Poliakrilonitrilin NaOH ile hidroliz kinetiğinin incelenmesi
Poliakrilonitrilin NaOH ile hidroliz kinetiğinin incelenmesi
|Soydam, A. Bahattin
|Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1996
|Poliakrilonitrilin homopolimeri ve kopolimeri kullanılarak, sodyum hidroksit ile hidrolizi incelenmiştir. Bundan önceki çalışmalarda da poliakrilonitrilin alkali hidroksitlerle hidrolizi incelenmiştir. Kullandıkları yöntem ise, poliakrilonitrilin, dimetilformamit (DMF), dimetillmetakrilat (DMA), dünetüsûlfonat (DMSO), sodyumsülfosiyanür (NaSCN) gibi çözücülerinden herhangi birinde çözerek riflaks edildikten sonra, potasyum hidroksit ilavesi şeklindedir. Bu yöntemde poliakrilonitrilin çok kısa bir zamanda (15-20 dakika) hidroliz olmasına karşılık teknolojik olarak çok zor ve pahali bir yöntemdir. Bu çalışmada ise bu sistemlerden farklı olarak atmosfer ortamında vakum yapmadan hidrolizi incelenmiş olup, deneyler poliakrilonitrilin sodyum hidroksit ve suyun belli oranlarda kanşünlarak, değişik sıcaklıklarda, farklı zaman dilimlerinde hidrolizi basit bir deney düzeneği kurularak yapılmıştır. Elde edilen ürünlerin İR, UV spektrumlan ve potansiyometrik thrasyonlan ile hidroliz için gerekli optimum koşulların sağlanması amaçlanmıştır.
|Of the vinyl polymers mentioned, only a few have found commercial acceptance, the most important being poly(sodium acrylate), introduced in 1949. It has found widespread application in noncalchim muds such as fresh water, sah water and sodiumsurfactant muds. In combination with other polymers, it has also found application in the newer low-solids mud systems. Although numerous techniques may be employed to prapare poty(sodium acrylate), hydrolysis of polyacrylonitrile is at attractive from a commercial viewpoint. Alkaline hydrolysis of polyacrylonitrile proceeds rapidly at atmospheric pressure to yield a copolymer containing 60-70 mole % sodium carboxylate groups and 30-40 mole % amide groups. The composition of a copolymer of this type is illustrated as below. Chemical composition of a polymer derived by alkaline hydrolysis of polyacrylonitrile further hydrolysis is difficult to achieve due to steric and ionic factors. If polymers having other comonomer ratios are desired, they may be readily prepared by copolymerization of acrylic acid with acrylamide or by simultaneously polymerizing and hydrolyzing acrylamide in an alkaline medium. Because of acrylomtrile high polarity, it is characterized by a high polymerizability. Although the pure monomer is thermally stable (when heated to ISO degrees °C, only a small amount of the cyclic dimer, dicyanocyclobutane, is formed), it is very readily polymerized under the action of x rays, gamma-radiation, ultraviolet radiation, and the like. vu The polymerization of acryionitrile is easily initiated by compounds acting as free-radical sources, such as peroxides or diazo compounds. In addition to the free-radical polymerization of acryionitrile, ionic polymerization is also known, which takes place at low temperatures under the action of such compounds as bortrifluoride, titaniumtetrachloride, and the like. Homogeneous polymerization is carried out in such a way that both the monomer and polymer are soluble in the reaction medium. Dimethylformamide is an example of a solvent which can be used in this method. Heterogeneous polymerization in bulk, emulsion or suspension is considerably more widely used. Pure acryionitrile does not polymerize readily without initiators or light, but polymerization proceeds rapidly and exothermically in the presence of free radicals or anionic initiators. Oxygen is a very strong inhibitor and forms peroxides. If oxygen is allowed to react to exhoustion, polymerization may then proceed at a very high rate through the thermal decomposition of peroxides, and explosion can ensue. Historically, synthetic fibers consume more than half of the acryionitrile produced throughout the world, and ABS-SAN copolymers are the second largest users. Nitrile elastomers have the longest history of acryionitrile usage. They are copolymers of butadiene with a broad range of acryionitrile content which gives a great variety of useful proporties, such as resistance to oils, greases, solvents, chemicals, heal; aging, and sunlight toughness, and ease of fabrication. The high nitrile-content copolymers are useful meterials for fiber production, having good resistance to stretch, heat, microorganisms, insects and many chemicals. The fibers also show good stability to washing and cleaning, good flex life and recovery from wrinkling, low moisture absorption, warm feel, and good bulking properties. The large-scale use of acryionitrile copolymers in the plastics industry is relatively recent; approximately 15% of the acryionitrile produced is used in this way. Applications in this field are likely to expand as new technology is devoloped to improve these copolymers. The nitril containing plastics have good dielectric proporties, light stability, high softening temperatures, high tensile and impact strengths, and good resistance to solvent and heat. vui Monomelic acrylic acid, CHr=CHCOOH, was prepared by oxidation of acrolein in 1843. Lineer polymers of acrylic acid may be prepared by the general methods used with other vinyl monomers, nCH2 = CHCOQH Mrtrator»»^, Ofr- CH- Ofr- CH" COOH COOH Polymerization in aqueous solution at concentrations of 25% or less is convenient. Polymarization of more concentrated solutions or of undiluted monomer is not recommended because the high heat of polymerization makes polymerization difficult to control and produces insoluble polymer. Aqueous solutions of acrylic and methacrylic acids can be polymerized in the presence of a peroxydisulfate initiator at 90-100°C. A convenient formulation uses 10 parts of methacrylic acid, 90 parts of water, and 0,2 parts of ammonium peroxydisulfate. Acrylic acid can be polymerized in nonaqueous media, such as benzene, which are solvents for monomer but nonsolvents for polymer. Initiation can be accomplished with initiators soluble in the medium, used, such as benzoyl peroxide on azobissisobutyronitrile, or by the action of light. Poly(acrylic acid) and copolymers have a variety of uses in such diverse fields as mining, textiles, cosmetics, and papermaking. One of the earliest uses of poly(acrylic acid) was as a thickener. For this purpose the poly(acrylic acid) or its copolymer was sold as a concentrated solution of a sodium or ammonium sah, or as a dry polymer, in the acid form, which could be dissolved and then neutralized. During processing, textile fibers are subjected to much mechanical handling. To prevent damage during kinitting and weaving fibers are treated with warp size. Copolymers of acrylic acid and acrylamide are used as drilling-mud additives. During the drilling of an oil well, mud is pumped into drill hole. In certain formations, this mud tends to lose water to the sides of the drill hole and to become dry and caked. IX Acrylic acid can be copolymerized with divinylbenzene to make ion-exchange resins. The aim of this study is, via a simple process, to obtain PAA which is difficult to isolate in known expensive processes and has a wide applications area. The polyacrylicacid (PAA) is obtained by hydrolizing alkaline hydroxide of polyacrylonitrile (PAN) that is produced commercially with a large amount in AKSA, TÜRKİYE. Hydrolysis of polyacrylonitrile in the presence of alkaline hydroxide was done. In this procedure the polymer was dissolved in one of the expensive solvents given below, N,Ndimethylformamide (DMF), dimethyimetaacrylate (DMA) dimethyisülfanate, (DMSO) sodium thiocyanate (NaSCN) and the solution refluxed in on a thermostate with a constant stirring. Potassiumhydrokside solution was added to get the predetermined degree of hydrolysis and stirring was continued. The precipitated products were filtered, washed with hexane and dried under vacuum. The polyacrylonitrile (PAN) is hydrolyzed in a short time, but this is difficult and so expensive from technological point of view. In this study, the polyacrylonitrile (PAN) is hydrolyzed without using expensive solvents. The experiment was done in atmospheric pressure. In the beginnig of the experiment the molecular weights of the reagents (homopolyacrylonitrile and copolyacrylonitrile) are determined by using viscosimetry. For the hydrolysis of homopolyacrylonitrile and copolyacrylonitrile 2,5 g sample (^omopolyacrylonitrile/copolyacrylonitrile), 5 g NaOH and 50 ml water were stirred on a water bath at 40°C and 80°C by performining two paraleli experiment sets at the same time. The experiment is repeated at different time intervals (1-2-3 and 9 hours) The chemical mechanism of the process is illustrated as below. -(oK-pf -MŞt-^pi -fc-Tİ CN COOH CN n=x+y In the infrared spectra nitrile groups of the species at 2300-2200 cm'1 disappear and stretching frequencies of the carboxyl groups are observed at 1500- 1450 cm'1. The values obtained of the potensiyometric titration data are similar to those of polyacrylicacid (PAA). So it can be concluded that the products may be the polymers which have carboxyl substituents.
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|Poliakrilonitrilin NaOH ile hidroliz kinetiğinin incelenmesi