Glossary

Plastics Glossary - U

UL Abbreviation for Underwriters Laboratories, the nonprofit safety testing organization. Phone 312-272-8800.

UL continuous use temperature The highest constant temperature at which a material will survive relative to the application requirements.

UL flammability Ratings given to materials after undergoing several tests to describe a material’s flammability.

UL properties Underwriters Laboratories certifies the results of several tests of a material’s properties that include: oxygen index, flammability, high voltage arc track rate, and continuous use temperature.

Ultimate elongation The maximum length a material will extend before breaking.

Ultimate Strength Term used to describe the maximum unit stress a material will withstand when subjected to an applied load in a compression, tension, flexural, or shear test.

Ultrasonic Emulsifer Machine that is used for the preparation of fine- particle-size emulsions. The emulsion is forced at high velocity against the edge of a blade. The acoustical waves of the vibration of the blade produce cavitation, which accomplishes the emulsification.

Ultrasonic welding Ultrasonic vibrations are produced by mechanical motion of a converter, expanding and contracting some 20,000 times/sec. The vibratory energy is channeled through a horn and applied to thermoplastic materials. This creates the frictional heat to produce a molecular interaction and weld materials.

Undercut A recess or depression in the plastic part that is not perpendicular to the parting line and causes the plastic part to stick in that half of the mold.

Unit mold or die Mold designed for quick-changing, interchangeable cavity parts.

Unstable Emulsions Those emulsions that separate into two immiscible phases, or otherwise lose homogeneity.

Urea formaldehyde See Aminoplastics.

USP United States Pharmacopeia.

U-V stabilizer A chemical additive that selectively absorbs or filters out light waves at the ultraviolet end of the spectrum, protecting plastics from their harmful effects such as embrittlement, discoloration, crazing and disintegration.