Wood and its properties = Древесина и ее свойства. Учебное пособие

LIGNIN

1. Read, translate and state to what parts of speech the following words belong.

Lignin, carbon, carbohydrate, glycol lignin, toxicity, rigidity, determinant, seaweed, bleaching, coarse, bulky, fiber, stiffness, newsprint.

2. Read and translate the text into Russian.

Lignin is a complex and high - molecular - weight polymer built on phenylpropane units (Picture 1). Although composed of carbon, hydrogen, and oxygen, lignin is not a carbohydrate nor even related to this class of compound. It is, instead, essentially phenolic in nature. Lignin is quite stable and difficult to isolate and occurs, moreover, in a variety of forms; because of this, the exact configuration of lignin within wood remains uncertain. One view is that lignin consists of a group of aromatic polymers, predominantly glycol lignin — an ordered polymer made up of multiples of a repeating unit consisting of 18 phenyl propane units. Lignin occurs between individual cells and within the cell walls. Between cells, it serves as a binding agent to hold the cells together. Within cell walls, lignin is very intimately associated with cellulose and the hemicelluloses, and it gives rigidity to the cell. Lignin is also credited with reducing dimensional change with moisture content fluctuation and has been said to add to wood’s toxicity, thus making it resistant to decay and insect attack. The rigidity provided by lignin is an important determinant of wood properties. Recollection of the very soft nature of cotton (almost pure cellulose) and the compliant nature of seaweed (which has very little lignin) are indications of how non-rigid wood would be without a stiffening ingredient. In its native form, lignin is only very lightly colored. However, even the mildest treatments available for removing lignin from wood cause appreciable degradation of its structure, resulting in a deepening of its color. Thus, chemical pulps that contain residual lignin require considerable bleaching to make them white in color. Because the pulping process used in making newsprint involves mechanical separation of fibers and not lignin removal, only a light brown color develops, which is readily removed by chemical bleaching. However, when the lignin present in newsprint is exposed to air, particularly in the presence of sunlight, the resulting lignin derivatives tend to become yellow or brown with age; a small part of yellowing with age is

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also traceable to the hemicelluloses. Because of the lignin in mechanical pulp, newsprint has a notoriously short longevity due to its high lignin content; it is also coarse, bulky, and of low strength because the fibers are difficult to bond to one another because of their inherent stiffness.

[From: Shmulsky R., Jones P. D. Forest Products and wood science / R. Shmulsky, P. D. Jones. – US : Willey-Blackwell, 2011. – P. 49]

[From: Shmulsky R., Jones P. D. Forest Products and wood science / R. Shmulsky, P. D. Jones. – US : Willey-Blackwell, 2011. – P. 49]

3. Write out new words and word combinations from the text and translate them into Russian.

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4. Answer the following questions using the words you’ve learned in exercise 3.

1.Can you give a definition of the term lignin?

2.Why does the exact configuration of lignin within wood remains uncertain?

3.Where can lignin occur?

4.What is lignin associated within cell walls with?

5.What is an important determinant of wood properties?

6.Where is the pulping process used in?

7.Why do the resulting lignin derivatives tend to become yellow or brown with age?

8.Why does newsprint have a notoriously short longevity due to its high lignin content?

LOCATION OF WATER IN WOOD

1. Read, translate and state to what parts of speech the following words belong.

Harvest, cell, lumen, organic, amount, liquid, photosynthesis, manufacture, vapor, dry, solution, product, property, adsorb, compounds, strength, sap, wood, location, materials, constant, freshly, dissolved.

2. Read and translate the text into Russian.

Water in green or freshly harvested wood is located within both the cell wall and the cell lumen. The amount of water within the cell wall structure of a living tree remains essentially constant from season to season, but the amount of water in the lumen may vary. The water in the lumen may contain dissolved food materials produced by photosynthesis as well as organic and inorganic compounds. This solution is commonly referred to as sap. When wood is dried during manufacture, all liquid water in the cell lumen is removed. The cell lumen always contains some water vapor, however. The amount of water remaining in the cell walls of a finished product depends on the extent of drying during manufacture and the environment into which the product is later placed. Once removed by drying, water will recur in the lumen only if the product is exposed to liquid water. Three common ways for this to occur are installing wood in the

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ground, placing it where it can be rained on, and locating it where condensation or leaking water occur. Picture 1 may help in visualizing the location of water in a wood cell. As long as there is any liquid water in the lumen, the wall of the cell will be saturated; that is, it will contain as much water as it can physically adsorb. Most physical properties of wood (other than weight) are not affected by differences in the amount of water in the cell lumen. For example, if the lumen is one - fourth full of liquid water, the cell and the wood will have the same strength as when the lumen is one - half full. The green wet cell is illustrated in Picture 1 A. As green wood begins to dry, water is first removed from the lumen. When wood is dried to the point that all the water in the lumen is removed, water then begins to leave the cell wall. Almost all wood products used in buildings or where there is no contact with the ground contain water in the form shown in Picture 1 B. The point at which all the liquid water in the lumen has been removed but the cell wall is still saturated is termed the fiber saturation point (FSP). This is a critical level because below this point the properties of wood are altered by changes in moisture content. If dry wood is used where it has no contact with a source of liquid water, the amount of water in the wood will always be less than the FSP.

[From: Shmulsky R., Jones P. D. Forest Products and wood science / R. Shmulsky, P. D. Jones. – US : Willey-Blackwell, 2011. – P. 141]

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NATURE OF WATER IN WOOD

1. Read, translate and state to what parts of speech the following words belong.

Liquid, lumen, structure, absorption, surface, chemical, molecules, sorption, cellulose, wood, cell, relatively, accumulation, remain, access, moisture, tightly, description, porous, increase.

2. Read and translate the text into Russian.

To simplify discussion, the liquid water found in the lumen of wood is often referred to as free water and the water within the cell wall is called bound water. This is an appropriate description because free water is relatively easy to remove and so is the first to be removed when wood is dried. Bound water is held more tightly because of surface adsorption within the wood structure. As moisture content decreases below the FSP, the strength of the wood – water bond increases. Adsorption forces, mainly hydrogen bonds, hold the water within the cell wall. This is not to be confused with the absorption that takes place, for example, when a synthetic sponge soaks up water. Absorption results from surface tension and capillary forces, and it results in a bulk accumulation of water in the porous wood. Adsorption, in contrast, involves the attraction of water molecules to hydrogen - bonding sites present in cellulose, hemicellulose, and lignin. Hydrogen bonding occurs on the hydrogen side of the hydroxyl (OH) groups found throughout the chemical elements of wood. Four water molecules are monomolecularly (one per site) adsorbed onto the wood. At higher moisture contents, additional water molecules first bind to the remaining hydroxyl groups and then begin to polymolecularly adsorbs, or piggyback, onto each other. In saturated green wood, as many as 6 - 10 water molecules may be attracted to each accessible sorption site. It is believed that the OH groups of adjacent cellulose molecules can be mutually bonded, or cross - linked.

[From: Shmulsky R., Jones P. D. Forest Products and wood science / R. Shmulsky, P. D. Jones. – US : Willey-Blackwell, 2011. – P. 207]

3. Write out new words and word combinations from the text and translate them into Russian.

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4. Answer the following questions using the words you’ve learned in exercise 3.

1.What does the term «free water» mean?

2.What does absorption involve?

3.Where are four water molecules absorbed?

4.How do the water molecules work at higher moisture contents?

5.How many can water molecules be attracted to each accessible sorption site in saturated green wood?

6.Which groups of adjacent cellulose molecules can be mutually bonded or

cross - linked?

7. What makes free water relatively easy to remove?

PAPER

1. Read, translate and state to what parts of speech the following words belong

Wood, cotton, raw, paper, ubiquitous, communications, industrial, capacity, source, globalization, lignin, chemicals, dominant, fibers, reeds, potential, fossil, flexible, profitable, important, pulp, straw, worldwide, disposable, major, facilities.

2. Read and translate the text into Russian.

It was not until the late 1800s that wood became an important source of papermaking fiber. Prior to that time, cotton and linen rags were the major source. In 1840, the groundwood pulping method was developed in Germany. In 1856, the soda chemical pulping process was developed in England, and in 1884, the kraftpulping process was developed in Germany. Currently, wood is the dominant raw material for paper manufacture. Worldwide, production of wood pulp for paper and paperboard is great with the quantity of nonwood fiber used in paper and board production. Nonwood fibers in use include primarily straw, bagasse, and bamboo. Other sources include reeds, abaca, esparto and Sabai grasses, oil palm, cotton linters, rags, sisal, and kenaf. Wood is clearly the dominant worldwide raw material for pulp.

Paper including paperboard and tissues has become so ubiquitous in

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people’s daily lives that most rarely consider its source or its importance.

Paper serves as a primary packaging product, communications medium, base for sanitary and disposable products, and industrial sheet material. Pulp and paper mills are generally large capacity and operate around the clock. Bark and lignin are commonly burned for energy that is used to heat the dryer rollers and, in some cases, to generate electricity. In the future, as energy costs increase and globalization improves, it is reasonable to assume that some pulp and paper mills will operate in a dual manner, that is, depending on the prevalent market cost structures for wood, paper, and energy, wood may be converted to pulp and paper or it may be converted to electricity. Another developing concept is that of the biorefinery. A biorefinery is essentially a mill that converts bio - based raw materials into chemicals, energy, and/or reconstituted products. Another developing concept is that of the biorefinery. A biorefinery is envisioned as a mill that will convert bio - based raw materials such as wood into chemicals, energy, and/or reconstituted products. Whereas kraft paper mills of today subject wood to chemicals that remove lignin and the hemicelluloses in the pulping step, with these compounds then burned for power, the chemical paper mill of the future may extract hemicelluloses from pulp chips prior to subsequent processing, with these used to produce a variety of chemicals and polymers. Then, in the biorefinery, the potential will exist for conversion of wood to syngas, liquid fuels, pulp, and a wide array of industrial chemicals and chemicals and feedstocks. Syngas consists primarily of carbon monoxide and hydrogen, is combustible, and about one - half the energy density of natural gas. Black liquor that results after pulping of the extracted chips will be used to generate power, as today, except that much more efficient gasification systems will be used. The net effect is that pulp and paper mills will become net providers of energy to the national energy grid, with pulpand paper but one of many product options for the biorefinery manager. In the process of conversion from paper mills to full biorefineries, wood processing facilities will switch from net emitters of carbon dioxide (traceable to use of fossil - based fuels for a portion of process energy) to facilities that sequester substantial quantities of carbon through avoided emissions. Such facilities will likely become more flexible, more responsive to societal needs, and potentially more profitable.

[From: Shmulsky R., Jones P. D. Forest Products and wood science / R. Shmulsky, P. D. Jones. – US : Willey-Blackwell, 2011. – P. 397]

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3.Write out new words and word combinations from the text and translate them into Russian.

4.Answer the following questions using the words you’ve learned in exercise 3.

1.When did wood become an important source of a papermaking fiber?

2.Which method was developed in 1840?

3.Where can nonfood fiber be used?

4.What happens during the process of conversion from paper mills to full biorefineries?

5.Can you explain the term «net effect»?

6.Which developing concepts are reasonable to assume in the future?

7.What does syngas consist of?

8.Which facilities will likely become more flexible, responsive to social needs and profitable in future?

STRENGTH AND MECHANICS

1. Read, translate and state to what parts of speech the following words belong.

Resistance, deformation, dependent, mechanical, selection, evolutions, omnipresent, property, expansion, distribution, humankind, property, argument, strength, application, elastic, critical, shape, product, various.

2. Read and translate the text into Russian.

The strength and resistance to deformation of a material are referred to as its mechanical properties. Strength is the ability of a material to carry applied loads or forces. Resistance to deformation, or stiffness, determines the amount a material is compressed, stretched, bent, or otherwise distorted by an applied load. Changes in shape that take place instantaneously as a load is applied and are recoverable when the load is removed are termed elastic deformation. If the deformation, on the other hand, develops slowly after the load is applied, it is termed a rheological or time - dependent

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