Multifunctional Polypyrrole-Based Textile Sensors for Integration into Personal Protection Equipment.

Integrated safety sensors for personal protection equipment increasingly attract research activities as there is a high need for workers in delicate situations to be physically monitored in order to avoid accidents. In this work, we present a simple approach to generate thin, homogeneous polypyrrole (PPy) layers on flexible textile polyamide fabrics. PPy layers of 0.5-1 µm were deposited on the fabric, which thus kept its flexibility. The conductive layers are multifunctional and can act as temperature and gas sensors for the detection of corrosive gases such as HCl and NH3. Using three examples of life-threatening environments, we were able to monitor temperature, atmospheric NH3 and HCl within critical ranges, i.e., 100 to 400 ppm for ammonia and 20 to 100 ppm for HCl. In the presence of HCl, a decrease in resistance was observed, while gaseous NH3 led to an increase in resistance. The sensor signal thus allows for distinguishing between these two gases and indicating critical concentrations. The simple and cheap manufacturing of such PPy sensors is of substantial interest for the future design of multifunction functional sensors in protective clothing.

Natural Fiber Reinforced Shoe Midsoles with Balanced Stiffness/Damping Behavior.

The comfort of walking depends heavily on the shoes used. Consequently, the midsole of shoes is designed in such a way that it can dampen force peaks during walking. This significantly increases the overall wellness during walking. Therefore, the midsole usually consists of rubber-like polymers, such as polyurethane and ethylene-vinyl acetate copolymer. Furthermore, the manufacturing process of these polymers results in a foam-like structure. This further enhances the damping behavior of the material. Nevertheless, it would be desirable to find a cheap and sustainable method to enhance the damping behavior of the shoe midsole. The purpose of this work is to see if hemp fibers, which are part of the polymer matrix material, could improve the stiffness without losing the damping behavior. The mechanical properties of such prepared fiber-reinforced composites were characterized by quasi-static tensile testing and dynamic mechanical analysis. The mechanical properties were examined in relation to the fiber type, weight fraction, and type of polyurethane used. Furthermore, the investigation of the embedding of these fibers in the polymer matrix was conducted through the utilization of optical and electron microscopy.

Imperfect cross-linking of xanthan for pH-responsive bio-based composite moist wound dressings by stencil printing.

The work addresses the use of bio-based and -degradable materials for the production of a moist, adaptive and anti-microbial wound dressing. The dressing is targeted to exhibit a pH-dependent active agent release. Xanthan hydrogel structures are coated on cellulose fabrics via stencil printing and subsequently cross-linked using glyoxal. By alteration of the cross-linker content from 1 to 6% by mass, the hydrogel elasticity can be tuned within a range of 2-16 kPa storage modulus. Increasing initial glyoxal concentrations also result in higher amounts of glyoxal release. Glyoxal, an anti-microbial agent with approval in veterinary medicine, is mostly released upon wound application supporting infection management. As wound simulation, normal saline, as pH 5 and pH 8 buffer solutions, were used. The release profile and magnitude of approx. 65%-90% glyoxal is pH-dependent. Increased release rates of glyoxal are present in pH 8 fluids, which mostly base on faster hydrogel swelling. Higher total glyoxal release is present in pH 5 fluid and normal saline after 3 days. Accordingly, a pH-dependent release profile was encountered. As glyoxal attacks any cell unselectively, it is expected to be effective against antibiotic resistant bacteria. By stencil printing the dressing size can be adjusted to minimize healthy glyoxal tissue exposure.

Cyclic Voltammetry of C.I. Disperse Orange 62 in an Aqueous Electrolyte.

Disperse dyes are an important group of colorants for dyeing polyester fibers. Approximately 30.000 tons of disperse dyes are released into the waste water annually from spent dyebaths. Therefore, methods for decolorizing such dyes are of general interest. The reductive after-treatment of disperse dyes using reducing agents, such as Na2S2O4, is a widely used process to improve rub fastness through dye reduction. Electrochemical dye reduction could be an alternative process for reductive dye treatment. In this work C.I. Disperse Orange 62 was used as a representative dye to study the direct cathodic reduction of a disperse dye with cyclic voltammetry. As anticipated for dispersed organic matter, relatively low current densities were observed, which strongly depend on the state of dispersion of the dye. The current density was increased by using dispersions prepared through dye precipitation from DMF solution and by the use of N-cetyl-N,N,N,-trimethyl-ammonium bromide as a cationic surfactant. The results demonstrate the successful cathodic reduction of a dispersed organic dye; however, the low solubility of the reaction products in the aqueous electrolyte hinders an efficient cathodic dye reduction.

Improvement of wet rub fastness in continuous dyeing with c.i. Sulphur Black 1 by ultrasonic treatment.

C.I. Sulphur Black 1 is among the most important dyes for cellulose textiles, as this dye offers a maximum colour depth at reasonable costs. In its final form the dye is present as solid pigment, thus limited wet rub fastness can be an issue. Controlled re-oxidation of the leuco form into the oxidised dye pigment and intensive washing and soaping are measures to achieve acceptable wet rub fastness. In this study pad-steam dyeing with C.I. Sulphur Black 1 was used to investigate the effects of an intensified washing process with use of ultrasonification on rub fastness. Ultrasound was applied following to steam fixation of the dye. Introduction of ultrasound into the following process steps was investigated: water seal, warm rinse, oxidation, soaping, cold rinse. Best results in rub fastness were obtained by combination of soaping and ultrasound processing. The high shear rate near to the fibre surface led to a reduction of the thickness of the stagnant diffusion layer and more intense removal of loosely bound dispersed dye. As a result of the treatment an improvement in wet rub fastness of the dyeings was achieved. Duration of 60 - 120 s was found sufficient to remove the major part of surface bound pigments which allows an integration into continuous pad-steam dyeing processing. The results demonstrate that ultrasound washing may lead to improved rub fastness of other dyeings where a pigment is the final form of the dye. The method thus could be extended to vat dyes including indigo, or naphthol dyes.

Investigation of the Functional Ageing of Conductive Coated Fabrics under Simulated Washing Conditions.

Conductive textiles play an important role in recent electronics development; however, one of the major challenges remains their machine-washing durability. For the investigation of the basic wash ageing mechanisms, we used copper-plated polyamide 66 and cellulose fabrics and developed a wet and dry operable flex tester with online resistance recording. The evaluation was supported by abrasion tests, cyclic elongation tests and tribological investigation of dry and wet textile-textile friction. It was found that the contribution of mechanical and chemical ageing to wash ageing strongly depends on the substrate material. A bad adhesion of copper on polyamide 66 leads to early fatigue while better stability of the copper on cellulose leads to a stronger resistance against ageing. For both substrates, the delamination of the copper layer was the root cause of the fatigue, which is facilitated by the washing solution. Finally, a cumulative fatigue model was developed and the determination of the end of lifetime by the intended use is discussed.

Dope Dyeing of Regenerated Cellulose Fibres with Leucoindigo as Base for Circularity of Denim.

Circularity of cellulose-based pre- and post-consumer wastes requires an integrated approach which has to consider the characteristics of the fibre polymer and the presence of dyes and additives from textile chemical processing as well. Fibre-to-fibre recycling is a condition to avoid downcycling of recycled material. For cellulose fibres regeneration via production of regenerated cellulose fibres is the most promising approach. Textile wastes contain dyes and additives, thus a recycling technique has to be robust enough to process such material. In an ideal case the reuse of colorants can be achieved as well. At present nearly 80% of the regenerated cellulose fibre production utilises the viscose process, therefore this technique was chosen to investigate the recycling of dyed material including the reuse of the colorant. In this work, for the first time, a compilation of all required process steps to a complete circular concept is presented and discussed as a model. Indigo-dyed viscose fibres were used as a model to study cellulose recycling via production of regenerated cellulose fibres to avoid downcycling. Indigo was found compatible to the alkalisation and xanthogenation steps in the viscose process and blue coloured cellulose regenerates were recovered from indigo-dyed cellulose. A supplemental addition of reduced indigo to the cellulose solution was also found feasible to adjust colour depth in the regenerated cellulose to the level required for use as warp material in denim production. By combination of fibre recycling and indigo dyeing the conventional yarn dyeing in denim production can be omitted. Model calculations for the savings in water and chemical consumption demonstrate the potential of the process. The proportion of the substitution will depend on the collection rate of denim wastes and on the efficiency of the fibre regeneration process. Estimates indicate that a substitution of more than 70% of the cotton fibres by regenerated cellulose fibres could be achieved when 80% of the pre- and post-consumer denim wastes are collected. Therefore, the introduction of fibre recycling via regenerated cellulose fibres will also make a substantial impact on the cotton consumption for jeans production.

Cellulose Fibre Degradation in Cellulose/Steel Hybrid Geotextiles under Outdoor Weathering Conditions.

Risks from rockfall and land sliding can be controlled by high-tensile steel nets and meshes which stabilise critical areas. In many cases, a recultivation of the land is also desired. However, high-tensile steel meshes alone are not always sufficient, depending on the location and the inclination of the stabilised slope, to achieve rapid greening. Cellulose fibres exhibit high water binding capacity which supports plant growth. In this work, a hybrid structure consisting of a nonwoven cellulose fibre web and a steel mesh was produced and tested under outdoor conditions over a period of 61 weeks. The cellulose fibres are intended to support plant growth and soil fixation, and thus the biodegradation of the structure is highly relevant, as these fibres will become part of the soil and must be biodegradable. The biodegradation of the cellulose fibres over the period of outdoor testing was monitored by microscopy and analytical methods. The enzymatic degradation of the cellulose fibres led to a reduction in the average degree of polymerisation and also a reduction in the moisture content, as polymer chain hydrolysis occurs more rapidly in the amorphous regions of the fibres. FTIR analysis and determination of carboxylic group content did not indicate substantial changes in the remaining parts of the cellulose fibre. Plant growth covered geotextiles almost completely during the period of testing, which demonstrated their good compatibility with the greening process. Over the total period of 61 weeks, the residual parts of the biodegradable cellulose web merged with the soil beneath and growing plants. This indicates the potential of such hybrid concepts to contribute a positive effect in greening barren and stony land, in addition to the stabilising function of the steel net.

Swelling of kappa carrageenan hydrogels in simulated body fluid for hypothetical vessel occlusion applications.

The swelling ability of kappa-carrageenan (KC) hydrogels was investigated in simulated body fluid (SBF). The SBF mimics the ionic concentrations in the vasa deferentia of human males. The study clarifies if these hydrogels can be adjusted to occlude the vasa deferentia by swelling. For this purpose, swelling to twice the initial volume is desirable. In this study, hydrogels of different primary potassium concentrations, biopolymer concentrations and ethanol-exchanged gels, were immersed in SBF either directly or after drying (pre-dried). We measured the absolute and relative swelling degree, and the swelling rates of the gels. Extensive pre-drying leads to irreversible gel densification and absolute swelling magnitudes decrease. We found that immersion into the SBF also leads to potassium ion accumulation, and network restructuring in the hydrogels. This markedly increases the storage moduli of the gel networks. The ion content in the gel structures also directly affects the swelling speed, the fastest swelling occurred in ethanol-exchanged and pre-dried gels. We found that by pre-drying and potassium content adjustment, swelling of the hydrogels is sufficient to render KC hydrogels as a possible candidate for the occlusion of the vasa deferentia.

Quantification of aniline and N-methylaniline in indigo.

Aniline and N-methylaniline are common contaminants in commercially produced indigo. It is known, that commercially produced indigo contains up to 0.6% aniline and 0.4% N-methylaniline by weight and indigo dye shows a small mutagenic effect, most probably due to the presence of these contaminants. The present work describes a new and powerful analytical method to determine the concentration of these contaminants in indigo. This method is based on the transformation of water insoluble indigo into soluble leucoindigo and allows therefore the acidic extraction of the aromatic contaminants. This transformation step is essential, because the main part of these contaminants are strongly included in the indigo crystals. The amount of extracted aniline and N-methylaniline from the leucoindigo solution was quantified with high performance liquid chromatography (HPLC, combined with a photo diode array detector). A possible accumulation of the aromatic amines at the indigo crystal surface was investigated using FTIR and by adsorption studies. Therefore this method allows an accurate monitoring of these toxic by-products in the indigo dye, which is important for an economic and environmental assessment of the denim production.

Towards the Functional Ageing of Electrically Conductive and Sensing Textiles: A Review.

Electronic textiles (e-textiles) have become more and more important in daily life and attracted increased attention of the scientific community over the last decade. This interdisciplinary field of interest ranges from material science, over chemistry, physics, electrical engineering, information technology to textile design. Numerous applications can already be found in sports, safety, healthcare, etc. Throughout the life of service, e-textiles undergo several exposures, e.g., mechanical stress, chemical corrosion, etc., that cause aging and functional losses in the materials. The review provides a broad and critical overview on the functional ageing of electronic textiles on different levels from fibres to fabrics. The main objective is to review possible aging mechanisms and elaborate the effect of aging on (electrical) performances of e-textiles. The review also provides an overview on different laboratory methods for the investigation on accelerated functional ageing. Finally, we try to build a model of cumulative fatigue damage theory for modelling the change of e-textile properties in their lifetime.

Multi-Point Flexible Temperature Sensor Array and Thermoelectric Generator Made from Copper-Coated Textiles.

The integration of electrical functionality into flexible textile structures requires the development of new concepts for flexible conductive material. Conductive and flexible thin films can be generated on non-conductive textile materials by electroless metal deposition. By electroless copper deposition on lyocell-type cellulose fabrics, thin conductive layers with a thickness of approximately 260 nm were prepared. The total copper content of a textile fabric was analyzed to be 147 mg per g of fabric, so that the textile character of the material remains unchanged, which includes, for example, the flexibility and bendability. The flexible material could be used to manufacture a thermoelectric sensor array and generator. This approach enables the formation of a sensor textile with a large number of individual sensors and, at the same time, a reduction in the number of electrical connections, since the conductive textile serves as a common conductive line for all sensors. In combination with aluminum, thermoelectric coefficients of 3-4 µV/K were obtained, which are comparable with copper/aluminum foil and bulk material. Thermoelectric generators, consisting of six junctions using the same material combinations, led to electric output voltages of 0.4 mV for both setups at a temperature difference of 71 K. The results demonstrate the potential of electroless deposition for the production of thin-film-coated flexible textiles, and represent a key technology to achieve the direct integration of electrical sensors and conductors in non-conductive material.

Investigation on the Behavior of κ -Carrageenan Hydrogels for Compressive Intra-Vessel Disintegration.

Gel disintegration via compression is a possible approach for the reversal of the occlusion of male vasa deferentia (VD) by hydrogels. κ -carrageenan (KC) hydrogels can be used for such an application. To determine the required forces for in-vessel compressive disintegration, a gel-tube model, preparing KC gels in different tubes, is studied. These gels are of alternating biopolymer (1-3% by mass) and potassium (100-300 mM) concentration. Gel-filled tubes are uniaxially compressed at two different compression speeds (1 and 0.3 mm s-1 ). Breakage compression strains are cross studied by shear breaking gel measurements using dynamic mechanical analysis. The measurements showed good agreement. Gel structure disintegration occurred below (62 ± 8) % strain. During compression, three stages of gel disintegration are present. Gel-tube wall detachment, gel rupture, and gel expulsion. The force required for gel disintegration and tube deformation can be added arithmetically. From the modulus of a human aortae model, it is estimated that average human pinch forces are insufficient to disintegrate 2% and 3% by mass KC hydrogels in VD by massage. The compressive disintegration would require a compression device while evading tissue damage.

Special Issue "Textile-Based Advanced Materials: Construction, Properties and Applications".

Developments in the science and technology of textiles is not only limited to apparel and fashion [...].

Piezo-Sensitive Fabrics from Carbon Black Containing Conductive Cellulose Fibres for Flexible Pressure Sensors.

The design of flexible sensors which can be incorporated in textile structures is of decisive importance for the future development of wearables. In addition to their technical functionality, the materials chosen to construct the sensor should be nontoxic, affordable, and compatible with future recycling. Conductive fibres were produced by incorporation of carbon black into regenerated cellulose fibres. By incorporation of 23 wt.% and 27 wt.% carbon black, the surface resistance of the fibres reduced from 1.3 × 1010 Ω·cm for standard viscose fibres to 2.7 × 103 and 475 Ω·cm, respectively. Fibre tenacity reduced to 30-50% of a standard viscose; however, it was sufficient to allow processing of the material in standard textile operations. A fibre blend of the conductive viscose fibres with polyester fibres was used to produce a needle-punched nonwoven material with piezo-electric properties, which was used as a pressure sensor in the very low pressure range of 400-1000 Pa. The durability of the sensor was demonstrated in repetitive load/relaxation cycles. As a regenerated cellulose fibre, the carbon-black-incorporated cellulose fibre is compatible with standard textile processing operations and, thus, will be of high interest as a functional element in future wearables.

Investigation of Interfacial Diffusion in PA/PP-g-MAH Laminates Using Nanoscale Infrared Spectroscopy.

The characterization of polymer-polymer interfaces is of great interest to understand the diffusion process and chemical interactions in polymeric multiphase systems. This study investigated the formation of the interface layer between polyamide (PA) and polypropylene (PP) and its dependency on the maleic anhydride (MAH) content in PP. New insights with a very high level of details on the formation of the interfacial layer are obtained by employing a special technique of atomic force microscopy (AFM) combined with infrared (IR) for chemical imaging at nanoscale spatial resolution. This enables the determination of the interface thickness and even the observation and visualization of the diffusion gradient across the PA/PP interface layer. Combined with classical investigation methods such as interfacial energy and rheology, the method of nano-IR spectroscopy represents a very powerful tool to obtain more insights and a deeper understanding of the interfacial phenomenon in multiphase polymeric systems.

Multivalent Ions as Reactive Crosslinkers for Biopolymers-A Review.

Many biopolymers exhibit a strong complexing ability for multivalent ions. Often such ions form ionic bridges between the polymer chains. This leads to the formation of ionic cross linked networks and supermolecular structures, thus promoting the modification of the behavior of solid and gel polymer networks. Sorption of biopolymers on fiber surfaces and interfaces increases substantially in the case of multivalent ions, e.g., calcium being available for ionic crosslinking. Through controlled adsorption and ionic crosslinking surface modification of textile fibers with biopolymers can be achieved, thus altering the characteristics at the interface between fiber and surrounding matrices. A brief introduction on the differences deriving from the biopolymers, as their interaction with other compounds, is given. Functional models are presented and specified by several examples from previous and recent studies. The relevance of ionic crosslinks in biopolymers is discussed by means of selected examples of wider use.

Water-based slurries for high-energy LiFePO4 batteries using embroidered current collectors.

Greater specific energy densities in lithium-ion batteries can be achieved by using three-dimensional (3D) porous current collectors, which allow for greater areal mass loadings of the electroactive material. In this paper, we present the use of embroidered current collectors for the preparation of thick, pouch-type Li-ion batteries. Experiments were performed on LiFePO4 (LFP) water-based slurries using styrene-butadiene rubber (SBR) as binder and sodium carboxymethyl cellulose (CMC) as thickener, and formulations of different rheological characteristics were investigated. The electrochemical performance (cyclic voltammetry, rate capability) and morphological characteristics of the LFP half-pouch cells (X-ray micro computed tomography and scanning electron microscopy) were compared between the formulations. An optimum electrode formulation was identified, and a mechanism is proposed to explain differences between the formulations. With the optimum electrode formulation, 350 µm casted electrodes with high mechanical stability were achieved. Electrodes exhibited 4-6 times greater areal mass loadings (4-6 mAh cm-2) and 50% greater electroactive material weight than with foils. In tests of half- and full-pouch embroidered cells, a 50% capacity utilization at 1C-rate and 11% at 2C-rate were observed, with a full recovery at C/5-rate. The cycling stability was also maintained over 55 cycles.

Textile-Integrated Thermocouples for Temperature Measurement.

The integration of conductive materials in textiles is key for detecting temperature in the wearer´s environment. When integrating sensors into textiles, properties such as their flexibility, handle, and stretch must stay unaffected by the functionalization. Conductive materials are difficult to integrate into textiles, since wires are stiff, and coatings show low adhesion. This work shows that various substrates such as cotton, cellulose, polymeric, carbon, and optical fiber-based textiles are used as support materials for temperature sensors. Suitable measurement principles for use in textiles are based on resistance changes, optical interferences (fiber Bragg grating), or thermoelectric effects. This review deals with developments in the construction of temperature sensors and the production of thermocouples for use in textiles. The operating principle of thermocouples is based on temperature gradients building up between a heated and a cold junction of two conductors, which is converted to a voltage output signal. This work also summarizes integration methods for thermocouples and other temperature-sensing techniques as well as the manufacture of conductive materials in textiles. In addition, textile thermocouples are emphasized as suitable and indispensable elements in sensor concepts for smart textiles.

Grafting of wool fibers through disulfide bonds: An advanced application of S-protected thiolated starch.

The purpose of this study is to develop a potential pathway for grafting polymers onto wool fibers based on thiol-disulfide exchange reactions. S-protected thiolated starch (PTS) was synthesized by coupling 3-(2-pyridyldithio) propanoic acid to starch through esterification, resulting in 417.3 ± 15.1 µmol ligand binding to 1 g of starch. PTS was labelled with fluorescein isothiocyanate (FITC) prior to grafting. Wool fibers were preactivated by raising the amount of thiol groups utilizing mild reducing agents. The highest degree of preactivation on the surface of wool fibers was achieved by a 0.2% (w/v) sodium borohydride and 1.5% (w/v) sodium bisulfite mixture pH 5.0 resulting in 182.6 ± 8.7 µmol thiol groups per gram of fibers. Different incubation times and ratios between FITC-labelled PTS and wool fibers were investigated. A graft yield of 58.5% was achieved at a ratio of 1:1.5 (w/w) between wool fibers and FITC-labelled PTS within 18 h of incubation. Successful coating of PTS on wool fibers was confirmed by confocal imaging, scanning electron microscopy and FT-IR. Mechanical properties of grafted wool fibers were tested regarding elongation and tensile strength. These results provide evidence for the potential of S-protected thiolated starch as a superior coating material for wool fibers.