EP4232632A1

EP4232632A1 - A moulding material, a method for preparing such material and a moulded product

Info

Publication number: EP4232632A1
Application number: EP21882295.5A
Authority: EP
Inventors: Lars Axrup; Cecilia LAND HENSDAL; Julia BROSZAT
Original assignee: Stora Enso Oyj
Current assignee: Stora Enso Oyj
Priority date: 2020-10-23
Filing date: 2021-10-22
Publication date: 2023-08-30
Also published as: WO2022084928A1

Abstract

The present invention relates to to a moulding material comprising 60-98 wt% of a dry wood-based material; 2-40 wt% of a fibrillated cellulose material; and 0-10 wt% of an additive, as calculated on the total dry solids in the moulded material. The invention also relates to a method for preparing such moulding material, as well as a moulded product prepared from said moulding material, and use of the moulding material in a moulded product.

Description

A MOULDING MATERIAL, A METHOD FOR PREPARING SUCH MATERIAL AND

A MOULDED PRODUCT

FIELD OF THE INVENTION

The present invention concerns a moulding material of biomass, a method for preparing such moulding material, as well as a moulded product prepared from said moulding material, and use of the moulding material in a moulded product.

TECHNICAL BACKGROUND

In our modern life, we depend heavily on plastics for multiple purposes, among others packaging for food or cosmetics. Those fossil-based materials are a problem for our nature and the climate.

During recent years there has been an increased awareness of the impact of packaging material on the environment and there is a demand for materials that cause less harm to the environment than petroleum-based plastics. There are ways to form packages by pressing and forming products out of fibre-based biomaterials. Plant-based materials can comprise cellulose, hemicellulose and lignin and be obtained from trees, shrubs, plants and agricultural crops. Cellulose has a special potential, as the most abundant renewable natural polymer on earth, with its crystalline structure, and the availability of methods for preparing large volumes on an industrial scale.

Moulded cellulose pulp provides for an environmentally friendly packaging material that is recyclable, compostable, and eventually biodegradable. In the literature, plastic-free composites are described that are made from pulp fibers, MFC and additives (e.g. Kojima el al., 2014; Diop et al., 2017; Pårs-Rosell, 2017). Another technique for making packaging products is pressing and stamping dry air-laid pulp, but the different shapes or products that can be produced are rather limited. Small packaging details with three-dimensional shapes are still usually made from fossil-based plastic materials. There is a need for an economically viable process that is rapid and requires a lower energy consumption and allows for the manufacturing large volumes of small packaging details with advanced three-dimensional structures, such as screw caps.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows moulded products in the form of capsules of a moulding material of biomass with increasing carboxymethyl cellulose (CMC) content from left to right; and

Figure 2 shows moulded products in the form of capsules of a moulding material of biomass with increasing microfibrillated cellulose (MFC) content from left to right.

DESCRIPTION OF THE INVENTION

The objective of this disclosure is to provide a moulding material prepared from biomass and that is suitable for manufacturing large volumes of small details, a method for preparing the moulding material, as well as a moulded product prepared from said moulding material, and use of the moulding material in a moulded product. A further objective is to provide a material comprising biomass suitable for moulding and that may be pressed under high pressure and heat for formation into packaging details and other end applications.

In a first aspect the present invention relates to a moulding material comprising 60-98 wt% of a dry wood-based material; 2-40 wt% of a fibrillated cellulose material; and 0-10 wt% of an additive, as calculated on the total dry solids in the moulded material. The wood-based material may be selected from dry particulate fibres, dry- cut cellulose, wood flour, sawdust and different combinations thereof. The fibre length distribution of the fibres can be modified, such as by grinding the fibres to reduce the size of the fibres. Preferably, the wood-based material comprises a cut, particulate or pulverized consistency, ranging in particle size dimension from 0.01 - 2mm, preferably 0.03 - 1mm, more preferably 0.05 - 0.3mm.

According to one aspect, the wood-based material range in particle size dimension from 10 - 300 μm. For instance, wood flour usually comprises an average particle diameter between 10 - 30 μm, whereas sawdust comprises an average particle diameter between 30 - 600 μm.

The moulding material may comprise 60-98 wt%, or 60-94 wt%, or 60-90 wt%, or 60-80 wt% of dry wood-based material, as calculated on the total dry solids in the moulding material.

The fibrillated cellulose is preferably microfibrillated cellulose (MFC). The source for the MFC may be various tree species, other plants, or bacteria. The fibrillated material may also be cellulose nanofibrils. The moulding material may comprise 2-40 wt%, or 5-30%, or 5-20%, or 5-15%, or 10- 20 wt% of a fibrillated cellulose material, as calculated on the total dry solids in the material. MFC will provide a barrier function against oxygen gas of the moulded end product.

The additive may be selected from carboxymethyl cellulose (CMC), latex, citric acid, crosslinkers and combinations thereof.

The total fibrous part of the moulding material may comprise at least 50 wt%, or at least 60 wt%, or at least 70 wt%, or at least 80 wt% or at least 90 wt% of fibres having a fibre length of less than 1 mm.

In a second aspect the present invention relates to a method for preparing the moulding material according to the present invention, the method comprising providing a suspension comprising the fibrillated cellulose material, e.g. MFC; optionally adding an additive, additional water, or both; and adding the dry wood-based material to the suspension to obtain a moulding material comprising 60-98 wt% of a dry wood-based material; 2- 40 wt% of fibrillated cellulose material; and 0-10 wt% of an additive, as calculated on the total dry solids in the moulding material.

The fibrillated cellulose material may be suspended in an aqueous media, preferably the fibrillated material is suspended in water. The suspension of fibrillated cellulose material contains 2-30 wt%, or 2-25 wt%, or 2-20 wt%, or 5-15 wt% solids, as calculated on the dry solid content in the suspension.

The addition of the dry wood-based material to the suspension of fibrillated material, may be made gradually during mixing. The wood-based material added to the suspension of the fibrillated cellulose material may have a dry content of from 80 to 100 wt%, or from 90 to 100 wt%, or from 90 to 98 wt%.

Said wood-based material is provided in a particulate form with a modified fibre length distribution, obtained e.g. by grinding wood-based material to reduce the size of its fibres, in order to improve the mouldability of the moulding material.

The additive is preferably added to the suspension of the fibrillated cellulose material before addition of the dry wood-based material. Adding the additive to the suspension of the fibrillated cellulose material before the addition of the dry wood-based material facilitates the formation of a homogeneous moulding material. Common papermaking additives and performance chemicals, such as antiflocculants, hydrophobation chemicals, latices, wet strength agents, and lubricants, may also be added. The method may further comprise transferring of the moulding material into a mould. The mould may have a three-dimensional shape. The moulding material according to the present invention has a sufficiently high moisture content to get a good mouldability, which provides for a good filling of every corner in the mould and allows for pressing of small objects with advanced three-dimensional shapes, such as screwcaps, coffee capsules, etc. The moisture content is also high enough to provide for hydrogen bonding to occur during drying, which results in a high material strength. If the dry solid content in the moulding material that is filled into the mould is too low, large amounts of water must be removed which slows down the process and may also require more energy. Thus, the dry solid content of the moulding material may be at least 40 wt%, or at least 65 wt%. The moulding material may have a dry solid content from 40 to 90 wt%, or from 65 to 80 wt%, most preferably from 65 to 75 wt%, as calculated on the total weight of the mixture. A relatively low moisture content also reduces the risk for liquid water flowing out during pressing and that functional additives escape from the material with the water.

The method may further comprise pressing the moulding material in the mould to form a moulded product. The pressing may be made at a temperature of from 120 °C to 200 °C, or from 130 °C to 180 °C, or from 140 °C to 170 °C. The pressing may be made at a pressure of from 0.5 to 600 MPa, or from 700 to 900 kPa. The pressing may be made for a time of from 10 seconds to 10 minutes, or from 15 seconds to 7 minutes, or from 30 seconds to 7 minutes, or from 1 minute to 7 minutes, or from 1 minute to 5 minutes. The pressing of the material in the mould may enhance the gas barrier properties of the moulded product such as oxygen gas barrier properties. The method may alternatively comprise injection moulding to form a moulded product. Thus, a further aspect of the present invention is a method for preparing a moulded product comprising the measures described herein. A benefit with the moulding material and the method according to the present invention is their simplicity, such as the possibility of making a moulded product using only chemicals that are already available in the regular papermaking industry. A further advantage with the moulding material is that normally only small changes are required in the standard compression moulding equipment used for shaping the corresponding articles in fossil-based plastic material.

Thus, the present invention also encompasses a moulded product comprising the moulding material according to the present invention. A still further aspect is a moulded product obtained with the method according to the present invention. The moulded product may have a moisture content of 35 wt% or less, preferably 0-10 wt%, as calculated on the total weight of the material. The moulded product may comprise an oxygen barrier, a moisture barrier or a combination of these. Moulded products prepared from the moulding material according to the present invention may be selected from screw caps, or containers for single or multiple use, such as bottles for oils or coffee capsules.

The moulded product may be provided with barrier properties, such as an oxygen barrier, a moisture barrier, grease resistance, or water repellence properties, or a combination of these. Such barrier properties may be provided by grafting the moulded product with fatty acid chloride, such as with the chromatogeny process; metallization, such as by vacuum deposition; coating with a barrier dispersion, such as a latex, an aqueous dispersion of fine polymer particles, preferably a bio-based latex; or coating with a polyolefin, e.g. PE, PP or PET, preferably a bio-based polyolefin; or a combination thereof. The barrier may be applied on the outside, the inside, or both sides of the pressed object. The moulded product may also be provided with at least one specific barrier layer, such as a layer comprising the composite material grafted with a fatty acid chloride; coated with a barrier dispersion, or a polyolefin, e.g. PE, PP or PET; or being metallized; or a combination thereof. Barrier properties may also be provided by blending an additive that may provide barrier properties into the moulding material, such as by adding, e.g. a hydrophobation chemical, or a latex; to the suspension of the fibrillated cellulose material;

An advantage with the moulded product according to the present invention is that it possesses a good barrier against fats, including grease and oil; as well as gases, such as air and oxygen.

The present invention also relates to the use of the moulding material according to the present invention in a screwcap, or in a container for single or multiple use, such as a bottle for oil, or a coffee capsule.

Cellulose is a polysaccharide consisting of a linear chain of β(1→ 4) linked D-glucose units and the main component in the cell walls of all plants. It can occur with different components depending on the type or part of the plant. While cellulose occurs together with lignin and hemicelluloses in wood, certain bacteria may produce a pure cellulose. Fibres of cellulose are significantly longer than wide. Cellulose fibres can have a mean width of 0.01 to 0.05 mm, while their length can vary considerably depending on the type of plant and its growing location. For example, the fibre length of softwood can be from 2.5 to 4.5 mm, while hardwood and Eucalyptus can have a fibre length from 0.7 to 1.6 mm. The aspect ratio, i.e. the ratio of the fibre length to the fibre width, can be at least 10, but also as large as 6500. The fibre length distribution can be modified, such as by grinding the cellulose fibres to reduce the size of the fibres. The cellulose constitutes the structural backbone of the material according to the present invention, and also provides some of the rigidity and strength.

Microfibrillated cellulose, MFC, is liberated from wood pulp or from other sources, for example selected from the group consisting of plants, tunicate, and bacteria, by means of mechanical disintegration, such as by homogenization, microfluidization, grinding, or using a supermass colloider (SMC), often preceded by a chemical pretreatment, such as by oxidation with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) or by carboxymethylation; or by enzyme-treatment, such as by endoglucanases. Other terms used for the microfibrillated cellulose are nanofibrillated cellulose (NFC), nanofibrillar cellulose (NFC), microfibrillar cellulose (MFC), cellulose microfibril (CMF) and cellulose nanofibre (CNF). MFC typically have a smallest dimension in the range 2-100 nm, while the length can be several micrometers, such as up to 10 μm, and therefore the aspect ratio of MFC (ratio of length to diameter) is very large.

The term "dry solid content" is used herein for the content of dry matter in a suspension as calculated on the total weight of the suspension.

EXAMPLES

Example 1

Preparation of moulding materials

Native MFC was prepared by high-pressure homogenization of enzyme treated bleached pulp. The dry solid content of the MFC was 11 wt%.

Carboxymethyl cellulose, CMC, Finnfix 5 (CPKelco) in powder form, 93 wt% dry solid content, was used as an additive.

The fibre material (i.e. the wood-based material) was a dry-cut, bleached pulp (Stora Enso, Skutskar Mill) with a particle size distribution between 40 - 300 μm. The dry solid content of the fibre material was 95 wt%.

First, the MFC was mixed together with the CMC powder with a spoon. Depending on the desired final moisture content, water was added in the required amount. The dry fibers were then mixed in gradually with a kitchen kneading machine (Kenwood) and mixed until everything was roughly distributed. The mixture was then filled into a lab extruder with twin screws for blending the material.

The final solids content was varied according to Table 1. For the most dry samples, final mixing was performed in a kitchen blender (Kenwood).

The MFC content was around 10 wt-% based on dry weight, and the CMC content was about 2 wt-% based on dry weight.

Mechanical properties

A stainless steel mould was used to produce round, flat samples with a diameter of 80 mm and a thickness of about 1.3 mm. An amount corresponding to 6 g of dry material was used. The mould with material in was put in a heated platen press, 150 °C for 5 min at the pressure 0.5 MPa. The samples were conditioned at 23 °C, 50% RH and then cut into 15 mm wide strips, and tensile properties were measured in a Zwick Z010 material tester at 2 mm/min crosshead speed. The results are found in Table 1.

Table 1. Results from tensile testing

Example 2

Pressing of capsules - varying CMC content

A native MFC was prepared by high-pressure homogenization of enzyme treated bleached pulp. Carboxymethyl cellulose, CMC, Finnfix 5 (CPKelco) was used as an additive. The fibre material (i.e. the wood-based material) was a dry cut, bleached pulp (Stora Enso, Skutskär Mill) with a particle size distribution between 40 - 300 μm. First, the MFC was mixed together with the CMC powder and water with a spoon. The dry fibers were then mixed in gradually with a kitchen kneading machine (Kenwood) into a "dough".

The solids content of the dough was 40 wt-%, the MFC content was 10 wt- % based on dry weight. One sample was prepared with no CMC content, and two samples with CMC content of 2 and 4 wt-% respectively, based on dry weight.

A stainless steel mould was used to produce simple capsule demonstrators. Moulding material was put in a heated platen press, 150 °C for 5 min at the pressure 0.8 MPa.

It was seen that an increased CMC content prevented the "walls" of the capsule to crumble, resulting in a higher capsule. The samples are shown in Figure 1, with increasing CMC content from left to right. The bottom of the capsule gets strong due to the high pressure acting on it, but the walls have a very high angle which do not bear load easily.

Example 3

Pressing of capsules - varying MFC content

A native MFC was prepared by high-pressure homogenization of enzyme treated bleached pulp. Carboxymethyl cellulose, CMC, Finnfix 5 (CPKelco) was used as an additive. The fibre material (i.e. the wood-based material) was a dry cut, bleached pulp (Stora Enso, Skutskar Mill) with a particle size distribution between 40 - 300 μm.

First, the MFC was mixed together with CMC powder and water. The dry fibers were then mixed in gradually with a kitchen kneading machine (Kenwood) into a "dough" corresponding to the "moulding material" according to the invention. The solids content of the dough was 40 wt-%, and content of CMC was 4 wt% based on dry weight. With this mixture as a base, four samples were prepared with varying MFC content: 0 wt%; 10 wt%; 14 wt% and 17 wt%.

Each of the four samples were used for producing a respective capsule demonstrator, using a stainless steel mould. Said stainless steel mould comprising the moulding material was put in a heated platen press, 150 °C for 5 min at the pressure 0.8 MPa.

The resulting four capsule demonstrators are shown in Figure 2, with increasing MFC content from left to right. It can be seen that with higher MFC content, the object was more intact and had higher walls.

Claims

1. A moulding material comprising:

- 60-98 wt% of a dry wood-based material comprising a particulate consistency and ranging in particle size dimension from 0.01 - 2mm;

- 2-40 wt% of a fibrillated cellulose material; and

- 0-10 wt% of an additive, as calculated on the total dry solids in the moulding material.

2. The moulding material according to claim 1, wherein the wood-based material is selected from dry cut cellulose, wood flour, sawdust, lignin powder and different combinations thereof.

3. The moulding material according to claim 1 or 2, wherein the additive is selected from carboxymethyl cellulose (CMC), latex, citric acid, crosslinkers and combinations thereof.

4. The moulding material according to any one of claims 1-3, wherein the fibrillated material is microfibrillated cellulose (MFC).

5. The moulding material according to any one of claims 1-4, wherein the total dry content in the moulding material is at least 40 wt%, preferably at least 50 wt%, more preferably at least 65-75 wt%, as calculated on the total weight of the material.

6. The moulding material according to any one of claims 1-5, wherein the material is further provided with barrier properties.

7. A method for preparing the moulding material according to any one of claims 1-6, the method comprising providing a suspension comprising fibrillated cellulose material; optionally adding an additive, additional water, or both of these; and adding the dry wood-based material to the suspension to obtain a moulding material comprising 60-98 wt% of a dry wood-based material; 2-40 wt% of fibrillated cellulose material; and 0-10 wt% of an additive, as calculated on the total dry weight in the moulding material.

8. The method according to claim 7, wherein the suspension medium is water.

9. The method according to claim 7 or 8, wherein the suspension of microfibrillated cellulose contains 2-30 wt% dry matter.

10 The method according to any one of claims 7-9, wherein addition of the dry wood-based material is made gradually during mixing.

11 The method according to any one of claims 7-10, wherein the suspension of the fibrillated cellulose material is mixed with additives before addition of the dry wood-based material.

12. The method according to any one of claims 7-11, further comprising transferring the moulding material into a mould.

13. The method according to claim 12, further comprising pressing the moulding material comprising the microfibrillated cellulose and the dry wood-based material, to form a moulded product.

14 The method according to claim 12 or 13, further comprising providing the moulded product with an oxygen barrier, a moisture barrier or a combination of these.

15 The method according to claim 14, where the barrier is provided on at least one side of the moulded product.

16. The method according to any one of claims 14-15, wherein the barrier properties are provided by blending in an additive that may provide barrier properties into the moulding material; grafting the moulding material or the moulded product with a fatty acid chloride; metallization; coating the moulding material with a barrier dispersion; coating with a polyolefin; or a combination of these.

17. A moulded product comprising the moulding material according to claim 1.

18. A moulded product according to claim 17, wherein the water content is 10 wt% or less, as calculated on the total weight of the product.

19 The moulded product according to claim 17 or 18 further comprising an oxygen barrier, a moisture barrier or a combination of these.

20 A moulded product obtained with the method according to anyone of claims 7-16.

21. The moulded product according to claim 21, which is a screwcap or a container for single or multiple use.

22 Use of the moulding material according to any one of claims 1- 6 in a screwcap or a container for single or multiple use.