Cellulose-based absorbent material and method for producing same

Abstract

The present invention relates to a method for producing a cellulose-based, biodegradable superabsorbent material suitable for use in applications such as wet wipes, disposable packaging, hygiene products, medical devices, and a wide range of other technical applications requiring a combination of high absorbency and water retention. The invention also relates to the material thus obtained.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a cellulose-based, biodegradable superabsorbent material suitable for use in applications requiring a combination of high absorbency and water retention, such as personal hygiene products, medical devices, and a wide range of other technical applications. The invention also relates to the material thus obtained. [Background technology]

[0002] Description of Related Art Superabsorbent polymers (SAPs) are polymers that can absorb large amounts of aqueous fluids. This absorption causes the SAP to swell, and therefore the absorbency of an SAP is often characterized in terms of its swelling capacity.

[0003] Currently commercially available SAPs are primarily synthetic and non-biodegradable, typically based on polyacrylic acid blended with sodium hydroxide, thus forming sodium polyacrylate. Due to the synthetic, non-biodegradable nature of the product, there is a need to replace these common SAPs with biodegradable and renewable alternatives.

[0004] Cationic starch has been used in absorbents in the past since the development of such products began in the early 1960s, but these starch-based absorbents lack the binding necessary for such products.

[0005] Cellulose-based absorbents have also been used in the past, and even before synthetic absorbents were developed, some of the oldest alternatives consisted of tissue paper, cotton or cotton pulp. More recent developments have also been made in cellulose absorbents, as described, for example, by Hubbe et al. (2013). However, these more recent cellulose absorbents typically use functionalized cellulose derivatives, thus resulting in lower levels of absorption compared to synthetic SAPs with free swelling capacities (FSCs) of 5-10 g / g and low absorption under load (AULs), or are grafted and crosslinked, such as with acrylic groups, thus compromising the biodegradability and compost stability of the product. WO 2012 / 127119 describes such materials with functionalized and crosslinked polysaccharide backbones. Due at least in part to these shortcomings of known cellulose-based absorbents, synthetic polyacrylate-based SAPs are more popular than cellulose-based alternatives. They have high absorbency and AUL, but are non-biodegradable and cannot be recycled. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2012 / 127119 [Non-patent literature]

[0007] [Non-Patent Document 1] Bachra, Y., Grouli, A., Damiri, F., Bennemara, A., Berrada, M. A new approach for assessing the absorption of disposable baby diapers and superabsorbent polymers: A comparative study. Results in Materials 8 (2020) 100156, doi.org / 10.1016 / j.rinma.2020.100156 [Non-patent document 2] Hubbe et al. (2013) “Review of cellulosic absorbents.” BioResources 8(4) 6556-6629 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, there is strong interest in further developing biodegradable and recyclable absorbent materials that have high absorption capacity in addition to being biodegradable. [Means for solving the problem]

[0009] The invention is defined by the features of the independent claims. Some particular embodiments are defined in the dependent claims.

[0010] According to a first aspect of the present invention, there is provided a process for preparing a cellulose-based absorbent material that does not require cross-linking, as the cross-linking can be replaced by natural bonds between the cellulose moieties.

[0011] According to a second aspect of the present invention, there is provided a method for preparing a cellulose-based absorbent material by utilizing a hydroxypropylation treatment to increase the accessibility of cellulose.

[0012] According to a third aspect of the present invention, there is provided a method for preparing a cellulose-based absorbent material, wherein high absorbency is achieved by a cationization treatment.

[0013] According to a fourth aspect of the invention, the functionalized material is prepared with a low degree of substitution (DS) so as not to impair the biodegradability of the material.

[0014] According to a further aspect of the present invention, there is provided a cellulose-based absorbent material suitable for use to provide high absorption and water retention in technical applications such as wet wipes or other similar hygiene products, disposable packaging, personal hygiene products such as diapers or feminine hygiene products, medical devices, or agricultural applications where large amounts of liquid need to be absorbed.

[0015] The present invention therefore relates to a method for producing a biodegradable absorbent material, comprising the functionalization of a polymeric raw material selected from cellulose, without crosslinking, by combining a low DS hydroxypropylation step with a low DS cationization step.

[0016] Several advantages are achieved using the invention, notably the ability to use renewable raw materials and simple chemical reactions. The combination of a low DS hydroxypropylation step and a low DS cationization step carried out on a cellulose raw material still results in a product with a low DS, so that a biodegradable and recyclable product is also obtained.

[0017] Furthermore, these processes result in highly absorbent materials with free swelling capacities (FSCs) several times higher than known cellulose-based cross-linked absorbents (typically >35 g / g), which are competitive with commercially available synthetic SAPs.

[0018] The lack of explicit cross-linking and low DS further allows for efficient utilization of the bulk of the cellulose without compromising biodegradability.

[0019] It may also be possible to prepare absorbents without a separate hydroxypropylation step, i.e., by directly cationizing the cellulose raw material. However, in such cases, a larger amount of cationization reagent is required to achieve the desired degree of substitution (DS), which, in the case of the commonly used glycidyltrimethylammonium chloride (GTAC), is expensive and hazardous. Separate hydroxypropylation activates the cellulose by opening its structure, thus helping the cationization reagent reach reactive sites on the cellulose and increasing the absorbency of the product.

[0020] Similarly, it is possible to prepare absorbents without a separate cationization step, i.e., by directly fluidizing the hydroxypropylated material, but in such cases, preparing a properly fluidized product requires increasing the DS value in the hydroxypropylation, thereby making it impossible to obtain a low DS superabsorbent.

[0021] A separate fluidization step is especially required for low DS products, as it has been found that low DS materials do not form dispersed gel-like materials without said step. DETAILED DESCRIPTION OF THE INVENTION

[0022] (definition) In this context, the "absorbency" of a material is defined as its free swelling capacity, which is typically >30 g / g for both conventional synthetic non-biodegradable SAPs and the cellulose-based SAPs of the present invention. The cellulose feedstock of the process is converted into chemically functionalized cellulose. The degree of substitution (DS) of the cellulose material after its functionalization is described in terms of "low DS" when the absorbent or intermediate products obtained during its preparation have a DS value of <2. In the materials of the present invention, the DS value is preferably even lower, with values ​​of <0.5. At low DS, the material still resembles natural cellulose sufficiently to be biodegradable.

[0023] The present invention relates to a method for producing a biodegradable absorbent material, which comprises functionalizing a polymeric raw material selected from cellulosic materials.

[0024] The method is carried out without crosslinking by combining a low DS hydroxypropylation treatment with a low DS cationization treatment, and is characterized by the following: - providing a polymeric feedstock formed from cellulose; - hydroxypropylating and cationizing a cellulose feedstock to form a chemically functionalized material having a degree of substitution (DS) of <0.5; - fluidizing the chemically functionalized material to convert it into a fibrillated gel-like material; and drying the fibrillated gel-like material to obtain a cellulose-based biodegradable absorbent product.

[0025] Preferably, the cellulose raw material is a dissolving pulp. In particular, pre-treated and pre-functionalized cellulose is avoided, as these may result in adverse consistency or poor biodegradability.

[0026] The hydroxypropylation step is intended to increase the accessibility of cellulose and is typically carried out using propylene oxide as the hydroxypropylating reagent. The temperature during the reaction is preferably 25-70°C and maintained for a period of time suitable to achieve the desired reaction, e.g., 3-10 hours, typically using an excess of hydroxypropylating reagent, e.g., >3 molar equivalents.

[0027] Typically, the reaction that occurs during the hydroxypropylation step is that of Scheme 1 below. [ka]

[0028] In one embodiment of the present invention, the hydroxypropylation is carried out at a degree of substitution (DS) of ≦0.5, preferably 0.2-0.5, or most suitably 0.3-0.4.

[0029] Cationization then provides the cellulose with the functional groups necessary for high absorbency. This cationization step is typically carried out using glycidyltrimethylammonium chloride (GTAC) as the cationization reagent. The reaction temperature is preferably 40-80°C and maintained for a period of time suitable to achieve the desired reaction, e.g., 6-20 hours, typically using an excess of cationization reagent, e.g., >4 molar equivalents.

[0030] Typically, the reaction that occurs during the cationization step is that of Scheme 2 below. [ka]

[0031] In one embodiment of the present invention, cationization is carried out to a degree of substitution (DS) of ≦0.4, preferably ≦0.2, or most suitably about 0.15.

[0032] In a preferred embodiment of the present invention, cationization is carried out directly on the hydroxypropylated material without isolating the hydroxypropylated material. This is possible because the hydroxypropylation and cationization reactions are carried out in similar environments. Furthermore, each isolation step typically reduces the product yield, so it is advantageous to omit them when possible.

[0033] Achieving the desired degree of substitution is critical to the present invention in order to obtain a natural and biodegradable product, and both the hydroxypropylation and cationization steps are typically optimized to facilitate this goal. However, the amounts of hydroxypropylation and cationization reagents added to the cellulose can also be adjusted to control the relative contribution of cellulose to the mass of the final product. In terms of dry matter, the final functionalized absorbent product should be comprised of 84-88% by weight of cellulose equivalent, preferably about 86% by weight. The remainder of the mass is provided by the hydroxypropyl moieties grafted onto the cellulose.

[0034] The next step in the process after hydroxypropylation and cationization is a fluidization step, which is essential to obtain a gel-form material. Preferably, fluidization is performed in a controlled manner, more preferably with the material in an aqueous suspension at a solids content of 0.3-0.75 wt %, such as about 0.5 wt %. Most suitably, microfluidization is used, typically using two or more passes, preferably two to three passes, through a microfluidizer to achieve a fiber length of less than 30 μm.

[0035] Once a suitable gel-like consistency is achieved for the fluidized material, the material can be dried, which is typically done in a controlled manner, preferably by freeze-drying, to avoid disrupting the structure achieved.

[0036] In conclusion of the above, the process of the present invention typically comprises four process steps: 1) Mild hydroxypropylation 2) Cationization of hydroxypropylated materials without isolation 3) Liquidation and 4) The resulting gel was dried.

[0037] The above process results in a biodegradable cellulose-based absorbent material. The present invention therefore also relates to said material prepared using the above method.

[0038] The preferred degree of substitution (DS) of this material is less than 0.5, as a sufficiently low DS value ensures that the material is still biodegradable.

[0039] In addition to being biodegradable, the materials of the present invention must also provide sufficient absorption. Accordingly, the biodegradable cellulose-based absorbent materials of the present invention preferably have a free swelling capacity (FSC) of >15 g / g, more preferably >30 g / g, and most preferably >35 g / g. Furthermore, the materials preferably have an absorption under load (AUL) of >8 g / g, more preferably >10 g / g, and most preferably >12 g / g in saline (0.9% NaCl) or synthetic urine (3.0% urea, 1.0% sodium chloride, 0.4% potassium chloride, 0.3% sodium sulfate).

[0040] The biodegradable cellulose-based absorbent materials described above are particularly suitable for use in technical applications such as wet wipes or other similar hygiene products, disposable packaging, personal hygiene products such as diapers or feminine hygiene products, medical devices, or agricultural applications that require the absorption of large amounts of aqueous solutions, and provide high absorbency and water retention.

[0041] It is to be understood that the disclosed embodiments of the invention are not limited to the particular structures, processing steps, or materials disclosed herein, but extend to equivalents thereof as would be recognized by one of ordinary skill in the art. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0042] Throughout this specification, 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, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily all refer to the same embodiment. For example, when a numerical value is referenced using terms such as about or substantially, the exact numerical value is also disclosed.

[0043] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in common lists for convenience. However, these lists should be construed as though each member of the list were individually identified as a separate and unique member. In addition, various embodiments and examples of the invention may be referenced herein, along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives should not be construed as de facto equivalents of each other, but should be considered as separate automatic representations of the invention.

[0044] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In this description, numerous specific details are provided to provide a thorough understanding of embodiments of the invention. However, one skilled in the art will recognize that the invention may be practiced without one or more of the specific details.

[0045] While the foregoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those skilled in the art that numerous modifications in embodiment, use, and detail can be made without the exercise of inventive faculty and without departing from the principles and concepts of the present invention. Accordingly, the present invention is not intended to be limited except as by the claims set forth below.

[0046] The following non-limiting examples are intended to merely illustrate the benefits provided by embodiments of the present invention. [Example]

[0047] Example 1 - Preparation of Cellulose-Based Superabsorbent Polymer 430 ml / g of dissolving pulp was obtained from Domsjo and used as the cellulose feedstock. A sample of the material was hydroxypropylated (DS≦0.5) with excess propylene oxide (4.1 molar equivalents) for 4 hours at 25°C and then directly cationized (without isolating the hydroxypropylated material) with excess GTAC (5.0 molar equivalents) for 16 hours at 45°C to a DS of approximately 0.15. The resulting cationized material was fluidized by passing it through a fluidizer (M-110EH, Microfluidics Ind.) using three passes (1000 bar, 1800 bar, and 1800 bar). The end point of the fluidization process was determined by microscopy and selected as the point at which visible fibers had almost disappeared. The resulting gel-form material was then dried by freeze-drying.

[0048] Control samples were prepared by omitting either functionalization (hydroxypropylation and cationization) or fluidization, or both.

[0049] The free swelling capacity in water at 5 min (FSC) was 41-58 g / g for the SAPs measured using an open cage. The FSC in synthetic urine was 22 g / g, and the absorption under load (AUL, 2 kPa / 0.3 psi static pressure) in synthetic urine was 12 g / g. The FSC was also measured for the controls. The FSC was 14 g / g for the non-functionalized fluidized control. The functionalized non-fluidized control material collapsed and could not be retained by the cage, but its swelling capacity could be measured in tea bags at 11 g / g. The AUL was measured using a method adapted from Bachra et al. [Industrial Applicability]

[0050] The material can generally be used as a replacement for conventional non-biodegradable synthetic absorbents in a wide range of applications requiring high absorption and water retention.

[0051] In particular, the material is useful in personal hygiene products such as wet wipes, disposable packaging, and hygiene products, medical devices, or agricultural applications.

Claims

1. A method for producing a biodegradable absorbent material, including the functionalization of polymeric raw materials, - A process of providing a polymeric raw material formed from cellulose. - A step of hydroxypropylating and cationizing a cellulose raw material to form a chemically functionalized material having a degree of substitution (DS) of <0.5, - A process of fluidizing a chemically functionalized material and converting it into a fibrillated gel-like material, and - A process of drying a fibrillated gel-like material to obtain a cellulose-based biodegradable absorbent product. A method characterized by the following.

2. The method according to claim 1, wherein the cellulose raw material is a pulp dissolving agent.

3. The method according to claim 1 or 2, wherein the hydroxypropylation is carried out with a degree of substitution (DS) of <0.

5.

4. The method according to claim 1 or 2, wherein hydroxypropylation is carried out using propylene oxide as the hydroxypropylating reagent, preferably at a temperature of 25 to 70°C maintained for 3 to 10 hours, and typically using an excess amount of hydroxypropylating reagent such as >3 molar equivalents.

5. The method according to claim 1 or 2, wherein the cationization is carried out with a degree of substitution (DS) of ≤0.2, preferably about 0.

15.

6. The method according to claim 1 or 2, wherein the cationization is carried out using glycidyltrimethylammonium chloride (GTAC) as the cationizing reagent, preferably at a temperature of 40 to 80°C maintained for 6 to 20 hours, and typically using a chloride cationizing reagent, for example, in an amount of >4 molar equivalents.

7. The method according to claim 1 or 2, wherein cationization is performed directly on the hydroxypropylated material without isolating the hydroxypropylated material.

8. The method according to claim 1 or 2, wherein the amounts of the hydroxypropylating reagent and the cationizing reagent added to the cellulose are adjusted to give an amount of cellulose equivalent to 84 to 88% by weight, preferably about 86% by weight, of the dry material in the final absorption product.

9. The method according to claim 1 or 2, wherein fluidization is carried out in a controlled manner, preferably by microfluidization, using a material in an aqueous suspension with a solid content of 0.3 to 0.75 wt%, more preferably by microfluidization, typically using two or more microfluidizers, to achieve a fiber length of <30 μm.

10. The method according to claim 1 or 2, wherein drying is carried out in a controlled manner, preferably by freeze-drying, to avoid collapse of the achieved structure.

11. A biodegradable cellulose-based absorbent material characterized by being prepared using the method described in claim 1 or 2.

12. The absorbent material according to claim 11, having a degree of substitution (DS) of <0.

5.

13. The absorbent material according to claim 11, having a free swelling capacity (FSC) of >15 g / g, preferably >30 g / g, and most preferably >35 g / g.

14. Use of a material manufactured according to the method of Claim 1 or 2 to provide high absorbency and water retention in personal hygiene products such as wet wipes or other similar hygiene products, disposable packaging, diapers or feminine hygiene products, medical devices, or technical applications such as agricultural applications, which require the absorption of large amounts of aqueous liquid.