The objective of the chemical pulping process is to solubilize and eliminate the lignin portion of the wood, which leaves industrial fiber composed of almost entirely pure carbohydrate material.
There are four primary processes used in chemical pulping: Kraft, Sulphite, Neutral Sulphite Semi-Chemical (NSSC), and Soda. Both Sulphate (Kraft/Alkaline) and Soda Pulping Processes are compared below: Kraft Pulping Process: In the kraft pulping process, a mixture of wood chips, cooking chemicals, and steam are placed in a digester. After the chemicals break down the lignin, the pulp is washed and screened to eliminate contaminants, resulting in a high-strength, high-quality pulp. It also produces more than 90% of the world's wood pulp. Furthermore, the Kraft process may be used with a variety of woods, including softwood and hardwood.
Soda Pulping Process: In the soda pulping process, wood chips are cooked at high temperatures and pressures in a sodium hydroxide (NaOH) solution, which breaks down the lignin. The pulp is screened and washed after being removed from the digester, and any leftover chemicals are eliminated. It's commonly used with hardwood species, and it's energy-efficient and produces a high yield. In comparison to kraft pulp, soda pulp is more prone to yellowing, has a lower strength, and contains more impurities.
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