Band 15, Heft 2

In this study, biodegradable microparticles of silk fibroin (SF)/chitosan (CS) blends with SF/CS blend ratios of 1:0, 2:1, 1:1, 1:2 and 0:1 (w/w) were prepared using the water-in-oil emulsification-diffusion method without any surfactants. An aqueous SF/CS blend solution and ethyl acetate were used as the water and oil phases, respectively. The plain SF had an irregular shape, while the CS microparticles were spherical. The blend microparticles were spherical in shape with a rough surface. Average microparticle sizes were in the range of 73–80 μm. The microparticle matrices had a sponge-like morphology. Conformational changes in the SF component, from random coil to the β-sheet form, were observed in the FTIR data. The dissolution of the blend microparticles was lower than those of the plain SF and CS microparticles. Microparticle density steadily increased and porosity slightly decreased as the amount of CS in the blend increased.

Atom transfer radical dispersion polymerization of acrylamide was successfully performed in ethyl acetate/ethanol with 2,2-azobisisobutyronitrile/FeCl 2 /succinic acid as the initiating system. Polyvinylpyrrolidone was used as the stabilizer. The “living” characteristics of the polymerization were studied. A linear relationship of ln([M] 0 /[M]) vs. polymerization time was obtained. Furthermore, the molecular weight increased with monomer conversion and agreed well with the theoretical values with a narrow molecular weight distribution (<1.5). Size-controlled submicrometer polyacrylamide (PAM) was obtained and characterized by transmission electron microscopy. The chemical structure of the obtained PAM was characterized by 1 H NMR. The living characteristics were confirmed by chain extension experiment.

Poly(acrylamide-co-acrylic acid)-spirulina (AAm-AAc-Sp) hydrogels were prepared by free radical solution polymerization of the monomer acrylamide (AAm) and the comonomer acrylic acid (AAc) with N , N -methylene bisacrylamide (BAAm) as the crosslinker in the presence of spirulina (Sp), which is a microalga species. The swelling ratios of the hydrogels were followed by gravimetric measurements. Hence, swelling kinetics and diffusion parameters were determined. Furthermore, the morphological structures and mechanical behaviors of the hydrogels were investigated by scanning electron microscopy and by using a uniaxial compression machine, respectively. All the results showed that spirulina had strong influence in the pH-dependent swelling behavior, as well as on the kinetic and diffusion parameters due to its interaction with the acrylic acid units. These interactions were attributed to spirulina, which caused a change in pore size and its distribution. The present novel hydrogels showed high swelling at neutral pH, but collapsed slowly at low and high pH values. Thus, these AAm-AAc-Sp hydrogels can be good candidates for pH-sensitive drug delivery systems.

Polyaniline (PANI) nanorods grown on layered porous graphitic carbon nitride (porous g-C 3 N 4 ) sheets (porous g-C 3 N 4 /PANI) were successfully synthesized by interfacial polymerization of aniline monomers in the presence of porous g-C 3 N 4 sheets. The experimental results suggest that porous g-C 3 N 4 obtained a good dispersion with intercalated and exfoliated nanostructure and interfacial adhesion in PANI, which improved the thermal stability and photocatalytic activity of the porous g-C 3 N 4 /PANI composites.

In this study, a polypropylene (PP) mesh was used to prepare proton- and Li + conducting composite membranes for fuel cells and lithium rechargeable batteries, respectively. For the preparation of Li + conducting membrane, polypropylene mesh was first immersed in an electrolyte solution, which was composed of LiBF 4 and ethylene carbonate. Then the swollen membrane was immersed in an acetone solution of polyethylene glycol diacrylate (PEGDA), polyvinylidenefluoride-co-hexafluoro-propylene and photoinitiator. Finally, PP fabric was taken out from the solution and exposed to UV irradiation. Furthermore, proton conducting membranes were prepared by immersing the PP mesh into a mixture of vinyl phosphonic acid, PEGDA and photoinitiator. Afterwards, samples were cured under UV light. PP-reinforced membranes designed for fuel cell applications exhibited a room temperature conductivity of 3.3×10 -3 mS/cm, while UV-cured electrolyte for Li batteries showed ionic conductivities in the range of 1.61×10 -3 –5.4×10 -3 S/cm with respect to temperature. In addition, for lithium-doped composite polymer electrolyte (CPE), the electrochemical stability window was negligible below 4.75 V vs. Li/Li + . It is concluded that lithium-doped CPE has suitable electrochemical stability to allow the use of high-voltage electrode couples.

The thermal conductivity of aerogel/epoxy composite based on the inexpensive powder form of silica aerogels by using water glass under ambient drying conditions was evaluated to investigate the relationship between the internal structure and the thermal conductivity of the composite. A high thermal conductivity was obtained for the composite fabricated by the typical liquid epoxy processing because the pores of the aerogels became filled with the epoxy resin during the processing of the composite. A new processing method for preserving the aerogel pores was then developed using ethanol evaporation, which lowered the thermal conductivity of the composite. The lowest thermal conductivity of 0.04 W/m K was obtained for the composite containing the as-received aerogel of 75 vol% with preserved pores. The preserved aerogel pores in the composite were the most significant physical factor in determining the thermal conductivity of the composite.

A low-emission catalyst for the preparation of flexible polyurethane (FPUR) foams was developed. Copper-amine complex solutions in ethylene glycol (EG), namely, Cu(OAc) 2 (en) 2 -EG and Cu(OAc) 2 (trien)-EG (en, ethylenediamine; trien, triethylenetetramine), were synthesized and used as catalysts for the preparation of FPUR foams. The synthesis of Cu(OAc) 2 (en) 2 -EG and Cu(OAc) 2 (trien)-EG is convenient because the synthesis of copper-amine complexes can be done in situ using ethylene glycol as a solvent and no purification step is needed. It was found that Cu(OAc) 2 (en) 2 -EG was a suitable catalyst for FPUR foam preparation. In comparison to Dabco EG (or triethylenediamine), which is a commercial catalyst for FPUR foam preparation, Cu(OAc) 2 (en) 2 -EG had a comparable catalytic activity in gelling reaction and a higher catalytic activity in blowing reaction. The FPUR foam prepared from Cu(OAc) 2 (en) 2 -EG had a lower density than that prepared from Dabco EG.

The purpose of this study was to investigate the validity of an artificial neural network (ANN) method in the prediction of nanofiber diameter to assess the parameters involved in controlling fiber form and thickness. A mixture of polymers including poly(vinyl alcohol) (PVA) and chitosan (CS) at different ratios was chosen as the nanofiber base material. The various samples of nanofibers were fabricated as training and testing datasets for ANN modeling. Different networks of ANN were designed to achieve the purposes of this study. The best network had three hidden layers with 8, 16 and 5 nodes in each layer, respectively. The mean squared error and correlation coefficient between the observed and the predicted diameter of the fibers in the selected model were equal to 0.09008 and 0.93866, respectively, proving the efficacy of the ANN technique in the prediction process. Finally, three-dimensional graphs of the electrospinning parameters involved and nanofiber diameter were plotted to scrutinize the implications.