Tannins

1
Tannins
2
David S. Seigler Department of Plant
BiologyUniversity of IllinoisUrbana, Illinois
61801 USAseigler_at_life.illinois.eduhttp//www.l
ife.illinois.edu/seigler
3
Tannins - Outline

• Importance
• Tanning leather
• Botanical
• o Wattle
• o Quebracho
• Isolation
• Commercial value

4
Reading

• CHAPTER 15 IN THE TEXT, 374 ff.

5
Introduction

• The conversion of raw animal hides into leather
  has traditionally been carried out with
  plant-derived tannins.
• Many different cultures have developed the
  process of tanning. The compounds that bind to
  the plant proteins are called (by definition)
  tannins.

6

• Leather sandals are found in Egyptian excavations
  from 3,300 years ago. By at least 1500 B.C.,
  records that indicate that tanning was carried
  out in the Mediterranean region are found.
  Clearly tanning was being done before that time.

7

• Some of the most commonly used plants for tanning
  are listed on page 376.
• Tannins are found in most plants, especially most
  woody plants. The quantities vary, often 1-5 is
  encountered.
• There are two major types of tannins condensed
  and hydrolysable. Both have been used for
  tanning. The tannins of the most important
  commercial tannins are condensed tannins.

8
Plants used in tanning

• In Europe, historically the most common tannin
  sources were sumac (Rhus species, Anacardiaceae)
  and oak (Quercus species, Fagaceae).
• Later in European history, spruce (Picea,
  Pinaceae) and pomegranate (Punica granatum,
  Punicaceae) were used.
• In England and Germany most tanning was done with
  oak bark. In North America, American Indians used
  many native plants to make leather.

9
Hemlock, Tsuga canadensis, Pinaceae
Courtesy Dr. Robert R. Robbins
10

• The colonists learned how to use many of these
  same plants. They especially favored hemlock
  (Tsuga canadensis, Pinaceae) and stripped the
  bark from this plant and almost extincted it in
  the northeastern U.S.
• Formerly hides were sent from South America to
  New York and New England and then hemlock was
  used to tan them. The leather was sent to Europe.
  This continued until the hemlock was almost all
  gone.

11

• As hemlock became depleted, emphasis shifted onto
  chestnut (Castanea dentata, Fagaceae). As the
  chestnut blight destroyed the chestnut forests,
  the logs of the trees became available and over
  100,000 tons of tannins from dead trees alone
  became available in the 1930's, especially in
  Pennsylvania.

12
Chestnut logs and stumps in the Smokies
Most of these trees died between 1910-1930
13

• In the tropics, mangroves are often used to make
  tannins. Several Rhizophora species
  (Rhizophoraceae) are especially important among
  these.
• Although these would seem to provide an almost
  limitless source of tannins, mangroves represent
  an unstable ecological community and their
  destruction has proven to be costly in terms of
  seafood.

14
Mangrove in Veracruz, Mexico. The principal tree
is Rhizophora mangle, Rhizophoraceae.
15

• Although the trees had been utilized earlier,
  quebracho (Schinopsis balansae and S. lorentzii,
  Anacardiaceae) and wattle (Acacia mearnsii,
  Fabaceae) became important tannin sources about a
  century ago.

16

• As other sources of tannins became depleted and,
  because of other economic factors, these trees
  now provide about 90 of all commercial tannins
  and almost all of those used in the U.S.

17
Quebracho (Schinopsis balansae or S. lorentzii,
Anacardiaceae)

• Quebracho (Schinopsis balansae or S. lorentzii,
  Anacardiaceae) is probably the best quality
  tannin material for many purposes. The wood of
  this tree from Argentina, Paraguay, and Brazil
  (the Chaco) is usually about 20 (up to 40)
  tannins.
• The tannins are extracted in water and then spray
  dried.
• Quebracho is largely wild harvested at present.

18
Quebracho (Schinopsis balansae, Anacardiaceae)
19
Quebracho (Schinopsis lorentzii, Anacardiaceae)
20
Wattle (Acacia mearnsii, Fabaceae)

• Wattle, Acacia mearnsii, (but a general name for
  many acacias in Australia) is native to
  Australia.
• The plant was introduced into South Africa about
  150 years ago and is widely cultivated there
  today.
• The bark of the tree as 30-40 tannins.

21

• The tree is mostly cultivated in South Africa,
  Sri Lanka, Australia, Brazil and a few other
  southern African countries.

22
Wattle, Acacia mearnsii, Fabaceae
Courtesy Bruce Maslin
23
Wattle under cultivation in Brazil
Debarking wattle logs in Brazil
Courtesy Dr. Geronimo Cano Cano
24
Other tannins

• Several other plants are still used for tannins.
  Among these are canaigre from the S.W. U.S. and
  Mexico. This plant (Rumex hymenocephalus,
  Polygonaceae) grows in sandy soils and has
  potential for being a row crop. The root is up to
  35 tannin.

25
Canaigre, Rumex hymenocephalus, Polygonaceae
Gary A. Monroe. USA, CA, San Bernardino Co.,
Mojave Desert Preserve.
Brother Alfred Brousseau. St. Mary's College of
California.
26

• However, the amount of starch present causes
  problems in tanning.
• European chestnut (Castanea sativa, Fagaceae)
  still accounts for much of the 10 of the market
  attributable to other tannins. Most of this comes
  from Italy, Spain and Portugal.

27
European chestnut (Castanea sativa, Fagaceae)
28

• Sumac (mostly hydrolyzable tannins) is used for
  certain types of tanning, but the color
  properties are not always desirable.
• The tannin content is high (20-35).

29
Sumac, Rhus spp., Anacardiaceae
30

• The cups of acorns have been widely used in the
  Middle East to make tannins.
• Acorns are the source of commercial tannic acid.
• Oak galls are also a source of tanning materials.

31
Acorn cups from Quercus spp., Fagaceae
32
Oak galls
33
How tanning works

• Animal skins are made up of protein called
  collagen (among other things). This protein is
  readily degraded by bacteria and fungi.
• When tannins bond to the collagen, the
  crosslinked fibers are no longer susceptible to
  attack.
• The tannin must effectively crosslink the
  protein, but must also have desirable color
  properties and meet many other requirements.

34
Tanning in the Sudan
Courtesy Dr. Dorothea Bedigian
35
Tanning of hides

• Hides are usually salted to prevent
  decomposition. The hides are first soaked in lime
  (or enzymes) to remove hair (depilatories).
• The proper concentration of tannin solution must
  be used because if it is too concentrated, it
  seals the outside of the hide and the inside
  portions don't get tanned.

36
Trimming salted hides
37
Pickled hides
38
Trimming pickled hides
39

• To avoid this problem, the hides are usually
  first soaked in a solution of "spent" tanning
  liquid.

40
Spent tanning fluid inside a tanning drum
41
A tanning drum in operation.
42
Curing tanned hides
43

• After tanning for an appropriate period, the
  hides are washed, dried and then treated with oil
  or grease for softness.
• The leather is finished and coated with a layer
  of gum, wax, or resin.

44

• About 15 of all tanning in the U.S. is initially
  carried out with vegetable tanning. Almost all
  thick leather products are still vegetable
  tanned. Shoe soles, brief cases, luggage, and
  belts are made in this manner.
• On the other hand, shoe uppers, are tanned with
  chrome alum. However, most of these inorganically
  tanned products are later retanned with vegetable
  tannins.

45
Prospects of tannin use

• Tannins are still widely used. Commercially
  produced quebracho and wattle have replaced local
  tannins in many countries. In some, however (such
  as India), locally produced products are still
  widely used.

46

• In the U.S. and Mexico, quebracho and wattle make
  up more than 90 of the tannins used in the
  leather tanning industry.
• Several billion pounds of hides are tanned
  annually. After tanning, about 30 of the weight
  of the leather is tannins.

47
Other uses of tannins

• Other uses of tannins account for about 15 of
  the total market.
• In the past, tannins and iron salts were used to
  make ink. Gums were also added.
• Tannins are sometimes used medicinally and are
  used in oil field drilling muds.

48
(No Transcript)