مجله ایرانی پلیمر
سال:1388 | دوره: | شماره: |تعداد مقالات:7

The graft copolymerization of styrene (St) onto poly(vinyl alcohol) (PVA) is studied by using a novel redox system of potassium diperiodatocuprate-PVA (Cu(III)-PVA) in alkaline medium. Cu(III)-PVA redox pair is an efficient initiator for this graft copolymerization which is proved by high graft efficiency (>97%) and high percentage of graft (>300%). Reaction conditions (monomer-to-PVA weight ratio, initiator concentration, pH, time and temperature) affect the graft parameters which have been investigated systematically. The optimum reaction conditions are found as St/PVA = 5.4, [Cu(III)] = 1×10-2 M, pH = 12.7, temperature = 50oC, time = 3.5 h. Further, the equation of the overall polymerization rate can be written as follows: Rp = k C1.9 (St) C1.7 (Cu(III)). The overall activation energy was calculated to be 42.0 kJ/mol based on the experimental data of the relations between Rp and C(St), Rp and C(Cu(III)), and Rp and temperature. A mechanism is proposed to explain the formation of radicals and the initiation. The structure of the graft copolymers is confirmed by Fourier transfer infrared spectroscopy (FTIR). Some peaks were compared with PVA at 3080.34-3001.79 cm-1 (=C-H stretching in the phenyl ring), 1600.34-1450.95 cm-1 (C=C stretching in the phenyl ring), 755.17 cm-1 and 698.64 cm-1 (=C-H out-off-plane bending in phenyl ring) which are considered to belong to the characteristic absorption bands of phenyl group of polystyrene. Therefore it proves that the graft copolymer is composed of PVA and PSt. TGA thermograms of PVA and PVA-g-PSt are investigated as well. As it is shown the initial decomposition temperature of PVA-g-PSt (377.3oC) is much higher than that of PVA (241.8oC), which indicates that the thermal stability of the PVA is obviously enhanced by grafting with PSt. X-Ray diffraction elucidates the incorporation of PSt with PVA which reduces the crystal degree of PVA.

This paper reports on the accuracy of the integral methods used for the kinetic analysis of degradation of synthesized optically active polyamides. For this purpose, thermogravimetric analysis is a technique, widely used in polymer science because of its simplicity. On analyzing data by integral methods, it is necessary to calculate the temperature integral, which does not have an analytical solution.Instead of performing the numerical integration, most of the researchers prefer to avoid the problem by using approximate expressions, not always adequate and several hundreds of citations to the original papers can be found in recent polymer science publications. The most important application of these equations is the determination of the kinetic parameters, in particular activation energies, and not the computation of the Arrhenius integral. A methodical analysis of the errors involved in the determination of the activation energy from these integral methods is invisibly missing. A comparative study on the precision of the activation energy as a function of u and T computed from different integral methods has been carried out. Furthermore, for a series of optically active polyamides, the interpretation of kinetic parameters (E, DS, DG and DH) of thermal decomposition stages has been evaluated and reported.

Aseries of rubber-like composite membranes were prepared for separation of gases such as propylene and nitrogen. The support layer was fabricated from different concentrations of polyethersulphone (20, 22 and 24% PES) and the coating layer was prepared from different concentrations of polydimethylsiloxane (3, 5, 7 and 9% PDMS). Permeances and selectivities of the prepared membranes for propylene and nitrogen gases and their mixtures were measured under transmembrane pressure of 1-10 bar. The influence of various parameters, such as PES concentration in support layer and PDMS concentration in coating layer at different pressures, on membrane performance were evaluated. It was shown that the membrane selectivity was increased with an increment in the feed pressure. At constant pressure for similar supports the propylene permeance and membrane selectivity were enhanced by increasing PDMS of the coating layer. For membranes with equivalent PDMS content in the coating layer, the performance of membrane was increased with PES decline in support layer. The permeability ratio of propylene over nitrogen in gas mixture (real selectivity) was low compared to the permeability ratio for pure gases passing through the membrane (ideal selectivity) at comparable operating pressure for similar membranes. At 5 bar pressure real selectivity of 3.6 was obtained while the ideal selectivity was 20.2.

Many biomaterials have been proposed as artificial articular cartilage in partial or total joint replacement. Poly(vinyl alcohol) (PVA) hydrogel is a kind of artificial cartilage and it exhibits excellent mechanical and biocompatibility properties. In this study, the friction tests under reciprocating motion were conducted to determine the tribological properties of PVA hydrogel in response to ceramic femoral component. The friction coefficient testing of PVA hydrogel against ceramic femoral component was performed by a three-factor, two-level designed experiment. The three factors studied were load, lubrication and sliding speed. Longer term friction tests were conducted under constant load and cyclic load to evaluate friction variations in 30 min. The friction coefficient between PVA hydrogel and ceramic femoral component was found to depend significantly on load, lubrication and sliding speed. The friction coefficient increased as load and sliding speed increased. The friction coefficient decreased when the lubricant was changed from Ringer's solution (RS) to hyaluronic acid (HA). In longer term tests, the friction coefficient in constant load tests was significantly lower than in cyclic load tests. The wear of PVA hydrogel under constant load was identified by environmental scanning electron microscopy (ESEM). It is indicated that the biphasic lubrication property is the key feature for PVA hydrogel. These results may be useful in the tribological design of artificial cartilage in joint replacement.

Polyvinylidene fluoride (PVDF)-perfluorosulphonic acid (PFSA) hollow fibre ultrafiltration (UF) blend membranes were prepared by wet-spinning method.Polyvinylpyrrolidone (PVP) and ethanol aqueous solutions were employed as additive and coagulants, respectively. The effect of PVP concentration in the dopes and ethanol concentration in the coagulants on morphology and performance of PVDFPFSA hollow fibre UF blend membranes were investigated. Blend membranes were characterized in terms of precipitation kinetics, morphology, thermal property and separation performance. The results showed that the increments of PVP concentration in the dopes and ethanol concentration in coagulants both resulted in higher pure water permeation flux (PWP) and worse rejection (R) of bovine serum albumin (with the increment of PVP concentration from 0 to 5 wt% in the dopes, PWP increased from 41.7 L.m-2.h-1 to 134 L.m-2.h-1 and R decreased from 99.8% to 84.4% as well as with the increase in ethanol concentration in coagulants from 0 to 40 wt%, PWP increased from 33.5 L.m-2.h-1 to 123 L.m-2.h-1 and R decreased from 97.7% to 88.7%). However, the proportion of sponge-like structure in the cross-section of membranes decreased with the increasing PVP concentration in the dopes and the proportion increased with the increased ethanol concentration in the coagulations. In addition, the location of the sponge-like structure in the cross-section of membranes was significantly influenced by ethanol concentrations in the coagulants and DSC results revealed that the crystallinity (Xc) of the blend membrane was in accordance with the proportion of sponge-like structure. These behaviours were attributed to the different roles of PVP in the dopes and ethanol in the coagulants, respectively. PVDF-PFSA hollow fibre membranes with different morphologies and performances were prepared by these two different routes. Meanwhile, the range of PVDF-PFSA hollow fibre blend membranes was extended.

At the present time coating industry is devoting much research in the direction of low volatile organic compounds to make eco-friendly coating material. In this study, such materials are developed from cellulose derived from bagasse, a sugar industry waste. Cellulose is converted to cellulose glycoglycoside by acid hydrolysis of cellulose under heterogeneous condition. Cellulose glycoglycoside is treated with polyethylene glycol having different molecular weights to give glycoglycosides which in turn are reacted with various diisocyanates to obtain polyurethane having free NCO groups. These materials are then reacted with hydroxyethylmethacrylate (HEMA) to give polyurethane acrylates. The acrylates are characterized for specific gravity, viscosity, colour and molecular weight as well as by FTIR spectroscopy. The UV-curable coating composition was prepared by blending PU-acrylate, reactive diluents and photoinitiator. Coating compositions were cured under UV-light and characterized for adhesion, flexibility, impact resistance, solvent resistance and for dynamic mechanical analysis as well as by TGA for thermal stability. The cured films give thickness of 23-24 microns and cure time required is less than 1.5-2.0 min. There is no liberation of any volatiles during curing and films have good adhesion to mild steel substrate. The cured coatings give excellent dynamic, mechanical and chemical properties. The scratch resistance was found to be satisfactory. The application was made in unpigmented form but it is found that various pigments can be used to give coloured UV-curable coatings.

Phenol formaldehyde (PF) resin was successfully produced from empty fruit bunch (EFB) fibres via liquefaction approach using sulphuric acid as catalyst.The produced PF resin was used to blend with EFB fibres as filler to produce PF-EFB composite boards. The effect of different percentages of EFB fibres on the density, water absorption, impact strength, flexural strength, hardness and thermal properties of the produced PF-EFB composite boards was investigated. The density of the PF-EFB composite boards increased with the increase in EFB fibre content due to the higher density of the EFB fibres relative to the PF resin. The water absorption of the PF-EFB composite boards was also found to be increased with the increase in EFB fibre content. This could be attributed to the hygroscopic nature of the EFB fibres, which had promoted the water absorption process. The mechanical properties (flexural, impact and hardness) of the produced PF-EFB composite boards were increased linearly and reached maximum value with the addition of 20% of EFB fibres. The electron micrographs suggested good compatibility between the PF matrix and the EFB fibres, which had enhanced the mechanical properties of the PF-EFB composite boards. Our results had suggested that the EFB fibres not only could be used to produce PF resin using liquefaction method, but also could be used as reinforcing fillers to enhance the physical and mechanical properties of the composite boards.