Plastics Glossary of Terms- Atlantic Poly

29 Jul 2013

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If you deal in plastics or need them in your business, there are some terms you will need to know. Over the last few blog posts, Atlantic Poly, a plastic bag and products company in MA, has been  acquainting you with some of the more necessary plastics terms. Here are the last few...

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.

For anything plastic related, contact Atlantic Poly.