Plastic Product Material and Process Selection Handbook Part 3 ppt

These TPs also possess good low temperature flexibility and heat resistance and have excellent electrical properties.. Polyvinyl Chloride The high volume PVCs worldwide market provides

54 Plastic Product Material and Process Selection Handbook

Polyolefin Thermoplastic Elastomer

TPEs are blends of various amorphous rubbers such as ethylene- propylene and of polyolefin semicrystalline plastics such as PP They are part of the family of TP olefins (TPOs) TPOs are mechanical blends consisting of a hard plastic and softer rubber They are considered different from blends that are dynamically thermoplastic vulcanized (TPV) a process in which the elastomer phase is cured during mixing of the polymers 84, 94

Ethylene-Propylene Elastomer

EP elastomcrs arc random, amorphous polymers with outstanding resistance to ozone, aging and weathering, mainly because of the saturated structure in their hydrocarbon backbone These TPs also possess good low temperature flexibility and heat resistance and have excellent electrical properties Their resistance to hydrocarbons and solvents is poor The low density of these elastomers plus their ability to accept very high levels of extender oils and fillers often gives them a cost advantage over other elastomers in many applications Principal applications are in automotive products, single-ply roofing, thermo- plastic olefins and viscosity index improvers for lubricating oils EP elastomers are the third-largest synthetic rubber consumed worldwide, after styrene-butadiene rubber and polybutadiene rubber World consumption of EP elastomers in 1998 was about 800 thousand metric tons

Polypropylene

PPs arc in the polyolefin family of plastics representing a major plastic used worldwide providing different performances They have low specific gravity and good resistance to chemicals and fatigue PP made with metallocene catalysts (mPP) has improved characteristics such as toughness, stiffness, heat resistance, clarity, barrier properties, high melt flow, and high melt strength 14, 95 Their densities are slightly lower than PEs but are much stiffer, more heat resistant, and have the same chemical and electrical resistance They arc semi-translucent and milky white in color, with excellent colorability Their chemical structure makes them stronger than other members of the polyolcfin family These versatile plastics are available in many grades as well as copolymers like ethylene propylene NEAT PP has a low density of 0.90, which, combined with its good balance of moderate cost, strength, and stiffness as well as excellent fatigue, chemical resistance, and thermal and electrical properties, makes PP extremely attractive for many indoor and outdoor applications There arc hundreds of formulations that are produced

2 9 Plastic property 5 5

.

PP is widely known for its application in the integral so called living hinges that are used in all types of applications; PP's excellent fatigue resistance is utilized in molding these integral living hinges 59 They have superior resistance to flexural fatigue stress cracldng, with excellent electrical and chemical properties This versatile polyolefin overcomes poor low temperature performance and other shortcomings through copolymer, filler, and fiber additions It is widely used in packaging (film and rigid), and in automobile interiors, under-the-hood and underbody applications, dishwashers, pumps, agitators, tubs, filters for laundry appliances and sterilizable medical components, etc 96

Electrical properties are affected to varying degrees by their service temperatures Its dielectric constant is essentially unchanged, but its dielectric strength increases and its volume resistivity decreases as temperature increases

They are unstable in the presence of oxidation conditions and UV radiation Although all its grades arc stabilized to some extent, specific stabilization systems are often used to suit a formulation to a particular environment, such as where it must undergo outdoor weathering PPs resist chemical attack and staining and are unaffected by aqueous solutions of inorganic salts or mineral acids and bases, even at high temperatures Most organic chemicals do not attack them, and there is

no solvent for this plastic at room temperature Halogens, fuming nitric acid, and other active oxidizing agents attack the plastics Also attacked

by aromatic and chlorinated hydrocarbons at high temperatures

PPs have limited heat resistance, but heat-stabilized grades are available for applications requiring prolonged use at elevated temperatures The useful life for products molded from such grades may be at least as long

as five years at 120C (250F), 10 years at 130C (230F), and 20 years at 99C (210F) Specially stabilized grades are UL rated at 120C (248F) for continuous service Basically, PP is classified as a slow burning material, but it can also be supplied in flame-retardant grades

Polybutylene

Part of the polyolcfin family are PBs They are similar to PPs and HDPEs but exhibit a more crystalline structure This crystallinity produces unusual high strength and extreme resistance to deformation over a temperature range o f - 1 0 to 190F Its structure results in a rubberlikc, elastomeric material with low molded-in stress Tensile stress that does not plateau after reaching its yield point makes possible films that look like PE but act more like polyester (TP) films Compared to other polyolefins, they have superior resistance to creep

56 Plastic Product Material and Process Selection Handbook

and stress cracking PB films have high tear resistance, toughness, and flexibility Their chemical and electrical properties arc similar to those of the PEs and PPs

Use includes pipe/tube, packaging, hot-melt adhesives, and sealants Piping for cold-water use out of PBs has a higher burst strength than pipe made from any other polyolefin Large diameter pipe has been successfully used in mining and power generation systems to convey abrasive materials PBs can be alloyed with other polyolefins to provide its inherent advantage Film made into industrial trash bags gives improved resistance to bursting, puncturing, and tearing

Cyclic Polybutylene Terephthalate

CBT| plastic is being developed by Dow with target date to have them commercially available by 2005 422 These plastic polymerize reactively like TSs but have the material properties of a TP Because its initial viscosity is like water it is easy to process CBT will provide significant performance improvements over traditional plastics as well as weight reduction, minimized scrap rates, lower tooling costs, and lower processing costs These cyclics with fiber reinforcements offers stiffness and toughness with a high level of resistance to heat and chemical attack They are dimensionally stable with low water absorption, provide electrical insulation, and can be made to be flame retardant Standard composites fabricating processes can be used (injection, compression, thermoforming, etc.) Parts can be welded, adhesively bonded, and painted Fabricated products are completely recyclable It

is possible to separate them back into their original components without any loss of properties

Applications include auto products such as vertical and horizontal external body panels, truck boxes and tailgates with Class A high quality surface appearances Other grades will be available for applications where structural strength is required Dow predicts many more traditional steel components being made of fiber reinforced plastic (FRP)

Vinyl

Vinyls are one of the most versatile families of plastics The term vinyl usually identifies the major very large production of polyvinyl chloride (PVC) plastics The vinyl family, in addition to PVCs, consists of polyvinyl acctals, polyvinyl acetates, polyvinyl alcohols, polyvinyl carbazoles, polyvinyl chloride-acetates, and polyvinylidene chlorides As

a family, they are strong and abrasion resistant They are unaffected, for the most part, by prolonged exposure to water, common chemicals,

2 9 Plastic property 5 7

and petroleum products However, they should be kept away from chlorinated solvents, such as many household-cleaning fluids Vinyls can withstand continuous exposure to heat up to 130F (54C) and perform satisfactorily at food freezing temperatures 98q~

forms of the materials They generally have in common excellent

elastomeric form vinyls usually exhibit properties superior to those of natural rubber in their flcxural life, resistance to acids, alcohols, sunlight, wear, and aging

They are slow burning and some types are self-extinguishing but they should be kept away from direct heat The vinyls may be given a wide range of colors and may be printed or embossed They generally have excellent electrical properties but with relatively poor weathering qualities are recommended for indoor use only unless stabilized wit suitable additives Vinyls literally can be processed by more techniques than any other plastic Reason is that it contains a relatively polar polymer that allows a large range of formations

Polyvinyl Chloride

The high volume PVCs worldwide market provides a wide range of low cost flexible to rigid plastic with moderate heat resistance and good chemical, weather and flame resistance The manufacture of a wide range of products is possible because of PVC's miscibility with an amount and variety of plasticizers PVC has good clarity and chemical resistance (Figures 2.2 and 2.3)

PVC can be chlorinated (CPVC) and be alloyed with other polymers like ABS, acrylics, polyurethanes, and nitrile rubbers to improve its impact resistance, heat deflection, and processability Although these vinyls differ in having literally thousands of varying compositions and properties, there are certain general characteristics that are common to nearly all these plastics Most materials based on vinyls are inherently

TP and heat sealable The exceptions are the products that have been purposely compounded with TSs or crosslinldng agents arc used

Rigid PVC, so-called poor man's engineering plastic, has a wide range

of properties for use in different products It has high resistance to ignition, good corrosion, and stain resistance, and weatherability However, aromatic solvents, ketones, aldehydes, naphthalenes, and some chloride, acetate, and acrylate esters attack it In general, the normal impact grades of PVCs have better chemical resistance than the high-impact grades Most PVCs arc not recommended for continuous use above 60C (140F) Chlorination to form CPVC increases its heat

80-50 ports PVC powder 20-50 ports ploshctzer (extendeC, fillers) slabilizers, pigments

I Mt

In,,

,rJ f o, oodc~"l mixer I

Sheets and h'Ims

Granules

Extruder

Profiles Covernngs and

tubes

Agglomerates, dry blends'

injection I I Costing and molding machine dipping mactu)~es

coverings and tapes

I Agitaler mixer, ! * Chemical or roll mill, if need ~ e~- physical blowing

foaming plants

Solid and foamed coab'ngs artificial leather, floor covc~ing, paneling

Open or closed flexible foams, sheet foams

Figure 2 ° 2 Examples o f p l a s t i c i z e d - f l e x i b l e PVC

CO D3

¢/t

" 0

8

e- e-i,

Pe ,-t

r n ~ I s

Powder mixing _J l

Slruclural

¢oom products, rigid foams

60 Plastic Product Material and Process Selection Handbook

resistance, flame retardancy, and density, depending on the amount of chlorination introduced In regard to flammability, note that the vinyls release a limited amount of hydrochloric acid during processing

Different blends can be prepared providing different properties Blends with non-compatible polymers such as polyolefin elastomers (POEs) are made to blend by using compatibilizers 143 These flexible PVC blends can be made with no plasticizers resulting in improved properties They are nontoxic, tasteless, odorless, and suitable for use as packaging materials that will come in contact with foods and drugs, as well as for decorative packaging requiring ordinary protection The vinyl plastics can be used in printing inks and be effectively used in coating paper, leather, wood, and, in some cases, plastics In most forms vinyl can be printed

They qualify in many markets such as for packaging, pipe, outdoor construction products (siding, window profiles, etc), and a host of low- cost disposable products [including FDA-grade medical uses in blood transfusion, storage, etc.96] Foam-vinyl strippables are used for metal parts packaging These PVC dispersion plastics are applied in liquid form Foaming takes place during their cure cycle (Chapter 8) PVCs come in a variety of grades, flexible to rigid They are tough, can be transparent (as in blow molded bottles and jugs), and are also a good alloying plastic to improve properties and reduce costs

PVCs inherent characteristics generally require special considerations to ensure the best melt processing conditions and the tool will not be damaged (corrode due to hydrochloric acid) by the PVC One such consideration is specifying the correct tool steel in order to meet products demanding appearances, meet long run production, etc (Chapter 17)

Ultra High Molecular Weight Polyvinyl Chloride

UHMWPVCs are versatile plastics that can provide superior mechanical properties and be formulated to produce a variety of products Because changes in formulations or equipment conditions may be required for processing, these plastics are generally used in plasticized applications; it

is in highly plasticized uses that they show the greatest advantages in producing compounds with improved properties They can bring to flexible vinyls improved tensile, modulus, abrasion, and solvent resistance; low and high temperature performance; and retention of properties during aging

Polyvinyl Acetate

The PVAc copolymers are odorless, tasteless, nontoxic, slow burning, lightweight, and colorless, with reasonably low water absorption They

2 9 Plastic property 61

are soluble in organic ketones, esters, chlorinated hydrocarbons, aromatic hydrocarbons, and alcohols, but insoluble in water, aliphatic hydrocarbons, fats, and waxes Water emulsions have extended the use

of this plastic Used perhaps most extensively as adhesives, they are also employed as coatings for paper sizing for textiles, and finishes for leathers, as well as bases for inks and lacquers, for heat-sealing films, and for flashbulb linings

They include vinyl acetate homopolymers and all copolymers in which vinyl acetate is the major constituent (50% or greater) The major PVAc copolymers are vinyl acetate-ethylene (VAE) and vinyl acetate-acrylic ester (vinyl acrylic) Vinyl acetate-versatic acid (vinyl versatate) and vinyl acetate- maleate are major PVAc copolymer emulsions used

Polyvinyl Chloride Acetate

PVCA is a copolymer of vinyl chloride and vinyl acetate It is a colorless thermoplastic solid with good resistance to water as well as concentrated acids and alkalis It is obtainable in the form of granules, solutions, and emulsions Compounded with plasticizers, it yields a flexible material superior to rubber in aging properties It is widely used for cable and wire coverings, in chemical plants, and in protective garments

Polyvinyl Chloride, Chlorinated

CPVC is a plastic produced by the post-chlorination of PVC Adding more chlorine raises the glass transition tempe::ature of CPVC at 115 to 135C (239 to 275F) and the resultant heat deflection under load from that of PVC at 70C (158F) to a level of 82 to 102C (180 to 219F) depending on formation CPVC has improved resistance to combustion and smoke generation with higher tensile strength and modulus while maintaining all the good properties that rigid PVC possesses Traditional uses are hot and cold-water distribution piping and fittings and industrial chemical liquid handling pipe, fittings, valves, and other different applications

Polyvinyl Alcohol

P V O H (or tradename PVAL) is a crystalline, white powder soluble in water and alcohols It is characterized by water solubility, low gas permeability barrier, high resistance to organic solvents other than alcohol, and crystallinity when stretch oriented Crystallinity allows the material to polarize light A series of hydrolysis levels of the plastic are available that range from room temperature solubility to those not soluble at all The major applications of the PVOHs are in elastomeric products, adhesives, films, and finishes Extruded P V O H hoses and tubing are excellent for use subjected to contact with oils and other chemicals P V O H is used as a sizing in the manufacture of nylon

62 Plastic Product Material and Process Selection Handbook

Polyvinyl Butyral

PVB is colorless, flexible, very tough solid plastic, soluble in esters, ketones, alcohols, and chlorinated hydrocarbons but insoluble in the aliphatic hydrocarbons They are stable in dilute alkali; but slowly decompose in dilute acids Since the year 1930s PVBs have been extensively used as shatterproof safety-glass interlayers and between sheets of acrylic to protect the enclosures of pressurized cabins in aircraft against shattering PVB film interlayers range from 10 to 40 mils They continue to be used as an important resource for the building glass windows, automotive, architectural industries, etc PVBs are also used as coatings for textiles and paper and also as adhesives

Polyvinyl Carbazole

PVCB is brown in color, obtained by reacting acetylene with carbazole The plastic has excellent electrical properties and good heat and chemical resistance Use includes high frequency dielectrics, impregnant for paper capacitors, and photoconductive plastics

Po lyvi n yl fluoride

PVF products are strong and tough, with good abrasion and staining resistance up to fairly high temperatures of 100 to 150C (212 to 302F) and they are classified as slow burning They are generally less chemical resistant than fully fluorinated plastics but show excellent UV resistance and good color retention and are not affected by water Their excellent weatherability has made them a choice material for exterior applications such as coatings for metals (slides, gutters, etc.), plywood finishes, architectural sheets, lighting panels, and glazing for solar energy collection Also for electrical wrapping tape and parting layers for laminates

Polyvinyl Formal

containers and electric wires It resistant greases and oils

Polyvinylidene Chloride

There are flexible and rigid PVDCs They have high strength, abrasion

durability This material is especially suited for injection molding at high speed that provides heavy, thick cross-sections Molded fittings and

Polyvinylidene Fluoride

PVDF is a fluorine-containing TP unlike other plastics It is a crystalline, high molecular weight polymer of vinylidene fluoride Compounds are available that contain at least 60wt% fluorine This nonflammable plastic is mechanically strong and tough, thermally stable, resistant to almost all chemicals and solvents It is also stable to

UV and extreme weather conditions with higher strength and abrasion resistance than PTFE; however, it does not match the high chemical and temperature resistance of PTFE Where unfavorable combinations

of chemical, mechanical, and physical environments may preclude the use of other materials, PVDF has been successfully used Examples include valve and pump parts, heavy wall pipefittings, gears, cams, bearings, coatings, and electrical insulations Its limitations include lower service temperatures than the highly fluorinated fluoropolymers,

no anti-stick qualities, and the fact that it produces toxic products upon thermal decomposition

Polystyrene

PS is a high volume worldwide consumed plastic It is used in many different formulations PS is noted for its sparlding clarity, hardness, low water absorption, extreme ease of processing general purpose PS (GPPS), excellent colorability, dimensional stability, and relatively low cost This amorphous TP often competes favorably with higher-priced plastics It is available in a wide range of grades for all types of processes

In its basic crystal PS form it is brittle, with low heat and chemical resistance, poor weather resistance High impact polystyrene is made with butadiene modifiers that provides significant improvements in impact strength and elongation over crystal polystyrene, accompanied

by a loss of transparency and little other property improvement Modifications available to the basic GPPS include grades for high heat and for various degrees of impact resistance Clarity and gloss are

64 Plastic Product Material and Process Selection Handbook

reduced, however, in the impact grades There are ignition-resistant polystyrenes (IRPSs) Some examples of members in the PS family are compounds of ABS, SAN, and SMA (styrene maleic anhydride) The structural characteristics of these copolymers are similar, but the SMA has the highest heat resistance

PS is soluble in most aromatic and chlorinated solvents but insoluble in such alcohols as methanol, ethanol, normal heptane, and acetone Most fluids in households, as well as drinks and foods, have no effect, but the oil in citrus-fruit rinds, gasoline, turpentine, and lacquer attack PS PSs are available in FDA-approved grades

Waste that occurs during the manufacturing and processing of PS has practically always been fed/recycled back into the processing cycle The reuse of municipal waste is feasible without any problems with uncontam- inated and contaminated materials Each is used in new market products

Polystyrene Copolymer

Copolymers of styrene include a large group of random, graft, and block copolymers Those with a high proportion of acrylonitrile used in barrier films as well as others such as methacrylic-butadiene-styrene copolymer (MBS) plastic is used as modifiers in PVC, SAN, ABS, ASA, etc The styrene-acrylonitrile copolymer (SAN) is the most important when considering volume and number of applications

Polystyrene, Expandable

Popular is expandable polystyrene (EPS) that is a specialized form of

PS Products have low heat resistance, as compared to most TPs Their maximum recommended continuous service temperature is below 93C (200F) Their electrical properties, that are good at room temperature, are affected only slightly by higher temperatures and varying humidity EPS is a modified PS prepared as small beads containing pentane gas which, when steamed, expand to form lightweight, cohesive masses for forms used to mold cups and trays, package fragile products for shipment, etc (Chapter 8) Similar dimensionally stable forms molded from EPS are used as cores for such products as automobile sun visors with surface overlays, etc

Polystyrene Maleic Anhydride

SMA is a copolymer made with or without rubber modifiers They are sometimes alloyed with ABS and offer good heat resistance, high impact strength and gloss but with little appreciable improvement in weatherability or chemical resistance over other styrene based plastics

Crystal Clear Polystyrene

The styrene-butadiene styrene block copolymers with a polybutadiene content of up to 30wt%, which are referred to as crystal clear, impact-

1 9 Introduction 2 9

electrical applications These ratings include separate listings for electrical properties, mechanical properties including impact, and mechanical properties without impact The temperature index is important if the final plastic product has to receive UL recognition or approval

Corrosion Resistance

Complex corrosive environments results in at least 30wt% of total yearly plastics production being required in buildings, chemical plants, transportation, packaging, and communications Plastics find many ways to save some of the billion dollars lost each year by industry due to the many forms of corrosion

Corrosion is fundamentally a problem associated with metals Since plastics are electrically insulating they are not subject to this type of damage Plastics are basically noncorrosive However, there are those that can be affected when exposed to corrosive environments It is material deterioration or destruction of materials and properties brought about through electrochemical, chemical, and mechanical actions

Corrosion resistance is the ability of a material to withstand contact with ambient natural factors or those of a particular artificially created atmosphere without degradation or change in properties Since plastics (not containing metallic additives) are not subjected to electrolytic corrosion, they are widely used where this property is required alone as

a product or as coatings and linings for material subjected to corrosion such as in chemical and water filtration plants, m o l d / d i e , etc Plastics are used as protective coatings on products such as steel rod, concrete steel reinforcement, mold cavity coating, plasticator screw coating, etc

Chemical Resistance

compatibility to chemicals, particularly to moisture, as compared to that

of other materials Because plastics are largely immune to the electro- chemical corrosion to which metals are susceptible, they can frequently

be used profitably to contain water and corrosive chemicals that would attack metals

Plastics arc often used in corrosive environments for chemical tanks, water treatment plants, and piping to handle drainage, sewage, and water supply Structural shapes for use under corrosive conditions often take advantage of the properties of RPs Today's underground tanks must last thirty or more years without undue maintenance To mect these criteria they must bc able to maintain their structural integrity and

66 Plastic Product Material and Process Selection Handbook

include foamed food trays, packaging, disposable cups, and printed displays

Syndiotactic Polystyrene

SPS is a crystalline plastic with far higher heat resistance than standard amorphous PS, lower moisture pick-up, and improved warp-resistance, and outstanding dimensional stability (eliminates the need for mineral fillers commonly used to counter warpage in other plastics such as nylon and PBT) It is made with metallocene catalyst technology This plastic has the highest melting point (518F) (270C) of any styrenic homopolymer It also has high chemical, water, and steam resistance, exceptional electrical properties, and well-balanced impact resistance and stiffness ~~

Po lystyre n e-A c r ylo n i tri le

SAN is hard, rigid, and transparent It has no butadiene as in ABS Excellent chemical and heat resistance, good dimensional stability, and ease of processing characterize it Special grades are available that have improved UV stability, vapor-barrier characteristics, and weatherability SAN is used for tinted drinking glasses, low-cost blender jars and water pitchers, and other consumer goods with longer life expectancies than ordinary PS

Polystyrene-Polyethylene Blend

The target of combining the lower water vapor permeability and good stress cracking of PE (or PP) with the problem free processing and high rigidity of PS in the past proved to be unattainable, because of their incompatibility This situation has been reduced through the use of mixing agents made up of styrene/olefin copolymers, etc PS-PE blends are primarily used as a substitute for PVC and ABS in the form of monofilm or multilayer film to produce thermoformed packaging for foods such as those that contain fat

Polystyrene-Polyphen ylene Ether Blend

The good compatibility of PS and polyphenylene ether (PPE) has been used for a long time to make blends that even with a PS content in excess of 50wt% still count as modified PPE The addition of PPE results in the increase of PS's heat resistance that can be raised to the same range as that for ABS Result is a lower cost plastic

Advanced Styrenic

These ASRs are produced either chemically in a reactor or by blending GPPS and rubber in downstream operations This family of plastics has good toughness and gloss, and very good processability ASRs can be processed on conventional sheet extrusion and thermo-forming equipment They are recommended for applications where intermediate

1 9 I n t r o d u c t i o n 31

coextrusion molding processes that combine different plastics, including those with specific permeability capabilities, are examples of methods used to reduce permeability while retaining other desirable properties (Chapters 2 and 6)

R a d i a t i o n

In general, plastics are superior to elastomers in radiation resistance but are inferior to metals and ceramics The materials that will respond satisfactorily in the range of 1010 and 1011 erg per gram are glass and asbestos-filled phenolics, certain epoxies, polyurethane, polystyrene, mineral-filled polyesters, silicone, and furane The next group of plastics

in order of radiation resistance includes polyethylene, melamine, urea formaldehyde, unfilled phenolic, and silicone resins Those materials that have poor radiation resistance include methyl methacrylate, unfilled polyesters, cellulosics, polyamides, and fluorocarbons

Craze/Crack

Many TPs will craze or crack under certain environmental conditions, and products that are highly stressed mechanically must be checked very carefully Polypropylene, ionomer, chlorinated polyether, phenoxy, EVA, and linear polyethylene offer greater freedom from stress crazing than some other TPs Solvents may crack products held under stress TSs is generally preferable for products under continuous loads

68 Plastic Product Material and Process Selection Handbook

devices, etc Used as an opaque colored sheeting thermoformed to produce an outer coating behind which glass-fiber-reinforced TS polyester plastics are sprayed to produce rigid camper tops, swimming- pool steps, plumbing fixtures with weatherability and repairability reported superior to polyester gel coats Like plywood, there are outdoor weather resistant grades and indoor nonweather resistant grades

Acrylic molding powders are used in different processed such as injection, extrusion, and casting Their mold shrinkage is low A semiviscous liquid casting syrup may be poured into a mold and cured

at temperatures of 150 to 250F to convert it into a hard, rigid solid Acrylic sheets of excellent clarity are made this way (Chapter 11) Products include siding and shutters, automotive and RV exteriors, tractor canopies, marine and leisure craft parts, sanitaryware, interior decorative panels, spas, glazing, and outdoor signs

Among the other forms of acrylics, coatings for protecting metal and acrylic enamels for cars and appliances are available in great variety Water emulsion acrylic paints give excellent service, both indoors and out, and acrylic adhesives are used to bond many carpeting fibers to their backing and provide nonsldd properties and dimensional stability

Polymethacrylic Acid

PMAA is water-soluble and essential in the formation of ionomer plastics

Po lymethyla c r yla te

PMA is used in adhesives, paints, and other products

Po lyethyl metha c r yla te

This is a special plastic in the acrylic family; PEMA provides the usual properties with flexibility

Polyglutarimide Acrylic Copolymer

Family of plastics that can be used in hot fill and retort packaging applications that provide clarity and heat resistance

1 9 I n t r o d u c t i o n 3 3

be accomplished by simply passing warm air over the material Moisture leaves the plastic in favor of the warm air resulting in drying the non- hygroscopic plastics

There are certain plastics that, when compounded with certain additives such as color, could have devastating results Day-to-night temperature changes is an example of how moisture contamination can be a source

of problems if not adequately eliminated when plastic materials are exposed to the air; otherwise it has an accumulative effect The critical moisture content (average material moisture content at the end of the constant-rate-drying period) is a function of material properties, the constant-rate of drying, and particle size

Although it is sometimes possible to select a suitable drying method simply by evaluating variables such as humidities and temperatures when removing u n b o u n d moisture, many plastic drying processes involve removal of bound moisture retained in capillaries among fine particles or moisture actually dissolved in the plastic Knowledge of internal liquid and vapor mass-transfer mechanisms applies Measuring drying-rate behavior under control conditions best identifies these mechanisms A change in material handling method or any operating variable, such as heating rate, may effect mass transfer

During the drying process at ambient temperature and 50% relative humidity, the vapor pressure of water outside a plastic is greater than within Moisture migrates into the plastic, increasing its moisture content until a state of equilibrium exists inside and outside the plastic But conditions are very different inside a drying hopper (etc.) with controlled environment At a temperature of 350F (170C) and - 4 0 F (-40C) dew point, the vapor pressure of the water inside the plastic is much greater than the vapor pressure of the water in the surrounding area Result is moisture migrates out of the plastic and into the surrounding air stream, where it is carried away to the desiccant bed of the dryer

Before drying can begin, a wct material must be heated to such a temperature that the vapor pressure of the liquid content exceeds the partial pressure of the corresponding vapor in the surrounding atmosphere Different &vices such as a psychometric chart can conveniently study the effect of the atmospheric vapor content on the rate of the dryer as well as thc effect of the material temperature It plots moisture content dry-bulb, wet-bulb, or saturation temperature, and enthalpy at saturation

First onc dctcrmincs from the matcrial supplier a n d / o r experience, the plastic's moisture content limit Next determine which procedure will

70 Plastic Product Material and Process Selection Handbook

transparency, or a saturated rubber may replace the polybutadiene, as in ASA and ACS, with an improvement in oxidation resistance

Uses are extensive such as electronic instrument housings, telephones, sports gear, automotive grilles, furniture, etc It is electroplatable, good

as a structural foam, and available as a tinted transparent Other appli- cations include luggage, truck caps, spas, RV and automotive interior and exterior panels and trim, appliances, refrigerator liners, table tops and leisure crafts

Acrylonitrile-Butadiene-Styrene, Transparent

When the refractive indices of the elastomer are matched usually by incorporating methyl mcthacrylate, transparent products are possible Progress in product development is achieved by further matching the properties of those of the standard ABS and also by increasing the light transmission up to 88% Another gain is better processing melt flow- ability of the products An example of an application is in products for medical packaging Other applications include paper feeds for copy machines, watch crystal, transparent building blocks for toy systems, transparent trays for freezers, and packaging for cosmetics

Acrylonitrile-Chlorinated Polyethylene-Styrene Copolymer

ACS is a terpolymcr obtained by the copolymerization of acrylonitrile and styrene in the presence of chlorinated polyethylene Properties are similar to ABS, except that it is more resistant to embrittlemcnt due to oxidative degradation, and has better fire resistance It has a very high flame-retardance; ACS is classified as UL 94 V-0 (1/16in thick specimen) ACS inherently resists the electrostatic deposition of dust resulting in no need for the addition of antistatic agents to the formulation The material's deflection temperature under load ranges from 78 to 90C (172 to 194F) Products made of ACS can be adhered

to each other, hot stamped and painted, and find their greatest use in cabinets and housings

Acrylon i trile-Ethylene/Propylene-Styrene Copo lymer

AES is a tcrpolymcr obtained by grafting styrene-acrylonitrile copolymer

to ethylene-propylenc or ethylene-propylene-diene monomer rubber Similar to ABS except with improved weathering resistance

Acr ylon i trile-Ethylene-Styrene

They are amorphous, opaque, tcrpolymers produced by suspension, emulsion, or continuous mass polymerization Properties arc similar to ABS, with the addition of weatherability or UV protection for outdoor use These materials are usually coextruded over ABS Typically applications have been exterior automotive and RV parts, truck caps, pool steps, outdoor signs, camper shells, and sidings