Farklı kil minerallerinin nanokompozitlere etkisi ve vermiküler/polimer nanokompozitlerinin özellikleri
The effect of the different types of clay minerals on nanocomposites and the properties of vermiculite/polymer nanocomposites
Yazar: YAVUZ İŞÇİ
Danışman: DOÇ. DR. SEVİM İŞÇİ TURUTOĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Fizik Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Fizik ve Fizik Mühendisliği = Physics and Physics Engineering

Özet:
Günümüzde polimerlerin kullanımı oldukça yaygındır ve polimer üzerine yapılan çalışmalar gün geçtikçe artmaya devam etmektedir. Polimerler üzerine yapılan çalışmalarda nano ölçekteki katkıların, polimerin özelliklerini oldukça geliştirdiği de bilinmektedir. Doğal olarak tabakalı yapıda bulunan killerin polimer içerisinde dağılabilmesi nedeniyle çok iyi birer katkı malzemesi olabilecekleri anlaşılmıştır ve böylece kil/polimer nanokompozitlerin hazırlanması, karakterizasyonları ve özelliklerinin belirlenmesi  üzerine yapılan çalışmalar başlamıştır.
Bu çalışmada, farklı kil çeşitleri incelenip, kil parçacıklarının birbirleri ile etkileşimleri, reolojik ve elektrokinetik ölçümlerle araştırılmıştır. Montmorillonit, sepiyolit ve vermiküler killeri araştırılarak killerin birbirleri ile olan etkileşimleri ve özellikleri incelendikten sonra, PVA polimeri ile en kolay nanokompozit hazırlama yöntemi olan çözeltilerin birleştirilmesi yöntemi kullanılarak nanokompozitler hazırlanmış ve bu nanokompozitler film haline getirilmiştir. Hazırlanan bu nanokompozitlerin karakterizasyonu yapılarak nanokompozit oldukları anlaşılmış, daha sonra nanokompozit filmlerin özelliklerinin incelenmesiyle PVA polimerine vermiküler kilinin katkısıyla mekanik özelliklerinin, montmorillonit kili katkısıyla da termal özelliklerinin geliştiğini görülmüştür. 
Mekanik özellik çalışmada daha ön planda olduğu için, yapılan ölçümlerde vermiküler kilinin istenildiği gibi yüksek elastik modülüne sahip olduğu görülmüş ve vermiküler kilinin anyonik, katyonik ve nanyonik yüzey aktiflerle etkileşimleri incelenmiştir. Bu yüzey aktif malzemelerle dispersiyonları hazırlandı. Karakterizasyonu yapılan ve özellikleri incelenen bu numunelerde, anyonik yüzey aktif SDS ve katyonik yüzey aktif ODTABr, vermiküler kilinin akış özelliğini değiştirmemiş ve tabakalar arası uzaklığı arttırmış veya tabakaları dağıtmıştır. Vermiküler kili, SDS ve ODTABr yüzey aktifleriyle modifiye edilerek organokil hazırlanmıştır. 
Hazırlanan bu organokil kullanılarak PVB polimeri ile ''organokil/polimer nanokompoziti'' hazırlanmıştır. Nanokompozit hazırlanırken polimerizasyon ve çözeltilerin birleştirilmesi tekniği olmak üzere iki farklı yöntem kullanılmıştır ve hangi yöntemle polimerin özelliklerinin daha çok geliştiği belirlenmeye çalışılmıştır. Hazırlanan nanokompozitlerin XRD, FTIR, TEM analizleri ile nanokompozit oldukları belirlemiştir. Ayrıca bu nanokompozitlerin termal ve mekanik özellikleri araştırılmıştır. 
Hazırlanan bu nanokompozitlerin XRD sonuçlarına bakıldığında, her iki yöntemde de tabakaların dağıldığı,  TEM resimlerine bakıldığında ise kil parçacıklarının 100 nm boyutundan daha küçük oldukları ve kil parçacıklarının tabakalarının hem dağılmış hem de tabakalı yapılarının bir arada oldukları görülmüştür.
PVB ve organokil nanokompozitlerinin orjinal PVB polimerine göre, termal dayanımları 2 kata kadar, mekanik dayanımları ise 8 kata kadar artmıştır.

Abstract:
Recently, the studies to improve the properies of the polymers increased with increasing industrial applications of the polymers. The studies to find which addition of the nano scale particles improved the properties of polymer. The naturally layered structure of the clay is understood to be an effective addition for polymer because it can be render easily in polymer matrix. Therefore, the studies for determine the preparation methods, the characterization, and properties of the clay/polymer nanocomposites have been started. 
In this thesis, firstly, different type of clay samples were investigated. The interaction between clay particles analysed by rheological and electrokinetical measurements. In this study, sepiolite, montmorillonite and vermiculite clays have been used. 
The first aim of this study is to determine and compare the effect of the clay minerals in a clay/polymer nanocomposites concerning the mechanical and thermal properties. The effects of the different clay minerals on different polymers have been researched frequently, but the comparison of the clay minerals never studied in an article at the literature. Since, clay minerals have different properties from each other such as surface area, crystal structure, surface properties, etc., the effect of the clay minerals on the nanocomposites would be different. 
At first, the characterization of clay particles were investigated. Clay minerals dispersed in water and were shaked for at least 24 hours. Dispersions of clay/water were dripped on the glass layer and were waited for drying for measurment of XRD measurments. According to XRD results, montmorillonite particle's gap between the layers were measured as 12.78 Å, for sepiolite it was found as 11.88 Å, and for vermiculite it was found as 11.33 Å. Another type of characterization is FTIR were used for investigation of bonding between particles. Also montmorillonit and vermiculite clay particles have the layered structure and sepiolite has the fiber stucture. Another type of characterization was FTIR for this samples. FTIR measurments have been done by FTIR spectrometer. Also samples were mixed with Kbr and were waited under pressure about 10 tons for preparing pellets. The results were discussed with modes of absorbance and transmittance of wave functions. In this method, the characteristic peaks of clay minerals were found.
In literature, there is a lot of appliance of clay/polymer nanocomposites with different types of clays but there is not any study about comparison of which clay is more effective to improve the specific properties of polymer. Thats why our next aim was investigating which clay improves the mechanical properties of polimer in nanocomposite application.
At the nanocomposite applience, layered particles are mostly preffered. Thats why montmorillonit and vermiculite clays are seems suitable for this project.
Montmorillonite (Mt), vermiculite (Verm) and sepiolite (Sep) clay minerals were used to prepare the nanocomposites for the comparison. A basic polymer, polyvinyl alcohol (PVA) were chosen as the polymer and the basic method, solution-casting method was used to prepare the nanocomposites. 
The structural and morphological characterizations were examined by using XRD (X-ray diffraction), TEM (Transmission electron microscopy), and FTIR (Fourier transform infrared) techniques and mechanical, thermal properties of the nanocomposites were determined by DMA (Dynamical mechanical analysis) and DSC (Differential scanning calorimetry) methods. 
XRD results shows that, due to the exfoluation of layered clay particles which are montmorillonit and vermiculite, the characteristic peaks of clay particles were disappeared. Because of the fiber structured sepiolite particles were not exfoluated, also were flocculated in nanocomposite. In nanocomposite applications, exfoluation of layers is needed to improve the interaction between polymer and particle's surface. Since sepiolite has not the layered structure, it is not suitable for nanocomposite applications. FTIR results showed that, there is hydrojen bonding between montmorillinite and polyvinly alcohol. According to thermal measurments, PVA polymer's glass transition temprature (Tg) is measured as 77.2 oC. The results showed that the layered clay minerals Mt, and Verm can be dispersed well in polymer and improved the mechanical, and thermal properties more than the fibrous sepiolite. Montmorillonit addition was improved the thermal properties about 2 times, vermiculite addition was improved the mechanical properties about 6 times of polyvinly alcohol. The bigger surface area of Verm caused to the bigger values of the elastic modulus while the more interaction between Mt with PVA caused to the higher values of glass temperature.
Due to bigger surface area of Verm causing to the bigger values of the elastic modulus, we prefer the Verm mineral in further experiments. 
According to rheological measurments, the dispertions of vermiculite in water, show the Bingam flow model and the according to electrokinetic analysis, zeta potantial measured as -17.4 mV. 
In the second part of the study, we modified the Verm minerals with different type of the surfactants in order to charge of the head parts of the surfactants. Vermiculite was modified with surfactants in order to enable intercalation of vermiculite layers. Since vermiculite has negative charges on its surfaces, it was expected that cationic surfactant would expand the clay layers more than an anionic surfactant. Nevertheless, OH- ions of the vermiculite surfaces were exchanged with negative parts of the anionic surfactant so unexpectedly the expansion of the layer was determined to be fully collapsed phase of vermiculite. 
Colloidal and structural properties of vermiculite dispersions were examined in presence of anionic, cationic and nonionic surfactants. 
The results showed that cationic surfactant covered the surface of the vermiculite with a second layer but the expansion of the clay layer was limited compared to the anionic surfactant. 
The anionic surfactant produced ion exchange with OH- ions of vermiculite and fully expanded the layer structure of the vermiculite. Also anionic and cationic surfactants didn't changed the rheological properties of dispertions. For further experiments, we choose the octadecyl trimethylammonium bromide and sodium dodecyl sulfate.
In the third part of the study, the organoclays were prepared with vermiculite; sodium dodecyl sulfate (SVerm) and octadecyl trimetylammonium bromide (OVerm). With this organoclays and polyvinyl butyral, nanocomposites were prepared. Polimerization and solution-casting methods were used in order to prepare the nanocomposites. 
The structural, and morphological characterizations were examined by using XRD (X-ray diffraction), TEM (Transmission electron microscopy), and FTIR (Fourier transform infrared) techniques and mechanical,  and thermal properties of the nanocomposites were determined by DMA (Dynamical mechanical analysis), and DSC (Differential scanning calorimetry) methods. 
Organoclay samples used with PVB polymer in order to prepare nanocomposites. According to XRD (X-ray diffraction) results, organoclay particles exfolieted, and dispersed in the nanocomposites. According to TEM images, the vermiculite particle's layers are not bigger than 100 nm. In solution-casting method, particle's layes are nearly 100 nm, and in polymerization methods, organoclays particle's layers are smaller than 100 nm. 
According to thermal analysis, the samples which prepared by solution-casting method; nanocomposites which prepared with vermiculite and SVerm, did not change the thermal properties of original PVB polymer, but the addition of OVerm to the PVB polymer increased the thermal properties. 
The samples which prepared by polymerization methods; nanocomposites which prepared vermiculite and SVerm increased the PVB polymer's glass transition temprature, and addition of vermiculite and SVerm increased the melting temprature at all concentration.