All issues / Volume 3 (2009) / Issue 3 (March)
A relation between surface free energy (σMHV) and Meyer’s lines cut-values has been established using Vickers microhardness (MHV) method and empirical physical laws. This relation allows the calculation of σMHV only from MHV data. The parameters required are Meyer’s lines cut-values and the mean value of diagonal length of the impression at different loads applied (drealmean). Our study of 12 samples of ultra high molecular weight polyethylene (PE-UHMW) showed that the new approach is applicable when the slope value of Meyer’s lines equals 2 (i.e. n = 2). A γ-60Co source was used for the irradiation of 11 samples (one of the samples investigated is un-irradiated) at room temperature in air. Doses of 1, 2, 5, 10, 20, 50, 100, 200, 500, 1000 and 1500 kGy were applied. The values of σMHV obtained are in a good agreement with the literature. The dependence of σMHV on the dose applied strictly corresponds to the radiation effects theory. MHV was measured at seven different loads – 0.0123, 0.0245, 0.049, 0.098, 0.196, 0.392, 0.785 N at a loading time of 30 s.
In this work carbon fiber/epoxy composites and MWCNT (multiwalled carbon nanotube)/carbon fiber/epoxy hybrid composites with 0.1, 0.3, 0.5 and 1 weight% nanotube filling of the matrix have been prepared and compared in terms of interlaminar properties. For the dispersion of the carbon nanotubes in the epoxy resin three roll milling has been utilized. The mechanical characterization has been carried out using standard DCB (double cantilever beam) tests assisted by acoustic emission. The test results have been evaluated by the conventional method provided by the standard and a novel method implementing acoustic emission signal localization for crack propagation tracing. According to the tests carbon nanotube filling of the matrix of the composites has a beneficial effect on their interlaminar properties: the interlaminar fracture toughness values of the composites have increased by a maximum of 13 and 33% at a 0.3 weight% carbon nanotube content of the matrix according to the conventional and AE based evaluation method respectively.
The modulus of filled and unfilled Ethylene-propylene diene rubber (EPDM) vulcanizates was used to predict the shape-factor of carbon black aggregation in the polymer. Four types of carbon black that vary in particle size and structure were used in this study. Quadratic curves relating the carbon black volume concentration and the modulus ratio of filled and unfilled rubber vulcanizates were used to adopt the shape factor of certain carbon black type. The shape factor of MT, HAF, SRF and Lampblack were 3, 3.75, 4 and 4.25 respectively. X-ray diffraction technique (XRD) was also used to evaluate the relative size of crystallite on the filler surface to that of the rubber and correlating it to the shape factor of carbon black aggregation in the polymer. Effect of the pH values and structure of carbon blacks used on the shape factor of filler aggregates were also studied. It was found that the shape factor is independent on the particle size while it is dependent on the pH value and structure of carbon black. Also the crystallites size of the filler is proportional to the shape factor.
Vinyl functionalized poly (ε-caprolactone) with molar mass ranging from 500–5000 Da were synthesized by ring opening polymerization and further photopolymerized. One-step synthesis and functionalization is achieved based on ring opening polymerization (ROP). Hydroxyl butyl vinyl ether (HBVE) was employed to play the role as the initiator of ROP, and photo-curable functional group. The presence of CH2=CH peak in Fourier Transform Infrared (FTIR) spectra confirmed that vinyl end groups were successfully attached to poly (ε-caprolactone) (PCL) macromolecule. Kinetic parameters of cationic photopolymerization of vinyl functionalized PCL were investigated. The activation energy was estimated at 11.33 kJ/mol, by assuming the cationic system followed second-order autocatalytic model.
In this paper, meso-2,3-dimercaptosuccinic acid-Ce(IV) redox couple is used for crosslinking polymerization of acrylamide (AAm) with N,N′-methylene bis(acrylamide) (MBAA) in acid aqueous medium. We have investigated the effects of crosslinker ratio, acid concentration and the molar ratio of AAm/Ce(IV) on the swelling behaviors of the synthesized P(AAm-MBAA) hydrogels. The experimental results show that the increase in the nAAm/nMBAA and nAAm/nCe(IV) result in an increase in the swelling ratio and rate of resulting hydrogels. However, the swelling equilibrium ratio and rate have been decreased with increasing of acid concentration. The k and n values in the equation of swelling rate have been determined. The n exponent decreases with increasing crosslinker, initiator and acid concentrations whereas k values increase. Kinetics and equilibrium swelling values have been discussed in terms of reaction parameters.
Nano crystalline powders of Barium Sodium Niobate (BNN) with the composition Ba3–2x Na4+x R Nb10 O30 with (R stands for rare earth = 0, x = 0) have been prepared by conventional ceramic technique. Barium Sodium Niobate can form a wide range of solid solutions, incorporating rare earth and alkali, alkaline earth elements with different compositions. The powder belonged to tungsten bronze type structure with tetragonal symmetry and lattice constants a = b = 1.2421 nm and c = 0.3903 nm. XRD (X-ray Diffraction) SEM (Scanning Electron Microscope) and AFM (Atomic Force Microscope) studies revealed that the particle size is in the nanometer range. Composites are prepared by mixing powders of BNN with polystyrene at different volume fractions of the BNN. Melt mixing technique is carried out in a Brabender Plasticoder at a rotor speed of 60 rpm (rotations per minute) for composite preparation. Mechanical properties such as stress-strain behavior, Young’s modulus, tensile strength, strain at break etc. are evaluated. Addition of filler enhances the mechanical properties of the polymer such as Young’s modulus and tensile strength. The composites showed the trend of perfect adhesion between the filler and the polymer. The filler particles are distributed relatively uniform fashion in all composites and the particles are almost spherical in shape with irregular boundaries. To explore more carefully the degree of interfacial adhesion between the two phases, the results are analyzed by using models featuring adhesion parameter. The experimental results are compared with theoretical predictions.
Polypropylene (PP) was blended with ethylene vinyl acetate copolymer (EVA) to form PP/EVA polymer blends. Wood powder (WP) was mixed into these blends at different weight fractions (50/50/0, 45/45/10, 40/40/20, 35/35/30 w/w PP/EVA/WP) to form PP/EVA/WP blend composites. The morphology, as well as thermal and mechanical properties, of these composites were investigated. The scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) results confirm the immiscibility of EVA and PP in the blends, and show that WP is primarily concentrated in the EVA phase. DSC results further show that the EVA crystallization behaviour is significantly influenced by the presence of WP. Dynamic mechanical analysis (DMA) results confirm immiscibility of PP and EVA, as well as an interaction between EVA and WP. Interaction between EVA and WP was further confirmed by Fourier-Transform infrared spectroscopy (FTIR). TGA results show that the blend composite degradation was also influenced by the presence of WP.