Presentation on theme: "Plants and People Wood & Paper. Plant Tissues Lateral meristems: located in the margins of the stem and root (vascular and cork cambium). Responsible."— Presentation transcript:
Plant Tissues Lateral meristems: located in the margins of the stem and root (vascular and cork cambium). Responsible for increase in girth. vascular cambium cork cambium (phellogen) Meristem is undifferentiated, embryonic tissue present throughout the life of the plant and can differentiate/mature into any other type of cell. Think the “stem cells” of the plant world!
What is Wood? In plants that become woody, a vascular cambium layer forms between the primary xylem and primary phloem cells. The vascular cambium is a laterally expanding meristem which divides to produce xylem to the inside and phloem to the outside. These secondary tissues are secondary xylem and secondary phloem. Only the cells closet to the cambium layer are alive and growing. Wood is an accumulation of secondary xylem. Herbaceous plants lack secondary growth even if a cambium layer is present.
What is Wood? Again, wood is an accumulation of secondary xylem. Sapwood is xylem which is still conducting water. Heartwood is the old, no-longer functional xylem. It may be filled with resins or tannins.
What is Bark? Bark consists partly of living and dead phloem cells and partly of periderm, which replaces the epidermis as a protective layer. Periderm is made by the cork cambium or phellogen, a secondary lateral meristem which produces cork or phellem. Because the bark must continually change to allow for the horizontal growth of the stem and to accommodate branches, new bark is continually being made from the underside while the outer layers slough off.
Where Does Cork Come From? Cork is derived from an oak tree, Quercus suber, which produces a thick, rugged bark. A tree must be about 25 years old before cork can be harvested, and the first year's harvest is poor. Later harvests are superior and can be harvested every 9 to 12 years. The harvesting of cork does not harm the tree, in fact, no trees are cut down during the harvesting process. Only part of the bark is extracted, and a new layer of cork regrows, making it a renewable resource.
Hardwoods vs. Softwoods Wood is divided into two major categories, hardwoods and softwoods. These terms refer to the plants that grew the wood, NOT to the character of the wood itself. Gymnosperms (non-flowering plants) produce softwood. The xylem consists only of tracheids, which are long cells that conduct water through openings in the side walls. Angiosperms (flowering plants) that are dicots produce hardwood. The xylem has both tracheids and vessels. Vessels are tube-like cells that conduct water through perforations in their end walls. Monocots have no vascular cambium and therefore no wood In addition to xylem and phloem, the cambium makes ray parenchyma cells in the living part of the xylem. These cells conduct water horizontally. Rays are present in both types of wood.
Tree Rings Seasonal variations in climate can be reflected in the cambium layer and hence the appearance of the xylem. In spring or the wet season, cambium makes many large xylem cells which appear lighter. In summer or the dry season, only a few small cells are made and the wood appears darker. In winter, cell production ceases. In the tropics where there is little variation in climate, the trees usually do not produce rings, but may be present if there is a marked wet and dry season. Dendrochronologists can coordinate tree ring patterns to reconstruct climate histories.
Characteristics of Wood Porosity refers to the vessel dispersion in a given year's growth. Grain describes the alignment of the xylem cells--straight, tipped, spiral, curled, etc. Figure is determined by the number of rays, the porosity, the grain, and the alignment of rings. The presence or absence of knots also contributes to the figure. Different woods have different densities, grains, and mechanical properties. Density is Mass/Volume. An oven-dried piece of wood 1 cubic cm in volume is used to measure density. Since the mass of 1 cc of water is 1 g at sea level, any wood with a density higher than 1 will sink, while any wood with a density below 1 will float. Balsa is the lightest wood; Lignum vitae is one of the densest, with a density of 1.3. Pine for construction is about 0.35; oak for furniture about 0.60.
XRT X is the cross-section of the wood. It shows rings, rays, and cells. R is a radial view of the wood. It shows the rings in side view. They appear as vertical streaks. Radially cut or quarter-sawn wood is expensive because only a few pieces can be obtained from each log. T refers to a tangential cut. It shows the ends of the rays. Annual rings appear as irregular bands of light and dark streaks or patches. This is the most common cut. This is also referred to as plain-sawed or slab-cut.
Seasoning Wood Wood must be seasoned or dried in the open air, in kilns, or with fans.
Wood Products - Veneer Veneer is thinly sliced wood used for decorative layers. Veneer may be shaved off a revolving log or from the side of a long rectangular block. See Figure 16.15 in textbook
Wood Products - Plywood Plywood is made of three or more thin layers of wood bonded together with an adhesive. Each layer of wood, or ply, is oriented with its grain running at right angles to the adjacent layer in order to reduce shrinkage and improve strength. Most plywood is pressed into large, flat sheets used in building construction. Plywood has limitations because its manufacture is dependent on the availability of large sheets of veneer. Three-ply all-veneer Three-lumber core Types of Plywood
Wood Products - Particleboard Particleboard is made from wood that is first reduced to small chips or sawdust by shaving or splintering. Once the chips of desired size have been produced, they can be mixed with resins, pesticides, and fire retardants and pressed into the desired shapes and sizes.
Wood Products - Fiberboard Fiberboard differs from particleboard in that wood fibers, not small pieces of wood, are used. The fibers are xylem elements that have been separated from one another by placing small wood particles in chemical solutions that dissolve the pectins that hold the fibers together. The processes used to reduce wood to fibers for fiberboard are the same as those used to make pulp for paper. MDF is “medium density fiberboard”.
Wood Products - Textiles Rayon and cellophane are the same product in different forms. Both are made from pure cellulose derived from wood that has been depolymerized and then dissolved into a strong alkaline solution. The final mixture is either extruded in thin sheets to produce cellophane or forced through small openings to produce rayon threads. Acetate is made from purified cellulose that has had one or more acetyl groups added. Lyocell, commonly sold under the name Tencel is the first new textile fiber produced in the last 30 years. Cellulose from plantation grown trees is extracted and strands of the fiber are produced by melting and spinning the cellulose using NMMO (N-methyl morpholine-N-oxide) as a solvent. Because the solvent is recovered and reused, the manufacture of lyocell is more environmentally friendly than other textile operations.
Paper Making Paper is separated plant fibers that have been matted together to form a sheet. What we want is the cellulose from the cell wall and NOT the lignin, pectin, or other cell wall components.
Wood Products - Paper History of Papermaking: video courtesy of www.paperrep.com click the button If the above video does not work, see the video at http://www.youtube.com/watch?v=sDGxy5ft6w8
Wood Products - Paper How Paper is Made: video courtesy of www.paperrep.com click the button If the above video does not work for you, watch it at http://www.youtube.com/watch?v=ZXzRrDQA9Ek
Alternatives to Wood In the Production Of Paper
Bamboo While bamboo is used much like wood, it has no secondary xylem and no cambium. Growth is by terminal meristem only. This is because bamboo a monocot. It is the largest member of the grass family, Poaceae. Bamboo can be processed into rayon and used for fabric production and also has been used to make paper in China since ancient times.
Flax (Linum usitatissimum) Linen fibers from the phloem of the flax plant have been used to make paper for centuries. The fibers are separated from the rest of the tissue by a process of controlled rotting known as “retting.” Formerly, old linen rags were broken down to make high-quality “rag” paper.
Kenaf Kenaf is a woody herb, Hibiscus cannabinus from the family Malvaceae. In 1960, the USDA surveyed more than 500 plants and selected kenaf as the most promising source of “tree-free” newsprint. Supposedly the energy requirements for producing pulp from kenaf are about 20% less than those for wood pulp because of the lower lignin content. Commercial operations of kenaf are greatest in southern Texas and Louisiana.
Cotton Cotton is a soft fiber that grows in a form known as a boll around the seeds of the cotton plant Cotton paper or rag paper is made from 100% cotton fibers. Cotton is superior in both strength and durability to wood-based paper. Certain cotton fiber paper is known to last hundreds of years without appreciable fading, discoloration, or deterioration and as such, is often used for important documents such as archival copies and banknotes
Hemp There is a niche market for hemp paper. The cost of hemp pulp is approximately 6x that of wood pulp because areas where it is grown have outdated equipment for harvesting and hemp can only be harvested once a year. Industrial hemp is produced around the world with major production in Canada, France, and China. Strains of Cannabis approved for industrial hemp production produce only minute amounts of the psychoactive drug, THC. While more hemp is exported to the USA than any other country, the US Government does not distinguish between marijuana and the non-psychoactive Cannabis used for industrial and commercial purposes. hemp fibers
Jute Jute is a long, soft, shiny vegetable fiber that can be spun into coarse, strong threads. It is produced from plants in the genus Corchorus, family Tiliaceae. Jute has many, many uses and has been used to make pulp and paper. India is the number one jute producing country with more than 2.14 million tons annually.
Lab this Week Examine the wood and paper materials provided on the lab benches and read and learn about the structure of wood, the different uses and types of wood, and the paper making process. Make a sheet of your own paper using the pulp and screens provided for you. Travel to the Cushing Library for a lecture about botany herbals and see a bunch of really old books!