K₂SiO₃.

The development of novel biomass carriers is an option for increasing the efficiency of processes at wastewater treatment plants (WWTPs). Biomass carriers support the adhesion of specific bacteria and the subsequent biofilm formation. As part of this work, a new type of microfibrous biomass carrier with a unique sandwich structure was developed. Technologically, the structure of the biomass carrier is based on warp knitted spacer fabric created on a double-needle bar machine. Commercially available microfiber materials were used to achieve a large specific surface area (SSA) and internal porosity of the carrier to ensure high microorganism capture. A yarn combination was chosen to reach a final carrier density slightly lower than water to float in an aqueous environment. As the first, was developed and described a three-dimensional warp knitted microfiber biomass carrier. Next, were evaluated the properties of this carrier for post nitrification on WWTPs and compared with commercially available biomass carriers. Testing biofilm (using respirometry, real-time polymerase chain reaction, and next-generation sequencing) growing on the developed carrier in a post-nitrification laboratory reactor showed excellent adhesion, stability, and abundance of microorganisms. A high rate (more than 95%) of ammonia nitrogen removal was achieved in post-nitrification, and molecular genetics methods confirmed the high concentration of nitrifying bacteria in the biofilm. The developed three-dimensional microfiber biomass carriers have proven their functionality and can be considered an advance in biofilm processes.

Textile-based carriers represent a promising alternative to conventional plastic media used in moving-bed biofilm reactors (MBBRs) for biological wastewater treatment. In this study, we developed and evaluated warp-knitted multifilament textile carriers intended to support biofilm growth, particularly under post-nitrification conditions. Four carrier variants were fabricated using combinations of polypropylene (PP) and polyester (PES) yarns to adjust material buoyancy (weight was in the range of 0.596 g to 0.612 g), dimension, 3D structures, and high surface availability for biofilm growth. The effective carrier area ranged from 4.6 × 10³ mm² to 5.3 × 10³ mm². Biofilm development was assessed through image analysis and oxygen uptake rate measurements. The positive effect of the holes on the water flowing through the carriers was not proven, but the long multifilament segment and the fibrous surface support bacterial growth. The warp-knitted spacer carriers developed in this study successfully supported the formation of active biofilms, as indicated by elevated oxygen consumption rates (OCR) reaching up to 8 mg O₂/L/h within six weeks of operation (OCR of 4–5 mg O₂/L/h was recorded for the plastic carrier). Only minor differences were observed between measurements taken at weeks 6 and 14, suggesting early stabilization of biofilm activity. Warp-knitted textile carriers show strong potential as biofilm-supporting media due to their structural flexibility, low weight, and scalability. Although compatibility with industrial systems has not yet been confirmed, the carriers were designed with this objective in mind and demonstrated rapid colonization and promising performance at the laboratory scale, suggesting their potential suitability for industrial applications. Graphical Abstract

Complex composite structure design is frequently practiced in today’s aerospace and automotive industries. This study deals with the winding optimization of polymer composite frames having complex 3D geometry using rovings, winding heads, and industrial robots. This problem is addressed mainly from a geometrical perspective using a novel mathematical model and approach. Attention is given to maintaining the required winding angles, avoiding gaps, minimizing roving overlaps during winding, and ensuring the homogeneity of the windings process. Determination of the optimal number of rovings used and their width during the winding process is solved first for the case of a straight frame, where the central axis of the wound roving forms a straight helix on the frame surface. The winding technology for curved parts of the frame is more complicated. In practice, the curved section of the frame often forms geometrically part of a ring torus. The central axis of the wound roving then forms a toroidal helix on the torus. Optimization procedures are also solved for this type of frame. The verification of the derived theoretical conclusions was done using practical examples is a part of the research.

The innovative designs come from the authors’ idea to similarity with commercially usable plastic media (AnoxKaldnes), which could be replaced with weft-knitted fabric with loose loops required for water flow during wastewater treatment. By a tailored mass fraction of polypropylene and polyester yarns, the necessary purpose of floating the sample due to the lower density, mimicking water, can be achieved. The textile-based microfiber structure supports bacterial attachment. The bacteria surface covering is examined with image analysis during the first period of the experimental bioreactor post-treatment process with the aim of helping media development. The surface bacteria covering is tracked in the location of media shape (inner, outer, held and transfer loops), and samples with high single jersey porosity improved the cell capture. Regarding initial adhesion and quick-up colonization process (advantage of fiber application), the results concerned yarn count and knitting parameters and recommended structure and patterning elements. Experimental tests did not confirm the necessity of openings in the media structure. A highly porous weft-knitted media of the spatial shape, including the simple pipe shape, could be an alternative to a plastic one, which would benefit while maintaining the existing infrastructure of the wastewater treatment process.