Document 5krnj7vNNd01MRzQ5VjnrQLLz

Fblyvinyl and vinyl copolymers ByJ.R. Mehall* andK.L. Brenisi \ Vinyl polymer* and copolymer* com prise one of the most important (roup* of thermoplastic*. The characteristic common to the members of this group is their derivation from vinyl chloridt (CH, - CHCI), vinyl acatate (CH, CHOCOCHj), or vinylidene chloride (CH, " CC1,). These thermoplastic polymer* include polyvinyl chloride (fvc) and copolymer*, chlorinated eve, polyvinyl acetate, polyvinylidene chlor ide, polyvinylidene fluoride, polyvinyl alcohol, and polyvinyl butyrate. eve and copolymen comprise 84% of the total polyvinyls produced and are therefore the largest family in the group. One of the primary reasons for this large use level is the wide range of properties possible for fvc by compounding with various lubricants, plasticiser*, process ing aids, stabilisers, impact modifiers, and other additives. These properties allow the production of a wide variety of products from rigid pipe to flexible thin film. PVC manufacturing pcocaasse All four basic manufacturing processes involve the polymerization of the monomer(s) in pressure vessels equipped with agitator* and heat-removal systems. Polymerization is initiated by free radi cals produced by the thermal decom position of peroxides and perozydicarbonates and proceeds exothermically at temperatures of 40 to 70* C. Reaction temperature, agitation characteristics, and reactor ingredient* are the primary determinants affecting polvmM- proper ties. In the most widely used process, sus pension polymerization, monomer drop- `MiMfct, and Kifoup Leader, FVC Tacfaaiea] Canicr, DiasoM Shamrock Crp,, HOC Superior Av,, Cleve land. Ok 44114. lets are suspended in an aqueous medium by a combination of agitation and pro tective colloids such as methyl cellulorn, gelatin, or partially hydrolyzed polyvinyl alcohol. Average fvc particle diameter is typically 100 to 125 microns. The resultant resin flurry is stripped to remove residual monomer, then is centri fuged and dried. In the moss polymerization process, the monomer is converted to fvc in the abeence at water in two specifically de signed reactors. This two-step polymeri sation process involves partial conversion in a vertical reactor followed by final conversion in a horizontal reactor. After stripping the residual monomer, the product is ready for uae. The emulsion polymerization process is similar to the suspension process ex cept that a colloidal dispersion of mono mer!*) is maintained with the addition of emulsifying agents. Water-soluble free radical initiators are used to produce particles which average 0.5 micron in diameter, This latex is stripped to remove residual monomer and used directly or spray-dried to produce a powder for use in plastiaols and organosols. In the least widely used process, solution polymerization, monomer(s) is first dissolved in an organic solvent, then polymerized. The resultant poly mer is precipitated from the solution followed by a solvent removal step. The process is used primarily to produce specialty copolymers for coating and ad hesive applications. Types of PVC fvc homopolymer resins are produced with various characteristics to meet specific end-use requirements. The primary differences between homopolymers are their molecular weight, surface characteristics and porosity, and particle size. High-molecular-weight resins generally have better physical properties while lower-molecular-weight resins are easier processing. Surface characteristics and porosity are impor tant determinants in the compounding process, especially if plasticizers are involved, Particle size is important in dis tinguishing between emulsion resins and suspension or mass resins. Homopolymers are used in the ma jority of fvc applications but copoly mers are favored in some applications. Vinyl chloride-vinyl acetate copolymers are used in solution coatings because of their greater eoiubility, and in vinyl asbestos floor tile because of their higher melt flow end pigment binding ebility. Poet chlorination of fvc homopolymers improves the beet deflection tempera ture sufficiently to allow cfvc pipe to be used in hot-water applications. PVC BsmpounJtag fvc by itaelf is not a commercially ueefut polymer. To achieve proceseibility and performance, various compounding in gredients must be added. The one addi tive common to all fvc compounds is s thermal stabilizer, fvc is a thermodegradable polymer and requires stabili zation to prevent degradation during processing. Depending upon type and level used, the stabilizer may ato con tribute to extending the service life of the end product. In addition to thermsi stabilizers, major additives may also include lubri cants, plasticisers, impact modifiers, process aids, fillers, end primary pig ments. Minor additives, used for specific purposes, include uv stabilizers, anti oxidants, blowing agents, flame retard ants, fungicides, antistatic agents, and antiblocking agents. Depending upon the type of fvc and i I i URL 14513 98 Modem Plastics Encyclopedia 1977- the proceesing method, eve compounds egg be powder*, pellet*, or liquid*. Pow der compounds are made by ribboo blending or high-istensity mixing of the fvc with all of the desired additives present. 'nmae powders are then pro- eresed directly. Pellet* are powder com- pouDde which have been put a vaeticitkn procedure and die-face cut or cubed to provide earn of shipment, handling, processing, and, in some case*, t provkto preliminary work input into the compound to improve end-product properties aucb a* clarity and absence of gel*. Liquid systems an plastieol* (emulsion resina^lasticizers and other additives) and organosols (emulsion resih/plasticizerm/solventa and other additives). Both can be mixed on low- ear planetary mixer* or medium- ibear, high-speed blade-type misers. Thermal stabilisers. The most common stabilisers for use with rvc are organo- meullic salts--usually tin, lead, barium, cadmium, calcium, and cine compounds. Epoxides, phosphite chelators, antioxi dants, etc., also are commonly used. While thermal stabilisers usually have little influence on most structural proper ties, they have a grass effect on such properties as electrical and outdoor weathering. Plasticisers impart flexibility to pvc. Properties of plasticised pvc depend greatly on the type and amount of plasti cizers used. The level of plasticiser used may vary from 10 parts per hundred of resin (p.h.r.) in semirigid compounds to 100 p.h.r. m very soft compounds. Phthalala esters are the most widely used types, but other organic acid esters, such at adipates, aselates, etc., and or ganic phosphate esters and epoxidized oils also are commonly used. Mixtures of various types of plasticisers often are used to obtain desirable coet-performance characteristics. End-use properties such as low migration, low-temperature flexi bility, flame retardance, and enhanced thermal stability are major considera tions in determining the use of one or a blend of plasticisers. Lubricant*. The primary lubricants used in the processing of pvc are waxes, fatty esters, and metallic soaps of fatty acids. Lubricants facilitate the melt flow and processing characteristics of pvc. Lubricants are classified as internal, external, or both, depending on chemical structure and compatibility. The correct types and amounts of lubricants are im portant for optimum processing and development of maximum physical prop erties. The choice of lubricants is also important to clarity, electrical proper ties, outdoor weathering and other char acteristics. Processing aid* such as methyl meth acrylate copolymers or styrene-acrylo nitrile copolymers frequently are used in rigid pvc compounds. They increase homogeneity end hot-melt strength dur ing processing. Impact modifiers are used most often with unplasticized rigid pvc compounds to improve impact resistance. Typical impact modifier* are elastomeric poly mer* such as sins, am, *va, and cm. De pending upon the degree of impact re sistance desired, use levels vary in the 6 to 15 p.h.r range. At Itvtls of 15 p.h.r. or higher these elastomeric modifiers have significant effect* on other physical properties, e.g., tensile, modulus, specific gravity, heat deflection temperature, etc. Fillers, by definition, are used pri marily to lower the raw material cost of pvc compounds. Calcium carbonate is the moet common filler used. Significant changes in finished product physical properties can be expected de pending upon the filler particle size, surface treatment, and use level in the compound. Primary pigments are used to impart color, opacity, and weatberability to pvc compounds. Both organic and in organic pigments can be used. Coat and end requirement* are the determining factors in the types and use levels of pigment*. FVC processing The most common methods of converting pvc compound* are by melt and liquid proceeding. Rigid and flexible pvc compounds in solid form, either powder or pellets, are converted by melt processing. The melt ing process is accomplished by internal (hear) and external heating in combina tion with pressure via several different type* ofprocessing equipment. in extrusion, both single and multiple screw extruders are used. Compounds run the range from rigid and semirigid to foil flexible compounds. Essentially any continuous shape, irregular or symmetri cal in croas-esetion, can be produced by the extrusion process. Some examples of products are profiles, pipe, blown film sheet, tubing, etc. Both rigid and flex ible cellular vinyls also are processed by extrusion. Injection molding of flexible vinyl com pounds is relatively easy. Injection mold ing of rigid vinyl has become practical with the development of reciprocatingscrew injection molding machines. Highsbear screws and lower-molecular-weight vinyl resins make it possible to generate low-viscosity melts which have accept able thermal stability and can flow into the outermost parts of the mold cavity. Injection molding is used to produce discrete parts varying in shape from very simple to very complex. In blow molding, extruded tubular parisons are damped in molds and airblown to conform to the mold. Pro grammed control of the parison provides a more uniform wall thickness and has helped significantly to reduce costs in blow molding operations. Blow molding is used extensively in the manufacture of rvc bottles or other container*. Injection molding of parisons, particularly for mall containers, allows lower scrap generation and more efficient utilization of compound. Calendering produces a product similar to that made by flat-die extrusion of film and sheet. It is a large-volume proceasing method requiring high capital equipment investment compared with the extrusion process. Calendering re quires prefluxinf of the compound on Banbury/roll q^l equipment at s rate matching tbs calender's capacity. Some times, m conjunction with the Banbury/ roll mill equipment, a abort-barreled extruder is used to feed the calender rolls. Calendering produces flexible and rigid vinyl sheeting in the 3 to 25 mil thickness range. Production rates are high and the process is particularly good for thin-film applications. Powder coating is another method which has been recently applied to both flexible and rigid vinyl powder com pounds. The principal application tech niques are electrostatic spray, fluidized bed, and slectroatatic fluid bed coating. Both rigid and flexible compounds can be applied as 100% solid coatings on metal and other substrates. This technol ogy is efficient and avoids problems associated with solvent-based costings. In the liquid processing of pvc resins there are usually throe basic types: piesUaols and organosols, solution coatings, and latexes. In liquid processing, fine particle aixe retins (0.2 to 2 microns), known as dispersion or emulsion resins, are dispersed in liquid plasticizers by low- to medium-shear agitation. The resin/plasticiser interaction must be minimised to obtain low viscosity which remains stable for an extended storage time at ambient temperatures. Formulating vinyl dispersion resins is similar to that for melt processed resins, except that all additives must be carefully chosen to obtain the desired rheological properties. Small-particle- ize suspension resins (blending resins) often are used to replace part of the dispersion resin to reduce cost and/or to adjust flow properties. If these disper sions contain little or no volatile ingredi ents, they are referred to as plastieols. Volatile solvents, nonpolar diluents, and/or more polar dispersants, are some times added to reduce viscosity and/or permit reduced plasticizer levels, in creasing hardness. In this case, the re sultant dispersion is known ss an organosol. Heat without pressure or shear is all that is required to convert plastieols and organoeols to flexible solid or cellular materials quite similar in physical and chemical properties to flexible vinyl products prepared by the melt process. Heating these dispersions to about 177 C. (350* F.) causes mutual solubilization of the resin and plasticizer, resulting in a homogeneous melt. No working of the hot melt is required, as is the case with melt processing. Simply cooling the melt to below 60* C. (140* F.) produces s tough, flexible vinyl product. Dispersion resin compounds are used for coatings and cast moldings. Roll casting, spraying, and dipping are all employed to coat s variety of substrates. Fabrics, coil metal, paper, and roll goods flooring usually are processed by knife or roll coating. Spray coating is URL 14514 Modem Plastics Encyclopedia 1977-1978 99 URL H515 used oc stamped or preformed metal- Racks, other complex parts, and eupported and unsupported flows are produced by dip coating. Rotational casting of plastiaok is used to sold open or closed hollow objects such as dolls, balls, and automotive arm rests. Slush molding is used to efficiently produce open hollow parta such as boots sod traffic cones. Organosols are used to produce thin filma of higher kardnese then can gen erally be obtained from plaetieols. 'Rte higher hardneee is possible due to the uee at volatile solvents and low coeeentra- tkos ofplasticisers. Organosols most commonty are processed by spray and roll costing. Foamed plastiaols account for a signifi cant portion of overall dispersion resin consumption. Foamed dispersions ere made by mechanical or chemical expan sion of plestieol before fusion, or by chemical expansion of fused melts. When pressure molded, vinyl foam is com pletely closed-cell end useful for thermal insulation end flotation applications. rvc and copolymers with vinyl acetate and vinylidene chloride can be dissolved by electron donor solvents to produce vinyl solution*. Viscosity depends upon the composition and molecular weight of the resin and the type and concentra tion of solvents. Some of the copolymers contain polar groups such as hydroxyl or carbonyl for improved adhesion to metal, end for cross)inking reactivity with epoxy, isocyanate, end methyloltype polymers. All common liquid coat ing methods at application can be used. Solution technology permits production of hard thin films at 1 mil or less at room temperatures. It does, however, impose some ecological problems at s result of the solvents used. rvc and copolymers also are available in latex form. This class of vinyls repre sents a relatively small part at the overall vinyl market. Latexes are true colloidal aqueous dispersions of vinyl resin which have particles of usually 0.2 micron or smaller average diameter. They are used for coating, impregnating, or satu rating paper, fabrics, and leather. All common liquid-coating methods--knife, roll, spray, brush, and curtain--can be used. good low-temperature properties, and up holstery material with Boftaeae and a wide range of colors. Packaging applications consume a largo portion at the extruded and film and sheet. Rigid dear sheet is used in blister packs and boa lide. Highly plasticised extruded filma are used in the packaging of food products, pvc bottles are used to contain codling oil, cosmetics, and liquid detergents. Growth of pvc bottles was slowed when trace amounts at vinyl chloride monomer (veu) were found in certain bottle contents. Since then, producers have lowered the residue) vest levels in the bottles to that vcm migration cannot reasonably be ex pected to occur. Growth in this area is ex pected to return. Houeehold uses and consumer goods require large quantities of pvc. Furni ture upholstery and wall coverings are the ma}re household uses; however, shower curtains, garden hoses, and smallappliance components an important products. Phonograph records are the largest pvc consumer product followed by footwear. Other consumer goods are toys, sporting goods, and outerwear. Transpoliation uses for pvc include upholatery, vinyl car tops, floor mats, and trim. Other pvc uses include medical tubing, credit cards, and a variety of miscellaneous items. Other potyvkiyla Other polyvinyls with commercial utility include polyvinyl acetate (pvac) homopolymer, and copolymers of vinyl ses tets with acrylates, maleate*, and ethylene. These are used primarily in emulsion or latex form for paints, ad hesives, textile sizing and coating, and pigment binders and coatings for paper. Special homopolymer* and copolymers are used as chewing gum bases. Chemical derivatives of polyvinyl acetate include polyvinyl alcohols, polyvinyl formal and polyvinyl butyral. Polyvinyl alcoholt are manufactured Bm different molecular weights and to Btate contents, pva resins usually an as aqueous solutions. In the textik ; I Bdustry, pva is used as a warp sis* Ba finishing resin to impart stiftun ; Bis useful for paper coatings, whet* h parts oil and grease resistance, ink hoc E out, and solvent resistance, pva aohitiou b are food adbeaivee for wood and ptp? E Major applications far pva u* j.f B moistansble adhesives for envelopei I labels and for water-resistant sdW F m food and beverage cartons, pva fils.. ( also are used for mold release in poK ( aster fabrication processes and for poU> [ izing optica. Cold water-soluble ft-, t are used for disposables such as hoep u t laundry bags and detergent packages ft Polyvinyl aeetaU are retina demr from the reaction of pva with sldebvda I Only polyvinyl formal* and polyvQt ft butyral* have any commercial imp* tance. Polyvinyl formal is used primarily; the manufacture of enamels for hti: resistant wire insulation, usually combination with phenolica. Polyvtr. butyral has an important use in sur primers for marine applications; but serves mainly si an adhesive interUve in safety glass, where clarity, imp*- resistance, and weathering stability t* critical properties. r Polyvinylidene chloride and copoi> X men with vinyl chloride, alkyl acrylic fc and acrylonitrile an soft, flexible plsstio S They are used mainly for film and costoi P applications in the packaging indunr V and for fibers. Resistance to oils, ftu ^ oxygen, and water vapor are their print.' * advantages. These polymer* may be usr- alone, usually as biaxially oriented, c supported films, or may be combine: with other substrates such as cellophts' R, pvc, paper and paperboard, either t lamination or coating techniques. Extruded monofilament* are used - household and automotive upholsten drapery fabrics, filter cloths, iwe. screening, and Venetian blind tapes. PVC applications rvc bomopolymere and copolymers are used in two basic compounded forms which become rigid or flexible vinyl products. Rigid vinyls are unplasticized thermo plastic materials that are bard and stiff. They cp" be transformed into trans parent, high-clarity film, sheet, and con tainers for packaging. A larger use is as opaque colored compounds used to make pipe, fittings, conduit, house siding, and a variety of profiles for the automotive, construction, and appliescsareas- Flexible vinyls are thermoplastic ma terials that contain plasticizers that impart flexibility. Flexible vinyls result in packaging films with good clarity, wire and cable coverings with good electrical properties, refrigeration gaskets with 102 Modem Plastics Encyclopedia 1977-19