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Although the typical antioxidant, N-(1,3-dimethylbutyl)-N’-phenyl-p-phenylenediamine (6PPD), ensures high durability and long lifespan for rubber compounds, it generates a highly toxic quinone in water, causing a serious environmental pollution. Herein, as an alternative material of 6PPD, we newly introduce eco-friendly amine-functionalized lignin (AL) to be incorporated in rubber, which can provide excellent combinatorial anti-aging properties of thermal stability and ozone/fatigue resistances through radical scavenging effect. The heterolytic ring-opening reaction of AL and sulfur can accelerate curing and improve crosslink density by 28% (v, 4.107 × 10−4 mol/cm3), consequently reducing ozone vulnerable areas of the matrix, and further improving aging resistance. Notably, AL allows its rubber compound to exhibit superior anti-ozone performance after ozone aging, with the arithmetic surface roughness (Sa) of 2.077 μm, which should be compared to that of 6PPD (4.737 μm). The developed chemically modified lignin and the methodology have enormous potential as a promising additive for the future eco-friendly rubber compounds.

A composite system with embedded bimodal-sized hybrid core–shell spheres is reported for electromagnetic interference (EMI) shielding applications, of which the shells are either wave-diffuse reflecting nickel/gold or wave-absorbing graphene.

The advances in modern intelligent electronic systems have a pressing need for smart electromagnetic interference (EMI) shielding capabilities in a frequency-selective manner to choose which electromagnetic waves in a certain range to be blocked. Herein, we present multilayered EMI shielding composites that can provide selective on-off characteristics for specific frequency ranges across a broad spectrum. The composites are composed of outermost dielectric layers and conductive interlayers fabricated via solution-printing, wherein hexagonal boron nitride (BN) and silver-coated BN particles are embedded, respectively. The EMI shielding frequency range and on-off selectivity are controllable by varying the configuration of the composite structure in terms of the BN content and the number of composite layers, providing different interstitial spaces between the fillers and interfacial dielectric properties. Furthermore, the optimal combination of these layers permits excellent combinatorial properties of EMI shielding (32–62 dB), thermal conductivity (7.61 W/m·K), and electrical insulation (4.03 kV/mm) in the through-plane direction. The developed composites and their synthetic pathways have enormous potential for tailored material design and flexible system integration in next-generation EMI shielding technologies.

Wearable devices have attracted increasing attention for development of personal healthcare. In this study, three-dimensional porous carbon aerogels reinforced polydimethylsiloxane nanocomposites with controllable and hierarchical open, semi-open and closed cell structures were developed for multifunctional wearable heating and sensing devices. This investigation reveals that the microstructures of the aerogels play a critical role in determining nanocomposites properties, particularly their heating and sensing performances. As thermotherapy heaters, the nanocomposite with semi-open cell structure is observed with the highest energy transduction efficiency (equilibrium temperature ∼138.9 °C under only 5 V) compared to the nanocomposites with open and closed cell structures, due to the well-defined conductive network and structural stability. As stimuli-responsive sensors, compared to the nanocomposite with closed cell structure, the nanocomposites with open and semi-open cell structures are observed with higher sensitivity (gauge factor ∼369.03) and much better repeatability, benefiting from their structural integrity. Finally, the nanocomposite with semi-open cell structure was investigated for practical potential on human body. Experimental results demonstrated the uniform temperature distribution and reliable sensitivity as a multifunctional wearable device. Therefore, by controlling and optimizing the microstructure of carbon aerogels, the nanocomposites with tailored microstructure could be exploited for various engineering applications including emerging multifunctional wearable devices.

Twisted and coiled actuators (TCAs), which are light but capable of producing significant power, were developed in recent times. After their introduction, there have been numerous improvements in performance, including development of techniques such as actuation strain and heating methods. However, the development of robots using TCA is still in its early stages. In this study, a bionic arm driven by TCAs was developed for light and flexible operation. The aim of this study was to gain a foothold in the future of robot development using TCA, which is considered as the appropriate artificial muscle. The main developments were with regard to the design (from actuator design to system design), system configuration for control, and control method. First, a process technology for repeatedly manufacturing TCA, which can be used practically and delivers sufficient performance, was developed. Based on the developed actuator, a joint was designed to move the elbow and hand. The final bionic arm was developed by integrating the TCA, pulley joint, and control system. It moved the elbow up to 100° and allowed the hand to move in three degrees of freedom. Using the control method for each joint, we were able to show the movement by using the hand and elbow.

Two-dimensional (2D) materials can offer high exposed surface area and reactive functional groups. Despite the tremendous progresses made in the 2D materials, carbonaceous 2D materials have not seen their light perhaps because of the overwhelming shadow cast by graphene. Here, we introduce a platform for carbonaceous 2D materials that are co-compounded carbonaceous nanoplates (Co-CANPs). Co-compounding carbonaceous nanoplates (CANPs) with another compound are accomplished by a one-pot process, and the synthesized Co-CANP does not require any separation for its use. It was confirmed that the mechanical properties were improved by adding the synthesized Co-CANP as a tire additive, thereby proving its efficacy. The platform introduced here opens the door to organic–inorganic Co-CANPs and also to many component Co-CANPs.

Electroadhesion device allows one to pick up almost all the objects regardless of their shape or types of materials by means of the electrostatic Maxwell force, which is developed by the dielectric...

Inspired by desert resurrection plant, Rose of Jericho, this study developed a new porous material with programmable multiple-stimuli responsive features. The first one is reversible shape-memory transformation of experiencing extremely large deformations upon dehydration and rehydration; superior to the plant, the aerogels display controllable responsiveness based on moisture amount with fast actuation. The second one is switchable flexibility depending on the polarity of exposed fluids; these aerogels are reversibly compressible with outstanding flexibility in polar solvents but sustain incompressibility with high stiffness in nonpolar solvents. The third one is programmable shape morphing capability driven by imbibition of liquid droplet; mimicking the movement of the plant but in different mechanisms, the aerogels can evolve into programmed V-shape or U-shape by simply controlling the liquid imbibition location. These multiple-stimuli responsive features arise from the unique ensemble of the porous morphology, and the interactions between solvent molecules and the chemical structures of the porous material engineered by two-step crosslinking mechanism. It can be foreseen that the synergistic effect of the intriguing features could allow for the applications of the aerogels as smart sensors/actuators, soft robotics, and biomedical devices, all of which typically require smart adaptability to external stimuli and/or extreme environments.

Development of lightweight porous structure with high compressibility and mechanical durability is in great demand to promote graphene-based materials from fundamental research to engineering applications. In this study, graphene oxide (GO)-based sponges with hierarchical porous structures were synthesized by a simple freeze-drying method. By controlling and optimizing their structures, the lightweight GO-based sponges can offer excellent structural integrity even after being compressed at 95% strain, indicating the extremely high compressibility. The outstanding mechanical durability were also demonstrated by cyclic compression testing at 50% strain for 10,000 cycles. Considering the severe dye pollution problem, the sponges were investigated for methylene blue adsorption. It was found that the sponges with high selectivity during adsorption can have the maximum adsorption capacity up to 476 mg g−1. More importantly, the sponges were demonstrated with extraordinary recyclability along with a very simple recycling process and also high recycling efficiency (above 86% after the 10th cycle). It was experimentally demonstrated that if their morphological structures are carefully designed and optimized, the GO-based porous structures can exhibit the ensemble of outstanding compressibility and durability, and equally importantly the excellent adsorption performance. Therefore, it could show great promise of such nanomaterial-based sponges as excellent adsorbents for wastewater purification.

Electroadhesive devices can lift materials of different shapes and various types using the electrostatic force developed at the interface between the device and the object. More specifically, the electrical potential generated by the device induces opposite charges on the object to give electrostatic Maxwell force. Although this technology has a great deal of potential, the key design factors based on the fundamental principles of interfacial polarization have yet to be clearly identified. In this study, we identify that the lifting force is quantitatively related to the total length of the boundary edges of the electrodes, where the induced charges are selectively concentrated. We subsequently propose a model equation that can predict the electrostatic lifting forces for different object materials as a function of the applied voltage, impedance, and electrode-boundary length. The model is based on the fact that the amount of induced charges should be concentrated where the equipotential field distance is minimal. We report that the impedance magnitude is correlated with the electroadhesive lifting forces by analyzing the impedance characteristics of objects made of different materials (e.g., paper, glass, or metal), as attached in situ to the electroadhesive device.

The static and dynamic compressive behaviors of glass fiber-reinforced polyurethane foams were characterized under cryogenic temperature conditions to help identify the essential design and parameters required to model the response of the foam accurately under the various loading conditions encountered in liquefied natural gas cargo containment systems. The material properties of polyurethane foams with varying concentrations and orientations of the glass fiber continuous strand mat were characterized by quasi-static, dynamic mechanical analysis (DMA), and low velocity impact testing. The testing results showed increased strength with increasing density and strain rate, as well as similar failure modes independent of the strain rate. In addition, the glass fibers dominated the DMA behavior and a glass transition temperature at or above 130 °C was observed for all foam varieties. Overall, the glass fiber reinforced polyurethane foam showed the typical static and dynamic compressive behaviors of foams at both room and cryogenic temperatures.

This study is a semi-empirical approach to effectively estimate the interfacial shear strength (IFSS) of short fiber-reinforced polymer composites by combining tensile and acoustic emission testing with finite element modeling. The short glass fiber–polycarbonate composites were fabricated using a solution mixing method and the tensile properties were characterized with a standard test. During the tensile tests, the debonding stresses at the interface between the glass fiber and polycarbonate were monitored with an acoustic emission sensor. Subsequently, a finite element model of the composites was developed using the experimentally obtained debonding stresses to estimate the IFSS of the composites. By employing this semi-empirical method, the IFSS was effectively determined and found to range from 83 to 126 MPa depending on the fiber orientation. This approach can be broadly applied to micron-sized short fibers and nanoscale fillers such as carbon nanotubes or graphene-reinforced composites.

Using a plasma enhanced chemical vapor deposition (PECVD) technique, a synchronous polymerization of 3,4-ethylenedioxythiophene (EDOT) and pyrrole monomers was investigated for the development of thin films with adjusted optoelectronic properties. Maintaining a constant amount of EDOT- and pyrrole-feed in the presence of a carrier gas, the PECVD reaction power was varied in the range of 10–100 W to give different physicochemical states of composite films composed of poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy). The deposition rate gradually increased with the reaction power reaching the highest deposition rate at 30 nm/min (100 W) in this study. The energy bandgap of the plasma-polymerized PEDOT/PPy copolymer films increased from 2.62 to 3.27 eV as the applied power density increased from 10 to 100 W in a continuous way, that could desirably ensure a tunable control of bandgaps in thin films. The electrical conductivity and the surface roughness of the thin films continuously increased from 1.59×10-4 to 2.28×10-2 S/m and from 0.2 to 1.9 nm respectively, as the applied power density decreased. The plasma-polymerized PEDOT/PPy copolymer is expected to find its application in various optoelectronic devices including the hole injection layer (HIL) in organic light-emitting diodes (OLEDs), and organic photovoltaics (OPVs) for the improved energy match.

Anti-corrosion metal protection of the 2D structured graphene oxide (GO) was investigated in this study using its intrinsic impermeability against reactive molecules stemming from the small geometric pore size and π-orbital repelling fields of graphene. The electrophoretic deposition (EPD) of GO sheets on metals is an attractive coating method but the negatively-charged GO only allows the anodic EPD process, which makes it difficult to achieve high-quality coating layers due to gas bubbling and electrochemical oxidation of metals. Thus, we imposed the positive charge to GO sheets using p-phenylenediamine (PPD) and successfully carried out the cathodic EPD in the ethanol aqueous solution. The cathodic EPD of GO on cupper provided a linear growth rate with both deposition time and voltage providing the thickness over 6.0 μm in a void-free and robust feature, which could hardly be achieved by other coating methods. Converting the GO coating to the reduced GO (RGO) by thermal reduction, we successfully increased the RGO adhesion strength up to the highest adhesion grade of 5B in the cross-cut adhesion test. An excellent anti-corrosion protection capability of the developed RGO coating was demonstrated by a decreased corrosion current density and increased corrosion potential in potentiodynamic polarization analysis.

As a family of smart functional hybrid materials, magnetic polymer composite particles have attracted considerable attention owing to their outstanding magnetism, dispersion stability, and fine biocompatibility. This review covers their magnetorheological properties, namely, flow curve, yield stress, and viscoelastic behavior, along with their synthesis. Preparation methods and characteristics of different types of magnetic composite particles are presented. Apart from the research progress in magnetic polymer composite synthesis, we also discuss prospects of this promising research field.

Magnetorheological (MR) elastomers become one of the most powerful smart and advanced materials that can be tuned reversibly, finely, and quickly in terms of their mechanical and viscoelastic properties by an input magnetic field. They are composite materials in which magnetizable particles are dispersed in solid base elastomers. Their distinctive behaviors are relying on the type and size of dispersed magnetic particles, the type of elastomer matrix, and the type of non-magnetic fillers such as plasticizer, carbon black, and crosslink agent. With these controllable characteristics, they can be applied to various applications such as vibration absorber, isolator, magnetoresistor, and electromagnetic wave absorption. This review provides a summary of the fabrication, properties, and applications of MR elastomers made of various elastomeric materials.

As highly integrated electronic devices and automotive parts are becoming used in high-power and load-bearing systems, thermal conductivity and mechanical damping properties have become critical factors. In this study, we applied two different fillers of aluminium nitride (AlN) and boron nitride (BN), having polygonal and platelet shapes, respectively, into ethylene-propylene-diene monomer (EPDM) rubber to ensure improved thermo-mechanical properties of EPDM composites. These two different shapes are considered advantageous in providing effective pathways of phonon transfer as well as facilitating sliding movement of packed particles. When the volume ratio of AlN : BN was 1 : 1, the thermal conductivity of the hybrid-filler system (EPDM/AlN/BN) increased in comparison to that of the single-filler system (EPDM/AlN) of 3.03 to 4.76 W m−1 K−1. The coefficient of thermal expansion (CTE) and thermal distortion parameter (TDP) substantially decreased from 59.3 ppm °C−1 and 17.5 m K−1 of EPDM/AlN, to 39.7 ppm °C−1 and 8.4 m K−1 of EPDM/AlN/BN, representing reductions of 33 and 52%, respectively. Moreover, the damping coefficient of EPDM/AlN/BN was greatly increased to 0.5 of at 50 °C, compared to 0.03 of neat EPDM. These excellent performances likely stem from the effective packing of AlN/BN hybrid fillers, which could induce facile energy transfer and effective energy dissipation by the sliding movement of the adjacent hybrid fillers in the EPDM matrix.

Although ceria particles are currently receiving great interest with their unique catalytic and optical properties, the problem of agglomeration is yet to be overcome, which is caused by their high density and surface energy, consequently hampering the practical applications. Herein, a novel method of preparing hierarchical shells of ceria (CeO2) and silica (SiO2) on a polystyrene (PS) core is introduced to control the shape and surface charge of the particle, which give rise to different dispersion conditions. The PS/CeO2/SiO2 hybrid core–shell microspheres provide a wide spectrum of surface charge via adjustment of the thickness of the outermost silica shell from 20 to 40 nm, which sets the isoelectric point (IEP) in the range of 5.1–8.6. Subsequently, the silica shell significantly extends the product’s stability and utilization windows due to the controlled surface charge and affinity between the particle surface and the dispersion medium. The developed multilayered core–shell microspheres and the method of synthesis have great potential for various applications that require sophisticated control of surface properties.

We investigated the rheological and mechanical properties of a polypropylene (PP) composite reinforced by microfibrillated cellulose (MFC) fibers, of which the size was fractionated at ca. 24 µm by removing substances such as lignin or hemicellulose out of natural plants to exert the maximum mechanical performance of cellulose fibers. Due to the poor compatibility of MFC with a non-polar hydrophobic PP matrix, the MFC surface was modified through silylation and acetylation to increase its wetting and dispersion characteristics. The content of silylated-MFC could increase up to 30 wt% in the PP composite through large-volume process such as extrusion and injection molding. In addition, all mechanical properties of the silylated-MFC/PP composite were improved compared to untreated MFC/PP, acetylated MFC/PP composite. It was ensured by a strong shear thinning characteristic of the PP composite with silylated MFC content 30 wt% exhibiting a 69% lower viscosity (337 Pa·s at 4.7 s−1) than the neat PP at 180 °C. The same 30 wt% silylated specimens gave a well-dispersed fibrous MFC in PP, providing a tensile modulus (3.09 GPa) and a flexural modulus (3133 MPa), which were 64 and 81% higher than the neat PP, and 16 and 15% higher than the untreated-MFC composites, respectively. The flexural strength and the heat distortion temperature were also increased by 10 and 22%, compared to neat PP, respectively. In the acetylation reaction, the fibril structure of MFC was damaged due to full substitution by acetyl groups, and the reinforcing effect was insignificant as a filler in PP matrix. The developed silylated-MFC/PP composites provided excellent mechanical properties and high-loading processability that would be difficult to achieve by other eco-friendly composite systems.

Microfibrillated cellulose (MFC) particles were synthesized by a low-pressure alkaline delignification process, and their shape and chemical structure were investigated by SEM and Fourier transformation infrared spectroscopy, respectively. As a novel electrorheological (ER) material, the MFC particulate sample was suspended in insulating oil to fabricate an ER fluid. Its rheological properties&mdash, steady shear stress, shear viscosity, yield stress, and dynamic moduli&mdash, under electric field strength were characterized by a rotational rheometer. The MFC-based ER fluid demonstrated typical ER characteristics, in which the shear stresses followed the Cho&ndash, Choi&ndash, Jhon model well under electric field strength. In addition, the solid-like behavior of the ER fluid was investigated with the Schwarzl equation. The elevated value of both dynamic and elastic yield stresses at applied electric field strengths was well described using a power law model (~E1.5). The reversible and quick response of the ER fluid was also illustrated through the on&ndash, off test.

Conducting polymer-coated nanoparticles used in electrorheological (ER) and magnetorheological (MR) fluids are reviewed along with their fabrication methods, morphologies, thermal properties, sedimentation stabilities, dielectric properties, and ER and MR characteristics under applied electric or magnetic fields. After functionalization of the conducting polymers, the nanoparticles exhibited properties suitable for use as ER materials, and materials in which magnetic particles are used as a core could also be applied as MR materials. The conducting polymers covered in this study included polyaniline and its derivatives, poly(3,4-ethylenedioxythiophene), poly(3-octylthiophene), polypyrrole, and poly(diphenylamine). The modified nanoparticles included polystyrene, poly(methyl methacrylate), silica, titanium dioxide, maghemite, magnetite, and nanoclay. This article reviews many core-shell structured conducting polymer-coated nanoparticles used in ER and MR fluids and is expected to contribute to the understanding and development of ER and MR materials.

More recently, three dimensional printing (3D Printing), also known as an additive manufacturing (AM), has been highlighted since it shows a great promise to realize almost any three dimensional parts or structures with computer aided design (CAD). Several different processes are available for 3D printing, which includes fused deposition modeling, selective laser sintering, stereolithography, photopolymerization, and etc. In particular, considerable attention is paid to the 3D printing technique with photopolymerization due to their high resolutions. Unfortunately, the 3D printed products with photopolymerization however possess poor mechanical properties. Understanding of this should be necessary for the advantages of the 3D printing to be fully realized. Here, this study experimentally investigates the mechanical properties of the 3D printed photopolymer through thermomechanical analysis and tensile testing. In this study, it is found that the printed specimens are not fully cured after the 3D printing with photopolymerization. DiBenedetto equation is employed to better understand the relationship between the curing status and tensile properties. In addition to the poor mechanical properties, anisotropic and size dependent tensile properties of the 3D printed photopolymers are also observed. Electron beam treatment is used to ensure the cure of the 3D printed photopolymer and the corresponding tensile properties are characterized and investigated.

Magnesium oxysulfate (MOS) whisker is considered as a promising inorganic material recently attracting a great attention for being used as a reinforcing filler for polymer composites due to high aspect ratio and extremely-low bulk density. In this study, the MOS was treated with 3-methacryloyloxypropyl-trimethoxy silane (MPS) via sol-gel condensation reactions, which successfully allowed melt mixing with polypropylene (PP) up to 30 wt% of MOS. The tensile strength at yield and modulus of the MOS/PP composites were substantially increased by 50.8% and 362%, respectively, when compared with the pristine PP. As a novel finding, the flame retardancy of MOS was proved by identifying water evolution at elevated temperatures giving out 9 wt% of water in 250–320 °C and 14 wt% in 350–420 °C in two steps. This work demonstrated that the MOS could be an excellent filler for PP not only increasing the mechanical properties in a great extent but also imposing flame retarding capability. Keywords: Magnesium oxysulfate, Surface modification, Mechanical properties, Flame retardant

The effects of ZnO particle size on crosslinking and thermal aging behavior of natural rubber (NR) were investigated. NR vulcanizates filled with nano ZnO allowed higher crosslink density, lower polysulfide crosslink, and stronger mechanical properties than those filled with micro ZnO. After thermal aging, NR filled with nano ZnO exhibited much more stable chemical and mechanical properties. The high crosslink density as well as the formation of more stable mono- and di-sulfidic crosslinks was attributed to the good dispersion and high surface area of the nano ZnO.

In the development of three-dimensional printable materials for high-speed and high-resolution printing, UV-curing polymers can guarantee fast and precise printing of high performance load-bearing structures, but the injected drops of the monomers tend to spread over the substrates due to their low viscosity. In this study, we imposed the self-standing and shape-memorable capability of an epoxy acrylate (EA) monomer to ensure continuous filamentary 3D printing while maintaining its low viscosity nature. Using octadecanamide (ODA) with EA, strong hydrogen-bond networks (−N−H⋯OC−, −N−CO⋯H–O–, –N–H⋯N–) were additionally achieved in the material system and the developed material distinctively exhibited rheological duality at different processing stages: a low-viscosity liquid-like behavior (viscosity of ∼50 Pa) while passing through the nozzle and a self-standing solid-like behavior (static yield stress of ∼364 Pa) right after being printed. This reversible liquid-to-solid transitional capability was quantified by viscoelastic complex moduli provided a dynamic yield stress (τy,G) of 210 Pa corresponding to the upright stacking up to ∼3.2 cm (3 wt% of ODA). The time (ty,G) required for conformational rearrangement was evaluated to be as fast as ∼10−2 s. After UV curing, the 3D printed layers exhibited no air pockets or weld lines at the stacked interfaces, which could guarantee excellent mechanical performance and structural integrity.

Suberin is an aromatic-aliphatic cross-linked polyester structure which constitutes cell wall structures of cork. It is particularly interesting for its use of monomeric compounds towards renewable bio-based polymers. In this study, the extraction of suberin monomers was successfully done by green method using alkaline hydrolysis combined with mechanical grinding. As the mechanical grinding was applied along with hydrolysis process, the maximum yield of depolymerized suberin monomer (DSM) with relatively low energy and less time was acheived. The polarity and functionality of DSM extracted in this study also showed higher values compared to conventional reflux hydrolysis process. Polyesterification and curing behavior of DSM were examined with molecular weights and mechanical properties of the ensuing polyesters. Tensile properties of suberin-based polyesters are reported for the first time that the maximum strength was found to be 7.3 MPa while Young‘s modulus was found to be 105 MPa. Furthermore, all natural cork composites were fabricated which comprise suberin-based polyester as matrix and lignocellulosic residue as reinforcement, and also reported their significantly enhanced tensile properties showing the great potential as an alternative green polymer composites for various engineering applications.

With a diffusion-assisted post-crosslinking method, polymer microspheres containing epoxy groups are crosslinked with ethylenediamine (EDA), gradually diffusing and reacting in the particles via amine/epoxy ring-opening reactions as confirmed by FT-IR and DSC results. Using a microcompression test, we find that the mechanical property (deformability under different applied force, breaking points, and recoverability) of the crosslinked microspheres is varied when different amounts of EDA are used in the system, resulting from different crosslinking density of the particles. An additional feature of the EDA treatment is to generate amine groups on the surface of the microspheres, enabling us to produce hybrid microspheres. We exploit them as immobilization sites for gold nanoparticles, forming gold-coated crosslinked microspheres. We also introduce a sequential functionalization method to fabricate crosslinked microspheres with selective functional groups on the surface. This approach can be a facile method to produce functional microspheres with controlled mechanical and surface properties.