Wen-Yen Chiu

Properties of the poly(vinyl alcohol)/chitosan blend and its effect on the culture of fibroblast in vitro

In this work, the properties of poly(vinyl alcohol) (PVA) and PVA/chitosan blended membranes were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and electron spectroscopy for chemical analysis (ESCA). The SEM photographs show the PVA/chitosan blended membrane undergoes dramatic changes on the surface and bulk structure during the membrane formation. The DSC analysis shows that PVA and chitosan are not very compatible in the PVA/chitosan blended membrane, whereas the combination of two polymer chains of constitutionally different features is revealed. In addition, the surface of the PVA/chitosan blended membrane is enriched with nitrogen atoms at the ESCA analysis. These reflect the PVA membrane can be modified by blending with chitosan that in turn may affect the biocompatibility of the blended membrane. Therefore, adhesion and growth of fibroblasts on the PVA as well as PVA/chitosan blended membranes were investigated. Cell morphologies on the membranes were examined by SEM and cell viability was studied using MTT assay. It was observed that the PVA/chitosan blended membrane was more favorable for the cell culture than the pure PVA membrane. Cells cultured on the PVA/chitosan blended membrane had good spreading, cytoplasm webbing and flattening and were more compacting than on the pure PVA membrane. Consequently, the PVA/chitosan blended membrane may spatially mediate cellular response that can promote cell attachment and growth, indicating the PVA/chitosan blended membrane should be useful as a biomaterial for cell culture.

Free radical degradation of chitosan with potassium persulfate

A thermal dissociation initiator, potassium persulfate (KPS), is added to the chitosan solution at 70 � C; immediately, the solution viscosity and the molecular weight of chitosan decrease in a very short time. Size exclusion chromatography, nuclear magnetic resonance and electron spin resonance were used to study the degradation mechanism. A free radical degradation mechanism of chitosan by KPS is then proposed. When KPS is thermally dissociated into anionic radicals, they are attracted to the cationic amino group in the chitosan ring. Subsequently, the anionic radical attacks the C-4 carbon and transfers the radical to the C-4 carbon by subtracting the hydrogen from it. The presence of free radical at C-4 carbon eventually results in the breakage of the glycosidic C– O–C bond in the chitosan main chain. According to this mechanism, the concentrations of KPS, total free radicals and the degraded chitosan chain at different degradation times are all calculated by solving the rate equations. Finally, the calculated average molecular weights of the degraded chitosan chains at different reaction times agree with the experimental values. # 2001 Elsevier Science Ltd. All rights reserved.

The effect of polymeric additives on the structure and permeability of poly(vinyl alcohol) asymmetric membranes

Abstract The manufacture and dextran-rejection properties of asymmetric poly(vinyl alcohol) (PVA) membranes have been described in this study. Membranes were prepared from a casting solution of PVA, water as solvent, and water-soluble polymeric additive by immersing them in Na 2 SO 4 /KOH/H 2 O as coagulant medium. Experiments showed that the dextran and poly(vinyl pyrrolidone) (PVP) additives exerted a different influence on the structure and permeability of membranes. Especially, the structure of skin layer strongly depended on the polymeric additives in the casting solution. The addition of dextran additives in the system could induce pores in the top layer. Conversely, the PVP additives effectively blocked the interstitial cavities within the top layer to generate a more compact structure. A mechanism describing that the affinity between additive and casting solution as well as between additive and coagulant medium was proposed to investigate the effect of dextran and PVP additives in the formation of PVA membranes. The results presented here offer a better understanding of relationships between the membrane formation mechanism and the skin structure when designing an asymmetric membrane by the addition of polymeric additives in the casting solution.

Ultrasonic spray pyrolysis for nanoparticles synthesis

This article presents new findings regarding the effects of precursor drop size and precursor concentration on product particle size and morphology in ultrasonic spray pyrolysis. Large precursor drops (diameter > 30 μm) generated by ultrasonic atomization at 120 kHz yielded particles with holes due to high solvent evaporation rate, as predicted by the conventional one particle per drop mechanism. Precursor drops 6–9 μm in diameter, generated by an ultrasonic nebulizer at 1.65 MHz and 23.5 W electric drive power, yielded uniform spherical particles 90 nm in diameter with proper control of precursor concentration and residence time. Moreover, air-assisted ultrasonic spray pyrolysis at 120 kHz and 2.3 W yielded spherical particles about 70% of which were smaller than those produced by the ultrasonic spray pyrolysis of the 6–9 μm precursor drops, despite much larger precursor drop size (28 μm peak diameter versus 7 μm mean diameter). These particles are much smaller than predicted by the conventional one particle per drop mechanism, suggesting that a gas-to-particle conversion mechanism may also be involved in spray pyrolysis.

The curing reaction and physical properties of DGEBA/DETA epoxy resin blended with propyl ester phosphazene

The influences of different amounts of propyl ester phosphazene (FR) on the curing kinetics and physical properties of diglycidyl ether of bisphenol A (DGEBA) epoxy prepolymer cured with diethylenetriamine (DETA) were investigated with DSC, SEM, DMA, and tensile testing. The results revealed that FR could be a catalyst or a diluent depending on the FR content. In addition, the blending systems were partially miscible. The tensile strength and modulus of blends decreased with increasing amounts of FR, but the elongation increased with increasing FR.

Kinetic model of thermal degradation of polymers for nonisothermal process

A new kinetic model was developed to describe the thermal degradation behavior of polymers. The model was applied to predict the degradation of poly(methyl methacrylate) (PMMA) blended with propyl ester phosphazene (FR). The results showed that the thermal degradation mechanism of pure PMMA was dominated by zero- and first-order reactions. For PMMA blended with FR, the thermal degradation mechanism was dominated by first- and second-order reactions due to the formation of anhydride from the ester groups of PMMA. In addition, the major thermal degradation temperature of blends was greater than pure PMMA. By using our model, the activation energy of the thermal degradation PMMA was calculated to be 180 kJ/mol; this activa- tion energy increased as FR was added to PMMA. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1855-1868, 1997

Fullerene bisadduct as an effective phase-separation inhibitor in preparing poly(3-hexylthiophene)–[6,6]-phenyl-C61-butyric acid methyl ester blends with highly stable morphology

This work demonstrates that the bis-adduct of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is an effective inhibitor of the aggregation of PCBM inside the poly(3-hexylthiophene) (P3HT) matrix. Substituting some of the PCBM with bis-PCBM apparently reduces the size of PCBM-rich clusters, enhancing both the short-circuit current density (JSC) and the fill factor (FF), leading to a ∼17% increment in power conversion efficiency (PCE) for a cell with 8.3 wt% bis-PCBM replacement. More importantly, a tiny amount of bis-PCBM significantly improves the morphological stability of P3HT–PCBM blend against high-temperature aging. All P3HT–PCBM:bis-PCBM devices exhibit extremely stable PCEs, which do not visibly change upon heating at 150 °C for 15 hours.

Thermal degradation behavior and flammability of polyurethanes blended with poly(bispropoxyphosphazene)

Polyurethanes containing different amount of flame retardant, poly(bispropoxyphosphazene), were synthesized by a two-step polymerization. The thermal degradation behaviors of these polyurethanes were then studied by the thermal gravimetric analysis (TGA), TGA coupled with Fourier transform infrared analysis and elemental analysis. A limiting oxygen index was used to evaluate the flammability of these polyurethanes. For these modified polyurethanes under nitrogen, a two-stage thermal degradation behavior was observed. The first stage was caused by the degradation of hard segments, whereas the soft segments were responsible for the second-stage degradation. The thermal degradation activation energies were calculated by using Ozawas method. It was found that the addition of flame retardant caused a decrease of the activation energy in the first stage, but an increase in the second stage, which was probably due to the formation of a thermal stable structure. As for the flame retardancy, the modified polyurethanes have a higher char yield at 550°C, and a higher limiting oxygen index than the neat polyurethane.

Kinetics study of imidazole-cured epoxy-phenol resins

The reaction kinetics of diglycidyl ether of bisphenol A (DGEBA) cured with different concentrations of imidazole and bisphenol A (BPA) were investigated by using differential scanning calorimetry. Both dynamic and isothermal DSC were stud- ied. Two initiation mechanisms were found to play roles in the curing reactions. One was based on adduct formation of epoxy groups with pyridine-type nitrogen and the other was based on ionic complexes of imidazole and BPA. The subsequent propagation was composed of three main reactions, viz. the epoxide/phenol reaction, the acid/base reaction, and the epoxide/R-O 2 reaction. A generalized kinetics model was developed and used to predict the conversion of epoxide groups using a wide range of imidazole and BPA concentrations, and cure temperature.

The effect of acetic acid on the structure and filtration properties of poly(vinyl alcohol) membranes

Abstract The role played by acetic acid in the formation of poly(vinyl alcohol) (PVA) membranes was investigated. Membranes were prepared from a casting solution of PVA, water, and acetic acid by immersion in Na 2 SO 4 /KOH/H 2 O coagulation bath. Experimental results show that the acetic acid additive exerts an influence on the structure and filtration properties of membranes. Not only the surface morphology but also the structure of cross-section could be modulated by adding the acetic acid in the casting solution. Obviously, the increase of the amount of acetic acid in the casting solution decreased the thickness of skin layer. This could be attributed to the fact that the increase of the amount of acetic acid in the casting solution increases H 3 O + ion of the casting solution enhancing the influx rate of coagulant medium for acid-base equilibrium. A mechanism describing the affinity between the PVA solution and the coagulant medium is proposed to estimate the PVA membrane structure by adding the acid. The results presented here offer a better understanding of relationships between the membrane formation mechanism and the skin structure when designing an asymmetric membrane with acetic acid as an additive.