FI124832B - Paper product and method and system for making a paper product - Google Patents

Description

A PAPER PRODUCT AND A METHOD AND A SYSTEM FOR MANUFACTURING A PAPER PRODUCT

Field of the Invention

This invention relates to a method and system for manufacturing a paper product comprising nanofibrillar cellulose material. In addition, this invention relates to a paper product.

Background of the Invention

Cellulose, which is an Abundant natural raw material, is a polysaccharide composed of a linear chain of several hundred to ten thousand linked D-Glucose units. Cellulose is typically used as a raw material for paper products. Papers may also include, for example, fillers and chemicals. Typically, the paper produced should have, among other things, good strength properties. In addition, the paper produced should typically be manufactured with good production efficiency.

It is an object of the present invention to present a novel solution for manufacturing paper.

Summary of the Invention

The present invention discloses a method and system for manufacturing paper comprising nanofibrillar cellulose. In addition, the invention discloses a paper product comprising nanofibrillar cellulose.

The invention is based on the use of nanofibrillar cellulose in paper furnish and in papers. Cellulose fibers, preferably chemically pre-treated and / or mechanically pre-treated cellulose fibers, can be reduced to nanofibrillar cellulose material that can be used as a reinforcing agent in paper. Nanofibrillar cellulose as such can provide a paper product with new functional properties.

It has been found that if release paper had lower grammage it would be possible to have a longer amount of paper in customer rolls. However, in order to lower the grammage of the paper, the initial wet strength of the paper should be improved to maintain the runnability of the paper and, moreover, to maintain the tensile strength of the paper without sacrificing the tear strength of the paper. Nanofibrillar cellulose, when used as a paper additive, has Surprisingly shown to achieve these needed properties.

The present invention is based on the use of nanofibrillar cellulose in paper furnish.

Advantageously in the method according to the present invention, the manufactured paper comprises nanofibrillar cellulose material, the method comprises: introducing raw materials to a system containing raw materials including pulp and nanofibrillar cellulose material, and conveying raw materials to a paper machine in order to produce paper having nanofibrillar cellulose content between 0.1 and 5% of dry weight of furnish.

Advantageously, in the system according to the present invention, the manufactured paper comprises nanofibrillar cellulose material, the method comprises: means for introducing cellulose pulp and nanofibrillar cellulose material to the system, at least one conveyor to convey raw materials to the paper machine in order to produce paper having nanofibrillar cellulose content between 0.1 and 5% of dry weight.

The nanofibrillar cellulose used in this invention can be produced with mechanical treatment from anionized cellulose fibers and / or from cellulose fibers that are not anionized. The anionization of the cellulose fibers may be effected, for example, by reaction with the primary hydroxyl groups of the cellulose being oxidized catalytically by the heterocyclic nitroxyl compound, or by the reaction of the cellulose fibers with the carboxymethylating agent to form lightly carboxymethylated cellulose. .

Therefore, in an embodiment of the invention, cellulose fibers are oxidized by nitroxyl-mediated oxidation of hydroxyl groups in the cellulose in order to achieve anionized cellulose fibers, after which the cellulose fibers are refined into the nanofibrillar cellulose material, which is added to the paper. .

In another embodiment of the invention, cellulose fibers are reacted with a car-boxymethylating agent in order to achieve anionized cellulose fibers, after which the cellulose fibers are refined into the nanofibrillar cellulose material that is added to the paper. In this embodiment, the cellulose fibers are reacted with the agents to form a lightly carboxymethylated cellulose having such a degree of substitution that it is not soluble in water, i.e. cellulose fibers have a degree of substitution preferably between 0.05 and 0.35 carboxymethyl group per anhydroglucose unit, more preferably between 0.10 and 0.30 carboxymethyl group per anhydroglucose unit.

In another embodiment of the invention, the cellulose fibers are refined into the nanofibrillar cellulose material without anionization step, which refined nanofibrillar cellulose material is added to the paper.

Thanks to the present invention, it may be possible to achieve at least some of the advantages mentioned below: - improved initial wet web strength properties, - especially internal bond strength properties, - low air permeability and absorption properties of the product, and - limited coating usage in case of coated paper, for example limited Silicon usage in case of release liner.

In addition, by using nanofibrillar cellulose in the paper furnish it may be possible to significantly reduce the basis weight of the paper, especially glassine type paper, without sacrificing the properties of the paper. Therefore, thanks to the present invention, it is possible to maintain the level of strength of the product and, in addition, to form a denser paper structure if compared to heavier reference papers.

Aspects of the invention are characterized by what is stated in the independent claims. Various embodiments of the invention are disclosed in the dependent claims.

Description of the Drawings

In the following, the invention will be illustrated by drawings in which

Figs 1a-1e show schematically some exemplary embodiments of the invention, and

Figs 2-3 show results from experimental tests.

Detailed Description of the Invention

In the following Disclosure, all percentages are by weight, unless otherwise stated.

Figures 1 to 3 show some advantageous embodiments of the invention. The following reference numbers are used: 1 paper, 2 cellulose pulp, 2a chemical pulp, 3 anionized cellulose material, 4 nanofibrillar cellulose material, 5 chemical pre-treatment, 8 refiner, 10 refined cellulose pulp, and 20 paper machine.

Cellulose is a renewable natural polymer that can be converted to many chemical derivatives. Derivatization takes place Mostly by chemical reactions of hydroxyl groups in the β-D-glucopyranose units of the polymer. By chemical derivatization, the properties of the cellulose can be altered in comparison to the original chemical form while retaining the polymeric structure.

The term "cellulose raw material" refers to any cellulose raw material source that can be used in the production of chemically and / or mechanically treated cellulose fibers. The raw material can be based on any plant material that contains cellulose. The plant material may be wood. The wood can be from Softwood trees such as spruce, pine, fir, larch, Douglas fir or hemlock, or from Hardwood trees such as birch, Aspen, poplar, alder, eucalyptus or acasia, or from a mixture of Softwood and Hardwood. Nonwood material can be from agricultural residues, grasses or other plant substances such as straw, leaves, bark, seeds, hulls, flowers, vegetables or fruits from cotton, corn, wheat, goat, rye, barley, rice, flax, hemp, Manila hemp, sisal hemp, jute, ramie, kenaf, bagasse, Bamboo or reed.

The term "chemical (cellulose) pulp" 2a refers to the cellulose fibers that are isolated from any cellulose raw material (s) by a chemical pulping process. Therefore, lignin is at least for the most part removed from the cellulose raw material. Chemical pulp pulp is preferably sulphate wood pulp. The used chemical cellulose pulp may be unbleached or bleached. Typically, the diameter of the fibers varies from 15 to 25 pm and the length exceeds 500 pm, but the present invention is not intended to be limited to these parameters. The term "mechanical (cellulose) pulp" refers to the cellulose fibers that are isolated from any cellulose raw material by a mechanical pulping process. The mechanical pulping process could be preceded by a chemical pretreatment, producing a chemimechanical pulp. The cellulose fibers used in this invention consist of mechanically and / or chemically and / or chemically-treated cellulose fibers. Herein they are also referred to as "raw material pulp".

The term "SEC" refers to specific energy consumption.

The term "SR" refers to the so-called Schopper-Riegler freeness of pulp.

The term "WRV" refers to the value of water retention.

It is possible to use nanofibrillar cellulose 4 in mechanical pulp containing papers such as printing paper. The method according to the present invention may be used, for example, in Light Weight Coated (LWC) or Super Calendered (SC) papers. Advantageously the method according to the present invention is used in paper grades having a high chemical pulp share, i.e. in papers comprising more chemical pulp 2a than mechanical pulp. In an embodiment, at least 80% of the dry weight, more preferably at least 90% of the dry weight and most preferably at least 95% of the dry weight of the cellulose fibers used in this invention is from a chemical pulp 2a.

The term "nanofibrillar cellulose" 4 refers to a collection of isolated cellulose microfibrils or microfibril bundles derived from cellulose raw material. There are several widely used synonyms for nanofibrillar cellulose. For example: nanofibrillated cellulose (NFC), nanocellulose, microfibrillar cellulose, cellulose nanofiber, nano-scale fibrillated cellulose, m icrof i bri 11 ated cellulose (MFC), or cellulose microfibrils. Nanofibrillar cellulose described in this application is not the same material as so called cellulose whiskers, which are also known as: cellulose nanowhiskers, cellulose nanocrystals, cellulose nanorods, rod-like cellulose microcrystals or cellulose nanowires. In some cases, similar terminology is used for both materials, for example by Kuth-carlapati et al. (Metals Materials and Processes 20 (3): 307-314, 2008) where the studied material was called "cellulose nanofiber" although they were clearly referred to cellulose nanowhiskers. Typically these materials do not have amorphous segments along the fibrillar structure as nanofibrillar cellulose does, which leads to a more rigid structure. Cellulose whiskers are also shorter than nanofibrillar cellulose.

Characterizations for nanofibrillar cellulose (advantageous examples) are presented in Tables 1 to 2.

Viscosity of Nanofibrillar Cellulose: There are several commercial Brookfield viscosimeters available for measuring apparent viscosity, which are all based on the same principle. The vane spindle is preferred because of its vane geometry, which is particularly suitable for testing heterogeneous viscous materials. Low rotation speed (10 rpm) is preferable because higher rotational speed can give falsely high viscosity values. The viscosity of anionized nanofibrillar cells is measured at 0.8% concentration. Attention should also be paid to the dilutions of nanofibrillar cellulose having a constant standard concentration to be able to compare the results correctly. Further, it is that flocking is avoided. Yield Stress of the nanofibrillar cellulose can be calculated from the viscosity measurement.

Turbidity of Nanofibrillar Cellulose: Typically, nanofibrillar cellulose is substantially transparent in an aqueous medium. More fibrillated cellulose materials have lower turbidity values when compared to less fibrillated ones. The units of Turbidity from a calibrated nephelometer are called Nephelometric Turbidity Units (NTU). The measurement is carried out at a concentration of 0.1%. Suitably a sample of nanofibrillar cellulose is diluted with water.

Charge of nanofibrillar cellulose: Charge can be determined by conductometric titration.

Yield Stress of Nanofibrillar Cellulose: Yield stress can be measured at 0.5% concentration.

Characterization of Nanofibrillar Cellulose Manufactured Using Catalytic Oxidation of Fibers is presented in Table 1.

Table 1: Characterization of Nanofibrillar Cellulose Manufactured Using TEMPO Pre-Treatment of Cellulose Material.

Characterization of a nanofibrillar cellulose manufactured using a carboxy-methylating reaction is presented in Table 2.

Table 2: Characterization of Nanofibrillar Cellulose Manufactured Using Carboxymethylation of Cellulose Material.

Advantageously, the present invention is used as a solution for manufacturing low basis weight paper comprising nanofibrillar cellulose. Preferably the manufactured paper is a so-called glassine type paper. The most advantageously manufactured paper is the so-called release paper of a label laminate.

The label laminate comprises two layers which are laminated together, i.e. a release liner and a face layer are provided between the release liner and the face layer. The term "face layer" refers to the "top layer" of the label laminate, also called the face stock. The face layer forms at least one layer that is attached to another surface with an adhesive layer when the label laminate is used.

The term "release liner" refers to a structure comprising at least one backing material layer as a base material and at least one release coating layer on a Backing material layer. In other words, the backing material layer is usually coated with a thin layer of release agent, such as Silicone. Therefore, the release liner can be easily removed from the face layer when the label is adhered to a substrate

Low basis weight release paper may be needed to maximize number of labels in reel of manufactured label laminate. Nanofibrillar cellulose used as an additive for paper offers a good combination of properties difficult to obtain otherwise in a cost-effective way. Therefore, due to the present invention, it may be possible to improve the competitiveness of fiber based release papers.

Advantageously, the basis weight range for manufactured paper is between 30 and 90 g / m2, more preferably between 40 and 50 g / m2

The amount of nanofibrillar cellulose in the manufactured paper is preferably between 0.1 and 5.0 w-%, more preferably between 0.5 and 2.5 w-% (dry weight), and most preferably between 1 and 2 w-% of manufactured paper (dry weight).

The produced paper may be, among other things, coated, surface sized and / or calendered. Advantageously the produced paper is coated with at least one Silicon coating layer in order to produce a release liner for a label laminate.

The pulp from which the handsheet is made is preferably collected from the pulp flow that is going to the headbox of a paper machine. In other words, the pulp preferably comprises every compound of the base paper to be manufactured, such as fillers, chemicals, pulps, etc., but the process parameters of the paper machine cannot have any effect on the results. Typically, nanofibrillar cellulose added in a small amount in paper has one, two, three or four of the following effects on the handsheet, if the handsheet is manufactured from the pulp produced according to the present invention: - Clearly lower air permeance if compared to a reference handsheets. - Improved initial wet strength if compared to reference handsheets. - Improved tensile strength if compared to reference handsheets. - Improved Scott Bond if compared to reference handsheets. - Higher SR or WRV without adjusting beating if compared to a reference handsheets.

Nanofibrillar cellulose 4 can be added to the system as an already manufactured nanofibrillar cellulose material as shown in Figures 1a, 1c and 1e, or it can be added to a system as material to be refined into nanofibrillar cellulose material as shown in Figures 1b and 1d .

The nanofibrillar cellulose material 4 may be dosed to a short circulation of a paper machine 20. In order to guarantee proper mixing to the basic furnish, the nanofibrillar cellulose material 4 is preferably dosed to a place where shear forces are present, such as a refiner 8, a pump, a mixer or a screen. In an embodiment of the invention, nanofibrillar cellulose material 4 is dosed to a thick stock and / or to a diluted stock.

The cationic polyelectrolyte such as Starch is preferably dosed to the cellulose pulp 2 before the dosage of the nanofibrillar cellulose material 4. The cationic polyelectrolyte should be added before the dosage of the nanofibrillar cellulose material in addition to the short circulation.

The cationic polyelectrolyte can be any retention or strength polymer used in paper manufacturing, e.g. cationic Starch, cationic Polyacrylamide (CPAM) or polydimethyldiallyl ammonium chloride (PDADMAC). Also, combinations of different polyelectrolytes can be used. Preferably, the cationic polyelectrolyte is cationic Starch (CS). The cationic polyelectrolyte is added in an amount of 0.01 to 5% of the dry weight of the fibers in the furnish, preferably approximately 0.15 to 1.50% of the dry weight.

The solution may comprise a chemical pre-treatment step 5 (shown in Figure 1b), which is at least part of the cellulose pulp 2 being anionized before it is at least partially refined into the nanofibrillar cellulose to be added to the paper 1.

The terms "anionized material 3" and "anionized cellulose fibers 3" refer to a material consisting of at least 90 w-% (dry weight) of cellulose material, in which - the cellulose is oxidized by nitroxyl-mediated (such as "TEMPO" -medi -ated) oxidation of hydroxyl groups of the cellulose, and / or - cellulose is reacted with a carboxymethylating agent in order to form lightly carboxymethylated cellulose having such a degree of substitution that it is not soluble in water, ie the cellulose fibers have a degree of substitution preferably between 0.05 and 0.35 carboxymethyl group per anhydroglucose unit, more preferably between 0.10 and 0.30 carboxymethyl group per anhydroglucose unit.

If the anionized cellulose fibers comprise the lightly carboxymethylated cellulose, the manufacturing of said lightly carboxymethylated cellulose Advantageously comprises a step in which a first chemical, i.e. an alkalizing agent, is dosed and absorbed into the cellulose raw material before or during dosing of the second chemical, i.e. an anionic agent. The first chemical added to the system, i.e. an alkalization agent, may be an alkali metal hydroxide and it is used for activating the pulp. In other words, the alkalization agent activates the fibers and contributes to the penetration of the second chemical into the fibers. The alkalization agent can be added to the reaction mixture, for example, in an aqueous solution and / or in a dry state. The most preferred said first chemical (i.e. the alkalization agent) is sodium hydroxide NaOH. The second chemical, i.e. the main chemical added to the system is preferably monochloroacetic acid or salt salt, and most preferably sodium mono-chloroacetic acid. The second chemical can be added to the system in a dry state and / or in an aqueous alkaline solution and / or in a gas form in order to produce cellulosic material. According to this embodiment of the invention, a third chemical, for example H2O2 may be added to the system in order to control (i.e. to decrease) the degree of substitution of the cellulose material.

The anionized cellulose fibers may form the cellulose material which is oxidized catalytically by a Heterocyclic nitroxyl compound, for example 2,2,6,6-tetramethylpiperidinyl-1-oxy free Radical, "which TEMPO", after which the The material is refined at least partly into the nano-fibrillar cellulose. Other Heterocyclic nitroxyl compounds are known to have selectivity in the oxidation of the C-6 carbon of the glucose units of the cellulose. refers to the oxidation of the hydroxyl groups (of the cellulose) to the aldehydes and / or carboxyl groups. It is preferred that the hydroxyl groups are oxidized to the carboxyl groups, ie the oxidation is complete before the refining step in at least one refiner is Implemented.

In an advantageous embodiment of the present invention, the anionized cellulose material 3 is added to the system as a material to be refined into the nanofibrillar cellulose material 4. implemented before at least one refiner stage of cellulose pulp 2a. Most preferably the addition of said anionized cellulose material 3 is done to the unbeaten chemical pulp to be conveyed to at least one refiner 8. The cellulose pulp 2 to be conveyed to at least one refiner 8 may, in addition or instead of, comprise fibers that is pre-refined by at least one refiner. The refiner 8 is preferably a conical refiner, a disc refiner or a cylindrical refiner. If the cellulose pulp 2 and the anionized cellulose material 3 are combined with each other before at least one refiner step, the anionized cellulose material 3 is fed together with the cellulose pulp 2 through a beating process in a paper machine approach system. In this case, fibrillating of nanofibrillar cellulose takes advantage of place at least partly during pulp beating, i.e. fibers get fibrillated due to the energy consumed during the beating process. Therefore, advantageously, a separate fibrillating stage to produce the nanofibrillar cellulose is not needed in the order to refine the nanofibrillar cellulose material from the anionized cellulose material 3. The anionized cellulose material 3 has a particularly high anionic charge and, thus, is relatively easily fibrillated under shear forces. Thanks to the present invention, it is possible to mix pulp 2 and nanofibrillar cellulose efficiently with each other without any separate mixing and fibrillating aggregates.

Due to the present invention it is possible to manufacture a paper product comprising at least some of the following properties: - high wet strength, - increased dry tensile strength, - greatly improved internal bonding, - lower air permeability, and - higher transparency.

The invention can cause an effective dispersion of nanofibrillar cellulose and a proper mixing with the base furnish. In addition, thanks to the present invention, paper properties can be improved without loss of drainage speed.

Experimental tests

In experimental tests, different kind of pulps for paper products were manufactured. The paper sheets were made from the produced Pulps and tested afterwards.

Example 1

Raw materials and a trial plan

The trial comprised: - a fourdrinier type former, - a press section with two nips, - running speed at 15 m / min, - bar coating, - calendering surface temperature ~ 100 ° C, pressure setting 140 kN / m, 2 nips

Coating and calendering were done in the laboratory and the paper was made with a pilot machine.

Trial plan was adjusted to 1% and 3% addition of nanofibrillar cellulose. Starch amount was varied from 1% to 2%. The trial plan is shown in Table 3.

Table 3. Trial plan for example 1.

The paper sample size used was A4. Coated sheets were moisturized overnight at RH 80%, + 23 ° C. Air conditioning before measurements was 50% RH, + 23 ° C.

Test Results

Results based on laboratory sheets. Air permeability results are shown in Figure 2a, and tensile strength results are shown in Figure 2b.

It was shown during the experimental tests that the weight of the paper produced could be reduced to 10 g / m2 with constant or improved dry paper strength properties if only a small amount of nanofibrillar cellulose (between 1 and 1.5%) was added to the pulp. Simultaneously original wet web strength of paper was increased. Air permeability was greatly reduced even in the case of lower basis weight paper compared to reference paper. In addition, Converting tests have shown a reduction in Silicon consumption. Release values of nanofibrillar cellulose trial points were comparable to reference samples with lower Silicon weight.

Especially good results were shown with an amount of approximately 3% of nanofibrillar cellulose. An addition of 2% of CS together with the addition of nanofibrillar cellulose showed some good properties.

Example 2

Raw materials and a trial plan

The trial was implemented with realistic running conditions: - glassine type furnish, - running speed at 600 m / min, - head box, - hybrid former, and - shoe press.

Two types of anionized cellulose fibers were fibrillated: 1) Tempo-treated nanofibrillar cellulose type 1 in Figures 3a-3b, and 2) lightly carboxymethylated nanofibrillar cellulose (nanofibrillar cellulose type 2 in Figures 3a-3b).

During the trial, the two anionized cellulose material were compared with each other. In addition, the basis weight and amount of nanofibrillar cellulose were studied.

Results

The trial showed very promising results. Thanks to the nanofibrillar cellulose used in the paper: - porosity level decreased by 20%, - 10 g / m2 basis weight reduction potential was shown at constant tensile level, - 1% -unit lower brightness but up to 4% -units lower opacity , - oil absorption decreased by 20%, - significant increase in wet web strength, - both tested anionized pulps to give good results, and - no major difference between 1% and 2% nanofibrillar cellulose dosing.

Drainage is an issue with nanofibrillar cellulose. However, in pilot scale, the trials for the dry matter after the wire section were only 1% -unit. Dry matter after wet pressing seems to depend on the press construction. In addition, the reduction of grammage can improve drainage.

Figure 3a shows the effect of nanofibrillar cellulose on the tensile strength of the produced paper. As can be seen, a small amount of nanofibrillar cellulose has a strong effect on tensile strength. Figure 3b shows the effect of nanofibrillar cellulose on air permeability of the produced paper. As can be seen, the addition of nanofibrillar cellulose clearly underlined the air permeability properties of the produced paper. The paper produced from the pulp manufactured according to the present invention may have many advantages. For example, a grammage of manufactured paper may be reduced. In addition, the amount of coating may be reduced due to the new properties of the paper. Thus, the competitiveness of renewable fiber based release products against plastic may be improved due to the present invention

One skilled in the art readily understands that different embodiments of the invention may have applications in environments where optimization of a paper product comprising nanofibrillar cellulose is desired. Therefore, it is obvious that the present invention is not limited to the above-presented embodiments, but it can be modified within the scope of the appended claims.

Claims (11)

A process for preparing a paper product comprising a nanofibrillary cellulosic material, the process comprising introducing into the system raw materials comprising a cellulosic pulp (2) and a nanofibrillary cellulosic material (4) into a papermaking machine (20) the manufactured release paper having a nanofibrillary cellulose content of 0.1-5% by dry weight, more preferably 0.5-2.5% by weight and preferably 1-2% by weight, and the released release paper having a basis weight of 40-50 g / m2, and the paper has improved wet and dry tensile strength of the web as compared to paper having the same basis weight of airborne fibril cellulose. A method according to claim 1, characterized in that the prepared paper is further coated with at least one silicone coating layer. Method according to claim 1 or 2, characterized in that at least some of the nanofibrillary cellulosic material is added before the at least one mill (8). Method according to one of the preceding claims, characterized in that the nanofibrillary cellulosic material (4) comprises a material made from an anionized cellulosic material (3). A method according to claim 4, characterized in that the at least a portion of the nanofibrillary cellulosic material is ground to an anionized pulp nano-fibrous cellulosic material in at least one refiner (8). Process according to Claim 4 or 5, characterized in that the primary hydroxyl groups of the cellulose are catalytically oxidized by oxidation to the heterocyclic nitroxyl compound before the material is made into a nanofibril cellulose material (4). Process according to claim 4 or 5, characterized in that the cellulose fibers are reacted with carboxymethylating agents to obtain anionized cellulose fibers having a degree of substitution of 0.05 to 0.35 carboxymethyl groups per anhydroglucose unit, after which the cellulose fibers are made into nanofibrillar material. A method according to any one of claims 4 to 7, characterized in that the anionic cellulosic pulp is fed to at least one refiner (8) together with the non-anionic chemical pulp, and that the anionic cellulose pulp is at least partially milled in at least one refiner (8). A method according to any one of the preceding claims, characterized in that at least a portion of the nanofibril cellulose (4) is added as a ready-made nanofibril cellulose to the short circulation of a papermaking machine. A release paper comprising a nanofibrillary cellulose material and a cellulose pulp, wherein: - the amount of nanofibrillar cellulose in the prepared paper blended in a paper blend ratio of 0.1-5%, more preferably 0.5-2.5%, and most preferably 1-2% dry weight, - the paper produced has a basis weight of 40 to 50 g / m 2, - the paper produced has: improved bond strength properties, improved web wet index, and reduced air permeability properties, all compared to paper having the same basis weight without nanofibril cellulose. Use of nanofibrillary cellulose as a blending agent for paper blend for the manufacture of release paper, wherein the released release paper has a nanofibrillary cellulose content of 0.1-5% dry weight and a basis weight of 40-50 g / m2, and has improved wet strength and dry tensile strength without nanofibrillar cellulose.