Preparation and Characterization of Hydrophobic Bagasse Hemicellulose-based Films

To improve the hydrophobicity of bagasse hemicellulose-based films, glutaraldehyde was applied when preparing films of original and cationic bagasse hemicellulose with the addition of polyvinyl alcohol and sorbitol. The results showed that the cationic modification could increase the hydrophobicity of the hemicellulose-based film, and the hydrophobicity of hemicellulose-based films crosslinked with glutaraldehyde also increased. However, cationic modification of hemicellulose decreased the stress of the hemicellulose-based film. While crosslinking with glutaraldehyde increased the stress of both the original and cationic hemicellulose-based films. Macrophotography indicated that the film formability of the original hemicellulose was better than that of cationic hemicellulose. Through SEM observation, the degree of bonding of different components of the films was found to be increased due to crosslinking with glutaraldehyde. The crosslinking reaction between glutaraldehyde and hemicellulose was further confirmed by FT-IR spectroscopy.     

单晶硅表层机械力学特性的各向异性分析

为探究挠性筋结构单晶硅材料的各向异性特性以及KOH腐蚀工艺对其力学性能的影响规律,进行纳米压痕实验,并结合原子力显微镜观察单晶硅表层3个主晶面上压痕裂纹形貌随晶向的变化规律,分析单晶硅材料表层弹性模量、硬度、断裂韧性等机械力学特性参数在(001)、(110)及(111)3个主要晶面上沿各个晶向的变化规律;分析挠性筋结构单晶硅材料(001)晶面的KOH腐蚀工艺对其材料表面机械特性的影响规律.结果表明:挠性筋单晶硅在(001)晶面上弹性模量的各向异性变化幅度明显,硬度及断裂韧性各向异性的变化幅度不大;挠性筋单晶硅在(110)晶面弹性模量和断裂韧性的各向异性变化幅度明显,硬度各向异性变化幅度不大;挠性筋单晶硅在(111)晶面硬度值、弹性模量及断裂韧性参数的变化幅度幅值均较小;确定了单晶硅表层3个晶面裂纹最易扩展的晶向方向,KOH腐蚀工艺使得单晶硅表面质量降低,腐蚀后暴露的表面微裂纹、缺陷等会使得单晶硅(001)晶面表层硬度、断裂韧性降低,从而降低了挠性筋结构的实际断裂强度.     

A highly active composite electrocatalyst Ni–Fe–P–Nb2O5/NF for overall water splitting

This work demonstrates a facile Nb₂O₅-decorated electrocatalyst to prepare cost-effective Ni–Fe–P–Nb₂O₅/NF and compared HER & OER performance in alkaline media. The prepared electrocatalyst presented an outstanding electrocatalytic performance towards hydrogen evolution reaction, which required a quite low overpotential of 39.05 mV at the current density of ?10 mA cm^?2 in 1 M KOH electrolyte. Moreover, the Ni–Fe–P–Nb₂O₅/NF catalyst also has excellent oxygen evolution efficiency, which needs only 322 mV to reach the current density of 50 mA cm^?2. Furthermore, its electrocatalytic performance towards overall water splitting worked as both cathode and anode achieved a quite low potential of 1.56 V (10 mA cm^?2).     

Deformation-induced bonding of polymer films below the glass transition temperature

Bonding between polymers through interdiffusion of macromolecules is a well-known mechanism of polymer adhesion. A new polymer bonding mechanism in the solid state, taking place at ambient temperatures well below the glass transition value (T_g), has been recently reported; in this mechanism, bulk plastic compression of polymer films held in contact led to adhesion over timescales of the order of a fraction of a second. In this study, we prepared various blends of plasticized polymer films with desirable ductility from amorphous and semicrystalline powders of hydroxypropyl methylcellulose and polyvinyl alcohol derivatives; then, we observed the bonding of these polymers at ambient temperatures, up to 80 K below T_g, purely through mechanical deformation. The deformation-induced bonding of the polymer films studied in this work led to interfacial fracture toughnesses in the range of 1.0–21.0 J/m² when bulk plastic strains between 3% and 30% were imposed across the films. Scanning electron microscopy observation of the debonded interfaces also confirmed that bonding was caused by deformation-induced macromolecular mobilization and interpenetration. These results expand the range of applicability of sub-T_g, solid-state, deformation-induced bonding processes.     

Bioinspired Triboelectric Soft Robot Driven by Mechanical Energy

A sustainable power source is a key technical challenge for practical applications of electrically responsive soft robots, especially the required voltage is over several thousand volts. Here, a practicable new technology, triboelectric soft robot (TESR) system with the primary characteristics of power source from mechanical energy, is developed. At its heart is TESR with bioinspired architectures made of soft-deformable body and two triboelectric adhesion feet, which is driven and accurately controlled through triboelectric effect, while reaching maximum crawling speeds of 14.9 mm s⁻¹ on the acrylic surface. The characteristics of the TESR, including displacement and force, are tested and simulated under the power of a rotary freestanding triboelectric nanogenerator (RF-TENG). Crawling of TESR is successfully realized on different materials surfaces and different angle slopes under the driven of RF-TENG. Furthermore, a real-time visual monitoring platform, in which TESR carries a micro camera to transmit images in a long narrow tunnel, is also achieved successfully, indicating that it can be used for fast diagnosis in an area inaccessible to human beings in the future. This study offers a new insight into the sustainable power source technologies suitable for electrically responsive soft robots and contributes to expanding the applicability of TENGs.     

高熔体流动速率薄壁注塑聚丙烯专用料的结构与性能分析

采用多种分析测试方法，对3类高熔体流动速率薄壁注塑聚丙烯（PP）专用料的熔融结晶性能、光学性能、分子量分布、力学性能、毛细管流变性能、热收缩性能进行了分析研究。结果表明，K1860与2种市售主流PP1、PP2各项性能相当，其中K1860分子量分布相对PP1、PP2较窄，弯曲性能、拉伸性能更优，可满足大型薄壁注塑制品的生产要求。     

Role of additives in fabrication of soy-based rigid polyurethane foam for structural and thermal insulation applications

Environmental concerns continue to pose the challenge to replace petroleum-based products with renewable ones completely or at least partially while maintaining comparable properties. Herein, rigid polyurethane (PU) foams were prepared using soy-based polyol for structural and thermal insulation applications. Cell size, density, thermal resistivity, and compression force deflection (CFD) values were evaluated and compared with that of petroleum-based PU foam Baydur 683. The roles of different additives, that is, catalyst, blowing agent, surfactants, and different functionalities of polyol on the properties of fabricated foam were also investigated. For this study, dibutyltin dilaurate was employed as catalyst and water as environment friendly blowing agent. Their competitive effect on density and cell size of the PU foams were evaluated. Five different silicone-based surfactants were employed to study the effect of surface tension on cell size of foam. It was also found that 5 g of surfactant per 100 g of polyol produced a foam with minimum surface tension and highest thermal resistivity (R value: 26.11 m²·K/W). However, CFD values were compromised for higher surfactant loading. Additionally, blending of 5 g of higher functionality soy-based polyol improved the CFD values to 328.19 kPa, which was comparable to that of petroleum-based foam Baydur 683.     

Rubber's dissipated energy quantification used in vibratory insulation and protection systems

In vibratory protection and insulation systems, the major problem consist to choose suitable passive elements (spring, damper, others), which are inserted between the resonator and the exciter which have the role of preventing or reducing the transmission of dynamic forces. This work consists of characterizing a synthetic rubber (SR) sample of hollow circular shape (design requirement) by determining the coefficient of energy dissipation at an average ambient temperature of 20°C with a humidity of 25%. The mechanical load and discharge tests make it possible to draw hysteresis curves through which the dissipation coefficient will be determined, the load values is between 500 and 1000 N, with 30, 60, and 90 mm/min loading speeds and a number of cycles 2, 3, and 5, these values have been chosen so as not to cause the effect of cyclic hardening and softening and also to take into consideration, that the vibration limits movement at 3 cycles, which makes this test different from other tests such as fatigue. The processing of different curves, allows to determine energy dissipation coefficient of rubber specimen and also to examine its variation as a function of load, loading speed, and number of cycles; it is possible to determine other characteristics from this coefficient, such as, damping ratio, dynamic amplification factor, and so on, necessary to study efficiency of protection systems, design, and manufacture, based on the curve of transmissibility of dynamic forces to evaluate performance rubber conditions use.     

Investigating the effect of silver nanorods embedded in polydimethylsiloxane matrix using nanoindentation and its use for flexible electronics

The stretchable electrodes with excellent flexibility, electrical conductivity, and mechanical durability are the most fundamental components in the emerging and exciting field of flexible electronics. This article proposes a method for fabrication of such a stretchable electrode by embedding silver nanorods (AgNRs) into a polydimethylsiloxane (PDMS) matrix that is grown by a unique glancing angle deposition technique. The surface, mechanical, and electrical properties of PDMS are significantly changed after embedding the AgNRs in it. The results show that surface roughness and polarity increase after AgNRs are embedded in the PDMS matrix. Elastic modulus (E) and hardness (H) decrease with an increase in the indentation load as a result of the indentation depth effect. Due to strong interfacial adhesion of AgNRs embedded in the PDMS matrix, the E and H of nanocomposite are increased by 167.6 and 93.3% compared with PDMS film, respectively. Furthermore, the AgNRs-PDMS film has an electrical resistivity value in the order of 10⁻⁷ Ωm. It remains conductive during various mechanical strains such as bending, twisting, and stretching, which is demonstrated using a light-emitting diode circuit. Simultaneously, the antimicrobial activity of silver could make it a promising candidate for wearable electronics.     

Variation of internal structure and performance of polyethylene- and polypropylene-modified bitumen during blending process

Linear-viscoelastic characteristics and performance are evaluated throughout the blending process of polyethylene and polypropylene with bitumen. Results indicate that type, form and percentage of polyolefin play a significant role in the time evolution of the composite's mechanical response. Toluene extraction of modified bitumen revealed, for the first time, the formation of a sponge-like polymer network. Visual inspection and Fourier transform infrared analysis of the polyolefins recovered after extraction indicates higher affinity of the polyethylene with bitumen in agreement with the rheological test results. The use of polypropylene is discouraged if rutting performance is a concern, and polyethylene in both pellets and powder form at 4%, and after 210 min of blending produces a modified bitumen with acceptable performance.