Browsing by Subject "Cryomilling"

Now showing 1 - 4 of 4

Open Access
Catalytic activity of novel thermoplastic/cellulose-Au nanocomposites prepared by cryomilling
(TUBITAK, 2020) Kwiczak-Yiğitbaşı, Joanna
Due to environmental concerns, increasing attention has been focused on the application and preparation of biobased polymers and their blends. In this study, cellulose, the most spread biopolymer on Earth, was used in the preparation of novel cotton/polypropyleneAu and cotton/polyethylene-Au nanocomposites via a green mechanochemical approach. First, mechanoradicals were generated by ball milling of the cotton and thermoplastics under cryo conditions, and then, these radicals were used in the reduction of Au ions to Au nanoparticles (Au NPs). Nanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The application of mechanochemistry in obtaining the cotton/thermoplastic blends allowed homogenous and fine blending of the samples and in addition, excluded the usage of toxic solvents. Since Au NPs exhibit a wide range of applications, e.g., in catalysis, cotton/thermoplastic-Au nanocomposites were used to catalyze the reduction reaction of 4-nitrophenol to 4-aminophenol, followed by UV-Vis spectroscopy. Finally, the hydrophobicity of the nanocomposites was alternated by tuning the blend composition. In the prepared nanocomposites, cotton and thermoplastics acted as very good supporting matrices for the Au NPs and provided satisfactory access to the NPs.
Open Access
Lignin as an antistatic additive for common polymers
(2018-01) Bedük, Tutku
Static electricity is a common phenomenon that can causes million-dollar loses in industries such as polymer, air and space, and drug manufacture due to the detrimental effects of electrostatic discharge of the accumulated charges on surfaces. Doping of the materials, i.e. polymers, with antistatic agents can reduce or prevent these problems. So far, the antistatic additives used were chosen to make the final material/composite conductive to dissipate the surface charges, by either directly doping with conductive materials (e.g. metals or carbon powder), or by doping with additives (e.g. ions) to increase surface humidity. The doped materials usually lose their inherent properties such as the mechanical properties because of the high concentrations of the additive. To provide a more universal solution to this problem and avoid the changes in the material properties after doping, the mechanism of static charge formation, which has been on debate for many years, should be clarified. Recent studies of our group and others have shown that the main mechanism behind the charge formation on electrified (polymer) materials is the bond-breakages on the surfaces of the materials, which lead to mechanoanion, mechanocation, mechanoradical active ends. The former two accounts for the charge on the surfaces and, as we have shown, the latter group (mechanoradicals) stabilizes the charged species. Previously, in our group, it was shown that by removing the mechanoradicals with radical scavenger antioxidants one can destabilize the charges – doping with antioxidants makes materials antistatic. However, the scavenger antioxidants we had used in this example to show the antistatic behavior were far from being practical in use for general polymers -that are produces in millions of tons per year- because of their individual prices. Lignin is the world’s second most abundant polymer. It has antioxidant properties, so it is a good candidate as an antistatic agent for common polymers. In this study we assess the lignin’s antistatic action by doping it into common polymers - elastomers (silicon rubber) and thermoplastics (PE, PP, PVC), and comparing the accumulated net charge on the doped and undoped polymers upon contact electrification. It was shown that the increase in lignin concentration and decrease in particle size of the lignin enhances the antistatic property in the polymers, due to an increase in radical scavenging OH groups, as verified by 31P-NMR analysis. We certify that the antistatic property is because of the radical scavenging action and not by increase in the surface conductivity. By doping polymers with cheap and abundant lignin, we provide a more universal, environment-friendly method for preventing electrostatic charge accumulation on common polymers, which are produced in millions of tons per year.
Open Access
Mechanochemical radical formation in cellulose ball milling and production of cellulose-metal nanoparticles composites
(2017-12) Bayrak, Özge
Cellulose is the most abundant biopolymer in nature, which contains linear chains of repeating D-glucose molecules connected by 𝛽-1,4-glycosidic linkages. Over the past decades, due to growing interest in sustainability and green chemistry, cellulosic materials have received much attention. Since cellulose is highly abundant, light weight, strong, biodegradable, and nonabrasive, composite materials including cellulose can be environmental friendly, biocompatible, low cost, low weight, and multifunctional. Cellulose composites including metal nanoparticles (cellulose-metal NPs composites) find application in many fields due to the combined properties of both metal NPs and cellulose matrices. However, current production methods of cellulose-metal NPs composites have generally multistep, long, and non-environment friendly procedures due to their requirement for hazardous chemicals to reduce the metal ion precursor and stabilize the metal NPs that form. This thesis work focuses on the investigation of cellulose mechanoradicals formation produced by ball milling qualitatively and quantitatively with the changes occurred in cellulose samples after mechanical treatment, and using formed cellulose mechanoradicals as reducing agent to reduce metal cations in cellulose matrices to obtain cellulose-metal NPs composites. Firstly, formation of cellulose mechanoradicals -free radicals that are formed by the homolytic breaking of the bonds in cellulose chains under mechanical input (ball milling)- was analyzed qualitatively and quantitatively. Qualitative analysis of cellulose mechanoradicals by ESR spectroscopy showed that, formed radicals could be generally peroxyl and alkoxyl types. The numbers of mechanoradicals formed by milling cellulose samples (cotton and microcrystalline cellulose) in wet and dry conditions were detected by using DPPH solutions with UV-Vis spectroscopy. It was shown that, dry grinding method led to the higher number of mechanoradicals formation. Changes in cellulose samples occurred after milling probed by using SEM, XRD, and FTIR-ATR analyses were found to follow the mechanoradical formation. Due to more efficient grinding in dry conditions, with increasing milling time, the progressive decrease in fiber size leading more accessible regions with smaller particle size of cellulose samples, and forming mostly amorphous cellulose samples were observed. FTIR-ATR analyses of ground cellulose samples, especially dry ground samples, showed the breaking of intra and intermolecular hydrogen bonds and 𝛽-1,4-glycosidic linkages. Lastly, cellulose-metal NPs composites were produced by using cellulose mechanoradicals as reducing agent for the first time. The composites were characterized by SEM, EDX, XRD, and XPS analyses. Au, Ag, Pt, and Pd NPs in their metallic forms, and Cu NPs in its metallic form Cu0 or in 1+ oxidation state as Cu2O, and Co in 2+ oxidation state as CoO NPs are successfully produced in cellulose matrices. This mechanochemical method can be proposed as a new and green method for cellulose-metal NPs composites production. Consequently, our findings can contribute to the area of mechanochemistry and composite materials.
Open Access
The morphological changes upon cryomilling of cellulose and concurrent generation of mechanoradicals
(Elsevier, 2019) Laçin, Özge; Kwiczak-Yiğitbaşı, Joanna; Erkan, Meltem; Cevher, Ş. C.; Baytekin, Bilge
With mechanical input, chemical bonds in polymers can be broken. Recently, it was shown that reactive ends formed by homolytic cleavage, so-called mechanoradicals, can be used in driving further chemical reactions or in making new composite materials. Cellulose, the most abundant polymer on earth, can also be subjected to mechanical input via ball-milling to produce mechanoradicals. Despite many reports on morphological changes in cellulose upon milling, there is only a limited understanding on how these changes affect the mechanoradical production, i.e., in which domains of cellulose the bonds are broken to produce the mechanoradicals. Here we show, the effect of the initial morphology of cellulose (cotton or microcrystalline cellulose) and the mode of grinding (dry or solvent-assisted) on the amount of generated cellulose mechanoradicals. The morphological and the chemical changes taking place upon milling of cellulose are monitored by SEM, XRD, and ATR, and the number of mechanoradicals is determined by a first-time quantitative analysis of cellulose mechanoradicals using radical scavenger DPPH. Our findings can help in efficient mechanofunctionalization of cellulose and to make useful mechanochemical reactions of cellulose using mechanoradicals, which stand as a promising economic and environment-friendly alternative to the conventional solvent-assisted chemistry of cellulose.