Band 37, Heft 2

Nanosized CdS/polymer composite fiber mats were fabricated via a facile electrospinning processing, and the as-prepared composite fiber mats showed excellent photodegradation ability to methylene blue (MB). Polymers bearing N and S atoms with affinity to Cd 2+ ions were first synthesized and then used to prepare CdS/polymer composite fibers. In this work, coaxial electrospinning was employed to achieve the preparation of the desired composite fibers using special polymers as core and cadmium acetate [Cd(CH 3 COO) 2 ] as shell. Then, fiber mats were immersed in thioacetamide (TAA) solution for several minutes, and CdS/polymer composite mats were obtained eventually. The photodegradation catalytic ability was tested using MB as a model dye under sunlight. The photocatalytic efficiency of the CdS/polymer composite fiber mat was recorded and studied by UV-visible spectra, and it showed high efficiency. Nanofiber mats will find real applications in the treatment of wastewater.

Waterborne epoxy-modified polyurethane-acrylate (EPUA) dispersions with nano-sized core-shell structure particles, with polyacrylate (PA) as core and epoxy-modified polyurethane (EPU) as shell, were successfully prepared via a two-step procedure. The waterborne EPU dispersions were first synthesized to serve as seeds, and then the butyl acrylate (BA) and methyl methacrylate (MMA) monomers were introduced into EPU particles to form polymeric core by radical polymerization under the assistance of ultrasonic treatment. Fourier transform infrared (FT-IR) spectroscopy revealed that the epoxy and PA components were successfully incorporated onto the chain of the PU and EPU to form EPU and EPUA, respectively. The transmission electron microscopy (TEM) photograph demonstrated that the EPUA particles have the core-shell structure. The as-prepared EPUA coating films exhibited good thermo-stability and mechanical properties, as revealed by thermogravimetric analysis (TGA) and tensile testing, respectively. The results of potentiodynamic polarization curves and immersion corrosion testing in 5 wt% NaCl aqueous solution both demonstrated that the anticorrosive properties of EPUA mainly depended on the mass content of PA, with the optimized value of 30 wt%.

A series of hyaluronan-heparin (HA-HP) hybrid hydrogels with an HP mass content from 1% to 10% were constructed by photo-crosslinking for the sustained delivery of growth factors (GFs) in soft tissue engineering. Glycidyl methacrylated HA (HAGMA) and glycidyl methacrylated HP (HPGMA) at a substitution degree of 33% and 17%, respectively, by 1 H nucleic magnetic resonance ( 1 H NMR) were synthesized and then used for gelation under ultraviolet radiation, followed by various characterizations, including elemental analysis, scanning electron microscopy (SEM), water swelling test, rheological analysis, and bone morphogenetic protein-2 (BMP-2) loading and delivery. The actual contents of HPGMA in HA-HP hydrogels were almost the same as their feeding ratios, indicative of a complete reaction by photo-crosslinking. The incorporation of HP into HA network gently influenced the morphology, water swelling property and rheological properties of hydrogels, but at 10% HP, it doubly increased the BMP-2 loading capacity to 65 ng/mg, alleviated the BMP-2 burst release to 40% within the initial 4 days and prolonged the BMP-2 sustained delivery to over 28 days. These results revealed that the long-term sustained delivery of BMP-2 from HA hydrogel could be achieved by conjugating HP into the crosslinked network with a controllable content.

In this work, polyacrylonitrile (PAN) was electrospun with and without magnetic nanoparticles (aluminum doped iron oxide) and was turned into magnetic nanofibers. The results showed that nanofibers diameter decreased from 700 nm to 300 nm by adding nanoparticles. Furthermore, pure PAN nanofibers were indicated to have low magnetic ability due to polar bonds that exist in their acrylonitrile groups. Obviously by adding only 4 wt% of the nanoparticles to PAN nanofibers, magnetic ability soared by more than 10 times, but at a higher percentage, it was shown to change just a little due to negative interaction among nanoparticles. This event relates to antiferromagnetically coupling of nanoparticles due to incomplete dispersion at higher percentage.

The objective of this study was to prepare linear low density polyethylene (LLDPE)/chitosan/closite nanocomposites by using various concentrations of LLDPE, chitosan, and closite clay mineral. The nanocomposites were then characterized for their thermal, mechanical, and rheological properties by using different analytical techniques including thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), rheological characterization, tensile strength study, and scanning electron microscopy. The TGA demonstrated that crosslinked composites are thermally more stable than non-crosslinked composites. The DSC stated that the percentage crystallinity of crosslinked composites is lower than the non-crosslinked composites. It is also observed that the increasing quantity of chitosan and closite also reduces the percentage crystallinity of the prepared nanocomposites. Rheological characterization revealed that, crosslinked composites are viscoelastic in nature and have high complex viscosities (η * ) and high dynamic shear storage modulus (G′), while non-crosslinked composites showed high dynamic shear loss modulus (G″). Tensile strength of crosslinked composites was much higher than non-crosslinked composites, however elongation at break (E b ) values of non-crosslinked composites are higher than crosslinked composites. The scanning electron microscopy displayed strong adhesion between matrix-filler-interphase in crosslinked composites, while some gaps were also observed in non-crosslinked composites. As a conclusion, chitosan, closite clay, and the LLDPE based nanocomposites with improved thermal, mechanical, and rheological properties can be successfully prepared by employing a peroxide-initiated melt compounding technique.

Molded interconnect devices offer great potential as a substitute for circuit boards, especially regarding three-dimensional shaping and functional integration. Applying circuits to polymer substrates can be performed by means of LPKF laser direct structuring ® (LDS). There, the matrix polymer is filled with a special metal additive, enabling laser activation and subsequent metallization. Important effects emerge from additional inorganic fillers inside the matrix polymer, e.g. the (thermo)mechanical behavior and the processing properties. In this work, the degree to which inorganic fillers affect the quality of metallization is investigated. An increase in the plating thickness was successfully achieved by adding varying amounts of talc platelets (diameter 7 μm) to a PA10T-based copolyamide filled with 4 and 8 wt% LDS additive, in contrast to poor metal deposition adding only LDS additive. Additionally, talc and glass spheres with a diameter of 50 μm were used, leading to unsatisfactory metallization results. To explain this behavior, adhering LDS particles were found on the talc platelets with a diameter of 7 μm on the surface of the laser-structured specimen. The talc platelets and glass spheres of 50 μm were not available in sufficient dimensions on the surface and thus led to worse plating results.

In this work, the posttreatment of an organic polymer is performed using an inorganic acid, nitric acid (HNO 3 ). We picked poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the base material and improved its electrical conductivity by acid treatment with different concentrations of HNO 3 . The acid treatment was able to achieve the optimum electrical conductivity of 197 S/cm, which is 115.5 times higher than the base material when treated with an aqueous solution containing 65% of HNO 3 . Moreover, the films showed higher transparency in the visible range while conducting Fourier transform infrared analysis. In addition, the treated films showed improved stability against outdoor operating conditions in terms of sheet resistance compared with untreated PEDOT:PSS films. We tried to develop a hypothesis to describe the reason behind the electrical conductivity enhancement by studying the thicknesses of all the samples at different acid concentration levels. The results from atomic force microscopy, the Hall effect, and the trend of film thickness suggest that the conformational change, the removal of excess PSS from the polymer, and the increase in carrier concentration are the reasons behind the improvement in electrical conductivity.

This paper describes the influence of thermal processing temperature on the microphase separation, hydrogen bonding, phase transitions and mechanical properties of 3,3-bis(azidomethyl)oxetane (BAMO)/tetrahydrofuran (THF) polyurethane binder, which is used for propellant. Fourier transform infrared (FTIR) spectroscopy confirmed that the intended polyurethane was synthesized and was used to determine the state of the local hydrogen bonding in these polyurethanes. The results showed that the thermal processing clearly imparts significant changes to the H-bonded environment and this was confirmed in a quantitative fashion using small-angle X-ray scattering (SAXS). The dynamic mechanical analysis (DMA) revealed rather significant changes in dynamic segmental relaxations and storage moduli for this series of BAMO/THF polyurethanes, which are in keeping with the findings from other experiments.

The aim of this study is to evaluate the effect of hybridizing Kevlar and glass fibers on the tensile and Charpy impact properties of their composites. Produced hybrid samples were designed as unbalanced and asymmetric structures in terms of different mixing ratios between woven Kevlar and S-glass fibers, and their tensile properties were determined using ASTM standards. A series of Charpy impact tests were performed to evaluate the amount of impact strength and absorbed energy by impacting each side of the hybrid composite samples. When the hybrid samples were impacted on the surface of the Kevlar side, they exhibited higher impact resistance compared with glass side impact. The resulting degree of hybridization effects showed that addition of Kevlar layers instead of glass layers contributed a significant increase in impact strength and absorbed energy of the overall composite laminate.

In this work, the effects of nano titania are investigated on mechanical, creep, and viscoelastic behaviors of epoxy resin. For this purpose, 0.25, 0.5, and 1 vol.% of TiO 2 nanoparticles were mixed with thermoset epoxy resin by mechanical and ultrasonic homogenizers and then the tensile, creep, and DMTA test samples were fabricated. The results of tensile tests show that the addition of TiO 2 nanopowder slightly increased the strength and Young’s modulus of epoxy resin. However, the ultimate tensile strain or the rupture strain of nanocomposites is decreased. In addition, to understand the viscoelastic behavior of nanocomposites, the DMTA and tensile creep tests have been done. Tensile creep test has been done by DMTA and universal test machine. Both results confirmed that the creep resistance of nanocomposites has extensively improved by adding the titania nanoparticles. Variations of storage modulus, loss modulus, and tan ( δ ) by adding TiO 2 nanopowder were examined in two modes of bending and tension. Storage and loss moduli of nanocomposite are considerably increased in all the states, but the storage modulus was more sensitive to TiO 2 loading intensity. Thus, test results showed that introduction of TiO 2 in the epoxy resin leads to the improvement of mechanical, creep resistance, and viscoelastic properties of nanocomposites. Due to the wide applications of epoxy resins in engineering devices, this method of reinforcement can be practical and useful to overcome some limitations of epoxy resins.

Binary fillers-filled silicone rubber (SR) matrix composites are prepared to improve the thermal and mechanical properties of SR as a lightweight thermal insulating material. Sepiolite and hollow glass microspheres (HGMs) can be evenly dispersed in SR matrix to obtain SR/sepiolite/HGM composites with superior performances at amounts of around 7.5 parts per hundreds of rubber (phr) and 20 phr, respectively, as observed from scanning electron microscopy (SEM). The density of the composites increases slightly with the addition of sepiolite in a linear trend, while the addition of HGMs results in the abrupt reduction in density lower than 0.7 g/cm 3 . Sepiolite exhibits a strengthening effect in the SR matrix; however, the addition of HGMs in this matrix slightly enhances the stress of the composite; its maximum elongation at break can increase up to 300%. The addition of sepiolite and HGMs improves the initial decomposition temperatures of SR composites a little; the excellent thermal insulating effect provided by HGMs is further verified by their significant decrease in thermal conductivity at 200°C, providing the facts that these SR/sepiolite/HGM composites can be used as lightweight materials for thermal insulating purposes.

In this research work, a two-dimensional model for randomly dispersed single-walled carbon nanotubes (SWCNT) in polymer hosts was used to predict the electrical percolation threshold (EPT) of the resulted composites in different concentrations of CNT. This was performed under a fixed DC voltage for different polymer matrices, such as high-density polyethylene, polymethyl methacrylate, polystyrene, polycarbonate, and polyethylene terephthalate via finite element method (FEM). The predicted EPT values in different composites were validated by experimental results published by other scientists. Results show that the electrical conductivity of the composites was strongly dependent on CNT weight percentages. Also, adding CNTs to the polymer matrix caused a decrease in the tunneling distance for various polymers in composites. Our results show that FEM could capture more details in the prediction of EPT in the nanocomposites.