paper industry

The Paper Making Process


All of us use paper every day. Yet, few realize all of the steps necessary to change plant material to this common, every day product. The fact that mankind ever stumbled upon this process is shear genius as the paper making process follows three steps: preparation of the fibers, sheet formation, and drying.


Preparation of the Fibers

During the first step of the paper making process, the material used to make the paper is converted to pulp, which is a concentrated mixture of fibers that are suspended in liquid. Generally, the fibers are those found naturally in softwood trees, hardwood trees, or other plants. The fibers can also come from recycled paper, such as from newsprint, old corrugated boxes, and mixed paper.

When plants are used to make paper, it is usually necessary to use a special chemical process to break down the lignin found inside the cell walls of the plant. Generally, this is done with the Kraft process. If the fibers used to make the paper are recycled, it is not necessary to undergo this process because the lignin has already been removed. If the lignin is not removed from the pulp, the resulting paper will turn yellow when it is exposed to light and air.

There are two ways to break down the pulp used to make paper: mechanically and chemically. When it is broken down mechanically, the resulting pulp is known as "groundwood pulp". This process does not require chemicals, but the lignin is not removed. This results in a relatively high yield of pulp, but the paper does turn yellow as it ages. Therefore, this type of paper is generally used for newspapers and other non-permanent types of paper.

Chemically broken down pulp is called "chemical pulp." The primary reason to break the pulp down in this manner is to remove the lignin by breaking it down and making it soluble. Removing the lignin also helps break down the wood chips to prepare them for the next step in the paper making process.

It is not necessary to pulp recycled fibers in either of these two ways because they have already been treated before. Therefore, a gentler process is utilized.

After the extraction of the fibers, they are dyed or bleached if necessary and any additional ingredients are added to change the appearance of the paper. Products such as Kaolin, for example, are sometimes added to make the paper look glossy for use in items such as magazines.

Sheet Formation

The next step is sheet formation. At this stage in the process, the pulp mixture is diluted some more with water. This is then strained through a moving screen made of fine mesh in order to create a fibrous web. At this time, a watermark may be impressed into the paper if desired. Then, the moving web of pulp is pressed and allowed to dry. Pressure may be applied to help squeeze out the water.

The resulting paper sheet can be removed from the mesh screen mould while it is still wet or it may be removed after it is completely dry in order to undergo additional processing. With most paper, it undergoes the Fourdrinier process in order to form a web of fibers or a reel in a thin sheet. Once try, the sheet can be cut to size.

Drying

The final stage of the paper making process is drying, which is accomplished with time and pressing of the paper. The exact method for drying depends on the overall process used to make the paper.

When pressing is used, the excess water is removed by force. Once forced out, an absorbent material is used to collect the water. Felt, which is not the same as the typical felt used in crafts and other projects, is usually used on paper machines to accomplish this task. When paper is made by hand, a blotter sheet is used to absorb excess water.

Air and heat are also used to remove the water. In the early years, this was accomplished by hanging the paper sheets out like laundry. Today, heated drying mechanisms are usually used, with the most common being the steam-heated can dryer. These dryers are capable of reaching over 200 degree Fahrenheit and can dry paper to less than 6% moisture.



 

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