ULTIMATE TENSILE STRENGTH: See TENSIL STRENGTH.
ULTRASONIC QUILTING: See PINSONIC® THERMAL JOINING MACHINE.
ULTRAVIOLET DEGRADATION: Weakening or deterioration caused by exposure to ultraviolet rays of sunlight or artificial light.
ULTRAVIOLET RESISTANCE: Ability to retain strength and resist deterioration on exposure to sunlight.
UNCRIMPING ENERGY: See CRIMP ENERGY.
UNDRAWN TOW: See DRAWN TOW.
UNDRAWN YARN: Extruded yarn (filaments), the component molecules of which are substantially unoriented. Undrawn yarn exhibits predominantly plastic flow in the initial stages of stretching and represents an intermediate stage in the production of a manufactured yarn.
UNEVEN DYEING: A fabric dyeing that shows variations in shade resulting from incorrect processing or dyeing methods or from use of faulty materials.
UNEVEN SHRINKAGE: A wavy, warpwise condition in the fabric that prevents it from lying flat on a horizontal surface.
UNEVEN SURFACE: An irregular surface characterized by nonuniformity in the physical configuration of the yarns or fibers making up the surface of the fabric.
UNEVEN YARN: A yarn that varies in diameter to an abnormal degree.
UNFINISHED WORSTED: A worsted fabric with a relatively soft hand and a light nap.
UNIDIRECTIONAL FABRIC: A fabric having reinforcing fibers in only one direction.
UNION CLOTH: A term describing a fabric woven from two or more types of yarn. For example, a union cloth may have a cotton warp and a wool filling. (Also see COMBINATION FABRIC.)
UNION DYEING: See DYEING.
UNOPENED STAPLE: Staple fiber in bunches or clusters in the bale in such a condition that it will not process smoothly through carding and subsequent operations in the spun-yarn plant.
UNRELAXED YARN: See RELAXED YARN.
UPDRAFT METIER: A dry spinning machine in which the air flow within the drying cabinet is countercurrent to the yarn path (upward).
UPTWISTER: A machine used for twisting yarns in an upward path from a rotating vertical supply package to a horizontal take-up package. Used for spun yarns and to a small extent for adding twist to some filament yarns.
UPTWISTING: The process of twisting yarn on the uptwister. The yarn to be twisted, which has been wound on a balanced support package, is placed on a revolving spindle. The yarn form the revolving supply package is fed upward through a gathering eye or guide, over a stop motion and a tension bar or bars, through a traversing guide, and onto the revolving collecting package.
URETHANE: The name of a group of organic chemical compounds or resins built from isocyanate, a very reactive material that liberates gas during reaction to produce foams of various types. Two types of compounds that react with isocyanate to form foam are polyesters and polyethers. Polyurethanes are used for foams and in other compounds in fiber form. The polyester variety should not be confused with polyester fibers. (Also see SPANDEX FIBER.)
USTER TESTER: An instrument that provides a continuous measurement of the variation in weight per unit length of sliver, roving, and yarn.
UV ABSORBERS: Polymer additives that absorb light in the UV region or that trap radicals produced in fiber during photooxidation. They provide stabilization against actinic degradation. Some critical applications include geotextiles, recreational surface polymers and fibers, tenting tarpaulins, etc.