دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و دوم شماره 2 (پیاپی 100، خرداد و تیر 1388)

A gel composite (based on polyacrylamide and crosslinker Cr(III) acetate) was prepared by solvent method (distillate and water formation) and nanoclay particle (kaolinite). Using XRD tests, d001 was evaluated for kaolinite nanoparticles in gel composite. Kaolinite modification using dimethyl-sulfoxide led to increase interlamellar spacing from 7.21 to 10.82 o A. Based on the results obtained for samples prepared from unmodified clay besides the pure clay, there is a wide peak at 2θ = 8o; which is a representative of polymer diffusion between the clay layers. For the sample prepared from modified clay, no increase in interlamellar space was observed. Addition of 15% clay (modified and unmodified) caused the syneresis to reduce by 20%. The gelation time for composites prepared from both types of clays increased due to increases in clay concentration, which this increase for the sample prepared from unmodified clay was greater. The viscosity of gel for samples prepared from modified clay increased due to increased clay concentration, which reached its maximum for 15% clay concentration. However for unmodified clay the maximum value of viscosity was observed for 30% clay concentration.

In this study the blends of acrylic/silicone pressure sensitive adhesive (PSA) were prepared, and their adhesion properties and surface morphology were evaluated. For this purpose appropriate amounts of acrylic (10- 90%w/w) were added to silicone PSA to obtain visually homogeneous solution. The resulting solution was evenly applied on a polyethylene terephthalate (PET) film with final specific thicknesses (35, 65 and 110 μm) by using a film applicator. The morphological analysis was performed through scanning electron microscopy (SEM) and by the study of thermal analysis using the differential mechanical thermal analysis (DMTA) behavior of the blends, and it was found that all acrylic/silicone blends were incompatible and showed two different glass transition temperatures. By addition of silicone from 10 to 50% to acrylic/silicone blends the continuous phase is acrylic and the dispersed phase is silicone. Equally by increasing the percentage of silicone in the blends the continuous and dispersed phases were interchanged. By study of surface analysis and peel strength results it was found that surface properties are the main factors to determine peel strength values. Viscoelastic studies of the blends were shown that tack values and G" showed the same changing trend.

Long-chain diacrylate crosslinkers based on linear α,ω-diols were synthesized and characterized using FTIR and 1H NMR spectroscopy. The highest reaction yield (99.5%) was due to polyethylene glycol diacrylate 1000 (PEGDA-1000). Then, kaolin-containing poly(potassium acrylate-acrylic acid) superabsorbent composites and kaolin-free counterparts were synthesized using PEGDA-1000.The effect of the crosslinker concentration on swelling, rheological and thermo-mechanical properties was investigated. Absorption capacity of the composite hydrogels (having ~38% kaolin) was unexpectedly higher than that of kaolin-free hydrogels. This was attributed to an interfering effect of kaolin during the polymerization. Glass transition temperature was increased with crosslinker concentration enhancement and addition of kaolin up to about 10oC and 28oC, respectively. Making such K-containing superabsorbents may be taken as an effective action to achieve more durable and cheaper superabsorbents for agricultural uses.

Elastomer compound based on NR/BR was prepared using different kinds of nano-ZnO and ZnO. The effect of zinc oxide as an activator of sulfur cure on the mechanical and morphological properties of the compound was studied. The result of the mechanical properties showed that the tensile strength, elongation-at-break, resilience, and abrasion resistance of the compound prepared by ZnO (4 phr) are equal to the compounds using nano-ZnO (Iran, 1 phr) and nano-Zno (China, 2 phr). The cure time of the compound with nano-Zno is less than that of the compound using ZnO while the scorch time of those compounds is the same. The SEM of the samples showed that the particle size of nano-ZnO (Iran) is smaller than that of ZnO and nano-Zno (China) and also uniformly dispersed.

Polyvinyl butyral (PVB) was synthesized by condensation reaction of polyvinyl alcohol (PVA) with butanal in aqueous medium containing an effective emulsifier and an inorganic acid as catalyst. The product was characterized by, IR, TG and DTG techniques. Percentage of vinyl alcohol groups in the PVB was determined by a chemical method according to a standard method. Some clear and soft film samples containing the PVB and some high boiling point plasticizers were made by hot press. For this purpose plasticizers such as bis(2-ethylhexyl)phthalate (DOP) and bis(2-ethylhexyl) terephthalate (DOTP) were purchased and the triethylene glycol bis(2-ethylhexanoate) (TEGB) was synthesized. The film samples containing 30 percent mixture of triethylene glycol bis(2-ethylhexanoate) and bis (2-ethylhexyl)phthalate with ratio 65/35 showed some improved mechanical and optical properties.

Polymerization of styrene in presence of two monofunctional initiators is studied kinetically in an ampoule scale. Polymerizations were ceased at different conversions for each ampoule while the temperature was increased almost linearly during the reaction. Three different initiator mixtures were used. The first mixtures were composed of benzoil peroxide (BPO) and t-butyl perbenzoate (TBPB) with various molar ratios and temperature programs. The second and third series were performed on mixtures of BPO and α,α'-azobisisobutyronitrile (AIBN) and AIBN with TBPB, respectively. The experimental results for these series revealed thatincreasing the percentage of TBPB in the initiator mixtures at the same reaction temperature intervals enhanced polymerization rate and molecular weight of the resulting polymers. On the other hand the results from the second series indicated that reducing AIBN in the mixture would have reduction effect on the reaction temperature intervals while both conversion and the polymer molecular weight are increased.

In this research, a braiding-pultrusion production line is developed by modifying a conventional textile maypole braiding machine and adding it to a pultrusion line for production of braid-pultruded (BP) composite rods. In order to evaluate the mechanical properties of BP rods and study the effect of some braiding parameters, they were produced with different braid roving linear densities and braid angles. The results are also compared to those of unidirectional (UD) pultruded rods which were produced without braided fabric cover, but with the same fiber volume fraction and diameter.The results showed BP rods had higher shear modulus, but lower tensile modulus and flexural rigidity compared to UD rods. It was also concluded that increasing the braid roving linear density leads to an improvement in shear modulus, but a reduction in tensile modulus and flexural rigidity. Moreover, the highest shear modulus is observed in the rod with braid angle of 45o. Tensile modulus and flexural rigidity decrease when braid angle increases.

Polymer/clay nanocomposites are considered as a new subject of research in Iran and the world. Addition of a minimum amount of clay (2-5wt%) can improve the mechanical properties, enhance barrier properties and reduce flammability dramatically. Polystyrene (PS) exhibits high strength, high modulus and excellent dimensional stability, but it has poor ductility, elongation, and flexural modulus. By incorporating clay into polystyrene these properties can be improved. In this study preparation of polystyrene/clay nanocomposite, effects of different types of clays (Cloisite 10A and Nanomer I.30TC) and maleic anhydride modified polystyrene on mechanical properties of the prepared polystyrene/clay nanocomposites were evaluated. Samples were prepared by a twin screw extruder. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques were employed to evaluate the extent of intercalation and exfoliation of silicate layers in the nanocomposites. Mechanical tests show that by addition of clay and maleic anhydride modified polystyrene the flexural modulus (~30%) and elongation-at-break (~40%) of prepared nanocomposites have been improved. XRD and TEM results show that nanocomposite have an intercalated structure with ability to change to further exfoliation structure.