Synthesis and characterization of clay/chitosan and organoclay/chitosan nanocomposites

Bu çalışmanın amacı, tıpta ve endüstride pek çok farklı kullanım alanı olan kitosan biyopolimerinin özelliklerini tabakalı yapıdaki montmorillonit kili katkısı ile geliştirmektir. Kil tanelerinin kitosan içinde en ideal şekilde dağıldığı ve iki bileşenin en iyi şekilde etkileşebildiği uygun koşullar reolojik, elektrokinetik ve morfolojik yapı çalışmaları ile araştırılmıştır. Öncelikle montmorillonit tipi kil; sedimantasyon, santrifuj, diyaliz, kurutma ve öğütme işlemleri ile saflaştırılmış ve boyutları küçültülerek saf kil (SMt) elde edilmiştir. Hidrofilik yapıda olan SMt kilinin kitosan biyopolimeri ile optimum etkileşimini sağlamak amacı ile, kil katyonik bir yüzeyaktif olan hekzadesiltrimetil amonyum bromür (HDTABr) ile modifiye edilerek organofilik yapıya dönüştürülmüş ve HDTABr/kil (OSMt) organokili elde edilmiştir. SMt ve OSMt killerinin su bazlı dispersiyonlarında reolojik, elektrokinetik ölçümler ve mikroyapı analizleri yapılarak özellikleri belirlenmiştir. Çözeltilerin birleştirilmesi yöntemi ile kil ve organokil, kitosan polimeri ile etkileştirilerek nanokompozit filmler elde edilmiştir. Kil ve organokil miktarı farklı olarak sentezlenen kil/kitosan nanokompozit filmlerinin mikro yapıları X ışını kırınımı (XRD) ve geçirmeli elektron mikroskobu (TEM) analizleri ile, termal özellikleri diferansiyel taramalı kalorimetri (DSC) ve termogravimetrik analiz (TGA) yöntemleriyle belirlenmiştir. Kompozitler kilin veya organokilin kitosan biyopolimeri ile etkileşimine göre yapraklanmış veya tabakalaşmış nanokompozitler olarak tanımlanmışlardır. Sentezlenen nanokompozit filmlerin geçirgenlikleri ve kilin polimer içinde ne şekilde dağıldığının anlaşılması için UV spektrofotometre ile de optik geçirgenlik testleri yapılmıştır. Filmlerin sert ve kırılgan özelliğinin giderilmesi, elastikliklerinin arttırılması için yapılan gliserin ilavesinin optik geçirgenliği azaltması nedeniyle; filmlerde UV geçirgenliğinin engellenmesi için gliserin kullanılabileceği anlaşılmıştır. Anahtar Kelimeler: Montmorillonit, kitosan, organokil, biyopolimer, kil/kitosan nanokompozit.Nowadays, the physical and engineering properties of polymers are improved by additon of nanosize clay to the clay/polymer nanocomposite materials. Clay/polymer nanocomposites exhibit various superior properties such as high strength, high modulus, and a high distortion temperature, compared to the pristine polymer. Montmorillonite (Mt) is the most widely used layered silicate in polymer nanocomposites due to its higher ion exchange capacity, surface area, and adsorption capacity, moreover that is friendly of environment, natural abundant and economic. Mt is composed of silicate sheets of 1 nm thickness with adsorbed exchangeable cations. The intercalation with organic materials increases the spacing between the silicate sheets and even lead to the complete dissociation of the sheets to form a Mt/organic composite with a nanometer scale. These nanoparticles have high aspect ratios (length-to-diameter (L/D) ratio for Mt clay ~ 220). Clay can be dispersed in polymeric matrix as conventional filler with aggregated particles, intercalated clay, ordered exfoliated nanocomposites, or disordered exfoliated nanocomposites. At very low loadings of nanoclay (~2-10 %), nanocomposites exhibit to increase in mechanical, thermal, electrical or barrier properties. Strong materials can be produced with inherent bioproperties (biocompatibility, biodegradability, antimicrobial) due to the completely biomolecular nature of the material. Biodegradable polymers which are provied from natural sources are desired polymers to make clay/polymer nanocomposite. Researches which were made to develope the properties of biopolymers are showed that the usage of clays, an inorganic material, as an additive gives positive effects. Physical and engineering properties of polymers can be improven by even a few amount of clay addition because of the crystal layer structure and characteristic properties of clays. The distribution of nano-size clay particles in polymers gets a strong interaction between clay and polymer that caused by superior properties clay/polymer nanocomposites. Chitosan is a biopolymer derived from chitin by N-deacylation. Chitin and chitosan are natural biodegradable and non-toxic linear heteropolysaccharides and waste products of the crab and shrimp industry. Chitosan is used in applications from health to agriculture to dyes for fabrics, because of its chemical and biological properties. There are even medical applications. The aim of  this  study, to improve the properties of the chitosan polymer, which has huge applications at medical and industrial fields, by adding clay particles. Clay particles were distributed homogenous in chitosan and suitable conditions for the best interaction of these two component are examined with using rheological, electrokinetical and morphological structure experiments. The clay samples were purified by using sedimentation, centrifuge, dialize, drying and grinding processes and called SMt. The purrified clay SMt and organoclay form of it, which was manifuctured by interaction of HDTABr surfactant with the aim of having optimum interaction between hydrophilic structured clay minerals and chitosan biopolymer were formed with chitosan. The micro structures of the composites were determined by using X-ray diffractometer (XRD) and transmission electron microscope (TEM) analysis. In addition, thermal properties of these samples were determined by using classical methods like differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Both rheological and electrokinetical properties of nanocomposite dispersions were obtaine and optical transparancy tests of nanocomposite films were experimented by using Ocean Optic HR 4000 UV/Visible spectrophotometer to determine light transmission of nanocomposite films beside how clay is distributed in polymer. The composite products were characterized by XRD, TEM to determine the microstructure, and DSC, TGA to find out the thermal properties. Besides, rheological and electrokinetic properties and optical transparancy of the nanocomposites were determined. We suggested that optical transparancy could help us to understand the distribution of the clay in polymer. The optical transparency tests was done and seen that the the transparancy of the films were decrease due to the aggregation of the particles. Also, glycerin which used to prepare the films caused to decrease the transparancy of the chitosan biopolymer, so it is determined that the films can be used as a UV light stopper materials. Keywords: Montmorillonite, chitosan, organoclay, biopolymer, clay/chitosan nanocomposite

Antibacterial mechanism with consequent cytotoxicity of different reinforcements in biodegradable magnesium and zinc alloys : A review

Benefits achieved by the biodegradable magnesium (Mg) and zinc (Zn) implants could be suppressed due to the invasion of infectious microbial, common bacteria, and fungi. Postoperative medications and the antibacterial properties of pure Mg and Zn are insufficient against biofilm and antibiotic-resistant bacteria, bringing osteomyelitis, necrosis, and even death. This study evaluates the antibacterial performance of biodegradable Mg and Zn alloys of different reinforcements, including silver (Ag), copper (Cu), lithium (Li), and gallium (Ga). Copper ions (Cu2+) can eradicate biofilms and antibiotic-resistant bacteria by extracting electrons from the cellular structure. Silver ion (Ag+) kills bacteria by creating bonds with the thiol group. Gallium ion (Ga3+) inhibits ferric ion (Fe3+) absorption, leading to nutrient deficiency and bacterial death. Nanoparticles and reactive oxygen species (ROS) can penetrate bacteria cell walls directly, develop bonds with receptors, and damage nucleotides. Antibacterial action depends on the alkali nature of metal ions and their degradation rate, which often causes cytotoxicity in living cells. Therefore, this review emphasizes the insight into degradation rate, antibacterial mechanism, and their consequent cytotoxicity and observes the correlation between antibacterial performance and oxidation number of metal ions

Study On The Effect Of Bdtdacl And Dtabr Catıonıc Surfactants On The Partıcle Interactıons In The Na-actıvated Bentonıte-water System By Usıng Rheologıcal And Electrokınetıc Methods

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2004Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2004Bu çalışmada % 3’lük su bazlı dispersiyonlara katyonik yapıdaki iki yüzey aktifin (benzyldimethyltetradecylammonium chloride (BDTDACl), dodecyltrimethylammonium bromide (DTABr)) 0-10 mmol/l aralığında ilavesi ile yüzey aktif moleküllerinin reolojik ve elektrokinetik parametreler üzerindeki etkileri belirlenmiş, partiküller arasındaki etkileşimler araştırılmıştır. Neticeler, yüzey aktif moleküllerinin kil partikül yüzeylerine elektrostatik olarak tutunmalarının yanısıra kilin birim hücre aralıklarına girerek basal aralığını (d001) arttırdıklarını ve parçacık boyutunun azalmasına sebep olduklarını göstermiştir. Ölçümler, her iki yüzey aktifin dispersiyonlar üzerinde flokülan etki yaptığını ancak tümüyle yüzeyi kaplamadıklarını ortaya koymuştur.In this study; the effect of the two cationic surfactants (benzyldimethyltetradecyl ammonium chloride (BDTDACl) , dodecyltrimethyl-ammonium bromide (DTABr)) on the rheological and electrokinetic properties of the Na-bentonite dispersion has been investigated at concentrations of BDTDACl and DTABr between 0-10 mmol/l. Experimental results reveal that cationic surfactants attached on the surface of negatively charged clay particles and also they impede into the interlayer of clay particles. This results in, BDTDACl and DTABr make increase the basal space of the clay layers (d001) and decrease the size of the clay particles. The measurements show that BDTDAC and DTABr flocculate the clay dispersion. These surfactants adsorbed on the clay surface but not cover the whole of surface of the particles.Yüksek LisansM.Sc

Poly (styrene) latex/modified na-activated bentonite nanocomposite films: a fluorescence study

We studied film formation of composites of surfactant-free polystyrene (PS) nanoparticles and modified Na-activated bentonite (MLB), by steady state fluorescence (SSF) technique. The films were prepared from a mixture of pyrene (P)-labeled PS particles and MLB at various compositions at room temperature. These films were annealed at elevated temperatures above the glass transition (T(g)) temperature of polystyrene for 10 min. Scattered light (I(S)) and fluorescence intensities (I(P)) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of the composite films was monitored by using photon transmission intensity, I(tr) Atomic force microscopy (AFM) was used to detect the variation in physical structure of annealed composite films. The nanocomposite films exhibited a percolation threshold at 20 wt.% MLB content. Below this fraction two distinct film formation stages were observed which are known as void closure and interdiffusion and above this fraction no film formation was detected. At 0-20 wt.% MLB, minimum film formation, T(0), void closure, T(v) and healing, T(h) temperatures were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. Void closure activation energies decreased as the percent of MLB increased, no variation was observed in backbone activation energies.Q1WOS:00026193270000

Microstructure and mechanical performance of low-cost biomedical-grade Titanium-316L alloy

A 316L stainless steel (SS) alloy was developed with 1, 3, and 5 vol% titanium (Ti) reinforcement using the powder injection molding route, representing a low-cost option for biomedical implants. The investigation encompassed 1300 °C, 1350 °C, and 1380 °C sintering temperatures to ascertain the optimal physical and mechanical properties. Both sintering temperature and Ti influenced sintered density, and Ti mitigated the deleterious effects of residual carbon. At higher sintering temperatures, carbon and silicon tended to migrate and accumulate at the brink of Ti, leading to the formation of intermetallic compounds and increased brittleness. Dispersed Ti particles within the 316L matrix acted as nucleation sites and enhanced solid solubility with improved density. An astounding 96.11 % sintered density was achieved at 3 vol% Ti sample sintered at 1380 °C. During the tensile test, 5 vol% Ti at 1380 °C exhibited a low modulus of 58.9 GPa, which is highly desirable for orthopedic implant application. The XRD, SEM, tensile test, and nano-indentation results collectively provide evidence of beta-titanium formation during the sintering process. Conversely, the sample incorporating 3 vol% titanium, sintered at 1380 °C, demonstrated a balanced performance, showcasing 432.94 ± 12.8 MPa ultimate tensile strength, 3.06 ± 0.17 % elongation, 74.2 GPa modulus, and 322 MPa and 423 MPa 0.2 % offset flexural and compressive yield strengths, respectively. Notably, an improvised wear resistance test underscored its aptitude for sliding wear resistance, solidifying its potential as a promising candidate for biomedical implants