Band 39, Heft 4

The effects of low-pressure RF N 2 -O 2 plasma produced using a 13.56 MHz hollow cathode discharge system on the polymeric materials in terms of both biological and chemical sides are studied. A complete inactivation of most of the studied bacteria has occurred within 30 min. However, this treatment caused an increase of the surface hydrophilicity, as manifested by the contact angle measurements. This increase was explained by the formation of the N and O functionalities revealed by the X-ray photoelectron technique analysis. A careful analysis of the high-resolution C 1s peak has also revealed some variations on the C–C, C–O and O=C– bonds and the emergence of a new C-N bond.

The present study investigates the effect of thermooxidative and photooxidative aging on the mechanical and bactericidal properties of elastomer nanocomposites (ENs) based on Nanobent ZR2. The mechanical properties and morphologies were analyzed before and after aging. The addition of nanoparticles had a significant effect on the mechanical properties of ENs. Samples containing Nanobent exhibited higher tensile strength before and after aging compared to the reference composition. The addition of nanoparticles attenuated elastomer aging at elevated temperatures and ultraviolet light. Aged nanocomposites showed an inhibitory effect on the growth of bacteria and yeasts. Antibacterial and antifungal activity was only partially reduced after aging using physical methods compared to the activity of probes without aging. Scanning electron microscopy micrograph analysis showed different rough but homogeneous structures, confirming the uniform dispersion of the modified nanoparticles in the elastomer matrix as well as the retention of mechanical properties after the aging process.

The objective of this investigation was to fabricate cross-linked polyvinyl alcohol (PVA) based laminate composites reinforced with biaxial cotton sheets. Cross-linking was done with sulfuric acid, to overcome the water solubility of PVA. A water uptake test was performed to evaluate the effect of cross-linking on the water absorption properties of the composites. Morphology, distribution and bonding between the matrix and reinforcement of the fabricated composites were studied using scanning electron microscopy. Mechanical properties such as the tensile strength (TS), modulus of elasticity and elongation of the fabricated composites material were evaluated. There was about a 56.25% increase in the TS of the cross-linked composite as compared to the neat PVA, and at 64 wt.% of cotton fiber, there was about a 56% increase in the TS as compared to the cross-linked PVA. The thermal degradation analysis of fabricated composites material was carried out by thermogravimetric analysis. The thermal stability increased with increase in cotton fiber wt.%. The viscoelastic properties of the fabricated composites material were determined by dynamic mechanical analysis. The effects of stress (4 MPa, 6 MPa and 8 MPa) and temperature (20°C and 40°C) on creep and recovery behavior of the laminated composites were studied.

The main aim of this work is to produce foam rubber using the Dunlop process from in-house creamed latex and compare it with commercial centrifuged latex. The dry rubber content of creamed latex is higher than that of fresh natural latex and traditional centrifuged latex. The creaming agent plays a major role during the preparation of foam rubber and therefore defines the density as well as the elastic and mechanical properties of the final product. Scanning electron microscopy images show lower porosity in rubber foam made from creamed latex compared to that from centrifuged latex. This methodology should have a highly positive impact on the rubber community in both upstream and downstream rubber industries.

The combination of double-fillers with synthetic polymers has been an attractive route for developing bone scaffolds. In this article, polycaprolactone (PCL) scaffolds were produced using a selective laser sintering (SLS) technique; multi-walled carbon nanotubes (MWCNTs) and eggshell (ES) were used as two fillers to improve their mechanical and osteogenic properties. The crystal phase, morphology, hydrophilicity, biocompatibility and mechanical properties of the composite scaffold were detected using X-ray diffraction, scanning electron microscope, water contact angle tester and in vitro cell test, respectively. Results show that ES improved the hydrophilicity and biocompatibility of the scaffolds obviously, whereas MWCNTs enhanced their compression and tensile strength. The PCL/ES/MWCNTs composited scaffold prepared by SLS possess excellent biocompatibility and mechanical strength, showing a potential application for bone repair.

The effectiveness of woven and nonwoven polyester support and coagulation time during membrane formation on the performance and characterization of prepared membranes was studied. The blend membranes of polyvinylchloride with cellulose acetate were prepared by the immersion precipitation process. The prepared membranes were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrophotometry and a mechanical test. Membrane performance was tested using a feed of different synthetic salt solutions. The results proved that the prepared membrane using woven support provided the highest permeate flux and good salt rejection (93.3%) for a salty solution concentration of 20,000 ppm. The stress-strain mechanical test indicated that the excellent mechanical behavior was shown for membranes prepared with a woven support, which has a strength of 12.6 N/cm 2 with an elongation of 25 mm for M8. A fouling test was carried out using a mixture solution of salt and humic acid. Using the prepared membranes with woven support provided the best antifouling properties with a flux recovery of 99.2% compared with a flux recovery of 96% using the prepared membrane without support.

Proton exchange membranes (PEMs), used as separators, are one of the important components in microbial fuel cells (MFCs). The efficiency of MFC is greatly influenced by PEM. Nafion, which is a commonly used membrane, has several disadvantages in addition to its high cost. The aim of the present work was to develop low-cost PEMs with higher conductivity. In the current work, membranes were prepared using comparatively cheaper material polyvinyl chloride with different concentrations of silica (SiO 2 ), citric acid and phosphotungstic acid (PWA) by the solution casting method. Different membrane properties such as surface morphology, water uptake capacity, ion exchange capacity (IEC), tensile strength, leaching test and potential applications in MFCs were investigated. The results showed that the prepared membrane with 10% silica has the highest water uptake of 55.8%. The IEC of prepared membranes was found to vary from 0.024 to 0.875 meq/g. The membranes showing better IEC were applied to the MFC. The maximum power density obtained was 43.91 m W/cm 2 in the case of a membrane with both 5% PWA and 5% silica. The results obtained make this membrane a promising and economically viable new material in MFC applications.

Graphene can be used as a functional filler in thermoplastics in order to improve the mechanical and electrical properties, among other things. In the case of high exfoliation and dispersion state, disproportionate increases in compound properties can be achieved even with the lowest filler content. Accordingly, dispersion plays a decisive role here. Up to now, it has not been possible to achieve sufficient dispersion under near-industrial conditions on a twin-screw extruder due to the achievable shear energy input and short residence times. Therefore, this study presents a two-stage compounding process with the aim of improving graphene dispersion. First of all, a predispersion step is carried out in a solvent with the aid of ultrasonic treatment. The predispersed graphene solution is then added to the twin-screw extruder for incorporation. The solvent is removed by a multi-stage degassing process. The results show an improved dispersion compared to conventional addition of the graphene in powder form. In particular, the elongation at break of graphene-based composites can be increased from 13.6% to 57.1% by the increased dispersion.

This paper reports the implementation of slip boundary conditions in the open-source computational library OpenFOAM. The linear and nonlinear Navier slip laws, which are newly implemented in this paper, can be used both for Newtonian and viscoelastic constitutive models. For the former case, the Couette flow assumption near the wall is employed, and for the latter, the cell-centered extra-stress tensor components are linearly extrapolated to the wall. The validation is performed by comparing the numerical results obtained for Newtonian and simplified Phan-Thien-Tanner constitutive model fluids in Couette and Poiseuille flows, with existing analytical solutions. The results obtained using different slip factors were shown to be in agreement with the analytical solutions, even for the most extreme cases where the slip factor is high enough to induce a plug flow pattern for the velocity field. The newly implemented boundary conditions are also used to study the influence of slip in polymer processing, namely in the production of an extruded profile. The results obtained show that the developed slip boundary conditions are able to deal with complex geometrical problems, and are an important tool to support the search of a balanced flow distribution in the design of profile extrusion dies.

An online and feasible clamping force measurement method is important in the injection molding process and equipment. Based on the sono-elasticity theory, an in situ clamping force measurement method using ultrasonic technology is proposed in this paper. A mathematical model is established to describe the relationship between the ultrasonic propagation time, mold thickness, and clamping force. A series of experiments are performed to verify the proposed method. Experimental findings show that the measurement results of the proposed method agree well with those of the magnetic enclosed-type clamping force tester method, with difference squares less than 2 (MPa) 2 and errors bars less than 0.7 MPa. The ultrasonic method can be applied in molds of different thickness, injection molding machines of different clamping scales, and large-scale injection cycles. The proposed method offers advantages of being highly accurate, highly stable, simple, feasible, non-destructive, and low-cost, providing significant application prospects in the injection molding industry.

In the precision thermoforming process, one of the main drawbacks occurs in the profile deviation of the produced part. In this study, the effect of different thermoforming process parameters on the mold replicability of a high impact polystyrene container produced by vacuum forming and drape forming processes has been experimentally and numerically investigated. According to experimental results, in the drape forming process, when the initial sheet thickness increases, the part will have higher mold replicability, whereas in the vacuum forming process, by increasing the initial sheet thickness, the mold replicability increases and reaches its peak, then decreases. The results also indicate that both temperature and vacuum pressure exhibit the most significant effect on mold replicability of the part. Furthermore, the finite element method is utilized by the implementation of a fully thermomechanically coupled hyperviscoelastic constitutive model in ABAQUS 6.13. By using this material model, it is possible to compare the sensitivity of the output (mold replicability of the part) to the changes in the range of the process parameters. The simulation results verified by the experimental data and the hyperviscoelastic model showed to be an outstanding and stable platform for the process simulation.