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Pulp

Orlando J. Rojas and Ronalds W. Gonzalez
North Carolina State University

Introduction

Pulp is the raw material used to make paper by mixing it with water forming a “pulp slurry”. This aqueous suspension consists of fibers, cellulose fines and, depending on the case, additives that are added to aid paper manufacture or to impart given functional (mechanical, optical or surface) properties to the paper or paperboard product. Pulp also generally refers to a dry or semi-dry lap or mass of cellulosic fibers obtained after processing wood (and non-wood plants). In some countries in the Americas the term “cellulose” is also loosely used to refer to the same material, even though “cellulose” in fact, refers to a linear polymer (specifically, a polysaccharide) which is the main constituent of the cell wall in most plants and the most abundant of all naturally occurring substances. Cellulose constitutes approximately a third of all vegetable matter (the others being hemicelluloses, lignin and extractives) and thus it exists in far greater quantity than any other polysaccharides. For the purpose of this entry we will use the term “pulp” as “wood or other lignocellulosic materials that have been broken down physically and/or chemically such that (more or less) discrete fibers are liberated and can be dispersed in water and reformed into a web” (Biermann 1996).

The fundamental material in pulp is the fiber. There are several ways to classify fibers, depending on their origin, length, or source:

    Origin

Wood fibers: Fiber that come from wood. They are the most commonly used source of fiber for paper and paper products manufacture.

Fibers from agricultural residues: These fibers usually come from residual lignocellulosic materials generated in agricultural processing, e.g., bagasse from sugar cane.

Short fibers: These are mostly found in hardwood, in species such as eucalyptus, poplar, etc. where the typical fiber lengths are around 2-3 mm.

Long fibers: These fibers are commonly found in softwoods such as pine, with fiber length of ca. 4-7 mm, depending on the species.

Virgin fibers: Fibers that have not been used/processed before; i.e., fibers that come directly from the raw material (wood and non-wood plants) and that underwent some type of pulping process.

Recycled fibers: Fibers that have already been used and recycled to produce paper again. Recycling implies drying cycles and a loss of some intrinsic strength properties of the fiber.

Pulping

In order to separate the fibers from wood or from the lignocellulosic material, several methods are commonly applied.  Wood can be grinded to produce groundwood (GW). Wood can also be crushed with refiners using steam at high pressures and temperatures to produce thermomechanical pulp (TMP). In addition to the refiners, chemicals can be used to facilitate cellulose fiber separation. Pulp produced this way is known as chemi-thermo-mechanical pulp (CTMP).

Chemical processes are commonly used in order to produce cellulosic pulp. A digester is used to combine wood chips (or non-wood lignocellulosics) with chemicals and steam to dissolve lignin, the material that holds the fibers together. Chemical pulps include kraft pulp (or sulphate pulp), sulphite pulps and others. By far the most common process to produce pulp is the Kraft process. The dissolved lignin plus any other dissolved substance that is generated during lignocellulosic digestion forms a by-product stream known as black liquor which is usually concentrated and burned as fuel. Finally, a slurry of fibers can be obtained by dispersing recycled paper and paperboard in water. In this case all types of fibers (long and short), coming from different processes (and bleached or unbleached) end up in the mixture that eventually (as such or mixed with virgin fibers) is used to make paper again.

Bleached and Unbleached Pulp

The pulp produced by chemical or mechanical process has a natural brown color; therefore, it could be bleached in order to produce brighter (bleached) pulp that is suitable for the manufacture of white paper products. The chemicals used to bleach pulp have been a source of environmental concern, and therefore the pulp industry has adapted a number of alternatives to eliminate the toxic chemicals used in the past. However, bleaching is optional and there are various pulp grades that don’t require added brightness (don’t require bleaching steps). The type of pulp and the brightness requirement depends on the specification of the paper product grade to be produced.  In the manufacture of paper a mixture of different pulps, fillers and a number of other additives (depending on the case) can be used in the paper machine, where the slurry is converted into a paper wet web which is then pressed and dried.

Pulp and Paper Grades

In mechanical pulps, since no (or little) chemical agents are used and rather physical/mechanical forces are used in the separation of fibers, the removal of lignin is minimal. Therefore, mechanical pulps are also called “high yield” pulps.  The ensuing characteristics and the lignin content make these pulps suitable for products that don’t require high strength, such as newsprint and paperboards.  GW, TMP and CTMP are all considered as mechanical pulps. The mechanical pulps tend to turn yellow in time, because of the binding material, lignin, in the pulp.

The removal of lignin in chemical pulps means the process has a lower yield compared to the mechanical and semi-mechanical counterparts. Chemical pulps are used for paper and paper products that demand high strength, this includes “kraft paper”, liner, etc. Semi-chemical pulps are produced in processes with intermediate yields and therefore the removal of lignin occurs in a lower extent. Typical products that are manufactured with semi-chemical pulps include medium paper used in box solutions. Finally, recycled pulp is most often used to make paperboard, newsprint or sanitary paper.

Production, Imports, and Exports

In 2005 the world produced ca. 188 million tons of pulp of which 67 % was chemical wood pulp, 19% mechanical wood pulp, 4.6 % semi-chemical wood pulp and 9.2 % other types of fiber pulp. In the same year the Americas produced ca. 49% of the total world pulp production. Table 1 shows the largest producers of pulp in the Americas (The tables are attached as separate document; access them by clicking on the attachment note at the bottom of the page).

< Tables 2 and 3 show the most important importers and exporters of pulp in the America. The U.S. is the largest importer of pulp followed by Mexico and Brazil. In the context of exports four countries are the major players, namely, Canada, USA, Brazil and Chile. Even though Uruguay is not included in Table 3, it is expected that with the pulp mills under construction in the next three years it could make the third largest exporter.

Raw Material Supply

The world pulp and paper industries are being affected by the emergent Chinese market; China and other fast emerging countries such as India and Russia will experience an increased consumption of recycled and virgin fibers. As an illustration of this fact we note China imported 4.9 million tons of recycled fiber in 2000; which increased to ca. 17.4 millions ton in 2005, an annual average growth equivalent to 23% (data from FAO 2007 (b)). Likewise, the imports of recycled fiber in India grew 100% in the same 2000-2005 period. It is expected that the increase in demand will make recycled fiber a more expensive commodity; this justifies the need to develop additional forest plantations as well as to implement strategies to increase the rate of recycling of paper products. Table 4 shows the total planted area per country in South America; a significant fact is that not all the plantations were established for pulpwood purposes. Nevertheless, this table provides insight regarding the (likely) availability of raw material in these countries.

The pulp and paper industry in Brazil benefits from a fiber supply from fast growing plantations. The most important species are Eucalyptus sp (75% planted area) and Pinus sp (24%).  Forestry companies in Brazil are world leaders in eucalyptus silviculture and tree improvement. In 1980 the average productivity of eucalyptus plantations was 24 m³/ha/year; 25 years later the average productivity increased to ca. 39 m³/ha/year, a dramatic improvement of 63% (BRACELPA 2007). Overall, forest research has resulted in a very impressive growth yield; nowadays a typical plantation of Eucalyptus dunii is harvested after seven years with an annual average growth of 43 m³/ha/year (Cubbage et al. 2007).

Chile with its 2.6 million hectares planted is positioned second after Brazil, in terms of plantation area in the South American region. The composition of the planted forests is 67.8 % Pinus radiata, 23.5 % Eucalyptus sp. and 8.7% other forest species (Papelnet 2007). Uruguay with 766 thousands hectares is the largest exporter of pulpwood in South America (1.5 million m³ per year). Interestingly, Venezuela has the largest single ownership, single plantation of Pinus caribaea var. hondurensis (400,000 ha). Its small pulp industry uses fast growing plantations of short fiber from Eucalyptus sp, and long fiber from Pinus caribaea var. hondurensis. The effective pulpwood plantation established by the industry is around 35,000 hectares.

In terms of recycled fiber, Brazil imported 13 thousand tons of recycled paper in 2005 (FAO (b), 2007). In 2006 the paper recovery rate in the same country was 46%. In 2005 Chile imported a total of 110 thousand ton of recycled paper (equivalent to US $ 17 million) (FAO 2007 (b)) while Venezuela imported 116 thousand ton of recycled paper in the same year (2005) (FAO 2007 (b)) (worth mentioning is the fact that this volume is almost nine-fold larger than that of Brazil). Table 4 shows the import volumes and percent of worldwide share of recovered paper by some countries in the region (it also includes the figures for China).

Outlook and Final Comments

South America is bound to be a key source of pulpwood and market pulp to satisfy the growing world demand.  Fertile forestland, fast growing species and relative political stability are main reasons for increased investments to improve or create production facilities.

In Brazil the pulp and paper industry launched an aggressive investment program including US$ 14.4 billions for the period 2003-2012, with the objective of increasing production and exports. In 2005 the annual reforested area was around 1.7 millions hectares (4.1 MM acres) and it is expected that it will reach a total of 2.6 millions hectares in 2012 (BRACELPA 2007).

In Uruguay the Stora Enso Company is installing a pulp mill with a capacity of 1 million ton per year with an invested capital of ca. US$ 1 billion. Likewise, the Finish company Botnia and the Spanish firm Ence have started or announced, respectively, two mills to produce annually 1 million ton of pulp each, although opposition from protesters and the government of Argentina may derail the latter. The combined investment amounts to ca. US$1.6 billion. These and other initiatives are expected to induce an increase in the forest planted area from 766 thousand hectares to 1 million hectares from 2005 to 2010. The target of these operations is mainly to export market pulp to their paper mills in the European and Chinese branches. Mill expansion and new production facilities are also underway in Chile, Argentina and Colombia.
 
In Venezuela expropriation of some forestland and nationalization policies have limited foreign investment; overall, the impact in the supply chain in the Venezuelan pulp and paper industry could witness important changes in the future (Gonzalez et al. 2007). A state-owned forest company has announced the creation of new pulp and paper mills to supply the local demand of mechanical pulp for newsprint (100 thousand ton/year) and kraft pulp for white paper (20 thousand ton/year) (Proforca 2007).

South America is playing a key role in market pulp supply, and with the new investments taking place in the region and the possibility to grow quick and low cost fiber raw material the region will help satisfy the growing demand of emergent economies. This region has clearly developed as an important player in the paper and packaging industry. Low-cost fiber, linked to developments in silviculture, seed improvement and plant genetics, especially in Brazil, has helped to position the region as a significant supplier of market pulp.

References

 
Associacao Brasileira de Celulose e Papel, 2007. Desempenho do Setor em 2006 e Projecao para 2007.  http://www.bracelpa.org.br, Accesed on 06/05/2007.

 Biermann, C. (1996). Handbook of Pulping and Papermaking, 2^nd Ed., Academic Press Ltd., London.

 Centeno, J. (1986). El mercado de pulpa y Papel en Venezuela 1970-2000. Instituto Forestal Latinoamericano, Merida, Venezuela 1986.

Cubbage, F. et al. 2007. Timber investment returns for selected plantations and native forests in South America and the Southern United States. New Forests (2007) 33:327-255

 FAO. (2005). Papier et carton. www.fao.org, Accessed on 06/05/2007.

FAO. (2007.) FAO STAT. www.fao.org, Accessed on 06/05/2007.

Gonzalez, et al (2007). The Performance of the Pulp and Paper Market in South America. In preparation.

Gonzalez, R., Plonczak, M., Stock J. (2004). Plantaciones Forestales e Industrias Asociadas en Venezuela. Aspectos Socioeconómicos. Revista Forestal Venezolana 48(2) 2004, 111-117

Hubbe, M. A., & Rojas, O. J. (2005) The paradox of Papermaking. Chemical Engineering Education,39(2): 146-155
 
Hunter, D., Papermaking –The History and Technique of an Ancient Craft, Dover, New York, 1947.

 Rojas, O.J., Hubbe, M.A. (2004). The Dispersion Science of Papermaking. Journal of Dispersion Science and Technology, 25 (6): 713-732.

 Smook, G. (1992).  Handbook for Pulp and Paper Technologists, 2^nd Ed., Angus Wilde Publ., Vancouver.

Orlando J. Rojas and Ronalds W. Gonzalez are Associate Professor and Graduate Student, respectively, Department of Wood and Paper Science, North Carolina State University, Raleigh, NC 27695

Posted 18 August 2007

Updated 22 August 2007