Last Updated on July 15, 2018 by Naeem Javid Muhammad Hassani
Short Notes of Forest Products (from Past Papers)
Softwoods are those which are derived from gymnosperms such as pines. These are evergreen, having needle-like leaves, and their seeds are in cones.
Hardwoods are those derived from angiosperms such as oak, poplar, and mulberry, with broad leaves, seeds enclosed and bearing flowers.
Wood portion responsible for the sap conduction is called sapwood.
Wood portion which is in the center which is darker, older and harder is heartwood
A series of cells to form an articulated (connected to a joint) tube-like structure of intermediate length, each segment is called vessel member.
When a secondary wall is laid down by protoplast, gaps are left to interchange the material b/w the cells. These gaps are known as Pits.
A cell in the trachea of conifers and other gymnosperm plants, with bands of lignin thickening the cell walls and adding structural support. Tracheid is a wood cell without end perforation as in a vessel, conducting and to some extent mechanical functions are performed by tracheid.
A storied or tired arrangement of wood rays or other wood elements like a vessel, parenchyma cells or fibers, produce on the tangential surface fine horizontal lines or band across the grain are called as ripple marks.
An Elongated cell with pointed ends and a thick or not infrequently a thin-walled included gelatinous fiber and libriform fiber. It is only formed in hardwood only.
Tissue consisting of short, relatively thin-walled cells with simple pits, convened with storage of food material and its distribution.
Ray is defined as a ribbon-like aggregate of parenchyma cells radiating from center to periphery. Ray initials and extends radially in the xylem and phloem.
A sac that forms in the water-conducting vessels of the older wood of a tree, often in response to drought or disease. Tylosis may cause blockage, and often filled with resins, gums, or pigments that may help to preserve, strengthen, or color the wood or provide a source of dyes.
Resin canals are sometimes confused with vessels. Resin canals are tubular intercellular spaces sheathed by secreting cells. Cavity and sheath cells both collectively called as Resin Canals.
Refers to the direction of fibers or cells relative to the long axis of the tree.
Refers to the relative size and amount of variation in a size of the cells
Refers to the pattern produced on a longitudinal surface of the wood as a result of the arrangement of wood elements and nature of the grain.
“Those abnormalities/ irregularities/ blemishes which tend to lower the economic value or decorative value of wood and also reduces the strength of wood, are known as wood defects”.
Those abnormalities which develop in the standing tree naturally, difficult to control but can be minimized up to some extent eg the development of knot (a natural phenomenon) is difficult to control but can be minimized by the Silvicultural operations such as pruning.
The abnormalities caused in a tree due to the biological agencies such as fungi, insects and can be controlled by the insecticides, pesticides, or fungicides and biological control is also done to reduce the biological defects in a wood.
These are the defects which are created during the seasoning of the wood. The defects created during the process are known as seasoning defects.
When sawn log makes width wise curve is called cupping.
When any converted log makes a lengthwise curve is called bowing.
When the four corners of a plank are in the same plane.
It is the separation of fiber that does not extend through the timber from one face to the other face.
It is the separation of fiber extending from face to face.
The portion of the branch wood embedded (fixed) in main trunk or bole of the tree is called a knot.
“It is an abnormal wood which is developed in leaning trunk or branches.”
Those reaction woods which are developed in leaning soft-woods trees are known as compression woods.
A type of reaction wood which is developed in the hard-wood leaning trees is called tension wood.
Breaking of wood at a force at which normal wood does not break is called brashness.
“Separation of fiber along the grain, this may be caused due to improper seasoning or in natural standing trees.”
It is also a natural defect in standing trees, occur in the cold climate areas. The abrupt variation in day and night temperature in the cold climatic areas results in the Frost Injuries.
It is a natural defect which normally develops in those trees which produce resin (in softwood trees) like Pinus roxbrughii.
A natural defect caused due to the excessive accumulation of minerals in the form of lines is called Mineral Streak.
Small patches of bark that are embedded in the wood apparently developed from some injury to the tree resulting in the death of small areas of cambium.
Stains of these sorts are caused by chemical changes in Lumina of cells.
Insects cause pith flecks (small marks or pieces), pinholes and grub holes in wood before it is utilized.
“The properties which are determined without any change in size, shape, and chemical composition of wood.”
“Property of wood elements and its contents which they have a tendency to reflect light.”
ODOR AND TASTE:
Many timbers have a characteristic odor, which is more effective during fresh conditions. But gradually disappears with the passage of time.
DENSITY OF WOOD:
Density may be defined as, “mass per unit volume.”
“The resistance offered by the wood to indentation (to make a dent)”
Fiber Saturation Point:
“Theoretical stage at which all moisture is removed from all cavity and is still retaining in the cell wall.” The moisture content of a wood at 25-30% this is also called as a green condition of wood or fiber saturation point.
Equilibrium Moisture Content:
Air dry condition or seasoned wood are other names of it. EMC is defined as, “Value of moisture content corresponding to the given combination of temperature and relative humidity of the atmosphere. Whenever moisture content is 12% called EMC.”
Whenever softwoods are dried from Fiber Saturation Point to oven dry condition. Shrinkage for common hardwood spp is from FSP (25 – 30%) to EMC (12% moisture content). Due to loss of moisture content size of wood changes.
Whenever moisture content of wood is increased from equilibrium moisture content (12%) to FSP (25 – 30%). Due to an increase of moisture content, the size of wood increases this phenomenon is regarded as swelling.
THERMAL AND ELECTRICAL CONDUCTIVITY:
The ability of the wood sample to conduct heat is called the Conductivity.
HEAT/ CALORIFIC VALUE OF WOOD:
It is the process in which the quantity of heat produced by complete combustion of unit mass wood substance.
Latent heat of vaporization:
“The minimum amount of heat required to evaporate the unit mass of water”.
The properties which are observed by applying an external force. Than establishment of data, from this data proper use is estimated. The mechanical properties of wood are also called as strength properties. There are some standards which are:
Weight / unit area or ‘force on unit area (kg / cm2)’.
Deformation / original length Or; = change in length / original length (length in longitudinal direction)
Modulus of elasticity is defined as, ‘the fiber stress at elastic limit.’ This can be understood by Hook’s law.
Modulus of rupture is defined as, fiber stress at maximums load which breaks the specimen.
Compression may be defined as a set of force acting on a similar piece of wood equal in magnitude and acting in the similar direction.
IMPACT BENDING/ TOUGHNESS/ DYNAMIC PROPERTY:
“Resistance by a wood sample to certain shocks.”
Tension may be defined as a set of forces acting on a wood sample equal in magnitude and acting opposite in direction.
Shear is defined as, “resistance offered by the wood sample to slipping or sliding of one position upon other.”
Cleavage is defined as, “resistance offered by the wood sample to splitting.” Standardized size for this test is 4.5cm × 2cm × 2cm is a cross section
NAIL OR SCREWING RESISTANCE:
It may be defined as, “resistance offered by the wood sample to withdraw (remove) a nail or screw from its surface.”
Those timbers which are most difficult to season and such timbers must be seasoned under highly controlled conditions. They are liable to cracks, splits, and wraps (cupping, bowing, twisting, crooks, etc) during seasoning.
Moderately Refractory Timbers:
These are comparatively easy to season. They are also liable to crack, splits, and wraps.
These are very easy to season and having staining, modulus, and decay
Air seasoning involves making of best use of prevailing winds and sun for seasoning while protecting wood from the rain.
This type of shed is closed from all the sides as well as from the top. Since there is no free circulation of air in this type of shed, the rate of evaporation is very slow. This type of shed is suitable for refractory timbers.
Open on North Sheds:
This type of shed is covered from the top as well as from three sides. The side which is towards the north is open. The rate of evaporation is comparatively more than in closed sheds. This is suitable for seasoning of moderately refractory timbers.
It is only covered from the top but all four sides are open. There is more circulation of air, so the rate of evaporation is high. This is suitable for non-refractory timbers.
A kiln is defined as a closed compartment in which conditions of temperature and humidity is always controlled.
CHEMICAL SEASONING OR SALT SEASONING:
When wood is seasoned with the help of chemical, it is termed as Chemical Seasoning.
Timbers in this class may be used with confidence for permanent structures in contact with the ground or in water eg transmission poles, railway sleepers, bridging, timbers, foundation timbers, hut holes and fencing. The life of the wood is over 25 years in service. Eg Dalbergia sissoo, Juniperus procera, etc.
Durable wood can be used for the exposed parts of permanent structures which are not in contact with the soil they are suitable for the frames, keels, and decking of boats, making vats for a window sill, etc. the service life of the wood is from 15-25 years. Eg Cedrus deodara, Eucalyptus camaldulensis, Juniperus procera, etc
Wood in this class should never be used in direct contact with the soil unless given preservative treatment, but for the short periods, they can withstand exposure to damp conditions. They are suitable for those parts of permanent structures that are given protection against the weather, such as rafters’ joints. They can also be used for vehicles and for some parts of boats, deck, and beams for example. Durable timbers offer their services 10-15 years. Eg Albizzia lebbek, A. procera, Cassia fistula, Eucalyptus camaldulensis, Eugenia jambolana, Quercus incana, etc
Non-durable woods should always receive treatment if there is any risk of their becoming damp in use. They can safely be used for internal joinery and furniture, though, if they carry a high protection of sapwood, they may require long-term protection against insect attack. Such wood spp have durability form 5-1- years. Eg Abies spp, Acacia nilotica, Cedrus toona, Dalbergia sissoo, Juglans regia, Mangifera indica, Morus alba, Picea spp, Pinus roxburghii, Populus spp, etc
Timbers described as perishable require rapid extraction, conversion, and seasoning, to avoid decay in the log and while they are being dried. They should not be used for constructional work even under cover unless they have received through preservative treatment. They are often used in turnery, and as veneers in plywood for indoor use, and for making matches and chip baskets. Perishable timbers have a service life of fewer than 5 years. Eg Bombax ceiba, Fraxinus spp (Ash), etc
WOOD PROTECTING CHEMICALS:
Preservatives are the chemical which enhances the durability of timber treated with different methods. The following characteristics of preservatives are the most important:
FIRE RETARDANTS AND THEIR APPLICATION:
The substances which are used for fireproofing are called fire retardants.
“This is the plant with different types of machines for sawing logs into planks, scants, etc.”
It is made by polymerization of glucose in the shape of a very long chain of cells. These contents should be in higher quantity for a suitable raw material.
The complex polymer in plant cell walls that gives the plant rigidity and strength, and is the major component of wood. It is a binding material for cells. Its ratio should be lower and there should be minimum lignin for suitable raw material.
If the number of joined molecules is less in the chain that is called hemicellulose and better than cellulose. Hemicellulose is unlike cellulose dissoluble in water. This should also be in less quantity.
These are actually mineral of soil taken up by plants through roots with soil moisture. They impart coloration to paper. They should not be more than 10% otherwise more chemicals will be required to whiten the paper, which is not economical.
This fraction termed extractive is composed of a variety of material that generally is not considered a part of the cell wall. These organic extraneous compounds may be included low molecular weight. They should also be in less quantity or amount.
A substance consisting of wood fiber isolated from wood by mechanical or chemical means and used for the manufacturing of paper called Pulp. The process of isolating wood fiber is called Pulping.
It is a Dutch word which means to fade the color. So bleaching means to fade the color and increase brightness.
When woods are broken down mechanically or chemically then reformed into a solid product with or without adhesive, these reconstructed woods are called composite woods. OR;
Composite Wood products:
Any wood product consisting of two or more than two types or raw materials is called a composite wood product.
A cross bounded assembly generally made up of veneers (or) of veneer in combination with lumber core/ pile, joined with adhesives are called plywood.
A sheet or board generally made up of fibers of wood or other lingo-cellulosic material is called fiberboard.
Resistance against a sudden shock is called impact resistant
It is very difficult to make solid wood as fire retardant but in plywood, it is much easier
A board/ sheet constituted of fragments of wood (discrete pieces) and lingo-cellulosic material, bounded with adhesives with the help of one or more agents like heat, pressure, humidity, are called Particle Boards. Eg chipboard, shoving board, flake board,
Hard gelatin obtained from hides, tendons, cartilage, bones, etc of animals.
The term used for better quality wood (or) A general term used for wood that has been specially treated in various ways to reduce the retard, wrapping or movement to increase its strength or other properties
A form of improved wood in which the wood is treated or is impregnated with synthetic resins
A form of improved wood in which the wood is compressed
A form of improved wood in which the wood is treated or impregnated with synthetic resin and compressed.
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