Bimodal or multimodal cellulosic materials and methods for their production - Patents.com

Abstract

According to one aspect of the present invention, a method for producing bimodal and / or multimodal cellulosic materials, such as films and filaments, is provided that combines the advantages of cellulosic raw materials having different average size (degree of polymerization) and / or molecular weight distributions.

Description

[Technical field]

[0001] The present invention relates to improved processability and mechanical performance of regenerated cellulose materials and to a method for producing bimodal or multimodal regenerated cellulose films and filaments having such properties, the bimodality in this case relating to combining cellulose pulps with different average molecular weights (or molar masses) via cellulose dissolution. [Background technology]

[0002] Currently, regenerated cellulose films are made from unimodal cellulose materials, which have only one maximum in their molecular weight distribution. The plastics industry uses bimodal and multimodal structures, for example in bimodal high density polyethylene (HDPE), linear low density polyethylene (LLDPE), and more recently polypropylene (PP) resins. The advantage of bimodality is that it retains the high stress crack resistance and processability of unimodal medium density polyethylene while providing the strength and stiffness of HDPE. For example, Yandi et al. (2009) characterized the microstructure of bimodal HDPE resins.

[0003] Processing of high molecular weight pulp has been impossible due to its high viscosity, limiting the performance of cellulose films alone, which is one of the fundamental reasons why regenerated cellulose films have not yet been able to compete with synthetic materials for similar applications.

[0004] There have been some recent partially related publications regarding cellulose films intended to replace synthetic raw materials. For example, WO2018 / 228744A1 discloses a composition comprising a combination of cellulose polymers that can be used to manufacture films or foils. The disclosed cellulose-based composition can replace films or foils based on fossil raw materials and is used as a packaging or wrapping material. However, the cellulose polymers described in the patent application 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 minor components such as molecular weight controlled cellulose or hemicellulose or lignin for regeneration processes.

[0005] WO2019 / 073370A1 discloses a method for improving the stretchability of films containing a large amount of microfibrillated cellulose (MFC) without adversely affecting the oxygen barrier properties. According to the disclosure, the film is formed from a suspension containing microfibrillated cellulose with a broad size distribution. However, the method described does not apply to dissolving cellulose.

[0006] Meanwhile, US2018 / 0371211A1 discloses a method for producing a cellulose material with a bimodal fibril distribution. This composition can be used to modify the rheological properties of the components. However, this US publication does not relate to a method for preparing a cellulose film, for example, via dissolution and regeneration. Furthermore, the fibril distribution is reflected in the size and shape of the particles, whereas the molecular weight distribution intended here only represents the size and any type of molecules.

[0007] US2019 / 0316293A1 aims to improve a mixture of high aspect ratio cellulose filaments, which includes providing a mixture of cellulose nanofilaments or a mixture of cellulose microfilaments, diluting the mixture of cellulose nanofilaments or the mixture of cellulose microfilaments to a target concentration, fractionating the diluted mixture of cellulose nanofilaments or the diluted mixture of cellulose microfilaments into at least a high solids content and a low solids content, and collecting a fraction of the diluted mixture of cellulose nanofilaments or a fraction of the diluted mixture of cellulose microfilaments. The disclosed method can be used to improve a mixture of high aspect ratio cellulose filaments used in, for example, plastic composite products, coating films, and concrete products. The ability to form a film is based on the assembly of individual cellulose fibers and the dense inter-fiber interactions that form upon drying. This US publication does not apply to dissolving cellulose, which destroys the intra- and intermolecular interactions between individual cellulose polymer chains that allow for structural changes in cellulose during regeneration, film forming ability, etc.

[0008] It is known in the art that high molecular weight cellulose solutions have poor processability but good mechanical properties of regenerated cellulose films. Low molecular weight cellulose solutions are easy to handle due to low solution viscosity, but the mechanical properties of the cellulose films produced are inferior. Similarly, high molar mass molecules can be processed to a certain extent in dilute solutions, but this procedure is limited and involves handling large amounts of solvent, resulting in process and economic challenges. Therefore, there is a need for new technologies to achieve regenerated cellulose films, fibers, etc. that combine the good processability of dissolved cellulose solutions with the good mechanical performance of regenerated cellulose products. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2018 / 228744 [Patent Document 2] International Publication No. 2019 / 073370 [Patent Document 3] US Patent Application Publication No. 2018 / 0371211 [Patent Document 4] US Patent Application Publication No. 2019 / 0316293 [Non-patent literature]

[0010] [Non-Patent Document 1] Berthold, F., Gustafsson, K., Sjoholm, E., Lindstrom, M., An improved method for the determination of softwood kraft pulp molecular mass distributions, In 11th International symposium on Wood and Pulping Chemistry, Nice, France, June 11-14, Vol. 1, 363-366, 2001. [Non-Patent Document 2] IUPAC., (1997). Compendium of chemical terminology. In: AD McNaught & A. Wilkinson, (eds). The "Gold Book". (2nd edn). Oxford: Blackwell Scientific Publications. DOI: 10.1351 / goldbook.M03706. [Non-Patent Document 3] Yandi F., Yanhu X., Wei N., Xiangling J., Shuqin B., Characterization of the Microstructure of Bimodal HDPE Resin, Polymer Journal vol. 41, pp. 622-628, 2009. Summary of the Invention [Problem to be solved by the invention]

[0011] The invention is defined by the features of the independent claims. Some particular embodiments are defined in the dependent claims.

[0012] According to one aspect of the present invention, a method is provided for producing bimodal or multimodal regenerated cellulose films and / or filaments, thereby combining the advantages of different cellulose raw materials at least in terms of processability and mechanical performance.

[0013] This and other aspects, together with the advantages thereof over known solutions, are accomplished by the present invention, as hereinafter described and claimed.

[0014] The method according to the invention is mainly characterized by what is stated in the characterizing part of claim 1.

[0015] The bimodal or multimodal film of the present invention is mainly characterized by what is stated in the characterizing part of claim 7.

[0016] The present invention provides many advantages. For example, the processability and mechanical properties of the regenerated cellulose material are improved and truly controlled in a desired manner, depending on the requirements of the final product. Better mechanical properties are beneficial from the perspective of processing and end use. This concept allows one to achieve rheological properties that are attractive for processing by adding low molecular weight cellulose, maintain high tensile modulus by adding high molecular weight cellulose, and achieve such properties even with high elongation and shorter side chain materials. Furthermore, the improved mechanical properties increase the usefulness of cellulose derivatives (modified long chain fatty acids), enabling the commercialization of the inventive concept.

[0017] The present technology will now be described in more detail with reference to specific embodiments.

[0018] The present technology consists in improving and controlling the processability and mechanical properties of bimodal or multimodal regenerated cellulose materials by combining low and high molecular weight cellulose (i.e., cellulose materials with different average degrees of polymerization). [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram illustrating the basic concepts of bimodal and multimodal molecular weight distribution cellulosic materials. [Diagram 2] FIG. 2 is a graph showing the molecular weight distribution, degree of polymerization (DP), average molecular weight (Mw) and polydispersity index of post-consumer pulp for regenerated cellulose film. [Diagram 3] FIG. 3 is a graph showing experimental results for solution viscosity (shear flow measured at 80° C.) for regenerated cellulose films. [Figure 4] FIG. 4 is a graph showing experimental results for solution viscosity (shear flow measured at 80° C.) for regenerated cellulose films. [Diagram 5] FIG. 5 is a graph showing experimental results for solution viscosity (shear flow measured at 80° C.) for regenerated cellulose films. [Figure 6] FIG. 6 is a graph showing the experimental results for measuring the tensile properties of a regenerated cellulose film. [Figure 7] FIG. 7 is a graph showing the experimental results for measuring the tensile properties of regenerated cellulose film. [Figure 8] FIG. 8 is a graph showing the experimental results for measuring the tensile properties of a regenerated cellulose film. [Figure 9] FIG. 9 is a graph showing the positive effect of hemicellulose on both the solution rheology (reduced viscosity) and mechanical properties (increased tensile strength and elongation) of regenerated cellulose films. [Figure 10]FIG. 10 is a graph showing the positive effect of hemicellulose on both the solution rheology (reduced viscosity) and mechanical properties (increased tensile strength and elongation) of regenerated cellulose films. [Figure 11] FIG. 11 is a graph showing the positive effect of hemicellulose on both the solution rheology (reduced viscosity) and mechanical properties (increased tensile strength and elongation) of regenerated cellulose films. [Figure 12] FIG. 12 is a graph showing the positive effect of hemicellulose on both the solution rheology (reduced viscosity) and mechanical properties (increased tensile strength and elongation) of regenerated cellulose films.

[0020] Low molecular weight (Mw) cellulose is intended to mean herein regenerated cellulose material less than 200 kDa, for example less than 100 kDa.

[0021] High molecular weight (Mw) cellulose is intended to mean herein regenerated cellulose material greater than 350 kDa-550 kDa, for example greater than 300 kDa.

[0022] The degree of substitution (DS) is the average number of substituents attached per base or monomer unit.

[0023] According to one embodiment of the present invention, cellulose raw materials with two different degrees of polymerization are dissolved, thereby forming a bimodal solution. Typically, bimodal systems are applied to, for example, polyolefins, but this phenomenon has not been applied to other polymers (such as cellulose). This phenomenon appears to be a universal behavior, and the inventors of the present invention have demonstrated this in a 4-methylmorpholine n-oxide solution / H2O / cellulose system. In the bimodal system, the processability of the solution is maintained and the strength and stiffness of the recycled film are improved.

[0024] New efficient solvents are essential to efficiently dissolve cellulosic materials and utilize high molecular weight cellulosic materials, which has not been shown or predicted before and is one of the key reasons that makes the idea of ​​thermoplastic and regenerated cellulosic materials in bimodal and multimodal properties feasible.

[0025] Thus, according to one embodiment of the present invention, a method for producing a regenerated cellulose film employs a bimodal cellulose fibril distribution to provide good mechanical properties while reducing viscosity during processing.

[0026] According to one embodiment of the invention, a method for producing bimodal or multimodal cellulose films and / or filaments comprises at least the following steps: mixing together cellulose raw materials having at least two different average degrees of polymerization or at least two different average molecular weights or molecular weight distributions, dissolving the mixed cellulose raw materials in a solvent to form a solution, and regenerating the solution into a film or any filament.

[0027] Reconstitution of the solution into films or filaments is accomplished by conventional reconstitution manufacturing methods.

[0028] According to one embodiment of the present invention, the average molecular weight of the cellulose raw material is 50 kDa-900 kDa, preferably 50-400 kDa.

[0029] According to one embodiment of the present invention, the molecular weight ratio of the different cellulose raw materials is less than 6, preferably greater than 2.5.

[0030] According to one embodiment of the present invention, the solution viscosity ratio of different dissolved cellulose solutions is 10s -1 At shear, less than 20, preferably more than 5.

[0031] According to one embodiment of the invention, the solvent used is selected from underivatized cellulose solvents, amine oxide cellulose solvents, and alkaline cellulose solvents such as, for example, 4-methylmorpholine n-oxide.

[0032] One aspect of the present invention is the inclusion of a dissolution step that disrupts the intra- and intermolecular interactions between cellulose chains, allowing for conformational changes etc. of cellulose during regeneration, improving film-forming ability.

[0033] Also included within the scope of the present invention are bimodal or multimodal cellulosic films having a tensile strength of at least 30 MPa and an elongation of at least 5%.

[0034] Throughout this specification, when referring to an embodiment or an embodiment, it means that the specific features, structures, or characteristics described in connection with that embodiment are included in at least one embodiment of the present invention. Thus, when the phrase "in one embodiment" or "in an embodiment" appears in various places throughout this specification, they do not necessarily all refer to the same embodiment. For example, when referring to a numerical value using terms such as "about" or "substantially", the exact numerical value is also disclosed.

[0035] For convenience, a plurality of items, structural elements, components, and / or materials may be presented in a common list herein. However, these lists should be construed as if each member of the list were individually identified as a separate and unique member. While the foregoing 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 changes in form, use, and details of implementation may be made without the exercise of inventive faculty and without departing from the principles and concepts of the present invention. Accordingly, it is not intended that the present invention be limited, except as by the claims set forth below.

[0036] The verbs "comprise" and "include" are used in this document as open limitations which do not exclude or require the presence of any unrecited features. Features recited in dependent claims may be freely combined with one another, unless expressly stated otherwise. [Industrial Applicability]

[0037] The plastics industry has adopted bimodal systems (HDPE, LLDPE, PP) that offer the benefits of bimodality by having the strength and stiffness of HDPE, while maintaining the high stress crack resistance and processability of unimodal medium density polyethylene. Currently, regenerated cellulose is made with unimodal cellulose materials. It is therefore advantageous and industrially attractive to apply bimodal and multimodal systems to cellulose materials as well, in order to combine the excellent properties of the various cellulose raw materials and provide new competitive solutions that can eventually compete and replace existing synthetic materials. It is important to realize that regenerated cellulose films, even though they are polymer films, are converted from a solution rather than from a melt, resulting in a unique film structure in molecular interactions and crystallinity, which does not mean that the material will not melt. The applications of regenerated films are partly the same as those of thermoplastic polymer films, but they surpass them, for example, in terms of stiffness and ability to be used at high temperatures. EXAMPLES

[0038] [Proof of concept – regenerated cellulose sample]: Commercially available dissolving grade softwood pulp was purchased from Domsjo Fabriker AB. The pulp was repulped overnight in deionized water and divided into three separate groups. Of these, two were ozone treated to reduce the average molecular weight. All pulps were then freeze-dried and ground through a 1 mm sieve (Fritsch Pulverisette variable speed rotor mill) to ensure even distribution of the dissolving solvent in the later step. The intrinsic viscosity of the pulps was measured using standard procedure ISO 5351_2010, and the viscosity average degree of polymerization (DP) of the pulps was calculated using the Mark-Houwink equation (IUPAC 1997). v ) were determined. Molecular weight and polydispersity were determined according to Berthold et al. (2001). The pulps and their properties are shown in Figure 2. Commercially available 4-methylmorpholine N-oxide monohydrate (NMMO, N content >95%) and propyl gallate (propyl-3,4,5-trihydroxybenzoate) were purchased from Sigma-Aldrich, Finland.

[0039] Cellulose was dissolved in a 6-slot Radleys Carousel Cooker (Tech 825W) with NMMO-H2O as the solvent. NMMO-H2O was added to a 250 mL glass flask and 0.1 wt% (per complete dry cellulose) propyl gallate (PG) was added as a stabilizer. The NMMO-H2O-PG mixture was heated to 80 °C to melt. Cellulose of three different molecular weights (65 kDa, 168 kDa, 375 kDa) was added to the mixture in various ratios (shown in Table 1). The total dry matter content of all the mixtures was kept at 7 wt%. The samples were mixed at 80 °C under constant shear of 30 rpm for 24 h. The solubility of cellulose in all the samples was confirmed by polarized microscope images (Microscope: Nikon Eclipse Ci, LV-UEPI-N, Japan, Lens: Nikon Plan 10x / 0.25 OFN22 Ph1 DL MRL20102).

[0040] [Table 1] The cellulose solution and its cellulose composition were investigated.

[0041] The shear flow viscosity of the solution was measured at 80°C. -1 From 1000s -1 A linear ramp-in interval of 1000 s and a measurement time of 6 s per point (data collected at 50 different points) were applied to quickly evaluate the effect of increasing shear stress on the solution viscosity. The results are shown in Figures 3-5.

[0042] The film was applied using an Erichsen K Coater film applicator (wet thickness 400 μm, cast speed 18 mm / s). -1 The films were prepared by casting the dissolved cellulose solution onto a glass surface at 80°C–90°C using a 300-mm immersion centrifuge (EMC) centrifuge. The cast films were precipitated in a water bath (tab water, 15°C) and dried between blotter papers at room temperature. The films were cut into 15 mm wide strips with a lab film cutter and conditioned at least overnight at 23°C and 50% RH. The tensile strength, Young’s modulus, and strain at break of the films were measured using a Lloyd LS5 materials testing machine (AMETEK Measurement and Calibration Technology, USA) and a 100 N load cell. The initial grip distance was 30 mm and the grip separation speed was 10 mm min -1 Each film was measured six times in replicates. The thickness of each strip was measured with a digital caliper from three different points and the average value was used in the calculations. The results are shown in Figures 6-8.

[0043] Effect of hemicellulose on viscosity and mechanical properties raw materials: Dissolution in ionic liquid: [mTBNH][OAc]: ·5-methyl-1,5,7-triaza-bicyclo-[4.3.0]non-6-enium acetate Liquid at room temperature, melting point 15℃, pH 6.5 ·C9H 17 N3O2, 119.19g / mol pulp: Dissolving sulfite pulp (DSP) · Metsa Fibre bleached kraft pulp (BK) Cold alkaline extraction (BK-CCE) Cold Alkaline Extraction, Molar Mass Control (BK-CCE-P) ·Molar mass control (BK-P)

[0044] a) Molecular weight distribution of untreated pulp by SEC analysis. Since the GGM of softwood pulp is poorly soluble in DMAc, SEC was measured by a derivatization method. The results are shown in Figure 9.

[0045] b) Molecular properties and sugar composition of the untreated pulp obtained by HPLC analysis were calculated to correspond to the polymers xylan (XYL), galactoglucomannan (GGM) and cellulose (CELL) according to Janson et al. (1970). The results are shown in Table 2.

[0046] [Table 2]

[0047] The change in solution viscosity of pulp (0.25 wt % and bone dry) in [mTNBH][OAc] in the presence of water as a function of time is shown in Figure 10 .

[0048] Mechanical properties: a) Stress-strain curves with standard deviation (n>5) of RC film (maximum 5.6 N, elongation rate 21 mm / min, actual elongation rate 10 mm / min) are shown in Figure 11. b) The thickness, ultimate tensile strength, strain at break, Young's modulus, and density of the RC films are shown in Table 3.

[0049] [Table 3]

[0050] Regenerated cellulose: a) Molecular weight distribution of untreated pulp by SEC analysis. Since the GGM of softwood pulp is poorly soluble in DMAc, SEC was measured by a derivatization method. The results are shown in Figure 12. b) Molecular properties and sugar composition of the untreated pulp obtained by HPLC analysis were calculated to correspond to the polymers xylan (XYL), galactoglucomannan (GGM) and cellulose (CELL) according to Janson et al. (1970). The results are shown in Table 4.

[0051] [Table 4]

Claims

1. 1. A method for producing bimodal or multimodal cellulose films and / or filaments, comprising: mixing together cellulose raw materials having at least two different average degrees of polymerization or at least two different average molecular weights or molecular weight distributions; dissolving the mixed cellulose feedstock in a solvent to form a solution; Regenerating the solution into a film or any filament; A method comprising at least

2. The average molecular weight of the cellulose raw materials mixed together is 50 kDa-900 kDa, preferably 50 kDa-400 kDa; The method of claim 1.

3. The molecular weight ratio of the different cellulose raw materials is less than 6, preferably more than 2.5; The method of claim 1.

4. The solution viscosity ratio of different dissolved cellulose solutions is 10 s －１ characterized by a shear of less than 20, preferably more than 5; The method of claim 1.

5. the solvent is selected from underivatized cellulose solvents, amine oxide cellulose solvents, or alkaline cellulose solvents; The method of claim 1.

6. The solvent is 4-methylmorpholine n-oxide monohydrate. The method of claim 5.

7. Characterized by having a tensile strength of at least 30 MPa and an elongation of at least 5%; Bimodal or multimodal cellulose films.

8. 10. A method for producing a cellulose acetate ester of cellulose acetate, comprising the steps of:

8. The bimodal or multimodal cellulosic film or filament of claim 7.

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