Blends of nylon 6 with a polyethylene functionalized by photooxidation

An easy and cheap method to prepare functionalized polyethylene is reported in which polyethylene is photooxidized and then melt-blended with nylon. Structural, rheological, and mechanical modifications indicate that carbonyl, formed during photooxidation, and amine groups react giving rise to copolymers which stabilize the blends. Photooxidized polyethylene from waste could be very effective in preparing polyethylene/polyamide blends with improved properties. This new approach improves over current methods in which compatibilization of polyolefines and polyamides is mostly performed by reacting functionalized polyolefines with polyamides in molten state. The functionalization is achieved by chemical modification of the polyolefines chains. This step could be very expensive.     

功能化石墨烯改性双马来酰亚胺复合材料的微观表征及性能

采用改进Hummers法制备氧化石墨烯（GO）,分别采用水合肼、壳聚糖、KOH还原得到了还原氧化石墨烯（rGO）并对三种还原方法做了对比,选择最佳方案;再通过离子液体（NH₂IL）对rGO功能化得到改性还原氧化石墨烯（NH₂IL-rGO）。以二烯丙基双酚A （BBA）和双酚A双烯丙基醚（BBE）为活性稀释剂,4,4'-二氨基二苯甲烷型双马来酰亚胺（MBMI）为反应单体,制备了MBMI-BBA-BBE （MBAE）树脂基体;同时以NH₂IL-rGO为增强体采用原位聚合法制备NH₂IL-rGO/MBAE复合材料。表征了石墨烯和复合材料的微观形貌并分析了石墨烯对复合材料性能的影响。结果表明：NH₂IL-rGO在树脂基体中以两相形式存在,结构完整,并赋予复合材料优异的性能。当NH₂IL-rGO含量为2%（质量）时,复合材料冲击强度和弯曲强度最大,分别为15.33 kJ/m²和142 MPa,热分解温度为435.73℃、当测试频率为100 Hz～10 kHz时介电常数发生突变达到84。     

Epoxy/p‐phenylenediamine functionalized graphene oxide composites and evaluation of their fracture toughness and tensile properties

In an attempt to enhance the mechanical properties of epoxy/graphene‐based composites, the interface was engineered through the functionalization of graphene oxide (GO) sheets with p‐phenylenediamine; this resulted in p‐phenylenediamine functionalized graphene oxide (GO–pPDA). The morphology and chemical structure of the GO–pPDA sheets were studied by spectroscopic methods, thermal analysis, X‐ray diffraction, and transmission electron microscopy. The characterization results show the successful covalent functionalization of GO sheets through the formation of amide bonds. In addition, p‐phenylenediamine were polymerized on graphene sheets to form crystalline nanospheres; this resulted in a GO/poly(p‐phenylenediamine) hybrid. The mechanical properties of the epoxy/GO–pPDA composite were assessed. Although the Young's modulus showed improvement, more significant improvements were observed in the strength, fracture strain, and plane‐strain fracture toughness. These improvements were attributed to the unique microstructure and strong interface between GO–pPDA and the epoxy matrix. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43821.     

The effect of the secondary relaxations on the fracture toughness of nylon 6/amorphous nylon 6IcoT blends

The fracture toughness of semicrystalline nylon 6, amorphous nylon 6IcoT, and their blends can be represented as the inherent toughness plus the toughness due to the formation of the crack tip plastic zone. The inherent toughness originates mostly from the molecular alignment near the crack tip plus a small contribution from chain scission. The plastic zone contribution is determined by its size and the energy dissipated by irreversible plastic deformation. The inherent toughness and the energy dissipated in the process zone are temperature dependent and primarily determined by the stress-induced molecular movement, which is related to the operative secondary β or γ relaxation.     

Increased optical nonlinearities of graphene nanohybrids covalently functionalized by axially-coordinated porphyrins

Two graphene oxide (GO)-based nanohybrid materials possessing covalent linkages to axially-coordinated tetraphenylporphyrin (TPP), GO–TPP, were prepared and were characterized by Fourier transform infrared (FT-IR), Ultraviolet–visible (UV–Vis) absorption, steady state fluorescence, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), thermogravimetric analysis (TGA), elemental analysis and Raman spectroscopic techniques. The nonlinear optical properties and optical limiting performance of GO, GO–TPP nanohybrids and the free porphyrins dihydroxotin(IV) tetraphenylporphyrin (SnTPP) and the phosphorus-cored porphyrin (PTPP) were investigated using nanosecond and picosecond Z-scan measurements at 532 nm. At the identical mass concentration of 0.2 mg mL⁻¹, GO–TPP nanohybrids exhibited enhanced nonlinear optical properties and optical limiting performance, ascribed to a combination of nonlinear scattering and/or two-photon absorption with reverse saturable absorption, and the photo-induced electron or energy transfer from the electron-donor porphyrin moiety to the acceptor graphene.     

Designed nitrogen doping of few-layer graphene functionalized by selective oxygenic groups

Few-layer nitrogen doped graphene was synthesized originating from graphene oxide functionalized by selective oxygenic functional groups (hydroxyl, carbonyl, carboxyl etc.) under hydrothermal conditions, respectively. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) observation evidenced few-layer feature of the graphene oxide. X-ray diffraction (XRD) pattern confirmed phase structure of the graphene oxide and reduced graphene oxide. Nitrogen doping content and bonding configuration of the graphene was determined by X-ray photoelectron spectroscopy (XPS), which indicated that different oxygenic functional groups were evidently different in affecting the nitrogen doping process. Compared with other oxygenic groups, carboxyl group played a crucial role in the initial stage of nitrogen doping while hydroxyls exhibited more evident contribution to the doping process in the late stage of the reaction. Formation of graphitic-like nitrogen species was controlled by a synergistic effect of the involved oxygenic groups (e.g., -COOH, -OH, C-O-C, etc.). The doping mechanism of nitrogen in the graphene was scrutinized. The research in this work may not only contribute to the fundamental understandings of nitrogen doping within graphene but promote the development of producing novel graphene-based devices with designed surface functionalization.     

用汉森溶解度参数评估功能化石墨烯在溶剂中的分散性

石墨烯独特的结构使其容易团聚,不溶于大多数的溶剂,应用受到极大限制。本工作用海藻酸钠(SA)和聚乙烯吡咯烷酮(PVP)表面改性石墨烯抑制石墨烯团聚,用扫描电子显微镜、傅里叶变换红外光谱、拉曼光谱和X射线衍射仪对其进行表征,考察了两种功能化石墨烯在溶剂中的分散性,并根据分散结果计算了汉森溶解度参数。结果表明,石墨烯成功功能化,经两种分散剂表面改性的石墨烯在溶剂中的分散性改变较大,在水中分散性较好,汉森溶解度参数和汉森球半径均发生改变。汉森球半径变大表明表面改性增大了石墨烯在溶剂中的溶解度。     

Enhanced toughness of zirconia ceramics with graphene platelets consolidated by spark plasma sintering

Graphene platelets reinforced zirconia (GPLs/ZrO₂) composites were prepared by spark plasma sintering in the present work. The effects of GPLs content on the densification route, microstructure feather, mechanical properties, and aging behaviors of such composites were investigated. In spite of the impeding effect of GPLs, high relative density of 98% was achieved for the composites owing to the uniform dispersion of GPLs. The addition of GPLs contributed to enhanced fracture toughness of the composites; when the added content was 1.0 wt.%, its fracture toughness reached up to 8.6 MPa·m^1/2. Also, aging behavior of the GPLs/ZrO₂ composites was investigated at 134°C for 24 hours. The monolithic ZrO₂ ceramic and GPLs/ZrO₂ composites presented residual ratio of 55% and 72% in fracture toughness, respectively. Thus, the incorporation of GPLs inhibited phase transformation from tetragonal phase to monoclinic phase of zirconia.     

Interpretive nonlinear viscoelasticity: Dynamic properties of nylon 6, nylon 66, and nylon 12 fibers

Nonlinear response of nylon 6, nylon 66, and nylon 12 fibers to sinusoidal straining under relatively large strain amplitude is analyzed in terms of the changes in properties during the straining, i.e., the change in modulus, change in internal friction and change in structure which involves energy release or absorption in straining. Modulus generally increases with strain but it decreases with increase of strain amplitude, the effect of strain amplitude being largest with nylon 6 and smallest with nylon 66. Mechanical loss increase with the increase of strain amplitudes in nonlinear manner, and the magnitude of change is largest with nylon 66 and smallest with nylon 6. During the extension phase, structural change occurring in nylon 6 is predominantly an increase in order or orientation while that with nylon 66 is crack opening or cavitation. Various aspects of the experiments and analysis of the data are described in detail.     

Modification and compatibilization of nylon 6 with functionalized styrenic block copolymers

Much work in recent years had focused on the improvements of the impact properties of engineering thermoplastics by the addition of a low modulus modifier that contains polar moieties as a result of polymerization or that has been modified to contain polar moieties as a result of various grafting techniques. Styrenic block copolymers (styrene-ethylene/butylene-styrene) functionalized with maleic anhydride have proved useful as impact modifiers and compatibilizers in blends with engineering thermoplastics. This paper focuses on the use of these functionalized elastomers to modify nylon 6. In such compositions, a nylon material with unique mechanical performance may be achieved using the functionalized elastomer either alone or in combination with an unfunctionalized styrenic block copolymer. The optimization of performance in these rubber toughened polyamide blends using various types of styrenic block copolymers is discussed. The morphology as it pertains to performance is also reviewed. The information contained herein may prove useful in obtaining a better understanding of the mechanisms of compatibilization and modification of nylon 6 systems.     

Highly-efficient fabrication of nanoscrolls from functionalized graphene oxide by Langmuir–Blodgett method

We report a Langmuir–Blodgett (LB) approach for highly-efficient fabrication of nanoscrolls from functionalized graphene oxide single sheets. Transmission electron microscope study reveals that the scroll has a tubular structure without caps at its ends. The scrolls align parallel to the moving barriers of the LB equipment and exhibit a loose-dense pattern during the LB compression process. We find that specific solvents can unwind the scrolled structures. Electrical characterization of the well-aligned scrolls was also performed. The method demonstrated here opens up a new avenue for high-yield fabrication of carbon nanoscrolls using functionalized graphene oxide as the building blocks.     

Monolithic carbons with spheroidal and hierarchical pores produced by the linkage of functionalized graphene sheets

We report a novel monolithic porous carbon constructed by the hydrothermal self-assembly of graphene oxide sheets with poly (vinyl alcohol) as the linker in the formation process of a three-dimensional (3D) structure. All the pores in this carbon have circular cross-sections and range from micropores to mesopores to macropores and are formed by the gradual removal of trapped water. This 3D graphene network together with unique spheroidal and hierarchical pore structure with macropore openings at the surface allows fast ion and electron transport into the innermost micropores. The carbon not only exhibits excellent capability for removal of dye pollutants and oils but also shows a good performance as an electrode material in lithium ion batteries. Moreover, it is also proved to be an ideal buffer for expanded active materials in electrochemical energy storage.     

Increasing the thermoelectric power generated by composite films using chemically functionalized single-walled carbon nanotubes

We prepared and characterized flexible thermoelectric (TE) materials based on thin films of single-walled carbon nanotube (SWCNT) composites with polyvinylalcohol. While pristine SWCNTs incorporated in a polymer matrix generated a p-type TE material, chemical functionalization of SWCNTs by using polyethyleneimine produced an n-type TE material. TE modules made of both p- and n-type composite were fabricated to demonstrate TE voltage and power generation. A single p–n junction made of two composite strips containing 20 wt.% of SWCNTs generated a high TE voltage of 92 μV per 1 K temperature gradient (ΔT). By combining five electrically connected p–n junctions an output voltage of 25 mV was obtained upon the applying ΔT = 50 K. Furthermore, this module generated a power of 4.5 nW when a load resistance matched the internal module resistance of 30 kΩ. These promising results show the potential of TE energy conversion provided by the SWCNT composite films connected in scalable modules for applications that require light weight and mechanical flexibility.     

用双螺杆挤出机制备丁腈橡胶/尼龙12热塑性弹性体

采用双螺杆挤出机通过动态硫化法制备了丁腈橡胶/尼龙12热塑性弹性体,考察了双螺杆挤出机的螺杆转速和机筒温度对所制备热塑性弹性体力学性能和微观形态的影响。结果表明,用双螺杆挤出机动态硫化制备的丁腈橡胶/尼龙12热塑性弹性体呈两相"海岛结构",即丁腈橡胶为分散相、尼龙12为连续相。随着挤出机螺杆转速的提高,弹性体的硬度、拉伸强度和扯断伸长率先增大后减小,撕裂强度和压缩永久变形逐渐降低;螺杆转速对弹性体耐油性能的影响不大;当螺杆转速增至400 r/min时,丁腈橡胶的粒径较小且分布均匀。随着双螺杆挤出机温度的升高,弹性体的硬度和拉伸强度逐渐增大,扯断伸长率、撕裂强度和压缩永久变形均先增大而后减小,耐油性能变差;温度升高使得丁腈橡胶难于在剪切作用下破碎,颗粒变大且分布不均。     

Spinodal decomposition in the Ta-Mo-Al-N films activated by Mo incorporation: Toward enhanced hardness and toughness

Spinodal decomposition in the transition metal aluminum nitrides, usually triggered by annealing, can enhance hardness via forming coherent nanometer-size domains, but it is still required to activate during fabrication. Herein, Mo was introduced into Ta-Al-N to obtain Ta-Mo-Al-N films by co-sputtering method, which induced two kinds of phase separations, including ~?15?at% Mo induced presence of stable wurtzite AlN phase and ~?28?at% Mo activated spinodal decomposition forming coherent fcc-Ta-Al-N and Mo-Al-N nano-domains. It is found that both hardness and toughness would be worsened by presence of hexagonal wurtzite AlN phase at incorporation of ~?15?at% Mo. On the contrary, once spinodal decomposition took place at ~?28?at% Mo, achieving the joint targets of enhanced hardness and toughness, together with reduced friction and improved wear-resistance. It may provide a new strategy to activate spinodal decomposition during fabrication by alloying additional elements.     

Enhancing toughness and strength of SiC ceramics with reduced graphene oxide by HP sintering

In this paper, the silicon carbide-reduced graphene oxide (SiC/rGO) composites with different content of rGO are investigated. The hot pressing (HP) at 2100?°C for 60?min under a uniaxial pressure of 40?M?Pa resulted in a near fully-dense SiC/rGO composite. In addition, the influence of graphene reinforcement on the sintering process, microstructure, and mechanical properties (fracture toughness, bending strength, and Vickers hardness) of SiC/rGO composites is discussed. The fracture toughness of SiC/rGO composites (7.9MPam^1/2) was strongly enhanced by incorporating rGO into the SiC matrix, which was 97% higher than the solid-state sintering SiC ceramics (SSiC) by HP. Meanwhile, the bending strength of the composites reached 625?M?Pa, which was 17.3% higher than the reference materials (SSiC). The microstructure of the composites revealed that SiC grains were isolated by rGO platelets, which lead to the toughening of the composite through rGO pull out/debonding and crack bridging mechanisms.     

Photochemistry of covalently functionalized graphene oxide with phenothiazinyl units

Phenothiazinyl units have been covalently attached to graphene oxide (GO) by nitrene insertion onto CC bonds. Laser flash photolysis of this material indicates that tethering of phenothiazinyl units to GO enhances significantly the interaction with respect to mixtures of both components, leading to the observation of photoinduced electron transfer.     

Structural evolution of functionalized graphene sheets during solvothermal reduction

Solvothermally reduced and functionalized graphene (SRFG) was obtained by refluxing graphene oxide in dimethyl formamide at 140 °C. The resultant simultaneous nitrogen-doping and presence of dangling bonds on SRFG prompted us to study the evolution of structural changes with refluxing time. It is shown that the removal of oxygen-containing functional groups leaves dangling bonds during the solvothermal reduction, which are responsible for the nitrogen-doping with longer refluxing time. The relationship between the defects of SRFGs and their lithium ion storage performances are also discussed.     

Increasing the strength and toughness of a carbon fiber/silicon carbide composite by heat treatment

The effect of heat treatment on the strengthening and toughening of a carbon fiber/silicon carbide composite (C/SiC) with a thin pyrolytic carbon (PyC) interphase was investigated. Tensile strength and modulus were measured using tensile tests, and toughness was obtained by calculating the area under the stress–strain curves. Results show that with increasing heat treatment temperature both the strength and toughness of the C/SiC composite increased, but the modulus decreased. After heat treatment at 1900 °C the tensile strength and toughness increased by a maximum of 42% and 252%, respectively, and the modulus decreased by 48%. X-ray diffraction analysis and microstructural observation confirmed that the heat treatment mainly increased the graphitization of the amorphous PyC interphase, and this was responsible for the property changes observed because it decreased the interfacial sliding resistance associated with long fiber pull-out, relieved the thermal residual stress and lower stress concentrations on the fibers to uniformly share the load for improving the strength and toughness.     

功能化石墨烯在防腐涂料中的应用

介绍了石墨烯的基本特性和作为新型纳米填料在防腐涂料领域发挥的重要作用,论述了采用共价键法和非共价键法修饰石墨烯的方法以及研究进展,并且通过对两种修饰方法对比,可根据不同的实验需求采取相应的修饰方法。同时结合近年来功能化石墨烯在防腐涂料中的研究及应用状况,针对功能化石墨烯在防腐涂料的应用过程中受到限制的原因进行了分析,对功能化石墨烯在防腐涂料中的前景进行了展望。