Iranian Polymer Journal
Year:2009 | Volume:18 | Issue:1 (103)|Papers Count:7

Conductive polymers are good candidates for preparation of conducting graft copolymers. Therefore, polyaniline was chemically grafted onto chitosan by using ammonium peroxydisulphate initiator, in the presence of 1 M HCl to obtain a product known as Chitaline (chit-g-PANi). Electrochemical polymerization was carried out by coating chitosan on the surface of Pt disk working electrode. Then, PANi grew onto chitosan in acidic solution and a graft copolymer was produced. The grafted copolymer was identified by FTIR, UV-visible, and 1H and 13C NMR spectroscopy techniques. Spectroscopic studies show the grafting and demonstrate that the electronic states are similar to those of the emeraldine and protonically doped emeraldine forms of polyaniline. The thermal properties of chit-g-PANi were studied by thermogravimetri  (TGA) and differential scanning calorimetry (DSC). Morphology properties of chit-g-PANi have been studied by SEM images which confirm grafting polymerization. The effects of concentration of APS, ANi, reaction time and temperature on graft copolymerization were studied by determining the grafting percentage, grafting efficiency and percentage add-on. Electrical conductivity of copolymer has been studied by four-point probe method of having produced 4.6×10-2 S/cm conductivity.

Textile cardiovascular prostheses are tubular structures made of polyester filaments. Woven prostheses are naturally tight but knitted ones are porous and can involve blood haemorrhage. Although compaction is necessary to reduce water permeability of knitted prostheses used for arterial replacement, it can induce degradation of mechanical properties of poly (ethylene terephthalate) (PET) yarns. We have studied the effect of chemical and thermal compaction process parameters on the physical and mechanical properties of PET yarns used for vascular prostheses manufacturing in order to find compaction systems that do not provoke important changes in the material characteristics. After chemical and thermal compactions, all yarn samples displayed longitudinal shrinkage accompanied by lateral swelling and a loss of mechanical properties. The analysis of chemical compaction results showed that fibre shrinkage and swelling are linked to the sizes of solvents' molecules and immersion duration. Compaction performances in thermal process are widely linked to treatment temperature. The effect of the two compaction treatments on a PET single jersey fabric permeability was studied as well.

The oxidative polycondensation reaction conditions of 4-[(2-methoxyphenylimino) methyl] phenol (2-MPIMP) were studied by using oxidants such as air and NaOCl in an aqueous alkaline medium between 50oC and 90oC. The structures of synthesized monomer and oligomer were confirmed by FTIR, UV-vis, 1H NMR, 13C NMR and elemental analysis. The characterization was afforded by TGA-DTA, size exclusion chromatography (SEC) and solubility tests. At optimum reaction conditions, the yield of oligo-4-[(2-methoxyphenylimino) methyl] phenol (O-2-MPIMP) was found to be 38.72% and 72.21% by air and NaOCl oxidants, respectively. According to the SEC analysis, the number average molecular weight (Mn), weight average molecular weight (Mw) and polydispersity index (PDI) values of O-2-MPIMP were respectively found to be 1400, 2350 g.mol-1, and 1.679 using air and 1650, 2350 g.mol-1, and 1.424 using NaOCl. TGA-DTA analyses of O-2-MPIMP were shown to be a stable compound against thermal decomposition. The weight losses of 2-MPIMP and O-2-MPIMP were found to be 57.09% and 59.11% at 1000oC, respectively. Also, electrical conductivity of the O-2-MPIMP was measured, showing that the oligomer was a semiconductor. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of monomer and oligomer were determined from the onset potentials for n-doping and p-doping, respectively. Optical band gaps (Eg) of 2-MPIMP and O-2- MPIMP were calculated from UV-vis measurements

The mechanical, thermal, morphological, dynamical mechanical and electrical properties of polymeric insulators are tested and reported. Low density polyethylene (LDPE), ethylene-propylene-diene monomer (EPDM) and blends of LDPE/EPDM are known polymers for use as low, medium and high voltage insulators. Several formulations containing EPDM and LDPE were prepared. EPDM was blended with LDPE in different weight ratios of LDPE/EPDM (100/0, 80/20, 60/40, 50/50, 40/60, 20/80, 0/100). The change in Haake-viscosity mixing torque with time for different blend compositions was obtained. The torque at any time is dependent on the blend composition. For EPDM the observed torque is directly influenced by its cross-linking density. However, for LDPE or blends of high percentage of LDPE the influence of cross-linking density on torque is relatively low. The mechanical properties of cross-linked EPDM are weaker than LDPE. Therefore changing the cross-link density of EPDM will not affect the blend properties significantly especially at high LDPE content. A drop shape analysis system G l0 (Kruss-USA) was used for hydrophobicity studies. Studies illustrate that in LDPE/EPDM blends, tensile strength of the blends are higher than either polymer component alone. But the synergism effect in LDPE/EPDM compound is stronger than HDPE/EPDM. Also the blends of LDPE/EPDM show good breakdown voltage strength and heat resistance comparing to LDPE. The result of mechanical measurement shows that mechanical properties such as tensile strength, modulus and elongation-at-break of blends can be enhanced with increase in LDPE in the formulation. Also tests were conducted to study various properties (mechanical, surface, electrical) under accelerated ageing condition. Because the life time of these compounds are generally too long to wait for a verdict on their behaviour in use. The ageing results show that mechanical properties follow the same trend as pre-ageing stage.

Based on our previous results of a good agreement between Monte Carlo simulation and DSC measurement for amide interchange reactions (AIRs) during PA6/PA66 melt blending processes, an improved Monte Carlo model comprising AIRs, polycondensation, and hydrolysis was established to illustrate the kinetic scheme of randomization for PA6/PA66 blending systems. Validity of the improved Monte Carlo model which transformed the macro-scale rate constant into a micro-scale rate constant in the simulation was testified by experiments. The effect of blending temperature on AIRs and the influence of AIRs on degree of transamidation, randomness, regularity, and number average block length of various sequences were analyzed in detail with the improved Monte Carlo model describing a kinetic process through a pseudorandom number. One-order exponential decay (Exp-decay 1) technique was employed to correlate melting points of copolyamides measured by differential scanning calorimeter (DSC) with degree of regularity simulated theoretically with the improved Monte Carlo model. First, the model established direct relationship between the mathematical simulation and the experiments then; it was applied to other polyamide blending systems after minor alteration of reaction parameter. It was found that degree of randomness and regularity are independent of blend molar ratio while melting point, molar fractions of amido linkages and number-average block length are blend molar ratio dependent.

Hydrogels are a unique class of macromolecular networks that can hold a large fraction of an aqueous solvent within their structures. They are particularly suitable for biomedical applications, including controlled drug delivery, because of their ability to simulate biological tissues. Many hydrogel-based networks have been designed and fabricated to meet the needs of pharmaceutical and medical fields. The objective of this paper is to give a brief review on the fundamentals and recent advances in the design of hydrogel-based drug delivery systems (DDS) as well as the description of the release mechanism of bioactive molecules from these hydrogels. The structure and classification of hydrogels, swelling behaviour of hydrogels, different mechanisms of solvent diffusion into and drug release from hydrogels and mathematical description of these phenomena are elucidated. The most important properties of hydrogels relevant to their biomedical applications are also identified, especially for use of hydrogels as drug delivery systems. Kinetics of drug release from hydrogels and the relevant mathematical modelling are also reviewed in this manuscript.

Poly (vinyl alcohol) (PVA) ultrafine fibres were prepared by gas-jet/electrospinning of its aqueous solutions. The morphology of the gas-jet/electrospun PVA fibres was investigated by controlling parameters such as: polymer solution concentration, gas flow rate and the polymer solution feeding rate. The morphology of the PVA fibres changed when the solution concentration was increased from 7 wt% to 12 wt%. With concentration of 7 wt%, a combination of smooth and some beads ultrafine PVA fibres was observed. With higher concentration, smooth fibres were obtained and the beads disappeared. The average diameters of PVA fibres increased gradually from 165±4 nm to 263±8 nm with the concentration from 7 wt% to 12 wt%. In addition, the average diameters of these ultrafine fibres were decreased from 317±10 nm to 219±5 nm after an initial increase in the gas flow rate from 2.5L/min to 7.5L/min and then increased to 287±9 nm as the gas flow rate increased to 10.0 L/min. The morphological structure changed with the variety of the solution feeding rates. At the solution feeding rate of 3.3mL/h, PVA fibres with beads were observed. The average diameters of PVA fibres increased with increasing solution feeding rate. Particularly, the production rate of the gas-jet/electrospinning of PVA solution could be up to 2.2 mL/h, which was 11 times higher than the conventional electrospinning (0.2 mL/h), while the difference between the average diameter of electrospun fibres and the gas-jet/electrospun fibres was slight.