Preparation and characterization of polyurethane-hectorite nanocomposites

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. 

A New method for the styrenation of triglyceride oils for surface coatings

Tez (Doktora)-- İTÜ Fen Bil. Enst., 1993.St irenin kuruyan yağlarla kopol imer i zasy onundan kuruma süreleri kısa. suya ve kimyasal maddelere karşı dayanıklı ve sert filmler oluşturan ürünler elde edilir. Klasik yöntemler ile yağların stirenlenmesinde yağla rın yapısındaki yag asitlerinin içerdikleri çift bağların sayısı ve pozisyonu önemlidir. Geliştirdiğimiz üretim yönteminde ise reaksiyonun gerçekleşmesinde yag asitlerin- deki çift bağların etkisi yoktur. Böylece kuruyan yağla rın yanı sıra yarı kuruyan yağlar da stirenlenebilmekte- dir. Geliştirilen yeni yöntemde, yağın yapısına, ısı etki si ile kolayca parçalanıp serbest radikal oluşturabilen azo grubu sokulmuş, daha sonra 70"C'da stiren ile kopol i- merizasyon reaksiyonu gerçekleştirilmiştir. Çalışmada yag komponenti olarak ayçiçeği yağı, tütün yağı, haşhaş yağı ve keten yağı kullanılmıştır. Elde edilen stirenlenmiş ürünlerin film özelliklerinin incelenmesi ile yüzey kapla- yıcı olarak kullanılabilecekleri sonucuna varılmıştır.Styrenation of drying oils and alkyds is a well known process which finds practical application in organic coatings. The term styrenation refers to copolymerization of styrene (St) with oils or alkyds induced in the presence or absence of an added initiator such as benzoyl peroxide. The mode of styrenation depends on the type of oil used. The presence of conjugation in the oil favors copolymerization which can be activated thermally even without initiator. In the case of non-conjugated oils, however, copolymerization can be motivated by adding peroxides, pre-blowing the oil, and Lewis acid catalysts such as BF3. Semi-drying and non-conjugated drying oils may be mixed with conjugated oils to yield better styrenated products. Typical reactions, postulated for the styrenation of non-conjugated drying oils in the presence of benzoyl peroxide, are depicted below. O 0 ı-C-0-O-C-Ph »» 2 Ph-C-O- Ph-C-0-O-C-Ph »» 2 Ph-C-O- (1) O Ph-C-O* » Ph- + C0a (2) CH CH CH !h Ph- + CHa - »> Ph-H + CH» (3) CH CH CH CH I I VI h CH' + n CHa=CH ^ Copolymer (4) CH Ph İH I Ph* + CHa=CH ^ Homopolystyrene (5) k Notably, homopolymerization of St can be initiated by the primary radicals, produced from the thermolysis of benzoyl peroxide, as indicated by reaction 5. Consequently, the resulting product is a mixture of copolymer and homopolymer. The practical application of St of non-conjugated oils by peroxides is» therefore, strongly hampered by the formation of homo-polystyrene, since polystyrene is not compatible with the oils, the mixture separates and the product is turbid and unsatisfactory. In the present work, the styrenation of several semi- drying oils, namely tobacco seed oil, poppy seed oil and sunflower oil and a drying oil, linseed oil, has been achieved by the use of a low molecular weigth azo initiator, (4,4'-azobis(4-cyanopentanoic acid) (ACPA) ) incorporated to the partial glycerides. Attachment of azo groups to the oils was achieved by condensation of ACPC with the partial glycerides according to the following reaction. VII O CH3 CH3 O - OH + Cl-C-CHa-CH2-C-N=N-C-CHa-CHa-C-Cl + CN CN HO l pyridine (6) h O CH3 CH3 O - 0-C-CHa-CHa-C-N=N-C-CHa-CH2-C-0- | CN CN Partial glyceride backbone Styrenation of the oils was achieved by the thermolysis of the lateral azo group attached to the glycerolysate. The overall reaction may be generalized as fol lows. h 0 CH3 CH3 O 0-C-CHa-CHa-C-N=N-C-CHa-CH3-C-0 CN CN 1 (?) h O CH3 O-C-CHa-CHa-C. İN I" (8) VIII h O CH3 )-C-CHa-CH2-C CN Partial glyceride segment Polystyrene segment In these experiments, overall conversion of St was in the range of 60-75 %. Typical results concerning viscosities of each styrenated oil based on partial glycerides with two initial hydroxy 1 values, are represented in Table 1. As can be seen, viscosities are significantly lower when the partial glycerides with lower hydroxyl values are utilised. As it was previously noted lower hydroxyl value corresponds to higher proportion of unfunctionalised glyceride molecules, as far as azo groups are concerned, which do not actively participate in the styrenation process and greatly reduce the viscosity of the final product. The applied tests for determining the film properties and the obtained results are given in Table 2. As stated in Table 2 gelation was observed after adding driers in the case of styrenated linseed oil glycerolysate of higher hydroxyl value. This indicates the importance of the type of oil used in the process. Although final film properties vary according to the type of oil used, it is quite clear that the oils styrenated via this procedure show much better alkali resistance and dry fast as the styrenated linseed oil samples obtained by classical methods. We have also performed styrenation experiments using allyl malonate as a degradative chain transfer agent. It is well known that termination of St polymerization occurs almost exclusively by a combination process for temperatu res up to 80 'C. This reaction leads crossl inking and eventual inhomogeneity in the styrenated product. One way to overcome crosl inking is the use of classical chain transfer agents during the styrenation process. However, because of the fact that propagating active radicals are transferred to the chain transfer agent, homopolystyrene formation is unavoidable and undesirable. IX 01 -p o 3.d o u a, ?d © ?p (O C © >,.P en © 42 4-> -P.M 01 o o 01 r-l © 43 E- -p c © -p c o o o 01 o.o o -p © c © 45 -P ?d © c c.H 45 -P © İM I 01 © ı-H CO © 4J 10 C O ı- I S O © o e (D oı A © ?P -o 03 İH (0 o. © İH Cm m ?d ©.p ıa c 0) İH >N.P cn d) X. -P oı (D ?rl -P İH © a o İH a, 6 r-H ?H En © r-4 « © rC ?P c o M O (0 İH u o c c o.rl ?P 3 rH O 01 § 10 ©aç oı CN "d © +J -rl «O rH c o.r! -P 3 rH O 01 o* X ut 3 «3 ü rC ü in cn -d c.rl O U +J 3 O -d ©.rl u u 01 © İH © -d a c a-ri a) oı rQ o rC -M © a -p 01 © +J I1 3 SO u ?d 4H d) O -rl rH İH 10 o m CN -p ? + RS« (9) H RS- + CH2=CH m- RS/^v^^^CH2-CH (10) Ph Ph R-SH : A mercaptan type chain transfer agent. In our styrenation experiments, the polymerization of St is regarded to proceed entirely with the unimolecular termination mechanism as shown below. For this reason allyl compounds may be termed more correctly as degenerative chain transfer agents. + CH2=CH-CH2-CH ( COOEt )2 ^ (11) + CH2=CH-CH-CH ( COOEt ) 2 H Because allyl compounds lead to degradative chain trasfer, the resulting allyl radical is quite stable due to the allyl resonance. CH2=CH-CH-CH ( COOEt ) 2 ^ - CH-CH=CH-CH ( COOEt ) 2 (12) In this case conversions were in the range of 45-60 %. Table 3 lists the film properties of the resultant products obtained in the presence of allyl malonate. It should also be noted that the use of allyl malonate improves the film flexibility and adhesion. This behaivor is expected since allyl compound regulates the chain length of St segment, e.g., short polystyrene chains are formed. This is also confirmed by the viscosity values of styrenated oils. Comparison of the viscosity data on the styrenated products in the presence and absence of allyl malonate (Table 1), shows that the XII © +J 10 c o ı-H S *P O © c -d d) d) tn -d a, o c © Tİ 43 -P © İH C (0 ?rt 03 ?d © O) f-H İh Q. -ı.ri m o ı-H.n -d O © © ?d to © c +J -ri (O ?-* c © "d u © 4J 0 Cfî c © 0 >, -p 01 03 ©.ı-l ı-H -P ıö u c © o O -P c © > c o ?rl O rt ~ cn © 43 «S -p © >. ri -P (0 i-H © !h â? o VO ?d d 10 B ı-H.ri l(H © 42 P d o X o (0 İH o o d d o.ri.P ı-H O 03 X O o © d? 03 d o.rt.p 3 r-H O 01 o* CO 3 10 O 4= ü m cti ?d d u -n o cj m. CM "d ©.P -rt JC).- ı a a 10 oı m o 43 -P rt 4J -H 3 >xO ü ?d m a) O -rt -p +j 03 03 © © o cn S3 -p 01 © m CM.p (0.p 3 O ?d © ?ri U IÖ ü 03 I.p 03 © ı0 43 ü -d © 03 ©.P 3 d.rt S 8 !h 3 O 43 © Öl d 10 43 O O d o d m.d d © bı ©,-1 XIII viscosity of the product in the presence of allyl malonate is 1 ower. These results show that a new initiation system based on the thermolysis of the azo groups incorporated to partial glycerides is found to be useful in styrenation of triglyceride oils. The advantages of using this system are manyfold, mainly, (1) it does not require additional initiator or catalyst (2) absence of homopolystyrene formation due to the direct generation of active radical sites on the oil backbone (3) cross linking reactions observed generally in styrenation process may be prevented by the addition of degradative chain transfer agent (4) more importantly, this process allows styrenation of semi- drying oils without mixing with oils having conjugated double bonds or using blown oils.DoktoraPh.D

High-performance supercapacitor electrolytes based on high-mole-ratio phosphoric acid/lauryl ether surfactant liquid crystalline gel

Proton-conducting gel electrolytes offer significant advantages for supercapacitors. Among various acids, phosphoric acid (H3PO4·H2O, PA) has the highest proton conductivity for use as a supercapacitor electrolyte. Compared with commonly used acidic and basic electrolytes (H2SO4 and KOH), a high specific capacitance of approximately 620 F g−1 was attained for PA under 0.1 A g−1 test conditions in combination with a reduced graphene oxide (rGO) symmetric electrode. Moreover, the PA electrolyte was further improved by confining it to a liquid crystal (LC) gel matrix. PA and a non-ionic surfactant (lauryl ether, C12H25[OCH2CH2]10OH) were used to form LC gels with PA:NI mole ratios 60 to 100:1, which had viscosity values in 800 to 5500 mPa s−1 range at a shear rate of 100 s−1 and provided a high gravimetric specific capacitance of approximately 1128 F g−1 when tested at 0.1 A g−1 with an rGO symmetric electrode. The mesophase of the LC gel at each PA:NI mole ratio was comprehensively analyzed using X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), and polarized optical microscopy (POM) to confirm that the mesostructure was responsible for the high specific capacitance. The electrochemical performance was studied using electrochemical methods and galvonastatic charge/discharge tests. Furthermore, to increase the energy density of supercapacitors, focusing on automotive applications, this LC gel electrolyte could be used in an asymmetrical pseudocapacitor design

Fmoc-PEG coated single-wall carbon nanotube carriers by non-covalent functionalization: an experimental and molecular dynamics study

Due to their structural characteristics at the nanoscale level, single-walled carbon nanotubes (SWNTs), hold great promise for applications in biomedicine such as drug delivery systems. Herein, a novel single-walled carbon nanotube (SWNT)-based drug delivery system was developed by conjugation of various Fmoc-amino acid bearing polyethylene glycol (PEG) chains (Mw = 2,000, 5,000, and 12,000). In the first step, full-atom molecular dynamics simulations (MD) were performed to identify the most suitable Fmoc-amino acid for an effective surface coating of SWNT. Fmoc-glycine, Fmoc-tryptophan, and Fmoc-cysteine were selected to attach to the PEG polymer. Here, Fmoc-cysteine and -tryptophan had better average interaction energies with SWNT with a high number of aromatic groups, while Fmoc-glycine provided a non-aromatic control. In the experimental studies, non-covalent modification of SWNTs was achieved by Fmoc-amino acid-bearing PEG chains. The remarkably high amount of Fmoc-glycine-PEG, Fmoc-tryptophan-PEG, and Fmoc-cysteine-PEG complexes adsorbed onto the SWNT surface, as was assessed via thermogravimetric and UV-vis spectroscopy analyses. Furthermore, Fmoc-cysteine-PEG5000 and Fmoc-cysteine-PEG12000 complexes displayed longer suspension time in deionized water, up to 1 and 5 week, respectively, underlying the ability of these surfactants to effectively disperse SWNTs in an aqueous environment. In vitro cell viability assays on human dermal fibroblast cells also showed the low cytotoxicity of these two samples, even at high concentrations. In conclusion, synthesized nanocarriers have a great potential for drug delivery systems, with high loading capacity, and excellent complex stability in water critical for biocompatibility

Preparation and Determination of In Vivo and In Vitro Performance of Doxycycline Imprinted Contact Lenses for Corneal Neovascularization Treatment

The aim of this study is to develop doxycycline imprinted contact lenses that will be used in the treatment of corneal neovascularization, which can eventually cause blindness. For this purpose, doxycycline imprinted contact lenses were first prepared, and then they were loaded with doxycycline and their in vitro and in vivo performances were determined. In the synthesis of the contact lenses, 2-hydroxyethyl methacrylate was used as a backbone monomer. The functional monomer was selected as itaconic acid using molecular simulations. Doxycycline release profile of the lenses was determined in NaCl solution and their cytotoxic response was investigated on retinal pigment epithelium cells. In vivo experiments in rat models were performed to study the treatment patterns. The rats were sacrificed fifteen days after treatment, and clinical examination under optical microscope was performed to evaluate neovascularization, infiltration of inflammatory cells, and corneal epithelial changes. In conclusion; doxycycline imprinted contact lenses promise as an effective treatment method for corneal neovascularization