For hundreds of years, paper has played a critical role in the evolution of human life. They are created by turning wood into pulp. The process is eco-friendly. Paper and pulp industry manufacturing process starts with the pulping procedure.
It all starts with the pulping procedure. Paper pulp manufacturers separate fibers and clean them, which leads to refining, dilution, fiber formation, and other steps. Paper and pulp, thus, get created from plant materials such as cellulosic fibers. Sometimes, a few synthetic materials are incorporated into the final product to impart some unique qualities.
Let’s discuss the paper and pulp industry manufacturing process in detail!
Raw material preparation
Wood reaches to a pulp manufacturing factory in many forms. The source of raw materials and its pulping process changes. Sometimes, the raw material contains short round wood logs attached to the bark. Other times, factories receive small chips in large quantities.
Depending on the condition of the raw material, professionals prepare it for pulping. Round-wood logs get debarked with the use of huge tumbling steel drums. Then, they get turned into small-sized chips, which get cleaned and stored for a while.
This stage involves a number of pulping technologies. High-temperature steam is used for fiber separation. This is called the digestion of chips. A digester or huge pressure cooker is used with appropriate chemicals to complete the process of chemical pulping. The digestion process allows wood chips to dissolve partially into various extractives including lignin.
After this, the pulp is transferred to a specially designed pressure vessel, where all the volatile materials and steam get separated. Then, the cooked pulp reaches the cycle of chemical recovery once again.
There is a mechanical procedure of separating fibers as well. The debarked logs go through a rotating wheel made of stone that grinds the wood. The pulp goes through thermos-mechanical refining, screening, cleaning, and water removal.
After fiber separation, the pulp contains several discoloration materials. Hence, bleaching is necessary to acquire the white, clean appeal. This process involves oxidation and chlorination of cellulose. The chemicals used in bleaching include chlorine gas, chlorine dioxide, hydrogen peroxide, sodium hypochlorite, and oxygen as well.
Sodium hydroxide is a pretty strong alkali chemical compound that helps in the dissolution of lignin discoloration from the surface of fibers. The type of bleaching agents used and their sequence in the process depend on various factors like the cost of chemicals, type of pulp and discoloration condition.
Mechanical pulp requires a different type of bleaching than chemical pulp. The bleaching process used for mechanical pulp ensures lignin removal minimization that would decrease fiber yields.
Chemicals are selectively used in the bleaching process of mechanical pulps. That way, the chemicals selectively remove coloring impurities without impacting the presence of cellulosic materials and lignin. Such chemicals include zinc or sodium hydrosulfite, sodium bisulfite, sodium or hydrogen peroxide, sodium or calcium hypochlorite, as well as Sulfur Dioxide-Borol method.
The unbleached or bleached pulp goes through more refining procedures to attain roughness on the surface of cellulosic fibers and cut them further. This process encourages bonding between fibers and improves the formation of collective structures. The process takes place in a papermaking machine.
A thin mix of pulp is created by adding water, which brings fiber concentration to one or lesser percentage. The slurry gets diluted, then, the cleaning process begins in the presence of cyclone cleaners. With that, the cleaned slurry goes to the centrifugal screens for screening. This prepares the material for the wet-end of paper-forming machinery. The diluted, cleaned and screened stock goes through the head-box of the machine, which evenly and uniformly distributes the slurry as per the desired paper sheet size.
And, that is how paper and pulp is prepared. The procedure might differ here and there depending on the type of product required. For instance, the construction process of the paper packaging board might not need bleaching.
So, now you know how the paper and pulp making industry works.