More than 48% of the raw material fiber used for paper production (chemical pulp or mechanical pulp) in the United States in 2002 was recovered or reclaimed, with recovered paper contributing 37.7% and wood residues 10.6%. The total has been more or less constant, with the percentage of recovered paper increasing and that of wood residues declining recently due to their increased use in oriented strand board and composite panels. Primary fibers are a renewable, domestic resource, much of which is currently supplied by tree plantations. Short-rotation forestry can be used to further increase the productivity of these plantations. Therefore, use of primary fibers need not mean cutting old-growth natural forests, with the implied loss of habitat, wilderness, and recreation land. However, monoculture may have environmental implications of its own, as does recycling; these should be taken into account during decision making about paper production and recycling policy.
For purposes of this article, virgin paper can be classified into two main types that have different chemical pulp compositions and physical properties. In reality, the industry produces a large variety of products, but these two classes cover most of them. The two types are distinguished by the processes used to make the pulp: chemical pulp or mechanical pulp. Kraft pulp (the most common type of chemical pulp) and thermo mechanical pulp (TMP), plus recycled fiber (chemical or mechanical), are the largest inputs to U.S. papermaking (85% of total pulp input), and their use is growing. This article focuses on these types. The energy and materials inputs to production of the different types of pulp differ, although both start with wood as the basic raw material. Papers made from different types of pulp are often kept separate in recycling because of the differences in material properties, but the secondary processing sequences are similar.
Chemical pulping separates wood chips and wood products into their components of cellulose, hemicellulose, and lignin and retains the cellulose fibers while rejecting most of the rest; therefore, the yields are less than 50%. However, much of the material removed is used for process fuel, so energy purchases are low. The two main types of chemical pulp are kraft (sulfate) and sulfite, indicating the types of chemicals used. Most printing and writing papers, packaging, and paperboard are made from kraft pulp because of its superior strength and economics. Sulfite pulp has a relatively small and declining market share and will not be discussed further. The total direct process energy requirement reported by the industry for pulping and making of printing and writing papers averages approximately 26 x 10e6 Btu/ton, but the energy required varies greatly with the product and with the degree of energy recovery included, ranging from a high of approximately 30–35 x 10e6 Btu/ton for kraft board to a low of 10–12 x 10e6 Btu/ton for recycled tissue. Process energy use is generally higher for products requiring extensive bleaching. Using paper that has undergone less bleaching could reduce fuel purchases more than recycling. There is a public misconception that virgin paper is white and recycled paper is brown. However, it is the degree of bleaching that determines brightness, so virgin paper can be brown and recycled paper can be white. Reducing bleaching also reduces environmental impacts. The primary purchased energy requirement for kraft paper, over half of which is bleached, is typically approximately 15 _ 10 6 Btu/ton.
It is hoped that the American Forest and Paper Association will publish actual industry data that will allow more accurate analysis. In addition, different mills use different mixes of purchased and self-generated electricity, affecting both the fuel mix and the primary fuel usage how to generate electricity. Also, the fuel mix for electricity generation varies from utility to utility, affecting the actual primary energy usage from electricity purchases (or the fuel displaced if electricity is sold back to the grid).
