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In this study, the accuracy of the analysis was improved by combining deformation analysis considering viscoelastic properties with heat transfer analysis considering radiation heating, which was used to optimize sheet temperature uniformity in the heating stage of the vacuum thermoforming process. The viscoelastic properties of the acrylonitrile butadiene styrene (ABS) sheet were measured using the dynamic mechanical analysis and a rheometer. A radiation camera was used to measure the emissivity at various temperatures. As a result of the analysis, the deformation caused the distance between the specimen and the heat source to shorten, leading to a higher temperature in the analysis that combined deformation analysis compared to the analysis that considered only heat transfer. To maintain uniform sheet temperature by adjusting the temperature distribution of the heat source, the temperature distribution was analyzed based on the positions of the heat source and the sheet, as well as the temperature variation within the sheet. The analysis showed that it is necessary to set the heater temperature higher in the outer region than in the central region. Finally, an optimization algorithm is used to obtain the process conditions that can produce a uniform temperature distribution.

A compression resin transfer molding (CRTM) process is a very useful composite manufacturing process owing to its high performance and productivity. A permeability variation of fiber preform with respect to fiber volume fraction was investigated by changing cavity thickness of mold in the one dimensional saturated flow in order to analyze resin flow during compression stage in a compression resin transfer molding (CRTM) process. In-situ variation of permeability was measured by tracking the pressure and flow rate while changing volume fractions of unidirectional carbon fabric from 45 % to 55 %, which was used to investigate the effect of fiber volume fraction and the additional flows on resin flow in the CRTM process. It is expected that this work would be helpful to understand the mechanism of resin flow in CRTM and optimize the process conditions such as compression thickness of mold, injection pressure, and mold clamping force.

Highly flexible and electrically-conductive multifunctional textiles are desirable for use in wearable electronic applications. In this study, we fabricated multifunctional textile composites by vacuum filtration and wet-transfer of graphene oxide films on a flexible polyethylene terephthalate (PET) textile in association with embedding Ag nanoparticles (AgNPs) to improve the electrical conductivity. A flexible organic transistor can be developed by direct transfer of a dielectric/semiconducting double layer on the graphene/AgNP textile composite, where the textile composite was used as both flexible substrate and conductive gate electrode. The thermal treatment of a textile-based transistor enhanced the electrical performance (mobility = 7.2 cm2·V−1·s−1, on/off current ratio = 4 × 105, and threshold voltage = −1.1 V) due to the improvement of interfacial properties between the conductive textile electrode and the ion-gel dielectric layer. Furthermore, the textile transistors exhibited highly stable device performance under extended bending conditions (with a bending radius down to 3 mm and repeated tests over 1000 cycles). We believe that our simple methods for the fabrication of graphene/AgNP textile composite for use in textile-type transistors can potentially be applied to the development of flexible large-area electronic clothes.

A strategy for fabricating microcrystalline cellulose-Ti 3 C 2 T x (MCC-MXene) nanocomposite films with high relative permittivity, high thermal conductivity, and excellent mechanical properties was developed. The MCC-MXene nanocomposite film was fabricated by casting a solution containing N,N-dimethylacetamide/lithium chloride (DMAc/LiCl)-soluble MCC and DMAc-dispersible MXene nanosheets, followed by humidity control drying. The MXene nanosheets greatly enhanced the permittivity of the nanocomposite films owing to interfacial polarization. Thus, the nanocomposite film with 20 wt.% MXene content achieved a desirable permittivity of 71.4 at 10 2 Hz (a 770% improvement against that of neat cellulose), while the dielectric loss only increased by 1.8 times (from 0.39 to 0.70). The obtained nanocomposite films with 20 wt.% and 30 wt.% MXene exhibited remarkable in-plane thermal conductivities of 8.523 and 9.668 W·m −1 ·K −1 , respectively, owing to the uniform dispersion and self-alignment of the MXene layered structure. Additionally, the uniformly dispersed MXene nanosheets in the MCC network with interfacial interaction (hydrogen bonding) and mechanical entanglement endowed the nanocomposite films with excellent mechanical properties and flexibility. Furthermore, the thermal stability, water resistance, and antibacterial properties of the nanocomposite films were effectively improved with the introduction of MXene. Moreover, using DMAc/LiCl as the solvent system not only improves the compatibility between MCC and MXene but also avoids the problem of easy oxidation of MXene in aqueous systems. With the high stability of the MCC-MXene solution and enhanced properties of the MCC-MXene films, the proposed strategy manifests great potential for fabricating natural biomass-based dielectric materials.

Polymeric liners, one of the main components of hydrogen tanks, have attracted significant research interest because of their lightweight and high-impact strength. Despite their advantages, high gas permeability limits their applications. Thus, numerous studies have been conducted to improve the gas barrier properties of polymer-based composites. In this study, we used a polyamide 6 (PA6)/ethylene vinyl alcohol (EVOH) blend as a matrix for high hydrogen gas barrier properties and ethylene propylene diene monomer (EPDM) rubber as reinforcement for injection moldability. The ternary polymer blends were successfully injection molded, and their morphology, mechanical properties, and gas permeability were measured. In addition, we performed a rheological investigation to analyze the processability of the ternary polymer blends. As a result, the developed material system showed a 28% reduction in hydrogen permeability and a 11% improvement in tensile strength compared to a commercial material. This study will be a valuable resource for the research of polymeric liners with efficient and reliable performance. Graphical Abstract

Mechanically robust, flexible and electrically conductive textiles are highly suitable for use in wearable electronic applications. In this study, highly conductive and flexible graphene/Ag hybrid fibers were prepared and used as electrodes for planar and fiber-type transistors. The graphene/Ag hybrid fibers were fabricated by the wet-spinning/drawing of giant graphene oxide and subsequent functionalization with Ag nanoparticles. The graphene/Ag hybrid fibers exhibited record-high electrical conductivity of up to 15,800 S cm −1 . As the graphene/Ag hybrid fibers can be easily cut and placed onto flexible substrates by simply gluing or stitching, ion gel-gated planar transistors were fabricated by using the hybrid fibers as source, drain and gate electrodes. Finally, fiber-type transistors were constructed by embedding the graphene/Ag hybrid fiber electrodes onto conventional polyurethane monofilaments, which exhibited excellent flexibility (highly bendable and rollable properties), high electrical performance (μ h  = 15.6 cm 2 V −1 s −1 , I on / I off  > 10 4 ) and outstanding device performance stability (stable after 1,000 cycles of bending tests and being exposed for 30 days to ambient conditions). We believe that our simple methods for the fabrication of graphene/Ag hybrid fiber electrodes for use in fiber-type transistors can potentially be applied to the development all-organic wearable devices.

Characteristic rheological behaviors of polymer nanocomposites were studied in shear flow and uniaxial elongational flow. Solid-like plateau storage modulus, strong shear thinning at low frequency regions, and strain hardening at elongational flow were observed. Especially, strain hardening was clearly observed for polymers without long chain branches if nanoparticles were homogeneously dispersed in the polymer matrix and interactions between nanoparticles and surrounding polymer molecules were sufficiently strong. Reptation models were used to model the nanoscale dynamics of nanoparticles and macromolecular chains, and the characteristic rheological behavior of nanocomposites could be explained. Brownian dynamics simulation of Doi-Edwards reptation model was applied and two particle constraint coefficients were introduced to express the influence of nanoparticles on molecular orientation and reptational diffusion of polymer chains. In the simulation, stress tensor including link tension coefficient which characterizes anisotropic friction coefficient of the molecular chain was used to obtain material functions by assuming that the anisotropy of friction was altered by the presence of nanoparticles. Additional frictional force between polymer chains and nanoparticles was considered and the suitable relaxation process and chain stretch were incorporated by considering the full chain geometry of polymer molecular chains. All the reptation models considering the effect of nanoparticles were verified by comparing the theoretical results with experimental data for polymer nanocomposites in shear and elongational flows.

It is very important to predict any defects occurring by undesired fiber deformations to improve production yields of resin transfer molding, which has been widely used for mass production of carbon fiber reinforced composite parts. In this study, a simple and efficient analytic scheme was proposed to predict deformations of a multi-layered fiber preform by comparing the forces applied to the preform in a mold of resin transfer molding. Friction coefficient of dry and wet states, permeability, and compressive behavior of unidirectional (UD) and plain woven (PW) carbon fabrics were measured, which were used to predict deformations of the multi-layered fiber preforms with changing their constitution ratios. The model predicted the occurrence, type, and position of fiber deformation, which agreed with the experimental results of the multi-layered preforms.

A fast-cure carbon fiber/epoxy prepreg was thermoformed against a replicated automotive roof panel mold (square-cup) to investigate the effect of the stacking sequence of prepreg layers with unidirectional and plane woven fabrics and mold geometry with different drawing angles and depths on the fiber deformation and formability of the prepreg. The optimum forming condition was determined via analysis of the material properties of epoxy resin. The non-linear mechanical properties of prepreg at the deformation modes of inter- and intra-ply shear, tensile and bending were measured to be used as input data for the commercial virtual forming simulation software. The prepreg with a stacking sequence containing the plain-woven carbon prepreg on the outer layer of the laminate was successfully thermoformed against a mold with a depth of 20 mm and a tilting angle of 110°. Experimental results for the shear deformations at each corner of the thermoformed square-cup product were compared with the simulation and a similarity in the overall tendency of the shear angle in the path at each corner was observed. The results are expected to contribute to the optimization of parameters on materials, mold design and processing in the thermoforming mass-production process for manufacturing high quality automotive parts with a square-cup geometry.

As the popularity of flexible devices that can be folded or bent rises, there is a need for developing supporting back cover panels that are both flexible and rigid, based on the direction of the force applied. In this study, a multiple-matrix-based carbon fiber reinforced plastic (CFRP) structure that is highly flexible on one side and rigid on the other is proposed for use as the back cover plate of flexible devices. To achieve this anisotropic flexibility, two different matrices were introduced, i.e., polyurethane for the flexible side and epoxy for the rigid side. After the epoxy-based rigid composite plate was fabricated using a resin infusion process, the polyurethane-based flexible composite was compression-molded onto the rigid composite. The effects of the thickness, the textile structure of each layer, and the adhesive layer between two different layers were investigated, and the optimized multiple-matrix composite panel reflected high anisotropic flexibility with a flexural strength of 0.55 MPa to the flexible side and 5.55 MPa to the rigid side. This result indicates the possibility of replacing structurally complex metal back covers with a simple-structured, lightweight CFRP.