Acetal plastics homopolymer

Polyvinyl acetate emulsions for manual application in the production of adhesive bound books were examined for stability. It was found, among other things, that plasticized homopolymers had poor or moderate stability, while copolymer types showed very high stability. The addition of calcium carbonate and calcium acetate could improve the lasting qualities of unstable materials but had little effect on the very stable ones. The addition of these buffering agents made the adhesive less acid and less damaging to papers (6). 

ISO/TS 20225 2001 Global medical device nomenclature for the purpose of regulatory data exchange ISO/ASTM 51650 2002 Practice for use of cellulose acetate dosimetry system NF EN ISO 4608 1998 Plastics. Homopolymer and copolymer resins of vinyl chloride for general use. Determination of plasticizer absorption at room temperature. 

Acetal Polyoxymethylene Homopolymer—POM PTFE Lubricated, azom.com Article ID 875. Source Plascams, Rubber and Plastics Research Association (RPRA). 

Since plastic materials are seldom supplied without the addition of certain additives and fillers, a classification system must be used to avoid confusion. For example, the specification for acetal materials covers three main types of acetal resins homopolymer, copolymer, and terpolyerm. The resin types are subdivided into classes according to the grade descriptions. The group 1, class 1 represents general-purpose homopolymer acetal resin, and group 2, class 3 represents impact modified copolymer acetal resin. Table 1-1 lists the detailed requirements for acetal materials. 

The most widely used resin in water-dispersion form is polyvinyl acetate in homopolymer and copolymer variety. Polyvinyl acetate latex is the basis for the common household white glue, of which Elmer s (www.elmers.com) is probably the most well known. Products of this type are good adhesives for paper, plastics, metal foil, leather, and cloth. Their major use is in packaging for flexible substrates. This... 

Acetal Resins. These are high performance plastics produced from formaldehyde that are used for automotive parts, in building products, and in consumer goods. Acetal resins (qv) are either homopolymers or copolymers of formaldehyde. Typically, the resin is produced from anhydrous formaldehyde or trioxane. The acetal resins formaldehyde demand are 9% of production (115). 

Copolymers wet and adhere well to nonporous surfaces, such as plastics and metals. They form soft, flexible films, in contrast to the tough, horny films formed by homopolymers, and are more water-resistant. As the ratio of comonomer to vinyl acetate increases, the variety of plastics to which the copolymer adheres also increases. Comonomers containing functional groups often adhere to specific surfaces for example, carboxyl containing polymers adhere well to metals. 

When more than routine water resistance is required, a copolymer vinyl acetate emulsion can be used. The plasticizing comonomer in the polymer particles increases their intrinsic coalescing ability thus, they can coalesce more readily than homopolymer particles to a film that has a higher resistance to water. This resistance to water does not extend to the organic solvents, however, which are better resisted by homopolymer films. The soft copolymers have lower solubility parameters than homopolymers and are more readily attacked by solvents of low polarity, eg, hydrocarbons. 

Properties of plastic LDPE LLDP E HDPE PP PVC (flexible ) PS ABS Polyacryhc (glazing) Polycarbonat e (glazing) Epoxy (minera 1 fihed) Acetal homopolym er... 

Vinyl chloride polymers are produced in two main types, homopolymers and copolymers, usually with vinyl acetate. Both types can be plasticized by a wide variety of plasticizers (qv), usually esters. Rigid or unplasticized PVC is used extensively for pipe. The plasticized material is used largely in floor coverings. The homopolymer itself is inherently fire-resistant, but addition of plasticizers, unless they are especially fire-resistant, considerably reduces this characteristic (see Elame retardants). 

Random copolymers of vinyl chloride and other monomers are important commercially. Most of these materials are produced by suspension or emulsion polymerization using free-radical initiators. Important producers for vinyl chloride—vinyUdene chloride copolymers include Borden, Inc. and Dow. These copolymers are used in specialized coatings appHcations because of their enhanced solubiUty and as extender resins in plastisols where rapid fusion is required (72). Another important class of materials are the vinyl chloride—vinyl acetate copolymers. Principal producers include Borden Chemicals Plastics, B. F. Goodrich Chemical, and Union Carbide. The copolymerization of vinyl chloride with vinyl acetate yields a material with improved processabihty compared with vinyl chloride homopolymer. However, the physical and chemical properties of the copolymers are different from those of the homopolymer PVC. Generally, as the vinyl acetate content increases, the resin solubiUty in ketone and ester solvents and its susceptibiUty to chemical attack increase, the resin viscosity and heat distortion temperature decrease, and the tensile strength and flexibiUty increase slightly. 

In addition to homopolymers of varying molecular and particle structure, copolymers are also available commercially in which vinyl chloride is the principal monomer. Comonomers used eommercially include vinyl acetate, vinylidene chloride, propylene, acrylonitrile, vinyl isobutyl ether, and maleic, fumaric and acrylic esters. Of these the first three only are of importance to the plastics industry. The main function of introducing comonomer is to reduce the regularity of the polymer structure and thus lower the interchain forces. The polymers may therefore be proeessed at much lower temperatures and are useful in the manufacture of gramophone records and flooring compositions. 

The polymerization of alkyl vinyl ethers is of some commercial importance. The homopolymers, which can be obtained only by cationic polymerization, are useful as plasticizers of other polymers, adhesives, and coatings. (The copolymerization of vinyl ethers with acrylates, vinyl acetate, maleic anhydride, and other monomers is achieved by radical polymerization but not the homopolymerizations of alkyl vinyl ethers.)... 

The industrial synthesis of polyformaldehyde [poly(oxymethylene)] occurs by anionic polymerization of formaldehyde in suspension. For this the purification and handling of monomeric formaldehyde is of special importance since it tends to form solid paraformaldehyde. After the polymerization the semiacetal end groups have to be protected in order to avoid thermal depolymerization (Example 5-13). This is achieved by esterfication with acetic anhydride (see Example 5-7). As in the case of trioxane copolymers (see Sect. 3.2.3.2) the homopolymers of formaldehyde find application as engineering plastics. 

Plastics for which the adhesion of coatings may be improved by plasma pre-treatment are reported to be polyethylene, polypropylene, polycarbonates, polyacetals, polyaromatic esters, polyimides, polyamides, polyphenylene ether, polyacrylates, acetal homopolymer, and poly(ether imide). 

Copolymerization with vinyl acetate has a strong effect on the nature of the surface of the polymer particles, but the plasticization effect is comparatively weak. With increasing content of vinyl acetate in the copolymer the latex stability will pass through a distinct maximum before decreasing below the stability level of the homopolymer. 

Polyvinyl acetate homopolymer emulsion. High molecular weight, large particle size resin. May be used with thermosetting resins, starches, softeners, nondurable water repellents and plasticizers. Base for adhesives. T(g) 28C. 

To illustrate this point consider the production of lacquers for PVC films and sheeting. Such lacquers contain a PVC homopolymer or low-acetate vinyl chloride-vinyl acetate copolymer, poly(methyl methacrylate), a plasticizer and perhaps some stabilizers, dulling agents (such as silica), pigments, and so on. Methyl ethyl ketone (MEK) is the solvent of choice because it gives the best balance of low toxicity, volatility, and low cost. Any other solvent is effectively... 

Adhesive Emulsions. Thermoplastic, synthetic polymers can be prepared as emulsions for use as adhesives. For example, while EVAc hot-melt adhesives described in the previous section contain less than 40% VAc, when the content of VAc in the copolymer is increased to 60%, and the copolymer is prepared in the form of aqueous emulsions, a very useful and versatile adhesive polymer is obtained. Although the VAc homopolymer, poly(vinyl acetate), is a brittle solid, with a Tg = 28 °C, the ethylene units present in the EVAc copolymer act as an internal plasticizer, and lower the Tg to below room temperature. The plasticization results from the reduction of interchain interaction of the VAc polymer chains by the ethylene units interspersed among the strongly interacting VAc units. This reduction of the Tg has important consequences because the formation of a flexible adhesive film from the emulsion depends upon the Tg of the polymer. 

Poly(vinyl chloride) may also be internally plasticized by copolymerization of vinyl chloride with vinyl acetate, as mentioned earlier. It is not possible to obtain the same result from a mixture of the same proportions of PVC and poly(vinyl acetate) homopolymers. Incorporation of vinyl acetate into the polymer chains produces the intimate association of components needed to lower the temperature required for processing in much the same way as an added plasticizer does. Important end uses for poly(vinyl chloride-co-vinyl acetate) at low levels of vinyl acetate incorporation are phonograph records and floor tiles, and also for sheeting, when added filler will also be used. 

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