All issues / Volume 1 (2007) / Issue 7 (July)
This is a revised manuscript submitted to the the Editorial Corner.
Semi-IPNs with varying contents of poly(vinyl alcohol) (PVA), poly acrylamide (PAM) and crosslinker N,N’-methylene bis acrylamide (MBA) were prepared by redox polymerization method. The structural and morphological properties were studied by Fourier transform infrared (FTIR) spectroscopy, environmental scanning electron microscopy (ESEM) and X-ray diffraction (XRD) methods, respectively. It was found that the surface of the hydrogel is heterogeneous with separated domains. XRD result shows the semi-crystalline nature of the semi-IPNs. The prepared semi-IPNs of different compositions were subjected to gamma irradiation (2 to 250 kGy) and the radiation induced effects on their strength of the semi-IPNs were studied by measuring the surface microhardness using a Vickers microhardness tester. Significant changes were observed in the Vickers microhardness, which were correlated with molecular architecture of the prepared semi-IPNs.
Non-isothermal crystallization kinetics were characterized by using differential scanning calorimetry (DSC) analysis on neat semicrystalline syndiotactic polystyrene (sPS) and its nanocomposites with polystyrene (PS) functionalized full-length single walled carbon nanotubes (SWNT-PS), which was prepared by copper (I) catalyzed click coupling of alkyne-decorated SWNTs with well-defined, azide-terminated PS. The crystallization behavior of neat sPS polymer was compared to its SWNT based nanocomposites. The results suggested that the non-isothermal crystallization behavior of sPS/SWNT-PS nanocomposites depended significantly on the SWNT-PS content and cooling rate. The incorporation of SWNT-PS caused a change in the mechanism of nucleation and the crystal growth of sPS crystallites, this effect being more significant at lower SWNT-PS content. Combined Avrami and Ozawa analysis was found to be effective in describing the non-isothermal crystallization of the neat sPS and its nanocomposites. The activation energy of sPS determined from non-isothermal data decreased with the presence of small quantity of SWNT-PS in the nanocomposites and then increased with increasing SWNT-PS content.
Electrical conduction characteristics in two different polyimide films prepared by the imidization of polyamic acid (PAA) and pre-imidized polyimide (PI) solution were investigated. It is found that the current density of the polyimide film from PAA was higher than that of the polyimide film from PI at the same electric field, even though the conduction mechanism in both polyimide films follows the ionic hopping model. The hopping distance was calculated to be 2.8 nm for PAA type and 3.2 nm for PI type polyimide film. It is also found that the decay rate of the residual electrostatic charges on the polyimide films becomes faster in the PAA type than in the PI type polyimide film.
Polyamide 6/silica nanocomposites were synthesized by in situ ring-opening anionic polymerization of ε-caprolactam in the presence of sodium caprolactamate as a catalyst and caprolactam-functionalized silica as an initiator. The initiator precursor, isocyanate-functionalized silica, was prepared by directly reacting commercial silica with excess toluene 2,4-diisocyanate. This polymerization was found to occur in a highly efficient manner at relatively low reaction temperature (170°C) and short reaction times (6 h). FTIR spectroscopy was utilized to follow the introduction and consumption of isocyanate groups on the silica surface. Thermogravimetric analysis indicated that the polyamide 6 was successfully grown from the silica surface. Transmission electron microscopy was utilized to image polymer-functionalized silica, showing fine dispersion of silica particles and their size ranging from 20 to 40 nm.
Rapid synthesis of poly[(pyrrole-2,5-diyl)-co-(benzylidene)] was achieved under microwave irradiation via the condensation of pyrrole and benzaldehyde in 1,2-dichloroethane using acid exchanged montmorillonite clay called Maghnite–H+ (Mag–H+) as an efficient catalyst. The effect of the amount of catalyst and of time on the polymerization yield and on the viscosity of the polymers was studied. Compared with conventional static interfacial polymerization, the microwave-radiation polymerization reaction proceeded rapidly and was completed within 35 s. The conjugated polymer was characterized by means of 1H-NMR, X-ray diffraction, FT-IR spectroscopy and AFM. The X-ray data showed the presence of a backbone form of the [(pyrrole-2,5-diyl)-co-(benzylidene)] formed.
Two novel azobenzene-functionalized polythiophenes, poly[4-((4-(phenyl)azo)phenoxy)butyl-3-thienylacetate] (P4) and the copolymer of 3-hexylthiophene and 4-((4-(phenyl)azo)phenoxy)butyl-3-thienylacetate (COP64) have been synthesized. The structure dependence of photoluminescence features and thermochromic behaviors of both azobenzene-functionalized polymers was investigated. The results show that polymer structure has a strong influence on the conformation and optical properties of the resulting polythiophene derivatives. The photochemical control of photoluminescence property was achieved with homopolymer P4 using photoactive azobenzene side chains.
Based on a previous optimisation of set-up parameters for injection moulding of polyamide 6-6 (PA 6-6) reinforced with 40-wt% of 10 mm long glass fibre, the aim of this paper is to define suitable guidelines to further improve the mechanical performances of PA 6-6/glass long fibre thermoplastic (LFT) injection mouldings. Different solutions have been considered: screw and non-return valve design modification so as to adapt them to LFT processing, increase of the initial fibre content (up to 50 wt%) and length (up to 25 mm) in the LFT pellets. Using a LFT dedicated plasticating unit has allowed decreasing the fibre breakage amount by about 80% at the nozzle exit, however without improving the flexural properties. Increasing the initial fibre content has logically permitted to improve the flexural properties. Increasing the initial fibre length has not brought any improvement of the properties and has even amplified the structural heterogeneities and anisotropy of the parts. These trends have been explained on the basis of cavity pressure records highlighting significantly different rheological behaviours, and of resulting residual fibre lengths and through-the-thickness fibre orientation profiles modifications.
This paper deals with plastic-wood composites based on low density polyethylene (LDPE) and olive husk flour (OHF). The problem of incompatibility between the hydrophilic wood filler and the LDPE hydrophobic matrix was treated by two methods: a chemical modification of the olive husk flour with maleic anhydride to esterify the free hydroxyl groups of the wood components and the use of a compatibilizer agent, i.e. an ethylene-butyl acrylate-glycidyl methacrylate (EBAGMA) terpolymer. The changes in the structure, the morphology, and the properties resulting from these treatments were followed by various techniques, especially FTIR spectroscopy, scanning electron microscopy (SEM), tensile measurements and water absorption. The experimental results indicated that both methods, i.e. the chemical treatment of the olive husk flour with maleic anhydride and the inclusion of EBAGMA terpolymer, improved the interactions between the two composite components and promoted better dispersion of the filler in the matrix. Moreover, ultimate tensile properties were also increased. However, the use of EBAGMA terpolymer as compatibilizer produced better enhancement of the properties of LDPE/OHF composites compared to those treated with maleic anhydride.
In this current investigation psyllium has been functionalized with acrylamide in the presence of potassium persulphate (KPS)-hexamethylene tetramine (HMTA) as an initiator-crosslinker system. After the initial optimization of different reaction parameters the resultant hydrogel was used for the absorption of water from different water-oil emulsions as a function of time, temperature, pH and NaCl concentration. 4216% of water absorption with 4.279·10–2 mol·l-1 HMTA concentration has been observed.