works as a redox catalyst by oxidizing cellulose and reducing lignin. This protects the cellulose from degradation and makes the lignin more water-soluble. An emulsion breaker can be added in the soap separation to speed up and improve the separation of soap from the used cooking liquors by flocculation. Defoamers remove foam and speed up the production process. Drainage of washing equipment is improved and gives cleaner pulp. Dispersing agents, detackifiers and complexing agents keep the system cleaner and reduce the need for maintenance stops. Fixation agents fix finely dispersed potential deposits to the fibers and thereby transport them out of the process. Comparison with other pulping processes Pulp produced by the kraft process is stronger than that made by other pulping processes and maintains a high effective sulfur ratio (sulfidity), an important determiner of the strength of the paper. Acidic sulfite processes degrade cellulose more than the kraft process, which leads to weaker fibers. Kraft pulping removes most of the lignin present originally in the wood whereas mechanical pulping processes leave most of the lignin in the fibers. The hydrophobic nature of lignin interferes with the formation of the hydrogen bonds between cellulose (and hemicellulose) in the fibers needed for the strength of paper (strength refers to tensile strength and resistance to tearing). Kraft pulp is darker than other wood pulps, but it can be bleached to make very white pulp. Fully bleached kraft pulp is used to make high-quality paper where strength, whiteness, and resistance to yellowing are important. The kraft process can use a wider range of fiber sources than most other pulping processes. All types of wood, including very resinous types like southern pine, and non-wood species like bamboo and kenaf can be used in the kraft process. Byproducts and emissions The main byproducts of kraft pulping are crude sulfate turpentine and tall oil soap. The availability of these is strongly dependent on wood species, growth conditions, storage time of logs and chips, and the mill's process. Pines are the most extractive rich woods. The raw turpentine is volatile and is distilled off the digester, while the raw soap is separated from the spent black liquor by decantation of the soap layer formed on top of the liquor storage tanks. From pines the average yield of turpentine is 5–10 kg/t pulp and of crude tall oil is 30–50 kg/t pulp. Various byproducts containing hydrogen sulfide, methyl