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1.
Gordon D. Airey 《Fuel》2003,82(14):1709-1719
The use of polymers for the modification of bitumen in road paving applications has been growing rapidly over the last decade as government authorities and paving contractors seek to improve road life in the face of increased traffic. Currently, the most commonly used polymer for bitumen modification is the elastomer styrene butadiene styrene (SBS) followed by other polymers such as styrene butadiene rubber, ethylene vinyl acetate and polyethylene. This paper describes the polymer modification of two penetration grade bitumens with SBS. Six polymer modified bitumens (PMBs) were produced by mixing the bitumens from two crude oil sources with a linear SBS copolymer at three polymer contents. The rheological characteristics of the SBS PMBs were analysed by means of conventional as well as dynamic mechanical analysis using a dynamic shear rheometer (DSR). The results of the investigation indicate that the degree of SBS modification is a function of bitumen source, bitumen-polymer compatibility and polymer concentration, with the higher polymer concentrations in a high aromatic content bitumen producing a highly elastic network which increases the viscosity, complex modulus and elastic response of the PMB, particularly at high service temperatures. However, ageing of the SBS PMBs tends to result in a reduction of the molecular size of the SBS copolymer with a decrease in the elastic response of the modified road bitumen. 相似文献
2.
This paper presents an investigation of artificial aging of polymer modified binders, prepared from three base bitumens and six polymers. Aging of the binders was performed using the Thin Film Oven Test (TFOT), the Rolling Thin Film Oven Test (RTFOT), and modified RTFOT (MRTFOT). The binders were characterized by means of infrared spectroscopy, different types of chromatography, and dynamic mechanical analysis. It was found that the effect of aging on the chemistry and rheology of the modified binders was influenced by the nature of the base bitumens and was strongly dependent on the characteristics of the polymers. For styrene–butadiene–styrene (SBS) and styrene–ethylene–butylene–styrene (SEBS) modified binders, aging decreased the complex modulus and increased the phase angle. Aging also increased the temperature susceptibility of these modified binders. The rheological changes of SBS modified bitumens were attributed to polymer degradation and bitumen oxidation. However, for SEBS modified bitumens, the mechanisms of aging are unclear. In the case of ethylene vinyl acetate (EVA) and ethylene butyl acrylate (EBA) modified binders, the process of aging increased the complex modulus and elastic response (decreased phase angle), and reduced temperature susceptibility. These changes were mainly due to the oxidative hardening of the base bitumens. The study also showed statistically significant correlation between TFOT, RTFOT, and MRTFOT. However, no definite conclusions could be drawn regarding the difference in severity of aging between these methods. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1811–1824, 2000 相似文献
3.
This article presents a laboratory evaluation of conventional, fundamental, rheological, and morphological characteristics of styrene‐butadiene‐styrene (SBS) and ethylene vinyl acetate (EVA) polymer modified bitumens. Polymer modified bitumen (PMB) samples have been produced by mixing a 50/70 penetration grade unmodified (base) bitumen with SBS and EVA copolymer at different polymer contents. The fundamental viscoelastic properties of the PMBs were determined using dynamic (oscillatory) mechanical analysis and presented in the form of temperature and frequency‐dependent rheological parameters. The morphology of the samples as well as the percent area distribution of polymers throughout the base bitumen have been characterized and determined by means of fluorescent light optic microscopy and Qwin Plus image analysis software, respectively. The results indicated that polymer modification improved the conventional and rheological properties of the base bitumen. It was also concluded that the temperature and frequency had a significant effect on complex modulus of PMBs. The behavior of EVA and SBS PMBs had exhibited quite difference at 50°C. Moreover, it was found out that at low polymer contents, the samples revealed the existence of dispersed polymer particles in a continuous bitumen phase, whereas at high polymer contents a continuous polymer phase has been observed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
4.
Three-dimensional microstructure analysis of numerically simulated cementitious materials 总被引:1,自引:0,他引:1
In order to predict the transport properties of porous media, such as permeability and electrical conductivity of cementitious materials, a better understanding of the microstructural characteristics, including the geometrical and topological properties, is required. In this contribution, the microstructure of cementitious materials is simulated by using the cement hydration model HYMOSTRUC. In this computer-based numerical model, the hydrating cement grains are modeled as gradually growing spheres, which become in contact while growing. The simulated porous medium can be described as a series of sections taken from three orthogonal directions, in which each unit (pixel) is filled either with a solid or a fluid phase (pores). Various algorithms based on a random walk process are utilized to determine the local geometrical information, such as gravity center's coordinate, perimeter and area of each individual pore. The percolating path of the fluid in three dimensions is traced by using an overlap algorithm. Both three-dimensional (3D) geometrical information and topological space characterization including branch node network and genus of the pores are derived. Calculation results of these algorithms are compared with results obtained by other microstructural models at various degree of hydration. 相似文献
5.
The pore structure of two ordinary Portland cement mortars at water-cement ratio of 0.35 and 0.70 was characterised using quantitative backscattered electron imaging. The mortars were cured and conditioned to produce a range of pore structure characteristics. Image analysis was used to characterise the pore structure in terms of simple morphological parameters such as resolvable porosity and the specific surface area. These were found to be correlated to measured transport coefficients (diffusivity, permeability and sorptivity), suggesting the feasibility of image analysis to derive valuable quantitative information describing the pore structure that can be used as input values for a transport prediction model. A simple analytical model incorporating tortuosity and constrictivity was used to predict oxygen diffusivity and a variant of the Kozeny-Carman model was used to predict oxygen permeability. The diffusion model tended to over-predict for the lower w/c ratio mortar, but the general agreement was reasonable, with 90% of the estimated values within a factor of two from the measured values. The modified Kozeny-Carman model, however, over-predicted all permeability values with an error of between half to one order of magnitude. 相似文献
6.
Thermomechanical properties of polymer blends seem to depend on their morphology on microscales and in particular on the size of the dispersed phase particles and/or their distances (ligament thickness). Precise characterization of morphologies by few simple geometrical parameters is often a quite delicate task, in particular because of the strong polydispersity of these systems. We present here a simple method based on image analysis of transmission electron micrographs (TEM) to estimate both distributions in particle size and ligament thickness. We first reconstruct three-dimensional distributions in particle size from two-dimensional measurements and show in particular that corrections from section thickness become significant when thickness is comparable to particle size. Knowing the distribution in particle size, we extend the model initially proposed by Wu to estimate the distribution in ligament thickness. This method provides a more detailed relation between the distribution in particle size and the distribution in ligament thickness. Advantages and limitations of the method are illustrated by practical examples on polyamide-12 systems filled with various particle dispersions. 相似文献
7.
Influence of aggregate size, water cement ratio and age on the microstructure of the interfacial transition zone 总被引:2,自引:0,他引:2
This paper presents the results of an investigation on the effect of water-cement ratio (w/c), aggregate size, and age on the microstructure of the interfacial transition zone (ITZ) between normal weight aggregate and the bulk cement paste. Backscattered electron images (BSE) obtained by scanning electron microscope were used to characterize the ITZ microstructure. The results suggest that the w/c plays an important role in controlling the microstructure of the ITZ and its thickness. Reducing w/c from 0.55 to 0.40 resulted in an ITZ with characteristics that are not distinguishable from those of the bulk paste as demonstrated by BSE images. Aggregate size appears to have an important influence on the ITZ characteristics. Reducing the aggregate size tends to reduce the ITZ porosity. The evolution of the ITZ microstructure relative to that of the bulk paste appears to depend on the initial content of the unhydrated cement grains (UH). The results suggest that the presence of a relatively low amount of UH in the ITZ at early age may cause the porosity of the ITZ, relative to that of the bulk paste, to increase with time. The presence of relatively large amount of UH in the ITZ at early ages may cause its porosity, relative to that of the bulk paste, to decrease with time. 相似文献
8.
A variety of nanocomposites were synthesised by bulk polymerisation of methyl methacrylate (MMA), and also by extrusion of poly(methyl methacrylate) (PMMA). These were characterised by wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). We applied image analysis to the TEM images of these PMMA-clay nanocomposites to quantify their structures; an analysis was made of the resulting parameters to determine which were most useful for quantifying the microscale and nanoscale structures. Frequently, these quantitative results differed from those expected on the basis of WAXD, demonstrating the limitations of using diffraction data as the sole measure of nanocomposite structure. By combining the quantitative parameters from TEM with the WAXD data, we have explored the effects of processing conditions and organoclay properties on final nanocomposite structure. Factors examined included the effect of the reactivity of the surface modifiers, platelet size, the incorporation of excess modifier within the organoclay, and bulk polymerisation versus extrusion. 相似文献
9.
Toughness of syndiotactic polystyrene/epoxy polymer blends: microstructure and toughening mechanisms 总被引:1,自引:0,他引:1
Thermoplastic/epoxy blends were formed using an amine-cured epoxy polymer and a semi-crystalline thermoplastic: syndiotactic polystyrene (sPS). Complete phase-separation of the initially soluble sPS from the epoxy occurred via ‘reaction-induced phase-separation’ (RIPS) or via ‘crystallisation-induced phase-separation’ (CIPS), depending upon the thermal processing history employed. Dynamic mechanical thermal analysis showed that no sPS was retained dissolved in the epoxy polymer. For RIPS, at concentrations of sPS of up to 8 wt%, the sPS is present solely as spherical particles. However, macro phase-separation, giving a co-continuous microstructure, accompanied by local phase-inversion, dominates the RIPS blends containing more than 8 wt% sPS. In the CIPS blends, the sPS is present as spherulitic particles, and this microstructure does not change over the range of sPS concentrations employed, i.e. from 1 to 12 wt% sPS. The pure epoxy polymer was very brittle with a value of fracture energy, GIc, of about 175 J/m2. However, the addition of the sPS significantly increases the value of GIc, though the toughness of the RIPS and CIPS blends differs markedly. For the RIPS blends, there is a steady increase in the toughness with increasing content of sPS and an apparent maximum value of GIc of about 810 J/m2 is obtained for 8-10 wt% sPS. On the other hand, the measured toughness of the CIPS blends increases relatively slowly with the concentration of sPS, and a maximum plateau value of only about 350 J/m2 was measured in the range of 8-12 wt% sPS. The relationships between the microstructure of the RIPS and CIPS sPS/epoxy blends and the measured fracture energies are discussed. Further, from scanning electron microscopy studies of the fracture surfaces and optical microscopy of the damage zone around the crack tip, the nature of the micromechanisms responsible for the increases in toughness of the blends are identified. For the RIPS blends, (i) debonding of the sPS particles, followed by (ii) plastic void growth of the epoxy matrix are the major toughening micromechanisms. The increase in toughness due to such micromechanisms is successfully predicted theoretically using an analytical model. In the case of the CIPS blends, the increase in the value of GIc results from (i) crack deflection and (ii) microcracking and crack bifurcation. 相似文献
10.
利用扫描电镜对聚乙烯(PE)、丙烯腈-丁二烯-苯乙烯共聚物(ABS)等高分子材料填料的分散性及表面与断裂界面进行了研究。结果表明,扫描电镜能够详细观察研究高分子材料的表面结构、微观相分离等,便于表征高分子材料微观结构形态,是分析高分子材料微观结构形态的有效手段。 相似文献
11.
《Ceramics International》2017,43(17):14642-14651
To improve the ablation resistance of C/C composites, ZrC modified composites were fabricated by precursor infiltration and pyrolysis combined with gradient chemical vapor infiltration process. The effects of ZrC precursor concentration on the microstructure, mechanical and ablation properties of the composites were studied. Results showed that with the increase of ZrC precursor concentration, the ZrC content and macroscopic uniformity of the composites increased but with obvious ZrC particle aggregation and the flexural strength decreased gradually. As the concentration of ZrC precursor improved to 60%, the fracture mode of the composites transformed from toughness to brittleness which was mainly attributed to the improved graphitization degree and reaction damage of carbon fiber in the precursor pyrolysis process. However, the ablation resistance was enhanced with the increasing precursor concentration which was resulted from the formation of ZrO2 in center ablation region and continuous ZrO2 coating in brim region serving as a barrier to heat and oxygen transfer. 相似文献
12.
《塑料、橡胶和复合材料》2013,42(6):177-186
AbstractThe research on rubber reinforcement is a traditional but vitally essential topic. However, many issues in this aspect are presently still not well understood and explained. Moreover, when rubber reinforcement is obtained by using nanoparticles, it is even more difficult to clearly understand the relationship between the microstructure and properties. The special character of rubber, being a multicomponent system (rubber, vulcanising agent, accelerants, reinforcements, etc.), complicates even more the analysis of the parameters affecting the rubber/nanoparticle composite formation. Therefore, we believe the results obtained by means of transport experiments represent a good approach for understanding the reinforcing capability of nanofillers. The reinforcing capability of nano-CaCO3 in natural rubber (NR) was characterised by means of transport properties such as diffusion, sorption and permeability coefficients, swelling ratio, enthalpy, entropy and activation energy. Concentration of nano-CaCo3 in NR was varied from 0 to 20 parts per one hundred parts of rubber by weight (phr). Transport process of toluene by use of equilibrium weight swelling of the NR and nanofilled composites have been studied in details. The effects of nanofiller concentration and temperature on transport of toluene through nano-CaCO3 filled NR vulcanisates were studied. The microstructure of the nanocomposites was investigated by scanning electron microscopy. The diffusivity data of the systems have shown the dependence on the temperature and microstructure of nanocomposite. Generally, the concentration of nano-CaCO3 plays an important role in transport process. 相似文献
13.
The process of deuterium desorption from single-wall carbon nanotubes (SWNTs) modified by atomic (D) and molecular (D2) deuterium treatment was investigated in an ultrahigh vacuum environment using thermal desorption mass spectroscopy (TDMS). Microstructural and chemical analyses of SWNT material, modified by this deuterium interaction, were performed by means of a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results disclose characteristic features in the TDMS spectra of deuterium evolved from the SWNT material, which can be correlated to the microstructure of nanocarbon material modified by D-treatment. The TDMS spectra of deuterium originating from the large diameter rope type nanotube structures, resulting from a prolonged low-pressure (D + D2) gas mixture treatment, exhibit three overlapping desorption peaks: a dominant one with a desorption activation energy (Edes) of approx. 2.86 eV and lower intensity peaks at Edes of ∼1.50 and 2.46 eV. On the other hand, the TDMS spectra of deuterium taken from the “coral reef”-like carbon nanostructures, obtained after prolonged treatment of SWNTs to a high-pressure (D + D2) gas mixture produced at high temperature, reveal the coexistence of four superimposed desorption peaks with Edes ranging from 1.23 to 4.4 eV. A dominant desorption peak with Edes ≈ 4.4 eV, can be attributed to bulk diffusion of D trapped within this nanocapsule bulk structure. 相似文献
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16.
Ti41.5Zr41.5Ni17 (at.%) powders from two batches having different size fractions have been vacuum plasma sprayed to form coatings using different
sets of spray parameters. The powders are composed mainly of the HCP alpha and Laves phases which transform to i-phase owing
to rapid quenching during plasma spraying. The coatings are examined using image analysis, hardness tester, XRD, SEM, and
TEM. TEM studies revealed that the coating has a microstructure constituted by extremely fine grains. It has been observed
that the polycrystalline to i-phase transformation occurs in both coatings irrespective of the differences in starting powder
size and other spray parameters. 相似文献
17.
利用化学活性物质对煤沥青进行改性处理,研究了改性煤沥青炭化产物的结构和性能。研究结果表明,改性煤沥青炭化产物的显微结构根据化学活性物质的添加量的不同可是流动状、细镶嵌状和光学各向异性结构;适量的添加化学活性物质,可得到微晶发育良好,抗氧化性优良的沥青炭化产物。 相似文献
18.
《Ceramics International》2021,47(2):2255-2260
This study firstly developed Hf1-xVxB2 (x = 0, 0.01, 0.02, 0.05) powders, which were derived from borothermal reduction of HfO2 and V2O5 with boron. The results revealed that significantly refined Hf1-xVxB2 powders (0.51 μm) could be obtained by solid solution of VB2, and x ≥ 0.05 was a premise. However, as the content of V-substitution for Hf increased, Hf1-xVxB2 ceramics sintered by spark plasma sintering at 2000 °C only displayed a slight densification improvement, which was attributed to the grain coarsening effect induced by the solid solution of VB2. By incorporating 20 vol% SiC, fully dense Hf1-xVxB2-SiC ceramics were successfully fabricated using the same sintering parameters. Compared with HfB2-SiC ceramics, Hf0.95V0.05B2-20 vol% SiC ceramics exhibited an elevated and comparable value of Vickers hardness (23.64 GPa), but lower fracture toughness (4.09 MPa m1/2). 相似文献
19.
Atomic force microscopy and nanoindentation have been applied to the study of thin molecularly templated polymer films. The template was chosen to be the readily hydrogen‐bonded cotinine molecule and three different polymer hosts, Elvamide® nylon, Nylon‐6, and poly(4‐vinylphenol) were compared. The host polymer was shown to affect the nature of the template‐host interaction resulting in varying surface morphologies and differences in the nanohardness. These observations were shown to reflect differences in the underlying interaction chemistry, specifically, whether or not the polymer may be imprinted in the film production process. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 877‐883, 2013 相似文献
20.
V. Matte M. Moranville F. Adenot C. Richet J. M. Torrenti 《Cement and Concrete Research》2000,30(12):1947-1954
Ultra-high performance cement-based materials expected to be used in nuclear waste containers were submitted to a leaching test in order to evaluate their long-term durability. Reactive powder concretes (RPC) were attacked by de-ionized water. Previous studies revealed a superficial degradation after leaching with a sound zone underneath an altered porous zone in which anhydrous silicates C3S and C2S were dissolved. To predict the long-term durability of RPC, the hydration rate of cement minerals, pozzolanic reactivity of silica fume, pore structure, and mechanisms of chemical reactions were needed. So first, the microstructure of RPC matrix was simulated using the NIST microstructural model. Then the transfer of Ca ions through percolating water was estimated using DIFFU-Ca, a model based on the local chemical equilibrium. This double modeling validates the damage process related to an instantaneous dissolution of anhydrous cement silicates at the degradation front which results in a higher connected pore space, and is in good agreement with experimental results. The long-term behavior is expressed as the depth of the altered zone, the leaching kinetics and the evolution of Ca concentration in the material. 相似文献