Iranian polymer journal
Volume:21 Issue: 8, 2012

Encapsulation of urea was performed in chitosan microspheres via emulsification followed by cross-linking with genipin, a natural cross-linker. The microspheres were prepared by varying different parameters, e.g., concentrations of chitosan, urea and cross-linker. The effect of these parameters on urea loading (%), urea content (%), entrapment efficiency (%) and release rate was studied. Higher amount of chitosan (1.0 g) and cross-linker concentration (0.75 mmol/g of chitosan) produced entrapment efficiencies of 99.0 and 78.5 %, respectively. Release rate was found to be dependent on the concentrations of urea, chitosan, cross-linker and temperature of the release medium. Higher concentration of loaded urea enhanced the release rate, whereas higher concentrations of chitosan and cross-linker reduced it. Higher temperature of the release medium improved the release rate. It was found that water uptake (%) increased through the increase of concentrations of urea and chitosan and decrease of that of cross-linker. Fourier transform infrared (FTIR) spectroscopy indicated the incorporation of urea in the chitosan microspheres. There was no significant interaction between chitosan and urea as evidenced by FTIR study. Surface of the urea-loaded microspheres appeared coarser and rough compared to that of unloaded microspheres as revealed by scanning electron microscopy.

Several novel kinds of poly (vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) based composite polymer electrolyte (CPE) membranes doped with ZSM-5 (Zeolite sieve of molecular porosity) were fabricated by steam bath technique. The desirable CPE membranes were further prepared by immersing them into the liquid electrolyte solution of 1.0 M LiPF6-ethylene carbonate /dimethyl carbonate/ethylmethyl carbonate (v/v/v:1/1/1) for 1 h to be activated at room temperature. Physical and chemical properties of the as-prepared CPEs are studied by scanning electron microscope, Fourier transform infrared, thermogravimetry and differential scanning calorimetry and electrochemical methods. The results showed that the thermal and electrochemical stabilities of the CPEs can be reached to 350 °C and 5 V, respectively. Reciprocal temperature dependence of corresponding ionic conductivity follows Vogel–Tamman–Fulcher relation, and ionic conductivity at ambient temperature can be up to 5.1 mS cm−1. The fabricated Li/CPEs/LiCoO2 coin cells with the CPE membranes prepared by steam bath technique can achieve a high discharge capacity about 144.97 mAh g−1 at 0.1 C. At 1.0 C, the capacity can be kept to 89.84 % of that at 0.1 C for the cell. After 26 cycles, the cell prepared with these CPE membranes can keep 97.5 % of its initial discharge capacity. These excellent physicochemical and battery properties indicate that these novel CPEs can be potentially used as electrolyte in lithium ion polymer battery.

Dodecylbenzenesulfonic acid (DBSA) -doped polyaniline (PAND) has been synthesized by redoping (PANDR) and aqueous polymerization (PANDA) methods. Silver nanoparticles were incorporated into the PANDR/tetrahydrofuran solution (PANDS) and then mixed with poly (vinyl chloride) (PVC) solution to prepare PANDS/PVC nanocomposites. In the present study، effects of silver nanoparticles on thermal properties of PAND/PVC blends have been investigated by employing thermal gravimetric analysis and heat flow microcalorimetry techniques. From these results it has been observed that the thermal stability of blends have increased by increasing the concentration of PAND in blends and nanocomposites. Addition of silver nanoparticles has suppressed the dehydrochlorination process and evolution/degradation of DBSA in PANDS/PVC nanocomposites. Presence of silver nanoparticles in PAND/PVC nanocomposites has reduced the mobility of PANI chains which in turn inhibited the transfer of free radicals formed during degradation of PAND and PVC through inter-chain reactions; hence، degradation process has been slowed down and thermal stability has been improved. Embedment of silver nanoparticles has reduced thermal weight loss corresponding to polymer degradation step and attains lower heat flow level in inert atmosphere for nanocomposites in contrast to those with no nanoparticles، thereby further improving thermal stability of nanocomposites. The heats of oxidation measured for blends and nanocomposites were independent of PAND/PVC blends composition.

Polyhedral oligomeric silsesquioxane (POSS) was synthesized via the hydrolytic condensation of γ-aminopropyltrimethoxysilane in the tetrahydrofuran solution catalyzed by concentrated hydrochloric acid and was further used as the grafting agent to react with graphite oxide (GO). The grafted product، which referred to as POSS-g-GO، was used to modify epoxy resin (EP) matrix. The epoxy/POSS-g-GO nanocomposites were fabricated using ultrasonication and the cast molding method and confirmed by Fourier transform infrared spectroscopy، X-ray diffraction، dynamic mechanical analysis (DMA)، and thermogravimetric analysis techniques. The results revealed that the incorporation of a small amount of POSS-g-GO caused a significant improvement in ultimate tensile strength، impact strength and roughness. With 2 wt% POSS-g-GO ultimate tensile strength and flexural strength of the composites were improved by 24. 8 and 56. 6 %، respectively. The impact strength was 42. 97 kJ/m2، which is 2. 5 times higher than that of the pure EP (17. 49 kJ/m2). The DMA results showed that the moduli of the nanocomposites in glass and rubbery states were significantly higher than those of the control epoxy. It indicated that incorporation of POSS-g-GO into epoxy networks was the efficient load transfer between the POSS-g-GO additives and epoxy matrix through covalent links. Morphological structure of the impact fracture surface of the epoxy/POSS-g-GO composites was observed by scanning electron microscope، as well.

Dynamically vulcanized thermoplastic elastomer based on Nitrile butadiene-rubber (NBR) /PVC with functionalized single-walled carbon nanotubes (f-SWNTs) and non-functionalized single-walled carbon nanotubes (SWNTs) were prepared using a brabender internal mixer. Effects of two types of SWNTs (functionalized and non-functionalized) on morphology and mechanical properties of NBR/PVC blends were studied. Results showed that the mechanical properties of NBR/PVC/SWNTs nanocomposites improved with the increasing of SWNTs content and in particular with the increase of f-SWNTs content. Moreover، the enhancement of mechanical properties of NBR/PVC blends reinforced with functionalized SWNT was higher than that of NBR/PVC blends with non-functionalized SWNT. Dispersion of SWNTs and morphology of NBR/PVC/SWNT nanocomposites were determined by scanning electron microscopy and transmission electron microscopy (TEM) techniques. TEM images illustrated that f-SWNTs were dispersed uniformly in NBR/PVC matrix while non-functionalized SWNTs showed much aggregation. Dynamic mechanical thermal analysis of NBR/PVC/SWNTs nanocomposites was also studied. The outcomes indicated that in the case of f-SWNTs، the intensity of tan δ peak was lower than that in the case of non-functionalized SWNTs. Meanwhile، the intensity of tan δ peak reduced when the content of f-SWNTs was increased.

Starch in its native form, may not be able to provide functional properties such as high or low temperatures and shear forces bearings expected in modern industries. Therefore, it is usually modified to make it compatible for different applications. The main aim of this research was to study the effects of dual modification using cross-linking and annealing on physicochemical properties of wheat starch. Therefore, starch was first cross-linked using different levels of POCl3 (0, 0.1, 0.2, 0.4 %, w/w, starch basis) and then annealed at 40 °C for 72 h. Scanning electron micrographs showed the presence of some spots on the granules of the dual-modified samples. The results of differential scanning calorimetry showed that the onset, peak and conclusion temperatures and enthalpy increased upon dual modification. The X-ray diffraction pattern of the modified samples remained unchanged while water solubility and swelling decreased. The results of rapid visco analyzing showed lower peak, setback, breakdown and final viscosities for the dual-modified samples. These samples produced stronger gels as determined using a texture analyzer. In total, annealing of the cross-linked starch could enhance some of its functional properties for further applications.

A series of poly (vinyl alcohol) (PVA) /regenerated silk fibroin (RSF) /nano-silicon dioxide (nano-SiO2) blend films were prepared by solution casting method، in which nano-SiO2 was obtained via sol–gel process. The structure، properties، and morphology of the films related to the compatibility were investigated by X-ray diffraction (XRD)، Fourier transform infrared spectroscopy (FTIR)، scanning electron microscopy (SEM)، transmission electron microscopy (TEM)، differential scanning calorimetry (DSC)، and thermogravimetric analysis (TGA). XRD peaks of PVA/RSF/nano-SiO2 (1. 0 wt %) blends decreased in intensity indicated that formation of PVA and RSF crystal lattices was hindered by nano-SiO2 particles. FTIR spectroscopy analysis of PVA/RSF/nano-SiO2 films confirmed that both Si–O–C linkage and hydrogen bonding were formed among PVA، RSF، and nano-SiO2. SEM showed that there was no obvious phase separation in PVA/RSF/nano-SiO2 (1. 0 wt %) film although small uniform blur particles can still be found. In addition، TEM showed nano-particles were well dispersed through the PVA/RSF polymer matrix. Besides، the observed shift in glass transition temperatures (T g) and improvement in thermal properties of composite films suggested the enhanced compatibility due to interfacial bonding and intermolecular interactions. Therefore، these results indicated that the compatibility of PVA/RSF was improved effectively by the addition of nano-SiO2.

Sodium ion conducting polymer electrolyte films based on poly(vinyl pyrrolidone) (PVP) were prepared using solution casting technique. Structural characterization was performed using X-ray diffraction (XRD) technique. Increase in amorphous phase with the increase of dopant concentration was observed. Temperature dependence of electrical conductivity was performed using AC impedance analyzing technique in the frequency range of 0.1 KHz to 1 MHz. Activation energy values were evaluated, as well. Optical absorption studies were carried out in the wavelength range 200–600 nm. Absorption edge, direct band gap, and indirect band gap values were also evaluated. Optical absorption edge and optical band gap (both direct and indirect) showed decreasing trend with increasing the concentration of the dopant. Dominant conducting species in the present electrolyte system was determined using Wagner polarization technique and dominant conducting species were found to be ions rather than electrons. Solid-state batteries were developed using the present solid polymer electrolyte system and discharge characteristics over the load of 100 kΩ. Cell parameters, e.g., open circuit voltage, short circuit current, current density, power density were evaluated, too. Among these cells, the cell made up of PVP/NaI (70/30) ratio for electrolyte was found to be more stable than the other two cells PVP/NaI (90/10) and (80/20) ratios and the obtained results were comparable with the results achieved by other studies.

Injection molding of foam articles has always attracted much interest because of elimination of sink mark, good dimensional stability and reduced production cost. In this study, the nanocomposite samples based on low-density polyethylene/ethylene vinyl acetate/organo montmorillonite were processed into foams by injection molding method. Nanocomposites were prepared by co-rotating a twin-screw extruder. The experimental design was based on Box–Behnken method and parameters such as injection rate, mold temperature and nanolayered silica content were examined in relation to physico-mechanical properties of foams using response surface methodology. Three levels of injection rate (30, 60 and 90 mm/s), nanoclay content (0, 3 and 6 phr) and mold temperature (160, 175 and 190 °C) were chosen. The mathematical model and response surface graphs were employed to illustrate the relationship between the variable parameters and foam properties. The results revealed that the cell size and cell density as the main characteristics of the foams were affected by all parameters. Cell density of samples was affected by mold temperature, injection rate and nanoclay content. At high level of nanocontent the increase of injection rate was accompanied by decreases in density. Tensile strength and specific compression modulus of samples passed through a maximum versus mold temperature due to competition between cross-linking reaction and cell growth. At high mold temperature and injection rate, the cell rupture occurred because of low viscosity of the compounds at these conditions.

Non-linear optical (NLO) dyes used as guests in polymeric films have recently attracted interests in optical applications. In this regard, dye-grafted polymeric systems can outperform conventional guest–host dye-containing films because they have lower loading limitations and aggregation problems. These give rise to enhanced molecular orientation. The work presented here is an attempt to study the laser-induced birefringence for a novel sol–gel based polymeric nanocomposite prepared by reacting an NLO dye (methyl red) and an epoxy silane coupling agent at different concentrations of dye. 3-Glycidoxy propyltrimethoxysilane was hydrolyzed and condensed to prepare a siloxane structure from which a dye-containing hybrid was obtained. The structural and morphological properties of the resulting nanocomposites were studied by FTIR spectroscopy, differential scanning calorimetry and transmission electron microscopy. Results showed that the dye was chemically attached to the siloxane structure built through sol–gel processing. This chemical modification leads to nanostructured morphology in which inorganic phase was entangled to the organic phase. The size of clusters formed was 60–80 nm in dimension. The optical responses of nanocomposites were investigated at different process parameters, including dye concentration, film thickness and curing regimes. These were then discussed based on the photochemical and photothermal properties of the dye molecules, the rotation dynamic of which was shown to strongly depend on the physical and chemical properties of the host. The samples with 8 wt% of dye revealed the maximum birefringence, while the sample with 10 wt% showed the best memory effect. The best condition for curing was found to be 24 h. By increasing the film thickness, there was an increase in the amount of induced birefringence.