In Brazil, the two main sources of the wood used to produce pulp are cultivated pine and eucalyptus trees, which account for over 98% of the volume produced. Pulp can also be obtained from other types of non-wood plants such as bamboo, the babassu palm, sisal (agave) and agricultural waste (sugarcane bagasse). Brazil is the fourth-largest producer of all types of cellulose, and is the worldwide leader in eucalyptus pulp.
After the trees are planted, grow, and are harvested, the bark is removed from the logs, which are then chopped into small pieces. These wood chips are sorted to remove wood shavings and sawdust, and next are subjected to mechanical and chemical processes to produce pulp.
Na primeira etapa desse processo, os cavacos são submetidos a um cozimento, em um equipamento chamado digestor, com a utilização de água, produtos químicos, pressão e temperaturas da ordem de 150ºC. O objetivo é separar as fibras de celulose da lignina – substância que une essas fibras, aumentando a rigidez da parede celular vegetal, e que constitui, juntamente com a celulose, a maior parte da madeira das árvores e arbustos.
In the first step of the pulping process, the wood chips are cooked in a piece of equipment called a digester, using water, chemicals, pressure, and temperatures of approximately 150°C (302°F). This cooking separates the cellulose fibers from lignin, which is the substance that binds these fibers together to make cell walls rigid and together with cellulose accounts for most of the wood in trees and shrubs.
After separation, the cellulosic fibers form a brown paste that is subjected to a series of processes and chemical reactions in the next stage of the process in order to screen, wash, and bleach the pulp to the desired degree of whiteness.
At the end of these steps, pulp may follow one of two distinct paths:
- It can be pumped into a paper machine, in the case of integrated mills (which have their own forest base and produce pulp and paper).
- It can undergo a drying process and be stored in bales for subsequent sale to paper mills as market pulp.
Lignin is not discarded after being separated from the fibers. Instead, it goes through another process that generates energy while at the same time recovering the chemicals used in pulping.
Types and Applications
Two types of pulp with different physical and chemical characteristics are used in papermaking.
Softwood pulp is made of long fibers between 2 and 5 millimeters in length, obtained from species like pine which are planted in Brazil. It is used to produce stronger papers like those for packaging and the inner layers of cardboard, as well as newsprint.
Hardwood pulp is made of short fibers 0.5 to 2 millimeters in length, mainly derived from eucalyptus wood. These fibers are ideal for producing paper for printing and writing and for tissue products (toilet paper, paper towels, and napkins). Eucalyptus fibers are also used in specialty papers as well as other products. The fibers are less resistant, very soft, and highly absorbent.
Unlike other industries in the Brazilian economy, the planted tree industry generates most of the energy it requires. In 2016, 67.5 million gigajoules of green electricity were produced, accounting for 69% of the industry's consumption. Furthermore, more modern pulp mills not only produce all of their own electricity, they generate a surplus that is sold back to the grid: around 11.9 million gigajoules, the equivalent of a medium-sized hydroelectric power plant.
The industry’s two main concerns are increasing energy efficiency in its processes and adopting renewable resources to generate electricity. In this sense, the plants in this sector almost exclusively use the byproducts from their processes to generate heat and electricity, principally forest biomass and black liquor (black liquor is a byproduct of the pulp production process).