دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و پنجم شماره 3 (پیاپی 119، امرداد و شهریور 1391)

The changes in the behaviour of mechanical properties of low density polyethylene-thermoplastic corn starch (LDPE-TPCS) nanocomposites were studied by an adaptive neuro-fuzzy interference system. LDPE-TPCS composites containing different quantities of nanoclay (Cloisite®15A، 0. 5-3wt%) were prepared by extrusion process. In practice، it is difficult to carry out several experiments to identify the relationship between the extrusion process parameters and mechanical properties of the nanocomposites. In this paper، an adaptive neuro-fuzzy inference system (ANFIS) was used for non-linear mapping between the processing parameters and the mechanical properties of LDPE-TPCS nanocomposites. ANFIS model due to possessing inference ability of fuzzy systems and also the learning feature of neural networks، could be used as a multiple inputs-multiple outputs to predict mechanical properties (such as ultimate tensile strength، elongation-at-break، Young’s modulus and relative impact strength) of the nanocomposites. The proposed ANFIS model utilizes temperature، torque and Cloisite®15A contents as input parameters to predict the desired mechanical properties. The results obtained in this work indicated that ANFIS is an effective and intelligent method for prediction of the mechanical properties of the LDPE-TPCS nanocomposites with a good accuracy. The statistical quality of the ANFIS model was significant due to its acceptable mean square error criterion and good correlation coefficient (values > 0. 8) between the experimental and simulated outputs.

Ablative materials play a strategic role in aerospace industry. These materialsproduce a thermal protection system which protects the structure، theaerodynamic surfaces and the payload of vehicles and probes duringhypersonic flight through a planetary atmosphere. In this work، we investigatedthe effect of refractory zirconium oxide on mechanical، heat stability and ablationproperties of asbestos/phenolic/zirconia composites. The asbestos/phenolic/zirconiacomposites were produced with different percentages of zirconia filler from 7 to 21%with average size of 7 μm and different number of layers of asbestos، say 3 to 6layers. These ablative composites were made by an autoclave curing cycle process. The densities of the composites were in the range of 1. 68 to 1. 88 g/cm3. Ablation properties of composites were determined by oxy-acetylene torch environment and burn-through time، erosion rates and back surface temperature in the first required 20 seconds. Thermal stability of the produced materials was estimated by means of thermal gravimetric analysis، in both air and nitrogen which consisted of dynamic scans at a heating rate of 10°C/min from 30 to 1000°C with bulk samples of about 20±1 mg. The results showed that when the amount of zirconia was raised from 7% to 21%، the erosion rate and the back surface temperature of composites increased by about 24% and 26% respectively، and the heat capacity of the composites increased byabout 85%. Also، the result showed that when the thickness of composites of 4. 2 mm was increased to 10. 1mm the burn-through time raised by about 226% and erosion rate dropped by about 41%. These composites displayed the maximum flexural strength when the amount of zirconia was about 14%.

Phase change materials (PCM) are substances with a high heat of fusion which، through melting and solidifying at certain temperatures، are capable to store or release a large amount of energy. This phenomenon can be utilized in designing heat protective materials as well as in thermal energy storage systems. One of the approaches to avoid materials leaching from a structure، where PCMs are incorporated، is to blend them with suitable polymers. To have a proper blend it is necessary to choose a compatible polymer with a PCM. It is important to assess the optimized concentration of PCM in polymer matrix and the phase structure and morphology of the blend، which causes the best heat protection. In this work، the influence of polyethylene glycol (PEG) as PCMs in epoxy resin matrix on heat protection was investigated. A special performance test was designed to study timetemperature behavior of the prepared samples and DSC and SEM tests to observe the melting point، heat of fusion and morphology of the samples. The results indicated that increases in PCM content led to better heat protection and the best concentration for PEG was found to be 60% wt. Time-temperature curves show that increases of temperature for PCM samples is very slow compared with net epoxy sample. PCM samples curves show plateau in melting region. In this region، they show nearly 15°C temperature lower than a net epoxy sample. The plateau region makes a delay time in temperature increment، which is about 22 min for PEG samples compared with a net epoxy.

This research is carried out to study some properties of polyethylene terephthalate (PET) as one of the most important synthetic polymers used in textile industry. PET based nanocomposites containing three differently modified silica particles were prepared by melt compounding. The influence of type and amount of nanosilica on various properties of nanocomposite was studied by Fourier transform infrared spectroscopy، scanning electron microscopy، contact angle determination، optical microscopy، differential scanning calorimetry، thermal gravimetry analyzer and dynamic mechanical thermal analyzer. ATR results indicated that the interactions of hydrophilic nanosilica mainly occur at the surface of nanocomposites. SEM was used to confirm the presence of silica on the surface of nanocomposites and it showed that surface properties depend on hydrophilicity of nanosilica. Studies on surface tension of nanocomposites showed that modified nanosilica particles have higher tendency to remain in bulk polymer as compared with unmodified one. Optical microscopy images from nanocomposites-containing silica illustrated the increment of the number of spherulites in the PET matrix with increases in silica percentage which were dependent on nano-silica type and content. Differential scanning calorimetry results of the nanocomposites showed a slight drop in the melting temperature compared to pure PET. The results obtained from thermal stability test showed that any improvement in thermal stability depends on the type of silica and dispersion of particles in polyethylene terephthalate. Moreover، the extent of interactions between nanosilica particles and polyethylene terephthatale chains affects on thermal stability of the composite.

Silica nanoparticles were modified with titanium tetraisopropoxide (TTIP) via a two-step sol-gel route. The modified silica nanoparticles were characterized using FTIR spectroscopy، thermal gravimetric analysis (TGA) and EDAX elemental analysis. Photocatalytic activity of the modified nanocomposites was evaluated by photo-activated degradation of Rhodamine B (Rh. B) dyestuff، as a colorant model، in distilled water. Reduction in Rh. B concentration in aqueous solution was evaluated by UV-visible spectroscopy and with the aid of visual observations. The FTIR spectroscopy results confirmed the formation of Ti-O-Si chemical bond on the surface of silica nanoparticles. TGA test results showed that the weight loss of the modified sample is due to deterioration of the alkoxy groups of the SiO2 surface. According to the results of EDAX elemental analysis، the presence of carbon and titanium in the structure of the modified samples and also reduction in oxygen levels are attributed to the chemical interactions due to surface chemical modification. Carbon detection in the composition can be attributed to the presence of isopropoxide in titanium tetraisopropoxide compound. The results also revealed that، with TiO2 grafting on the silica nanoparticles surface، absorption in UV region is increased and that the silica nanoparticles modified with titanate compound show photocatalytic characteristics and degradation ability of Rh. B dyestuff under UV light irradiation. It became also evident that the photocatalytic activity of the modified nanoparticles is less than TiO2 nanoparticles. However، by inclusion of modified silica nanoparticles into the polymeric coating، the photocatalytic properties of the coating can be established. Although modified silica nanoparticles have less photocatalytic activity compared to TiO2 nanoparticles، but they cause less damage to the polymer matrix.

Atheoretical hypothesis was put forward on the effect of nanoparticle size on cell nucleation in polystyrene (PS) matrix foam. At first the heterogeneous factor was calculated in different wetting angles from zero to 180º. Then، to verify this hypothesis a combination of the solution and melting methods was used to prepare PS-nanosilica nanocomposites at different concentrations and different sizes of nanosilica. In this regard a novel apparatus، including a high-pressure/ high-temperature vessel capable of instantaneous pressure release and stabilization control، was used to prepare a polystyrene-nanosilica nanocomposite foam in its melt state. To reach the foaming conditions، the vessel was pressurized with dry ice at the specified temperature. After reaching the foaming conditions، the sample was saturated with supercritical carbon dioxide (CO2) for 8 more hours. Then، the pressure was released with an on/off valve and the temperature was instantaneously dropped to below glass transition temperature. The scanning electron microscopy pictures were used to calculate the effect of nanosilica on the main foaming parameters including cell density and cell size. The results showed that a small amount of nanosilica has substantial effect on decreasing cell size and increasing the cell density. Moreover، the foam quality and structure was improved by addition of the nanoparticle.

The effect of mixing on rheological behavior of 6% wt epoxy-clay nanocomposites was studied. The mixing processes were carried out by low shear mixer، homogenizer and ultrasonic and combination of different mixing techniques at medium and maximum power. All these methods led to intercalated structure. The XRD results showed that the ultrasonic has the best effect on dispersion while a low shear mixer has the least positive effect. Opposite to an ultrasonic mixing method، the homogenization process through maximum power does not change the dispersion state significantly. The best condition would be to use an ultrasonic mixer after a homogenizer، otherwise the reverse process may result in lower dispersion. Small amplitude oscillatory measurements were carried out on linear regime over 0. 1-100 Hz. According to the fact that rheological responses are very sensitive to polymerparticle interactions and accessible surface area، the slope of storage modulus and shear thinning exponent of viscosity are proportional to the level of dispersion. This implies that more increases in intergallary height may lead to less terminal slope. The continuous relaxation profile and zero shear viscosity were generated by experimental data via computer software based on neural network approach. To check the validity of software، the experimental data were recovered with very low deviation using relaxation spectrum. The experimental observations showed that a solid-like behavior، as a result of better dispersion، can prevent the profile from falling especially at longer times.