Wood Pulp Article Index for
Wood 		Website Links For
Wood 		 

Information About

Wood Pulp
  CATEGORIES ABOUT WOOD PULP
   
wood
   
papermaking
   
pulp and paper industry
   
APPAREL
BABY
BEAUTY
BOOKS
CAR TOYS
CELL PHONES
DVD'S
ELECTRONICS
GOURMET FOOD
GROCERIES
HEALTH & PERSONAL
HOME & GARDEN
JEWELRY
MUSIC
MUSIC INSTRUMENTS
OFFICE PRODUCTS
SOFTWARE
SPORTING GOODS
TOOLS & HARDWARE
TOYS
VIDEO GAMES
SHOPPING HOME
MORE SHOPPING...



Wood pulp is the most common material used to make Paper . The timber resources used to make Wood pulp are referred to as Pulpwood . Wood pulp generally comes from Softwood trees such as Spruce , Pine , Fir , Larch and Hemlock , but also some Hardwood s such as Eucalyptus and Birch .


MANUFACTURE OF WOOD PULP


See Also: Pulp mill



Wood pulp is made in several stages:

# First the Bark is removed from the wood. This can be done with or without water (wet stripping). The bark is generally recovered to use as fuel in the pulp and paper making process.
# The Cellulose fibres that keep the wood together are then separated. This can be done in a number of ways:
  • The wood can be crushed with grinders (huge grindstones) and then soaked in water to produce groundwood (GW). Mechanical pulps are used for products that require less strength, such as Newsprint and Paperboard s.

  • The wood can be crushed with Refiners using steam at high pressures and temperatures to produce thermomechanical pulp (TMP). TMP differs in quality from groundwood.

  • In addition to the refiners, chemicals can be used to break up the cellulose fibres. Pulp produced this way is known as chemithermomechanical pulp (CTMP). GW, TMP and CTMP are all considered as mechanical pulps. The mechanical pulps tend to turn yellow in time, because of the binding material, Lignin , in the pulp.

  • Chemical pulp is produced by combining wood chips and chemicals in huge vats known as digesters. The effect of the heat and the chemicals dissolves the lignin, that binds the cellulose fibers together, without breaking the wood fibres. The fluid that contains lignin and other dissolved material is then dried and used as fuel. Chemical pulp is used for materials that need to be stronger or combined with mechanical pulps to give a product different characteristics. Chemical pulps include ''' Kraft Pulp ''' (or '''sulphate pulp''').

  • Pulp can also be made out of waste paper and paperboard. Recycled pulp is most often used to make paperboard, newsprint or sanitary paper.

  • Research is under way to develop biological pulping, similar to chemical pulping but using certain species of Fungi that are able to break down the unwanted lignin, but not the cellulose fibres. This could have major Environment al benefits in reducing the pollution associated with chemical pulping.

    • # The pulp produced up to this point in the process can be bleached to produce a white paper product. The chemicals used to bleach pulp have been a source of environmental concern, and recently the pulp industry has been using alternatives to Chlorine , such as Chlorine Dioxide , Oxygen , Ozone and Hydrogen Peroxide .

# The pulp mixture is now sent to the paper machine, where it is shaped and dried.


HISTORY

Using wood to make paper is a fairly recent innovation. In the 1800s, Fiber Crop s such as Linen fibres were the primary material source, but a shortage led to contemporaries as Dime Novel s or Penny Dreadfuls .

The major environmental impacts of wooding come from its impact on forest sources and from its waste products.

The number of trees consumed depends on the type of paper, whether made by using the groundwood process or the kraft process. It has been estimated that based on a mixture of softwoods and hardwoods 40 feet tall and 6-8 inches in diameter, it would take a rough average of 24 trees to produce a ton of printing and writing paper, using the kraft chemical (freesheet) pulping process. On the assumption that the groundwood process is about twice as efficient in using trees, it takes about 12 trees to make a ton of groundwood and newsprint. {Link without Title}
However, a Kraft Pulp mill is self-sufficient in bioenergy.

When the paper is bleached with elemental in the environment continues to be waste-burning Incinerator s and also backyard burn-barrels.) Elemental Chlorine Free technology utilizes Chlorine Dioxide (ClO2) in place of chlorine (Cl2). Total chlorine free bleaching utilizes no chlorine in the bleaching process.

The wastewater effluent can also be a major source of pollution, containing lignins from the trees, high Biological Oxygen Demand (BOD) and dissolved organic carbon (DOC), along with Alcohol s, Chlorate s, heavy metals, and Chelating agents. Reducing the environmental impact of this effluent is accomplished by closing the loop and recycling the effluent where possible, as well as employing less damaging agents in the pulping process. The most important way to mitigate the impacts is the biological effluent treatment.

In the Kraft Process , the largest volume byproduct from the Pulping process is weak black liquor. This liquor contains the pulping chemicals and the lignin from the trees. The lignin is high in heat content, so this weak black liquor (about 15% solids) is concentrated into heavy black liquor (usually 68% to 75% solids) by use of multiple effect evaporation. Multiple effect evaporation is a process in which one pound of steam is used to boil 4.5 to 5.5 pounds of water. The heavy black liquor is burned in a recovery boiler and the chemicals fall to the bottom of the boiler in a semi-liquid state called smelt. The smelt then flows out of the boiler and is dissolved in water or weak wash to form green liquor. The green liquor is then clarified. Quick Lime (CaO) is added to the clairified green liquor to convert a majority of the Sodium Carbonate (Na2CO3) to Sodium Hydroxide (NaOH). The green liquor with the quick lime is then clarified and the resulting liquid is white liquor. The white liquor is used as pulping chemicals and the process begins again. The spent lime ( CaCO3 ) is then calcined at approximately 1800 degrees Fahrenheit (1000 degrees Celsius ) to yield quick lime to be used again in the clarified green liquor.

Paper made from wood pulp can typically be recycled four to seven times before the fibres become too short. To solve this problem recycled paper is usually mixed with virgin wood pulp to ensure a high quality paper.


ALTERNATIVES

Today, some people and groups are advocating using Field Crop Fiber or agricultural residues instead of wood fiber as being more Sustainable . However, wood is also a renewable resource.


SEE ALSO




EXTERNAL LINK