Method for producing sanitary pulp

Abstract

A method for producing sanitary pulp is provided. Also provided are sanitary pulps, uses of sanitary pulps in the production of paper, boards, molded fibrous articles or other fiber-based articles comprising the sanitary pulps.

Description

Technical Field

[0001] This disclosure generally relates to methods for producing hygienized pulp, and additionally to hygienized pulp. Background Technology

[0002] This section provides useful background information, but does not acknowledge that any technology described herein represents prior art.

[0003] Currently, the most common hygienic board grades used for food packaging (folding board boxes, FBB, and liquid packaging boards, LPB) are produced from virgin fibers. Examples of such packaging include food service items, beverage packaging, beverage service items, cargo packaging, cargo service items, and packaged items such as oven-safe trays, microwave-safe trays, clamshell boxes, other food containers, soup cups, fresh meat and poultry trays, plates, and cup lids.

[0004] Sustainability discussions have sparked growing interest among consumers and packaging manufacturers in the use of recycled fibers.

[0005] Recycled fibrous materials typically contain high levels of bacteria and bacterial endospores. Fiber materials collected from consumer and industrial sources for recycling often contain contaminants such as food or oil residues, which provide an excellent culture medium for bacterial growth. Even recycled fibrous materials with a relatively clean appearance (such as collected office waste paper) often contain high levels of endospores because endospore levels are not actively monitored in the production of non-hygienic / non-food grade packaging paper or board. Furthermore, collected fibrous materials are often packaged and stored under dirty, damp, and / or warm conditions, which increase the risk of significant bacterial growth. Therefore, fiber suspensions produced from recycled fibrous materials typically contain high levels of bacteria and bacterial contaminants in the form of bacterial endospores.

[0006] If paper or board products are intended for use in food or beverage packaging, the permissible amount of bacterial endospores in the final paper and board products is strictly limited to avoid potential contamination of the packaging materials. These limitations result in the practical absence of recycled fiber materials in hygienic paper and board products designed for food and beverage packaging.

[0007] WO2022112663A1 relates to a method for producing paper, board, tissue paper, etc. In this method, bacterial endospores are reduced in an aqueous fiber suspension containing recycled cellulose fibers having an initial endospore content of ≥10,000 CFU / ml, which is reduced to ≤1000 CFU / ml by adjusting the oxidation-reduction potential (ORP) of the fiber suspension to ≥200 mV and the pH to an acidic value with a first oxidant, followed by introducing a certain amount of performic acid as a second oxidant into the fiber suspension. The treated fiber suspension is further processed using chemicals such as retention agents, internal sizing agents, wet strength and / or dry strength agents commonly used in the manufacture of paper, board, tissue paper, etc.

[0008] There is a need for effective methods to reduce the amount of bacterial endospores in aqueous fiber suspensions containing cellulose fibers (such as recycled cellulose fibers) in order to produce sanitary pulp products in a simpler way. Summary of the Invention

[0009] The following is a simplified overview of the features disclosed herein to provide a basic understanding of some exemplary aspects of the invention. This overview is not a comprehensive summary of the invention. It is not intended to identify key / critical elements of the invention or to define the scope of the invention. Its sole purpose is to present some of the concepts disclosed herein in a simplified form as a prelude to a more detailed description.

[0010] Using the method according to the invention, dried sanitary recycled pulp can be produced in one production line. Then, on another production line (e.g., for the production of sanitary packaging boards), functional chemicals (such as strength chemicals and hydrophobic chemicals) can be added to the sanitary pulp to obtain the desired functional properties of the final packaging board. Pulp made from virgin fibers can be used with sanitary recycled pulp in any suitable ratio.

[0011] In a first aspect, the present invention provides a method for producing sanitary pulp, the method comprising:

[0012] Provides cellulose fibers;

[0013] During the pulping stage, a fiber suspension containing cellulose fibers with a primary endospore content of >1000 CFU / ml is formed.

[0014] During the screening stage, impurities are removed from the fiber suspension to produce a purified fiber suspension.

[0015] The purified fiber suspension is subjected to a thickening stage; subsequently

[0016] (i) Adjust the pH of the fiber suspension to a pH value <6.5.

[0017] (ii) Adjust the oxidation-reduction potential (ORP) of the fiber suspension to an ORP value >200 mV using a first oxidizing agent.

[0018] (iii) A certain amount of performic acid is introduced into the fiber suspension as a second oxidant to reduce the amount of endospores in the fiber suspension.

[0019] A paper web in which a fiber suspension is formed on a wire; and

[0020] The paper web is pressed and dried to obtain dried pulp with a bacterial endospore count of <1000 CFU / g, preferably <50 CFU / g.

[0021] The method essentially does not use functional chemicals, such as strength chemicals and hydrophobic chemicals, and preferably does not use functional chemicals, such as strength chemicals and hydrophobic chemicals.

[0022] In a second aspect, the present invention provides sanitary pulp produced using the method of the present invention.

[0023] In a third aspect, the present invention provides the use of sanitary pulp produced by the method of the present invention, or sanitary pulp of the present invention, for the production of paper, board, molded fiber-based articles or other fiber-based articles.

[0024] In a fourth aspect, the present invention provides paper, board, molded fiber-based articles or other fiber-based articles comprising sanitary pulp produced by the method of the present invention or sanitary pulp of the present invention.

[0025] Surprisingly, it has been found that, using the method of the present invention, sanitary pulp (such as recycled pulp) can also be produced under acidic and high-conductivity process conditions. This method does not require the use of any typical functional chemicals (such as strength chemicals and hydrophobic chemicals, which are typically used to obtain the desired functions of off-the-shelf packaging boards), thereby allowing sanitary pulp (such as recycled pulp) to be produced also under acidic and high-conductivity process conditions.

[0026] The advantage of this invention is that, instead of expensive and requiring high doses of mild organic acids (such as citric acid), the process pH can be adjusted with a cheaper strong acid, with expected lower consumption compared to organic acids.

[0027] Furthermore, centralized manufacturing of toilet pulp (such as recycled toilet pulp) allows for better management of impurities. The pulping and cleaning stages remove impurities such as plastics, polystyrene foam, tape, glass, sand, metal, and other insoluble impurities. These dirty process stages are performed in the first section of the first production line and do not interfere with hygienic operating practices in the second production line that produces the final packaging paper or board. Additionally, undesirable trace chemicals may be present in the recycled fiber raw material and are soluble in process water. These can be removed in the first production line (e.g., in several thickening stages) before forming the final dried toilet pulp, which is then sent to the second production line.

[0028] The purpose or objective of the method of this invention is not to target the functional properties of the final fiber-based product (such as the final board or paper product), but rather to surprisingly allow for the production of sanitary pulp (such as recycled sanitary pulp) in a simpler manner with less chemical consumption. The method of this invention is also more economical because it eliminates the need for functional chemicals.

[0029] Another advantage of the method of the present invention is that, by using the pulping, screening and thickening stages of the production line, followed by sanitizing steps (i), (ii) and (iii), the method of the present invention can utilize a typical production line originally designed for manufacturing linerboard (such as recycled linerboard).

[0030] In the manufacture of fiber-based products, sanitary pulp (such as sanitary recycled pulp produced by the method of the present invention) can be used as sanitary pulp.

[0031] The appended claims define the scope of protection. Attached Figure Description

[0032] Figure 1 A flowchart of a typical production line designed for manufacturing recycled cardboard is shown.

[0033] Figure 2 A flowchart is shown of an exemplary production line designed for producing sanitary pulp using the method according to the present invention. Detailed Implementation

[0034] In a first aspect, the present invention provides a method for producing sanitary pulp, the method comprising:

[0035] Provides cellulose fibers;

[0036] During the pulping stage, a fiber suspension containing cellulose fibers with a primary endophytic spore count of >1000 CFU / ml is formed.

[0037] During the screening stage, impurities are removed from the fiber suspension to produce a purified fiber suspension.

[0038] The purified fiber suspension is subjected to a thickening stage; subsequently

[0039] (i) Adjust the pH of the fiber suspension to a pH value <6.5.

[0040] (ii) Adjust the oxidation-reduction potential (ORP) of the fiber suspension to an ORP value >200 mV using a first oxidizing agent.

[0041] (iii) A certain amount of performic acid is introduced into the fiber suspension as a second oxidant to reduce the amount of endospores in the fiber suspension.

[0042] Paper webs that form fiber suspensions on the web; and

[0043] The paper web is pressed and dried to obtain dried pulp with a bacterial endospore count of <1000 CFU / g, preferably <50 CFU / g.

[0044] The method essentially does not use functional chemicals, such as strength chemicals and hydrophobic chemicals, and preferably does not use functional chemicals, such as strength chemicals and hydrophobic chemicals.

[0045] This method essentially does not use, and preferably does not use, functional chemicals, i.e., reagents that provide functional properties or are used to adjust the functional properties of the product (paper or board), such as strength chemicals (strength agents) and hydrophobic chemicals (hydrophobic agents).

[0046] In one embodiment, during the thickening stage, the consistency of the fiber suspension is adjusted to 1-30%, preferably 4-20%, more preferably 4-12%, or even more preferably 4-10%.

[0047] In one implementation, impurities are removed in the pulping section, in the thickening stage, in the pressing section, and / or from the process water via a membrane cleaning system.

[0048] In one embodiment, a specific amount of process chemicals (i.e., agents for auxiliary processes, such as defoamers and retainers) is preferably added to the process in the mixing tank, the pulping tank, or in a short loop where the wet fiber web is formed in the headbox, to remove excess water in the wire section and collect it in the wire silo for recycling. The amount of process chemicals can be selected to achieve predetermined and / or desired effects.

[0049] In one embodiment, a certain amount of biocide is added to the method, preferably to the spray water of the method. The amount of biocide can be selected to obtain the predetermined and / or desired effect.

[0050] In one implementation, pH and ORP are monitored and measured in steps (i) and (ii), preferably in online manner.

[0051] In one implementation, steps (i), (ii), and (iii) are performed during the thickening stage.

[0052] In one embodiment, steps (i), (ii), and (iii) are performed before or after the thermal disperser. In another embodiment, steps (i) and (ii) are performed before the thermal disperser, and step (iii) is performed after the thermal disperser.

[0053] In one embodiment, the dryness of the dried pulp is at least 85%, preferably at least 87%, more preferably 87%-97%, and most preferably 87%-93%.

[0054] In the context of this invention, the term "oxidation-reduction potential" (abbreviated as ORP) refers to the oxidation or reduction potential of an aqueous fiber suspension. The ORP value of an aqueous fiber suspension can be determined by using a chemically inert electrode immersed in the suspension and measuring its potential relative to a reference electrode. Several commercial sensors are available for measuring ORP values.

[0055] In the context of this invention, the term "bacterial endospore" is understood to refer to a dormant, non-reproductive structure formed by bacteria. Bacterial endospores contain the bacteria's DNA and a portion of its cytoplasm enclosed by a protective outer covering. Bacterial endospores can germinate under favorable conditions to a metabolically active state, i.e., a vegetative state. According to one embodiment of the invention, the method of the invention is used to reduce the amount of bacterial endospores, such as those of the genera *Bacillus*, *Bacillus brevis*, and / or *Bacillus* morphologica*. These genera are known to grow under the process conditions of paper, board, and tissue paper machines, etc. These bacterial genera are capable of producing heat-resistant endospores that are resistant to the heat of the drying section used in processes producing cellulosic fiber paper webs (such as paper, board, tissue paper, etc.).

[0056] The fiber suspension comprises a liquid phase and a solid phase, the liquid phase typically being water, and the solid phase comprising at least cellulose fibers and optionally inorganic particles suspended in the liquid phase. In the method of the invention, the initial aqueous fiber suspension subjected to bacterial endospore reduction treatment in steps (i), (ii), and (iii) comprises cellulose fibers, such as recycled cellulose fibers, and has an initial bacterial endospore content of at least 1000 CFU / ml, typically at least 5000 CFU / ml, more typically at least 10000 CFU / ml. The fiber suspension comprises an aqueous liquid phase and a solid phase, the solid phase comprising recycled fibers. The cellulose fibers in the fiber suspension may be bleached, unbleached, or a mixture of bleached and unbleached fibers, such as recycled fibers. The cellulose fibers in the fiber suspension are non-synthetic natural fibers originally obtained by any mechanical or chemical pulping method or by any combination of mechanical and chemical pulping methods. Cellulose fibers can be wood fibers and / or non-wood fibers, preferably wood fibers, such as hardwood, softwood, or any combination thereof. Recycled fibers can be derived from any available recycled industrial and / or consumer fiber materials. Recycled fibers can be derived from, for example, old corrugated cardboard boxes (OCC), office waste paper, mixed office waste paper, sorted office waste paper, or any mixture thereof. Recycled fibers can be derived from, for example, recycled pre-consumer fiber materials and / or recycled post-consumer fiber materials. Recycled fibers can even be secondary fibers from the production processes of paper, board, tissue paper, etc., such as broke paper.

[0057] In one embodiment, the cellulose fiber comprises recycled cellulose fiber. In another embodiment, the cellulose fiber consists of recycled cellulose fiber.

[0058] In one embodiment, the cellulose fibers comprise natural cellulose or lignocellulose fibers derived from molded pulp products.

[0059] In one embodiment, the cellulose fiber comprises recycled cellulose fiber, natural cellulose or lignocellulose fiber derived from molded pulp products, or a mixture thereof.

[0060] Molded pulp products are primarily composed of cellulose, lignin, and hemicellulose. Natural fibers can be derived from a variety of resources, such as wood obtained through chemical and mechanical pulping methods, recycled fibers, agricultural biomass waste such as canola straw, wheat straw, rice straw, hemp fiber, bagasse and bamboo fiber, sugar beets and mixtures thereof.

[0061] In one embodiment, the recycled cellulose fibers are sorted recycled cellulose fibers, preferably double-sorted recycled cellulose fibers.

[0062] In one embodiment, the recycled cellulose fibers include used corrugated cardboard boxes, sorted office waste paper, mixed waste paper and board, mixed office waste paper, mixed newspapers and magazines, used kraft paper, used corrugated kraft paper, used kraft paper bags, used beverage cartons, unprinted bleached sulfate board, white mechanical pulp-based coated and uncoated paper, liquid board packaging, sorted office paper, new kraft paper, new carrier kraft paper, unsold magazines and newspapers, unused corrugated kraft paper, unused corrugated material, unused kraft paper bags, recycled pre-consumer fiber materials, recycled post-consumer fiber materials, secondary fibers from paper, board, tissue paper, and other production processes, waste paper or mixtures thereof, preferably used corrugated cardboard boxes, unused corrugated material, used beverage cartons or mixtures thereof.

[0063] In one embodiment, the amount of recycled cellulose fibers, natural cellulose or lignocellulose fibers derived from molded pulp products, or mixtures thereof in the fiber suspension to be treated is at least 60% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, or at least 95% by weight, calculated from the total dry fiber weight of the suspension.

[0064] Aqueous fiber suspensions typically have negative initial oxidation-reduction (ORP) values, for example, in the range of -500 mV to -50 mV, more typically -400 mV to -100 mV, or even more typically -300 mV to -200 mV.

[0065] In one embodiment, the fiber suspension may contain inorganic particles, such as particles of calcium carbonate, kaolin, talc, gypsum, etc. These inorganic particles are typically derived from internal fillers, inorganic coatings, labels, adhesives, etc., and are already present in the collected fiber material for recycling. The amount of inorganic particles (given by the ash content of the cellulose fiber material used) can range from 5-30% by weight, typically 5-25% by weight or 10-20% by weight. Complete removal of inorganic particles from cellulose fiber (such as recycled fiber) material during the repulping process is generally difficult and / or uneconomical, meaning that typically at least some inorganic particles accompany the cellulose fiber material (such as recycled fiber) into the fiber suspension.

[0066] Fiber suspensions typically contain at least some dissolved carbonate ions.

[0067] The fiber suspension formed during the pulping stage contains hydrophobic contaminants such as plastics, tape, and / or adhesive residues. These contaminants, along with other impurities, large particles, etc., are removed in one or more screening steps following the pulping stage, typically removing contaminants and / or impurities with a size greater than 200 micrometers.

[0068] The fiber suspension is typically subjected to fiber grading, in which the fibers are separated into at least long fiber fractions and short fiber fractions according to their length.

[0069] In one implementation, the pH of the fiber suspension is adjusted by introducing an acidifying agent into the fiber suspension.

[0070] In one embodiment, the pH of the fiber suspension is adjusted to a pH value <6.5, preferably by introducing an acidifying agent into the fiber suspension. The pH of the fiber suspension can be adjusted to a pH range of 4-6.5, preferably 4.5-6.5, more preferably 5-6.5, and even more preferably 5.5-6.3. The acidifying agent can be any chemical compound suitable for adjusting the pH of the fiber suspension to the desired level, such as polyaluminum chloride, alum, etc. The acidifying agent can be an organic acid (such as citric acid, formic acid, etc.), or an inorganic acid (such as hydrochloric acid, sulfuric acid, etc.), or a mixture of organic and / or inorganic acids. The acidifying agent can be an acidifying gas, such as carbon dioxide gas. When the acidifying agent is an acid in liquid form, it is added to the fiber suspension, and when the acidifying agent is in gaseous form (e.g., carbon dioxide gas), it is introduced into the fiber suspension. The acidifier is preferably introduced or added to the fiber suspension in an amount that adjusts the pH of the fiber suspension to the desired pH value without causing a significant increase in the conductivity of the fiber suspension. Effective mixing is advantageous when the acidifier is added to the fiber suspension.

[0071] The acidifier can be selected based on the properties of the fiber suspension to be treated, particularly its buffering capacity. For example, a fiber suspension with high buffering capacity (e.g., containing recycled fibers derived from sorted office waste and fiber suspensions with high calcium carbonate particle content) can be treated with an acidifier selected from the organic or inorganic acids or mixtures thereof to achieve an economically appropriate consumption of the acidifier and avoid large pH changes, which can lead to undesirable changes in the conductivity of the fiber suspension.

[0072] In a preferred embodiment, the conductivity of the fiber suspension does not change significantly during the reduction of bacterial endospores in the fiber suspension according to the method of the present invention. This means that the fiber suspension typically has an initial conductivity value in the range of 2-10 mS / cm, preferably 2-7 mS / cm, measured before pH and ORP adjustment and the introduction of performic acid, and a final conductivity value in the range of 2-10 mS / cm, preferably 3-7 mS / cm, measured after pH and ORP adjustment and the introduction of performic acid.

[0073] In one embodiment, the fiber suspension has a final conductivity value in the range of 2 mS / cm to 10 mS / cm, preferably 2 mS / cm to 7 mS / cm, measured after adjusting the pH and ORP values.

[0074] The oxidation-reduction potential (ORP) of the fiber suspension is adjusted to an ORP value >200 mV using a first oxidant (which is added to or introduced into the fiber suspension). Preferably, the ORP value of the fiber suspension can be adjusted to an ORP value >250 mV, more preferably >300 mV. It has been observed that when the ORP value of the fiber suspension is adjusted to a level >200 mV, performic acid can effectively eliminate and destroy bacterial endospores present in the fiber suspension.

[0075] In one embodiment, the ORP value of the fiber suspension can be adjusted to a range of +100 mV to +500 mV, preferably +200 mV to +400 mV, and more preferably +300 mV to +400 mV.

[0076] The first oxidant used to adjust the ORP value is different from performic acid; that is, the first oxidant is not performic acid. Preferably, the first oxidant used does not contain performic acid. Other organic peracids besides performic acid can be used as the first oxidant for adjusting the ORP value. However, preferably, the first oxidant can be hydrogen peroxide, H2O2, or percarbonate, preferably sodium percarbonate. Hydrogen peroxide and percarbonate are readily available on an industrial scale, and they can effectively adjust the ORP value of the fiber suspension to the desired level. The first oxidant can be considered a sacrificial treatment agent, by which performic acid consumption is kept as low as possible. The use of the first oxidant does provide an effective means of adjusting the ORP value to a level at which the full potential of performic acid can be realized.

[0077] In one embodiment, the first oxidant is H2O2 or percarbonate.

[0078] The first oxidant can provide the required ORP value for the fiber suspension containing cellulose fibers by introducing an amount into the fiber suspension.

[0079] In one embodiment, the first oxidant may be introduced into the fiber suspension in an amount of 300-1000 ppm, preferably 400-800 ppm, and more preferably 500-700 ppm, in grams of activator per m³. 3 The form of the fiber suspension is given.

[0080] Adding the first oxidant to the fiber suspension does not provide a bleaching effect. This means that the ISO brightness of the fiber suspension does not change significantly after the addition of the first oxidant. Typically, the change in ISO brightness of the fiber suspension (if any) is less than 5 ISO%, preferably less than 3 ISO%, more preferably less than 1 ISO%, as measured using standard ISO2470-1:2016.

[0081] In one embodiment, performic acid is introduced as a second oxidant, i.e., for the treated fiber suspension, performic acid is added to the fiber suspension in an amount that reduces the amount of bacterial endospores to <1000 CFU / ml, preferably <500 CFU / ml, more preferably <250 CFU / ml, even more preferably <150 CFU / ml, and sometimes even <100 CFU / ml. In one embodiment, performic acid may be introduced into the fiber suspension in an amount that reduces the amount of bacterial endospores to <50 CFU / ml, even to <30 CFU / ml, or even <10 CFU / ml.

[0082] In one embodiment, performic acid is introduced into the fiber suspension in an amount such that the amount of endospores in the final dried sanitary pulp is reduced to <1000 CFU / g, preferably to <50 CFU / g.

[0083] In one embodiment, formic acid may be introduced (i.e. added) into the fiber suspension in an amount of 50-500 ppm, preferably 100-400 ppm, more preferably 200-300 ppm, at a concentration of gram of surfactant per cubic meter. 3 The form of the fiber suspension is given. The amount of bacterial endospores can be determined using conventional techniques known to those skilled in the art.

[0084] Performic acid is introduced into the fiber suspension in the form of an aqueous solution. Performic acid can be prepared by mixing an aqueous solution of hydrogen peroxide with an aqueous solution of formic acid and an optional catalyst (e.g., sulfuric acid). Preferably, the aqueous performic acid solution is used as an equilibrium solution comprising performic acid, formic acid, water, hydrogen peroxide, and an optional catalyst. The performic acid solution typically has a concentration of at least 10% (by weight / volume), typically about 13.5% or 14% (by weight / volume) of performic acid.

[0085] Preferably, at elevated fiber suspension temperatures, performic acid can interact with bacterial endospores in the fiber suspension. In one embodiment, the temperature of the fiber suspension in steps (i), (ii), and (iii) is at least 20°C, such as 20-120°C, preferably at least 40°C, such as 40-50°C, more preferably at least 60°C, such as 60-100°C, and even more preferably at least 65°C, such as 65-100°C. The temperature of the fiber suspension in steps (i), (ii), and (iii) may preferably be <100°C, more preferably <85°C, and even more preferably <75°C. In particular, it is advantageous when the pH of the fiber suspension is adjusted to the range of 5.5-6.5, when performic acid is introduced into the fiber suspension in steps (i), (ii), and (iii), and / or when performic acid interacts with bacterial endospores, if the temperature of the fiber suspension is in the range of 30-100°C, preferably 30-99°C, more preferably 40-80°C, such as 40-50°C, or even more preferably 50-80°C. It has been observed that maximum endospore-destructive effect can be achieved in this manner. Assuming no theoretical constraints, the increased temperature when performic acid is introduced into the fiber suspension can further sensitize the bacterial endospores and make them susceptible to destruction. Advantageously, effective reduction or destruction of endospores has been achieved at fiber suspension temperatures below 100°C. This avoids the need for expensive and complex process equipment, such as pressurized hot steam treatment tanks.

[0086] The temperature of the fiber suspension can be raised to the desired value by heating it to the desired temperature in a separate process step. For example, the fiber suspension can be transferred to a separate tank, located after the pulper, preferably after the screening stage. In this separate tank, the fiber suspension can be heated to the desired temperature.

[0087] Preferably, the temperature of the fiber suspension is adjusted to the elevated temperature specified above, and then performic acid is introduced into the fiber suspension.

[0088] In one embodiment, after treating the fiber suspension with formic acid, at least a portion of the aqueous liquid phase of the fiber suspension is separated from the solid phase of the fiber suspension containing cellulose fibers, and the separated aqueous liquid phase is recycled back into the process and reused to form the initial fiber suspension. The separated aqueous phase typically contains a basic concentration of unconsumed first and / or second oxidants. This means that recycling the aqueous phase in the method provides the possibility of reducing the amount of the first and / or second oxidants required to adjust the ORP value to the desired level and to destroy or reduce bacterial endospores.

[0089] After the performic acid has interacted with the cellulose suspension and the amount of bacterial endospores in the cellulose suspension has decreased, the pH of the cellulose suspension can be adjusted (e.g., neutralized) to the desired value using a strong base (e.g., NaOH or sodium bisulfite), if necessary. Neutralization is typically performed after a suitable treatment or interaction time following the introduction of the performic acid. The treatment time required for the interaction between the performic acid and bacterial endospores can be, for example, 5-30 min, preferably 10-15 min.

[0090] Figure 1 A flowchart of an exemplary production line designed for manufacturing linerboard (such as recycled linerboard) is shown. Recycled cellulose fibers are subjected to a pulping stage (1) to form a fiber suspension containing cellulose fibers, and this fiber suspension is transferred to a pouring tank (2). Impurities are removed from the fiber suspension in a screening stage (3) to produce a purified fiber suspension. The purified fiber suspension is graded (4) into a suspension containing long fibers and a suspension containing short fibers, preferably subjected to thickening stages (5) and (15) respectively via disc filters. In thickening, the consistency of the fiber suspension increases, i.e., the fiber suspension is thickened to a predetermined consistency.

[0091] From the thickening stage (5, 15), the thickened suspension is (optionally) heated in a thermal disperser (6, 16) to manage the viscous hydrophobic compounds, such as those derived from recycled fiber materials. The fiber suspension is directed to a storage tower (7, 17), from which it is transferred at the desired mixing ratio to a mixing tank (8), and further to a pulping tank (9), and from there to a headbox (10). The headbox (10) distributes the fiber suspension onto a wire to form a wet fiber web, from which excess water is first removed in the wire section (11), then through a press section (12), and finally in a drying section (13) to dry the fiber web. Surface strength chemicals are then added to the dried web at a sizing press (20), resulting in a dried recycled facing board.

[0092] Fresh water can be introduced into the system, for example via cleaning sprayers for the wire, felt, and rolls at the wire section (11) and / or the press section (12). Water discharged from the wire section (11) and the press section (12) can be distributed for reuse, either directly after the pulping tank (9) or via water storage tanks (19, 14) to various locations in the process, including the pulper (1). Waste paper can be stored at a waste paper storage tower (18) from which it can be delivered to the mixing tank (8).

[0093] In the production of linerboard, functional chemicals (i.e., reagents that provide functional properties or reagents that are used to regulate the functional properties of recycled linerboard (such as strength chemicals (strength agents) and hydrophobic chemicals (hydrophobic agents)) are added to the wet end (i.e., the mixing tank (8) and the pulping tank (9)) and the dry end (i.e., the sizing press (20)).

[0094] Figure 2 A flowchart of an exemplary production line designed for producing sanitary pulp using the method according to the invention is shown. Cellulose fibers are subjected to a pulping stage (1) to form a fiber suspension containing cellulose fibers, and the fiber suspension is transferred to a pouring tank (2). Impurities are removed from the fiber suspension in a screening stage (3) to produce a purified fiber suspension. The purified fiber suspension is graded (4) into a suspension containing long fibers and a suspension containing short fibers, and these suspensions are preferably subjected to thickening stages (5) and (15) respectively through a disc filter. In the thickening stage, the consistency of the fiber suspension is adjusted to 1-30%, preferably 4-20%, more preferably 4-12%, and even more preferably 4-10%. After adjusting the consistency, the fiber suspension with high consistency is subjected to the treatments in steps (i), (ii), and (iii).

[0095] Following treatment, the treated fiber suspension is optionally heated in a thermal disperser (6, 16) to manage potential sticky hydrophobic compounds, such as those originating from cellulose materials (e.g., recycled cellulose materials). The fiber suspension is directed to a storage tower (7, 17), from which it is transferred at the desired mixing ratio to a mixing tank (8), and further to a pulping tank (9), and from there to a headbox (10). The headbox (10) distributes the fiber suspension onto a wire to form a wet fiber web, first removing excess water from the wet fiber web in a wire section (11), then passing it through a pressing section (12), and finally drying it in a drying section (13). After drying the web, dried sanitary pulp is obtained. In the process section beginning from the storage towers (7, 17), a certain amount of process chemicals (i.e., agents for auxiliary processes, such as defoamers and retainers or biocides) may be added to the process.

[0096] Fresh water can be introduced into the system, for example via cleaning sprayers for the wire, felt, and rolls at the wire section (11) and / or the press section (12). Water discharged from the wire section (11) and the press section (12) can be distributed for reuse, either directly after the pulping tank (9) or via water storage tanks (19, 14) to various locations in the process, including the pulper (1). Waste paper can be stored at a waste paper storage tower (18) from which it can be delivered to the mixing tank (8).

[0097] In the method according to the invention, no functional chemicals (such as strength agents and hydrophobic agents) are added in the wet end (i.e., the mixing tank (8) and the slurry tank (9)), preferably no functional chemicals are added, and no strength chemicals are applied on the drying plate after the drying section (13), preferably no strength chemicals are applied.

[0098] In a second aspect, the present invention provides sanitary pulp produced using the method of the present invention.

[0099] In one embodiment, the bacterial endospore count of the sanitary pulp is <1000 CFU / g dry pulp, preferably <50 CFU / g dry pulp.

[0100] In one embodiment, the dryness of the dried pulp is at least 85%, preferably at least 87%, more preferably 87%-97%, and most preferably 87%-93%.

[0101] In one embodiment, the sanitary pulp comprises sanitary recycled cellulose fibers, sanitary natural cellulose or lignocellulose fibers derived from molded pulp products, or mixtures thereof.

[0102] In one implementation, the toilet paper pulp is in the form of rolls, sheets, or sheet packs.

[0103] In a third aspect, the present invention provides the use of sanitary pulp produced by the method of the present invention, or sanitary pulp of the present invention, for the production of paper, board, molded fiber-based articles or other fiber-based articles in another production line.

[0104] In one embodiment, the sanitary pulp comprises sanitary recycled cellulose fibers, sanitary natural cellulose or lignocellulose fibers derived from molded pulp products, or mixtures thereof.

[0105] Toilet pulp can be used to produce any fiber-based product that requires sanitary fiber pulp. Toilet pulp can be used with virgin fibers in any suitable ratio.

[0106] In a fourth aspect, the present invention provides paper, board, molded fiber-based articles or other fiber-based articles comprising sanitary pulp produced by the method of the present invention or sanitary pulp of the present invention.

[0107] In one embodiment, the sanitary pulp comprises sanitary recycled cellulose fibers, sanitary natural cellulose or lignocellulose fibers derived from molded pulp products, or mixtures thereof.

[0108] Fiber-based products can be used for food packaging (folding trays, FBBs, and liquid packaging trays, LPBs). Examples of such packaging include food service items, beverage packaging, beverage service items, cargo packaging, cargo service items, and packaging items such as oven-safe trays, microwave-safe trays, clamshell boxes, other food containers, soup cups, fresh meat and poultry trays, plates, and cup lids.

[0109] Various implementation schemes have been presented. It should be understood that in this document, the words contain, include, and contain are used as open-ended expressions and are not intended to be exclusive.

[0110] The foregoing description has provided a comprehensive and informative account of the best mode of carrying out the invention as currently conceived by the inventors, through specific examples of implementation methods and embodiments. However, it will be apparent to those skilled in the art that the invention is not limited to the details of the foregoing embodiments, but may be implemented in other embodiments using equivalent means or in different combinations of embodiments without departing from the characteristics of the invention.

[0111] Furthermore, some features of the exemplary embodiments disclosed above can be used advantageously without the need for corresponding use of other features. Therefore, the foregoing description should be considered merely illustrative of the principles of the invention and not limiting of them. Thus, the scope of the invention is limited only by the appended claims.

Claims

1. A method for producing sanitary paper pulp, the method comprising: Provides cellulose fibers; During the pulping stage, a fiber suspension containing the cellulose fibers with an initial endophytic spore amount of >1000 CFU / ml is formed. During the screening stage, impurities are removed from the fiber suspension to produce a purified fiber suspension. The purified fiber suspension is subjected to a thickening stage; Subsequently (iv) Adjust the pH of the fiber suspension to a pH value < 6.

5. (v) Adjust the oxidation-reduction potential (ORP) of the fiber suspension to an ORP value >200 mV using a first oxidant. (vi) A certain amount of performic acid is introduced into the fiber suspension as a second oxidant to reduce the amount of endospores in the fiber suspension; The paper web on which the fiber suspension is formed, and The paper web is pressed and dried to obtain dried pulp with a bacterial endospore count of <1000 CFU / g, preferably <50 CFU / g. The method described herein does not use functional chemicals, such as strength chemicals and hydrophobic chemicals, and preferably does not use functional chemicals, such as strength chemicals and hydrophobic chemicals.

2. The method of claim 1, wherein the cellulose fiber comprises recycled cellulose fiber, natural cellulose or lignocellulose fiber derived from molded pulp products, or a mixture thereof.

3. The method according to claim 1 or 2, wherein during the thickening stage, the consistency of the fiber suspension is adjusted to 1-30%, preferably 4-20%, more preferably 4-12%, or even more preferably 4-10%.

4. The method according to any one of claims 1-3, wherein impurities are removed in the pulping section, in the thickening stage, in the pressing section, and / or from the process water by a membrane cleaning system.

5. The method according to any one of claims 1-4, wherein, A certain amount of process chemicals, such as defoamers, retainers and / or biocides, are added in the mixing tank, the pulping tank, or in the short loop where the wet fiber web is formed in the headbox to remove excess water in the wire section and collect it in the wire silo for recycling.

6. The method according to any one of claims 1-5, wherein the pH and the ORP are monitored and measured in steps (i) and (ii), preferably the pH and the ORP are monitored and measured online in steps (i) and (ii).

7. The method according to any one of claims 1-6, wherein steps (i), (ii) and (iii) are performed during the thickening stage.

8. The method according to any one of claims 1-7, wherein the dryness of the dried pulp is at least 85%, preferably at least 87%, more preferably 87%-97%, and most preferably 87%-93%.

9. The method according to any one of claims 1-8, wherein the fiber suspension comprises inorganic particles, such as calcium carbonate particles, and the pH of the fiber suspension is adjusted to a range of 5-6.5, more preferably 5.5-6.5, or even more preferably 6-6.

5.

10. The method according to any one of claims 1-9, wherein, The temperature of the fiber suspension in steps (i), (ii) and (iii) is at least 20°C, preferably at least 40°C, such as 40-50°C, more preferably at least 60°C, and even more preferably at least 65°C.

11. The method according to any one of claims 1-10, wherein the fiber suspension has a final conductivity value in the range of 2 mS / cm-10 mS / cm, preferably 3 mS / cm-7 mS / cm, measured after adjusting the pH and ORP values.

12. The method according to any one of claims 1-11, wherein the ORP value is adjusted to a range of +100 mV to +500 mV, preferably +200 mV to +400 mV, more preferably +300 mV to +400 mV.

13. Sanitary pulp produced by the method according to any one of claims 1-12.

14. Use of sanitary pulp produced by any one of claims 1-12 or sanitary pulp according to claim 13 for the production of paper, board, molded fiber-based articles or other fiber-based articles.

15. Paper, board, molded fiber-based articles or other fiber-based articles comprising sanitary pulp produced by the method according to any one of claims 1-12 or sanitary pulp according to claim 13.

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