Iranian Journal of Polymer Science and Technology
Year:2007 | Volume:20 | Issue:4 (ISSUE NO. 90)|Papers Count:10

Polymer-graphite powder composite behaves as a low-conductive material which can be used as an automatic fuse for adhesive connector in electrical circuits. The conductivity of this composite, below its transition temperature, Tt, depends on concentration of carbon powder, slowly decreases as the temperature increases. Meanwhile, the electrical resistivity of this material in transition temperature region severely increases. The amount of Tt was found to be ~148oC for polyethylene-carbon independent of its concentration. In this work, the rate of change in electrical resistance of this composite in terms of temperature, carbon concentration and g-ray irradiation dose has been investigated. Also, the values of Tt and the peak resistance temperature, Tp of samples in each case were determined. The results show that both values of Tt and Tp decrease with increasing of irradiation dose. It has been found that the concentration of carbon powder has no significant effect on the transition temperatures of samples.

Phenolic resins are synthetic low molecular weight thermoset resins which are polymerized and cured to higher molecular weights by condensation method. These resins have high weathering resistance, high oxidative thermal properties and good chemical resistance. Phenolic resins can be cured thermally or by acid curing. The most common method of curing phenolic resin is by thermal curing that takes place in the range of 130-180oC. At room temperature, however, phenolic resins are cured by acid catalysts. In this paper, room temperature curing of resol phenolic resin by para toluene sulphonic acid has been investigated. The acid quantity has been determined for room temperature curing of two types of resols to achieve a reasonable hardness and gelation time. Temperature curing and thermal stability of respective resins have been investigated by DSC and TGA, respectively. A glass-phenolic composite plate has been prepared and cured by these two methods. The results show that the optimum amount of acid is 20% by weight. Optimum mechanical properties, chemical resistance and thermal properties have been achieved for acid cured system. The hot cured resin, however, has better properties.

In the traditional hole drilling method the in-plane stresses are studied in detail and the interlaminar stresses are not taken seriously. The interlaminar stresses on the free edge of composite materials are important and can cause matrix cracking and delamination. Inserting holes in composite laminates causes free edges and it can induce interlaminar shear and normal stresses. In this research, using a finite element method and the simulated hole drilling method for isotropic and orthotropic materials, the three dimensional state of stresses are studied. The number of steps for hole drilling, the uniform and non-uniform pre-stresses, and uniaxial and biaxial stresses are considered. The results show if the number of drilling steps changes from one to four, the ratio of the maximum three-dimensional stresses to the induced uniaxial stress is changed. The mechanical properties of each layer, number of layers, and the stacking sequence are important parameters for laminated composites. Therefore, unidirectional plies under uniaxial and biaxial state of stresses are considered. Then, the interlaminar stresses for the cross-ply, angle-ply and quasi-isotropic laminated are studied. The effects of interlaminar stresses on the residual stresses on the point of measurement of strains by strain gauges are studied in detail.

These days, most of the marine structures which are constructed and used in Persian Gulf, are made of ST37 steel. Due to oil and gas sources excavated, the number of these structures is constantly increasing. On the other hand, these types of structures are exposed to corrosive environments and it is seriously critical for these structures to be used for many years. Coal tar epoxy (trade name), one of the popular coating layers, is used in different parts of steel constructions which are in use in the Persian Gulf. Several works have been carried out on the functioning quality of this coating in tidal zones, under splashing water and atmospheric conditions, but up to now no report is made in submerge zone. Hence in this investigation, three coating systems have been considered that coal tar epoxy is being used in each of one of the three layers of primer, middle and top. Two systems of laboratory and in field have been investigated for 6 months and an isolated system in field type has been also investigated. All the mechanical and chemical tests which have been performed are according to NACERPO176-64 standard which is for investigating the function of all marine coatings. All corrosion tests have been performed in Refinary Laboratory of Petroleum Industry and all the fields samples have been investigated in Steel Harbor located in the south of Bandar Abbas every week during 6 months. The test results have indicated that the coal tar epoxy which were being used in the last layer is not suitable for submerge zone. By preparing, however, a suitable surface in the first layer using zinc ethyl silicate and the last layer with antifouling, the coal tar epoxy can function properly in the middle layer.

In this study, the possibility of producing wood-plastic panels was studied using two different blending methods including melt blend and dry blend. Wood-plastic panels were made from recycled high density polyethylene (as resin) and MDF waste (as natural fiber) at 60, 70 and 80% by weight filler loading. Nominal density and dimensions of the panels were 1g/cm3 and 35×35×1 cm, respectively. The mechanical properties of the panels including flexural elastic modulus, flexural strength, screw and nail withdrawal resistance, and impact strength were studied. Maximum values of flexural modulus of wood-plastic panels were found at 70% fiber content in both methods. Flexural strength, screw and nail withdrawal resistance and impact strength of wood-plastic composites reduced with the increase in fiber content from 60% to 80%. Mechanical properties of samples made with dry blend method were generally higher than those of samples made with melt blend method for all corresponding formulations.

Denim is a casual garment normally used by young people and extremely influential in shaping the fashion industry. Among various garments, these garments are subjected to innovations. This work is an attempt to compare the different methods of stone washing using pumice stones, acid cellulases and neutral cellulases or in combination of these methods. The effects of different processing conditions on the garment are compared and reported. Color differences of samples are probed by reflective colorimeter on the front side as well as the backside and also the white pocket of the garment. The abrasion resistance, tensile strength and crease recovery angle of samples are also reported. The XRD spectra are used to calculate the crystalline degrees of the selected samples. Moreover, fiber surfaces of some treated samples have been observed by SEM. The results indicate that treatment of denim with pumice stone with equal weight of garment causes a small color differences. The addition of cellulases to the washing, however, accelerates the color fading. Also, lower staining observed on the white pocket when the garment was treated with cellulases. However, the neutral cellulases increase the garment fading and decrease the staining on the white pocket. It is also observed that pumice stone with cellulases damages the fabric surface, although it is of a minimal damage.

In this article, hybrid organic-inorganic materials were prepared by free radical copolymerization of 2-hydroxyethyl methacrylate (HEMA) and 3-methacryloxy-propyltrimethoxysilane (MPTMS) via sol-gel process. The methoxysilane-containing copolymer precursors were synthesized at different compositions. These copolymer precursors were then hydrolyzed and condensed to produce PHEMA-SiO2 nanocomposites. The samples were characterized by FTIR spectra and TGA thermograms. Optical properties and hardness were measured by visible spectroscopy and Shore D, respectively. Morphological characteristics were investigated with SEM images and finally the formation and distribution of nano SiO2 particles were characterized by AFM images. FTIR spectra showed the formation of silica bonds (Si-O-Si) and TGA thermo grams showed high thermal resistance up to 340oC for hybrid samples. Also samples possessed very good transparency in visible wavelength range. Microscopical images showed the existence and suitable distribution of nano silica particles.

In this work, leather fibers were employed as a component of elastomeric compounds based on NBR, CR and EPDM and studied were made on their effects upon curing characteristics and mechanical properties of the prepared compounds. Evaluation of curing characteristics of the compounds demonstrated that leather fibers have no considerable effect on initial viscosity and curing time of the compounds. The study of mechanical properties of the vulcanized compounds showed that inclusion of leather fibers leads to increasing of tensile strength in NBR based compound due to compatibility between NBR and leather fibers. It is also found that increase in tensile strength in NBR compounds depends on the curing system of the compounds. The results of this work showed considerable increase in hardness for all of the prepared compounds. Abrasion resistance and resilience of the compounds were also measured and reported.

Hydrolysis of ethylene-vinyl acetate copolymer in alkaline conditions using two systems of NaOH/methanol and KOH/isopropanol has been studied and the formation of ethylene-vinyl alcohol copolymer was systematically examined using NMR spectroscopy and DSC measurements. Vinyl acetate weight percentage and the degree of hydrolysis were calculated from NMR spectroscopy and it is shown that hydrolysis by NaOH/methanol system has higher rate and reaches a maximum of nearly 100 percent compared with KOH/isopropanol system. DSC was used to follow melting temperature and DH of the hydrolysis products. The results have shown that the obtained copolymers have higher melting temperature and DH indicating that ethylene-vinyl acetate copolymer is converted to ethylene-vinyl alcohol. Moreover, DSC confirms the results of NMR in which higher degree of hydrolysis is reached using NaOH/methanol system. Based on the experimental results and system used, the hydrolysis is reached its maximum between 10 and 30 min in this study.