WO2023073539A1

WO2023073539A1 - A method for manufacturing a purified fiber fraction from used beverage carton

Info

Publication number: WO2023073539A1
Application number: PCT/IB2022/060223
Authority: WO
Inventors: Carl-Henrik LJUNGQVIST; Isto Heiskanen; Kaj Backfolk
Original assignee: Stora Enso Oyj
Priority date: 2021-10-29
Filing date: 2022-10-25
Publication date: 2023-05-04
Also published as: SE2151331A1

Abstract

The present invention relates to a method for manufacturing a purified fiber fraction from used beverage carton (UBC), said method comprising the steps: a) subjecting a UBC starting material to a polymer and aluminum film separation method to obtain a UBC polymer and aluminum fraction and a raw UBC fiber fraction; b) optionally subjecting the raw UBC fiber fraction to a coarse screening method to remove coarse particles; c) subjecting the raw UBC fiber fraction to a fine screening method to remove cellulose fines and fine particulate contaminants, wherein the fine screening method comprises at least one fine screening step and at least one dilution step; d) optionally subjecting the fine screened UBC fiber fraction to a bleaching method; e) subjecting the fine screened, and optionally bleached, UBC fiber fraction to an electro-osmosis method to remove further contaminants; f) optionally subjecting the fine screened, and optionally bleached, UBC fiber fraction to a dewatering method to a consistency of at least 20 wt%; and g) subjecting the optionally dewatered UBC fiber fraction to a deactivation method to obtain a purified UBC fiber fraction.

Description

A METHOD FOR MANUFACTURING A PURIFIED FIBER FRACTION FROM

USED BEVERAGE CARTON

Technical field

The present disclosure relates to methods for recycling a fiber fraction from used beverage carton (UBC).

Background

The multilayer construction of beverage cartons provides a resource efficient, lightweight and recyclable packaging solution that can be made from renewable resources. Sustainably sourced virgin cellulose fibers provide strength and stiffness whilst the other layers provide barriers to liquid, water vapor, oil/grease, oxygen and light to protect the packed contents. The correct combination of materials ensures food transport and storage safety, while preventing food spoilage and waste by protecting the contents from deterioration. These barrier layers may consist of various polymers or a combination of polymers and aluminum foils or coatings, depending on the type of product to be packaged, and whether the product is kept refrigerated or if it is distributed and stored at room temperature.

Beverage carton in its simplest form comprises at least one paperboard layer and at least one liquid barrier layer, typically a polyolefin layer. Beverage carton may further comprise an additional barrier layer, typically an aluminum foil or coating layer, or a high barrier polymer layer such as polyamide or EVOH. Such beverage carton is often used for aseptic packaging and is therefore often referred to as aseptic beverage carton.

The typical structure of an aseptic carton includes a polyolefin, typically LDPE (low density polyethylene), outer layer which provides a moisture and liquid barrier, protects the printing ink layer applied to the board and enables the package to be heat sealed. The type of paperboard used depends on the product being packed, the market where it will be sold and the manufacturing conditions, but it is commonly a two or three ply or even up to five ply material with a bleached or clay-coated outer layer and often contains CTMP (chemithermomechanical pulp), TMP (thermomechanical pulp), brown pulp or high yield pulp; the paperboard gives the package the required mechanical rigidity and typically represents about 65-75% of the total weight of the package. The inner side of the paperboard is coated with LDPE to tie it to the aluminum foil layer that provides an odor, light, and gas barrier. Adhesion of the aluminum foil to the innermost plastic layer is achieved through the use of a tie layer, e.g. of EMAA (poly(ethylene-co- methacrylic acid). Finally, an inner layer of LDPE is applied to enable heat sealing of the carton.

The term used beverage carton (UBC) is used herein to denote post-consumer beverage carton, and particularly post-consumer aseptic beverage carton, obtained from containers and packaging materials which have been collected after being used.

The composition of UBC is different compared to many other recycled sources. UBC is typically characterized by:

• High amount of bleached or unbleached chemical, semi-chemical, or mechanical fibers

• High plastic content

• High content of aluminum from foils and coatings

• Food or liquid residues

• High microbe (microorganism) content

• High amount of organic materials including different fats and oils

• High content of single and multivalent ions or salts

• Possible presence of heavy metals

• Non-intentionally added substances (NIAS)

• Mixed waste containing packaging and packaging items such as single use components (caps, straws and long stringy materials such as baling wire, etc) The collected UBC can contain printing ink and varnish. Although usually most of the fiber is not directly subjected to printing ink, the dissolved ink or ink fragments can re-redeposit onto the fibers during the disintegration step.

Recycling can be categorized as primary, secondary, tertiary, and quaternary recycling. Primary recycling refers to reprocessing the material back into its original use or comparable products with equivalent or higher quality, but this is currently not an option for post-consumer cartons as they cannot be directly converted back into their original use. Secondary recycling, wherein materials are processed and used in applications not requiring virgin material properties is the most widespread recycling option for UBC. The paper fibers are separated from the polymer and aluminum residual (also referred to herein as the PolyAI residual) and the fibers are incorporated into paper products. Another secondary recycling process involves converting the shredded UBC into construction materials.

Tertiary recycling involves breaking a product down into its chemical building blocks, and then recycling those chemicals into various products. Quaternary recycling of UBC involves incineration with energy recovery, although this process is not considered as recycling in many countries.

Due to its multilayer structure and characteristic composition, it is difficult to efficiently recycle and reuse UBC. As a result, UBC is today often collected and then either disposed as landfill, burned or processed into different lower value fractions (e.g. a polymer-rich fraction, a fiber-rich fraction, and a waste water or sludge fraction). The fiber-rich fraction is typically used in composite materials, non-food packaging applications and other grades where higher contents of impurities are tolerated, such as tissues, towels, liner and writing paper.

As the paperboard typically constitutes 65-75% of the total weight of the carton, recovery of this fraction has been the predominant focus of carton recycling approaches. Recycling may be accomplished at a paper mill by recovering the paper fibers using a conventional hydrapulper or a drum pulper. Hydrapulpers are large cylindrical vessels with impellers at the bottom which break apart the paper fibers and produce a relatively dilute slurry of fibers that can be further processed within the mill. Contact between the water and the paper layer occurs in the hydrapulper, and the layers separate due to the hydraulic forces inside the pulper. No chemicals are required, but solvents or acid or alkaline solutions may sometimes be used to improve the separation efficiency. The consistency of the pulp in the hydrapulper is typically below 15 wt%. Hydrapulpers are generally equipped with a ragger which removes the PolyAI residual, caps, straws and long stringy materials such as baling wire from the slurry. After removal from the pulper, the PolyAI residual is washed in a perforated rotating cylinder to recover any entrained fibers. A drum pulper is basically a rotating, inclined drum with baffles, which separates the debris from the fibers in pulping and screening sections with minimal fiber loss.

While many paper mills have hydrapulpers that could recycle UBC, the fact that the maximum theoretical yield is just 75% compared to 85% or more for other paper packaging is a disincentive, as is the challenge of economically processing the PolyAI residual. Furthermore, the high amounts of impurities in recovered UBC fibers, particularly from food residues and non-intentionally added substances (NIAS), can make them unsuitable for mixing into virgin or less contaminated pulp streams. Today, there are strict regulations and limitations on the use of recycled material in paperboard manufacturing processes. Fibers obtained from UBC may contain components that should not be allowed back into a paperboard making process. Examples include plastic particles, metals metal compounds, optical brightening agents (OBA) or fluorescent whitening agents (FWA), ink residuals or mineral oils, and in particular microbes, toxic components, and food residues. These impurities can interfere with wet end chemistry (process performance), but also end product properties (mechanical or product performance, barrier properties, impurities, microbial growth, etc.).

Fibers obtained from UBC may often exhibit high microbial activity, or high microbial load, and microbial deactivation or sterilization of the fibers or pulps is typically required before they can be reused.

Another challenge with recycled UBC is that fibers obtained from UBC are considered as downgraded when they are recycled and reused. This downgrading is partly due to reduced mechanical properties caused by excessive mechanical and chemical treatment. The recycled fibers may be mechanically damaged or treated using methods that affect, e.g., their strength and mechanical performance.

Generally, only virgin paper fibers are used in the manufacture of paperboard for food or beverage packaging applications. There is a need to increase the amount of recycled fiber content in paperboard for food packaging applications. Due to the high degree of contamination, microbial load, and downgrading of the recycled material it is commonly assumed that fibers from UBC cannot be efficiently reused in food or beverage packaging laminates or products.

Thus, there is a need to find methods that allow pulp from UBC to be used in food or beverage packaging substrates and laminates, especially in higher contents, without affecting mechanical properties of the substrates and laminates or causing risks for contamination of packaged contents.

Description of the invention

It is an object of the present disclosure to provide a method that allows pulp from used beverage carton (UBC) to be reused in applications and products where typically only virgin paper fibers are used, such as in food or beverage packaging substrates and laminates.

It is an object of the present disclosure to provide a fiber fraction from UBC, which has suitable chemical purity for being reused in food or beverage packaging substrates and laminates.

It is an object of the present disclosure to provide a fiber fraction from UBC, which has a reduced content of optical brightening agents (OBAs).

It is an object of the present disclosure to provide a fiber fraction from UBC, which has suitable or required biological purity for being reused in food or beverage packaging substrates and laminates. It is an object of the present disclosure to provide a fiber fraction from UBC, which has suitable mechanical properties for being reused in food or beverage packaging substrates and laminates.

The above-mentioned objects, as well as other objects as will be realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure.

The present invention is based on the inventive realization that subjecting a fine screened UBC fiber fraction to an electro-osmosis method to remove further contaminants not only leads to an efficient removal of metallic and non-metallic ions and salts, but also to a reduction of the OBA content of the fiber fraction and a reduction of the microbial activity of the UBC fiber fraction.

The present invention is further based on the realization that subjecting the raw UBC fiber fraction obtained after removal of the PolyAI residual to a fine screening method to remove fines and fine particulate materials has been found to significantly facilitate subsequent washing, electro-osmosis, bleaching and deactivation of the UBC fiber fraction.

A relatively small portion of fines in recycled UBC fiber fractions is responsible to a high degree for the high levels of impurities, high water retention and/or high drainage resistance of the fiber fractions. Fine screening to remove fines and fine particulate materials can remove a significant portion of the particulate contaminants, and the reduced drainage resistance allows for repetitive washing steps to be performed in a shorter period of time, resulting in a fiber fraction with higher purity.

The fine screening method to remove fines and fine particulate materials also facilitates bleaching and deactivation of the UBC fiber fraction by reducing the amount of bleaching or deactivation chemicals required to achieve a required bleaching or deactivation result, respectively. Furthermore, the removal of fines, fine particulate materials, and contaminants may also reduce the interference with wet end chemistry when the UBC fiber fraction is reused in a pulping process or a process for making paper or paperboard or moldable fiber.

According to a first aspect illustrated herein, there is provided a method for manufacturing a purified fiber fraction from used beverage carton (UBC), said method comprising the steps: a) subjecting a UBC starting material to a polymer and aluminum film separation method to obtain a UBC polymer and aluminum fraction and a raw UBC fiber fraction; b) optionally subjecting the raw UBC fiber fraction to a coarse screening method to remove coarse particles; c) subjecting the raw UBC fiber fraction to a fine screening method to remove cellulose fines and fine particulate contaminants, wherein the fine screening method comprises at least one fine screening step and at least one dilution step; d) optionally subjecting the fine screened UBC fiber fraction to a bleaching method; e) subjecting the fine screened, and optionally bleached, UBC fiber fraction to an electro-osmosis method to remove further contaminants; f) optionally subjecting the fine screened, and optionally bleached, UBC fiber fraction to a dewatering method to a consistency of at least 20 wt%; and g) subjecting the optionally dewatered UBC fiber fraction to a deactivation method to obtain a purified UBC fiber fraction.

The purified UBC fiber fraction obtained according to the inventive method is preferably suitable for demanding end uses such as for direct or indirect food contact.

In addition to cellulose fiber, collected UBC, referred to herein as the UBC starting material, also comprises a high content of plastic materials, mainly polyolefins, and a high content of aluminum from foils and/or coatings. In some embodiments the UBC starting material in step (a) comprises at least 15 wt%, and in some embodiments at least 20 wt% of plastic, based on dry weight. In some embodiments the UBC starting material in step (a) comprises at least 0.3 wt%, and preferably at least 1 wt% of aluminum or aluminum compounds, based on dry weight. In some embodiments the UBC starting material in step (a) comprises at least 15 wt% plastic and at least 0.3 wt% aluminum or aluminum compounds preferably at least 20 wt% plastic and at least 1 wt% aluminum or aluminum compounds, based on dry weight.

In some embodiments the UBC starting material in step (a) comprises less than 1 wt% optical brightening agent (OBA). In some embodiments the UBC starting material in step (a) comprises 0.1-1 wt% optical brightening agent (OBA).

In order to obtain a raw fiber fraction suitable for further washing and deactivation, plastics and/or aluminum content is first removed. This is done by subjecting a UBC starting material to a polymer and aluminum film separation method to obtain a UBC polymer and aluminum fraction and a raw UBC fiber fraction. If the UBC starting material does not contain aluminum, the UBC polymer and aluminum fraction may only comprise polymer and no aluminum. The obtained raw UBC fiber fraction is mainly comprised of cellulosic material and comprises significantly less plastics and aluminum than the UBC starting material. The polymer and aluminum film separation method may comprise shredding the UBC starting material and mixing the shredded UBC starting material with water or an aqueous solution. As the mixture is stirred, the fibers absorb moisture and the plastic and aluminum layers of the laminate are loosened. Through mechanical filtration and/or flotation, various fractions are separated to obtain a UBC polymer and aluminum fraction and a raw UBC fiber fraction.

The raw UBC fiber fraction obtained in step (a) preferably comprises at least 80 wt% cellulose fiber, based on dry weight. In some embodiments, the raw UBC fiber fraction obtained in step (a) preferably comprises at least 90 wt% cellulose fiber, preferably at least 95 wt% cellulose fiber, based on dry weight.

In some embodiments, the raw UBC fiber fraction obtained in step (a) has a Schopper-Riegler (SR) value in the range of 15-35, preferably in the range of 18- 30, as determined by standard ISO 5267-1. In some embodiments, the raw UBC fiber fraction obtained in step (a) has a water retention value (WRV) in the range of 110-200%, preferably in the range of 120- 180%, and more preferably in the range of 125-175% as determined by standard ISO 23714.

In some embodiments, the raw UBC fiber fraction obtained in step (a) has a content of “Fines A” as measured using an FS5 optical fiber analyzer (Valmet) of above 22 %, preferably above 25 %.

In some embodiments, the raw UBC fiber fraction obtained in step (a) comprises above 1 wt% plastic, preferably above 1 .2 wt% plastic, based on dry weight.

In some embodiments, the raw UBC fiber fraction obtained in step (a) comprises above 0.2 wt% aluminum, preferably above 0.5 wt% aluminum, based on dry weight.

In some embodiments, the raw UBC fiber fraction obtained in step (a) comprises above 20 mg/kg mineral oil saturated hydrocarbons (MOSH), preferably above 50 mg/kg MOSH, based on dry weight.

In some embodiments, the raw UBC fiber fraction obtained in step (a) comprises above 20 mg/kg mineral oil aromatic hydrocarbons (MOAH), preferably above 50 mg/kg MOAH, based on dry weight.

In some embodiments, the raw UBC fiber fraction obtained in step (a) comprises above 5000 mg/kg extractives, preferably above 10 000 mg/kg extractives, based on dry weight.

In some embodiments, the raw UBC fiber fraction obtained in step (a) comprises above 1000 mg/kg unsaturated fatty acids, preferably above 2000 mg/kg unsaturated fatty acids, based on dry weight. In some embodiments, the raw UBC fiber fraction obtained in step (a) comprises above 400 mg/kg resin acids, preferably above 500 mg/kg resin acids, based on dry weight.

The amounts of extractives, unsaturated fatty acids, and resin acids were determined using the SCAN-CM 49 method with acidification of pulp to pH < 3 using acetic acid. Extraction was made by ASE (Accelerated Solvent Extraction) with acetone at temperature of 100 °C, pressure 2000 psi, and 2 cycles. The extracts were analyzed with GC-FID and then calculated against internal standards.

In some embodiments, the raw UBC fiber fraction obtained in step (a) has an ash content (525 °C) above 4 % and/or and an ash content (925 °C) above 4 %. Raw UBC fiber fractions obtained from some types of sources, e.g. from sources containing mineral or pigment coated carton, may also have significantly higher ash contents.

In some embodiments, the raw UBC fiber fraction is subjected to a screening method to remove coarse particles. The term coarse particles as used herein refers generally to particles having a diameter or width above 1 mm.

The raw UBC fiber fraction may still comprise minor quantities of plastics and aluminum, predominantly in the form of fine particulates not removed by conventional polymer and aluminum film separation methods. These fine particulates, together with cellulose fines formed by degradation of the cellulosic material, is responsible to a high degree for the retention of high levels of impurities, high water retention and/or high drainage resistance of the fiber fraction.

The term cellulose fines as used herein generally refers to cellulosic particles significantly smaller in size than cellulose fibers.

In some embodiments, the term cellulose fines as used herein refers to fine cellulosic particles, which are able to pass through a 200 mesh screen (equivalent hole diameter 76 pm) of a conventional laboratory fractionation device (SCAN-CM 66:05). There are two major types of fiber fines, namely primary and secondary fines. Primary fines are generated during pulping and bleaching, where they are removed from the cell wall matrix by chemical and mechanical treatment. As a consequence of their origin (i.e., compound middle lamella, ray cells, parenchyma cells), primary fines exhibit a flake-like structure with only minor shares of fibrillar material. In contrast, secondary fines are generated during the refining of pulp. Both primary and secondary fines increase drainage resistance of the pulp and reduce the dewatering speed in the forming section of a paper machine. Because of their large specific surface area in comparison to pulp fibers, fines affect the retention of process chemicals and hence greatly influence the process stability and end product performance.

In contrast to conventional papermaking methods involving wire dewatering, the retention of fines in this system is preferably kept low so that dewatering/drainage in the subsequent washing, bleaching and deactivation becomes more efficient.

In some embodiments, the term fine particulate contaminants as used herein refers to fine particles not derived from a cellulosic material, which are able to pass through a 200 mesh screen (equivalent hole diameter 76 pm) of a conventional laboratory fractionation device (SCAN-CM 66:05).

In order to remove a portion of the cellulose fines and fine particulate contaminants from the raw UBC fiber fraction, the raw UBC fiber fraction is subjected to a fine screening method to remove cellulose fines and fine particulate contaminants, wherein the fine screening method comprises at least one fine screening step and at least one dilution step.

The fine screening method used to remove cellulose fines and fine particulate contaminants from the raw UBC fiber fraction includes at least one fine screening step. The fine screening step may include screening using one or more pressure screens, one or more hydrocyclones, one or more belt filters, or a combination thereof. Other screening methods known by the skilled person for removing fines from a fiber mixture may also be employed. The fine screening method used to remove cellulose fines and fine particulate contaminants from the raw UBC fiber fraction includes at least one dilution step. The dilution step preferably comprises adding a dilution liquid, preferably water or an aqueous solution to reduce the consistency of the UBC fiber fraction. The dilution step may be performed before and/or after the fine screening step Preferably, dilution is performed at least before the fine screening step in order to reduce the consistency of the UBC fiber fraction before the fine screening step. The consistency of the UBC fiber fraction after dilution may vary depending on the screening or fraction method used. In some embodiments, the dilution factor (DF) is >2, preferably >2.5, >3.0, >3.5, >4, >4.5 or >5. Preferably, the dilution step comprises diluting the UBC fiber fraction to a consistency in the range of 0.1-7 wt%, preferably in the range of 0.3-5 wt%, and more preferably in the range of 0.5- 2 wt%. It is also possible to perform screening at higher consistency, especially at the end of a fine screening method comprising more than one screening step.

The inventive method may preferably comprise an extended fine screening sequence, wherein at least two fine screening steps and/or at least two dilution steps are performed.

In some embodiments, the fine screening method of step (c) includes at least two, preferably at least three, fine screening steps. The fine screening steps can be the same or different.

In some embodiments, the fine screening method of step (c) includes at least two, preferably at least three, dilution steps. The dilution steps may be the same or different.

In some embodiments, the fine screening steps of step (c) are repeated in sequence at least two times, preferably at least three times.

Examples of possible screening/dilution sequences: screening - dilution - screening screening - dilution - screening - dilution screening - dilution - screening - dilution - screening dilution - screening - dilution dilution - screening - dilution - screening - dilution dilution - screening - dilution - screening - dilution - screening

In some embodiments, the fine screening method of step (c) reduces the content of fines and fine particulate contaminants in the UBC fiber fraction by at least 20 %, preferably by at least 30 %, and more preferably by at least 40 %. More specifically, in some embodiments, the fine screening method of step (c) reduces the content of fines in the UBC fiber fraction by at least 20 %, preferably by at least 30 %, and more preferably by at least 40 %, wherein the fines content is the content of “Fines A” as measured using an FS5 optical fiber analyzer (Valmet).

In some embodiments, the fine screening method of step (c) reduces “Fines A” as measured using an FS5 optical fiber analyzer (Valmet) to less than 20 %, preferably to less than 17 %, and more preferably to less than 15 %.

In some embodiments, the fine screening method of step (c) removes 0.1-10 wt% or 0.1 -7.5 wt% or 0.1 -5 wt% of the solid content of the raw UBC fiber fraction.

The fine screened UBC fiber fraction is optionally subjected to a further washing method to remove further contaminants subjected to a washing method to remove further contaminants, particularly dissolved, dispersed, soluble, or extractable contaminants. Any suitable pulp washing method for removing contaminants from a pulp mixture may be used. The washing method used to remove further contaminants from the raw UBC fiber fraction may include washing using one or more rotary vacuum washers, rotary pressure washers, pressure and atmospheric diffusion washers, horizontal belt washers and dilution/extraction equipment, or a combination thereof. Other washing methods known by the skilled person for removing fines from a fiber mixture may also be employed. The washing method may preferably comprise two or more washing steps. In some embodiments, the fine screened UBC fiber fraction is subjected to a bleaching method. The bleaching method may before or after the electro-osmosis method. The bleaching method may for example be selected from the group consisting of hydrogen peroxide bleaching, ozone bleaching, oxygen bleaching, chloride bleaching, hypochlorite bleaching, and extraction bleaching. In a preferred embodiment, the bleaching method is combined with heating the screened and washed UBC fiber fraction to a temperature of 50 °C or higher, such as 80 °C or higher, preferably 90 °C or higher, and more preferably 100 °C or higher. The bleaching method may for example comprise a combination of heating and hydrogen peroxide bleaching or heating and hypochlorite bleaching. Such a bleaching method may preferably also lead to an at least partial deactivation of the UBC fiber fraction.

The fine screened, and optionally bleached, UBC fiber fraction is subjected to an electro-osmosis method to remove further contaminants. The electro-osmosis method involves subjecting the UBC fiber fraction to an electric field, inducing motion of water around charged particles. The electro-osmosis method may also involve electrophoresis, whereby charged particles in the electrical field are attracted and move towards the electrode with the opposite charge. The electric field may for example be created by providing electricity to anode and cathode electrodes of an electro-osmosis device.

In some embodiments, the electro-osmosis method comprises the following steps: providing a slurry comprising the UBC fiber fraction and liquid, subjecting the slurry to an electric field inducing the liquid of the slurry to flow, separating liquid from the UBC fiber fraction thus obtaining a liquid depleted slurry, adding a washing liquid, preferably water, to the liquid depleted slurry subjecting the liquid depleted slurry to an electric field inducing the washing liquid of the slurry to flow, and separating the washing liquid from the UBC fiber fraction, thus obtaining a purified UBC fiber fraction. Examples of electro-osmosis methods that could be applied in the present invention include, but are not limited to, those described in US patent 9447541 B2 and US patent 10913759 B2.

The electro-osmosis method leads to removal of metallic and non-metallic ions and salts from the UBC fiber fraction, but also to a reduction of the OBA content of the UBC fiber fraction. The electro-osmosis method has also been found to reduce the microbial activity of the UBC fiber fraction.

The electro-osmosis is also generally accompanied by dewatering of the UBC fiber fraction. The degree of dewatering is related to the amount of contaminants removed by the electro-osmosis method, but may also be affected by drainage resistance of the UBC fiber fraction, additional pressure or vacuum applied, press fabric permeability, speed, filter cake thickness, consistency etc. The dewatering is preferably done in a continuous mode such as on a belt or wire or press fabric.

In some embodiments, the electro-osmosis method in step (e) leads to dewatering of the UBC fiber fraction.

In some embodiments, the electro-osmosis method in step (e) leads to dewatering of the UBC fiber fraction to a consistency of at least 20 wt%.

In some embodiments, the screened and washed, and optionally bleached, UBC fiber fraction is subjected to an additional dewatering method to a consistency of at least 20 wt%. In some embodiments, the UBC fiber fraction in step (f) is dewatered to a consistency of at least 30 wt%, preferably at least 40 wt%. The dewatering improves the efficiency of the subsequent deactivation method.

The present inventors have further found that the mechanical properties of the UBC fiber fraction can be further improved for use in in food or beverage packaging substrates and laminates by subjecting the UBC fiber fraction to a heat treatment at a consistency of at least 20 wt%, preferably at least 30 wt%, and more preferably at least 40 wt%. The heat treatment may for example comprise subjecting the UBC fiber fraction to drying at elevated temperature. In some embodiments, the UBC fiber fraction is subjected to drying at elevated temperature to a consistency of at least 70 wt%, preferably at least 80 wt%, and more preferably at least 90 wt%, before or during or after being subjected to the deactivation method. Without wishing to be bound to any specific scientific theory, it is believed that hornification of the UBC fiber fraction caused by the heat treatment at high consistencies can improve the mechanical properties of the fiber fraction when used in a food or beverage packaging substrate or laminate. Thus, in some embodiments, the drying at elevated temperature leads to hornification of the UBC fiber fraction. The elevated temperature is preferably 80 °C or higher, preferably 90 °C or higher, and more preferably 100 °C or higher.

In some embodiments, the heat treatment is performed in a hot disperger (also known as a hot disperser). A hot disperger is a device which uses a combination of heat and mechanical treatment of fibers at high consistency to liquefy, break down and disperse tacky and visible contaminants. The temperature in the hot disperger is preferably 80 °C or higher, preferably 90 °C or higher, and more preferably 100 °C or higher, such as in the range of 110-180 °C. The heat treatment in the hot disperger may typically be performed for a duration of 5 seconds to 120 minutes, preferably for 5 seconds to 30 minutes. Heat treatment in a hot disperger can improve dissolution of e.g. starch and residual barrier polymers and additives. Heat treatment in a hot disperger may preferably also lead to an at least partial deactivation of the UBC fiber fraction.

The dewatered UBC fiber fraction is subjected to a deactivation method to obtain a purified UBC fiber fraction. The term “deactivation” as used herein refers to microbial deactivation, i.e. a method or treatment which reduces the microbial activity or microbial load of the UBC fiber fraction. The deactivation method kills or deactivates microorganisms and other potential pathogens present in the UBC fiber fraction. The deactivation method may lead to a complete sterilization or a partial deactivation, i.e. a disinfection or a sanitization, of the fiber fraction.

The deactivation preferably reduces the microbial actvity of the UBC fiber fraction by at least 30%, preferably at least 40%, at least 50%, or at least 60%, such as in the range of 60-100%. Preferably, the deactivation method reduces the activity of microorganisms and other potential pathogens present in the UBC fiber fraction to a level which is normally accepted for fibers for use in food or beverage packaging substrates and laminates. The deactivated purified UBC fiber fraction has suitable chemical purity, suitable biological purity, and suitable mechanical properties for being reused in food or beverage packaging substrates and laminates.

In some embodiments, the deactivation method comprises heat deactivation, chemical deactivation, and/or irradiation deactivation. The heat deactivation may for example be selected from the group consisting of steam deactivation and dry heat deactivation. The chemical deactivation may for example be selected from the group consisting of ethylene oxide, nitrogen dioxide, ozone, glutaraldehyde and formaldehyde, hydrogen peroxide, and peracetic acid deactivation. The irradiation deactivation may for example be selected from the group consisting of non-ionizing radiation deactivation, and ionizing radiation deactivation. The deactivation method may also comprise a combination of two or more deactivation techniques.

In some embodiments the deactivation method is performed using chemicals conventionally used for bleaching of fibers for use in paper and paperboard. Deactivation may for example be performed using hydrogen peroxide or ozone. Such deactivation using chemicals conventionally used for bleaching of fibers may be advantageous as it may also lead to an at least partial bleaching of the UBC fiber fraction.

In some embodiments, wherein the deactivation method involves elevated temperature the heat treatment and the deactivation method may be combined. For example, deactivation by autoclaving at 121 °C will also constitute a heat treatment of the UBC fiber fraction. As another example, heat treatment in a disperger at a temperature leading to deactivation of the fiber fraction may also constitute a deactivation method.

The purified UBC fiber fraction obtained according to the inventive method is preferably suitable for demanding end uses such as for direct or indirect food contact. The resulting purified UBC fiber fraction obtained in step (g) is suitable for being reused in food or beverage packaging substrates and laminates. Although purified UBC fiber fraction may advantageously be reused in food or beverage packaging substrates and laminates, it is understood that the fiber fraction may also be reused in other types of products, such as in liner or tissue.

In some embodiments, the purified UBC fiber fraction in step (g) comprises at least 96 wt% cellulose fiber, preferably at least 98 wt% cellulose fiber, based on dry weight.

In some embodiments, the purified UBC fiber fraction in step (g) has Schopper- Riegler (SR) value in the range of 15-35, preferably in the range of 18-30, as determined by standard ISO 5267-1.

In some embodiments, the purified UBC fiber fraction in step (g) has water retention value (WRV) in the range of 110-200%, preferably in the range of 120- 180%, and more preferably in the range of 125-175% as determined by standard ISO 23714.

In some embodiments, the purified UBC fiber fraction in step (g) has a content of “Fines A” as measured using an FS5 optical fiber analyzer (Valmet) of less than 20 %, preferably less than 17 %, and more preferably less than 15 %.

In some embodiments, the purified UBC fiber fraction in step (g) has a Kappa number above 5, preferably above 10, and more preferably above 20, as determined according to standard ISO 302:2015. Purified UBC fiber fractions obtained from some types of sources, e.g. sources containing mechanical pulp, may also have significantly higher Kappa numbers, such as above 30 or above 40 as determined according to standard ISO 302:2015.

In some embodiments, the purified UBC fiber fraction in step (g) comprises less than 0.5 wt% plastic, preferably less than 0.1 wt% plastic, based on dry weight. In some embodiments, the purified UBC fiber fraction in step (g) comprises less than 0.5 wt% aluminum, preferably less than 0.1 wt% aluminum, based on dry weight.

In some embodiments, the purified UBC fiber fraction in step (g) comprises less than 0.1 wt% OBA, preferably less than 0.05 wt% OBA, based on dry weight.

In some embodiments, the purified UBC fiber fraction in step (g) comprises less than 50 mg/kg mineral oil saturated hydrocarbons (MOSH), preferably less than 20 mg/kg MOSH, based on dry weight.

In some embodiments, the purified UBC fiber fraction in step (g) comprises less than 50 mg/kg mineral oil aromatic hydrocarbons (MOAH), preferably less than 20 mg/kg MOAH, based on dry weight.

In some embodiments, the purified UBC fiber fraction in step (g) comprises less than 5000 mg/kg extractives, preferably less than 4000 mg/kg extractives, based on dry weight.

In some embodiments, the purified UBC fiber fraction in step (g) comprises less than 800 mg/kg unsaturated fatty acids, preferably less than 600 mg/kg unsaturated fatty acids, based on dry weight.

In some embodiments, the purified UBC fiber fraction in step (g) comprises less than 200 mg/kg resin acids, preferably less than 100 mg/kg resin acids, based on dry weight.

The amounts of extractives, unsaturated fatty acids, and resin acids were determined using the SCAN-CM 49 method with acidification of pulp to pH < 3 using acetic acid. Extraction was made by ASE (Accelerated Solvent Extraction) with acetone at temperature of 100 °C, pressure 2000 psi, and 2 cycles. The extracts were analyzed with GC-FID and then calculated against internal standards. In some embodiments, the purified UBC fiber fraction in step (g) has an ash content (525 °C) below 2 % and/or and an ash content (925 °C) below 1 %. Purified UBC fiber fractions obtained from some types of sources, e.g. from sources containing mineral or pigment coated carton, may also have significantly higher ash contents.

Preferably, at least 99 wt% more preferably at least 99.5 wt%, and most more preferably at least 99.9 wt% of the purified UBC fiber fraction obtained in step (g) can be identified by chemical analysis.

In some embodiments, the purified UBC fiber fraction obtained in step (g) is mixed with non-UBC fibers obtained from a chemical pulp, chemimechanical pulp (CMP), chemi-thermomechanical pulp (CTMP), high-temperature chemi- thermomechanical pulp (HT-CTMP), thermomechanical pulp (TMP), or broke. The fibers may be softwood fibers, hardwood fibers or non-wood fibers and may be bleached or unbleached.

In some embodiments, the purified UBC fiber fraction obtained in step (g) is corefined with non-UBC fibers obtained from a chemical pulp, CMP, CTMP, HT- CTMP, TMP, or broke.

According to a second aspect illustrated herein, there is provided a paper or paperboard product comprising a purified UBC fiber fraction obtained according to the method of the first aspect. In a preferred embodiment the paper or paperboard product is a food or beverage packaging substrates or laminate. In some embodiments, the paper or paperboard product is a liquid packaging board (LPB).

While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention should not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Brief description of the drawings

Fig. 1 is a diagram showing the Schopper Riegler value plotted versus the applied specific refining energy for unrefined and refined recycled UBC pulps.

Fig. 2 is a diagram showing the Schopper Riegler value plotted versus water retention value, WRV for unrefined and refined recycled UBC pulps.

Fig. 3 is a diagram showing tensile index plotted versus sheet density for unrefined and refined recycled UBC pulps.

Fig. 4 is a diagram showing tear index plotted versus sheet density for unrefined and refined recycled UBC pulps.

Examples

Example 1 - Preparation of raw UBC pulp

Collected post-consumer UBC starting material was subjected to a polymer and aluminum film separation method to obtain a polymer and aluminum fraction and a fiber fraction. The UBC was treated with water in a drum pulper (drum speed 10.7 U/min) for 25 minutes at about 50 °C and at a consistency of ca 18-20 wt%. The polymer-aluminum fraction was separated from the UBC and the remaining pulp is denoted here as Raw UBC pulp (1 ). The screening drum was equipped with 8 mm holes. The polymer and aluminum fraction constituted about 30-35 wt% of the dry weight of the UBC starting material. The fiber composition of the raw UBC pulp was as follows:

Bleached softwood kraft: 12 wt%

Unbleached softwood kraft: 25 wt%

Unbleached hardwood kraft: 20 wt%

Softwood CTMP: 33 wt%

Hardwood CTMP: 10 wt% The results of fiber and water analysis of the raw UBC pulp, denoted as sample (1 ) are shown in Tables 1 , 2 and 3.

The amount of extractives in this pulp sample was 13900 mg/kg (acetone extract), whereas the amount of unsaturated fatty acids (free and bound) were 2365 mg/kg. The amount of resin acids were 511 mg/kg, whereof free sterols were 49 mg/kg and bound sterols were 37 mg/kg.

The pH of the filtrate was 6.74, the amount of suspended solids was 33 mg/l and BOD after 5 days was 500 mg/l and COD was 820 mg/l. Phosphorous content and total nitrogen content of the filtrate were 2.1 mg/l and 26 mg/l, respectively.

Example 2 - Coarse screening of Raw UBC

The raw UBC pulp prepared in Example 1 was then diluted and subjected to a coarse screening at a consistency of 1 .6 wt%. The screener had a step rotor alongside the contour-hole screen basket so that large flat contaminants were efficiently removed (rotor speed 730 m/min). The holes in the screen were 1 .6 mm in diameter. The accepted stream (output, consistency 1 .4 wt%) was then collected and analysed. The reject (reject rate 14 wt%), was subjected to another screening and deflaking unit having screening holes of 2.4 mm. The accept was then collected and used as the output stream, whereas the reject was subjected to a reject sorter having 2.4 mm holes in the screens (Reject sorter, rotor speed 1600 m/min, consistency 2.2 wt%, dilution water 50 L/min). Temperature of the obtained accept flows (consistency 1 .4 wt%) were about 37 °C. The output stream, denoted as sample (2), was analyzed and the results are presented in Tables 1-3.

Example 3 - Fine screening and washing

The output stream obtained in example 2 was diluted to a consistency of 1 wt% with hot water (68 °C) and then subjected to high-speed washing/dewatering and fractionation by feeding the pulp suspension by wire tension around a smooth roll in a belt-type washer. The consistency of the pulp after washing and drainage was about 12 wt% and the temperature of the pulp was about 60 °C. Washing/dewatering in the belt-type washer reduced the ash content of the fiber fraction by 49%. Basis weight of the dewatered fiber substrate was about 31 gsm.

The treated UBC was further subjected to a dilution step and then to fine screening using 2 forward screener cleaners (hydrocyclones) at a consistency of 1 .4 wt% (reject quantity 4.7 wt%, dilution water 60 l/min) and then a second forward cleaner step at a consistency of 1 .2 wt% (reject quantity 5.7 wt%, dilution water 65 l/min) and to 2 rotor screeners based on centrifugal screening principle (Multifoil rotor) operated in cascade mode at a consistency of 1 .3 wt% and then subjected to a thickener step (inlet consistency 1 .2 wt% and accept consistency 6.1 wt%. The accept had an ash content of 2.1 wt%). The temperature of the pulp was about 60-70 °C. The slit size in the screens was 0.15 mm. The obtained purified UBC pulp, denoted as sample (3), was analyzed and the results are presented in Tables 1 -3.

Example 4 - Thickening, heat dispersion and dewatering

The fine screened, washed and thickened material obtained in Example 3 was further fed to a screw press and heating screw and heater (inlet consistency 3.4 wt%, accept consistency 40 wt%, Screw speed 50 U/min) followed by a hot disperger operated at about 115 °C (rotor speed 1500 U/min, inlet consistency 35 wt%, gap 4.4 mm, accept consistency 10.5 wt%). After the disperger, the consistency of the pulp was 10.5 wt%. A dilution and washing at low consistency were performed (with high-speed washing/dewatering unit) before dewatering in a screw press to a consistency of about 30 wt%.

The washed and screened material denoted as sample (4), was analyzed and the results are presented in Tables 1 -3. The results showed that a significant amount of extractives could be removed compared to the reference sample 1 (Raw UBC pulp). The amounts of extractives in this pulp sample was 3200 mg/kg (acetone extract), whereas the amount of unsaturated fatty acids (free and bound) were 591 mg/kg. The amount of resin acids was 62 mg/kg, whereof the amounts of free and bound sterols were to 15 and 8 mg/kg, respectively. The pH of the filtrate was 8.4, the amount of suspended solids was 16 mg/l and BOD after 5 days was 13 mg/l and COD was 44 mg/l. Phosphorous content and total nitrogen content of the filtrate were 0.7 mg/l and <1 mg/l, respectively.

Example 5 - Heating and high consistency deactivation

The material obtained in Example 4 was further subjected to a screening press and heating screen operated at T > 80 °C and further to a high consistency disperger, also operating at higher temperature. The purpose was to further dewater the pulp and to deactivate microbial activity at higher consistency. After the high consistency disperger, the pulp was subjected to deactivation at high consistency with 3.3% peroxide and NaOH and Silicate at a temperature of ca 85 °C. The purpose of this treatment was to deactivate remaining microbial activity.

The obtained deactivated UBC pulp, denoted as sample (5), was analyzed and the results are presented in Tables 1-3. The results show that, e.g., the amounts of extractives could be further reduced, but also that the microbial activity is significantly reduced. The amounts of extractives in this pulp sample was 2500 mg/kg (acetone extract), whereas the amount of unsaturated fatty acids (free and bound) were 495 mg/kg. The amount of resin acids was 49 mg/kg, whereof free and bound sterols were reduced to 11 and 8 mg/kg, respectively.

Example 6 Comparative - UBC treatment in OCC plant

In this case, the collected UBC pulp was subjected to a drum pulper and fractionation based on a conventional OCC plant concept. The obtained UBC pulp, denoted as sample (6), was analyzed and the results are presented in Tables 1-2. The results show that the plastic content is relatively high and that also Al and Ca concentrations remains on a high level.

Example 7 Comparative - UBC treatment in OCC plant

Similar as Example 6, but the pulp was further treated in a hot disperger, which is designed and intended for treatment of OCC. The obtained UBC pulp, denoted as sample (7), was analyzed and the results are presented in Tables 1-2. A small improvement in fiber yield could be seen as well as a small reduction in plastic content. Compared to (6), a small improvement in the metal salts could be seen although these are still on a high level.

The solid content of this suspension was 7.6 wt%, the SR value was 33, and the WRV value was 163, which indicates a high drainage resistance.

Table 1

(dry matter basis. % (means wt%) Table 2 Microbology and cultivations (mirobes, spores, mould, yeast)

Table 3 Pulp and fiber properties

Example 8 - Manufacturing trial of a 3-ply liquid paperboard

The paperboard manufacturing tests were performed on a pilot machine based on Fourdrinier technology having 3 wires and 3 headboxes, following a press section, drying and surface sizing and calendering section and finally winding station. Starch was added as a ply bonding agent at an amount of 1 .8 gsm between the top and mid ply and between the mid and back ply.

The pulp mixtures and composition of the layers are shown in Table 4 and the test results for the obtained 3-ply board are shown in Table 5. The total grammage of the 3-ply board was 250 g/m². Targeted moisture content was 7.5%.

A trial point with raw UBC pulp was not performed due to high bacterial activity and unpleasant odor and high content of impurities. Instead, as a reference, a high kappa (brown) pulp was used in the mid ply together with broke (internal furnish, i.e. reused pulp).

Example 9 - High amount of pulp from UBC in mid-ply

The purified UBC pulp obtained in Example 4 was used in a paperboard manufacturing trial of a 3-ply liquid paperboard. The purified UBC pulp was prepared at a solid content of 35 wt%. During the trials, no smell or odor were observed and bacterial activity for this particular pulp was normal for papermaking conditions.

The total amount of UBC pulp in the paperboard corresponded to 30% of the total board grammage (fiber), whereas the percentage in the mid ply was 53%.

A small reduction in some strength properties of the board could be seen, whereas for example Z-strength was still above the benchmark. The example confirms that high yield pulp or high kappa pulp can be replaced with pulp from UBC.

Example 10 - Low amount of pulp from UBC in mid-ply

In this case, the mid-ply composition was changed so that the UBC pulp was mixed in lower amount and with higher content of high yield pulp than in the previous example. The total amount of pulp from UBC in the board was about 15%. The example confirms that high yield pulp or high kappa pulp can be replaced with pulp from UBC.

Example 11 - High amount of pulp from UBC, highly refined

In this case, more highly refined pulp from UBC was added to mid ply (53%) together with broke and high yield pulp. This amount corresponded to the use of 30% pulp from UBC in the whole board structure. Despite the high amount of UBC pulp, no effect on optical properties or mechanical properties were seen, see Table II. In fact, a significant improvement in the Z-strength was obtained.

Example 12 - Low amount of pulp from UBC, highly refined

In this case, the mid-ply composition was changed so that the highly refined pulp from UBC was mixed in lower amount and with higher content of high yield pulp than in the previous example. The total amount of pulp from UBC in the board was about 15%. This example confirms that the UBC pulp can be used with higher content of high yield pulp and it actually improves some strength properties such as Scott bond and Z-strength. Table 4

Table 5

Example 13 - Effect of washing and refining on strength properties of the treated LIBC pulp

The UBC pulps obtained from Examples 1 , 4 and 5 were used as starting material. Three samples of each pulp were prepared, one was unrefined and two were subjected to two different levels of refining in a Voith LR40 refiner (consistency 4%, fillings 3-1 , 0-60C, specific edge load 2.5 J/m). 160 gsm sheets of each sample pulps were prepared according to a standard procedure, and the strength and physical properties of the sheets were examined. The results are presented in the diagrams in Fig. 1-4. In the diagrams, “RAW UBC” refers to the UBC pulp obtained from Example 1 , “UBC + WT” refers to the UBC pulp obtained from Example 4, and “UBC WB” refers to the UBC pulp obtained from Example 5.

Although impurities and fines are removed during the extensive purification and thermal treatment of the UBC pulps obtained from Examples 4 and 5, the results surprisingly show that strength properties of the recycled and purified pulps can be maintained or improved.

Unless specified otherwise, the following parameters were measured according to the specified standard methods: Dry matter content: ISO 638

WRV 100 mesh: ISO 23714

Fiber length Lc(l) FS5 ISO: ISO 16065

Drainability (SR): ISO 5267-1 pH: DIN 38404-05:2009-7

Suspended solids: DIN EN 872:2005-04

BOD: DIN EN 1899-1 :1998-05

COD: DIN 38409-H41/SFS 5504:1988

Total Phosphorus: DIN EN ISO 11885:2009-09 Total Nitrogen: DIN EN 25663:1993-11

Claims

32 CLAIMS

1 . A method for manufacturing a purified fiber fraction from used beverage carton (UBC), said method comprising the steps: a) subjecting a UBC starting material to a polymer and aluminum film separation method to obtain a UBC polymer and aluminum fraction and a raw UBC fiber fraction; b) optionally subjecting the raw UBC fiber fraction to a coarse screening method to remove coarse particles; c) subjecting the raw UBC fiber fraction to a fine screening method to remove cellulose fines and fine particulate contaminants, wherein the fine screening method comprises at least one fine screening step and at least one dilution step; d) optionally subjecting the fine screened UBC fiber fraction to a bleaching method; e) subjecting the fine screened, and optionally bleached, UBC fiber fraction to an electro-osmosis method to remove further contaminants; f) optionally subjecting the fine screened, and optionally bleached, UBC fiber fraction to a dewatering method to a consistency of at least 20 wt%; and g) subjecting the optionally dewatered UBC fiber fraction to a deactivation method to obtain a purified UBC fiber fraction.

2. The method according to claim 1 , wherein the UBC starting material in step (a) comprises at least 15 wt% plastic and at least 0.3 wt% aluminum or aluminum compounds, preferably at least 20 wt% plastic and at least 1 wt% aluminum or aluminum compounds, based on dry weight.

3. The method according to any one of the preceding claims, wherein the UBC starting material in step (a) comprises less than 1 wt% optical brightening agent (OBA).

4. The method according to any one of the preceding claims, wherein the raw UBC fiber fraction in step (a) comprises at least 90 wt% cellulose fiber, preferably at least 95 wt% cellulose fiber, based on dry weight. 33

5. The method according to any one of the preceding claims, wherein the purified UBC fiber fraction in step (g) has a Schopper-Riegler (SR) value in the range of 15-35, preferably in the range of 18-30, as determined by standard ISO 5267-1 .

6. The method according to any one of the preceding claims, wherein the purified UBC fiber fraction in step (g) has a water retention value (WRV) in the range of 110-200%, preferably in the range of 120-180%, and more preferably in the range of 125-175% as determined by standard ISO 23714.

7. The method according to any one of the preceding claims, wherein the purified UBC fiber fraction in step (g) comprises at least 96 wt% cellulose fiber, preferably at least 98 wt% cellulose fiber, based on dry weight.

8. The method according to any one of the preceding claims, wherein the purified UBC fiber fraction in step (g) comprises less than 0.5 wt% plastic, preferably less than 0.1 wt% plastic, based on dry weight.

9. The method according to any one of the preceding claims, wherein the purified UBC fiber fraction in step (g) comprises less than 0.5 wt% aluminum, preferably less than 0.1 wt% aluminum, based on dry weight.

10. The method according to any one of the preceding claims, wherein the purified UBC fiber fraction in step (g) comprises less than 0.1 wt% OBA, preferably less than 0.05 wt% OBA, based on dry weight.

11 . The method according to any one of the preceding claims, wherein the purified UBC fiber fraction in step (g) has an ash content (525 °C) below 2 % and/or and an ash content (925 °C) below 1 %.

12. The method according to any one of the preceding claims, wherein the fine screening method of step (c) includes at least two, preferably at least three, screening steps.

13. The method according to any one of the preceding claims, wherein the fine screening method of step (c) includes at least two, preferably at least three, dilution steps.

14. The method according to any one of the preceding claims, wherein the fine screening steps of step (c) are repeated in sequence at least two times, preferably at least three times.

15. The method according to any one of the preceding claims, wherein the fine screening method of step (c) removes 0.1-5 wt% of the solid content of the raw UBC fiber fraction.

16. The method according to any one of the preceding claims, wherein the electro-osmosis method in step (e) leads to dewatering of the UBC fiber fraction.

17. The method according to any one of the preceding claims, wherein the electro-osmosis method in step (e) leads to dewatering of the UBC fiber fraction to a consistency of at least 20 wt%.

18. The method according to any one of the preceding claims, wherein the UBC fiber fraction in step (f) is dewatered to a consistency of at least 30 wt%, preferably at least 40 wt%.

19. The method according to any one of the preceding claims, wherein the UBC fiber fraction is subjected to drying at elevated temperature to a consistency of at least 70 wt%, preferably at least 80 wt%, and more preferably at least 90 wt%, before or during or after being subjected to the deactivation method.

20. The method according to claim 19, wherein the drying at elevated temperature leads to hornification of the UBC fiber fraction.

21 . The method according to any one of the preceding claims, wherein the deactivation method of step (g) comprises heat deactivation, chemical deactivation, and/or irradiation deactivation.