دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و هفتم شماره 1 (پیاپی 129، فروردین و اردیبهشت 1393)

The effect of organically modified clay on the structure and deformation mechanism of polymeric matrices was investigated. For this purpose، the role of organoclay in deformation control of polymeric matrices، with different deformation mechanisms، has been studied methodically in order to determine a relationship between the structure and deformation mechanisms. In this respect polypropylene and polystyrene composites systems were designed using montmorillonite through melt intercalation technique using a twin، co-rotating extruder with starve feeding system. Also an epoxy was employed to design a nanocomposite system prepared by in-situ polymerization technique. The structure and deformation mechanism of nanocomposites were investigated using appropriate techniques. X-Ray diffraction and transmission electron microscopy were used to explore the structure of various systems while، the reflection and transmission optical microscopy were used in order to study their corresponding deformation mechanisms. The bulk polymer was also studied for its deformation mechanism by reflection optical microscopy and the notch tip of the samples were examined by transmission optical microscopy. The results of experiments showed that organoclays acted as initiator sites for shear yielding mechanism as the dominant deformation mechanism in epoxies. It may be noted that، these particles may act as initiator sites for crazing، the dominant deformation mechanism of polystyrene، and alter the mechanism from local to massive. In polypropylene systems، which may exhibit both shear yielding and crazing organoclays can facilitate or postpone both mechanisms in different conditions، related to PP morphology and other conditions.

Application of ultrasound process is growing in food industry for different purposes including homogenization، extraction، blanching and removal of microorganisms، etc. On the other hand، starch is a natural polymer which exists in many foods or added into the food as an additive. Therefore، determination of the effects of ultrasound on starch characteristics can be useful in interpretation of the properties of starch-containing products. The main aim of this study was to determine the physicochemical changes of wheat starch treated by ultrasound waves. Therefore، an ultrasound probe device was used which ran at 20 kHz، 100 W and 22°C. Starch suspension in distilled water (30% w/w) was prepared and treated with ultrasound for 5، 10، 15 and 20 min. The results showed that increases in processing duration led to increases in water solubility of starch، water absorption and gel clarity (as determined by spectrophotometry). Starch intrinsic viscosity as measured using an Ostwald U-tube showed lower intrinsic viscosity with increases in ultrasound time. Gel strength of the samples as determined using a texture analyzer was reduced by longer processing time. The scanning electron microscopy revealed that increasing the duration time of the ultrasound treatment could produce some cracks and spots on the surface of the granules. In total، it was concluded that the ultrasound treatment resulted in some changes from the starch granular scale to molecular levels. Some of the starch molecules were degraded upon ultrasound processing. Such changes may be observed for the starch-containing foods treated with ultrasound and they are enhanced with increases in ultrasound time intervals.

The bis (indenyl) zirconium dichloride catalyst was synthesized by a modified method at room temperature. Terpolymerization of ethylene، propylene and diene monomers were carried out using this metallocene catalyst under different conditions of different feed ratios of monomers، co-catalyst/catalyst ratios and polymerization temperatures. Methylaluminoxane (MAO) was used as a co-catalyst. The highest activity of catalyst was obtained at total pressure 4 bar، co-catalyst/catalyst ratio [Al] / [Zr] =600، polymerization temperature 60°C and E/P=67:33 and momomer feed ratio of 1700 kgEPDM/molZrh. The activity of catalyst showed bell-shaped behaviors versus co-catalyst/catalyst ratio ([Al] / [Zr]) and polymerization temperatures. The viscosity-average molecular weight (Mv) of terpolymers increased with increasing total pressure at different feed ratios of monomers. However، the viscosity-average molecular weight of terpolymers decreased at higher co-catalyst/catalyst ratios ([Al] / [Zr]) and higher polymerization temperatures. The increases in propylene and diene monomers in the feed ratios decreased the catalyst activity and viscosity-average molecular weight of terpolymers. The ratio of maximum average rate of terpolymerization to an average rate of terpolymerization at the end of the polymerization (DI) for different terpolymerization conditions was relatively high; an indication of the decay kinetics for this type of metallocene catalyst. Increasing the co-catalyst/catalyst ratio up to [Al] / [Zr] = 500 increased the Et% and ENB% in the final obtained polymers. However، increasing the polymerization temperature، diene and propylene concentrations in the feed ratio decreased the Et% and increased the ENB% contents in the final obtained polymers. Tg of the final terpolymers was between -64 and -52°C. The study on microstructures of some polymer revealed block type of chain microstructures.

The protein-polysaccharide complex-based nanocapsule is one type of polymeric nanocarrier which can be potentially useful for encapsulation of hydrophobic nutraceuticals. In this research، caseinate-carrageenan complex was used for encapsulation of vitamin D. The complex formation between caseinate and carrageenan was carried out by lowering the pH under isoelectric point of protein. The Fourier transform infrared spectroscopy (FTIR) and differential scanning colorimetry (DSC) confirmed complex formation between carrageenan، caseinate and vitamin D. The particle size of 1% caseinate particles was in the range of 150-300 nanometer and by addition of vitamin D the particle size increased to 450-750 nanometer. Moreover، carrageenan of all concentrations (at constant concentration of caseinate (1%) and pH4. 9) resulted in lower particle size below 100 nanometer. The stability of caseinate and its complex formation with carrageenan showed that encapsulation was achieved at 45% efficiency and also vitamin D stability (during 5 days storage) was higher in nanocomplex compared to pure caseinate particles (60-63% compared to 53%). The complex formation between caseinate and carrageenan was carried out by pH decreasing under isoelectric point of protein. The FTIR and DSC confirmed complex formation between carrageenan، caseinate and vitamin D. The particle size of caseinate 1% particles were in the range of 150 -300 nanometer and with adding vitamin D، particle size increased to 450-750 nanometer. Moreover، adding carrageenan at all used concentration (at constant concentration of caseinate (1%) and pH4. 9) resulted in reduced particle size to less than 100 nanometer and vitamin D stability (during 5 days storage) was higher (60-63%) in nanocomplex compared to pure caseinate particles (53%). The protein-polysaccharide complex based nanocapsule is one type of the polymeric nanocarriers which can potentially be used for encapsulation of hydrophobic nutraceuticals. In this research، carageenan- caseinate complex was used for encapsulation of vitamin D. The complex formation between caseinate and carageenan was carried out by pH decreasing under isoelectric point of protein. The Fourier transform infrared spectroscopy (FTIR) and differential scanning colorimetry (DSC) confirmed complex formation between carageenan، caseinate and vitamin D. The particle size of caseinate 1% particles were in the range of 150 -300 nanometer and with adding vitamin D، particle size increased to 450 -750 nanometer. Moreover، adding carageenan at all used concentration (at constant concentration of caseinate (1%) and pH=4. 9) caused to decrease of particle size to below of 100 nanometer. The results of encapsulation efficiency and stability showed that caseinate and complex particles confront from 45% efficiency and also vitamin D stability (during 5 days storage) was higher in nanocomplex compared to pure caseinate particles (60-63% in comparison to 53%).

Nanocomposites based on polyoxymethylene (POM)، containing 1. 5 to 9 wt% of CaCO3 nanoparticles، were prepared by melt compounding، using a co-rotating twin screw extruder، followed by injection molding process. The thermal behavior، mechanical properties as well as morphology were characterized. The inclusion of CaCO3 nanoparticles into POM slightly affected the melt flow index. The differential scanning calorimetry (DSC) results indicated that the incorporation of CaCO3 nanoparticles has nucleating effect and can raise the temperature and the degree of crystallinity. The results of shrinkage assessments revealed that crystal nucleation and filling effects of CaCO3 nanoparticles have counter effects on thermal contractions. Incorporation of the CaCO3 nanoparticles into POM improved tensile and flexural properties as well as the impact resistance at the same time. The maximum tensile strength، tensile modulus، flexural strength، flexural modulus and impact strength were achieved in the order given by applying 1. 5، 6، 3، 6، 3 wt% of CaCO3 nanoparticles، which corresponded to 13، 40، 33، 15 and 20% higher than those of pure POM. The notable improvements of tensile، flexural and impact properties as a result of incorporating 3 wt% of CaCO3 nanoparticles were attributed to the nucleation and crystallinity enhancements as well as relatively uniform dispersion of CaCO3 nanoparticles in POM matrix. The morphology studies indicated that CaCO3 nanoparticles inclusion can alter the fracture mechanism from brittle-to-ductile-brittle، a sharp transition from ductile-to-brittle fracture observed in POM/CaCO3 nanocomposite.

Polyacrylonitrile (PAN) micro/ultrafiltration membranes were prepared by phase inversion method. The effects of various preparation conditions including polymeric solution concentration، evaporation time، temperature، composition and residence time of the coagulation bath were investigated. Various important membrane characteristics such as pore size، bulk porosity، and mechanical and morphological properties were taken into the consideration. The characterizations were performed by measuring the bubble point، water flux، tensile strength and scanning electron microscopy (SEM) analyses. The results showed that by increasing the polymeric solution concentration from 13 to 17 wt%، the porosity and water flux were decreased. Moreover، the membrane skin layer was considerably thickened with a very significant decrease in its pore sizes which was achieved in ultrafiltration region. By increasing the evaporation time at atmospheric pressure، membrane skin layer was thickened and the pore sizes were decreased. Low coagulation bath temperatures (below 30°C) resulted in lower pore size، water flux، and an increase in membrane mechanical strength. Introduction of isopropanol (IPA) into the water coagulation bath led to lower coagulation rate and consequently، the formation of smaller pores became possible by using pure isopropanol as coagulation bath. Furthermore، by increasing the residence time in coagulation bath، a more porous structure with more uniform pore sizes were formed that showed better mechanical properties. Finally، the so-called ultrafiltration membranes were applied in concentration process of protein and milk fat. A protein rejection more than 93% was attained while a complete removal of milk fat was achieved.

Atom transfer radical polymerization (ATRP) of styrene in presence of mesoporous silica nanoparticles was carried out at 110 °C. Reverse atom transfer radical polymerization (RATRP) and simultaneous reverse and normal initiation for atom transfer radical polymerization (SR&NI ATRP) techniques were used as two appropriate introduced techniques for circumventing oxidation problems. Usage of metal catalyst in its higher oxidation state was the main feature of these initiation techniques in which deficiencies of normal ATRP were circumvented. Structure، surface area and pore diameter of synthesized mesoporous silica nanoparticles were evaluated using X–ray diffraction and nitrogen adsorption/desorption isotherm analysis. Average particle size was estimated around 600 nm by electron microscopy images. In addition، according to these images، nanoparticles revealed an appropriate size distribution. Particles size and their distribution were examined using scanning. Final monomer conversion was determined by using gas chromatography. The number and weight average molecular weights (Mn and Mw) and polydispersity indexes (PDI) were also evaluated by gel permeation chromatography. According to the results obtained، addition of mesoporous silica nanoparticles in both RATRP and SR&NI ATRP systems revealed similar effects: decrement of conversion and Mn and also increment of PDI values observed by increasing of mesoporous silica nanoparticles content. Improvement in thermal stability of the nanocomposites in comparison with neat polystyrene was demonstrated by thermogravimetric analysis (TGA). Moreover، in case of nanocomposites، thermal stability was obtained by higher loading of nanoparticles. A decrease in glass transition temperature by higher content of mesoporous silica nanoparticles has been demonstrated by differential scanning calorimetry analysis.