D. Stojanović

Application of cellulose acetate for controlled release of thymol

Cellulose acetate (CA) was investigated as a carrier towards development of material with controlled release of thymol as a natural substance with strong antibacterial properties using high pressure techniques. Effect of thymol content on CA was confirmed by SEM, FTIR and DSC methods. Kinetic of thymol release from CA was tested using simulated gastric and intestinal fluids (hydrochloric acid and phosphate buffer saline). Results were correlated with Korsmeyer-Peppas and Weibull model. Depending on the thymol content and chemical nature of the release medium, the time of thymol release varied from one to three days indicating CA as a promising carrier of thymol with potential uses from medicine to agriculture. The impregnated CA showed antibacterial activity against 23 tested bacterial strains including methicillin-resistant Staphylococcus aureus (MRSA) which is particularly important bearing in mind that this strain causes fatal infections in humans and animals.

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.

Processing and characterization of UHMWPE composite fibres with alumina particles in poly(ethylene-vinyl acetate) matrix:

Processing of hybrid composites represents a challenge for engineers where the aim is to establish compatibility among several materials. The aim of this study is to evaluate the effects of different sizes and morphologies of alumina fillers on the mechanical and thermal properties of the composite fibres based on ultra-high molecular weight polyethylene fibres (UHMWPE). These fibres have an outstanding elastic modulus and they are compatible with nonpolar sequences of the poly(ethylene-co-vinyl acetate) (EVA) matrix. Compared to the fibres, inferior mechanical properties of the matrix can be improved using alumina particles. Commercial aluminium oxide (Al2O3) nanoparticles, commercial whiskers and synthesized particles of Al2O3 doped with iron oxide, incorporated in different weight percentages, were used as fillers. The UHMWPE fibres were impregnated using the solution of EVA in toluene with dispersed particles. Fourier transform infrared spectroscopy and field emission scanning electron microscope were used for structural examination. Tensile testing revealed increasing of modulus of elasticity and strengths of obtained hybrid composite fibres. Thermal gravimetry showed improved thermal stability up to 350°C of the hybrid composite fibres with alumina particles doped with iron oxide. Results of tested samples showed that the best mechanical properties were for hybrid composite fibres with 1 wt% of iron doped alumina filler.

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.

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.

Preliminary analysis of the possibility of preparing PVB/IF-WS2 composites. Effect of nanoparticles addition on thermal and rheological behavior of PVB

A possibility of using inorganic fullerene-like tungsten disulfide, IF-WS2, nanoparticles as a filler in poly (vinyl butyral), PVB, for improving its thermal and rheological properties is examined. PVB is a thermoplastic polymer with excellent properties, widely used: in ballistic protection, for protection of safety glass, in metal primers and coatings, temporary binders. Two different molecular weights of PVB were previously examined in this research: Mowital B60H and B75H. Both grades of PVB were dissolved in different solvents: ethanol and 2-propanol. Thin films were prepared by solvent casting technique. The glass transition temperature (Tg) of the tested samples was determined using differential scanning calorimetry (DSC), at three different heating rates (5°C/min, 10°C/min and 20°C/min). After choosing a solvent and PVB grade, IF-WS2 nanoparticles were added to PVB solutions and dispersed by ultrasonic irradiation. Compatibility, i.e. interaction of IF-WS2 with the dissolved PVB was examined by microcalorimetry method. The nanoparticles dispersion and deagglomeration in matrix of PVB was analyzed by scanning electron microscope (SEM). The effect of IF-WS2 on rheological properties of the chosen samples has been examined using Dynamic Mechanical Thermal Analysis (DMTA), observing storage modulus, loss modulus and the loss factor as functions of temperature for the tested composites.