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Note: The definitions in this section were derived from the following sources:
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Adhesive - A substance which applied as an intermediate is capable of holding materials together by surface attachment.
Aliphatic - Any organic compound in which the main structure is a chain of carbon atoms joined to each other is classified as being aliphatic.
Alloy - Composite material made up by blending polymers or copolymers with other polymers or elastomers under selected conditions, e.g., styreneacrylonitryle copolymer resins blended with butadiene-acrylonitrile rubbers.
Anti-blocking and slip agents - Surface-modifying additives to reduce friction and tackiness of polyolefin films.
Antistatic Agents - Methods of minimising static electricity in plastic materials. Such agents are of two basic types: (1) metallic devices which come into contact with the plastics and conduct the static to earth. Such devices give complete neutralization at the time, but because they do not modify the surface of the material it can become prone to further static during subsequent handling; (2) chemical additives which, mixed with the compound during processing, give a reasonable degree of protection to the finished products.
Aromatic - Aromatics are a highly reactive group of hydrocarbons with unsaturated rings of carbon atoms, producing a great variety of products. As their name implies, they have a strong odor, which is not unpleasant.
Autoclave - Closed strong vessel for conducting chemical reactions under high pressure; (2) in low-pressure laminating, a round or cylindrical container in which heat and gas pressure can be applied to resin-impregnated paper or fabric positioned in layers over a mold.
Autoclave Molding - Modification of the pressure bag method for molding reinforced plastics. After lay-up, entire assembly is placed in steam autoclave at 50 to 100 psi. Additional pressure achieves higher reinforcement loadings and improved removal of air.
Bloom - A visible exudation or efflorescence on the surface of a material.
Blow Molding - A widely used process for the production of hollow thermoplastic shapes. The process is divided into two general categories: extrusion blow molding and injection blow molding. These processes are typically used to manufacture plastic bottles and containers.
Blown Film - A thermoplastic film which is produced by extruding a tube, applying a slight internal pressure to the tube to expand it while still molten and subsequent cooling to set the tube. The tube is then flattened through guides and wound up flat on rolls. The size of blown tubing is determined by the flat width in inches as wound rather than by the diameter as in the case of rigid types of tubing.
Chalking - A powdery residue on the surface of a material often resulting from degradation.
Chlorinated Polyvinyl Chloride Plastics - Plastics based on chlorinated polyvinyl chloride in which the chlorinated polyvinyl chloride is in the greatest amount of weight.
Clarifier - An additive that increases the transparency of a material.
Clarity - The amount of clearness in plastic materials.
Closed Cell - An expanded structure consisting of a multitude of individual, nonconnecting, gas-tight cells.
Coefficient of Expansion - The fractional change in length (sometimes volume, specified) of a material for a unit change in temperature. Values for plastics range from 0.01 to 0.2 mils/in., C.
Compound - An intimate mixture of (a) polymers(s) with all the materials necessary for the finished product.
Compounding - The incorporation of additional ingredients needed for processing in order to have optimal properties. These ingredients may include additives to improve a polymer's physical properties, stability or processability.
Compression Ratio - In an extruder screw, the ratio of volume available in the first flight at the hopper to the last flight at the end of the screw.
Coextrusion - Involves a process where parts are blow-molded with walls containing two or more layers of different material. Coextrusion offers wide latitude for material selection and also allows the use of recycled materials. A material with good barrier properties, for example, can be used for the inside and outside surfaces of a blow molded bottle, while recycled material can be used for the internal layer.
Compression Set - The residual decrease in thickness of a test specimen measured 30 minutes or 24 hours after removal from a suitable loading device in which the specimen had been subjected for a definite time to compressive deformation under specified conditions of load application and temperature.
Crazing - Fine cracks which may extend in a network on or under the surface or through a layer of a plastic material.
Copolymer - Two monomers polymerized together to form a polymer.
Creep - The dimensional change with time of a material under load, following the initial instantaneous elastic deformation. Creep at room temperature is sometimes called Cold Flow.
Cross Laminate - A laminate in which some of the layers of material are oriented approximately at right angles to the remaining layers with respect to the grain or strongest direction in tension.
Cross-Linking - Applied to polymer molecules, the setting-up of chemical links between the molecular chains. When extensive, as in most thermosetting resins, cross-linking makes one infusible super-molecule of all the chains.
Crystallinity - A state of molecular structure in some resins which denotes uniformity and compactness of the molecular chains forming the polymer. Normally can be attributed to the formation of solid crystals having a definite geometric form.
Cure - To change the properties of a polymeric system into a more stable, usable condition by the use of heat, radiation, or reaction with chemical additives. NOTE: Cure may be accomplished, for example, by removal of solvent or cross-linking.
Density - Weight per unit volume of a substance, expressed in grams per cubic centimeter, pounds per cubic foot, etc.
Die C-Tear Strength - The maximum force required to cause a rupture by tearing action of the right angle test specimen; the force divided by the thickness of the specimen. The force acts parallel to the tab ends of the specimen or at 45° to the 90° center angle. Refer to ASTM Method D624.
Die Gap - The distance between the metal faces forming the die opening.
Die Lines - Vertical marks on the parison caused by damage of die parts or contamination.
Dimensional Stability - Ability of a plastic part to retain the precise shape in which it was molded, fabricated, or cast.
Discoloration - Any change from the original color, often caused by overheating, light exposure, irradiation, or chemical attack.
Dispersion - Finely divided particles of a material in suspension in another substance.
Draw Down Ratio - The ratio of the thickness of the die opening to the final thickness of the product.
Ductility - The extent to which a solid material can be drawn into a thinner cross section.
Durometer - An instrument for determining the hardness of polymer by measuring its resistance to the penetration (without puncturing) of a blunt indented point impressed on the rubber surface against the action of a spring. A hand and a special scale indicate the resistance to penetration or "hardness". The scale of the Shore hardness testers reads from 0 to 100, 0 being very soft and 100 being very hard. There are several Shore hardness gauges available and the proper durometer depends on the hardness of the surface being measured (Shore A, D and 00).
Elastomer - A polymer with the properties of rubber. Polymers that can be formulated as elastomers are polyurethane, butyl rubber, silicones and specially treated ethylene-propylene copolymers. At room temperature the material stretches under low stress to at least twice its length and snaps back to the original length upon release of stress.
Elongation - The fractional increase in length of a material stressed in tension.
Embossing - Techniques used to create depressions of a specific pattern in plastics film and sheeting.
Encapsulating - Enclosing an article (usually an electronic component or the like) in a closed envelope of plastic, by immersing the object in a casting resin and allowing the resin to polymerize or, if hot, to cool.
Environmental Stress Cracking - The susceptibility of a thermoplastic article to crack or craze formation under the influence of certain chemicals and stress.
Ester - The reaction product of an alcohol and an acid.
Ethylene Plastics - Plastics based on polymers of ethylene or copolymers of ethylene with other monomers, the ethylene being in greatest amount by mass.
Exothermic Reaction - A chemical reaction in which heat is evolved.
Extruder - Equipment for melting, pressurising and homogenising plastics by means of a rotating screw. Different configurations are possible; the most simple one being a single screw extruder mainly used for conversion processes like cast film extrusion, fibre spinning, film blowing or pipe and profile extrusion. For more demanding applications like compounding of polymer powder before pelletization or the mixing of polymers, twin screw extruders are used where the two normally intermeshing screws can be moved in a corotating (same direction) or counterrotating (opposite direction) fashion. These machines normally contain different mixing elements, most important being kneading blocks for the local creation of extensional flow.
Extrusion - One of the most common plastics processing techniques covering a vast range of applications in which resins are melted, heated and pumped for processing. Extrusion machines accomplish these tasks by means of one or more internal screws. In extrusion, the material to be processed is sheared between the root of the screw and the wall of the barrel that surround it. This process produces frictional energy that heats and melts the substance as it is conveyed down the barrel. Melted extrudate from the machine is further processed after the extrusion phase, which typically produces pellets, sheet, cast film, blown film, fibers, coatings, pipes, profiles or molded parts.
Extrusion Coating - The resin is coated on a substrate by extruding a thin film of molten resin and pressing it onto or into the substrates, or both, without the use of an adhesive.
Film - An optional term for sheeting having a nominal thickness not greater than 0.010 inch.
Finish - The plastic forming the opening of a container shaped to accommodate a specific closure. Also, the ultimate surface of an article.
Fish Eye - A fault in transparent or translucent plastics materials, such as film or sheet, appearing as a small globular mass and caused by incomplete blending of the mass with surrounding materials.
Flame Retardant Resin - A resin which is compounded with certain chemicals to reduce or eliminate its tendency to burn. For polyethylene and similar resins, chemicals such as antimony trioxide and chlorinated paraffins are useful.
Flame Treating - A method of rendering inert thermoplastic objects receptive to inks, lacquers, paints, adhesives, etc. in which the object is bathed in an open flame to promote oxidation of the surface of the article.
Flammability - Measure of the extent to which a material will support combustion.
Flexural Modulus - A measure of the strain imposed in the outermost fibers of a bent specimen.
Flexural Strength - The strength of a material in blending, expressed as the tensile stress of the outermost fibers of a bent test sample at the instant of failure. With plastics, this value is usually higher than the straight tensile strength.
Foaming Agents - Chemicals added to plastics and rubbers that generate inert gases on heating, causing the resin to assume a cellular structure.
Gel - unmelted raw material (resin) that manifests as a cosmetic blemish that will usually not affect performance of the final film. Gel can also result from using materials in the recipe that have slightly different chemistry or melt properties. In severe cases, they can apear as larger, solid pieces of material that can cause a tear or void in the film during secondary processing or end use.
Gloss - The shine or luster of the surface of a material.
Granulating (see also Regrind) - A size-reduction process used for production scrap, post-consumer plastic packaging, industrial parts, or other materials that must be downsized for further processing. Granulators consist of a feed hopper, cutting chamber, classifying screen, and rotating knives that work in concert with stationary-bed knives to reduce the plastic scrap until it is small enough to pass through the classifying screen. The resulting particles, called regrind, can vary in size from 3 mm to 20 mm.
Hardness - Resistance of a (polymer) surface to deformation. The different hardness measures applied for characterising polymers are: (a) Shore hardness (two scales, A for softer and D for harder materials) (b) Ball indentation hardness (also useable on profiled surfaces because of bigger measuring device).
Haze - The degree of cloudiness in a plastic material.
Heat Sealing - A method of joining plastic films by simultaneous application of heat and pressure to areas in contact. Heat may be supplied conductively or dielectrically.
Hydrocarbon - An organic compound that consists exclusively of the elements carbon and hydrogen. Generally, the term hydrocarbon is used for the chemicals that are derived from natural gas, oil and coal.
Hydrolysis - Chemical decomposition of a substance involving the addition of water.
Impact Resistance - Relative susceptibility of plastics to fracture by shock, e.g., as indicated by the energy expended by a standard pendulum type impact machine in breaking a standard specimen in one blow.
Impact Strength - (1) The ability of a material to withstand shock loading. (2) The work done in fracturing, under shock loading, a specified test specimen in a specified manner.
Impulse Sealing - A heat sealing technique in which a pulse of intense thermal energy is applied to the sealing area for a very short time, followed immediately by cooling. It is usually accomplished by using an RF heated metal bar which is cored for water cooling or is of such a mass that it will cool rapidly at ambient temperatures.
Injection Blow Molding - A blow molding process in which the parison to be blown is formed by injection molding.
Injection Molding - A molding procedure whereby a heat-softened plastic material is forced from a cylinder into a relatively cool cavity which gives the article the desired shape.
Instron - An instrument utilized to determine the tensile and compressive properties of material.
Light-resistance - The ability of a plastics material to resist fading after exposure to sunlight or ultra-violet light. Nearly all plastics tend to darken under these conditions.
Masterbatch - A plastics compound which includes a high concentration of an additive or additives. Masterbatches are designed for use in appropriate quantities with the basic resin or mix so that the correct end concentration is achieved. For example, color masterbatches for a variety of plastics are extensively used as they provide a clean and convenient method of obtaining accurate color shades.
Melt Flow - The flow rate obtained from extrusion of a molten resin through a die of specified length and diameter under prescribed conditions of time, temperature and load as set forth in ASTM D1238.
Melt Index - a measure of the rate of flow of a polymeric material through an orifice over a specific period of time.
Melt Temperature - The temperature of the molten plastic just prior to entering the mold or extruded through the die.
Melting Point - The temperature at which solid and liquid forms of a substance are in equilibrium. In common usage the melting point is taken as the temperature at which the liquid first forms in a small sample as its temperature is increased gradually.
Modulus of Elasticity - The ratio of stress to strain in a material that is elastically deformed.
Moisture Vapor Transmission - The rate at which water vapor permeates through a plastic film or wall at a specified temperature and relative humidity.
Opaque - Descriptive of a material or substance which will not transmit light. Opposite of transparent. Materials which are neither opaque nor transparent are sometimes described as semi-opaque, but are more properly classified as translucent.
Orientation - The alignment of the crystalline structure in polymeric materials so as to produce a highly uniform structure. Can be accomplished by cold drawing or stretching during fabrication.
Pigment - Any colorant, usually an insoluble powdered substance used to produce a desired color of hue.
Plastic - (1) One of many high-polymeric substances, including both natural and synthetic products, but excluding the rubbers. At some stage in its manufacture, every plastic is capable of flowing, under heat and pressure if necessary, into the desired final shape. (2) Made of plastic; capable of flow under pressure or tensile stress.
Plastic Memory - A phenomenon of plastic to return to its original molded form. Different plastics possess varying degrees of this characteristic.
Plasticity - The quality of being able to be shaped by plastic flow.
Plasticize - To soften a material and make it plastic or moldable, either by means of a plasticizer or the application of heat.
Plasticizer - Chemical agent added to plastic compositions to make them softer and more flexible.
Polyamide - A polymer in which the structural units are linked by amide or thioamide groupings. Many polyamides are fiber-forming.
Polybutylene - A polymer prepared by the polymerization of butene as the sole monomer.
Polycaprolactone - a specialty ester polyol which provides improved hydrolytic stability over conventional polyesters and high cut, tear, and abrasion resistance when incorporated into a polyurethane compound.
Polyester - A resin formed by the reaction between a dibasic acid and a dihydroxy alcohol, both organic. Modification with multi-functional acids and/or bases and some unsaturated reactants permit cross-linking to thermosetting resins. Polyesters modified with fatty acids are called Alkyds.
Polyether - a polymer in which carbon atoms of the repeating units are joined by a single oxygen atom. Polyethers used in polyurethane technology contain reactive hyroxyl end groups.
Polyethylene - A thermoplastic material composed by polymers of ethylene. It is normally a translucent, tough, waxy solid which is unaffected by water and by a large range of chemicals.
Polymer - A high-molecular-weight organic compound, natural or synthetic, whose structure can be represented by a repeated small unit, the mer; e.g., polyethylene, rubber, cellulose. Synthetic polymers are formed by addition or condensation polymerization of monomers. If two or more monomers are involved, a copolymer is obtained. Some polymers are elastomers, some plastics.
Polymerization - A chemical reaction in which the molecules of a monomer are linked together to form large molecules whose molecular weight is a multiple of that of the original substance. When two or more monomers are involved, the process is called copolymerization or heteropolymerization. See also Degree of, Condensation, and Polymer.
Polyolefin - A polymer prepared by the polymerization of an Olefin(s) as the sole Monomer(s).
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.
Polyurethane Resins - A family of resins produced by reacting diisocyanate with organic compounds containing two or more active hydrogens to form polymers having free isocyanate groups. These groups, under the influence of heat or certain catalysts, will react with each other, or with water, glycols, etc., to form a thermosetting material.
Polyvinyl Chloride (PVC) - A thermoplastic material composed of polymers of vinyl chloride; a colorless solid with outstanding resistance to water, alcohols, and concentrated acids and alkalies. It is obtainable in the form of granules, solutions, lattices, and pastes. Compounded with plasticizers it yields a flexible material superior to rubber in ageing properties. It is widely used for cable and wire coverings, in chemical plants, and in the manufacture of protective garments.
Regrind - Plastic that is re-introduced into the production stream.
Resin - Any of a class of solid or semi-solid organic products of natural or synthetic origin, generally of high molecular weight with no definite melting point. Most resins are polymers.
Rockwell Hardness - A common method of testing a plastic material for resistance to indentation in which a diamond or steel ball, under pressure, is used to pierce the test specimen. The load used is expressed in kilograms and a 10-kilometer weight is first applied and the degree of penetration noted. The so-called major load (60 to 150 kilograms) is next applied and a second reading obtained. The hardness is then calculated as the difference between the two loads and expressed with nine different prefix letters to denote the type of penetrator used and the weight applied as the major load.
Shear Stress - The stress developing in a polymer melt when the layers in a cross section are gliding along the wall of the channel (in laminar flow).
Sheet (thermoplastic) - A flat section of a thermoplastic resin with the length considerably greater than the width and 10 mils or greater in thickness.
Shore Hardness - Resistance of a (polymer) surface to deformation. The different hardness measures applied for characterising polymers are: (a) Shore hardness (two scales, A for softer and D for harder materials) (b) Ball indentation hardness (also useable on profiled surfaces because of bigger measuring device).
SI Units - The International System of Units (Systems International) is a modernized version of the metric system established by international agreement. It provides a logical and interconnected framework for all measurements in science, industry and commerce. Officially abbreviated SI, the system is built upon a foundation of seven base units.
Slip Additive - A modifier that acts as an internal lubricant which exudes to the surface of the plastic during and immediately after processing. In other words, a non-visible coating blooms to the surface to provide the necessary lubricity to reduce coefficient of friction and thereby improve slip characteristics.
Stabilizer - An ingredient used in the formulation of some plastics, especially elastomers, to assist in maintaining the physical and chemical properties of the compounded materials at their initial values throughout the processing and service life of the material. Sustainable Development - To meet the needs of the present without compromising the ability of future generations to meet their own needs.
Tear Resistance - The force required to tear completely across a specifically nicked rubber test specimen, or right angle test specimen, by elongating at a specific rate. See ASTM Method D 624.
Tear Strength - Film must have certain resistance to tear loading. Tear strength indicates the average force required to propagate tearing through a specified length of the film sample. This test is suitable for investigation of orientation balance of the film. Normally tear strength is measured in two directions, parallel and transverse to the extrusion direction of the film.
Tensile Strength - The pulling stress, in psi, required to break a given specimen. Area used in computing strength is usually the original, rather than the necked-down area.
Thermal Conductivity - Ability of a material to conduct heat; physical constant for quantity of heat that passes through a unit cube of a substance in a unit of time when difference in temperature of two faces is 1 degree.
Thermal Degradation - Deterioration by heat.
Thermal Expansion Coefficient - The fractional change in length (sometimes volume, specified) of a material for a unit change in temperature. Values for plastics range from 0.01 to 0.2 mils/in., degrees C.
Thermal Stress Cracking (TSC) - Crazing and cracking of some thermoplastic resins which results from over-exposure to elevated temperatures.
Thermoforming - Any process of forming thermoplastic sheet which consists of heating the sheet and pulling it down onto a mold surface.
Thermoplastic - Capable of being repeatedly softened by heat and hardened by cooling (n.) - A material that will repeatedly soften when heated and harden when cooled. Typical of the thermoplastics family are the styrene polymers and copolymers, acrylics, cellulosics, polyethylenes, vinyls, nylons, and the various fluorocarbons materials.
Thermoset - A material that will undergo or has undergone a chemical reaction by the action of heat, catalysts, ultra-violet light, etc., leading to a relatively infusible state. Typical of the plastics in the thermosetting family are the aminos (melamine and urea), most polyesters, alkyds, epoxies, and phenolics.
Translucent - Descriptive of a material or substance capable of transmitting some light, but not clear enough to be seen through.
Transparent - Descriptive of a material or substance capable of a high degree of light transmission e.g., glass. Some polypropylene films and acrylic moldings are outstanding in this respect.
Ultrasonic Sealing - A film sealing method in which sealing is accomplished through the application of vibratory mechanical pressure at ultrasonic frequencies (20 to 40 KC.). Electrical energy is converted to ultrasonic vibrations through the use of either a magnetostrictive or piezoelectric transducer. The vibratory pressures at the film interface in the sealing area develop localized heat losses which melt the plastic surfaces effecting the seal.
Ultraviolet - Zone of invisible radiation beyond the violet end of the spectrum of visible radiation. Since UV wavelengths are shorter than the visible, their photons have more energy, enough to initiate some chemical reactions and to degrade most plastics.
UV Stabilizer - Any chemical compound which, when mixed with a thermoplastic resin, selectively absorbs UV rays.
Vacuum Forming - Method of sheet forming in which the plastic sheet is clamped in a stationary frame, heated, and drawn down by a vacuum into a mold. In a loose sense, it is sometimes used to refer to all sheet forming techniques, including Drape Forming involving the use of vacuum and stationary molds.
Vinyl (Polyvinyl Chloride or PVC) - In addition to its stable physical properties, PVC has excellent transparency, chemical resistance, long-term stability, good weatherability, flow characteristics and stable electrical properties. The diverse slate of vinyl products can be broadly divided into rigid and flexible materials. Rigid applications, accounting for 60 percent of total vinyl production, are concentrated in construction markets which include pipe and fittings, siding, carpet backing and windows. Bottles and packaging sheet are also major rigid markets. Flexible vinyl is used in wire and cable insulation, film and sheet, floor coverings, syntheticleather products, coatings, blood bags, medical tubing and many other applications.
Virgin Material - A plastic material in the form of pellets, granules, powder, flock, or liquid that has not been subjected to use or processing other than that required for its initial manufacture.
Viscosity - Internal friction or resistance to flow of a liquid. The constant ratio of shearing stress to rate of shear. In liquids for which this ratio is a function of stress, the term "apparent viscosity" is defined as the ratio.
Voids - (1) In a solid plastic, an unfilled space of such size that it scatters radiant energy such as light.(2) A cavity unintentionally formed in a cellular material and substantially larger than the individual cells.
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