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聚氯乙烯(PVC)的热稳定性较差,在加工过程中必须通过添加2%~4%热稳定剂才能有效地阻止其热降解。工业上广泛应用铅、镉、钡、钙、锌的硬脂酸盐或油酸盐等的复合物作为PVC的复合热稳定剂,通常是二元或三元复合体系,如铅钡、镉钡、镉钡锌、钙锌体系等,由于体系内组分之间有协同热稳定性,不仅使PVC加工时期的色泽好,而且有非常好的长期稳定性。 相似文献
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合成了月桂酸镧/铈/钕,分别与硬脂酸钙、季戊四醇复配得到了硬质PVC用月桂酸稀土复合热稳定剂。采用刚果红法、转矩流变仪、动态力学谱仪等考察其对PVC热稳定性、流变性能、力学性能的影响,利用红外光谱初步探讨了其热稳定机制。结果表明:稀土复合热稳定剂中月桂酸镧(铈/钕)/硬脂酸钙/季戊四醇最佳比例为3∶1∶1;具有良好的热稳定性,静态、动态热稳定时间均达到为90和50 min以上;其加工性能和力学性能与铅盐体系相当,断裂伸长率明显高于铅盐体系。 相似文献
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N-苯基马来酰胺酸根合镧(Ⅲ)的合成及对PVC的热稳定作用 总被引:6,自引:0,他引:6
以马来酸酐、苯胺和氧化镧为原料合成了N-苯基马来酰胺酸根合镧(Ⅲ).对产品进行了红外光谱分析及其物性常数测定,通过刚果红法和热重法对其PVC热稳定性进行评价.结果表明,N-苯基马来酰胺酸根(OA)合镧(Ⅲ)为淡黄色粉末,熔点181℃,其化学组成符合La(OA)3·H2O,酰胺氮和羧基氧与镧离子发生了配位作用.配合物对PVC的热稳定性良好,可作为PVC的热稳定剂使用,当稳定剂加入量为PVC的2.5%时,稳定时间可达到31 min,热失重温度提高30℃;并且与硬脂酸钙之间有明显的协同作用,当配合物与硬脂酸钙按质量(1+3)形成的复合物的加入量为PVC的2.5%时,对PVc的稳定时间可以达到38 min,热失重温度提高60℃.该化合物主要通过镧与PVC中活泼的Cl反应和其有机部分的稳定作用来提高PVC的热稳定性. 相似文献
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为了进一步研发性价比高且"无铅化"的稀土复合热稳定剂,研究了系列硬脂酸轻稀土盐(镧/铈/镨/钕/钐/铕/混合)与其他常用PVC热稳定(助)剂的复配效果。通过刚果红试纸法、红外光谱分析(FT-IR)、转矩流变仪等探究了复合热稳定剂对PVC性能的影响。结果表明:复合热稳定剂配方为硬脂酸轻稀土盐0.7~1.0份、硬脂酸锌0.8~0.9份、β-二酮0.3~0.6份和季戊四醇0.8~0.9份。将3份复合热稳定剂添加到100份PVC树脂中,静态及动态热稳定时间延长至100和35 min左右;动态热稳定性能和力学性能优于市售钙锌热稳定剂,与市售铅盐较接近。红外光谱分析表明复合热稳定剂可在加热初期减缓PVC氧化降解,较好地抑制初期着色,对PVC性能影响顺序为:镧组钕组混合组铈组镨组钐组铕组。 相似文献
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稀土复合稳定剂在PVC塑料门窗型材中的应用 总被引:3,自引:1,他引:3
根据人们对环保产品的需求,对新型环保产品RE-4稀土复合稳定剂的热稳定性,流变性,抗硫化污染等方面铅盐体系进行了分析对比,其结果表明RE-4稀土复合稳定剂不但具有良好的热稳定性而且对配方中的无机成分具有良好的包覆与分散作用;从而能提高物料的流动性能和产品质量。 相似文献
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The toxicity of inorganic trivalent arsenic for living organisms is reduced by in vivo methylation of the element. In man, this biotransformation leads to the synthesis of monomethylarsonic (MMA) and dimethylarsinic (DMA) acids, which are efficiently eliminated in urine along with the unchanged form (Asi). In order to document the methylation process in humans, the kinetics of Asi, MMA and DMA elimination were studied in volunteers given a single dose of one of these three arsenicals or repeated doses of Asi. The arsenic methylation efficiency was also assessed in subjects acutely intoxicated with arsenic trioxide (As2O3) and in patients with liver diseases. Several observations in humans can be explained by the properties of the enzymic systems involved in the methylation process which we have characterized in vitro and in vivo in rats as follows: (1) production of Asi metabolites is catalyzed by an enzymic system whose activity is highest in liver cytosol; (2) different enzymic activities, using the same methyl group donor (S-adenosylmethionine), lead to the production of mono- and di-methylated derivatives which are excreted in urine as MMA and DMA; (3) dimethylating activity is highly sensitive to inhibition by excess of inorganic arsenic; (4) reduced glutathione concentration in liver moderates the arsenic methylation process through several mechanisms, e.g. stimulation of the first methylation reaction leading to MMA, facilitation of Asi uptake by hepatocytes, stimulation of the biliary excretion of the element, reduction of pentavalent forms before methylation, and protection of a reducing environment in the cells necessary to maintain the activity of the enzymic systems. 相似文献
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Electrochemistry is one of the most advanced techniques for monitoring neurochemical activities in the living brain because electrochemical approaches bear the advantageous features of high spatial and temporal resolutions, which facilitate its tremendous potential in investigating the highly spatially heterogeneous brain system and the fast dynamics of neurochemical activities. On the other hand, since brain is the most complicated organ in the sense of its numerous kinds of neurochemical species, high selectivity is always required for any analytical methods that approach the brain. In this review, we will discuss various electrochemical methodologies to achieve selective detection of neurochemicals in mammalian brain and the strategies developed mainly by our group towards selective monitoring of both electrochemically active and inactive neurochemicals. At the end, we will discuss possible solutions towards brain mapping of neurochemical species and combination of neurochemical detection strategy with electrophysiology as the direction of future development of electroanalysis in living brain. 相似文献
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Lothar Dunsch 《Journal of Solid State Electrochemistry》2011,15(7-8):1631-1646
To consider the past, present and future of in situ spectroelectrochemistry, a review on the recent state of modern spectroelectrochemistry and trends in the development of spectroelectrochemcial techniques is presented for the combined application of different in situ spectroelectrochemcial methods like ESR spectroelectrochemistry, NMR spectroelectrochemistry, Raman spectroelectrochemistry or IR spectroelectrochemistry to electrode systems. Starting with a discussion of the first steps in spectroelectrochemistry in the past, the main part of this review is focused on the advantages of the combined application of spectroelectrochemical techniques in the analysis of electrode reactions. The spectroelectrochemical methods are demonstrated to be successful in electrode reactions both for solid structures like polymers or carbon nanotubes and for molecular structures like fullerenes and oligothiophenes. The final outlook is attributed to future developments in spectroelectrochemistry. 相似文献
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G. den Boef 《Fresenius' Journal of Analytical Chemistry》1981,305(2):127-129
Summary At the session of the WPAC of Fechem on education in analytical chemistry it was concluded that it is now essential to include chemometrics and basic knowledge of computers in all courses on analytical chemistry.
Tendenzen in der analytisch-chemischen Ausbildung
Zusammenfassung Bei einer Tagung der WPAC über die Lehre auf dem Gebiet der analytischen Chemie wurde bei der Betrachtung neuer Aspekte festgestellt, daß vor allem Chemometrie und Grundkenntnisse in Computertechnik in die Ausbildung aufgenommen werden sollten.相似文献
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A. P. Grimanis N. Kalogeropoulos V. Kilikoglou M. Vassilaki-Grimani 《Journal of Radioanalytical and Nuclear Chemistry》1997,219(2):177-185
Neutron activation analysis (NAA) is a very sensitive and accurate multielement analytical method that is widely applied to the investigation of environmental and archaeological problems. The first part of this paper is a review of pollution studies of toxic trace elements in sediments, seawater and marine organisms of Saronikos Gulf, Greece by NAA. The second part of this paper is a review of provenance studies based on minor and trace element research in ancient ceramics, obsidian, flint, limestone, marble and lead by Instrumental NAA, performed at the NCSR Demokritos. 相似文献