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.

CottonOriginally, 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 non-metallic 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.

sapwoodheartwood

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.