气相生长碳纤维填充聚苯乙烯的熔体动态流变行为

采用修正的两相模型讨论加工条件对不同体积分数(ψ=0～0.05)气相纳米碳纤维(VGCF)填充聚苯乙烯(PS)熔体(200℃)频率(ω)依赖性动态流变的影响.与弱剪切条件(190℃;30 r/min-5 min)下所制备的材料相比,VGCF在强剪切条件(190℃;120 r/min-10 min)下所制备材料中分散均匀,“粒子相”应变放大因子A,(ψ)较低,而松弛指数n较高.将应变(γ)依赖性G″(ω,ψ)应变放大因子A,(ψ,γ)与“粒子相”特征模量G″fψ(,γc),G″f(ψ,γc)引入两相模型,讨论加工条件对γ依赖性非线性流变行为的影响.研究结果表明,两相模型可定量讨论填充熔体动态流变行为.加工条件影响VGCF在基体中的分散性,但不影响“粒子相”弹性贡献R′f(ψ)与n的关系、G′f(ψ,γc)与非线性应变幂律指数x的关系以及G″f(ψ,γc)与非线性应变幂律指数y的关系,说明“粒子相”对填充熔体黏弹性的贡献与其弛豫特性及结构稳定性密切相关.     

加工工艺对气相生长碳纤维填充聚苯乙烯复合体系导电逾渗与动态流变特性的影响

研究了加工工艺对气相生长碳纤维(VGCF)填充聚苯乙烯(PS)复合体系导电逾渗与动态流变特性的影响.结果表明,低转速、短时间混合有利于VGCF形成较为完善的逾渗网络结构,其复合体系逾渗阈值低、导电性能好.使用作者提出的两相模型描述VGCF/PS复合体系的流变特性,发现低转速、短时间(30 r/min、5 min)混合条...     

Y2O3/ZrO2中空纤维陶瓷膜的制备与表征

本文结合相转化技术和干湿法纺丝工艺制备了以YSZ(以摩尔分数为8%的Y2O3稳定的ZrO2)为原料的中空纤维陶瓷膜, 考察了YSZ粉体的粒度分布和形貌, 并研究了YSZ中空纤维陶瓷膜的气密性、 孔特性、 机械性能、 微观结构及晶型变化等.     

Analytical investigation of plasma-treated carbon fibres

As-grown and heat-treated vapour grown carbon fibres (VGCF) in the as-prepared state, washed in HCl/H(2)O, and treated in O(2) plasma for different periods have been investigated by means of XPS and scanning electron microscopy (SEM). The surface energy of the carbon fibres before and after plasma treatment was determined from the wetting contact angle. Washing introduced hydroxyl, carbonyl and carboxyl groups onto the fibre surfaces and oxygen plasma treatment increases the total atomic concentration of oxygen up to 17%. This is in good agreement with the value of the polar component of the surface energy. Plasma treatment also enhanced the fibre surface porosity (by etching).     

Electrical conductivity of carbon fibres/polyester resin composites in the percolation threshold region

The electrical conductivity of composites of a polyester resin filled with short carbon fibres has been investigated with a special attention to the properties in the percolation threshold region. A very low percolation threshold (0.7-0.8 vol% of the filler) was confirmed. In contrast to S-shaped curves calculated according to the percolation theory of composites of globular particles, the experimental conductivity vs. fibre content dependence, after a steep increase in the percolation region, increased almost linearly. This atypical behaviour was explained by a different mechanism of formation of fibrous and globular conducting structures above the percolation threshold. An increase in scatter of conductivity values observed at percolation threshold as a consequence of great fluctuation of fibre arrangement manifested itself also in the conductivity-temperature dependences.     

改性壳聚精膜用于醇水混合液分离的研究──Ⅲ．超细粉末填充壳聚精膜

首次制备了用Ｓｉ３Ｎ４，ＳｉＯ２，ＴｉＨ４超细粉末填充的改性壳聚精膜，并将其用于乙醇／水混合液的分离中。实验表明壳聚糖膜经超细粉末填充后强度增大，溶胀度减小。用于乙醇／水混合液渗透蒸发分离时，分离因子和渗透通量都有提高，并在填充量为１６．７％附近出现极大值。随着料液中乙醇含量的增大，渗透通量减小，分离因子增大；随着料液温度的升高渗透通量显著增大，分离因子则稍有下降。并简单讨论了超细粉末在乙醇／水混合液分离中的作用。     

Evaluation of the thermophysical and heating properties of a composite rubber membrane with energy harvesting purposes

This paper evaluates the thermal behaviour of recycled rubber membranes from End of Life Tyres (ELTs) reinforced with steel wool fibres, and their potential use as solar collectors. The thermophysical and heating properties of the rubber membranes with different steel wool fibre contents were evaluated. The thermal performance of a solar collector prototype manufactured with these membranes was also evaluated. It was proven that the addition of metallic fibres can increase the amount of heat absorbed and the heating rate in the membranes. However, fibre addition over 0.5%/v does not contribute to an increase in the temperature reached. A solar collector prototype fabricated with rubber membranes with 0.5%/v of fibres can transmit the heat absorbed by the membrane to the water, reaching a temperature of 45 °C, thus demonstrating that it can be used as new sustainable construction material for energy harvesting applications.     

The ageing phenomenon of polyethersulphone hollow fibre membranes for gas separation and their characteristics

We have studied the ageing behaviour of PES/NMP (polyethersulphone/N-methyl pyrrolidone) hollow fibres for gas separation that were prepared from 35% and 37% dope. The effect of ageing on hollow fibres spun from low and high shear rate (103 vs. 862 s⁻¹) has also been investigated, in terms of their transport properties (permeation flux and separation performance), thermal, mechanical and tensile properties. Hollow fibres in this study were aged for around four months in ambient air at room temperature prior to testing.In general, the gas permeation flux drops steeply during the 40 days following fabrication and levels off thereafter. The O₂/N₂ selectivity decreases slightly over time. Hollow fibres spun with high shear rate seem to age faster than those spun with low shear rate. The gas fluxes of both membranes were found to follow a log–log relationship with ageing time. For almost all the gases used in this study, the gas flux decay rate, calculated from the slope of the log–log plot of gas flux vs. ageing, is higher for membranes spun with high shear rate. The effect of shear rate on ageing is less significant for smaller gas molecules that travel faster such as He and H₂. No significant effect of ageing on gas selectivity was observed. Experimental results also indicate that the storage modulus and loss modulus of the hollow fibres increase with ageing. Hollow fibres spun with high shear rates give a slightly higher increase in these moduli than those spun at low shear rates. Surprisingly, tangent δ (energy dissipation) and glass transitional temperature are not sensitive to ageing. We also found that the tensile yield strength and Young's modulus of the hollow fibres increase slightly with ageing. The hollow fibre membranes spun at high shear rates also show a higher increment in tensile yield stress. However, the change in Young's modulus due to ageing was similar for fibres spun with high and low shear rates.     

Dehydration of 1,4-dioxane by pervaporation using filled and crosslinked polyvinyl alcohol membrane

Polyvinyl alcohol (PVOH) membrane, was modified both physically and chemically by incorporation of inorganic filler, sodium aluminosilicate and chemical crosslinking with maleic acid and glutaraldehyde. The change of morphology and crystallinity of PVOH by this physical and chemical modification was studied by FTIR, DSC, TGA, SEM and XRD. These membranes were evaluated in terms of its potential for dehydration of dioxane by preferential sorption and permeation using pervaporation (PV) technique. These membranes were cast in the laboratory by solution casting from the polymer and other additives. The performance of the unfilled (containing no filler) glutaraldehyde (GA) crosslinked PVOH-1 and maleic acid (MA) crosslinked PVOH-2 membranes were compared with filled (containing aluminosilicate filler) but GA crosslinked PVOH-3 and filled but MA crosslinked PVOH-4 membranes. The filled membranes were found to show higher flux and water selectivity. Among all the four used membranes, the MA crosslinked filled PVOH-4 membrane was found to show best results in terms of both water selectivity and flux.     

Poly(ε-caprolactone) filled with electrospun nylon fibres: A model for a facile composite fabrication

Electrospun fibres are very rarely used as reinforcing agents in polymer-based composites. A fabrication approach is presented that allows to easily prepare composites based on polycaprolactone (PCL) filled with nylon 6 electrospun fibres by compression moulding. At very low filler contents (3%), the obtained composites exhibited improved stiffness with a simultaneous increase in ductility, differently from what is usually found in PCL nanocomposites with a variety of fillers, in which increases in modulus happen at the expense of elongation at break. The presence of fibres with a very small diameter, typical of the products of electrospinning, favoured a good interfacial adhesion between matrix and filler. Being of a similar order of magnitude than polymer lamellae, electrospun fibres can be used to shape the morphology of lamellar stacks, and therefore the final properties of the composites.     

Moisture Removal from Natural Jute Fibre by Plasma Drying Process

Low temperature plasma process is an effective alternative method compared to the conventional vacuum drying method for removing moisture. Plasma drying removes the moisture from fibres faster and to a lower level than conventional methods. It also improves the surface properties of the fibres. The jute fibre was treated with inert gas argon plasma without damaging the fibre. The OES was used to monitor the moisture desorbed from the fibre during processing. The XRD results revealed a change in the macromolecular structure as well as the crystallinity of the treated fibre. The FTIR and TGA provided the evidence of moisture removal from the fibres. It was found that the plasma treated fibres contain less than 1.8% (wt.) moisture which is a promising result when compared with conventional drying processes.The average tensile strength of the plasma treated fibres increased by 12.5% compared with those treated with the conventional vacuum dry process.     

Evaluation of the mechanical and morphological properties of long fibre reinforced polyurethane rigid foams

This paper examines the effect of glass fibre reinforcements on the mechanical and morphological properties of polyurethane rigid foams. The processing parameters of the polyurethane foam were maintained constant while the influence of the filler was evaluated in terms of fibre mass content variation (5%, 10% and 20%) and fibre length variation (12.5 mm, 25 mm and 50 mm). Tests were carried out in compression, three-point bending, tension and shear for all material configurations, the variation in fibre mass content having a larger influence on mechanical properties than fibre length. The structure of the specimens was investigated using Scanning Electron Microscopy and Computer Tomography in order to investigate the filler influence on morphology and the scatter in results.     

Silica filled poly(4-methyl-2-pentyne) nanocomposite membranes: Similarities and differences with poly(1-trimethylsilyl-1-propyne)–silica systems

The performance of poly(4-methyl-2-pentyne) (PMP)/silica nanocomposites was studied for membranes with a filler content between 10 and 40 wt%. An increase in permeability and a constant vapor selectivity were measured with increasing filler content. The constant selectivity was in contrast to earlier published results for silica filled poly(1-trimethylsilyl-1-propyne) (PTSMP) membranes. Therefore, a comparison between both materials was made. Free volume sizes and interstitial mesopore sizes were determined by use of positron annihilation lifetime spectroscopy (PALS) and image analysis was performed on transmission electron microscopy (TEM) pictures of both materials. Although both materials possessed interstitial mesopores, a difference in membrane structure was noticed, explaining the difference in membrane performance.     

Influence of plasma treatment on the adhesion between a polymeric matrix and natural fibres

The aim of this work is to study the influence of low-pressure plasma treatment on cellulose fibres to improve the adhesion between a polymeric matrix and natural fibres used as reinforcement. To evaluate fibre wettability, contact angle measurements were carried out on flax fibres after treatment with plasma under several conditions. Similarly, contact angle measurements were performed without plasma treatment. A comparison between all the samples led to the definition of the optimal plasma treatment conditions. Once the latter were determined, composite materials were prepared with treated and untreated flax fibres and a low-density polyethylene matrix. Composites, with different fibre contents (5 and 40%) and different fibre lengths (1 and 10 mm), were manufactured using a mixer and a hot plate press. The tensile strengths of the composites were assessed to determine optimal fibre content and length, and the plasma treatment effect was also quantified. It was found that the higher the fibre content, the higher the tensile strength, and the higher the Young’s modulus; however, fibre length did not affect tensile strength. Regarding plasma treatment, composites with treated fibres exhibited a considerably improved tensile strength and Young’s modulus. Plasma treatment effects were also studied by X-ray photoelectron spectroscopy and by differential scanning calorimetric. Finally, an analysis of the fibre surface and an interaction study between the matrix and the fibres was conducted with scanning electron microscopy.     

Combination of glass fibres and minerals in polyamides

Polyamides reinforced with glass fibres are characterised by high values for modulus of elasticity and notched impact strength but also have the negative properties of rough surfaces and anisotropy - particularly anisotropic shrinkage. Mineral-filled polyamides have good surface properties, are isotropic and have high impact strength, however, the elasticity modulus is only slightly better than for normal polyamides and notched impact strength values are relatively low. Through a combination of glass fibres and mineral filler, surface properties can be improved and anisotropy reduced. In order to achieve the optimum mechanical properties a range of 0 - 50 wt.-% glass fibre content and 0 - 40 wt.-% mineral content was systematically examined using statistically designed experiments. This investigation showed the relationship between the “Responses”, surface appearance, shrinkage, modulus of elasticity, impact strength and tensile properties and the “variables”, glass fibre and mineral content. Optimal products, based on the model functions, can be chosen in this way.     

The influence of hemicellulose on fibril aggregation of kraft pulp fibres as revealed by FE-SEM and CP/MAS 13C-NMR

Three Norway spruce pulps were produced using different kraft pulping methods, in order to obtain large differences in cellulose and hemicellulose proportions at a similar lignin content. The hemicellulose content in the three pulps varied between 10% and 22%. The aim of the study was to evaluate the influence of cellulose and hemicellulose on fibre ultrastructure and correlate this with the differences observed in the mechanical properties between the pulps. The ultrastructure of the pulp fibres were studied using Field Emission Scanning Electron Microscopy (FE-SEM) and Solid-State Cross Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance (CP/MAS ¹³C-NMR) in combination with spectral fitting. CP/MAS ¹³C-NMR measured the average bulk properties of the pulp fibres, while FE-SEM allowed for observations on the ultrastructure of fibre surfaces. The ultrastructure of the fibres varied with varying hemicellulose content. The pulp with a high hemicellulose content had a porous surface structure. In fibres with a low hemicellulose content, the fibril aggregates (macrofibrils) formed a much more compact surface structure. With CP/MAS ¹³C-NMR this change was reflected by an increase in average fibril aggregate width with decreasing hemicellulose content. Results from FE-SEM and CP/MAS ¹³C-NMR correlated well. The changes recorded in ultrastructure may explain the very different mechanical properties reported previously for pulps with different hemicellulose content.     

Characterisation of carbon fibres grown from carbonaceous gases by measurements of their density and oxidation resistance

In the present work it has been demonstrated, by measurements of their density and air oxidation resistance, that different sorts of carbon fibres grown from a gaseous stage, vapour grown carbon fibres (VGCF), present a duplex structure. By means of these two experimental techniques, structural differences between both constituent phases of this kind of fibres have been determined. It has been proved that the catalytic phase or nucleus presents higher level of crystalline perfection than the pyrolytic or cortical phase. This is corroborated by the fact that thin VGCF show better mechanical properties than thick fibres.In this way, it has been possible to determine the mean nucleus diameter of a batch of VGCF, and to established a mathematical expression, of the rule of mixtures type, for their density.     

界面改性剂在聚丙烯／高岭土二相复合体系中的作用

从高岭土（Ｋａｏｌｉｎ）填充聚丙烯（ＰＰ）体系的界面分子设计入手，研究了界面改性剂对填料的分散性，聚丙烯基体的结晶行为，填充熔体流变性质以及材料力学性能的影响．结果表明，界面改性剂降低了填料的高表面能，改善了填料分散状况．界面改性剂的加入，填充熔体粘度接近纯聚丙烯数值．经界面改性剂处理后，填充材料缺口悬臂梁冲击强度随填料量的增加而急剧升高，在填料量为３０Ｗｔ％时，冲击强度达到４８０Ｊ／Ｍ，是未处理材料的十二倍，添加至填料量为５０ｗｔ％时，冲击强度没有明显降低．     

Preparation and characterisation of SrCe0.95Yb0.05O2.975 hollow fibre membranes

A mixed proton and electronic conducting hollow fibre membrane, SrCe_0.95Yb_0.05O_2.975 (SCYb), has been prepared by spinning a polymer solution containing suspended SCYb particles to a hollow fibre precursor, which is then sintered at elevated temperatures. The SCYb powders having a sub-micron size, i.e. an essential size for fabrication of the hollow fibre with good mechanical strength, were synthesised through a polymerised water-soluble complex method. By controlling weight ratio of the SCYb ceramic powder to the polymer binder and sintering temperatures, the SCYb ceramic hollow fibres with gas-tight properties can be prepared. Some primary factors affecting microstructures, gas tightness and mechanical strength of the mixed conducting hollow fibre membranes were studied in details.     

Measurement of thermal diffusivity of filler-polymide composites by flash radiometry

Thermal diffusivity D of filler-polyimide composites was investigated using flash radiometry. The fillers used were: diamond, alumina, boron nitride, aluminium nitride, silicon carbide, and silicon carbide whiskers, Composite films were prepared by casting a polyamic acid solution with dispersed filler on a glass plate and then annealing. The effects of filler type, size, content, and shape on D were studied. D increased with increasing average filler particle diameter and filler content. For the composite filled with fine Al₂O₃ whose average particle diameter is about 0.2 μm, aggregates of filler were observed with dimensions up to a few microns. The formation of thermal paths through this aggregate enhances thermal diffusion. For the composites filled with high thermal conductivity filler such as BN and AIN, there was a strong increase in D above a filler content of 20 vol %. D was ten times larger than that of unfilled polyimide when the BN content was 54 vol %. D of the SiC-whisker composite increased strongly up to a filler content of 18 vol %. Above this content D significantly decreased, probably because of interconnected voids formed by mold shrinkage.