Plastics Glossary - I

Immiscible Incapable of mixing. Oil and water are immiscible.

Impact bar A test bar of specified dimensions, used to determine the relative resistance of a plastic to fracture by shock.

Impact modification A means of modifying a polymer to increase the impact resistance.

Impact modifier A material such as rubber, an elastomer or some plastics with excellent impact resistance, that is blended with a resin to improve its impact resistance. The impact modifier usually has a glass transition temperature that is well below room temperature.

Impact Resistance The resistance of plastic articles to fracture under stresses applied at high speeds.

Impact Strength The ability of a material to withstand shock loading.

Impact tests Measures the energy necessary to fracture a standard notched bar by an impulse load.

Impeller Rotating member of an agitating or pumping device.

Implosion Inward collapse.

Inhibiter Substance that prevents or slows down a chemical reaction.

Initiator Peroxides used as sources of free radicals. They are used in free radical polymerizations, curing thermosetting resins, as cross-linking agents for elastomers and polyethylene, and for polymer modification.

Injection blow molding Suited for containers that have very close tolerance threaded necks, wide mouth openings, and highly styled shapes. In the basic process, plastic melt is injected as a parison into a preform cavity forming the preform around a core rod. A completely finished injection molded neck is formed at this station. The preform is indexed to the flow station where it is blown through an opening in the core rod into the final shape.

Injection mold See Mold, Injection

Injection molding Injection molding is a repetitive process in which plastic is melted or plasticated and injected into a mold containing a cavity in the shape of the desired article. In thermoplastics, the mold is kept at a temperature below the solidifying point of the plastic, causing the injected polymer to “freeze,” thus forming the article. When processing thermosets, the material is kept below the temperature at which it would cause solidification due to its exothermic reaction until it enters the cavity. In turn, the cavity temperature is kept high to cause the melt to solidify.

Injection pressure Pressure applied to the injection ram to force the plastic from the barrel and into the mold (measured in psi).

Injection ram The ram or screw that applies pressure on the molten plastic material to force it into the mold cavities.

Insert molding Process by which components, such as terminals, pins, studs, and fasteners, may be molded into a part. Instrumented impact testing A mechanically or hydraulically driven dart is driven at a constant velocity through a plastic test specimen. The dart tip or driving mechanism has transducers and high-speed data-gathering computers to measure and analyze the energy required to break the specimen.

Insert An article of metal or other material which is incorporated into a plastic molded part either by pressing the insert into the finished molded part or by placing the insert in the cavity so that it becomes an integral part of the molding.

Instrumented impact testing A mechanically or hydraulically driven dart is driven at a constant velocity through a plastic test specimen. The dart tip or driving mechanism has transducers and high speed data gathering computers to measure and analyze the energy required to break the specimen.

Interfacial Film A film of material (usually liquid) that forms at the point of contact of two immiscible liquids. The film may prevent coalescence.

Interfacial Viscometer Instrument used for the measurement of the physical properties of surface and interfacial films.

Internal Phase Dispersed or discontinuous phase of an emulsion.

Intumesce Foaming, swelling, or bubbling that may be a result of heating.

Intumescent coating Coatings formulated to protect an object from intense heat or flames by decomposing into a foam barrier.

Inversion Transposition of the two phases of an emulsion (internal phase becomes external phase and vice-versa).

Ion Electrically charged portion of matter of atomic or molecular dimensions.

Ionic Solutions Solutions of substances such as acids, bases and salts that dissociate in solution into charged particles called ions.

Ionic Surfactants Surfactants that dissociate in solution into an organic lipophilic group and a hydrophilic group. The molecules produce two ions, one positively charged (cation), the other negatively charged (anion).

Ionomer Thermoplastic that combines transparency with toughness, particularly at low temperatures. The polymer’s main component is ethylene, but it contains both inorganic and organic materials lined by both covalent and ionic bonds. Film is used in skin packaging.

Irradiation Subjecting plastics or other compounds to radiant energy to cure or produce some change in the material, or to test the results. Cross-linking of thermoplastics is accomplished in this way. Some medical applications require parts to be irradiated with gamma rays for sterilization.

Iso Prefix meaning equal.

ISO Abbreviation for the International Standards Organization.

Isocyanate resin One of the two major components in making polyurethane foams. It is reacted with a polyol, usually a polyether. The two types most widely used are toluene diisocyanate (TDI) and methylphenylene diisocyanate (MDI).

Isoelectric Point pH value of a hydrophilic sol (electrolyte) at which it will not migrate in an electrical field.

Isotactic Pertaining to a type of polymeric molecular structure containing a sequence of regularly spaced asymmetric atoms arranged in like configurations in a polymer chain.

Isothermal Constant temperature system.

Isotropic Fluid Fluid whose properties are independent of the rotation of the axis of reference along which the properties are measured.

Isotropic shrinkage Shrinkage that occurs the same in all directions and with unfilled materials.

Isotropic The ability to react the same regardless of the direction of the measurement. Isotropic materials will react consistently even if stress is applied in different directions. Stress-strength ratio is uniform throughout material.

Izod Impact Strength A measure of impact strength determined by the difference in energy of a swinging pendulum before and after it breaks a notched specimen held vertically as a cantilever beam.

Izod impact test A test for shock-loading in which a notched sample bar is held at one end and broken by swinging a pendulum.