BACKGROUND:
Individual fibers have
unique characteristics. Natural fibers have very characteristic features. Cotton is a flat
fiber that is twisted. Linen
looks jointed like bamboo. Wool looks like scaly corkscrews. Silk has double
strands. However synthetic fibers are less distinguishable. Rayon
is smooth glass-like rods; nylon is smooth clear rods; and
polyester is rod shaped like nylon but not as clear. All fibers are polymers
which are monomers that repeat and are aligned in a stretched pattern.
This allows fibers to be spun into threads and used as textiles.
In 1884, Louis Bernigaut successfully created an
artificial silk, which was the precursor to rayon. Unfortunately,
the synthetic fabric was highly flammable and burnt a young lay's ball
gown (while she was still in it!) Rayon was finally generated from a cellulose polymer in
1926 by the DuPont Company.
Cellulose is a polymer common in nature like wood, paper, and
cotton. Cotton over the course of human civilization has been
used to weave many different fabrics. Nylon a synthetic fiber,
was first used in woman's stockings in 1940's. Nylon is a light and
durable fabric used in parachutes and ropes. Many bulletproof fabrics
are also in the nylon family.
Olefin is a lightweight synthetic fiber found
in sportswear and thermal underwear. Acrylic and modacrylic
fibers are used with cotton to make fake sheep fleece, deep pile
coats, and even teddy bears. Spandex is a stretchable fiber
used in bathing suites and other sports wear.
Paper is not a fabric because paper is made by pressing
and flattening fibers by forcing them to "stick" together. Remember
most fabrics or cloth fibers are interlocked by weaving, knitting, or crocheting.
Felt is a cloth made by pressing together, but it is not used to make clothes.
Paper is usually made up of vegetable fibers that are laid down on
a fine screen from a water suspension and then are pressed together through
the action of heat, moisture, chemicals, and pressure. Other natural
fibers are used as well as synthetic or mixed fibers.
In lab the students will be
observing different fibers so they can identify them. Then in the
post lab, students will look at the fibers in the lint they have from home.
Investigators
use fibers many times to identify criminals. After this unit the
students will be able to understand why. Fibers are unique
and can be traced from a criminal to the crime.
PROCEDURE:
- Read the poem "Poly Mer" so students
are familiar with the term polymer. Emphasize that all fibers are
polymers whether naturally occurring or synthetically produced. This
is an introduction to the term. The "mer" refers to the
Greek meaning part.
The basic conceptual building unit of a polymer is a monomer that is
repeated in a chain or branched form. A molecule is repeated over
and over. In a polymer fiber the chain is elongated.
- You may want students to "research"
about one fiber. If you have a computer lab this would be a good way to
introduce searching for information.
If your school has a library this is a good
opportunity to investigate what types of books the library has. You might go over the procedure on using references, what an index is,
and how to ask for help. In lab their research
will help them to distinguish the different types of fibers.
- You may want students to research types of paper. Some possible
suggestions are: papyrus, rice paper, wax paper, cardboard, tracing paper,
history of paper, or even fibers in forensic science.
