B-Keratin (Silk)
Technical Name: Beta-Keratin, Fibroin. Common Name: B-Keratin, Silk.
(Beta-Keratin) silk is a synthetic polymer. The name silk is thought to have originated from the Greek word “seres”.
Most of the world’s silk is derived from the cocoons of the moth Bombyx mori which lives exclusively
on the leaves of “Morus alba”, the white mulberry tree. There are other species of silkworm
but their contribution to world silk is small. One cocoon is made of a single silk thread between
300 and 900 meters long. A silk strand consists of two silk filaments encased by a protein called sericin.
The sericin can be dissolved in mild alkaline leaving the pure silk threads.

Silk is a natural fiber, coming from the cocoons of the larvae of mulberry silkworms.

silkworm_cocoon.JPG (Silkworm cocoons)

Monomer Unit! :

Linking Monomers: The silk polymer is a linear molecule composed of the protein fibroin.
This protein is composed of sixteen amino acids of which three - alanine, glycine and serine -
constitute 80% of the polymer. There are no amino acids containing sulphur in fibroin and so no disulphide bonds.
The silk polymer system is about 65-70% crystalline giving a high tensile strength to the fibres.

Acids can degrade silk fairly easily since once the peptide groups are hydrolysed there
are no disulphide bonds (as are found in wool) to hold the structure together.Alkali causes the silk fibre
to swell. Prolonged exposure to alkali results in the complete degradation of the polymer structure.

Hydrogen bonding is holding the polymers together to form chains.This explains why silk is so fluid and flowing.
Monomers are linked by addition, not condensation. They are not linked by condensation because there is no
water involved in the linking.

Physical Characteristics: Silk has a smooth, soft texture that is not slippery, unlike many synthetic fibers.
Its denier (
a unit of measurement of linear density of textile fiber mass) is 4.5 g/d when dry and 2.8-4.0 g/d
when wet. B-Keratin (Silk) is one of the strongest natural fibers but loses up to 20% of its strength when wet.
It has a good moisture regain of 11%. Its elasticity is moderate to poor: if elongated even a small amount
it remains stretched. It can be weakened if exposed to too much sunlight. It may also be attacked by
insects, especially if left dirty.
Silk is a poor conductor of electricity and thus vulnerable to static cling.
Unwashed silk chiffon may shrink up to 8% due to a relaxation of the fiber macrostructure-
So silk should either be pre-washed prior to garment construction, or dry-cleaned.
Dry cleaning may still shrink the chiffon up to 4%. There is almost no gradual shrinkage
or shrinkage due to molecular-level deformation.
Silk does not recycle.
Chemical Characteristics: Silk is made up of the amino acids GLY-SER-GLY-ALA-GLY
and forms Beta pleated sheets. Interchain H-bonds are formed while side chains are above
and below the plane of the H-bond network.
Small residue (Gly) allows tight packing and the fibers are strong and resistant to stretching.
The tension is due to covalent peptide bonds. Since the protein forms a Beta sheet, when stretched
the force is applied to these strong bonds and they do not break. The 50% Gly composition means
that Gly exists regularly at every other position.
Silk is resistant to mineral acids. It is yellowed by perspiration and will dissolve in sulfuric acid.
Silk is thermoplastic. It is thermoplastic because it changes shape if certain things are done to it. For instance,
If you stick silk in the dryer, it will shrink.

Silk fibers have a triangular cross section with rounded corners.This allows light to hit at many
different angles, so silk is a bright fiber and has a natural shine. It has a smooth,
soft texture that is not slippery, unlike many synthetic fibers.
B-Keratin molecules do not
form a helix; instead they lie on top of each other to give ridged sheets of linked amino acids,
with glycine appearing on only one side of the sheets. The sheets then
stack one on top of the other. This planar structure is felt when you touch the smooth surface of silk.

Therefore, cross-linkage does not occur because it does not have sulfur or nitrogen.

Natural Roles: B-Keratin adds much more rigidity to reptile skin. Β-keratin is impregnated into the
stratum corneum of the reptilian skin, providing waterproofing and the prevention of dehydration.
Bird's beaks, claws and feathers are also made from β-keratin.
B-keratin is taken from silkworm,
lizards, and spiders.
Silk's good absorbency makes it comfortable to wear in warm weather and while
active. Its low conductivity keeps warm air close to the skin during cold weather.
It is often used for clothing such as shirts, blouses, formal dresses, high fashion clothes,
negligees, pajamas, robes, sun dresses and underwear.

Practical Uses: Silk's elegant, soft luster and beautiful drape makes it perfect for many
furnishing applications. It is used for upholstery, wall coverings, window treatments
(if blended with another fiber), rugs, bedding and wall hangings. Silk is also used for parachutes,
bicycle tires, comforter filling and artillery gunpowder bags. Early bulletproof vests were
made from silk in the era of black po
wder weapons until roughly World War I.
A special manufacturing process makes it suitable as non-absorbable surgical sutures.Chinese doctors
have used
it to make prosthetic arteries.Silk cloth is also used as a material on which to write.

(Silk duvet)

(Silk dresses)

Enough chemistry?
Click here to find out more about the history of silk!


OR here to learn about spider silk!


Please feel free to check out any of the following
websites for more information on B-Keratin/Silk!


Works Cited:
"Beta-keratin." Wikipedia, The Free Encyclopedia. 21 Apr 2007, 23:43 UTC. Wikimedia Foundation, Inc. 15 May 2008 <http://en.wikipedia.org/w/index.php?title=Beta-keratin&oldid=124733478>.
"Bombyx mori." Wikipedia, The Free Encyclopedia. 15 May 2008, 00:54 UTC. Wikimedia Foundation, Inc. 15 May 2008 <http://en.wikipedia.org/w/index.php?title=Bombyx_mori&oldid=212494207>.<span style="color: red">
Brush, Alan. b-keratin. 30 April 2000. 11 May 2008 <http://dml.cmnh.org/2000Apr/msg00705.html>.
"Keratin." Wikipedia, The Free Encyclopedia. 5 May 2008, 01:52 UTC. Wikimedia Foundation, Inc. 15 May 2008 <http://en.wikipedia.org/w/index.php?title=Keratin&oldid=210231253>.
Online, Pine. Summer Weight Duvet. 14 May 2008 <http://www.pineonline.co.uk/shopscr1133.html>.
"Silk." Wikipedia, The Free Encyclopedia. 13 May 2008, 14:28 UTC. Wikimedia Foundation, Inc. 15 May 2008 <http://en.wikipedia.org/w/index.php?title=Silk&oldid=212114564>.
TEXTILES F.R. LIMITED. Textile Silk Fibres. 2006. 13 May 2008 <http://www.textilesfr.co.uk/TFSilk.html>.
Yahya, Harun. The Miracle in the Atom. 2004. 13 May 2008 <http://images.google.com/imgres?imgurl=http://www.evidencesofcreation.com/images_atom/051.jpe&imgrefurl=http://www.evidencesofcreation.com/atom06.htm&h=171&w=270&sz=15&hl=en&start=1&um=1&tbnid=rVaVyDJaDbwGeM:&tbnh=72&tbnw=113&prev=/images%3Fq%3DB-Keratin%>.