Iranian Journal of Polymer Science and Technology
Year:2007 | Volume:19 | Issue:5 (ISSUE NO. 85)|Papers Count:9

The effect of reaction conditions on mechanical properties, before and after modification treatment, is investigated. The results show that increasing chemical reagent concentration, reaction time and temperature can increase the chemical groups in fibers, however the mechanical properties decrease and modified fibers lose their performance. While with selection of optimum concentration, temperature and time length of reaction, fibers with suitable adsorbent properties and good mechanical properties under pH range of 2-12 can be obtained. The experimental results show that by using cross-linking treatment at optimized condition, the modified fibers experience lower decrease in mechanical properties compared to noncross-linked modified fibers.

The chlorination and its effect as a surface treatment method on friction coefficient and physical properties of rubbery wiper blades are investigated. The results show that chlorination of the surface of rubbery wiper blades reduces the friction coefficient. The effect of chlorination time length on controlling the thickness of treated layer and friction coefficient in desired ranges is also studied.

The quality of the pipes produced by extrusion, and the quality of extrudate depends heavily on the detailed design of the die. The production of the pipes using extruder equipped with plain die is not sufficiently correct, because of axial orientation of polymeric chains and the existence of weld line (s) due to spiders. The pipes produced in this manner have no significant strength in the hoop direction. One of the methods to produce weldless pipes with reasonable hoop strength is by rotating die system. In this system, the inner or outer members or both rotate. The simple shape of rotating die is assumed as an annulus with rotating capability for each inner or outer members. The fluid flows through the nip of annulus under the pressure gradient across the pipe, i.e. DP/L, also is influenced (affected) with shear (drag) flow. In this work, to describe the non Newtonian behaviour of fluid, a power Law model was used. Non-Newtonian fluid flow and fiber orientation in the pile-like die were investigated using the finite element method. The results were compared with experimental data for short fiber orientation. This comparison clearly shows the validity of the resultant velocity vector as a controlling factor for fiber orientation.

Macroporous styrene-divinylbenzene (S-DVB) with cross-link density of 40% was synthesized by suspension polymerization technique in the presence of toluene-n-heptane and toluene-cyclohexane as diluents. The effect of diluents composition was studied by scanning electron microscopy (SEM) and BET. The porosity of beads was increased with increasing of poor solvent portion. Also, the porosity was increased as the cross-linking agent percentage was. Raised to 40% from 16%.

Blend fibers of silk fibroin and polyamide 6 were prepared by the wet spinning method. The effects of blend ratio were studied on the tensile strength and elongation-at-break of cast films and wet spun fibers. It was found that the tensile strength and elongation-at-break of the wet spun fibers decreased with the increase of fibroin weight ratio in the blends. However, fibers with good mechanical properties can be prepared up to 30% fibroin in the blend. SEM observation showed a nearly circular cross sectional shape for the prepared fibers. FTIR of the fibers with different blend ratios were recorded and discussed.

In this work biodegradable polymers have been formulated for packaging purposes and with a view to reduce the environmental accumulation of plastic waste. Degradation of the polymers under the specific weathering conditions of Tehran was studied. In this work low-density polyethylene (LDPE) was formulated with two wheat starch concentrations, maleic anhydride, glycerol as well as a pro-oxidant system of oleic acid, benzoyl peroxide and ferric stearate. The formulated master batches were mixed by using a laboratory two-roll mill at 190°C.The prepared master batches were mixed with the commercial LDPE to prepare compounds 1 and 2 containing 1.2 and 6.4 percents wheat starch. The LDPE control films as well as the formulated compounds were compression moulded in a hot press at 130oC.The films were subjected to three general conditions of atmospheric exposure, buried in soil and combined conditions of soil burial! atmospheric exposure. The three environmental conditions impact upon the formulated and control films were investigated through tensile strength, elongation-at-break, carbonyl index, water absorption, weight loss as well as SEM analysis. The microbial investigation was followed by growing the Penicillium Asymmetrica, which had the main population in microbial flora of the soil, on formulated and control films. The studies revealed that the incorporation of this pro-oxidant system with the addition of 6.4% wheat starch enhance the degradation rate of commercial LDPE films to a significant degree.

Light cured dental composite resins are extensively used in dentistry. The purpose of this study was to investigate the effect of different wavelengths, power densities and irradiation time of an argon laser on the physical and mechanical properties of a Bis-GMA dental resin based monomer. The resin was prepared by mixing Bis-GMA and TEGDMA with a mass ratio of 75/25. A tuneable argon laser was used to cure the samples at 488 nm and 514 nm wavelengths separately. Degree of conversion (DC%) of samples was measured using FTIR spectroscopy. The water sorption and solubility were also measured. The temperature rise during polymerization reaction was measured using a K-type thermocouple. The flexural strength, flexural modulus and microhardness of samples were also measured and compared. The results revealed that the resin cured at 488 nm with 1075 mW/cm2 showed higher degree of conversion (52.2±4.8), flexural strength (51.19±2.10 MPa), flexural modules (1112.75±48.28 MPa), microhardness (l9.59±1.61 kg/mm2), and lower water sorption (23.7 mg/mm3) and solubility (2.20 mg/mm3) in comparison the resin cured at 514 nm with 700 mW/cm2 exhibited lower degree of conversion (26.6±2.3), flexural strength (8.42±0.97 MPa), flexural modulus (107.76±10.63 MPa), microhardness (1.20±0.15 kglmm2), and higher water sorption (56.3 mg/mm3) and solubility (16.4 mg/mm3).The specimens cured at 488 nm and 1075 mW/cm2 showed the highest temperature rise due to reaction(13.5oC), which was in agreement with the results of DC%. On the other hand curing the resin at 514 nm and 700 mW/cm2 resulted in lowest temperature rise due to reaction (3.5oC).No significant difference between water sorption, solubility and flexural strength of specimens was observed when cured with 488 nm at different power densities. The results showed that using 488 nm wavelength at relatively high power densities of an argon laser can be useful in clinical applications with regard to achieving acceptable chemical and physical improvement.

By using radio frequency glow discharge, polystyrene samples were treated with argon and oxygen plasmas at different time lengths and constant power. The changes were characterized by atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared (ATR-FTIR), scanning electron microscopy (SEM) and contact angle measurements. AFM and SEM observations demonstrated that after plasma treatments, roughness of polystyrene surface was increased. Contact angle measurement indicated higher wettability of the treated polystyrene with both argon and oxygen plasmas compared to the untreated polystyrene. The data from ATR-FTIR spectra showed the induction process of oxygen based functional group in both polystyrene samples treated with Ar and O2 plasmas. The formation of these functional groups and increasing in roughness led to increased surface wettability.