Iranian Polymer Journal
Year:2008 | Volume:17 | Issue:11|Papers Count:7

Nano hydroxyapatite (HA) is a potential artificial cartilage material. To study its friction and wear properties, nano hydroxyapatite (HA) particles filled with polyvinyl alcohol hydrogel (PVA-H) composites were slid against a stainless steel disk under water lubrication condition using an improved four-ball tester. The worn surfaces were investigated by using a scanning electron microscope (SEM) to determine the wear mechanisms of pure PVA-H and PVA-H/HA composites prepared by different methods. Experimental results show that the addition of HA slightly decreases the friction coefficient of composites with the increase of HA content under water lubrication condition. The wear resistance of the PVA-H matrix was also improved by the introduction of HA inorganic component. It was also found that the PVA-H/HA composites prepared by in situ synthesis have better tribological properties than the composites prepared by mixed method with the same components and test conditions. The SEM photos show that the wear mechanisms of PVA-H/HA composite prepared by the mixed method with high HA content showed abrasion and adhesion, while that of the composite prepared by in situ synthesis was slightly scratched and fatigued. These results may be useful in the tribological designs for artificial articular cartilage material.

The changes in microstructural parameters of edible polymer films of hydroxypropylmethylcellulose (HPMC) with plasticizers such as glycerol (GLY) and polyethylene glycol (PEG) have been studied using wide angle X-ray scattering (WAXS) data and line profile analysis (LPA). Exponential function for the column length distribution has been used for the determination of microstructural parameters. The crystal imperfection parameters such as crystal size <N>, lattice strain %(g) and orientational parameters have been computed and correlated with the amount of plasticizers. Comparison of orientational parameter with increase in plasticizers suggests that there is increase in the orientation in HPMC films. The flexibility of the films is expected to increase due to decrease in the number of weak inter- and intramolecular hydrogen bonds with the addition of plasticizers. From these investigations it is also observed that there is increase in unit cell volume with increase in the plasticizers in HPMC films indicating greater stability of the blends which are essential in packing industry.

One of the basic problems in the mixing of non-Newtonian fluids and especially diluted polymer solutions is the determination of the prevailing shear rates during the mixing process. The significant method of Metzner and Otto for calculation of the effective shear rate is limited to the laminar region and it is not valid in the transition region. In this article, the local shear rate and the Metzner-Otto method for helical ribbon impeller have been studied using laser Doppler anemometry (LDA) for viscoelastic liquids. It is also shown that the variation of the local shear rate against the impeller speed is better correlated by a power equation, i.e., g= k´s.Nb´ in the transition region, i.e., 70<Re<6700. In addition, a correlation between the improved coefficient, k´s, and the elasticity number of the viscoelastic liquid is given that can be helpful in designing the mixing of viscoelastic as well as inelastic non-Newtonian fluids by means of relating the rheological properties to the kinematical and dynamical parameters of the mixing process.

The antifungal activities of chitosan with different molecular weights and concentrations against Aspergillus niger were studied in vitro. The results showed that the antifungal activity of chitosan against Aspergillus niger is molecular weight and concentration dependent. The smaller the molecular weight, the stronger would be the antifungal activity. Chitosan with higher molecular weight and concentration has no antifungal but promotion activity towards Aspergillus niger. It is only the chitosan with proper molecular weight and concentration which possesses preferable antifungal activity towards Aspergillus niger. The effects of chitosan on Aspergillus niger and hyphal ultrastructure were examined to gain more information on its mode of action. The ultrastructure morphology investigated by transmission electron microscopy results indicated that chitosan acts on Aspergillus niger by inhibiting the growth of sporules. The fluorescein isothiocyanate labelled chitosan observation has elucidated the antifungal activity of chitosan to be caused mainly by inhibiting the DNA to RNA transcription. So the antifungal activity of chitosan towards Aspergillus niger was the combined effect of the above two observations. The study has provided sufficient scientific evidence for careful application of chitosan in food and medical industry.

The thermal degradation behavior and service lifetime of poly (p-phenylenbenzobisoxazole) (PBO) fibers, prepared by our group, were investigated. The thermal degradation processes of the PBO fibres were studied using TG-DTG at heating rates of 5.0, 10.0, 15.0, 20.0 K.min-1 under atmospheric air and at heating rate of 10.0 K.min-1 under nitrogen atmosphere, respectively. The thermal decomposition process of PBO fibre occurs in a single step in the air, being especially prominent between 900 K and 960 K. The thermal degradation kinetics of the PBO polymer under the non-isothermal condition, gave values for activation energy E and the pre-exponential factor A as 142.51±10 kJ.mol-1 and 2.43×107±105 min-1, respectively. Under nitrogen condition, the thermal degradation has started above 907 K. The thermal stability of PBO in the nitrogen atmosphere was 80 K higher than that in the air atmosphere. Moreover, the oxygen played an important role in the degradation, which initiated the degradation of PBO. The decomposition gases of the PBO were analyzed by TG- FTIR. It was found that CO, CO2 and H2O were the main compounds during the PBO degradation in the air. PBO fibre is transformed into charred material which is stable enough and has no aromatic species. The PBO fibre can be used for long time as the temperature is less than 300ºC in air. The service lifetime of the PBO fibres was estimated by the kinetics of thermal degradation, and the lifetime equation at weight-loss of 5% was deduced from the equation In t = -19.954 + 17141 / T.

Renewable resources in the field of fibre-reinforced polymeric materials with their new range of applications represent an important basis in order to fulfil the ecological objective of creating eco-friendly materials. Because of their low density, renewable origin, relatively high specific strength, light weight, unlimited availability, low price, resistance to corrosion and abrasion, ease of processing, good mechanical performance and problem-free disposal, natural fibres offer a real alternative to the technical reinforcing fibres presently available. Keeping in mind these immense advantages of natural fibres, in the present communication a study on the fabrication of Hibiscus Sabdariffa (HS) fibre reinforced urea-formaldehyde matrix based polymer composites has been reported. Urea-formaldehyde resin matrix was prepared by the technique developed in our laboratory. Urea-formaldehyde matrix was reinforced with Hibiscus Sabdariffa fibres to prepare natural fibre reinforced composites. These polymer composites were subsequently subjected to evaluation of their mechanical, morphological (SEM), and thermal (TGA/DTA/DTG) properties. Present work reveals that mechanical properties such as: tensile strength, compressive strength, flexural strength, and wear resistance, etc. of the composite increase with increase in fibre loading up to 30% loading and beyond this loading these properties decrease. In case of morphological (SEM) behaviour, morphological results clearly show that when polymer resin matrix is reinforced with the different loadings of fibre, morphological change takes place depending on loading of the fibre. In case of thermal behaviour, results indicate that the presence of cellulose fibres affects the thermal stability of polymer matrix. The IDT and FDT values for composite have been found in between those of matrix and the fibre which indicate that the composite is thermally slightly less stable as compared to resin matrix.

Asulphone-nitrogen containing heterocyclic ring, tetraphenylthiophene diamine (TPTDA) was prepared and used as curing agent together with triphenylphosphine (PPh3) to cure diglycidyl ether of a bisphenol A-based epoxy resin (DGEBA). Activation energies (Ea) for curing DGEBA/TPTDA and DGEBA/ TPTDA/PPh3 systems by using DSC data and Kissinger equation are 66.6 kJ/mol and 76.6 kJ/mol, respectively. The increase in Ea can be due to polymerization of DGEBA by PPh3 and formation of larger molecules with reduced mobility before curing with TPTDA to start. Ea of thermal degradation of cured DGEBA/TPTDA and DGEBA/TPTDA/PPh3 systems by using TGA data and Horowitz-Metzger equation are 56.0 kJ/mol and 128.0 kJ/mol, respectively. The onset decomposition temperature and the char yield have increased from 230oC to 320oC and from 21.4% to 32.5% for the above systems, respectively. The addition of PPh3 to the curing mixture enhanced char formation and improved thermal stability of the resin.