Eucalyptus belongs to the hardwood, is a kind of wood pulp, however, due to its low lignin content and it is easy to be diffluent, structural tests have shown that it is easy to cook and bleach. The required material per ton of pulp produced by eucalyptus is small. Therefore, the eucalyptus pulp for papermaking will have higher economic benefits. Eucalyptus pulp is an excellent short-fiber hardwood pulp, and due to its relatively uniform fiber, simple cell structure of the fiber, low degree of lignification, its smoothness, bulk, opacity and softness, water absorption are all superior to softwood pulp. Eucalyptus pulp can be widely used in high-grade writing paper, copy paper, white paperboard, security paper, cigarette paper, toilet paper, napkin and other paper manufacture.
Eucalyptus robusta Smith, also known as the Eucalyptus tree, is the collective name for the myrtaceae and the genus Amaranthus. There are many values such as medicinal and economic. The vast majority of eucalyptus origins grow on the Australian continent, with a small portion growing in neighboring New Guinea, Indonesia, and the Philippine Islands. Introduced to the rest of the world in the 19th century, as of 2012, there are 96 countries or regions cultivated. The main distribution centers are in Oceania, with a certain number of distributions in China, including Fujian, Guangxi, Guangdong, Yunnan and Sichuan.
It is worth noting that there are great differences in paper properties between different species. There are many kinds of eucalyptus trees, so the eucalyptus paper making needs to pay attention to the problem of introduction and cultivation.
There are many existing pulping process for eucalyptus wood. Eucalyptus can be used to produce various chemical pulps, chemical mechanical pulps and mechanical pulps. However, it is mainly used to produce KP pulp, the output accounts for more than 80° of the total output of eucalyptus wood pulp.
The KP pulping of the eucalyptus wood mainly uses the NaOH and Na2S. The OH and HS of cooking liquor attack the susceptibility structure in lignin. Alkalization fracture, sulfurization fracture and other reactions occur, so that most of the lignin macromolecules are disintegrated into small molecules to dissolve, thereby raw materials are dispersed into pulp. Currently, about 75% pulp is made by Kraft pulping in the world. The Kraft pulp paper has high strength, but the disadvantages of low yield and serious pollution.
In addition to, there are many other pulp processes for eucalyptus wood, such as RDH cooking, biological pulp, monosulfite pulping, CMP、 CTMP、 BCTMP and APMP pulping.
The continuous tubular digester is typical pulp cooking equipment in the eucalyptus pulp production. The earliest continuous tubular digester was built in 1957 as a cold-discharge digester, and in 1997 a compact cooking system – COMPACT COOKINGTM system was designed.
There are different types of washing equipment, such as drum washers, pressure diffusion washers, atmospheric pressure diffusion washers, net presses, dewatering spirals and washing presses. Since the washing press has the characteristics of clean water consumption and low wastewater discharge, it is widely used in pulp production, especially in the bleaching section.
Nowadays, the use of oxygen deferens in the kraft pulp production line has become the standard. The low-cost, highly selective two-stage oxygen delignification process (DUALOXTM) has been used for hardwood pulp and softwood pulp.
ECF bleaching has an advantage in bleaching technology and is known as the “most effective bleaching technology”. Over the years, the bleaching stages of eucalyptus wood pulp ECF bleaching has decreased. At first, ECF bleaching mostly have five stages, but now many new bleaching sections have only three stages. Because the pulp cooking process is improved, the pulp is easily bleached, and the oxygen delignification can be carried out efficiently, and H202 or a small amount of ozone can be used as the bleaching agent. The constant reduction in chemical consumption will have a negative impact on the pulp quality, such as the yellowing of the pulp. For many wood pulp producers, the stability of whiteness and whitening is the most important characteristic of pulp. Researchers have recognized that the factors affecting the Kappa number are not just lignin content, which has led to a new development in bleaching technology, namely the hot CI02 segment.