دو ماهنامه علوم و تکنولوژی پلیمر
سال بیست و نهم شماره 1 (پیاپی 141، فروردین و اردیبهشت 1395)

Interactions between polyelectrolytes and oppositely charged vesicular particles have many possible applications in drug delivery or gene therapy. Formation of vesicular structures by 2-(propylcarbamoyl) terephthalic acid heptaisobutyl POSS (POSS DCA) in a solvent mixture comprising acetone, ethanol, and 1-propanol has been already proved by the same authors. Particle size and morphology of POSS DCA vesicular particles were investigated as a function of ultrasonication (sonicated vs. non-sonicated) and concentration (23 or 34 mM) and correlated to the interactions occurring between the vesicles and a cationic random terpolymer. Concentrated solutions (56% w/w) of the terpolymer i.e., poly(dimethylaminoethyl methacrylate-co-methyl methacrylate-co-butyl methacrylate) were prepared in the above solvent mixture containing POSS DCA particles. Morphological changes of the particles in the concentrated solutions were studied by atomic force microscopy (AFM) and conformity of the AFM findings with rheological results was investigated. Interactions between the terpolymer and spherical vesicular particles (mean diameter c.a. 4.5 μm in non-sonicated state; C=23 or 34 mM) led to disappearance of the particles and formation of smaller elliptical particles (mean diameter ranging 70 to 700 nm), respectively. At 34 mM POSS DCA concentration, the interactions between the terpolymer chains and sonicated vesicular particles (mean diameter c.a., 4.5 μm with approx. 8 μm length) led to formation of irregular, aggregated, lamellar structures. Some of these findings were confirmed by the rheological results. The results were interpreted considering self-assembly of the terpolymer chains, vesicle shell peeling by the polyelectrolyte chains, and diffusion of the chains into the shells.

The bed of an open wound is prone to infection because of good conditions for microorganisms to grow in a moist, warm and nutritious environment. Using an antibacterial wound dressing, the healing of the wound can be accelerated. Antibacterial properties of natural dyes have been studied by researchers in recent years. On the other hand, the efficiency of fine fibers in wound dressing has been demonstrated due to increasing its contact area with the skin and simulation of extracellular matrix. In this study, polyvinyl alcohol (PVA) microfibers were fabricated by electrospinning process and heat treatment was used to increase the stability of microfibers against aqueous solutions. It is notable to say that untreated PVA microfibers dissolve in aqueous solutions easily. XRD spectrum was used for structural characterization of PVA microfibers after heat treatment. The results showed an increase in the crystallinity of the microfibers after heat treatment. Antibacterial properties of some natural dyes (green walnut shells, Punicagranatum, Urticadioica) were investigated by dipping PVA microfibers in the natural dyes solutions extracted by different solvents such as water and ethanol. In the end, the antibacterial property of PVA microfibers dipped in Punicagranatum extract solution for both pathogenic strains of gram-positive (Staphylococcus aureus) and gram-negative (Pseudomonas aeruginosa) was demonstrated. PVA microfibers dipped in aqueous solution of Punicagranatum showed stronger antibacterial property than those dipped in ethanolic Punicagranatum extract solution. The SEM images indicated that morphology of PVA microfibers preserved after dipping in the natural dyes solution extracted by water and ethanol, confirming stability of PVA microfibers after heat treatment.

One of the major concerns of using a non-biodegradable polymer product is its disposal at the end of its life cycle. Development of biodegradable plastics promises an alternative solution to combat this problem. Blending of poly(lactic acid) with non-biodegradable polymers is a practical and economical method for modifying the biodegradability properties of non-biodegradable polymers. In this study, soil biodegradability of the blends of high density polyethylene (HDPE) and variable amounts of recycled poly(lactic acid) (r-PLA) plastic flakes at 0, 5, 10, 20, 30, 40 and 50 wt% was studied. The behavior of the force-elongation profile of the blends having r-PLA content of lower than 30 wt% was approximately the same as that of pure HDPE while, it was completely different for the other blends. Tearing force and elongation-at-yield-point of the blends films with the 20 to 50 wt% r-PLA were decreased significantly after 60 days of soil biodegradability test. Morphological study showed that biodegradability of the blend films at surface of the samples (deep pores and grooves) was increased with extended biodegradability time and higher r-PLA content, while, this variation was significant for the blend films of more than 20 wt% r-PLA content. Thermal properties evaluation by differential scanning calorimetry (DSC) curves indicated that the glass transition temperature and enthalpy peaks during the heating stage were eliminated with increasing the biodegradability testing time. Also, reduction in the crystallinity degree of the r-PLA component with increasing the biodegradability testing time coincided with the earlier results.

Polymer materials have been increasingly accumulated in the environment and led to an interest in solving waste disposal problems through replacement of inert and non-biodegradable materials by biodegradable alternatives. A very high demand on low density polyethylene (LDPE)/ethylene-vinyl acetate (EVA) copolymers as suitable film materials applicable in the agricultural industry, because of their flexibility and high quality features, has particularly increased concerns over the degradation of these films. The effect of organoclay Cloisite15A and calcium stearate on the photo-degradation behavior of lowdensity polyethylene (LDPE)/ethylenevinyl acetate (EVA) (70/30) films was investigated in this study. First the best feeding sequence was found by X-ray diffraction (XRD) for nanoclay dispersion, and the extruded cast films of LDPE/EVA (60-80 μm) containing 2% w/w calcium stearate and 2% w/w organoclay were prepared. Photocatalytic degradation of the LDPE/EVA composite films was carried out under ultraviolet (UV-A) light irradiation for 72 h. The progress of degradation was followed by monitoring the changes incurred in the samples using Fourier transform infrared spectroscopy (FTIR) and carbonyl index calculation, thermogravimetric analysis (TGA) and tensile properties (tensile strength and elongation-at- break). It was observed that the LDPE/EVA samples with no additives did not exhibit significant changes when subjected to photooxidation but calcium stearate showed a strong accelerating effect on the rate of photooxidation of films. The presence of organoclay, in enhancing the mechanical, thermal and barrier properties, did not influence the photooxidation mechanism significantly. In other word, the susceptibility of LDPE/EVA composite containing calcium stearate and organoclay to photooxidation was similar to that of LDPE containing Ca-stearate.

A numerical and experimental low-velocity impact behavior of sandwich plates have been presently studied with regard to the compressibility and viscoelasticity features of their cores. Face sheets were assumed to be anisotropic composites or isotropic aluminum materials and a viscoelastic behavior has been considered for core. The boundary conditions are assumed to be simply supported or rigid. Abaqus, as FEM software, and its python script programming feature, have been used to model the specimens. To model hyper-viscoelastic nonlinear behavior of the core, Ogden hyper-foam elasticity and Prony series approach are manipulated. To solve the numerical problem, dynamic explicit solver option with sufficient solving amplitude has been used. Prony series have been used to model the core time-dependent behavior. In conjunction with a simple indentation experiment, FEM used to formulate a novel method for finding the Prony series coefficients. By performing some low-velocity impact experiments, the impact force and displacement of the composite sandwich plates have been investigated. The results indicate that increasing the structural damping increases the contact time and missing energy and decreases the stored energy of the system. The structures with composite face sheets have a minimum ratio of upper face sheet displacement to lower face sheet displacement in comparison to those with the isotropic face sheets. Impact behavior of isotropic face sheet specimens are more flattened than that of the composite face sheets. In addition, the specific energy stored in the sandwich plates with composite face sheets, on different supports, is greater than that stored in the aluminum face sheets.

This study addresses the effect of temperature and nanoparticle on PS foam structure in order to control its structure more accurately. For this purpose, a theoretical hypothesis was proposed by explaining the classical nucleation theory. The PS in the presence of nanosilica and CO2 was foamed. Foaming process was carried out in a vessel suitable under high pressure and temperature conditions, and with instantaneous pressure release and high-speed stabilization capabilities. The most important factors affecting foam properties including foaming temperature, size, content and surface properties of nanosilica were investigated. Increasing of foaming temperature was effective on the initial nuclei formation and cell growth. These two effects determined the final foam structure. When the temperature was changed from 90 to 180°C, cell density of PS foam increased thousand fold to 2.2×1012 number of cells per unit volume of foam (cell/cm3). The results showed that a small amount of nanosilica had a substantial effect on decreasing the cell size and increasing the cell density. An increase in nanoparticle concentration also increased its effectiveness. Moreover, the quality and structure of foam were improved by adding the nanoparticle. As the size of nanosilica increased from 20 to 40 nm, its cell density decreased from 3.3×109 to 1.78×109 numbers of cells per unit volume of foam (cells/cm3). Surface treatment of the nanosilica using triethoxysilane, in addition to improving nanoparticle dispersion, increased its cell density. The efficiency of nanosilica in improving cell density after surface treatment increased by more than double.

Silk fibroin (SF) as an important natural polymer has been extensively used as a suitable matrix in controlled drug release systems because of its biocompatibility feature, slow degradation rate and unique mechanical properties. In this study, a new β-cyclodextrin/silk fibroin nanofibrous membrane (β-CD/SF) with the function of molecular capture was successfully prepared by electrospinning of homogeneous solutions of β-CD and SF in formic acid. The effects of cyclodextrin on the nanofibers properties and its drug release properties were investigated. The morphology, microscopic structure, chemical composition and heat treatment of the β-CD/SF nanofibrous membrane were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Scanning electronic microscopy images showed that defect free mats with a uniform structure were generated, and the average diameter of the nanofibers was mainly affected by weight ratio of the blend. The result revealed that increasing the β-CD content in the blends lowered the average fiber diameter. In this report these observations are discussed with respect to the viscosity data of the electrospinning solutions which have been decreased with increasing β-cyclodextrin concentration. Differential scanning calorimetry results showed that drug was loaded into the β-cyclodextrin cavities. In vitro drug delivery profile of salicylic acid, as a drug model, was examined by UV spectroscopy at body temperature (37˚C) in phosphate buffer saline (pH 7.4). The molecular capturing ability of β-cyclodextrin /silk fibroin composite was improved with the amount of β-cyclodextrin in composite nanofibrous membrane which resulted in lower drug release.