Poly Vinyl Alcohol

Major polymer applications sizing agents, binders, protective colloids, photographic papers, toners, fihn, water-soluble laundry bags, seed tapes, sanitary pads, belts, printing rolls, controlled drug delivery, membranes 

Typical fillers carbon black, silica, calcium carbonate, clay, zinc oxide, titanium dioxide, sand, aluminum oxide, magnesium oxide, zirconia, ferrite, graphite 

Special methods of incorporation in situ precipitation of filler  

Poly(vinyl acetate) is too soft and shows excessive cold flow for use in moulded plastics. This is no doubt associated with the fact that the glass transition temperature of 28°C is little above the usual ambient temperatures and in fact in many places at various times the glass temperature may be the lower. It has a density of 1.19g/cm and a refractive index of 1.47. Commercial polymers are atactic and, since they do not crystallise, transparent (if free from emulsifier). They are successfully used in emulsion paints, as adhesives for textiles, paper and wood, as a sizing material and as a permanent starch . A number of grades are supplied by manufacturers which differ in molecular weight and in the nature of comonomers (e.g. vinyl maleate) which are commonly used (see Section 14.4.4) 

The polymers are usually supplied as emulsions which also differ in the particle size, the sign of the charge on the particle, the pH of the aqueous phase and in other details. 

Being an amorphous polymer with a solubility parameter of 19.4 MPa, it dissolves in solvents with similar solubility parameters (e.g. benzene 8 = 18.8 MPa, chloroform 8 = 19.0MPa, and acetone 8 = 20.4 MPa.  

Vinyl alcohol does not exist in the free state and all attempts to prepare it have led instead to the production of its tautomer, acetaldehyde. 

The term hydrolysis is sometimes incorrectly used to describe this process. In fact water does not react readily to yield poly(vinyl alcohol)s and may actually retard reaction where certain catalysts are used. 

Poly(vinyl alcohol) [9002-89-5] is obtained by hydrolysis of poly(vinyl acetate). Commercial grades of poly(vinyl alcohol) differ in the degree of polymerization (molecular mass) and degree of hydrolysis [residual poly(vinyl acetate) content]. 

Poly(vinyl alcohol) is used in the coating sector (e.g, as a thickening agent for aqueous systems), in adhesives, for finishing paper and cardboard, for coating paper, as a binder for strippable coatings, and as a protective colloid for dispersions. 

Commercial products include Airvol (Air Products), Elvanol (Du Pont), Ertivinol (ERT), Gohsenol (Nippon Gohsei), Mowiol (Clariant), Polyviol (Wacker), Poval (Kuraray, Denka, Shinet-Su), and Rhodoviol (Rhone-Poulenc). 

Poly(vinyl alcohol) is a synthetic pol3mier of a linear structure type [38, 59, 60] and it contains only secondary alcoholic groups as shown in the following structure [d)  

The primary and secondary alcoholic groups in either PVA or polysaccharides tend to protonate in acidic media forming the more reactive alkoxnium ions [61-68] for either primary (Eq. 12.24) or secondary alcohols (Eq. 12.25), respectively, as follows  

On the contrary, these primary and secondaiy alcoholic groups possess a high tendency for deprotonation in alkaline medium to give the corresponding alkoxides [49-60] as shown by Eqs. (12.25) and (12.26), respective.  

Vinal fibers, or poly(vinyl alcohol) fibers, are not made in the United States, but the fiber is produced commercially in Japan, Korea, and China where the generic name vinylon is used. These materials are the subject of this article (see also Vinyl polymers, vinyl alcohol polymers). 

Vinyl alcohol does not exist as a monomer, but Herrmann and Haehnel (1) were able to obtain the desired product poly(vinyl alcohol) [9002-89-5] (PVA), by polymerizing vinyl acetate and then hydrolyzing the resultant poly(vinyl acetate). This process is employed for the commercial production of PVA even now. The principal concern of the discoverers was development of a suture for surgical operations the fiber then obtained was not suited for clothing use (2). 

Commercial production of PVA fiber was thus started in Japan, at as early a period as that for nylon. However, compared with various other synthetic fibers which appeared after that period, the properties of which have continuously been improved, PVA fiber is not very well suited for clothing and interior uses because of its characteristic properties. The fiber, however, is widely used in the world because of unique features such as high affinity for water due to the —OH groups present in PVA, excellent mechanical properties because of high crystallinity, and high resistance to chemicals including alkah and natural conditions. 

The People s RepubHc of China introduced Kuraray technology and started production of PVA fiber by a wet spinning process in 1965. Its annual capacity reached 165,000 tons in 1986 (9). The Democratic People s RepubHc of Korea produce PVA and reportedly have an annual production capacity of 50,000 tons (9). 

Raw Material. PVA is synthesized from acetjiene [74-86-2] or ethylene [74-85-1] by reaction with acetic acid (and oxygen in the case of ethylene), in the presence of a catalyst such as zinc acetate, to form vinyl acetate [108-05-4] which is then polymerized in methanol. The polymer obtained is subjected to methanolysis with sodium hydroxide, whereby PVA precipitates from the methanol solution. 

Photoirradiation of poly(vinyl alcohol) in vacuum causes formation of three kinds of radicals which give singlet, quartet and triplet ESR spectra [1621]. These spectra were assigned to alkoxy and methyl radicals which originated from the acetyl group remaining in the sample, and to carbon radicals gen- 

Scission of some of the C—C bonds results in the formation of carbonyl end-groups. Aldehyde and acid ends are expected to form according to the reactions  

Scission of the C—O bond of the polymer oxyradical results in the formation of an intramolecular hydrogen bridge  

FTIR spectroscopy, the rate of increase of the concentration of degradation products was monitored as the parameter determining polymer degradation. Significantly better stability was expressly confirmed by the statistical analysis of the results for the film containing Mg(OH)2 as thermal stabiliser. The presented results confirmed that a good stabiliser must effectively eliminate acidic compounds in PVA melt to avoid degradation reactions. 

The biodegradabdity of vinyl ester-based polymers with a special emphasis on poly(vinyl acetate) and poly(vinyl alcohol) (PYA) has been reviewed (15). Also, the general physical and chemical properties of these polymers and on the relationships, how these properties can influence the biodegradabdity are discussed. 

As already mentioned, PVA is a water soluble polymer used in applications such as packaging films where water solubility is desired. It is the most readily biodegradable of the vinyl polymers, which makes it a potentially useful material in biomedical, agricultural, and water treatment areas, for example, as a flocculant, or scavenger of metal ions. Moreover, due to its water solubility, PVA can also be used as a model for particle dispersion in aqueous suspensions, especially those from CNWs and some clays. As a consequence, PVA has been largely used to produce nanocomposites with clays, cellulose, and chitin whiskers, silver nanoparticles, graphite oxide, and carbon nanotubes. 

PVA is produced by hydrolyzing poly(vinyl acetate). PVA fiber is an almost exclusively Japanese product some production takes place in Korea and China, based on Japanese technology. The fiber has Vinylon as a general name and Kuraray is the largest producer (Kuralon). Poly(vinyl alcohol) is water-soluble, which makes the choice of a solvent easy. And, of course, it has proved possible to make the fibers water-insoluble. 

Hot drawing of PVA, at 210-240°C, takes place after drying. Draw ratios ( 10) and tenacities achieved ( 900 mN tex ) are high, and the resulting yams are highly crystalline (40-50%) and no longer water-soluble. For staple fiber the draw ratios may be lower, and a heat treatment for 0.5-3 min at 210-230°C is given to further crystallize the fibers. 

For complete insolubility in water, the hydroxyl groups can be made to react with formaldehyde to a maximum degree of 85%. This takes 10-20 min, however, and only seems interesting in tow processing. 

2 Synthesis Methods and Structural Properties of Nanotubes/PVA Composites 

In this section, we present different approaches that have been used to produce various forms of PVA/nanotube composite films and the morphological studies that have been performed to enlighten the interactions between PVA and nanotubes. 

Most of PVA/CNT composites are processed under the form of films. Generally, films are casted and dried from water-based PVA and nanotube dispersions. Different types of water-based dispersions have been used. Carbon nanotubes come from various production sources and can be covalently functionalized. The PVA molecular weight and hydrolysis rate can also be varied as well as the nanotube fraction. This is why comparisons between all the contributions in the literature can sometimes be difficult. Nevertheless some general and important features can still be deduced from all the studies reported on this topic. 

In 1999, M. Shaffer and A. Windle reported the first study of the thermo-mechanical and electrical properties of PVA/MWNT composite films (18). In this work, a high hydrolysis rate PVA was used (98-99%), with a large range molecular weight (between 85,000 and 146,000 g/mol). Water solutions of PVA were prepared at 90°C. 

In order to achieve deeper understanding of the interaction between nanotubes and PVA, the influence of the nature of the CNTs was examined by Cadek et al. (23). Free standing composite films were prepared from PVA and raw nanotube soot, again with no surfactant. Six different sources of nanotubes were studied. 

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Resins formed from the reaction of poly(vinyl alcohol) with aldehydes. The formal derivative (from methanal) is used in wire coatings and adhesives and the bulyral (from butanal) is used in metal paints, wood-sealers, adhesives and in safety glass interlayers. 

Prepared generally by ester interchange from polyvinylacelate (ethanoate) using methanol and base also formed by hydrolysis of the acetate by NaOH and water. The properties of the poly(vinyl alcohol) depend upon the structure of the original polyvinyl acetate. Forms copolymers. Used as a size in the textile industry, in aqueous adhesives, in the production of polyvinyl acetates (e.g. butynal) for safety glasses. U.S. production 1980... 

Poly(vinyl alcohol) is a useful water soluble polymer It cannot be prepared directly from vinyl alcohol because of the rapidity with which vinyl alcohol (H2C=CHOH) isomenzes to acetaldehyde Vinyl acetate however does not rearrange and can be polymerized to poly(vinyl acetate) How could you make use of this fact to prepare poly(vinyl alcohol)" ... 

Poly(vinyl alcohol) Poly(vinyl acetate)... 

Poly (vinyl Alcohol). Poly( vinyl alcohol) has the following formula ... 

First, we consider the experimental aspects of osmometry. The semiperme-able membrane is the basis for an osmotic pressure experiment and is probably its most troublesome feature in practice. The membrane material must display the required selectivity in permeability-passing solvent and retaining solute-but a membrane that works for one system may not work for another. A wide variety of materials have been used as membranes, with cellophane, poly (vinyl alcohol), polyurethanes, and various animal membranes as typical examples. The membrane must be thin enough for the solvent to pass at a reasonable rate, yet sturdy enough to withstand the pressure difference which can be... 

VINYLPOLYTffiRS - VINYL ALCOHOLPOLYTffiRS] (Vol 24) PVA. See Poly(vinyl alcohol). 

Acetals are readily formed with alcohols and cycHc acetals with 1,2 and 1,3-diols (19). Furfural reacts with poly(vinyl alcohol) under acid catalysis to effect acetalization of the hydroxyl groups (20,21). Reaction with acetic anhydride under appropriate conditions gives the acylal, furfuryUdene diacetate... 

Dichromated Resists. The first compositions widely used as photoresists combine a photosensitive dichromate salt (usually ammonium dichromate) with a water-soluble polymer of biologic origin such as gelatin, egg albumin (proteins), or gum arabic (a starch). Later, synthetic polymers such as poly(vinyl alcohol) also were used (11,12). Irradiation with uv light (X in the range of 360—380 nm using, for example, a carbon arc lamp) leads to photoinitiated oxidation of the polymer and reduction of dichromate to Ct(III). The photoinduced chemistry renders exposed areas insoluble in aqueous developing solutions. The photochemical mechanism of dichromate sensitization of PVA (summarized in Fig. 3) has been studied in detail (13). 

Fig. 3. Chemistry of dichromated poly(vinyl alcohol) resist. Initially the dichromate ion absorbs light the light-activated species undergoes an...

Currently, almost all acetic acid produced commercially comes from acetaldehyde oxidation, methanol or methyl acetate carbonylation, or light hydrocarbon Hquid-phase oxidation. Comparatively small amounts are generated by butane Hquid-phase oxidation, direct ethanol oxidation, and synthesis gas. Large amounts of acetic acid are recycled industrially in the production of cellulose acetate, poly(vinyl alcohol), and aspirin and in a broad array of other... 

About half of the wodd production comes from methanol carbonylation and about one-third from acetaldehyde oxidation. Another tenth of the wodd capacity can be attributed to butane—naphtha Hquid-phase oxidation. Appreciable quantities of acetic acid are recovered from reactions involving peracetic acid. Precise statistics on acetic acid production are compHcated by recycling of acid from cellulose acetate and poly(vinyl alcohol) production. Acetic acid that is by-product from peracetic acid [79-21-0] is normally designated as virgin acid, yet acid from hydrolysis of cellulose acetate or poly(vinyl acetate) is designated recycle acid. Indeterrninate quantities of acetic acid are coproduced with acetic anhydride from coal-based carbon monoxide and unknown amounts are bartered or exchanged between corporations as a device to lessen transport costs. 

Many of these reactions are reversible, and for the stronger nucleophiles they usually proceed the fastest. Typical examples are the addition of ammonia, amines, phosphines, and bisulfite. Alkaline conditions permit the addition of mercaptans, sulfides, ketones, nitroalkanes, and alcohols to acrylamide. Good examples of alcohol reactions are those involving polymeric alcohols such as poly(vinyl alcohol), cellulose, and starch. The alkaline conditions employed with these reactions result in partial hydrolysis of the amide, yielding mixed carbamojdethyl and carboxyethyl products. 

Suitable protective coUoids for the preparation of acryhc suspension polymers include ceUulose derivatives, polyacrylate salts, starch, poly(vinyl alcohol), gelatin, talc, clay, and clay derivatives (95). These materials are added to prevent the monomer droplets from coalescing during polymerisation (110). Thickeners such as glycerol, glycols, polyglycols, and inorganic salts ate also often added to improve the quahty of acryhc suspension polymers (95). 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Lead azide is not readily dead-pressed, ie, pressed to a point where it can no longer be initiated. However, this condition is somewhat dependent on the output of the mixture used to ignite the lead azide and the degree of confinement of the system. Because lead azide is a nonconductor, it may be mixed with flaked graphite to form a conductive mix for use in low energy electric detonators. A number of different types of lead azide have been prepared to improve its handling characteristics and performance and to decrease sensitivity. In addition to the dextrinated lead azide commonly used in the United States, service lead azide, which contains a minimum of 97% lead azide and no protective colloid, is used in the United Kingdom. Other varieties include colloidal lead azide (3—4 pm), poly(vinyl alcohol)-coated lead azide, and British RE) 1333 and RE) 1343 lead azide which is precipitated in the presence of carboxymethyl cellulose (88—92). 

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