Low Molecular Weight PVA Research Articles

Effect of Poly(Vinyl Alcohol) Concentration and Chain Length on Polymer Nanogel Formation in Aqueous Dispersion Polymerization.

Nanotechnology has attracted increasing interest in various research fields for fabricating functional nanomaterials. In this study, we investigated the effect of poly(vinyl alcohol) (PVA) addition on the formation and thermoresponsive properties of poly(N-isopropyl acrylamide)-based nanogels in aqueous dispersion polymerizations. During dispersion polymerization, PVA appears to play three roles: (i) it bridges the generated polymer chains during polymerization, (ii) it stabilizes the formed polymer nanogels, and (iii) it regulates the thermoresponsive properties of the polymer nanogels. By regulating the bridging effect of PVA via changing the PVA concentration and chain length, the size of the obtained polymer gel particles was maintained in the nanometer range. Furthermore, we found that the clouding-point temperature increased when using low-molecular weight PVA. We believe that the knowledge gained in this study regarding the effect of PVA concentration and chain length on nanogel formation will aid in the future fabrication of functional polymer nanogels.

Chitosan/PVA Nanofibrous Membranes as Air Filter Material

Nanofiber membranes made of polymer materials are being extensively investigated and developed as air filter materials. This research aims to make and characterize the nanofiber membranes as filter materials capable of filtering gaseous pollutants from cigarette smoke. The electrospinning method manufactured the chitosan (CS)/PVA blend nanofiber membranes with CS/PVA ratios of (0/100, 20/80, 30/70, and 40/60 w/w) using low molecular weight (LMw) PVA and the ratios of (0/100, 10/90, 20/80, and 30/70 w/w) with high Mw (HMw) PVA. The CS concentration increased the CS-PVA solution‘s electrical conductivity and decreased the membrane‘s average fiber diameter and tensile properties. The filtration test on neat PVA and CS/LMw PVA (20/80) membranes set on the metallic substrate with a 0.08 mm hole size was conducted by varying membrane thickness (20, 35, and 45 µm). The filtration efficiency increased with the membrane thickness because membrane pores tend to be smaller, indicating that reducing the fiber diameter by adding CS increases pore size. The filtration test on CS/HMw PVA (20/80) membranes with 45 µm thickness on different substrate¢s hole sizes of (0.08, 1.19, and 1.41 mm) showed that the larger the hole size, the lower the filtration efficiency. By similar CS/PVA ratio, membrane thickness, and substrate size hole, the CS/HMw PVA's filtration efficiency (87.15%) is higher than CS/LMw PVA (85.79%). However, the CS/LMw PVA membrane showed higher tensile strength, low stiffness, and more economical air filtration material than CS/HMw PVA.

Effect of Vinyl Acetate Ethylene Emulsion Formulation and Poly (vinyl alcohol) Molecular Weight on the Quality of Inkjet Paper

The study aim was to evaluate the effect of mixing of a water-soluble polymer, poly (vinyl alcohol) (PVA), and an emulsion binder, vinyl acetate ethylene (VAE), on the properties of the coating color and to identify the factors affecting the design of the coating color formulation for inkjet paper. The test compositions of the coating color used PVA and VAE emulsion binders of different molecular weights, and the properties of the prepared coating color and coated paper were analyzed. As the mixing ratio of the VAE emulsion to PVA increased, the viscosity of the coating solution decreased, but when the mixing ratio was constant, the coating color using low-molecular weight PVA had low viscosity. As the VAE emulsion mixing ratio and PVA molecular weight increased, the contact angle of the coated papers increased, but the ink density of the coated paper decreased.

Pillared-bilayer metal-organic framework membranes for dehydration of isopropanol

Metal-organic frameworks (MOFs) possess ordered micropores with high variety in surface functionality, and are considered excellent candidates for membrane pervaporation. However, only very few successful examples of pure MOF membranes for pervaporation have been reported to date. In this work we report on an emerging pillared-bilayer MOF, Zn-aip-azpy, with a pore limiting diameter of 3.57 Å for the pervaporation of water-IPA mixture. We find that the seeding procedure is crucial to the formation of high-quality dense membrane comprising Zn-aip-azpy. The deposition of low-molecular weight PVA is also found to be an effective approach to form a protective layer on the pure Zn-aip-azpy membrane. The optimized Zn-aip-azpy membrane presents a water-to-IPA separation factor of as high as ~2000 with a mass flux of 0.043 kg-m−2-h−1. This is for the first time that the water-to-alcohol selectivity of a pure MOF membrane can exceed 1000. A correlation between air permeance of a membrane and its separation performance is developed in this work, which can be applied to diagnose the pinhole type defects in pure MOF membranes. Molecular simulations conducted herein suggest that, while the interior surface of Zn-aip-azpy is largely alcohol selective, the narrow bottleneck in its one-dimensional channel imposes a large diffusion barrier for IPA and thus renders this membrane high water-to-IPA selectivity.

Solution Blow Spinning Poly(vinyl alcohol) Sub-microfibers Produced from Different Solvents

Poly (vinyl alcohol) (PVA) presents a good chemical stability at room temperature, and interesting physical and mechanical properties that enable a wide range of applications of this material. The relationship between the type of polymer-solvent interaction and the physical properties of the gel can be considered, as a key factor to produce PVA micro- and nanofibers by solution blow spinning (SBS) technique. In this work, the influence of changes in the polymer-solvent interaction as a function of the solvent composition on SBS fiber formation are presented. The low molecular weight PVA solutions were obtained by dissolving the PVA in deionized water, and then adding a more volatile solvent to adjust the final concentration at 0.08 g/mL. The addition of different solvents was performed to modify the chemical nature of the solvent and consequently the polymer-solvent interaction. The viscosity measurements were performed as a function of temperature and shear rate. The rheological characterization of the solutions revealed significant changes in the viscosity value as a function of the solvent nature, although the solution´s rheological behavior showed no significative changes. Finally, the solutions showed potential to produce homogeneous PVA sub-microfibers by solution blow spinning technique. DOI: http://dx.doi.org/10.17807/orbital.v12i1.1169

Modified low molecular weight poly-vinyl alcohol as viscosity enhancer

Dry Eye Disease (DED) is a multifactorial disease that provokes a reduced vision quality and eye fatigue. It is often treated with artificial tears that must have enhanced viscosity in comparison with human tears. Phosphorylated low molecular weight PVA was synthesized to obtain a viscosity enhancer for the production of artificial tears. Three different concentrations were analyzed, verifying that, thanks to the combined action of low molecular weight and presence of anionic groups inserted along the chains, formulations can be sterilized by filtration without losing their viscosity properties, stability and transparency (light trasmittance >85%). Formulations were characterized by Infrared and UV spectroscopy, thermal analyses and rheology. The developed viscosity enhancer shows adequate viscosity values for the foreseen application. Indeed, its viscosity is higher than natural tears (1.5 mPa.s) but lower than 30 mPa.s (sticky sensation) at the shear stress values the eye is subjected. It shows a mean viscosity value of 20 mPa.s at shear rate 1 s−1 (interblinking phase: open eye), and 10.5 mPa.s at 10,000 s-1 (blinking phase).

Strategy of Constructing Light-Weight and Highly Compressible Graphene-Based Aerogels with an Ordered Unique Configuration for Wearable Piezoresistive Sensors.

Three-dimensional (3D) graphene aerogels (GAs) have attracted huge attention from researchers due to their great potential in vast applications. The hydrothermal reaction combined with freeze-drying using graphene oxide (GO) as a precursor has proven to be an effective method for obtaining relatively well-structured pure GAs. However, insufficient mechanical strength and low compressibility of the materials still limit their practical applications. Here, we report the microstructure-induced strong mechanical anisotropy of these monolithic GAs in transverse direction (TD) and longitudinal direction(LD), which has never been considered to be related to structural vulnerability. To overcome this anisotropy and enhance the structure, we hereby introduce our self-made poly(vinyl alcohol)- co-polyethylene (PVA- co-PE) nanofibers and low-molecular weight PVA as structural enhancers into the original 3D network to form a novel nanofiber-graphene composite aerogel. Intriguingly, a unique configuration is formed in the GA, in which the highly aligned stacked reduced GO sheets serve as the framework (cellular walls) and the nanofibers act as cross-linking columns anchored between the walls to support the structure along the TD, whereas the micro/nanosized PVA lamellae serve as binders. The resulting aerogel (referred to as graphene-PVA- co-PE nanofibers-PVA aerogel (GNPA)) has excellent compressive resilience along the TD and exhibits an ultrahigh gauge factor (14387%) at a very subtle strain (0.23%) in piezoresistive properties. The GNPA-TD has also been assembled into a variety of wearable sensors and demonstrates great potential for wireless human pressure sensing. In short, this study offers an extremely simple and effective method for developing graphene aerogels with a strong mechanical structure and paves the way for the application of 3D graphene in wearable sensors.

Self-Healing Hydrogels of Low Molecular Weight Poly(vinyl alcohol) Assembled by Host-Guest Recognition.

Poly(vinyl alcohol) (PVA) is a cytocompatible synthetic polymer and has been commonly used to prepare hydrogels. Bile acids and β-cyclodextrin are both natural compounds and they form stable host-guest inclusion complexes. They are attached covalently onto a low molecular weight PVA separately. Self-healing hydrogels can be easily formed by mixing the aqueous solutions of these PVA based polymers. The mechanical properties of the hydrogels can be tuned by varying the molar fractions of bile acid units on PVA. The dynamic inclusion complexation of the host-guest pair of the hydrogel allows the self-healing rapidly under ambient atmosphere and their mechanical properties could recover their original values in 1 min after incision. These PVA based polymers exhibited the good cytocompatibility and high hemocompatibility as shown by their biological evaluations. The use of natural compounds for host-guest interaction make such gels especially convenient to use as biomaterials, an advantage over conventional hydrogels prepared through freeze-thaw method.

Dehydration performance of double-network poly(vinyl alcohol) nanocomposite membranes (PVAs-DN)

Double-network poly(vinyl alcohol) nanocomposite membranes (PVAs-DN) were prepared from interpenetrating of two PVA networks. The sequential method was employed in which the first PVA network was completely established from crosslinking of high molecular weight PVA (HPVA) in the presence of silica nanospheres (SNSs) prior to a formation of the second network by the thermal crosslinking of low molecular weight PVA (LPVA). SNSs particle loading was varied at 1 and 3.5wt% which assured an even distribution of the particles in PVAs-DN matrix. Introducing of SNSs enhanced the crystallinity and mechanical properties of PVAs-DN as revealed by XRD and DMA analysis. Furthermore DMA result indicated that HPVA and LPVA networks in PVAs-DN membranes, despite their chemically identical structure, established a separate network and possessed its own relaxation. Effect of temperature on the sorption and the pervaporation was performed using 90wt% ethanol solution. The results showed that the permeability and the selectivity of water were pronouncedly improved in SNSs-filled PVAs-DN membranes compared with unfilled one and HPVA-SN membranes. Consequently thermodynamic parameters and Arrhenius activation parameters were determined.

Physical, mechanical, and transdermal diltiazem release analysis of nanosilica tailored various poly(vinyl alcohol) membranes

ABSTRACTHybrid membranes based on poly(vinyl alcohol) (PVA) of widely different molecular weights and ex situ nanosilica were synthesized and characterized as transdermal delivery device for Diltiazem hydrochloride. Investigations showed that change in PVA molecular weight strongly influenced physico‐mechanicals of the hybrids especially at low nanosilica content than at higher levels. As for example at 1 wt %, low molecular weight PVA induced finer dispersion of silica nanoparticles resulting into higher dry state crystallinity and mechanical strength but slightly lower biocompatibility as compared to high molecular weight PVA. Those variations in physico‐mechanicals finally affected Diltiazem retention and its elution from those membranes under physiological conditions. Low molecular weight PVA produced highest drug retention as well as slowest yet steady release than both high molecular weight PVA and neat PVA membranes. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2076–2086, 2013

Uniquely different PVA-xanthan gum irradiated membranes as transdermal diltiazem delivery device

This paper reports interesting differences between physical and mechanical properties of various membranes prepared from high and low molecular weight poly (vinyl alcohol) (PVA) and xanthan gum (XG) blends irradiated under low dose electron beam. The membranes were designed for sustained delivery of diltiazem hydrochloride through skin. Electron beam irradiation produced crosslinks and turned PVA into crystalline phase from its amorphous organization in the unirradiated state. PVA crystals were fibrillar at low XG content (1wt.%) when the molecular weight was high while similar orientation at higher XG content (5wt.%) when the molecular weight was low. Low molecular weight PVA–XG membranes showed equivalent physical properties under dry condition but wet-mechanical properties were superior for high molecular weight PVA–XG hybrids. Both of them showed slow and sustained diltiazem release but the later induced slightly slower release despite low drug encapsulation efficiency due to its better wet mechanical strength.

A transdermal diltiazem hydrochloride delivery device using multi-walled carbon nanotube/poly(vinyl alcohol) composites

Membranes with high strength and elasticity are of great demand in patch therapy. Similar membranes have been developed by combining carboxy-functionalized multiwalled carbon nanotube (c-MWCNT) with different poly(vinyl alcohol) (PVA) as potential diltiazem delivery device through aqueous mixing. High molecular weight PVA (PVAH) produced stronger interaction with c-MWCNT than low molecular weight PVA (PVAL) preferably at low concentration. Positive changes in favor of PVAH in infrared and solid state 13C nuclear magnetic resonance spectroscopy, wide angle X-ray scattering, thermal stability, morphology and dry and wet mechanical properties clearly demonstrate that. Fibrillar c-MWCNT array at 1wt.% in PVAH (PVAH/1) has drastically improved PVA crystalline cell dimension, tensile strength (201%) and elongation (196%) than neat PVAH whereas the similar improvement is much less (100% and 185%) in PVAL (PVAL/1) due to globular morphology. Instead, c-MWCNT performed better at 0.5wt.% in PVAL (PVAL/0.5). The kinetic data reflects better encapsulation and slower release by PVAH (5.87%) than PVAL (10.17%) due to greater interfacial interaction.

Interesting correlation between structure, physicomechanical, swelling and sustained transdermal release behavior of diltiazem hydrochloride in various poly(vinyl alcohol) hydrogel membranes

AbstractInteresting correlation between physicomechanical and in vitro release behavior of diltiazem hydrochloride has been obtained in physically treated poly(vinyl alcohol) (PVA) membranes of widely different molecular weights. Physical treatment could not raise crystallinity in dry state, but some of them show significant postswelled crystallinity and achieves elastomeric character. They also retain lot of equilibrium water, ideally suited for drug‐impregnated transdermal patches. In effect, low molecular weight PVA and dimethyl sulfoxide‐modified high molecular weight PVA membranes have shown acceptable release of diltiazem hydrochloride when compared with thermally treated high molecular weight PVA membrane. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Introducing different poly (vinyl alcohol)s as new flocculant for kaolinated waste water

High hydrolyzed grade, different poly (vinyl alcohol)s (PVA) are introduced as new eco-friendly flocculants for aqueous kaolin suspension. Sedimentation efficiency is investigated as a function of PVA molecular weight, pH and presence of different surfactants in the suspension media. Results are interesting. Low molecular weight PVA (Mn 14,000) at pH 4 excels over other high molecular weight polymers (Mn 30,000 and 115,000) by producing fastest sedimentation followed by low residual turbidity and minimum fresh water removal from the medium. Presence of surfactants has largely delayed sedimentation and has produced exceedingly high residual turbidity except cetyltrimethyl ammonium bromide, CTAB which shows turbidity slightly less than the low molecular weight PVA at its best working pH (pH 4).

Preparation of water‐soluble, syndiotacticity‐rich, low molecular weight poly(vinyl alcohol) microfibrils in high yields with the low‐temperature polymerization of vinyl pivalate in tetrahydrofuran and saponification

AbstractTo prepare water‐soluble, syndiotacticity‐rich poly(vinyl alcohol) (PVA) microfibrils for various industrial applications, we synthesized syndiotacticity‐rich, low molecular weight PVA by the solution polymerization of vinyl pivalate (VPi) in tetrahydrofuran (THF) at low temperatures with 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN) as an initiator and successive saponification of poly(vinyl pivalate) (PVPi). Effects of the initiator and monomer concentrations and the polymerization temperature were investigated in terms of the polymerization behaviors and molecular structures of PVPi and the corresponding syndiotacticity‐rich PVA. The polymerization rate of VPi in THF was proportional to the 0.91 power of the ADMVN concentration, indicating the heterogeneous nature of THF polymerization. The low‐temperature solution polymerization of VPi in THF with ADMVN proved to be successful in obtaining water‐soluble PVA with a number‐average degree of polymerization (Pn) of 300–900, a syndiotactic dyad content of 60–63%, and an ultimate conversion of VPi into PVPi of over 75%. Despite the low molecular weight of PVA with Pn = 800, water‐soluble PVA microfibrillar fibers were prepared because of the high level of syndiotacticity. In contrast, for PVA with Pn = 330, shapeless and globular morphologies were observed, indicating that molecular weight has an important role in the in situ fibrillation of syndiotacticity‐rich PVA. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1103–1111, 2002

Evaluation of Poly(vinyl alcohol) for Protein Tailoring: Improvements in Pharmacokinetic Properties of Superoxide Dismutase

Conjugation of poly(vinyl alcohol) (PVA) containing a thiol group to superoxide dismutase (SOD) was performed by using N-(∈-maleimido caproyloxy)succinimide (EMCS) as a coupling agent. Various chemical charac teristics and pharmacokinetic parameters were evaluated. Two different molec ular weight PVA-SOD conjugates were prepared. Both retained at least 92% of the native SOD activity whereas the plasma half-life increased from 4.8 min for the native SOD to 3.0 and 7.8 h for the low and high molecular weight PVA conjugates, respectively. Tissue distribution studies revealed that in travenously administered PVA-SOD had a high concentration primarily in the circulation, followed by the kidney, the lung, the liver, and the spleen. Un modified SOD was rapidly excreted via the urine, with the exception of high retention in the kidney (36% of the injected dose). PVA-SOD was also rapidly ex creted in the urine, which suggests that the kidney is the main route of excre tion of the derivatives. PVA-SOD exhibited a lower antigenicity and immuno genicity and an enhanced therapeutic effect against ischemic edema of the mouse foot pad compared with the native form. PVA with a thiol functional group appears to be useful for the preparation of protein drug-polymer conju gates, with significant diminution of immunogenicity but retention of almost full biological activity attributable to both mild conjugation conditions and selective reaction.

Characterization and Physical Properties of Low Molecular Weight Poly(vinyl acetate) and Poly(vinyl alcohol)

Low molecular weight poly(vinyl acetate) (PVAc) and poly(vinyl alcohol) (PVA) having a 2-hydroxyethylthio group at one end were synthesized using 2-mercaptoethanol as a chain transfer agent. The dependence of physical properties of PVAc and PVA on the degree of polymerization was investigated. It became clear that vapor pressure osmometry was useful as well as 1H NMR analysis to determine the number average degree of polymerization of the low molecular weight PVAc and PVA. The glass transition temperature of the PVAc decreased below 150 as the number average degree of polymerization (Pn), and the melting temperature and degree of crystallinity of the PVA had no or little change above around 100 of Pn, but changed below 100, estpcially at less than 50. The effect of chemical structure of the end groups on the swelling was also studied.

Polyvinyl alcohol containing N‐derivatives of cytosine, uracil, or adenosine‐5′‐phosphate as pendant groups

AbstractPolyvinyl alcohols (P̄n ca. 500) having a nucleotide or one of its analogs, such as adenosine‐5′‐phosphate, N‐[(2′‐dihydrogenphosphato)ethyl]‐uracil and ‐cytosine, as pendant group were synthesized by condensation using DCC as dehydrating agent in refluxing DMF. The resulting polyvinyl alcohols showed a hypochromic effect up to 4% when mixed with denaturated RNA or DNA in aqueous solution. Low molecular weight PVA (P̄n = 8) containing nucleotide analogs showed no hypochromic effect with DNA or RNA.