Polyvinyl alcohol permeability

Release of tetracycUne hydrochloride from PCL fibers was evaluated as a means of controlled administration to periodontal pockets (69). Only small amounts of the drug were released rapidly in vitro or in vivo, and poly(ethylene-co-vinyl acetate) gave superior results. Because Fickian diffusion of an ionic hydrochloride salt in a UpophiUc polymer is unlikely, and because PCL and EVA have essentially identical Fickian permeabilities, we attribute this result to leaching of the charged salt by a mechanism similar to release of proteins from EVA (73). Poly-e-caprolactone pellets have been found unsuitable for the release of methylene blue, another ionic species (74,75). In this case, blending PCL with polyvinyl alcohol (75% hydrolyzed) increased the release rate. 

How do the polyvinyl alcohol platelets reduce gas permeability in polyethylene terephthalate soda bottles ... 

The results of a reverse osmosis study of radiation crossllnk-ed and heat treated polyvinyl alcohol(PVA) membranes are reported. In the framework of this study the permeability of water and salt through these membranes was investigated. In parallel, the diffusive transport of salt through PVA was also studied. The results suggest that the transport of salt and water through PVA is uncoupled, The salt transport data can be rationalized in terms of a modified solution-diffusion model. 

Polymers may exhibit non-Fickian diffusion below the Tgt but a transition to Fickian diffusion is noted as the temperature is raised above the Tr The permeability of a gas, such as oxygen, is much greater through a silicone membrane than through a polyvinyl alcohol (PVA) membrane. Permeability of specific gases may be controlled by the use of composite membranes. 

The polyvinyl acetate and polybutyral polymers were useful for forming films, but the other materials were not. Polyvinyl alcohol is only soluble in water and not capable of being blended with other polymers. Also, any polymer with a large percentage of polyvinyl alcohol will absorb too much water and become permeable to bacteria. 

The observations in Sect. 2.6.1 clearly apply to the barrier effects in Fig. 2.62 especially with regard to the moisture or water vapor permeability. The permeability of water vapor for polyvinyl alcohol is unacceptable compared to acceptable levels in polyvinyl acetate, polybutyral and cyanoacrylate. A high level of moisture... 

It should be noted that the given sensor is much more sensitive than a sensor based on composite films CuS-polyvinyl alcohol prepared by a classical liquid-phase method [88]. In these films the sensor effect is caused by increase in probability of tunnel transitions between CuS semiconducting particles owing to increase in macroscopical dielectric permeability of a hydrophilic matrix absorbing water from the surrounding atmosphere [88]. 

In addition to these materials, several others, such as polyurethanes, polysulfones, polyvinyl alcohol, and various copolymers, have been tried or are under development. Recently, silicon hydrogel lenses with high oxygen permeability were marketed. The future... 

It was mentioned earlier that composite membranes have superior properties as compared with asymmetric memberanes. There is better control on memberane active and support layers concerning chemical stability, wider pH range, selectivity, solubility, and permeability. The active layer can be made as thin as possible for higher permeability (low-pressure operation). They can be designed with good control on properties for any particular application. Finally, the pH range of application is normally much wider than for asymmetric memberanes as was shown in Table 1. Active surface layer of composite membranes is made from cellulose acetate, aromatic polyamide, polyvinyl alcohol, etc., whereas the support layer is typically made from cellulose acetate, polysulfone, polyester, etc. 

For instance, Yadav and Ahuja prepared nanoparticles using gum cordia as the polymer and to evaluate them for ophthalmic delivery of fluconazole. A w/o/w emulsion containing fluconazole and gum cordia in aqueous phase, methylene chloride as the oily phase, and dioctyl sodium sulfosuccinate and polyvinyl alcohol as the primary and secondary emulsifiers, respectively, were cross-linked by the ionic gelation technique to produce a fluconazole-loaded nanoreservoir system. The formulation of nanoparticles was optimized using response surface methodology. Multiple response simultaneous optimizations using the desirability approach were used to find optimal experimental conditions. The optimal conditions were found to be concentrations of gum cordia (0.85%, w/v), di-octyl sodium sulfosuccinate (9.07%, w/v), and fluconazole (6.06%, w/v). On comparison of the optimized nanosuspension formulation with commercial formulation, it was found to provide comparable in vitro corneal permeability of... 

Exceptions to the low permeability of polyvinyl alcohol to gases are ammonia and water vapor. 

Wash gloves appropriately before removing them. (Note some gloves, e g., leather and polyvinyl alcohol, are water-permeable.)... 

Shao et al. have coated polyvinyl alcohol (PVA) him on the surface of the Nahon membrane to prodnce a Nahon/PVA composite membrane by immersing the Nahon membrane in a PVA casting solution (Shao et al. 2002). Subsequent cross-linking and snlfonation treatment were also applied on the composite membrane to enhance the mechanical strength and proton conductivity of the casting him. The best result was with the modihed membrane of 50 50 ratio, which exhibited the lowest methanol permeability. 

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