Self-lubrication and tribological properties of polymer composites containing lubricant

The purpose of this study was to improve the tribological properties of polydimethylsiloxane (PDMS) by mixing lubricants into it. The chemical composition, physical/chemical bonding state, and mechanical properties of the PDMS/lubricant composites (PLCs), prepared by mixing PDMS and lubricants at different ratios, were analyzed. With increasing lubricant content, the friction coefficient initially decreased, reaching a minimum value at a PDMS/lubricant ratio of 100 : 10; however, it gradually increased with a further increase in the lubricant content. The mechanical properties of PLCs with lubricant contents of 10% and higher decreased owing to the lubricant addition, so that the contact area with the sliding counter tip increased with lubricant content, but the frictional resistance was still decreased owing to the self-lubricating effect. In addition, owing to the effect of the lubricating film, there was no direct contact between the PLC surface and counter tip, and almost no damage was done to the PLC surface. Finite element analysis of the changes in stress during indentation and sliding confirmed that the stress applied to the PLCs was lower than that for bare PDMS.

The purpose of this study was to improve the tribological properties of polydimethylsiloxane (PDMS) by mixing lubricants into it.     

Stabilizing decontamination foam using surface-modified silica nanoparticles containing chemical reagent: foam stability,structures, and dispersion properties

The stabilization of decontamination foams containing a chemical reagent is a crucial requirement for their use in the decontamination of nuclear power plants. We have investigated the effects on decontamination foam stability of adding silica nanoparticles (NPs) modified with various functional groups, namely propyl (–CH₃), amine (–NH₂), and thiol (–SH) groups. The surface properties of these silica NPs were characterized with ATR-FTIR, solid NMR, and TGA analyses. We also established that the agglomeration in such foams of the amine-modified silica NPs is weaker than that of the other modified silica NPs due to their thorough dispersion in the liquid film. Further, the foam containing amine-modified silica NPs was found to be stable for 60 min at a pH of 2, i.e. under decontamination conditions. The bubble structure analysis showed that this decontamination foam has a bubble count that is approximately 5–8 times higher than the foams containing NPs modified with the other functional groups, which indicates that the decontamination foam with amine-modified silica NPs has the best foam structure of the three investigated foams. The well-dispersed and smaller amine-modified silica NPs enhance the foam stability by providing a barrier between the gas bubbles and delaying their coalescence. In contrast, the thiol- and propyl-modified silica NPs form aggregates with large diameters that reduce the maximum capillary pressure of coalescence and hence decrease the foam stability.

The stabilization of decontamination foams containing a chemical reagent is a crucial requirement for their use in the decontamination of nuclear power plants.     

Preparation and sound absorption properties of barium titanate/nitrile butadiene rubber-polyurethane foam composites with stratified structure

Barium titanate/nitrile butadiene rubber (BT/NBR) and polyurethane (PU) foam were combined to prepare sound-absorbing materials with different stratified structures including a double-layer structure and alternating multilayered structure, respectively. The effects of the cell size of the PU foam and the thickness of the PU foam layer on the sound absorption efficiency of the BT/NBR-PU foam composite with a double-layer structure were studied, and the effects of the alternating unit number on the sound absorption efficiency of the BT/NBR-PU foam composite with an alternating multilayered structure were studied. The results show that the sound absorption peak of the double-layer structure composites would move toward low frequency with a decrease of the cell size of the PU foam or with an increase the thickness of the PU foam layer. With increasing alternating unit number, the composites with an alternating multilayered structure have good sound absorption performance in a wider frequency bandwidth. The sound absorption frequency range of the stratified composite could be adjusted by changing the cell size of the PU foam, the thickness of the PU foam layer and the alternating unit number. Each stratified structure BT/NBR-PU foam, whether with a double-layer structure or alternating multilayered structure, shows excellent sound absorption efficiency at low frequency owing to the combination of airflow resistivity, resonance absorption and interface dissipation.

BT/NBR-PU foam composites with two different stratified structures including double-layer and alternating multilayered have excellent low-frequency sound absorption performance.     

Effects of magnesium hydroxide on the properties of starch/plant fiber composites with foam structure

In this study, magnesium hydroxide (MH) flame-retarded starch/plant fiber composites containing various MH contents (0%, 5%, 15%, 15%) were prepared and named as TF-MH0, TF-MH5, TF-MH10, TF-MH15. Thermal degradation, flame retardancy, mechanical and microscopic characteristics were discussed. The reduction in the maximum thermal degradation rate revealed that the addition of MH provided improvement in the thermal stability of the composite. The horizontal burning test and the limiting oxygen index analysis suggested enhancement in flame retardancy with increasing MH content. Moreover, the density of composites initially decreased and then increased as the MH content increased. The tensile strength was positively correlated with the density, whereas the cushioning performance was negatively correlated with the density. Microscopic analysis showed that there was an interfacial interaction between MH and thermoplastic starch, which not only improves the thermal stability, but also promotes bubble nucleation as a nucleating agent. The cells of TF-MH10 were uniform and dense, thus TF-MH10 had the best buffering performance. Furthermore, the cell structure of TF-MH15 was short in diameter, small in number, and large in skeleton thickness; therefore, TF-MH15 had the highest tensile strength.

The process and the property of starch-based composite.     

琼脂-羟基磷灰石复合物的仿生合成及细胞相容性

背景:以有机大分子作为矿化模版进行骨组织修复材料的仿生构建,是目前骨修复材料的研究热点.而将琼脂应用于骨修复材料的报道较少.目的:仿生合成一种由琼脂和羟基磷灰石组成的新型纳米复合骨组织修复材料,评价其理化性能和细胞相容性.方法:①将一定量的非纳米羟基磷灰石的盐酸溶液,加入一定量的琼脂溶胶中,调整反应体系的pH值至7～8,然后将反应形成的复合物冷冻干燥后即得琼脂-羟基磷灰石复合材料.②将第3代SD大鼠骨髓基质细胞与琼脂-羟基磷灰石复合材料共培养,于培养1,3,5 d时观察细胞生长情况.结果与结论:X射线衍射仪,傅里叶变换红外光谱仪,热分析仪,透射电镜和扫描电镜对材料进行表征分析,显示琼脂良好控制了磷灰石晶体的生长,纳米的磷灰石晶体均匀分布在琼脂纤维中,琼脂-羟基磷灰石复合物具有多孔结构.共培养3,5 d时骨髓基质细胞在复合物中生长良好,并有较明显的细胞骨架形成.提示琼脂-羟基磷灰石复合物具有良好的理化性质和细胞相容性.     

Water-soluble and adjustable fluorescence copolymers containing a hydrochromic dye: synthesis,characterization and properties

Water solubility and adjustable fluorescence properties have been successfully implemented in the hydrochromic amino rhodamine via copolymerization. Four copolymers have been synthesized and clearly characterized by UV-Vis spectroscopy, proving greater detail than the commonly used NMR and IR technologies. The four copolymers have good solubility in pure water and in many common organic solvents, while preserving the hydrochromism of the dye monomer. Based on aggregation and dispersion of the copolymers as adjusted by solvent media and temperature, reversible fluorescence properties were successfully realized. Furthermore, their luminescence in solid state was observed. These studies are of great significance for expanding the application of hydrochromic dyes in biological fields and promoting green industrialization.

Water solubility and adjustable fluorescence adjustable properties have been successfully endowed to established in a hydrochromic dye via copolymerization.     

Photoluminescence,thermal and surface properties of triarylimidazole-containing polyimide nanocomposite films

In this work, a triarylimidazole-containing diamine 2-(4-methylphenyl)-4,5-bis(4-(4-amino-2-trifluoromethylphenoxy)phenyl)imidazole (MPBAI) was firstly synthesized and polymerized with 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) to prepare transparent polyimide (PI) films by means of thermal imidization. Then, inorganic nanoparticles including silica (SiO₂), alumina (Al₂O₃) and silicon nitride (Si₃N₄) were separately introduced into the PI(MPBAI-CBDA) with different mass fractions of 0.02%, 0.10%, 0.50% and 2.50% to obtain three series of PI nanocomposite films. All these films were close to colorless and transparent, although the light transmittance showed a downward trend due to the introduction of nanoparticles. Moreover, as the content of inorganic nanoparticles increased, the fluorescence intensities of these films were increased. Comparatively, the improvement effect of nano-SiO₂ was the most obvious. When the content of SiO₂ was 2.50%, the maximum intensity of the fluorescence absorption peak was increased by 9.6 times, and the absolute fluorescence quantum yield reached 17.2%, about 5.2 times that of the original PI film. Moreover, the maximum absorption peak produced a red shift of 85 nm due to the addition of 2.50% Si₃N₄, which was probably caused by the weakening of fluorescence quenching effect and high permittivity. The nanocomposites exhibited high glass transition temperatures of around 300 °C and excellent thermal stabilities. The surface hydrophobicity was changed by adjusting the mass and type of nanoparticles. Thus, this work provided a simple way to improve the photoluminescence effect by introducing the nanoparticles. The functional films will be expected to be applied in some optical applications.

Three series of triarylimidazole-containing polyimide nanocomposite films were prepared via thermal imidization. Due to the introduction of inorganic nanoparticles including SiO₂, Al₂O₃ and Si₃N₄, the fluorescence intensities of these composite films were clearly increased.     

Multifunctional biphenyl derivatives as photosensitisers in various types of photopolymerization processes,including IPN formation, 3D printing of photocurable multiwalled carbon nanotubes (MWCNTs) fluorescent composites

A series of 2-(diethylamino)-4-(1-ethylpropyl)-6-phenyl-benzene-1,3-dicarbonitrile derivatives were investigated in terms of photosensitisation in various photopolymerization processes in UV-A and vis light conditions. A full spectroscopic analysis of the tested compounds was performed. In addition to excellent spectroscopic properties, these compounds enable highly efficient photopolymerization processes, including free-radical, cationic and hybrid photopolymerization. As proven by a real-time FTIR study, these photosensitisers allow the formation of both thin and thick layers from different monomers. Finally, the investigated 2-(diethylamino)-4-(1-ethylpropyl)-6-phenyl-benzene-1,3-dicarbonitrile derivatives were used to obtain multiwalled carbon nanotubes (MWCNTs) composites for which the degree of conversion was determined using real-time FT-IR and Photo-Differential Scanning Calorimetry (Photo-DSC). Selected derivatives were applied as photosensitisers in two-component photoinitiating systems, operating according to the mechanism of photo-oxidation and photo-reduction, for the preparation of photo-cured MWCNTs composites. The importance of the quantity of multiwalled carbon nanotubes (MWCNTs) added to the polymeric matrix on the curing degree is also discussed in this study. The structures of the MWCNTs composites were analysed using an optical and fluorescence microscope. Moreover, this study also examines the applicability of new photoinitiator systems for printing nanocomposites by vat photopolymerization, which has gained increasing attention in recent years. Therefore, photocurable nanocomposite resin based on methacrylates was used for 3D printing in room temperature and atmospheric conditions, under a visible LED with emission at 405 nm, in order to obtain fluorescent photocurable patterns.

Summary of properties and applications of multifunctional of biphenyl derivatives as photosensitisers in various types of photopolymerization processes, including IPN formation, 3D printing of photocurable multiwalled carbon nanotubes (MWCNTs) fluorescent composites.     

Retention of supportive properties by eggcrate and foam wheelchair cushions

This study investigated the reported lack of ability of the eggcrate cushion (EC) to provide wheelchair users with adequate support necessary for comfort and tolerably low-peak sitting pressures over time. The primary parameter used to quantify the ability of the cushion to distribute load was the indention force deflection (IFD) metric. The EC was compared to a high-density planar foam cushion (HD). The IFD was measured for both cushions after successive periods of compression to simulate use. Study results failed to support the common perception that the soft EC would lose its supportive properties more rapidly than the much firmer HD cushion. Although the initial IFD of the EC was much lower than that of the HD, a smaller percentage of its IFD was lost after compression. This difference between the two cushions likely was due to differences in packaging. The EC was rolled into a cylinder, compressing it to 60% of its original thickness; the HD was packaged without compression.     

Effects of hydrotalcite on rigid polyurethane foam composites containing a fire retarding agent: compressive stress,combustion resistance,sound absorption,and electromagnetic shielding effectiveness

Polyether polyol, isocyanate, and a flame retardant (10 wt%), hydrotalcite (0, 1, 3, 5, 7, and 9 wt%) are used to form a rigid PU foam, while a nylon nonwoven fabric (400 g m⁻²) and a polyester aluminum foil are combined to serve as the panel. The rigid PU foam and the panel are then combined to form the rigid foam composites. The cell structure, compressive stress, combustion resistance, thermal stability, sound absorption, and electromagnetic shielding effectiveness of the rigid foam composites are evaluated, examining the effects of using hydrotalcite. When the hydrotalcite is 5 wt%, the rigid foam composites have an optimal density of 0.168 g cm⁻³, an average cell size of 0.2858 mm, a maximum compressive stress of 479.95 kpa, an optimal LOI of 29, an optimal EMSE of 45 dB, and the maximum thermal stability and sound absorption.

The synthesis of rigid polyurethane foam.     

光固化复合树脂的乳光及荧光性能

背景：光固化复合树脂在现代牙科美容修复中占重要位置,广泛用于临床牙体缺损的直接修复,可产生与牙体相似的颜色效果。目的：综述光固化复合树脂乳光、荧光效应的影响因素及研究现状。方法：由第一作者检索1989-01/2010-11中国期刊全文数据库和PubMed数据库,中文检索词＂光固化复合树脂,颜色,乳光,荧光＂,英文检索词＂resin composite,illumination,filler,scattering,opalescence,fluorescence,color＂,初检到129篇文献,依纳入排除标准,保留34篇归纳总结。结果与结论：光固化复合树脂材料能模拟天然牙的乳光性、荧光性,其中,光固化复合树脂中直径接近蓝光的无机填料对蓝光的散射、感光的有机基质对紫外光的吸收可以模拟天然牙,分别产生材料的乳光或荧光效应;它们受光源条件、材料状态以及临床相关操作等的影响,也可以影响光固化复合树脂的遮色力。     

光固化复合树脂的乳光及荧光性能

背景:光固化复合树脂在现代牙科美容修复中占重要位置,广泛用于临床牙体缺损的直接修复,可产生与牙体相似的颜色效果。目的:综述光固化复合树脂乳光、荧光效应的影响因素及研究现状。方法:由第一作者检索1989-01/2010-11中国期刊全文数据库和PubMed数据库,中文检索词"光固化复合树脂,颜色,乳光,荧光",英文检索词"resin composite,illumination,filler,scattering,opalescence,fluorescence,color",初检到129篇文献,依纳入排除标准,保留34篇归纳总结。结果与结论:光固化复合树脂材料能模拟天然牙的乳光性、荧光性,其中,光固化复合树脂中直径接近蓝光的无机填料对蓝光的散射、感光的有机基质对紫外光的吸收可以模拟天然牙,分别产生材料的乳光或荧光效应;它们受光源条件、材料状态以及临床相关操作等的影响,也可以影响光固化复合树脂的遮色力。     

Synergistic effect of proton irradiation and strain on the mechanical properties of polyimide fibers

The damage behaviors of polyimide fiber after 150 keV proton irradiation and the synergistic effect of proton irradiation and strain were investigated. Changes in the mechanical properties, free radicals, element content, and element chemical state of the polyimide fiber before and after 150 keV proton irradiation were investigated. The results showed that the tensile strength and elongation at break of the material decreased significantly after proton irradiation. The synergistic effect of proton irradiation and strain weakened the reduction of mechanical properties caused by single proton irradiation. After proton irradiation and the combination of proton irradiation and strain, pyrolytic carbon free radicals were generated. According to XPS analysis, the proton-irradiated polyimide fiber underwent complex denitrification and deoxygenation reactions, and carbon enrichment appeared on the surface of the material.

Compared with the single irradiated sample, the tensile strength and elongation at break after the combination of proton irradiation and strain increased, indicating that introducing strain during irradiation will weaken the damage of irradiation.     

Effects of chain extender on properties and foaming behavior of polypropylene foam

Polypropylene (PP) foam offers superior thermal and mechanical properties and versatile applications. However, the linear structure of PP hinders the fabrication of a uniform and fine foam, owing to changes in the melt strength with variations in the temperature. The foamability of the material can be improved by fabricating modified PP by introducing long-chain branches by grafting and chain extension reactions, using glycidyl methacrylate (GMA) and adipic acid (AA). Adding 5 phr GMA to PP optimizes the graft ratio. AA as a chain extender forms a long-chain branched structure, as confirmed by the melt flow index, morphology, and thermal and dynamic viscoelastic properties. Variations in foaming characteristics according to the AA content, temperature, volume expansion ratio, and oven residence time have also been observed. An optimal volume expansion ratio of ∼14 is obtained at an AA content of 1.5 phr and foaming for 11 min at 240 °C.

The mechanism of the grafting and chain extension reaction and changes in the PP structure and foamability.     

Enhanced mechanical properties of hBN–ZrO2 composites and their biological activities on Drosophila melanogaster: synthesis and characterization

In this study, six compositions in the system [x(h-BN)–(100 − x)ZrO₂] (10 ≤ x ≤ 90) were synthesized by a bottom up approach, i.e., the solid-state reaction technique. XRD results showed the formation of a novel and main phase of zirconium oxynitrate ZrO(NO₃)₂ and SEM exhibited mixed morphology of layered and stacked h-BN nanosheets with ZrO₂ grains. The composite sample 10 wt% h-BN + 90 wt% ZrO₂ (10B90Z) showed outstanding mechanical properties for different parameters, i.e., density (3.12 g cm⁻³), Young''s modulus (10.10 GPa), toughness (2.56 MJ m⁻³), and maximum mechanical strength (227.33 MPa). The current study further checked the in vivo toxicity of composite 10B90Z and composite 90B10Z using Drosophila melanogaster. The composite 10B90Z showed less cytotoxicity in this model, while the composite 90B10Z showed higher toxicity in terms of organ development as well as internal damage of the gut mostly at the lower concentrations of 1, 10, and 25 μg mL⁻¹. Altogether, the current study proposes the composite 10B90Z as an ideal compound for applications in biomedical research. This composite 10B90Z displays remarkable mechanical and biological performances, due to which we recommend this composition for various biomedical applications.

In this study, six compositions in the system [x(h-BN)–(100 − x)ZrO₂], (10 ≤ x ≤ 90) were synthesized by a bottom up approach, i.e., the solid-state reaction technique.     

Hydrothermal-template synthesis and electrochemical properties of Co3O4/nitrogen-doped hemisphere-porous graphene composites with 3D heterogeneous structure

Despite the high capacity of Co₃O₄ employed in lithium-ion battery anodes, the reduced conductivity and grievous volume change of Co₃O₄ during long cycling of insertion/extraction of lithium-ions remain a challenge. Herein, an optimized nanocomposite, Co₃O₄/nitrogen-doped hemisphere-porous graphene composite (Co₃O₄/N-HPGC), is synthesized by a facile hydrothermal-template approach with polystyrene (PS) microspheres as a template. The characterization results demonstrate that Co₃O₄ nanoparticles are densely anchored onto graphene layers, nitrogen elements are successfully introduced by carbamide and the nanocomposites maintain the hemispherical porous structure. As an anode material for lithium-ion batteries, the composite material not only maintains a relatively high lithium storage capacity (the first discharge specific capacity can reach 2696 mA h g⁻¹), but also shows significantly improved rate performance (1188 mA h g⁻¹ at 0.1 A g⁻¹, 344 mA h g⁻¹ at 5 A g⁻¹) and enhanced cycling stability (683 mA h g⁻¹ after 500 cycles at 1 A g⁻¹). The enhanced electrochemical properties of Co₃O₄/N-HPGC nanocomposites can be ascribed to the synergistic effects of Co₃O₄ nanoparticles, novel hierarchical structure with hemisphere-pores and nitrogen-containing functional groups of the nanomaterials. Therefore, the developed strategy can be extended as a universal and scalable approach for integrating various metal oxides into graphene-based materials for energy storage and conversion applications.

The Co₃O₄/N-HPGC nanocomposites synthesized by a hydrothermal-template approach with polystyrene microspheres as the template possess excellent electrochemical performance.     

The effective photocatalysis and antibacterial properties of AgBr/AgVO3 composites under visible-light

With the discharge of large amount of organic pollutants and antibiotics into the water environment, the water cycle has been seriously polluted, and at the same time, various drug-resistant bacteria have emerged in succession, which poses a serious threat to human health. In recent years, photocatalytic nanomaterials have become a research hotspot in the antimicrobial area. In this study, AgBr/AgVO₃ photocatalysts were prepared by a hydrothermal process and an in situ growth method. The composites were tightly connected by the (501) plane of AgVO₃ and the (200) lattice plane of AgBr. The photocatalytic activity was tested by degrading Rhodamine B (RhB) solution under visible-light, and the result indicated that the photodegradation rate for RhB solution was 92.3% by the photocatalysis with 0.5AgBr/AgVO₃ and the photocatalytic performance of 0.5AgBr/AgVO₃ was improved compared to pure AgVO₃ and AgBr. In addition, more than 99.997% of E. coli, S. aureus, and P. aeruginosa cells were killed by the photocatalysis with 0.5AgBr/AgVO₃ within 30 min. These results demonstrated that the 0.5AgBr/AgVO₃ heterojunction photocatalyst could be widely used in the treatment of environmental pollution and in the antibacterial field.

With the discharge of large amount of organic pollutants and antibiotics into the water environment, the water cycle has been seriously polluted, and at the same time, various drug-resistant bacteria have emerged in succession, which poses a serious threat to human health.