Natural fibers - fibers obtained from plant (cellulosic), animal (protein)  or mineral sources

     NATURAL CELLULOSIC
            Seed - from seed of plant
            Bast - from stem of plant
           Leaf - from leaf of plant

  Properties of natural cellulosic fibers:
     -    Low elasticity and resilience
     -   Burns readily and completely
     -    Do not melt but will scorch and burn
     -    Good resistance to most chemicals
     -    Attacked by plant-loving insects such as silverfish
     -    Attacked and destroyed by mold and mildew
     -     Very hydrophilic
     -    Shrink in presence of heat and moisture

     Cotton is a seed cellulosic fiber.  The fibers form around the seed; the seed must be removed and fibers removed from
     the plant before it can be used.  READ THE INFORMATION ABOUT CULTIVATION AND PRODUCTION OF
     THE FIBER

     The quality of the fiber depends on the length, the growing conditions, the weather.

     Most cotton grows as a white fiber; however naturally colored cottons (which have been around for thousands of years,
     but grown in obscurity) are being grown in locations around the world.  The naturally colored cotton requires no
     chemical dyes.  The colors tend to be muted greens, browns, and reds.  In recent years, cotton producers/researchers
     have been genetically improving the naturally colored cottons so they are better quality.

    A unique property of cotton that differs from the general properties of natural cellulosic fibers is that it is stronger wet
     than dry.

     STUDY THE DIAGRAM AND PHOTOMICROGRAPH ON PAGE 74, 75 OF YOUR TEXTBOOK.

Photomicrograph of cotton fibers taken from Cotton Science magazine

Other cellulosic fibers generally have the same properties as cotton.

     Bast                                        Leaf
     Flax (linen)                            Sisal
     Jute                                       Pina
     Ramie                                    Henequen
     Hemp
     Kenaf

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     Natural Protein Fibers

     Wool from sheep
     Camel
     Alpaca
     Vicuna
     Llama
     Cashmere
     Mohair
     Qiviut
     Cashgora

     Properties of natural protein fibers (the discussions of wool and silk will not usually list these
     again)
     Hydrophilic
     Hygroscopic (especially wool)
     Difficult to burn
     Attacked by some insects such as carpet beetles and moths
     Damaged by some acids and alkalis (detergents, perfumes, perspiration, etc.)
     Good resilience
     Damaged by continuous exposure to sunlight

     WOOL - the protein in wool is keratin.
     The sheep's wool is the most common and plentiful.  Most wool comes from the Merino sheep.
     The sheep are sheared in the spring and produce an average of 8 pounds of wool/year.  About 3-5
     pounds is useable.

 Products made from new or used wool are covered under the Wool Products Labeling Act (1939).
     In addition to the requirements of TFPIA, there are the following:
     - The term "wool" means it is a new wool, never used before
     - If any part is recycled, it must be stated on the label
     - Specialty fibers other than wool must be identified

     Wool that has been taken from animals that have been slaughtered for meat is called pulled wool.
     Pulled wool is less elastic and lustrous because it has been treated to remove the skin.
 

     Lambs wool comes from sheep 8 months old or younger.
 
 

Physical properties
 The physical structure of wool includes scales on the outside (see page 104) and cortical cells on the
     inside of the fiber..  The cortex consists of long, spindle-shaped cells.  The cortex is divided into two
     distinct sections - paracortex and orthocortex. These cortical cells respond differently to heat and
     moisture and give wool the 3-dimensional crimp.
 

The wool polymer is helical (see your class notes).
 

Chemical Properties
Wool is hydrophilic and hygroscopic (absorbs readily but does not release the moisture)..
     Wool provides good thermal insulation due to the dead air spaces in the scales and the crimp in the
     fibers.  The fibers cannot get close to each other thus providing a large volume of dead air space.

     Wool is one of the least flammable textile fibers; it burn slowly and gives off a smoky flame; it often
     self-extinguishes when removed from the flame.  When it burns, it smells like rotten eggs (due to
     sulfur) - the same as when your hair burns.

     Care
     Wool shrinks due to felting shrinkage when subjected to agitation .  The scales entangle making the product (sweater, socks, etc.) smaller.

     Alakline substances usch as detergents cause degradation.  Bleach decomposes the fibers.

     Usually wool fabrics have a label recommending dry cleaning.  Washable wool is on the market.  It
     is usually blended with another fiber such as polyester to avoid felting shrinkage or it has been
     treated with a resin to cover the harsh edges of the scales.

     SPECIALTY WOOLS  are similar to sheep's wool in structure and properties.  Most are more rare,
     less durable, and have finer diameter than sheep's wool.
     ========================================================
     SILK  the protein in silk is fibroin.  Silk fiber is produced by the larva of certain insects used in
     building webs and cocoons -  the silkworm the bombyx mori produces the most silk..
     (See Page 119 in your textbook)
 
 

     Silk is the only natural filament fiber.  The longest fibers are 1500-2000 feet long but usually are
     more like 1000 feet.
     Sericin is the gum surrounding the silk when it is secreted.

Cultivated silk is obtained from the cocoons of silkworms under controlled diet and environmental
     conditions.  The silkworm is killed inside with heat and does not damage the cocoon.

     Wild silk (Tussah) is obtained from the cocoons of silkworms left unattended in their natural
     habitat.  The silkworm is allowed to come out of the cocoon.

     Raw silk is the silk that has not had the sericin removed.  Removing the sericin removes about 1/4
     of the weight.

     Duppioni silk results when two cultivated silkworms spin their cocoons together.

     Weighting  is a finish applied to silk fabrics to add back some of the weight when the sericin is
     removed.  Large percentages of weighting of metallic salts damage the silk fibers.
     Today silk that is weighted more than 15% for black or 10% for other colors must be labeled.
 

     Silk is damaged by alkalis and acids, particularly detergents and perfumes, perspiration, bleaches.
     Sunlight causes fiber damage.  Silk is attacked by carpet beetles, but not moths.
     Ultraviolet light causes breakdown of the polymers and fiber degradation.

     Care. - most silk is labeled "dry clean".
     The absorption of water breaks the bonds in the silk fiber and causes silk to lose approximately 20%
     of its strength.
        The new "washable silks" result from a modification in the dye or a resin treatment to prevent
     fiber degradation.