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  • 1.
    Lund, Anja
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Melvinsson, Rebecca
    Malm, Veronica
    University of Borås, Faculty of Textiles, Engineering and Business.
    Wand, Charlie
    The University of Manchester · School of Chemical Engineering and Analytical Science.
    Tahir, Mohammad Waseem
    Högskolan i Skövde.
    Skrifvars, Mikael
    Stigh, Ulf
    Högskolan i Skövde.
    Bolton, Kim
    University of Borås, Faculty of Textiles, Engineering and Business.
    Nierstrasz, Vincent
    University of Borås, Faculty of Textiles, Engineering and Business.
    Melt Spun PVDF Actuator Fibres: the Effect of Spin-Line Orientation and MW on Actuation2015In: Regional Conference Polymer Processing Society Graz 2015: Book of Abstracts, 2015, p. 306-Conference paper (Other academic)
    Abstract [en]

    This paper presents the melt spinning and characterisation of polymer actuator fibres; fibres that reversibly contract along the fibre axis in response to heat. Recently, Haines et al (1) showed that low-cost filaments, e.g. fishing lines, can be relevant precursors for artificial muscles. They demonstrated a reversible fibre-direction thermal contraction, which was significantly amplified when the fibres were twisted and coiled. The effect was explained to result from an increase in the conformational entropy of the amorphous phase. In earlier studies on negative thermal expansion in anisotropic polymer structures, it has been shown that the negative thermal expansion in oriented highly crystalline polymers approaches values typical of polymer crystals (2).

     

    To further investigate the mechanisms behind these seemingly simple artificial muscles, we have melt spun fibres from poly(vinylidene fluoride) (PVDF) – Solef  1006 and 1008 kindly provided by Solvay (Milan, Italy) – and compared their properties to a commercially available PVDF-fishing line. The fibres were characterised with respect to their thermal actuation properties, crystal morphology and degree of orientation along the spin-line axis.

     

    We have further done modelling on the molecular and macroscopic levels examining the possible mechanisms of negative thermal expansion in semi-crystalline PVDF. We believe that tie molecules (a polymer chain linking two crystalline regions) are the predominant factor influencing actuation. Two mechanisms are considered: an entropic effect and a conformational change effect. The entropic effect causes an increase in the elastic stiffness with an increase in temperature, effectively resulting in a contraction of a strained fibre. The conformational change effect is also expected to contribute to contraction as tie molecules, under strain, revert to their unloaded preferred conformation when heated.

    1. C. S. Haines et al., Artificial Muscles from Fishing Line and Sewing Thread. Science 343, 868-872 (2014).
    2. C. L. Choy et al., Negative Thermal Expansion in Oriented Crystalline Polymers. Journal of Polymer Science: Polymer Physics Edition 19, 335-352 (1981).
  • 2.
    Malm, Veronica
    University of Borås, Swedish School of Textiles.
    Colour-changing textile coatings containing multi-layered mica pigments: an experimental study2014Licentiate thesis, monograph (Other academic)
    Abstract [en]

    This study investigates the possibility of producing angle-dependent colour-changing textiles with thickened polyurethane (PU)-based aqueous dispersion containing multi-layered mica pigments using a direct coating method. Colour changing textile coatings with the latest generation of layered mica pigment (EP) have a promising future for functional purposes such as authentication and aesthetic eye-catching applications. The surface structure and colour of the substrate as well as the coating formulation combined with different coating parameters will strongly influence the colour-changing effects of textile coatings containing EPs. Scanning electron microscopy (SEM) showed that the substrate surface roughness increased when constructed of multifilament yarns with high thread count, spun staple-fibre yarns with higher and spun staple-fibre yarns with lower thread counts. Multi-angle spectrophotometer measurements of EP-coated samples showed that the colour differences in form of CIE L*a*b*-coordinates varied to a great extent, depending on detection angles, surface roughness and colour of the substrates. Increased surface roughness generated less plane-parallel orientated EP-platelets and consequently a less pronounced colour-changing effect on coated textiles. The lightness, L*-values, for white substrates were much higher than the corresponding values obtained with black substrates. Thus white substrates greatly affect the colour-changing effects, which become less intense and much more difficult for the human eye to distinguish. Different types of rheology modifiers (RMs), dispersion in oil of sodium polyacrylates (LDPSAPs), hydrophobically modified alkali-swellable acrylic emulsions (HASEs) and hydrophobically modified ethoxylated polyurethanes (HEURs) provided EP-formulations with similar viscosity profiles. However, it was found that the choice of RM as well as variations in gap heights and coating speed could increase the solids deposit, corresponding to more and better dispersed EPs within the coated layer as well as more plane-parallel oriented platelets as confirmed by SEM. Multi-angle spectrophotometer measurements with six detection angles showed that the variations of the absolute values of L* and a* were more pronounced between detection angles of -15° and 15°, corresponding to the angles where the strongest colour changes can be visually observed. Slow-coated samples with a higher deposit were measured to be lighter and of higher chroma compared to samples coated at a higher speed. The colour-changing effects were found to be governed by the choice of RM and coating parameters in terms of variations of the amount of coating deposited onto the samples.

  • 3.
    Malm, Veronica
    University of Borås, Faculty of Textiles, Engineering and Business.
    Functional Textile Coatings Containing Flake-shaped Fillers: investigations on selected optical and electrical properties2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis investigates the manufacturing and characterisation of functionalised textile coatings containing different types of flake-shaped fillers with angle-dependent colour-changing and electrically conductive properties, respectively. Common benefits of these types of flakes are their high aspect ratio, which offers low filler loading with high functional performance. However, when applied on flexible fabric, their impact on the mechanical properties and durability leads to that a trade-off between, for example, flexural rigidity and functional performance need to be taken into account. Both experimental studies, with different functional approaches, explore how formulation additives e.g. rheology modifiers and cross-linker and knife coating parameters e.g. gap height and speed influence the formulation viscosity, which in turn strongly influences the amount of solids deposited on the fabric, and the functional performance.

    Multilayered mica pigments can provide an angle-dependent colour change based on the phenomenon of interference, and has great potential in application within the textile design and product authentication fields. However, optimal conditions for intense colour-changing effects using these types of flake-shaped pigments depend on a plane-parallel orientation to a flat substrate. The pigment orientation is challenged by textile substrates, which have a textured surface due to the cross-sectional shape of the fibre, the yarn composition and fabric construction. In addition, the semi-transparent nature of these types of pigments means that the substrate colour highly influences the colour-changing effects.

    Metal flake-shaped fillers for high electrical conductivity applications are particularly advantageous for reliable power and signal transferring interconnections in the field of electronic textiles. As the conductivity depends on the electron transport between the metal flakes, the challenge is to establish and maintain the three-dimensional network of contacting surfaces between flakes. Although the network is held together and adhered to the substrate by an insulating polymer film matrix, it is highly sensitive to dimensional impact upon different

  • 4.
    Malm, Veronica
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Nierstrasz, Vincent
    University of Borås, Faculty of Textiles, Engineering and Business.
    Seoane, Fernando
    University of Borås, Faculty of Textiles, Engineering and Business. University of Borås, Faculty of Caring Science, Work Life and Social Welfare.
    Electrical resistance characterisations and durability of textile coatings containing metal flake fillers2018Conference paper (Refereed)
  • 5. Malm, Veronica
    et al.
    Seoane, Fernando
    University of Borås, Faculty of Caring Science, Work Life and Social Welfare. University of Borås, Faculty of Textiles, Engineering and Business.
    Nierstrasz, Vincent
    University of Borås, Faculty of Textiles, Engineering and Business.
    Characterisation of Electrical and Stiffness Properties of Conductive Textile Coatings with Metal Flake-shaped Fillers2019In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 21, p. 1-18Article in journal (Refereed)
    Abstract [en]

    Two conductive formulations containing different types of micron-sized metal flakes (silver-coated copper (Cu) and pure silver (Ag)) were characterised and used to form highly electrically conductive coatings (conductors) on plain and base-coated woven fabrics, the latter in an encapsulated construction. With e-textiles as the intended application, the fabric stiffness, in terms of flexural stiffness and sheet resistance (Rsh), after durability testing (laundering and abrasion) was investigated and related to user friendliness and long-term performance. Bare and encapsulated conductors with increasing amounts of deposited solids were fabricated by adjusting the knife coating parameters, such as the coating gap height (5, 20, 50, and 200 μm), which reduced the Rsh, as determined by four-point probe (4PP) measurements; however, this improvement was at the expense of increased flexural stiffness of the coated fabrics. The addition of a melamine derivative (MF) as a cross-linker to the Cu formulation and the encapsulation of both conductor types gave the best trade-off between durability and Rsh, as confirmed by 4PP measurements. However, the infrared camera images revealed the formation of hotspots within the bare conductor matrix, although low resistances (determined by 4PP) and no microstructural defects (determined by SEM) were detected. These results stress the importance of thorough investigation to assure the design of reliable conductors applied on textiles requiring this type of maintenance.

  • 6.
    Malm, Veronica
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Seoane, Fernando
    University of Borås, Faculty of Textiles, Engineering and Business.
    Nierstrasz, Vincent
    University of Borås, Faculty of Textiles, Engineering and Business.
    Fused deposition modelling – Towards 3D printed electrodes on fabric for surface electromyography (sEMG)2018Conference paper (Other academic)
    Abstract [en]

    Surface electromyography (sEMG) monitoring has promising applications within the field of human robot communication where wearable electrodes are used as the interface. This research investigates the production of flexible 3D printed electrodes using electrically conductive filaments, of thermoplastic polyurethane containing carbon black, and polyester fabric as substrate. Dry 3D printed electrodes of varying thickness, due to increased number of layers, were compared to conventional electrolytic gel electrodes. Initial tests show that the volume resistivity of 3D printed electrodes increased with increased number of layers. This because, with increased number of layers the diffusion between layers deteriorates and hinders conductive particle connections. Additional heat-treatments using hot press plates to improve diffusion between layers were promising as volume resistivity decreased with 200 % for all samples. As a first step to evaluate the 3D printed electrodes, skin-electrode impedance measurements were performed, and compared with measurements of conventional electrodes. Results showed that resistance and reactance versus frequency curves had similar trending slopes, decreasing with increasing frequency. However, this corresponded only between the thinnest (200 μm) 3D-printed dry electrode having a volume resistivity of 6.2 Ω cm and the conventional gel electrode. Future studies regarding the influence of platform and extruder temperature are planned for, focusing on improved diffusion between layers and increased conduction for proper electron transfer. 

  • 7. Malm, Veronica
    et al.
    Seoane, Fernando
    University of Borås, Faculty of Caring Science, Work Life and Social Welfare. University of Borås, Faculty of Textiles, Engineering and Business.
    Nierstrasz, Vincent
    University of Borås, Faculty of Textiles, Engineering and Business.
    Stability of encapsulated electrical interconnections coated on fabric exposed to mechanical strain.In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069Article in journal (Refereed)
    Abstract [en]

    In this study, two different conductive coating formulation containing silver (Ag) and silver-coated copper (Cu) flakes are studied to evaluate the electromechanical stabilityof encapsulated conductors coated on textiles in a multilayer construction. Consideringe-textiles as a possible application area with integrated conductors functioning as interconnections, the purpose is to obtain a fundamental understanding of the deformation behaviour when subjected to tensile and compressive strains during bending. The results show that an increased Ag conductor thickness with flakes <5 μm was a favourable combination regardless of encapsulation thickness providing samples with minimal stress responses upon bending deformations at angles of -180°, -90°, 90°and 180°, and, sheet resistance (Rsh) values of 0.01 Ω/sq. It was shown that the conductor layer changed shape depending on the bending angle resulting in alternating convex and concave arcs at -180° and a more uniform curvature at 180°. The findings were correlated to lower and larger Rsh ratios, respectively, which are denoted as the thinner encapsulated Ag conductors and the Cu conductors of different thicknesses, respectively. Up to ten repetitive bendings at angles between -180° and 180° did however induce stresses within the material resulting in an increased Rsh by a factor of>10.

  • 8.
    Malm, Veronica
    et al.
    University of Borås, Swedish School of Textiles.
    Strååt, Martin
    Walkenström, Pernilla
    Effects of surface structure and substrate color on color differences in textile coatings containing effect pigments.2014In: Textile research journal, ISSN 0040-5175, E-ISSN 1746-7748, Vol. 84, no 2, p. 63-77Article in journal (Refereed)
    Abstract [en]

    Textiles with dynamically color-changing effects depending on the observation angle were achieved by applying a coating paste containing multicolor effect pigments using a knife-over-table coating method. Black and white textile substrates with different structure characteristics depending on yarn type (multifilament and spun) and thread count (high and low) were studied and compared to a paper test chart as a smooth reference. The influence of surface structures on effect pigment coatings were investigated and compared with TiO2 coatings. Scanning electron micrographs showed that the substrate surface roughness increased when constructed of multifilament yarns with high thread count, spun yarns with higher thread counts and spun yarns with lower thread counts. Multi-angle spectrophotometer measurements of effect pigment-coated samples showed that the color differences in form of the CIE L*a*b*-coordinates varied to great extents, depending on detection angles, surface roughness and color of the substrates, compared to TiO2-pigment coatings with insignificant color-changing effects. The parallel alignment of effect pigment platelets was more easily achieved on the test chart. As a result, the color-changing effect was less intense on coated textiles. The effect were approximately reduced by half when coated on a substrate constructed of spun yarns compared to one made of multifilament yarns.

  • 9.
    Malm, Veronica
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business. University of Borås.
    Tadesse Abate, Molla
    University of Borås, Faculty of Textiles, Engineering and Business.
    Seipel, Sina
    University of Borås, Faculty of Textiles, Engineering and Business.
    Nierstrasz, Vincent
    University of Borås, Faculty of Textiles, Engineering and Business.
    Supercritical Carbon Dioxide: A Sustainable Medium For Textile Dyeing And Finishing To Expand The Possibilities For A Resource Efficient Production Technology2019In: Autex 19th World Textile Conference: Textiles at the Crossroads, 2019, 2019Conference paper (Other academic)
    Abstract [en]

    In our research group focusing on resource efficient processes, we explore the waterless supercritical carbon dioxide (SC-CO2) technology as a promising sustainable alternative to the traditional textile wet dyeing and water based finishing processes. Already, it is industrially implemented for textile dyeing, in particular for synthetic fabrics, and, being a dry color process it is regarded as only using ¼ of the physical footprint compared to conventional dyeing. This, does not only account for water and energy savings, but also includes advantages such as reduced emissions of harmful effluents, less amount of used dye, no or minimal use of auxiliaries (dispersing agents, carriers and surfactants) and low waste of material. To expand the industrial capabilities of this technology and open up for new business opportunities, our research focuses on textile functionalization in SC-CO2, either by only applying a functional material or to combine dyeing and functionalization of fabric in a single-step process. For polyethylene terephthalate (PET) fabric dyeing (step 1) and functionalization (step 2) in a sequential process where similar processing parameters (high temperature and pressure) was used, it was found that the color was extracted in the second step. The PET dyeing kinetics using SC-CO2 as a solvent depend on the transition in the amorphous regions of the fiber and diffusion properties and solvating power of the SC-CO2 with the dye. Hence, extensive studies on compatibility between fiber, dye and functional compounds include solubility of dye and functional material in SC-CO2, optimization of process parameters (pressure and temperature) and depressurization. This is crucial for understanding the adhesion mechanism between fiber and chemicals, and, particularly for a proper adhesion with a durable functional performance. Furthermore, as SC-CO2 is a good solvent for hydrophobic compounds, nonionics and organic compounds with low molecules weight, there are challenges in modifying conventional compound or using co-solvents. Activities within this domain in our research group stretch between dyeing and functionalization of textiles with end-use properties such as antimicrobial, photochromic, moisture management, water repellency, soil repellency and flame retardant.

  • 10.
    Malm, Veronica
    et al.
    University of Borås, Swedish School of Textiles.
    Walkenström, Pernilla
    Influence of rheology modifiers and coating parameters on the color-changing effects of textile coatings with multi-layered mica pigments2014In: Textile research journal, ISSN 0040-5175, E-ISSN 1746-7748, Vol. 85, no 9, p. 936-948Article in journal (Refereed)
    Abstract [en]

    In order to optimize the color-changing effects of textile knife-coatings containing multi-layered mica pigments (effect pigments; EPs), the properties and structure of the coating formulation/layer during and after application were investigated. Three pigment coating formulations were prepared by first mixing the EP dispersion into a water-based polyurethane binder. Different types of rheology modifiers (RMs), liquid dispersion of sodium polyacrylates (LDPSAP), hydrophobically alkali swellable emulsions (HASEs) and hydrophobically modified ethoxylated polyurethane, were then added to the dispersion. The rheological behavior of the coating formulations was characterized in terms of the shear rate dependence of the viscosity. The formulations were applied onto the same type of textile substrate using a knife-coating technique. The choice of RM as well as variations in gap height and coating speed increased the solids deposit. The increased amount of coating deposits (thicker coating layers) corresponded to more and better dispersed EPs within the coated layer as well as more horizontally oriented platelets as confirmed by scanning electron microscopy. Multi-angle spectrophotometer measurements showed that the CIE L*a*b* color coordinates varied strongly depending on detection angle. The variations of the absolute values of L* and a* were more pronounced between –15° and 15° detection angles, corresponding to angles with the greatest visual color changes. The slowly coated samples with higher solids deposit were measured to be lighter and of higher chroma compared to samples coated at a higher speed. Generally, the color-changing effects were governed by the choice of RM and coating parameters in terms of variations of the amount of coating deposited onto the samples.

  • 11.
    Malm, Veronica
    et al.
    University of Borås, Faculty of Textiles, Engineering and Business.
    Walkenström, Pernilla
    University of Borås, Faculty of Textiles, Engineering and Business. Swerea IVF, Department of Textile and Plastics.
    Nierstrasz, Vincent
    University of Borås, Faculty of Textiles, Engineering and Business.
    Flexible and durable highly conductive coatings for smart textile applications2015In: Bio-Boosting Today's Technology, 2015, p. 1-199Conference paper (Other academic)
    Abstract [en]

    The aim of this research is to develop highly conductive coating compounds for the emergence of comfortable and durable garments with integrated technology. Metals as filler particles for coating and printing pastes are the focus in this work. This, due to that metal provides excellent conductive properties particularly important for producing reliable electronic circuits used in e.g. wearable body monitoring systems. The research presented center on the frequently reported research challenges; to overcome the stiffening effects of metals and the poor mechanical resistance of the conductive film, commonly shown during folding, abrasion and washing [1,2]. This affects the comfort for the wearer and the durability. A prior concern is also the toxicological effects of certain metal particles, possibly leaking out into the environment during washing or wearing. Therefore the mechanical resistance and adhesion of these types of coatings are further investigated.

    Today, the use of metal compounds for flexible electronic fabrics are frequently reported including their use for electromagnetic shielding and even antimicrobial effects [3]. In this work, conductive coatings containing silver-coated copper flakes are evaluated for their electrically and thermally conductive properties, using square resistance measurements and infrared camera imaging respectively. Different approaches for improving the durability of the conductive films are comprised, such as addition of a cross-linking agent and encapsulation of the conductive film.

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