Bioinspired Design of LDH‐Based Mobile Building Materials with Enhanced Mechanical and Ultraviolet‐Shielding Performance

Glass fiber reinforced polytetrafluoroethylene composites (PTFE/GF composites) with the excellent performance have been given considerable attention due to their increasing applications in large architecture areas such as stadiums, amusement parks, parking lots, etc. However, the brittleness of glass fiber can hinder the performance of PTFE/GF composites. The PTFE/MLDH (modified ZnAl‐layered double hydroxide)/GF composites inspired by layer‐layer structure are prepared via the multi‐layered dipping method, which consists of GF acting as a reinforcement, PTFE acting as matrix, and MLDH acting as the layer‐layer structure. The results of study show that the high strength and surperflexibility of PTFE/MLDH/GF composites are higher than pure PTFE/GF composites. Especially, when the PTFE/MLDH/GF composites contain 1.6 wt% MLDH, the folding endurance reaches up to 39 035 times, the tensile strength reaches up to 163.57 MPa, and strain reaches up to 8.33%. More significantly, the strength and surperflexibility are illustrated by a mechanism model and it is used to further broaden the application of PTFE/GF composites in mobile building materials. Moreover, it is discovered that the PTFE/MLDH/GF composites have unique translucent performance and excellent ultraviolet‐shielding properties in this study, which further broaden its range of applications.     

Pseudo-ductile fracture of 3D printed alumina triply periodic minimal surface structures

Additive manufacturing enables the fabrication of periodic ceramic lattices with controllable micro-architectures. Many studies reported their catastrophic brittle fracture behaviour. However, ceramic lattices may fail by a layer-by-layer pseudo-ductile fracture mode, by controlling micro-architectures and porosities. Moreover, their fracture behaviour can be optimised by introducing strut/wall thickness gradients. This paper investigates the fracture behaviour and the fracture mode transition of ceramic triply periodic minimal surface (TPMS) structures. Alumina TPMS structures with relative densities of 0.14-0.37 are fabricated by ceramic stereolithography. Quasi-static compression tests validate a transition density range for non-graded samples: low (<0.21) and moderate (>0.25) relative density samples show layer-by-layer pseudo-ductile and catastrophic brittle fracture modes, respectively. The pseudo-ductile failure mode increases the energy absorption performance, enabling load-bearing capacity for a compressive strain up to 50%. With appropriate thickness gradients, graded structures exhibit significant increase of energy absorption without a decrease of fracture strength compared to their non-graded counterparts.     

Thermoreversible rheological responses of biscarbamates and tricarbamates in uncured epoxy composite pastes caused by their self‐assembly in an epoxy matrix

We investigated the rheological behaviors of diglycidyl ether of bisphenol A (epoxy resin) composite pastes with fumed SiO₂, biscarbamates, and tricarbamates with the same terminal alkyl chains of C₁₆, respectively. The rheological measurement results show that the rheological responses of both carbamates in the epoxy composite pastes were stronger than that of fumed silica at the same concentrations, especially at low concentrations, and the rheological behaviors of the epoxy composites with them were thermally reversible and concentration dependent. IR, thermal, differential scanning calorimetry, and polarized microscopic analyses demonstrated that their different excellent rheological responses in epoxy composite pastes came from their different self‐assemblies in the epoxy matrix, which were caused by the different intermolecular interactions, mainly including hydrogen‐bonding and van de Waals interactions, and the intermolecular interactions for carbamates were closely related to their molecular structures. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46032.     

Drape behavior of 3D woven glass‐epoxy composites

This article deals with the drapability of 3D woven glass fabrics for composite applications. The study focuses on forming a 3D fabric over the mold, the result is a preform, which generally is then injected with a polymer matrix by so called Liquid Composite Molding (LCM) technique. When draping pre–impregnated composites, the fabric is embedded in the epoxy resin as matrix material. Various drape models for dry and pre‐impregnated fabrics have been proposed in the work. Solidworks and ANSYS are the software used for modeling and simulation of 3D woven fabric composites. Given the linear density (tex) and density of E‐glass fiber, the radius of the yarn was calculated. So far the cross section of yarn is assumed to be perfectly circular in shape, keeping the perimeter of yarn constant the circular cross section was deformed into a race track shape which is a much more practical and realistic shape of a yarn cross section. After calculating all the required dimensions, all the three 3D woven structures namely angle interlock, warp interlock and orthogonal were developed in solidworks. All the parameters like total number of warp and weft yarn per unit distance and thickness of the fabric were kept constant in all three structures. The analysis is based on first principles and the parameters of yarn and fabric construction. Results obtained through simulation are reported. These are validated with experimental composite samples. The model used to predict drapability of 3D woven glass‐epoxy composite gives good results. Orthogonal structure proves to be the best as far as resistance to deformation is concerned. However, if a relatively more flexible and formable prepreg is desired, it is advisable to use angle interlock or warp interlock structures. Warp interlock 3D structure proves most beneficial for draping on a mold. POLYM. COMPOS., 37:472–480, 2016. © 2014 Society of Plastics Engineers     

Excellent lubrication properties of 3D printed ceramic bionic structures

Three-dimensional (3D) printed ceramic structures loaded with lubricating materials could exhibit excellent lubrication effect. In this paper, various bionic petal structures and tree frog toe end structure of 3D-printed alumina (Al₂O₃) ceramic are designed to study the effects of lubricating structures and tungsten disulfide (WS₂) solid lubricant on the friction performance. Compared to the friction properties of various bionic lubricating structures loaded with WS₂, the bionic small petal structure with hexagonal arrangement exhibits a lowest friction coefficient of 0.411 and moderate wear resistance due to more storage of lubricant and debris. The maximum friction coefficient of 1.177 and optimum anti-wear ability are offered by the bionic tree frog toe end structure. In particular, the friction coefficient of the bionic petal lubricating structures loaded with WS₂ are lower than that of blank printed Al₂O₃ ceramic, indicating that the lubricating structures provide positive effect on improving friction performance. Therefore, the 3D printed ceramic lubricating structures provided a novel strategy for achieving lubrication in advanced applications.     

A review on direct assembly of through‐the‐thickness reinforced metal–polymer composite hybrid structures

Constant efforts to reduce the structural weight of transportation systems as a solution to control emission levels are currently shaping the way modern cars and airplanes are designed and manufactured. Increased attention has been given to innovative metal–composites multi‐material concepts for the production of lightweight structures. However, the nature of these very dissimilar materials makes their joining a rather complicated task. Recently several technologies have been proposed to overcome process limitation and increase the load transfer between metal and composite in hybrid structures. One of the promising solutions is a new concept known as direct assembling with through‐the‐thickness reinforcements. In this concept, the composite material of a hybrid joint is directly assembled upon a surface‐structured metallic part. Features structured on the metallic part, by a manufacturing phase, act as a through‐the‐thickness reinforcement improving the out‐of‐plane strength and load transfer capabilities of such joints. The current status and state‐of‐art direct assembling technologies are reviewed in this article. Examples of reviewed metal structuring techniques include micromachining, stamping, Surfi‐Sculpt, additive manufacturing, cold metal transfer, and metal injection molding structuring. Direct assembling techniques addressed in this article are vacuum‐assisted resin infusion, resin transfer molding, prepreg/autoclave assembly, and ultrasonic joining. POLYM. ENG. SCI., 59:661–674, 2019. © 2018 The Authors. Polymer Engineering & Science published by Wiley Periodicals, Inc. on behalf of Society of Plastics Engineers.     

Electrolyte‐resistant epoxy for bonding batteries based on sandwich structures

Adhesives that are stable in Li‐ion battery electrolytes are required to realize the potential of new battery designs that integrate structural elements with energy storage. Here, several polymers, commercial adhesives, and sealants were investigated to bond and seal a Li‐ion battery sandwich panel. Gravimetric electrolyte uptake measurements were compared with Hansen solubility parameters to predict long‐term durability of the materials exposed to battery electrolyte. The durability of adhesively bonded joints with an epoxy adhesive, which was selected as the lowest electrolyte uptake material, was examined using single lap shear strength tests and three‐point bending tests in a fabricated sandwich panel. The strength of the epoxy decreased after exposure to battery electrolyte due to solvent uptake in the bond. The addition of lithium hexafluorophosphate to the ethylene carbonate/dimethyl carbonate mixture severely decreased the strength with respect to the pure solvents. In device testing, the sandwich panel did not show any visible damage or leakage when loaded to above 1000 N during three‐point bending tests. Using sol extraction measurements and differential scanning calorimetry analyses, the optimized curing temperature for the epoxy adhesive ranged from 80 to 100 °C. At these temperatures, the cured adhesive had a highly crosslinked structure with low sol extraction. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46059.     

Impact response of carbon‐epoxy laminates containing buffer‐strip layers

This work looks at the dynamic behavior of laminated carbon‐epoxy (C‐E) composites with inserted interleaf polytetrafluoroethylene (PTFE)‐coated material. Instrumented impact tests performed on the interleaved test samples showed significant differences in the energy absorption characteristics that could be correlated with the failure mode. It was inferred that with the introduction of small amounts of less adherent layers of material at specific locations, the load‐carrying ability decreased while the energy‐absorbing capability was found to improve considerably. These and other experimental observations are discussed in this article. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 752–761, 2002     

Fabrication of 3D structures via direct ink writing of kaolin/graphene oxide composite suspensions at ambient temperature

Kaolin/graphene oxide composite has been widely utilized in aero-space and architectural engineering applications due to its excellent mechanical property. Direct ink writing (DIW) is a freeform rapid prototyping technology that could be used to accurately fabricate the resulting size with complex shapes. In this study, we reported the DIW of kaolin/graphene oxide (GO) composite suspensions (KGCS) to assemble 3D structures at ambient temperature for the first time. The effects of GO on the chemical constitution and microstructure of kaolin suspensions were investigated. Rheology was characterized to ensure printability of KGCS. The addition of GO in kaolin suspensions quickened a flocculation structure, which dramatically changed their rheology properties. The DIW of 3D structures from the optimal KGCS sample maintained their initial shape without spreading. The flexural and compressive strengths of the dried optimal KGCS samples were obviously enhanced due to the improvement and reduction of the micro-defects compared from cured kaolin matrix.     

Facile synthesis of graphene/polypyrrole 3D composite for a high‐sensitivity non‐enzymatic dopamine detection

One kind of nanocomposite consisting of graphene and polypyrrole was synthesized via a facile and mild way with the assistant of microwave irradiation. The synthesis route was embedding the polypyrrole into the graphene flakes to form a 3D structure, to achieve larger active surface and higher electro‐catalysis property. Structures and components of the composite were measured by X‐ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. A stronger electrochemical response of electrode with modified resultant was observed in the electrochemical test. Dopamine sensor based on the composite showed a sensitivity of 363 μA mM ^?1 cm^?2, a linear range of 1 × 10^?4 M to 1 × 10^?3 M , and a detection limit of 2.3 × 10^?6 M (S/N = 3). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44840.     

Preparation,characterization, and improvement of hollow epoxy particle‐toughened vinyl ester composites for high‐end applications

Spherical hollow epoxy particles (HEPs) that can serve as advanced reinforcing fillers for vinyl ester thermosets were prepared using the water‐based emulsion method. The HEP fillers were incorporated into the vinyl ester matrices at different loading amounts, ranging from 0 to 9 wt %, to reinforce and toughen the vinyl ester composite. The optimum mechanical properties of the HEP‐toughened epoxy composite can be achieved by the addition of 5 wt % HEP filler into the vinyl ester matrices. The toughening and strengthening of the epoxy composites involved the interlocking of vinyl ester resins into the pore regions on the HEP fillers. The toughening and interlocking mechanisms of HEP‐toughened vinyl ester composites were also proposed and discussed. The addition of HEP fillers into vinyl ester matrices increased the glass transition temperature (T_g) and thermal stability of the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Study on synthesis of polyurethane‐epoxy composite emulsion

The stable polyurethane‐epoxy composite emulsion with the epoxy‐amine oligomer (DEA‐EP) and the epoxy resin oligomer has been prepared by step‐growth polymerization and controlled crosslinking technique. The emulsion forming transparent films can be cured at room temperature with trimethylolpropane tris (1‐ethyleneimine) propionate (TMPTA‐AZ). The DEA‐EP structure and its reaction with urethane prepolymers were proved by Fourier transform infrared spectra (FTIR). The studies on particle size, the particle size distribution, viscosity, and the films' transmittance (Tr) indicated that both trimethylol propane (TMP) and DEA‐EP contributed to improving the resin blends' compatibility and reducing the viscosity. The epoxy resin content can increase up to 20.0 wt % (based on the total content of the polyurethane and epoxy resin) and the emulsion was still stable. The data from the tensile test experiments showed that with the epoxy content increasing, the tensile strength (σ_b) and Young's modulus were proportionately raised, but the elongation at break (ε_b) decreased. Tensile tests also revealed that introducing TMPTA‐AZ as an outside‐crosslinker can increase the tensile strength. By adding 0.3 wt % of TMPTA‐AZ, the ε_b reduced from 429% to 371% and the σ_b increased from 4.4 to 13.73 MPa; by adding 1.8 wt % of TMPTA‐AZ, ε_b of the film was 67% of ε_b of the film with 0.3 wt % of TMPTA‐AZ, but its σ_b was 24.77 MPa and 180% of σ_b of the film with 0.3 wt % of TMPTA‐AZ. The cured films possessed excellent water and toluene resistance: water uptake (48 h, 3.1%; degree of curing: 70%), toluene uptake (210 h, 8%. degree of curing: 70%). Better properties of the composite emulsion will confer it as a potential application in low volatile industrial coatings. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fracture toughness of silica particulate‐filled epoxy composite

The relationship between the postcuring conditions and fracture toughness on three silica particulate‐filled epoxy composites was investigated. The glass transition temperature, T_g, and the fragility parameter, m, derived from the thermo‐viscoelasticity, were used to characterize the composites, which were postcured under various conditions. The glass transition temperature and fragility both depended on both of the curing conditions and the volume fraction of silica particles. The glass transition temperature increased with the postcuring time and temperature, while the fragility generally decreased as the volume fraction increased. There was no direct correlation between the glass transition temperature and fragility. The fracture toughness depended on both the glass transition temperature and fragility. The composites with a high glass transition temperature and low fragility had high fracture toughness. These results indicate that the glass transition temperature and fragility are useful parameters for estimating the fracture toughness of the silica particulate‐filled epoxy composites. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2261–2265, 2002     

Self‐assembly of rod‐coil molecules into lateral chain‐length‐dependent supramolecular organization

In this article, we report synthesis and characterization of the self‐assembly behavior of coil‐ rod‐coil molecules, consisting of four biphenyls and a p‐terphenyl unit linked together with ether bonds as a rod segment. These molecules contain lateral methyl or ethoxymethyl groups at 2 and 5 positions of the middle benzene ring of p‐terphenyl. The self‐assembling behavior of these materials was investigated by means of DSC, POM, and SAXS in the bulk state. The results reveal that self‐assembling behavior of these molecules is dramatically influenced by a lateral methyl or ethoxymethyl groups in the middle of rod segment. In addition, molecule with PEO (DP = 17) coil chains of identical coil volume fraction to the corresponding molecule connected by PPO (DP = 12) coil chains, shows diverse self‐organizing behavior that may result from the parameters of cross‐sectional area of coil segment and the steric hindrance at the rod/coil interface. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Bio‐orthogonal Fluorescent Labelling of Biopolymers through Inverse‐Electron‐Demand Diels–Alder Reactions

Bio‐orthogonal labelling schemes based on inverse‐electron‐demand Diels–Alder (IEDDA) cycloaddition have attracted much attention in chemical biology recently. The appealing features of this reaction, such as the fast reaction kinetics, fully bio‐orthogonal nature and high selectivity, have helped chemical biologists gain deeper understanding of biochemical processes at the molecular level. Listing the components and discussing the possibilities and limitations of these reagents, we provide a recent snapshot of the field of IEDDA‐based biomolecular manipulation with special focus on fluorescent modulation approaches through the use of bio‐orthogonalized building blocks. At the end, we discuss challenges that need to be addressed for further developments in order to overcome recent limitations and to enable researchers to answer biomolecular questions in more detail.     

In‐situ grown silica/water‐borne epoxy shape memory composite foams prepared without blowing agent addition

Shape memory (SM) silica/epoxy composite foams were successfully synthesized via latex technology and prepared without blowing agent addition. Silica was synthesized via tetraethoxysilane (TEOS) hydrolysis. Silica/epoxy foams were obtained from the TEOS solution and water‐borne epoxy mixtures after freeze‐drying and foaming in the presence of residual moisture as the blowing agent under a vacuum at 110°C. The morphologies of the resulting foams were evaluated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Compression and thermo‐mechanical cycle tests were performed to measure the mechanical and SM properties of the foams. Experimental results indicated that the micrographs and mechanical properties of the foams were closely related to freeze‐drying time. The final composite foams exhibited high shape recovery and fixity ratios and could maintain both properties at more than 90% even after five thermo‐mechanical cycles. The properties obtained in the epoxy foams may offer new opportunities for their use in future structural applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42599.     

UV induced microcellular foaming—A new approach towards the production of 3D structures in offset printing techniques

The generation of microcellular foams via a photochemical initiation mechanism is a new approach aimed at the one step production of three dimensional structures in offset printing techniques. The photochemical foaming involves the excitation of a selected photoacid generator with ultra-violet (UV) light to release Brønsted acids. Carbon dioxide, formed upon the reaction of the Brønsted acid with calcium carbonate particles, is used as blowing agent. In order to achieve efficient proton formation and consequently generate a sufficient amount of blowing agent, photosensitizers are employed. Long wavelength absorbing anthracene derivates are added to capture a higher fraction of the light source, a conventional mercury arc lamp, to sensitize the photolysis of the photoacid generator. The microcellular foaming was performed with a commercially available UV curable offset ink formulation containing triacrylate oligomers. To ensure that the gas bubbles are trapped in the cured resin a balance has to be found between the curing speed of the ink and the foaming speed. In the present study crucial process parameters including photoacid generator level, choice of photosensitizer, light intensity and concentration of calcium carbonate particles are evaluated and their influence on the foam properties are discussed. Both the cell morphology and the expansion of the film thickness are characterized with optical microscopy and mechanical methods. The results clearly show that the UV assisted foaming leads to the formation of dense and uniform microcells by applying optimized process parameters. Moreover, the relative thickness of the ink layer can be raised up to 90% which makes the one-step production of three dimensional structures (e.g. reliefs) at short reaction times and ambient temperatures feasible.     

Experimental and numerical study of distortion in flat,L‐shaped,and U‐shaped carbon fiber–epoxy composite parts

In this study, flat composite panels were fabricated to find the effect of different manufacturing parameters, including stacking sequence, part thickness, and tooling material, on distortion of carbon fiber‐epoxy composite parts. L‐shaped and U‐shaped panels were also made to investigate the effect of stacking sequence on spring‐in angle and warpage of the curved panels. Results showed that distortion of the flat panels caused by asymmetry in the stacking sequence was an order of magnitude greater than distortion of the panels with an unbalanced stacking sequence; whereas in the curved panels, the panel with an asymmetric stacking sequence showed the least spring‐in angle, and the largest angle was observed in the symmetric panel. MSC Marc was used to predict distortion of the panels, and the simulation results were compared with the experimental results for several stacking sequences of the flat and the L‐shaped panels. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40439.     

Direct ink writing of 3D piezoelectric ceramics with complex unsupported structures

Piezoelectric ceramic, as a typical smart material, shows great potential in applications of sensing & actuation, smart structure and energy harvesting. However, the use of traditional methods to fabricate complex and high-precision piezoelectric ceramic devices faces huge technical difficulties and high molding costs. Direct ink writing is a typical additive manufacturing technology, but has limited capabilities when preparing ceramic products with complex unsupported structures. In this work, a combined process of direct ink writing (DIW) and secondary shaping of flexible ceramic green body has been developed and proved to produce complex piezoelectric ceramics. The PZT ink shows shear thinning behavior and appropriate viscoelasticity such as moderate viscosity and high storage modulus. The printed green body can be flexibly deformed and the samples after polarization show good piezoelectric properties, with an average d₃₃ up to 265 pC/N. This work demonstrates an attractive method for geometrically complex piezoceramic with unique macro structure due to its simplicity and low cost, and provides a solution to the key problems in the existing manufacturing technology of 3D ceramics.