Iranian polymer journal
Volume:12 Issue: 5, 2003

In this work Flory-Huggins theory has been extended to satisfy the hard sphere limit. The resulting equations are used to correlate the solvent activity and to calculate the polymer size parameter. Based on the extended model new equations have been derived to predict the enthalpy and entropy of dilution of various polymer solutions with diverse molecular weights in different solvents. The results obtained from the extended Flory-Huggins theory are compared with those of the original theory and with the experimental data. The comparisons indicate that the proposed extension improves the predictability of the theory for thermodynamic properties of polymer solutions.

Compounding studies of a fluoroelastomer grade (Viton GF) has been carried out. The effect of peroxide cross-linking system is compared with hexamethylene- N,N’-bis(tert-butyl peroxycarbamate) (HBTBP). HBTBP in fluoroelastomer produced a comparative cure response as the conventional peroxide system. Whereas, coagents are necessary to bring about cure in peroxide systems, it was found that HBTBP does not need co-agents to cure this fluoroelastomer grade. Also, only calcium oxide and magnesium oxide are compatible with HBTBP cure.

The effects of recycle rubber powder (RRP) content and conventional (CV), semiefficient (semi-EV) and efficient vulcanization (EV) systems on curing characteristics and mechanical properties of natural rubber (NR)/recycle rubber powder (RRP) blends were examined. The minimum torque, maximum torque and torque difference are increased with increasing recycle rubber powder (RRP) content in NR/RRP blends, whereas, the scorch time and cure time show the opposite trend. NR/RRP Blends cured with the CV system showed the highest minimum torque, maximum torque and torque difference but longest cure time, t90. Increasing RRP content in NR/RRP blends increases the tensile modulus and hardness but decreases the tensile strength, tear strength, resilience and elongation-at-break. Although the CV system exhibits the highest tensile modulus and hardness but NR/RRP blends cured with EV system show the highest tensile strength, tear strength, resilience and elongation-at-break followed by semi-EV and CV systems.

The interlaminar fracture behaviour of unidirectional carbon/epoxy composites has been studied under flexural loading by using end-notched flexure (ENF) specimens. GIIc values were calculated as total fracture toughness energy at the maximum load sustained by the materials as the delamination extended. The results showed that high temperature moulding systems (XHTM45) have the highest GIIc values well above 1000 J/ m2. For medium temperature systems (MTM), GIIc has also increased significantly after post cure. For compression strength after impact (CSAI), the behaviour to a certain extent is related to that found for GIIc tests. Comparison of the GIIc values with CSAI also indicated a relationship between two test results. SEM Micrographs revealed their excellent delamination resistance as good crack stoppers with the evidence of strong fibre/matrix interface. Dynamic mechanical analysis (DMA) indicated the increased Tg and modulus retention of the LTM and MTM prepregs after post-curing at elevated temperatures. The failure mechanisms seem to be different for different tough matrix materials and appear to be strongly dependent on the cure and post-curing conditions. This is particularly noticeable for curing at 135°C and 80°C of medium and low temperature moulding systems.

Enzymatic synthesis has been used to prepare a water-soluble and conducting poly (2-ethylaniline) in the presence of sulphonated polystyrene (SPS). The polymerizationof 2-ethylaniline was performed with horseradish peroxidase (HRP) as a catalyst to form conducting poly(2-ethylaniline)/SPS complex with moderate electrical conductivity. The polymerization is simple and can be carried out at room temperature in pH 4.0 phosphate buffered solution. This electrochemically active polymer shows strong pH dependence of absorption and other characteristics. The formation of conducting and electroactive form of poly(2-ethylaniline)/SPS complex was confirmed through UV-vis, FTIR and NMR spectroscopy. Cyclic voltammetry studies show only one set of redox peaks over the potential range of -0.2 to 1.0 V.

In a monolithic controlled drug release system, the effect of drug and additives on release behaviour and mechanical properties of silicone elastomer were investigated. For this purpose the silicone matrixes containing different concentrations of progesterone, calcium carbonate and silicone oil as additives were prepared by mixing in thermo-mixer Haake and cured in specific conditions. Then the released drug was evaluated by a new analytical method and the mechanical properties were studied according to ASTM D 2240. The results indicate that the release profile that has been found by experimental data is in good agreement with Higuchi''s model. When silicone oil and progesterone concentration were increased in polymer matrix, the drug release was increased but the hardness was decreased. The drug release was decreased by addition of calcium carbonate but this additive had no effect on hardness.

Mucoadhesive formulations have been of great interest in recent years. One approach to study mucoadhesion is the technique of dynamic oscillatory rheology (DOR). In this study the use of an extended frequency sweep DOR, instead of the routine limited DOR studies, as a more comprehensive and realistic means of investigating the process of mucoadhesion was investigated. For this purpose polymeric discs were directly placed in contact with natural mucus samples and incubated for various time intervals (15, 60 and 120 min) at 37°C, and then they were rheologically examined across a frequency of 0.0001-10 Hz. Results showed that in the presence of anionic mucoadhesive discs containing Carbopol 934P (C934) and sodium carboxymethyl cellulose (NaCMC), the G'' (storage modulus) and to a smaller extent G" (loss modulus) values of the weakly viscoelastic mucus samples are strengthened much more than the non-ionic polymer hydroxypropyl cellulose and the calcium containing Carbopol EX83, and far less reduced at frequencies below 1Hz. However, in the presence of potassium thiocyanate (hydrogen-bond breaking agent), unlike G" values, the G'' values of particularly the anionic polymers C934 and NaCMC suffered a sharp decline at frequencies below 1Hz. These findings support the theory of mucoadhesive polymer chain interpenetration and formation of hydrogen-bonds with the mucus gel network, and shows that by using an extended frequency sweep rather than a normal limited frequency sweep, a more detailed and realistic approach for studying the process of mucoadhesion and putative mucoadhesive polymers and formulations, could be provided.

Polypropylene filament yarns, when compared with polyethyleneterephthalate and polyamide yarns have lower stretchability after being false twist textured. To overcome this deficiency, other researchers have tried to lower the degree of crystallinity of this fibre by either tension annealing or blending it with polyethyleneterephthalate and polystyrene. These physical or chemical modifications have not yet achieved a satisfactory level of enhancement of the textureability of polypropylene. Considering the importance of BCF polypropylene yarns, in this research, the effect of blending polypropylene with12.5 and 25 % of polyamide 6 on the bulk of the final bulked continuous filament (BCF) yarn has been investigated. The results show that although both crimp contraction and crimp modulus increase with the temperature and pressure of hot air during texturing, but blending polypropylene with even 25% of polyamide 6 does not enhance the textureability of BCF yarns. Also, the reduction in the crystallinity of the yarns does not lead to any improvement in the textureability of the polypropylene BCF yarns.