Z94.12.6 Plastics

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TACK. Stickiness of an adhesive. This property is measured as the pull resistance to effect division without failure or deformation occurring in the adherend surroundings or at the interface while the adhesive still exhibits viscous or plastic flow. The measured value may vary with time, temperature, film thickness, etc.

TEMPER. To reheat after hardening to some temperature below the critical temperature, followed by air cooling to obtain desired mechanical properties and to relieve hardening strains.

THERMALLY FOAMED PLASTICS. Cellular plastics produced by applying heat to effect gaseous decompositon or volatilization of a constituent.

THERMOELASTICITY. Rubber-like elasticity exhibited by a rigid plastic and resulting from an increase of temperature.

THERMOFORMING. The processes for forming thermoplastic sheet by heating the sheet and using air, vacuum, or mechanical methods to form it onto the surface contour of a mold.

THERMOPLASTICS. Polymers that are capable of being repeatedly softened by heating and hardened by cooling.

THERMOSET. A material that will undergo or has undergone a chemical reaction by the action of heat, catalysts, or ultraviolet light and will achieve or has achieved a relatively infusible state.

THERMOSETTING. Capable of being changed into a substantially infusible or insoluble product when cured by application of heat or chemical means. Thermosetting polymers form bridges between molecule chains referred to as cross-links.

THIXOTROPIC. A thixotropic fluid is one whose apparent viscosity decreases with time, to some constant value at any constant rate of shear; i.e., its apparent viscosity can be gradually decreased to that limit by stirring. When stirring is discontinued, the apparent viscosity increases gradually back to the original value.

TRANSFER MOLDING. A method of molding thermosetting materials, in which the plastic is softened by heat and pressure in a transfer chamber, then forced by high pressure through sprues, runners, and gates into a closed mold for final curing.

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