How is Paper Made?

The process is a little different for different papers. Watch the Paper Making Process Video.

1. The basic raw material for making paper is trees in the form of logs.

 

 



2. Tree bark is not used for paper production. The second step is to de-bark the logs.

 


3. Pulping - In this process a thick liquid mixture (slurry) of wood pieces is prepared. There are two broad types of pulping.

Mechanical Pulping - the debarked wood is ground into very small chips and mixed with water. Here, the yield can be as high has 95% and so the paper produced is relatively cheap. The disadvantage is the fibers constituting the output paper are not very strongly woven up, resulting in low quality product.

Chemical Pulping - here the debarked wood is chemically treated to remove "Lignin" - lignin is a resin-like adhesive holding the fibers together. Various processes (sulphate process, sulphite process to name few) are used for this removal process. The water mixture is also heated for better lignin removal. Here the yield is as low as 50% which leads to higher cost paper.

 


4. Bleaching
What we get from the third step is still brownish in color. To get the strong white uniform appearance it has to be bleached. You might have seen that paper with "whiter" sheets are costlier. This is because to make it whiter you have bleach it more. The bleaching is usually done using Chlorine, hydrogen peroxide or other compounds.

(Some environmental papers are marked Chlorine free - means no chlorine is used for the bleaching process)

Here is progressive bleaching... The more you bleach, the whiter it becomes.

 

 

5. Pressing, Squeezing, Drying, & Slicing - The final steps of the paper making process. After bleaching, the main aim is  to remove the excess of water & get the desired thickness. For colored sheets, additional dyes are added. For glossy finishes, a variety of other coatings and chemicals are added.

The paper which ultimately comes out from the process is made up of cellulose fibers. These fibers were bound together by lignin and other resins from inside the core of tree. The fibers get woven up in patterns different in different directions (forming grains). This difference makes it weaker in either longitudinal direction or perpendicular to it.

Small experiment: Try tearing up a newspaper (fast) in either direction. You will notice in one direction the tear is more or less straight while in other it goes at an angle. It is because of these grains.

Recycling is a very good alternative to the above process. Very much similar except that instead of using wood for pulping, recycled papers are used as the pulp.

Why to recycle -
two reasons
                  1.)  a single ton of paper recycled can save 20 trees.
                  2.)  a single ton of paper requires 100 000 liters of water. Recycling uses much less.

Paper currency - these are made from a much different process and has different constituents. To get better tear resistance and a higher life; Cotton, hemp and other fibers are added to the pulp.