Paper is wood fiber
Wood is made largely of cellulose fibers held together by a natural glue-like substance called lignin. Paper is made by separating those fibers, suspending them in water, spreading them thinly and letting them bond together as the water drains and dries. Everything from newsprint to cardboard to tissue follows this general idea, with differences in the fiber, the treatment and the finishing.
What pulpwood is
Pulpwood is wood grown or gathered for fiber and not for lumber. It tends to be smaller in diameter, crookeder or lower in quality than sawlogs, because fiber does not need straight, knot-free boards. Common sources include:
- Thinnings, small trees removed from a stand early to leave more room for the rest. This is part of the logic of stand thinning.
- Dedicated plantations, where fast-growing species are grown for fiber and harvested on short cycles. Such tree plantations supply a large share of pulpwood in many regions.
- Residues from sawmills, including chips from the outer parts of logs, which are sold to pulp mills instead of being discarded.
- Recovered paper, which is not wood in the forest sense but is a major source of fiber.
Both conifers and broadleaved trees are used. Softwood fibers are generally longer, which gives strength, and hardwood fibers are shorter, which gives a smoother surface. Mills often blend them to get the properties they want, a distinction touched on in the article on hardwood and softwood.
From chips to pulp
Logs are debarked and chipped into small pieces of consistent size. Chips are then turned into pulp in one of two broad ways.
Mechanical pulping grinds or shreds the wood, separating fibers physically. It keeps most of the wood in the pulp, so the yield is high, but the lignin remains. The lignin makes paper darken and become brittle with age, which is why newspapers yellow. This kind of pulp is used for products where lasting quality matters less.
Chemical pulping cooks chips with chemicals under heat and pressure to dissolve most lignin and free the fibers. The most widespread version is the kraft process. The pulp is stronger and can be bleached to be bright, but less of the wood ends up as pulp. The dissolved material and spent chemicals are generally concentrated and burned in the mill, which recovers the chemicals and produces energy that helps run the plant. This is a notable example of a facility using the by-products of its own process as a fuel source.
Between the two lie hybrid methods that combine heat, mild chemicals and mechanical action.
From pulp to paper
The pulp is diluted into a watery mix, cleaned and sometimes refined to improve how fibers bond. It is spread on a moving screen where water drains away, then pressed and dried on heated rollers. Additives can improve smoothness, brightness or water resistance, and coatings add gloss for printing.
Paper mills use large amounts of water and energy. Many have reduced their use over time, and wastewater treatment is a regulated part of the operation, but the footprint depends on the mill and its location.
Packaging, tissue and printing paper
The mix of paper products has been shifting. Demand for printing and writing paper has declined in many countries as reading and office work move to screens, though patterns vary by region. Packaging has been a growing area, especially boxes and cartons for shipping goods. Tissue, towels and hygiene products are another large category. Other uses include filters, labels and specialty papers.
Compared with plastic, paper packaging is based on a renewable material, but a fair comparison depends on weight, durability, the energy used and what happens afterward, and the results vary by case.
Recycling and fresh fiber
Used paper is one of the most commonly recycled materials, and recovered fiber is a substantial input to the industry. Each time paper is recycled, fibers get shorter and weaker, and so they can be reused a limited number of times, often described as several cycles. This means recycling cannot supply the whole industry alone, and some fresh fiber from forests is needed to keep the system going. Some products, such as food-contact papers and certain high-strength boards, rely more heavily on fresh fiber.
Where the forest enters the picture
The key question for forests is how the pulpwood was grown and where. Fiber from well-managed forests and plantations that were established on previously used land is quite different from fiber that comes from clearing natural forest. The practices of sustainable forestry and the documentation provided by forest certification help buyers distinguish between them. Because paper products pass through long and complicated supply chains, tracing the source is not always easy.
Plantations raise their own issues. They can produce a lot of fiber from a small area, which may reduce pressure on natural forest, but monocultures usually support less wildlife than diverse stands and can use more water in dry places. Replacing natural forest with plantations is widely regarded as harmful, while planting on degraded or former farmland is viewed more favorably. Wood residues that cannot be pulped may also be used for energy, a topic covered under forest bioenergy.
Reading a paper label
Labels on paper can tell you the share of recycled content and sometimes the forest management standard behind fresh fiber. Using less paper, using it twice and recycling it afterward all reduce the demand placed on forests, and choosing sources with credible documentation supports better practice at the forest end.