Paper manufacturing has also evolved in the years with the advent of better technology. There used to be a time when raw materials like linen (from rags) were used. They were then washed and macerated into pulp, paper moulds were made, and then sent for pressing, sizing and finishing.

Increase in demand of paper and wood pulp, paper industry has started harvesting trees for commercial purposes and replacing the same after they are cut. Paper mills use all parts of the tree at various stages of production for energy and for pulping unlike other industries hence nothing is wasted. The various steps taken to manufacture paper are:

1. Pulping:

The main raw material in manufacturing paper is cellulose fiber which is produced from wood as it consists of 40- 50% cellulose and rest is lignin and hydrocarbons. Pulping is the process in which the wood fibers are separated from each other either chemically or mechanically leading to surfacing of cellulose. The hydrogen bonding is what gives paper its strength. The quality of paper depends upon the cellulose content in the pulp and the length of fibers.

i) Chemical Pulping:

This process is also known as the Kraft process. It breaks the fibers and produces lignin and other hydrocarbons along with cellulose. Lignin has property of holding the fibers together but since chemical pulping alters its chemical structure, it gets washed away with water and pulp is formed. Though the process results in only about 50% yield, it results in unbleached paper which can be used as it is as well.

ii) Mechanical Pulping:

There are two ways of making pulp in the mechanical process. One is where wood logs are fed into grinders where the fibers are separated called Ground Wood Pulping. The other is where chipped wood is put between rotating steel discs and hot water or steam are added to assist the separation process called Thermo Mechanical Pulping. This process yields has over 90% yield but does not remove lignin from the pulp. Lignin has a property of turning brown in sunlight hence, with time paper made from this pulp turns yellow and is bulky in nature.

Chemical pulp yields stronger paper but costs more than mechanical pulp. Also, chemical pulping helps in saving energy as the lignin can be used to produce heat and electricity needed for the process whereas in mechanical pulping, the lignin cannot be separated.

2. Bleaching:

Depending on the lignin content in the pulp and nature of end use of paper, appropriate bleaching process is initiated. It may be treated with hydrogen peroxide, chlorine or Elementary Chlorine Free (ECF) or Totally Chlorine Free (TCF) methods may also be used in order to yield bright white pulp.

3. Beating:

The pulp is then beaten in the refiners in order to break down the stiff cellulose fibers. They are then flattened before they are ready to bind in a sheet of paper.

4. Making the Sheet:

After bleaching the pulp, water is added to the paper machine where the cellulose fibers will be retained on the wires to make a paper web and water is drained out. Thus, the new sheet is transferred for pressing to drain out remaining water.

5. Pressing and Drying:

Pressing may be used to remove excess water by force. Drying is also done by using air or by using metal cylinder dryers heated with steam.

6. Cutting and sizing:

Sizing is done to alter the physical properties of the paper by adding a solution to improve its strength, make it less absorbent and will thereby effect its reaction to various inks. This new paper can be used directly and can be cut into sheets.

7. Finishing:

It is during this process that additional characteristics are added to the paper like glossy look etc. as per requirements. After coating and then drying, the paper sheet is smoothened through calendaring and the sheet is collected on the roll and can be removed from the paper machine. Some types of paper require further smoothening by using a super calendar where they may be embossed by designs etc.