Yarn Surface Research Articles

Flexible and strain conductive cotton yarn enabled by low-temperature sintering of silver paste with multifunctional sensing capability in human motion detection and wearable applications

Flexible wearable textiles have attracted increasing attention, due to their potential applications in human motion detection, electric heating and humidity monitoring. However, the rigidity of metal materials contradicts the flexibility of textiles, and the complex preparation process and unfriendly environment hinder the development of metal materials as conductive materials of smart textiles. This study proposed a simple and environmentally friendly solution for smart textile preparation. Drawing on the bionic design principle of long-horned beetle’s exocuticle, the conductive layer on the surface of cotton yarn (CY) was formed by sintering the silver paste under low temperature of 200 ˚C. Silver Paste (SP) mainly composed with silver particles, terpineol (TE) and ethyl cellulose (EC). The resultant conductive yarn was characterized with high flexibility and high conductivity (4.08 × 103 S/cm). The conductivity of the yarn increases under tensile force, while decreases under non-tensile bending action. The strain sensor prepared by the yarn has a wide working range and high sensitivity, with distinguish performances of signal output according to the motion of different human body parts. The sensing behavior was also highlighted with the capability of micro-vibration strain of the human body, such as response to the pulse and throat. Furthermore, the conductive property of sintered silver paste cotton yarn (SSP-CY) has the capability of electric heating. The electric heating device based on SSP-CY can realize wired and radio heating, which resulted a maximum temperature of about 41 ℃. Therefore, the novel conductive cotton yarn has great potential in the application of high-sensitive wearable electronic devices.

Effect of Core Yarn on Linear Actuation of Electroactive Polymer Coated Yarn Actuators

AbstractSmart textiles combine the features of conventional textiles with promising properties of smart materials such as electromechanically active polymers, resulting in textile actuators. Textile actuators comprise of individual yarn actuators, so understanding their electro‐chemo‐mechanical behavior is of great importance. Herein, this study investigates the effect of inherent structural and mechanical properties of commercial yarns, that form the core of the yarn actuators, on the linear actuation of the conducting‐polymer‐based yarn actuators. Commercial yarns were coated with poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) to make them conductive. Then polypyrrole (PPy) that provides the electromechanical actuation is electropolymerized on the yarn surface under controlled conditions. The linear actuation of the yarn actuators is investigated in aqueous electrolyte under isotonic and isometric conditions. The yarn actuators generated an isotonic strain up to 0.99% and isometric force of 95 mN. The isometric strain achieved in this work is more than tenfold and threefold greater than the previously reported yarn actuators. The isometric actuation force shows an increase of nearly 11‐fold over our previous results. Finally, a qualitative mechanical model is introduced to describe the actuation behavior of yarn actuators. The strain and force created by the yarn actuators make them promising candidates for wearable actuator technologies.

A novel method for reducing yarn hairiness with dynamic and static friction rollers on the yarn guide

Fiber torsional control is critical for reducing the hairiness of high-quality yarns during the yarn formation process. However, the applied fiber torsion that facilitates fiber motion and transfer in conventional ring spinning is still under exploration. In this study, we designed a device with dynamic- and static-friction rollers for reducing harmful hairiness. The key mechanisms and mechanical model of the applied forces on fiber torsion and motion contacting dynamic- and static-friction rollers were theoretically analyzed. Exceptional fiber torsion was obtained by creating gradient friction resistance from the varied applied pressures while providing full internal and external transfer to forcibly capture and trap exposed fibers into the main yarn body. Compared to conventional ring-spun yarns, yarns spun by the dynamic-friction roller exhibited reduced harmful hairiness, improved tensile properties, a tighter yarn surface, and improved yarn irregularity. However, the excessive force applied by the static-friction roller deformed exposed fibers to cause fiber accumulation and fiber loss, resulting in reduced yarn performance. These results can be used to develop novel spinning methods for various fiber materials for high-quality yarn production.

Mechanical performance of cementitious composites reinforced with weft-knitted spacer fabrics under static flexural and impact loading

Though weft-knitted spacer fabric made from high-performance continuous fiber offers great potential for lightweight composite with high energy absorption characteristic, it has yet to be substantially studied in the field of cement-based structural materials. In this paper, a series of newly developed aramid weft-knitted spacer fabrics were applied to reinforce the eco-friendly cementitious matrix. The mechanical properties and failure behaviors of composites were investigated via the three-point bending test and impact test systematically. XCT was then performed to reveal the underlying damage mode of composites. The experimental results indicated that aramid weft-knitted spacer fabrics were highly beneficial reinforcements for cementitious composites due to their great bonding and mechanical anchoring with matrix. The larger ductile deformation and higher damage tolerance of composites were obtained by the increase of spacer yarn density and surface yarn density. The asymmetrical structure corresponding to the different density of surface layer could further enhance bearing capacity by altering the stress transfer.

Realistic fabric rendering with yarn models

Modeling fabrics with yarn models makes the fabric structure more realistic in detail. In this paper, a fiber-level rendering method is proposed to simulate different yarns and fabrics. The fibers are divided into three categories: the ply, the loop hairiness and the short hairiness. Geometric tubes are modeled to match these fibers according to the input yarn parameters. Different fibers can be selected depending on the yarn type, which is flexible to reduce the computation amount. Texture mapping is applied to simulate the yarn surface, reducing the memory and time cost of rendering large numbers of fibers. Several single yarns and fabric with different structures are simulated, demonstrating that this is an effective method for fabric modeling and rendering.

Film-Formation and Binder-Free Pigment Printing of Fluorosilicone-Modified Polyacrylate/Pigment Hybrid Latex: Effect of Cross-Linking Degree

Binder-free pigment dyeing/printing of textiles is a type of environmentally friendly and clean production technology that utilizes polymer/pigment hybrid latex. Although it has widespread use, the manner in which the nature of the hybrid latex influences the film formation and how systems can be designed to improve softness and air-permeability is still unclear. In this study, we synthesized a series of fluorosilicone-modified polyacrylate/pigment hybrid latexes to explore how cross-linking degree affects film-formation behavior and binder-free pigment printing performance on fabric, where the cross-linking structure is controlled by a silane coupling agent. Our results show that the cross-linking degree of the fluorosilicone-modified polyacrylate chain plays a vital role in chain diffusion, latex particle packing, and deformation. Further, it controls “skin” formation during the process of hybrid latex drying. The dried hybrid films not only have homogeneity and good barrier performance but also exhibit a soft state (low Tg, – 28.3 °C) owing to the silicone chain segment and bound water with a plasticizing effect. Interestingly, our results show that the cross-linking degree of hybrid latex particles changes as a function of the morphology of the printed polyester (PET) fiber. Further, as a result of the improvement of the softness and air-permeability of the binder-free printed PET fabric, the surface of single yarns is uniformly wrapped by hybrid films with a high cross-linking degree. These insights allow for effective development of textile pigment printing technology controlled by the film-formation behavior of hybrid latex.

Collagen Nanoyarns: Hierarchical Three-Dimensional Biomaterial Constructs.

Hierarchical fibrous scaffolds (HFS) consist of nanoscale fibers arranged in larger macroscale structures, much in the same pattern as in native tissue such as tendon and bone. Creation of continuous macroscale nanofiber yarns has been made possible using modified electrospinning set-ups that combine electrospinning with techniques such as twisting, drawing, and winding. In this paper, a modified electrospinning setup was used to create continuous yarns of twisted type I collagen nanofibers, also known as collagen nanoyarns (CNY), from collagen solution prepared in acetic acid. Fabricated CNYs were cross-linked and characterized using SEM imaging and mechanical testing, while denaturation of collagen and dissolution of the scaffolds were assessed using circular dichroism (CD) and UV-vis spectroscopy, respectively. HeLa cells were then cultured on the nanoyarns for 24 h to assess cell adhesion on the scaffolds. Scanning electron micrographs revealed a twisted nanofiber morphology with an average nanofiber diameter of 213 ± 60 nm and a yarn diameter of 372 ± 23 μm that shrank by 35% after covalent cross-linking. Structural denaturation assessment of native collagen using circular dichroism (CD) spectroscopy showed that 60% of the triple-helical collagen content in CNYs was retained. Cross-linking of CNYs significantly improved their mechanical properties as well as stability in buffered saline with no sign of degradation for 14 days. In addition, CNY strength and stiffness increased significantly with cross-linking although in the wet state, significant loss in these properties, with a corresponding increase in elasticity, was observed. HeLa cells cultured on cross-linked CNYs for 24 h adhered to the yarn surface and oriented along the nanofiber alignment axis, displaying the characteristic spindle-like morphology of cells grown on surfaces with aligned topography. Collectively, the results demonstrate the promising potential of collagen nanoyarns as a new class of shapable biomaterial scaffold and building block for generating macroscale fiber-based tissues.

Linear flexible capacitive sensor with double helix structure based on multi-needle water-bath electrospinning technology

Capacitive flexible sensors stand out due to their advantages of simple structure, strong adaptability and low power consumption, and become the mainstream technology for the preparation of wearable flexible devices. In this study, polyamide 6 (PA6) nanofibers were coated on the surface of a silver-coated nylon (SCN) core yarn using a novel multi-needle water-bath electrospinning method. The SCN/PA6 nanofiber core-spun yarns were prepared, and linear flexible capacitive sensors with a double helix structure (double helix structure capacitive sensors, DHSCSs) were produced by winding two nanofiber core-spun yarns in parallel, with different winding densities, on elastic rubber strings. We then characterized the nanofiber core-spun yarn, analyzed its sensing performance, and explored an application in human motion monitoring. Our results confirm that a nanofiber coating with a complete structure can be formed on the surface of the SCN core yarn by multi-needle water-bath electrospinning. The nanofiber diameter was in the 80–100 nm range, which provides a soft and deformable dielectric layer for the sensor. The capacitance of the DHSCSs gradually decreased with an increase in strain. When the strain was small, it exhibited good linearity (R 2 > 0.99) and sensitivity (gauge factor of ∼4). With an increase in strain, the linearity and sensitivity of the DHSCSs gradually decreased. The capacitances of the DHSCSs were stable under extended duration cyclic stretching, and their repeatability and stability were good. At different tensile speeds, the sensing performance of the DHSCSs did not change, and the capacitance change was not affected by the tensile speed. The higher winding density of the sensor made it more sensitive. The DHSCS could monitor intermittent and continuous knee bending and walking, effectively monitoring human motion in real time. This sensor has the potential for application in flexible wearable human motion, health monitoring, and other fields.

Sericin eco-friendly biomaterial as a spin finish in drawn textured PET yarn production

Purpose This paper aims to extracted sericin from the cocoons of Bombyx mori silkworms, and sericin powder was applied onto drawn textured polyethylene terephthalate (PET) yarns as a spin finish. The reactivity on the surface of PET yarns was analyzed through Fourier transform infrared spectrophotometry–attenuated total reflectance (FTIR-ATR) and dyeing with methylene blue as a reactive dye. Also, investigations were conducted on the effects of sericin, citrc acid (CA) (as a crosslinking agent), and sodium hypophosphite (as a catalyst) concentrations on some properties of false-twist textured PET yarns. Design/methodology/approach A false-twist texturing machine (Scragg-Shirley minibulk, England) was used with the draw ratio of 1.05, heating temperature of 120°C, texturing speed of 100 m min−1 and applied twist of 3,000 TPM. The aqueous extraction of sericin was carried out by the boiling of the raw silk in distilled water with L:R: 40:1 for 120 min. The aqueous solution was filtered with a filter paper to remove the impurities and insoluble fibroin. Finally, the sericin solution was freeze-dried to obtain the sericin powder. The sericin solution was applied on the drawn textured PET yarns using the “pad-dry-cure” method. Findings Sericin fixation onto the PET yarns was confirmed by FTIR-ATR. The results showed that there were no significant changes in the tensile strength, linear density, crimp contraction and crimp modulus, elongation at break and shrinkage. In contrast, a substantial increase was observed in moisture regain, vertical wicking, dye uptake and ultraviolet protection. There was also a reduction just in the electrical resistivity, in the presence of sericin. Originality/value Although sericin has been known to have numerous beneficial properties, its application in textile industry as a spin finish has not been reported yet.

Mass-Produced Flexible Strain Sensors Based on Dip-Coating and Water Bath for Human–Computer Interaction

Flexible strain sensors play a key role in the field of human–machine interaction because of their ability to sense deformation. To meet the needs of mass production of wearable electronic devices, it is very necessary to develop a strain sensor with excellent sensing performance and low-cost mass fabrication. In this article, a fabrication process of a flexible resistive strain sensor, which is perfectly matched by the combined method with dip-coating and water bath, is proposed. A layer of conductive polymers containing carbon black/multiwall carbon nanotubes/thermoplastic polyurethane (CB/MWCNTs/TPU) was quickly and evenly wrapped on the surface of the core-spun elastic yarn. Combining the synergistic conductive effect of the filler and the high elasticity of the yarn matrix, the designed flexible strain sensor has high sensitivity (gauge factor (GF) to 68), low detection limit, wide strain range, fast response time, fast recovery time, and high stability. The designed strain sensor exhibits outstanding sensing performance and wearability, which can be used for real-time monitoring of human joint bending and breathing state. Furthermore, a wireless operating system based on wearable data gloves has been developed to realize the remote synchronous movement of the human hand/the bionic manipulator. The results indicate that the proposed strain sensor has great potential in human–machine interaction and its fabrication technology provides guidance for the sensor in mass production.

Preparation of Acrylic Yarns with Durable Structural Colors Based on Stable Photonic Crystals.

Structural coloration of photonic crystals (PCs) is considered an ecological and environmental way to achieve colorful textiles. However, constructing PCs with obvious structural colors on traditional flexible yarns is still a great challenge. As a secondary structure that forms textiles, compared with fibers and fabrics, the yarns are rougher, hindering the construction of regular PCs. In this work, the flexible acrylic yarns with vivid structural colors, named PC-based structural color yarns, were prepared by constructing regular PCs via assembling poly(styrene-butyl acrylate-methacrylate) (P(St-BA-MAA)) colloidal microspheres on yarns. Specifically, the properties of P(St-BA-MAA) colloidal microspheres were investigated. The PCs with better structural stability and obvious structural colors were prepared by presetting the acrylic adhesive layer on yarns. Moreover, the color durability and color regulation methods of prepared PC-based structural color yarns were evaluated and discussed. The results showed that the P(St-BA-MAA) colloidal microspheres exhibited even particle sizes, excellent monodispersity, and a typical hard core-soft shell structure. And the glass-transition temperature (T g) of the microspheres was tested to be about 65.6 °C. The cationic acrylate regarded as a pretreatment agent could not only improve the combination between the PC layers and the yarns by acting as a "bridge" but also enhance the structural color effect by smoothing the yarn surface. The results showed that when the mass fraction of cationic acrylate was 3 wt %, the microspheres were beneficial to access regular PCs with obvious structural colors. The PCs with bright structural colors could be constructed on black acrylic yarns, and the colors of yarns were still bright after rubbing and washing tests, indicating that the prepared PC-based structural color yarns have good color fastness. Moreover, the color hue of PC-based structural color yarns could be regulated by adjusting the particle sizes and viewing angles. This study provides strategic support for the structural coloration of flexible materials.

Recycled fibers from pre- and post-consumer textile waste as blend constituents in manufacturing 100% cotton yarns in ring spinning: A sustainable and eco-friendly approach

The usage of recycled fibers has achieved enormous importance in the textile sector due to growing environmental awareness, legal requirements for more sustainability and the cost of raw materials. Recycled cotton fibers derived from mechanical shredding of textile waste possess lower quality values and therefore they are spun through blending with other fibers in rotor spinning system for the production of coarse yarns (10–20 Ne) to make denim, towel and home furnishing. Owing to low fiber migration, rotor yarns require high twist during spinning which makes them stiffer and poorly moisture absorbent. Rotor yarns also feel harsh in skin contact due to the presence of wrapper fibers in the yarn surface. Intending to make knit top garments like T-shirts and polo shirts, apparel manufacturers nowadays demand recycled fiber-contained soft and high moisture absorbent yarn that can be produced in ring spinning system. In the current endeavor, cotton fibers reclaimed from pre- and post-consumer textile waste were blended with virgin cotton and soft-twisted 30 Ne yarns were manufactured in ring spinning frame on an industrial scale in a spinning mill. A thorough analysis of the structure and properties of the yarns revealed that up to 25% recycled cotton fibers can be used as an alternative to virgin cotton to manufacture medium count (30 Ne) yarn in ring spinning suitable to produce knit top garments.

Enzymatic construction of temperature-responsive PDMAPS-decorated textiles for oil-water separation

In view of the frequent occurrence of oil-containing pollutant discharge events, many optimal strategies for oil-water separation were proposed. However, the large-scale application of these strategies is severely limited by the lack of environmental unfriendliness and intelligent response capability. To address these issues, we developed a thermo-responsive fabric with switchable wettability that can be applied for efficient oil-water separation by an eco-friendly enzymatic method. Briefly, 3-(trimethoxysilyl) propyl methacrylate (KH-570) and boron nitride (BN) nanosheets were introduced to the surfaces of cotton fabric, followed by enzymatic graft polymerization of N,N-dimethyl (methacryloylethyl) ammonium propane sulfonate (DMAPS) onto the fibers using horseradish peroxidase (HRP). Thanks to the switchable wettability of the composite layer on the yarn surfaces, oil and water can pass through the cotton fabric at the temperatures below and above 28 °C, respectively, realizing highly efficient oil-water separation. The resulting temperature-responsive textiles exhibit encouraging separation performance, and the separation efficiency, oil flux, and water flux reach as high as 95%, 542.57 L·h−1m−2, and 477.26 L·h−1m−2, respectively. Meanwhile, the cyclic separation capability, acid-alkali tolerance, and mechanical friction stability of the composite textiles are encouraging. The present work provides an alternative for construction of oil-water separation materials, which inspires further research on the smart oil-water separation strategies.

Surface Modification on Polyimide Yarn by Plasma Treatment to Enhance Adhesion with Polypropylene Resin.

Polyimide yarn as a kind of high performance fiber material has to improve the adhesion between the material surface and the resin in order to get a deeper application. The surface of polyimide yarn is modified by low temperature plasma treatment, and the effect of plasma treatment parameters on the adhesion between polyimide yarn and polypropylene resin is studied. By comparing the extraction force on the surface of polyimide yarn before and after treatment, the effect of plasma treatment parameters such as treatment time, processing gas and treating power on yarn adhesion is investigated. Furthermore, the adhesive force between polyimide yarn and polypropylene resin is analyzed by a single factor to optimize the process parameters to obtain higher adhesive force. Additionally, the Box–Behnken design is utilized to optimize the plasma treatment parameters, and the significance of the influence of the plasma treatment parameters on the adhesion between the polyimide fiber and the resin is discussed. The optimal process parameters are obtained through analysis: the treatment time 90 s, the processing gas oxygen, and the treating power 150 W.

Numerical study of flows for slub yarn transmission in an air jet

This paper focused on the investigation of the slub yarn parameters and the relationships of the aerodynamic friction along the surface of the slub yarn. The calculation of the frictional drag force was analyzed for spun yarns, which proves it has an irregular surface due to the irregularity of the yarn diameter along its length. In the case of slub yarns, the main descriptive parameters such as slub length, slub distance, slub multiplier, and base yarn count, will affect the air drag coefficient. A methodology for the calculation of the coefficient of air drag along the yarn in an airstream was developed for both regular and slub yarns under different conditions. The air frictional drag coefficients of yarn samples were calculated accordingly. Finally, empirical equations were developed. Calculations of the air friction drag coefficient of slub yarn were determined. The experimental results agreed well with the model predictions and showed that the present model had a high prediction accuracy.

Fabrication and characterization of polyester composite yarn with PVB/ZrC/Al2O3 coating

As a functional textile, photothermal textile materials are receiving more and more attention. A composite yarn was prepared by coating polyvinyl butyral/zirconium carbide/alumina oxide on the surface of polyester yarn through a sizing coating method with the aim to provide a textile substrate with controlled photothermal efficiency. The Box–Behnken design combined with response surface analysis and regression method was used to study the effects of input variables (polyvinyl butyral, zirconium carbide and alumina oxide concentration) on the temperature of the fabric made of polyester/polyvinyl butyral/zirconium carbide/alumina oxide composite yarn under infrared light irradiation. It was found that the effect of polyvinyl butyral and zirconium carbide content on the fabric surface temperature was more significant than that of alumina oxide content. The established regression model could predict the response value (fabric temperature) precisely. The optimal conditions for preparing the polyester/polyvinyl butyral/zirconium carbide/alumina oxide composite yarn were obtained by response surface analysis: 5.9% polyvinyl butyral, 5% zirconium carbide and 0.5% alumina oxide. The structure and properties of the yarn prepared under the optimal conditions were characterized. The results showed zirconium carbide and alumina oxide deposited on surface coating without obvious deterioration of thermal stability and tensile strength. The near-infrared light absorption rate of the composite yarn reached 96.71% and its surface temperature reached 104.0°C after 180 s irradiation under an infrared lamp. The photothermal temperature can still reach 101.5°C after 20 cyclings. The excellent photothermal conversion capacity indicates the polyester/polyvinyl butyral/zirconium carbide/alumina oxide yarn can realize solar energy utilization and be applied in heat management textiles.

Modeling of filament level plain woven Kevlar 49 fabric for accurate prediction of yarn pull-out behavior

This paper proposes two numerical and one analytical yarn pull-out models to investigate pull-out behavior and its energy transfer mechanism. First, the microgeometry of a two-dimensional woven fabric is generated with 112 fibers per yarn mesh implementing the digital element approach. In this approach, one yarn consists of a bundle of fibers and one fiber is made of a chain of rod elements. As such, the realistic yarn surface and yarn cross-section shapes are derived from fiber alignment. Meanwhile, a yarn-level fabric model with constant yarn cross-sectional shape is built on commercial textile modeling software TexGen. Then, both numerical and analytical yarn pull-out models are proposed to investigate the fabric performance. Results show the pull-out force and transferred energy of the digital element approach model is higher than the other two models and closer to the experimental data. This indicates that the realistic yarn surface introduces more contact points and the period of the pull-out force is determined by material properties rather than detailed fabric geometric configuration. Second, a detailed parametric study is carried out with a broad range of friction coefficient and tensile preload. The simulation results find out, when the tensile pre-load is between 50 N and 300 N, the transverse force drops immediately after the pull-out process begins. When the tensile pre-load reaches 400 N, the transverse force increases instead. This phenomenon indicates that the transverse force is sensitive to tensile pre-load and can be used as an indicator to detect residual stress in fabric.

Effect of Fibre Diameter, Prickle Factor and Coarse Fibre Bias on Yarn Surface Hairiness in South American Camelids (SAC) Fibre

It is well known that objectionable fibres emerge from the surface of the yarn due to the centrifugal force of the spinning device. Furthermore, the hair removal process is based on the same physical principles. However, the fibres that are >30 µm (PcF) are the fibres that appear in the hairiness of the yarn and are eliminated by dehairing. It has always been presumed that the PcF was linearly correlated with the diameter of the fibre (MFD) in llamas, but not so in alpaca fibres. Nevertheless, there is evidence that this relationship is curvilinear and behaves the same way in both species. The objectives of this study are to explore the relationship between MFD and PcF in both llamas and alpacas, to explore the existence of a breaking point (BP) in this curvilinear relationship, and to determine the frequency of fleeces that do not require dehairing because the PcF ≤ 3.2%. In addition, the existence of a positive bias of coarse fibre content on the hairy surface (CFs) of the yarn to coarse fibre content within the yarn fibres (CFy) was determined, which may explain the effect of the dehairing on the prickle factor of SAC fibres. The relationship of PcF on MFD behaves the same way in alpacas and llamas. It conforms to a power distribution and presents a BP of 23 µm, with PcF being constant before the BP and increasing significantly after it. Most animals (≤91% of alpacas and ≤87% of llamas) are above the threshold (≤3.2%), requiring dehairing to correct it. By means of a shaving technique on the surface of the fabric sample, it was established that the objectionable CFs content is 8.15% higher than the objectionable CFy content. In the evoked-coarse fibre in the dehaired samples, a CFs-CFy difference below 5.9% (p > 0.05) is not significantly detected by panellists. The surface MFD is more than 2.7 µm coarser than the yarn MFD.

An Eco-Friendly Surface Modification Method of Para-Aramid by Supercritical CO<sub>2</sub>

The structures and properties of para-aramid yarn were investigated under different treatment temperatures from 80 °C to 200 °C with supercritical CO2 and air, respectively, which were observed by Scanning electron microscopy (SEM), Dynamic wetting measurements, Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), and Thermogravimetric instrument (TG). It is confirmed that the surface morphology of para-aramid yarn was changed remarkably with the supercritical CO2 treatment temperature increasing compared to untreated yarn and treated with air, and the oligomers and disaggregates of yarn were migrated to the yarn surface. Furthermore, the water contact angle of para-aramid was reduced significantly from 136.22° to 91.37° with supercritical CO2 treatment at 200 °C, and the wettability was improved. Overall, supercritical CO2 modification for para-aramid has been proved to be feasible.

Efficient plant fibre yarn pre-treatment for 3D printed continuous flax fibre/poly(lactic) acid composites

To address the issue of high void contents in 3D printed continuous flax fibre reinforced composites (CFFRCs), an efficient fibre pre-treatment method was proposed to improve the compatibility between plant fibre and resin matrix so that the high-quality manufacturing and excellent mechanical performance were achieved. The surface of flax yarns was treated by silane coupling agents to improve the wettability and interfacial performance. The CFFRCs were then prepared by the customised 3D printing technology, and the mechanical tests were conducted to measure their mechanical properties. It was found that the mechanical properties of the CFFRCs were greatly improved after the treatments which induced very low void contents of less than 1.1%, due to the improved wettability and the interfacial bonding between the flax yarns and resin matrix. The mechanical properties of the CFFRCs prepared by 3D printing in the present work were comparable to those manufactured by compression moulding in literature.