All issues / Volume 2 (2008) / Issue 10 (October)
Polyaniline (PANI) was synthesized via oxidative coupling polymerization in acid conditions and de-doped in ammonia solution. The electrorheological (ER) properties of the PANI/silicone oil suspensions were investigated in the oscillatory mode shear, with particular focus on the high frequency region, where a crossover in G′(ω) and G″(ω) signals the onset of a dissipative relaxation process, presumed to be associated with motion of PANI particles within the fibrillar structures generated by the electric field. The relationship between the crossover frequency, ωc, and the electric field strength (E) was investigated as a function of matrix viscosity and shear strain. We find that ωc increases with increasing electric field strength, and decreases with increases of matrix viscosity and strain amplitude. These observations are in qualitative agreement with a theoretical model, which relates the relaxation mechanism to the competition between hydrodynamic and electrostatic forces between PANI particles within thick fibrillar structures. At the crossover point, a critical scaling relation is found relating two dimensionless parameters, the Mason number (Mn), and the Peclet number (Pe), viz. Mn~(Pe)0.09.
The effects of carbon blacks on vulcanization and mechanical properties of filled ethylene-propylene-diene rubber (EPDM) are investigated, by comparing with five types of rubber-grade carbon blacks. Curing kinetics is studied by rheometer and the results indicate that the curing characteristics are influenced by combination of surface area of carbon black and sulphur content on the filler surface, because the former one enhances the physical cross-linking and the latter one introduces the additional chemical cross-linking. Both the degree of cross-linking and cure rate increase with increasing surface area and sulphur content, whereas the optimum cure time and scorch time decrease. The reinforcing nature of the carbon black is assessed from mechanical measurements. It is suggested that the surface area of carbon blacks strongly affects the physical properties of EPDM/carbon black composites. Conductive carbon black (N472) can be used as desirable reinforcing filler due to the higher degree of cross-linking of EPDM with N472 than other EPDM/carbon black composites. The morphology and distribution of particles are studied by using scanning electron microscope. The sound reinforcing ability of N472 is also supported by scanning electron microscope due to the notable dispersibility of N472 within EPDM matrix. N472 ensures the EPDM/N472 composite the most conductive sample among the five composites.
The abrasive sliding friction and wear behaviours of silicon carbide (SiC) filled vinylester (VE) composites were investigated. The average grain size of the incorporated SiC particles was varied, holding the volume content of them in every case at 16 vol%. Mechanical properties (hardness, compression modulus, yield stress) of the filled and neat VE were determined. The tribological properties were investigated in block (composite) – on – ring (steel) test configuration. The steel counter bodies were covered with abrasive papers of different graining. Coefficient of friction (COF) and specific wear rate of the VE + SiC composites were determined. It was observed that the wear resistance increases with increasing average filler grain size and with decreasing abrasiveness of the counter surface. The COF of the VE + SiC composites is independent of the size of the incorporated particles, but it is strongly influenced by the abrasiveness of the counter body. The worn surfaces of the VE + SiC systems were analysed in scanning electron microscope (SEM) to deduce the typical wear mechanisms. The size effect of the SiC filler particles onto the abrasive wear characteristics was investigated by assuming that the roughness peaks of the abrasive paper and the indenter of the microhardness test cause similar micro scaled contact deformations in the composites. Therefore FE method was used to simulate the micro scaled deformation process in the VE + SiC systems during microindentation tests. The FE results provided valuable information on how to explain the size effect of the incorporated SiC filler.
Dielectric properties of polymer matrix – ceramic BaTiO3 composites were examined by means of Broadband Dielectric Spectroscopy (BDS) in the frequency range of 10–1–107 Hz and over the temperature range of 30–160°C, varying the content of ferroelectric particles. Experimental results provide evidence that the recorded relaxation phenomena include contributions from both the polymeric matrix and the presence of the reinforcing phase. Obtained results are analysed via the electric modulus formalism. Polymer matrix exhibits two distinct relaxation processes attributed, with ascending relaxation rate, to glass/rubber transition, and local motions of polar side groups. Interfacial polarization or Maxwell-Wagner-Sillars process is present in the low frequency range and at high temperatures. Finally, in the vicinity of the characteristic Curie temperature (TC) an abrupt variation of the real part of dielectric permittivity with temperature is recorded. This peak is probably related to the ferroelectric to paraelectric phase transition of the employed ceramic inclusions.
The acrylate monomer, 7-acryloyloxy-4-methyl coumarin (AMC) has been synthesized by reacting 7-hydroxy-4-methyl coumarin, with acryloyl chloride in the presence of NaOH at 0–5°C. Copolymers of 7-acryloyloxy-4-methyl coumarin (AMC) with vinyl acetate (VAc) were synthesized in DMF (dimethyl formamide) solution at 70±1°C using 2,2′-azobisisobutyronitrile (AIBN) as an initiator with different monomer-to-monomer ratios in the feed. The copolymers were characterized by Fourier transform infra red (FTIR) spectroscopy. The copolymer composition was evaluated by 1H-NMR (proton nuclear magnetic resonance) and was further used to determine reactivity ratios. The monomer reactivity ratios for AMC (M1)-VAc (M2) pair were determined by the application of conventional linearization methods such as Fineman-Ross (r1 = 0.6924; r2 = 0.6431), Kelen-Tüdõs (r1 = 0.6776; r2 = 0.6374) and extended Kelen-Tüdõs (r1 = 0.6657; r2 = 0.6256). Thermo gravimetric analysis showed that thermal decomposition of the copolymers occurred in single stage in the temperature range of 263–458°C. The molecular weights of the polymers were determined using gel permeation chromatography. The homo and copolymers were tested for their antimicrobial properties against selected microorganisms.
Multi-walled carbon nanotube filled polypropylene nanocomposites based on masterbatch route: Improvement of dispersion and mechanical properties through PP-g-MA addition
K. Prashantha, J. Soulestin, M. F. Lacrampe, M. Claes, G. Dupin, P. Krawczak
Vol. 2., No.10., Pages 735-745, 2008
Vol. 2., No.10., Pages 735-745, 2008
Multi-wall carbon nanotubes (MWNTs) filled polypropylene (PP) nanocomposites were prepared through diluting a PP/MWNT masterbatch in a PP matrix by melt compounding with a twin screw extruder. Polypropylene grafted maleic anhydride (PP-g-MA) was used to promote the carbon nanotubes dispersion. The effect of PP-g-MA addition on the rheological, mechanical and morphological properties of the nanocomposites was assessed for different MWNTs loadings. Scanning electron microscopy (SEM) has shown that nanotubes are distributed reasonably uniformly. A better dispersion and good adhesion between the nanotubes and the PP matrix is caused by wrapping of PP-g-MA on MWNTs. When PP-g-MA is added, dynamic moduli and viscosity further increases compared to PP/MWNT nanocomposites. The rheological percolation threshold drops significantly. Tensile and flexural moduli and Charpy impact resistance of the nanocomposites also increases by the addition of PP-g-MA. The present study confirms that PP-g-MA is efficient to promote the dispersion of MWNTs in PP matrix and serves as an adhesive to increase their interfacial strength, hence greatly improving the rheological percolation threshold and mechanical properties of PP/MWNT nanocomposites.
Binary and ternary composites composed of polyoxymethylene (POM), polyurethane (PU) and synthetic boehmite alumina (AlO(OH)) were produced by water-mediated melt compounding technique. PU latex and/or aqueous alumina suspension were injected into the molten POM in a twin-screw extruder to prepare toughened and/or reinforced polymer composites. The dispersion of the alumina and PU was studied by transmission- and scanning electron microcopy techniques (TEM and SEM, respectively), and discussed. The crystallization of the POM-based systems was inspected by polarized optical microscopy (PLM). The mechanical and thermomechanical properties of the composites were determined in dynamic-mechanical thermal analysis (DMTA), short-time creep tests (performed at various temperatures), uniaxial static tensile and notched Charpy impact tests. Incorporation of alumina increased the stiffness and resistance to creep and reduced the tensile strength, elongation at break and impact toughness. The change in the above parameters was opposite for the POM/PU binary blends. Additional incorporation of alumina in the POM/PU blend enhanced the resistance to creep, elongation at break and maintained the impact toughness compared to the POM/PU blend.