Abstract
Paper is one of the most recycled materials globally. In the United States, the average recycling rate was 60 to 64% in 2024. In response to sustainability goals, producers are increasingly incorporating recycled fibers over virgin wood. This study evaluates the repulpability and fiber characteristics of various paper grades using laboratory repulping and screening. Tissue paper, used brown kraft, Old Corrugated Containers and Sorted Clean News showed the highest repulping yields, above 80%, while Aseptic Packaging, Sorted Office Paper, magazines presented the lowest yields on average at 60%. On average uncoated products demonstrate lower total ash content compared to coated products, except for printing grades and non-domestic containerboard. These results highlight the impact of fillers and coatings on fiber recovery. Fiber quality analysis revealed significant variation between grades, with tissue, Old Corrugated Containers, Sorted Clean News, printed unbleached board, aseptic packaging, and fiber cores displaying the greatest weighted fiber lengths (1.6–1.8 mm) and widths (20–33 µm). Lower fiber yield led to higher fiber costs for raw materials, which is essential to consider in fiber procurement cost analysis. These findings offer practical insights for optimizing recycled fiber use, balancing cost, and maintaining product quality.
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Assessing the Paper Recycling Repulping Yield and Fiber Properties of Recovered Paper Products
Amelys Brito, Adeena Khan, Antonio Suarez, Ronalds Gonzalez, Richard Venditti,* and Hasan Jameel *
Paper is one of the most recycled materials globally. In the United States, the average recycling rate was 60 to 64% in 2024. In response to sustainability goals, producers are increasingly incorporating recycled fibers over virgin wood-derived fibers. This study evaluates the fiber yield and fiber characteristics of various paper products using laboratory repulping and screening. Tissue paper, used brown kraft, old corrugated containers, and sorted clean news showed the highest repulping fiber yields, above 80%, whereas aseptic packaging, sorted office paper, and magazines presented the lowest yields, on average about 60%. On average uncoated products exhibited lower total ash/inorganic fillers content compared to coated products, except for printing grades and non-domestic containerboard. These results highlight the impact of filler and coating content on fiber yield in different paper products. Fiber quality analysis revealed significant differences between grades, with tissue, Old corrugated containers, sorted clean news, printed unbleached board, aseptic packaging, and fiber cores displayed the longest length-weighted fiber lengths (1.6 to 1.8 mm) and widths (20 to 33 µm). These findings offer practical insights from a unique set of data for estimating the fiber yield, balancing cost, and maintaining product quality for a very wide range of paper products.
DOI: 10.15376/biores.21.3.7025-7059
Keywords: Recycled fiber; Repulpability test; Paper substrates; Fiber yield; Ash content; ISO brightness; Fiber Quality Analysis (FQA)
Contact information: Department of Forest Biomaterials, North Carolina State University, Raleigh, NC, 27695-8005, United States; *Corresponding author: richardv@ncsu.edu, jameel@ncsu.edu
INTRODUCTION
Paper products are one of the most widely recycled groups of materials globally. Approximately 232 million metric tons of recovered paper were collected in 2023 (Statista 2025). In the United States alone, about 46 million tons of paper were recycled in 2024, with an average recovery rate of 60 to 64% (American Forest & Paper Association 2025). Specifically, Old Corrugated Containers (OCC) are one of the most recycled grades in the United States, followed by mixed papers, high-grade deinking (printed pre-consumer scrap), newspapers, and pulp substitutes (unprinted pre-consumer scrap) (American Forest & Paper Association 2020).
Studies indicate that consumers are becoming increasingly sustainability-conscious and are willing to pay premium prices for environmentally friendly products to reduce their environmental footprint (Business Wire 2021). Consequently, producers have increasingly turned to recycled fibers to produce various paper products instead of relying solely on virgin wood (Hensley et al. 2020). The proportion of recycled paper in the total fiber used at U.S. mills rose from 36.6% in 2005 to 44.4% in 2024 (American Forest & Paper Association 2025). Therefore, to ensure a consistent supply of recycled fiber and to understand the quality of the fiber obtained from sorting facilities, it is essential to have a comprehensive knowledge of the potential fiber yield on recycling of various paper grades.
Repulpability refers to the ability of paper to be disintegrated in hydropulpers to yield fibers for subsequent paper sheet formation. Papers that have low repulpability generate large amounts of large unpulped materials that are discarded as recycling rejects. Repulpability is evaluated most commonly through a recognized procedure in the United States in the voluntary standard for repulping and recycling created by the Fibre Box Association (FBA) and the American Forest and Paper Association (AF&PA) (Fibre Box Association 2013) and recently revised in 2025 (Fibre Box Association 2025). Although it was initially intended for evaluating linerboard, containerboard, and corrugated medium, with and without water barrier coatings, this method has been adapted to evaluate most paper products. It is now widely used by paper manufacturers to understand the repulpability and recyclability of different paper grades. In the method, the sample is soaked in water, pulped in a blender, followed by disintegration, and then screened with 0.010 inch slots. Accepts are caught on a fine screen mesh that allows small particles (fines and fillers) and soluble materials (such as starch) to pass through the mesh and to be separated from the accepts fibers. The known sample input weight, the collected accepts and the collected rejects can be used to determine the percent accepts fiber yield, the percent large unpulped rejects blocked by the screen. The difference between the initial sample weight and the sum of the accepts and rejects can be used as a rough estimate of expected yield losses in a recycling operation.
Usable fiber yields of recovered paper products is a key critical variable that determines operating costs in a paper recycling process, with implications to fiber costs, sludge reject costs, and water treatment costs. Surprisingly, there has been no publication that details the fiber yields from product level paper materials. Estimates of non-fiber content have been presented (Ervasti 2016; Keranen and Ervasti 2014) but these lack any granularity on a paper product level. For instance, in Europe the reported non fiber material including minerals and additives was reported as 0.1% for newsprint, 11.3% for printing and writing grades, 0.2% for tissue, 0.6% for corrugated board, 1.1% for cartonboard (Ervasti 2016). However, this type of study is not product-level. Note that paper furnishes are evolving with time and older studies are informative but may not represent current and future paper compositions with respect to fillers, pigments, and additives. Thus, more recent evaluation of fiber, filler and additives in paper are needed.
This study aimed to analyze a broad range of paper products available in the United States on the market to gain a comprehensive understanding of their fiber yield and fiber length of accepts aligned with the FBA/AFPA repulpability method. It also analyzed the presence of total ash (non-fibrous inorganic material) in the original substrates and the effect of coating on the fiber yield. Furthermore, Fiber Quality Analysis (FQA) and ISO brightness measurements were performed on the recovered pulp to demonstrate fiber quality characteristics of recovered paper products.
The study addresses the following questions.
- How strongly correlated is the overall fiber yield to the ash content of a paper product?
- Can the ash content be used as a fast predictor of fiber yield from a paper product?
- Is there a general and significant difference between coated and uncoated paper products in fiber yield?
- Can the fiber length of a paper product be used as a predictor of the overall fiber yield?
The overall novelty of this study lies in it being the first and only comprehensive and consistent laboratory-scale recycling evaluation of a robust and large set of paper products with regard to their fiber yield and fiber quality. Product level data like this does not exist in literature. The resulting findings have significant implications for the impact of incoming paper types on both the paper recycling mill economics and environmental burdens. The findings show which measurables of recovered paper might be used to predict recycling yield and fiber quality.
EXPERIMENTAL
Materials and Selected Substrates
The paper industry offers a wide variety of products made through different processes. In this work, 69 paper substrates representative of the industry were selected and categorized into 13 groups according to the ISRI Scrap Specification Circular Guidelines (Institute of Scrap Recycling Industries 2022), when possible. The grade definitions used in the guidelines refer to how paper products should be sorted and packed in a sorting facility Also, it is important to note that every effort was made to accurately categorize the substrates based on the ISRI Scrap Specification Circular Guidelines. However, this was not possible for some specific products due to the lack of clearly following a grade definition within the guidelines, such as tissue paper or molded products.
Table A1 in the Appendix shows the different groups of paper products collected in the United States used in this study, along with information on whether the sample is coated, contains stickies (tacky adhesive contaminants), and whether it contains bleached or unbleached fibers. The samples were used products that were collected in the Raleigh, NC area. The samples were not sourced from industrial collection or recycling centers. To unambiguously document each paper product, images of each are shown in Table A2. Some of the paper products collected were considered to reflect compositions of pre-consumer waste such as clippings and over-issue products; this is why hygienic tissue paper was evaluated.
Equipment
A balance accurate to 0.001 grams (Mettler Toledo, Columbus, OH, USA) was used to measure the oven-dry equivalent weight of the substrates. A specimen-cutting device was used to cut the substrates. A commercial blender (Waring, Stamford, CT, USA) with a marine-type impeller was used to repulp the substrate with water as is prescribed in the Voluntary Standard for Repulping and Recycling (Fibre Box Association 2013). This impeller was used in order to better reflect industrial pulping as it decreases the amount of fiber cutting that a normal blender impeller blades might. The fiber blend was then placed in a standard pulp disintegrator (British Pulp Disintegrator, Testing Machines Inc., New Castle, DE, USA) to deflake the re-pulped material. A MasterScreen (MasterScreen PULMAC, Williston, VT, USA) with 0.010” slots was used to separate the accepts that were collected on a basket with 200 mesh screen bottom (75-micron openings). The screen accepts held in cheesecloth were using a Sharples 2-foot diameter centrifuge. A laboratory oven (Fisher Scientific, Waltham, MA, USA) was used to dry the rejects at 105˚C to obtain the dry (OD) weight.
Lab-scale Simplified Recycling Procedure
The lab-scale simplified recycling procedures utilized steps in the Voluntary Standard for Repulping and Recycling (Fibre Box Association 2013), and it is shown in Fig. 1. For the starting weight, 25 g of oven dry (OD) substrate was weighed out and cut into small strips of 1 1/4 in. (31.8 mm) by 4 in. (102 mm). The substrate and 1,500 mL of hot water (52°C ± 5°C) were placed in the blender as shown in the Appendix. The mixture was blended at low speed (15,000 rpm) for four minutes. The mixture was poured into the disintegrator. Additional fibers were rinsed out of the blender with 500 mL of hot water and poured into the disintegrator. The mixture (2,000 mL) was deflaked for five minutes at 3,000 rpm. The pulp was poured into a Pulmac MasterScreen with slots of 0.010” to separate accepts and rejects. The screening accepts were collected in a receiving basket of 200 wire mesh (75 micron openings) bottom that collected the screen accepts, then manually placed into a grade 60 cheesecloth 32/28 mesh (about 600-micron openings). The pulp was centrifuged, fluffed, and placed into separate plastic bags. Note that the mechanical retention of solids in the centrifuge was a function of the pulp mat that was formed as well as the cheesecloth. The pulp consistency was measured to obtain the pulp OD weight. The rejects collected on filter paper were dried in a laboratory oven at 105 °C before obtaining the OD weight. Both accepts and rejects were placed into separate plastic bags and stored until tested.
It is important to mention that the results obtained in this work are not a certification of the repulpability of selected paper products and constitute an exploratory study to understand fiber yield, screen rejects and fine particle and soluble material losses under the same experimental conditions that model a simplified paper recycling operation. These results should be used as directional indicators and not as absolute values for paper products.
Fig. 1. Lab-scale simplified recycling procedure (based on the Fibre Box Association 2013)
Testing Procedure
To study the repulping behavior of the samples, fiber accepts and rejects yields were obtained. Equation 1 expresses the yield as the accepts percentage calculated based on the OD weight charged to the pulper. Equation 2 expresses the yield as the accepts percentage calculated based on the accepts plus rejects (OD material). The accepts and rejects percentages are expressed by Eqs. 3 and 4 in the same manner. Finally, losses refer to the amount of soluble, fines, and fillers in the sample that are washed away during the repulping, screening and collection procedure and were calculated using Eq. 5.
Fiber Morphology – Fiber Quality Analysis (FQA)
The morphological properties of the repulped fiber after the screened process were analyzed using an optical fiber quality analyzer (HiRes FQ, OpTest Equipment Inc, Hawkesbury, ON, Canada). Fiber length, fiber width, and coarseness were measured.
Ash Content and ISO Brightness
The total ash content of the starting material was determined according to TAPPI T211 om-02 (2002), where the sample was ignited in a muffle at 525 ⁰C. This test determines the amount of inorganic matter in paper products, which varies depending on the product’s manufacturing process and end use. This ashing temperature allows the practical measurement of CaCO3 within the ash residuals.
To measure ISO brightness, handsheets were prepared with 5 g OD of 100% repulped and screened accepts fiber, following the ISO standard 2470 (2016). Pulp ISO brightness was measured using a spectrophotometer (ColourtouchX, Technydine, New Albany, IN, USA) (ISO 2016; Ragnar 2005).
Cost of Usable Repulped Fiber
To demonstrate the actual total cost of the usable fiber after a simplified repulping, screening, and collection on a 200 mesh screen recycling model, the recovered paper product cost was divided by the fractional fiber yield to determine the $/Bone Dried Short Ton of (BDST) of usable fiber. The prices for the recovered paper at the mill gate were obtained from the RISI database (Fastmarkets RISI 2025). The cost of the recovered paper was an average of what American paper mills paid for different types of recovered paper in the first two quarters of the year 2025. Three groups of paper products that are commonly recycled in the United States were chosen for this part of the analysis, Old Corrugated Containers (OCC), Magazines (OMG), and Sorted Office Paper (SOP).
RESULTS AND DISCUSSION
The laboratory recycling experiment provided valuable data, including the percentages of accepts and rejects for each paper product. These percentages were estimated through Eqs. 1 and 3, where the amounts of recovered or rejected material were divided by each substrate’s OD weight charged to the pulper (starting weight). The losses incurred during the repulping process were also quantified. This lost material was small enough to pass through the 200 wire-mesh receiving basket and the pulp pad within the cheesecloth in the centrifugation, including the soluble and insoluble materials. Moreover, the study determined the ISO brightness of each repulped fiber and the total ash content of the original material. The experiment also evaluated the morphological characteristics of the repulped fiber, adding another layer of insight to the value of the recovered fiber.
Fiber Yields for Different Paper Substrates
Table 1 displays the maximum, average, and minimum of the repulping accepts, rejects, and losses yield per recycled paper grade. The data revealed that 58% of the samples produced repulping yields (Eq.1) above 70%. On average, unused tissue paper, used brown kraft, OCC, and SCN showed the highest average repulping fiber yield with 93.6%, 81.9%, 78.9% and 78.9% respectively. Overall, these substrates shared the characteristic of having a small amount of ash content, i.e. fillers, little rejects, and no coating, which resulted in higher fiber yields. Notably, unused tissue products, such as paper towels, had very high fiber yields. While used tissue paper is generally not recycled due to the nature of the contaminants present in the product after its use (Corny 2021), unused tissue products, such as pre-consumer scrap generated during converting operations can be repulped and transformed into other paper products.
On the other hand, Aseptic Packaging, Sorted Office Paper (SOP), and Old Magazines (OMG) groups presented the lowest fiber yields of 62.0%, 61.5% and 60.1% respectively, Table 2. This is due to the high presence of fillers or coating components, such as kaolin, talc, calcium carbonates, and titanium dioxide, used to increase opacity and improve printing surfaces (Hubbe and Gill 2016). In the case of aseptic packaging, a high rejects content of ca. 22% contributed to the lower yield; in these cases, the large aluminum and polyethylene layers that would have plugged the Pulmac MasterScreen slots were manually removed after pulping and added to the screen rejects. It is important to mention that printed bleached cup stock (#2) also presented a high level of rejects of 11%, mostly due to the presence of a plastic film covering the interior of the cup. Interestingly, plates made from non-wood fibers, categorized as molded products, presented considerable rejects, due in part to the presence of shives in the product.
In terms of losses, OMG, SOP, UOP, and printed bleached board presented the highest losses with values between ca. 30% and ca. 40%, probably due to the high quantity of fillers in the paper and coating used during its production, which is washed away during the collection of accepts. The quantification of losses is also important because they contribute to the solid waste that would end up as sludge if removed in water clarification (suspended solids) that would be most likely be landfilled. Both the suspended solids and soluble organics that are not removed in water clarification and are present in the disposed waste water would contribute to the Biochemical Oxygen Demand (BOD), color, and chemical characteristics of the waste water. In particular, the BOD in the wastewater from a paper recycling mill can contribute significantly to the overall operating expenses. It is not practical to recycle these inorganic materials and re-use them again since they are heavily contaminated, variable in their composition, and compete with extremely inexpensive virgin materials.
Even low-valued and high-volume applications for sludge such as burning for energy value, construction or land applications have significant issues. For burning to obtain fuel value, the high moisture content (circa 50%) and high ash content cause the heating value to be extremely low. Further, when burning, there are issues with the high ash content fouling the boiler, sometimes leaving glass-like deposits on walls and boiler tubes. In construction, structural applications are hindered by the variability of the sludge composition that prevent their use when the material needs to be certified for a consistent composition. Land applications are limited, since soils need a balance of carbon to nitrogen and most lands do not require the amount of carbon found in sludges. Other concerns in land filling consist of the introduction of microplastics, metals, and other contaminants to the soil.
Table 1. Fiber Yield (Eq. 1), Screen Rejects (Eq. 2) and Losses (Eq. 3) by Product Group
Finally, it is important to highlight the large range of fiber yields for some paper products (Table 1). For example, for the OCC group the range was 35%, whereas it was only 2.5% for the sorted clean news. This variation could be attributed to the range of manufacturing processes and the vast number of process variables, such as fiber composition, additives, coatings, and processing conditions, used to manufacture similar products. Such heterogeneity constitutes an operational challenge for paper mills, which must attempt to ensure a consistent product produced from a variable supply of raw materials. Thus, the lack of raw material uniformity and the desire to meet minimum quality standards can affect yield, product quality, and resource efficiency, negatively affecting mill operations.
Ash Content and ISO Brightness for Different Paper Substrates
Table 2 shows the results for ISO brightness (%) of the screened fiber and the total ash content of different recovered paper grades. The paper groups that presented the highest average ISO brightness were tissue, SOP, printed bleached cup stock, printed bleached board, and OMG, with values between ca. 75% and 80%. This is expected, since these grades are made of bleached fibers. High brightness recovered fiber are valued in recycled printing and writing grades or tissue grades, since these fibers require less treatment to produce high brightness papers. On the other hand, high brightness fibers are not needed and may create color matching problems for many packaging applications.
In terms of ash content, OMG, printed bleached board, SOP, UOP, and aseptic packaging presented the highest ash content, with values between ca. 16.5% and ca. 28.0% (Table 2). This elevated ash level could be primarily attributed to the presence of inorganic materials in surface coatings and other inorganic fillers added to the bulk of the paper, which remain as non-combustible residues when subjected to thermal treatment at 525 °C. These inorganics are almost entirely washed away during the paper repulping process and end up mainly in sludge that is normally landfilled with significant associated costs. Interestingly, aseptic packaging presented one of the highest ash contents due to the aluminum layer in the container (Kaye 2011), but this would be rejected as a gross contaminant in screening. On the other hand, tissue, SCN and printed bleached cup stock were observed to have very low ash contents of under 2% on average.
Figure 2 depicts the repulped fiber yield and the total ash content for the different paper products ordered in terms of decreasing ash content from top to bottom. Coated card products had the highest ash content, which was likely due to the filler and coating of the paper, followed by Tetra Pak cartons due to the presence of aluminum layers, and then by glossy-coated magazines, sticker papers, and envelopes which probably contain coatings and the presence of fillers.
Moreover, in some cases, the manufacturing origin of the product also influenced the yield. For instance, domestic OCC and white top exhibited higher yields and lower ash content compared to their non-domestic counterparts. Overall, products with ash content above 20% presented lower yields, with some exceptions such as paper cups. The paper cups, although having low ash content, showed lower yields, which was likely due to high repulping rejects, such as plastic films. These screen rejects for paper cups ignited at the high temperature of the ash content test. Therefore, it is important to note that although ash content, often associated with losses, may serve as a useful indirect indicator for fiber yield, understanding the quantity of screen rejects is also essential for estimating potential fiber yields.
Table 2. Ash Content in the Original Recovered Paper (%) and ISO Brightness of the Accepts Fiber by Group
The correlation between fiber yield and ash content for both coated and uncoated products is presented in Fig. 3. There is significant scatter in the fiber yield versus ash content and there is significant overlap of the coated and uncoated data. For samples with very low ash content less than 5% it is clear that the uncoated products have in general higher yield than the coated products. It is also evident that only coated products have ash contents above 25%. This is expected, since the amount of filler in uncoated products generally resides between 5 and 25%. There is a large number of products with the highest fiber yield that have very low ash and are uncoated.
Fig. 2. Comparison of the repulped fiber yield (Eq.1) and ash content of the initial sample
Fig. 3. Repulped fiber yield vs. the total ash content of the initial sample for coated and uncoated products
Fiber Quality Analysis (FQA) for Different Paper Substrates
Fiber morphology characteristics in recovered paper highly influence the mechanical properties of the recycled paper products. For instance, longer fibers are associated generally with faster draining paper stock and higher paper strengths. Shorter fibers and fines are associated with slower draining paper stock and lower paper strengths. Therefore, understanding the morphology of recovered paper grades is crucial to making informed decisions to achieve the desired product quality.
The morphology of pulps made from softwoods, hardwoods, and other fibers has been widely reported (De Assis et al. 2018). For instance, fiber length can generally vary from 2.34 to 2.58 mm in bleached softwood pulps, and from 0.70 mm to 1.11 mm in bleached hardwood pulps, whereas widths have been reported to be approximately 28 µm in softwood pulps and to range between 16.4 µm and 18.5 µm in hardwood pulps (De Assis et al. 2018).
Table 3 depicts the fiber morphology results for all the recovered fiber groups. In terms of length weighted fiber length and width, tissue, OCC, SCN, printed unbleached board, aseptic packaging and fiber cores presented the highest average weighted lengths and widths with values between ca. 1.6 and ca. 1.8 mm, and ca. 20 µm and ca. 33 µm respectively. This could be attributed to a greater concentration of softwood fibers, although it is known that some of these grades also contain considerable amounts of hardwood fibers to improve surface properties such as smoothness for printing or better softness for tissue. Nevertheless, determining the furnish composition of the studied products based on fiber morphology is challenging and was outside of the scope of this study. Specific wood fiber supply, pulping processes, refining, and recycled content can affect fiber morphology.
Table 3. Fiber Length Weighted Length (mm), and Mean Width (µm) by Group
Figure 4 compares the repulped fiber yield and fiber length of different paper products ordered from longest to shortest average fiber length from top to bottom. The top 10 substrates with the highest fiber length were primarily packaging products such as OCC, coated cardboard, and used brown bags (Table 3). Most of these products had a high repulping yield above 80%. However, some substrates, such as glossy coated magazines and Tetra Pak containers, also had a high fiber length but a low fiber yield of approximately 50%.
Fig. 4. Comparison of the repulped fiber yield and weighted fiber length
These lower repulping yields may be caused by several reasons. For example, the coated magazine could present high content of coating or a specific type of coating that was washed away during repulping, resulting in very low yields. In the case of Tetra Pak containers, which have a large proportion of aluminum and polyethylene (Kaye 2011), the repulping fiber yields were lower than other products. Samples did not show a clear trend regarding the relationship between fiber repulping yield and fiber length.
The relationship between fiber yield and fiber length for both coated and uncoated products is shown in Fig. 5. Overall, no strong correlations were observed. However, uncoated products generally exhibited the highest fiber yields and longer weighted fiber lengths. In this type of product, surface properties could be less critical depending on the grade, and therefore the content of shorter fibers could be expected to be lower. For example, the peeled liner from the linerboard presented a yield of 95% and fiber lengths of up to 2.4 mm, which is characteristic of softwood fiber.
Fig. 5. Repulped fiber yield (%) versus weighted fiber length (mm) of the initial sample for coated and uncoated products
Nevertheless, some exceptions arise, such as non-domestic OCC, which is known to contain a lot of printing and writing grades that are known for having shorter fibers and high quantities of fillers. In both cases of the non-domestic OCC, the yields were low. Additionally, non-domestic white top exhibited lower repulping yields (63%) compared to domestic white top, which yielded 88%. For coated products, only the cracker box and beer carrier showed fiber lengths above 2.3 mm and fiber yields above 80%. In coating grades, smoothness is critical, leading to increased use of shorter fibers to improve surface properties. Also, as explained earlier, coating material is not recovered during recycling and repulping processes, leading to lower yields. Thus, it is not reasonable to estimate fiber yield with fiber length, even within coated or uncoated grades, due to the influence of multiple other factors, such as the presence of fillers and the specific application for which the paper grade is used.
Cost of Usable Repulped Fiber
Table 4 provides an example of the estimated cost of recovered paper for three different grades (OCC, OMG and SOP). The equivalent fiber cost is based on the repulping yields without taking into consideration any additional treatment that the raw material might require for the product application, such as starch addition to increase strength. Note that the price of recovered paper changes considerably with time due to supply and demand impacts and this is just an example of an estimate, which will change considerably as fiber costs change. Also note that the cost of fiber as well as the composition of paper products varies significantly among different countries. The results highlight the negative impact of low but not uncommon fiber yields on the overall cost of fiber at the headbox. For instance, SOP and OMG presented a lower repulping fiber yield than OCC, resulting in higher fiber costs for raw materials at the paper machine. By understanding the cost implications, manufacturers can make informed decisions about the types of fiber they use and how to optimize their processes to minimize costs while maintaining product quality.
Table 4. Assessment of Cost of Repulped Fiber in the United States by Group
CONCLUSIONS
- Paper products in this study exhibited a broad range of repulping yields. This was mainly attributable to the myriad of processes, furnishes, and related variables involved in their production. Nevertheless, the repulpability experiment provided valuable results for assessing the repulpability of these products and identifying the main factors affecting it.
- Overall, substrates with low ash content, few large rejects, and no coating presented higher repulping yields. Nevertheless, no single factor alone was enough to predict high repulpability.
- Repulping yield did not present a strong correlation with recovered fiber length. Nevertheless, uncoated products generally exhibited higher repulping yields along with longer fiber lengths than their coated counterparts. Exceptions included non-domestic packaging and printing and writing grades.
- Lower fiber yields resulted in higher costs associated with fiber. Based on prices at the time of writing of the article, domestic old corrugated container pulp (OCC), with higher repulpability yield, presented a cost of 96.1 USD at the paper machine, whereas OMG and SOP presented costs of 154.6 and 209.9 USD, respectively.
- It was determined that tissue paper, used brown kraft, OCC, and sorted clean news (SCN) showed the highest repulping yields, above 80%, whereas aseptic packaging, sorted office paper (SOP), and old magazine (OMG) paper groups presented the lowest repulpability yields, averaging around 60%.
- Non-domestic OCC exhibited lower yields (63 to 70%) compared to domestic United States OCC (72 to 98%). Additionally, non-domestic white top exhibited lower repulping yields (63%) compared to domestic United States white top board (88%).
- In terms of losses, OMG, SOP, UOP (unsorted office paper) and printed bleached board presented the highest losses, ranging from 31% to 52%, indicating that the amount of sludge generated from processing these materials will be very high.
- Tissue paper, SOP and OMG groups presented the highest ISO brightness, with most of the samples exhibiting values between ca. 75% and 80%.
- The samples categorized as OMG, printed bleached board, SOP, UOP and aseptic packaging presented the highest ash contents with most of the samples presenting values between ca. 15% and ca. 36%.
- Tissue paper, OCC, SCN, printed unbleached board, aseptic packaging and fiber cores presented the highest average weighted fiber lengths (circa 1.6 to 1.8 mm) and widths (circa 20 to 33 µm).
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Article submitted: September 12, 2025; Peer review completed: October 25, 2025; Revised version received: October 30, 2025; Accepted: June 10, 2026; Published: June 16, 2026.
DOI: 10.15376/biores.21.3.7025-7059
APPENDIX
Cost of Usable Repulped Fiber
Table A1. Paper Products Classification by Group, with Description, Coating, Presence of Stickies, Bleached and Brown Fiber. Numbers in the descriptions indicate different samples.
Pictures of Tested Products
Table A2. Pictures of Tested Products
