A method for producing a cellulose regenerated material

Abstract

The application relates to a preparation method of a cellulose regenerated material, which comprises the following steps: soaking cellulose in water to swell and activate the cellulose to obtain activated cellulose; providing a hydrated molten salt system of hydrated zinc chloride and anhydrous lithium chloride as a mixed molten salt solvent, the content of the hydrated zinc chloride being 65.0wt%-90.0wt%, and the content of the anhydrous lithium chloride being 10.0wt%-35.0wt%; slowly adding the activated cellulose into the mixed molten salt solvent after the mixed molten salt solvent is heated to 80.0-120 DEG C, and the temperature is kept at 80.0-120.0 DEG C to obtain a cellulose concentrated solution; and regenerating the cellulose concentrated solution through a water coagulation bath to obtain the cellulose regenerated material. According to the preparation method of the cellulose regenerated material, the hydrated molten salt solvent system of the hydrated zinc chloride and the anhydrous lithium chloride is configured, the cellulose has excellent dissolving performance, and the cellulose regenerated material can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to cellulose, more particularly to a method for preparing a cellulose regenerated material. BACKGROUND

[0002] With the development of society and the population explosion, the demand for energy continues to rise, and the use of a large amount of fossil fuels leads to resource shortage and ecological environment deterioration. Therefore, exploring cheap and clean renewable energy has become a hot issue of global concern. As the most abundant biomass natural polymer on earth, cellulose is favored by researchers due to its advantages of renewability, good biocompatibility, biodegradability, green and pollution-free. In recent years, cellulose and its derivatives as raw materials for fibers, films, additives and composites show great potential in the fields of tissue engineering, drug carriers, adsorption, food packaging, textiles, medical devices, flexible wearable electronic devices and so on. However, due to the strong intramolecular / intermolecular hydrogen bonding in the natural structure of cellulose, it is insoluble in water and ordinary organic solvents, which greatly limits its application in industrial production. Therefore, developing a solvent system suitable for cellulose and improving the solubility of cellulose has important significance for the development and utilization of cellulose functional materials.

[0003] In order to solve the problem of cellulose dissolution, in recent years, researchers have developed a series of solvent systems such as: sodium hydroxide / carbon disulfide system, carbamate system, protonic acid system, polyformaldehyde / dimethyl sulfoxide system, copper ammonia solution system, N-methyl morpholine oxide (NMMO), ionic liquid system, alkali / urea or thiourea / water system, etc. However, due to the problems of biological toxicity, environmental pollution, high cost, insufficient solubility and the like, the existing solvent systems cannot well solve the problems of cellulose dissolution and regeneration. As a new cellulose solvent system, molten salt has the advantages of green environmental protection, low cost, biological non-toxicity, neutral system, good stability and recyclability, and has become the focus of research. The current molten salt solvent system is mainly divided into two types: one is the hydrated molten salt solvent system mainly composed of lithium ion, such as LiBr·3H2O, LiI·H2O, LiCl·8H2O and the like. The lithium salt system has the characteristics of good solubility stability and is not easy to cause cellulose degradation, but the temperature required for dissolution is high, and the solubility and dissolution rate are low; the other is the hydrated molten salt solvent system mainly composed of zinc ion, such as ZnCl2·3H2O, ZnCl2·4H2O, Zn(NO3)2·xH2O and the like. The zinc salt system has the advantages of fast dissolution rate and low dissolution temperature, although the solubility is improved, but it still cannot reach the solubility of the traditional solvent system, and due to the stability problem of the solvent system itself, the cellulose after dissolution has a significant degradation problem, which seriously affects the performance of the regenerated cellulose functional material. Therefore, how to solve the problems of insufficient solubility, poor stability and the like of the existing molten salt solvent system and the performance of the regenerated material has become an urgent problem to be solved. SUMMARY

[0004] In order to solve the problem of low solubility of the existing cellulose molten salt solvent system in the prior art, the application provides a preparation method of a regenerated cellulose material.

[0005] The preparation method of the regenerated cellulose material according to the application comprises the following steps: S1, swelling and activating cellulose by immersing it in water to obtain activated cellulose; S2, providing a hydrated zinc chloride and anhydrous lithium chloride hydrated molten salt system as a mixed molten salt solvent, wherein the content of the hydrated zinc chloride is 65.0wt%-90.0wt%, and the content of the anhydrous lithium chloride is 10.0wt%-35.0wt%; S3, after the mixed molten salt solvent is heated to 80.0-120℃, the activated cellulose is slowly added into the mixed molten salt solvent, and stirred for 3.0-5.0h, the temperature is kept at 80.0-120.0℃, until the cellulose is completely dissolved, to obtain a concentrated cellulose solution; S4, the concentrated cellulose solution is regenerated by a water coagulation bath to obtain a regenerated cellulose material.

[0006] Preferably, in step S1, the mass ratio of cellulose to water is (0.7-7):10.

[0007] Preferably, in step S1, the soaking time is 8.0-24.0 h.

[0008] Preferably, in step S1, the natural cellulose is activated by soaking in deionized water.

[0009] Preferably, the molecular weight of the natural cellulose is up to 8.0 x 10 5 It should be understood that the molecular weight is that of the raw material long-staple cotton. In fact, cellulose with a small molecular weight can be directly dissolved in water without a solvent system, but this does not mean that the solvent system of the present application cannot dissolve cellulose with a small molecular weight.

[0010] Preferably, the hydrated zinc chloride is zinc chloride trihydrate or zinc chloride tetrahydrate or zinc chloride pentahydrate or zinc chloride hexahydrate. In a preferred embodiment, the hydrated zinc chloride is zinc chloride trihydrate, which has been shown in practice to have the best solubility.

[0011] Preferably, in step S2, the hydrated zinc chloride is melted at 50.0-80.0 °C to obtain a hydrated zinc chloride molten salt, and then anhydrous lithium chloride is slowly added to the hydrated zinc chloride molten salt, and the temperature is raised to 65.0-90.0 °C to obtain a mixed molten salt solvent. In a preferred embodiment, the hydrated zinc chloride is heated to 60-80 °C to obtain a hydrated zinc chloride molten salt, and then anhydrous lithium chloride is slowly added to the hydrated zinc chloride molten salt, and the temperature is raised to 65-90 °C to obtain a transparent solution as a mixed molten salt solvent.

[0012] Preferably, in step S3, the mass ratio of the activated cellulose to the mixed molten salt solvent is (1-7): 100.

[0013] Preferably, in step S3, the stirring speed is 1000-1800 rpm.

[0014] Preferably, in step S4, the concentrated cellulose solution is poured into a mold, and the mold is placed in a deionized water coagulation bath to regenerate and coagulate the cellulose, and the cellulose regenerated material is obtained after standing for 1.0-4.0 h. This process uses deionized water as a medium to promote the formation of hydrogen bonds. Although there is a small amount of metal ion loss during the process, the metal ions remaining in the cellulose can still play a bridging role to link the cellulose chains, effectively enhancing the mechanical properties of the cellulose regenerated material. It should be understood that the addition of deionized water in the regeneration process is a physical reaction to wash out excess free salt components.

[0015] Preferably, the mold is a polytetrafluoroethylene mold.

[0016] Preferably, the cellulose regenerated material comprises regenerated cellulose hydrogel or regenerated cellulose membrane.

[0017] The cellulose regenerated material preparation method according to the present application configures a cellulose hydrating molten salt solvent system (MHY solvent system) with hydrated zinc chloride and anhydrous lithium chloride as raw materials, has the performance advantages of lithium salt and zinc salt solvent systems, has excellent dissolving performance, for example, the solubility can reach 7.0%, a stable high-concentration cellulose solution can be obtained after dissolving, has the advantages of safe raw materials, green and pollution-free, low price, and recyclable. The MHY solvent system is simple to obtain, low in price, easy to recycle, green and pollution-free, high in solubility, and the dissolved cellulose can be stably stored in the molten salt system. According to the cellulose regenerated material preparation method of the present application, the high-solubility cellulose solution obtained can quickly regenerate a cellulose hydrogel or cellulose film with high transparency and good mechanical strength by a deionized water coagulation bath, for example, the maximum pressure value of the gel at a 50% deformation is 0.6 MPa. According to the cellulose regenerated material preparation method of the present application, the process of dissolving natural cellulose is pollution-free, the system is neutral, green and environmentally friendly, and is suitable for large-scale production. In summary, the present application is green and efficient, and can effectively solve the problems of low solubility, slow dissolving rate, insufficient stability and poor regenerated cellulose performance of the existing cellulose molten salt solvent system, and expand the application of cellulose in the field of biomass functional materials. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the infrared spectrum of the cellulose raw material and regenerated cellulose according to Example 1 of the present application.

[0019] Figure 2 is the nuclear magnetic resonance spectrum of the cellulose raw material and regenerated cellulose according to Example 1 of the present application.

[0020] Figure 3 is a display of the regenerated cellulose gel sample according to Example 1 of the present application.

[0021] Figure 4 is a display of the mechanical properties of the regenerated cellulose gel sample according to Example 1 of the present application. DETAILED DESCRIPTION

[0022] The preferred embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0023] Example 1

[0024] Step 1: Soak 0.5 g of natural cellulose in 1.0 g of deionized water for 8.0 h for sufficient activation.

[0025] Step 2: Heat 6.6 g of zinc chloride trihydrate to 60℃ to obtain a zinc chloride trihydrate molten salt, then slowly add 3.4 g of anhydrous lithium chloride to the zinc chloride trihydrate molten salt, and raise the temperature to 65℃ to obtain a transparent solution.

[0026] Step 3: The mixed molten salt solvent obtained in step 2 was heated to 80.0°C, and then 0.5 g of the activated natural cellulose (Mz = 8.0 x 10 5 ) was slowly added to the mixed molten salt solvent. The mixture was stirred at 1000 rpm for 4.0 h at 80.0°C to obtain a concentrated cellulose solution.

[0027] Step 4: The concentrated cellulose solution obtained in step 3 was poured into a polytetrafluoroethylene mold, and then the polytetrafluoroethylene mold was placed in a deionized water coagulation bath for regeneration. After standing for 3.0 h, a regenerated cellulose hydrogel or cellulose film was obtained.

[0028] The dissolution process of cellulose is a physical process without chemical reaction, which is a process of decreasing crystallinity and enhancing molecular chain movement. The structure of the cellulose raw material and the regenerated cellulose was characterized, and the infrared spectrum as shown in Figure 1 , the nuclear magnetic resonance spectrum as shown in Figure 2 , Figure 1 , and Figure 2 all can observe that the dissolved and regenerated cellulose materials have similar chemical structures, but the peak position, peak shape and size are significantly changed. The hydrogel sample prepared by regeneration as shown in Figure 3 , the change of the characteristic peak of the functional group in the figure can prove that the MHY molten salt system is a green and efficient cellulose solvent, which can be used to dissolve cellulose.

[0029] Next, the mechanical properties of the obtained regenerated cellulose hydrogel were investigated. The regenerated cellulose hydrogel sample was subjected to continuous bending, as shown in Figure 4 , when the external force was applied, the hydrogel deformed, and after the mechanical properties were removed, the hydrogel could quickly recover to the initial state without damage or fracture, indicating that the regenerated cellulose hydrogel obtained by using the MHY solvent system showed excellent mechanical properties. The maximum pressure value of the 50% deformation of the gel was 0.6 MPa. This is because the metal ions remaining in the cellulose during the regeneration process can act as a bridge to link the cellulose molecular chains, effectively enhancing the mechanical properties of the regenerated cellulose gel.

[0030] Example 2

[0031] Step 1: 0.2 g of natural cellulose was soaked in 0.3 g of deionized water for 15.0 h for sufficient activation.

[0032] Step 2: 9.0 g of zinc chloride trihydrate was heated to 70°C to obtain a zinc chloride trihydrate molten salt, and then 1.0 g of anhydrous lithium chloride was slowly added to the zinc chloride trihydrate molten salt, and the temperature was increased to 80°C to obtain a transparent solution.

[0033] Step 3: After the mixed molten salt solvent obtained in step 2 was heated to 100.0 °C, 0.2 g of the activated natural cellulose (Mz = 8.0 x 10 5 ) was slowly added into the mixed molten salt solvent. The stirring was carried out at 1500 rpm for 3.0 h at 100.0 °C, and a concentrated cellulose solution was obtained.

[0034] Step 4: The concentrated cellulose solution obtained in step 3 was poured into a polytetrafluoroethylene mold, and then the polytetrafluoroethylene mold was placed in a deionized water coagulation bath for regeneration. After standing for 1.0 h, a regenerated cellulose hydrogel or cellulose membrane was obtained.

[0035] Example 3

[0036] Step 1: 0.84 g of natural cellulose was soaked in 8.4 g of deionized water for 24.0 h for sufficient activation.

[0037] Step 2: 10.0 g of zinc chloride trihydrate was heated to 80 °C to obtain a zinc chloride trihydrate molten salt. Then, 2.0 g of anhydrous lithium chloride was slowly added into the zinc chloride trihydrate molten salt, and the temperature was increased to 90 °C to obtain a transparent solution.

[0038] Step 3: After the mixed molten salt solvent obtained in step 2 was heated to 120.0 °C, 0.84 g of the activated natural cellulose (Mz = 8.0 x 10 5 ) was slowly added into the mixed molten salt solvent. The stirring was carried out at 1800 rpm for 5.0 h at 120.0 °C, and a concentrated cellulose solution was obtained.

[0039] Step 4: The concentrated cellulose solution obtained in step 3 was poured into a polytetrafluoroethylene mold, and then the polytetrafluoroethylene mold was placed in a deionized water coagulation bath for regeneration. After standing for 4.0 h, a regenerated cellulose hydrogel or cellulose membrane was obtained.

[0040] Example 4

[0041] Step 1: 0.7 g of natural cellulose was soaked in 7.0 g of deionized water for 20.0 h for sufficient activation.

[0042] Step 2: 12.0 g of zinc chloride trihydrate was heated to 80 °C to obtain a zinc chloride trihydrate molten salt. Then, 2.0 g of anhydrous lithium chloride was slowly added into the zinc chloride trihydrate molten salt, and the temperature was increased to 80 °C to obtain a transparent solution.

[0043] Step 3: After the mixed molten salt solvent obtained in step 2 was heated to 100.0 °C, 0.7 g of the activated natural cellulose (Mz = 8.0 x 10 5Slowly add it to the mixed molten salt solvent, stir at 1800 rpm for 5.0 h, and keep the temperature at 100.0℃ to obtain a concentrated cellulose solution.

[0044] Step 4: Pour the concentrated cellulose solution obtained in Step 3 into a polytetrafluoroethylene mold, and then place the polytetrafluoroethylene mold into a deionized water coagulation bath for regeneration. Let it stand for 4.0 hours to obtain a regenerated cellulose hydrogel or cellulose membrane.

[0045] Example 5

[0046] Step 1: Soak 0.396g of natural cellulose in 0.3g of deionized water for 15.0h to fully activate it.

[0047] Step 2: Heat 10.0g of zinc chloride tetrahydrate to 70℃ to obtain zinc chloride tetrahydrate molten salt. Then, slowly add 3.2g of anhydrous lithium chloride to the zinc chloride tetrahydrate molten salt and raise the temperature to 80℃ to obtain a transparent solution.

[0048] Step 3: Heat the mixed molten salt solvent obtained in Step 2 to 100.0℃, then add 0.396g of activated natural cellulose (Mz = 8.0 × 10⁻⁶). 5 Slowly add it to the mixed molten salt solvent, stir at 1500 rpm for 3.0 h, and keep the temperature at 100.0℃ to obtain a concentrated cellulose solution.

[0049] Step 4: Pour the concentrated cellulose solution obtained in Step 3 into a polytetrafluoroethylene mold, and then place the polytetrafluoroethylene mold into a deionized water coagulation bath for regeneration. Let it stand for 1.0 h to obtain regenerated cellulose hydrogel or cellulose membrane.

[0050] Example 6

[0051] Step 1: Soak 0.396g of natural cellulose in 0.3g of deionized water for 15.0h to fully activate it.

[0052] Step 2: Heat 10.0g of zinc chloride pentahydrate to 70℃ to obtain zinc chloride pentahydrate molten salt. Then, slowly add 3.34g of anhydrous lithium chloride to the zinc chloride pentahydrate molten salt and raise the temperature to 80℃ to obtain a transparent solution.

[0053] Step 3: Heat the mixed molten salt solvent obtained in Step 2 to 100.0℃, then add 0.396g of activated natural cellulose (Mz = 8.0 × 10⁻⁶). 5 Slowly add it to the mixed molten salt solvent, stir at 1500 rpm for 3.0 h, and keep the temperature at 100.0℃ to obtain a concentrated cellulose solution.

[0054] Step 4: The cellulose concentrated solution obtained in step 3 was poured into a polytetrafluoroethylene mold, and then the polytetrafluoroethylene mold was placed in a deionized water coagulation bath for regeneration, and was left to stand for 1.0 h to obtain a regenerated cellulose hydrogel or cellulose membrane.

[0055] Example 7

[0056] Step 1: 0.396 g of natural cellulose was soaked in 0.3 g of deionized water for 15.0 h for sufficient activation.

[0057] Step 2: 10.0 g of zinc chloride hexahydrate was warmed to 70 °C to obtain a zinc chloride hexahydrate molten salt, and then 3.34 g of anhydrous lithium chloride was slowly added to the zinc chloride hexahydrate molten salt, and the temperature was raised to 80 °C to obtain a transparent solution.

[0058] Step 3: The mixed molten salt solvent obtained in step 2 was warmed to 100.0 °C, and then 0.396 g of the activated natural cellulose (Mz = 8.0 x 10 5 ) was slowly added to the mixed molten salt solvent, and was stirred at a rotation speed of 1500 rpm for 3.0 h while the temperature was maintained at 100.0 °C to obtain a cellulose concentrated solution.

[0059] Step 4: The cellulose concentrated solution obtained in step 3 was poured into a polytetrafluoroethylene mold, and then the polytetrafluoroethylene mold was placed in a deionized water coagulation bath for regeneration, and was left to stand for 1.0 h to obtain a regenerated cellulose hydrogel or cellulose membrane.

[0060] Comparative Example 1

[0061] 1.0 g of zinc chloride trihydrate was prepared, 10.0 g of anhydrous lithium chloride was slowly added to the zinc chloride trihydrate molten salt, and the mixture was placed in an oil bath, and was warmed to 65 °C, but a colorless and transparent mixed molten salt solvent could not be obtained.

[0062] Comparative Example 2

[0063] Step 1: 10.0 g of zinc chloride trihydrate was prepared, 1.0 g of anhydrous lithium chloride was slowly added to the zinc chloride trihydrate molten salt, and the mixture was placed in an oil bath, and was warmed to 65 °C to obtain a transparent solution.

[0064] Step 2: The mixed molten salt solvent obtained in step 1 was warmed to 120.0 °C, and then 0.1 g of natural cellulose (Mz = 8.0 x 10 5 ) was slowly added to the mixed molten salt solvent, and was stirred at a rotation speed of 1000 rpm for 5.0 h while the temperature was maintained at 120.0 °C to obtain a cellulose concentrated solution.

[0065] Step 3: The cellulose concentrated solution obtained in step 2 was poured into a polytetrafluoroethylene mold, and then the polytetrafluoroethylene mold was regenerated in a deionized water coagulation bath, and was placed for 8.0 h. The regenerated cellulose hydrogel obtained was opaque and not shaped.

[0066] In summary, the present application proposes a simple, efficient and green method for dissolving cellulose in MHY molten salt solvent, and successfully prepares cellulose hydrogel or film with high transparency and good mechanical strength. The prepared molten salt system exhibits excellent dissolving performance, good stability and recycling characteristics, and the degradation rate of the dissolved cellulose is low. The above problems existing in the prior art are effectively solved. In addition, the hydrogel regenerated by deionized water has high transparency and good mechanical strength.

[0067] The above is only a preferred embodiment of the present application, and is not intended to limit the scope of the present application. The above embodiment of the present application can also be variously changed. That is, any simple, equivalent change, modification and the like made according to the content of the claims and the specification of the present application fall within the scope of protection of the present application. The present application is not described in detail.

Claims

1. A method for producing a cellulose regenerated material, characterized by, The preparation method comprises the following steps: S1, soaking cellulose in water to swell and activate for 8.0-24.0 hours to obtain activated cellulose; S2, providing a hydrated molten salt system of zinc chloride and anhydrous lithium chloride as a mixed molten salt solvent, wherein the content of the hydrated zinc chloride is 65.0wt%-90.0wt%, the content of the anhydrous lithium chloride is 10.0wt%-35.0wt%, and the hydrated zinc chloride is zinc chloride trihydrate; S3, after the mixed molten salt solvent is heated to 80.0-120℃, the activated cellulose is slowly added into the mixed molten salt solvent, the mass ratio of the activated cellulose to the mixed molten salt solvent is (1-7):100, stirring is carried out for 3.0-5.0 hours, the temperature is kept at 80.0-120.0℃, until the cellulose is completely dissolved, to obtain a concentrated cellulose solution; S4, the concentrated cellulose solution is regenerated by a water coagulation bath to obtain a regenerated cellulose material.

2. The production method according to claim 1, characterized by, In step S1, the mass ratio of the cellulose to water is (0.7-7):

10.

3. The preparation method according to claim 1, characterized in that, In step S1, the natural cellulose is soaked in deionized water for activation.

4. The method of claim 1, wherein, In step S2, the hydrated zinc chloride is melted at 50.0℃-80.0℃ to obtain a hydrated zinc chloride molten salt, then the anhydrous lithium chloride is slowly added into the hydrated zinc chloride molten salt, and the temperature is increased to 65.0℃-90.0℃ to obtain the mixed molten salt solvent.

5. The preparation method according to claim 1, characterized in that, In step S3, stirring is carried out at a rotation speed of 1000-1800 rpm.

6. The method of claim 1, wherein, In step S4, the concentrated cellulose solution is poured into a mold, the mold is placed in a deionized water coagulation bath, cellulose regeneration coagulation is carried out, and the mold is placed for 1.0-4.0 hours to obtain a regenerated cellulose material.

7. The production method according to claim 6, wherein The mold is a polytetrafluoroethylene mold.

8. The method of claim 1, wherein, The regenerated cellulose material comprises a regenerated cellulose hydrogel or a regenerated cellulose film. The preparation method comprises the following steps: S1, soaking cellulose in water to swell and activate for 8.0-24.0 hours to obtain activated cellulose; S2, providing a hydrated molten salt system of zinc chloride and anhydrous lithium chloride as a mixed molten salt solvent, wherein the content of the hydrated zinc chloride is 65.0wt%-90.0wt%, the content of the anhydrous lithium chloride is 10.0wt%-35.0wt%, and the hydrated zinc chloride is zinc chloride trihydrate; S3, after the mixed molten salt solvent is heated to 80.0-120℃, the activated cellulose is slowly added into the mixed molten salt solvent, the mass ratio of the activated cellulose to the mixed molten salt solvent is (1-7):100, stirring is carried out for 3.0-5.0 hours, the temperature is kept at 80.0-120.0℃, until the cellulose is completely dissolved, to obtain a concentrated cellulose solution; S4, the concentrated cellulose solution is regenerated by a water coagulation bath to obtain a regenerated cellulose material. In step S1, the mass ratio of the cellulose to water is (0.7-7):

10. In step S1, the natural cellulose is soaked in deionized water for activation. In step S2, the hydrated zinc chloride is melted at 50.0℃-80.0℃ to obtain a hydrated zinc chloride molten salt, then the anhydrous lithium chloride is slowly added into the hydrated zinc chloride molten salt, and the temperature is increased to 65.0℃-90.0℃ to obtain the mixed molten salt solvent. In step S3, stirring is carried out at a rotation speed of 1000-1800 rpm. In step S4, the concentrated cellulose solution is poured into a mold, the mold is placed in a deionized water coagulation bath, cellulose regeneration coagulation is carried out, and the mold is placed for 1.0-4.0 hours to obtain a regenerated cellulose material. The mold is a polytetrafluoroethylene mold. The regenerated cellulose material comprises a regenerated cellulose hydrogel or a regenerated cellulose film.

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