Fabrication and Optimization of Poly(vinyl alcohol)/Zirconium Acetate Electrospun Nanofibers Using Taguchi Experimental Design

This paper presents an investigation regarding poly(vinyl alcohol)/zirconium acetate (organic–inorganic) (PVA/Zrace) nanofibers prepared by electrospinning which could be used as a precursor for fabricating ceramic metal oxide nanofibers. The effect of some processing variables, including polymer solution concentration, tip to collector distance and applied voltage of electrospinning, and the amount of Zrace and their interactions, on the diameter of the nanofibers were studied. Taguchi experimental design and a statistical analysis (ANOVA) were employed and the relationship between experimental conditions and yield levels determined. It was concluded that to obtain a narrow diameter distribution as well as maximum fiber fineness, a polymer concentration of 10 wt%, tip to collector distance of 18 cm and applied voltage of 20 kV variables were the optimum. Furthermore, it was also concluded that the ratio of Zrace (6 g) to PVA solution (10% wt) played an important role for achieving the minimum fiber diameter. Under these optimum conditions, the diameters of the electrospun composite fibers ranged from 86 nm to 381 nm with a diameter average of 193 nm. The experiments were done with Qualitek-4 software with “smaller is better” as the quality characteristics. The optimized conditions showed an improvement in the fibers diameter distribution and the average fibers diameter showed good resemblance with the result predicted using the Taguchi method and the Qualitek-4 software. The ANOVA results showed that all factors had significant effects on the fibers diameter and distribution, but the effect of PVA concentration and zirconium acetate were more significant than the other factors.     

Studies on Poly(Dialkoxyphosphazenes) for the Medical Applications

Abstract

The presence of trace of chlorine in poly(diorganophosphazenes) [-N=P(OR)2-]., where R = C₂H₅, CH₂CF₃, C₂F₅, C₄H₅, C₆H₁₃, C₈H₁₇, C₁₂H₂₅, CH₂C₆H₅ in many cases leads to the substantial changes of their physicochemical properties and limits application possibilities of this class of polymers especial for the medical materials. Despite the optimization of reaction conditions for each nucleophilic alkoxy substituent, the obtained poly(dia1koxyphosphaenes) exhibited some physicochemical anomalies.     

Highly improved crystallization behavior of poly(L‐lactide) induced by a novel nucleating agent: substituted‐aryl phosphate salts

In this work, a novel nucleating agent (NA) based on substituted‐aryl phosphate salts was introduced into poly(L‐Lactide) (PLLA). The nonisothermal and isothermal crystallization behaviors of nucleated PLLA samples were investigated through differential scanning calorimetry (DSC), wide angle X‐ray diffraction, and polarized optical microscope (POM). Furthermore, the effect of annealing treatment on the cold crystallization behaviors of nucleated samples was also investigated. The results show that the crystallization of PLLA, whether for the melt crystallization (including nonisothermal and isothermal crystallization process) or for the cold crystallization (including the cold crystallization occurring during the DSC heating process and during the annealing process), is greatly dependent upon the content of NA. At relatively lower NA content (≤0.1 wt%), the nucleation effect of NA is inconspicuous, however, at higher NA content (≥0.2 wt%), it exhibits great nucleation effect for the crystallization of PLLA. Further results show that the double endothermic peak of PLLA depends on the temperature applied for the crystallization. Copyright © 2012 John Wiley & Sons, Ltd.     

Anti‐static Agent Containing Zinc Oxide and its Modification for PA6 Fiber

A new anti‐static agent was synthesized from zinc oxide‐adipic acid‐polyethylene glycol and caprolactam by three‐step reactions. The antistatic agent (called poly(ether ester amide zinc oxide) or PEEAZ) was analyzed by IR and DSC. The results showed that zinc oxide existed in the main chain of PEEAZ. The glass temperature and melt temperature of poly(ether ester amide zinc oxide) (referred to as PEEAZ in the following) decreased with increasing poly(ether ester zinc oxide) increasing in PEEAZ. Antistatic PA6 fiber was obtained by adding PEEAZ 2–8% (wt/wt) to PA6 during blend spinning. The specific resistance and the static half‐value period of PA6 fiber was less than 10⁹Ω · cm and 60 sec, respectively. Excellent antistatic property remained after being washed 30 times.     

Cure Kinetics of Poly(acrylonitrile-butadiene-styrene) Modified Epoxy–Amine System

The cure kinetics of epoxy based on the diglycidyl ether of bisphenol A (DGEBA) modified with different amounts of poly(acrylonitrile-butadiene-styrene) (ABS) and cured with 4,4′-diaminodiphenylsulfone (DDS) was investigated by employing differential scanning calorimetry (DSC). The curing reaction was followed by using an isothermal approach over the temperature range 150–180°C. The amount of ABS in the blends was 3.6, 6.9, 10 and 12.9 wt%. Blending of ABS in the epoxy monomer did not change the reaction mechanism of the epoxy network formation, but the reaction rate seems to be decreased with the addition of the thermoplastic. A phenomenological kinetic model was used for kinetic analysis. Activation energies and kinetic parameters were determined by fitting the kinetic model with experimental data. Diffusion control was incorporated to describe the cure in the latter stages, predicting the cure kinetics over the whole range of conversion. The reaction rates for the epoxy blends were found to be lower than that of the neat epoxy. The reaction rates decreased when the ABS contents was increased, due to the dilution effect caused by the ABS on the epoxy/amine reaction mixture.     

Kinetic Investigation of Poly(ethylene glycol) Hydrogel Formation via Perfusion‐Based Frontal Photopolymerization: Influence of Free‐Radical Polymerization Conditions on Frontal Velocity and Swelling Gradients

Poly(ethylene glycol) diacrylate (PEGDA) hydrogels are extensively used as scaffolds in tissue engineering. The ability to spatially control hydrogel properties is critical for designing scaffolds that direct cell behavior and tissue regeneration. To this end, we have recently developed a polymerization technique, perfusion‐based frontal photopolymerization, to generate tunable gradients in PEG hydrogels. This study explores the effects of polymerization conditions on the velocity of the propagating front and its influence on gradients in hydrogel swelling. Alterations in photoinitiator perfusion rate result in the largest variations in frontal velocity and in the magnitude of the swelling gradient among all polymerization conditions investigated.

     

Novel Method for Soluble‐Polymer‐Supported Synthesis of 3,4,5‐Trisubstituted Isoxazoles

A practical and efficient liquid‐phase synthesis of 3,4,5‐trisubstituted isoxazoles using poly(ethylene glycol) as supported is described. Soluble‐polymer‐supported nitrile oxide generated in situ reacted with chalcones to afford polymer‐supported isoxazolines, which were cleaved by sodium methoxide to generate 3,4,5‐trisubstituted isoxazoles instead of 3,4,5‐trisubstituted isoxazolines. This sequential process provided a novel method to synthesize 3,4,5‐trisubstituted isoxazoles.     

Modification and Application of Poly(Ethylene Terephethalate) Nonwoven Fiber Using Octadecyl Acrylate and Acrylic Acid as Oil Sorbers

Three series of crosslinked octadecyl acrylate and acrylic acid copolymers were prepared through suspension copolymerization based on acrylic acid content (10, 30, 50%wt. ratio). Divinyl benzene (DVB) was used as a crosslinker with different weight ratios (1, 4 and 10%). Isopropyl alcohol or dioctyl phthalate and methyl benzoate were used as two different reaction solvents in the presence of ABIN as initiator. The prepared crosslinked copolymers were characterized by SEM, TGA and FTIR spectroscopic analyses. The prepared polymers were coated onto poly(ethylene terephethalate) nonwoven fiber (NWPET). The effect of copolymerization feed composition, crosslinker wt% and reaction media or solvent on swelling properties of crosslinked polymers were studied through the oil absorption tests in toluene and 10% of diluted crude oil with toluene. It was noticed that the maximum swelling of crosslinked copolymers was increased from 30 to 100 g/g after grafting of copolymers onto NWPET.     

The State of NaOH in NaOH/Poly(Sodium Acrylate) Composite

NaOH/poly(sodium acrylate) composites were prepared by in situ polymerization of acrylic acid with an overneutralization level by adding excess NaOH. The composites were studied by XRD, IR and ²³Na MAS NMR spectroscopy. The results showed that the high neutralization degree (>100%) may lead to a complete polymerization. Both XRD and ²³Na MAS NMR spectra did not show any peaks of phase-separated NaOH or Na₂CO₃ until the neutralization degree was up to 217.5%. It can be presumed that the aggregates of Na⁺ ions can contain approximately two Na⁺ units for every carboxyl group before the phase separation.