دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و ششم شماره 6 (پیاپی 128، بهمن و اسفند 1392)

Drug delivery through skin is often obstructed by low permeability of skin towards most drugs; however، such problem would be solved by application of skin penetration enhancers in the formulations. In the present study، a drug in adhesive patch with buprenorphine as active ingredient was prepared. Drug-in-adhesive transdermal drug delivery systems with different chemical penetration enhancers were designed. For this purpose a response-surface experimental design was used. Response surface methodology based on a three-level، three-variable Box–Behnken design was used to evaluate the interactive effects of dependent variables such as: the rate of skin permeation and adhesion properties including peel strength and tack value. The parameters such as drug release and adhesion were used as independent variables. Levulinic acid، lauryl alcohol and Tween 80 were used as penetration enhancers. In order to prepare samples، buprenorphine with constant concentration was incorporated into acrylic pressure sensitive adhesive with carboxylic functionality and this mixture was added to chemical penetration enhancer with different concentrations. The results show that the cumulative amount of drug release in presence of Tween 80 is 462. 9 ± 0. 006 μg so it is higher than cumulative amount of drug release in presence of levulinic acid (357. 9 ± 0. 005 μg) and lauryl alcohol (269. 5 ± 0. 001 μg). Results of adhesion properties such as peel strength and tack reveal that using levulinic acid and lauryl alcohol will increase peel strength while Tween 80 will decrease it. Besides، the results show that all these permeation enhancers have increased tack values.

Poly (dimethyl siloxane) (PDMS) has received special attention due to its unique properties such as high surface tension، high gas permeability، high hydrophobicity، high chain flexibility at room temperature، good biocompatibility and very low glass transition temperature. One of the simplest methods to impart these properties in copolymers is to use PDMS as a macroinitiator in the controlled radical polymerization. In the present study، hydroxyl-ω PDMS was characterized by FTIR، 1H NMR and GPC analyses. The results showed that there is an impurity present in the commercial hydroxyl-ω PDMS. Functionalization reactions were used to investigate the reactivity of the impurities. Hydroxyl-terminated PDMS was brominated via 2-bromopropionyl bromide and α-bromoisobutyryl bromide. Brominated PDMS، used as a macroinitiator in the atom transfer radical polymerization، was then iodinated by sodium iodide in anhydrous acetone as a solvent to prepare iodinated PDMS. Bromination and iodination were verified by FTIR، 1H NMR and GPC analyses. GPC results showed that a high molecular weight impurity present in the sample can be removed after functionalization and purification of PDMS though there may be still impurities remain in the purified product. 1H NMR spectrum of the brominated and iodinated PDMS showed that the peaks related to the impurity do not show any change in intensity and chemical shift in comparison with those appeared in the 1H NMR spectrum of the hydroxyl-ω PDMS، indicating that impure species are not reactive in chemical modifications. In other words، these impurity species do not have any hydroxyl reactive functional group.

ICellulose nanofibers (CNF) -reinforced poly (lactic acid) (PLA) nanocomposite was prepared by casting method. In order to improve the compatibility and miscibility of the whole system with respect to PLA matrix، CNFs were treated with oleic acid. The resulting modified nanofibers (MCNF) exhibited reduced polarity and crystalline structure as compared with unmodified CNF. These MCNF were subsequently introduced into a PLA polymeric matrix and the effect of nanofiller on physicochemical properties of the nanocomposites was studied. Surface morphologies of PLA films studied by atomic force microscopy and it was revealed that the surface roughness of nanocomposites increased by increasing the nanofiber content. The morphology of fracture surface، evaluated by scanning electron microscopy، confirmed the uniform dispersion of MCNF at low levels. However، a higher level of MCNF (12 wt%) led to less dispersion uniformity and more agglomeration of the nanofibers. The thermal analysis by differential scanning calorimetry showed that the melting temperature of the PLA-MCNF nanocomposites was significantly higher than that of pure PLA film. Also، the degree of crystallinity increased with an increase in MCNF content. X ray diffraction patterns confirmed that the addition of MCNF resulted in increased crystalline structure in PLA matrix. At MCNF content of 12 wt%، the tensile strength and Young’s modulus of the nanocomposites increased by 2. 5 and 2 folds than those of pure PLA films، respectively. These improvements were primarily attributed to the effect of surface modification and uniform dispersion of the MCNF in the PLA matrix. However، the MCNF formed aggregates in the higher loading levels (12 wt %).

This study was an effort to control foam structure with controlled shear rate in a slit die with addition of nanosilica in the extrusion process. We used general purpose polystyrene as the matrix، nanosilica as a nucleating agent and nitrogen gas as the blowing agent. For better dispersion of nanoparticles in the matrix، a combination of solution and melt methods were employed. The foams were produced in a twin screw extruder by studying the effects of shear rate on the slit die، size and weight percentage of nanosilica on foam density، cell density and average cell size. Scanning electron microscopicy (SEM) pictures were used to obtain the main characterizing parameters of the foams i. e.، cell density and cell size. The results showed that when the shear rate of 8 min-1 on the slit die was increased to 12 min-1، due to the breakage of the large cells into several smaller cells، there were observed 61% enhancement in cell density and 18% reduction in average cell size. When the size of nanosilica was decreased from 40 to 12 nm، the cell density was increased from 1. 24×108 to 1. 73×108 cells/cm3 and average cell size was decreased from 11. 5 to 9 micrometer. By changing the nanosilica content from 0. 1 to 4% (by weight)، it was observed that at 2% (by weight) of nanosilica، the maximum cell density was obtained. In conclusion it was observed that the nanocomposite was produced by 2% (by weight) of 12 nm silica nanoparticles at 12 min-1 shear rate shows the maximum cell density and minimum cell size.

In the synthesis of mesoporous silica particles، the geometry، pore size، and specific surface area and pore volume of the particles can be greatly influenced by selected media and method، selection of co-solvent and co-surfactant. In this study، new SPB particles (silicone mesoporous particles، prepared by sol-gel method using block copolymers as template) were synthesized in a water/n-octane system from the mixture of two copolymers based on poly (ethylene oxide) -b-poly (propylene oxide) -b-poly (ethylene oxide) (PEO-b-PPO-b-PEO) and poly (propylene oxide) -b-poly (ethylene oxide) -b-poly (propylene oxide) (PPO-b-PEO-b-PPO) triblock copolymers. Tetraethyl orthosilicate (TEOS) as precursor، cyclohexanol as co-surfactant، n-octane as co-solvent and citric acid catalyst were used. The specific surface area and pore volume، pore diameter، morphology، microstructure and porosity of the SPB particles were characterized by X-ray diffraction (XRD)، nitrogen adsorption-desorption (BET method) and scanning electron microscopy (SEM). The obtained results revealed that، using the mixture of two block copolymers in the synthesis of SPB1،2 particles، could produce mean pore diameters around 9 nm and control the pore size distribution of silica particles from non-normal to a normal distribution. Furthermore، the effect of chair conformation of cyclohexanol as a large co-surfactant on the mixed block copolymers due to increase in the uniformity and yield of the SPB1،2 mesoporous silica particles compared to the SPB1 particles، there is approximately a two fold increase in SPB1،2 particle yield. In this regard، the effect of cyclohexanol and the second block copolymer in making the new templates and micellization process were discussed.

Carbon aerogels are comprised of a class of low density open-cell foams with large void space، nanometer pore size and composed of sparsely semi-colloidal nanometer sized particles forming an open porous structure. Phase change materials are those with high heat of fusion that could absorb and release a large amount of energy at the time of phase transition. These materials are mostly used as thermal energy storage materials but in addition they could serve as an obstacle for passage of heat during phase changes and this has led to their use in thermal protection systems. In this study، the effect of magnesium chloride hexahydrate، as a phase change material (melting point 115°C)، on thermal properties of carbon aerogels is investigated. Thermal performance tests are designed and used for comparing the temperature-time behavior of the samples. DSC is applied to obtain the latent heat of melting of the phase change materials and the SEM tests are used to analyze the microstructure and morphology of carbon aerogels. The results show that the low percentage of phase change materials in carbon aerogels does not have any significant positive effect on carbon aerogels thermal properties. However، these properties are improved by increasing the percentage of phase change materials. With high percentage of phase change materials، a sample surface at 300°C would display an opposite surface with a significant drop in temperature increases، while at 115-200°C، with carbon aerogels، having no phase change materials، there is a severe reduction in the rate of temperature increase of the sample.

Cure kinetics of an epoxy-novolac resin with tetrabromo-bisphenol-A، as a flame retardant، was investigated in the presence of nadic methyl anhydride as a curing agent. Different amounts of benzyl dimethyl amine were used as accelerator. The studies on kinetics were carried out using isothermal DSC experiments at 100، 110، 120 and 130°C. The conversions were calculated based on the total heat of curing reaction obtained from non-isothermal DSC analysis at a heating rate of10°C/min. Kinetic parameters were obtained from isothermal analysis and by a model especifically for autocatalytic curing reactions which have been developed by Kamal and Sourour. The results obtained illustrate that the reaction is controlled by kinetic and diffusion parameters at different reaction stages. In other words، before a glassy state is reached the reaction mainly proceeds with autocatalytic behavior and can be well explained by the equation containing k1 and k2 as the rate constants and n and m as the reaction orders. At higher conversion levels، at about 65%، at the onset of network formation the system turns to a glassy state، the curing reaction is mainly controlled by diffusion (diffusion-controlled system). We conclude therefore that، theoretical and experimental data would be confirmed by considering the diffusion parameters in the corresponding model.