Made from wood pulp or plant fiber, papers are the world’s favorite material. For more than nineteen centuries until the advent of the World Wide Web, almost all written information was transmitted in printed form.
The era of the “paperless world” has been predicted for decades, and it still is not anywhere near. In fact, we use more paper than ever before — more than 400 million metric tons of paper are produced worldwide each year.
Today, different types of papers are not just used for printing but also for packaging, writing, cleaning, filtering, decorating, laminations, tissues, and various industrial and construction processes.
The first papermaking method was probably developed in China in 105 CE, though the oldest archaeological fragments of paper are known to be derived from the 2nd century BCE.
Although papers are now produced by large automated machines to fulfill the demands of developing society, handmade papers are still appreciated for their distinctive uniqueness as well as the skilled craft involved in creating every sheet. Let’s dig deeper and find out how paper is made.
Where Does Paper Come From?
The paper you use on a daily basis is usually produced from trees. It can be made from cotton, hemp, flax, and other plant fibers. However, large amounts of paper are produced from logs or recycled paper that was itself produced from logs.
More specifically, almost 50% of the total fiber used to produce papers comes from wood that has been deliberately harvested. The rest of the material comes from wood fiber from sawmills, recycled cloth, recycled newspaper, and some vegetable matter.
Papermaking industries prefer coniferous trees (softwood), such as fir and spruce, because they have long cellulose fibers in the pulp, which makes the paper stronger. Deciduous trees (hardwood), such as elm and poplar, are also used to fulfill the growing demand for paper.
In regions without significant forests, bamboo, sugarcane, and straw could be used for pulp. Linen and cotton rags are used to make fine-grade papers such as security certificates, resume sheets, and letterheads.
Did you know that American paper currency is made from cotton?
Other materials used for papermaking include fillers (chalk and clay), sizings ( rosin and starch), bleaches, and dyes.
The industrial process of making paper begins with a forest. A bulldozer cuts down a large number of trees (including eucalyptus, beech, and birch) quickly. The fibers obtained from these trees are called cellulose. Generally, conifer trees have longer fibers, which is required for producing strong papers.
Once enough amount of trees are cut down, they are taken to a factory and fed to a large machine that strips the bark and makes wood chips. These wood chips are then sent to another automated machine known as a digester. It breaks down the wood into a soft mixture of various substances, including cellulose, fiber crops, and rags.
Cellulose is separated (chemically or mechanically) from other substances, and then it is mixed with water and chemical additives to produce a lignocellulosic fibrous material called the pulp. Finally, the pulp is converted into paper using a large roller machine.
The overall manufacturing process involves four key processes:
1. Producing Pulp
There are two processes to turn logs into wood pulp: mechanical and chemical process. In the former, logs are tumbled in tankers to remove the bark. And then they are passed through grinders, which press the wood between large revolving slabs, breaking the wood down into the pulp.
Fibers in wood pulp
The chemical process usually involves boiling wood chips in a solution of sodium sulfide and sodium hydroxide at high pressure. This is done in large digesters. When chips get dissolved into pulp, it is filtered to remove other wood parts. Bleach or colorings are often added in this step.
The pulp is pounded and squeezed appropriately. This process is carried out by machine beaters. At this stage, several filler substances and chemicals are added, such as clays, chalks, and titanium oxide, to influence the qualities of the final product.
Sizings are also included to control how the paper will react with different inks. Starch, for example, makes the paper ‘somewhat’ water-resistant so that the ink can sit on top of the paper instead of sinking in.
A worker inspecting wet, bleached wood pulp at a mill near Pensacola (1947)
3. Turning Pulp Into Paper
The pulp is pumped or fed into large, automated machines. Almost all modern papermaking machines are based on the principles of the Fourdrinier Machine, which was invented in London in the early 19th century.
The machine filters out the unwanted materials from the stock and produces a continuously moving wet mat of fiber. It is then dried within the machine to create a strong paper web.
The dried paper is wrapped on large metal rollers, where it is further processed according to its intended use. It may be coated with chemicals or pigments before running it through the smooth rollers (calenders) for the final time. Eventually, it is cut and packed for distribution.
How Fourdrinier Machine Works?
Different sections of the Fourdrinier machine
These machines are large and complex, containing four main sections:
Wet Section: The soft, wet mass of pulp starts off in a large vat known as the headbox. It typically contains a mixture of recycled paper fibers and wood pulp.
Wet Press Section: This is where a significant amount of water from the pulp is removed through mesh and suction boxes. The forming paper (shown in blue color) runs over a rotating felt belt (dark black) that absorbs the moisture. A large roller could also be used to put a pattern, texture, or watermark on the paper.
Dryer Section: The paper passes through a series of internally steam-heated rollers that evaporate the remaining moisture.
Calender Section: Placed vertically in a stack, calender rolls make the paper surface glossy and extra smooth.
Paper leaving the machine is rolled onto a reel
A large machine may have 40-70 drying rollers. When operated at full potential, it can produce paper at an astounding rate of 40 mph (or 65 km/h).
The paper leaving the machine is rolled onto a jumbo reel, which can weigh several tonnes and be a few meters long. It is inspected by automated measuring devices that identify imperfections. Good quality paper is unwound, cut into smaller rolls as orders by customers, and labeled for shipment.
Papermaking By Hand
Despite advances in technologies and material sciences, the method of manual papermaking hasn’t changed very much. It is still similar to how the Chinese did it centuries ago.
The overall process can be generalized into five steps:
- Separate the crucial fiber (such as cellulose) from the rest of the wood parts.
- Beat down the fiber into pulp.
- Use additives to adjust the color and mechanical/chemical properties of the paper.
- Screen the resulting mixture
- Press and dry the thick mixture to obtain the actual paper
The fourth step involves using a very basic frame to form sheets of paper. This frame is made of two parts: a metal mesh called a mold, and a wooden frame called a deckle. The mold sits inside the deckle (just like a picture frame).
The mold is pushed into the thick solution and gently agitated in a way that a uniform coating forms on top, with some of the pulp draining through.
Dipping frame in the pulp
The fifth step involves removing the deckle from the mold and placing the soggy mat on a felt sheet. The wet mat is then squeezed under extreme pressure to squash out the remaining water.
Once all the water is removed, the paper sheet is taken out and dried using different methods such as simple air drying or vacuum drying. The sheet is often rolled to harden and flatten the surface. Finally, it is cut to the desired shaped and packed.
Since it is made by hand, the edges of the papers look quite irregular and wavy. These papers usually fold and tear more evenly along the laid lines that are caused by the wires in the mold. One can also put watermarks by weaving a design into the mold’s wire.
Since the use of paper has risen by 400 percent in the past four decades, deforestation has become a major issue in both developed and developing regions. Pulp and paper mills contribute to:
Air pollution: In 2015, over 313,000 tonnes of toxic waste was released into the air in the United States. Of that emission, pulp and paper accounted for 20 percent. This industry produces sulfur oxides, nitrogen oxides, carbon dioxide, and fine particulate matter (PM2.5) that can penetrate the respiratory system and have a severe impact on health.
Water pollution: Paper industries are one of the major sources of dissolved matter, such as lignin in wastewater discharges. Other complex compounds and agents like chlorates and alcohols are also involved. These substances pollute lakes and rivers that they are released into. They also discolor the water leading to reduced aesthetics.
A paper manufacturing factory in New Brunswick, Canada
Paper waste: Nearly 26 percent (67 million tons) of solid waste dumped in dumping sites is discarded paper and paperboard. Like other wastes, these could be potentially carcinogenic when incinerated or mixed with groundwater.
Sulfur-based compounds: Dimethyl sulfide, dimethyl disulfide, hydrogen sulfide, and other sulfur-based compounds are used for making wood pulp, especially in the kraft process and the sulfite process. Sulfur dioxide released from these processes are highly toxic and could cause immune and hormonal problems.
Greenhouse gas emission: The paper and print industry accounts for approximately 0.8% of global carbon dioxide emissions. The carbon footprint is further added by the disposal of paper in landfill sites and subsequent methane production.
The rise in such issues and global climate change have forced several national governments to increase regulations. In the past few years, many environmental impacts of the pulp and paper industry have been addressed, and there is a movement towards sustainable practices.
Efforts to recycle paper have been effective in mitigating the need for destroying woodlands, and recycled paper has now become a crucial ingredient in various types of paper manufacturing techniques.
Source: Resource Information Systems Inc.
China, the United States, and Japan are the largest paper producing countries. They account for more than 50% of the world’s total paper production, while the leading paper exporting and importing countries are the United States and Germany.
Increasing middle-class population and urbanization, along with the surge in literacy rates in developing countries, will create significant demand for paper products such as writing pad, newsprint, and packaging.
Furthermore, changing customer preferences towards green, sustainable packaging solutions will reduce the demand for plastic packaging and hence fuel the pulp and paper industry.
All in all, the paper industry is morphing and developing rapidly. It is currently going through the most substantial transformation it has seen in several decades.