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Highly sensitive and flexible capacitive sensors are in great demand for wearable electronics, which can be achieved by preparing micropatterns on their dielectric layer surface. However, most micropatterns are often molded with the silicon template acquired by complex processes which are very time-consuming and costly. Here, a dielectric layer with micropatterned arrays was prepared on the thermal plastic polyurethane (TPU) film with the help of a hot-air-gun, then assembled with an ITO/PET electrode to develop a capacitive sensor with a sandwich structure. The capacitive sensor based on TPU/ITO/PET composites exhibits sensitivity of over 0.026 kPa−1, shorter response/recovery time of 99 ms, wide working range (0–13 kPa) and remarkable stability over 5000 cyclic pressing or bending. Interestingly, such sensor can monitor various physiological signals of people (e.g., voice signal, finger bending and breath). More importantly, it can distinguish different sign languages according to capacitive changes in the case of different finger gestures. The method proposed in this study will paves a new avenue for the facile preparation of micropatterned surface to improve the performance of flexible capacitive sensors. The present work represents a facile and efficient method to achieve capacitive sensor that can not only exhibit excellent sensing performances, but also it can detect a series of physiological signals and realize sign language interpretation. [Display omitted] • A cost-effective method is proposed to fabricate micropatterned surface. • Micropatterned capacitive sensor has remarkable sensing performances. • Capacitive sensor can monitor various physiological signals in the body. • Capacitive sensor can realize sign language interpretation. [ABSTRACT FROM AUTHOR]

To explore the possibility of using surface coating to reduce environmental stress cracking (ESC) of transparent polycarbonate (PC) parts, silicone coated and SiO 2 coated PC were tested in a self-made three-point bending apparatus in the presence of ethanol. The variation of stress with time was recorded, and the surface cracking was observed to evaluate the ESC resistance of samples. Slower stress relaxation rates and fewer surface cracks indicated that silicone coating improved the ESC resistance of PC, but SiO 2 coated PC was found to be no better than that of uncoated PC. Silicone coating reduced the absorption of ethanol in PC, weakening the surface plasticization, thus hindering the formation and development of cracks in PC. Nanoindentation test results showed that the mechanical properties such as hardness and elastic modulus of silicone coating are a better match for PC than SiO 2 coating. This allows the silicone coating to have a favorable effect in providing continuous protection for PC under the combined action of ethanol and stress. [ABSTRACT FROM AUTHOR]

The influence of crystalline memory effect on poly(lactic acid) (PLA) crystallization was probed by time-resolved Fourier transform infrared spectroscopy (FTIR). The melt with different degrees of order was prepared by melting at various temperatures. The vibrational changes associated with inter- and intra-chain interactions during crystallization were monitored. In the initial period of crystallization, the order of intensity changes is as follows: 1458 cm −1 > 1210 cm −1 ≫ 921 cm −1 , 1458 cm −1 > 1210 cm −1 > 921 cm −1 , and 1458 cm −1 > 1210 cm −1 ∼ 921 cm −1 for PLA melted at 190, 170, and 168 °C, respectively. With increasing the degree of order, both the formation of skeletal conformational-ordered structure and, especially, the 10 3 helix structure are accelerated. The influence of memory effect on the crystallization kinetics was also discussed based on the Avrami model. [ABSTRACT FROM AUTHOR]

Melt-stretched isotactic polypropylene (iPP) filled with different weight fractions (0, 0.1, 0.2 and 0.4 wt %) of β-nucleating agent (β-NA) was extruded via a single screw extruder with a slit die and immediately melt-stretched at the die exit. The microstructure and mechanical properties (i.e., monotonic tensile, step-cycle and stress relaxation behavior) of these samples were analyzed. Unexpectedly, the lamellar branching of β-crystal, which is similar to lamellar branching of α-crystal, is observed in melt-stretched β-nucleated iPP. More interestingly, it is found that, compared with other samples, iPP containing 0.2 wt % of β-NA has the best mechanical properties. Through thorough analysis of various structural characterizations, the improved tensile strength obtained from step-cycle tests and viscous force obtained from stress relaxation measurements for iPP with 0.2 wt% of β-NA is ascribed to lamellar branching of β-crystal. The study is an example of preparing high performance polymers via practical polymer processing methods. [ABSTRACT FROM AUTHOR]

In this letter, both the viscoelastic and electrical properties of poly(methyl methacrylate)/carbon black (PMMA/CB) nanocomposites with different CB concentrations prior to and after annealing were investigated. The linear steady-state recoverable compliance of pure PMMA is independent of annealing as it reflects only polymer-polymer interactions. While the conductivity of PMMA/CB nanocomposites increases gradually with annealing, and the viscoelastic properties show different regions of response depending on the CB concentration. At CB contents below the percolation threshold the recoverable compliances increase after annealing, whereas the reverse trend is found at CB contents above the percolation threshold. This behavior is related to the interplay between network formation and particle-particle interactions. [ABSTRACT FROM AUTHOR]

The strain sensing behavior of multi-walled carbon nanotubes (MWCNT)/epoxy (EP) conductive composites subjected to tensile strain was studied in detail. With increasing the load to rupture, the responsivity (ΔR/R 0 , R 0 is the original resistance, ΔR is instantaneous change in resistance) increased in a linear fashion and then began to decrease at a critical strain ( ε c ), which was remarkably different from the thermoplastic conductive composites only with a monotonic increase of the responsivity. It was attributed to the decrease of the nanotube contact points, the increase in the gaps before ε c , and the reorientation and violent alignment of nanotubes in the zones of high local deformation (after ε c ). In addition, when the extension-retraction cycles were applied, the values of max ΔR/R 0 showed a distinct tendency with different strains around the ε c . These behaviors were attributed to the competition of network destruction and reconstruction during the cyclic deformation. The mechanism of this unique sensing behavior was proposed as well. [ABSTRACT FROM AUTHOR]

Flexible and wearable strain sensors based on conductive polymer composites (CPCs) for human motion detection have been highlighted recently. Herein, two flexible conductive composites were fabricated by mixing matrix polydimethylsiloxane (PDMS) with zero-dimensional conductive filler carbon black (CB) and one-dimensional carbon nanotubes (CNTs), respectively. A low percolation threshold of CB/PDMS (0.48 vol%) was achieved, while this value was higher than that of CNTs/PDMS (0.13 vol%). In strain-dependent response tests, compared with CNTs/PDMS with a gauge factor ( GF ) of 4.36 (a strain of 10%), CB/PDMS composites showed a higher sensitivity with a larger GF of 15.75 (a strain of 10%). A good reproducibility was obtained in stretching-releasing process for the two composites. In long-term cyclic test, CB/PDMS showed more stable sensing behaviors, while a slight drifting and fluctuation was observed for CNTs/PDMS. Generally, two composites both possessed satisfactory durability. Mathematical models were proposed to explain the mechanism of the distinct strain sensing behaviors. A smart glove was assembled to monitor the finger motion to evaluate the application of the two composites as flexible strain sensors. [ABSTRACT FROM AUTHOR]

To explore the effect of physical aging on environmental stress cracking (ESC) behavior of polycarbonate (PC), sub-T g annealing was utilized as a method for accelerated aging. Injection molded samples were annealed at 130 °C for different time varying up to 96 h. A three point bending apparatus was used to evaluate critical stress for crazing and to record the variation of stress with immersion time at constant strain. The ESC results indicated that the critical stress for crazing initiation of PC in ethanol is increased by sub-T g annealing. However, the resistance of annealed PC to ESC with immersion time during the stress relaxation test depends on the level of initial stress. When a relatively low initial stress was used, a short time (24 h) of sub-T g annealing reduced the stress relaxation rate and decreased the number of cracks on the surface of PC. However, under higher initial stress, the stress relaxation rate of PC had a slight change only when the annealing time was prolonged about threefold (72 h). This can be explained by the formation of cohesional entanglement sites during the sub-T g annealing process, which was demonstrated by the thermal and dynamic mechanical tests. [ABSTRACT FROM AUTHOR]

Isotactic polypropylene (iPP)/glass fiber (GF) composites with different specific interfacial features ( viz ., α-spherulite, α-cylindrite and β-cylindrite) were prepared via shear-induced interfacial crystallization. α-spherulite, α-cylindrite and β-cylindrite were successively encouraged at the interface between iPP matrix and GF with increasing the fiber-pulling speed. Moreover, the composite specimens containing β-cylindrite exhibited remarkably higher interfacial shear strength (IFSS) than those containing α-spherulite or α-cylindrite, as demonstrated by the single fiber fragmentation test (SFFT). More interestingly, simultaneously improved tensile strength and toughness were observed in the presence of β-cylindrite. This study offers a new insight that β-cylindrite produced by shear is an alternative approach to achieve comprehensive mechanical properties for the iPP/fiber composite systems. [ABSTRACT FROM AUTHOR]

The electrically conductive nanocomposites composing of different concentrations (0.05–1.5 wt%) of reduced graphene oxide (RGO) in the thermoplastic polyurethane/polypropylene (TPU/PP, 55/40) matrix with a fine co-continuous structure were fabricated by solution-flocculation and melt-mixing process using a micron twin-screw extruder. Both thermodynamic and kinetic theoretical analysis predicated the preferential location of RGO in the TPU rather than PP phase. Both optical microscope and field emission scanning electron microscopy (FESEM) observations verified this theoretical dispersion predication. The homogeneous dispersion of RGO in the TPU matrix is confirmed by wide-angle X-ray diffraction (WAXD) patterns and transmission electron microscope (TEM) observation. A very low percolation threshold of 0.054 wt% was achieved owing to high conductivity of RGO and favorable double percolation effect. The tensile strength and elongation at break of the composites with RGO content of only 0.5 wt% were improved by 341.9% and 354.3%, respectively. The present work provides a guideline for an efficient, facile fabrication technique of graphene based conductive polymer nanocomposites with high electrical conductivity and improved mechanical properties. [ABSTRACT FROM AUTHOR]

With the rapid development of new-generation wireless communication technologies and portable intelligent electronic devices, the development of composites with excellent thermal conductivity and electromagnetic shielding properties has become an urgent challenge. In this work, a unique fibers-induced segregated-like structure strategy for fabricating thermoplastic polyurethane/polydopamine/silver (TPU/PDA/Ag) composites film with high thermal conductivity (TC) and excellent electromagnetic interference (EMI) shielding performance is demonstrated via electrospinning-electroless depositing-pressing technology. The TPU/PDA/Ag composites film exhibit excellent in-plane TC of 20.9 W/(m⋅K) at 75 wt% Ag loading, which shows excellent thermal management capability as heat spreaders of high-power light-emitting diode (LED) modules in practice. Meanwhile, the composites film presents outstanding EMI shielding efficiency of 109 dB (8.2–12.4 GHz) with a thickness of 45 μm and prominent EMI shielding reliability after 1000 cycles of bending. In addition, the composites film shows good tensile strength (12.1 MPa), elongation at break (108.0%), and toughness (11.59 MJ/m3). The obtained TPU/PDA/Ag composites film achieves the desired balance among thermal conductivity, EMI shielding, and mechanical properties, indicating broad application prospects in new-generation wireless communication technologies and portable intelligent electronic devices. [ABSTRACT FROM AUTHOR]

Stretchable strain sensors with integrated attributes of flexibility and robustness are urgently required owing to their promising applications in healthcare monitoring and environment detection. Herein, we achieved a highly stretchable thermoplastic polyurethane (TPU) mat (PUM) through electrospinning, then decorated with polyaniline (PANI) nanoparticles bridged by reduced graphene oxide (rGO) nanosheets by in-situ polymerization and ultrasonication. The rGO/PANI/TPU mat (GPTM) was then assembled as the strain sensor (GPTSS), showing a wide sensing range of 0.1%–300% strain, high gauge factor (GF) of 3000.2, favorable sensing stability, short response time (90 ms) and excellent long-term durability after 10000 stretching/releasing cycles, which endows the strain sensor with high discernibility for detecting intricate human motions. The GPTSS shows the capacity to precisely monitor ammonia gas (as low as 5 ppm), which can be used to detect harmful gases. The integrated capabilities of strain sensing and environmental monitoring promote the progress of high-performance electronics. [Display omitted] [ABSTRACT FROM AUTHOR]

A biomimetic nanocomposite scaffold with HA formation on the electrospun poly(ɛ-caprolactone) (PCL)/nanocellulose (NC) fibrous matrix was developed in this study. The electrospun PCL/NC fiber mat was built and then biomineralized by treatment in simulated body fluid (SBF). Using such a rapid and effective procedure, a continuous biomimetic crystalline HA layer could be successfully formed without the need of any additional chemical modification of the substrate surface. The results showed that the introduction of NC into composite fibers is an effective approach to induce the deposition of HA nucleus as well as to improve their distribution and growth of a crystalline HA layer on the fibrous scaffolds. The water contact angle (WCA) of the PCL/NC/HA scaffolds decreases with increasing NC content and mineralization time, resulting in the enhancement of their hydrophilicity. These results indicated that HA-mineralized on PCL/NC fiber can be prepared directly by simply using SBF immersion. [ABSTRACT FROM AUTHOR]

In this paper, carbon black (CB), carbon fiber (CF), and hybrid CF/CB were introduced into polypropylene (PP) to fabricate different conductive composites by melt mixing, respectively. The combined effects of CF and CB on the electrical and liquid sensing properties of PP-based composites were investigated in detail. In virtue of the co-supporting conductive network, percolation threshold of the CF/CB/PP composite was reduced apparently upon the addition of 8 wt.% CF. For liquid sensing measurements, CF/CB/PP conductive polymer composites (CPCs) exhibited a superior liquid sensing behavior with higher responsivity, rapider response and better stability in contrast to the counterpart CB/PP. In addition, the response curves are found to be remarkably characteristic for discriminating different kinds of organic solvents. The present paper provides a new route to tailor the liquid sensing properties of CPCs. [ABSTRACT FROM AUTHOR]

Isotactic polypropylene (iPP) based single-polymer composites (SPCs) were prepared by introducing iPP fibers into the molten or supercooled homogeneous iPP matrix. The influences of fiber introduction temperature ( T i ) on the resultant morphology of transcrystallinity (TC) and mechanical properties of SPCs were investigated via a polarized optical microscopy (POM) and a universal tensile test machine. The effects of interfacial crystallization on mechanical properties were also studied. The tensile strength of SPCs was observed to increase firstly and to reach a maximum value at T i = 160 °C, and then to decrease with further increasing the T i . Wide-angle X-ray diffraction (WAXD), scanning electron microscopy (SEM) and POM were employed to understand the mechanical enhancement mechanism. It is found that the enhanced tensile strength of SPCs was strongly dependent on the synergistic effects of TC, high orientation degree of iPP fibers and good adhesion between the iPP fiber and the matrix. [ABSTRACT FROM AUTHOR]

Conductive polymer composites (CPCs) have found applications as eco-friendly vapor sensor. In this study, ramie fiber (RF) was incorporated into poly (lactic acid) (PLA), an eco-friendly polymer, through a premixing process of conductive fillers (carbon black (CB) and carbon nanotubes (CNTs)) and RF. The introduction of RF increases the crystallinity of composites without sacrificing electrical properties. The influence of RF on the vapor sensing behaviors of the CPC was investigated in detail. Compared with those systems with only conductive fillers, i.e. , CB/PLA and CNT/PLA, the RF embedded CPCs show higher electrical conductivity with lower percolation threshold, better shape stability toward ‘good solvent’ such as dichloromethane, and excellent reversibility upon ‘poor’ solvent. The increased crystallinity and the interaction between conductive fillers and RF are responsible for the phenomenon. To illustrate the conductive network evolution during tests, a schematic was proposed. The results suggest that conductive polymer composites containing RF can be applied as a promising eco-friendly vapor sensor. [ABSTRACT FROM AUTHOR]

The degraded polycarbonate (PC) chains were successfully grafted onto the surface of silica nanoparticles (nano-SiO 2 ) by melt blending. Covalent linkage (Si–O–C bond) was formed between the degraded PC chains and nano-SiO 2 under the condition of strong shear force and high temperature. The alcoholysis between carbonate and Si–OH groups, coupled with the condensation reaction between silicon hydroxyls and hydroxyl end groups of degraded chains, mainly contributed to the formation of Si–O–C bond. As expected, the tensile strength and toughness of PC were simultaneously enhanced by incorporating functionalized SiO 2 . The improvement in tensile properties was attributed to the strong interfacial adhesion between functionalized SiO 2 and PC matrix. [ABSTRACT FROM AUTHOR]

In the present work, pre-shear was elaborately introduced into melting HDPE and then such pre-sheared melt was injection molded. The hierarchical structure and crystalline morphology of injection-molded HDPE part were investigated by using WAXD and SEM. It was found that pre-shear can enhance the formation of oriented crystals in core region of HDPE part. More interestingly, such enhancing effect becomes more remarkable if pre-shear was exerted at low temperature just slightly above the melting point of HDPE. Naturally, mechanical property was promoted due to the oriented crystals induced by pre-shear at low temperature and the narrowed orientation gap between shear region and core region. [ABSTRACT FROM AUTHOR]

This work investigated the influence of two-dimensional boron nitride (BN) on the phase transformation kinetics of isotactic polybutene-1 (iPB-1) with differential scanning calorimetry, wide angle X-ray diffraction, and small angle X-ray scattering technique. The phase transition time (t tra) from form II to I largely decreases with the increasing content of BN nanosheets. Different from that in pure iPB-1, the phase transition is accomplished without residual form II in a relatively short time. It's speculated that the addition of BN leads to the irregular lamellae packing of form II (demonstrated by the SAXS result). The irregular packing can avoid the accumulation of negative stress that is induced by the lamellae deformation of the transformed form II, which may hider the chain movement of the residual un-transformed form II. The dispersion of the negative stress obviously accelerated phase transition kinetics from form II to I in iPB-1/BN blends. In addition, it's found that the thickness of form I in iPB-1/BN blends is thicker than that in pure iPB-1. By investigation on the melting temperature of partially transformed form II/I, it showed that the thickness of form I in iPB-1/blends increased continually during the whole phase transition process, which is different from that in pure iPB-1. The continuously lamellae thickening of form I during phase transition may be due to the dispersion of negative stress which benefits the chain movement. [Display omitted] • The effect of 2D nanofillers on the phase transition from form II to I in iPB-1 is investigated. • The transformation kinetics is obviously accelerated. • Lamellar thickening of form I during phase transition is observed. [ABSTRACT FROM AUTHOR]

Herein, a porous polycarbonate blend monolith with hierarchical micro-nano structure using fluorine-free and low-cost material via a simple thermally induced phase separation is successfully prepared. The unique micro-nano structure endows the monolith with high porosity (90%) and low density (93 mg/cm3), as well as strong superhydrophobicity (water contact angle of 159°) and superoleophilicity. It shows high saturation adsorption capacity (6.25–10.58 g/g) and rapid adsorption rate (20 s reach adsorption equilibrium). Furthermore, outstanding environmental resistance in a variety of harsh conditions, such as contact angle varies slightly under various pHs (1–14) and the constant adsorption capacity at different temperatures (0–100 °C), is found. Additionally, the monolith displays good recycling performance for at least 10 cycles by simply pumping and evaporating, indicating a good application prospect in the field of practical oil-water separation. [Display omitted] • Superhydrophobic PDMS/PC monolith with hierarchical micro-nano structure is prepared. • Monolith endows the high porosity (90.8%) and low density (93 mg/cm3). • It has outstanding environmental resistance and constant adsorption capacity at 0–100 °C. [ABSTRACT FROM AUTHOR]

Removing the solid skin of polymer foams is a challenging approach for supercritical carbon dioxide (scCO 2) foaming. Herein, a surface-constrained foaming method was used to fabricate skinless cellular poly (vinylidene fluoride) (PVDF) films. The use of organosilicone and nature latex as gas barrier layers resulted in low CO 2 diffusion rates of 2.16 × 10−11 m2/s and 4.73 × 10−13 m2/s, and trigger heterogeneous nucleation of cells on the PVDF/barrier layer interface. The skin layer and the cell size gradient in the region close to the surface were successfully eliminated, and the surface cell density and cell size could be controlled in the range of 7.2 × 106 cells/cm3, and 13–41 µm, respectively. Moreover, the fabricated skinless cellular PVDF films exhibited an enhanced melting temperature and crystallinity due to the plasticizing effect of scCO 2. The present study provides new thoughts for the fabrication of skinless polymer films using surface-constrained scCO 2 foaming. [Display omitted] • Fabricating skinless PVDF cellular films via surface-constrained scCO 2 foaming. • Organosilicone and nature latex were used as constrained layers. • Low CO 2 diffusivity and high interfacial adhesion assisted cell nucleation. • Skinless PVDF cellular films have negligible cell size gradient close to surface. • Skinless PVDF cellular films exhibit enhanced cystallinity and melting temperature. [ABSTRACT FROM AUTHOR]

Shear-induced interfacial sheath structure was generated by pulling a single glass fiber (GF) in the supercooled isotactic polypropylene (iPP) melt. Its morphological evolution and microstructure were investigated by means of polarized optical microscopy (POM), ex-situ polarized Fourier transform infrared spectroscopy (FTIR), ex-situ two-dimension wide-angle X-ray diffraction (2D-WAXD) and scanning electron microscopy (SEM). The results revealed that higher fiber-pulling speed was crucial to promote the formation of sheath structure. Such sheath structure was proved to be the most thermodynamically stable α-crystal that could effectively induce the generation of β-cylindrite. Meanwhile, the thickness and orientation level of the sheath structure were increased with the increasing fiber-pulling speed. More interestingly, the sheath structure was composed of aligned shish-kebabs, and the lamellar-branched β-iPP crystals directly “rooted” in these kebabs, viz., β-iPP crystals grew at the growth front of oriented fibrillar lamellae. This study on the interfacial sheath structure provides another direct evidence for the formation mechanism of β-iPP crystals upon shear field. [ABSTRACT FROM AUTHOR]

Uniaxial deformation of amorphous poly(lactic acid) (PLA) film was performed at 60 °C (around the glass transition temperature). The deformed samples revealed a strain-induced mesophase, and its fraction and thermal stability increased with draw strain. Further annealing was performed in situ at constant length, at the drawing temperature for the films drawn to strains of 100% and 230%. Interestingly, the orientation of amorphous phase relaxed more rapidly for the 100% sample compared with the 230% one. This could be ascribed to the constraint effect of mesophase on the amorphous chains. In addition, the chains of mesophase relaxed slightly for the 100% sample while it retained high orientation for the 230% sample. Meanwhile, the mesophase fraction decreased, and the trend was more significant for the sample drawn to 100%. These effects can be ascribed to the melting of mesophase and the different thermal stabilities of the mesophases. [ABSTRACT FROM AUTHOR]

The impacts of both shear temperature and shear rate on both the self-assembled β-nucleating agent (β-NA) in the hosting isotactic polypropylene (iPP) matrix and the subsequent crystallization of the hosting iPP matrix were investigated by polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD), and small-angle X-ray scattering (SAXS) measurements, respectively. Under static condition, β-NA could self-assemble into snowflake-like aggregate. Once shear was applied, three kinds of self-assembled aggregates could be developed prior to the crystallization of matrix depending on the applied shear temperatures, that is, snowflake-like self-assembled aggregate at 200 °C, deformed snowflake-like one with smaller branches at 180 °C, tiny and dense needle-like one if shear temperature was further decreased to 160 °C. Since β-NA with various self-assembled aggregates can act as nucleating templates for the subsequent nucleation of iPP matrix, it is conceivable that the crystallization behavior of the iPP matrix can be altered. As expected, β-phase crystallinity, long period and lamellar thickness are steadily dependent on the shear temperature and shear rate. That is, when shear was applied at 200 °C, β-phase crystallinity, long period and lamellar thickness keeps almost constant regardless of the shear rate. If melt was sheared at 180 °C, β-phase crystallinity was decreased while long period and lamellar thickness remained unchanged with elevating shear rate. At lower shear temperature (i.e., 160 °C), β-phase crystallinity, long period and lamellar thickness were further decreased with increasing the shear rate. These results are of practical significance to understand the long-term ignored issue: apart from the loading of β-NA, different self-assembled aggregates formed in flow field are another crucial factor in determining the microstructure development of matrix. [ABSTRACT FROM AUTHOR]

In recent years, the essential work of fracture (EWF) method has been extensively employed for assessing a material's toughness by specific essential fracture work, especially for polymers showing ductile failure. However, most research has studied either the in-plane stress mode or the out-of-plane stress mode. To obtain a more in-depth understanding of the EWF theory, the specific essential and non-essential fracture work of polypropylene random copolymer (PP-R) was investigated in both in-plane stress mode and out-of-plane stress mode. The effects of ligament length, amount of pre-cracking and pre-cracking method on the specific essential and non-essential fracture work were explored. The specific essential fracture work obtained in both stress modes is compared and discussed. [ABSTRACT FROM AUTHOR]

The effects of drawing temperature ( T d ) and draw strain on the orientation and structure of semicrystalline poly(lactic acid) (PLA) films were investigated by wide angle X-ray diffraction and polarized Fourier transform infrared spectroscopy. Semicrystalline PLA samples with two initial levels of crystallinity, X c = 1% and 11%, were prepared by cold crystallization at 80 ° C. Whatever X c and T d , the total amount of the ordered phases ( i.e. crystalline + mesophase) increased with draw strain, which could be ascribed to the formation of strain-induced mesophase at T d = 60 or 70 ° C but crystalline at 80 ° C. Also, the molecular orientation of both the amorphous and ordered phases increased with draw strain. Whatever X c , the orientation of the ordered phases was insensitive to T d , whereas higher orientation in the amorphous phase was achieved at lower T d , and the trend was more significant for X c = 1% compared with 11%. [ABSTRACT FROM AUTHOR]

Polycarbonate nanocomposites filled with pristine and modified silica were prepared by simple melt compounding. The thermal degradation behavior of composites was investigated by thermogravimetric analysis coupled with differential scanning calorimetry (TGA/DSC). To understand the thermal degradation mechanism, the chemical structures of gaseous and solid degradation products were detected by thermogravimetric analysis coupled with Fourier transform infrared spectrometry (TGA/FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods were employed to analyze the thermal degradation kinetics. High thermal degradation temperature was obtained by incorporating both types of nanoparticles into matrix, but the maximum mass loss rate increased. According to the DSC curves for degradation process, the change of the number and position of absorption peaks meant that the degradation mechanism of composites was different from that of neat PC. The analysis for TGA chars confirmed the presence of alcoholysis reaction between PC and silica nanoparticles during the thermal decomposition. TGA/FTIR results proved that no new degradation volatiles were produced during the thermal degradation of composites, but the total amounts of all gaseous products decreased by adding silica nanoparticles. The degradation activation energies of both composites increased significantly relative to neat PC, especially for the composite with modified silica. [ABSTRACT FROM AUTHOR]

The nonisothermal and isothermal crystallization behavior of pre-crystallized poly(lactic acid) (PLA) after partial or complete melting was investigated. After partial melting, the maximum crystallization peak shifts to higher temperature by 30 °C during subsequent cooling, indicating that self-nucleation greatly enhances the overall crystallization rate of PLA. Partial melting leads to predetermined athermal nucleation at higher temperature, while complete melting results in sporadic nucleation at lower temperature. Spherulitic and irregular morphologies are formed for the sample partially melted at 178 °C and 176 °C (or 175 °C), respectively. The isothermal crystallization data were analyzed by the Avrami model. The values of the Avrami exponent for partially melted PLA are comparable to that of completely melted material, indicating that self-nucleation does not change the crystallization mechanism of PLA. Irregular spherulites are formed for PLA partially melted at 176 °C during subsequent isothermal crystallization, and the nucleation density decreases with increasing crystallization temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • A cost-effective method was proposed to fabricate single-layer polymer actuator. • Such actuator exhibits excellent actuation performance and durability. • Such actuator can further realize programmed deformation. • Soft robots that mimic snake wrapping and frog jumping were successfully constructed. Polymer actuators that can produce programmed deformations upon environmental stimulation (e.g., heat, light, electricity and chemical vapor) have attracted more attention due to their great potential in some emerging fields of soft robots, sensors, biomimetic devices, artificial muscles, etc. Unfortunately, interfacial failure is frequently happened in bilayer or multilayer actuators due to the poor compatibility between their heterogeneous components. Although some reported single-layer polymer actuators are free of such irritating interfacial failure, facile fabrication of such actuators remains a huge challenge. Herein, a facile but cost-effective strategy to fabricate single-layer homogeneous-polymer Janus actuator (SHJA) based on thermoplastic was proposed. With the help of vacuum-assisted hot-press molding, micro-ridge arrays were introduced onto homogeneous polyvinylidene fluoride (PVDF) film surface, enabling such micropatterned surface to swell asymmetrically and bend in controllable direction in acetone vapor. Such SHJA exhibits excellent actuation behaviors and durability. Interestingly, diversely biomimetic motions including wrapping and jumping can be realized, which highlights its promising potential for applications in soft robots, sensors, biomimetic devices and artificial muscles. Moreover, considering the facile preparation process, low-cost and recyclable substrate material, this approach can be easily scaled up for industrial production. [ABSTRACT FROM AUTHOR]

Compared to polymer fibers, it is still challenging for fabricating large-scale polymer products with superb mechanical properties. Herein, high density polyethylene (HDPE) films reinforced with carbon nanotubes (CNTs) were prepared via an ingenious high-speed melt stretching strategy. With employing a homemade two-drum extensional rheometer, the maximum 80 × stretch ratio of supercooled melt was realized within very short time of 220 ms. The achieved nanocomposite films present the highest tensile strength of 147 MPa in reported HDPE-based composites, while the Young's modulus keeps simultaneously a high level of 2300 MPa in spite of low filler fraction of 3 wt%. Furthermore, the nanocomposite films display an excellent erosion resistance, ensuring the durability in harsh using environments. Microstructural characterization indicates a strong synergy between high-speed melt stretching and CNTs in (1) forming the densely distributed shish-kebab superstructures, (2) making a nearly perfect orientation of shish-kebab crystal and (3) reinforcing the physical connectivity of shish-kebab network. The construction of such characteristic microstructures greatly improves the transfer of mechanical load and underlies a significant enhancement on the mechanical performance. Due to the ultrastrong nanocomposite films fabricated directly by melt processing, the current work is of guiding significance in engineering practice and lights a feasible path towards expanding applications of general plastics to some special occasions like collision protection and structural materials. [Display omitted] • PE/C nanocomposite films are fabricated by high-speed melt stretching. • Films show ultrahigh mechanical properties and excellent erosion resistance. • Dense shish-kebab superstructures with nearly perfect orientation are formed. • CNTs greatly reinforce physical connectivity of shish-kebab crystal network. [ABSTRACT FROM AUTHOR]

Precise control and regulation of the cell structure in supercritical CO 2 (scCO 2) foaming is the key to boost the performance and extend the application of polymer foams. In this work, dynamic scCO 2 foaming method is proposed to fabricate thermoplastic polyurethane (TPU) foams with unique wrinkly structures by introducing a continuous scCO 2 flow field during scCO 2 saturation. The scCO 2 flow field applied on the TPU matrix generated intramolecular stress and resulted in the formation of wrinkles on the surface of cells. The structure of wrinkles was controlled by pivotal processing factors including foaming temperature, pressure, scCO 2 flow rate, and scCO 2 flow time. Attributing to the wrinkly structure, the wrinkled foams possessed superior compressive modulus, strength, recoverability, and energy absorption performance than conventional TPU foams, which make them a promising material for buffering and energy absorption applications. The dynamic scCO 2 foaming method opens avenue for scCO 2 foaming process involves dynamic field. [Display omitted] • Dynamic scCO 2 foaming process that involves scCO 2 flow field during saturation. • Fabrication of wrinkled foams with dense and controllable wrinkly structures. • Intramolecular stress release and cell contraction behaviors resulted in the formation of wrinkly structure. • Wrinkled foams have superior compressive modulus, recovery rate, and energy absorption performances. [ABSTRACT FROM AUTHOR]

Abstract: The effect of one of the 1,3,5-benzenetrisamide derivatives, N,N',N''-tricyclohexyl-1,3,5- benzenetricarboxylamide (defined here as TMC), on the crystallization behavior of isotactic polypropylene (iPP) was investigated by differential scanning calorimetry. TMC shows excellent nucleating effect on iPP. The nucleation efficiency of the blends reaches 30% even at a very low loading of 0.05 wt% TMC. For 0.1 wt% TMC, the crystallization half-time of the blend decreases from 39.41 to 3.97 min at 136 °C, compared with pure iPP. The isothermal crystallization data were further analyzed by the Avrami model. The values of the Avrami exponent of the blends are comparable to that of pure iPP, indicating that the presence of TMC does not change the crystallization mechanism of the matrix. The presence of TMC increases significantly the nuclei density of iPP but has no discernible effect on its crystalline structure, evidenced by polarized optical microscopy and wide angle X-ray diffraction measurements. [Copyright &y& Elsevier]

Abstract: Ultra-thin LLDPE parts were prepared by microinjection molding. Mechanical properties and microstructure of samples before and after annealing at different temperatures (60, 80, 100 °C) were analyzed. Tensile test indicates that toughness has been enhanced at least 7 times after being annealed in parallel with significant increase of tensile strength. Microstructure characterizations, including differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), scanning electronic microscope (SEM) and polarized Fourier transform infrared spectroscopy (FTIR) were performed to investigate the variations of microstructure and to further establish the relationship between microstructure and mechanical properties. It is suggested that the increased crystallinity and perfection of crystals upon annealing are beneficial to the reinforcement. Formation of a stronger physical cross-linking network due to the increase of connecting points is in favor of the enhanced strength as well. Moreover, the notable improvement of toughness in the annealed ultra-thin LLDPE parts is ascribed to combined effects of microvoids developed in both the annealing and deformation process. This work offers a simple approach to prepare ultra-thin LLDPE parts with excellent toughness and strength. [Copyright &y& Elsevier]

Frequent oil spills on water have always generated serious ecological disasters and environmental crises in recent years. Unfortunately, the traditional oil/water separation and collection process is in an intermittent mode and therefore suffers from expensive, time-consuming and complicated procedures. Undoubtedly, it is necessary to develop a facile method to selectively separate and collect oil from the oil/water mixture in a continuous mode. Herein, we present a low-cost, efficient and simple approach (co-extrusion molding) to continuously fabricate polymer microfibrillar tube (PMT). It shows high porosity, excellent oleophilicity and good hydrophobicity, and thereby excellent absorption and transportability is obtained. More interestingly, it is capable of continuously separating/collecting oil from flowing oil/water mixture and there is no secondary treatment (i.e., desorption) involved in such one-step process for oil/water separation and collection. This study proposes a new concept for fabricating polymer porous tube consisting of microfibril through a low-cost, efficient, simple and continuous way, showing promising potential application in continuous oil/water separation and collection. The present work represents a facile, cost-effective and environmentally friendly method to fabricate polymer microfibrillar tube (PMT). Interestingly, such PMT can one-step separate and collect oil from the oil/water mixture in a continuous way. This study proposes a new concept for fabricating polymer porous tube consisting of microfibril through a low-cost, efficient, simple and continuous way, showing promising potential application in continuous oil/water separation and collection. [Display omitted] • A low-cost, facile method through co-extrusion molding and water leaching method to fabricate PMT. • PMT exhibits excellent oleophilicity and hydrophobicity. • PMT has the ability of continuously separating/collecting oil from flowing oil/water mixture. • No secondary treatment (i.e., desorption) is involved in separation/collection process. [ABSTRACT FROM AUTHOR]

Cellulose has attracted an increasing attention for piezoelectric energy harvesting. However, the limited piezoelectricity of natural cellulose constraints the applications. Therefore, we demonstrate the development of piezoelectric nanogenerators based on robust, durable layered membranes composed of cotton cellulose interfaced maleic-anhydride-grafted polyvinylidene fluoride (PVDF- g -MA) nanofibers. Exploiting polydopamine@BaTiO 3 (pBT) nanoparticles as interlayer bridges, interlocked layer–layer interfaces that covalently bind component layers are constructed by a facile and scalable approach. As-obtained membranes exhibit significantly improved piezoelectricity with a maximum piezoelectric coefficient of 27.2 pC/N, power density of 1.72 μW/cm2, and stability over 8000 cycles. Substantial enhancement in piezoelectricity over pristine cellulose is ascribed to the synergy of components and the localized stress concentration induced by pBT nanoparticles. The self-powered device could also be used to detect human physiological motions in different forms. Such cellulose-based membranes can be up-scaled to fabricate ecofriendly, flexible and durable energy harvesters and self-powered wearable sensors. [Display omitted] [ABSTRACT FROM AUTHOR]

Most cellulose products lack water resistance due to the existence of abundant hydroxyl groups. In this work, microfibrillated cellulose (MFC) was modified via 3-aminopropyltriethoxysilane (APTES)-assisted ball milling. Under the synergism between high-energy mechanical force field and APTES-modification, the fibrillation and hydrophobization of MFC were achieved simultaneously. Free-standing translucent cellulose films made of modified MFC were fabricated. The original crystal form of cellulose is maintained. The hydrophobicity of cellulose film markedly increases and the water contact angle goes up to 133.2 ± 3.4°, which might be ascribed to the combined effects of APTES-modification and rough film surface. In addition, the thermostability and mechanical properties of cellulose film are also improved via mechanochemical modification. This work provides a novel one-step fibrillation-hydrophobization method for cellulose. [Display omitted] • Microfibrillated cellulose (MFC) was modified by aminosilane-assisted ball milling. • The fibrillation and hydrophobization of MFC were achieved simultaneously. • The obtained translucent cellulose films exhibited excellent hydrophobicity. • The thermostability and mechanical properties of cellulose film were also improved. [ABSTRACT FROM AUTHOR]

In this study, the crystallization behavior of oriented isotactic polypropylene during solid-state stretching was investigated by in-situ wide-angle X-ray scattering. Results showed that a new arc appeared on the (040) reflection with the previous arcs remained when the stretching direction was inclined to the initial orientation direction, as a result of stretching induced crystallization. The crystallization process occurred later than the yielding but earlier than the strain hardening. The crystallinity of the newly formed crystal showed a linear dependence on the Hencky strain, and the slope of the plot was more sensitive to the stretching angle rather than the stretching temperature. Lastly, the stress relaxation test showed that the crystallinity was linear correlated to the amorphous phase orientation. The Pearson correlation coefficient was as high as −0.99, suggesting that the crystallization process is originated from the orientation of the chain network during stretching. [Display omitted] • The crystallization behavior of oriented iPP during solid state stretching is studied by in-situ wide angle X-ray scattering. • The crystallinity shows a linear dependence on the macroscopic Hencky strain. The slope of the plot is more sensitive to the stretching angle instead of the stretching temperature. • The crystallization during solid-state stretching correlates with the orientation of chain network in the amorphous phase. [ABSTRACT FROM AUTHOR]

Abstract: Macroscopically aligned isotactic polypropylene (iPP) fibers with different diameters ranging from 0.7 to 13.2 μm were successfully fabricated by high-temperature solution electrospinning using an infrared (IR) heating system. Polarized optical microscope (POM), scanning electron microscope (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and polarized Fourier transform infrared (FTIR) were employed to characterize the surface morphology and microstructure of the electrospun fibers. From SEM images, three macroscopically structural models have been found: (1) cylindrical fibers, (2) twisted fibers and (3) beaded fibers. Interestingly, regardless of fiber's shape and size, they (especially for cylindrical fibers) exhibit well-defined self-similar morphology. That is, the tertiary, secondary and primary morphology are similar with each other. Thermally induced phase separation (TIPS) is the most pertinent origin to explain the formation of self-similar morphology. WAXD and DSC results show that α-form crystal prevails in the electrospun iPP fibers. For comparison, the solution-cast film was also prepared under the same conditions as those adopted in electrospinning except that the voltage was 0 kV. Compared with the solution-cast film, lower crystallinity, smaller average crystallite size and higher melting point are achieved in the electrospun iPP fibers. The results of polarized FTIR spectra demonstrate that the macroscopically aligned electrospun fibers are highly oriented along the fiber's longitudinal axis at molecular level. Furthermore, when the electrospun iPP fibers were embed in iPP matrix, surface-induced crystallization is significantly enhanced and finally develops into transcrystalline layer which can be even revived after recrystallization. As a result, it is logical that long-lived thermodynamically stable structure has been formed in the electrospun iPP fiber. Combined with FTIR result, the α-form crystal formed in the fiber is conjectured to be a kind of oriented structure with thermodynamically long-lived stability which is similar to "shish-kebab" structure. [Copyright &y& Elsevier]

Abstract: On the laboratory scale, pre-shear induced orientation at high temperature can considerably influence the subsequent crystallization, which has been intensively investigated by various sophisticated methods. Unfortunately, during conventional polymer processing (e.g., injection molding), the preservation of pre-shear induced orientation is a practical challenge because oriented chains are prone to relax as far as possible. Motivated by the studies on pre-shear induced crystallization, a Mixing-Injection Molding (MIM) machine was designed and built to study pre-shear induced crystallization under practical processing conditions. Its main features contain two aspects: (1) polymer composites or blends can be simultaneously plasticized and melt mixed in the barrel by a rotating screw. Logically, pre-shear is introduced to the homogeneously mixed melt; (2) the pre-sheared melt can be in-situ injected into a mold once the mixing-plasticization process finishes. In the present study, an unusual distribution of β-form isotactic polypropylene (iPP) prepared by the MIM is discovered. That is, in the core region, crystallinity of β-form (X β ) is unexpectedly equal to that in the intermediate region, while β-form is almost absent in the core region of a conventional injection molded counterpart. Taking into account the main features of MIM and the evidence of supplementary experiments, this interesting result can be attributed to the fact that precursors can be induced by pre-shear. Such precursors are most likely to be short α-row-nuclei, which can act as nucleating sites for the growth of β-spherulites once the material is in-situ injected into the mold cavity. [Copyright &y& Elsevier]

Among the appearance defects of injection molded products, sink mark near the gate accounts for a large proportion, especially for the precision products that require a high appearance quality. The traditional method to relieve gate sink mark is to increase packing pressure and packing time. Even so, the problem cannot be completely solved. In current study, a three-dimensional numerical simulation method was employed to analyze the formation mechanism of gate sink mark. The analyses point out that high shear in the filling stage, melt refilling in packing stage and high mold temperature lead to the imbalance of shear heat generation and cooling between the gate and other regions, and finally result in the relatively high temperature and the sink mark defect in the gate region. Based on these results, a novel and simple method for improving gate sink mark by adding beryllium copper insert in the runner was proposed and implemented. Further simulation shows that the method is effective in eliminating the gate "hot spot" and improving the temperature uniformity of the entire product. The experiment results also prove that the heat sink mark in the gate area can be effectively avoided by using the mold with insert for both amorphous ABS and semi-crystalline PP products. The proposed method can not only solve the sink mark problem effectively, but also has the advantage of being simple and easy to achieve because the slide type side gate design is adopted. [ABSTRACT FROM AUTHOR]

Boron nitride/multiwalled carbon nanotubes/carbon (BN/MWCNTs/C) networks were prepared via a rape pollen (RP) biological template assisted strategy. The highly thermally conductive epoxy resin (EP) composites were prepared by impregnating EP into the 3D BN/MWCNTs/C networks. Fourier transform infrared spectra and X-ray photoelectron spectroscopy analyses indicated that the successful modification of BN (m-BN) and the interaction between RP, carboxyl functionalized MWCNTs (c-MWCNTs) and m-BN. Scanning electron microscopy images clearly present the network morphology constructed by MWCNTs connected to m-BN. Thermogravimetric analyzer curves determine the mass concentration of m-BN in EP-based composites. The thermal conductivity (K) reached 1.84 W/(m·K) in the composites at a BN content of 21.3 wt%, displaying a significant enhancement of 868% compared with pure EP. The enhanced K is attributed to the effective connection of BN by the MWCNTs covered on the surface of RP. Meanwhile, the composites exhibit a tensile strength of 39.2 MPa, electrically insulating with a volume electrical resistivity about 9.17 × 1010 Ω cm and good flame retardancy. [Display omitted] • 3D BN/MWCNTs/C thermal conductive networks were prepared via a biological template assisted strategy. • Epoxy-based composites were prepared by a vacuum-assisted impregnation method. • Thermal conductivity was significantly enhanced in this system. • Electrical insulation and flame retardancy performances were observed as well. [ABSTRACT FROM AUTHOR]

The rapid development of electronic devices has led to widespread demand and research on electronic packaging materials with electromagnetic shielding and thermal conductivity (TC) properties due to the inevitable issues of the electromagnetic radiation and thermal accumulation. However, there exists a huge challenge to simultaneously achieve high electromagnetic shielding and TC as well as the electrical insulation requirement as electromagnetic shielding predominantly relies on electrical conductivity of materials. Multilayer structure can endow composite materials with a variety of properties. Therefore, in this work, we fabricated sandwiched cellulose nanofiber/boron nitride nanosheet/Ti 3 C 2 T x MXene films by using a simple and effective alternating vacuum filtration method, and as a result, the special sandwich structure endows the film with excellent electromagnetic shielding, insulation and TC performance. The composite film has an extremely high electromagnetic shielding effectiveness up to 60.7 dB at 8.2 GHz as well as still maintains good electrical insulation properties due to the presence of the CNF/BNNS layer on the surface. Moreover, when the content of BNNS in the CNF/BNNS layer reaches 70 wt%, the sandwiched film has excellent in-plane TC of 19.97 W m−1 K−1. The sandwiched film with excellent electromagnetic shielding and high TC yet insulation performance has great application value in highly integrated electronic devices. [Display omitted] [ABSTRACT FROM AUTHOR]

The durability and large-scale production of Ti 3 C 2 T x MXene-based composites are the main obstacles in industrialized application. Herein, a scalable blade coating method is demonstrated for fabricating the flexible and durable polyvinylidene fluoride (PVDF)/Ti 3 C 2 T x MXene layered films with compact hierarchical brick-and-mortar structure. The highly aligned MXene nanosheets make the obtained PVDF/MXene films with high electrical conductivity from 21.1 to 214.6 S cm−1. In combination to the multiple wave reflection in hierarchical layered structure and the interfacial polarization between dielectric matrix and MXene, PVDF/MXene films reveal excellent electromagnetic interference (EMI) performance with an optimal specific EMI shielding effectiveness (SSE/t) of 19504.8 dB cm2 g−1 at only 17 μm thickness. More importantly, the PVDF/MXene film can withstand the damages from mechanical deformation, hot/cold attack and chemical corrosion, meanwhile maintain a stable EMI shielding performance within floating of 5%. Besides, arising from the surface plasmon resonance effect and high electrical conductivity, the PVDF/MXene film reveals photo/electro-thermal heating abilities with rapid response time, high stability and controllability, which ensure their reliable EMI shielding performance under extremely cold conditions. [Display omitted] • A scalable blade coating method was reported for fabricating PVDF/MXene layered film. • The film with compact brick-and-mortar structure reveals good EMI shielding property. • PVDF/MXene film shows superior durability with stable EMI SE in various environments. • PVDF/MXene film exhibits multifunctional photo/electro-thermal conversion capacities. [ABSTRACT FROM AUTHOR]

• Superhydrophobic CA/OMWNTs monolith with unique porous structure was prepared. • The introduction of OMWNTs improved the overall performance of monolith. • The CA/OMWNTs monolith possessed outstanding oil/water separation capability. • The CA/OMWNTs monolith presented excellent durability and recyclability. • The CA/OMWNTs monolith could continuously separate oil/water mixture by device. Porous cellulose acetate/carboxylated multiwalled carbon nanotubes (CA/OMWNTs) monolith with superhydrophobicity (155°) and superoleophilicity (∼0°) was first prepared using a facile and green phase separation method. Benefiting from the unique three-dimensional (3D) fiber cluster network structure, the as-prepared CA/OMWNTs monolith reveals a high porosity (93.7 %) and a large specific surface area (85.36 m2/g). As an oil adsorption material, the superhydrophobic porous monolith is able to adsorb the different kinds of organic solvents and oils from water efficiently and selectively with saturated adsorption capacities from 7.39 to 19.84 g g−1. Moreover, the porous monolith exhibits an excellent durability with the highly stable wettability and oil/water separation no matter at different pH (1–14) conditions or extreme temperatures (−20−160 °C). Besides, the CA/OMWNTs monolith also could continuously and rapidly separate oils/organic solvents from oil/water mixtures via a simple and home-made pump-assisted adsorption device, showing potential application in large-area remediation of oily wastewater. [ABSTRACT FROM AUTHOR]

• Entransy dissipation thermal conductivity varies with boundary conditions. • Thermal conductivity with equal boundary temperature gradient is higher than others. • Upper and lower bounds of the entransy dissipation thermal conductivity is found. • The minimum thermal resistance principle is mathematically proved. The prediction of equivalent thermal conductivity (ETC) and resistance (ETR) is an important topic in the composite material field. Many expressions of ETCs and ETRs have been proposed using different homogenization methods in last several decades. Especially, expressions defined by the entransy dissipation rate, k e f f and R e f f , excel for their wide range of application. Usually, it was agreed that k e f f and R e f f were determined by the thermal conductivity distribution inside. However, we find that they are also vary with the boundary temperature gradient distribution (TGD). In this paper, we simulate and mathematically prove the influence of boundary TGD on k e f f. The results indicate that k e f f with uniform boundary TGD is higher than that with non-uniform boundary TGD. In addition, the mathematical proof after a little adjustment is applied to confirm the minimum thermal resistance principle based on the uniform TGD inside. The results show that k e f f is the maximum when TGD are uniform in all regions including boundaries, and k e f f reaches the minimum when the non-uniformity of TGD extends to the limit. Upper and lower bounds of k e f f and R e f f found in this paper are greatly valuable for optimizing the heat transfer ability and heat insulation ability of materials. And the methodology as well as conclusion in this paper can be reproduced in some generalized irreversible transport systems. [ABSTRACT FROM AUTHOR]

Flexible and wearable strain sensors with multi-functionalities have aroused tremendous attention for various applications in disease diagnostics, environment detection and healthcare monitoring, etc. However, limited electromechanical performance and complicated fabrication process of strain sensors restrict their extensive applications in full-range stimuli monitoring. Herein, we fabricated flexible and wearable strain sensors, consisting of a robust fiber with helical structure and two polyaniline (PANI) layers bridged by reduced graphene oxide (rGO) layer through in-situ polymerization and ultrasonication. The flexible and wearable sensor possesses wide healthcare monitoring range (0.1%–200% strain), high sensibility especially for subtle deformation, excellent response stability, fast response/recovery time (100 ms/100 ms) and favorable durability. Meanwhile, our conductive PANI-rGO-PANI fiber (CPGPF) is assembled as a wearable sensor with the capability of precisely monitoring human body motions, temperature fluctuation and poisonous gas, indicating a promising multifunctional application in human-machine interaction and environment monitoring. [ABSTRACT FROM AUTHOR]

Hybrid fillers of different geometries are increasingly utilized for the development of functional polymer composites. We herein report the role of HDPE-g-MAH as a compatibilizer for ternary composites consisting of HDPE, multi-walled carbon nanotubes and hexagonal boron nitride (BN). Through melt blending, HDPE-g-MAH can reduce the agglomeration of fillers and facilitate the formation of network structure. Due to the synergistic effect, ternary composites have demonstrated significantly higher thermal conductivity than those binary composites, and their maximum increase relative to the matrix is 262%. The mechanical performance and thermal conductivity are explained from perspectives of the morphology and crystallinity of the composites. The rheological properties of both binary and ternary composites have close relationship with their thermal conductivity. Although a high fraction of BN nanosheets can greatly reduce the electrical conductivity of ternary composites, they posed little effect on the electromagnetic interference shielding performance, owing to their electrical insulating nature. This research can provide new clues for the development of functional materials. Image 1 [ABSTRACT FROM AUTHOR]

With the rapid development of the flexible electronics industry, the range of multifunctional applications of materials has become extensive. But it is still a challenge to apply flexible materials to different fields while ensuring corresponding performance. Herein, a simple and available approach is addressed to fabricate conductive polymer composite films supported on Ag flakes and waterborne polyurethane (WPU) by spraying. The WPU/Ag films with uniform structure show outstanding flexibility and electromagnetic interference shielding effectiveness of 68.9 dB with thickness of only 50 μm, and could sustain a high standard even undergoing excessive mechanical deformations. Besides, the resulted films possess prominent electro-thermal effect, which can achieve a temperature of over 120 °C by applying a low voltage of 2 V, and the heat can be dissipated rapidly along with the connecting Ag network. Moreover, it shows a high gauge factor (229.2), good durability and reproductivity (over 1000 cycles), and rapid response time to strain (50 ms), which can be potentially used in the field of human movement monitoring and wearable electronic devices. These results indicate the multifunction of the WPU/Ag film, which could widen its practical applications after the corresponding treatment. Image 1 • Multifunctional WPU/Ag composite films were prepared by the solution blending and spraying technique. • The film with a thickness of 50 μm exhibits superior conductivity (1101.32 S cm−1) and EMI SE (68.97 dB). • The film can be rapidly heated to 125 °C under 2.0 V at 1 min. • The film shows high gauge factor (229), goodreproductivity (over 1000 cycles), and rapid response time (50 ms). [ABSTRACT FROM AUTHOR]

Multifunctional polymer foam becomes the tendency due to the single-functional foam is difficult to adapt the various complicated environments. However, preparing multifunctional porous ultra-high molecular weight polyethylene (UHMWPE) material with high porosity is still challenge. Thus, it is desirable to develop a simple and effective method that could integrate multiple functions into polymer foam. Herein, a multifunctional UHMWPE foam was fabricated via a facile thermally induced phase separation method. The foam displays a low density of 8.23 mg cm−3, high porosity of 99.2% and robust superhydrophobicity (water contact angle of 152°), thus exhibiting excellent adsorption capacity in oil-water separation under different extreme environments. Moreover, the thermal conductivity of the foam goes down to 11.6 mWm−1K−1, which endows the foam with great thermal insulation performance under various temperature conditions. Thus, this foam can meet the demands of various practical applications. Image 1 • Multifunctional UHMPE foam was fabricated via thermally induced phase separation method. • The foam displays an ultra-light property (8.23 mg cm−3) and robust superhydrophobicity (water contact angle of 152°). • It shows excellent adsorption capacity in oil-water separation under different extreme environments. • The foam with 11.6 mWm−1K−1 thermal conductivity exhibits great thermal insulation performance. [ABSTRACT FROM AUTHOR]

The construction of heat conduction paths in the polymer matrix is essential to improve the thermal management performance of polymer composites. A three-dimensional (3D) thermally conductive network with regular filler structures is very attractive for building fast conductive paths in polymer composites. Herein, a unique 3D interconnected tannic acid modified boron nitride (BN) and C network (M-BN/C) was successfully fabricated by the carbonization of M-BN/thermoplastic polyurethane (TPU) skeletons, which were obtained via simple salt template assisted strategy to enhance the thermal transfer properties of composites. The highly thermally conductive epoxy composites (M-BN/C/EP) were then prepared by impregnating epoxy resin (EP) into the 3D M-BN/C network. The thermal conductivity of the composites with a M − BN loading of 23 wt% is as high as 1.524 W/(m·K), which exhibits a significant enhancement of 702% compared with pure EP. In addition, our composite exhibited outstanding thermal behaviors during heating and cooling processes. Furthermore, the finite element heat conduction simulation further analyzes the heat conduction mechanism of epoxy composites from the theoretical level. This work provides a new idea to significantly enhance the thermal conductivity of thermal management materials. [ABSTRACT FROM AUTHOR]