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Plastics Glossary of Terms

Acetate: A derivative of acetic acid. Used in polymers for film extrusion.

Additive: A compound or substance added to a polymer to improve or alter some characteristic of the polymer. Examples include pigments, anti-statics and flame retardant.

Antiblock Agent: A slip additive incorporated in film to prevent the adhesion (sticking) of touching layers of poly films during fabrication, storage, or use.

Antioxidant: An additive which inhibits the degradation and oxidation of material when exposed to ambient air during processing and subsequently in the end product form.

Antistatic Agent: Additive which imparts a slight degree of electrical conductivity to plastics, permitting the dissipation of static electricity. In general terms, stops the passing of static electricity between objects.

Average Molecular Weight: Molecular weight of polymers is determined by viscosity of the material in solution at a specific temperature. This results in an average molecular weight of the molecular chains independent of specific chain length. The value obtained falls between weight and number average molecular weight.

Banbury Mixer: A compounding apparatus consisting of two contra-rotating spiral-shaped blades encased in intersecting cylindrical housings so as to leave a ridge between blades.

Barrel: The tubular portion of the extruder or injection molding machine in which the extruder screw is placed and rotates.

Barrier Resins: Polymers which have very low permeability to gases.

Beta Gauge: A thickness measuring device used for sheeting or extruded pans. The device operates by beta radiation being emitted on one side of the pan and a detector placed on the opposite side. When a pan is passed through the beam, some of the beta radiation is absorbed, which is indicative of the pan thickness.

Biaxial Orientation: The process of stretching a hot plastic film or other article in two directions under conditions resulting in molecular orientation in two directions.

Biodegradation: The degradation of plastics by microorganisms when buried in the soil. Some plastics can be modified to become biodegradable by the incorporation of a biodegradable additive such as corn starch.

Blend: The mixing of polymers with other polymers or copolymers, usually where the mixture results in the desired physical properties.

Blocking: An undesirable adhesion between layers of film or sheeting which may have developed during processing or storage. Blocking can be prevented by adding antiblock agents to the resin.

Bloom: A thin, greasy film on the surface of a plastic film or pan usually caused by the exudation of an additive. Slip additives are designed to migrate or bloom to the surface of films.

Breaker Plate: A perforated plate located at the rear end of an extruder head or die adapter serving to support the screen pack. The breaker plat also helps to generate back pressure in extrusion.

Bulk Density: The density (mass per unit of volume) of a resin in solid form (granular, nodular, pellet, powder, etc.) expressed in g/cm3 or lb/ft3.

Calcium Carbonate: A filler and extender used in thermoplastics. It occurs naturally in the form of minerals such as calcite, chalk, limestone, marble, and whiting.

Cast: The cast film process involves the extrusion of molten polymers through a flat slot die to form a thin film or sheet. This film of molten polymer is then quenched by passing through a set of chill rolls (typically water-cooled). The film quenches immediately, and the edges are trimmed prior to winding or stacking.

Centerfold: Folding a film along the length to obtain a two layered product with half the width.

Cfold: Folding of a film along the length to obtain a two layered product with flaps folded on each side of the folded product. The folded film profile looks like a stapled pin from a stapler.

Chill Roll: A cored roll, usually temperature controlled with circulating water, which cools a molten polymer web on contact before winding.

Coextrusion: Fabrication of a multi-layer film by pumping materials through separate extruders and then merging the extruded material into a common die assembly. These die assemblies are constructed to maintain distinct material layers with fusion occurring at the boundaries due to the pressures and temperature of the extruded material.

Color Concentrate: A plastics compound which contains a high percentage of pigment to be blended into base resins. The term masterbatch is sometimes used for color concentrate as well as for concentration of other additives.

Comonomer: A monomer which copolymerizes with another monomer.

Copolymer: A polymer resulting from the polymerization reaction of two chemically different monomers.

Corona Treat: The process by which the surface energy of plastic films, foils and paper is increased in order to allow improved wettability and adhesion to inks, coatings and adhesives.

Degradation: A deleterious change in the chemical structure, physical properties, or appearance of a plastic caused by exposure to heat, light, oxygen, or weathering.

Density: Weight per unit volume of a substance usually reported in g/cm3 or lb/ft3.

Die: A steel block containing an orifice through which plastic is extruded, shaping the extrudate to the desired form.

Die Gap: Distance between the metal faces forming the die opening.

Die Lines: Vertical or horizontal marks on the extrudate and in the finished product caused by damaged die elements or by contamination held up in the die land.

Differential Scanning Calorimetry (DSC): Method used to determine thermal histories of polymers such as melting points and glass transition points.

Drawdown: In extrusion, the process of pulling the extrudate away from the die at a linear speed higher than that at which the melt is emerging from the die, thus reducing the cross-sectional dimensions of the extrudate.

Elasticity: The property (of plastic materials) of recovering original size and shape after deformation.

Elastomer: A material which, at room temperature, can be stretched under low stress to at least twice its original length and, upon immediate release of the stress, will return with force to its approximate original length.

Elongation: Deformation caused by stretching; the fractional increase in length of a material stressed in tension.

Embossing: The process used to modify the surface texture of a smooth film to achieve special surface properties such as surface area, coefficient of friction, gloss, adhesion, etc., and alter the bulk density of the film. For example, embossing forms a waffle from a pancake.

Erucamide: A fatty acid-based slip additive used in polyolefin resins.

Ethylene Vinyl Acetate (EVA): Copolymeric member of the polyolefin family derived from random copolymerization of vinyl acetate and ethylene.

Extruder, Single Screw: Basic machine consists of a screw, barrel, drive mechanism, resin feed arrangement and controls. The constantly turning screw augers the resin through the heated barrel where it is heated to proper temperature and blended into a homogeneous melt. Before the melt can leave the barrel, it must pass through a breaker plate and screen pack. The melt is then extruded through the die into the desired shape.

Extrusion:Compacting and melting a plastic material and forcing it through an orifice in a continuous fashion.

Blown Film: Process involves extruding a continuous thin walled tube of plastic and inflating it immediately after it leaves the die. The pressure is such that the tube stretches, increasing its diameter and reducing its wall thickness to desired gauge. Air is trapped within the blow tube (bubble) between the die and collapsing rolls which convert it to layflat film to facilitate winding onto a roll.

Cast Film: Process by which a polymer is extruded from a slot die onto the surface of a water-cooled roll. Film is clearer and has more sparkle than blown film.

Coating: Coating of a substrate by extruding a thin film of molten polymer and pressing it onto the substrate.

Foam: Process for producing plastic sheet or molded article with a cellular construction. Either a chemical or gaseous blowing agent is introduced into the polymer melt while the melt is being prepared in the extruder barrel. As the plastic melt exits the die, it expands a predetermined amount forming a cellular wall.

Film: Sheet material having a nominal thickness not greater than 10 mil.

Flame Retardant: Reactive compounds and additive compounds to render a polymer fire resistant. Reactive compounds become an integral part of the polymer.

Gauge: Thickness of plastic film measured in decimal inches or mils.

Gel: Small globular mass which as not blended completely into the surrounding material resulting in a fault in the film or sheet.

Glass Transition Temperature: The temperature at which a reversible change occurs in an amorphous polymer when it is heated to a certain temperature and undergoes a rather sudden transition from a hard, glassy, or brittle condition to a flexible or elastomeric condition.

Gloss: Brightness or luster of a plastic resulting from a smooth surface.

Gravure Printing: The depressions in an engraved printing cylinder or plate are filled with ink, the excess raised portions being wiped off by a doctor blade. Ink remaining in the depressions is deposited on the plastic film or other substrates as it passes between the gravure roll and resilient back-up roll.

Haze: Cloudiness in plastic film. Measured as percent haze, anything below 5 percent is generally considered high clarity.

Heat Sealing: The process of joining two or more thermoplastic films or sheets by heating areas in contact with each other to the temperature at which fusion occurs, usually aided by pressure.

High-Density Polyethylene: This term is generally considered to include polyethylene's ranging in density from about 0.940 to 0.960 and over.

Homopolymer: The result of the polymerization of a single monomer, a homopolymer consists of a single type of repeating unit.

Jfold: Folding of a film along the length to obtain a two layered product with one layer wider than the other.

Lamination: Bonding of a polymeric or non-polymeric substrate to a polymeric film using heat and pressure.

Linear Polymer: A polymer in which the monomeric units are linked together in linear fashion with little or no long chain branching. Examples are linear low-density polyethylene and high-density polyethylene.

Linear Low-Density Polyethylene: Includes polyethylene's ranging in density from 0.915 to 0.935.

Low-Density Polyethylene: This term is generally considered to include polyethylene's ranging in density from about 0.915 to 0.925. In low density polyethylene's, the ethylene monomeric units are linked in random fashion, with the main chains having long and short side branches. This branching prevents the formation of a closely knit pattern, resulting in material that is relatively soft, flexible and tough, and which will withstand moderate heat.

Masterbatch: A concentrated blend of pigment, additives, filler, etc. in a base polymer.

Melt Fracture: Is a phenomenon of melt extrudate in which the surface appears rough or wavy upon exit from the die. Melt fracture may appear uniformly or in certain sections only.

Melt Index: The number of grams, of a thermoplastic resin which can be forced through a 0.0825 inch orifice when subjected to 2160 grams force in 10 minutes at 190°C.

Melting Point: The temperature at which a resin changes from a solid to a liquid.

Modulus of Elasticity: The ratio of stress to strain below the yield point of the material.

Molecular Weight (MW): The sum of the atomic weights of all atoms in a molecule.

Molecular Weight Distribution (MWD): The relative amounts of polymers of different molecular weights (MW) that make up a specific polymer.

Mono layer: A homogenous film formed by pumping molten polymer from an extruder through a die assembly to form a film or sheet.

Neck-In: In extrusion coating, the difference between the width of the extrusion die opening and the width of the coating on the substrate.

Nip: The V-shaped gap between a pair of calender rolls where incoming material is nipped and drawn between the rolls.

Octene: A comonomer used in the production of linear low-density polyethylene's.

Offset Printing: A printing process in which the image to be printed is first applied to an intermediate carrier such as a roll or plate, then is transferred to a plastic film or molded article.

Oleamide: An ivory-colored powder used as a slip additive in polyolefin's.

Orange Peel: An uneven surface texture of a plastic article or its finished coating somewhat resembling the surface of an orange, see Melt Fracture.

Pellets: Tablets of uniform size, consisting of resins or mixtures of resins with compounding additives which have been prepared for molding operations by shaping in a pelletizing machine or by extrusion and chopping into short segments.

Perforating: Processes by which plastic film or sheeting is provided with holes ranging from relatively large diameters for decorative effects (by means of punching or clicking) to very small, even invisible, sizes. The latter are attained by passing the material between rollers or plates, one of which is equipped with closely spaced fine needles or by spark erosion.

Permeation: The passage or diffusion of a gas, vapor, liquid, or solid through a barrier without physically or chemically affecting it.

Permeability: Permeability is the property of a material, i.e. the degree to which it allows permeation to occur.

Photodegradation: Degradation of plastics due to the action of light. Most plastics tend to absorb high-energy radiation in the ultraviolet portion of the spectrum, which results in the formation of free radicals and causes oxidation, cleavage, and other degradative reactions.

Polyethylene: A family of resins obtained by polymerizing the gas ethylene.

Polymer Process Aid (PPA): Additives incorporated into plastics as a modifier to aid in the extrusion of film, pipe, sheet, etc.

Polymerization: A chemical reaction in which the molecules of a simple substance (monomer) are linked together to form large molecules whose molecular weight is a multiple of that of the monomer.

Polyolefins: The class of polymers made by polymerizing relatively simple olefins, including ethylene, propylene, butenes, isoprenes, and pentenes.

Polypropylene: A tough, lightweight, rigid plastic made by the polymerization of high-purity propylene gas in the presence of an organometallic catalyst at relatively low pressures and temperatures.

Pressure Roll: In extrusion coating, a roll used to apply pressure to consolidate the substrate and the plastic film with which it has been coated.

Random Copolymer: A copolymer consisting of alternating segments of two monomeric units of random distribution, including single molecules.

Reinforced Plastics: Molded, formed, filament wound, or shaped plastic parts consisting of resins to which reinforcing fibers, mats, fabrics, etc., have been added before the forming operation. Strength properties are improved.

Resin: An organic substance of natural or synthetic origin characterized by being polymeric in nature.

Screen: Woven metal screens are installed across the flow of plastic in an extruder. They are located between the tip of the screw and the die. Supported by a breaker plate, the screens strain out contaminants and increase back pressure.

Sheeting: Sheets are distinguished from films in the plastics and packaging industry only according to the thickness. A web under 10 mils (.010 inch) thick is usually called a film, whereas a web 10 mils and over in thickness is usually called a sheet. Sheeting is most commonly made by extrusion, casting, and calendering.

Shelf Life: The length of time over which a product will remain fit for use during storage under specific conditions.

Silica: Naturally occurring silica occurs in deposits which are 99 percent silicon dioxide. The hardness provides both mechanical strength and abrasion resistance. Silica's are an economical extender-filler which is thermally stable, pure, low in ionic impurities, and hard. They are often used as antiblocking agents in polyolefin's.

Slip Agent: Provides surface lubrication following the processing of plastics. Compounded into the plastic, the additive gradually migrates to the surface where it reduces the coefficient of friction.

Slitting: The conversion of a given width of plastic film, tube, or sheeting to several various widths by means of knives.

Specific Gravity: The ratio of weight of a given volume of a substance to that of an equal volume of water at the same temperature. The temperature selected varies among industries, 15°C (60°F) being the usual standard.

Specific Heat: THe amount of heat required to raise a specified mass by one unit of a specified temperature, usually expressed as Btu/lb/ °F. or cal/g/°C.

Stabilizer: Ingredient used in the formulation of some polymers to assist in maintaining the physical and chemical properties of the compounded materials, for example, heat and UV stabilizers.

Static Eliminators: Mechanical devices for removing electrical static charges from plastic articles. Types of static eliminators include static bars, ionizing blowers, and air guns.

Stearamide: A slip additive used in polyolefin's.

Strain: In tensile testing, the ratio of the elongation to the gauge length of the test specimen, that is, the change in length per unit of original length.

Stress: The force producing or tending to produce deformation divided by the area over which the force is applied.

Surface Tension: A fluid in contact with a surface exhibits phenomena, due to molecular attractions, which appears to arise from a tension in the surface of the fluid. It may be expressed as dynes per centimeter or as ergs per square centimeter.

Tack: The stickiness of an adhesive, measurable as the force required to separate an adherent from it by viscous or plastic flow of the adhesive.

Tackifier: A substance such as a resin ester which is added to synthetic resins or elastomeric adhesives to improve the initial and extended tackiness of the film.

Talc: A natural hydrous magnesium silicate, used frequently as a filler such as steatite, talcum, mineral graphite.

Tear Resistance: Resistance of a material to a force acting to initiate and then propagate a failure at the edge of a test specimen.

Tensile Strength: The maximum tensile stress sustained by the specimen before failure in a tension test. Usually expressed in pounds per square inch or megapascals. The cross-sectional area used is that of the original specimen, not at the point of rupture.

Thermoforming: The process of forming a thermoplastic sheet into a three-dimensional shape by clamping the sheet in a frame, heating it to render it soft, then applying differential pressure to make the sheet conform to the shape of a mold or die positioned below the frame.

Thermoplastics: Resins or plastic compounds which, in their final state as finished articles, are capable of being repeatedly softened by an increase of temperature and hardened by a decrease of temperature.

Thermosets: Resins or plastic compounds which in their final state as finished articles are substantially infusible and insoluble.

Titanium Dioxide: A white powder available in two crystalline forms, the anatase and rutile types.

Transition Temperature: The temperature at which a polymer changes from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one.

Treater: Equipment and process used to render a surface of inert plastics, such as polyethylene, more receptive to inks, adhesives, or coatings.

Vapor Barrier: A layer of material through which water vapor will not pass.

Vicat Softening Point: The temperature at which a flat-ended needle of 1 square millimeter circular or square cross section will penetrate a thermoplastic specimen to a depth of 1 mm under a specified load using a uniform rate of temperature rise.

(ASTM D-1525-58T).

Virgin Material: Any plastic compound or resin that has not been subjected to use or processing other than that required for its original manufacture.

Viscosity: The measure of the resistance of a fluid to flow (either through a specific orifice or in a rotational viscometer).

Wrinkle: A surface imperfection in plastic films that has the appearance of a crease or wrinkle.

Yellowness Index: A measure of the tendency of plastics to turn yellow upon long-term exposure to light or heat.