Petar S. Uskoković

Oxidized and Ethylenediamine-Functionalized Multi-Walled Carbon Nanotubes for the Separation of Low Concentration Arsenate from Water

In this work multiwalled carbon nanotubes (MWCNTs) modified by oxidation (o-MWCNTs) and by aminofunctionalization (e-MWCNTs) were examined as potential adsorbents for arsenate removal from water. Adsorption characteristics of raw and modified MWCNTs were investigated in batch adsorption experiments. The influence of solution pH (pH range 3–10), contact time, and temperature (25, 35, and 45°C) were studied. Ethylenediamine-functionalized MWCNTs have the greatest affinity for arsenate ions, followed by o-MWCNTs and raw-MWCNTs. The obtained experimental data for raw- and o-MWCNTs fitted Sips isotherm model, while for the e-MWCNTs, the Freundlich model provided the best fit to the experimental points. The maximum adsorption capacity for arsenate ions was achieved using e-MWCNTs, 12.18 mg g−1. The presence of the arsenate on the adsorbent is confirmed by FTIR spectroscopy. Thermodynamic studies indicated the spontaneity and endothermic nature of the adsorption. Sodium hydroxide solution (0.1 M) was found to desorb about 70% of arsenate from e-MWCNTs. The results with spiked drinking water samples demonstrated that e-MWCNTs, due to the present basic and acidic groups, were very efficient for the removal of arsenate ions, as well as of some cations, at pH 4.

Wood-Thermoplastic Composites Based on Industrial Waste and Virgin High-Density Polyethylene (HDPE)

This article investigated the water resistance, mechanical and thermal properties, and the microstructure of wood–plastic composites, which were made by hot pressing using either virgin or high-density polyethylene (HDPE) as industrial waste with wood filler. The waste polyethylene was collected from residues of polymer production from Petrochemical plant, and wood particles were obtained from a local sawmill. The mechanical and thermal properties of the composites based on waste polyethylene were lower to those based on virgin HDPE, and the water resistance was shown to be higher. Adding ethylene maleated anhydride copolymer (MP) by 0.5–1.5 wt% in the composite formulation significantly improved both the stability and mechanical properties. Microstructure analysis of the fractured surfaces of MP modified composites confirmed improved interfacial bonding.

Keratin–polyethylene oxide bio-nanocomposites reinforced with ultrasonically functionalized graphene

Polyethylene oxide (PEO) functionalized graphene (f-G) was prepared by ultrasonication of pristine graphene in PEO aqueous solution. The feasible sonication protocol of PEO degradation and graphene functionalization enabled fabrication of solvent cast nanocomposites. Additionally, the steps to form new bio-nanocomposite films have been described. Taking the advantage of the combination of graphene, PEO and keratin fibers from poultry feather waste, the aforementioned bio-nanocomposite films were designed with extraordinary properties allowing the films to have promising applications as eventual packaging materials and enabling bio-waste keratin to be converted into value-added materials. Compared to neat PEO, addition of only 0.3 wt% f-G provided an increase of 92% to the storage modulus. These findings are similar to the nanoindentation results, which yielded increases in the reduced modulus of the same composition by about 92%. Nanoindentation testing shows that the incorporation of 0.3 wt% f-G increased the reduced modulus and hardness of the keratin–PEO blend by about 155 and 99%, respectively.

Dynamic mechanical and impact properties of composites reinforced with carbon nanotubes

This study presents dynamic mechanical and impact properties of the new form of hybrid thermoplastic composites. The six composites of polyurethane/p-aramid multiaxial fabric forms (Kolon fabrics) were impregnated with 10 wt% poly(vinyl butyral) (PVB)/ethanol solution with the addition of pristine multiwalled carbon nanotubes (MWCNT) where the PVB/fabric ratio was 20 wt%. All the composites consisted of four layers of the impregnated fabrics. The MWCNT/PVB content was 0, 0.5 and 1 wt%. The surface of the three composites with different MWCNT/PVB content was modified with γ-aminopropyltriethoxy silane (AMEO silane)/ethanol solution. The physical and dynamic mechanical properties of the prepared composite samples were analyzed by dynamic mechanical analysis (DMA) and high speed puncture impact tester. The structures of the composite samples were investigated by scanning electron microscopy (SEM). The results showed that the Kolon/AMEO/PVB/1 wt% MWCNT sample yielded a 60 % improvement in the storage modulus and a 73 % improvement in the impact absorbed energy compared to the Kolon/PVB sample. The carbon nanotubes (MWCNT) were added to improve the dynamic mechanical and impact properties of the materials for ballistic protection.

Formulation and characterization of nanofibers and films with carvedilol prepared by electrospinning and solution casting method

ABSTRACT The preparation and characterization of films and nanofibers with carvedilol as a poorly water‐soluble drug in poly (ethylene oxide) (PEO) polymer were investigated. Films are prepared by solution casting method, and nanofibers by electrospinning from a polymer solution. Water and mixture of ethanol and water were used as solvents. FT‐IR analysis of the samples showed that there was no interaction between the polymer and the drug substance. DSC analysis revealed that carvedilol was dissolved in the polymer and influenced the degree of crystallinity of PEO. Carvedilol release rate for all of the formulations was increased in comparison with pure carvedilol. Significant differences in the rate of release of carvedilol from the films and nanofibers were observed. Field Emission Scanning Electron Microscope (FESEM) images of the obtained fiber was revealed the dependence of the fiber diameter of formulation and electrospinning process parameters, and consequently influence the amount and distribution of carvedilol in the encapsulated fibers. Graphical abstract Figure. No Caption available.

Effect of Silane Coupling Agents on Mechanical Properties of Nano-SiO2 Filled High-Density Polyethylene Composites

Composites with nano-SiO2 particles and high density polyethylene (HDPE) matrix were produced by hot pressing with various particle contents and particle surface treatment using commercially available silane coupling agents: γ-methacryloxypropyltrimethoxy silane and γ- glycidyloxypropyltrimethoxysilane. The influence of the particle treatment on the mechanical properties of composites was determined by compression and indentation tests. Additionally, numerical analysis was performed in order to calculate Young’s modulus and stress concentrations for various particle contents in order to provide reference data by simulating micro- and macro particle composites with perfect bonding to the matrix.

Effect of the vinyl modification of multi-walled carbon nanotubes on the performances of waste poly(ethylene terephthalate)-based nanocomposites

Production of high-performance nanocomposite materials obtained from unsaturated polyester resin, based on products of the waste poly(ethylene terephthalate) recycling, and modified multi-walled carbon nanotubes is presented. Di-hydroxy functional glycolysates, synthesized by catalytic depolymerization of poly(ethylene terephthalate) with propylene glycol, were used for the unsaturated polyester resin synthesis. The structure of the obtained glycolysis product and unsaturated polyester resin were characterized by using FTIR and NMR spectroscopy, and by acid, iodine, and hydroxyl value. Nanofillers were prepared by direct and two-step amidation of oxidized multi-walled carbon nanotubes. Direct amidation with diallylamine produced multi-walled carbon nanotube-diallylamine reactive nanofiller. Two-step modification with diamines: hexamethylenediamine and p-phenylenediamine gave multi-walled carbon nanotube-hexamethylenediamine and multi-walled carbon nanotube-p-phenylenediamine nanofiller, respectively, whose amidation with methyl ester of linseed oil fatty acids gave multi-walled carbon nanotube-hexamethylenediamine/methyl ester of linseed oil fatty acid and multi-walled carbon nanotube-p-phenylenediamine/methyl ester of linseed oil fatty acid nanofiller, respectively. Influences of vinyl functionalities on mechanical properties of nanocomposite were analyzed from tensile strength (σb), elongation (ɛb) and Young’s modulus (E) determination. An increase of 97.4, 119 and 139% of σb was obtained for nanocomposites with addition of 0.25 wt.% of diallylamine, p-phenylenediamine/methyl ester of linseed oil fatty acid and hexamethylenediamine/methyl ester of linseed oil fatty acid multi-walled carbon nanotubes, respectively. Short techno-economic analysis, performed on the basis of fixed and variable unsaturated polyester resin production costs, showed satisfactory potential profit, which could be realized by the implementation of the presented technology.

Stress Field Analysis in Composite Laminates with Embedded Optical Fiber

A typical intensity-modulated optical fiber sensor system consists of a light source, a sensing device, within which the intensity of light is altered by the measurand in some way, a detector to measure the intensity of the transmitted signal and optical fibers to carry light between these components. The optical fiber coating interaction with the host material plays a major role in determining the proper transfer of load from the structure to the optical fiber. Three-dimensional (3D) finite element (FE) model of the structure was performed to study and predict the behaviour of the stress/strain fields in and around acrylate coated embedded optical fibers in flexural test coupons of carbon fiber composite. The modeling results and the fracture surface scanning electron micrographs suggest that the soft acrylate coating is debonding.

Processing of hybrid wood plastic composite reinforced with short PET fibers

ABSTRACT Poly(ethylene terephthalate) (PET) fibers (virgin, waste, and mixed) were incorporated in the composite poly(methyl methacrylate) (PMMA)–wood. Hybrid composite panels were prepared by pressure molding. Toluene-2,4-diisocyanate (TDI) and (3-mercaptopropyl)trimethoxysilane (MPTMS) were used as cross-linking bonding agents for modification of wood fibers. Influence of cross-linking bonding agents, structure, and composition of PET fibers was examined by studying thermomechanical properties as well as moisture absorption. Moisture absorption was lower for composites with bonding agents. Mechanical testing revealed that the addition of PET fibers drastically enhances properties of the composites. Covalent and hydrogen bonds formed with the addition of bonding agents have also improved mechanical properties compared to the untreated composites.

Healing efficiency of polystyrene electrospun nanofibers with Grubbs’ catalyst in thermosetting composite

The study presents a novel method for the protection of Grubbs’ catalyst, by incorporation in polystyrene fibres via electrospinning technique. Epoxy-glass fibre composite with embedded self-healing agents (polystyrene fibres with Grubbs’ and microcapsules with dicyclopentadiene) was processed. Fibres retained pale purple colour during processing, revealing that fibres provided good protection of the catalyst from the amine hardener. The influence of self-healing agents’ content and thermal treatment on self-healing efficiency was investigated. Fourier transform infrared spectroscopy revealed that a polydicyclopentadiene formed at the healed interface. Thermal analysis revealed that ‘bleed’ at the healing sites from different samples had similar concentration of polydicyclopentadiene, indicating that the same amount of the catalyst has been provided to dicyclopentadiene for polymerization. This finding lead to assumption that electrospun polymer fibres enabled good dispersion of the catalyst in the composites. The low energy impact tests of the samples showed a recovery of 90% after 24 h at room temperature and up to 111% after repeated heating cycles.