Testing thermoplastic elastomers selected as flexible three-dimensional printing materials for functional garment and technical textile applications

Purpose The utilization of three-dimensional (3D) printing in composite materials reduces constraints and opens new possibilities for the development of protective textiles compared to conventional manufacturing processes. Previous studies have predominantly focused on investigating critical parameters that influence the adhesion quality of 3D printed layers on textile substrates, along with the structural characteristics of two-dimensional (2D) textile substrates. However, 3D fabrics with superior properties have not been extensively explored. This study aims to develop innovative 3 days printing auxetic structure–spacer fabric composites with enhanced protection and comfort. Design/methodology/approach Using an entry-level Fused Deposition Modeling (FDM) printer, polymer materials were directly deposited onto 3D spacer fabrics. A series of printing trials determined the optimal process parameters, after which composites with various tilting angles were fabricated. Their deformation behavior and energy absorption characteristics were then evaluated through systematic compression tests. Findings It is found that Thermoplastic Polyurethane (TPU) is more suitable for composite with spacer fabrics compared to Polylactic Acid (PLA). Optimal printing conditions were identified as a speed of 30–40 mm/s, a preheating temperature of approximately 209 °C and an extrusion temperature between 215 and 220 °C. Additionally, an appropriate Z-axis distance effectively combines the 3D printed components with the fabric while maintaining the comfort of the spacer fabric. Composites with a 45°tilting angle demonstrated the best compressive and energy absorption performance under 80 and 50% strain conditions. Practical implications The composites we fabricated with a single-layer thickness below 9 mm, especially the 45° tilting angle structure is only about 7 mm, meeting dimensional requirements for protective equipment (e.g. helmet liners and protective pads). Additionally, the uniform microporous array on the composites surface enhancing breathability without compromising surface smoothness, and contributing to improve comfort in wearable protective applications. The good performance in compressive strength and energy absorption capacity underscoring its potential in applications requiring efficient energy absorption at low strain, such as protective padding and sportswear components. Social implications The increasing demand for personal safety protection has driven the development of high-performance textile composites. Personal protective equipment must not only provide excellent protective functionality but also ensure comfort and portability. Composites with multifunctional gradually replace traditional textiles by balancing protection, flexibility and wearer comfort. Moreover, flexibility of 3D printing can meet the needs of different markets for customization of high-performance personal protective equipment. Originality/value These findings demonstrate the potential of composite materials in applications requiring high energy absorption at low strain conditions and also reflect the promise of integrating FDM 3D printing technology with spacer fabrics for the design and manufacturing of advanced auxetic materials for personal protective equipment.

This study evaluates the three-dimensional (3D) printing materials used in Fused Deposition Modeling (FDM) printing technology. 3D printing technology has been developing strongly, becoming an effective support tool in production and research. The 3D printing process involves many stages, with many parameters affecting the quality and properties of the product, in which 3D printing material is one of many essential factors affecting that process. The study conducts a comprehensive assessment of the most common materials in 3D printing technology to determine the advantages and limitations of precisely five types of materials: Polylactic acid, acrylonitrile butadiene styrene, polyethylene terephthalate glycol-modified, thermoplastic polyurethane, and acrylonitrile styrene acrylate. With 3D printing, parameters such as sintering temperature, printing speed, and layer thickness are kept constant. These parameters are applied equally to all five material samples. The experiment evaluates the tensile strength of materials. The study results provide an overview of the properties and applicability of 3D printing materials, helping to select materials suitable for specific FDM 3D printing technology applications.

Cell growth on fiber surfaces is an important aspect of many applications of technical textiles. The need to prevent clogging in artificial blood vessels or in textiles used for blood or water filtration as well as the anti-fouling properties of outdoor technical textiles are examples in this context. Since the adsorption of proteins forms the initial step of cell growth, a promising way to avoid biofouling is to prohibit protein adsorption by means of a suitable, permanent and non-toxic surface functionalization. Today, the deposition of poly(ethylene glycol)s (PEGs) is a well-known approach to decrease non-specific protein adsorption. In this work, a photo-chemical method to graft or cross-link PEGs on fiber surfaces was studied. Monomethacrylated PEG300MA and PEG2080MA as well as dimethacrylated PEG400DMA and PEG600DMA were considered, the numbers indicate average molar mass in g/mol. Textile fabrics made of poly(ethylene terephthalate) (PET) were impregnated with solutions of the PEGs and irradiated using either a KrCl* or a XeCl* excimer lamp (emission wavelengths 222 or 308 nm, respectively). Surface properties of the treated textiles were characterized as a function of process conditions using various surface sensitive analyses. UV cross-linking of PEG400DMA resulted in the deposition of a thick layer which effectively masked the texture of the fabric and its pore system. Much less coverage was observed in case of monomethacrylated PEGMAs, with a significant reduction in drop penetration time already after deposition of a marginal layer (less than 0.01 mg/mg). Highest reductions in adsorption of bovine serum albumin (BSA) were observed for samples prepared using PEG300MA or PEG400DMA under conditions where also the drop penetration time was at its minimum. The longer chain PEG2080MA was less effective. All results show clearly that the protein adsorption tendency can be significantly reduced by choice of suitable combinations of PEGylated monomer and UV irradiation conditions.

Thermoplastic polyurethane (TPU) is one of the most widely used thermoplastic elastomers (TPE) due to its high strength and tear resistance, good elasticity, flexibility and damping properties. Enhancement of TPU properties can be achieved by either varying the hard-soft segment composition ratio or by the reinforcement with micro or nanoscale fillers. In the last decade, cellulose nanocrystals (CNC) have gained an increasing degree of interest from both academics and industries as ‘sustainable nanomaterials’, as they have high-axial mechanical properties and reinforcing capability, abundance, low density, renewability and biodegradability. Contemporary research activities centred on the reinforcement of TPU with CNC have typically employed solvent-based fabrication methods (solution/wet casting). For the successful translation of this new class of nanocomposite materials from laboratory research to widespread applications, processing via scalable approaches has to be demonstrated. The utility of CNC as TPU reinforcers has also been limited by the poor thermal stability of CNC, which are typically isolated via acid hydrolysis, as well as the poor quality of dispersion achieved when more scalable methodologies are used (eg. melt compounding). Thus, this study firstly aims to explore, optimise and develop CNC with enhanced thermal stability, and secondly, to incorporate these more thermostable CNC into high performance TPU nanocomposites via scalable melt-compounding and reactive extrusion methods. The research thesis is presented in three main parts. The first part is focused on the production/isolation of CNC with enhanced thermal stability and at a high production yield. CNC has been isolated via two methods, acid hydrolysis using mild acid and a scalable high energy bead milling process. Both processes have been optimised to isolate CNC with requisite thermal stability and dispersibility for TPU host polymers. The second part is focused on the processability of CNC into the TPU matrix via an intermediate-scale traditional twin screw extrusion melt compounding method. The third and final part is focused on the processing TPU/CNC nanocomposites via a large-scale reactive extrusion method, by pre-dispersing CNC in polyol and then performing in-situ polymerisation in a twin-screw extruder (i.e. reactive extrusion). The main outcomes or observations from this study are: • Isolation of CNC with enhanced thermal stability and dispersibility via mild acid hydrolysis, and with a higher production yield than the previously reported methods • Acid-free isolation of CNC with enhanced thermal stability at high production yields • Organic solvent-free processing of TPU/CNC nanocomposites • The performance of the host TPU matrix, a “workhorse” aromatic polyether grade, is remarkably enhanced by the incorporation strategies reported, without negatively affecting the important elastic properties and compliance of the TPU

Recently, responsive structure color fibers and fabrics have been designed and prepared for colorimetric detecting of volatile organic compounds (VOCs). Fabric substrates can offer greater flexibility and portability than flat and hard substrates such as glass, silicon wafers, etc. At present, one-dimensional photonic crystal (multilayer films) and three-dimensional dense photonic crystal layers are mainly constructed on fabrics to achieve the response to VOCs. However, the binding force between these structural color coatings and the fabrics was poor, and the dense structures inevitably hindered the diffusion of VOCs. Here, thermoplastic polyurethane (TPU) inverse opal (IOs) fabrics were prepared by sacrificing the SiO2 photonic crystal templates to achieve colorimetric detecting of VOCs. The IOs layer of TPU was cured directly on the fabric surface, TPU infiltrated into the fabric yarns, and bonded the fabrics and IOs layer into a whole, which greatly improved the binding force, and the porous structure and large specific surface area of IOs were conducive to the diffusion of VOCs. The results showed that the TPU IOs fabrics have large reflection peak shifts to DMF, THF, toluene and chloroform vapors, and its concentration has a good linear relationship with the maximum reflection peak value of TPU IOs fabrics. The theoretical detection limits are 1.72, 0.89, 0.78 and 1.64 g m−3, respectively. The response times are 105, 62, 75 and 66 seconds, with good stability. Finally, it was calculated that the discoloration of the TPU IOs fabrics in VOCs was due to the joint-effects of lattice spacing and effective refractive index increase.

Thermoplastic natural rubber (TPNR) is widely used across industries due to its unique blend of elasticity and processability. Thermoplastic vulcanizates (TPVs) based on thermoplastic polyurethane (TPU) offer excellent mechanical properties and flexibility, yet often require enhanced elasticity and durability. Blending TPU with natural rubber (NR) is promising; however, phase incompatibility reduces mechanical strength and thermal stability. To address this, epoxidized NR (ENR) was employed as a compatibilizer in TPU/NR blends. ENR’s hydrocarbon backbone interacts with crosslinked NR, while epoxy groups enhance adhesion with TPU. Incorporating 3 phr of ENR significantly improved crosslinking, increased tensile strength by 41.1%, enhanced stress relaxation, and lowered the glass transition temperatures of both TPU and NR phases in the TPU/NR blends. These effects are attributed to improved chemical bridging between TPU and NR. However, excess ENR disrupts phase compatibility, causing polymer entanglement and reduced strength. Optimizing ENR content is essential for developing high-performance TPU/NR blends. Printability was demonstrated using the material extrusion additive manufacturing (MEx-AM) fused deposition modeling (FDM), showing potential for flexible applications like splints and medical devices.

During the past few years, the use of technical textiles has grown rapidly. Natural, synthetic, and high-performance fibers are being used in many technical textile applications. Some of which are explained in detail, while others are in brief in this book. This chapter reviews the application and use of natural, synthetic, and high-performance fibers for Indutech, Hometech, Clothtech, Buildtech, Packtech, and Oekotech. As the strength of natural fibers is not so good, the use of synthetic and high-performance fibers is increasing in industrial and technical products. One of the major applications of technical textiles is in the filtration media. The performance of a specific filter is based on the selection of fiber, textile material, and the way they have been assembled. The properties of fluid for which the filter has to be designed must be considered carefully as well. Human beings have been using regular clothing to protect themselves from a very hot and cold environment. The workers in some occupations (like military, police, firefighting, and healthcare) are exposed to different hazards, so they are required to wear protecting textile clothing, which is discussed further in the chapter. For centuries, textiles are being used for construction materials whether it is for insulation or reinforcement of any other application. However, the use of advanced construction material specifically textile fibers has increased extensively these days. It is important to have appropriate knowledge about textile fibers in the light of current climate change and other global challenges, as textiles in any form (fiber, yarn, or fabric) provide excellent thermal and mechanical properties with low weight. Today the people around the world have become more educated with higher living standards. Therefore, the use of high technology products, which offer enhanced performance, durability, hygienic conditions, and aesthetic, has become the need of the day. The demand for eco-friendly and bio-degradable packaging is growing now as they have a great impact on human health and the environment. The use of natural fibers for environmental protection is not new. While the use of synthetic and high-performance fibers for environmental protection is a revolutionary change in the current century. One of its uses is in protecting the crops and soil artificially by weather changes to increase productivity. The new and advanced developments for environmental protection keep on increasing across the world in the coming years. In this chapter, an overview of such types of textiles; fibers being used; and their applications, advantages, and drawbacks have been provided briefly.

Recently, composite filament development for three-dimensional printing has emerged and is used for numerous applications. The present research work develops neat polylactic acid and Almond Shell Particles reinforced polylactic acid bio-composites for three-dimensional printing and investigates the effects of printing orientation, including 0°, 45° and 90° orientation, on the tribological and mechanical behaviours of three-dimensional printed materials. The novel almond shell particles reinforced polylactic acid filaments are extruded by the filament extrusion method with the presence of 10% almond shell particles in the polylactic acid matrix, and the samples are three-dimensional printed by the fused filament fabrication technique. Mechanical characteristics such as tensile, flexural, compressive strength, and shore hardness are evaluated with respect to various three-dimensional printing orientations. The surface quality of the three-dimensional printed polylactic acid composite samples is analysed with respect to length and diameter deviation. Length accuracy of the 90° oriented polylactic acid and almond shell particles reinforced polylactic acid bio-composite samples exploits a better accuracy of 99.12% and 98.81%, respectively. It is shown that adding almond shell particles to the polylactic acid matrix decreases the flexural and tensile strength. Among the printing orientations, 0° flat samples result in the maximum tensile strength of 36 and 28 MPa for the neat polylactic acid and almond shell particles reinforced polylactic acid composites, respectively. The lowest contact angle of 54° is observed on the almond shell particles reinforced polylactic acid bio-composites three-dimensional printed with a 90° orientation. The highest contact angle value of 94° is observed on the neat polylactic acid three-dimensional printed with a 0° printing orientation. A tribological study is carried out under dry conditions on the pin-on-disc tribometer by varying the sliding speed (1, 2, and 3 m/s) and load (10, 20, and 30 N). The result shows that the lowest coefficient of friction of 0.22 is achieved for the almond shell particles reinforced polylactic acid bio-composite samples with a 0° printing orientation under a sliding load of 10 N. These kinds of newly developed compostable materials can be used for developing disposable orthotic foot appliances.

In this study, the foaming of nonwoven fabrics and bulk polymers was investigated. Four different polymers that are commonly used for textiles including polyethylene terephthalate, thermoplastic polyurethane, thermoplastic polyether ester elastomer and polypropylene were foamed by batch foaming. Among the polymers, thermoplastic polyurethane seems to be the most promising material since it possesses the highest cell density and smallest cell size. In addition, nanoclay was added to thermoplastic polyurethane to promote cell nucleation and to increase the cell density. The results showed that well dispersed nanoclay in thermoplastic polyurethane served as an excellent nucleation agent and the cell structure was improved. The cell size of thermoplastic polyurethane nanocomposite foam decreased to 1 µm while the cell density increased to 3 × 1011 cells/cm3.

Thermoplastic polyurethane (TPU) is a highly elastic linear polymer composed of soft segments, usually flexible polyester, or polyether. It is widely used in 3D printing technologies, being FFF the most common technique. However, stiffness and hardness values of 3D printed TPU in filament form are higher than would be desirable for some applications, which require softer parts. Therefore, it was seen necessary to find a new methodology for 3D printing soft TPU. In this way, the present study seeks to be the first research study that focuses on the possibility of 3D printing TPU using DIW (Direct Ink Writing) technology with UV light. Firstly, the optimal 3D printing and curing parameters to print soft TPU are determined and then two different TPU formulations are 3D printed. Then, both bulk and 3D printed TPU samples were characterized in terms of shear strength using the Warner-Bratzler shear test and hardness using the Shore hardness test. It was seen that the 3D printed samples showed higher softness than bulk samples compared to TPU filament. Finally, it was concluded that the 3D printing of TPU is challenging due to several points: (1) the viscosity of the TPU; (2) their main issue is their sticky behavior; and (3) the shrinkage which takes place after the thermal treatment and for some applications, it might be a problem. Despite that, TPU appears to be a promising material to be used in different industrial applications.

The latest advances in additive manufacturing methods (AMM) generally called as three-dimensional (3D) printing has been permitted to design and generate complicated profiles which are not possible with conventional techniques. A new method of creation of an object by layer by layer called it as rapid prototyping technique which is also known as three-dimensional printing. If these methods of printing supposed to be implemented for self-healing smart materials, then it is known as four-dimensional printing. Also, day-to-day advancements in fashion in the lifestyle of public, industries are not capable to satisfy their requirements with conventional manufacturing techniques with conventional materials because of increased cost to alter the design, manufacture and process layout for each fashion style. It is impossible to satisfy with conventional materials as well as processing methods so more competition existed in the present industrial sectors according to market demands as per customer requirements. Advancements in additive manufacturing techniques covered this gap by day-to-day developments in materials and their methods. In this review article, discussed about recent developments of smart materials, innovations in 4D printing and challenges which are faced in the research and development (R&D) divisions, also described about variety of application areas almost in all fields. This paper provides the basic information to the young researchers who are interested in this area.KeywordsRapid prototyping4D printingSelf-healing smart materialsTemperature responsive materialsLight/electric current/magnetic field materials

11 - Elastomers and Rubbers

With the purpose of making soft robotic structures with embedded sensors, additive manufacturing techniques like fused deposition modeling (FDM) are popular. Thermoplastic polyurethane (TPU) filaments, with and without conductive fillers, are now commercially available. However, conventional FDM still has some limitations because of the marginal compatibility with soft materials. Material selection criteria for the available material options for FDM have not been established. In this study, an open-source soft robotic gripper design has been used to evaluate the FDM printing of TPU structures with integrated strain sensing elements in order to provide some guidelines for the material selection when an elastomer and a soft piezoresistive sensor are combined. Such soft grippers, with integrated strain sensing elements, were successfully printed using a multi-material FDM 3D printer. Characterization of the integrated piezoresistive sensor function, using dynamic tensile testing, revealed that the sensors exhibited good linearity up to 30% strain, which was sufficient for the deformation range of the selected gripper structure. Grippers produced using four different TPU materials were used to investigate the effect of the Shore hardness of the TPU on the piezoresistive sensor properties. The results indicated that the in situ printed strain sensing elements on the soft gripper were able to detect the deformation of the structure when the tentacles of the gripper were open or closed. The sensor signal could differentiate between the picking of small or big objects and when an obstacle prevented the tentacles from opening. Interestingly, the sensors embedded in the tentacles exhibited good reproducibility and linearity, and the sensitivity of the sensor response changed with the Shore hardness of the gripper. Correlation between TPU Shore hardness, used for the gripper body and sensitivity of the integrated in situ strain sensing elements, showed that material selection affects the sensor signal significantly.

A novel green and low friction composite reinforced by lignum vitae chips

Designers are continuously searching for materials or meta-structures, also inspired by nature, that exhibit favourable strength-to-weight ratios, substantial heat transfer capabilities, and efficient energy absorption. One particular example includes fractal geometries, which usually consist of intricate three-dimensional geometrical structures and are challenging to produce through traditional manufacturing methods. In this regard, this study analyses the performance of a three-dimensional cross-based fractal structure (3D-CFS) designed for energy absorption and manufactured using polymeric materials. Mathematically, the geometry is obtained using a 3D Greek cross repeated in the 3D space according to the fractal principle. Owing to the intricate final structure, samples are fabricated using an Additive Manufacturing system based on powder bed fusion with a laser beam and infrared light. The study is carried out using two polymeric materials, polyamide and thermoplastic polyurethane, and the mechanical response of the structure is analysed under dynamic compression tests. The tested geometries consisted of samples with a single 3D-CFS cell, various volume fractions and a configuration with multiple cells that emulated a possible layout for linear helmet application. The findings indicate that the 3D-CFS is a promising geometry for eventual implementation into shock absorption applications, specifically in personal protective equipment (PPE) usage.