WO2025032396A1

WO2025032396A1 - A method for manufacturing a cellulose pulp composition for a moldable cellulose fiber-based web

Info

Publication number: WO2025032396A1
Application number: PCT/IB2024/056646
Authority: WO
Inventors: Isto Heiskanen; Titta Lammi; Jari RÄSÄNEN; Teemu Karhu; Nina Miikki
Original assignee: Stora Enso Oyj
Current assignee: Stora Enso Oyj
Priority date: 2023-08-09
Filing date: 2024-07-08
Publication date: 2025-02-13
Anticipated expiration: 2026-02-09
Also published as: SE2330347A1; SE547210C2

Abstract

The present invention relates to a method for manufacturing a cellulose pulp composition for a moldable cellulose fiber-based web, said method comprising: a) providing a cellulose pulp composition comprising at least 50 wt% chemical or semi-chemical wood pulp based on dry weight, b) subjecting the cellulose pulp composition provided in step a) to low consistency (LC) refining at a consistency in the range of 1-7 wt% to an SR value in the range of 18-50 as determined by standard ISO 5267-1, c) subjecting the LC-refined cellulose pulp composition obtained in step b) to high consistency (HC) refining at a consistency in the range of 12-40 wt% with a refining energy of at least 150 kWh/t, and d) diluting the HC-refined cellulose pulp composition obtained in step c) to a consistency in the range of 0.1-10 wt%. The invention further relates to a method for manufacturing a moldable cellulose fiber-based web and a method for manufacturing a molded cellulose fiber-based product.

Description

A METHOD FOR MANUFACTURING A CELLULOSE PULP COMPOSITION FOR A MOLDABLE CELLULOSE FIBER-BASED WEB

Technical field

The present disclosure relates to methods for manufacturing cellulose pulp compositions for moldable cellulose fiber-based webs, to methods for manufacturing cellulose fiber-based webs, and to methods for manufacturing molded cellulose fiberbased products.

Paper based packaging materials, as renewable materials, have a growing market potential due to their sustainability. However, the development of new packaging concepts requires improvement in the mechanical properties of paper. High stretchability is one of these properties. Highly stretchable papers would have the potential to replace certain kinds of plastics used for forming packaging by three dimensional (3D) forming sheets into products and articles, for example deep drawing processes.

In general, the forming processes for paper-based materials can be divided into two main categories: sliding and fixed blank processes. In the forming process with sliding blank, forming proceeds due to the sliding of paper into the mold and lateral contraction of paper that causes microfolding of the paper. In the fixed blank process (e.g. deep drawing) paper is formed via straining of the paper.

Usually, the sliding blank process is used to produce molded products with a relatively high depth, while products produced using the fixed blank typically have significant limitations in depth. This is due to the fact that in the fixed blank process tensile deformation of paper prevails over compressive deformation. This means that only paper grades with high stretchability, high strength and post-forming stiffness are suitable for the fixed blank forming process. Moreover, fixed blank forming process yields molded products with smooth and even edges that enables the gastight sealing of formed products with barrier films. In contrast, the products produced in the sliding blank process have limitations in sealability due to microfolding/ wrinkling, which also causes shape instability and impaired visual appearance.

Formability of a paper-based material can be defined as the ability of a material to deform without breaking. However, formability is not a specific mechanical property, but can be regarded as a generic term for explaining how well the paper deforms during a particular forming process. Formability can for example be estimated on the basis of a 2D experimental test method that simulates the process conditions in a fixed blank thermoforming process as described by Vishtal & Retulainen, 2014 (Improving the stretchability, wet web and dry strength of paper by addition of agar, Nord Pulp Pap Res J, 29:434-443). In the fixed blank process, the formability is determined by the stretchability and tensile strength of the paper. As yet, the fixed blank forming process has not been widely applied in industry for paperboard.

Pulp fibers constitute the load-bearing components of paper. Kraft pulp fibers primarily consist of cellulose and hemicellulose. Cellulose is a crystalline, strong and stiff material with low stretchability making cellulosic fibers strong and stiff.

Different technologies and solutions have been proposed to improve the stretchability of paper.

Addition of chemicals such as thermoplastic polymers or fibers has been applied in order to improve the formability of the paper. However, there is a need to replace thermoplastic polymers or fibers with more sustainable materials.

Mechanical refining at high consistency has been shown to improve the stretchability potential of paper. However, the problem with most refining methods is that they result in fiber cutting and formation of significant amounts of fines. The fiber cutting and fines formation leads to reduced mechanical strength of the formed paper.

Paper substrates with improved stretchability might open up new possibilities in the preparation of molded products by fixed blank forming. There remains a need to find an industrially scalable and implementable solution for improving the 3D forming of fiber-based substrates on commercial machines, without having risks of cracking or pinhole formation. Therefore, there remains a need for new strategies for preparing paper and paperboard with improved stretchability.

Summary of the invention

It is an object of the present disclosure to alleviate at least some of the problems with cellulose fiber-based materials for use in manufacturing three dimensional molded cellulose fiber-based products, for example by fixed blank forming.

It is a further object of the present disclosure to provide a method for manufacturing a cellulose pulp composition useful for manufacturing a moldable cellulose fiberbased web with improved formability, i.e. improved stretchability and strength, or toughness.

It is a further object of the present disclosure to provide a method for manufacturing a cellulose pulp composition useful for manufacturing a moldable cellulose fiberbased web without using synthetic polymers.

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.

According to a first aspect illustrated herein, there is provided a method for manufacturing a cellulose pulp composition for a moldable cellulose fiber-based web, said method comprising: a) providing a cellulose pulp composition comprising at least 50 wt% chemical or semi-chemical wood pulp based on dry weight, b) subjecting the cellulose pulp composition provided in step a) to low consistency (LC) refining at a consistency in the range of 1-7 wt% to an SR value in the range of 18-50 as determined by standard ISO 5267-1 , c) subjecting the LC-refined cellulose pulp composition obtained in step b) to high consistency (HC) refining at a consistency in the range of 12-40 wt% with a refining energy of at least 150 kWh/t, and d) diluting the HC-refined cellulose pulp composition obtained in step c) to a consistency in the range of 0.1-10 wt%.

A pulp suspension with a high portion of curled fibers can be obtained by high consistency (HC) refining of a chemical or semi-chemical wood pulp. Mechanical refining of chemical or semi-chemical wood pulps at high consistency has been shown to improve the stretchability potential of paper formed from the pulps. HC refining produces less fines and fiber cutting than LC refining, but less fibrillation. Less fibrillation in HC refining gives lower mechanical strength and more curl compared to LC refining, in which a higher degree of fibrillation causes more fiber bonding. LC refining on the other hand straightens curled fibers, and due to the presence of more straight fibers and less curled fibers, tensile strength is improved by LC refining. The present invention is based on the realization that the HC refining is preferably preceded by low consistency (LC) refining of the chemical or semichemical wood pulp to an SR value in the range of 18-50, as determined by standard ISO 5267-1 . This produces fibers having both curl and surface fibrillation.

The cellulose pulp composition provided in a) comprises at least 50 wt% chemical or semi-chemical wood pulp based on dry weight. In some embodiments, the cellulose pulp composition provided in a) comprises at least 60 wt%, at least 70 wt%, at least 80 wt%, or at least 90 wt% of chemical or semi-chemical wood pulp based on dry weight. In some embodiments, the cellulose pulp composition provided in a) comprises 100 wt% of chemical or semi-chemical wood pulp based on dry weight.

The pulp used as the starting material for preparation of the modified pulp is a chemical or semi-chemical wood pulp. Chemical pulps are composed of cellulose, hemicelluloses and lignin, the latter of which is often present in very small quantities. However, unbleached and especially mechanical pulps have significantly higher lignin contents. Mechanical pulps are not preferred in the present invention, since the high lignin content may have a negative effect on paper stretchability. Webs prepared from mechanical pulps therefore typically have significantly lower stretchability than webs prepared from chemical or semi-chemical pulps. In some embodiments, the chemical or semi-chemical wood pulp is a softwood pulp, preferably pine pulp, spruce pulp, or a combination thereof. The chemical or semichemical wood pulp may be bleached or unbleached. The chemical or semichemical wood pulp is preferably unbleached. In some embodiments, the chemical or semi-chemical wood pulp has a Kappa number below 90, preferably below 70, more preferably below 50, and more preferably in the range of 0-40, as determined according to standard ISO 302:2015.

In some embodiments, the chemical or semi-chemical wood pulp is a never dried chemical or semi-chemical wood pulp. The term never dried pulp refers to pulp fibers that have not undergone any drying process after being separated from their source material.

The pH value of the cellulose pulp composition is typically in the range of 5-7. In some embodiments, the pH value of the cellulose pulp composition is raised to above 7, such as above 8 or above 9 before the LC refining step in step b) or before the LC refining in step c).

The remaining portion of the cellulose pulp composition may comprise other types of pulp or other additives.

The cellulose pulp composition provided in step a) is subjected to low consistency (LC) refining at a consistency in the range of 1-7 wt% to an SR value in the range of 18-50, as determined by standard ISO 5267-1.

In some embodiments, the cellulose pulp composition in b) is subjected to LC refining to an SR value in the range of 20-50, preferably to an SR value in the range of 25-50, and more preferably to an SR value in the range of 30-50, as determined by standard ISO 5267-1 .

During LC refining, pulp fibers are subjected to mechanical forces in the presence of water, which leads to the breaking down of fiber bundles and the separation of individual fibers. LC refining can be performed by any of the LC refining methods known in the art. Examples of refiners useful for the LC refining process include, but are not limited to, conical refiners or disk refiners. The temperature of the pulp composition during LC refining is typically in the range of 10-90 °C, such as in the range of 25-80 °C. A consistency in the range of 1-7 wt% of the cellulose pulp composition can be achieved by dilution or concentration of the composition provided in step a) as required using methods known in the art.

The LC-refined cellulose pulp composition obtained in step b) is subjected to high consistency (HC) refining at a consistency in the range of 12-40 wt% with a refining energy of at least 150 kWh/t.

In some embodiments, the cellulose pulp composition in c) is subjected to HC refining with a refining energy of at least 200 kWh/t, preferably at least 250 kWh/t, and more preferably at least 300 kWh/t.

In some embodiments, the cellulose pulp composition in c) is subjected to HC refining at a temperature in the range of 70-120 °C.

In HC refining, the pulp composition is subjected to refining in a concentrated form, meaning that a significant amount of the mixture consists of pulp fibers. HC refining is performed at a significantly higher consistency than the consistency used for the LC refining. A consistency in the range of 12-40 wt% of the cellulose pulp composition can be achieved by concentration of the composition obtained in step b) as required using methods known in the art. The HC refining can be performed by any of the HC refining methods known in the art. Examples of refiners useful for the HC refining process include, but are not limited to, conical refiners, wing defibrators or compactors. Conical refiners are well known to the person skilled in the art of pulp refining. Wing defibrators are high intensity mixers fitted with rotating blades, commonly used in the preparation of mechanical pulp. Compactors are machines typically used for compressing or compacting loose biomass or other materials, for example saw dust, into denser and uniform briquettes. One example of compactor type useful for HC-refining in the inventive method is an e-compactor as described in published PCT patent application WO 2012/113990 A1. Due to high transfer of stresses between the fibers in HC refining, microcompressions are imparted leading to that curled and kinked fibers are created. Curly fibers produce high flocculation, and 3D flocks have relatively high strength and flock stretchability compared to stiff non-curly fibers due to mechanical interlocking. The skilled person understands that “curled” refers to curved cellulose fiber and “kinks” refers to sharp changes in an axial direction of a cellulose fiber. The curl % is measured by means of a fiber image analyzing instrument, such as Valmet FS5, and is determined by measuring individual fiber contours and projected lengths. Curl % is based on length-weighed curl of cellulose fibers and is calculated as 100% *(1/L) where I is the fiber contour length and L is the projected end-to-end distance of the fiber, i.e. the distance between the two points on the fiber that are furthest apart.

The HC refining leads to a high degree of curl in the cellulose fibers of the chemical or semi-chemical wood pulp. In some embodiments, the cellulose fibers of the obtained HC-refined cellulose pulp composition have a fiber curl of at least 9%, preferably at least 15%, and more preferably at least 20%. The fiber curl of the HC- refined cellulose pulp composition is measured by standard methods using a Valmet FS5 image analyzer.

The present inventors have found that subjecting a cellulose pulp composition comprising at least 50 wt% chemical or semi-chemical wood pulp based on dry weight to LC refining followed by HC refining according to the present disclosure produces cellulose fibers providing significantly improved formability properties when used in a moldable cellulose fiber-based web for forming molded products by fixed blank 3D forming.

Using fibers with high fiber curl, such as a fiber curl at least 9% increases the stretch of the web of the fibrous cellulosic material. This stretch is useful in fixed blank forming. For example, the fiber curl of the cellulose fibers of the chemical or semichemical wood pulp may be in the range of 9-40%, such as in the range of 15-35%, or such as in the range of 20-30%.

Following the HC refining the HC-refined cellulose pulp composition obtained in step c) is diluted to a consistency in the range of 0.1-10 wt%. The diluent used for the dilution is preferably water or an aqueous solution. Dilution to a consistency of 10 wt% or less allows for the HC-refined cellulose pulp composition to be pumped and or subjected to further treatment. To avoid straightening of the curly fibers formed during the HC-refining of the cellulose pulp, the dilution is preferably performed without further refining of the pulp composition.

In some embodiments, the method further comprises adding 0.1-25 kg/tn, preferably 1-20 kg/tn, and more preferably 1-15 kg/tn, based on dry weight of the cellulose pulp composition, of an anionic or non-ionic polymer to the cellulose pulp composition prior to subjecting it to the HC-refining in step c). A suitable amount of anionic or non-ionic polymer depends on the type of anionic or non-ionic polymer used.

The anionic or non-ionic polymer aids the HC refining by reducing the friction between the cellulose fibers, preventing fiber cutting, and enhancing fiber curling.

The anionic or non-ionic polymer may be added to the cellulose pulp composition before, during or after the LC-refining in step b), but before the HC-refining in step c). In some embodiments, the anionic or non-ionic polymer is added to the cellulose pulp composition before the LC-refining in step b). In some embodiments, the anionic or non-ionic polymer is added to the cellulose pulp composition during the LC-refining in step b). In some embodiments, the anionic or non-ionic polymer is added to the cellulose pulp composition after the LC-refining in step b), but before the HC-refining in step c).

In some embodiments, the anionic or non-ionic polymer is selected from the group consisting of cellulose ethers, natural gums, and anionic polyacrylamide.

The anionic or non-ionic polymer is preferably a natural polymer or a derivative of a natural polymer, and more preferably a natural polysaccharide or a derivative of a natural polysaccharide. In some embodiments, the anionic or non-ionic polymer is selected from the group consisting of cellulose ethers, and natural gums. Cellulose ethers are a group of polymers that are derived from cellulose. Cellulose ethers are created by chemically modifying the cellulose molecule, resulting in improved or altered properties that make them useful in various industrial applications. Cellulose ethers are typically water-soluble polymers. Examples of cellulose ethers useful as the anionic or non-ionic polymer herein include, but are not limited to, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), hydroxypropyl cellulose (HPC), and methyl ethyl hydroxyethyl cellulose (MEHEC). These cellulose ethers may also be functionalized with functional groups to increase their hydrophobicity. Natural gums are hydrocolloids derived from various plant sources. Examples of cellulose ethers useful as the anionic or non-ionic polymer herein include, but are not limited to, gum arabic, guar gum, xanthan gum, locust bean gum, gum tragacanth, karaya gum, tara gum, alginates, carrageenan, and agar-agar.

In some embodiments, the anionic or non-ionic polymer is carboxymethyl cellulose. The carboxymethyl cellulose may generally have a degree of substitution above 0.25 or above 0.3. In some preferred embodiments, the carboxymethyl cellulose has a degree of substitution above 0.4, preferably above 0.6, and more preferably above 0.8. The amount of carboxymethyl cellulose added is preferably in the range of 0.5- 15 kg/tn, based on dry weight of the cellulose pulp composition.

In some embodiments, the method further comprises adding 0.1-50 kg/tn, based on dry weight of the cellulose pulp composition, of a metal salt to the cellulose pulp composition prior to subjecting it to the HC-refining in step c). In some embodiments, the metal salt is added to the cellulose pulp composition before the LC-refining in step b). In some embodiments, the metal salt is added to the cellulose pulp composition during the LC-refining in step b). In some embodiments, the metal salt is added to the cellulose pulp composition after the LC-refining in step b), but before the HC-refining in step c). The metal salt is preferably added together with the anionic or non-ionic polymer, more preferably wherein the anionic or non-ionic polymer is CMC. The metal salt is preferably CaCl2. The metal salt can improve chemical adsorption of the anionic or non-ionic polymer, particularly CMC, onto cellulose fibers.

In some embodiments, the cellulose pulp composition in c) is subjected to HC refining at a temperature in the range of 70-120 °C. Without wishing to be bound to any specific scientific theory, it is believed that an increased temperature in the range of 70-120 °C during HC refining leads to better chemical adsorption of the anionic or non-ionic polymer onto cellulose fibers. In some embodiments, the method further comprises adding 5-50 kg/tn, preferably 10-50 kg/tn, and more preferably 20-50 kg/tn, based on dry weight of the cellulose pulp composition, of a polysaccharide based strength enhancement agent to the cellulose pulp composition after subjecting it to the HC-refining in step c).

The inventors have found that in order to get acceptable bonding without straightening the fibers, a relatively large amount of a polysaccharide based strength enhancement agent may be used. The polysaccharide based strength enhancement agent is preferably added to the HC-refined cellulose pulp composition at an amount which is much higher than the amounts normally contemplated when a polysaccharide based strength enhancement agent is used in paper/board production.

The polysaccharide based strength enhancement agent is added to the cellulose pulp composition after subjecting it to the HC-refining in step c). Preferably, the polysaccharide based strength enhancement agent is added to the cellulose pulp composition during or after subjecting it to the dilution in step d). In some embodiments the polysaccharide based strength enhancement agent is added to the cellulose pulp composition after subjecting it to the dilution in step d). In some embodiments, the polysaccharide based strength enhancement agent is added to the cellulose pulp composition with the diluent water used for the dilution in step d).

In some embodiments, the polysaccharide based strength enhancement agent is a cellulose based strength enhancement agent, preferably selected from the group consisting of highly refined cellulose having an SR value in the range of 70-92, cellulose fines, microfibri Hated cellulose, or combinations thereof.

The term highly refined cellulose as used herein refers to cellulose that has been subjected to refining to a Schopper-Riegler (SR) value in the range of 70-92, as determined by standard ISO 5267-1 . Refining, or beating, of cellulose refers to mechanical treatment and modification of the cellulose fibers in order to provide them with desired properties. 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.

Microfibrillated cellulose (MFC) shall in the context of the patent application mean a cellulose particle, fiber or fibril having a width or diameter of from 20 nm to 1000 nm. Various methods exist to make MFC, such as single or multiple pass refining, prehydrolysis followed by refining or high shear disintegration or liberation of fibrils. One or several pre-treatment steps is usually required in order to make MFC manufacturing both energy efficient and sustainable. The cellulose fibers of the pulp used when producing MFC may thus be native or pre-treated enzymatically or chemically, for example to reduce the quantity of hemicellulose or lignin. The cellulose fibers may be chemically modified before fibrillation, wherein the cellulose molecules contain functional groups other (or more) than found in the original cellulose. Such groups include, among others, carboxymethyl (CM), aldehyde and/or carboxyl groups (cellulose obtained by N-oxyl mediated oxidation, for example "TEMPO"), or quaternary ammonium (cationic cellulose). After being modified or oxidized in one of the above-described methods, it is easier to disintegrate the fibers into MFC.

In some embodiments, the polysaccharide based strength enhancement agent is a starch based strength enhancement agent. The starch based strength enhancement agent may for example be native starch, cooked starch, cationic starch, chemically modified starch, physically modified polymer grafted starch, enzyme modified starch, anionic starch, amphoteric starch, crosslinked starch, pre-gelled starch, swelled starch, or any combination thereof. In some embodiments, the starch based strength enhancement agent comprises cationic starch.

In some embodiments, the polysaccharide-based strength enhancement agent is a combination of a cellulose based strength enhancement agent and a starch based strength enhancement agent. The addition of microfibri Hated cellulose may increase the strength enhancement agent loading capacity of the pulp composition. This allows for a higher total amount of a strength enhancement agent, such as starch, to be added and bound to the pulp than would otherwise have been possible.

The inventors found that by adding a high amount of polysaccharide-based strength enhancement agent to the HC-refined cellulose pulp composition, straightening of the curly fibers during subsequent processing of the HC-refined cellulose pulp composition can be avoided.

The addition of this high amount of a polysaccharide-based strength enhancement agent to the pulp suspension allows for higher degree of fiber curl from the HC- refined pulp composition to be retained also in a moldable cellulose fiber-based material, such as a moldable web, formed from the pulp composition and as a result the stretchability properties of the moldable cellulose fiber-based web are improved.

The cellulose pulp composition is preferably prepared without, or substantially without addition of synthetic polymers. In some embodiments, the obtained HC- refined cellulose pulp composition comprises less than 2 wt%, preferably less than 1 wt%, and more preferably less than 0.5 wt%, based on dry weight, of synthetic polymers.

In some embodiments, the steps a)-d) are performed as an integrated process. This allows for full control of delay times and curl behaviors.

The HC-refined cellulose pulp composition obtained by the method of the present disclosure is especially useful in moldable webs used as a precursor for preparation of 3D formed products obtained by means of fixed blank forming. The term web as used herein refers generally to a continuous blank or sheet of paper or paperboard manufactured or undergoing manufacture on a paper machine. The term web as used herein further refers to paper or paperboard substrate used for conversion into other physical forms, e.g. in the preparation of molded products by fixed blank forming.

According to a second aspect illustrated herein, there is provided a method for manufacturing a moldable cellulose fiber-based web, said method comprising: i) manufacturing a cellulose pulp composition for a moldable cellulose fiber-based web according to any one of the preceding claims, ii) forming a wet web of the cellulose pulp composition, optionally together with additional components, ill) dewatering the wet web, and iv) drying the dewatered wet web to obtain a moldable cellulose fiber-based web.

Preferably, no further refining of the cellulose composition is performed after the HC refining. Further fibrillation, and excessive disintegration, mixing and pumping, of the HC refined pulp is preferably avoided or minimized to avoid reducing the curl of the fibers.

In some embodiments, the steps i)-iv) are performed as an integrated process. This allows for full control of delay times and curl behaviors.

The forming of the wet web in ii) may be done using conventional paper or paperboard forming techniques known in the art. Although different arrangements for performing the steps of the inventive method could be contemplated by the skilled person, the inventive method may advantageously be performed in a paper machine, more preferably in a Fourdrinier type paper machine, i.e. a paper machine based on based on the principles of the Fourdrinier Machine. The Fourdrinier type paper machine uses a moving dewatering fabric or woven mesh, commonly referred to as a “wire”, to create a continuous web by filtering out the fibers held in the cellulose pulp composition and producing a continuously moving wet web of fiber. This wet web is subsequently dried in the machine to produce paper or paperboard. The forming and dewatering steps of the inventive method are preferably performed at the forming section of the paper machine, also commonly referred to as the wet end. The cellulose pulp composition is typically applied to the wire at a consistency in the range of 0.1 -1.5 wt%, and more typically below 0.5 wt%, using a so-called headbox.

The forming of the wet web in ii) may for example comprise water forming or foam forming.

In some embodiments, the forming of the wet web in ii) comprises foam forming. In foam forming fibers and other furnish components are mixed with foam instead of water. The foam consists of water, foaming agent and air.

In foam forming, a large amount of air is added to the cellulose pulp composition in the presence of a foaming agent. The air bubbles formed prevent fiber flocculation, enhance dewatering, and enables production of light weight structures. Foam forming is also expected to maintain curl of the fibers in a batter way that conventional water forming, leading to better stretchability of the formed web.

The terms foam and foamed, as used herein, refer to a substance made by trapping air or gas bubbles inside a solid or liquid. Typically, the volume of gas is much larger than that of the liquid or solid, with thin films separating gas pockets. Three requirements must be met in order for foam to form. Mechanical work is needed to increase the surface area. This can occur by agitation, dispersing a large volume of gas into a liquid, or injecting a gas into a liquid. The second requirement is that a foam forming agent, typically an amphiphilic substance, a surfactant or surface active component, must be present to decrease surface tension. Finally, the foam must form more quickly than it breaks down.

In some embodiments, the foaming required for the foam forming is achieved using a foam generator. The pulp suspension may be pumped through a foam generator one or several times in order to reach a desired gas content or foam density. In some embodiments, the pulp suspension is pumped via a high shear mixer or refiner which generates the foam. Foam can be generated either offline or inline at the paper machine.

Typical air content is in the range of 50-70 vol% based on the volume of the foam. The air bubbles prevent flocculation of fibers in the headbox. In some embodiments, the foam is brought to an air content of 60-70 vol% before being applied to the forming fabric. The consistency of the cellulose pulp composition pulp being subjected to foaming may typically be in the range of 2-5 wt%.

The foam is formed and stabilized using a foaming agent present in the pulp suspension. The foaming agent may be a small molecule surfactant or a polymeric foaming agent or a mixture thereof. The amount of foaming agent in the foam may typically be in the range of 0.005 to 30 wt% based on the total dry weight of the foam, but will be easily determinable by a skilled person. An example of a small molecule surfactant useful for the foam forming is sodium dodecyl sulfate (SDS). The amount of SDS in the foam may typically be in the range of 0.005 to 10 wt%, for example about 0.02 wt% based on the total dry weight of the foam. Examples of a polymeric foaming agent useful for the foam forming include polyvinyl alcohol (PVOH) and partially hydrolyzed polyvinyl acetate (PVOH/Ac). The amount of polyvinyl alcohol (PVOH) or partially hydrolyzed polyvinyl acetate (PVOH/Ac) in the foam may typically be in the range of 0.01 to 30 wt%, for example about 5 wt%, based on the total dry weight of the foam.

When foam forming is used, the cellulose pulp composition may be applied to the wire at a consistency significantly higher than the 0.1-1 .5 wt% typical for water forming. When foam forming is used, the cellulose pulp composition is preferably applied to the wire at a consistency in the range 2-5 wt%.

The wet web is first subjected to dewatering on the wire. Dewatering on the wire may be assisted by various dewatering devices such as blade, table and/or foil elements, suction boxes, friction less dewatering, ultra-sound assisted dewatering, couch rolls, or a dandy roll. The dewatering typically further comprises pressing the wet web to squeeze out as much water as possible. The dewatering may for example include passing the formed wet web through a press section of the paper machine, where the wet web passes between large rolls loaded under high pressure to squeeze out as much water as possible. The removed water is typically received by a fabric or felt. In some embodiments, the dry solids content of the wet web after dewatering is in the range of 15-65 wt%, preferably in the range of 18-60 wt%, and more preferably in the range of 22-55 wt%.

The drying step may for example include drying the dewatered wet web by passing the dewatered wet web around a series of heated drying cylinders. Drying may typically reduce the water content in the web down to a level of about 1-15 wt%, preferably to about 2-10 wt%.

In some embodiments, the drying in step iv) leads to a drying shrinkage in the cross direction (CD) of at least 4%, preferably in the range of 5-20%, and more preferably in the range of 6-12%.

The obtained moldable cellulose fiber-based web according to the invention preferably has properties, such as basis weight, thickness and stretchability, which makes the material suitable for converting the web into molded packaging products by 3D forming techniques, such as fixed blank forming, including molding- and/or deep drawing techniques.

In some embodiments, the obtained 3D-formable cellulose fiber-based web has a grammage, i.e. a basis weight, in the range of 50-500 g/m², or in the range of 120 - 200 g/m², or 150 - 200g/m². A grammage between 120 to 200g/m² may be preferred as it will be less prone to breaking and can withstand the forces implied during the 3D forming process.

In some embodiments, the obtained moldable cellulose fiber-based web has a stretchability according to standard ISO 1924-3:2005 of at least 5% in the machine direction (MD) and at least 9% in the cross direction (CD). For example, the stretchability is at least 6% percent in both directions (MD and CD). In another example, the stretchability is at least 10% or at least 12% in cross direction (CD). In yet another example, the stretchability in CD direction is between 8 - 15% according to standard ISO 1924-3:2005, preferably between 10-14%.

In some embodiments, the obtained moldable cellulose fiber-based web comprises less than 2 wt%, preferably less than 1 wt%, and more preferably less than 0.5 wt%, based on dry weight, of synthetic polymers.

In some embodiments, the obtained moldable cellulose fiber-based web has a total reject according to PTS RH 021/97 test method for Category II products of less than 10 %, and preferably less than 5 %.

In some embodiments, the moldable cellulose fiber-based web is formed as one ply of a multi-ply moldable cellulose fiber-based web.

According to a third aspect illustrated herein, there is provided a method for manufacturing a three-dimensional (3D) cellulose fiber-based product, said method comprising: i) manufacturing a cellulose pulp composition for a moldable cellulose fiber-based web according to any one of claims 1-14, ii) forming a wet web of the cellulose pulp composition, optionally together with additional components, iii) dewatering the wet web, iv) drying the dewatered wet web to obtain a moldable cellulose fiber-based web, and v) forming a molded cellulose fiber-based product from the moldable cellulose fiber-based web, for example by fixed blank forming.

In some embodiments, the steps i)-v) are performed as an integrated process. This allows for full control of delay times and curl behaviors.

In some embodiments, step iv) is followed by compacting the dewatered web in a Clupak unit before forming a product in step v). In such a case, the web comprises a moisture content between 20-50% during Clupak compacting. As known by the skilled person, Clupak method is an in-plane compacting treatment of moist fiber layer resulting in improved extensibility of the material. The production process involves running the web through a nip in a compactor wherein said web is subjected to recoil action of an elastic surface, such as an endless rubber surface, resulting in compaction of the web and thus to mechanically added stretch to the same. It has been noted that foam-formed webs tolerate Clupak treatment particularly well due to the improved stretchability as previously described. Thus, in one embodiment the web to be subjected to Clupak compacting is foam formed.

In some embodiments, the fixed blank forming is performed with a mold depth of at least 20 mm. In some embodiments, the fixed blank forming is deep drawing.

The molded product may for example be a molded receptacle. Non-limiting examples of such receptacles include trays, containers, plates, bowls and cups. The receptacles may for example have a substantially square (e.g. quadratic or rectangular), substantially polygonal (e.g. hexagonal) or substantially round (e.g. circular or elliptic) geometry. The receptacle may be used, among other purposes, for storage and transport of fresh or frozen food. In some embodiments, the containers may also be used for conventional or microwave preparation of food. The receptacle is preferably formed from a single piece of substrate material. Within the context of this document, the phrase a "single piece of material" includes a single piece of material that comprises a single layer or multiple layers of the same material or multiple layers of different materials. These multi-layered materials could include, for example, layers of two or more paper and/or paperboard substrates completely bonded together and/or partially bonded together, such as a corrugated board material, with or without any other layer or layers of any other materials such as metal, foil, plastic, and so forth. Thus, laminates formed from two or more differing types of material are nonetheless encompassed by the phrase a "single piece of material".

The molded product is preferably prepared by fixed blank forming techniques using a moldable cellulose fiber-based web obtained according to the second aspect. In a preferred embodiment, the molded three-dimensional product is formed from of a single piece of the moldable cellulose fiber-based web. In a preferred embodiment, the molded product is formed from of a single piece of the moldable cellulose fiberbased web, wherein said web has a grammage above 120 g/m², or above 150 g/m²

Although the inventive methods described herein are mainly contemplated for fixed blank forming, it is noted that the methods, and the obtained cellulose pulp compositions and moldable cellulose fiber-based webs obtained by the methods, are also useful in other forming techniques, such as hydro forming, thermoforming, and press forming. Thus, in any aspect or embodiment described herein, fixed blank forming may be replaced by, and/or encompass, deep drawing, hydro forming, thermoforming, or press forming.

The inventive methods described herein are mainly contemplated for the manufacture of cellulose pulp compositions and moldable cellulose fiber-based webs for use in the manufacture of 3D molded cellulose fiber-based products. However, the stretchability and strength of the moldable cellulose fiber-based webs may also be useful in other applications where these properties are desired. Specifically, the obtained cellulose pulp compositions and moldable cellulose fiber-based webs may also be useful in the manufacture of cellulose based mulch films for agricultural applications. The moldable cellulose fiber-based webs may be used to replace conventional synthetic polymer mulch films.

While the invention is described herein 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 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.

Claims

1 . A method for manufacturing a cellulose pulp composition for a moldable cellulose fiber-based web, said method comprising: a) providing a cellulose pulp composition comprising at least 50 wt% chemical or semi-chemical wood pulp based on dry weight, b) subjecting the cellulose pulp composition provided in step a) to low consistency (LC) refining at a consistency in the range of 1-7 wt% to an SR value in the range of 18-50 as determined by standard ISO 5267-1 , c) subjecting the LC-refined cellulose pulp composition obtained in step b) to high consistency (HC) refining at a consistency in the range of 12-40 wt% with a refining energy of at least 150 kWh/t, and d) diluting the HC-refined cellulose pulp composition obtained in step c) to a consistency in the range of 0.1-10 wt%.

2. The method according to claim 1 , wherein said chemical or semi-chemical wood pulp is a softwood pulp, preferably pine pulp, spruce pulp, or a combination thereof.

3. The method according to any one of the preceding claims, further comprising adding 0.1 -25 kg/tn, preferably 1-20 kg/tn, and more preferably 1 -15 kg/tn, based on dry weight, of an anionic or non-ionic polymer to the cellulose pulp composition prior to subjecting it to the HC-refining in step c).

4. The method according to claim 3, wherein said anionic or non-ionic polymer is selected from the group consisting of cellulose ethers, natural gums, and anionic polyacrylamide.

5. The method according to claim 4, wherein said anionic or non-ionic polymer is selected from the group consisting of cellulose ethers, and natural gums.

6. The method according to any one of the preceding claims, further comprising adding 5-50 kg/tn, preferably 10-50 kg/tn, and more preferably 20-50 kg/tn, based on dry weight of the cellulose pulp composition, of a polysaccharide-based strength enhancement agent to the cellulose pulp composition after subjecting it to the HC- refining in step c).

7. The method according to claim 6, wherein said polysaccharide-based strength enhancement agent is a cellulose based strength enhancement agent, preferably selected from the group consisting of highly refined cellulose having an SR value in the range of 70-92, cellulose fines, m icrofibrillated cellulose, and combinations thereof.

8. The method according to claim 6, wherein said polysaccharide-based strength enhancement agent is a starch-based strength enhancement agent.

9. The method according to claim 6, wherein said polysaccharide-based strength enhancement agent is a combination of a cellulose based strength enhancement agent and a starch-based strength enhancement agent.

10. The method according to any one of the preceding claims, wherein the cellulose pulp composition in b) is subjected to LC refining to an SR value in the range of 20-50, preferably to an SR value in the range of 25-50, and more preferably to an SR value in the range of 30-50.

11. The method according to any one of the preceding claims, wherein the cellulose pulp composition in c) is subjected to HC refining with a refining energy of at least 200 kWh/t, preferably at least 250 kWh/t, and more preferably at least 300 kWh/t.

12. The method according to any one of the preceding claims, wherein the cellulose pulp composition in c) is subjected to HC refining at a temperature in the range of 70-120 °C.

13. The method according to any one of the preceding claims, wherein the cellulose fibers of the obtained HC-refined cellulose pulp composition have a fiber curl of at least 9%, preferably at least 15%, and more preferably at least 20%.

14. The method according to any one of the preceding claims, wherein the obtained HC-refined cellulose pulp composition comprises less than 2 wt%, preferably less than 1 wt%, and more preferably less than 0.5 wt%, based on dry weight, of synthetic polymers.

15. A method for manufacturing a moldable cellulose fiber-based web, said method comprising: i) manufacturing a cellulose pulp composition for a moldable cellulose fiber-based web according to any one of the preceding claims, ii) forming a wet web of the cellulose pulp composition, optionally together with additional components, iii) dewatering the wet web, and iv) drying the dewatered wet web to obtain a moldable cellulose fiber-based web.

16. The method according to claim 15, wherein the obtained moldable cellulose fiber-based web has a dry basis weight in the range of 50-500 g/m² or 120 - 200 g/m², or 150 - 180g/m².

17. The method according to any one of claims 15-16, wherein the drying in step iv) leads to a drying shrinkage in the cross direction (CD) of at least 4%, preferably in the range of 5-20%, and more preferably in the range of 6-12%.

18. The method according to any one of claims 15-17, wherein the obtained moldable cellulose fiber-based web has a stretchability according to standard ISO 1924-3:2005 of at least 5% in the machine direction (MD) and at least 9% in the cross direction (CD).

19. The method according to any one of claims 15-18, wherein the obtained moldable cellulose fiber-based web comprises less than 2 wt%, preferably less than 1 wt%, and more preferably less than 0.5 wt%, based on dry weight, of synthetic polymers.

20. The method according to any one of claims 15-19, wherein the obtained moldable cellulose fiber-based web has a total reject according to PTS RH 021/97 test method for Category II products of less than 10 %, and preferably less than 5 %.

21. A method for manufacturing a molded cellulose fiber-based product, said method comprising: i) manufacturing a cellulose pulp composition for a moldable cellulose fiber-based web according to any one of claims 1-14, ii) forming a wet web of the cellulose pulp composition, optionally together with additional components, iii) dewatering the wet web, iv) drying the dewatered wet web to obtain a moldable cellulose fiber-based web, and v) forming a three-dimensional molded cellulose fiber-based product from the moldable cellulose fiber-based web.