Salt-responsive material and use thereof

Abstract

To develop a material which has a salt-stimulus-responsive switching mechanism while possessing mechanical strength, and has marine degradability.SOLUTION: The present invention provides a method for controlling marine degradability of a salt-responsive material by applying a salt to the salt-responsive material containing an ionic supramolecular polymer composed of an ion pair of chitosan and a polycarboxylic acid, the control being effected through the salt response of the ionic supramolecular polymer.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to salt-responsive materials and their use, etc.

Background Art

[0002] As a measure to prevent marine pollution by plastics, attention has been increasing on marine-degradable polymers that decompose in the ocean. However, marine-degradable polymers are limited to poly(3-hydroxybutyrate), polycaprolactone, etc. Therefore, the development of marine-degradable plastics with a switching mechanism that exhibits biodegradability by an external stimulus during ocean outflow has been underway. The present inventors have hitherto developed disulfide-containing polymers that switch in the reducing environment of seafloor sediment to initiate biodegradation (Non-Patent Document 1) and spore-embedded polymers that switch by abrasion stimulation during external outflow to initiate biodegradability (Patent Document 1).

[0003] In addition, the present inventors have developed a switching mechanism that is expressed in response to salts (NaCl) in the ocean. However, there is a demand for salt-responsive polymers having further mechanical strength.

[0004] As salt-responsive materials, Non-Patent Document 2 shows the salt responsiveness and marine degradability of a polyion complex (PGAIC) formed between poly-γ-glutamic acid (PGA) and a quaternary ammonium compound (QA), but does not show a supramolecular polymer network material formed between chitosan and a polyvalent carboxylic acid. Although the salt responsiveness and marine degradability of a polyion complex (PGAIC) formed between poly-γ-glutamic acid (PGA) and a quaternary ammonium compound (QA) are shown in Non-Patent Document 2, a supramolecular polymer network material formed between chitosan and a polyvalent carboxylic acid is not shown.

[0005] Non-Patent Document 3 shows a citric acid-crosslinked chitosan / PVA composite having a chemical crosslink between chitosan and citric acid, but does not show an ionic supramolecular polymer.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Non-Patent Literature

[0007]

Non-Patent Literature 1

Non-Patent Literature 2

Non-Patent Literature 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] In view of the above situation, it is an object to develop a material that has a salt-stimulus-responsive switching mechanism while having mechanical strength and is ocean-degradable.

Means for Solving the Problems

[0009] As a result of intensive studies to solve the above problems, the present inventors have found that by mixing chitosan nanofibers (ChNF) having an amino group, which is a basic functional group, on the fiber surface and a polyvalent carboxylic acid having a carboxy group, which is an acidic functional group, a supramolecular polymer network (SPN) is constructed, and a material having mechanical strength and expressing a salt-stimulus-responsive switching mechanism is obtained. Based on such findings, the present invention has been completed. That is, the gist of the present invention relates to the following.

[0010] [1] A method for controlling the ocean degradability of a salt-responsive material containing an ionic supramolecular polymer composed of an ion pair of chitosan and a polyvalent carboxylic acid by acting a salt on the salt-responsive material and by the salt response of the ionic supramolecular polymer. [2] The method according to [1], wherein the chitosan is chitosan nanofibers. [3] The method according to [1], wherein the polyvalent carboxylic acid is at least one selected from tartaric acid and citric acid. [4] The method according to [1], wherein the mixing ratio of chitosan and the polyvalent carboxylic acid is more than 1:0.5 to less than 1:3 in terms of the molar ratio of the amino group contained in chitosan to the carboxy group contained in the polyvalent carboxylic acid. [5] A method for cleaving a salt-responsive material containing an ionic supramolecular polymer composed of an ion pair of chitosan and a polyvalent carboxylic acid by acting a salt on the salt-responsive material and by the salt response of the ionic supramolecular polymer. [6] A method for biodegrading a salt-responsive material containing an ionic supramolecular polymer composed of an ion pair of chitosan and a polyvalent carboxylic acid in a marine environment by acting seawater on the salt-responsive material and by the salt response of the ionic supramolecular polymer. [7] An ionic supramolecular polymer composed of an ion pair of chitosan and a polyvalent carboxylic acid. [8] The ionic supramolecular polymer according to [7], wherein the chitosan is chitosan nanofibers. [9] The ionic supramolecular polymer according to [7], wherein the polyvalent carboxylic acid is at least one selected from tartaric acid and citric acid.

[10] The ionic supramolecular polymer according to [7], wherein the content ratio of chitosan and the polyvalent carboxylic acid in the salt-responsive material is more than 1:0.5 to less than 1:3 in terms of the molar ratio of the amino group contained in chitosan to the carboxy group contained in the polyvalent carboxylic acid.

[11] A salt-responsive material comprising the ionic supramolecular polymer.

[0011] The present invention can also be embodied in the following aspects.

[12] A method for producing an ionic supramolecular polymer, comprising mixing chitosan and a polycarboxylic acid. Effect of the Invention

[0012] According to the present invention, it is possible to provide a new material that has mechanical strength and decomposes in response to an external stimulus such as salt (for example, NaCl). In other words, the chitosan and polycarboxylic acid that constitute the material of the present invention are derived from natural products and are inherently biodegradable in the environment, so once the molecular bonds of the material of the present invention are cleaved, it is rapidly biodegraded into water, carbon dioxide, etc. in the ocean, etc. [Brief description of the drawings]

[0013] [Figure 1] Figure 1 shows the BOD biodegradation curves of ChNF using soil and marine inoculants. [Figure 2] Figure 2 shows SPN films prepared from ChNF and polycarboxylic acids (photos used as drawing substitutes): (a) ChNF, (b) ChNF / TA (tartaric acid) (1:1), (c) ChNF / CA (citric acid) (1:0.5), (d) ChNF / CA (1:1), (e) ChNF / CA (1:1.5), (f) ChNF / CA (1:2). The ratio in parentheses is the NH2:COOH mixture ratio. [Figure 3] Figure 3 shows the FT-IR spectra (diamond, ATR) of ChNF (top line), SPN film of ChNF / TA (1:1) (middle line), and TA (bottom line). [Figure 4] Figure 4 shows the FT-IR spectra (diamond, ATR) of ChNF (top line), SPN film of ChNF / CA (1:1) (middle line), and CA (bottom line). [Figure 5]FIG. 5 is a schematic diagram showing the NaCl stimulus response of a carboxylic acid crosslinked film of chitosan. [Figure 6] FIG. 6 shows the results of a disintegration test at 30° C. for 14 days in various ChNF / TA (1:1) solutions (photographs used as drawing substitutes). [Figure 7] FIG. 7 is a schematic diagram showing a multipoint ionic supramolecular polymer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be described below. However, the present invention is not limited to the following preferred embodiments, and can be freely modified within the scope of the present invention. In this specification, when a numerical range is expressed as "lower limit to upper limit," the upper limit may be "equal to or less than" or "less than," and the lower limit may be "equal to or greater than" or "more than."

[0015] <Ionic supramolecular polymer> One aspect of the present invention relates to an ionic supramolecular polymer comprising an ion pair of chitosan and a polycarboxylic acid (hereinafter, sometimes referred to as "the ionic supramolecular polymer of the present invention").

[0016] The ionic supramolecular polymer according to the present invention was designed from the following viewpoints. The inventors have investigated "acid-base ion pairs" as an environmentally responsive cleavage unit. Taking advantage of the fact that the ionic bond of an acid-base ion pair weakens and ionizes in a solution containing salt (e.g., NaCl), the inventors have previously developed an external stimulus-responsive material that cleaves in response to salt by forming a readily biodegradable unit into a supramolecule using an ion pair.

[0017] When this technology is used for the connection between polymer side chains, in addition to the switching function, it also leads to the technology for controlling the physical properties of the original polymer. Therefore, an ionic supramolecular polymer composed of chitosan, a biodegradable polymer with functional groups in its side chains, and crosslinked by a polyvalent carboxylic acid was developed, and a switching mechanism based on salt response was established. In addition, a composite material containing the ionic supramolecular polymer was developed, and a switching mechanism based on salt response was established. Figure 7 is a schematic diagram showing the above molecular design and cleavage by salt response of the ionic supramolecular polymer of the present invention.

[0018] The ionic supramolecular polymer of the present invention can be formed by mixing chitosan and a polyvalent carboxylic acid in a dispersed solution state at a specific mixing weight ratio, and after forming the ionic supramolecular polymer, the ionic supramolecular polymer can be isolated by distilling off the solvent from the solution.

[0019] More specifically, for example, an ionic supramolecular polymer can be formed by mixing chitosan and a polyvalent carboxylic acid in a solvent and reacting them at room temperature for about 0.1 to 12 hours. The pH of the solvent used for forming the ionic supramolecular polymer of the present invention depends on the chitosan and polyvalent carboxylic acid used, etc., but is usually about pH 3 to 8.

[0020] The solvent used for forming the ionic supramolecular polymer of the present invention is not limited as long as it can uniformly disperse and dissolve chitosan and a polyvalent carboxylic acid. For example, solutions using water as a solvent such as water and buffer solutions, organic solvents such as alcohols (e.g., methanol), and mixed solvents composed of water and at least one kind of hydrophilic organic solvent can be mentioned. The solvent may contain one kind or more.

[0021] The concentrations of chitosan and polycarboxylic acid contained in the dispersion solution may be appropriately adjusted within the range where chitosan and polycarboxylic acid are uniformly dispersed and dissolved in the solvent, and are not limited, but may be 0.001 g / mL or more, 0.005 g / mL or more, or 0.01 g / mL or more respectively, and may be 1 g / mL or less, 0.1 g / mL or less, or 0.05 g / mL or less, and may be these non - contradictory combinations. The concentration may be, for example, 0.001 to 0.05 g / mL.

[0022] The mixing ratio of chitosan and polycarboxylic acid can be changed according to the types of chitosan and polycarboxylic acid used, etc., and is not limited. However, the amino group, which is a reactive functional group contained in chitosan, and the carboxy group, which is a reactive functional group contained in polycarboxylic acid, are reacted under the condition that the molar ratio is usually more than 1:0.5 to less than 1:3. Also, the molar ratio may be 1:0.75 to 1:2, 1:1 to 1:1.5 or 1:1 to 1:1.25, etc., and may be these non - contradictory combinations.

[0023] The formation of the ionic supramolecular polymer can be confirmed by particle size measurement by light scattering method, IR analysis, NMR analysis, visual observation, etc. It can be confirmed by visual observation and the like.

[0024] ≪Chitosan≫ Chitosan is a polysaccharide in which 2 - amino - 2 - deoxy - D - glucose (glucosamine) is linearly bonded. Industrially, it is generally produced by subjecting chitin contained in the shells of crustaceans such as crabs and shrimps, and the skeletons of squids, etc. to deproteinization treatment by alkali treatment, etc., and then subjecting the obtained chitin to de - calcium treatment by acid treatment, etc., and then performing de - acetylation by alkali treatment, etc.

[0025] ​As the chitosan constituting the ionic supramolecular polymer of the present invention, for example, those prepared by the usual preparation methods of chitosan as described above or commercially available products can be used without particular limitation. As commercially available products, for example, chitosan manufactured by Tokyo Chemical Industry Co., Ltd., chitosan nanofibers manufactured by Sugino Machine, etc. can be used.

[0026] In the deacetylation step, the degree of deacetylation can be adjusted by appropriately changing the alkali concentration, temperature, and treatment time used. Generally, the degree of deacetylation is 60% or more. The average molecular weight of chitosan used in the present invention is not particularly limited. For example, the weight average molecular weight (calculated by GPC molecular weight measurement using pullulan as a standard product) is 10,000 to 4,000,000 or about 100,000 to about 1,000,000.

[0027] The molecular weight of chitosan can be measured by the GPC method or the like. The degree of deacetylation can be measured by colloidal titration with a polylithium sulfate potassium solution or the like.

[0028] Note that chitosan may be derivatized as long as the functional groups forming the ionic supramolecular polymer are maintained.

[0029] As the chitosan used in the present invention, chitosan nanofibers can be preferably used. Chitosan nanofibers can be obtained, for example, by subjecting a chitin-containing biological-derived material to at least one deproteinization step, at least one deashing step, and at least one deacetylation step as described above, and then performing fibrillation treatment. For the fibrillation treatment, devices such as a mortar type grinder, a high-pressure homogenizer, a freeze pulverizer, etc. can be used, and preferably, grinder treatment is performed using a mortar type grinder or the like. The diameter of chitosan nanofibers is usually about 2 nm to about 40 nm

[0030] ​​The chitosan nanofibers used in the present invention may be prepared by the usual chitosan nanofiber preparation method as described above, or may be commercially available products, without any particular limitation. Examples of commercially available products that can be used include chitosan nanofibers manufactured by Sugino Machine Co., Ltd.

[0031] <Polycarboxylic acids> Examples of the polycarboxylic acid constituting the ionic supramolecular polymer of the present invention include aliphatic polycarboxylic acids, alicyclic polycarboxylic acids, aromatic polycarboxylic acids, and oxypolycarboxylic acids.

[0032] Aliphatic polycarboxylic acids are compounds that have an aliphatic skeleton (excluding alicyclic skeletons) and two or more carboxy groups in the molecule. Examples of aliphatic polycarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid, fumaric acid, and itaconic acid. Alicyclic polycarboxylic acids are compounds having an alicyclic skeleton and two or more carboxy groups in the molecule. Examples of alicyclic polycarboxylic acids include hexahydrophthalic acid and tetrahydrophthalic acid. Aromatic polycarboxylic acids are compounds having an aromatic skeleton and two or more carboxy groups in the molecule. Examples of aromatic polycarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, and pyromellitic acid. The oxypolycarboxylic acid is a compound having a hydroxy group and two or more carboxy groups in the molecule. Examples of the oxypolycarboxylic acid include tartronic acid, malic acid, tartaric acid, and citric acid.

[0033] Among these, the polycarboxylic acid is preferably a di- or tricarboxylic acid having two or three carboxy groups, more preferably an oxypolycarboxylic acid, and more preferably tartaric acid or citric acid.

[0034] The polycarboxylic acid may be derivatized as long as the functional group that forms the ionic supramolecular polymer is maintained. The polycarboxylic acid may be used alone or in combination of two or more.

[0035] The polycarboxylic acid used in the present invention can be produced by a known synthesis reaction, and commercially available products can also be used.

[0036] <Salt-responsive materials> A further aspect of the present invention relates to a salt-responsive material (hereinafter, sometimes referred to as "the salt-responsive material of the present invention") comprising the ionic supramolecular polymer of the present invention. The matters explained in the section on <ionic supramolecular polymer> above are all applicable to the explanation of the <salt-responsive material> of the present invention.

[0037] The salt-responsive material of the present invention is a material containing the ionic supramolecular polymer of the present invention, and the ionic supramolecular polymer is salt-responsively cleaved in a solution containing salt, and the ionic supramolecular polymer units whose molecular bonds have been cleaved are rapidly biodegraded into water, carbon dioxide, etc. in the ocean, etc., and therefore the salt-responsive material of the present invention can be suitably applied to marine biodegradable products, etc.

[0038] The salt-responsive material may be composed of the ionic supramolecular polymer of the present invention, and may optionally contain various additives such as solvents, excipients, stabilizers, blended polymers, etc. The additives may be used alone or in combination of two or more.

[0039] The blending ratio of the ionic supramolecular polymer in the salt-responsive material is not limited, but can be, for example, about 1 to 100 wt %, 50 to 99 wt %, 60 to 90 wt %, or 70 to 80 wt % of the total amount of the salt-responsive material.

[0040] The form of the salt-responsive material is not particularly limited, and it may be in the form of a powder, pellet, film-like solid, or dissolved or dispersed in a hydrophilic or lipophilic liquid, sol, or gel. Salt-responsive materials can be produced by conventional methods.

[0041] The salt-responsive material of the present invention can be formed into articles, containers, etc. having a shape suitable for use, such as films and sheets, and molded articles such as fibers and non-woven fabrics by molding. There are no particular restrictions on the method for obtaining a film or sheet using the salt-responsive material of the present invention. Except for using the salt-responsive material, it is formed into a film shape or a sheet shape by a known molding method. For example, methods of forming into a film shape or a sheet shape by a T-die molding method, an inflation molding method, a calendar molding method, a hot press molding method, etc. can be mentioned. Further, these films and sheets may be stretched in at least one direction. There are no particular restrictions on the stretching method, but examples include a roll stretching method, a tenter method, an inflation method, etc.

[0042] There are no particular restrictions on the method for obtaining a molded article having a shape suitable for use using the salt-responsive material of the present invention. Except for using the salt-responsive material, it can be manufactured by a known method. For example, methods such as performing extrusion molding or injection molding on a mold can be mentioned.

[0043] Various additives can be added to the salt-responsive material of the present invention according to the purpose. Examples of the additives include blend polymers, plasticizers, fillers, antioxidants, ultraviolet absorbers, heat stabilizers, flame retardants, mold release agents, inorganic additives, crystal nucleating agents, antistatic agents, pigments, antiblocking agents, etc. The additives can be used alone or in combination of two or more.

[0044] The method for adding various additives to the salt-responsive material of the present invention is not particularly limited. For example, it can be carried out by mixing using a Henschel mixer, a super mixer, a tumbler-type mixer, etc., and then continuously kneading using a single-screw or twin-screw extruder.

[0045] <Cracking method, method for controlling marine degradability, marine degradation method> One aspect of the present invention relates to a method of causing a salt to act on a salt-responsive material containing an ionic supramolecular polymer composed of an ion pair of chitosan and a polyvalent carboxylic acid, and cleaving the material by the salt response of the ionic supramolecular polymer (hereinafter sometimes referred to as "the cleavage method of the present invention"). Note that the matters described in the sections of <ionic supramolecular polymer> and <salt-responsive material> are all applicable to the descriptions of <cleavage method, method for controlling marine degradability, marine degradation method> of the present invention.

[0046] The ionic supramolecular polymer of the present invention is a structure that is responsive to an external stimulus of a salt. That is, the ionic supramolecular polymer of the present invention is responsive to an external stimulus of a salt and cleaves into a salt of chitosan and a salt of a polyvalent carboxylic acid. The salt-responsive material containing the ionic supramolecular polymer of the present invention is immersed in a salt-containing solution, for example, at 0 to 40 ° C, and can be cleaved by reacting for about 4 weeks immediately after immersion in the salt-containing solution. The pH of the solvent used for cleaving the salt-responsive material containing the ionic supra molecular polymer of the present invention depends on the salt, ionic supramolecular polymer, etc. used, but is usually about pH 6 to 8, or about 6.5 to 7.5.

[0047] The cleavage of the ionic supramolecular polymer can be confirmed by particle size measurement by light scattering method, IR analysis, NMR analysis, visual observation, etc.

[0048] ≪Salt≫ The salt used for cleaving the ionic supramolecular polymer of the present invention may be any salt that can react with the ionic supramolecular polymer of the present invention and cleave into a salt of chitosan and a salt of a polyvalent carboxylic acid. Although not limited, for example, at least one cation selected from alkali metal ions, alkaline earth metal ions, metal ions, and ammonium ions, and, for example, at least one anion selected from halide ions such as chloride ions, bromide ions, and iodide ions, hydroxide ions, acetate ions, carbonate ions, sulfate ions, nitrate ions, nitrite ions, and phosphate ions, etc. It is preferably a salt composed of a pair.

[0049] Further, it is preferable that the cation of the salt is sodium ion, potassium ion, magnesium ion, calcium ion, iron ion, or ammonium ion, and the anion is chloride ion. It is more preferable that the cation of the salt is sodium ion or potassium ion, and the anion is chloride ion. The salt is preferably sodium chloride or potassium chloride, and more preferably sodium chloride. As the salt, a solution containing the salt, such as seawater, can also be used.

[0050] The concentration of the salt in the system acting on the ionic supramolecular polymer depends on the ionic supramolecular polymer, the salt, etc. used, but is usually more than 0% by weight to a saturated solution, 0.1 to 5% by weight, preferably 1 to 3.5 % by weight. The concentration of the saturated solution may be, for example, about 35% by weight. For the cleavage of the ionic supramolecular polymer of the present invention, one or more salts may be used.

[0051] ≪Solvent≫ The solvent used for the cleavage of the ionic supramolecular polymer of the present invention is not limited as long as it can uniformly disperse and dissolve the salt and the ionic supramolecular polymer. For example, a solution using water as a solvent such as water or a buffer solution, an organic solvent such as alcohols (e.g., methanol), water and at least one of hydrophilic organic solvents, such as a mixed solvent, can be mentioned. The solvent may contain one or more kinds.

[0052] Thus, in the presence of a salt, the ionic supramolecular polymer of the present invention weakens and cleaves ionic bonds by salt exchange, resulting in a decrease in molecular weight. The resulting chitosan and polyvalent carboxylic acid can be biodegradably decomposed by being rapidly decomposed by microorganisms. That is, in the marine environment, the salt-responsive material containing the ionic supramolecular polymer of the present invention undergoes salt-responsive cleavage of the ionic supramolecular polymer by seawater, resulting in a decrease in molecular weight and biodegradation. That is, as one aspect of the present invention, a method for controlling the marine degradability of a salt-responsive material containing an ionic supramolecular polymer composed of an ion pair of chitosan and a polyvalent carboxylic acid by acting a salt on the salt-responsive material (hereinafter sometimes referred to as "the method for controlling the marine degradability of the present invention") is provided.

[0053] Further, as another aspect of the present invention, a method for biodegrading the material in a marine environment by acting seawater on a salt-responsive material containing an ionic supramolecular polymer composed of an ion pair of chitosan and a polyvalent carboxylic acid (hereinafter sometimes referred to as "the marine degradation method of the present invention") is provided.

[0054] Here, the biodegradability of a biodegradable polymer can be the property that the biodegradable polymer is cleaved, fragmented into low molecules, and mineralized. The biodegradability of a biodegradable polymer can be confirmed, for example, by International Standards ISO 18830, ISO 19679, ISO 22403, ISO 22404, ISO 22766, ISO 23832, ISO 23977-1, and ISO 23977-2.

Examples

[0055] Hereinafter, the present invention will be specifically described by way of examples, but these are merely examples of the present invention and the scope of the present invention is not limited thereto.

[0056] <Evaluation of Biodegradability of Chitosan Nanofibers> As the basic nanofibers, chitosan nanofibers (ChNF), which are fibers derived from marine organisms having an amino group, were employed. Chitosan can be obtained by deacetylating chitin contained in marine organisms (such as shrimp and crab), and is commercially available as chitosan nanofibers (ChNF), which are fibers having an amino group. First, it was evaluated from a BOD biodegradation test whether this could be used as an easily degradable unit. In this test, BiNFI-s (manufactured by Sugino Machine) was used as ChNF.

[0057] The results are shown in Fig. 1. In the BOD biodegradation test using soil planting sources, ChNF rapidly biodegraded after a 3-day induction period and showed a biodegradation degree of approximately 70% in 60 days. Also, in the ocean, ChNF started biodegradation after a 5-day induction period and showed a BOD biodegradation degree of approximately 60% in 60 days. From this it can be expected that the composite material prepared by mixing ChNF and polycarboxylic acid will be rapidly biodegraded in the ocean as well.

[0058] <Development of Chitosan nanofiber-based salt-responsive composite materials> Tartaric acid (TA) or citric acid (CA) having a dicarboxylic acid at the end was mixed with a 2% ChNF aqueous dispersion at various mixing ratios (molar ratio of the NH2 groups contained in ChNF and the COOH groups contained in the dicarboxylic acid) and stirred at room temperature for 12 hours, transferred to a petri dish, and dried at 30 °C under air to prepare cast films of ChNF / TA or ChNF / CA.

[0059] The films were self-standing films that could be held with tweezers (Fig. 2; (a) ChNF, (b) ChNF / TA (1:1), (c) ChNF / CA (1:0.5), (d) ChNF / CA (1:1), (e) ChNF / CA (1:1.5), (f) ChNF / CA (1:2). The numbers in parentheses are the NH2:COOH mixing ratios).

[0060] <Confirmation of ionic bond formation by FT-IR measurement> Considering the functional group ratio, it is expected that ionic bonds are most efficiently formed when NH2:COOH is 1:1. Therefore, the FT-IR spectra of ChNF / TA (1:1) and ChNF / CA (1:1) were measured and compared with the compounds before mixing to confirm the presence or absence of ionic bond formation.

[0061] ​The obtained FT-IR spectra are shown in Figures 3 and 4. The absorption bands of ChNF and carboxylic acid were assigned from previous studies (Carbohydrate Polymers. 2023, 312, 120842.; ACS Omega. 2020, 5, 1086.; Carbohydrate Polymers. 2018, 195, 329.).

[0062] ChNF showed absorption bands derived from NH stretching vibration and OH stretching vibration at 3600 - 2990 cm -1 . Also, an absorption band derived from CH stretching vibration was observed at 2880 cm -1 . As characteristic absorption peaks , absorption bands derived from NH bending vibration were observed at 1660 cm -1 and 1590 cm -1 . An absorption band derived from CH bending vibration was observed around 1380 cm -1 .

[0063] Tartaric acid (TA) showed absorption bands derived from OH stretching vibration at 3390 cm -1 and 3340 cm -1 . Also, an absorption band derived from C=O stretching vibration was observed at 1710 cm -1 . In the ChNF / TA(1:1) film mixed at a functional group ratio of 1:1 , the absorption bands derived from NH bending vibration of ChNF at 1660 cm -1 and 1590 cm -1 were shifted to 1570 cm -1 and 1510 cm -1 . This indicates that the amino group (-NH2) of ChNF changed to an ammonium group (-NH3 + ) due to mixing with TA and is undergoing ionic interaction . Also, the broad absorption band around 3200 cm -1 is considered to be derived from hydrogen bonding . These results indicate that SPN was formed by ionic interaction.

[0064] Citric acid (CA) has absorption bands derived from OH stretching vibrations at 3490 cm -1 and 3290 - 3190 cm -1 as shown. Also, it has absorption bands derived from CO stretching vibrations at 1740 cm and 1690 cm -1 and 1690 cm -1 Shown. ChNF / CA (1:1) mixed with these in a functional group ratio of 1:1 has absorption bands derived from NH bending vibrations in ChNF at 1660 cm -1 and 1590 cm -1 shifted to 1550 cm and 1520 cm -1 and 1520 cm -1 This indicates that upon mixing with CA, the amino group (-NH2) of ChNF changes to an ammonium group (-NH3 + ) and is involved in ionic interactions. Also, the broad absorption band near 3200 cm is considered to be derived from hydrogen bonding. These results indicate that SPN was formed by ionic interactions. -1 near is considered to be due to hydrogen bonding. These results indicate that SPN was formed by ionic interactions. From these results, it is shown that SPN was formed by ionic interactions.

[0065] <Disintegration test of chitosan nanofiber - based salt - responsive composite materials> This film was immersed in deionized water or 3.5% NaCl solution adjusted to pH 8.0 at each temperature and left standing at room temperature for 14 days. The experimental scheme is shown in Fig. 5, and the results of evaluating the presence or absence of the film's disintegration behavior are summarized in Table 1.

[0066] The film made of only ChNF did not disintegrate in deionized water or 3.5% NaCl solution. Next, using succinic acid (SA) and DL - malic acid (MA) which have a chemical structure similar to tartaric acid , films with ChNF were prepared. However, salt responsiveness was not exhibited in the SPN composite materials of SA or MA. came to be. The film prepared from tartaric acid (TA) with a ratio of amino groups to carboxyl groups of 1:1 and ChNF did not disintegrate in deionized water at 30 °C, but rapidly disintegrated (dissolved) in 3.5% NaCl solution. When using citric acid (CA), a tricarboxylic acid, more complex network formation can be expected. Prepared from citric acid (CA) with a ratio of amino groups to carboxyl groups of 1:0.75 or 1:1.5 and ChNF the film did not disintegrate in deionized water at 30 °C, but rapidly disintegrated (dissolved) in 3.5% NaCl solution. The ChNF / CA film with a ratio of amino groups to carboxyl groups of 1:3 easily disintegrated (dissolved) in deionized water at 4 °C and in 3.5% NaCl solution. Considering these results in terms of the number of functional groups, it was found that the composite material with an excess of carboxyl groups relative to amino groups easily disintegrated. On the other hand, it was suggested that salt responsiveness was exhibited when the carboxyl groups were approximately 1 equivalent relative to the amino groups. Since this film specifically disintegrates in salt water it is suggested that a supramolecular network structure is formed via ionic bonds and that the ionic bonds are cleaved in response to salt. Therefore, it was shown that SPN composite materials composed of ChNF / TA and ChNF / CA prepared from an appropriate mixing ratio are capable of biodegradation control due to salt responsiveness was demonstrated.

[0067]

Table 1

[0068] Furthermore, the NaCl responsiveness of the film, pH dependence in seawater, and disintegration behavior in BOD buffer solution were evaluated. Deionized water was used to prepare the ISO14855 buffer solution. Also, seawater filtered through a membrane filter was used to prepare the ASTM6691-17 buffer solution.

[0069] The results are shown in Fig. 6 and Table 2. The ChNF / TA (1:1) film was found to be salt-responsive, disintegrating even with a slight salt stimulus. Furthermore, it rapidly disintegrated (dissolved) in seawater with a pH of 6.0-8.0, indicating that it is pH-dependent. Furthermore, it was found that the ChNF / TA film rapidly disintegrated (dissolved) in a seawater buffer solution in the absence of microorganisms. From the results of the disintegration tests conducted so far, it was found that the optimal mixing ratio of ChNF to TA is greater than 1:0.7 and less than 1:1.6, more specifically, 1:0.8 to 1:1.5, in order to achieve salt concentration responsiveness and selective disintegration in seawater.

[0070] The ChNF / CA (1:0.5) film did not disintegrate in freshwater or 0.1% or 3.5% NaCl solutions, but disintegrated in 1.0% NaCl solution. Furthermore, we confirmed that the disintegration of ChNF / CA (1:0.5) was dependent on the pH of seawater. Furthermore, we found that ChNF / CA (1:0.5) disintegrated slowly in a seawater buffer solution without microorganisms.

[0071] The ChNF / CA (1:1) film did not disintegrate in freshwater or 0.1% NaCl solution, but was completely dissolved in 1.0% and 3.5% NaCl solutions. Therefore, a clear salt concentration dependence of the disintegration behavior of ChNF / CA (1:1) was confirmed. Furthermore, ChNF / CA (1:1) did not disintegrate in alkaline seawater. Furthermore, it disintegrated in a seawater buffer solution without the presence of microorganisms.

[0072] The ChNF / CA (1:1.5) film did not disintegrate in freshwater, but disintegrated or completely dissolved in NaCl solution, confirming a clear salt concentration dependency of the disintegration behavior of ChNF / CA (1:1.5). Furthermore, ChNF / CA (1:1.5) disintegrated in all seawater adjusted to pH 6.0-8.0. , it was revealed that ChNF / CA (1:1.5) disintegrates regardless of the pH of seawater. Also, it disintegrated in a seawater buffer solution without microorganisms. Based on these, it can be expected that ChNF / CA (1:1.5) will disintegrate in response to salt concentration in the actual environment.

[0073] Since the ChNF / CA (1:2) film did not disintegrate in fresh water but disintegrated or completely dissolved in the NaCl solution, a clear salt concentration dependence was confirmed regarding the disintegration behavior of ChNF / CA (1:2). Also, it disintegrated in a seawater buffer solution without microorganisms.

[0074] From the results of the disintegration tests so far, it was found that for salt concentration responsiveness and selective disintegration expression in seawater, the mixing ratio of ChNF and CA should be more than 1:0.5 and less than 1:3, more specifically, 1:0.6 to 1:2 is optimal.

[0075]

Table 2

Industrial Applicability

[0076] Since the salt-responsive material of the present invention is based on the material properties of chitosan itself, it becomes a mechanically rigid film or bulk material. Therefore, the salt-responsive material of the present invention can be applied to food containers, agricultural materials, etc. that require marine degradability. to be applied.

Claims

**Claim 1** A method of controlling the marine degradability of a salt-responsive material containing an ionic supramolecular polymer composed of an ion pair of chitosan and a polycarboxylic acid by applying a salt to the salt-responsive material and relying on the salt response of the ionic supramolecular polymer. **Claim 2** The method according to claim 1, wherein the chitosan is chitosan nanofibers. **Claim 3** The method according to claim 1, wherein the polycarboxylic acid is one or more selected from tartaric acid and citric acid. **Claim 4** The method according to claim 1, wherein the mixing ratio of chitosan and the polycarboxylic acid is more than 1:0.5 to less than 1:3 in terms of the molar ratio of the amino group contained in chitosan to the carboxy group contained in the polycarboxylic acid. **Claim 5** A method of cleaving a salt-responsive material containing an ionic supramolecular polymer composed of an ion pair of chitosan and a polycarboxylic acid by applying a salt to the salt-responsive material and relying on the salt response of the ionic supramolecular polymer. **Claim 6** A method of biodegrading a salt-responsive material in a marine environment by applying seawater to the salt-responsive material containing an ionic supramolecular polymer composed of an ion pair of chitosan and a polycarboxylic acid and relying on the salt response of the ionic supramolecular polymer. **Claim 7** An ionic supramolecular polymer composed of an ion pair of chitosan and a polycarboxylic acid. **Claim 8** The ionic supramolecular polymer according to claim 7, wherein the chitosan is chitosan nanofibers. **Claim 9** The ionic supramolecular polymer according to claim 7, wherein the polycarboxylic acid is one or more selected from tartaric acid and citric acid. **Claim 10** The ionic supramolecular polymer according to claim 7, wherein the content ratio of chitosan and the polycarboxylic acid in the salt-responsive material is more than 1:0.5 to less than 1:3 in terms of the molar ratio of the amino group contained in chitosan to the carboxy group contained in the polycarboxylic acid. **Claim 11** A salt-responsive material containing the ionic supramolecular polymer according to any one of claims 7 to 10. ​ ​

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