Debris from a Yellow Bodied Acoustic Ceiling Tile
This field contains glass fiber with yellow phenolic binder
and a few associated particles.
Transmitted Off Crossed Polarized Light Illumination
Definition/Function:
Glass fiber is a fiber composed of a material in a "glassy" state. A "glass" is any of a
large class of materials that
solidify from a molten state without crystallization and with random molecular
orientation. They are regarded physically
as supercooled liquids rather than true solids (based on the definition in the AMERICAN
HERITAGE DICTIONARY). Chemically
they generally contain silicon along with a number of other elements though carbon-based
glasses are also common in some
environments. It is estimated that there are in excess of 50,000 different chemical
compositions for glass (MATERIALS
HANDBOOK, by George S. Brady and Henry R. Clauser). Glass is easily formed at elevated
temperature and can be made into
fibers intentionally, as an artifact of thermal forming, or as a natural process as in
the case of volcanic glass fiber
(Pele's Hair).
"Glass fiber", as identified by light microscopy, is defined by its morphology and a few
optical properties. Its
cylindrical shape (a result of surface tension at elevated temperature) is best seen by
the relief gradient at
the edge of the fiber when viewed with transmitted oblique illumination. The random
molecular structure is demonstrated by
the fact that the fiber is isotropic (disapears in all orientations when viewed between
linear polarizing filters at 90
degrees to one another). The brittle nature of the fiber is shown by the lack of plastic
deformation at the terminations
of the fiber.
Glass fiber from acoustic ceiling tile is identified by the binders and fillers stuck to
the outside of the fiber and the
lack of impacted debris adhering to the fibers. Ceiling tile is a molded material and
the molding process imposes
certain compositional demands and limitations. A binder must be present in sufficient
quantity to impart some rigidity to
the tile. The binder is relatively expensive so it is often extended by adding mineral
fillers. Flexible fibers, such as
paper fiber or plastic fiber, may be added to impart greater durability to the tile. The
presence of these materials
physically attached to the glass fiber identifies the fiber as being from acoustic
ceiling tile. The type of acoustic
ceiling tile is identified by the composition of the attached materials.
Significance in the Environment:
Glass fiber on surfaces has been associated with a number of health complaints and with
the "Sick Building Syndrome" in
general. This is not true of glass fiber collected in air samples. The reason for this
seems to be that in most cases
in offices, schools, and homes the transport to the upper respiratory system is the
result of mechanical disturbance and
transport from contaminated surfaces and not from elevated airborne loading (see
references in the microlabnw paper cited
below).
Characteristic Features:
Glass fiber may be distinguished from bird feather barbules by the low birefringence of
the barbules and by accessory
structures (nodes) on the barbules, if present.
Glass fiber may be distinguished from silaceous phytoliths by accessory structures on
the phytoliths, the low refractive
index of the phytoliths (less than 1.500), by surface texture on the phytoliths, or by
the non-cylindrical shape of the
phytolith. These properties exclude most silaceous phytoliths from confusion with glass
fiber unless a lower refractive
index glass fiber is present, such as fused quartz (refractive index of 1.48).
Associated Particles:
The source of glass fiber in an environment is identified by the types of materials
associated with the glass fiber.
Chemical composition is often unreliable because of variations in the chemical
composition of the glass itself and because
of surface films or particle adhering to the fiber that alter its chemical signature.
Binders and the fillers, extenders,
and pigments that may be associated with the binders attached to the fiber are a good
indication of the fibers source. In
addition to the binder there are often other fiber types attached to the glass fiber by
the binder that further clarify the
source of the glass fiber.
References:
Brady, George S. and Henry R. Clauser, MATERIALS HANDBOOK, 11th Edition, ISBN
0-07-007069-5, pp. 341-350
http://www.microlabnw.com/index/Glass%20Fiber%20and%20Health%20Complaints.pdf
Parker, Sybil P. (ed), McGRAW-HILL ENCYCOPEDIA OF PHYSICS, ISBN 0-07-045253-9, p.27.