Mikrodalga ile kürleştirilen epoksi nanokompozitlerin polidimetil siloksan ile modifikasyonu

Nanocomposites are materials that comprise dispersion of nanometer-size particles in a (polymer/ceramic/metal) matrix. The polymers containing layered silicate clay minerals as reinforcing agent can be classified as "intercalated" or "exfoliated depending on dispersing of clays in the matrix. Smectite (especially montmorillonite), saponite, and synthetic mica are among the commonly used layered silicate minerals for effective dispersion of nanolayers into an organic polymer matrix to form a nanocomposite.  The inorganic clay minerals must be modified by organic groups for dispersing of clay in the polymer matrix. For this purpose, clay must be put in the form of organoclay, firstly. Clay minerals are commonly composed of sandwiched sheets between alumina and silica layers. One of the typical properties of the clay is having a ion-exchange capacity. Generally, natural or synthetic clay minerals have a cation-exchange capacity of  50 to 200 milliequivalent/100 g. Clays whose cation-exchange capacity are  200 milliequivalent/100 g, have the interlayer bonding force too strong for exfoliation. On other hand, the capacity is  50 milliequivalent/100 g, the ion exchange of a swelling agent will not be sufficient. Therefore, having cation-exchange capacity of 50 to 150 milliequivalent/100 g. montmorillonite is a suitable clay mineral on account of organic cation swelling agent. In this work, powder formed layered silicates sodium montmorillonite, which is a member of smectite clay group, are used whose cation exchange capacity and medium particle size are 80 milliequivalent/100 g and 10 m, respectively. The polymer used in the work is bisphenol-A type epoxy resin, which is commonly used in industry as a thermoset polymer. Epoxy resins contain crosslinked epoxide groups in the polymer. For preparing epoxy polymers, crosslinked agent must be added to the epoxy monomer and applying any curing process to the mixture must do curing. In this work, bisphenol-A based epoxy resin cured with an aliphatic polyamino curing agent by applying electro magnetic radiation (microwave radiation). For the purpose of the surface modification,  diacrylate poly (dimethylsiloxane) (PDMS V-Si 21) was added to the mixture before curing process. The three different organophilic clay treated sodium montmorillonite was prepared by using different length long alkyl chain terminated amines such as dodecylamine, octadecylamine, and hexadecylamine. These organoclays was used for preparing polymer nanocomposites. Bisphenol-A based epoxy resin was mixed with the predetermined amount of organoclay ( 3%, 5%) and PDMS V-Si 21 (5%, 10%), and then the blend was mixed at  for 30 minutes. After that the curing agent was added to the mixture. Epoxy resin/curing agent ratio were taken as 2/1 in all samples prepared. Approximately 2 mg. well-mixed samples were poured into the 10 x 70 x 2 mm3 in size finger shaped Teflon mould to prepare the film samples. Microwave curing time was taken constant as 20 minutes at 400 W  power. After microwave radiation, the clear film-formed samples were removed and then cooled and stored in a freezer to use in some characterization tests. The prepared organoclays and polymeric samples were investigated by X-ray diffraction (XRD) analyses to calculate the difference between the layers. Thermal characterization was detected by differential scanning calorimeter (DSC) and E-Modulus, maximum strength, maximum strain, strenght at break was determined by universal testing machine. Shore D hardness were measured by applying on the both sides of the prepared nanocomposites. Fractured surface of samples were investigated by scanning electron microscope (SEM). The microwave curing is very effective due to the fast reaction technique for supporting intragallery epoxy curing. Incorporation of siloxanes improved both the compatibility and thermal stability of nanocomposites were observed by thermal characterization results. The mechanical properties of the nanocomposites were significantly improved for each sample containing 5% organoclay and 5% siloxane, in which interlayer spacing was increased and elastic properties. Hardness measurements of the nanocomposite samples showed siloxane accumulation on the film-air surface and their hardness were decreased by increasing siloxane content.In morphological study, the contribution of siloxane made the fractured surface smoother. Keywords: Nanocomposites, epoxy resin, montmorillonite, organoclay.Nanokompozitler, nanometre büyüklüğünde parçacıkların bir (polimer/seramik/metal) matriks içerisinde dağılmasıyla oluşan maddelerdir. Tabakalı silikat yapıdaki kil minerallerinin kuvvetlendirici katkı maddesi olarak kullanıldığı polimerler, kilin polimerde dağılma şekline göre “intercalated” veya “exfoliated” yapılarda nanokompozitler olarak adlandırılırlar. Bu çalışmada, önce, katyon değiştirme kapasitesi 80 meq./100 g sodyum montmorillonit, dodesilamin, hekzadesilamin ve oktadesilamin ile üç farklı zincir uzunluğunda organokil haline getirilmiş ve hazırlanan bu organokiller polimer nanokompozit hazırlanmasında kullanılmışlardır. Bisfenol A bazlı epoksi içerisine daha önceden belirlenen miktarlarda (%3, %5) organokil ve (%5, %10) silikon (PDMS V-Si 21) eklenerek mikrodalga kürleşme tekniği ile  farklı içerikli nanokompozitler hazırlanmıştır. Hazırlanan organokil ve polimerik örneklerin X-ışınları kırınımı (XRD) yöntemi ile incelenmesi sonucunda kil tabakalarının aralıkları incelenmiştir. Diferansiyel taramalı kalorimetre ile termal özelliklerdeki değişiklik, üniversal çekme cihazı ile E-modülü, çekme mukavemeti, maksimum kuvvette uzama ve kopma mukavemeti belirlenmiştir. Örneklerin her iki yüzeyinin Shore-D sertlik ölçümleri yapılmıştır. Örneklerin kırık yüzeylerinin yapısı taramalı elektron mikroskobu (SEM) ile incelenmiştir. Nanokompozit sentezinde mikrodalga ile kürleştirme tekniğinin, hızlı kürleşme tekniği olarak galeriler içi epoksi kürleşmesini desteklemesinden ötürü, çok etkili  olduğu görülmüştür Silikonun katılması nanokompozitin uyumluluğunu ve ısıl kararlılığını iyileştirdiği termal karakterizasyon sonuçlarından görülmüştür. %5 organokil ve %5 silikon içeren nanokompozitlerin tabakalar arası uzaklıkları da dikkate almak üzere mekanik özelliklerinde belirgin iyileşmelere neden olduğu yapılan çalışmanın sonuçlarından görülmüştür. Anahtar Kelimeler: Nanokompozit, epoksi reçinesi, montmorillonit, organokil

Copolymers of linear and crosslinked N-isopropylacrylamide/Monoitaconates

Sıcaklığa duyarlı N-izopropilakrilamit (NIPAAm)in nötral ve, hidrofobik dimetilitakonat (DMI), hidrofilik itakonik asit (IA), hidrofilik/hidrofobik monoester komonomerlerini içeren NIPAAm/DMI, NIPAAm/IA veNIPAAm/monoitakonat hidrojelleri, çapraz bağlayıcı bileşen olarak hem hidrofilik N,N’-metilenbis(akrilamid) (BIS) hem de hidrofobik vinil sonlu poli(dimetilsiloksan) (VTPDMS) varlığında, potasyum persulfat (KPS)-N,N,N’,N’-tetrametiletilendiamin (TEMED) redoks başlatıcı çifti ve AIBN kullanılarak su/metanol karışımında ve dioksanda serbest radikal çözelti polimerizasyonu ile sentezlendi ve bunların sıcaklığa bağlı şişme özellikleri ve sıkıştırma modülleri hesaplandı. Hidrofobik makro çapraz bağlayıcı VTPDMS kullanılarak elde edilen nötral NIPAAm hidrojellerinin mekanik dayanımlarının, BIS gibi dört fonksiyonlu çapraz bağlayıcılar kullanılarak elde edilen jellere göre yaklaşık 10 kat daha fazla olduğu gözlendi. Hidrofobik komonomerler (monobutil itakonat (MBuI), mono oktil itakonat (MOcI) ve mono setil itakonat (MCeI) ile iki farklı çapraz bağlayıcı BIS konsantrasyonunda NIPAAm hidrojelleri sentezlendi ve bunların mekanik dayanım deneyleri yapıldı. BIS kullanılarak sentezlenen NIPAAm hidrojellerinin sıkıştırma modülleri ve çapraz bağ yoğunlukları, alkil zincirlerinin uzunluğunun artmasına paralel olarak MCeI>MOcI>MBuI sıralamasına göre beklendiği şekilde artış gösterdi. Elde edilen bu sonuçlar doğrultusunda ilaç salımında kullanılmak için çapraz bağlayıcı olarak BIS ve VTPDMS kullanılarak sentezlenen NIPAAm, NIPAAm/IA, NIPAAm/monoitakonat homopolimer ve kopolimer hidrojelleri seçildi. IA, DMI, MMI, MBuI, MOcI ve MCeI komonomerlerini kullanılarak, AIBN ve KPS/TEMED redoks başlatıcı çifti eşliğinde 1,4-dioksan ve metanol/su çözücü karışımında toplam monomer konsantrasyunu 0.7 mol/L sabit tutularak, NIPAAm in doğrusal kopolimer ve terpolimerleri serbest radikal çözelti polimerizasyonu ile sentezlendi ve bu kopolimerlerin alt kritik çözelti sıcaklıkları incelendi. Anahtar Kelimeler: Poli(NIPAAm) jelleri, NIPAAm/IA, LCST, poli(dimetilsiloksan), mekanik dayanım, sıkıştırma modülü, kontrollü ilaç salınımı.Poly(N-isopropyl acrylamide) (PNIPAAm) has become the most popular member of a class of polymers that exhibits inverse solubility in aqueous solutions. This property is contrary to the solution behavior of most polymers in organic solvents under atmospheric pressure near room temperature. Its macromolecular transition from a hydrophilic to a hydrophobic structure occurs at a temperature which is known as the Lower Critical Solution Temperature (LCST). This temperature, being a function of the micro-structure of the polymer chains lies between 30oC and 35oC. PNIPAAm has been used in many forms including single chains, macroscopic gels, micro gels, latexes, thin films, membranes, coatings and fibers. Moreover, wide ranges of disciplines have examined PNIPPAm, encompassing chemistry, physics, rheology, biology and photography. PNIPAAm has been synthesized by a variety of techniques. Free radical initiation in organic solvents and aqueous media is only one of these experimental methods. Various initiators and solvents such as potassium persulfate (KPS), Ammonium persulfate (APS), azobis(isobutyronitrile) (AIBN), benzoylperoxide, laurylperoxide and water, methanol, benzene, 1,4-dioxane, tetrahydrofuran (THF), respectively, have been used in free radical polymerization produced in organic solvents and in aqueous media.Redox polymerization of NIPAAm typically uses APS or KPS as the initiator and either N,N,N?,N? tetramethylethylenediamine (TEMED) as the accelerator. In this study, taking into account the above literature results, we have attempted to investigate the effect of initiator type and concentration, hydrophobic and ionizable comonomers, and synthesis-solvent composition on the swelling behaviour of NIPAAM gels. For this purpose, NIPAAM gels, initiated with two different initiator concentrations, in water, and NIPAAM/DMI (dimethyl itaconate) and NIPAAM/ IA and NIPAAm/monoesters of IA copolymer gels in water/methanol mixtures and 1,4-dioxane were synthesized and their volume phase transitions were examined. Conventional swelling theory is used to characterize the interactions between the polymer and solvent molecules. Monoitaconates containing methyl, butyl, octyl and cetyl groups were synthesized. The copolymers containing these monoitaconates, IA and DMI were obtained by free-radical solution polymerization of NIPAAm. Hydrogels composed of NIPAAm, BIS, vinyl terminated poly(dimethyl siloxane) (VTPDMS) (commercial product) and IA as hydrophobic monomer, hydrophilic crosslinker, hydrophobic crosslinker and weakly ionizable comonomer, respectively, were prepared to investigate the effect of hydrophobic component, i.e., VTPDMS on the compression moduli of the samples attained equilibrium swollen state in distilled-deionized water at 25oC. For the NIPAAm/monoitaconate copolymer hydrogels crosslinked with BIS, the effects of hydrophobic component i.e., monobutyl itaconate (MBuI), monooctyl itaconate (MOcI) and monocetyl itaconate (MCeI) on the compression moduli of the samples attained equilibrium swollen state in distilled-deionized water at 25oC were investigated. Compression moduli and crosslinking densities of NIPAAm hydrogels containing 2.50 and 5.0 mole % of monoesters of IA in the feed and crosslinked with BIS increased with alkyl chain length in the order of MCeI > MOcI > MBuI. Theophylline was used as a drug for controlled-release of PNIPAAm, NIPAAm/IA and NIPAAm/ monoitaconate copolymer hydrogels crosslinked with BIS and VTPDMS. PNIPAAm hydrogel crosslinked with VTPDMS has the lowest drug release capacity because of the unresemble structures to each other. The presence of hydrophilic and ionizable IA molecules in the structures of NIPAAm hydrogels increases the release capacities and rates of hydrogels crosslinked with BIS or VTPDMS because repulsive forces between the ?COO- groups controls the shrinking rate at 37oC and so the drug molecules do not trap in the polymeric network. PNIPAAm, poly(dimethyl itaconate) (PDMI) and, copolymers of NIPAAm with IA, DMI, MMI, MBuI, MOcI and MCeI were obtained by free radical solution polymerization using AIBN and KPS/TEMED redox pair, as initiator, in 1,4-Dioxane and in MetOH/DDW with a total monomer concentration of 0.7  mol/L. The sensitivity of NIPAAm copolymers to change in pH and temperature suggest that they could be useful in biotechnology and drug delivery applications where small changes in pH and temperature. Keywords: poly(NIPAAm) gels, poly(NIPAAm-co-IA), LCST, Poly(dimethylsiloxane), mechanical strength, compression module, drug delivery systems

Study of the morphological and thermal properties of polystyrene nanocomposites based on modified halloysite nanotubes with styrene-maleic anhydride copolymers

In this study, the melt blending method was used to prepare the polystyrene/halloysite nanotubes (PS/HNTs) nanocomposites instead of in-situ bulk polymerization of styrene monomer in the presence of HNTs. Surface modification of HNTs with styrene-maleic anhydride copolymers (SMA) was performed in THF medium to improve the HNTs distribution and compatibility in the PS matrix. PS/HNTs nanocomposites were prepared in a twin-screw micro compounder containing 5, 10, and 15 wt.% of nanoclays. The influences of the surface modification of HNTs on the properties of the nanocomposites were studied by XRD, SEM, DSC, TGA, and tensile test. The SEM images showed that the modified HNTs samples were uniformly distributed in the PS matrix compared to the pristine HNTs. The thermal stability of nanocomposites was also improved by increasing of modified HNTs content. Consequently, the surface modification increased the dispersion of HNTs in the PS nanocomposites prepared by melt blending method

Experimental and MD simulation study on the physical and mechanical properties of organically modified montmorillonite clay and compatibilized linear low density polyethylene nanocomposites

Understanding the interfacial interactions plays a key role in controlling mechanical and physical properties of polymer/clay nanocomposites (PCNs). In this work, the surface interactions between constituents of experimentally prepared PCNs which are the pristine linear low density polyethylene (PE) chains, PE compatibilizers, montmorillonite clay surface layer, and surfactants were studied quantitatively by employing molecular dynamics simulation technique. The interaction energy between the polymer and the clay was found to be inversely proportional with the volume of the surfactant which decreases the electrostatic interactions between the compatibilizer and the hydrophilic clay surface. However, the van der Waals (vdW) interactions between alkyl tails of surfactants and the PE chains increase with the tail length of the surfactants. The most attractive interaction was between the surfactant's head group and the clay surface. We showed that there existed fine balance between the electrostatic and vdW type forces on the stability and the enhanced properties of the PE-organoclay nanocomposites. Calculated interaction energies were then correlated to the experimentally measured mechanical properties. (c) 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45817