Palletizing - A process of producing pellets.

Parison - The hollow plastic tube from which a container, toy, etc. is blow molded.

Parison Swell - In blow molding the ratio of the cross-sectional area of the parison to the cross-sectional area of the die opening.

Parting Agent - A lubricant, often wax, used to coat a mold cavity to prevent the molded piece from sticking to it, and thus to facilitate its removal from the mold. Also called Release Agent.

Parting Line - Mark on a molding or casting where halves of mold met in closing.

Partitioned Mold Cooling - A large diameter hole drilled into the mold (usually the core) and partitioned by a metal plate extending to near the bottom end of the channel. Water is introduced near the top of one side of the partition and removed on the other side.

Pellet - A small ball or spherical shape.

Permanent Set - The increase in length, expressed in a percentage of the original length, by which an elastic material fails to return to original length after being stressed for a standard period of time.

Permeability - (1) The passage or diffusion of a gas, vapor, liquid, or solid through a barrier without physically or chemically affecting it. (2) The rate of such passage.

PH - An expression of the degree of acidity or alkalinity of a substance. Neutrality is pH -acid solutions being under 7 and alkaline solution over 7. pH meters are commercially available for accurate readings.

Phenolic Resin - A synthetic resin produced by the condensation of an aromatic alcohol with an aldehyde, particularly of phenol with formaldehyde. Phenolic resins from the basis of thermosetting molding materials, laminated sheet, and varnishes. They are also used as impregnating agents and as components of paint, varnishes, lacquers, and adhesives.

Pigment - Any colorant, usually an insoluble powdered substance used to produce a desired color of hue.

Pinpoint Gate - A restricted orifice of 0.030 inches or less in diameter through which molten resin flows into a mold cavity.

Pitch - The distance from any point on the flight of a screw line to the corresponding point on an adjacent flight, measured parallel to the axis of the screw line or threading.

Plastic Deformation - A change in dimensions of an object under load that is not recovered when the load is removed; opposed to elastic deformation.

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.

Plastics Wood Composites - a range of materials that resemble wood. It combines the advantages of wood with those of plastics.

Plastisols - Mixtures of resins and plasticizers which can be molded, cast, or converted to continuous films by the application of heat. If the mixtures contain volatile thinners also, they are known as Organosols.

Plate Dispersion Plug - Two perforated plates held together with a connecting rod which are placed in the nozzle of an injection molding machine to aid in dispersing a colorant in a resin as it flows through the orifices in the plates.

Plate-mark - Any imperfection in a pressed plastic sheet resulting from the surface of the pressing plate.

Platens - The mounting plates of a press to which the entire mold assembly is bolted.

Platform Blowing - A special technique for blowing large parts. To prevent excessive sag of the heavy parison the machine employs a table which after rising to meet the parison at the die descends with the parison but at a slightly lower rate than the parison extrusion speed.

Plug Forming - A thermoforming process in which a plug or male mold is used to partially preform the part before forming is completed using vacuum or pressure.

Plug-and-ring - Method of sheet forming in which a plug, functioning as a male mold, is forced into a heated plastic sheet held in place by a clamping ring.

Plunger - See Force Plug.

Pneumatic - A system in which energy is transferred by compression, flow and expansion of air.

Poise - The unit of viscosity expressed as one dyne per second per square centimeter.

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.

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.

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.

Polyimide Resins - A new group of resins recently introduced in the United States. The material is an aromatic polyimide made by reacting pyromellitic dianhydride with aromatic diamines. The polymer is characterized by the fact that it has rings of four carbon atoms tightly bound together, and the manufacturers claim that the new resin has greater resistance to heat than any other unfilled organic material yet discovered. Suggested applications include components for internal combustion engines.

Polyisobutylene - The polymerization product of isobutylene. It varies in consistency from a viscous liquid to a rubber-like solid with corresponding variation in molecular weight from 1,000 to 400,000.

Polyliner - A perforated longitudinally ribbed sleeve that fits inside the cylinder of an injection molding machine; used as a replacement for conventional injection cylinder torpedoes.

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.

Polymethyl Methacrylate - A thermoplastic material composed of polymers of methyl methacrylate. It is a transparent solid with exceptional optical properties and good resistance to water. It is obtainable in the form of sheets, granules, solutions, and emulsions. It is extensively used for aircraft domes, lighting, fixtures, decorative articles, etc.; it is also used in optical instruments and surgical appliances.

Polyolefin - A polymer prepared by the polymerization of an Olefin(s) as the sole Monomer(s).

Polyoxymethylene - A polymer in which the repeated structural unit in the chain is oxymethylene.

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.

Polystyrene - A water-white thermoplastic produced by the polymerization of styrene (vinyl benzene). The electrical insulating properties of polystyrene are outstandingly good and the material is relatively unaffected by moisture.

Polytetrafluoroethylene (PTFE) Resins - Members of the fluorocarbons family of plastics made by the polymerization of tetrafluoroethylene. PTFE is characterized by its extreme inertness to chemicals, very high thermal stability and low frictional properties. Among the applications for these materials are bearings, fuel hoses, gaskets and tapes, and coatings for metal and fabric.

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 Acetal - A member of the family of vinyl plastics. Polyvinyl acetal is the general name for resins produced from a condensation of polyvinyl alcohol with an aldehyde. There are three main groups: polyvinyl acetal itself; polyvinyl butyl, and polyvinyl formal. Polyvinyl acetal resins are thermoplastics which can be processed by casting, extruding, molding and coating, but their main uses are in adhesives, lacquers, coatings and films.

Polyvinyl Acetate - A thermoplastic material composed of polymers of vinyl acetate in the form of a colorless solid. It is obtainable in the form of granules, solutions, lattices, and pastes, and is used extensively in adhesives, for paper and fabric coatings, and in bases for inks and lacquers.

Polyvinyl Carbazole - A thermoplastic resin, brown in color, obtained by reacting acetylene with carbazole. The resin has excellent electrical properties and good heat and chemical resistance. It is used as an impregnate for paper capacitors.

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.

Polyvinyl Chloride Acetate - A thermoplastic material composed of copolymers of vinyl chloride and vinyl acetate; a colorless solid with good resistance to water, and concentrated acids and alkalies. 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.

POM - The chemical abbreviation for Acetal, also known as Polyoxymethylene.

Postcure - Those additional operations to which a cured thermosetting plastic or rubber composition are subjected to enhance the level of one or more properties.

Postforming - The forming, bending, or shaping of fully cured, C-stage thermoset laminates that have been heated to make them flexible. On cooling, the formed laminate retains the contours and shape of the mold over which it has been formed.

Powder Molding - General term used to denote several techniques for producing objects of varying sizes and shapes by melting polyethylene powder, usually against the inside of a mold. The techniques vary as to whether the molds are stationary (e.g., as in variations on slush molding techniques) or rotating (e.g., as in variations on rotational molding).

Power Factor - In a perfect condenser, the current leads the voltage by 90 degrees. When a loss takes place in the insulation, the absorbed current, which produces heat, throws the 90 degree relationship out according to the proportion of current absorbed by the dielectric. The power factor is the cosine of the angle between voltage applied and the current resulting.

Preform - (n.) A compressed tablet or biscuit of plastic composition used for efficiency in handling and accuracy in weighing materials. (v.) To make plastic molding powder into pellets or tablets.

Preheat Roll - In extrusion coating, a heated roll installed between the pressure roll and unwind roll whose purpose is to heat the substrate before it is coated.

Preheating - The heating of a compound prior to molding or casting in order to facilitate the operation or to reduce the molding cycle.

Preimpregnation - The practice of mixing resin and reinforcement before shipping it to the molder.

Prepreg - A term generally used in reinforced plastics to mean the reinforcing material containing or combined with the full complement of resin before molding.

Pressure Forming - A thermoforming process wherein pressure is used to push the sheet to be formed against the mold surface as opposed to using a vacuum to suck the sheet against the mold.

Pressure Pads - Reinforcements or hardened steel distributed around the dead areas in the faces of a mold to help the land absorb the final pressure of closing without collapsing.

Pressure Roll - In extrusion coating, the roll which with the chill roll applies pressure to the substrate and the molten extruded web.

Prototype Mold - A simplified mold construction often made from a light metal casting alloy or from an epoxy resin in order to obtain information for the final mold and/or part design.

Pulp - A form of cellulose obtained from wood or other vegetable matter by prolonged cooking with chemicals.

Pulp Molding - Process by which a resin-impregnated pulp material is preformed by application of a vacuum and subsequently oven cured or molded.

Purging - Cleaning one color or type of material from the cylinder of an injection molding machine or extruder by forcing it out with the new color or material to be used in subsequent production. Purging materials are also available.

Push Up - The bottom contor of a plastic container designed in such a manner as to allow an even bearing surface on the outside edge and to prevent the bottle from rocking.