All issues / Volume 4 (2010) / Issue 6 (June)
The magnetite (Fe3O4) nanoparticles (MNPs) coated with poly(N-vinyl pyrrolidone) (PVP) via covalent bonds were prepared as T2 contrast agent for magnetic resonance imaging (MRI). The surface of MNPs was first coated with 3-(trimethoxysilyl) propyl methacrylate (silan A) by a silanization reaction to introduce reactive vinyl groups onto the surface, then poly(N-vinyl pyrrolidone) was grafted onto the surface of modified-MNPs via surface-initiated radical polymerization. The obtained nanoparticles were characterized by FT-IR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), TEM (transmission electron microscopy), VSM (vibrating sample magnetometer), and TGA (thermogravimetric analysis). The MNPs had an average size of 14 nm and exhibited superparamagnetism and high saturation magnetization at room temperature. T2-weighted MRI images of PVP-grafted MNPs showed that the magnetic resonance signal is enhanced significantly with increasing nanoparticle concentration in water. The r1 and r2 values per millimole Fe, and r2/r1 value of the PVP-grafted MNPs were calculated to be 2.6 , 72.1, and 28.1(mmol/l)–1•s–1, respectively. These results indicate that the PVP-grafted MNPs have great potential for application in MRI as a T2 contrast agent.
Syndiotactic polystyrene (sPS) samples were quenched at low temperature (0°C) in the presence of Multi-Walled Carbon Nanotubes (MWCNT) at different concentrations. The influence of carbon nanotubes on the structure and physical properties of sPS composites was investigated by SEM, X-ray diffractograms, DSC (Differential Scanning Calorimetry), and Dynamic Mechanical Analysis (DMA). A good dispersion of the carbon nanotubes in the sPS matrix was found, at least for the low MWCNT concentration, whereas opposite effects were noticed on Tg and elastic modulus, depending on concentration. The pristine sPS sample was almost amorphous at 0°C, whereas in the filled samples the crystallinity increased on increasing the MWCNT concentration, indicating a strong nucleation effect of the nanotubes. Interestingly, in spite of the low temperature, the β crystallinity was induced and this crystalline form increases on increasing the carbon nanotube concentration, being dominant (68% of the total crystallinity) already at 3 wt% of MWCNT concentration.
A novel engineering plastic, poly(decamethylene 2,6-naphthalamide) (PA10N) was prepared via a reaction of 2,6-naphthalene dicarboxylic acid and 1,10-decanediamine. The structure of synthesized PA10N was characterized by elemental analysis, Fourier transform infrared (FT-IR) spectroscopy and proton nuclear magnetic resonance (1H-NMR). The thermal behavior was determined by differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Melting temperature (Tm), glass transition temperature (Tg) and decomposition temperature (Td) of PA10N are 320, 144 and 495°C, respectively. The solubility, water-absorbing capacity, and mechanical properties of PA10N have also been investigated. Pyrolysis products and thermal decomposition mechanism of PA10N were analyzed by flash pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The results show that the heat resistance and mechanical properties of PA10N are near to those of poly(nonamethylene terephthalamide) (PA9T), and PA10N is a promising heat-resistant and processable engineering plastic.
The usual sol-gel process was applied to precipitate silica or titania particles in a preformed poly(dimethylsiloxane) (PDMS) network under the presence of dibutyltin diacetate used as a catalyst. The resulting structures of the reinforcing fillers were studied by transmission electron microscopy and small-angle neutron scattering. Stress-strain measurements in elongation and equilibrium swelling experiments revealed distinct behaviors mainly attributed to the nature and the size of the generated particles and to the formation, in the case of titania, of a filler network even at low filler loadings.
Wood and natural fiber reinforced plastic composites are established for several fields like decking, transportation and automotive applications. In the last decade, extensive researches were conducted to improve the mechanical properties, such as incorporating additives like maleic anhydride grafted polypropylene (MAH-PP). The major challenge is to keep the properties in face of the environmental influence the parts are exposed to. Therefore it’s necessary to find the hardest impact factor concerning the mechanical properties. Water absorption (static and cyclic) of the composites was examined at two different temperatures (23, 50°C). A correlation between duration, kind of conditioning, temperature and modification was established. The results indicate that the coupling agent MAH-PP improved significantly the water resistance of the wood plastic composites under climatic conditions and higher temperature accelerated the rate of water absorption of the composites. The decrease of mechanical properties related to cyclic conditions is partially reversible and therefore the cyclic exposition shows less effects compared to static conditions.
The surface modification of the anatase titania nanoparticles prepared via a controlled nonhydrolytic sol-gel process is achieved by the formation of the bidentate coordination between titania and methacrylic acid (MAA) molecules. The in situ photocatalytic polymerization of methyl methacrylate (MMA) monomer is initiated by surface modified anatase titania nanoparticles under Xe lamp irradiation. A variety of techniques including differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and scanning electron microscopy (SEM) are employed to characterize the resulting materials. The glass transition temperatures and the thermal stabilities of polymethyl methacrylate (PMMA) composite materials prepared via photocatalytic polymerization are enhanced compared with pure polymer. The partial aggregation of titania nanoparticles in PMMA composite films is derived from the surface polymerization of MMA, which makes the inorganic particles hydrophobic and drives them to the water/oil interfaces.
The effect of fumed silica on the curing of a trimethylolpropane epoxy resin was investigated by thermal analysis methods like Differential Scanning Calorimetry (DSC), and Dynamic Mechanical Analysis (DMA). The fumed silica used here is a by-product of the silicon and ferrosilicon industry, consisting of micro and nanosized particles. Both the curing reaction and the properties of the obtained composites were affected by the filler content. Different trends were observed for filler contents above and below the 30 wt%. Up to 30 wt%, the behaviour can be explained as a predominantly agglomeration effect. For 30 wt% and higher filler contents, single particles seem to play a more important role.