SE1951393A1 - Water-resistant cellulose-based substrate with improved repulpability - Google Patents

Abstract

The present invention relates to a water-resistant cellulose-based substrate comprised of one or more plies, wherein said substrate has a basis weight in the range of 120-500 g/m2, and a density below 1000 kg/m3, wherein said substrate has been subjected to grafting with a fatty acid halide through the entire thickness of said substrate such that the substrate has a Cobb6o value (as determined according to standard ISO 535:2014 after 60 seconds) below 30 g/m2. The present invention further relates to a method for manufacturing the water-resistant cellulose-based substrate.

Description

WATER-RESISTANT CELLULOSE-BASED SU BSTRATE WITH IMPROVEDREPULPABILITY Technical fieldThe present disclosure relates to water-resistant cellulose-based substrates, such as paper, paperboard or containerboard, for use in wet or damp environments.

BackgroundWater resistance is an important property in many paper, paperboard or containerboard applications. Some examples include packaging, such as boxes,corrugated board and other containers; fresh and aseptic liquid packaging; boxes,corrugated board, trays, or cups for hot, cold, dry, wet and frozen food andbeverages; products for outdoor use such as boxes, signs and posters; pots, traysand covers for plants; packages for construction materials, and construction material.

Paper, paperboard or containerboard for use in wet or damp environments areusually treated with sizing agents to enhance certain qualities; and above all, toincrease the resistance to penetration of water and other liquids into the cellulose-based substrate. There are two main types of sizing: internal sizing and surfacesizing. For internal sizing, chemicals are added to the pulp at the wet end, forexample alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA) or rosinsizing agent. Common surface-sizing agents include, e.g., starch or acrylic co- polymers.

Coating of paper, paperboard or containerboard with plastics is often employed tocombine the mechanical properties of the paperboard with the barrier and sealingproperties of a plastic film. Also in plastic coated paperboard, the board is oftentreated with a hydrophobic sizing agent to prevent so-called edge wick, i.e.absorption of liquid at the cut edges (or so-called raw edges) of the paperboard.

Edge-wick resistance is an important parameter in many applications.

A problem with internal sizing agents, such as AKD, is that they interfere with thehydrogen bonding between the cellulose fibers, giving a debonding effect and 2 hence a weaker material. To compensate for the weaker material, the grammageof paper and board is increased leading to higher carbon footprint due to overuseof wood fibers and higher transport weight at all stages downstream the production.

To improve the wet strength of the material, the internal sizing agent can becombined with a wet strength agent. A wet-strength agent improves the tensileproperties of the paper or paperboard in the wet state by for example covalentlybinding to the cellulose fibers and also form a crosslinking network between thefibers that do not break upon wetting. Common wet strength agents include urea-formaldehyde (UF), melamine-formaldehyde (MF) and polyamide-epichlorohydrin(PAE). Other wet strength agents can give wet-strength by other mechanisms, andsome of these wet strength agents can also have a temporary wet-strength function.

A problem with the addition of wet strength agents is that the repulpability of the paperboard is severely reduced.Thus, there remains a need for improved solutions to render cellulose-basedsubstrates such as paper, paperboard or containerboard water resistant, without weakening the material and without reducing the repulpability of the material.

Description of the invention lt is an object of the present disclosure to provide a water-resistant cellulose-based substrate with high repulpability. lt is an object of the present disclosure to provide a method for rendering acellulose-based substrate water resistant, without weakening the material andwithout reducing the repulpability of the material. lt is a further object of the present disclosure to provide a water-resistant cellulose-based substrate with improved wet strength and similar repulpability as compared to a corresponding non water-resistant cellulose-based substrate. 3 lt is a further object of the present disclosure to provide a water-resistant cellulose-based substrate which can reduce the grammage of the cellulose-based substrateand still meet strength requirements. lt is a further object of the present disclosure to provide a water-resistant cellulose-based substrate which is free from added hydrophobic sizing agents, for examplea|ky| ketene dimer (AKD), alkenyl succinic anhydride (ASA) and/or rosin-sizing agent. lt is a further object of the present disclosure to provide a water-resistant cellulose-based substrate which is free from added wet strength agents, particularlycrosslink-forming wet strength agents, for example urea-formaldehyde (UF),melamine-formaldehyde (MF) and/or polyamide-epichlorohydrin (PAE).

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

According to a first aspect illustrated herein, there is provided a water-resistantcellulose-based substrate comprised of one or more plies, wherein said substrate has a basis weight in the range of 120-500 g/m2, and a density below 1000 kg/m3, wherein said substrate has been subjected to grafting with a fatty acid halidethrough the entire thickness of said substrate and that the substrate has a Cobbßovalue (as determined according to standard ISO 535:2014 after 60 seconds) below30 g/m2.

The cellulose-based substrate is preferably a sheet or web of material formed from a pulp of wood or other fibrous substances comprising cellulose fibers. 4 The cellulose-based substrate is preferably paperboard, containerboard or high-grammage paper having a basis weight in the range of 150-500 g/m2, and adensity below 1000 kg/m3.

Paper generally refers to a material manufactured in sheets from the pulp of woodor other fibrous substances comprising cellulose fibers, used for e.g. writing,drawing, or printing on, or as packaging material. Paper used in the presentdisclosure is paper having a basis weight in the range of 150-500 g/m2. Examplesof containerboard or high-grammage paper types for use in the present disclosureinclude, but are not limited to, paper qualities used in the manufacture ofcorrugated board, such as fluting, liner and testliner.

Paperboard generally refers to strong, thick paper or cardboard comprisingcellulose fibers used for example in boxes and other types of packaging.Paperboard can be comprised of one or more plies. Paperboard can either bebleached or unbleached, coated or uncoated, and produced in a variety ofthicknesses, depending on the end-use requirements.

The cellulose-based substrate is preferably for use in wet or damp environments.ln some embodiments, the cellulose-based substrate is for use in packaging, suchas boxes, corrugated board and other containers; fresh and aseptic liquidpackaging; boxes, corrugated board, trays, or cups for hot, cold, dry, wet andfrozen food and beverages; products for outdoor use such as boxes, signs andposters; pots, trays and covers for plants; packages for construction materials, andconstruction material. ln some embodiments, the cellulose-based substrate is foruse in the manufacture of corrugated board.

The present disclosure is based on the inventive realization that a cellulose-basedsubstrate of certain basis weight and density can be conveniently subjected tografting with a fatty acid halide such that grafting of fatty acids to the substrate material is achieved through the entire thickness of the substrate.

Besides improved hydrophobicity (e.g. water contact angle, Cobbßo value, andwick index), the fatty acid halide grafting through the entire thickness of the substrate has been found to also provide a range of other properties especiallyuseful in thicker paperboard. Improved properties include, but are not limited to,wet strength improved compared to the untreated cellulose-based substrate,tensile strength, bending resistance and Z-strength similar to the untreatedcellulose-based substrate and significantly improved compared to the samecellulose-based substrate with added internal sizing agent (AKD) and/or wetstrength agent (PAE). ln fact, the wet tearing strength of the grafted cellulose-based substrate has been found to be considerably higher than the wet tearingstrength of the same cellulose-based substrate with added internal sizing agent(AKD) and/or wet strength agent (PAE). Furthermore, the repulpability of thegrafted cellulose-based substrate was found to be on the same level as theuntreated cellulose-based substrate and significantly improved compared to thesame cellulose-based substrate with added wet strength agent (PAE). Thecombination of improved wet strength and high repulpability is surprising and ofcourse very useful in paper, paperboard and containerboard products.

The fatty acid halide grafting results in a cellulose-based substrate having aCobbßo value below 30 g/m2. ln some embodiments, the cellulose-based substratesubjected to grafting with a fatty acid halide has a Cobbßo value below 20 g/m2,preferably below 10 g/m2.

The cellulose-based substrate useful in the present disclosure should have a basisweight in the range of 150-500 g/m2, and a density below 1000 kg/m3. Higherdensity and basis weight prevent grafting through the entire thickness of thesubstrate. Cellulose-based substrates of lower basis weight is typically of limiteduse in the intended applications. ln some embodiments, the basis weight of the cellulose-based substrate is in therange of 200-400 g/m2. ln some embodiments, the density of the cellulose-based substrate is below 800kg/m3 or below 400 kg/m3. 6 ln some embodiments, the thickness of the cellulose-based substrate is above 150 pm, preferably above 200 pm or 250 pm. ln some embodiments, the fatty acid halide grafted on the cellulose-basedsubstrate is a C16 or C18 fatty acid halide, or a mixture thereof. ln some preferredembodiments, the fatty acid halide grafted on the cellulose-based substrate is palmitoyl ch|oride or stearoy| ch|oride.

Grafting of the fatty acid halide to the cellulose-based substrate having availablehydroxyl group can be achieved by applying a fatty acid halide to the surface ofthe substrate, followed by penetration of the reagent upon heating, which alsopromotes the formation of covalent bonds between the fatty acid halide and thehydroxyl groups of the substrate. The reaction between the fatty acid halide, e.g.fatty acid ch|oride, and the hydroxyl groups of the substrate results in ester bondsbetween the reagent and the substrate. Ungrafted and thereby unbound fatty acidsmay also be present to a certain extent. Upon the reaction with the hydroxylgroups in the substrate, and/or with water in the substrate and/or in the air,hydrohalic acid, e.g. hydrochloric acid, is formed as a reaction byproduct. Thegrafting may preferably be followed by removal of the formed hydrohalic acid, andoptionally by removal of the ungrafted residues. One example of a grafting processwhich could be used in production of the water-resistant cellulose-based substrateof the present disclosure is described in detail in the international patentapplication WO2012066015A1. Another example of a grafting process, whichcould be used in production of the water-resistant cellulose-based substrate in thepresent disclosure, is described in detail in the international patent applicationWO2017002005A1. The grafting process may preferably be repeated, in order toincrease the amount of grafted and free fatty acids in the cellulose-basedsubstrate. ln order to achieve fatty acid halide grafting through the entire thickness of thecellulose-based substrate having a basis weight in the range of 150-500 g/m2, anda density below 1000 kg/m3, it has been found that the cellulose-based substrateshould preferably be subjected to grafting with a fatty acid halide at least twice. lnsome embodiments, the cellulose-based substrate has a front surface and a back 7 surface and said substrate has been subjected to grafting with a fatty acid halideon both the front surface and the back surface, or subjected to grafting with a fattyacid halide at least twice on the same surface.

The fatty acid halide grafting preferably results in a total amount of grafted andfree fatty acids in the cellulose-based substrate in the range of 0.5-10 kg/ton of thetotal dry weight of the substrate.

A surface of the cellulose-based substrate subjected to grafting with a fatty acid halide preferably has a water contact angle above 90°, preferably above 100°.

The fatty acid halide grafting through the entire thickness of the cellulose-basedsubstrate removes the need for a hydrophobic sizing agent. Thus, in preferredembodiments the substrate is free from added hydrophobic sizing agents, forexample alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA) and/or rosin- sizing agent.

The fatty acid halide grafting through the entire thickness of the cellulose-basedsubstrate also removes the need for an added wet strength agent to improve thewet strength of the substrate. Thus, in some embodiments the cellulose-basedsubstrate is free from added wet strength agents. ln some embodiments thecellulose-based substrate is free from added crosslink-forming wet strength agents, for example polyamide-epichlorohydrin (PAE). ln some embodiments, the cellulose-based substrate subjected to grafting with afatty acid halide has an edge wick index (Lactic acid 1% solution, 1 h at 23 °C and 50 % relative humidity) below 1 kg/m2h, preferably below 0.5 kg/m2h. ln some embodiments, the cellulose-based substrate subjected to grafting with afatty acid halide has an edge wick index (hydrogen peroxide 35 % solution, 10 minat 70 °C) below 5 kg/m2h, preferably below 1.5 kg/m2h. 8 ln some embodiments, the cellulose-based substrate subjected to grafting with afatty acid halide has an edge wick index (warm water, 90 min at 55 °C) below 3 kg/m2h, preferably below 1 kg/m2h. ln some embodiments, the cellulose-based substrate subjected to grafting with afatty acid halide has a relative wet strength (in machine direction and crossdirection, determined according to standard ISO 3781 :201 1) of at least 5%,preferably at least 10%. ln some embodiments, the cellulose-based substrate subjected to grafting with afatty acid halide has a relative wet strength (in machine direction and cross direction, determined according to standard ISO 3781 :2011) of at least two timeshigher, preferably at least four times higher, as compared to the same cellulose- based substrate not subjected to said grafting. ln some embodiments, the cellulose-based substrate subjected to grafting with afatty acid halide has a relative wet tearing strength (in machine direction and crossdirection, determined according to TAPPI T 496 sp-13 (T 496 cm-85) and ISO1974:2012) of at least 30%, preferably at least 50%. ln some embodiments, the cellulose-based substrate subjected to grafting with afatty acid halide has a relative wet tearing strength (in machine direction and crossdirection, determined according to standard ISO 3781:2011) of at least two timeshigher, preferably at least four times higher, as compared to the same cellulose- based substrate not subjected to said grafting. ln some embodiments, the cellulose-based substrate subjected to grafting with afatty acid halide has a tensile strength (in machine direction and cross direction,determined according to standard ISO 1924-3:2005) of at least 90%, preferably atleast 95%, of the same cellulose-based substrate not subjected to said grafting. ln some embodiments, the cellulose-based substrate subjected to grafting with afatty acid halide has a L&W bending resistance (in machine direction and crossdirection, determined according to standard ISO 2493-1:2010, bending length 50 9 mm, bending angle 15°) of at least 90%, preferably at least 100%, of the same cellulose-based substrate not subjected to said grafting. ln some embodiments, the cellulose-based substrate subjected to grafting with afatty acid halide has a Z-strength (determined according to standard ISO15754:2009) of at least 90%, preferably at least 100%, of the same cellulose-based substrate not subjected to said grafting. ln some embodiments, the cellulose-based substrate subjected to grafting with afatty acid halide has a repulpability characterized by a reject rate (as determinedaccording to the PTS RH 021/97 test method) below 20%, preferably below 10%, more preferably below 5%, and most preferably below 1%.

According to a second aspect illustrated herein, there is provided a method formanufacturing a water-resistant cellulose-based substrate, said method comprising: a) providing a cellulose-based substrate comprised of one or more plies, whereinsaid substrate has a basis weight in the range of 150-500 g/m2 and a densitybelow 1000 kg/m3, and b) subjecting said substrate to grafting with a fatty acid halide on both the frontsurface and the back surface thereof, or at least twice on the same surface, suchthat said substrate is subjected to grafting with the fatty acid halide through theentire thickness of said substrate and the substrate has a Cobbßo value (asdetermined according to standard ISO 535:2014 after 60 seconds) below 30 g/m2.

The fatty acid halide grafting in step b) results in a cellulose-based substratehaving a Cobbßo value below 30 g/m2. ln some embodiments, the cellulose-basedsubstrate subjected to grafting with a fatty acid halide has a Cobbßo value below 20g/m2, preferably below 15 g/m2.

The cellulose-based substrate in step a) should have a basis weight in the rangeof 120-500 g/m2, and a density below 1000 kg/m3. Higher density or basis weight prevents grafting through the entire thickness of the substrate. Cellulose-basedsubstrates of lower basis weight is typically of limited use in the intended applications. ln some embodiments, the basis weight of the cellulose-based substrate is in therange of 200-400 g/m2. ln some embodiments, the density of the cellulose-based substrate is below 800kg/m3 or below 400 kg/m3. ln some embodiments, the grafting in step b) involves contacting the cellulose-based substrate with fatty acid halide in a liquid, spray and/or vapor state. ln order to achieve fatty acid halide grafting through the entire thickness of thecellulose-based substrate having a basis weight in the range of 120-500 g/m2, anda density below 1000 kg/m3, it has been found that the substrate should preferablybe subjected to grafting with a fatty acid halide at least twice. ln someembodiments, the cellulose-based substrate has a front surface and a backsurface and said substrate has been subjected to grafting with a fatty acid halideon both the front surface and the back surface, or subjected to grafting with a fattyacid halide at least twice on the same surface.

The fatty acid halide grafting preferably results in a total amount of grafted andfree fatty acids in the cellulose-based substrate in the range of 0.5-10 kg/ton of thetotal dry weight of the cellulose-based substrate.

A surface of the cellulose-based substrate subjected to grafting with a fatty acidhalide preferably has a water contact angle above 90°, preferably above 100°.

The fatty acid halide grafting through the entire thickness of the cellulose-basedsubstrate removes the need for a hydrophobic sizing agent. Thus, in preferredembodiments the cellulose-based substrate is free from added hydrophobic sizingagents, for example alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA) and/or rosin sizing agent. 11 The fatty acid halide grafting through the entire thickness of the cellulose-basedsubstrate also removes the need for an added crosslink-forming wet strengthagent to improve the wet strength of the cellulose-based substrate or tocompensate for a reduced tensile strength caused by the presence of ahydrophobic sizing agent. Thus, in some embodiments the cellulose-basedsubstrate is free from added wet strength agents. ln some embodiments thecellulose-based substrate is free from added crosslink-forming wet strengthagents, for example polyamide-epichlorohydrin (PAE).

The water-resistant cellulose-based substrate may further comprise at least oneprotective polymer layer disposed on a surface thereof. The protective polymerlayer preferably comprises a thermoplastic polymer. The polymer layer may forexample comprise any of the polymers commonly used in paper-based orpaperboard-based packaging materials in general. Examples include polyethylene(PE), polyethylene terephthalate (PET), polypropylene (PP) and polylactic acid(PLA). Polyethylenes, especially low-density polyethylene (LDPE) and high-density polyethylene (HDPE), are the most common and versatile polymers used.Thermoplastic polymers, and particularly polyolefins are useful since they can beconveniently processed by extrusion coating techniques to form very thin andhomogenous films with good barrier properties. ln preferred embodiments, thepolymer layer comprises a polyethylene, more preferably LDPE or HDPE.

The basis weight (corresponding to the thickness) of the protective polymer layeris preferably less than 50 g/m2. ln order to achieve a continuous and substantiallydefect free film, a basis weight of the polymer layer of at least 8 g/m2, preferably atleast 12 g/m2, is typically required. ln some embodiments, the basis weight of thepolymer layer is in the range of 8-50 g/m2, preferably in the range of 12-50 g/m2.

According to a third aspect illustrated herein, there is provided a carton blankcomprising a water-resistant cellulose-based substrate according to the firstaspect. 12 According to a fourth aspect illustrated herein, there is provided a container,comprising a water-resistant cellulose-based substrate according to the firstaspect.

While the invention has been described with reference to various exemplaryembodiments, it will be understood by those ski||ed in the art that various changesmay be made and equivalents may be substituted for elements thereof withoutdeparting from the scope of the invention. ln addition, many modifications may bemade to adapt a particular situation or material to the teachings of the inventionwithout departing from the essential scope thereof. Therefore, it is intended thatthe invention not be limited to the particular embodiment disclosed as the bestmode contemplated for carrying out this invention, but that the invention willinclude all embodiments falling within the scope of the appended claims.

ExamplesThree-plies bleached boards at 240 g/m2 were produced containing: no sizing (sample B0), 4 kg/ton AKD sizing (sample Ref-BA) and both 2.1 kg/ton AKD sizingand 1.5 kg/ton wet-strength agent PAE (Ref-BAW), respectively. The thickness ofthe board was around 370 um and the density was around 650 kg/m3.

Sample B0 was grafted by subjecting both sides of the board to palmitoyl chlorideas a liquid and thereafter it was heat treated at 190 °C. The total amount of fattyacids in the board (sample BOG) after the reaction was 2.4 kg/ton.

The method for measurement of contact angle (CA) is based on the standard ISOTC 6/SC 2/WG 41: Paper and board - Measurement of water contact angle byoptical methods. Contact angle was measured for 10 seconds and values for eachsecond and at 0.1 s were noted. The values are an average from 5 drops. Theliquid used was Milli-Q water, drop size was 4 ul and drops were evaluated by the software calculation program Circle.

The contact angle values for all boards except B0 were above 120° with no biggerdifferences between the boards; B0 absorbed the droplet. 13 Cobbßo analyses were performed by ISO 535:2014 for 60 seconds.

Edge-wick penetration testing was performed with a lactic acid (LA) solution (1 %)for 1 h at conditioned climate of 23 °C and 50% RH. The thickness of the sheetswas determined, and the surfaces were masked with a plastic film on both sides,prior to cutting them into five pieces to reveal raw edges. These were thereafterimmersed into the LA bath for 1 h, and the amount of absorbed liquid wassubsequently weighed. Thereafter the edge penetration wick index can be calculated in kg/m2h.

Edge-wick penetration testing was also performed with hydrogen peroxide andwith warm water, respectively. For the hydrogen peroxide (HP) edge wick, a 35%solution was utilized at 70 °C for 10 min. For the warm water edge wick, water at55 °C was utilized for 90 min.

The Cobbßo and edge-wick values of the four samples are presented in Table 1.

Table 1. Cobbßo and edge wick values.

SAMPLES Cobbßo LA wick HP wick Warm water wick(g/m2) (kg/m2h) (kg/m2h) (kg/m2h)B0 Not 10.3 Not 18measurable measurable BOG 17.9 0.45 0.84 0.49Ref-BA 18.5 0.35 1.74 2.00Ref-BAW 20.0 0.49 3.59 2.20 The unsized sample B0 gave very poor results with either high or unmeasurablevalues. Compared to the AKD and AKD/WS-containing samples, the Cobbßo valuebecame slightly better for the grafted sample (BOG), and its LA wick value was at agood level. The biggest and surprising difference could be seen for the HP and warm water wick, where the uptake of the solution was surprisingly low for the 14 grafted board; despite the fact that the amount of fatty acids were lower than theamounts of AKD and/or WS.

The tensile strength and tensile stiffness were measured according to standardISO 1924-3:2005.

The L&W bending resistance 50 mm 15° MD was measured according to standardISO 2493-1:2010.

The Z-strength was measured according to standard ISO 15754:2009. lt can clearly be seen in Table 2 that the addition of the AKD has a negativeimpact on the strength and stiffness compared to the unsized board B0. The samedamaging effect cannot be seen for the grafted board, and here the stiffness wasalso slightly improved. This trend also held for the bending resistance and the Z-strength.

Table 2. Tensile properties.

SAMPLES Tensile Tensile Bending Z-strengthstiffness MD strength MD resistance MD(kN/m) (kN/m) (mN) (kPa) B0 2300 20.5 358 360 BOG 2340 19.7 380 364Ref-BA 2100 17.3 331 320Ref-BAW 2130 18.5 330 313 The wet strength was measured according to standard ISO 3781 :2011 for theboards without sizing and with fatty acid grafting, AKD sizing and/or WS agent,respectively. The relative wet strength is the difference between the tensilestrength and the wet strength in percentage (in accordance with the samestandard).

The wet tearing strength was measured based on TAPPI T 496 sp-13 (T 496 cm-85). Test species was cut out and subsequently soaked in distilled water for 60min. Excess water was removed by couching. A small cut was made prior tosubjecting the samples for tearing according to ISO 1974:2012. The relative wettearing strength is the difference between the tearing strength and the wet tearing strength in percentage (in accordance with the same standard).

Table 3 summarizes the wet strength and wet tearing strength in MD as well asthe relative wet strength and the relative wet tearing strength in MD of the differentboards. The grafting of fatty acids to the unsized board had a positive impact onthe wet strength compared to when only AKD was utilized, and it was almost onthe same level as when wet-strength agent also was added. Surprisingly, the wettearing strength was much higher for the grafted sample compared to the others, with a relative wet tearing strength of 90 %.

Table 3.SAM PLES Wet strength Wet tearing Relative wet Relative wetMD strength MD strength MD tearing strength (kN/m) (kN/m) (%) MD (%) B0 0.5 545 2 16 BOG 2.3 2670 12 90Ref-BA 1 .8 544 10 17Ref-BAW 2.6 612 14 18

Claims (26)

1. Water-resistant cellulose-based substrate comprised of one or more plies, wherein said substrate has a basis weight in the range of 120-500 g/m2, and adensity below 1000 kg/m3, wherein said substrate has been subjected to grafting with a fatty acid halidethrough the entire thickness of said substrate such that the substrate has a Cobbßovalue (as determined according to standard ISO 535:2014 after 60 seconds) below30 g/m2.

2. Cellulose-based substrate according to any one of the preceding claims,wherein the basis weight of said substrate is in the range of 200-400 g/m2.

3. Cellulose-based substrate according to any one of the preceding claims, wherein the density of said substrate is below 800 kg/m3 or below 400 kg/m3.

4. Cellulose-based substrate according to any one of the preceding claims,wherein the thickness of said substrate is above 150 um, preferably above 250 um.

5. Cellulose-based substrate according to any one of the preceding claims,wherein said substrate has a front surface and a back surface and said substratehas been subjected to grafting with a fatty acid halide on both the front surface andthe back surface or subjected to grafting with a fatty acid halide at least twice on the same surface.

6. Cellulose-based substrate according to any one of the preceding claims,wherein the total amount of grafted and free fatty acids in the substrate is in therange of 0.5-10 kg/ton of the total dry weight of the substrate. 17

7. Cellulose-based substrate according to any one of the preceding claims,wherein a surface of said substrate subjected to grafting with a fatty acid halidehas a water contact angle above 90°, preferably above 100°.

8. Cellulose-based substrate according to any one of the preceding claims,wherein said substrate is free from added hydrophobic sizing agents, for examplea|ky| ketene dimer (AKD), alkenyl succinic anhydride (ASA) and/or rosin sizingagent.

9. Cellulose-based substrate according to any one of the preceding claims,wherein said substrate is free from added wet-strength agents.

10. Cellulose-based substrate according to any one of the preceding claims,wherein said substrate subjected to grafting with a fatty acid halide has a Cobbßovalue (as determined according to standard ISO 535:2014 after 60 seconds) below20 g/m2, preferably below 10 g/m2.

11. Cellulose-based substrate according to any one of the preceding claims,wherein said substrate subjected to grafting with a fatty acid halide has an edgewick index (Lactic acid 1% solution, 1 h at 23 °C and 50 % relative humidity) below1 kg/m2h, preferably below 0.5 kg/m2h.

12. Cellulose-based substrate according to any one of the preceding claims,wherein said substrate subjected to grafting with a fatty acid halide has a relativewet strength (in machine direction and cross direction, determined according tostandard ISO 3781 :201 1) of at least 5%, preferably at least 10%.

13. Cellulose-based substrate according to any one of the preceding claims,wherein said substrate subjected to grafting with a fatty acid halide has a relativewet tearing strength (in machine direction and cross direction, determinedaccording to TAPPI T 496 sp-13 (T 496 cm-85) and ISO 1974:2012) of at least30%, preferably at least 50%. 18

14. Cellulose-based substrate according to any one of the preceding claims,wherein said substrate subjected to grafting with a fatty acid halide has a tensilestrength (in machine direction and cross direction, determined according tostandard ISO 1924-3:2005) of at least 90%, preferably at least 95%, of the samecellulose-based substrate not subjected to said grafting.

15. Cellulose-based substrate according to any one of the preceding claims,wherein said substrate subjected to grafting with a fatty acid halide has a L&Wbending resistance (in machine direction and cross direction, determinedaccording to standard ISO 2493-1:2010, bending length 50 mm, bending angle15°) of at least 90%, preferably at least 100%, of the same substrate not subjectedto said grafting.

16. Cellulose-based substrate according to any one of the preceding claims,wherein said substrate subjected to grafting with a fatty acid halide has a Z-strength (determined according to standard ISO 15754:2009) of at least 90%,preferably at least 100%, of the same substrate not subjected to said grafting.

17. Cellulose-based substrate according to any one of the preceding claims,wherein said substrate subjected to grafting with a fatty acid halide has arepulpability characterized by a reject rate (as determined according to the PTSRH 021/97 test method) below 20%, preferably below 10%, more preferably below5%, and most preferably below 1%.

18. Cellulose-based substrate according to any one of the preceding claims, wherein said substrate is for use in wet or damp environments.

19. A method for manufacturing a water-resistant cellulose-based substrate,said method comprising: a) providing a cellulose-based substrate comprised of one or more plies, whereinsaid substrate has a basis weight in the range of 120-500 g/m2 and a densitybelow 1000 kg/m3, and 19 b) subjecting said substrate to grafting with a fatty acid halide on both the frontsurface and the back surface thereof, or at least twice on the same surface, suchthat said substrate is subjected to grafting with the fatty acid halide through theentire thickness of said substrate and the substrate has a Cobbßo value (asdetermined according to standard ISO 535:2014 after 60 seconds) below 30 g/m2.

20. The method according to claim 19, wherein the basis weight of saidcellulose-based substrate is in the range of 200-400 g/m2.

21. The method according to any one of claims 19-20, wherein the density ofsaid cellulose-based substrate is below 800 kg/m3, preferably below 400 kg/m3.

22. The method according to any one of claims 19-21, wherein the graftinginvolves contacting the cellulose-based substrate with fatty acid halide in a liquid,spray and/or vapor state.

23. The method according to any one of claims 19-22, wherein the total amountof grafted and free fatty acids in the cellulose-based substrate is in the range of0.5-10 kg/ton of the total dry weight of the substrate.

24. The method according to any one of claims 19-23, wherein a surface of saidcellulose-based substrate subjected to grafting with a fatty acid halide has a water contact angle above 90°, preferably above 100°.

25. The method according to any one of claims 19-24, wherein said cellulose-based substrate is free from added hydrophobic sizing agents, for example alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA) and/or rosin sizing agent.

26. The method according to any one of claims 19-25, wherein said cellulose-based substrate is free from added wet strength agents.