ABSTRACT
In this study, nanofibers of poly (acrylic acid) (PAAc), polyacrylamide (PAAm) and poly (vinyl alcohol) (PVOH) were prepared using the electrospinning technique. Based on the Taguchi DOE (design of experiment) method, the effects of electrospinning parameters, i.e., needle tip to collector distance, polymer solution concentration, applied voltage, polymer solution feed rate and polymer type, on the diameter and morphology of polymer nanofibers were evaluated. Analyses of the experiments for the diameters of the polymer nanofibers showed that the type of polymer was the most significant factor. The optimal combination to obtain the smallest diameters with minimum deviations for electrospun polymer nanofibers was also determined. For this purpose, the appropriate factor levels were determined as follows: polymer PAAm, applied voltage 10 kV, delivery rate 0.1 mL/h, needle tip to collector distance 10 cm, and polymer solution concentration 8%, to obtain the thinnest nanofibers. This combination was further validated by conducting a confirmation experiment, and the average diameter of the polymer nanofibers was found to be close to the optimal conditions estimated by the Taguchi DOE method.
ABSTRACT
In this paper, novel microgels containing nano-SiO2 were prepared by in situ copolymerization using nano-SiO2 particles as a reinforcing agent, nanosilica functional monomer (silane-modified nano-SiO2) as a structure and morphology director, acrylamide (AAm) as a monomer, acrylic acid (AAc) as a comonomer, potassium persulfate (KPS) as a polymerization initiator, and N,N'-methylene bis (acrylamide) (MBA) as a crosslinker. In addition, a conventional copolymeric hydrogel based on poly (acrylamide/acrylic acid) was synthesized by solution polymerization. The microgel samples, hydrogel and nanoparticles were characterized by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). A FESEM micrograph of copolymeric hydrogel showed the high porosity and 3D interconnected microstructure. Furthermore, FESEM results demonstrated that when nano-SiO2 particles were used in the AAm/AAc copolymerization process, the microstructure and morphology of product changed from porous hydrogel to a nanocomposite microgel with cauliflower-like morphology. According to FESEM images, the copolymerization of AAm and AAc monomers with a nanosilica functional monomer or polymerizable nanosilica particle as a seed led to a microgel with core-shell structure and morphology. These results demonstrated that the polymerizable vinyl group on nano-SiO2 particles have controlled the copolymerization and the product morphology. FTIR analysis showed that the copolymeric chains of polyacrylamide (PAAm) and poly (acrylic acid) (PAAc) were chemically bonded to the surfaces of the nano-SiO2 particles and silane-modified nano-SiO2. The particulate character of microgel samples and the existence of long distance among aggregations of particles led to rapid swelling and increasing of porosity and therefore increasing of degree of swelling.
ABSTRACT
The effect of SiO2 nanoparticles on the formation of PAA (poly acrylic acid) gel structure was investigated with seeded emulsion polymerization method used to prepare SiO2/PAA nanoparticles. The morphologies of the nanocomposite nanoparticles were studied by transmission electron microscopy (TEM). Fourier-transform infrared (FTIR) spectroscopy results indicated that the PAA was chemically bonded to the surface of the SiO2 nanoparticles. Additionally, the resulting morphology of the nanocomposite nanoparticles confirmed the co-crosslinking role of the SiO2 nanoparticles in the formation of the 3D structure and hydrogel of PAA. SiO2/PAA nanocomposite hydrogels were synthesized by in situ solution polymerization with and without toluene. The morphology studies by field emission scanning electron microscopy (FESEM) showed that when the toluene was used as a pore forming agent in the polymerization process, a macroporous hydrogel structure was achieved. The pH-sensitive swelling behaviors of the nanocomposite hydrogels showed that the formation of pores in the gels structure was a dominant factor on the water absorption capacity. In the current research the absorption capacity was changed from about 500 to 4000 g water/g dry hydrogel. Finally, the macroporous nanocomposite hydrogel sample was tested as an amoxicillin release system in buffer solutions with pHs of 3, 7.2, and 9 at 37 °C. The results showed that the percentage cumulative release of amoxicillin from the hydrogels was higher in neutral and basic mediums than in the acidic medium and the amoxicillin release rate was decreased with increasing pH. Additionally, the release results were very similar to swelling results and hence amoxicillin release was a swelling controlled-release system.
