Plastics Glossary - A

Abrasion Resistance The ability of a material to withstand mechanical actions such as rubbing, scraping, or erosion, that tend progressively to remove material from its surface.

ABS (Acrylonitrile-Butadiene-Styrene) A terpolymer produced from acrylonitrile, butadiene, and styrene in a variety of ratios to produce the family of ABS resins. These resins are used for their balance of appearance, toughness, heat distortion and ease of processing. Need to be dried for processing. Amorphous material.

Absolute (Dynamic) Viscosity Ratio of stress to rate of shear strain.

Absolute Viscosity The tangential force on unit area of either of two parallel planes at unit distance apart when the space between the planes is filled with the fluid in question and one of the planes moves with unit differential velocity in its own plane. The C.G.S. unit for absolute (or dynamic) viscosity is poise (dyne-sec./sq. cm.). Centipoise (0.01) is often used.

Accelerated Ejection Rack and pinion linkages used to extend the reach of the ejector pins, so that the ejector pins move before the main ejector plate comes all the way forward.

Accelerator A chemical additive that hastens a chemical reaction.

Accumulator An auxiliary ram cylinder for fast delivery of plasticated melt. It is filled from the main barrel. Used on injection molding machines and blow molding machines. Also, a container for storing hydraulic oil under pressure and used on a molding machine to boost injection rate.

Acetal (POM) Highly crystalline (as high as 97%) thermoplastic made from linear polyoxymethylene. Excellent creep resistance and fatigue endurance. Two main classes: homopolymer and copolymer. May need to be dried for processing. Semicrystalline material.

Acid Number Number of mg of KOH required to neutralize the free fatty acids in 1 gram of fat, wax, or resin.

Acrylic Acrylic polymer is the common name for polymethylmethacrylate, or PMA, which is made from monomer methacrylate, or MMA.

Acrylonitrile A monomer with the structure (CH2:CHCN). It is most useful in copolymers. Its copolymer with butadiene is nitrile rubber, and several copolymers with styrene exist that are tougher than polystyrene. It is also used as a synthetic fiber and as a chemical intermediate.

Adaptive control A method by which input from sensors automatically and continuously adjusts in an attempt to provide near optimum processing conditions. In cyclic processes such as injection molding, this means adjusting the process with data from one cycle for the next cycle. This algorithm assumes a process trend. The technique should not be used in a process under statistical control.

Addition polymerization Chemical reaction in which simple molecules (monomers) are added to each other to form long-chain molecules (polymers) and no by-produces are formed (as opposed to condensation polymerization).

Additive Materials added in minor amounts to basic resins or compounds to improve a polymer's performance during processing, or tailor a polymer's performance capabilities for end use.

Adhesion Condition in which unlike substances stick to each other.

Adhesional Wetting Formation of a solid/liquid interface at the expense of solid/air and the liquid/air interface.

Adhesive Assembly The process of joining two or more plastic parts by means of an adhesive.

Adhesive Material that can hold other materials together by physical or chemical attachment at the surfaces.

Adiabatic A process condition in which there is not gain or loss of heat from the environment.

Adsorbate Material that adheres to the surface of another.

Adsorbent Material on whose surface adsorption takes place.

Adsorption Adhesion of a substance to the surface of a solid or liquid.

Adsorption Curve Amount adsorbed from a solution plotted as a function of the concentration of the solute.

Aerosol Colloidal suspension in which gas is the dispersant. Dispersionor suspension of extremely fine particles of liquid or solid in a gaseous medium.

Agglomerate Cluster of particles adhering to one another.

Aging The process of, or the results of, exposure of plastics to natural or artificial environmental conditions for a prolonged period of time.

Air shot Injecting plastic into the air from the nozzle of an injection molding machine.

Air trap Occurs when melt fronts converge and trap air in the cavity of a mold. Will not occur if there is "perfect" venting.

Alginates Vegetable products made from kelp and seaweed .

Aliphatic Hydrocarbon Straight-chain organic compounds such as the paraffins and their derivatives; e.g. propane, ethylene, acetylene.

Alkyd Group of thermoplastic synthetic resins made from dibasic organic acids, anhyrides, alohols, and drying oils.

Alkyd molding compound Compound based on unsaturated polyester resins and formulated with relatively low amounts of cross-linking monomer and fillers, lubricants, pigments, and catalysts into a thermosetting material for use in compression, transfer, or injection molding.

Alloy A composite material produced by blending polymers or copolymers with other polymers under selected conditions to achieve greater physical properties.

Alumina trihydrate An inert mineral filler that provides flame retardancy and arc/track resistance.

Ambient Temperature The temperature of a medium surrounding an object. The term is often used to denote prevailing room temperature.

Aminoplastics Thermoset plastic made of amino compounds (compounds derived from ammonia) such as urea-formaldehyde and melamine-formaldehyde. Amorphous material.

Amorphous material Pinch-off A raised edge around the mold cavity that seals off the part and separates excess material as the mold closes around the parison in the blow-molding process.

Amorphous phase Devoid of crystallinity (non crystalline). Most plastics are amorphous at processing temperatures.

Amorphous polymers A family of polymers characterized by the randomness of entangled polymer chains. Generally have lower shrinkage than semi-crystalline polymers.

Amorphous Without structure. Amorphous plastics do not form the uniform, compact, ordered chains of crystalline plastics.

Ampholytic Capable of acting either as a base or as an acid, depending on the nature of the surrounding medium.

Amphoteric Reacting chemically as an acid to strong bases and as a base to strong acids.

Angle pin The fixed pin that engages a mold slide to move it when the mold opens and closes.

Angstrom Unit of wavelength equal to 10-10m.

Anhydrous Not containing water of hydration, or completely dry.

Anion Negatively charged ion such as hydroxide (OH-), carbonate (CO3=), phosphate (PO4=).

Anionic Surfactants Ionic surface-active agents in which the portion that associates with the internal phase is the anion, negatively charged hydrophobe; they include car boxylic acids, sulfuric acid esters, and sulfonic acids.

Anisotropic shrinkage Shrinkage that is not the same in all directions. Occurs in filled material due to the restriction of shrinkage along the fiber length which tends to be in the flow direction.

Anisotropy The tendency of a material to react differently to stresses applied in different directions, especially with respect to flow orientation.

Anistrophic shrinkage Shrinkage that is not the same in all directions. Anistrophic shrinkage occurs in filled materials due to the restriction of shrinkage along the fiber length that tends to be in the flow direction. Anistrophic shrinkage also occurs in unfilled polymers relative to direction of flow as compared to across flow.

Annealing The process of relieving stresses in molded plastic articles by heating to a predetermined temperature, maintaining this temperature for a predetermined length of time, and slowly cooling the articles to be painted which might craze due to solvent attack.

ANSI Abbreviation for American National Standards Institute.

Antifoamer Liquid of low intrinsic surface tension that prevents formation of a foam.

Antifogging Agents Additives which prevent or reduce the condensation of water on a plastic film in the form of small droplets which resemble fog.

Antimony oxide A white, odorless, fine powder which is used as a flame retardant as well as pigment, catalyst, chemical intermediate, and lubricant (Sb₂O₃).

Antioxidant Additive to prevent degradation of plastics through exposure to either processing or the environment. Deterioration may be caused by heat, age, radiation, chemicals, stress, etc.

Antistatic agent Antistatic agents are additives that eliminate the charge potential in a polymer. Almost all polymers are good electric insulators, thus major sources of static electricity. Static electricity is caused by the contact and then separation of two non-conductive surfaces. As these surfaces separate, electrons go to one surface leaving the other positively charged. This stored charge is only relieved by coming in contact with a conductive surface; i.e., metal, human skin, dust, etc.

API American Petroleum Institute.

A-plate A mold plate used to house the cavities or cavity blocks. Located on the stationary half of an injection molding machine.

Apparent Viscosity Viscosity of a complex (non-Newtonian) fluid under given conditions.

Application The act of applying or putting to use. What the molded plastic article will be in its final form.

Aramid fiber Lightweight polyaromatic amide fibers offer excellent high temperature, flame, and electrical properties. These fibers are used in protective clothing and as high strength reinforcement in plastic composites, tires, flack jackets.

Arc Resistance The ability of a plastic material to resist the action of a high voltage electrical arc, usually stated in terms of time required to render the material electrically conductive.

Aromatic Hydrocarbons Organic compounds that contain a benzenoid structure or ring. The simplest such compound is benzene, C6H6.

ASA American Standards Association.

Ash Content The solid residue remaining after a substance has been incinerated or heated to a temperature sufficient to drive off all combustible or volatile substances.

Aspect ratio The ratio of length to diameter of a fiber or other object.

Asphalt Base Oil Type of petroleum that yields a pitch-like residue on distillation.

Assembly The process of joining parts by any of several methods.

Association Combination of molecules of the same substance, resulting in multiple molecules.

ASTM Time Tube Viscometer of the rising-bubble type.

ASTM American Society for Testing and Materials. Located at 1916 Race Street, Philadelphia, PA 19103.

Atactic A random arrangement of pendant groups on a polymeric chain.

Atlantic Viscometer Apparatus used to determine the kinematic viscosities of transparent Newtonian liquids of 0.6-5000 cS.

Attrition Pulverization through abrasion.

Autoclave Closed vessel for conducting a chemical reaction or other operation under pressure and heat.

Automatic operation The machine is set up to run each cycle immediately after the previous one is completed, without assistance from the technician.

Automation The science and practice of machinery or mechanisms that are so self-controlled and automatic that manual input is not necessary during operation. The technique of making a process automatic or self-controlling.

Average molecular weight The molecular weight of a polymer in solution at a specific temperature. This gives an average molecular weight of the molecular chains in the polymer independent of the specific chain length. The value falls between weight average and number average molecular weight.