Sonbahar Atığı Yapraktan Poliüretan Üretimi

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Tarih
2015-06-25
Yazarlar
Büyüklimanlı, Ayşegül
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Fen Bilimleri Enstitüsü
Institute of Science and Technology
Özet
Son yıllarda yüksek performanslı ve uygun maliyetli yeni malzemeler için büyük çapta bir arayış başladı. Bu süreçte polimerik malzemeler bir çok malzemenin önüne geçti. Fakat petrol temelli monomerlerden üretilen polimerlerin doğada uzun yıllar yok olmayışı ve çevrede yarattığı kirlilik yüzünden daha doğal yöntemler  aranmaktadır. Artan çevre bilinci ile bu arama özellikle yenilenebilir ve sürdürülebilir sloganları altında toplanmaktadır. Bu kavramların ön plana çıktığı günümüzde doğal liflerin kompozit malzemelerde ve polimerlerde kullanımı hızla artmaktadır. Yeni istihdam alanları yaratmasının yanında doğal liflere olan ilginin artmasının nedenlerinden bir diğeride selüloz, hemiselüloz ve lignin gibi lignoselülozik malzemelerin yapısının daha iyi anlaşılmış olmasıdır.  Doğada yaygın olarak bulunan selüloz sert, fibröz ve suda çözülmeyen doğal bir polimerdir. Selüloz,  hemiselüloz ve lignin ile beraber bitki hücrelerinde, hücre duvarının temel yapısında bulunur. Selüloz odunun büyük kısmını oluşturur doğrusal ve dallanmamıştır ve 10000 15000 Dglukoz birimi içeirir. Glukoz konfigürasyonundadır. Selülozun yapısında glukozlar glukozidik bağla bağlanmıştır. Doğal bir makromolekül olan selüloz, sentetik moleküller ile birleştirilerek çeşitli polimerizasyonlar ile kompozit malzemeler elde edilebilir. Çok kullanılan polimerlerden olan poliüretanlar genel olarak bakıldığında bir diol grubu ile bir diizosiyanat grubunun kondenzasyon polimerizasyonu ile ardarda birleşmesinden oluşurlar. Poliüretanlar yumuşak ve sert kısımdan oluşan parçalı bir yapıya sahiptir. Yumuşak kısım poliollerden oluşurken, sert kısım izosiyanat ve zincir uzatıcıdan oluşur. Yumuşak kısmın camsı geçiş sıcaklığı sert kısma göre daha düşüktür ve yapıya esneklik özelliği kazandırır. Bu iki yapısal bileşenin oranına baglı olarak son ürünün mekanik özellikleri geniş bir aralıkta değişmektedir. Bu çalışmada sonbahar atığı olarak nitelendirilen ve içinde lignoselülozik birimler barındıran yapraklar toplanarak içindeki selülozdan yararlanılmak istendi. Elde edilen selülozun endüstride değerlendirilebilmesi için poliol olarak poliüretan polimerizasyonunda kullanılmıştır.  Çalışmamızda İstanbul Teknik Üniversitesi’nden toplanan yapraklar selüloz geri kazınımı için soksilet ektraksiyonunda toulen etanol veya toulenm etanol ile ekstrakte edildi. Ekstrakte edilen yaprak hidrojen peroksit ve sodyum hidroksit ile oksidasyon yapıldı. İdeal koşulların belirlenmesi için baz miktarı, süre gibi koşullar değiştirildi. Analitik bir yöntem olan alkali delignifikasyonun literatürdeki emsallerinden farklı olarak, çalışmalar oda sıcaklığında gerçekleştirildi. Yapılan denemeler sonucunda oda sıcaklığında selüloz sentezinde zamanın uzamasının selülozu parçaladığı, selülozunda hemiselüloz ve lignin ile beraber çözeltiye katıldığı  ve ideal sürenin 24 saat olduğu gözlendi. Baz miktarının kullanılanılanın üzerine çıkarılmasının verimi negatif etkilediği baz peroksit oranının 0,8 1,0 arasında  sabit tutulması gerektiği gözlendi. İdeal parametreler doğrultusunda yapılan denemede verim yüzde 65 bulundu. Selüloza yapılan FTIR incelemelerinde 3400 cm-1 civarındaki yayvan OH bandları ve 895 cm-1 civarındaki  glukozit bandları gözlendi ve taramalı elektron mikroskobu ile alınan görüntüde selülozun mikrofibril yapısı görüldü. Kısacası bu tez çalışmasında öncelikle yapraktan selüloz sentezlendi. Sentezlenen bu selüloz poliüretan polimerizasyonuna katıldı. Daha sonrasında yapılan denemelerin spektral ve morfolojik incelemeleri yapıldı.
A large scale search has begun for new high-performance and cost-effective materials in recent years. With increasing environmental awareness, this search has been gathered under the slogans of “particularly renewable and sustainable”.  These concepts are coming into prominence today, and the usage of natural fibers with composite materials and polymers is increasing rapidly. The improvement of these materials are really important for not just science, but for creating new employment opportunities. The non-nutrient agricultural wastes create new business opportunities in countryside.  Polymeric materials replaced a lot of materials over the last few years, but polymers synthesized from petroleum based monomers can do a lot of harm to the environment and the bad effects of those polymers doesn’t dissolve quickly and pollutes the environment for a long time, and the researchers’ interest headed towards more natural procedures and natural products. The interest to the natural fibers increased rapidly after 1990’s, because researchers tried to find environment friendly products. Also,  the petroleum resources weren’t infinite, and the structure of lignocellulosic materials (such as cellulose, hemicellulose and lignin) were studied and understood a lot better, compared to petroleum based products. Cellulose, hemicellulose and lignin can be found in the plant cells;  in the structure of the cell wall. Our country has a high potential in terms of renewable energy sources. Turkey accounts for two-thirds of these resources according to the report biomass energy. This is a result of studies to assess the causes  biomass. Cellulose which is widespread in nature is a tough, fibrous, and hydrofobic natural polymer.The structure of wood is heavily consisted of cellulose. It can be found on plants’ branches, and all of the woody parts of the plants. The molecular structure is not branched, and it includes 10000 15000 DGlukose unit. The glukose units in the cellulose structure are bonded with glucosidic bonds. The secondary cell wall, primary cell wall microfibrils are microfibrils and more intense than those of cellulose crystals. Cellulose nature almost never does it alone. Usually found in combination with other herbal substances. This affects the degradation of cellulose in the natural environment. Cellulose fibers are primarily hemicellulose, being embedded in the matrix of other polymers, including pectin and protein. The chemical properties of cellulose are determined almost exclusively by functional groups. These groups are usually participate in any chemical reaction cellulose. Functional groups in the cellulose molecules within the three alcoholic hydroxyl group in each glukozanhidrit units are oxygen bridge between units.  The polyurethanes from requently used polymers are  produced from condensation reactions of a diol group and a diisocyanate group, whose merge one after another. Polyurethanes consist of a scattered structure, which are soft and hard parts. The soft parts consists of polyols, and the hard parts consists of isocyanate and chain lenghtener. The glass transition temperature of the soft part is lower compared to the hard part, and it adds flexibility to the structure. The mechanical characteristics of the final product changes in a wide range, and it depends on the ratio of those two structural components. The hard part is formed by diisocyanate effective in the formation of cross-linking. By phase separation between the hard segment urethane polyol soft segment is available. This structure results in the dispersion in the matrix of the soft segment, the hard segment areas occurs. Physical and mechanical properties of the polyurethane will depend largely on the distribution of hard and soft segments of the material. Changing the phase distribution of the material between the soft and hard segments, mechanical, physical properties and biocompatibility may be varied. Polyurethane may be a single step or two-step synthesis. Isocyanate in a one-step process, the polyol, chain extender is also added to the solvent. The reaction temperature is above 80C. Catalyst can be used if necessary. The two-step synthesis by reacting the polyols excess isocyanate prepolymer is obtained. The resulting structure is a low melting solid or viscous prepolymer. This prepolymer is reacted with chain extenders and high molecular weight polyurethane is obtained afterwards. Structure polyols used in polyurethane production are at least two or more hydroxyl group bearing compound. Polyols provide high elasticity to the main chain, so are referred to as soft segments. Polyols can be divided into two groups in terms of structural differences. The first group of propylene glycol, ethylene glycol, low molecular weight polyols, such as glycerin. The second group are the molecular weight oligopoliol containing terminal OH groups of up to 10 000 daltons. The intent of this study was to collect autumn wastes (autumn leaves which contains lignocellulosic units) and use the cellulose inside the structure of those wastes. The cellulose gathered from the wastes used in polyurethane polymerisation as polyol, to evaluate in industry. The leaves gathered from Istanbul Technical University has been extracted with soxhlet extraction, and toluen ethanol and toluen:methanol have beed used for extraction for cellulose retrieval. Soxhlet phase methanol: toluene and ethanol: toluene solvent grade ethanol, including two types: toluene was determined that the impurities are more expenses. After the extraction, the leaves have been oxidated with hydrogen peroxide and sodium hydroxide. Conditions like base quantity or the elapsed time has been altered to determine the ideal conditions. After the experiments, it turned out that lenghtening the reaction time in cellulose synthesis would lead to the fragmentization of the cellulose in room temperature, the ideal time was 24 hours, increasing the base quantity would reduce the efficiency, and the ideal ratio of baseperoxide need to be fixed at 0,8  1,0. Determination was made of the amount of lignin with lignin kappa method to detect analytically. In the FTIR examination of cellulose, broad OH bands at 3400 cm and  glycoside bands at 895 cm-1 has been observed, and the microfibril structure of cellulose has been observed with the SEM. All carbohydrates such as cellulose can enter the hydroxyl group in the structure and acetal and the reaction of the aldehyde group in the structure. The most important reactions in acid and alkaline degradation reactions, oxidation, esterification, etherification and is polymerized. The cellulose units gathered from alkaline peroxide oxidation has been mixed to make a charge mixture. The polyurethane experiments continued with this mixture. In the polyurethane synthesis, the surface area has been widened by mixing the cellulose inside acetone and Nmethylprolydon . Then hexamethylendiisocyanate , and 0,10 ml dibuthyltinlaurathe  or triethylenamine  has been added to the mixture. Then triethanolamine  has been added to the gathered prepolymer after this steps, after one hour. To end the reaction, 15 mL water has beed added after 3 hours.  The celluloseHDI ratio, chain lenghtener quantity or catalytic had been changed in these experiments to determine the ideal conditions. It turned out that the ideal ratio of celluloseHDI should be under 0,80, when the ratio lowers during the prepolymer sythesis, all of the NCO groups would react with OH groups, and there wouldn’t any NCO group left to react with the chain lenghtener. With the chain lenghtener addition, more durable and stronger products had been synthesized, and the best catalytic was determined as DBTL, by measuring the elapsed time. In the FTIR examination of polyurethane experiments, broad NH bands at 3330 cm-1 and CO bands between 1710 cm-1 and 1680 cm-1 has been observed.In all experiments, a band at 2270 cm-1 has been observed, this shows that all of the hexamethylendiisocyanate joined the reaction. PU polymers with trans-cis isomerism indicated characteristic bands such as NH stretching at 3323 cm-1, CN and NH stretching at 1532 cm-1 and asymmetric and symmetric stretching NCO-O and COC at around 1247 and 1249 cm-1 respectively. 1HNMR results showed characteristic. . FTIR studies that some of the polyurethane synthesized in cis-cis or trans-trans conformation of the owners of some products cis-trans, structure and showed that the vast majority of product urea-urethane has the structure. Stirring the obtained cellulose in a single sample when employed in polyurethane trials "result HDI  cellulose ratio should be below 0,80'n was observed. When the ratio falls during the prepolymer obtained is reacted with OH group of the cellulose of all the -NCO groups and a chain extender was found to not participate in the reaction of NCO group is added. Products of the addition fragmentation chain extender easily obtained. DBTDL as the catalyst was observed in a shorter time complete the reaction. To conclude;  cellulose has been sytnthesized from leaf in the first step of this thesis experiment. Unlike their alkali cellulose was obtained at room temperature delignification methods. The obtained sample was observed where the fiber lignin in the FTIR spectrum analyzed. The gathered cellulose has been used in polyurethane polymerisation, and the spectral and morphologic analysis of the experiments has been done. Polyurethane-polyurea structure in the product were confirmed on the desired mechanical properties of the product may be obtained by the change ratio of hard segment and soft segment.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2015
Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2015
Anahtar kelimeler
Polimer,  poliüretan, Selüloz, Polymer, Polyurethane, Cellulose
Alıntı