Bimodal or multimodal cellulosic materials and methods for their manufacture

Abstract

According to an exemplary embodiment of the present invention, a method is provided for producing bimodal and / or multimodal cellulosic materials, such as films and filaments, that combine the advantages of cellulosic feedstocks having different average molecular weight distributions and / or side chain lengths.

Description

[Technical field]

[0001] The present invention relates to improved processability and mechanical performance of thermoplastic cellulosic materials and to a method for producing bimodal or multimodal thermoplastic cellulose films having such properties, where bimodality or multimodality refers to combining cellulosic pulps with different average molecular weights (or molar masses) via cellulose dissolution. [Background technology]

[0002] There are some recent and partially related publications related to cellulose films aiming to replace synthetic raw materials. For example, WO2018 / 228744A1 discloses a composition comprising a combination of cellulose-based polymers that can be used to manufacture a film or foil. The disclosed cellulose-based composition may replace films or foils based on fossil raw materials and used as packaging or wrapping materials. However, the cellulose-based polymers described in WO2018 / 228744A1 are selected from the group consisting of cellulose acetate butyrate, cellulose acetate propionate and ethyl cellulose, and are not naturally occurring cellulose materials, whether or not they contain trace components necessary for the regeneration process, such as molecular weight controlled cellulose or hemicellulose or lignin.

[0003] WO2019 / 073370A1 relates to a process for improving the stretchability of films made of a large amount of microfibrillated cellulose (MFC) without adversely affecting the oxygen barrier properties. According to this disclosure, the film is formed from a suspension containing microfibrillated cellulose with a broad size distribution. However, the method described in WO2019 / 073370A1 does not apply to the dissolution of cellulose or the use of thermoplastic cellulose.

[0004] On the other hand, Patent Document 3 (US2018 / 0371211A1) discloses a method for producing a cellulose-based material with a bimodal fibril distribution. This composition can be used to modify the rheological properties of the components. However, this Patent Document 3 does not relate to a method for preparing a cellulose film, for example by dissolution, or a method for preparing a thermoplastic cellulose product. Furthermore, while fibril distribution is reflected in particle size and morphology, molecular weight distribution as intended here means only molecular size and any type. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2018 / 228744 Brochure [Patent Document 2] International Publication No. 2019 / 073370 Brochure [Patent Document 3] US Patent Publication No. 2018 / 0371211 [Non-patent literature]

[0006] [Non-Patent Document 1] Willberg-Keyrilainen P., Talja R., Asikainen S, Harlin A, Ropponen J., The effect of cellulose molar mass on the properties of palmitate ester, Carbohydrate Polymers, Vol. 151, pp 988-995, 2016, doi: 10.1016 / j.carbpol.2016.06.048. [Non-Patent Document 2] Willberg-Keyrilainen P., Vartiainen J., Harlin A, Ropponen J., The effect of side-chain length of cellulose fatty acid esters, Cellulose, 24, pp 505-517, 2017, doi: 10.1007 / s10570-016-1165-x. Summary of the Invention [Problem to be solved by the invention]

[0007] It is known to those skilled in the art that high molecular weight cellulose solutions have poor processability, but the mechanical properties of the cellulose films are usually good. Solutions of low molecular weight cellulose are easy to manipulate due to their low solution viscosity, but the mechanical properties of the prepared cellulose films are poor. Similarly, high molar mass molecules can be processed in dilute solutions to a certain extent, but this approach is limited and involves handling large amounts of solvent, which then creates challenges in the process and its economics. Therefore, there is a need for new technologies to achieve thermoplastic cellulose films, fibers, etc. that combine both the good processability of dissolved cellulose solutions and the good mechanical performance of thermoplastic cellulose products. [Means for solving the problem]

[0008] The invention is defined by the features of the independent claims. Some particular embodiments are defined in the dependent claims.

[0009] According to one aspect of the present invention, there is provided a method for producing bimodal or multimodal thermoplastic cellulose films and / or filaments, thereby combining the advantages of different thermoplastic cellulose derivatives and / or side chain lengths at least in terms of processability and mechanical performance.

[0010] This and other aspects, together with the advantages thereof over known solutions, are accomplished by the present invention, as hereinafter described and claimed.

[0011] The method according to the invention is mainly characterized by what is stated in the characterizing part of claim 1.

[0012] The bimodal or multimodal film is mainly characterized by what is stated in the characterizing part of claim 5.

[0013] The present invention provides considerable advantages. For example, the processability and mechanical properties of thermoplastic cellulose materials can be improved and controlled in a pure manner according to the requirements of the final product. Better mechanical properties are beneficial from the processing and end-use point of view. This concept allows the addition of low molecular weight cellulose to reach rheological properties that are attractive for processing, while the addition of high molecular weight cellulose maintains a high tensile modulus, even with materials with high elongation and short side chains. Furthermore, the improved mechanical properties increase the usefulness of cellulose derivatives (modified long chain fatty acids) and allow the commercialization of the inventive concept.

[0014] The present technology will now be described in more detail with reference to specific embodiments.

[0015] The present technology provides improved and controlled processability and mechanical properties of bimodal or multimodal thermoplastic cellulosics by combining low and high molecular weight cellulosics and / or different side chain lengths. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram illustrating the basic concept of bimodal and multimodal molecular weight distribution cellulosic materials. [Diagram 2]1 is a chart illustrating the effect of molar mass on elastic modulus for thermoplastic cellulose films. For example, the label 16H90_16L10 means that the thermoplastic cellulose derivative mixture consists of 90% high molecular weight thermoplastic cellulose derivatives with side chain length C16 and 10% low molecular weight thermoplastic cellulose derivatives with side chain length C16. The same type of label is used in Figures 2-7. [Diagram 3] 1 is a chart illustrating the effect of side chain length on elastic modulus for thermoplastic cellulose films. [Figure 4] 1 is a chart illustrating the effect of molar mass on tensile strength for thermoplastic cellulose films. [Diagram 5] 1 is a chart illustrating the effect of side chain length on tensile strength for thermoplastic cellulose films. [Figure 6] 1 is a chart illustrating the effect of molar mass on elongation for thermoplastic cellulose films. [Figure 7] 1 is a chart illustrating the effect of side chain length on elongation for thermoplastic cellulose films. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] In the present context of thermoplastic cellulose derivatives, low molecular weight (Mw) cellulose can be anything that is essentially lower than high Mw cellulose, for example 1 / 3 (low / high).

[0018] In the present context of thermoplastic cellulose derivatives, high molecular weight (Mw) cellulose can be anything that is essentially higher than low Mw cellulose, for example, 1.5 to 2 times higher (high / low).

[0019] The degree of substitution (DS) is the average number of substituents attached per base or monomer unit.

[0020] According to one embodiment of the present invention, there is provided a method for producing bimodal or multimodal cellulose films and / or filaments, the method comprising at least the following steps: - mixing thermoplastic cellulose derivatives having at least two different average molecular weights or molecular weight distributions and / or side chain lengths; - dissolving the blended thermoplastic cellulose derivative in a solvent to form a solution; and - forming said solution into a film or optionally a filament by a solvent casting process; Equipped with.

[0021] According to one embodiment of the present invention, it is preferred to mix together said thermoplastic cellulose derivatives having at least two different average molecular weights between 50 and 200 kDa.

[0022] According to one embodiment of the present invention, it is preferred to mix together said thermoplastic cellulose derivatives having at least two different side chain lengths from C8 to C16.

[0023] According to one possible embodiment of the invention, at least two of said thermoplastic cellulose derivatives are dissolved in chloroform.

[0024] Also within the scope of the invention are bimodal or multimodal cellulosic films having a modulus of elasticity of at least 100 MPa, a tensile strength of at least 6 MPa, and an elongation of at least 40%.

[0025] Throughout this specification, a reference to an embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, although the phrase "in one embodiment" or "in an embodiment" appears in various places throughout this specification, not all necessarily refer to the same embodiment. For example, when a numerical value is referred to using terms such as about or substantially / nearly, the exact numerical value is also disclosed.

[0026] As used herein, a plurality of items, structural elements, components, and / or materials may be presented in a common list for convenience. However, these lists should be construed as if each member of the list were individually identified as a separate and unique element. While the above-described examples illustrate the principles of the present invention in one or more specific applications, it will be apparent to those skilled in the art that numerous modifications can be made in the form, use, and details of implementation without the exercise of the inventive faculty and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the present invention be limited except as by the scope of the claims set forth below.

[0027] In this specification, the verbs "to comprise" and "to include" are used as open limitations which neither exclude nor require the presence of any unrecited features. Features recited in the dependent claims may be freely combined with one another, unless expressly stated otherwise. [Industrial Applicability]

[0028] It would be advantageous and industrially attractive to combine the outstanding properties of different cellulosic feedstocks, providing novel and competitive solutions, and applying bimodal and multimodal systems to cellulosic materials, so that they can eventually compete with and replace existing synthetic materials. EXAMPLES

[0029] Proof of concept – thermoplastic cellulose sample: [Table 1]

[0030] Thermoplastic cellulose samples were prepared using the homogeneous method presented by Willberg-Keyrilainen et al. (2016 and 2017). The molecular weight of the starting pulp and the degree of substitution (DS) of the final product were varied.

[0031] Films were prepared from thermoplastic cellulose samples by the solvent casting method. Two grades of thermoplastic cellulose were dissolved in chloroform and poured into petri dishes (diameter 50-100 mm). Before film formation, the solvent was evaporated in air at room temperature.

[0032] The tensile properties of the thermoplastic cellulose films were measured in the same manner as described above for the regenerated cellulose films, and the results are shown in Figures 2-7.

Claims

1. A method for producing bimodal or multimodal cellulose films and / or filaments, the method comprising at least the following steps: - mixing thermoplastic cellulose derivatives having at least two different average molecular weights or molecular weight distributions and / or side chain lengths; - dissolving the blended thermoplastic cellulose derivative in a solvent to form a solution; and - forming said solution into a film or optionally a filament by solvent casting; A method comprising:

2. 2. The method of claim 1, wherein said thermoplastic cellulose derivatives having at least two different average molecular weights between 50 and 200 kDa are mixed together.

3. 2. The method of claim 1, wherein said thermoplastic cellulose derivatives having at least two different side chain lengths from C8 to C16 are mixed together.

4. 10. The method of claim 1, wherein at least two of said thermoplastic cellulose derivatives are dissolved in chloroform.

5. A bimodal or multimodal cellulose film characterized by having a modulus of elasticity of at least 100 MPa, a tensile strength of at least 6 MPa, and an elongation of at least 40%.

6. The bimodal or multimodal cellulose film according to claim 5, characterized in that it is produced by the method according to any one of claims 1 to 4.

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