Heat-treated PVA Research Articles

Study on Stabilized of Poly(Vinyl Alcohol) Nanofibers Based Sandwich Structure Purification Material

PVA nanofibers are generally required to be modified because of its poor stability in water. The water stability of PVA nanofibers was improved by heat treatment in this paper. The DSC test results showed that the crystallinity of heat-treated PVA nanofibers at 150°C for 10 min reached the maximum which increased by 12% compared with PVA nanofibers. From the SEM images it was observed that the heat-treated fibers didn’t dissolve in water but showed certain degree of agglutination and swelling. PVA nanofibers were taken as the inner layer of the sandwich structure purification material prepared with the hot pressing technology. The filtering experiments showed that the filtration properties were better when the area density of PVA nanofibers was 2.5 g/m2.

Cellular response to poly(vinyl alcohol) nanofibers coated with biocompatible proteins and polysaccharides

A PVA nanofibrous matrix was prepared by electrospinning an aqueous 10wt% PVA solution. The mean diameter of the PVA nanofibers electrospun from the aqueous PVA solution was 240nm. The water resistance of the as-spun PVA nanofibrous matrix was improved by physically crosslinking the PVA nanofibers by heat treatment at 150°C for 10min. In addition, the heat-treated PVA nanofibrous matrix was coated with biocompatible polysaccharides (chitosan (CHI) or hyaluronic acid (HA)) and proteins (collagen (COL) or silk fibroin (SF)) to construct biomimetic nanofibrous scaffolds. The coating of proteins or polysaccharides on the PVA nanofibrous matrix was confirmed by ATR-IR spectra, and the degree of coating was determined by elemental analysis based on nitrogen content. The coated PVA matrices exhibited less hydrophilicity, except for the HA coating, and better tensile properties than the pure PVA nanofibrous matrix. The increase in tensile properties was due to interfiber bonds formed by the coating. The effect of protein and polysaccharide coating on normal human keratinocytes (NHEKs) and fibroblasts (NHEFs) was examined by cytocompatibility assessment in vitro. Among the CHI-, COL-, HA- and SF-coated PVA matrices, the SF-coated PVA nanofibrous matrix was found to be the most promising scaffold for the attachment and spreading of NHEKs and NHEFs as compared to the pure PVA matrix. This approach to controlling the surface properties of nanofibrous structures with SF may be useful in the design and tailoring of novel matrices for skin regeneration.

Membrane Separation of Ethanol from Mixtures of Gasoline and Bioethanol with Heat-Treated PVA membranes

The pervaporation performance of heat-treated PVA membranes with varying degrees of saponification was examined for the separation of ethanol from mixtures with n-heptane, which simulates the on-bo...

Epidermal cellular response to poly(vinyl alcohol) nanofibers containing silver nanoparticles

A heat-treated PVA nanofibrous matrix containing silver (Ag) was prepared by electrospinning an aqueous 10 wt% PVA solution and followed by heat treatment at 150 °C for 10 min. The average diameter of the as-spun and heat-treated PVA nanofibers was 330 nm. The heat-treated PVA nanofibrous matrix containing Ag was irradiated with UV light to transform the Ag ions in the nanofibrous matrix into Ag nanoparticles. The in vitro cytotoxicity of the Ag ions and/or nanoparticles on normal human epidermal keratinocytes (NHEK) and fibroblasts (NHEF) cultures was examined. The PVA nanofibrous matrix containing Ag showed slightly higher level of attachment and spreading in the early stage culture (1 h) than the PVA nanofibers without Ag (control). However, compared with the PVA nanofibers without Ag, the heat-treated and UV-irradiated PVA nanofibers, containing mainly Ag ions and nanoparticles, respectively, showed reduced cell attachment and spreading. This shows that both Ag ions and Ag nanoparticles are cytotoxic to NHEK and NHEF. There was no significant difference in cytotoxicity to NHEK and NHEF between Ag ions and Ag nanoparticles. NHEF appeared to be more sensitive to Ag ions or particles than NHEK. In addition, the residual nitrate ions (NO 3 −) in the PVA nanofibers had an adverse effect on the culture of both cells.

Electrospun poly(vinyl alcohol) nanofibers: effects of degree of hydrolysis and enhanced water stability

The effects of the degree of hydrolysis (DH) of poly(vinyl alcohol) (PVA) on electrospinning and water resistance of electrospun PVA/poly(acrylic acid) (PAA) composite fibers were explored. At a constant concentration of PVA solution (∼8wt%), the average diameter of electrospun PVA fibers increased with increasing DH. The water resistance of heat-treated PVA/ PAA composite fibers was dramatically enhanced, and was also affected by PAA weight fractions (φPAA) in PVA/PAA blend solutions.

Chitosan‐coated poly(vinyl alcohol) nanofibers for wound dressings

A PVA nanofibrous matrix was prepared by electrospinning an aqueous 10 wt % PVA solution. The mean diameter of the PVA nanofibers electrospun from the PVA aqueous solution was 240 nm. The water resistance of the as-spun PVA nanofibrous matrix was improved by physically crosslinking the PVA nanofibers by heat treatment at 150 degrees C for 10 min, which were found to be the optimal heat treatment conditions determined from chemical and morphological considerations. In addition, the heat-treated PVA (H-PVA) nanofibrous matrix was coated with a chitosan solution to construct biomimetic nanofibrous wound dressings. The chitosan-coated PVA (C-PVA) nanofibrous matrix showed less hydrophilic and better tensile properties than the H-PVA nanofibrous matrix. The effect of the chitosan coating on open wound healing in a mouse was examined. The C-PVA and H-PVA nanofibrous matrices showed faster wound healing than the control. The histological examination and mechanical stability revealed the C-PVA nanofibrous matrix to be more effective as a wound-healing accelerator in the early stages of wound healing than the H-PVA nanofibrous matrix.

Improvement of the water resistance of atactic poly(vinyl alcohol) nanowebs by a heat treatment

Nanoscale materials can be rationally designed to exhibit significantly changed physical, chemical, and biological properties because of the extremely small dimensions. Therefore, atactic poly(vinyl alcohol) (a-PVA) nanowebs by an electrospinning technique have very high water solubility because of their nanoscale in comparison with microscale materials such as fibers and films. In this study, a-PVA nanowebs were prepared via electrospinning under suitable conditions to form PVA webs with uniform nanofibers (fiber average diameter = 200 ± 50 nm), not a bead or bead-and-string morphology. Furthermore, to improve the water resistance of the water-soluble a-PVA nanowebs, the PVA nanowebs were heat-treated at various heat-treatment temperatures. The melting temperature of the heat-treated PVA nanowebs shifted toward a lower temperature with an increase in the heat-treatment temperature, and this indicated that micronetwork domains formed. Moreover, with the exception of a PVA nanoweb treated at an excessive heat-treatment temperature, the heat-treated PVA nanowebs showed higher crystalline and mechanical properties than a pure PVA nanoweb. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Studies On The Crosslinking Of Poly (Vinyl Alcohol)

This paper is concerned with the cross-linking of poly(vinyl alcohol) (PVA) using maleic acid as the cross-linker. The curative (maleic acid) dose and the curing temperature and time were varied between 2.5 and 60% (w/w), 120 and 160 °C and 30 and 120 min, respectively. From a thorough swelling study in both hot and cold water (percentage swelling, gel content, swelling ratio, etc-) the optimum curative dose and curing conditions have been evaluated. The molecular weight between the cross-links exhibited a sharp fall up to a maleic acid dose of 20% (w/w). A comparative evaluation of maleic acid cross-linked and heat-treated PVA films has been done. Better heat stability for maleic acid cross-linked PVA was observed from thermogravimetric analysis. A shift in glass transition temperature was observed for both heat-treated and maleic acid treated PVA compared with the virgin one. IR spectroscopic study indicated the presence of an ester linkage and an olefinic double bond in maleic acid treated and heat-treated PVA films, respectively. Maleic acid cross-linked PVA is quite stable in different polar and nonpolar solvents. A definite structural pattern has been observed in maleic acid cross-linked PVA films through scanning electron microscopy.

Semicrystalline poly(vinyl alcohol) ultrafiltration membranes for bioseparations

Semicrystalline poly(vinyl alcohol) (PVA) ultrafiltration (UF) membranes were fabricated for use in bioseparations to separate small molecular weight solutes from macromolecules. PVA was chosen because of its hydrophilic nature and these membranes are expected to minimize membrane fouling due to protein adsorption. The membranes were annealed at temperatures above the polymer’s glass transition temperature to crystallize them in order to improve their mechanical properties. The degree of crystallinity of these membranes was measured using differential scanning calorimetry. Studies were conducted to measure the selectivity of separation of two different sized solutes using these membranes. These studies showed that heat-treated PVA membranes had a higher selectivity compared to the untreated PVA membranes. The effects of heat treatment, stirring speed, membrane thickness, average molecular weight of PVA and the addition of Pluronic ® F127 and Pluronic ® F68 on the separation of fluorescein isothiocyanate-dextran and myoglobin from l-tryptophan were studied. The mechanical strength of heat-treated PVA membranes and the selectivity of separation of these membranes were compared with commercial polyethersulfone (PeS) membranes. Mechanical studies using dynamic mechanical analysis showed that the tensile modulus of commercial PeS membranes was significantly higher than the heat-treated PVA membranes that were swollen in deionized water for 1 and 5 h. However, the compressive moduli of PVA membranes were found to be of the same order as the compressive moduli of PeS membranes. The tensile and compressive moduli of heat-treated PVA/1% (w/v) Pluronic ® F127 membranes were considerably lower than PeS and PVA membranes. It was found that the PVA membranes were more resistant to fouling than the PeS membranes.

Rate Constants of the Photodegradation and Photoisomerization of Polyenes Produced in Heat-Treated PVA Film

Abstract The rate constants of two parallel reactions, photodegradation and photoisomerization of polyenes,n with n = 2–5, produced in heat-treated PVA film are estimated by an analysis of the spectral changes on monochromatic irradiation (200–250 nm). The rate constants for isomerization is found to be ten times as large as that of degradation.H=CH

Dichroism analysis of polyenes produced in heat-treated PVA

Dichroism analysis of polyenes produced in PVA films was carried out for films stretched (at 80°C) after heat treatment (at 170°C) and films heat-treated after stretch. The relation between R s (stretch ratio of the film) and R d, n (dichroic ratio of n conjugated polyene) in the former case fitted the theoretical curves, but in the latter, high R d, n values regardless of R s were observed. Stretching of the film might promote both polyene formation and cross-linking dehydration, especially on the segments oriented in the stretch direction.

Absorption coefficients of polyenes in heated poly(vinyl alcohol) film and distribution of polyenes formed by its photodegradation

The absorption coefficients of polyenes (CHCH) n with n = 2–5 in heat-treated poly(vinyl alcohol) (PVA) film were determined approximately by the analysis of selective photodegradation. The distribution of polyenes formed by photodegradation of the heat-treated PVA film was estimated using the absorption coefficients obtained. It indicated that the reactivity of the terminal double bond of polyenes decreased as the conjugation number increased.

Assignment of Conjugate Double Bond Systems Produced in Heated PVA Film by Absorption and Excitation Spectra

Abstract Absorption, emission and excitation spectra of heat-treated PVA film have been interpreted as corresponding to mixtures of –(CH=CH)n– and –(CH=CH)n–CO–, which are distinguishable from each other according to whether spectrum is accompanied with fine structures or not. The former shows fine structures and has had n determined to be 2–14 by analysis of peak locations on the basis of linearity for Lewis-Calvin’s plot. For the latter, n has been determined to be 1–7, and Lewis-Calvin’s plot between the wavelength of band maximum and n also shows a good linearity.

EXCITATION SPECTRA OF HEAT-TREATED POLY(VINYL ALCOHOL) FILM

Abstract Among species of general structure (\( \llap–CH=CH \llap–)\)n produced in the heat-treated PVA substrate, the existence of polyene systems with n=2 to 5 were successfully confirmed by means of the excitation spectra and the Lewis–Calvin’s plot.

CARBAMOYLETHYLATION OF POLYVINYL ALCOHOL FIBFRS WITH ACRYLAMIDE

The partial carbamoylethylation of polyvinyl alcohol fibers with acrylamide was studied, using the aqueous solution or curing method. Suitable reaction conditions are as follows;For the aqueous solution method, -AM/PVA mol ratio 0.6, AM concentration 30g/l, Na2SO4 25%, Na3PO4 2%, 60°C, 4hr.For the curing method, -composition of impregnating solution; AM 35%, NaOH 7%curing condition; 120°C, 5min.Under both conditions, the, value of the degree of substitution was 2_??_4 mol%, for the unheated and heat-treated PVA fibers.From the improvement of elastic recovery by the formalization of partial carbamylethylated fibers, a certain degree of intermolecular cross-linking is deduced. Also, The Mannich reaction was observed when the amine treatment of partial carbamoylethylated fibers was caried out.The affinities for some dyestuffs of these after-treated fibers are improved, and especially good result is obtained for dimethylamine-treated and then formalizee fibers.