All issues / Volume 4 (2010) / Issue 3 (March)
This is intended for the Editorial Corner
To overcome the disadvantages generated by the loose nano-partilce agglomerates dispersed in polymer composites, a chemical grafting method was applied to modify nano-Si3N4 by covalently bonding glycidyl methacrylate (GMA) onto the particles. The tribological behavior of the epoxy composite filled with nano-Si3N4 or GMA treated Si3N4 (Si3N4-g-PGMA) was studied using a ring-on-block wear tester under dry sliding, and the worn surface of the filled epoxy composite and the surface roughness of the composites after the sliding wear test were investigated by SEM (scanning electron microscopy) and AFM (atomic force microscopy), respectively. In comparison to the composites filled with untreated nano-Si3N4 particles, the composites with the grafted Sinano-3N4 exhibit improved sliding wear resistance and reduced friction coefficient owing to the chemical bonding at the filler/matrix interface.
The non-isothermal crystallization kinetics of ethylene-vinyl acetate copolymer (EVA, 14 wt% vinyl acetate content), low density polyethylene (LDPE) and their binary blends with different blending ratio were investigated via differential scanning calorimetry. Jeziorny theory and Mo’s method were utilized in evaluating the crystallization behavior of both neat materials successfully. In the primary crystallization stage both EVA and LDPE had three-dimensional spherulitic growth mechanism. Apparently the crystallization rate of LDPE was faster than that of EVA at a low cooling rate. Increase in cooling rate limited the spherulites’ growth, which narrowed their rate difference. Influences from blending on the crystallization kinetics of each component in EVA/LDPE mixture were evaluated by Kissinger’s activation energy (ΔE) and Khanna’s crystallization rate coefficient (CRC). Inter-molecular interaction in the melt increased the ΔE of both EVA and LDPE components at the beginning of cooling. During the primary crystallization stage of LDPE, dilution effect from EVA facilitated the crystal growth in LDPE. Co-crystallization between EVA component and the secondary crystallization stage of LDPE component also increased the CRC of EVA. In blend of EVA/LDPE = 7/3, LDPE obtained the maximal CRC value of 174.2 h–1. Results obtained from various approaches accorded well with each other, which insured the rationality of conclusion.
Influence of processing on the ethylene-vinyl alcohol (EVOH) properties: Application of the successive self-nucleation and annealing (SSA) technique
E. Franco-Urquiza, O. O. Santana, J. Gamez-Perez, A. B. Martinez, M. Ll. Maspoch
Vol. 4., No.3., Pages 153-160, 2010
Vol. 4., No.3., Pages 153-160, 2010
Films of EVOH copolymers, processed three times by twin-screw extrusion were prepared using a cast-film line. The variation on the melt flow rate (MFR) and rheological behaviour of the films were determined, as well as the thermal properties assessed by differential scanning calorimetry (DSC) and dynamic-mechanical thermal analysis (DMTA). As the results showed that the reprocessing induced an increase in the viscosity and orientation of the films, it was suggested that structural modifications from chain-extension or cross-linking reactions promoted by hydroxyl and residual acetoxyl groups, could be occurring. The successive self-nucleation and annealing (SSA) technique was applied, evidencing the structural modifications on the EVOH copolymer.
An investigation was made of grafting trans-ethylene-1,2-dicarboxylic acid (TEDA) onto metallocene-linear low-density polyethylene (mLLDPE) and low-density polyethylene (LDPE) in the course of reactive extrusion. The initiator was 1,3-bis-(tert-butyl-peroxyisopropyl)benzene. The graft efficiency of TEDA has been shown to increase with increasing initiator concentration, irrespective of polyethylene type. The graft values for LDPE were higher than for mLLDPE over the initiator concentration range (0.05 to 0.4 wt%). The rheological properties of mLLDPE were found to undergo more tangible changes during functionalization than those of LDPE. These changes were caused by side reactions, mainly macromolecular crosslinking. It has been established that some carboxyl groups get transformed to anhydride groups in the grafted product. The concentration of end double bonds reduces, but intramolecular unsaturation in both polyethylenes increases. Data are presented on thermal and stress-strain (mechanical) properties of virgin and functionalized polymers, as well as rheological and viscoelastic properties of their melts.
Natural fibres such as jute, coir, sisal, bamboo and pineapple are known to have high specific strength and can be effectively used in composites in various applications. The use of hemp fibres to reinforce the polymer aroused great interest and expectations amongst scientists and materials engineers. In this paper, composites with isotactic polypropylene (iPP) matrix and hemp fibres were studied. These materials were manufactured via the patented FIBROLINE process based on the principle of the dry impregnation of a fibre assembly with a thermoplastic powder (iPP), using an alternating electric field. The aim of this paper is to show the influence of fibre/matrix interfaces on dielectric properties coupled with mechanical behaviours. Fibres or more probably the fibre/matrix interfaces allow the diffusion of electric charges and delocalise the polarisation energy. In this way, damages are limited during mechanical loading and the mechanical properties of the composites increase. The structure of composite samples was investigated by X-ray and FTIR analysis. The mechanical properties were analysed by quasistatic and dynamic tests. The dielectric investigations were carried out using the SEMME (Scanning Electron Microscope Mirror Effect) method coupled with the measurement of the induced current (ICM).
Organo-modified ferroferric oxide superparamagnetic nanoparticles, synthesized by the coprecipitation of superparamagnetic nanoparticles in presence of oleic acid (OA), were incorporated in polystyrene (PS) by the facile in situ bulk radical polymerization by using 2,2-azobisisobutyronitrile (AIBN) as initiator. The transmission electron microscopy (TEM) analysis of the resultant uniform ferroferric oxide/polystyrene superparamagnetic nanocomposite (Fe3O4/PS) showed that the superparamagnetic nanoparticles had been dispersed homogeneously in the polymer matrix due to the surface grafted polystyrene, confirmed by Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric analysis (TGA). The superparamagnetic property of the Fe3O4/PS nanocomposite was testified by the vibrating sample magnetometer (VSM) analysis. The strategy developed is expected to be applied for the large-scale industrial manufacturing of the superparamagnetic polymer nanocomposite.
A novel polymer Al2(SO4)3-poly(acrylamide-co-2-acrylamido-2-methyl-1-propanesulfonate) (Al2(SO4)3-P(AM/AMPS)) had been synthesized by dispersion polymerization in an aqueous solution of ammonium sulfate and aluminum sulfate, using poly(2-acrylamido-2-methyl-1-propanesulfonate) P(AMPS) as stabilizer, acrylamide (AM) and 2-acrylamido-2-methyl-1-propanesulfonate (AMPS) as monomers, poly(2-acrylamido-2-methyl-1-propanesulfonate) (PAMPS) as stabilizer and [2-(2-imidazdino-2-yl)propane]dihydrochloride (VA-044) as initiator. The average particle size of polymer dispersion ranged from 0.2 to 0.3 µm, the molecular weight was from 4.3•106 to 5.7•106 g•mol-1. The polymer was characterized by infrared (IR) spectroscopy, thermogravimetry (TGA) and transmission electron microscopy (TEM). The swelling property of the dispersion polymer was studied by particle size distribution. When the polymer dispersion was diluted with deionized water, particle sizes decreased several times. When the polymer dispersion was diluted with salt water, the particle size increased with increasing concentration of salt. The effects of Al2(SO4)3 and stabilizer on the particle size and the relative molecular weight of the polymer were investigated, respectively. The optimum conditions for the stable Al2(SO4)3-P(AM/AMPS) dispersion were that the concentration of Al2(SO4)3 was 1.12 wt%, the concentration of PAMPS stabilizer was 3 wt% and the concentration of initiator was 0.2 mol•l-1 and the monomers concentration was 14 wt%.