Vinylidene COATINGS

Polymeric vinylidene chloride generally produced by free radical polymerization of CH2 = CCl2. Homopolymers and copolymers are used. A thermoplastic used in moulding, coatings and fibres. The polymers have high thermal stability and low permeability to gases, and are self extinguishing. 

Poly(vinyhdene chloride) (PVDC) film has exceUent barrier properties, among the best of the common films (see Barrier polymers). It is formulated and processed into a flexible film with cling and tacky properties that make it a useful wrap for leftovers and other household uses. As a component in coatings or laminates it provides barrier properties to other film stmctures. The vinyUdene chloride is copolymerized with vinyl chloride, alkyl acrylates, and acrylonitrile to get the optimum processibUity and end use properties (see Vinylidene chloride monomer and polymers). 

Poly(vinylidene chloride). Poly(viayHdene chloride) [9002-85-1] (PVDC), most of which is produced by Dow Chemical, is best known in its saran or PVC-copolymerized form (see Vinylidene chloride and poly(VINYLIDENE chloride)). As solvent or emulsion coating, PVDC imparts high oxygen, fat, aroma, and water-vapor resistance to substrates such as ceUophane, oriented polypropylene, polyester, and nylon. 

Vinylidene Chloride Copolymer Latex. Vinyhdene chloride polymers are often made in emulsion, but usuaUy are isolated, dried, and used as conventional resins. Stable latices have been prepared and can be used direcdy for coatings (171—176). The principal apphcations for these materials are as barrier coatings on paper products and, more recently, on plastic films. The heat-seal characteristics of VDC copolymer coatings are equaUy valuable in many apphcations. They are also used as binders for paints and nonwoven fabrics (177). The use of special VDC copolymer latices for barrier laminating adhesives is growing, and the use of vinyhdene chloride copolymers in flame-resistant carpet backing is weU known (178—181). VDC latices can also be used to coat poly(ethylene terephthalate) (PET) bottles to retain carbon dioxide (182). 

Vinyhdene chloride copolymers are available as resins for extmsion, latices for coating, and resins for solvent coating. Comonomer levels range from 5 to 20 wt %. Common comonomers are vinyl chloride, acrylonitrile, and alkyl acrylates. The permeability of the polymer is a function of type and amount of comonomer. As the comonomer fraction of these semicrystalline copolymers is increased, the melting temperature decreases and the permeability increases. The permeability of vinylidene chloride homopolymer has not been measured. 

In order to reduce the tendency of the film to shrink oriented film may be annealed at about 100°C whilst under tension immediately after drawing. The film is often coated with another polymer sueh as a vinylidene ehloride-based copolymer. This both improves the barrier properties and improves the heat scalability. 

Copolymers of acrylonitrile and vinylidene chloride have been used for many years to produce films of low gas permeability, often as a coating on another material. Styrene-acrylonitrile with styrene as the predominant free monomer (SAN polymers) has also been available for a long time. In the 1970s materials were produced which aimed to provide a compromise between the very low gas permeability of poly(vinylidene chloride) and poly(acrylonitrile) with the processability of polystyrene or SAN polymers (discussed more fully in Chapter 16). These became known as nitrile resins. 

By copolymerising the vinylidene chloride with about 10-15% of vinyl chloride, processable polymers may be obtained which are used in the manufacture of filaments and films. These copolymers have been marketed by the Dow Company since 1940 under the trade name Saran. Vinylidene chloride-acrylonitrile copolymers for use as coatings of low moisture permeability are also marketed (Saran, Viclan). Vinylidene chloride-vinyl chloride copolymers in which the vinylidene chloride is the minor component (2-20%) were mentioned in Chapter 12. 

Figure 6. Partly assembled, 5-gallon, low density polyethylene liner in a corrugated carton. Liner is coated with poly(vinylidene chloride) (Saran) to block oxygen entry and prevent loss of aroma used for cola concentrate.

Some polymers like PE and NR get cross-linked on exposure to radiation while others like those based on vinylidene polymers, e.g., polymethylmethacrylate (PMMA), polyisobutylene, degrade. Certain other types of polymer stmctures (high aromatic content or thermoset) resist degradation by high-energy radiation. Coating polymers usually contain acrylic, methacryUc, or fumaric vinyl unsaturation along or attached to the backbone. 

Concern over the migration of plasticisers from packaging materials has led to various studies, amongst which monitoring levels of various phthalates from coatings of regenerated cellulose film [433] and of acetyl-tributyl citrate (ATBC) from vinylidene chloride/vinyl... 

At present, a wide range of solid substrates are available for protein immobilization. According to the protein attachment strategies, namely, adsorption, affinity binding, and covalent binding, all these substrates can be separated into three main parts. Surfaces like ploy(vinylidene fluoride) (PVDF), poly(dimethylsiloxane) (PDMS), nitrocellulose, polystyrene, and poly-1-lysine coated glass can adsorb proteins by electrostatic or hydrophobic forces. A potential drawback of such substrates is the difficulty... 

Beside SILP experiments with silica as support material, reports have also been made on the use of membranes coated with ionic liquid catalyst solution for the hydrogenation reaction of propene and ethene. The membranes were obtained by supporting various ionic liquids, each containing 16 to 23 mmol Rh(I) complex Rh(nbd)(PPh3)2 (nbd=norbornadiene), in the pores of poly(vinylidene fluoride) filter membranes [118]. 

Another specialty area is coil coating, which involves coating metal coils by continuous operation. Modern roller systems afford speeds of up to 200 m/min. Most coils are made of cold-rolled and surface treated steel, aluminum, or alloys of the latter with manganese or magnesium. Coating systems are based on alkyd or acrylic resins, oil-free polyester, silicone-modified polyester or acrylic resin, poly(vinylidene fluoride), or poly(vinyl fluoride). Water-reducible systems, mainly based on acrylic resins, have been developed for aluminum as well as for steel coils [21-24], Drying is carried out by continuous operation in gas- or oil-heated multichamber ovens. 

Plasticizers are used in the polymer industry to improve flexibility, workability, and general handling properties. Dibutyl sebacate and phthalates, such as dibutyl phthalate, diethyl phthalate, dicyclohexyl phthalate, butylbenzyl phthalate, and diphenyl-2-ethylhexyl phosphate, serve widely as plasticizers in vinylidene chloride copolymers, nitrocellulose-coated regenerated cellulose film, and cellulose acetate (Castle et ah, 1988a). In PVC, di(2-ethylhexyl)... 

Uses Synthetic fibers and adhesives chemical intermediate in vinylidene fluoride synthesis production of poly(vinyl dichloroethylene) and LLl trichloroethane comonomer for food packaging, coating resins, and modacrylic fibers. 

Uses. Production of copolymers of high vinylidene chloride content, the other major monomer usually being vinyl chloride such as Saran and VELON for films and coatings... 

Poly(vinylidene chloride) (XLII) and its copolymers with vinyl chloride, acrylonitrile, and acrylates, usually produced by the suspension or emulsion process, are useful as oil, fat, oxygen, and moisture-resistant packaging films (Saran wrap), containers, coatings, tank liners, and monofilaments in drapery fabrics and industrial filter cloths. 

Tlie use of polymer blends has been a very important approach in the development of new materials for evolving applications, as it is less costly than developing new polymers. The compatibility of poly(vinylidene fluoride) (PVDF) with various polymers has been comprehensively evaluated and has led to useful applications in coatings and films. Poly(methyl methacrylate) has been the most studied compatible polymer with PVDF owing to cost and performance advantages. Other acrylic polymers such as poly(ethyl methacrylate), poly(methyl acrylate), and poly(ethyl acrylate) have also been found to be compatible with PVDF. ... 

Copolymers of acrylonitrile and methyl acrylate and terpolymers of acrylonitrile, styrene, and methyl methacrylate are used as bamer polymers. Acrylonitrile copolymers and multipolymers containing butyl acrylate, ethyl aciylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, methyl methaciylate. vinyl acetate, vinyl ethers, and vinylidene chlonde are also used in bamer films, laminates, and coatings. Environmentally degradable polymers useful in packaging are prepared from polymerization of acrylonitrile with styrene and methyl vinyl ketone. 

Poly(vinylidene chloride-co-acrylonitrile) is widely used as a latex coating for cellophane, polyethylene and paper. Since this copolymer is soluble in organic solvents, it is also used as a solution coating. Tile resistance to vapor permeability and the ease of printing on polyethylene and cellophane is increased by coating with this vinylidene chloride copolymer. 

Copolymerization. Vinyl chloride can be copolymerized with a variety of monomers. Vinyl acetate, the most important commercial comonomer, is used to reduce crystallinity, winch aids fusion and allows lower processing temperatures. Copolymers are used in flooring and coatings. This copolymer sometimes contains maleic add or vinyl alcohol (hydrolyzed from the poly(vinyl acetate ) to improve the coating s adhesion to other materials, including metals, Copolymers with vinylidene chloride are used as barrier films and coatings. Copolymers of vinyl chlonde with acrylic esters in latex from are used as film formers in paint, nonwoven fabric binders, adhesives, and coatings. Copolymers with olefins improve thermal stability and melt flow, but at some loss of heat-deflection temperature,... 

Vinylidene chloride polymers have several properties that are valuable in the coatings industry excellent resistance to gas and moisture vapor transmission, good resistance to attack by solvents and by fats and oils, high strength, and the abilrtv to be heat-sealed. 

Vinylidene chloride polymers are often made in emulsion, bul usually are isolated, clned, and used as conventional resins. Stable latices have been prepared and can be used directly for coatings. The principal applications for these materials are as barrier coatings on paper products and, more recently, on plastic films,... 

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