Bu çalışmada polimerler içerisinde üretim hacmi sürekli artan bir polimer olan poliüretan ve Türkiye’nin yerli kaynaklarından elde edilen doğal hektorit kili kullanılarak poliüretan nanokom-pozitleri hazırlanmıştır. Kimyasal ve mineralojik analizleri yapılan doğal hektorit kili saflaştırma işlemi yapılmadan ve herhangi bir organik yüzey aktif maddeyle modifiye edilmeden kullanılmıştır. Polimer nanokompozitlerin yapıları, X-ışınları kırınımı ve Fourier transform infrared spektroskopisi kullanılarak aydınlatılmıştır. Yapılan deneyler sonucunda hazırlanmış nanokompozitlerin çok başarılı şekilde hazırlandıkları X-ışınları kırınım yöntemiyle tespit edilmiştir. Fourier transform infrared sprektroskopisiyle de poliüretanın killere moleküler seviyede etkileşmesi sonucunda poliüretanın yapısının değiştiği ve kilin polimer yapısına çok iyi şekilde katıldığı tespit edilmiştir. Nanokompozitlerin ara yüzeyinin morfolojik özellikleri taramalı elektron mikroskobuyla incelenmiştir. Polimer nanokompozitindeki killerin tamamen delamine olmuş yapılarını gözlemlemek için geçirimli elektron mikroskobu kullanılmıştır. Yapılan çalışma sırasında geçirimli elektron mikroskobunda inceleme yapabilmek için çok yeni bir numune hazırlama yöntemi geliştirilmiştir. Nanokompozitlerin ısıl özellikleri ısıl ağırlık analizi ile karakterize edilmiştir. Hazırlanmış olan nanokompozitlerin viskoelastik özelliklerini ve mekanik özelliklerdeki sıcaklığa bağlı değişimini gözlemlemek için dinamik mekanik analiz çalışmaları yapılmıştır. Polimerin hidrofilik özelliğinin belirlenmesi için su temas açısı test yöntemi kullanılmıştır. Nanokompozitlerin çekme-uzama mukavemetlerini belirlemek için mekanik testler yapılmıştır. Yapılan çalışmalar sonucunda çok iyi delamine olmuş nanokompozit yapılar elde edilmiştir ve bunun da neticesinde poliüretanın mekanik özellikleri iyileştirilmiş ve ısıl kararlığı arttırılmıştır. Anahtar Kelimeler: Poliüretan, nanokompozit, kil, hektorit, mekanik özellikler, ısıl kararlılık. Polyurethanes are unique polymeric materials in terms of various applications such as biomedical, coatings, adhesives, thermoplastic elastomers and composite. Polyurethanes have a copolymer structure synthesized with the isocyanates and polyols forming the hard domains and soft domains as a consequence of the isocyanates and polyol part, respectively. The properties of the polyurethanes can be adjusted by two main routes. The first method is the chemical route changing the isocyanate/polyol ratio and using different amounts of chain extender. The second method is the materials route altering the properties of the polyurethanes with different fillers. The versatile types of these two main reactants (isocyanates and polyols), different ways to synthesize the polymer and finally the processing of the polymer change the structure and the properties of the polymer. The properties of the polyurethanes can be improved by using reinforcing material such as talc, mica and glass fiber in the form of polymer matrix composite material. The polymer composites prepared with glass fibers have been used since 1950s. They have been applied in the industrial scale as well. These materials increase the tensile strength and improve the mechanical properties but they sacrifice the elongation at break. Currently new composite materials are based on the reinforcing agents at the nano-scale enabling the increase in strength without loss in the elasticity of the material and even getting more tough materials. There are two other advantages of nanocomposites. The one is the increase of thermal properties and the other one is better optical properties. Within this context clays form important family of nano fillers. The clays used in the preparation of polymer nanocomposites are generally from the smectite family with well ordered crystalline structure. Clay mineral is abundant in nature. It is a very cheap raw material for preparation of industrial product, if it is used without any modification and purification. The clays can be found in the polymer matrix in three forms such as intercalated, flocculated or exfoliated structure. The best structure is the exfoliated structure due to the best dispersion of clay can be obtained in the polymer matrix and level of utilization for the reinforcement is maximum. In this work, we have improved the properties of the polyurethanes with the materials route using the clays as the nano-scale reinforcing agent. In previous studies, the montmorillonite clay has always been examined to reinforce the polyurethane polymer. No work has been reported using the clay hectorite. In this work, we have investigated the effect of the hectorite content on the properties of the polyurethane. In some polymers such as polyethylene and starch, it has been observed that hectorite improves the mechanical properties of the matrix polymer. These led us to use the hectorite in the polyurethane matrix forming very novel nanocomposites. In this study, very novel polyurethane nanocomposites were prepared with the natural nanoclay hectorite without purification and organical modification. Generally, in the preparation of the polymer-clay nanocomposites, the organically modified clays have been used to create partial delamination before interacting with the polymer. In this study the exfoliated structures could be obtained without organic modification of the clays because of the hydrophilic nature of the polyurethane and swelling capacity of hectorite in the solvent, dimethylformamide. Exfoliated structures were identified using the X-ray diffraction analysis. Moreover the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to support the findings of the X-ray analysis. A novel sample preparation for transmission electron microscopy technique was used. With SEM, the clay particles could not be observed which shows the good dispersion of the clay platelets. With TEM, the individual layers of clay which could not be seen with SEM, were easily investigated with the thickness given in the pictures. Fourier infrared spectroscopy was used to determine the interactions at the molecular level. It was determined that the polyurethane and the clay interacted at the molecular level changing the structure of the polyurethane. Mechanical testing and thermal gravimetric tests were done for further investigations of the material. As a result of this successful nanocomposite preparation, the mechanical properties increased 113 wt % and thermal properties were also improved. Keywords: Polyurethane, nanocomposite, clay, hectorite, mechanical testing, thermal stability.
