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.
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 . COMBINATION
FABRIC.)
UNION DYEING- . 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- . 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 . 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.