改性膨润土对乙草胺-海藻酸钙制剂释放性能的影响

在海藻酸钙制剂中添加改性膨润土以延缓其对乙草胺的释放,采用50%活性成分被释放所消耗时间(t50)来评价改性膨润土对乙草胺释放速率的影响.结果表明,膨润土经改性后吸附能力显著提高,加入海藻酸钙制剂中使乙草胺释放速率明显下降,t50值由纯海藻酸盐制剂FA20的38.4 h分别延长到羟基铁柱撑膨润土复合制剂FF24的85.7 h、酸活化膨润土复合制剂FS24的102.4 h和羟基铝柱撑膨润土复合制剂FL24的108.5 h,相对提高两倍以上.根据拟合方程得到复合制剂的n值(0.473～0.519)近似Fickian扩散模型(n=0.5),说明乙草胺由该制剂中的释放主要受扩散控制.     

聚电解质微胶囊的制备及其对2,4-二氯苯氧乙酸的控制释放

[目的]制备缓释型聚电解质微胶囊,解决2,4-二氯苯氧乙酸(2,4-滴)有效成分释放速度快、药效持续时间短的问题。[方法]将除草剂2,4-滴乳液成功地包埋入具有良好机械性能的聚丙烯酸-阳离子淀粉聚电解质微胶囊中,研究不同pH值、温度和盐浓度对2,4-滴释放性能的影响。[结果]聚电解质微胶囊具有良好的机械性能,当pH值为4、温度为15℃、盐浓度为1.5%时,微胶囊对2,4-滴的释放性能最佳。[结论]聚电解质微胶囊对2,4-滴具有良好的控制释放性能。     

除草剂在土壤中的分解(二)

Ⅳ.各种除草剂的分解下面叙述各种除草剂的分解,而有关各除草剂在土壤中的残留期可参阅另外文献。 1.苯氧基乙酸类除草剂除2,4-滴(2,4-D或2,4PA)、2-甲-4-氯(MCP)之外,还有2,4-PS(SES)、MCPE、除草佳(MCPCA)等。在日本除2,4-滴盐、2-甲-4-氯盐之外,用于水田杂草防治的还有2,4-滴乙酯、2-甲-4-氯乙酯。2,4,5-T作为高效除草剂,过去大量使用,但是因为产品中存在杂质二噁因(dioxin)的毒性问题,故近年来已不使用。     

微波一步法合成颗粒有机膨润土及其柱试验吸附废水中2,4-二氯酚

以膨润土粉末为原料制得颗粒膨润土,在微波作用下,用十六烷基三甲基溴化铵(CTMAB)对其改性,合成了颗粒有机膨润土.SEM图表明改性后的膨润土片层变小,由XRD测定结果计算出改性后颗粒膨润土层间距由0.91 nm增加到1.02 nm.通过柱试验考察了CTMAB用量对有机膨润土颗粒吸附2,4-二氯酚效果的影响,结果表明,当CTMAB用量由25％ CEC增加到100％ CEC时,吸附柱被穿透的时间由80 min延长到220 min.再生试验表明颗粒有机膨润土可以重复利用.     

聚胺类功能性2,4-滴制剂的制备与控释性能评价

[目的]提高2,4-滴等有机酸类农药的有效利用率。[方法]使用聚N,N-二甲基乙烯基胺、聚N,N-二甲基烯丙基胺、甲基化聚乙烯亚胺(PEI)、聚脒等4种聚胺类功能性高分子与2,4-滴结合形成水溶性制剂,并测试其对2,4-滴透析释放情况的影响。[结果]水中透析以甲基化PEI、聚N,N-二甲基烯丙基胺、聚N,N-二甲基乙烯基胺的控释能力为佳。叔胺度69.0%的甲基化PEI质量≥42.6%时,释放率在32%左右达到控释平衡,且药剂释放比较集中。[结论]聚胺类高分子与2,4-滴的结合可以改善2,4-滴的控释性能。     

激素型除草剂抗性概况、机制和对农作物阔叶杂草管理意义

2,4-滴、2甲4氯(MCPA)和麦草畏等激素型除草剂被广泛用于谷物田选择性地防除阔叶杂草,而毒莠定用于非农业领域(如电力线走廊或草地)控制阔叶杂草.2,4-滴和2甲4氯是在二次世界大战期间开发的首类选择性有机除草剂,此后北美开始大量地生产2,4-滴.进而,2,4-滴在谷物田的使用使全世界掀起了农业生产改革的浪潮.2,4-滴成功的商业化带动人们合成了其他一些化合物,如麦草畏、二氯吡啶酸、毒莠定和二氯喹啉酸,这些化合物目前正被用作选择性除草剂.激素型除草剂价格不高,土壤中的残留期短(吡啶羧酸类除外,图1).这些除草剂选择性强,活性高,杀草谱宽,使用成本低,是全球使用十分广泛的除草剂,已被使用60多年.自从2,4-滴、麦草畏和其他激素型除草剂商业化用于中耕作物以及非作物系统后,它们在美国、加拿大和其他国家的使用量大大增加了.     

未来2,4-滴的市场前景依然看好

正2,4-滴在农药历史上具有里程碑的意义,该品种1945年引入市场,迅速应用于小麦、玉米、水稻及其他禾谷类作物防除农田杂草,成为第1例成功的选择性除草剂,历经半个多世纪还在农业生产中发挥重要的作用。2,4-滴在我国是大吨位的除草剂,其制剂2,4滴-丁酯以其广谱、价格优势一直在我国农业生产上起主导作用,目前在我国有8000吨/年的使用量。     

从我国除草剂登记情况看中国除草剂发展现状

1942年,2,4-滴的发现开创了有机除草剂发展的新纪元。70年代,发达国家除草剂的产量、产值、使用面积开始超过杀虫剂和杀菌剂。我国从1956年起在稻、麦田使用2,4-滴防除杂草,除草剂应用开始起步,90年代我国除草剂得到了较快的发展。但从目前看,除草剂的产量与杀虫剂相比还很少,1997年除草剂产量为6.7万吨(100%有效成分,下同)、杀虫剂27.5万吨,分别占农药总产量(39.5万吨)的17.0%、69.6%(原化工部化工统计年报1998)。截止2000年7月底,国内外共有404个厂家在我国登记除草剂,总数达1421个,其中国内厂家登记制剂数1078个(表1),占我国制剂登记总数…     

2,4-滴的用途广

2,4-滴是四十年代研制的一个除草剂老品种。历史上许多除草剂老品种,在除草剂的竞争中正在或已经被新品种代替,可是,2,4-滴这个品种却在竞争中一直保持着它的优势。据大田作物文摘(Field cropabstracts)1977-1978报导,有关2,4-滴作除草剂和植物激素应用仍很多。它在使用的几百个除草、激素药剂中,仍处在领先的地位。2,4-滴所以有这么强的竞争能力,其中一个重要的原因是它具有广泛的用途。2,4-滴作为除草剂已有悠久的历史,早已为人们所熟悉。然而,近年来它作为大田作物除草剂,不     

活化黏土对羧甲基壳聚糖控制吡虫啉释放的强化作用

[目的]以活化黏土为吸附剂,与羧甲基壳聚糖复合制备颗粒状控制释放制剂,以延缓吡虫啉释放、提高药效并控制其污染。[方法]分别采用水中释放实验、土壤表层淋出实验,考察颗粒制剂控制吡虫啉释放及抑制其淋溶的效果。[结果]颗粒制剂中吡虫啉在水中的半数释放时间(t50)延长至25.5 h,释放过程受费克扩散控制,9次淋洗后吡虫啉的累计淋出率仅为28.6%。[结论]活化黏土可以进一步延缓吡虫啉的释放,显著减少其对地下水的污染。     

Carboxylmethylcellulose/bentonite composite gels: Water sorption behavior and controlled release of herbicide

The composite gels were prepared by adding bentonite or its acid‐activated derivative into the carboxylmethylcellulose (CMC) gel, and the resulted products were characterized with infrared spectroscopy. Different from ordinary swellable hydrogels, the CMC/bentonite hydrogel beads shrinked in water. The water sorption of dried gels was limited below 120% of their own weight, and a sorption equilibrium reached quickly within 20–40 min. The water of swollen gels exists mainly in bound status according to the DSC analysis. The release experiments in water were carried out to evaluate the release of herbicide metolachlor from gel formulations. The release mechanism dominated by a Fickian diffusion might be related to the quick and limited swelling of dried gels. Addition of bentonites in CMC gel is beneficial for slowing the release of metolachlor, especially when the acid‐activated bentonite was added. The time taken for 50% of metolachlor to be released, t₅₀ was prolonged to 158 h for the composite gel formulation based on acid‐activated bentonite from the 61.1 h for pure CMC gel formulation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Controlled release of the herbicides 2,4-D and dichlobenil from alginate gels

The herbicides 2,4-D [(2,4-dichlorophenoxy)acetic acid] and dichlobenil (2,6-dichlorobenzonitrile) were individually incorporated into 1.6–2.8-mm alginate gel beads by using calcium chloride and barium chloride as gellants. The release rate of each herbicide from the beads into water was greatly influenced by drying and the choice of gellant cation. Slowest release was obtained with dried samples that were gelled with barium chloride. At the slowest rates, release of 2,4-D was complete in 14 days, while only 59% of the less-soluble dichlobenil was released in 150 days.     

Optimization of an herbicide release from ethylcellulose microspheres

Summary The herbicide 2,4-D was microencapsulated using ethyl cellulose to develop controlled release formulations that protect it from photodegradation and evaporation and to reduce the environment pollution. Ethyl cellulose microspheres loaded with 2,4-D were prepared by the emulsion solvent-evaporation technique. We have obtained the desired microspheres with higher drug entrapment and encapsulation yield by varying certain conditions as stirring speed, polymer-solvent ratio, drug-polymer ratio, pH of continuous phase and organic phase solvent. The shape and size of microspheres were analysed by scanning electron microscopy. The herbicide release was studied at 25 °C and the release data were analysed according to Fick’s Law. The results demonstrate that we can control the release rate by modifying the process parameters.     

Electrochemical process for 2,4-D herbicide removal from aqueous solutions using stainless steel 316 and graphite Anodes: optimization using response surface methodology

In this experimental study, an electrochemical cell (100 cc) equipped with anode electrodes of SS316 and graphite and the cathode electrode of SS316 in parallel form at a distance of 1 cm from each other was used to degradation the 2,4-Diclorophenoxy acetic acid (2,4-D) herbicide. The results showed that the removal efficiency of 2,4-D herbicide in initial concentrations of 50 and 100 mg/L under optimum conditions (pH = 7, electrolysis time = 50 min and current density = 3 mA/cm²) using the graphite anode electrode was 73.5% and 47.76%, respectively; however, using the SS316 electrode, the removal efficiency was 44.23% and 17.65%, respectively. The highest removal of 2,4-D in electrochemical process was 95.87% for herbicide initial concentration of 50 mg/L by graphite anode electrode. Considering the efficiency of 2,4-D removal, the determined coefficients were found to be 0.91–0.93. The amount of energy consumed for SS316 and graphite electrodes was obtained to be 6.308 and 5.99 kWh/m³, respectively. Results revealed that the electrochemical process with graphite anode electrode has an acceptable efficiency in removing the 2,4-D herbicide and can be used as an appropriate pretreatment in treating the wastewater containing the resistant compounds such as phenoxy group herbicides (2,4-D).     

The Effect of Single, Binary and Ternary Anions of Chloride, Carbonate and Phosphate on the Release of 2,4-Dichlorophenoxyacetate Intercalated into the Zn–Al-layered Double Hydroxide Nanohybrid

Intercalation of beneficial anion into inorganic host has lead to an opportunity to synthesize various combinations of new organic–inorganic nanohybrids with various potential applications; especially, for the controlled release formulation and storage purposes. Investigation on the release behavior of 2,4-dichlorophenoxyacetate (2,4-D) intercalated into the interlayer of Zn–Al-layered double hydroxide (ZAN) have been carried out using single, binary and ternary aqueous systems of chloride, carbonate and phosphate. The release behavior of the active agent 2,4-D from its double-layered hydroxide nanohybrid ZANDI was found to be of controlled manner governed by pseudo-second order kinetics. It was found that carbonate medium yielded the highest accumulated release of 2,4-D, while phosphate in combination with carbonate and/or nitrate speeds up the release rate of 2,4-D. These results indicate that it is possible to design and develop new delivery system of latex stimulant compound with controlled release property based on 2,4-D that is known as a substance to increase latex production of rubber tree, Hevea brasiliensis.     

草甘膦与2,4-滴丁酯防除紫茎泽兰应用技术

通过草甘膦和2,4-滴丁酯对不同生长时期的紫茎泽兰活性测定,采用正交旋转组合设计,研究2种除草剂混用后的效果及最佳配比,并通过田间药效试验进行检验.结果表明：一次性施药处理,草甘膦效果较2,4-滴丁酯好,连续2次施药,效果相反;草甘膦防除大龄紫茎泽兰群体的效果较2,4-滴丁酯好;2种除草剂合理混用对紫茎泽兰表现出明显的增效作用,通过混用可减少除草剂用量.     

有机膨润土对印楝素的缓释和稳定作用

采用有机膨润土做载体以延缓印楝素的释放,提高其在水中和光照下的稳定性。印楝素A(Aza-A)的水解和光降解过程可以用一级反应动力学描述,其半衰期分别为67.5、5.35h。有机膨润土能够降低印楝素A在水中的释放速率,且膨润土改性时有机阳离子用量越多,印楝素A释放越慢。有机膨润土做载体可以提高印楝素A在水中的稳定性,并可将其光降解半衰期延长到6.94h。     

Controlled release of polymer conjugated agrochemicals. System based on poly(methyl vinyl ether‐alt‐maleic anhydride)

Controlled release formulations were prepared by using commercially available poly(methyl vinyl ether‐alt‐maleic anhydride) (I) and 2,4‐dichlorophenoxy acetic acid herbicide (2,4‐D). The copolymer (I) was reacted with various diamines to produce amido‐amine containing carboxylate copolymers. The produced copolymers were reacted with the acid chloride of herbicide 2,4‐D as model herbicide for carboxylic group functionalized herbicides. The formulations produced were characterized by IR and elemental analyses. The release of the herbicide 2,4‐D from the formulations was studied under different aqueous medium conditions and the effect of copolymer microstructure on release profiles was investigated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 415–421, 2001     

Silver nanoparticles embedded gum ghatti-graft-poly(N,N-dimethylacrylamide) biodegradable hydrogel: evaluation as matrix for controlled release of 2,4-dichlorophenoxyacetic acid

The present work explores the use of a nanocomposite hydrogel made using Gum ghatti (Gg), N,N-dimethylacrylamide (DMA) and N,N- methylene- bis-acrylamide (MBA) as a matrix for controlled release of 2,4-dichlorophenoxy acetic acid (2,4-D). Stable and uniformally distributed silver nanoparticles (Ag NP) were formed by the reduction of AgNO₃ using TCS within the gel network. The Gg-g-PDMA and Ag NPs entrapped gel (Gg-g-PDMA-SN) were characterized by FT-IR, XRD, TGA, SEM, EDS and TEM techniques. The presence of Ag NPs is observed to enhance the swelling ability and the release efficiency of the Gg-g-PDMA gels significantly and also showed higher biodegradability. The gels exhibited prolonged release of the 2,4-D indicating good potential to be used as matrix for controlled release applications in agriculture.     

Adsorption of 2,4-Dichlorophenoxyacetic Acid and Phenoxyacetic Acid on Sibunit

The kinetics of adsorption of the typical herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and phenoxyacetic acid (the product of 2,4-D decay in the natural environment) on the activated carbon Sibunit was studied in an aqueous medium. The porosity and surface structure of the carbon were studied. The orders of 2,4-D and phenoxyacetic acid adsorption were determined. The high adsorption capacity of Sibunit for these substances was found.