Adjusting the properties of silicone rubber filled with nanosilica by changing the surface organic groups of nanosilica

A series of nanosilica (denoted as nano-SiO₂) surface-capped with organic modifiers hexamethyldisilazane (denoted as HMDS; molecular formula: C₆H₁₉NSi₂) and KH570 (molecular formula: C₁₀H₂₀O₅Si) containing CC double bond were prepared by in situ surface-modification method. As-obtained nano-SiO₂ particles were characterized by Fourier transform infrared spectrometry and transmission electron microscopy, and they were also used to reinforce silicone rubber (denoted as SR) in order to improve the mechanical properties. Moreover, a universal material testing machine was performed to determine the mechanical properties of the SR-matrix nanocomposites. Results showed that the surface properties of nano-SiO₂ can be adjusted by changing the ratio of these modifiers. The tensile strength, tear strength and elongation at break of nano-SiO₂/SR nanocomposites are comparable to or even better than those of R-106/SR nanocomposite (R-106 refers to commercially obtained fumed SiO₂ nanoparticles that was modified with silane coupling agent). The mechanical strength of nano-SiO₂/SR nanocomposites especially for tear strength largely improve with adding a small amount of CC content of the surface-capped nano-SiO₂. More importantly, it could be feasible to manipulate the mechanical properties of silicone rubber by properly adjusting the dosages of surface-modifiers HMDS and KH570 during the preparation of in situ surface-capped nanosilica, which could be of special significance to developing high performance SR-matrix nanocomposites.     

Reaction products and their solidification process of the plasma sprayed Fe2O3–Al composite powders

Fe₂O₃–Al composite powders were deposited onto steel substrate by plasma spraying. The reaction products of the Fe₂O₃–Al composite powders in the plasma flame and their solidification process were investigated. The results showed that the reaction products of the Fe₂O₃–Al composite powders in the plasma flame were Fe–Al–O ceramic melt and Fe melt. Fe was not always formed in the reaction products of each composite particle, and the formation of Fe was dependent on the composition distribution and the reaction kinetics process of each composite particle. The composition inhomogeneity, discontinuity and porousness of the composite particles resulted in the difference of the reaction kinetics of each composite particle and the composition difference of the droplets. Hercynite solid solution, Fe, Al₂O₃ and FeAl phases were formed by non-equilibrium solidification of the Fe–Al–O ceramic melt. For the smaller size droplet, when it spread on the substrate, the spreading droplet was quickly chilled to form equiaxed grains with size of 100–200 nm. Nano-sized or submicron equiaxed grains, nano-sized columnar grains and cellular structure were formed in the larger spreading droplet. Fe rich hercynite solid solution nucleated and grew preferentially and then Al rich hercynite solid solution grew, which form composition segregation in the columnar grains. The main phases in the composite coating were hercynite solid solution.     

Hyperfine interactions and structural features of Fe–44Co–6Mo (wt.%) nanostructured powders

Nanocrystalline Fe–44Co–6Mo (wt.%) powders have been prepared by high-energy ball milling from elemental Fe, Co and Mo pure powders in a P7 planetary ball mill. The obtained powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Mössbauer spectrometry techniques. The influence of milling process and Mo substitution for Co in equiatomic FeCo have been examined in order to study structural evolution and formation mechanism of nanostructured Fe(CoMo) solid solution. XRD results show the formation of a BCC Fe(CoMo) solid solution (a = 0.2874 nm) where unmixed nanocrystalline Mo with a BCC structure is embedded. Disordered Fe(CoMo) solid solution is characterized by a broad hyperfine magnetic field distribution with two regions centered at B₁ = 35.0 T and B₂ = 30.7 T, respectively, attributed to disordered Fe(Co) solid solution and CoMo enriched environments. Prolonged milling and Mo addition cause the decrease of average hyperfine magnetic field while the average isomer shift remains nearly constant.     

PAN初生纤维拉伸性能试验研究

为了提高聚丙烯腈(PAN)初生纤维的可拉伸性能,将溶液纺丝得到的初生纤维进行不同时间的恒温干燥处理,研究其拉伸性能随干燥时间的变化规律。结果表明,干燥处理可以大幅度提升PAN初生纤维的力学性能,其拉伸强力可达10.3cN,断裂伸长可达263.5%;随着干燥时间的延长,纤维的可拉伸性能增强,经过10h干燥后的初生纤维具有最佳可牵伸性能;而拉伸速率的提高可以有效促进未干燥初生纤维的拉伸变形,而对干燥处理后纤维的拉伸性能的影响不大。用SEM观察纤维断裂形貌发现,PAN纤维的致密性随牵伸比的增加而提高。     

Study of some physical properties of biodegradable films based on blends of gelatin and poly(vinyl alcohol) using a response-surface methodology

The aim of this work was to study the effect of the hydrolysis degree (HD) and the concentration (C_PVA) of two types of poly(vinyl alcohol) (PVA) and of the type (glycerol and sorbitol) and the concentration (C_P) of plasticizers on some physical properties of biodegradable films based on blends of gelatin and PVA using a response-surface methodology. The films were prepared with a film forming solutions (FFS) with 2 g of macromolecules (gelatin+PVA)/100 g de FFS. The responses analyzed were the mechanical properties, the solubility, the moisture content, the color difference and the opacity. The linear model was statistically significant and predictive for puncture force and deformation, elongation at break, solubility in water, moisture content and opacity. The C_PVA affected strongly the elongation at break of the films. The interaction of the HD and the C_P affected this property. Moreover, the puncture force was affected slightly by the C_PVA. Concerning the solubility in water, the reduction of the HD increased it and this effect was greater for high C_PVA values. In general, the most important effect observed in the physical properties of the films was that of the plasticizer type and concentration. The PVA hydrolysis degree and concentration have an important effect only for the elongation at break, puncture deformation and solubility in water.     

Memory effects in exchange coupled Fe/Co3O4 nanocomposites

Nanocomposites comprising a ferromagnet and an antiferromagnet have drawn attention recently because of their interesting physical properties and variety of technological applications. In the present work, structural, hyperfine and magnetic properties of Fe/Co₃O₄ nanocomposites prepared by a chemical route having 10–70 wt.% of Fe, have been investigated. XRD and TEM measurements confirmed polycrystalline nature of the samples having grain size in the nanometer regime. FTIR measurements show the presence of two bands of Co–O corresponding to Co²⁺ and Co³⁺. Mössbauer spectra recorded at room temperature confirm the presence of Fe in the blocked state. Presence of exchange bias at Fe–Co₃O₄ interfaces is confirmed by the magnetization measurements. Irreversibility in temperature dependent FC–ZFC measurements points to interface effect. Frequency dependent ac susceptibility measurements as well as memory effect observed in dc magnetization measurements indicate the superspin glass nature of the nanocomposites.     

Sugarcane bagasse cellulose/HDPE composites obtained by extrusion

Natural fibers used in this study were both pre-treated and modified residues from sugarcane bagasse. Polymer of high density polyethylene (HDPE) was employed as matrix in to composites, which were produced by mixing high density polyethylene with cellulose (10%) and Cell/ZrO₂·nH₂O (10%), using an extruder and hydraulic press. Tensile tests showed that the Cell/ZrO₂·nH₂O (10%)/HDPE composites present better tensile strength than cellulose (10%)/HDPE composites. Cellulose agglomerations were responsible for poor adhesion between fiber and matrix in cellulose (10%)/HDPE composites. HDPE/natural fibers composites showed also lower tensile strength in comparison to the polymer. The increase in Young’s modulus is associated to fibers reinforcement. SEM analysis showed that the cellulose fibers insertion in the matrix caused an increase of defects, which were reduced when modified cellulose fibers were used.     

水相悬浮聚合制备MWCNTs/PAN复合微球及其电纺纤维

先用Fenton试剂（过氧化氢/硫酸亚铁）对多壁碳纳米管进行改性处理（-fMWCNTs）,再通过水相悬浮聚合法制备了多壁碳纳米管/聚丙烯腈（-fMWCNTs/PAN）复合微球,用静电纺丝技术制备了-fMWCNTs/PAN复合纤维膜。通过扫描电镜（SEM）、热重分析仪（TGA）和万能试验机研究了-fMWCNTs对电纺纤维...     

(Fe,Cr)7C3/Fe surface gradient composite: Microstructure,microhardness, and wear resistance

In this study, the (Fe,Cr)₇C₃/Fe surface gradient composite was produced by in situ synthesis process with subsequent heat treatment. According to the results of thermal analysis, the as-cast specimen was subjected to heat treatment at 1180 °C for 3 h in argon atmosphere. The phase composition, microstructure, microhardness, and wear resistance of the samples were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers hardness tester, and wear resistance tester, respectively. The XRD results show that α-Fe and (Fe,Cr)₇C₃ are the predominant crystalline phases in the composite obtained. The volume fraction of (Fe,Cr)₇C₃ particulates has a gradient distribution from the surface to the matrix, and the morphology of (Fe,Cr)₇C₃ particulates changes considerably. A dense ceramic layer is formed on the upper surface of (Fe,Cr)₇C₃/Fe surface gradient composite with a volume fraction of 90%. The microhardness of the dense ceramic layer is 1484 HV_0.1, and its relative wear resistance is five times higher than that of the iron matrix.     

Effect of C<Subscript>60</Subscript> fullerene additives on the structure and mechanical properties of thin organic glass films

We have studied the effect of small additives of C₆₀ fullerene on the mechanical properties (strength, Young’s modulus, elongation at break) of thin organic glass films tested for uniaxial extension.     

Hierarchical poly(p-phenylene benzobisoxazole)/graphene oxide reinforcement with multifunctional and biomimic middle layer

A new hierarchical reinforcement developed by coating biomimic polydopamine (PDA) on the surface of poly(p-phenylene benzobisoxazole) (PBO) fibers, which served as a platform for the graphene oxide (GO) grafting, using branched polyethyleneimine (b-PEI) as a bridging agent. The surface morphologies and chemical structures of PBO fibers were characterized for confirming the formation of covalent bond between GO and PBO fibers. The surface roughness (R_a) and wettability of the obtained fibers, denoted as PBO@PDA-PEI-GO, were obviously increased in comparison with those of untreated one. The reinforcement offered a 68.8% enhancement in the interfacial shear strength (IFSS) without degrading the base fiber. The PDA layer on the PBO fiber surface led to improved UV resistance. The hydrothermal aging resistance of PBO/epoxy composite was also greatly improved. This biomimic surface modification approach is facile to prepare, highly efficient to enhance interface, adaptable to all high-performance fibers, and meaningful in multifunctional applications.     

Influence of strain amplitude on damping property of aluminum foams reinforced with copper-coated carbon fibers

Aluminum foams containing 0.35, 1.0, 1.7 vol.% copper-coated carbon fibers were fabricated by a melt route. The room temperature damping property of Al/C_f foam was studied at different strain amplitude in two directions. The experimental results show that the critical strain amplitude decreases and the damping capacity of Al/C_f foam increases with the copper-coated carbon fibers contents. It can be attributed to the interfacial micro-slip increasing with the C_f contents and the microplasticity deformation arises from the micro-crack among the C_f–Al interface. Moreover, the damping property in the transverse direction is higher than that in the longitudinal direction. The ratio of longitudinal loss factor to transverse loss factor is almost independent of the C_f contents and strain amplitude.     

气氛中硫和氯导致Fe-15Cr-10Al合金表面氧化铝膜退化

研究了Fe-15Cr-10Al合金在700℃还原性H_2-CO_2和H_2-HCl-H_2S-HCl混合气氛中的腐蚀行为.结果表明,添加到H_2-CO_2气氛中的微量HCl和H_2S导致合金表面氧化铝膜退化,在合金表面生成了铁铬铝混合氧化物层.这种退化与腐蚀过程中生成的硫化物和氯化物密切相关.计算混合气氛中平衡时的氯势、氧势和硫势预测了合金与气氛可能发生的反应,并解释了腐蚀机制.     

Mechanical properties of wood–fiber reinforced polypropylene composites: Effect of a novel compatibilizer with isocyanate functional group

Natural fibers are increasingly being used as reinforcement in commercial thermoplastics due to their low cost, high specific properties and renewable nature. While the maleic anhydride modified polypropylene (MAPP) is most commonly used as compatibilizer to improve interfacial adhesion between hydrophilic wood–fibers and hydrophobic polypropylene, in this study, a novel compatibilizer (m-TMI-g-PP) with isocyanate functional group was synthesized by grafting m-isopropenyl-α,α-dimethylbenzyl-isocyanate (m-TMI) onto isotactic polypropylene (PP) in a twin screw extruder. The effect of filler concentration on the mechanical properties of wood–fiber filled composites, prepared by using m-TMI-g-PP as the compatibilizer, was investigated. The addition of the compatibilizer resulted in greater reinforcement of composites, as indicated by the improvement in mechanical properties. Tensile strength of composites so prepared increased by almost 45%, whereas 85% increase in flexural properties was observed. However the addition of wood–fibers resulted in a decrease in elongation at break and impact strength of the composites.     

Changes of polyacrylonitrile fiber fine structure during thermal stabilization

In this article regularities of length changes of polyacrylonitrile (PAN) fiber, as well as its structure transformation into the structure of thermally stabilized fiber, have been studied in detail. The fiber has been manufactured with the use of dimethyl sulfoxide (PAN¹) and dimethyl formamide (PAN²), with methylacrilate content of 5% (mass). Thermal stabilization has been carried out under isothermal conditions at 245, 255 and 265, 275, 285 and 290 °C in atmospheric air at constant load of 0.6 g/tex. By X-ray structural analysis it has been shown that the structure of PAN fiber crystal component is depicted by two kinds of coherent-scattering regions (CSR), differing in the average size by an order of magnitude. Phase transition of PAN into the new highly dispersed phase is accompanied by dispersion of PAN larger CSR. Qualitative and quantitative regularities of fine structure evolution have been determined at thermal treatment in the indicated temperature range. It has been shown that the transition of PAN¹ fiber into the new two-phase state during thermal stabilization progressed more actively than the same process in PAN², by ~25%. Increase of thermal treatment temperature leads to significant acceleration of PAN crystal phase dispersion and formation on the new highly dispersed phase. At that instance, average sizes of CSR of highly dispersed components of thermally stabilized fiber equal ~1 nm at the end of the process, when aromatization index of the material amounts to 51–58%.     

Effect of C<Subscript>60</Subscript> fullerene additives on the mechanical properties of low-density polyethylene films

We have studied the effect of C₆₀ fullerene additives on the mechanical properties (strength, Young’s modulus, elongation at break) of thin low-density polyethylene films tested for uniaxial extension.     

Mechanical properties of basalt fibers and their adhesion to polypropylene matrices

This work is aimed to study the mechanical properties of basalt fibers, and their adhesion to polypropylene (PP) matrices. Single filament tensile tests were used to calculate the strength of different types of fibers, characterized by different providers and surface treatment. Single fiber fragmentation tests (SFFT) were used to calculate the critical length of the fibers, in a homopolymer PP matrix and in a maleic anhydride modified PP matrix. It was shown that the tensile strength of the fibers is not significantly influenced by the origin or the surface treatment. Only fibers without any sizing show very reduced mechanical properties. On the other hand, the tensile strength was shown to be severely dependent on the filament length. Weibull theory was used in order to calculate the fitting parameters σ₀ and β, which were necessary in order to extrapolate the tensile strength to the critical length determined by SFFT. This allowed calculating the adhesion properties of the basalt fibers. It was shown that fiber–matrix adhesion is dependent on both the presence of sizing on the fiber surface, as well as on the modification of the matrix.     

Thermal shock behavior of as-sintered and pre-oxidation Zr2Al4C5–20SiC composites

A water-quenching technique was adopted to evaluate the thermal shock behavior of as-sintered and pre-oxidation Zr₂Al₄C₅–20 vol.%SiC composites in an air atmosphere. The strength retention of the two kinds of composites was measured after varying temperature (ΔTc) up to 800 °C. As-sintered Zr₂Al₄C₅–20 vol.%SiC showed rapidly drop in flexural strength above ΔT of 400 °C. However, the pre-oxidation Zr₂Al₄C₅–20 vol.%SiC composite showed a higher retained strength up to 800 °C, and the critical thermal shock temperature difference (ΔTc) is as high as 660 °C. The main reasons for a great improvement of thermal shock resistance (TSR) were also discussed and analyzed.     

Enhancement of mechanical properties of TiO2 nanofibers by reinforcement with polysulfone fibers

The titania (TiO₂)/polysulfone (PSF) blend fibers were prepared by hybrid electrospinning to impart mechanical stability to the TiO₂ fibers. The TiO₂/PSF blend fibers (2/1 and 1/1, w/w) were prepared by adjusting the flow rate of PSF solution with the flow rate of the TiO₂ sol fixed. The PSF fibers in the blend fibers provided the mechanical stability for the TiO₂ fibrous mat. Both the tensile strength and modulus of the TiO₂/PSF blend fibers increased gradually with increasing PSF content, whereas the breaking elongation decreased. This suggests that PSF fibers play an important role in the mechanical resistance of blend fiber mats.     

C6位选择性氧化竹浆纤维的壳聚糖改性处理

采用H_3PO_4/HNO_3-NaNO_2氧化体系对竹浆纤维C6位进行选择性氧化,然后与壳聚糖溶液交联反应制备生态的抗菌壳聚糖改性竹浆纤维。固相CP/MAS 13 C核磁共振分析显示,H_3PO_4/HNO_3-NaNO_2已将竹浆纤维C6位上的伯羟基选择性氧化成羧基,且红外光谱和扫描电镜测试表明,壳聚糖的氨基与氧化竹浆纤维分子上的羧基发生酰胺化反应,壳聚糖分子通过C-N化学键共价交联在竹浆纤维上,并在竹浆纤维表面形成壳聚糖薄膜。通过分析H_3PO_4/HNO_3-NaNO_2氧化和壳聚糖处理过程中竹浆纤维羧基含量、机械强力、壳聚糖含量等指标,得出最佳工艺参数。Kjeldahl定氮分析得出壳聚糖在氧化竹浆纤维上的最大含量为3.92%。壳聚糖接枝竹浆纤维的断裂强度变化不明显,但其断裂伸长率降低。抗菌试验结果显示,与壳聚糖处理的原竹浆纤维抗菌性相比,壳聚糖改性竹浆纤维对大肠杆菌和金黄色葡萄球菌的抗菌效果明显提高,抑菌率均在96%以上,且壳聚糖改性竹浆纤维具有良好的抗菌耐洗涤性能。