Iranian polymer journal
Volume:16 Issue: 6, 2007

Monofilaments precursor of linear ultra-high molecular weight polyethylene (UHMWPE) were produced by gel spinning at controlled conditions. The rheological behaviour of UHMWPE solution (gel) was studied in paraffin oil at 175ºC with deformation rates in the range 600-11000 s-1 which was in good agreement with power law model. The effect of paraffin concentration of the extraction bath was determined on the amount of paraffin remained in the precursor fibre and on the extraction time. The desorption behaviour of paraffin/UHMWPE system is in accordance with Flory-Huggins model. The precursor fibre structure and its morphology before drawing process is a determining parameter in drawability and properties of the produced fibre. Thus, the effects of processing conditions such as spinning speed, spinneret geometry, and temperature of the region between the die and the quench bath were investigated on the crystallinity of the precursor fibre. High deformation rates () caused by decreasing the die diameter or increasing the spinning speed result in more macromolecular orientation and increased degree of crystallinity. Significant recrystallization or crystal perfection took place during the solvent extraction step which increased the melting point of the precursor fibre from118.5ºC to 147ºC.

The thermal protection of space crafts during hypersonic re-entry into the Earth’s atmosphere by ablative composite and nanocomposite has been the subject of intensive investigation in recent years. An evaluation has been made on the advantages of relative performances of various ablation materials which is based on the thermal degradation mechanism and thermal stability of these materials. The objective of this work is to investigate the effect of kaolinite nanocrystal on the thermal degradation of resol-type phenolic/asbestos nanocomposite during pyrolysis using thermogravimetric analysis and to compare the results with that of the phenolic/asbestos composite. Thermal degradation and char forming mechanisms could be obtained from parametric adjustments of the process model to the thermogravimetric experimental data. The results of this work are the kinetic parameters of thermal degradation, i.e., the activation energy, frequency factors, and degree of thermal degradation which are employed to clarify the degradation mechanism.

Polyaniline (PANI) doped with dodecyl benzene sulphonic acid (DBSA) was directly synthesized by aniline polymerization in the presence of DBSA in an aqueous medium. The temperature and colour changes of the polymerization reaction were carefully recorded and found that the polymerization of aniline begins after 80 min with changing reaction colour from white to pale blue. Fourier transform infrared (FTIR), elemental analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques were used to characterize and analyze the thermal characteristics of the doped PANI sample. In the FTIR spectrum, the peak related to NH+…SO3 - interactions between the polymer chain and the dopant appeared at 1026 cm-1. The obtained TGA curve has illustrated three major stages in the weight loss of the doped PANI. These three weight loss stages were accounted to the evaporation of moisture, evaporation of DBSA, and the chemical structure degradation of PANI. The moisture, DBSA, and PANI contents ofthe product were calculated from TGA curve and it was shown that approximately 6.65aniline repeating units have been doped with one DBSA molecule. The DSC thermogramhas shown two endothermic peaks around 120ºC and 280ºC due to the evaporationsof moisture and DBSA, respectively. The analysis of XRD spectra confirmedthat a chemical cross-linking reaction occurs between the PANI chains during thermaltreatment and increases the amorphous state of the sample. The resultant electricalconductivity examination at the heating temperature of 100ºC has shown that at theheating time of 30 min the doped PANI possessed maximum electrical conductivitywhich decreased by increase in heating time.

The kinetics of capillary rise follows the Lucas-Washburn equation. Capillary flow is studied in core-spun yarns by image analysis of coloured liquid rising into the core-spun yarn and the distance of liquid rise was determined as a function of time. The great variations of the experimental results in the cross and along the yarns are attributed to the yarn heterogeneity of the interfibre space. Yarn construction features, such as twist, linear density, and pretension of core component of core-spun yarns are shown to be related to the rate of liquid transport in such fibre assemblies. The liquid transport properties of yarns in general provide useful information about fibre orientation in yarns. The results show that the continuity of capillaries formed by the fibres decreases either by random arrangement of fibres due to low pretension of core component or by increasing yarn twist. Also, decrease in the size of capillaries was governed by three parameters, namely; increased pretension of core component, decreased linear density of core component, and increased yarn twist. The presentstudy indicates that an appropriate choice in production parameters of core-spun yarns is all important in obtaining the desired properties of capillary rise.

The mechanical properties of plain woven fabrics have been investigated under tensile fatigue. It is proposed that the mechanism of their fatigue consists of two stages: yarn slippage in the fabric and yarn elongation. The yarn slippage in the fabric occurs at the initial stage of fatigue. This mechanism which arises from interyarn friction in the fabric structure causes sharp variations in the fabric viscoelastic properties. Finally the region of the steady variations of the fabric viscoelastic properties seems to be due to yarn elongation. In this study plain woven fabrics were produced with different weft density and their viscoelastic properties have been analyzed by the dynamic mechanical analyzing technique at two different strains and frequencies. It is found that by increasing weft density, the fabric storage modulus and loss modulus increase for all testing conditions, while damping factor decreases at 0.5% strain and 1 Hz frequency. No particular trend was observed in the variations of fabric percentage elongation versus weave density. It has been demonstrated that fabrics at low strain have shown better recovery from extension and greater stability against repeated tensile fatigue, but an increase in lifetime when frequency was increased.

Anovel randomly-arranged experimental design method (random-design) was employed to optimize the technology of emulsion polymerization with high solid content. In the case of the emulsion copolymerization of styrene, butyl acrylate (BA), and acrylic acid, six principal factors were chosen for random-design process. Then, regression analysis was used for the random-design experimental results by a known statistical analysis system (SAS). In turn, the optimal regression equations were established between the principal factors and the emulsion properties. It is shown that the particle size and size distribution are greatly affected by the following factors: the square values of the solid and emulsifier contents and the interactions between the initiator concentration and functional monomer concentration, BA concentration and reaction temperature, emulsifier content and reaction temperature, solid content and reaction temperature, and BA and functional monomers.

Athermo-sensitive hydrogel designed for controlled drug delivery was prepared and its properties were studied. The hydrogel was made of konjac glucomannan (KGM), copolymerized with N-isopropylacrylamide (NIPAAm) and crosslinked by N,N-methylene-bis-(acrylamide) (BIS). Several key parameters influencing the equilibrium swelling ratios of the hydrogels were studied. The swelling ratio was mainly controlled by the content of BIS, and influenced by the ratio of NIPAAm/KGM, slightly. It was possible to control the degree of swelling of the gels by changing crosslinking density of the polymer. The gels swelling ratio has possessed sensitive response to the environmental temperature. In vitro release of model drug bovine serum albumin (BSA) was studied at 20ºC and 37ºC in phosphate buffer solution (PBS) of pH 7.4. The accumulative release percentages are nearly 80% and 30% after 5 h at 20ºC and 37ºC, respectively.