共查询到20条相似文献,搜索用时 31 毫秒
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M. Kattan C. Cabot E. Dargent J. Bayard J. Grenet 《Journal of Thermal Analysis and Calorimetry》1998,52(3):765-772
The analysis of DSC experimental data from solidification is improved, thanks to a modified isoconversional method. The validity
of the proposed method is tested for a polyethylene glycol with a mean molecular weight of 6000. The temperature-cooling rate-transformation
diagrams reveal good agreement between the experimental and calculated data.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Francesca Lionetto Antonella Tarzia Miriam Coluccia Alfonso Maffezzoli 《Macromolecular Symposia》2007,247(1):50-58
Air-coupled ultrasound in one-side transmission mode has been applied to monitor the curing process of an unsaturated polyester resin, commonly used as a matrix in glass reinforced composites. The evolution of the resin mechanical properties during cure has been measured from the variation of longitudinal velocity. The technique has demonstrated to be a very powerful tool for detecting the structural changes occurring at gelation and vitrification. The no-contact ultrasonic results have been compared with those obtained using conventional contact ultrasonic measurements, characterized by direct coupling between the transducer and the resin, and with the rheological measurements. The good agreement among the results of the different techniques demonstrates the reliability of air-coupled ultrasound in monitoring the changes of viscoelastic properties occurring during the cure of thermosetting polymers. A further advantage of the proposed one-side ultrasonic technique is the absence of physical contact between the transducers and the sample, which is relevant during composite manufacturing, where probe contact could adversely affect the part quality or access from both sides is not practicable. No-contact ultrasonic cure monitoring is suitable for both stationary and moving liquid or solid samples in several process conditions such as moulding, filament winding, etc., opening the way to new applications of ultrasound in the composite industry. 相似文献
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J. Grenet S. Marais M. T. Legras P. Chevalier J. M. Saiter 《Journal of Thermal Analysis and Calorimetry》2000,61(3):719-730
This work reports on the curing kinetics of unsaturated polymer resins (UPRs) cured with styrene, studied by differential
scanning calorimetry and Fourier transform infrared spectroscopy. The data lead to determination of the experimental conditions
with which to obtain a fully cured material and open the way for study of the relaxation phenomena by means of thermally stimulated
depolarization current analysis (TSDC). In relaxation studies on fully cured resins, the TSDC spectra revealed important overlapping
of the main relaxation peak with an extra upper peak. The importance of this extra peak a priori prevents further analysis
of the main relaxation. To identify the origins of this peak (space charge or other), the purity of the resin was checked
by X-ray fluorescence spectroscopy. The use of UPR specimens with different compositions (in terms of the resin/activator/initiator
ratio) demonstrated that the bulk of the impurities Cl, K, Ca, Sr, Zr and Ba are due to the promoter. Decoupling of the mixed
peaks (α-relaxation and extra) revealed that the a peak is independent of the proportion of the promoter in the resin and
that the extra peak is principally due to the presence of these impurities.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Médout-Marère V Belarbi H Haouzi A Giuntini JC Douillard JM Zanchetta JV Vanderschueren J 《Journal of colloid and interface science》2000,223(1):61-73
This work shows that hydration of clays can be studied by means of a new interpretation of thermally stimulated depolarization currents technique. These measurements have been performed on four exchanged natural clays: Na-montmorillonite, Ca-montmorillonite, kaolinite, and illite. The results are analyzed using both the recently developed analysis of relaxation times distribution and the electronegativity equalization method. They provide evidence of the surface heterogeneity of clays. It is established that sites, identical from a crystallographic point of view, are different when the energy of the phenomenon is considered. The main interest of this work is to give for the first time a value of the hydration energy of cation onto clay surfaces. Copyright 2000 Academic Press. 相似文献
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Susana S. Pinto Joaquim J. Moura Ramos Hermínio P. Diogo 《European Polymer Journal》2009,45(9):2644-2652
The relaxational processes in amorphous solid poly(vinyl acetate) are studied by Thermally Stimulated Depolarisation Currents (TSDC) in the temperature region from −165 °C (108 K) up to 60 °C (333 K). The influence of aging on the current peaks of the secondary relaxation is discussed, and it is concluded that some modes of motion of this mobility are aging independent, while others are affected by aging. A particular attention is focused on the discussion of the degree of cooperativity of the motional modes of the secondary relaxation, and the conclusion to be driven from the results is that all these modes do not show any appreciable cooperative character. The method of determination of the temperature dependent relaxation time is discussed in the case of non-exponential relaxations. The fragility (or steepness index) of poly(vinyl acetate) is calculated from TSDC data and the obtained value is compared with that obtained by broadband dielectric spectroscopy. 相似文献
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不饱和聚酯/聚氨酯互穿网络聚合物的合成 总被引:8,自引:1,他引:8
以醋酸酐封端的不饱和聚酯(FUPR)与交联聚氨酯预聚物制备了具有互穿聚合物网络(IPN)的不饱和聚酯/聚氨酯,通过红外,DSC和扫描电镜等分析了FUPR/PUIPN网络形成的动力学,微相分离行为及力学性能,结果表明,当FUPR/PU达到某一比值时,产生网络互穿效应,可改善聚氨酯的刚性,提高不饱和聚酯的抗冲性。 相似文献
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Xiu Xia WANG Zhi Gang JIANG Yi Feng ZHANG 《中国化学快报》2006,17(1):125-128
Epoxy resins are widely used in coatings, adhesives and polymer composites, but the applications of cured epoxy resins are often restricted by their poor toughness. HBP can be used as toughener to improve the toughness of epoxy resins due to its high-dens… 相似文献
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以芝麻秸秆粉、水稻秸秆粉、玉米芯秆粉、菠萝叶粉、甘蔗渣粉五种不同植物纤维粉为填充体、不饱和聚酯树脂(UPR)为基体制作植物纤维粉/UPR复合材料,对比研究了秸秆种类对复合材料密度、力学性能及吸水性能的影响。结果表明,植物纤维粉粒径为100目、添加量为UPR用量的10%时,芝麻秸秆粉/UPR复合材料的综合力学性能最好,拉伸强度、弯曲强度和冲击强度分别为41.320 MPa、67.467 MPa和2.815 KJ/m^2,且每一浸泡阶段吸水率均最低。 相似文献
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Thermoset unsaturated polyesters (UP) are usually obtained by crosslinking of alkyd chains dissolved in an unsaturated reactive monomeric diluent, usually styrene. Recently we found that UP-alkyd chains (without styrene) are intrinsically cured into a crosslinked matrix in the presence of peroxide. The thermal, mechanical, dynamic mechanical and chemorheological properties and the network molecular structure of the crosslinked UP-alkyd are a function of the peroxide content used. All properties change considerably upon the addition of small amounts of peroxide (between 1 and 2%wt.) and change to a lesser extent upon employing higher peroxide concentrations (up to 6%wt.). Due to co-occurrence of crosslinking and scission events, the crosslinked system contains both gel and sol fractions. The sol fraction demonstrates a plasticizing effect on the crosslinked network, affecting the thermal and mechanical properties of the crosslinked polymer. The new materials developed in this work are interesting for utilization in innovative styrene-free UP-alkyd/organo-clay nanocomposites. It was found that inducing high shear levels for prolonged durations promotes the intercalation and exfoliation of the silicate layers, resulting in a better dispersion of clay particles. Crosslinking of the UP-alkyd/organo-clay nanocomposites alters their nanostructure, particularly affected by the peroxide content used. Thus, depending on the content employed, either an exfoliated or a combined intercalated/exfoliated structure may be realized. 相似文献
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J. Bayard J. Grenet C. Cabot M. Jutigny E. Dargent 《Journal of Thermal Analysis and Calorimetry》1997,50(3):441-453
In this paper we present an electrical model of simulation. This model is used to simulate Thermally Stimulated Depolarization Current measurements. The time constant of the model shows the same temperature behaviour as that observed for amorphous materials. The computations by means of SPICE software give results which are very close to be behaviour laws used in the theory of relaxation in amorphous materials. 相似文献
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Mayank Shah Edwin Zondervan Maarten Oudshoorn Andre de Haan 《Macromolecular Symposia》2011,302(1):46-55
Summary: Unsaturated polyester is traditionally produced in a batch wise operating reaction vessel connected to a distillation unit. An attractive alternative for the synthesis of unsaturated polyester is a reactive distillation. To value such alternative synthesis route reliable process models need to be developed. In this paper, the strategy is described for the development of the reactive distillation model. Essential parts of the reactive distillation model are kinetic and thermodynamic which are subsequently validated with the experimental data of the traditional batch process such as acid value of the polyester, weight of the distillate and glycol concentration in the distillate. We find that the models predict these important variables reliably. Unsaturated polyester production time is around 12 hours in the traditional batch process. However, the simulation study of the reactive distillation process shows that the total production time of unsaturated polyester in a continuous reactive distillation system is between 1.5 hours to 2 hours for the same product quality as during batch production. The equilibrium conversion is raised by 7% compared to the traditional batch process. The model demonstrated that reactive distillation has the potential to intensify the process by factor of 6 to 8 in comparison to the batch reactor. 相似文献
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B. Chowdhury 《Journal of Thermal Analysis and Calorimetry》2001,64(2):433-441
Pyrolysis of normally insulating aromatic polyimide is known to impart electrical conductivity to the polymer due to the formation
of carbonized regions in an insulating matrix with a concomitant change in the polymer’s structural arrangement. The wholly
pyrolyzed polyimide is potentially useful for specific applications in certain types of semiconductor devices because of the
polyimide’s insulator/conductor transition which creates a barrier type conduction. Pyrolysis, however, degrades the required
mechanical integrity of the polyimide for construction of such devices. In order to evaluate the fundamental aspects of barrier
conduction by high voltage electron transfer from metal contact that can still produce measurable current in thermally treated
non-pyrolyzed polyimide, the nature of depolarization in Kapton was assessed by the thermally stimulated depolarization current
(TSDC) technique. The results show that thermal treatment of polyimide without pyrolysis and therefore without loss of mechanical
integrity offers a viable means of steady electron conduction for semiconductor operation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献