Polyfvinyl alcohol

Commercial polyfvinyl alcohol) (e.g. Gelvatol, Elvanol, Mowiol and Rhodo-viol) is available in a number of grades which differ in molecular weight and in the residual acetate content. Because alcoholysis will cause scission of branched polymers at the points where branching has proceeded via the acetate group, polyfvinyl alcohol) polymer will have a lower molecular weight than the poly (vinyl acetate) from which it is made. 

Poly(vinyl acetate) is an atactic material and is amorphous. Whilst the structure of polyfvinyl alcohol) is also atactic the polymer exhibits crystallinity and has essentially the same crystal lattice as polyethylene. This is because the hydroxyl groups are small enough to fit into the lattice without disrupting it. 

Because of its high polarity, polyfvinyl alcohol) is very resistant to hydrocarbons such as petrol. Although the polymer will dissolve in lower alcohol-water mixtures, it does not dissolve in pure alcohols. As it is crystalline as well as... 

Poly(vinyl alcohol) has the structure 10.67. Poly(vinyl acetate) is the fully esterified derivative of polyfvinyl alcohol), in which the -OH groups are replaced by -OCOCH3 groups. As indicated in Table 10.5, commercial polyvinyl sizes are effectively copolymers of polyfvinyl acetate) and polyfvinyl alcohol) that vary in the degree of saponification of the ester groups. These products may comprise 100% of either polymer, or combinations of the two monomers in any proportions. Crotonic acid (2-butenoic acid), widely used in the preparation of resins, may also be a component. This compound exhibits cis-trans isomerism (Scheme 10.17). The solid trans form is produced readily by catalysed rearrangement of the liquid cis isomer. 

The desizing of water-soluble size polymers can be summarised as follows. Batchwise or continuous methods can be used in both cases an adequate supply of hot water is needed during the washing-off. Hot water and detergent are needed to remove polyfvinyl alcohol) or carboxymethylcellulose. The addition of alkali may be beneficial with carboxymethylcellulose. Alkali is essential with modified starches and acrylic acid copolymers. Polyfvinyl alcohol) can be degraded effectively by alkaline oxidation. 

Clearly, one option to reduce the add-on is to use high-efficiency size formulations. However, there is a limit to what can be achieved by this approach. Even if the add-on is reduced to only 5%, the pollution load is still substantial. The two main options to facilitate disposal are (a) recovery of size polymers and (b) biological effluent treatment. Recovery of size polymers, particularly from water-soluble synthetic sizes, is based on extraction washing using the minimum quantity of water. Recovery rates in the region of 50% have been quoted for polyfvinyl alcohol) and carboxymethylcellulose size formulations. It is necessary to apply one of three concentration techniques precipitation, condensation or ultrafiltration [205]. 

Hassan, C. M. and Peppas, N. A. Structure and Applications of Polyfvinyl alcohol) Hydrogels Produced by Conventional Crosslinking or by Freezing/Thawing Methods. Vol. 153, pp. 37-65. 

The oxidative degradation of polyfvinyl alcohol) is followed at 25 °C by viscosity measurements in an Ostwald viscometer (capillary diameter 0.4 mm). One proceeds as follows ... 

In the same way, 5 ml of the polyfvinyl alcohol) solution are diluted to 10 ml with distilled water and the flow time t of this solution is determined. 

If It is assumed that the contribution of the periodic add to the viscosity is negligible then the specific viscosity of the original polyfvinyl alcohol) is given by ... 

The polymerization proceeds in an autoclave, by dissolving vinyl acetate, polyfvinyl alcohol) (PVA), ferrous sulfate heptahydrate, and acetic acid in water. 

Figure 9.4 The effect of permeate pressure on the separation of ethanol/water mixtures with a polyfvinyl alcohol) membrane. The feed solution contains 20 wt% water and 80 wt% ethanol. The line drawn through the experimental data points is calculated from Equation (9.11)...

FIGURE 2.25 Pore volume and pore size distribution of mesoporous carbons obtained from the mixture of Mg citrate with polyfvinyl alcohol). 

Divinylbenzene, styrene, a,a -azoisobutyronitrile and methacrylic monomers di(methacryloyloxymethyl)-naphthalene (DMN), methacrylic ester of p,p -dihydroxydiphenylpropane diglycidyl ether (MEDDE), and dimethacrylglycol-ethylene (DMGE) were received from Fluka and used without further purification. Polyfvinyl alcohol), /7-dccanol, ethanol, acetone and toluene (Merck), fumed silica with specific surface area of 300 m2/g (Kalush), triethoxysilane (Kremnepolimer) and hexamethyldisilazane (Fluka) were applied. 

Polyfvinyl alcohol) is an important example. Inspection of the structure reveals that this is a typical alkene polymer but the monomer would have to be vinyl alcohol—the unstable enol of acetaldehyde. The way to make the polymer is to start with something else and only later... 

Polymers such as polyfvinyl alcohol), dextrans, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, and polyfethylene oxide) can be used as dynamic or permanent coatings. The latter mode is generally more effective. 

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