Transcript Plants as sources of non-food products

Plants as sources of non-food products
Plant products we’ll consider here use fiber from plant
tissues. The fiber, however, comes from different plant
parts…
Fiber cells are elongate and have thickened secondary
cell walls. Most of those cell walls are cellulose, but
there may also be lignin, and they may be impregnated
with tannins, gums, pectin, or other polysaccharides.
Much of the fiber we use comes from xylem tubes, and
is comprised of elongate strings of many fiber cells.
Cellulose is extremely strong in tensile strength (how
much force it takes to pull the fiber apart lengthwise).
The basic structure of cellulose as linked β-glucose (2
units) is:
What gives these strings of glucose great tensile
strength is hydrogen bonding (cross linking) of hydroxyl
groups from individual ‘strings’.
Cellulose is strongest when it’s white and ‘pure’. The
presence of lignin makes the fiber weaker, as well as
frequently giving it color.
Plant fiber can be classified by source: surface fibers
come from coverings of seeds, leaves or fruit; bast fiber
comes from phloem from inner bark; hard fiber comes
from vascular bundles (phloem & xylem) of leaves.
We now understand the genetic control over cellulose
biosynthesis. Control comes from one gene: RSW1.
Synthesis occurs at the cell membrane at what are
called rosette terminal complexes (RTCs).
Here’s what happens when synthesis is blocked in
Arabidopsis:
Table 18.1 lists a number of sources for fibers, where
they come from within the plant, and how they are used.
The general categories are:
textile fiber (cotton cloth, linen, hemp cloth, piña
cloth, ramie cloth)
cordage fiber (rope, twine and matting from hemp,
musa, and sisal)
filling fiber (coir, kapok)
The methods for extracting fiber from all these plants
are basically similar for each fiber source:
Surface fiber is extracted by ginning. The most obvious
example is ginning of cotton.
Cotton
Originally, ginning was done by hand.
Then, in 1793, James Whitney invented the cotton gin. It
increased the efficiency of ginning by 50x.
To understand why it made such a difference, we need
to look at the cotton plant and how cotton is harvested.
Cotton species (different ones) originate in both New
and Old World regions. All are in the genus Gossypium.
New World species are G. hirsutum and G. barbadense.
Both are tetraploid and ‘long staple’, meaning the seed
hairs that are cotton are long, sometimes >2 cm. The
tetraploid genetics may have resulted from hybridization
of the Old World species. However it originated, it comes
from southern Mexico and Central America. G. hirsutum
is now the most commonly grown cotton.
Old world species are G. herbaceum and G. raimondii.
Both are diploid and produce shorter fibers, generally <2
cm.
Today, the cotton grown in the American South is largely
mechanically harvested.
Cotton fiber has a basic microstructure that includes a
natural ‘twist’.
On the left are cotton bolls on a plant following spraying
of the plants with defoliants to make harvesting easier.
On the right is an opened boll that indicates how ‘hairy’
cotton seeds are.
The modern saw gin (much like Whitney’s gin) grabs
and pulls fiber, while the seeds cannot get past a screen.
A Whitney-type gin
A modern ginning plant
Ginned fiber is packed in bales. There are a number of
black folk songs about loading bales of cotton onto
ships, about working in the mills, and about the pest
problems in producing cotton –
“Gonna jump down, turn around, pick a bale o’cotton
Gonna jump dpwn, turn around, to pick a bale a day”
“Now, the first time I seen the boll weevil
He was settin’ on the square
The next time I saw the boll weevil,
Had his whole family there
Just a lookin’ for a home…
The baled cotton was shipped to the mills, where the
fibers were straightened (called carding), combed, and
spun into yarn.
The yarn is bleached. Today, chlorine-based bleaching
is used. In the 1700s in England, bleaching involved
soaking in sour milk and cow dung, then steeping the
yarn in lye. Finally, the yarn was bathed in buttermilk
and spread out in the sun to dry and bleach it. That
must have made for quite a smell.
The next stage for most cotton used for thread and
some cotton cloth is mercerization. Cotton is passed
through a bath of NaOH. The thread or cloth fibers
swell, become stronger and has greater affinity for dyes.
Cotton yarn or cloth is dyed with many of the different
natural or synthetic dyes, of course including indigo to
colour jeans.
The last point to make about cotton is that most
American cotton is now a bioengineered product. It is
called Bollgard (Monsanto) (or Bt) cotton. A bacterial
toxin has been introduced that acts as an insecticide
against various bollworms. How much cotton is Bt?
How much difference does Bt make?
In the U.S., with heavy use of pesticides, the
improvement in yield is only about 10%. However, in
India, where pesticide, due to expense, is much less
heavily used, the increase in yield is 50 – 60%.
Flax -The second most important fiber for clothing
comes from Linum usitatissimum. Flax is grown both for
the fiber and for oil from the seeds. Linseed oil is used in
paints, wood finishes, linoleum and as a drying oil.
Flax is the oldest source of fiber for clothing. Bast fiber
from stem phloem has been found in archaeological
sites at least 10,000 years old. Egyptian linen fragments
~6500 years old are in museums. Use was not limited to
the Old World; there are also very old pieces of cloth
from the American southwest.
Linen manufacture begins by harvesting flax stems
around 1m long, then ‘retting’ [rotting] those stems.
Retting can be done in a pond or stream, or in a nonmetallic container. At the end of retting, the fibers are
soft and easily separated from the wood.
The separation process is called dressing or scutching.
After scutching, the fiber is combed (or hackled), then
spun into yarn that can be woven.
Linen is used both for fine fabrics (Lace and tablecloths,
as well as clothing), towels, and rougher fiber is used in
cordage.
There are many other bast fiber sources and products:
Ramie – derived from Boehmeria nivea, a member of
the nettle family. Ramie originated in China and the
Malay Peninsula (two different forms), and has been
cultivated for fiber for 6,000 years.
Production of fiber requires first de-barking the stems,
scraping the outer bark, then separating bark from
parenchyma, washing, drying, and de-gumming the
parenchyma fiber to extract spinnable fiber.
Ramie is strong, but not particularly durable or dyeable.
It is used for industrial sewing thread, packing materials,
fishing nets, and filter cloths. It is also made into fabrics
for household furnishings and clothing, frequently in
blends with other textile fibers
Ramie clothing
The plant
Jute – made into burlap, ropes, upholstery, carpet
backing, and coarse clothing, comes from Corchorus
species (dominated by C. olitorius). The plant family is
the Tiliaceae, which we encounter locally as linden trees.
The jute plant is an annual native to Asia, but was
converted into the ‘sackcloth’ worn in medieval Europe.
Cannabis sativa, marijuana for one use, but hemp for its
fiber, is also used for both rope and cloth. During WWII it
was cultivated widely for the strong rope that could be
made. However, its fiber is much like linen, and can be
made into strong, durable, fine clothing.
hemp stem
hemp fiber
The U.S. has prohibitions on growing hemp, but does
permit importation of finished clothing. Canada is now
allowing pilot plantations. The plants must have <3%
THC.
Hemp clothing is not new. Levi Strauss jeans were
originally made with hemp cloth – that’s where the
name denim came from [‘Serge de Nimes’ – hemp cloth
from Nimes = denim]
Other fibers
Manila hemp – from Musa textilis, a congeneric relative
of banana
Sisal – from Agave sisalana leaf fibers, used to make
rope and mats, and from the surface fiber of this plant,
kapok used to make stuffing, including in life vests.
Piña – from pineapple plants, made into shirts in the
Philippines
Coir – seed fiber from coconuts, used to make rope and
mats
Artificial fiber?
Rayon is sometimes called an artificial fiber, but it’s
really a reconstituted cellulose fiber fabric. The first form
of viscose fabric was developed in 1855, and various
alternatives continued to be developed until 1910 [the
name rayon was not attached until 1924]. The same
basic process that produces rayon fiber also produces
cellophane.
There are many steps in the process of making viscose
(rayon) fiber from wood pulp. Here’s the full list (from
Wikipedia):
1. Cellulose: Production begins with processed
cellulose (wood pulp)
2. Immersion: The cellulose is dissolved in caustic soda
3. Pressing: The solution is then pressed between
rollers to remove excess liquid
4. White Crumb: The pressed sheets are crumbled or
shredded to produce what is known as "white crumb"
5. Aging: The "white crumb" aged through exposure to
oxygen
6. Xanthation: The aged "white crumb" is mixed with
carbon disulfide in a process known as Xanthation
7. Yellow Crumb: Xanthation changes the chemical
makeup of the cellulose mixture and the resulting
product is now called "yellow crumb"
8. Viscose: The "yellow crumb" is dissolved in a caustic
solution to form viscose
9. Ripening: The viscose is set to stand for a period of
time, allowing it to ripen
10. Filtering: After ripening, the viscose is filtered to
remove any undissolved particles
11. Extruding: The viscose solution is extruded through
a spinneret, which resembles a shower head with many
small holes
12. Acid Bath: As the viscose exits the spinneret, it
lands in a bath of sulfuric acid resulting in the formation
of rayon filaments
13. Drawing: The rayon filaments are stretched, known
as drawing, to straighten out the fibers
14. Washing: The fibers are then washed to remove
any residual chemicals
Trees, Wood, and Wood Products
Trees cover 25% of land in the U.S., 40% in Canada,
and ~33% of the Earth’s land surface. 60% of forests are
in the tropics.
Use of forests has been so intense that 30 – 50% of
forest land has been cleared for lumber, fuelwood, or
agriculture. In the tropics ~2% of what’s left is being
destroyed annually.
Only ~2% of forests are protected in parks, reserves,
etc. and only 13% is managed.
Reforesting land from which trees are harvested is a
logical answer, but…
Even in Canada, reforestation is a legal requirement
only on Federally or Provincially owned land.
In tropical forests density is high and light penetration
low, so that a seedling cannot simply be planted in the
place of a harvested tree. Instead, an area has to be cut
around the harvested tree, meaning loss of a diverse
group of trees to permit growth of one new, valuable
tree.
Time is also a factor. It takes 25-40 years for a softwood
tree to reach harvesting size for pulp. It takes 90-150
years for a hardwood tree to reach harvesting size.
What do we mean by ‘hardwood’ and ‘softwood’?
Hardwood generally refers to trees from angiosperm
species; softwood to coniferous (or gymnosperm) trees.
Hardwoods occupy 65% of the world’s forests, conifers
35%. That does not necessarily indicate wood
properties. Poplar (aspen) and Balsa wood are
‘hardwoods’ that are of low density and ‘soft’, while
yellow pine is harder and denser than many hardwoods.
There is a real meaning to ‘hard’ in hardwoods:
Hardness is determined by the thickness of cell walls
and the proportion of vessels, tracheids, and fibers.
The other distinction is between heartwood – the inner
secondary xylem, dry and darker because cells contain
tannins, gums and resins (which act as preservatives) –
and sapwood, which is the active xylem lying outside
the heartwood. It is wet due to its function of water and
mineral transport.
heartwood
sapwood
There are differences in heartwood colour and
properties that are important in how species are used…
Wood, in general, is second only to food in importance
as a plant product.
Wood is used in various ways: as lumber plainsawn or
quartersawn, as veneer, as plywood (thin layers glued
with wood grain at right angles on adjacent sheets), as
fiberboard (typically MDF) and as OSB (oriented strand
board)
The most important species of softwoods are: Pine
(Pinus spp.), Douglas Fir (Pseudotsuga spp.), and
spruce (Picea spp.)
The most important species of hardwoods from North
America are: oak (Quercus spp.), maple (Acer spp.),
cherry (Prunus spp.; this genus also includes apricot,
almond, peach and plum), and walnut (Juglans spp.)
In the less developed countries the major use is as fuel.
In the industrialized countries, 50% of harvested wood is
used as pulp. Most of that is used in the manufacture of
paper. This use is relatively recent; before the middle of
the 19th century paper was made from straw, leaves,
and rags. The U.S. Declaration of Independence and
Constitution were originally written on hemp paper.
There are older ways of making paper.
In ancient Egypt paper was made from papyrus
(Cyperus papyrus), a wetland sedge (like a grass, but
with triangular stems) from the Nile delta. The same
plant was called bublos when used in
other products – that’s where words like
bibliography and bible come from.
Papyrus ‘paper’ was made by stripping
off outer layers of the stem, then laying
strips of the pith together, with additional
layers at right angles (usually when wet
to increase adherence), and pounding
the layers together between hard tablets
and drying the result.
Because papyrus (a cellulose ‘paper’) can be sensitive
to decay, it was replaced by ‘paper’ made from animal
tissues.
Parchment is a thin sheet made from calf, goat or sheep
skin. It is produced by stretching a skin, then scraping
and drying it under tension. Vellum is a parchment made
from the skin of a young calf. When you get your
‘sheepskin’ at the end of your undergraduate career, it
will not be on parchment.
engraving of a parchmenter
1568
The steps in paper manufacturing using wood pulp:
1. Pulping – Chemically the Kraft process is used;
crushed wood is ‘cooked’ in a liquor [the liquor
contains NaOH, sulphites or sulphates; each of these
as a waste product has environmental impact] that
dissolves out the lignin and separates the fiber.
Mechanically, chipped wood is fed into a steam
pressure cooker; the ‘oatmeal-like’ output is then
pressed between rollers. Since the lignin remains,
paper produced by mechanical pulping is cheaper,
but is weaker and yellows with age.
The pulp may then be bleached using chlorine. In
addition to bleaching, this treatment produces
organochlorine compounds including dioxins.
2. Drying - prepared pulp is spread over a web, then
pressed to remove water. The remainder is taken up by
an absorbent felt. Then heating completes the process.
The wood pulp can also be used to make cardboard,
fiberboard, cellophane, or cellulose acetate, which is
then used to make molded plastics.
The last two products are made by treating pulp with
either acetic acid or acetic anhydride (remember
rayon). You probably used a cellulose acetate product
when you brushed your teeth or combed your hair.
There are a number of other products made from trees:
Resins – resins are insoluble in water, and have
therefore been used in waterproofing (pine pitch to seal
lapboard construction of ships).
A simple distillation of conifer resin produces turpentine.
What’s left over is rosin, used by string-playing
musicians and baseball players.
Part of what makes Band-Aids stick to your skin is resin!
Another important product from the periderm of the cork
cambium is cork (called phellem in describing plant
structure earlier). Cork is light, tough, and a good
insulator. We use it in flooring and, of course, to seal
wine bottles. Instead of natural cork (largely from cork
oaks), a significant fraction of what is used today is
synthetic.
What about ‘wood’ products not from trees?
Bamboo (a generic name for products from the stems of
grasses within the subfamily Bambusoidea) is used in
hundreds of different products, from furniture and
flooring to the Japanese shakuhachi, a wood flute.
Bamboos do not have secondary growth (the
enlargement of stems over years). Instead, the culm is
an annual growth, approximately fixed in diameter.
Species with large diameters are used in construction;
we use species with smaller diameters as stakes to hold
up plants.
Bamboo is also >90% of the food for pandas, and China
has protected some bamboo forests for pandas.
Finally, bamboo is the chief source of pulp for
papermaking in India.