PT115074B - MINERAL LOAD FLAKES CONJUGATED WITH MICROFIBRILLES AND CELLULOSE NANOFIBRILLES FOR APPLICATION IN THE PRODUCTION OF PAPER MATERIAL WITH IMPROVED PAPER PROPERTIES - Google Patents

Abstract

THIS INVENTION INTENDS TO SOLVE THE CURRENT PROBLEM OF THE USE OF SYNTHETIC, HARMFUL AND DIFFERENT ADDITIVES, IN THE PROCESS OF PRODUCTION OF PAPER MATERIAL WITH IMPROVED PAPER PROPERTIES, WITH REGARD TO THE INCREASE IN THE CONTENT OF THE STRAIN (). WITH GREATER MINERAL LOAD RETENTION, GREATER MECHANICAL RESISTANCE AND AIR RESISTANCE (SUITABLE FOR PACKING APPLICATIONS), LESS ROUGHNESS, GREATER OPACITY AND EVEN LESS CAPILLARY WATER ABSORPTION THIS INVENTION CONSISTS OF FLAKE PRODUCTS (1), FOR APPLICATION IN CELLULOSIC FIBERS (2), CONSTITUTED BY MINERAL LOADS CONJUGATED WITH MICROFIBRILLES OR CELLULOSE NANOFIBRILLES, AND THEIR USE IN THE PRODUCTION OF PAPER MATERIAL AND PAPER PRODUCTS.

Description

DESCRIPTION

MINERAL LOAD FLAKES CONJUGATED WITH MICROFIBRILLES AND CELLULOSE NANOFIBRILLES FOR APPLICATION IN THE PRODUCTION OF PAPER MATERIAL WITH IMPROVED PAPER PROPERTIES

Invention Area

The present invention is inserted in the field of paper material production, namely on products consisting of mineral fillers combined with cellulose microfibrils and nanofibrils, obtained by an enzymatic process or by a TEMPO-mediated oxidation (N-oxyl-2,2, 6,6-tetramethylpiperidine), which improve all paper properties, making it possible to reduce the amount, or without the need to add, additives that are normally expensive and harmful to the environment.

State of art

Competitiveness in the paper industry has increased significantly. In order to improve paper properties, it is essential to optimize the underlying processes, with a view to new horizons, such as the synthesis of new materials. Cellulose nano and microfibrils (CNF and CMF, respectively) are a relatively recent material that have proven to significantly improve the strength of the paper. These have unique characteristics, such as small size and high specific surface area, high tensile strength, crystallinity and transparency, therefore being an object of high interest, mainly as reinforcement material in composite structures. For the production of these new fibrous structures, different raw materials and methodologies can be used, and mechanical treatments are usually used to defibrillate the fibers. In order to avoid high energy consumption and overcome technical difficulties inherent to the process, pre-treatment of fibers through chemical or enzymatic strategies has become common.

The use of CNF / CMF in paper production has been the subject of several studies since they improve the strength of paper, content of mineral fillers and other specific properties, such as absorption. In paper production, these tend to appear in combination with additives commonly used in the industry, such as internal resistance agents (eg cationic starch), internal sizing agents (eg ASA-Alkenyl Succinic Anhydride or AKD-Alkyl Ketene Dimmer) or agents retention (eg cationic polyacrylamides). The published inventions refer that the mixture of CNFs with the aforementioned additives interferes positively in the bonds between cellulosic fibers and mineral fillers. In this sense, it is extremely important to understand the diverse and complex interactions and mechanisms involved between the different components of the role.

WO2018100524A1 describes the invention in which microfibrillated cellulose is mixed with at least two retention agents (cationic polymer, e.g. starch, and micro or nanoparticles, e.g. silica or bentonite) as a premix before paper production. Mixtures with mineral fillers are not described.

The EP2236664A1 invention refers to the mixture of cellulosic fibers with mineral fillers only for the purpose of producing nanofibrilated cellulose, through a more efficient process. It does not demonstrate any simultaneous improvement of a plurality of paper properties of the paper produced with the new product obtained by the described method.

Publication WO2016 / 185397A1 also mentions the production of mineral fillers directly in a suspension of microfibrillated cellulose, which can be used to produce paper with better drainability. There is no reference in the document cited about the simultaneous improvement of a plurality of paper properties, such as an increase in the tensile index, with greater retention of mineral fillers, greater mechanical resistance and resistance to air, less roughness, greater opacity and even less capillary absorption. of water. Additionally, mineral charges, and their effect, are associated with the use of a precursor, in this case carbon dioxide with a certain size of its gas bubbles.

EP publication 2978894 B1 defines the papermaking process which consists of mixing microfibrillated cellulose with a resistance agent (e.g. starch) and later a microparticle (e.g. silica or bentonite).

article He et al. (2017) states that a composite of CMF, precipitated calcium carbonate (PCC) and cationic starch gives rise to large flakes that allow for improved PCC retention.

EP 2425057 BI discloses the methodology for preparing an aqueous suspension to be used in the production of paper. The suspension mentioned is composed of mineral fillers, fibers, nanofibrilated cellulose and a cationic polyelectrolyte (preferably cationic starch). It is stated that the retention of mineral fillers and the strength of the paper are improved if the combination of fillers, CNF and starch is used.

The publication WO2015101498A1 discloses a methodology that provides a composition of pretreated fillers, containing PCC, cationic polyacrylamide and nanofibrilated cellulose. The aggregates of pre-treated loads referred to were characterized by Measurement of Reflectance by a Focused Light Beam (FBRM) and are considered responsible for the improvement of paper properties.

Publication US2017 / 0284030A1 refers to the application of cellulose microfibrils and inorganic particles in a layer on the surface of a paper structure. Although the described surface layer (containing the cellulose microfibrils and inorganic particles) does not contain additives, the document describes that the paper structure must contain approximately 2% of additives, such as flocculants, drainage / formation additives, thickeners, starch and retention agents. Additionally, 3 there is no reference to flakes made up of mineral fillers and cellulose fibrils with a certain intrinsic viscosity, refloculation capacity and associated size. Nor is it mentioned the simultaneous improvement of a plurality of paper properties, such as an increase in the tensile index, with greater retention of mineral fillers, greater mechanical resistance and resistance to air, less roughness, greater opacity and even less capillary water absorption.

Taking into account the published knowledge, there remains a need to achieve an overall improvement of a plurality of paper properties, using efficient, economical and environmentally friendly products and methodologies, with the possibility of reducing the quantity, or without the need to add , of additives normally expensive and harmful to the environment.

Reference Author Title WO 2018 Kaj Backfolk, Pre-mix useful in the 100524 Al Isto Heiskanen, Esa Saukkonen manufacture of a fiber based product EP 2978894 BI Mikko Virtanen Process for production of paper or board He et al. Ming He, Guihua Effects of addition method (2017) Yang, Byoung-Uk Cho, Yong Kyu Lee, Jong Myoung Won and fibrillation degree of cellulose nanofibrils on furnish drainability and paper properties EP 2425057 Janne Laine, Method for producing BI Monika Österberg, Delphine Miguel, Leila Pohjola, Irmeli Sinisalo, Harri Kosonen furnish, furnish and paper WO 2015 Matti A method for providing a 101498 Al Hietaniemi, Mikko Virtanen, Katariina Torvinen, Terhi Saari, Hellén Erkki pretreated filler composition and its use in paper and board manufacturing

EP 2236664 Al Patrick A. C. GaneJoachim SchoelkopfDaniel GantenbeinMichel SchenkerMichael PohlBeat Kíibler Process for the production of nano-fibrillar cellulose suspensions WO 2016/185397 Al This HeiskanenKaj Backfolk Production of nanosized precipitated calcium carbonate and use in improving dewatering of fiber webs US 2017/0284030 Al Per SvendingJonathan Stuart PhippsJohannes KritzingerTom LarsonTania SelinaDavid Skuse Paper and paperboard Products

Summary of the invention;

This invention aims to solve the current problem of the use of synthetic additives, harmful to the environment and expensive, in the process of producing paper material with a plurality of improved paper properties.

This invention consists of flake products consisting of mineral fillers conjugated with cellulose microfibrils and nanofibrils, obtained, respectively, by enzymatic route or via an oxidation mediated by N-oxyl-2,2,6,6tetramethylpiperidine - TEMPO - which, unexpectedly, they confer a plurality of globally improved paper properties to the paper material and it is possible to reduce the amount, or without the need to add, of additives normally expensive and harmful to the environment.

Additionally, this invention consists of paper material, produced from flakes of mineral fillers and cellulose microfibrils or nanofibrils (obtained through enzymatic hydrolysis and TEMPO-mediated oxidation (N-oxyl-2,2,6,6- tetramethylpiperidine), respectively), described above. The product obtained has a globality of improved paper properties, such as an increase in the tensile index (dry and wet), greater retention of mineral fillers, greater mechanical resistance and resistance to air, less roughness, greater opacity and even less capillary absorption. of water, making it possible to reduce the amount, or even without the need for the addition, of expensive additives, such as starches, ASA, and cationic polyacrylamides.

Brief description of the figures:

Figure 1. Characterization of the different CNF / CMF produced and the bleached pulp for comparison.

Figure 2. Quantities (in%) of the different components for the different series of formulations for the production of sheets of white eucalyptus pulp.

Figure 3. Evolution of the average particle size in the suspension containing PCC and CNF / CMF. A PCC-only test was also considered for comparison.

Figure 4. Evolution of the average particle size in the suspension containing PCC and CMF-E1 produced with an increasing number of passages in the HPH. A PCC-only test was also considered for comparison.

Figure 5. Retention of PCC in the leaves produced with the flakes produced with the CNF / CMF from different processes and additives. The horizontal line represents the one normally used, that is, sheets without flakes and with PCC and with all additives.

Figure 6. Standardized PCC-traction factor for the same PCC content of sheets produced with flakes produced with CNF / CMF obtained by different processes and with different additives, and relationship with the current reference (without flakes and with PCC and with additives).

Figure 7. Leaf tensile index produced with CMF-E1 flakes, with and without additives. The black column refers to sheets produced with an extra 5% addition of PCC.

Figure 8. Factor PCC-tear normalized to the same content in PCC of sheets produced with flakes produced with CNF / CMF obtained by different processes and with different additives, and relationship with the current reference (without flakes and with PCC and with additives).

Figure 9. Standardized PCC-opacity factor for the same PCC content of sheets produced with flakes produced with CNF / CMF obtained by different processes and with different additives, and relationship with the current reference (without flakes and with PCC and with additives).

Figure 10. Wet tensile index of leaves produced without additives with flakes produced with CNF-T3 or CMF-E1 and reference sheets (without flakes and with PCC and with additives).

Figure 11. Influence of the addition of PCC + CMF-E1 flakes on the leaf tensile index produced with refined pulp at different ° SR. The PCC-traction factor was calculated based on the reference produced with 2 9 ⁰ SR paste + PCC + additives.

Figure 12. Structural properties of the leaves produced with the flakes produced with the different CNF / CMF and additives.

Figure 13. Value of water retention (WRV) and capillary water absorption (Klemm test) of laboratory sheets with flakes produced with the different CNF / CMF and additives.

Figure 14. CNF / CMF production costs and the respective addition of 3% to the paper production process.

* Fiber cost estimated at 700euros / metric ton ** Energy cost assumed to be 0.02 euros / MJ, excluding water consumption costs

Figure 15. Flakes (1) attached to a cellulosic fiber (2), by scanning electron microscopy with field emission of a sheet produced with cellulosic fiber and flakes.

Detailed description of the invention:

In this invention enzymatic microfibrillated (CMF) and nanofibrillated (CNF) celluloses by TEMPO oxidation are individually combined with mineral fillers for use in the production of paper material, increasing their paper properties with the reduction of the quantity, or without the need for addition, other additives.

Microfibrillated (CMF) and nanofibrillated (CNF) celluloses can be synthesized through different processes, mechanical, enzymatic and / or chemical.

The sizes of the fibrils make it possible to distinguish between nanofibrils and cellulose microfibrils (Kargarzadeh H., Mariano M., Gopakumar D., Ahmad I., Thomas S., Dufresne A., Huang J., Lin N. (2018 ) Advances in cellulose nanomaterials, Cellulose 25: 2151-2189). In the proposal for standard TAPPI WI 3021 (TAPPI Standard proposal WI 3021. Standard terms and their definition for cellulose nanomaterials, draft), cellulose nanofibrils are defined as having a width of 5-30nm and cellulose microfibrils with a width of 10-100nm. Additionally, the nanofibrillation yield, that is, the nanofibril ratio of the different samples, was determined, Figure 1. For this, centrifugation and gravimetry are used (as defined in the ISO / CD TS 21346). Samples composed mainly of nanofibrils (that is, with a nanofibril ratio - nanofibrillation yield - greater than 50%) and CMF are samples composed mainly of microfibrils (ie, with a nanofibril ratio - nanofibrillation yield below 50) %).

In addition to microfibrillated cellulose (CMF) produced by enzymatic hydrolysis with endoglucanases (according to the methodology proposed by Tarrés et al. 2016) and identified here as CMF-E1 and CMF-E2, and nanofibrillated cellulose (CNF) produced by TEMPO-mediated oxidation, N-oxyl-2,2,6,6-tetramethylpiperidine (according to the methodology proposed by Saito et al. 2007), commonly referred to by experts in the art as TEMPO nanofibrillated cellulose, CNF-TEMPO, and here identified as CNF-T3 and CNF-T9, were also considered CNF / CMF produced in different ways, namely by mechanical refining (identified here as CMF-Mec) and by carboxymethylation with different amounts of 9% monochloroacetic acid and 27% (identified as CNFC9 and CNF-C27, respectively).

In the case of enzymatic cellulose microfibrils (CMF), they are produced from 0.03 kg of bleached eucalyptus kraft pulp, which was disintegrated and refined at 4000 rotations in a PFI type refiner. Then the fibers undergo an enzymatic hydrolysis with different commercial enzymes: El enzyme (endocellulase, 10% exocellulase and 5% hemicellulose) and E2 enzyme (endocellulase with 10% hemicellulose). The protein content of the enzymes was determined by the Bradford method (Bradford, 1976) with bovine whey protein (BSA), with values of 5.0 and 5.8 kg / m ^{3 being obtained} for the enzymes E1 and E2, respectively. The fibers are suspended in water, at a consistency of 3.5%, and the pH is adjusted to the value of 5, with a sodium citrate buffer. The suspension is then heated to 323.15 K, with continuous mechanical stirring, and the enzyme is finally added (3x10 ^-4 kg per kg of paste). The hydrolysis is terminated after 7200 s, by heating the suspension to 353.15 K and for 900 s. The resulting suspension is cooled to room temperature.

In the case of CNF produced by oxidation, the refined fibers were mixed in an aqueous suspension containing NaBr and TEMPO at room temperature. Then, a solution of sodium hypochlorite (NaClO) in the proportion of 3 or 9 mol per kilogram of fiber was added slowly to the previous mixture, maintaining the pH at 10 with NaOH for two 9 hours, producing the samples CNF-T3 and CNF -T9, respectively.

Both the enzymatic samples and the TEMPO were thoroughly washed with demineralized water until a low conductivity of the filtrate was obtained. After these enzymatic and fiber oxidation treatments, they are finally mechanically treated, to a consistency of 1%, in a high pressure homogenizer (HPH, GEA Niro Soavi, model Panther NS3006L), first at 5x10 ⁷ Pa and then to 10x10 ⁷ Pa. This mechanical treatment is intensive, preferably two passes (total pressure 15x10 ⁷ Pa).

It was also possible to characterize the CNF / CMF produced by different methods, with regard to nanofibrillation yield, content of carboxylic groups, intrinsic viscosity (degree of polymerization) and surface electrical charge (zeta potential), as shown in Figure 1. One Adequate characterization of this type of material is essential and the parameters to be measured may vary depending on the type of intended use. Usually the amount of material at the nanoscale, the average particle size and size distribution, surface chemistry and mechanical properties are the most measured, but also the crystallinity, specific surface area and rheology of the suspensions depending on the future application.

The intrinsic viscosity was measured by dissolving in cupriethylenediamine, according to the ISO 5351: 2010 standard, and the degree of polymerization was calculated using the Mark-Houwink equation, using the parameters defined by Henriksson et al. 2008.

In Figure 1, the amount of nanofibrils allows to distinguish the nanofibrillated samples (CNF), which also correspond to the functionalized samples and therefore with a high degree of carboxylic groups and high zeta potential (absolute value), from the microfibrillated samples (CMF).

Five different series of formulations were prepared and used in the preparation of laboratory sheets, with regard to the content in bleached eucalyptus pulp 10 refined up to 33 ° SR (degree of refining, Schopper Riegler), in CNF / CMF, in carbonate of precipitated calcium (PCC), in cationic starch, in alkenyl succinic anhydride (alkenyl succinic anhydride (ASA)), and / or in linear cationic polyacrylamide (CPAM). These compounds are those commonly used to improve paper properties in the production of paper sheets.

Figure 2 indicates the quantities considered.

In the next step, PCC flakes are produced with cellulose micro or nanofibrils. Initially, an aqueous suspension of precipitated calcium carbonate (1% by weight) and an aqueous suspension of the enzymatically obtained cellulose microfibrils or TEMPO nanofibrils (0. 2% by weight) are prepared. The calcium carbonate and the cellulose micro or nanofibrils, in a mass ratio of 10: 1, respectively, and in a total solids concentration of approximately 0.01% also by weight, are mixed under agitation (2000 rpm). After 1200 s of agitation, sonication is applied for 900 s to break the flakes. At the end of 900 s, the stirring continues for another 1800 s.

An important factor in the improvement of the papermaking potential will be the evaluation of the interaction of the CNF / CMF with the PCC, through flocculation tests. In fact, mineral fillers, such as PCC, are not able to form sufficiently strong bonds with cellulosic fibers and therefore in the sheet formation process a large amount is lost through the web. The efficient flocculation of these, which promotes particle sizes high enough to prevent their loss, but with controlled sizes so as not to harm the subsequent formation of the leaf, is essential. As mentioned, usually the flocculation of inorganic fillers is done using synthetic additives, such as cationic polyacrylamides or cationic starch.

Thus, the size of the flakes is controlled over time by light diffraction measurements on a Mastersizer 2000 equipment (Malvern Instruments), equipped with the Hydro2000 module and using a PCC refractive index of 1.57 and Mie's theory for processing measurements. The measurement technique was initially reported by Rasteiro et al. (2008) for mineral loads (without CNF).

It was possible to verify, as seen in Figure 3, that the CMF obtained mechanically do not cause flocculation of the PCC and in the case of CNF via TEMPO, only one case originated flocculation, the CNF-T3, with a final flake size of approximately 50 μm. For CNF obtained by carboxymethylation, a strong flocculation was observed. In the case of enzymes, there was also a strong flocculation, obtaining flakes with dimensions of 27 μm. The size of the flakes varies significantly with the properties of the CMF. In the case of enzymes, the intrinsic viscosity should be less than 0.75 m ³ / kg, more preferably in the range 0.45-0.70 m ³ / kg, corresponding to a degree of polymerization between 1000 to 2000, in order to produce flakes with the sizes mentioned above. Supplementary studies for this work indicate that CNF-TEMPO should have an intrinsic viscosity greater than 0.10 m ³ / kg, more preferably in the range 0.12 0.21 m ³ / kg, which corresponds to a degree of polymerization between 300-500, and a amount of carboxylic groups less than 1.4 mol / kg, in order to be able to cause an efficient flocculation of PCC particles, namely, with flakes of sizes between 20 to 50 pm (after breaking the flakes and refloculation). In the case of CMF-E1, the influence of the number of passes in the homogenizer on the PCC flocculation was also studied. Thus, 2, 4 or 6 passes (corresponding to a total pressure of 12.5 ^{x 10 7} , 27.5 x 10 7 and 42.5 ^{x 10 7} Pa, respectively) gave rise to microfibrils with decreasing degrees of polymerization (1834, 1747 and 1504, respectively) and with decreasing capacities flocculation (Figure 4). The CMF-E1 produced with two passes (total of 12.5 x 10 ⁷ Pa) in the HPH originated the largest flakes, with average sizes of 28 pm (after breaking the flakes and subsequent refloculation).

For the preparation of the leaves, with the formulations and quantities described in Figure 1, the flakes produced are added to the bleached refined eucalyptus fiber, under agitation. After 120 seconds, the remaining additives are added. The cationic starch + ASA mixture is stirred with the previous mixture for 150 seconds and the cationic polyacrylamide for 5 seconds. The formulations go to the leaf former, where the steps of agitation (5 seconds), decantation (5 seconds) and drainage (time dependent on the formulations) are automatically carried out. The sheets are pressed, dried and conditioned according to the ISO 5269-1 standard. The structural, optical and mechanical properties are measured according to the corresponding standards: grammage (ISO 536: 2011), Gurley air resistance (ISO 5636-5: 2003), Bendtsen roughness (ISO 8791-2: 2013), index of traction (ISO 1924-2: 2008), tear index (ISO 1974: 2012), opacity (ISO 2471: 2008) and Klemm capillary water absorption (ISO 8787: 1986). The retention of mineral charges in the fibrous matrix was evaluated by the TAPPI T 211 om-93 standard.

The increase in the content of mineral fillers in the paper material is desirable, not only for environmental reasons, since the use of cellulosic fibers is reduced, but also for economic reasons since the fibers are normally much more expensive and papers with a high content of loads lead to more effective sheet drying. In addition, its use is useful in controlling important properties, such as opacity, surface smoothness and printability. However, mineral fillers have a negative effect on the strength of the paper, due to the breakage of fiber-fiber connections, and losses through the web, as mentioned above, make it necessary to add retention agents to the process, in addition to problems underlying formation and printing (delamination of the sheet and / or detachment of material on the surface of the paper). For this reason, the content of mineral fillers is usually limited to values below 30% of the total weight of the leaf.

In this way, sheets were prepared according to the different formulations specified in Figure 2, in a discontinuous type bench former (300-1 model, LabTech), using a 120 mesh web.

The percentage of PCC retention was thus measured for the 5 different series of formulations mentioned above and used for the production of bleached eucalyptus pulp sheets. Figure 5 represents the retention of PCC in leaves produced with CNF / CMF from different processes and additives.

As explained above, with the exception of CNF-T9, the presence of CNF / CMF, and the consequent strong PCC flocculation, leads to high PCC retention, even in the absence of additives. When comparing with the method that simulates what is currently used in the paper production process, that is, use of PCC with all additives but without CNF, an increase in PPC retention is observed with the benefit of not using additives expensive, like CPAM.

Paper materials have a high mechanical resistance requirement in order to overcome all the stresses to which they are subjected in the paper machine, but also in industrial printers. However, there are several factors that negatively influence this factor, such as the use of recycled fibers and mineral fillers or the need to reduce grammage (to save on the use of virgin fibers, for example). The strength of the paper material depends on the strength of the fibers used as well as the strength of the bonds between them. The tensile index is the property most commonly used to assess mechanical strength, being directly associated with the content of mineral fillers in the paper. Thus, another way to analyze the results obtained will be through a mineral load-traction factor, which consists of a correction of the traction index, when considering the effective content of PCC (mineral load) in the leaves. We then have:

Mineral load factor - traction: (traction index x load content) with flakes / (traction index x load content) with PCC and with additives. If the value of this factor is greater than 1, we will have sheets with a tensile index value higher than that of the reference sheets, that is, without flakes and with PCC and with additives.

same factor and respective considerations were applied to the tear index and opacity.

These values are shown in Figures 6, 7 and 8.

When using the TEMPO nanofibrils with lower load (CNF-T3) in the production of the flakes, it appears that the tensile index is only improved compared to the reference, if additives are not used. In fact, the negative charge of the nanofibrils seems to attract the added cationic additives, which are therefore not available to bind to the fibers and improve the mechanical strength, as observed in Figure 6 in the series containing additives. It is also possible to observe that with the enzymatic CMF flakes the traction index is always improved in relation to the reference, either in the presence or in the absence of additives, with factors greater than one. In addition, when removing the CPAM, the greatest increase in traction is also obtained with the enzymatic CMF flakes, which seems to suggest that the long chain length of these microfibrils can overcome the effect of the CPAM. Due to the great improvement of the paper properties with the flakes produced with the enzymatic CMF El, an additional series of sheets was made, with an extra incorporation of 5% of PCC and without additives (Figure 2). The results of the tensile index (Figure 7) reveal that it is possible to produce sheets with the same mineral filler content as the reference (without flakes and with all additives), and a higher tensile index, but without the need to add additives.

effect of the flakes on the tear index did not follow the same trend (Figure 8). In this case, only with the flakes with CNF-C27 there was an improvement in the tear rate in the absence of additives. However, in the presence of starch + ASA or in the presence of all additives, it is noted that with the flakes produced with non-functionalized CMF (CMF-Mec, CMF-E1 and CMF-E2) there is a great increase in this property.

Additionally, with the CMF-E1 flakes, better results were observed (both in the tensile and tear index) than with the CMF-E2 flakes, probably due to the presence of exocellulase in the composition of the enzyme El.

The optical properties, here assessed by opacity (Figure 9), were also improved, both in the absence and in the presence of additives.

In addition to dry resistances, wet resistance has also been significantly improved with the use of flakes. Figure 10 represents the tensile index obtained for different degrees of humidity of leaves produced without additives and with the flakes produced with CNF-T3, CMF-E1 and CNF-C9. Reference sheets (without flakes and with PCC and with additives) are also shown. All the sheets represented have the same content of mineral fillers (26 to 28% effective). In addition, reference sheets produced under the same conditions (with additives), but containing 25% long fiber, which is normally used to provide resistance to breaks in a paper machine, were analyzed. These results are extremely important for the operation of the paper machine: for common humidity levels in the drying section (7 to 50%), the flakes can contribute to the reduction of breaks in the paper sheet and / or to the increase of the machine speed due to improved wet mechanical resistance. Thus, it can be seen in Figure 10 that the flakes used are also able to replace the need to use long fiber, since the wet resistance is the same as that of the reference sheets.

Figure 11 shows the results of the production of leaves with bleached eucalyptus pulp with different degrees of refining (1300, 1800 and 2300 rotations corresponding to degrees of refining of 25, 27 and 29 ° SR (Schopper Riegler degree), respectively). It is possible to observe that the addition of the PCC flakes with CMF-E1 to laboratory sheets without additives allows to save more than 4 ° SR in the refining of the matrix paste and still obtain the same mechanical strengths. However, load retention is slightly affected, so a PCC-traction index was calculated, based on the reference produced with refined pulp at 2300 rotations PFI (29 ° SR) + PCC + additives (7XA + P). It appears that the limit for improvements is above 26 ° SR, that is, by adding the PCC flakes with CMF-E1, it is possible to produce sheets with the same content of mineral fillers and with the same tensile index as the than the reference sheets, but saving on the refining of the used pulp.

Figure 12 shows results for air resistance, measured by the Gurley method and for Bendtsen roughness, structural properties of relevance for the different sheets produced. As widely reported, the use of CNF / CMF leads to less drainage capacity, as the structure becomes more closed. However, compared to the performance of the flakes produced with CNF obtained by chemical treatments (such as TEMPO oxidation or carboxymethylation), the air resistance is not as altered when the enzymatic CMF flakes are used.

The ability of the fibrous matrix to retain water was assessed by the water retention value (WRV) and the ability to absorb water by the Klemm capillary rise test (Figure 13). In the absence of additives the flake sheets retain less water than the reference, but in the presence of any of the additives the flake leaves retain much more water than the reference, which may hinder the drying process in a paper machine. However, when using an extra 5% of PCC in the paper formulation with starch + ASA and flakes produced with CMF-E1, it was possible to obtain the same WRV value as that of the reference sheet with all additives (WRV = 1.22 ± 0.02 kg / kg), in addition to the high mechanical strength mentioned above. On the other hand, capillary water absorption has always been reduced in the presence of flakes, which means that there will be less penetration of liquids than in reference sheets without flakes, such as surface bonding formulations applied to the paper machine. .

It is also possible to show that the production of flocs with enzymatic CMF and its addition to the production of paper material is one of the ones with the lowest costs, as shown in Figure 13.

Example

In a preferred form of this invention, the microfibrillated and nanofibrillated celluloses are obtained by enzymatic hydrolysis or by TEMPO-mediated oxidation (N-oxyl2,2,6,6-tetramethylpiperidine), followed by high pressure homogenization (intensive mechanical treatment of two passages with a total pressure of 15 x 10 ⁷ Pa). CMFEnzimáticas have an intrinsic viscosity of less than 0.75 m ³ / kg, more preferably comprised in the range 0.45-0.70 m ³ / kg, corresponding to a degree of polymerization between 1000 to 2000, while CNF-TEMPO have less than 1.4 mol / kg of carboxylic groups and should have an intrinsic viscosity greater than 0.10 m ³ / kg, more preferably in the range 0.12-0.21 m ³ / kg, which corresponds to a degree of polymerization between 300-500, in order to flocculate mineral particles ( such as precipitated calcium carbonate, natural calcium carbonate and kaolin). The flakes formed are able to reflect after forced breaking, e.g. using sonication, and have an average size (measured by laser diffraction spectroscopy) of 20 to 50 pm. The use of these flakes, constituted by the described microfibrils and nanofibrils and mineral particles, in the production of paper material allows the improvement of paper properties, with regard to the increase in mechanical resistance (increases of 41% and 99% for tensile index dry and with 50% humidity, respectively, and 20% increase for tear index), slight increase of 2.2% in the retention of mineral loads, greater air resistance, less surface roughness (decrease of 65%), greater opacity (increase of 0.2%) and even lower capillary water absorption (Klemm test, decrease of 24%), when compared to the reference (paper material without flakes and with PCC, starch, ASA and CPAM, which are commonly used additives, expensive and possibly negative for the environment). In addition, these increases are possible when reducing or even eliminating the use of any other additives.

We have then described here the use of the flakes (Figure 15) disclosed in this document in papermaking production processes, with a plurality of improved papermaking properties, and which allows a reduction in the commonly used amount of paper additives, or even without the use of any paper additive.

These flakes can thus be used in processes with greater retention of mineral fillers and reduction in the amount of paper additives, when compared to paper material produced under the same conditions but without the said flakes.

The resulting paper material and which incorporates the flakes described in this invention has improved paper properties, namely mechanical, structural and optical, and with a lower amount of added paper additives or even without any amount of added paper additives.

These flakes work as well as reducing the amount of internal resistance agents, internal bonding agents and retention agents commonly used in papermaking processes and incorporated in papermaking material.

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Aveiro, September 18, 2020

Claims (4)

Claims 1. Flakes for improving the paper properties of paper material, with or without the use of paper additives, characterized by having a size between 20-50 pm in refloculated form and by comprising mineral fillers selected from the group consisting of calcium carbonate precipitate, natural calcium carbonate or kaolin and cellulose fibrils selected from the group consisting of: enzymatic cellulose microfibrils with an intrinsic viscosity between 0.45-0.70 m ³ / kg or, cellulose nanofibrils via N-oxyl-2,2,6,6tetramethylpiperidine - TEMPO with an intrinsic viscosity between 0.12-0, 21 m ³ / kg and an amount of carboxylic groups less than 1.4 mol / kg. 2. Use of the flakes, described in the previous claim, characterized by being used in the production of paper material. 3. Use of flakes, according to the previous claim, characterized by being used as reducers of the amount of internal resistance agents, internal sizing agents and retention agents used in papermaking production processes. 4. Paper material characterized by comprising the flakes described in claim 1. Aveiro, September 18, 2020