LU500847B1

LU500847B1 - Use of hydrophilic zeolites in the production of cellulose-based (cardboard) packaging

Info

Publication number: LU500847B1
Application number: LU500847A
Authority: LU
Inventors: Andrej Kovic; Tomaz Fakin; Alenka Ristic; Janja Zule; Logar Natasa Zabukovec; Marko Zmazek; Tea Kapun; Alenka Pusar-Jeric
Original assignee: Kolicevo Karton D O O; Kemijski Institut Nat Institute Of Chemistry; Silkem D O O
Priority date: 2021-11-11
Filing date: 2021-11-11
Publication date: 2023-05-11
Also published as: EP4180573A1

Abstract

The present invention is related to the field of chemical technology, specifically paper technology. It refers to the use of zeolites in the production of cellulose-based products or cellulose fibres for the purpose of controlling the sensory and mechanical properties of the final products.

Description

USE OF HYDROPHILIC ZEOLITES IN THE PRODUCTION OF LU500847

CELLULOSE-BASED (CARDBOARD) PACKAGING

FIELD OF THE INVENTION

BACKGROUND OF THE INVENTION

Several types of raw materials can be used for the production of products based on fresh pulp or freshly harvested cellulose fibres. The most common raw materials for the production of the cellulose-based products or cellulosic fibres are: bleached cellulose, semi-bleached cellulose, unbleached cellulose and wood pulp. Some other raw materials can also be used, which are not so often represented, but are not excluded from the processes described. The composition of the wood fibres contains besides cellulose, lignin, hemicellulose and extracts, also metals such as manganese, copper, iron, and others metals can also be found. These metals, in free form, can act as catalytic centres for the reactions of an autocatalyzed radical reaction of fatty acid oxidation (referred to as "fatty acid oxidation" or "oxidation"). Manganese, copper and iron are the most problematic, but other elements may be involved in the oxidation as well. In the wood pulp, the presence of manganese is the highest, meanwhile copper and iron form more complexes with other components of lignocellulose components. The oxidation of fatty acids results in the breakdown of the molecules into smaller volatile organic compounds, which can be detected either by gas chromatography or by smell, as the product’s own odor. One of the most commonly present fatty acid degradation products is hexanal, which is measured in the final products by gas chromatography or spectroscopy methods. The beginning of the free radical oxidation reaction is gradual and the intensity changes over time according to the amount of the fatty acids and resins that are presented. This reflects in the unpleasant odor of the cellulose based packaging. For this purpose, various complexants and chelating agents are added to the production of the fibres and packaging products. They enable the binding and fixation of metal ions into their structures and thus prevent the oxidation. Unfortunately, chelating agents are in many cases expensive, even more they are environmentally and healthy hazardous materials, therefore new solutions are being sought. The most common and long-term most effective chelating agents are DTPA, EDTA, HEDTA, GLDA, MGDA, NTA,

EDG and their derivatives. Their mechanisms of the complex formation are not selective and they affect all free cations in the suspension where they have high stability which ensures their efficiency. Furthermore, they are deposited in the sediments and tissues of living organisms and can cause poisoning. Nevertheless, EDTA and HEDTA can be found as additives in the food industry. There are other complexes based on organophosphorus acids and other organic complexes, but their long-term effectiveness may be questionable and the initial formation of inhibition may be limited by the production process, having several different factors such as LU500847 pH, saturation of the suspension with other ions, moisture in the product, etc.

Zeolites are crystalline aluminosilicate materials with a microporous structure containing channels and / or cavities of molecular dimensions. The zeolite framework is composed of SiO4 and AIO, tetrahedra that connect to each other via common oxygen atoms into a three- dimensional network. À framework structure is formed of channels and / or cavities containing cations and water molecules. Channel structures can have one-, two- or three-dimensional channel systems, with two or three-dimensional systems interconnected or not interconnected.

Cavity structures are characterized by cavities with shapes of different polyhedra that are interconnected through common multi-membered rings. The use of synthetic zeolites in catalysis, separation and adsorption processes is due to their unique properties such as crystallinity, thermal stability, large specific surface area, ordered microporous structure, presence of catalytically active acid sites, ion-exchange capacities and ability to selectively separate according to the size of the molecules. Due to their different Si / Al molar ratios, they have hydrophilic (low Si / Al) or hydrophobic (high Si / Al) properties. The ion exchange ability of zeolites allows the exchange of metal cations from the environment with cations in the pores of the zeolite. The cations in the pores enable the crystal lattice of the zeolites to be stabilized by neutralizing the charge of the present embedded aluminium atoms in the silicate structure.

The most important ion-exchange zeolites include zeolites: zeolite 4A with Linde Type A structure type (LTA), zeolite P with gismondine structure type (GIS) and zeolite X with faujasite structure type (FAU). These are hydrophilic zeolites. The LTA structure type consists of associated sodalite cages. The pores form of an 8-membered ring having a diameter of 0.4 nm. The faujasite structure type consists of sodalite cages that are associated with hexagonal prisms. The pores form of a 12-membered ring having a relatively large diameter of 0.74 nm.

The inner cavity is 1.2 nm in diameter. The gismondine structure type is constructed of double chainsthat are connected by 4-membered rings to form a channel of 8-membered rings leading to the formation of a two-dimensional channel system. Channel apertures are 0.31 x 0.45 nm and 0.28 x 0.48 nm in size.

The use of zeolites in the production of bleached cellulose fibres has been recorded in the past. The main purpose of using zeolite was to bind metal ions in order to prevent the breakdown of the bleaching agent, i.e. hydrogen peroxide (US5227022). Complexation processes for various metal ions (iron, magnesium, manganese, copper, etc.) were also used in the processes of delignification and bleaching of cellulose fibres. These metal ions are disruptive at the yield of the delignification process, because the added reactants change only the oxidation state of the unwanted metal cations, which are present. The described problems are known in technological processes, chloride or hypochlorite bleaching, sulphite and sulphate bleaching, and oxygen-based bleaching processes (bleaching with hydrogen peroxide or other peroxo compounds, oxygen bleaching, and ozone bleaching). EP0540076 (EKA NOBEL AB, 5.5.1993) and (NZ244868) disclose the use of a high SiO; : AlO; molar ratio of the hydrophobic type for the manufacture of sized paper by forming and dewatering a suspension of lignocellulose-containing fibres. Due to the inert nature of zeolite, it can be used in paper production in a very wide pH range. The document also relates to the use of a high

SiOz : AlzO3 (from 25:1 to 50:1) molar ratio of the hydrophobic pentasil-type zeolite (ZSM-5) zeolite for the manufacture of packaging paper. In the case of cardboards intended for solid or liquid food, tobacco or medical products, such hydrophobic zeolite is also used to reduce the transfer of undesirable taste from the package to its content of the substance by adsorption of the non-polar organic substances. Patents US2003051637 and US2005269050 describe the LU500847 use of natural zeolite as a filler to facilitate the production of coated inkjet and digital printing papers with improved quality and economy, to improve the properties of coated paper and cardboard for flexographic and water engraving, for low wear, to provide improved coefficient of friction retention of microparticles in paper making and to improve the efficiency of degreasing processes. The addition of zeolite can improve the whiteness and opacity of the paper (FR2494736), while the zeolite molecular sieve in the filter paper increases the porosity so that the specific surface area of the resulting paper is larger. In addition, such filter paper is moisture resistant and has a long life time (CN104005273). Zeolites have also been used to clean wastewater from paper production (CN104370413). JP 62299/80 discloses paper containing hydrophilic zeolite, mordenite, which increases the water's adsorption capacity of the paper. The inventions (CN108589427, TW201024085) disclose high performance corrosion-resistant corrugated cardboard containing zeolite in the core layer. High performance of the corrugated cardboard has a very high impact resistance, burst and tear resistance in all directions, and moisture resistance. Zeolites (zeolite X, A, Beta) are used as a filler to improve optical properties - whiteness (US2002084049), for high-strength packaging paper (CN 108277698), as a medium for size (CH678636), massiveness, printability, and retention enhancements. US 5205907 describes the removal of manganese, which has a detrimental effect on hydrogen peroxide bleaching, from the mechanical pulp using a chelating agent and at least 500 ppm of magnesium sulphate, which is added before the mechanical pulp concentration.

Cellulose-based packaging is mainly used for the production of packaging for food, technical and other products. Unlike other types of packaging, which are based on different polymeric materials, packaging material from cellulose fibres is more environmentally friendly. The basis of the production of cellulose-based packaging are cellulose fibres, which are produced by wet grinding of the wood, which can then be further chemically treated (delignification and bleaching) or the wood is being mechanically treated to obtain wood pulp. Such pulp needs to be disintegrated in water, further on refined and mixed with other additives such as retention aids, fillers, starch, sizing agents etc. The paper sheet is being formed on paper machine. In the paper production, only one layer is formed, while two or even more layers are usually joint together by adhesives (most often starch) and mechanical pressing. Board is used for food packaging, so some additional chemicals need to be added to ensure safety for food contact in terms of microbiology and transmission of chemicals substances as well as sensory properties. To achieve the biological and chemical safety of products, biocides and preservatives are used in in the production in strictly limited and regulated quantities. The control of sensory values is a more difficult process that cannot be predicted in advance. For this purpose, chelating agents based on DTPA, EDTA, HEDTA, GLDA, MGDA, NTA, EDG and their derivatives are used in most cases. They ensure the sensory stability of cellulose-based packaging, as the formation of complexes with metal ions results in the prevention of oxidation of fatty acids and resins in the raw material. By preventing oxidation, the formation of unpleasant odor and the transmission of this odor and taste to the food are almost completely prevented.

However, there is still a need for improving the manufacture of cellulose-based materials, in particular packaging materials for food, technical and other products. In this context, it is desirable to use additives that give the material advantageous properties and are not harmful tothe products to be packaged.

DESCRIPTION OF THE INVENTION

According to the present invention, this aim is achieved by adding hydrophilic zeolite to the pulp used for the manufacture of cellulose-based material or cellulose fibres. It was found, that hydrophilic zeolite is suitable for controlling the sensory and mechanical properties of the final products. It prevents the autocatalytic free radical reaction of fatty acid oxidation in the cellulosic raw materials, cellulose and other raw materials for the manufacture of cellulose- based packaging products.

Thus, a first aspect of the present invention is the use of hydrophilic zeolite in the manufacture of cellulose-based material or cellulose fibres from pulp, wherein the hydrophilic zeolite is added to the pulp in an amount of about 3 to 10 % by weight. In this amount, the hydrophilic zeolite does not negatively affect the mechanical properties of the final product. Preferably, hydrophilic zeolite is added in an amount of about 4 to 9 % by weight, about 5 to 8 % by weight or about 6-7 % by weight, based on the total weight of the pulp.

Zeolites are crystalline aluminosilicate materials with a three-dimensional microporous structure. Their structures are acid and base resistant under moderate conditions (pH 3 to pH 12). Thermal stability is high as the structure breaks down at temperatures above 600 °C.

Synthetic zeolites have crystal sizes from 1 to 5 um with a narrow size distribution curve, with only 10 % of particles smaller than 2 microns and 90 % of particles smaller than 10 microns.

Zeolite is also characterized by high optical whiteness.

The addition of zeolites to the mechanical pulp for the production of cellulose-based materials or cellulose fibres, in particular for cardboard production is multifunctional. First of all, the addition of zeolite to the pulp reduces the concentration of metals, especially manganese, copper and iron in the pulp. The hydrophilic zeolite acts as ion exchanger for metal cations present in the mechanical pulp from which cellulose- or cellulose fibres-based products are produced. By ion exchange, the metal cations are trapped in the zeolite particles. Thus, in the final product, e.g. cardboard, the amount of undesirable free metal cations is significantly reduced. The lowering of the concentration of these metals consequently reduces the rate of fatty acid oxidation and thus the formation of volatile organic compounds (aldehydes), which affect sensory properties. Hexanal is one of the most dominant aldehydes that affect sensory properties, while being considered the standard for quantitative traceability of sensory values in cardboard. The function of the zeolite is to exchange structure-forming cations (Na, K) with metal cations (Mn, Cu, Fe) from the mechanical pulp. Manganese exchange and binding is favourited, since the concentration of the latter in the pulp is the highest. On the other hand, iron and copper are more complexly bonded and thus reveal weaker catalytically active centres for fatty acid oxidation.

The amount of the required addition of zeolite for the efficient bonding of metal cations is not negligible from the point of view of the mechanical and optical properties of the prepared product, e.g. cardboard. It was found that the mechanical and optical properties do not significantly deteriorate in the case of the use of the hydrophilic zeolite in an amount of about 3to 10 % by weight in comparison to common additives, e.g. CaCO; filler.

As used herein, the term “pulp” refers to the raw material used in papermaking and in the industrial production of other paper products. Pulp comprises a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fibre crops, LU500847 waste paper, rag or other materials, preferably mixed with water and other chemical or plant- based additives. It can be mechanical pulp, thermomechanical pulp, chemi-thermomechanical pulp, chemical pulp, recycled pulp, organosolv pulp, etc., preferably mechanical pulp.

Hydrophilic zeolite is added to the pulp as particles, preferably with a mean particle size d50 in arange of 1 um to 10 um. More preferably, the particle size d50 is in a range of 2 um to 8 pm, 3 um to 7 um or 4 um to 6 um.

The hydrophilic zeolite for use according to the present invention preferably comprises a low

Si / Al molar ratio, in particular a ratio in the range of 0,9 : 1 to 1,5: 1.

According to a particular preferred embodiment, the hydrophilic zeolite comprises or consists of zeolite A with crystalline structure type Linde Type A (LTA), zeolite B of crystalline gismondine structure type (GIS) in tetragonal or cubic form, or a mixture thereof.

The hydrophilic zeolite may comprise or consist of a sodium zeolite, or a potassium sodium exchanged zeolite or a mixture thereof. Particularly preferred is a hydrophilic zeolite comprising or consisting of a sodium form of the zeolite B of crystalline gismondine structure type (GIS) in tetragonal or cubic form and a potassium sodium exchanged zeolite A (20 - 70 %) or a mixture thereof.

According to the invention, the hydrophilic zeolite can replace commonly used additives and conventional fillers such as CaCO;, DTPA, EDTA, HEDTA, GLDA, MGDA, NTA, EDG or derivatives thereof. Preferably, no such additives and fillers are added to the pulp.

The use of the above hydrophilic zeolite provides the final product with surprisingly improved properties. Autocatalytic free radical reaction of fatty acid oxidation in cellulosic raw materials, cellulose and other raw materials is prevented. The sensory and mechanical properties of the final products are improved. In particular, zeolite addition according to the invention results in an increased breaking length. The burst indexes are increased compared to commercial fillers such as HydroPlex filler. The tear index is lower and the bending resistance increases.

Additionally, ISO whiteness of the final product is increased due to zeolite addition. These properties are particularly advantageous for packaging materials, in particular cellulose-based packaging products such as cardboard.

A further aspect of the invention is a method for the manufacture of a cellulose-based material or cellulose fibres from pulp, comprising a step of adding hydrophilic zeolite to the pulp in a proportion of 3 to 10 % by weight. It is understood that the features described above in connection with the use according to the invention apply analogously to the manufacturing method.

The present invention will be further supported by the following figures and examples of embodiments showing the positive effects of the added zeolite in mechanical pulp before manufacturing the cardboard.

FIGURES

Fig.1 Hexanal concentration after aging simulation of the pulp with the addition of 6 % of LU500847 zeolite A and zeolite B

Fig.2 Hexanal concentration after aging simulation of the pulp containing 3 % of the mixture of zeolite A and zeolite B

EXAMPLES

The mechanical pulp was prepared by the process of mechanical grinding. A large amount of sample with a concentration of 3-4 g/l was taken. The water used for the experiments was from the press section of board machine. Samples from 500 mL of mechanical pulp and 500 mL of water were prepared. In this mixture, the commercial complexant or zeolite (Dissolvine

D50 or zeolite with LTA structural type with sodium and / or potassium cations or zeolite with

GIS structural type with sodium and / or potassium cations) was added. Then the prepared suspension was stirred for 10 minutes. After stirring, the filtration of the suspension was followed by a funnel. The pulp sample was then dried by the press under the pressure of 3 bar for 5 minutes. Then forced drying by convection in an oven at 40 °C was conducted. The aging simulation was performed, which was carried out at 90 °C for 72 hours. Determination of hexanal contents from the prepared samples in aging simulation was performed at baseline (Oh) and after 8, 24, 32, 40, 48, 56 and 72 hours. The data collected are plotted in a time- dependent graph that illustrates the full potential for hexanal formation in the natural aging process.

The zeolites, which were added to the mixture in different mass percentages, possessed the following characteristics: low molar ratio of Si / Al (high aluminium content) and small pores.

The typical chemical composition is shown in the table below.

Na;O/ % K:0/ % SiOz / % ALO; I % H:O0 / % 14 +/- 6 30 +/- 2 27+/-2 19 +/- 3

Zeolite A: a zeolite with LTA structure type. XRD diffractogram of this structure shows typical diffraction peaks at °2Theta values: 7.18, 10.16, 12.45, 14.38, 16.09, 17.64, 20.45, 21.4, 22.89, 24.04, 26.16, 21.17, 27.25, 29.10.

Zeolite B: a zeolite with gismondine (GIS) structure type. XRD diffractogram of gismondine structure shows typical diffraction peaks at °2Theta values: 12.45, 17.65, 21.65, 25.06, 28.07 and / or °2Theta: 12.45, 13.48, 17.65, 18.63, 21.65, 22.8, 25.06, 28.07, 29.31, 29.93.

The typical chemical composition is shown in the table below.

Naz0 / % K20 / % SiOz! % ALO; | % H20/% 19 +/- 6 39 +/- 2 31+/- 2 10 +/- 2

Example 1

A mixture of about 500 ml of mechanical pulp and 500 ml of press water was prepared in the LU500847 laboratory. The complexant (Dissolvine D50 or zeolite) was added to this mixture followed by stirring for 10 minutes. After stirring, the prepared mixture was filtered using a funnel. The mechanical pulp samples were then dried by means of a press where the sample was pressurized for 3 minutes under pressure at 5 °C for 5 minutes and for one hour in a forced convection oven at 40 °C. The addition of the commercial organic Dissolvine D50 complexant is 0.25 %. The zeolite addition is 6 %.

Aging simulation was performed at 90 °C for 72 hours. Measurements are taken on the calibrated GC-MS system at the beginning (0 h) and after 8, 24, 32, 40, 48, 56, 72 hours. The data collected are plotted in a time-dependent graph that illustrates the full potential for hexanal formation in the natural aging process.

Example 2

Similar to Example 1, except 3 % of a mixture of zeolite A and zeolite B was added to a different mechanical pulp.

Example 3

The purpose of the tests was to determine the effect of added zeolite on the mechanical properties of the cardboard. Two zeolites (zeolite A and zeolite B) were tested against the reference (commercial HydroPlex filler). The recipe for the laboratory sheets was the same for all samples: 1 % bleached pulp, 93 % pulp, 1.5 % starch, 0.075 % Percol cationic retention agent and 6 % filler / zeolite. The grammage of the lab sheets was 80 g/m2. All basic mechanical properties are determined to this grammage.

The filler and / or zeolite content were added to such an extent that an ash content of 6 + 2 % was obtained.

RESULTS

The diagrams represent the results of the performance of two hydrophilic zeolites in fixed proportions with respect to the weight of the pulp in order to eliminate hexanal from the pulp during rapid aging. Each diagram shows concentration of hexanal after aging simulation for a sample without an additive, which is designated as a REFERENCE. Also, each diagram contains a sample to which a commercial metal ion binding complexant has been added, which is designated as a COMMERCIAL COMPLEXANT. Figure 1 shows the cardboard containing 6% of zeolite A and zeolite B. The concentration of hexanal after aging simulation of cardboard is lower to that of the cardboard with the commercial complexant.

The results show that the use of zeolite A or B can replace the use of the commercial organic complexant and thus better reduce the oxidation of fatty acids in the cardboard, which is reflected in decrease of the hexanal concentration after aging simulation of the cardboard.

Figure 2 shows the hexanal concentration after aging simulation of cardboard, containing 3 % of the mixture of zeolite A and B is shown in Figure 2. It can be seen lower hexanal concentration of the cardboard containing the mixture of zeolites compared to that of the cardboard with the commercial complexant.

Table 1 shows mechanical and optical properties of the cardboards with zeolite A and zeolite LU500847

B (6 %), while the reference sample does not contain the zeolite.

Table 1: Mechanical properties of the cardboards containing 6 % of the hydrophilic zeolite A and zeolite B.

Breaking| Burst | Tear [Bending | so

Grammage index index resistance, _. Ash [Thickness [length , whiteness … [9/m?] [kPam?2/g]|[mNm?/g]| L&W ° [9%] [um] [km] [%] [mN]

The results of the Table 1 show that the addition of the zeolite affects some of mechanical and optical properties, such as: - The breaking length increases in both cases of zeolite addition; - The burst indexes are higher in both cases of zeolite additives compared to the commercial

HydroPlex filler; - The tear index is lower for both zeolites compared to the reference; - The bending resistance increases in both cases of zeolite addition; - ISO whiteness increases in both cases of the zeolite addition compared to the reference.

Claims

CLAIMS LU500847

1. Use of a hydrophilic zeolite in the manufacture of a cellulose-based material or cellulose fibres from pulp, wherein the hydrophilic zeolite is added to the pulp in a proportion of 3 to 10 % by weight.

2. The use according to claim1, wherein the hydrophilic zeolite is added as particles with a mean particle size d50 in a range of 1 um to 10 um.

3. The use according to any one of the preceding claims, wherein the hydrophilic zeolite comprises a low ratio of Si : Al, in particular a ratio in the range of 0,9 : 1 to 1,5 : 1.

4. The use according to any one of the preceding claims, wherein the hydrophilic zeolite comprises or consists of zeolite A with crystalline structure type Linde Type A (LTA), zeolite B of crystalline gismondine structure type (GIS) in tetragonal or cubic form, or a mixture thereof.

5. The use according to any one of the preceding claims, wherein the hydrophilic zeolite comprises or consists of a sodium zeolite, or a potassium sodium exchanged zeolite or a mixture thereof.

6. The use according to any one of the preceding claims, wherein the hydrophilic zeolite comprises or consists of a sodium form of the zeolite B of crystalline gismondine structure type (GIS) in tetragonal or cubic form.

7. The use according to any one of the preceding claims, wherein the hydrophilic zeolite comprises or consists of a potassium sodium exchanged zeolite A (20 - 70 %).

8. The use according to any one of the preceding claims, wherein the cellulose-based material is a packaging material, in particular a cellulose-based packaging product, e.g. cardboard.

9. The use according to any one of the preceding claims, wherein the pulp is a mechanical pulp.

10. The use according to any one of the preceding claims, wherein no conventional fillers are added to the pulp, in particular no CaCO;, DTPA, EDTA, HEDTA, GLDA, MGDA, NTA, EDG or derivatives thereof.

11. The use according to any one of the preceding claims, for preventing autocatalytic free radical reaction of fatty acid oxidation in cellulosic raw materials, cellulose and other raw materials.

12. The use according to any one of the preceding claims, for controlling the sensory and mechanical properties of the final products.

13. A method for the manufacture of a cellulose-based material or cellulose fibres from pulp, comprising a step of adding hydrophilic zeolite to the pulp in a proportion of 3 to 10 % by weight.