Molecular Weight PVA Research Articles

Physical stabilisation of electrospun poly(vinyl alcohol) nanofibres: comparative study on methanol and heat-based crosslinking

Methanol crosslinking and heat-treatment methods for physical crosslinking of electrospun poly(vinyl alcohol) (PVA) nanofibres were investigated to assess their stability in water. For this purpose, PVAs with low and high molecular weights were selected. Morphology of the crosslinked membranes was characterised by scanning electron microscopy. Crystallinity of the resultant crosslinked fibres were analysed by FT-IR and differential scanning calorimetry. It has been shown that physical crosslinking increases the crystallinity of the fibres. High molecular weight PVA nanofibres showed better stability and better preservation of nanofibrous structure. Stability of the crosslinked membranes was also tested by immersion into water at room temperature and boiling water. Combined methanol and heat treatments at different temperatures and exposure periods were also investigated. Treatment at 180 °C HMW PVA nanofibres for longer durations exhibited best results in terms of water stability, although it exhibited somewhat lower swelling ratios as compared to those subjected to only methanol treatment.

Freeze-Thawed Hybridized Preparation with Biomimetic Self-Assembly for a Polyvinyl Alcohol/Collagen Hydrogel Created for Meniscus Tissue Engineering

Freeze-thawed hybridized preparation and the biomimetic self-assembly technique were used to fabricate hydrogel as tissue engineered scaffolds for meniscus tissue. Because of the advantages of both techniques, they were hybridized together as an interesting preparation for hydrogel. Three molecular weights (high, medium, and low) of PVA were prepared in a biomimetic solution before formation into hydrogel by freeze-thawing. The most suitable molecular weight PVA for hydrogel formation was chosen to be mixed with collagen. PVA, PVA/collagen, and collagen were prepared in biomimetic solutions and freeze-thawed into hydrogels. The hydrogels were analyzed and characterized by FTIR, DSC, and SEM. FTIR characterization indicated that high molecular weight PVA formed molecular interaction better than the other molecular weights, and PVA molecules formed molecular interaction with collagen molecules via –OH and C=O groups. DSC characterization showed that the hybridized preparation of freeze-thawing and biomimetic self-assembly kept the characteristics of PVA and collagen. SEM analysis demonstrated that the morphological formation of PVA/collagen was hybridized during freeze-thawing and collagen self-assembly. The morphological structure was organized into a porous network structure. The porous structure showed a rough wall that was formed by the hybridized structure of the crystal domain dispersed in amorphous and collagen self-assembly.

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

Fabrication of protein-loaded PLGA nanoparticles: effect of selected formulation variables on particle size and release profile

In this study, the processing conditions for fabricating bovine serum albumin (BSA)-loaded poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles via a water/oil/water double emulsion technique were adjusted and release profiles were studied. Particle size and surface morphology of the BSA-loaded PLGA nanoparticles were comprehensively controlled as a function of processing determinants. The nanoparticles were intended as a carrier for controlled delivery of therapeutic proteins; however, BSA was chosen as a hydrophilic model protein encapsulated within PLGA nanoparticles to investigate the effective formulation parameters. Several key processing parameters were changed including surfactant(s) concentration in the internal and external aqueous phases, BSA concentration, poly(vinyl alcohol) (PVA) characteristics, and power of ultrasonicator probe to investigate their effects on the morphological characteristics and size distribution of the nanoparticles (NPs). The prepared NPs showed spherical shape with smooth and pore-free surfaces along with a relatively narrow particle size distribution. The mean particle size of the optimized formulation was 251.3 ± 8.5 nm, which is ideal for drug delivery applications. Our results demonstrate that using PVA with Mw 13–23 kDa and degree of hydrolysis approximately 87–89 % yields better results than PVA of higher molecular weight and higher degree of hydrolysis. Surfactants concentrations in internal (Span 60) and external phase (Tween 80) of the emulsions, which play a key role in determining NP characteristics and cumulative percentage BSA released, were optimized at 14 % (w/w) and 4 % (w/v), respectively. Optimal level of ultrasonication power (50 W) was also determined. According to the results, the optimized protein-loaded NPs with proper shape, size, and surface properties were prepared and these may act as a good candidate for protein delivery.

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).

THE EFFECT OF RESIDUAL POLY(VINYL ALCOHOL) ON BIOPHYSICAL INTERACTION OF NANOPARTICLES WITH ENDOTHELIAL CELL MODEL MEMBRANE

Poly(vinyl alcohol) (PVA) is commonly used as an emulsifier in the formulation of nanoparticles (NPs) comprising poly DL-lactide co-glycolide and polylactide-based biodegradable polymers for drug and gene delivery applications. A fraction of PVA remains associated with the NPs at the interface despite their repeated washing (residual PVA). We hypothesize that this residual PVA influences the interfacial properties of NPs and hence their biophysical interactions with membrane lipids. In this study, we formulated NPs using PVA of different molecular weights to determine the effects of the residual PVA on biophysical interactions of the formulated NPs with the endothelial cell model membrane using a Langmuir balance. Despite similar physical properties (particle size and zeta potential), NPs formulated with different PVA demonstrated significant variations in their intrinsic surface properties and biophysical interactions with the model membrane. This was evident from the difference in the surface pressure–area (π–A) isotherms prepared in the presence of different formulations of NPs and the change in surface pressure of the model membrane following interaction with NPs. The variation in the biophysical properties was observed even with the NPs formulated using the same molecular weight PVA but obtained from different lots. Since the interfacial properties of NPs can significantly influence NP interactions with cells and tissue, their biophysical characterization could prove to be an important parameter not only to obtain consistent results with NPs but also to optimize their properties for drug/gene delivery applications.

Flow Instability of Polyvinyl alcohol)/Dimethyl Sulfoxide Solution under Steady Shear

The effects of solution temperature and molecular weight on the rheological responses of poly(vinyl alcohol) (PVA) semidilute solutions (13 g/dL- 19 g/dL) in dimethyl sulfoxide (DMSO) have been studied using PVA with two different number-average degrees of polymerization (Pn): 1700 and 4000. For the rheological experiments using dynamic shear, the PVA solution with a Pn of 1700 showed rather simple Newtonian fluid behaviour, whereas that with Pn of 4000 exhibited non-Newtonian shear thinning behaviour. Steady shear rheology experiments suggested that the lower Pn PVA solutions were Newtonian fluids, which is consistent with the dynamic shear rheology results. However, an abrupt decrease of shear viscosity at high shear rates was observed for the higher Pn PVA solutions at lower temperatures, such as 30 °C and 50 °C. At higher temperatures of 70 °C and 90 °C, the higher molecular weight PVA solutions exhibited simple shear thinning behaviour without any further complications of flow instability. The fact that temperature plays a critical role in controlling the observed flow instability of the PVA solutions in DMSO strongly suggests that there exist enhanced inter-chain interactions by hydrogen bonding of PVA chains beyond the chain entanglements, particularly for the higher Pn PVA semidilute solutions at low temperatures. Therefore, it is important to consider both chain entanglements and hydrogen bonding interactions in order to process PVA solutions without causing undesirable flow instability.

High molecular weight PVA-modified PVA/PAMPS proton-conducting membranes with increased stability and their application in DMFCs

A series of proton-conducting composites has been synthesized from PVA/PAMPS [poly(vinyl alcohol)/poly(2-acrylamido-2-methyl-1-propanesulfonic acid)] using high molecular weight PVA (HMw-PVA). By applying high molecular weight PVA as a polymer matrix, a greater hydrophobicity of the membranes emerged, which endows them with reduced water uptake (70-90%) but high proton conductivity (0.06-0.1 S cm - 1 ), low methanol permeability (1/3 to 1/5 that of Nafion 117), and excellent oxidative stability towards Fenton's reagent. A DMFC fabricated with the above membrane showed a high power density of 15.8 mW cm - 2 at 30 °C, which reached 42.9 mW cm - 2 at 80 °C. An initial lifetime performance assessment in DMFC mode yielded a value of 70 h for stable cell operation.

Effect of gel spinning accompanied with cross‐linking using boric acid on the structure and properties of high‐molecular‐weight poly(vinyl alcohol) fiber

AbstractTo enhance the thermal stability of poly(vinyl alcohol) (PVA) fiber, the fiber was prepared from the gel spinning of high molecular weight (HMW) PVA by using dimethyl sulfoxide/water (8/2, v/v) as a solvent, accompanied with the cross‐link by boric acid (B‐PVA). In addition, the structure and properties of the B‐PVA fiber were compared with those of the HMW PVA fiber obtained by using the same spinning system without cross‐linking (NB‐PVA). Through a series of experiments, it turned out that cross‐linking actualized by an optimum amount of boric acid (0.3 wt % based on PVA) and zone drawing caused significant changes in the properties of HMW PVA gel fiber. That is, cross‐linking increased thermal degradation temperatures at each degradation step and amounts of final residues, resulting in improving thermal properties of the PVA fiber. On the contrary, it was found that in the case of the B‐PVA fiber, some broadening of the original PVA unit cell occurred, which was identified by the peak shift to lower angle in X‐ray diffractogram. The tensile strength and Young's modulus of B‐PVA fiber with draw ratio of 15 are 23.1 and 308.3 g/d, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Performance Enhancement of PVA/PAMPS Conducting Composites using High Molecular Weight PVA

PVA/PAMPS proton conducting composites have been presented for low temperature DMFCs using high molecular weight PVA (HMw- PVA). By using high molecular weight PVA as polymer matrices, the membrane micro-phase structure is improved and this brings about a performance enhancement of the membrane such as low water uptake, high proton conductivity, low methanol permeability and excellent longevity towards the Fenton's reagent.

Performance Enhancement of PVA/PAMPS Conducting Composites using High Molecular Weight PVA

not Available.

Swelling and mechanical properties of glycol chitosan/poly(vinyl alcohol) IPN‐type superporous hydrogels

Glycol chitosan/poly(vinyl alcohol) interpenetrating polymer network type superporous hydrogels were prepared using a gas foaming/freeze-drying method. The effect of the molecular weight of the strengthener, poly(vinyl alcohol) (PVA), on the swelling and mechanical behavior of the superporous hydrogels was investigated. The introduction of a small amount of high molecular weight PVA significantly enhanced the mechanical strength but slightly reduced the swelling capacity. The freezing/thawing (F/T) drying process had a significant effect on the physical properties of the glycol chitosan/PVA superporous hydrogels, because hydrogen bonds were formed between the PVA molecules as a result of the number of F/T cycles. The swelling ratio decreased but the mechanical strength increased with increasing freezing time. However, this effect was not as strong as the number of F/T cycles. The differential scanning calorimetry was used to examine how the thermal behavior associated with the hydrogen bond-induced crystalline structure was affected by the F/T process.

Poly(vinyl alcohol) nanofibres by electrospinning: influence of molecular weight on fibre shape

AbstractPoly(vinyl alcohol) (PVA) nanofibres were obtained by electrospinning of PVA/water solutions. Formation of beaded fibres combined with decreased fibre diameters was observed for low PVA concentrations. Electrospinning of blends of PVA of different molecular weight resulted in less bead formation and smaller fibre diameters as compared to corresponding homopolymers of similar viscosity.

Novel associated hydrogels for nucleus pulposus replacement.

Hydrogels of poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) blends may provide a material suitable for replacement of the nucleus pulposus of the intervertebral disc. This research examined the stability of these hydrogels under simulated physiological conditions. Polymer dissolution and stability were characterized over 120 days immersion, chemical surface analysis over 56 days immersion, and tensile mechanical behavior over 56 days immersion. Rubber elasticity theory was used by combining mechanical results with swelling data to calculate network characteristics such as the molecular weight between physical crosslinks and density of crosslinks. Properties were examined as a function of PVA/PVP composition as well as PVA molecular weight and PVP molecular weight. Results indicated that PVA/PVP blends prepared with moderate amounts of PVP (0.5-5%) resulted in a polymer network stabilized through interchain hydrogen bonding between hydroxyl groups on PVA chains and carbonyl groups on PVP chains. Most notably, a significant decrease in percentage of polymer mass loss was seen for blends prepared with 143K molecular weight PVA. Surface chemical analysis revealed that PVP unincorporated in the network structure suffered significant dissolution out of the polymer network and into solution. The molecular weight of PVA and PVP were shown to have a significant influence on the blends' network properties. Gels prepared with lower molecular weight PVA resulted in a more stable blend containing a higher density of crosslinks. However, blends prepared with a higher molecular weight PVA showed superior polymer network stability in dissolution studies. The blend that had the best combination of network stability under physiological conditions and a relatively tight, stable, and crosslinked network was prepared with 99% PVA (143K) and 1% PVP (40K). This material is proposed as an implant material for replacement of the degenerated nucleus pulposus.

Preparation of ultrahigh molecular weight syndiotactic poly(vinyl alcohol) microfibrillar fibers by low‐temperature solution polymerization of vinyl pivalate in tertiary butyl alcohol and saponification

AbstractVinyl pivalate (VPi) was solution polymerized in tertiary butyl alcohol (TBA) and in dimethyl sulfoxide (DMSO) with a low chain transfer constant using a low temperature initiator, 2,2′‐azobis(2,4‐ dimethylvaleronitrile) (ADMVN). The effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of poly(vinyl pivalate) (PVPi) and its saponification product poly(vinyl alcohol) (PVA). TBA was absolutely superior to DMSO in increasing the syndiotacticity and molecular weight of PVA. In contrast, TBA was inferior to DMSO in causing conversion to polymer, indicating that the initiation rate of VPi production in TBA was lower than that in DMSO. These effects could be explained by a kinetic order of ADMVN concentration, calculated by the initial rate method. Low‐temperature solution polymerization of VPi in TBA or DMSO by adopting ADMVN proved to be successful in obtaining PVA of ultrahigh molecular weight [maximum number‐average degree of polymerization (Pn): 13,500–17,000] and of high yield (ultimate conversion of VPi into PVPi: 55–83%). In the case of bulk polymerization of VPi at the same conditions, maximum Pn and conversion were 14,500–17,500 and 22–36%, respectively. The Pn and syndiotactic diad content were much higher and the degree of branching was lower with PVA prepared from PVPi polymerized at lower temperatures in TBA. Moreover, PVA from the TBA system was fibrous, with a high degree of orientation of the crystallites, indicating the syndiotactic nature of TBA polymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1992–2003, 2002

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

Characterizations of poly(vinyl pivalate) polymerized in tertiary butyl alcohol and resulting syndiotactic poly(vinyl alcohol) microfibrils saponified

Vinyl pivalate (VPi) was solution-polymerized in tertiary butyl alcohol (TBA) and in dimethyl sulfoxide (DMSO) with low chain transfer constant using a low temperature initiator, 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN). TBA was absolutely superior to DMSO in increasing the syndiotacticity and molecular weight of poly(vinyl alcohol) (PVA). Low-temperature solution polymerization of VPi in TBA or DMSO by adopting ADMVN proved to be successful in obtaining PVA of ultrahigh molecular weight (maximum number-average degree of polymerization (Pn): 13,500–17,000) and of high yield (ultimate conversion of VPi into PVPi: 55–80%) to a much higher conversion than that from bulk polymerization. Moreover, PVA from TBA system were fibrous, with a high degree of orientation of the crystallites, indicating the syndiotactic nature of TBA polymerization.