Unusual swelling behavior of polymer-clay nanocomposite hydrogels

The swelling behavior and the elastic properties of nanocomposite hydrogels have been investigated. The hydrogels were prepared by free-radical polymerization of the monomers acrylamide (AAm), N,N-dimethylacrylamide (DMA), and N-isopropylacrylamide (NIPA) in aqueous clay suspensions at 21 °C. Laponite with a radius of gyration in distilled water of 20 nm was used as clay particles in the hydrogel preparation. The reactions with AAm monomer were carried out in the presence of the chemical crosslinker N,N′-methylenebis(acrylamide) (BAAm). It was found that the volume of nanocomposite hydrogels immersed in water rapidly increases and attains a maximum value after about one day. Surprisingly, further increase in the swelling time results in the deswelling of the gels until they reach a limiting swelling ratio after about 5 days. This unusual swelling behavior is observable only when the clay concentration in the hydrogel is above the overlap threshold c^∗. Swelling measurements combined with the elasticity tests show that the effective crosslink density first decreases, but then increases with increasing time of swelling of the hydrogels. The results were explained in terms of the rearrangements of the highly entangled polymer chains and clay particles during the gel volume change.     

Characterization of cationic water-soluble polyacrylamides

Copolymers of poly(acrylamide-co-acryloyloxyethyltrimethylammonium chloride or AM–CMA) and poly(acrylamide-co-methacryloyloxyethyltrimethylammonium chloride or AM–CMA) prepared by inverse emulsion polymerization were characterized by different analytical techniques. The chemical composition of the copolymers was estimated by elemental analysis and by nuclear magnetic resonance spectroscopy (NMR). NMR spectroscopy and computer simulation were further used for investigating the polymers' sequence distribution. The poly(AM–CMA) copolymers are chemically more homogeneous than are the poly(AM–CMA). The configurational propagation of dyads and triads for the homopolymers obeys Bernouilli's statistics. For the copolymers, the chemical sequences distribution is governed by Markov's first-order statistics.     

Hydrodesulfurization of model diesel using Pt/Al2O3 catalysts prepared by supercritical deposition

Pt/Al₂O₃ catalysts with Pt loadings ranging from 0.5 to 11 wt.% were synthesized by supercritical carbon dioxide (scCO₂) deposition method. Transmission electron microscopy (TEM) images showed that the synthesized catalysts contained small Pt nanoparticles (1–4 nm in diameter) with a narrow size distribution, no observable agglomeration, and uniformly dispersed on the alumina support. The catalysts were found to be active for hydrodesulfurization of dibenzothiophene (DBT) dissolved in n-hexadecane (n-HD) without sulfiding the metal phase. The reaction proceeded only via the direct hydrogenolysis route in the temperature range 310–400 °C and at atmospheric pressure. The activity increased with increasing the metal loading. Increasing [H₂]₀/[DBT]₀ by either increasing [H₂]₀ or decreasing [DBT]₀, increased the DBT conversion. At a fixed weight hourly space velocity and feed concentration, conversion did not increase with increasing temperature beyond 330 °C. The presence of toluene inhibited the catalyst activity presumably due to competitive adsorption between DBT and toluene. Under the operating conditions, the reaction was far from equilibrium.     

Fatty acids of the seeds of <Emphasis Type="Italic">Origanum onites</Emphasis> L. and <Emphasis Type="Italic">O. vulgare</Emphasis> L.

Seed oils of Origanum onites L. from the Antalya and Mugla regions and O. vulgare L. from the Kirklareli region of Turkey were extracted with hexane in a Soxhlet apparatus. The oil yields were 14.1–20.0 and 18.5%, respectively. FA compositions of the seed oils were determined by GC and GC/MS. Twenty FA were identified in both O. onites and O. vulgare seeds. The major FA of both species were linolenic (56.3–57.0%; 61.8%), linoleic (21.5–21.7%; 18.8%), oleic (8.7–8.9%; 5.9%), palmitic (5.9–6.5%; 5.5%), stearic (2.1–2.4%; 2.1%), and (Z)-11-octadecenoic (0.6–0.8%; 0.5%), respectively.     

Polypropylene photostabilization by hindered amines in the presence of acidic species

Some volatile acids were found to dramatically reduce the effectiveness of additives based on 2,2,6,6-tetramethylpiperidine as photostabilizers for polypropylene films. Strong acids such as HCl, HBr, and HNO₃ had the largest effect with sulfurous acid somewhat less detrimental. Weak organic acids did not impair the effectiveness of the hindered amine light stabilizers. The role of acid concentration and contact time were explored for the HCl–piperidyl additive system. Secondary and tertiary amines were included in the study as well as oligomeric additives and an N-oxyl derivative. The latter is less basic than the free amines, and it was correspondingly less effected by acid exposures. The possibilities for acid exposure during the compounding, fabrication, and use of stabilized polyolefin articles is discussed as well as the effects of acids in terms of proposed stabilization mechanisms for the hindered amines.     

Improving Dewaterability and Other Properties of Citric Acid Wastewater Treatment Sludge by Ozone and Peroxone

ABSTRACT

The efficacies of ozonation and peroxone (O₃/H₂O₂) pretreatments were compared for citric acid wastewater sludge conditioning with the objective of improving dewatering characteristics of the sludge. Treatment with 84 mg O₃/g dry solid (DS) and 12.5 mg/g DS H₂O₂ greatly enhanced the effectiveness of ozonation, providing sludge dewaterability similar to that obtained by ozonation at 250 mg O₃/g DS. Most importantly, treatment of citric acid wastewater sludge with 84 mg O₃/g DS and 12.5 mg/g DS H₂O₂ led to the preservation of the nutrient elements nitrogen, phosphorus, and potassium in the sludge with a minimal volatile suspended solids/total suspended solids reduction of 5.5%, which is much lower than that with ozonation at 250 mg O₃/g DS.     

Synthesis,characterization, and antitumor activity of poly(maleic anhydride‐co‐vinyl acetate‐co‐acrylic acid)

The ternary copolymerization of maleic anhydride (MA), vinyl acetate (VA), and acrylic acid (AA) [P(MA‐co‐VA‐co‐AA)], which is considered to be an acceptor–donor–acceptor system, was carried out in 1,4‐dioxane with benzoyl peroxide as an initiator at 70°C under a nitrogen atmosphere. Constants of complex formation for the monomer systems in the study were determined by UV–visible (hydrogen‐bonding complex) and ¹H‐NMR (charge transfer complex) methods, respectively. The results show that polymerization of the P(MA‐co‐VA‐co‐AA) system proceeds by an alternating terpolymerization mechanism. It is shown that the synthesized copolymers have typical polyelectrolyte behavior, ability for reversible hydrolysis–anhydrization reactions, and semicrystalline structures. In these cases, including radical polymerization, and formation of semicrystalline structures, the hydrogen‐bonding effect plays a significant role. The in vitro cytotoxicities of the synthesized terpolymer and alternating copolymer were evaluated using Raji cells (human Burkitt lymphoma cell line). The antitumor activities of prepared anion‐active copolymers were studied using methyl–thiazol–tetrazolium colorimetric assay and 50% of the cytotoxic dose of each copolymer and terpolymer were calculated. Hydrolyzed P(MA‐co‐VA‐co‐AA) and P(MA‐alt‐AA) copolymers have sufficiently high antitumor activity, which depends on the amount of hydrogen‐bonding carboxylic groups and their regular distribution in the side chain of functional macromolecules. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3425–3432, 2006     

H_2-THF水合物形成过程研究

利用定容恒温法研究了H2-5.56 mol%THF-水在2℃,不同压力下的水合物形成特性,比较2种不同的氢气水合物形成方法:1)氢气-THF水溶液体系;2)氢气-THF水合物颗粒体系,考察形成过程,并计算储氢量。实验结果表明,在上述条件下,不同的方法氢气水合物的形成速率不同,第2种方法下氢气水合物的形成速率相对较快,且储氢量也高,约为质量分数0.33%,2种体系下的储氢量均随着压力的增高而增加。最后对2个体系下的氢气水合物的形成机理进行分析。     

高新区知识创新能力影响因素的实证研究

考虑到知识经济全球化背景下,高新区知识创新能力对于国家高新区二次创业和国际化发展的至关重要性,以西安高新区为研究对象,对高新区知识创新能力进行了分析,指出了高新区影响知识创新的两个因素是社会资本和区域基础环境.通过逻辑分析推导出9个假设,并进行了实证分析.     

基于改进粒子群的航空军械保障调度优化

针对航空单机军械保障中出现的保障周期长、资源配置不合理等问题,在给出改进粒子群算法的基础上,分析单机军械保障问题中多约束条件,构建多资源约束下的军械保障调度数学模型.将改进算法应用于航空单机军械保障问题中,利用优先值方法编码,提出一种优先进度生成机制作为解码方式求解.通过对实际算例优化分析,得到单机保障的最小时间为64min,远小于未优化时保障周期,而且资源的使用基本趋于均衡,说明改进的方法能快速、正确地解决单机军械调度的优化问题.