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More than 1,900 years ago, Cai Lun invented the papermaking process using raw materials such as tree bark, rags, and fishing nets. The method involved several steps, including cutting, soaking, fermenting, pounding, scooping, and drying, to produce handmade paper.
By the 17th century, Europeans had developed pulpers and paper machines, along with mechanical and chemical pulping techniques. As a result, traditional hand papermaking was gradually replaced by mechanized production.
Over time, papermaking technology has continuously evolved. Throughout thousands of years, pulp and paper manufacturing processes have undergone significant advancements. While early fundamental principles have been preserved, they have been refined and adapted to modern standards.
During this evolution, new technologies, processes, equipment, paper grades, and chemical additives have emerged, while certain outdated methods and materials have either disappeared or are nearing obsolescence.
The transformation of the industry-marked by the replacement of old practices with innovative ones-not only reflects historical shifts in papermaking but also highlights the critical role of innovation in industrial progress.
1. Blueprint (Diazo Paper)
One of the major developments in the engineering design field during the 20th century was the transition from blueprints to white-line drawings. Blueprints, also known as diazo paper, are specialized sheets used for reproducing technical drawings and documents. The surface of diazo paper is coated with a photosensitive layer composed of diazonium salts and coupling agents. When developed with an alkaline solution, it produces a characteristic blue background with purple lines.
In the pre-digital era, engineers manually created original drawings, traced base copies, and then exposed them to produce blueprints. These rolls of blueprints were essential at construction sites, although their development process released ammonia fumes. Despite these drawbacks, blueprinting enabled efficient reproduction and long-term preservation of technical documentation.
With the advent of computer-aided design (CAD), digital workflows became dominant. Advances in computing power, coupled with improvements in printers and copiers-featuring high speed, large format capability, high quality, multifunctionality, and low cost-led to widespread adoption of digital printing. This shift fundamentally transformed engineering documentation, making the use of white-line drawings standard practice.
2. Wood Grinder
Decades ago, visiting a newsprint mill would typically include seeing large, noisy wood grinders operating in the pulping车间. In this process, logs were pressed hydraulically or mechanically against rotating grinding stones, where they were reduced to pulp before being collected through underground channels. The resulting product, known as groundwood pulp, was produced entirely through mechanical means.
Today, many younger professionals may be unfamiliar with wood grinders, reflecting how significantly pulping methods have changed. Several types of wood grinders existed, including chain-type, bag-type, bin-type, and ring-type models, with chain-type and bag-type being most common in China.
However, mechanical grinding was an inefficient process characterized by high energy consumption. For many years, groundwood pulp remained the primary material for newsprint production, with stone grinding being the dominant method.
This began to change in the latter half of the 20th century with the introduction of two key innovations. First was the development of chip-based mechanical pulping technologies, including refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), and bleached CTMP (BCTMP), starting in the 1960s. Compared to traditional grinding, these methods broadened the range of usable wood resources, improved automation, enhanced pulp quality, increased efficiency, and reduced environmental impact-leading to rapid adoption.
Second, newsprint mills increasingly turned to recycled fiber. In November 1992, Guangzhou Paper Mill commissioned an 80-ton-per-day deinked waste paper pulp (DIP) line imported from Andritz of Austria for newsprint production. In 1998, Shanghai Hansong Potential Paper Industry Co., Ltd. began producing newsprint using a blend of 90% DIP and 10% BCTMP, later transitioning to 100% DIP. Since then, all newly installed newsprint machines in China have primarily used recycled paper as raw material.
3. Cylinder Machine
In 1809, British inventor John Dickinson developed the cylinder mold paper machine. This machine utilized one or more cylindrical molds and was capable of producing papers ranging from light household grades (tens of grams per square meter) to heavy multi-ply board (hundreds of grams per square meter).
Although introduced a decade after the Fourdrinier machine and adopted later in China, the cylinder machine gained popularity due to its simple structure, ease of operation, lower investment costs, and straightforward maintenance. Most early provincial paper mills in China relied on cylinder machines.
During the period of rapid growth in small-scale papermaking, cylinder machines were ubiquitous. By the end of 1985, China's light industry sector operated over 5,000 paper machines, of which approximately 600 were Fourdrinier types and the remainder cylinder machines.
The traditional cylinder machine uses a rotating cylindrical wire for sheet formation. However, as demand grew for higher speeds, wider widths, and better quality, this forming method proved inadequate. It was gradually superseded by more advanced systems: the jacketed wire machine (for cultural papers), crescent former (for tissue), and multi-layer former (for cardboard).
Today, modern paper mills undertaking expansion projects rely on digital design tools. Printers, copiers, and computers dominate the workspace, and documentation is now predominantly printed on white paper.
4. Formation Aid
For centuries, Chinese papermakers have used a substance known as "paper medicine," derived from plant mucilage. When added to pulp, it acts as a dispersant, regulating water drainage on the forming fabric, improving fiber dispersion, and enhancing paper uniformity-a practice that continues to some extent today.
Following China's reform and opening-up policy, rising living standards led to increased demand for toilet paper. At that time, only Fourdrinier and cylinder machines were available. Due to the low basis weight and thinness of tissue paper, achieving uniform formation was challenging. To address this, the industry revisited the concept of "paper medicine," replacing natural plant extracts with more effective synthetic polymers.
Initially, nonionic polyethylene oxide (PEO) was used, followed by anionic polyacrylamide (APAM). PEO offered superior performance but was costly; APAM was less effective but more economical.
Both are high-molecular-weight polymers with high solution viscosity. When added to pulp, they increase inter-fiber repulsion, slow down dewatering, and reduce fiber flocculation, thereby improving sheet uniformity. These chemicals are now referred to as dispersants or formation aids.
However, this application declined after 1997, when China began importing advanced tissue machines-specifically vacuum suction roll type (Bestformer) and crescent formers. Their unique forming mechanisms inherently ensured excellent sheet uniformity, reducing reliance on chemical additives. As Fourdrinier and cylinder machines phased out of tissue production, the market for dispersants diminished accordingly.
5. Beater
Historically, papermakers used wooden mallets or stone mortars to beat fibrous raw materials-a process aptly named "beating." This step modifies fiber morphology and enhances bonding strength between fibers, which is essential for producing high-quality paper. Indeed, the phrase "paper comes from the beater" underscores its importance.
In archaeological studies, whether fibers have undergone beating is a key criterion in determining if unearthed fibrous materials qualify as true paper.
In 1680, the Dutch invented the Hollander beater, which became widely adopted. In this device, pulp circulates in a tub, where rotating knives interact with stationary bottom knives to achieve refining.
However, the Hollander beater occupies considerable space, consumes substantial electricity, operates intermittently, and imposes high labor intensity. These limitations made it inherently transitional. By the late 20th century, it was largely replaced by continuous refiners.
Modern practice refers to the process as "refining" rather than "beating," and the equipment is now called a "refiner." Correspondingly, the English terminology shifted from "beating" to "refining," and "beater" to "refiner."
6. Yellow Straw Board
Yellow straw board, commonly known as "horse dung paper," was formerly termed yellow board paper. In earlier times, when living standards and papermaking technology were limited, this low-grade board served as a primary packaging material, used for wrapping goods or as backing plates.
It is produced from rice and wheat straw, processed via fermentation or alkali cooking with lime or caustic soda. Due to low-quality raw materials and rudimentary processing, the resulting board exhibits poor appearance and low mechanical strength.
By the end of the 20th century, domestic production of white-faced corrugated board and folding boxboard expanded significantly. Market preferences shifted toward higher-quality alternatives, leading to a sharp decline in the use of yellow straw board. After 1996, it was no longer included in official statistics published by the paper industry authorities. Today, only a few small paper mills continue to produce it, primarily for low-end packaging applications.
7. Bronze Wire
Since the invention of the paper machine, copper mesh has been used as the forming and dewatering component. Typically, phosphor bronze wire is used for the warp and brass wire for the weft.
After the founding of the People's Republic of China, trial production of phosphor bronze mesh began in 1949 under the Northeast Enterprise Administration Bureau. This led to the establishment of Shenyang Copper Mesh Factory-the first dedicated papermaking mesh manufacturer in China.
Copper, tin, and zinc-key components of copper mesh-are valuable non-ferrous metals, so copper mesh was classified as a "precious item" within paper mills and managed accordingly.
In the late 1950s, following international trends, China began exploring plastic alternatives to copper. In the 1960s, foreign-made plastic nets were imported for testing.
In 1977, the Ministry of Light Industry tasked Tianjin Copper Wire and Copper Mesh Factory with developing polyester forming fabric. In December 1982, the Tianjin Paper Research Institute hosted an appraisal meeting for this innovation, which was successfully approved.
Subsequently, the factory produced trial batches of polyester mesh for pilot use in various paper mills.
In January 1986, a national conference on polyester mesh promotion was held in Tianjin, attended by 139 representatives from 25 provinces and municipalities. A consensus was reached on replacing copper mesh with polyester mesh, initiating nationwide adoption.
By the end of 1986, seven domestic mesh factories had produced 1.6 million square meters of forming fabric, of which 1.03 million were copper mesh.
By 2009, China had 14 large-scale mesh manufacturers (excluding wholly foreign-owned enterprises), producing a total of 1.8 million square meters of forming fabric, with only 139,000 square meters still made of copper.
8. Rosin Size Glue
Rosin was first used as a sizing agent in papermaking in 1807 and remained the dominant sizing chemical for over a century. Its development progressed from regular rosin size to strengthened and dispersed forms, and from anionic to cationic variants. Despite improvements, rosin sizing always required aluminum sulfate, making it suitable only for acidic papermaking environments.
In the mid-20th century, the industry shifted toward neutral and alkaline papermaking, particularly for cultural papers using calcium carbonate as filler. Although modified rosin sizes extended usability to pH 6–7 (neutral conditions), they could not function effectively at pH 8–9 (alkaline conditions).
This limitation spurred the development of synthetic sizing agents such as alkyl ketene dimer (AKD) and alkenyl succinic anhydride (ASA). In China, Shanghai Jiangnan Paper Mill pioneered AKD-based neutral sizing in 1989 for coated base paper. In 1992, Jinan Chemical Research Institute established a production facility in Longkou, Shandong, through Longquan Joint Venture Fine Chemical Factory, producing 100 tons of AKD powder and 1,000 tons of emulsion annually-marking the beginning of domestic AKD manufacturing.
In the late 1990s, Cytec (USA) successfully introduced ASA sizing at Ningbo Zhonghua Paper Industry Company for coated white board production.
Currently, AKD and ASA are widely used in the production of cultural paper, packaging materials, board, and specialty papers.
Nevertheless, rosin remains a renewable resource and a historically effective sizing agent. The main constraint lies in its dependence on aluminum sulfate. If future research enables rosin-based sizing in alkaline systems, it could experience a resurgence.
9. Spherical Digester
Not long ago, steaming balls were common pulping vessels in Chinese paper mills, which often produced their own chemical pulp. The steaming ball is a spherical, rotating vessel that operates intermittently, with limited capacity.
Available in volumes of 14, 25, and 40 cubic meters, a 25 m³ unit produces about 10 tons of dry pulp per day, while a 40 m³ unit yields 16 tons-resulting in annual outputs of only a few thousand tons.
Additionally, the steaming process requires repeated venting of steam, which is difficult to recover or treat, leading to significant energy loss and environmental pollution.
As pulp mills scaled up, increasing output through larger or multiple steaming balls became impractical. Consequently, steaming balls lost relevance.
Modern pulp mills, with annual capacities exceeding one million tons, rely exclusively on continuous digesters or large-scale batch digesters.
10. Sulfite Pulping
Industrial chemical pulping primarily employs two methods: the alkali process and the sulfite process. The sulfite method, invented in the U.S. in 1866 and industrialized in 1874, uses sulfite solutions to cook plant fibers into pulp. Variants include acidic, neutral, basic, and bisulfite processes, with cations such as calcium, magnesium, sodium, or ammonium.
The acidic sulfite process operates at very low pH and is suitable only for wood, not grass-based materials.
In the 1960s and 1970s, due to shortages of caustic soda and low alkali recovery rates in kraft pulping, interest in neutral ammonium sulfite pulping rose. In 1967, the Ministry of Light Industry organized trials on its application, with waste liquor used as fertilizer.
In 1968, with support from the Ministry's Paper Research Institute and other research units, Tai'an Paper Mill in Shandong successfully implemented ammonium sulfite pulping using straw, applying the spent liquor directly to farmland.
Recognized as a national demonstration project in 1976, this method spread to small paper mills across provinces including Shandong, Sichuan, Hebei, Shanxi, Henan, Yunnan, Shaanxi, and Xinjiang.
However, sulfite pulping suffers from high equipment corrosion, long cooking cycles, and difficult effluent treatment. Once kraft pulping achieved breakthroughs in alkali recovery and bleaching, the sulfite process declined.
Since the end of the 20th century, sulfite pulping lines in China have been progressively shut down. All new and expanded pulp mills-whether for wood or non-wood fibers-now adopt alkaline pulping processes.
