Mathis Bruns

Electropolymerized polypyrrole (PPy) is considered as one of the promising polymers for use in ionic-electroactive or conducting polymer (CP) actuators. Its electromechanical properties surpass those of other prominent CPs such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) or polyaniline. However, freestanding and linear contracting actuator fibers made solely of electropolymerized PPy are not available yet. This work therefore targets the development of all-CP-based actuator fibers: electromechanically active PPy is electropolymerized on the surface of wet-spun, also electromechanically active PEDOT/PSS fibers. The thickness of the PPy fiber sheath is varied by using different electropolymerization durations. Mechanical and actuation properties of the different PEDOT/PPy core-sheath actuator fibers are investigated via tensile tests and isotonic actuation strain and isometric actuation force measurements, respectively. The fiber actuators show high tensile stability in both dry and aqueous conditions, rendering them highly suitable for actuation in aqueous electrolyte media. Regarding linear, untwisted, and uncoiled CP fiber actuators, the presented actuation measurements demonstrate to the best of our knowledge the highest reported linear contractile actuation strains of up to 2.2% in electrolytes and remarkable tensile actuation stresses of 1.64 MPa, as well as a high long-term cyclic actuation stability using varying actuation durations. This renders the fibers as a highly promising material, particularly with regard to their further structural textile processing for use in actuating wearables or soft robots.

Melt‐spun polypropylene/carbon nanotube (PP/CNT) monofilaments hold great promise for use in structural health monitoring (SHM) due to their low density, mechanical flexibility, and piezoresistive properties. However, achieving homogeneous CNT dispersion, optimizing processing parameters, and enhancing strain sensitivity remain key challenges for their practical implementation. This study systematically examines the influence of CNT and carbon black (CB) content as extrinsically conductive fillers, the incorporation of polyethylene glycol (PEG) as processing aids, and the effect of extruder screw speeds on the morphology, mechanical properties, and electrical behavior of PP/CNT monofilaments. Spinning pressure measurements reveal PEG effectively reduces spinning pressure. Morphological analysis indicates that higher CNT content results in rougher filament surfaces, while PEG enhances fiber uniformity. Tensile testing demonstrates a strong dependence of Young′s modulus and tensile strength on CNT content and processing parameters, with PEG‐modified samples exhibiting improved ductility. Electrical characterization confirmed a stable strain‐dependent resistance variation, with gauge factors up to 1.5. Mechanical testing showed that Young’s modulus could be tailored from 0.8 to 16 GPa depending on CNT and PEG content. These results demonstrate the feasibility of producing lightweight PP/CNT monofilaments with tunable electromechanical properties for scalable SHM sensor integration.

Poly(3,4‐ethylenedioxythiophene) (PEDOT), an inherently electrically conductive or conjugated polymer (CP), exhibits the potential to play a significant role in the development of innovative fiber materials for use in smart textiles, such as wearables. Furthermore, these fibers can function as artificial muscles in the emerging field of interactive fiber rubber composites. This study introduces a straightforward and efficient method for creating PEDOT‐based, biomimetic, fiber‐shaped, linearly contracting ionic electroactive polymer actuators. To achieve this, a wet‐spinning technique is presented, which enables a continuous production of PEDOT:polystyrene sulfate (PSS) fibers at high production rates of 34 m h⁻¹, an additional fiber washing step and a sulfuric acid posttreatment step to increase the fibers conductivity. The fibers provide a high conductivity of 1028 S cm⁻¹, maximum tensile strength reaching 182 MPa, and a maximum elongation of 24%. When utilized as CP actuators in an aqueous sodium dodecylbenzenesulfonate electrolyte medium, the fibers demonstrate a repeatable maximum isometric contractile force of 1.64 mN and repeatable linear contractile strain up to 0.56%. Furthermore, a high level of cyclic long‐term actuation stability can be demonstrated. Notably, these contractile strains are, to the best of knowledge, the highest reported values for pristine PEDOT:PSS fibers.

Warp knitting is a highly productive textile manufacturing process and method of choice for many products. With the current generation of machines running up to 4400 min⁻¹, dynamics become a limit for the production. Resonance effects of yarn-guiding elements and oscillations of the yarn lead to load peaks, resulting in breakage or mismatches. This limits material choice to highly elastic materials for high speeds, which compensate for these effects through their intrinsic properties. To allow the processing of high-performance fibers, a better understanding of the viscoelastic yarn behavior is necessary. The present paper shows a method to achieve this in longitudinal yarn direction using a dynamic mechanical analysis approach. Samples of high tenacity polyester and aramid are investigated. The test setup resembles the warp knitting process in terms of similar geometrical conditions, pre-loads, and occurring frequencies. By recording the mechanical load resulting from an applied strain, it is possible to calculate the phase shift and the dissipation factor, which is a key indicator for the damping behavior. It shows that the dissipation factor rises with rising frequency. The results allow for a simulation of the warp knitting process, including a detailed yarn model and representation of stitch-formation process.

Warp knitting is appointed as a manufacturing method for high-performance and high-quality textiles due to its versatility and production speed. To ensure a continuous and error-free manufacturing process under highly dynamic production conditions, a high level of knowledge of the yarn and machine interaction is required. Mechanical stresses from the machine are transferred to the yarn via friction points, as well as during the stitching process from one yarn to another, where the yarn is subjected to high stresses.Therefore, the focus of this research is the investigation of the friction between the yarn and yarn guiding elements and the friction between the yarns themselves during the stitch formation. For this reason, all contact points between yarn and yarn guiding elements as well as between the yarns themselves are examined and classified. A test rig is set up to determine all occurring frictions as a function of various machine parameters.The knowledge gained and the derived analytical expressions between machine settings and occurring friction can thus become the basis for modeling the friction points of the warp knitting machine, which is also presented. Furthermore, based on the findings a design improvement of the machine can be achieved and the friction model can serve as part of a simulation model of the entire warp knitting machine, which will be the focus of further publications.

Soft actuators are a promising option for the advancing fields of human-machine interaction and dexterous robots in complex environments. Shape memory alloy wire actuators can be integrated into fiber rubber composites for highly deformable structures. For autonomous, closed-loop control of such systems, additional integrated sensors are necessary. In this work, a soft actuator is presented that incorporates fiber-based actuators and sensors to monitor both deformation and temperature. The soft actuator showed considerable deformation around two solid body joints, which was then compared to the sensor signals, and their correlation was analyzed. Both, the actuator as well as the sensor materials were processed by braiding and tailored fiber placement before molding with silicone rubber. Finally, the novel fiber-rubber composite material was used to implement closed-loop control of the actuator with a maximum error of 0.5°.

Electrically conductive filaments are used in a wide variety of applications, for example, in smart textiles and soft robotics. Filaments that conduct electricity are required for the transmission of energy and information, but up until now, most electrically conductive fibers, filaments and wires offer low mechanical elongation. Therefore, they are not well suited for the implementation into elastomeric composites and textiles that are worn close to the human body and have to follow a wide range of movements. In order to overcome this issue, the presented study aims at the development of electrically conductive and elastic filaments based on a coating process suited for multifilament yarns made of thermoplastic polyurethane (TPU). The coating solution contains TPU, carbon nanotubes (CNT) and N-Methyl-2-pyrrolidone (NMP) with varied concentrations of solids and electrically conductive particles. After applying the coating to TPU multifilament yarns, the mechanical and electrical properties are analyzed. A special focus is given to the electromechanical behavior of the coated yarns under mechanical strain loading. It is determined that the electrical conductivity is maintained even at elongations of up to 100%.