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Micro-nano structure regulation of polyaniline and impedance-matching design of its composites are two crucial but challenging works in microwave absorption. In this study, an in situ sacrificial templates polymerization is applied to regulate the porous structures of polyaniline decorated on vapor-grown carbon fiber (VGCF). By manipulating porous polyaniline structures, heterogeneous interfaces, polarization centers, and geometric structures are introduced into porous VGCF@polyaniline nanohybrids. Porous VGCF@polyaniline demonstrated robust microwave absorption ability with a minimum reflection loss of − 55.9 dB at 10.3 GHz with a filler loading of 18 wt% and a thinner thickness of 1.33 mm. The investigation of the novel porous polyaniline structures and composition relationship suggest that the microwave absorption ability of porous VGCF@polyaniline is originated from the optimal impedance-matching ratio, enhanced dielectric loss, and synergistic effect, which is enhanced by conductive loss and interfacial polarization. A universal approach was proposed to address the critical issue of hybridizing porous VGCF@polyaniline with flexible polyurethane sponge as practical electromagnetic absorption structures. The hybrids exhibited interesting dual absorption properties with minimum reflection loss of − 28.8 and − 35.5 dB at frequencies of 8.5 and 8.7 GHz, respectively. This study provides a new approach for designing lightweight and practical microwave absorbers.

Highly aligned nonwoven vapor grown carbon fibre (VGCF) based polyurethane (PU) fibrous membrane (VGCF@PUFM) was fabricated by rotation spinning based on DMF-H2O exchange for directional microwave shielding. This VGCF@PUFM showed obviously different electrical conductivity and mechanical strength in parallel and perpendicular directions. Variational microwave shielding effectiveness (SE) could be observed by changing the rotation angles of VGCF@PUFM with vibrational direction of electromagnetic (EM) wave. There was the shielding difference more than 10 dB (above 20 dB in 0°, below 8 dB in 90°). Greater shielding effectiveness could be expected by enhancing the anisotropy of electrical conductivity of the VGCF@PUFM. In addition, oriented alignment of VGCF in fibre is promising for further improvement of the electrical conductivity in fibre direction.

A novel ternary nanocomposite of Fe3O4 functionalized porous biomass carbon decorated by aligned polyaniline (A-PANI/Fe3O4/PBC) was successfully fabricated by hydrothermal and in situ oxidative polymerization. The morphology and structure of the composite was characterized by X-ray diffraction, fourier transform infrared spectra, scanning electron microcopy, transmission electron microscopy, X-ray photoelectron spectra and vibrating sample magnetometer. The microwave absorbing properties of A-PANI/Fe3O4/PBC composite were investigated in the frequency of 2–18 GHz. The results indicated that the A-PANI/Fe3O4/PBC composite possess excellent microwave absorbing performance, and the minimum reflection loss can be up to −44.8 dB at 10.67 GHz, effective absorbing bandwidth (RL

Multi-layer graphene oxide (MLGO) coated shape memory polyurethane (MLGO@SMPU) with different layers was fabricated by multiple dipping for adjustable shape memory switching devices. The MLGO, which stacked together in parallel, evenly covered the surface of the SMPU. Stress strain testing indicated that the coating of GO improved the mechanical strength of these MLGO@SMPU composites in the stretching stage below the strain of approximately 6%. Adhesive force testing suggested that the first GO layer could adhere well to the SMPU surface, but the interaction force between GO layers was weak. The angle recovery ratio and time, bending recovery force, and angle fixity ratio of these MLGO@SMPU composites were evaluated using homemade evaluation apparatus. Results indicated that with the increase of GO layers from one to five layers, the MLGO@SMPU gave an angle recovery ratio reduced to 83.2%, recovery time decreased to 7.6 s, bending recovery force increased to 18.3 mN, and angle fixity ratio decreased to 83.3%. This novel and straightforward approach of dipping graphene oxide onto shape memory substrates for adjustable recovery ratio, time and force has the potential to be applied to smart switching devices including sensors and actuators.

Three-dimensional aerogel has been expected to be a promising candidate for lightweight absorber. Here, polypyrrole (PPy) aerogels with elasticity characteristic have been obtained via facile oxidative polymerization and freeze-drying techniques. The low density (54 − 61 mg/cm3) and mechanical strength (15.4 − 18.7 kPa at 50% strain) of the PPy aerogels can be achieved by adjusting the FeCl3/Py molar ratios from 1:1.5 to 1.5:1. And as a microwave absorber for the PPy aerogel (FeCl3/Py = 1:1.5, 10 wt% mixed with paraffin), at the thickness of 2 mm, the minimum reflection loss (RL) could reach − 55 dB at 14 GHz and the efficient bandwidth (RL ≤ − 10 dB, 90% absorption) is 5.5 GHz. Increasing the FeCl3/Py molar ratio to 1:1, the efficient bandwidth of the prepared PPy aerogel expands to 5.6 GHz. The high-performance microwave absorption properties and well mechanical capacities of the PPy aerogels highlight their potential application in the microwave absorbing systems.

Shape memory driving thickness adjustable graphite (G) micro-flakes@shape memory polyurethane (G@SMPU) sponge was fabricated by two-step dipping separately in G-dispersed aqueous solution and SMPU/THF solution for high-performance microwave shielding. The sponge exhibited an ultrahigh G loading ratio (G/sponge, wt/wt) up to 490 wt%. For the first time, dipping coating of SMPU onto the sponge was proposed, and the obtained G@SMPU sponge exhibited a good recovery effect at least above 90% after thorough compression. And also, the thickness could be adjusted by utilizing its shape memory property. For microwave shielding, G-9@SMPU and G-18@SMPU sponges achieved the shielding effectiveness over 20 and 30 dB, respectively. Moreover, varying thickness or compressing repeatedly even up to 100 times would not obviously decrease the shielding effect of the G@SMPU sponge. This suggests the steady distribution and adhesion of G micro-flakes inside the three-dimensional sponge substrate due to the fixing of SMPU.

In this study, a new design method for a three-dimensional hollow structure woven fabric was proposed and the effect of cellular size on the cushioning property of the fabric-reinforced polyurethane elastomer composite was investigated. The fabric structure was analyzed from a cross-section view and the theoretical equations for the warp and weft yarns were proposed, using the fabric layer and cellular size as parameters. Nine kinds of fabrics with different layers and cellular size were fabricated with a Jacquard loom and reinforced with polyurethane elastomer to yield fabric composites. Then the effect of cellular size on the cushioning property of the fabric composites was discussed. The results showed that upon increasing the cellular size, the cellular fabric composite exhibited lower compression resistance. Moreover, the stress at a strain of 65% and the energy absorbed in the loading process were increased with decreasing cellular size. Moreover, the compression resilience was also changed with the cellular size. It can be concluded that the cellular size had an important effect on the cushioning property of the fabric composite, which can be considered as a design parameter for cushion material based on its usages.

Glass fiber fabrics/hollow glass microspheres (HGM)–waterborne polyurethane (WPU) textile composites were prepared using glass fiber, WPU, and HGM as skeleton material, binder, and insulation filler, respectively, to study the effect of HGM on the thermal insulation performance of glass fiber fabrics. Scanning electron microscopy, Instron 3367 tensile test instrument, thermal constant analysis, and infrared thermal imaging were used to determine the cross-sectional morphology, mechanical property, thermal conductivity, and thermal insulation property, respectively, of the developed materials. The results show that the addition of HGM mixed in WPU significantly enhanced thermal insulation performance of the textile composite with the reduction of thermal conductivity of 45.2% when the volume ratio of HGM to WPU is 0.8 compared with that of material without HGM. The composite can achieve the thermal insulation effect with a temperature difference of 17.74 °C at the temperature field of 70 °C. Meanwhile, the tensile strength of the composite is improved from 14.16 to 22.14 MPa. With these results, it is confirmed that designing hollow glass microspheres (HGM) is an effective way to develop and enhance the high performance of insulation materials with an obvious lightweight of the bulk density reaching about 50%.

A facile method for fabricating intelligent microwave absorber of vapor grown carbon fibers/Polydimethylsiloxane-epoxy resin shape memory composites (VGCFs/PDMS-SMEP) was proposed to deliver intelligently tunable and broadband microwave absorption performance. The maximal absorption intensity was regulated by varying the deformation of the composites driven by the superior shape memory property of SMEP, where practical the minimum reflection loss (RLmin) reaches −55.7 dB at 16.0 GHz with the thickness of 2.0 mm. The effective absorption bandwidth (EAB) reached 9.8 GHz, which covered the whole applied frequency range (8.2–18.0 GHz). The intelligent microwave absorption performance of the sample was attributed to robust conductive loss and dielectric loss enhanced by the dipole relaxations and multi-reflections. Thus, VGCFs/PDMS-SMEP composites serves as the key that really opens up opportunity for the application as flexible, shape memory and tunable high performance broadband microwave absorption absorber in frontiers such as wearable electronic devices, chips protection, stealth technology and information security.

Over recent years, researchers have noticed that recovery rates of shape memory composites (SMCs) would vary due to the addition of fillers. So far, although several superficial reasons are discussed, a thorough analysis has not been presented yet probably due to the absence of a microscopic mechanism of SMCs. Here, a molecular mechanism of SMCs is clarified by identifying the differences lying in molecular motions of shape memory polymers and SMCs. On the basis of the molecular mechanism of SMCs, both a positive effect and a negative effect of fillers on recovery rates are revealed. Because interfaces between fillers and matrices play a decisive role in the two effects of fillers, several experiments are designed to verify the role of interfaces. The experimental results prove that the interfaces are benefit and harmful for recovery rates at the same time. Moreover, the results are able to qualitatively predict that the recovery rates of SMCs would increase or decrease with more addition of fillers.

A class of functional composites are compounded by piezoelectric particles and shape memory polymers, and the resultant composites perform both shape memory effect and piezoelectric effect. Although many kinds of piezoelectric composites have been developed, few papers report the effect of interfacial bonding between fillers and matrices on piezoelectric performances. Here, two groups of samples are investigated to clarify the role of interfaces in piezoelectric performances and permittivity properties. The experimental results testify that the samples with poor interfaces exhibit lower relative permittivity and are unable to show usable piezoelectric effect. The piezoelectric effect critically depends on interfacial bonding. Compared with pristine shape memory polymers, interfaces efficiently improve thermodynamics but influence the glass transition temperature very little. Moreover, shape recovery rates all reach at least 95% in the third cycle, even though decrease with the addition of fillers because of increasing interfaces.

To combine the piezoelectric effect and shape memory effect, various kinds of smart composites are developed through compounding lead zirconate titanate (PZT) particles with average diameters of 400 nm and shape memory polyurethane (SMPU) matrices. Compared with pristine SMPU, the resulting composites are enhanced by more than 133% in the maximum recovery stresses. Additionally, the film actuators made from these composites can generate 1 nm resolution displacements without any control method in a common laboratory environment when the step voltage signals are applied to them. This feature partly profits from the softness of SMPU matrices which, to some extent, protects PZT particles from ambient noise. Moreover, taking the advantage of shape memory effect easily deforms the film actuators into a variety of designed shapes. As a consequence, the shaped actuators are able to produce many more displacements while the positioning errors remain the same. The displacements of the “U” type actuator and the “Z” type actuator are respectively 18 nm (about 4.7 times displacement of the corresponding film actuator) at 840 V and 75 nm (about 13.3 times displacement of the corresponding film actuator) at 600 V. The proposed smart composites strongly show the potential to lower the requirements of nanopositioning and reduce costs.

In light of the rapid increasing demand for high-precision ultrasonic technologies for damage detection in composite structures, it is necessary to give a further study on the ultrasonic attenuation characteristics, with consideration of the combined effects of material anisotropy and viscoelasticity, and the frequency characteristics of the individual attenuation component. In the present paper, based on the time-domain finite element analysis of ultrasonic wave propagation in a two-layered fiber/matrix composite material, a new method is presented. In the method, by means of extracting the individual attenuation components (viscoelastic attenuation, scattering attenuation due to interface defects, and energy dissipation at the interface) from the overall attenuation respectively, the variation behavior of them with material anisotropy and viscoelasticity, and incident wave frequency, are quantitatively evaluated. The change of proportion of individual attenuation components in overall attenuation under different conditions are also investigated. From the results, the energy loss at the interface is always a major part in ultrasonic attenuation characteristics. Each attenuation component shows frequency dependence, especially the viscoelastic attenuation and energy dissipation at the interface. The simulation results also clarified the detailed effect mechanism of material viscoelasticity and anisotropy on the attenuation characteristics, which will encourage the further development of attenuation measurements for damage detection in composite structures.

In this paper, electrically actuated shape memory composites were prepared by compounding shape memory polyurethane (SMPU) with conductive antimony-doped tin oxide/TiO2 (ATO/TiO2) whiskers. The resultant composites, ATO/TiO2/SMPU, can be activated by electric voltages because of heating Joule and enhancement of heating efficiency by the conductive network resulting from the overlaps of whiskers. In addition to conductivity, ATO/TiO2/SMPU composites featured lighter color than most electroactive shape memory composites, which exhibit black color due to the addition of carbon materials. The composites exhibited uniform electrical resistance and rapid heat transfer performances. When the composites with 50 wt% ATO/TiO2 whiskers were used in a switch electric circuit as the switch, the circuit can turn off within 30 s. ATO/TiO2 whiskers improved Young's moduli by at least 390% and recovery stresses by more than 250% compared with pristine SMPU. Although the recovery rates were unsatisfactory in the first test cycle, composites with 40 wt% ATO/TiO2 whiskers and 50 wt% ATO/TiO2 whiskers still showed recovery rates higher than 96% and 94% in the third cycle, respectively. Keywords: Electrical actuation, Shape memory composite, Switch, Electric circuit, Morphing performance

In this study, a tube actuator was successfully fabricated by incorporating shape memory polyurethane (SMPU) with dibutyl adipate (DBA) plasticizer, which distinctly produces softness and glass transition temperature switching close to human body temperature. The plasticized SMPU tube was activated at 37 °C, which is faster than the pure SMPU tube. The effect of thermal triggering on tensile and viscoelastic properties was investigated. Adding DBA plasticizers to SMPU demonstrated a quicker recovery rate than pure SMPU during tube compression and expansion. In addition, according to thermomechanical analysis results, the shape recovery ratio of the DBA plasticizer-doped tube is up to 83%, and its shape recovery ratio during tensile deformation is up to 99%. Particularly, mouse cell adhesions and proliferation on SMPU-DBA gel provide biocompatibility and nontoxicity. The bio-based mechanical properties of the tube make sensing under human temperature control an appealing possibility. The developed tube actuators can be used as artificial blood vessels and in other clinical applications.

In this study, a new weaving technology with a modified heddle position system based on a self-built three-dimensional (3D) weaving loom is designed, and four typical 3D woven-structure textile groups are manufactured: layer-to-layer orthogonal weaving, through-thickness orthogonal weaving, layer-to-layer angle-interlock weaving, and through-thickness angle-interlock weaving. The new weaving technology has great potential for manufacturing various 3D woven structures effectively and efficiently. The fabricated 3D woven textile-reinforced epoxy-resin composites undergo quasi-static three-point bending tests to study the influence of the woven structure on the flexural performance and failure modes along the textile warp and weft directions. The composites along the weft direction (weft-direction beams) have a larger flexural modulus but smaller failure strain compared with the warp direction (warp-direction beams) for all woven-structure types. Among the designed 3D textile composites, the angle-interlock woven structures have a larger flexural strength (50%), modulus (40%), and failure resistance than have the orthogonal-woven structures. Overall, the through-thickness angle-interlock woven structure has the best flexural-failure resistance among all textile structures, and is the optimal structural design based on this modified weaving technology.

In this paper, an epoxy resin mixture composed of epoxy and phenol monomers is used to prepare thermoplastic epoxy polymer (EP-TP) through a polymerization reaction and shape memory thermoplastic epoxy filament (SMEF-TP) was successfully developed for the first time through a melt-drawing process. Tensile tests showed that the yield stress of the developed SMEF-TP reached 63 MPa, which is an increase of 54% compared with EP-TP films. Shape memory experiments showed that the developed SMEF-TP has excellent shape memory performance, with a shape fixation rate of 97%, a shape recovery rate of over 97%, and good stability in cycling. Based on the shape memory performance analysis, the shape recovery stress of the SMEF-TP was characterized. Shape recovery stress responded to temperature stability and increased with the increase of strain, reaching 1.45 MPa at a strain of 35%. The SMEF-TP can reach an energy density of 0.066 J/cm3 during thermal actuation and shows greater application potential when processed into textiles. In addition, the chemical structure, thermal performance, and dynamic mechanical performance of SMEF-TPs are analyzed. The developed SMEF-TP shows excellent shape memory performance, and the output shape recovery stress is more than 5 times that of EP-TP film, which provides huge application potential in the fields of artificial muscles and smart textiles.

The traditional approach toward improving the crystallization rate as well as the mechanical and barrier properties of poly(lactic acid) (PLA) is the incorporation of nanocelluloses (NCs). Unfortunately, little study has been focused on the influence of the differences in NC morphology and dimensions on the PLA property enhancement. Here, by HCOOH/HCl hydrolysis of lyocell fibers, microcrystalline cellulose (MCC), and ginger fibers, we unveil the preparation of cellulose nanospheres (CNS), rod-like cellulose nanocrystals (CNC), and cellulose nanofibers (CNF) with different aspect ratios, respectively. All the NC surfaces were chemically modified by Fischer esterification with hydrophobic formate groups to improve the NC dispersion in the PLA matrix. This study systematically compared CNS, CNC, and CNF as reinforcing agents to induce different kinds of heterogeneous nucleation and reinforce the effects on the properties of PLA. The incorporation of three NCs can greatly improve the PLA crystallization ability, thermal stability, and mechanical strength of nanocomposites. At the same NC loading level, the PLA/CNS showed the highest crystallinity (19.8 ± 0.4%) with a smaller spherulite size (33 ± 1.5 μm), indicating that CNS, with its high specific surface area, can induce a stronger heterogeneous nucleation effect on the PLA crystallization than CNC or CNF. Instead, compared to PLA, the PLA/CNF nanocomposites gave the largest Young's modulus increase of 350 %, due to the larger aspect ratio/rigidity of CNF and their interlocking or percolation network caused by filler-matrix interfacial bonds. Furthermore, taking these factors of hydrogen bonding interaction, increased crystallinity, and interfacial tortuosity into account, the PLA/CNC nanocomposite films showed the best barrier property against water vapor and lowest migration levels in two liquid food simulates (well below 60 mg kg-1 for required overall migration in packaging) than CNS- and CNF-based films. This comparative study was very beneficial for selecting reasonable nanocelluloses as nucleation/reinforcing agents in robust-barrier packaging biomaterials with outstanding mechanical and thermal performance.

Hollow silica spheres (HSS) have attracted considerable attention in recent years because of their unique physical and chemical properties, as well as can be used for wide range potential applications. In this study, a novel HSS was successfully synthesized via silica sol self-templated route and vacuum freeze-drying assistant method. The experimental results revealed that the HSS exhibited bowl-like and deflated balloon-like morphology structure and thin sphere shell was approximately 30 nm. The particle size of the HSS was almost between 0.20 and 2.50 µm. The possible mechanism for the formation of the HHS was discussed and proposed.

The scaffold which provides space for cell growth, proliferation, and differentiation, is a key factor in bone tissue engineering. However, improvements in scaffold design are needed to precisely match the irregular boundaries of bone defects as well as facilitate clinical application. In this study, controllable three-dimensional (3D) porous shape memory polyurethane/nano-hydroxyapatite (SMPU/nHAP) composite scaffold was successfully fabricated for bone defect reparation. Detailed studies were performed to evaluate its structure, apparent density, porosity, and mechanical properties, emphasizing the contribution of nHAP particles on shape recovery behaviors and biological performance in vitro. The effect of nHAP particles in porous SMPU/nHAP composite scaffold was found to enhance the compression resistance by 37%, shorten the compression recovery time by 41%, reduce the tensile resistance by 78%, reach the shape recovery ratio of 99%, and promote the cell proliferation by 13% after 7 days of culture. These results revealed that the 3D structure and aperture of as-prepared scaffold were controllable. And in minimally invasive surgery and bone repair surgery, this porous composite scaffold could significantly reduce the operative time and promote the bone cell growth. Therefore, this porous SMPU/nHAP composite scaffold design has potential applications for the bone tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 244-254, 2018.

This work is dedicated to a high-precision ultrasonic testing technology for dynamic mechanical evaluation of particle reinforced composite materials. The detailed ultrasonic wave propagation due to multi-reflection and scattering waves by particles and matrix viscoelasticity, especially the mutual interactions among particles, are systematically clarified. Through a unique material evaluation method, Ultrasonic Dynamic Mechanical Analysis (U-DMA), the dynamic viscoelasticity of particulate composites with different types and contents of particles are measured directly in high frequency domain. Furthermore, based on the experiment data, the ultrasonic propagation behaviors are detailedly investigated by a newly developed time-domain finite element analysis code, Pzflex, for investigating the detailed mechanisms of particles. The results clarify that the particle interactions are playing a major role in ultrasonic wave propagation and attenuation properties, which can significantly affect the viscoelastic characteristics of developed particulate composite materials. And the feasibility and effectiveness of U-DMA are verified from both simulation and practical experiments.

Damages such as fiber breakage and delamination are likely to occur inside CFRP composites when subjected to external forces, such as impact and fatigue load. These damages are mostly invisible and cause safety hazards during the service of the products. This study proposes a new type of nondestructive testing (NDT) method using electromagnetic wave (EMW) technique, EMW-NDT. It was proven that the proposed EMW-NDT method is effective in detecting damages such as delamination, crack or other defects in CFRP composites. The EMW-NDT method's detection capacity to the delamination size, delamination thickness, and slits in CFRP composites was investigated. A reasonable sensitivity to the damage volume change in delamination was confirmed with a damage area ratio of 12.6%/dB and a thickness change of 5.5 dB/mm. It was found that the incident angle of the EM wave plays a vital role in detecting sensitivity because of the skin effect in CFRP composites. The results confirmed that the proposed method demonstrates good detection sensitivity to delamination size and thickness. In terms of crack damage, the slit and its length were detected and the slit direction was successfully identified in this study based on the characteristics of the electromagnetic interference (EMI) shielding anisotropy in CFRPs. Moreover, the proposed EMW-NDT method with specified designed free-space measurement system is contactless, and no coupling medium is required; thus, it exhibits huge potential to be widely used as a new damage detection technique for CFRP composites.

Energy expenditure in buildings and transportation is about 63% of all global energy consumption, making them major targeted sectors for energy conservation and carbon dioxide (CO2) emission reduction. To save energy in cooling of automobiles and buildings, transparent passive-cooling films with 90-nm-diameter zinc oxide (ZnO) particles dispersed in low density polyethylene were manufactured. These films filter out the high-energy region of visible light (Vis), block ultraviolet (UV) light, and allow infrared light to pass through by utilizing light scattering due to nanoparticles (NPs) and refraction from lamellar crystals in the film. Transmissivities of the films decrease as NP concentration, film thickness, and crystallinity increase. Passive-cooling performance tests show that the films have a temperature reduction (ΔT) of up to 14.95 °C around midday, which is substantially better than that reported for similar films. The volume involved in the passive-cooling test is found to be critically important. ΔT initially declines exponentially and then levels-off as the enclosed volume to window area ratio, or specific volume (SV), increases. An empirical model is proposed for the relationship between ΔT and SV for more appropriate measurements of passive-cooling performance. SVs of passenger cars and office buildings are located within the most sensitive range of the ΔT-SV curve of the fabricated films.

The proposed 3D orthogonal woven ramie/Kevlar reinforced poly (lactic acid) composite in this paper is a new type composite in which the 3D orthogonal structure has great advantages of high impact and delamination resistance due to the Z yarns and the hybridization of natural and manmade fibers provides not only partial environment friendly benefit but also efficient compensation for the relatively low mechanical properties from pure natural fibers. Eight types of the aforementioned composites were designed and fabricated. The results showed that as the volume fraction of Kevlar was increased, the tensile properties showed increasing trends, while the flexural properties were predominantly dependent on the fabric structures, especially, the weft yarns properties in the first and second layers from the upper and bottom surfaces. Furthermore, the impact strength was enhanced as the volume fraction of Kevlar increased to 5.5% and leveled off when Kevlar yarns continuously increased.

Shape memory polymers (SMPs) have received great attention and scientific interest in widespread technological development during last few decades. Besides the development of novel SMPs, various techniques have been practiced for characterization of shape memory effect (SME) of SMPs. In this study, the shape memory effect and recovery stress property of the carbon nanotube (CNT)/waterborne epoxy (WEP) nanocomposites below and above the glass transition temperature (Tg) of the nanocomposites and under isostrain and isostress were systematically investigated via thermal mechanical analysis (TMA), respectively. The experimental results showed that the nanocomposites exhibit excellent shape memory effect. The shape memory fixity and recovery ratios were approximately 100% even below glass transition temperature (Tg). A remarkable point is that the strain of the nanocomposites suddenly increased with the temperature decreasing in a certain period of the heating-cooling cycles under isostress condition and the strain increment increased with temperature in general. Especially at low temperature, the recovery stress was very sensitive to temperature under isostrain condition of ±0.25 °C temperature with differential of 25.5 °C developed pressure difference of 0.20 MPa. Moreover, TMA is a practical method for quantifying the SME and recovery stress properties of SMPs and their composites.

Plasma-electrolytic oxidation (PEO) is a corrosion prevention technique which produces a protective oxide layer on a metal surface by high-voltage oxidation to increase its corrosion resistance. Traditionally, PEO processing on a magnesium alloy surface has been investigated via the voltage-time response measured during the treatment. Thus far, the information extractable from voltage-time measurements has been limited due to the sporadic nature of coating evolution. The current study presents a new approach to examine the mechanisms governing PEO coating formation and the subsequent influence of process parameters. The instantaneous voltage-time response has been recorded and analyzed using a statistical approach. Combining the voltage-time measurements with structural analysis (XRD/SEM/EDX), a multi-step coating formation mechanism has been proposed. The first stage of the treatment process was similar to traditional anodization. When the voltage was sufficiently high to induce dielectric breakdown of the existing oxide material, plasma discharging occurred and a silica containing layer was formed. Two predominant types of discharge governed the oxidation process; discharge through deep pores, and discharge through micro-voids. Increasing the current density proportionally accelerated the rate of oxide development. Increasing the temperature of the electrolyte resulted in thinner coatings due to an increased oxide dissolution rate. From an application point of view, the PEO coating process can be accelerated by choosing a high current density, but the problem of localized heating by the discharges must be addressed to avoid severe dissolution of coating.

An analytical solution is proposed for the low velocity impact response of laminated plates with an elastic medium layer. In the theoretical model, the medium materials between laminated plates are considered to be a spring model with elastic constants. The influences of impactor parameters such as velocity and mass on the impact response are investigated based on the proposed model and a numerical simulation. The simulation result shows that the impact response of two-layer laminated plates is quite different when a medium layer is inserted into the laminated plates. Impact loads acting on the laminated plate significantly decrease due to deformation energy absorption by the elastic medium layer in laminated plates.

Polymer melt blending has become a main and important method to modify polymer materials for overcoming defects and obtaining excellent performance. The mechanical properties, compatibility, tribological properties and modification mechanisms of polyphenylene sulfide (PPS) alloys have been investigated over the last decades. However, there are few researches on PPS/polyvinylidene fluoride (PVDF) alloys, and material researchers have paid little attention to the manufacture and properties of PPS/PVDF alloys. In our research, the morphology, thermal properties and mechanical properties of PPS/PVDF alloys were first studied. PPS/PVDF alloys were prepared by a simple polymer melt blending. Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the morphology of PPS/PVDF alloys. It was found that the PPS/PVDF alloys had a “sea-island” structure with a poor adhesion at the interface between the PVDF phase and PPS matrix. The addition of PPS may also promote the transformation of α-phase to β-phase in PVDF. The thermal properties of PPS/PVDF alloys were confirmed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It indicated the addition of PVDF would accelerate the crystallization of PPS and increase the crystal perfection of PPS. It was clearly that the thermal stability of PPS/PVDF alloys could be improved by the addition of PVDF especially when the PVDF content is lower than 20 wt %. When the content of PVDF was only 5 wt %, the tensile strength and tensile modulus of PPS/PVDF alloys had a significant improvement compared with pure PPS. Furthermore, it was also found that the addition of PVDF could also increase breaking elongation rate in a small degree.

Agricultural wastes such as rice husks (RHs) are valuable due to their feasibility to be converted into carbon materials, low cost, and abundancy in contrast to the conventional carbon material sources. In this study, RHs are carbonized at various temperatures from low to high temperatures, and their electromagnetic (EM) wave absorption properties are evaluated. Carbon materials, silicon carbide (SiC) whiskers, and SiC particles are obtained from RHs carbonized at 1500 °C (CRH1500) for 0.5 h with presence of Ar gas at 1 atm. In order to evaluate their EM wave absorption performance, complex permittivity and permeability are measured by using vector network analyzer, and the values are utilized in the reflection loss (R.L.) calculation according to the transmission line theory. CRH1500, 40 wt% with thickness of 1.6 mm exhibits minimum R.L. of ≈−55.4 dB (>99.9997% absorption) at 11.37 GHz and response bandwidth (R.L. < 10 dB, > 90% absorption) of 4.21 GHz. Low‐cost and abundant RHs, carbonized at various temperatures, show significant absorption performance. Their absorption performance and response bandwidth are highly dependent on matching thickness, indicating that they can be easily modulated for promising electromagnetic wave absorber materials.

Gradient vapor grown carbon fiber (VGCF) based shape memory polyurethane foam (VGCF@SMPUF) was fabricated by alternate dipping in a gradually diluted VGCF@SMPU/DMF solution and distilled water for shape memory driven microwave shielding. Shape memory performance for this VGCF@SMPUF was achieved by heat transfer of thermally conductive VGCF. Shielding effectiveness (SE) was adjusted through different degrees of angle recovery. A consistent shielding effect from either side indicated that electromagnetic reflection may take place at both the surface and inside of the non-homogeneous composite shield. For shape memory effect, hot compression made this VGCF@SMPUF achieve a faster recovery time and higher recovery ratio owing to improved thermal conductivity. Moreover, VGCF@SMPUF, which was bent to the positive side (PS) with a higher VGCF content, showed shorter recovery time and higher recovery ratio than that bent to the negative side (NS) with a lower VGCF content. We attribute this result to the relatively small mechanical compression strength of the negative side with the lower VGCF content at the bending point when expanding from the positive side. Furthermore, hot compression obviously improved the shielding effectiveness of the VGCF@SMPUF, mainly through a considerable increase of the electrical conductivity. The VGCF@SMPUF hot compressed to a thickness of 0.11 mm achieved a SE value of ∼30 dB, corresponding to a shielding efficiency of ∼99.9%.

Poly(ethylene terephthalate) (PET) fabric-reinforced polyvinyl chloride (PVC) composites have a wide range of applications, but the interface bonding of PET fabric/PVC composites has remained a challenge. In this work, a new in-situ SiO2/tributyl citrate sizing agent was synthesized according to the principle of &ldquo, similar compatibility.&rdquo, The developed sizing agent was used as a PET surface modifier to enhance the interfacial performance of PET fabric/PVC composites. The morphology and structure of the PET filaments, the wettability and tensile properties of the PET fabric, the interfacial adhesion, and the tensile and tearing properties of the PET fabric/PVC composites were investigated. Experimental results showed that many SiO2 nanoparticles were scattered on the surface of the modified PET filaments. Moreover, the surface roughness of the modified PET filaments remarkably increased in comparison with that of the untreated PET filaments. The contact angle of the modified PET filaments was also smaller than that of the untreated ones. The peeling strength of the modified PET fabrics/PVC composites was 0.663 N/mm, which increased by 62.50% in comparison with the peeling strength of the untreated ones (0.408 N/mm). This work provides a new approach to the surface modification of PET and improves the properties of PET fabric/PVC composites.

Continuous carbon fiber reinforced polymers (CFRP) composites, particularly prepreg stacked composites, have anisotropic properties, including anisotropy of electrical conductivity and dielectric characteristics. These features lead to electromagnetic interference (EMI) shielding anisotropy of the CFRP. The coaxial transmission line method was used to test the EMI shielding of CFRP to clarify the EMI shielding anisotropy of CFRP. Moreover, the optimization of EMI shielding performance of CFRP by changing the composites’ structure were also investigated systematically. The anisotropy of EMI shielding was confirmed for the first time by the coaxial transmission line method. The results showed that a quasi-radial sample had the highest shielding effectiveness (25.8 dB) at 15 GHz, and the carbon fibers in this sample aligned in the direction of the electric field of electromagnetic waves. The orientation of fibers relative to the direction of electric field clearly affected the EMI shielding performance of the CFRP composites. The four-ply CFRP (0°/90°/0°/90°) with three cross-layers had the excellent shielding value of 28.9 dB at 15 GHz, that was far superior to that of a unidirectional CFRP (0°/0°/0°/0°) composite (SE = 18.6 dB), and it even outperformed an eight-ply unidirectional CFRP composite (SE = 22.6 dB). Laminated structures governed SE, and the number of cross-layers in the composites improved their EMI shielding performance. The shielding mechanisms of cross-layer CFRPs were also discussed and clarified based on both experimental and theoretical analysis. We believe that these findings could provide a scientific basis and potential in designing high-performance EMI shielding materials.

The energy harvesting performance of the shape memory materials (SMM) depends on the recovery rate and recovery force of SMM. In this work, the shape memory vapor grown carbon fiber/graphene oxide/epoxy (VGCF/GO/EP) were prepared, and the thermodynamic coupling behaviors and the energy harvesting property of the composites were investigated via homemade evaluation apparatus, respectively. The experimental results showed that the addition of VGCF-GO fillers can effectively improve the thermal response recovery rate of EP in the stretching stage below the strain of approximately 10%. At 10% pre-strain, the maximum thermal response recovery rate of the VGCF/GO/EP composites was 57%, 158%, and 22% higher than that of the pristine EP, GO/EP composites, and VGCF/EP composites, respectively. The synergistic effect of VGCF and GO significantly improves the output work of the EP films, and the VGCF/GO/EP composite films can easily lift 300 g weight under 30% pre-strain. Especially under 100 g load, the VGCF/GO/EP composite films can stably output up to 275 J kg−1 work in the heating and cooling cycle (40 °C–95 °C). Furthermore, the VGCF/GO/EP composite films and piezoelectric ceramic (PZTC) were combined to form a thermal energy collector, which realized the conversion from thermal energy to electrical energy. The thermal energy collectors can output 1.5 V peak voltage under the ambient temperature change of 40 °C–90 °C.

To investigate the influence of cross-linking/sulfonation on the viscosity stability, adhesion, film properties and desizability of corn starch for ameliorating its end-use ability in application of warp sizing, a series of itaconic acid cross-linked and sulfonated starch (IACLSS) samples with different levels of cross-linking (LCL) and degrees of substitution (DS) were synthesized by the cross-linking of acid-converted starch (ACS) with itaconic acid (IA) and subsequent sulfonation with NaHSO3. The apparent viscosity and viscosity stability were determined and adhesion was evaluated using a standardized method (FZ/T 15,001–2008). Film properties were also estimated in terms of tensile strength, breaking elongation, bending endurance, and moisture regain and the desizability of the IACLSS samples was investigated by measuring the time required to break the films in hot water. The experimental results showed that cross-linking/sulfonation was capable of improving the viscosity stability of cooked starch paste, enhancing the adhesion of starch to cotton and polyester fibers, increasing breaking elongation, bending endurance and moisture regain of starch film as well as decreasing its tensile strength, thereby stabilizing paste viscosity, ameliorating the adhesion to fibers and diminishing film brittleness. In addition, modification could reduce the time required to break the films in 80 °C water, indicating that modification favored the desizing of starch in hot water. Increasing sulfonation levels whilst decreasing the LCL values favored improvement in stability and desizability, enhancement in the adhesion to cotton and polyester fibers, and decrease in brittleness. The IACLSS showed potential in the applications of cotton and polyester sizing.

In recent years, shape memory polyurethane (SMPU) as a smart material has been used in various applications owing to its desirable shape memory effect and biocompatibility. In this study, unidirectional SMPU nanofibers are innovated by electrospinning to clarify the mechanical and shape memory properties with nanofiber directions. The results showed that when the nanofiber alignment degree is 0° (parallel to the tensile direction), the aligned SMPU nanofibers achieved the obvious improvement of tensile strength (increased to 135%) and elastic modulus (increased to 313%), compared with the random SMPU nanofiber. Moreover, the developed aligned nanofibers exhibited good ability against stress relaxation and creep under constant strain or constant stress conditions in cyclic loading. The aligned SMPU nanofibers with a 0° alignment degree exhibited excellent shape memory properties with shape recovery rates larger than 93% and shape fixity rates larger than 90%, and a dramatic increase of shape recovery stress.

In this study, flexible energy harvesters based on lead zirconate titanate (PZT)/shape memory polyurethane (SMPU) nanofibers were prepared and made wearable for energy harvesting from human body movements while ensuring flexibility. The results obtained showed that there is a relationship between the piezoelectric and energy harvesting properties of the proposed PZT/SMPU energy harvesters, and the alignment degrees and motion modes. The 0°-aligned energy harvester—wherein nanofibers are parallel to the longitudinal direction—showed higher piezoelectric properties and induced higher output voltages because of the bending motion compared to nanofibers aligned randomly-, at 90°-, and at 45°-. Practical tests showed that flexible energy harvesters can efficiently convert mechanical energy into electricity when subject to different body motions such as bending, twisting, and applied pressure. The maximum output voltages generated by energy harvesters with 0°- and 45°-aligned nanofibers were 537 and 55 mV when they were subjected to finger bending and wrist twisting motions, respectively; this represents an increase of at least 28% compared to that of other samples. Therefore, these findings provide insights and strategies related to the optimal arrangement of nanofibers in wearable energy harvesters and improvement in their energy harvesting efficiency with respect to different body part motions.

In this work, shape memory materials were developed for use as soft actuators. Shape memory polymers (SMPs) generally demonstrate good actuation on direct thermal heating. Here, we also demonstrate SMPs with good electric actuation via the incorporation of dibutyl adipate (DBA) plasticizers with shape memory polyurethane to form an SMP gel, which is a soft dielectric material. The effect of the plasticizer on the shape memory behavior under thermal stimulus was investigated. The SMP gel had faster shape recovery than the pure SMP and almost fully recovery. A dielectric SMP actuator was prepared and its two-way shape deformation of contraction and expansion, were investigated over 6 electric on-off cycles. The largest contraction reached 6.76 % with an electric field of 34.24 V/μm. The developed dielectric elastomer actuator displayed a multifunctional response to thermal and electric stimuli. This material has potential for alternative actuation applications including biomaterials.

To improve the interfacial performance of carbon fiber (CF) and epoxy resin, the surface of CF was modified using magnetron sputtering technology, and a CF epoxy resin (CFER) composite was prepared using injection molding technology. The influence of magnetron sputtering technology on the surface properties of CF was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and dynamic contact angle analysis (DCAA). The influence of the surface modification of the CFs by magnetron sputtering on the mechanical and interfacial properties of CF composites was analyzed by testing the tensile and bending properties of the CFER composites. The results indicated that the surface morphology of CF can be modified by magnetron sputtering, and a nano sized carbon film was deposited on the surface of the CFs. The morphology of the carbon film on the surface of the CFs was different from that on the silicon pellet. The surface roughness of the CF increased after it was modified by magnetron sputtering. The surface wettability of the CFs may be improved by increasing the surface free energy of the fiber owing to the deposition of the carbon film. Tests of the tensile and bending properties of the CFER composites showed that the surface modification of CFs by magnetron sputtering can effectively improve the mechanical properties of the CFER composites, which not only improves the tensile strength and bending strength, but also increases the tensile modulus and bending modulus. The SEM images showed that the interfacial adhesion between the modified CF and the epoxy resin was significantly improved. The stress–strain curves showed that the failure mode of the CFER composite modified by magnetron sputtering CF surface changed, and a stress yield phenomenon was observed.

When ultrasonic waves propagate in composite materials, the propagation behaviors result from the combination effects of various factors, such as material anisotropy and viscoelastic property, internal microstructure and defects, incident wave characteristics and interface condition between composite components. It is essential to make it clear how these factors affect the ultrasonic wave propagation and attenuation characteristics, and how they mutually interact on each other. In the present paper, based on a newly developed time-domain finite element analysis code, PZflex, a unique approach for clarifying the detailed influence mechanism of aforementioned factors is proposed, in which each attenuation component can be extracted from the overall attenuation and analyzed respectively. By taking into consideration the interrelation between each individual attenuation component, the variation behaviors of each component and internal dynamic stress distribution against material anisotropy and matrix viscosity are separately and quantitatively evaluated. From the detailed analysis results of each attenuation component, the energy dissipation at interface is a major component in ultrasonic wave attenuation characteristics, which can provide a maximum contribution rate of 68.2 % to the overall attenuation, and each attenuation component is closely related to the material anisotropy and viscoelasticity. The results clarify the correlation between ultrasonic wave propagation characteristics and material viscoelastic properties, which will be useful in the further development of ultrasonic technology in defect detection.

In the present study, the effect of epoxy-graft-polyoxyethylene octyl phenyl ether (EP-g-TX100) on the processing and properties of the novel carbon nanotube (CNT)/water-borne epoxy (WEP) triple-shape memory nanocomposites was investigated. Generally, common epoxy or CNT/epoxy nanocomposites only possess dual-shape memory effect (DSME) that can remember only one temporary shape. In addition, CNTs aggregation and chemically inactive surface have remained a vexing problem that limits CNTs in composite application. In order to obtain excellent CNT/epoxy triple-shape memory effect (TSME) nanocomposites prepared via environmental friendly approach, EP-g-TX100 was synthesized and introduced to the CNT-epoxy system as a reactive emulsifier for epoxy emulsion, a non-covalent dispersant for CNTs, and a new reversible phase for TSME epoxy system. The multifunction self-made TX100-dangled epoxy surfactant for preparing CNT/epoxy TSME nanocomposites was first reported. The experimental results show that EP-g-TX100 had a good emulsifying ability to emulsify epoxy in water. CNTs were homogenously dispersed and well incorporated into WEP matrix and significantly improved the mechanical properties of the CNT/WEP nanocomposites. The final nanocomposites exhibited excellent TSME as we expected.

A new method to evaluate dynamic stress distribution of composite materials is presented using ultrasonic wave propagation analysis. In this method, a two-dimensional bimaterial composite with elliptical defect is modeled by using finite element analysis software. Based on elastic wave propagation analysis, the deformation and dynamic stress fields against different material properties are simulated. As the material properties change, the stress distribution at free edge and interface also change causing different stress wave propagation behavior. By investigating the dynamic stress distribution, the interaction of stress singularities at free edge, mode conversion at interface and wave propagation is clarified. The simulation results show that ultrasonic wave propagation analysis is a convenient and effective way to evaluate the correlation between material properties, stress singularities and dynamic internal stress distribution in composite materials.

The electromagnetic wave absorption properties of single- and double-layer silver nanoparticle/carbon nanotube (Ag/CNT) nanocomposites were evaluated. The reflection loss (R.L.) of the samples was calculated based on the measured complex permittivity and permeability. The double-layer composites constructed from CNT 30 wt.% and Ag/CNT 30 wt.% with total thickness of 3.3 mm showed a minimum R.L. of ∼−52.9 dB (over 99.999% absorption) at 6.3 GHz. The bandwidth of reflection loss less than −10 dB was observed at 3 regions, with wideness of 3.5, 0.8, and 1.5 GHz. Thin absorber with large R.L. and wide response bandwidth at low and high frequency regions can be obtained with double-layer composites. The capability to modulate the absorption and bandwidth of these samples to suit various applications in different frequency bands indicates that these nanocomposites could be an excellent electromagnetic wave absorber.