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EP-4739836-A1 - A METHOD FOR PRODUCING A MICROFIBRILLATED CELLULOSE WEB

EP4739836A1EP 4739836 A1EP4739836 A1EP 4739836A1EP-4739836-A1

Abstract

The present invention relates to a method for producing a microfibrillated cellulose (MFC) web. The method comprises preparing an MFC suspension and forming a wet MFC web from the MFC suspension by casting on a non-porous support. The wet MFC web positioned on the non-porous support is subjected to water removal by means of dewatering and/or drying to form a dry MFC web. Broke material is discharged and collected. Collected broke material is mixed with water to provide at least one broke suspension wherein at least 90 weight- % of each broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05. The broke suspension(s) is/are subjected to a mechanical treatment. The broke suspension(s) is/are used in the preparation of the MFC suspension. The mechanical treatment is performed to increase the viscosity of the broke suspension(s) to at least 60% of the viscosity of the MFC suspension without the broke suspension(s).

Inventors

  • NYLÉN, Otto
  • KARPPINEN, Anni
  • BACKFOLK, KAJ

Assignees

  • Stora Enso Oyj

Dates

Publication Date
20260513
Application Date
20240611

Claims (20)

  1. 1 . A method for producing a microfibrillated cellulose (MFC) web, wherein the method comprises the steps of: a) preparing an MFC suspension comprising between 50 weight-% to 100 weight-% MFC based on total dry weight; b) forming a wet MFC web of said MFC suspension by casting on a non- porous support; c) subjecting said wet MFC web positioned on said non-porous support to water removal to form a dry MFC web, wherein the water removal comprises dewatering said wet MFC web in at least one dewatering step and/or drying said wet MFC web in at least one drying step; d) discharging and collecting broke material comprising wet broke and/or dry broke, wherein said wet broke comprises wet MFC web waste, wherein said dry broke comprises dry MFC web waste; e) subjecting collected broke material to mixing with water to provide at least one broke suspension, wherein at least 90 weight-% of each broke suspension of said at least one broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05; f) subjecting said at least one broke suspension to a mechanical treatment to increase the viscosity of said at least one broke suspension, and g) using said at least one broke suspension subjected to said mechanical treatment in said preparation of said MFC suspension of step a), wherein said mechanical treatment of step f) is performed such that each broke suspension of said at least one broke suspension has, after said mechanical treatment, a viscosity of at least 60% of the viscosity of said MFC suspension without any inclusion of said at least one broke suspension.
  2. 2. The method according to claim 1 , wherein each mechanical treatment step of the mechanical treatment of step f) is selected from the group of: a homogenization treatment, a fluidization treatment and a fibrillation treatment.
  3. 3. The method according to claim 1 or 2, wherein step d) comprises discharging and collecting first broke material comprising wet broke and/or dry broke, wherein step e) comprises subjecting collected first broke material to said mixing with water to provide a first broke suspension, wherein at least 90 weight-% of said first broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05, wherein step f) comprises subjecting said first broke suspension to said mechanical treatment to increase the viscosity of said first broke suspension, and wherein step g) comprises using said first broke suspension subjected to said mechanical treatment in said preparation of said MFC suspension of step a), wherein said mechanical treatment of step f) is performed such that said first broke suspension has, after said mechanical treatment, a viscosity of at least 60% of the viscosity of said MFC suspension without any inclusion of said first broke suspension.
  4. 4. The method according to claim 3, wherein step g) comprises mixing said first broke suspension after said mechanical treatment with an MFC stock suspension in said preparation of said MFC suspension.
  5. 5. The method according to claim 3, wherein said mechanical treatment of step f) comprises a mechanical treatment step being a fibrillation treatment which comprises subjecting said first broke suspension to co-fibrillation with pulp or pre-treated pulp to provide an MFC stock suspension and wherein step g) comprises using said MFC stock suspension in said preparation of said MFC suspension.
  6. 6. The method according to any one of claims 3-5, wherein the method further comprises subjecting said first broke suspension to at least one first purification treatment, wherein each of said at least one first purification treatment is selected from the group of: screening, filtration, treatment with one or more microbial deactivation agents, deaeration, defoaming, treatment with one or more bleaching chemicals, flotation, sterilization, enzymatic hydrolysis, chemical hydrolysis and fractionation, and wherein step g) comprises using said first broke suspension in said preparation of said MFC suspension after said at least one first purification treatment.
  7. 7. The method according to any one of claims 3-6, wherein said first broke material comprises dry broke.
  8. 8. The method according to any one of claims 3-7, wherein said first broke material comprises wet broke consisting of waste of said wet MFC web being dewatered and/or partially dried.
  9. 9. The method according to any one of claims 1 -8, wherein step d) comprises discharging and collecting second broke material comprising wet broke, wherein step e) comprises subjecting collected second broke material to said mixing with water to provide a second broke suspension, wherein at least 90 weight-% of said second broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05, wherein step f) comprises subjecting said second broke suspension to said mechanical treatment to increase the viscosity of said second broke suspension, and wherein step g) comprises using said second broke suspension subjected to said mechanical treatment in said preparation of said MFC suspension of step a), wherein said mechanical treatment of step f) is performed such that said second broke suspension has, after said mechanical treatment, a viscosity of at least 60% of the viscosity of said MFC suspension without any inclusion of said second broke suspension.
  10. 10. The method according to claim 9, wherein step g) comprises mixing said second broke suspension after said mechanical treatment with an MFC stock suspension in said preparation of said MFC suspension.
  11. 11 . The method according to claim 9 or 10, wherein the method further comprises subjecting said second broke suspension to at least one second purification treatment, wherein each of said at least one second purification treatment is selected from the group of: screening, filtration, treatment with one or more microbial deactivation agents, deaeration, defoaming, treatment with one or more bleaching chemicals, flotation, sterilization, enzymatic hydrolysis, chemical hydrolysis and fractionation, and wherein step g) comprises using said second broke suspension in said preparation of said MFC suspension after said at least one second purification treatment.
  12. 12. The method according to any one of the preceding claims, wherein the method further comprises a step of air removal of said broke material before said mixing with water of step e).
  13. 13. The method according to any one of the preceding claims, wherein the non- porous support is a metal belt.
  14. 14. The method according to any one of the preceding claims, wherein the dewatering of step c) comprises at least one press dewatering step.
  15. 15. The method according to claim 14, wherein each press dewatering step comprises applying a press fabric into direct or indirect contact with said wet MFC web positioned on said non-porous support and conducting said wet MFC web, arranged between said press fabric and said non-porous support, through a pressing equipment to remove water from said wet MFC web by transferring water from said wet MFC web into the press fabric.
  16. 16. The method according to any one of the preceding claims, wherein said drying of step c) comprises at least one non-contact drying step and/or at least one contact drying step.
  17. 17. The method according to claim 16, wherein each non-contact drying step comprises hot gas impingement drying, microwave drying, ultraviolet drying, electron beam drying, infrared drying, near infrared drying or a combination thereof.
  18. 18. The method according to 16 or 17, wherein each contact drying step comprises contacting said wet MFC web with at least one heated belt or heated cylinder.
  19. 19. The method according to any one of the preceding claims, wherein said wet broke comprises wet MFC web edges and/or waste of wet MFC web breaks.
  20. 20. The method according to any one of the preceding claims, wherein said dry broke comprises dry MFC web edges and/or waste of dry MFC web breaks and/or reel waste.

Description

A METHOD FOR PRODUCING A MICROFIBRILLATED CELLULOSE WEB Technical field The present disclosure relates to a method for producing a microfibrillated cellulose (MFC) web, such as an MFC film, involving web formation by casting on a non- porous support, which method enables improved reuse of material rejected or wasted during the production. Oxygen, grease, water vapor and/or aroma barrier properties are required in many uses of paper and paperboard packaging. However, paper and paperboard substrates do not have these properties inherently. Most commonly barrier characteristics of paper and paperboard substrates are created by adding one or more barrier coatings and/or laminated barrier layers which are based on plastics or other non-renewable materials. The disadvantage with these coatings and barrier layers is their non-renewable raw material basis that can increase the carbon dioxide footprint of the material as well as make the otherwise biodegradable paper or paperboard non-biodegradable and in some cases non-recyclable. More recently, microfibrillated cellulose (MFC) webs have been developed, in which cellulosic fibrils, provided by fibrillation of cellulose fibers, have been suspended, e.g., in water and thereafter re-organized and re-bonded together to form a web. For example, MFC webs in the form of MFC films, which are dense films with barrier properties, such as oxygen, aroma and grease barrier properties, have been developed. MFC webs, such as MFC films, are recyclable and biodegradable as well as based on renewable raw material. One approach to produce MFC webs, such as MFC films, is to use a casting method in which a wet MFC web is formed by casting of an MFC suspension comprising MFC and water as suspension medium on a non-porous support, such as a plastic or metal support, and thereafter dewatering and/or drying to remove water from the wet MFC web and form a dry MFC web. This type of web casting method has been shown to enable production of MFC films with very smooth surfaces with good barrier properties, such as oxygen barrier properties and/or water vapor barrier properties. There is still a need for a method for producing an MFC web on a non-porous support with a casting method, which enables improved reuse of material rejected or wasted during the production. Description of the invention It is an object of the present invention to provide a method for producing an MFC web, such as an MFC film, involving web formation by casting on a non-porous support, which enables improved reuse of material rejected or wasted during the production It is a further object of the present invention to provide a method for producing an MFC web, such as an MFC film, involving web formation by casting on a non-porous support, which enables improved broke handling. 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 invention is defined by the appended independent claim. Embodiments are set forth in the appended dependent claims and in the following description. According to a first aspect illustrated herein, there is provided a method for producing a microfibrillated cellulose (MFC) web, wherein the method comprises the steps of: a) preparing an MFC suspension comprising between 50 weight-% to 100 weight-% MFC based on total dry weight; b) forming a wet MFC web of said MFC suspension by casting on a non- porous support; c) subjecting said wet MFC web positioned on said non-porous support to water removal to form a dry MFC web, wherein the water removal comprises dewatering said wet MFC web in at least one dewatering step and/or drying said wet MFC web in at least one drying step; d) discharging and collecting broke material comprising wet broke and/or dry broke, wherein said wet broke comprises wet MFC web waste, wherein said dry broke comprises dry MFC web waste; e) subjecting collected broke material to mixing with water to provide at least one broke suspension, wherein at least 90 weight-% of each broke suspension of said at least one broke suspension passes a Mesh 30 screen according to SCAN-CM 66:05; f) subjecting said at least one broke suspension to a mechanical treatment to increase the viscosity of said at least one broke suspension, and g) using said at least one broke suspension subjected to said mechanical treatment in said preparation of said MFC suspension of step a), wherein said mechanical treatment of step f) is performed such that each broke suspension of said at least one broke suspension has, after said mechanical treatment, a viscosity of at least 60% of the viscosity of said MFC suspension without any inclusion of said at least one broke suspension. The method according to the first aspect enables the production of an MFC web, such as an MFC film, with casting technique on a non-porous support, wherein improved reuse of material rejecte