دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و یکم شماره 1 (پیاپی 93، فروردین واردیبهشت 1387)

In this study, rice husk and sodium silicate solution were used to produce particleboards. Sodium silicate was used as bonding aid by 25, 20, 15, 10, 5 and zero percent (based on rice husk dry weight). To modify the mechanism of bondability, one percent of 4,4’-diphenylmethane diisocyanate (MDI) was added for every five percent less sodium silicate solution. The effect of diisocyanate on bondability was evaluated by measuring the bending strength, internal bond, thickness swelling and water absorption. Data were statistically analyzed with SPSS software and comparison was made on the data obtained employing Dancan test. Generally the results have shown that increase in sodium silicate replacement with diisocyanate improves the mechanical and physical properties of particleboard. Economically, the best condition obtained in this study was to use 15% sodium silicate solution with 2% diisocyanate to produce rice husk particleboard.

Nowadays, polymer blends usages increase more and more in order to produce materials with better properties. According to many research works, the blends of polyolefins have shown industrial importance. The purpose of this project was to carry out some investigations on fibers melt spun from the polypropylene and low density polyethylene blends. PP and LDPE are immiscible. PP/LDPE blend filament yarns with the blend ratios of 100/0, 99/1, 97/3, 95/5, 93/7, 90/10 were produced by the melt spinning process. Microstructure (density, DSC, birefringence) and physical properties (tenacity, breaking elongation, initial modulus and shrinkage of samples) were measured and compared. The results showed that presence of LDPE in blend samples does not influence the density and crystallinity of PP. However, increasing the fraction of LDPE in blend samples also increases the shrinkage of drawn yarns. The tenacity of as-spun and drawn yarns displayed a downward trend by increasing the LDPE in blend. But the breaking elongation presented an upward trend. Tensile properties of textured yarns spun from PP/LDPE blends were higher than those of pure PP at all applied texturing temperatures (apart from 150C). Increasing the texturing temperature resulted in the increasing of crimp properties. However, the rate of increase is lower when the fraction of LDPE is higher.

Because of inhomogeneity and anisotropy of composite materials, defining a unique fatigue criterion to be suitable for different loading conditions is much more difficult in comparison with traditional materials. For this reason many tests on evaluating the damages such as crack density, stiffness reduction and residual strength are used by various researchers to monitor the fatigue process. In this research the residual strain energy density is defined as a suitable fatigue measure and used in a micromechanical static failure model to predict the fatigue life of unidirectional composites in different fiber load angles. In contrast to stress based fatigue models the new developed model employed both stiffness and strength reduction to predict the fatigue life with more accuracy. To measure the residual strain energy density stiffness and strength failure of models given by Shokrieh et al. are modified and used in this research. Available experimental data on unidirectional carbon/epoxy composites with the stress ratios of R=0 and 0.1 on stress states of 50, 60, 70 and 80 percent of static strength are used to evaluate the proposed model. The results predicted by the model underestimates the fatigue life in comparison with the experimental data.

The thin gelatin films, prepared by casting of gelatin solutions at different drying temperatures, had different molecular morphologies as monitored, using wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) techniques. It was revealed that gelatin films dried at lower temperatures showed markedly higher crystalline or helical structure with slightly higher Tg and lower ΔCp than those for the hot dried film with more coiled structure. These films exhibited different interactions with water, which were assessed, using dynamic vapour sorption experiments. The sorption capacity of these films increased with increasing the degree of molecular order. There was no difference between the diffusion coefficients obtained upon sorption and desorption steps for each gelatin samples. The diffusion coefficient did not show any significant dependence on water content.

Polyethylene imide was synthesized from the reaction of high density polyethylene grafted maleic anhydride (PE-g-MA) and 1,4-diaminobutane in boiling xylene. The chemical compositions of the reaction products were examined by Fourier transform infrared spectroscopy. Different conditions and parameters like the effect of temperature, time, monomer concentration and oxygen on the extent of reaction and gel content were studied and the best conditions of the reaction were determined. Thermal analysis using differential scanning calorimetry and thermogravimetry analysis was carried out to determine thermal stabilities and properties of the reaction products. Rheometry experiments were also performed to determine the rheological properties. The results show that PE-g-MA and PE-g-imide have better properties.

The growing interest in using natural fibers as reinforcing agents of polymer-based composites is mainly due to their advantages such as lower cost, lower density, ease of preparation, lower energy requirements for processing, biodegradability, wide availability and relative non-abrasiveness over traditional reinforcing fibers such as glass and carbon. In this study, wood-plastic composite (WPC) containing 40 wt % of wood was prepared using an intermeshing co-rotating twin screw extruder. The effect of wood particle size in three levels (100, 250, and 400 μm) was studied on the physicalmechanical properties of WPC such as: tensile properties, heat distortion temperature (HDT), melt flow index (MFI) and notched Izod impact resistance. In addition, the rheological behaviors were studied as function of wood particle size. The data showed an increase in the modulus and a decrease in the tensile strength with increase of wood particle size while there was no considerable change in the elongation-at-break. The results also showed that MFI decreased and impact resistance increased with decreases of wood particle size. HDT was independent from variation of wood particle size. Complex viscosity and storage modulus increased with decrease of wood particle size while Tan δ did not change with variation of particle size.

The influence of flour content and immersion time in water on the creep behavior of composites made from high density polyethylene (HDPE) waste and MDF (medium density fiberboard) flour was investigated. Mixing was carried out by a twin screw extruder and the sample was manufactured by flat hot press. Firstly, the modulus of elasticity and bending strength of various MDF flour-polyethylene composites (WPCs) were measured before performing the creep test. It was shown that the modulus of WPCs increases with an increase in MDF flour content from 60 to 70% and then decreases as the flour content reaches 80%. It is found that the bending strengths of WPCs significantly and linearly decrease with the increase in flour content from 60 to 80%. The results showed that, the creep strain decreases as the lignocellulosic flour level increases. Water absorption has negative effect on creep behavior of MDF flour/HDPE composites. For all filler contents, it can be seen that the creep strain increases when the immersion time increases.

The objective of this research work is to evaluate the surface roughness of polyacrylonitrile (PAN) nanowebs. For this purpose the nanowebs have been prepared in different concentrations of PAN solution from 11 to 15% (by wt). Surface roughness of nanowebs was evaluated by entropy algorithm (ENT) as well as atomic force microscopy (AFM) and then the results of two methods have been compared. To evaluate surface roughness using AFM, four roughness parameters such as maximum height, ten point height, arithmetic mean of roughness (AMR), and root mean square were measured and AMR parameter was used as surface roughness. Based on the results obtained, the increase in concentration of PAN solution from 11 to 15% (by wt) would increase nanofiber diameter from 195 to 524 nm. The results obtained from two methods show that increasing the fiber diameters of nanowebs lead to the enhancement of surface roughness of samples. The correlation coefficient of surface roughness obtained from these two methods and nanofibers diameter is more than 0.90. Statistical analysis shows that there is a good agreement of surface roughness between the two methods.

The molecular weight distribution of 4 commercial isotactic polypropylene (iPP) samples was estimated using rheological data. The dynamic moduli data, obtained from rheological measurements in linear viscoelastic region was used for calculation of relaxation time spectrum, h(τ) and then shear relaxation modulus, G(t). Finally, applying Thimm Kernel function and relaxation modulus data in generalized mixing rule, the molecular weight distribution was calculated and compared to the experimental results obtained by gel permeation chromatography (GPC). The results showed that normalized relaxation time spectrum is a good measure for qualitative comparison of molecular weight distributions of various samples. Furthermore, using Thimm Kernel function, it is possible to calculate the molecular weight averages of iPP samples with good accuracy. However, good agreement between the molecular weight distributions determined by GPC and by rheological data evaluation can be achieved only by changing the β mixing parameter value from 3.84 to about 1 and subtraction of Rouse part of relaxation time spectrum.

Polyhydroxyalkanoates (PHAS) is known to be temporarily stored by microorganisms in activated sludge, especially in the anaerobic-aerobic processes. The main objective of this study was to investigate the effects of fatty acids (VFAs) compounds coexistence in substrate of SBR on PHAs productivity of activated sludge. It has been found that addition of different concentrations of VFAs results in an increase of PHAs content of activated sludge in the range of 90-130% as compared to the one acclimatized with only sucrose as a carbon source. In this study the optimum concentration of acetate and propionate as the sole carbon sources in the PHAs production reactor was also found to be 30-35 and 15-20 mgC/L.h.gSS, respectively. Finally, the work was conducted in order to try and control PHAs composition by applying carbon sources with different acetate to propionate ratios. It has been observed that inclusion of propionate in the carbon sources lowered PHAs productivity. The produced PHAs is composed mainly of 3-hydroxy-butyrate and 3-hydroxy-valerate, and when the propionate in the substrate was increased from 0 to 100% the mass ratio of 3HV produced is increased from 6 to 85%.