A
Ablative Plastics
A material which absorbs heat (while part of it is being consumed by heat) through a thermal composition process known as pyrolysis, which takes place in the near surface layer exposed to heat.
Absorption
1) The penetration into the mass of one substance by another. 2) The process whereby energy is dissipated within a specimen placed in a field of radiation energy. Since processes other than absorption occur, e.g., scattering, only a fraction of the energy removed from a beam is retained in the specimen
Accelerator
A substance that hastens a reaction. For example, sulfur-containing compounds that speed up the vulcanization of rubber. Alo known as promoter. Often used to denote a substance that hastens the action of an initiator or catalyst.
Acetal resins
Polymers containing the acetal linkage ( ). One example would be polyoxymethylene.
Acrylic resin
A synthetic resin prepared from acrylic acid or from a derivative of acrylic acid.
Addition polymer
A polymer formed by a chain reaction, e.g., polyethylene and polystyrene.
Aging
The change of a material with time under defined environmental conditions, leading to improvement or deterioration of properties.
Alkyd resin
Polyesters made from dicarboxylic acids and diols, primarily used as coatings, modified with vegetable oil, fatty acids, etc.
Alloy
Composite material made up by blending polymers or copolymers with other polymers or elastomers under selected conditions, e.g., styrene-acrylonitrile copolymer resins blended with butadiene-acrylonitrile rubbers. See Polyblends.
Alternating copolymer
Copolymer in which the molecules of each monomer alternate in the polymer chain. See also Block and Random copolymers
Amino
Indicates the presence of an -NH2 group.
Amorphous phase
Devoid of crystallinity - no definite order. At processing temperatures a plastic is normally in an amorphous state.
Annealing
A process of holding a material at an elevated temperature below its melting point, the objective being to permit stress relaxation without distortion of shape. It is often used on molded articles, to relieve stresses set up by flow into the mold.
Antioxidant
Substances which prevent or slow down oxidation of a polymeric material exposed to air.
Antiskid aggregate
Hard grain of natural or artificial origin, used to provide antiskid qualities for the road markings.
Antistatic agents
Agents which minimize static electricity in plastics. Such agents are of two basic types: 1) metallic devices which come into contact with the plastics conducting 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, when mixed with the compound during processing, give a reasonable degree of protection to the finished products.
Arc resistance
Time required for a given applied electrical voltage to render the surface of a material conductive because the carbonization by the arc discharge.
A-stage
An early stage in the reaction of a thermosetting resin in which the material is still linear in structure, soluble in certain liquids and fusible. (See also B- and C- stage.)
Autoclave
1) Closed vessel for conducting chemical reactions under high pressure and temperature; 2) in low-pressure laminating, a round or cylindrical container in which heat and pressure can be applied to resin-impregnated paper of fabric positioned in layers over a mold.
Average molecular weight
Most synthetic polymers are a mixture of individual chains of many different sizes, hence a molecular weight assigned to such a mixture is of necessity an average molecular weight. See Number-, Weight-, z and Viscosity-.average molecular weights.
