METHOD OF PRODUCING A MOLDED FIBER PRODUCT AND MOLDED FIBER PRODUCT

Abstract

The invention discloses a method for producing a three dimensional molded product from cellulose fibers, comprising the steps of: providing a cellulose fiber composition comprising 1-30 wt % lignin, said cellulose fiber composition further having a solid content between 0.1-95%; providing a forming tool having a three dimensional shape including a forming surface, and bringing said forming surface into contact with the cellulose fiber composition; and press drying the cellulose fiber composition contacted by the forming tool at temperatures>200° C. to a dry content of at least 70%.

The invention also relates to a three dimensional fiber based product obtainable by means of said method.

Claims

1. A method for producing a three dimensional molded product from cellulose fibers, comprising the steps of: providing a cellulose fiber composition comprising 1-30 wt % lignin, said cellulose fiber composition further having a solid content between 0.1-95%; providing a forming tool having a three dimensional shape including a forming surface, and bringing said forming surface into contact with the cellulose fiber composition; and press drying the cellulose fiber composition contacted by the forming tool at temperatures>200° C. to a dry content of at least 70%.

2. The method according to claim 1, wherein said cellulose fiber composition is a pulp suspension of cellulose fiber material having a consistency between 0.1-1 wt %, and wherein said forming tool is brought into contact with said pulp suspension so that said forming surface of said forming tool is covered with a layer of pulp from said pulp suspension, whereafter the layer of pulp present on said forming tool is press-dried and dewatered to a dry content of at least 70 wt %.

3. The method according to claim 1, wherein said cellulosic fiber composition is a fiber based sheet material having a solid content of 30-95 wt %.

4. The method according to claim 1, wherein said cellulose fiber composition comprises mechanical pulp selected from a group consisting of: TMP, CMP, CTMP, cTMP, HTCTMP and mixtures thereof.

5. The method according to claim 1, wherein said cellulose fiber composition is selected from a group consisting of: wood pulps, non-wood pulps, unbleached chemical pulp, defibrated fiber material, bagasse, straws, bamboo, spruce CTMP, eucalyptus CTMP, and spruce HT CTMP.

6. The method according to claim 1, wherein the cellulose fiber composition is press dried at temperatures>250° C.

7. The method according to claim 1, wherein at least a portion of the fibers in the cellulose fiber composition have been subjected to treatment with an oxidant for inducing radicals in the cellulose fiber molecules to induce covalent cross bindings.

8. The method according to claim 7, wherein said oxidant is ozone gas or ozone water.

9. The method according to claim 1, wherein at least a portion of the fibers in the cellulose fiber composition have been subjected to treatment with laccase enzyme for cross linking lignin polymers present in said suspension.

10. A three dimensional fiber based product obtained by the method according to claim 1, said product comprising: a fiber based material having a density of less than 650 kg/m.sup.3, and a bending stiffness index greater than 0.8 Nm 7/kg.sup.3.

11. A three dimensional fiber based product obtained by the method according to claim 1, said product comprising: a fiber based material having a density<650 kg/m.sup.3.

12. The product according to claim 10, comprising a burst greater than 1 kPam.sup.2/g.

13. The product according to claim 10, comprising a Z-strength greater than 200 kPa.

14. The product according to claim 10, comprising a compressive strength greater than 15 Nm/g.

15. The product according to claim 1, wherein the product comprises a food packaging product.

Description

DESCRIPTION OF EMBODIMENTS

[0028] The present description is directed to a thermoforming method for manufacturing a molded pulp product from a lignin-containing cellulose fiber composition. Examples of “lignin-containing fiber composition” are mechanical pulp such as thermomechanical pulp (TMP), chemi mechanical pulp (CMP), chemi-thermomechanical pulp (CTMP), cTMP, high-temperature chemithermomechanical pulp (HTCTMP) and mixtures thereof.

[0029] Other cellulosic material such as chemical or semi-chemical pulp of wood or none-wood material can also be added as a part of the fiber composition.

[0030] Thermoforming refers to a fiber molding method where press forming is combined with application of heat so that the product is densified and dried. Press forming (here also referred to as press drying) may be performed by means of providing two complementary forming tools, a first and a second tool, arranged to essentially match each other, and pressing the two tools together such that the cellulose fiber composition is sandwiched between the first and the second tool. The press forming can be applied in one or several consequtive steps depending on the end product. For example, a two-step press forming could be advantageous to obtain a product with double sided smooth surface.

[0031] The present invention covers at least two options for performing thermoforming: wet forming and dry forming.

[0032] An example of wet forming a fiber product by means of thermoforming according to the invention is now to be described.

[0033] A cellulose fiber composition in the form of a pulp suspension containing mechanical pulp is provided, said pulp suspension having a consistency between 0.1-1% by weight. The pulp suspension is herein referred to as one example of a “cellulose fiber composition”. A three dimensional forming tool arranged on a tool holder is immersed into said suspension thus contacting the pulp therein so that at least a forming surface of said forming tool is covered with a layer of pulp from said pulp suspension. The layer of pulp on the tool can be accomplished in various ways, e.g. by means of applying a suction through the forming tool when it is immersed in the pulp suspension. The layer of pulp present on said forming tool is then press dried at temperatures above 200° C., or above 250° C., such as above 280° C., and simultaneously dewatered to a dry content of at least 70% by weight.

[0034] During the press drying step of the method, the pulp layer is subjected to high temperatures above 200° C., such as above 250° C., for instance by means of drying between hot tools in one or several steps with the help of vacuum and compressed air. This leads to efficient and quick drying, as the water present in the pulp is pressed out in combination with being evaporated, which in turn gives better productivity. The applied high temperature also leads to that the lignin in the pulp is plasticized and cross linked, thus improving strength properties in the end-product.

[0035] According to the invention, said pulp suspension comprising cellulose fiber material may be pretreated with an oxidant for inducing radicals in the fiber components to induce covalent cross bondings. Suitable oxidants are ozone gas or ozone water. Another possible way of oxidizing the pulp is pre-treatment with laccase enzyme for cross linking lignin polymers. Oxidizing of the pulp is preferably performed on the so-called start preparation pulp having a consistency between 3-5% by weight. The pulp is thereafter diluted to 0.1-1% by weight and fed into the forming step of the molded fiber line.

[0036] An example of dry forming a fiber product by means of thermoforming according to the invention is now to be described.

[0037] A fiber based sheet or web is produced from a lignin-containing cellulose material, for example made from mechanical pulp. The fiber based sheet material is herein referred to as one example of a “cellulose fiber composition”.

[0038] Said sheet material could comprise hardwood or softwood chemical pulp or mechanical pulps, having a ligning content of 1-30% by weight, and with a basic density of 100-900 kg/m3. The fiber based sheet is dampened so that it acquires a moisture content of between 10-40% by weight, and is thereafter transferred to a forming station. A three dimensional forming tool arranged on a tool holder is provided and brought into contact with the dampened sheet. Thermomolding is then performed by pressing the forming tool against the sheet under heat treatment so that the sheet is shaped in accordance with the three dimensional surface of the forming tool. A second mating tool can be used for sandwiching the sheet layer during press forming. Analogously with the wet forming, during the press drying step of the method the sheet is subjected to temperatures above 200° C., such as above 250° C. This leads to efficient and quick drying, as the water present in the pulp is pressed out in combination with being evaporated. The applied high temperature also leads to that the lignin in the pulp is plasticized and cross linked, thus improving strength properties in the end-product.

[0039] The product formed by means of the molding method of the invention can thus be produced from lignin-containing mechanical pulp, it will have a low density and yet provide good strength and exhibit material properties that are as good as (or even better than) material produced from chemical pulp.

[0040] Measurement and Evaluation Methods

[0041] The following methods and standards apply both to the definitions of the appended claims and to the measurements performed in the example below.

[0042] Drainage resistance: SCAN C19:65

[0043] Density (pulp sheet density, table 1): ISO 534:2011

[0044] Density (sheet density table 2): ISO 534:2011

[0045] Tensile Index: ISO 1924-3:2005

[0046] Tensile stiffness index ISO 1924-3:2005

[0047] Stretch at break: ISO 1924-3:2005

[0048] Tensile energy abs. index: ISO 1924-3:2005

[0049] Burst index: ISO 2758:2014

[0050] Tear index: ISO 1974:2012

[0051] Z-strength: SCAN-P 80:98

[0052] Bending resistance: ISO 2493-1:2010

EXAMPLE

[0053] In order to evaluate the quality of the molded fiber product of the invention, a test series was performed in which thermomolded products made from chemical pulp (Ref 1 and Ref 2) were compared with thermomolded products having a lignin content of at least 1 wt % (Samples A, B and C).

[0054] Pulp properties such as drainage resistance, strength and density for the different pulp tests (Ref. 1; Ref. 2; Sample A; Sample B; and Sample C) were evaluated. All tests were performed according to the methods and standards as indicated above and all analyses were carried out according to available standards after conditioning at 23° C., 50% RH.

[0055] The properties of the pulps used in the molded fiber samples are presented in Table 1, and the tested properties of the molded fiber materials are presented in Table 2.

[0056] Product Formation

[0057] A slurry was provided for each of Ref. 1-2, and samples A-C respectively. Each slurry had a consistency between 0.3-0.6 wt %.

[0058] Said slurry was transferred to a forming section, where a three dimensional forming tool was brought into contact with said slurry.

[0059] Said forming tool had a forming surface having a three dimensional tray-like shape, and comprised channels for vacuum suction. By means of vacuum suction, a pulp layer was formed on the forming surface of the tool.

[0060] The forming tool comprising the layer of slurry was transferred to a press molding unit where heat was supplied at temperature exceeding 250° C. Press drying was conducted under heat in several steps until the compression-molded fibre product had reached a dry content of at least 70%.

[0061] The measured handsheet properties of the pulp suspensions as well as the resulting molded fiber products are presented in Tables 1 and 2 respectively.

TABLE-US-00001 TABLE 1 Pulp properties of tested pulps. Property Unit Ref 1 Ref 2 A B C Sample description BI Chem BI Chem Spruce Spruce Eucalyptus Pine pulp Eucalyptus CTMP HT CTMP pulp CTMP Lignin content % <1 <1 27 27 25 Drainage °SR 20.8 35 15.6 17.8 30.4 resistance, SR Sheet density kg/m3 728 670 276 364 452 Tensile index Nm/g 75.04 59.16 23.61 22.43 34.4 Tensile stiffness kNm/g 7.82 7.26 2.94 3.29 4.56 index Stretch at break % 3.72 3.03 1.46 1.46 1.53 Tensile energy J/g 1.93 1.29 0.22 0.23 0.35 absorption index Burst index kPam2/g 3.8 5.89 1.39 1.2 1.55 Tear index mNm2/g 11.6 8.3 12.2 7.8 4.7 Z-strength kPa 530 520 88 118 235 FT* average length mm 2.111 0.785 1.886 1.373 0.88 (>0.2 mm) Coarseness on mg/m 181.4 78.4 335.6 302.3 119.1 fibers (>0.2 mm) FT + Fiber width μm 30.8 18 37.6 37.2 21.1 (>0.2 mm) *FT = Fibertester, an instrument for fiber testing; (>0.2 mm): a standard method to exclude fractions smaller than 0.2 mm in the test method. CTMP = Chemi-thermomechanical pulp

TABLE-US-00002 TABLE 2 Product properties of molded fiber Property Unit Ref 1 Ref 2 A B C Sample description BI Chem BI Chem Spruce Spruce Eucalyptus Pine pulp Eucalyptus CTMP HT CTMP pulp CTMP Sheet density kg/m3 603 535 496 462 534 Tensile index Nm/g 51.1 38.4 34.9 33.9 46.71 Tensile stiffness kNm/g 5.130 5.600 4.910 4.380 5.75 index Stretch at break % 4.110 1.990 1.480 1.460 1.82 Tensile energy J/g 1.48 0.56 0.35 0.33 0.59 absorption index Burst index P25 kPam2/g 4.57 2.23 1.82 2.07 2.17 Z-strength kPa 377 372 310 265 369 SCT index Nm/g 22.5 21.8 21.6 18.4 28.3 Bending Nm7/kg3 0.80 0.90 1.10 1.20 1.3 stiffness index 50 mm 15°

[0062] In table 1 it is shown that samples A, B and C have much lower mechanical strength, especially Z-strength, burst strength and tensile stiffness, compared to Ref 1 and Ref 2 both comprising chemical pulp.

[0063] As seen in Table 2, however, the molded fiber products made of samples A, B and C, however, have dramatically improved mechanical strength. Not only Z-strength, burst and tensile stiffness are improved to the same level as Ref 1 and Ref 2, but also the products have significantly higher bending stiffness. Sample C has a bending stiffness index which is 40% larger than for Ref 2 at similar mechanical strength, despite the significantly lower mechanical strength of the pulp material. Both Sample C and Ref 2 are produced from eucalyptus as raw wood material.

[0064] The strength properties of mechanical pulp products are comparable to, or even higher than properties of chemical pulp products. This is due to the improved consolidation and bonding of the lignin containing fibers at the elevated temperature. The effect of the high temperature treatment is softening of the fiber structure. This in turn improves consolidation and bonding Z strength and tensile strength of the product.

[0065] Also, thanks to the high stiffness of the mechanical pulp fibers, the CTMP based products have much better bending stiffness, enabling for reduce basis weight—i.e. resulting in source reduction.

[0066] The present invention has been described with regard to preferred embodiments. However, it will be obvious to a person skilled in the art that a number of variations and modifications can be made without departing from the scope of the invention as described herein.