Cüneyt H. Ünlü

Chitosan is an antimicrobial biopolymer with significant potential for manufacturing biodegradable and biocompatible materials through further functionalization. These materials could be highly suitable for biomedical applications. In this study, in order to obtain better properties such as antimicrobial activity and adjustable hydrophilicity for biopolymer‐based applications, N‐vinylpyrrolidone (VP) and methylmethacrylate (MMA) were simultaneously grafted onto chitosan by a ceric‐initiated emulsion polymerization method. The chemical structure, thermal, morphological, and antimicrobial properties of the resulting materials were investigated. The results revealed that PMMA and PVP pendant groups were grafted onto the chitosan main chain. According to SEM measurements, the obtained materials had spherical shapes with diameters ranging from 250 to 950 nm for the components. In vitro antibacterial activity against both Gram‐positive and Gram‐negative bacteria was significantly improved in the obtained materials compared to pristine chitosan.

Corn cob and tea leaves waste are used as raw materials for condensed phenolic structures. In this study phenolics were extracted from these waste materials, characterized, and modified to obtain surface active materials. The phenolic structures of corn cob were HGS-type lignin with 10% by mass of initial dry weight, while of tea waste were condensed tannin with catechin-like fragments with 15% by mass. Hydroxymethylation reactions were carried out to increase the reactive sites and also the water solubility. The phenolics of the corn cob were hydroxymethylated to a higher rate than the phenolics of the tea leaves waste (85 vs. 48%). Subsequent modification with maleic anhydride was carried out at a rate of about 40% for both types. Visual determinations indicated that all the materials obtained behaved like non-ionic surfactants. However, sulfonation of tannin structure (at a rate of 40%) resulted in an anionic surfactant structure, as expected.

This study covers the synthesis and release behavior of chitosan-graft-polyacrylamide copolymers in aqueous media at different pH values. The copolymers were synthesized using redox polymerization with ceric ammonium nitrate (CAN) in 1% aqueous acetic acid solution as the initiator. Optimum condition for the graft copolymer synthesis was determined as 3.85 g/L chitosan, 0.27 M acrylamide (AAm) monomer at 40 °C with a CAN per gram chitosan as 6 mmol using 0.05 M stock solution in 0.1 N HNO3. Then the crosslinked copolymers were synthesized using methylenebisacrylamide (MBA) as a crosslinker varying mass proportions of AAm:MBA as 15:1, 20:1, and 30:1. Obtained material amount (polymer yield) and molecular weight of crosslinked copolymers were lower than the graft copolymer as expected. Acetylsalicylic acid (ASA) release behaviors of all copolymers were monitored with UV-visible spectroscopy at different pH values (2, 6, and 8.5) corresponding to different media in the body (stomach, skin, and intestine, respectively). According to the results, the release behavior changed the least among the samples with respect to medium pH and of was the most affected.

Polyester and/or polythioester grafted chitosan copolymers were synthesized. For that, poly(ε-caprolactone) (PCL), poly(ε-thiocaprolactone) (PTCL), and their copolymers were first synthesized by ring opening polymerization. Copolymers with caprolactone:thiocaprolactone (CL:TCL) molar ratios of 2:1, 1:1, 1:2 were synthesized. All of the synthesized macromolecular architectures were characterized using different spectral (Fourier transform infrared (FTIR), proton nuclear magnetic resonance (¹H-NMR), X-Ray diffraction (XRD)) and thermal (Differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA)) methods. Grafting was then performed according two distinct routes: (i) using a blend of both homopolymers (PCL and PTCL) or (ii) using pre-synthesized copolymers with controlled CL:TCL ratios. Hexamethylene diisocyanate was used as a grafting/coupling agent through urethane bonds with high yield. Grafting preferentially occurred at sulfur sites. The results indicated that PTCL is more reactive and favorable than PCL for grafting onto chitosan. With the homopolymers blend grafting route, the corresponding materials mostly had a higher PTCL portion than expected. To obtain polyester grafted chitosan with a determined CL:TCL ratio, the copolymer grafting route would yield better results.

This study is about preparation of two different organoclays with cationic surfactants and their poly(vinyl alcohol) nanocomposites with increased thermal and mechanical behavior. Organoclays were prepared modifying clay mineral with solution intercalation method using aqueous solutions of cationic surfactants dodecyltrimethylammonium bromide (DTABr) and cetylpyridinium bromide (CPBr). Obtained organoclays (D-MMT and C-MMT for DTABr/MMT and CPBr/MMT, respectively) were characterized using different methods including zeta potential and XRD. Results indicated an absolute decrease in zeta potential about 20 mV for C-MMT, and 14 mV for D-MMT indicating flocculation and coating of the surface. Moreover measurements indicated that interlayer distance increased based on basal spacing peak shift whose value was 1.27 nm for NaMMT, whereas 1.40 nm for D-MMT, and 1.75 nm for C-MMT. The organoclays were used in preparation of PVA/clay nanocomposites; thermal stability of the nanocomposites were determined using TGA, while mechanical strength measurements were done using DMA. Maximum thermal decomposition temperature of the pristine PVA and nanocomposites were compared and an average increase of 4°C were observed. Also activation energy of the decomposition was observed ca. 40 kj mol-1 higher than pristine PVA.

A Koran written by Mehmed Şevki is the subject of this comparative analysis. This manuscript displayed an extensive degree of deterioration in 28 of the folios, while the rest of the manuscript is in considerably better condition. The aforementioned deteriorated sections of the book proved to be brittle and much darker in colour compared to the rest of this manuscript. The possible cause for this condition was ascertained using complementary techniques including the utilisation of micro-chemical (spot) tests, SEM-EDS, FTIR and Raman spectroscopy. The Micro-chemical Herzberg test indicated rag fibres in the paper used for the Koran, while the Raspail test #1 revealed rosin only in the sizing material of the deteriorated folios. SEM-EDS identified the presence of iron in all layers of the deteriorated folios but not in the stable folios. These results led subsequently to the conclusion that the deterioration of the folios was in fact related to the acid-catalysed hydrolysis due mainly to the presence of rosin and oxidation processes promoted by iron ions. This finding was also supported by FTIR analysis. The analyses indicated that different sizing materials had been used in the papermaking process of the two types of folios. In addition, Raman, EDS and HPLC techniques were also applied for the characterization of the inks and dyes. The results showed that inks and dyes were consistent throughout the entire text, thus suggesting calligrapher Mehmed Şevki and illuminator Hüseyin processed the book continually. It is plausible that calligrapher Mehmed Şevki changed his paper supply during the writing process which is why today we see a variety of differences in the condition of the papers.