6 best pulp quality parameters

Table of Contents

The six best pulp quality parameters include fiber characteristics (length 1-5 mm for strength and smoothness), brightness (80-90% for premium paper), purity (fewer than five defects per 10,000 m²), freeness (350-450 mL for tissue paper), consistency (0.5-0.6% density for uniformity), and viscosity (15-20 centipoises for durability).

Fiber Characteristics

When determining the quality of pulp, fiber characteristics are one of the more transparent measures. They consist mainly of fiber length, width and strength, which directly affect the paper product’s strength, texture, and printability. Long fibers, as found in softwood in most cases, impart strength which is essential for products for which durability is the most important such as construction paper or packaging. The softwood fibers used for kraft papers are on average 3 to 5 mm long, and as they are longer, they thus help to achieve stronger bonds between fibers. On the other hand, hardwood fibers, which are typically about 1 to 2 mm long, create a more even surface of paper which is typical for fine stationary.

The width of fibers somewhat reflects their strength, as wider fibers are usually older, but also rougher. Wide fibers are often used in heavy weight papers or grocery bags, as strength is the most valued characteristic in those cases. Younger fibers are thin and less strong but typically make for a smoother paper product used in facial tissues or paper towels. By mixing these types of fibers in different ratios, the paper product can be created to have properties more suitable for different uses. If for example, 70% long fibers are mixed with 30% short fibers, the resulting office paper will be less likely to tear and still smooth enough for the purpose of high-quality printing.

If the paper is created with fibers of appropriate characteristics, the whole manufacturing process also stands to benefit. Papers developed to have optimal fiber characteristics require less treatment with chemicals and use less energy in general. Considering the number of paper produced worldwide – nearly 400 million tonnes – a reduction of 5 to 10 percent can save a great deal of production costs for the producers.


Brightness and Color

Pulp’s brightness and color are the most important characteristics for the type of application processes. For high-quality or even decorative papers, the brightness of the fiber is necessary due to its positive or negative connotations. The characteristic indicating how much light is reflected can range from 80 to 90 percent of all light in papers for magazines and important documents. Such a feature becomes critical not only from an appeal standpoint but also from a usage side: only brighter papers can allow the colors used in the printing to be conveyed in the correct way.

In a field such as coloring using natural pulp, such color needs to be consistent, especially in cards for holidays or business purposes. To account for it, the producer must control the bleaching and selection of chemicals that will remove the natural and artificial contaminants sensed by the pulp. In industrial application, controlling color is vital in any product from magazines to trees because in applications like grocery packaging, a variation in color may indicate the paper was exposed to water. One dyed piece of the paper, or even the cardboard, will discolor; the two prints will display two different colors. If chemicals’ eyelids change too much in the bleaching process, the pulp will be whiter care of those chemicals.

The concentration of chemicals can change the product by only 2 to 3 percent, but the customer will notice the incontinence. A simple example is printing paper for office printers that are almost always printed on brighter paper. Because of contrasts in brightness, this paper is more comfortable for the eyes, making readability more convenient. It directly regulates how the brightness of the paper over 85 percent is directly linked to consumer-design help and a perception of its quality based on the paper. It helps to preserve the necessary strengths when modifying the chemical compounds used in bleaching. As a simple example, a small one percent reduction in the use of a chemical care of, for example, a blue substance could save a pulp mill than $100,000 in annual chemical costs.


Purity in the context of pulp production indicates the absence of any contaminants that might interfere with the end paper’s appearance, performance, or processing. For example, contaminants are usually dirt, metal particles, or residual chemicals. Purity is critical to the highest grade of paper of the type used to pack pharmaceuticals or food, as even the slightest impurities can cause significant health hazards or degrade the taste and safety of the packed products. To ensure the highest possible purity, manufacturers use different processes of cleaning and screening.

The methods used are devised to cleanse paper of small enough particles and contaminants that would lead to a defect in the end product, like spots or holes. Such defects are unacceptable in production of paper for medical use or art paper. For high-grade office paper, the acceptable standard is no more than five particles or defects that are visible in 10,000 square meters of paper. A particularly illustrative example would be purity requirements for production of paper for use in inkjet printers. To avoid clogging of the tiny nozzle that supplies the ink to the sheet, the paper has to be perfectly clean, and there must be no inconsistency in ink absorption across the sheet.

Mills can afford no more than one defect in purity out of 1,000 square meters of paper to avoid any perceptible problems with prints, and purity is preserved at such high levels, contributing to an appropriate price for the paper. The cost of maintaining such levels of purity can be as high as 20% due to additional expenses on filtration systems, but these costs are justified by the possibility of getting higher prices for premium products. For example, the price of art paper can be more than 30% higher than standard drawing paper due to the remoteness and purity of materials spent on producing it, as well as the comparative lack of imperfections and defects and the suitability of such paper for high-quality photographic reproductions.



The freeness of pulp is the rate at which the water drains from the pulp slurry; it is a critical indicator of how well the pulp is prepared for papermaking. It mainly affects the production process of paper sheets and the energy included. The lower freeness suggests that the pulp has not been appropriately processed, thus the water drains slowly. It means that the fiber still needs to retain water, thus drying will take more energy. Consequently, the higher freeness assumes that the pulp is well-processed, and dried fiber has to drain water quickly so that the paper requires less energy for drying.

Tissue papers shall be made highly absorbent and will have a freeness of approximately 350-450 mL in Canadian Standard Freeness test, which indicates the very short fiber that allows water to be absorbed quickly. This freeness optimizes the drying of the tissue and consequently its manufacture process, allowing it to be entirely made and packaging in a few hours. On the other hand, high-grade writing papers are required to be strong enough, and for this matter, a freeness of approximately 200-300mL is usually chosen. It dictates that the fiber bonds should be strong enough, while the energy of the ink was able to be absorbed by paper and no escape to the other side.

It thus allows to choose a surface of desired smoothness that has less possibility of smearing and eliminating the risk of writing on the paper on the other side..reibung.auss. Changing the fiber freeness has also consequences for energy consumption. The drying of paper is the process that demands the most energy, and it can take up to 42% of total energy consumption. Changing the fiber freeness may allow to reduce the time of paper drying and save up to 10% of energy, which at large pulp mill scales may achieve saving of $1,000 a ton of the produced paper, or even more in countries with the high price of electricity.


One of the indicators used in pulp to check if each batch of paper produced has the same quality as the last batch is the consistency. Consistency involves testing if the fibers and any additives within the pulp material are evenly spread. High consistency means that every sheet will exhibit the same quality attributes as the one printed before it. It is crucial for products that require consistent quality such as currency paper or photographic paper. Every day, people use the level of consistency of the notebook paper they use for school. Both students and teachers are aware of the extreme smoothness of the paper and that their pencils, pens, or markers do not wear off so quickly due to the buffer.

Printed notebooks paper aims for a reading of 0.5, 0.6% due to density. The mixture of fibers, water, and additives is constantly monitored. The process calls for the use of reliable control systems with sensors that have to analyze several parameters such as viscosity, density, etc., such as in, for example, refiner filling. The correct measurement depends on the stable and reproducible dampening of the web or solids.

Producing the perfect amount of fill water for the paper stock generated before ensuring it remains the same varies in weight and volume. Approximately 45% of the total waste produced is due to poor consistency in the manufacture of graphic paper or printing and writing paper with a high weight ratio. These high-precision management systems could increase the loss by less than 5% of overall variable revenue due to product returns and customer complaints.


Viscosity is the parameter of high significance in the course of pulp processing. When it is high, it means that the polymerization of the cellulose fibers in the pulp is high. High viscosity presupposes the high quality of fiber and the final paper product in general. The importance of viscosity can be particularly acute for some products that need to have high tear resistance and tensile strength since the high viscosity accounts for paper strength.When producing paper for banknotes, it is vital that the viscosity be high enough for the paper not to rip when subjected to mechanical stress. Perspiration, crumpling, and countless other types of effect the banknote is exposed to in everyday life do not negatively affect a 15-20 centipoises’ paper. The added polymer also does not cause any harm but assists in the implementation of the great variety of individual security features that are the banknote alone.

The viscosity of the pulp may be considered a finalized product that needs to be preserved at a certain level. It requires the particular preservation regime in the course of pulp processing. Nevertheless, this characteristic feature also presupposes the usage of specialized equipment to measure the definite parameter and preserve the high viscosity levels throughout the process. The viscosity of the viscous fibers may be considered a regulated input product for which defined equipment or testing methods are used in the course of pulp processing. The viscosity of pulp can be changed with the help of the fine-tuning of the cooking and bleaching processes. In general, reducing the cooking time or temperatures usually help the matter be preserved at high levels.

From the economic point of view, the necessity of achieving proper viscosity accounts for the considerable portion of costs saved. Precision manufacturing when the parameter processing is kept at the required level provides low waste rates that can be nearly 85%. It also reduces costly process errors and resource consumption, such as chemicals and water. Moreover, it enables to keep pace with specific market needs and ensure the level of paper durability and longevity in the case of archival and legal writings. Only high viscosity-level pulp may ensure that the cellulose structure will last for decades without decay.

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