Preparation method of cellulose regenerated silk

Abstract

The invention belongs to the technical field of fiber preparation, and particularly relates to a preparation method of cellulose regenerated silk. According to the method, the cosolvent is formed by the hydrated calcium salt and the organic carboxylic acid which are low in price, then the cellulose is dissolved and esterified, and the dissolution rate of the cellulose can reach 12% or above. A'dry-jet wet-spinning 'technology is adopted to promote high orientation of cellulose molecular chains, and under the induction of coagulating bath molecules, the cellulose molecular chains are self-assembled into cellulose gel filaments, so that tough regenerated cellulose filaments are formed. Collecting the used coagulating bath, and respectively recovering the coagulating bath and an esterification system through separation; the recycled esterification system is used for dissolving the cellulose again, the recycled coagulating bath can be returned to the coagulating and forming process to be continuously used, and tough regenerated cellulose filaments can still be obtained. The process not only proves that an efficient closed-loop production system can be constructed by dissolving the cellulose and preparing the cellulose regenerated silk, but also shows huge potential of the method in industrial application.

Description

Technical Field

[0001] The invention belongs to the technical field of fiber preparation, and particularly relates to a method for preparing cellulose regenerated silk. Background Art

[0002] Cellulose is the most abundant natural polymer on earth and is widely distributed in wood, cotton, flax, algae and various herbs. Since plants in nature are constantly growing and renewing, cellulose is considered to be an inexhaustible renewable biomass resource, and its processing and utilization will help promote the development of the circular economy. Through advanced dissolution technology, cellulose can be converted into a variety of new materials, such as high-strength fibers, biodegradable films, bioplastics, etc. The application areas of these products are wide and diverse, covering a wide range of fields from textiles and clothing to environmentally friendly packaging, as well as sustainable building materials. Although current cellulose dissolution and modification technologies have made significant progress, these methods are difficult to meet modern industrial needs such as low-cost, sustainable, and closed-loop production, and have become a key bottleneck restricting the high-value utilization of cellulose resources.

[0003] The prior art discloses a method for esterifying cellulose, which uses an esterification system composed of zinc chloride, formic acid and water to dissolve cellulose at room temperature. However, the esterification system is difficult to recycle, which is not conducive to reducing process steps and production costs. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing cellulose regenerated silk. The method provided by the present invention can prepare high-strength cellulose regenerated silk, and the esterification system therein can be recycled, thereby shortening the process and reducing the production cost.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing regenerated cellulose silk, comprising the following steps:

[0007] The hydrated calcium salt and the organic carboxylic acid are heated to react to obtain an esterification system;

[0008] Mixing cellulose and the esterification system to carry out esterification reaction to obtain a spinning solution;

[0009] Spinning the spinning solution, passing the obtained filaments into a coagulation bath for coagulation and forming, thereby obtaining the cellulose regenerated filaments;

[0010] The used coagulation bath is separated to obtain a recovered esterification system and a recovered coagulation bath, respectively. The recovered esterification system is returned to the esterification reaction for recycling, and the recovered coagulation bath is returned to the coagulation molding process for recycling.

[0011] Preferably, the hydrated calcium salt includes one or more of hydrated calcium chloride, hydrated calcium bromide and hydrated calcium acetate.

[0012] Preferably, the organic carboxylic acid includes one or more of formic acid, acetic acid and propionic acid.

[0013] Preferably, the mass ratio of the hydrated calcium salt to the organic carboxylic acid is 1:1.8-2.

[0014] Preferably, the temperature of the heating reaction is ≥70°C and the time is 15 to 30 minutes.

[0015] Preferably, the mass ratio of the cellulose to the esterification system is 7.5-13.7:100.

[0016] Preferably, the temperature of the esterification reaction is room temperature to 60°C.

[0017] Preferably, the coagulation bath comprises methanol or ethanol.

[0018] Preferably, after the coagulation forming, the spinning fibers are washed and dried to obtain the cellulose regenerated fibers and washing liquid;

[0019] The washing liquid and the used coagulation bath are mixed and separated to obtain a recovered esterification system, recovered water and recovered coagulation bath respectively. The recovered esterification system is returned to the esterification reaction for recycling, the recovered water is returned to the water washing process for recycling, and the recovered coagulation bath is returned to the coagulation molding process for recycling.

[0020] The invention provides a method for preparing cellulose regenerated silk, comprising the following steps: subjecting hydrated calcium salt and organic carboxylic acid to a heating reaction to obtain an esterification system; mixing cellulose and the esterification system to an esterification reaction to obtain a spinning solution; spinning the spinning solution to pass the obtained filaments into a coagulation bath for coagulation and forming to obtain the cellulose regenerated silk; separating the used coagulation bath to respectively obtain a recovered esterification system and a recovered coagulation bath, wherein the recovered esterification system is returned to the esterification reaction for recycling, and the recovered coagulation bath is returned to the coagulation forming process for recycling.

[0021] The present invention utilizes low-cost hydrated calcium salt and organic carboxylic acid to form a co-solvent, and then dissolves and esterifies cellulose, and the dissolution rate of cellulose can reach more than 12%. The "dry-jet wet spinning" technology is used to promote the high orientation of cellulose molecular chains, and under the induction of the coagulation bath molecules, they self-assemble into cellulose gel fibers to form strong and tough cellulose regenerated fibers. The used coagulation bath is collected, and the coagulation bath and the esterification system are recovered after separation; the recovered esterification system is used to dissolve the cellulose again, and the recovered coagulation bath is returned to the coagulation molding for continued use, and strong and tough cellulose regenerated fibers can still be obtained. This process not only proves that the dissolution of cellulose and the preparation of cellulose regenerated fibers can construct an efficient closed-loop production system, but also shows the great potential of this method in industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of the preparation method provided by the present invention;

[0023] Figure 2 A physical diagram of the process of obtaining the spinning solution in the preparation method provided by the present invention;

[0024] Figure 3 This is a polarizing microscope photo of the cellulose dissolution process in Example 2;

[0025] Figure 4 A schematic diagram of the process of solidification molding in the preparation method provided by the present invention;

[0026] Figure 5 This is a physical picture of the cellulose regenerated silk obtained in Example 2;

[0027] Figure 6 This is a test diagram of the tensile strength of the cellulose regenerated silk obtained in Example 2;

[0028] Figure 7 is the XRD pattern of the cellulose raw material and the cellulose regenerated silk in Example 2;

[0029] Figure 8 is the infrared spectra of the cellulose raw material and the cellulose regenerated silk in Example 2;

[0030] Fig. 9 A physical diagram of the process for recovering the coagulation bath and the washing liquid in the preparation method provided by the present invention;

[0031] Fig.10 This is a tensile strength test chart of the cellulose regenerated silk prepared using the recycled esterification system in Example 2. DETAILED DESCRIPTION

[0032] The present invention provides a method for preparing regenerated cellulose silk, comprising the following steps:

[0033] The hydrated calcium salt and the organic carboxylic acid are heated to react to obtain an esterification system;

[0034] Mixing cellulose and the esterification system to carry out esterification reaction to obtain a spinning solution;

[0035] Spinning the spinning solution, passing the obtained filaments into a coagulation bath for coagulation and forming, thereby obtaining the cellulose regenerated filaments;

[0036] The used coagulation bath is separated to obtain a recovered esterification system and a recovered coagulation bath, respectively. The recovered esterification system is returned to the esterification reaction for recycling, and the recovered coagulation bath is returned to the coagulation molding process for recycling.

[0037] In the present invention, unless otherwise specified, all raw materials are commercially available products well known to those skilled in the art.

[0038] The invention heats a hydrated calcium salt and an organic carboxylic acid to react to obtain an esterification system.

[0039] In the present invention, the hydrated calcium salt preferably includes one or more of hydrated calcium chloride, hydrated calcium bromide and hydrated calcium acetate; the hydrated calcium chloride further preferably includes dihydrated calcium chloride. In the present invention, the organic carboxylic acid preferably includes one or more of formic acid, acetic acid and propionic acid. In the present invention, the mass ratio of the hydrated calcium salt to the organic carboxylic acid is preferably 1:1.8-2, and more preferably 1:1.88. In the present invention, the temperature of the heating reaction is preferably ≥70°C; the time is preferably 15-30min, and more preferably 20min.

[0040] After obtaining the esterification system, the present invention mixes cellulose and the esterification system to carry out an esterification reaction to obtain a spinning solution.

[0041] The present invention has no special limitation on the type of cellulose, and any type known to those skilled in the art can be used. In a specific embodiment of the present invention, the cellulose is preferably industrial grade softwood pulp, and the degree of polymerization of the industrial grade softwood pulp is preferably 1539, and the crystallinity is preferably 53.58%.

[0042] In the present invention, the mass ratio of the cellulose to the esterification system is preferably 7.5 to 13.7:100, and more preferably 13.7:100; the temperature of the esterification reaction is preferably room temperature to 60°C. In the present invention, as the temperature of the esterification reaction increases, the time required for the esterification reaction decreases accordingly. Specifically, when the temperature of the esterification reaction is room temperature, the time of the esterification reaction is preferably 3 hours; when the temperature of the esterification reaction is 60°C, the time of the esterification reaction is preferably 1 to 1.5 hours. In the present invention, the esterification reaction is preferably carried out under stirring. In the present invention, the dissolution rate of the cellulose is preferably above 12%. After the esterification reaction, the present invention also preferably includes centrifuging the obtained system to remove bubbles.

[0043] The actual process diagram of obtaining the spinning solution in the preparation method provided by the present invention is as follows Figure 2 shown.

[0044] After obtaining the spinning solution, the present invention spins the spinning solution, and the obtained filaments are passed into a coagulation bath for coagulation and molding to obtain the cellulose regenerated fibers.

[0045] In the present invention, the spinning process preferably includes: loading the spinning solution into a syringe, and then using a syringe pump to extrude the spinning solution from the syringe, the syringe outlet and the coagulation bath liquid surface are kept at a certain distance, and the ejected filaments are oriented and stretched in the air due to their own gravity. In a specific embodiment of the present invention, the diameter of the syringe outlet is 900 μm; the distance between the syringe outlet and the coagulation bath liquid surface is 20 cm, and the extrusion speed is 0.6 mL / min. In the present invention, the coagulation bath preferably includes methanol or ethanol. In the present invention, the anchoring and tight assembly of the molecular chains of the cellulose esterification product are achieved during the coagulation molding process.

[0046] The schematic diagram of the process of solidification molding in the preparation method provided by the present invention is as follows Figure 4 shown.

[0047] After the coagulation molding, the present invention also preferably includes washing and drying the fibers obtained by spinning to obtain the cellulose regenerated silk and washing liquid; mixing the washing liquid and the used coagulation bath and separating them to obtain a recovered esterification system, recovered water and recovered coagulation bath respectively, the recovered esterification system is returned to the esterification reaction for recycling, the recovered water is returned to the washing process for recycling, and the recovered coagulation bath is returned to the coagulation molding process for recycling.

[0048] In the present invention, when the recycled esterification system is used for the esterification reaction, the extrusion speed during the spinning process is preferably 1 mL / min.

[0049] The present invention has no particular limitation on the separation method, and any method known to those skilled in the art may be used. In the present invention, the separation method preferably includes rotary distillation, fractional distillation, azeotropic distillation, membrane separation technology or steam reforming.

[0050] In the present invention, when separation is performed by rotary evaporation, the rotary evaporation temperature of the recovered coagulation bath is preferably 45-55°C; the rotary evaporation temperature of the recovered water is preferably 70-90°C. In the present invention, after the water and the coagulation bath components are evaporated, the remaining liquid is the recovered esterification system. In the present invention, when the recovered esterification system is returned to the esterification reaction for recycling, it is also preferably included to add organic carboxylic acid to the recovered esterification system. The present invention has no special limitation on the amount of the organic acid added, as long as the ratio of the hydrated calcium salt and the organic carboxylic acid in the original esterification system can be met.

[0051] After obtaining the cellulose regenerated silk, the present invention separates the used coagulation bath to obtain a recovered esterification system and a recovered coagulation bath, respectively. The recovered esterification system is returned to the esterification reaction for recycling, and the recovered coagulation bath is returned to the coagulation molding process for recycling.

[0052] The actual process diagram of the recovery of the coagulation bath and the washing liquid in the preparation method provided by the present invention is as follows: Fig. 9 The schematic diagram of the preparation method provided by the present invention is as shown in Figure 1 shown.

[0053] In the present invention, the separation conditions are preferably consistent with the separation conditions described in the above technical solution, which will not be repeated here. In the present invention, when the recycled esterification system is used for esterification reaction, the extrusion speed during the spinning process is preferably 1 mL / min.

[0054] In the present invention, the used coagulation bath or washing liquid is recycled, and the recycled coagulation bath and water can be returned to the production process for continued use, and the recycled esterification system can be returned to the esterification reaction to continue reacting with cellulose. At the same time, the cellulose regenerated silk prepared using the recycled esterification system still has high-strength performance, thereby reducing the production cost in the entire production process, realizing the closed-loop production of dissolving cellulose and preparing cellulose regenerated silk, and having prospects for industrial application.

[0055] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] In the following examples, the cellulose used is industrial grade softwood pulp with a degree of polymerization of 1539 and a crystallinity of 53.58%.

[0057] Example 1

[0058] Calcium chloride dihydrate and formic acid were heated to react at 70°C (the mass ratio of calcium chloride dihydrate to formic acid was 1:1.88) and kept warm for 20 minutes to obtain an esterification system;

[0059] Cellulose was added to the esterification system, the mass ratio of cellulose to the esterification system was 13.7 g:100 g, the obtained mixture was stirred at room temperature for 3 hours, and the dissolution of cellulose was observed by polarizing microscope. The cellulose solution was centrifuged to remove bubbles to obtain a spinning solution, in which the dissolution rate of cellulose was 12%;

[0060] The spinning solution is loaded into a syringe, and then the spinning solution is squeezed out of the syringe by a syringe pump. The ejected filaments will produce a directional structure under the action of gravity, wherein the diameter of the syringe outlet is 900 μm, the height of the syringe outlet from the coagulation bath liquid surface is 20 cm, and the extrusion speed is 0.6 mL / min; thereafter, the filaments are passed into a methanol coagulation bath to self-assemble into gel filaments, and the residual solvent and impurities are washed away with water to obtain cellulose hydrogel filaments and washing liquid, and finally the water molecules are volatilized in the air to obtain cellulose regenerated filaments (recorded as fiber A1-1).

[0061] The used coagulation bath and washing liquid are collected and mixed, and the recovered coagulation bath (rotary evaporation temperature is 50° C.), the recovered water (rotary evaporation temperature is 70° C.) and the recovered esterification system (evaporation residual liquid) are obtained respectively by means of reduced pressure rotary evaporation;

[0062] 83 g of the recovered esterification system and 17 g of formic acid were mixed, heated and mixed at 70°C, and kept warm for 10 minutes to obtain an esterification system. The cellulose was dissolved and esterified according to the above method and then spun, wherein the extrusion rate was 1 mL / min, to obtain cellulose regenerated silk prepared from the recovered esterification system (referred to as fiber A1-2).

[0063] Example 2

[0064] Cellulose regenerated silk (referred to as fiber A2-1) was prepared in the same manner as in Example 1, except that the coagulation bath was replaced with ethanol.

[0065] The used coagulation bath and washing liquid are collected and mixed, and the recovered coagulation bath (rotary evaporation temperature is 50° C.), the recovered water (rotary evaporation temperature is 70° C.) and the recovered esterification system (evaporation residual liquid) are obtained respectively by means of reduced pressure rotary evaporation;

[0066] 83 g of the recovered esterification system and 17 g of formic acid were mixed, heated and mixed at 70°C, and kept warm for 10 minutes to obtain an esterification system. The cellulose was dissolved and esterified according to the above method and then spun, wherein the extrusion rate was 1 mL / min, to obtain cellulose regenerated silk prepared from the recovered esterification system (referred to as fiber A2-2).

[0067] Comparative Example 1

[0068] Cellulose regenerated silk (referred to as fiber B1-1) was prepared in the same manner as in Example 1, except that the coagulation bath was replaced with isopropanol;

[0069] The used coagulation bath and washing liquid are collected and mixed, and the recovered coagulation bath (rotary evaporation temperature is 60° C.), the recovered water (rotary evaporation temperature is 70° C.) and the recovered esterification system (evaporation residual liquid) are obtained respectively by means of reduced pressure rotary evaporation;

[0070] 77 g of the recovered esterification system and 23 g of formic acid were mixed, heated and mixed at 70°C, and kept warm for 10 minutes to obtain an esterification system. The cellulose was dissolved and esterified according to the above method and then spun, wherein the extrusion rate was 1 mL / min, to obtain cellulose regenerated silk prepared from the recovered esterification system (referred to as fiber B1-2).

[0071] Comparative Example 2

[0072] Mixing formic acid, zinc chloride and water in a molar ratio of 4:1:1 to obtain an esterification system;

[0073] Add cellulose to the esterification system, the mass ratio of cellulose to the esterification system is 7.6g:100g, stir the obtained mixture at room temperature for 2h, and observe the dissolution of cellulose by polarizing microscope; centrifuge the cellulose solution to remove bubbles, and obtain a spinning solution, in which the solubility of cellulose is 7%;

[0074] The spinning solution is loaded into a syringe, and then the spinning solution is squeezed out of the syringe by a syringe pump. The ejected filaments will produce a directional structure under the action of gravity, wherein the diameter of the syringe outlet is 900 μm; the height of the syringe outlet from the coagulation bath liquid surface is 25 cm; then the filaments are respectively passed into two coagulation baths of calcium chloride aqueous solution (mass fraction 40%) and ethanol to self-assemble into gel filaments, and the residual solvent and impurities are washed away with water to obtain cellulose hydrogel filaments and washing liquid, and finally the water molecules are volatilized in the air to obtain cellulose regenerated silk (recorded as fiber B2-1).

[0075] Since the zinc chloride component in the esterification system and the calcium chloride component in the coagulation bath are difficult to separate after being mixed, the esterification system cannot be recovered.

[0076] Performance Testing

[0077] Test Example 1

[0078] Figure 3 is a polarizing microscope photo of the cellulose dissolution process in Example 2; Figure 3 It can be seen that the cellulose raw material is completely dissolved in the solvent system;

[0079] Figure 5 This is a physical picture of the cellulose regenerated silk obtained in Example 2. Figure 7 The XRD diagrams of the cellulose raw material and the cellulose regenerated silk in Example 2 show that the cellulose raw material belongs to the cellulose type I crystal structure, and the cellulose regenerated silk belongs to the cellulose type II crystal structure, indicating that the crystal form of cellulose changes after dissolution;

[0080] Figure 8 The infrared spectra of the cellulose raw material and the cellulose regenerated silk in Example 2; the cellulose regenerated silk has an infrared spectrum of 1710 cm -1 A new absorption peak appears at the bottom, indicating that cellulose undergoes esterification during the dissolution process.

[0081] Test Example 2

[0082] The properties of the cellulose regenerated silk obtained in the examples and comparative examples were tested, and the test results are shown in Table 1; Figure 6 This is a test diagram of the tensile strength of the cellulose regenerated silk obtained in Example 2; Fig.10 This is a test graph of the tensile strength of the cellulose regenerated silk prepared by using the recycled esterification system in Example 2;

[0083] Table 1 Performance test results of the fibers obtained in the examples and comparative examples

[0084]

[0085] As can be seen from Table 1, the fibers A2-1 and A2-2 in Example 2 exhibited high tensile strength and elongation, indicating that the fibers had high toughness. In addition, this also proves that the esterification system can be effectively used to dissolve cellulose and prepare cellulose regenerated silk, while achieving closed-loop production of the two, and is expected to be widely used in the textile field.

[0086] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing regenerated cellulose silk, characterized in that: The following steps are involved: The hydrated calcium salt and the organic carboxylic acid are heated to react to obtain an esterification system; Mixing cellulose and the esterification system to carry out esterification reaction to obtain a spinning solution; Spinning the spinning solution, passing the obtained filaments into a coagulation bath for coagulation and forming, thereby obtaining the cellulose regenerated filaments; The used coagulation bath is separated to obtain a recovered esterification system and a recovered coagulation bath, respectively. The recovered esterification system is returned to the esterification reaction for recycling, and the recovered coagulation bath is returned to the coagulation molding process for recycling.

2. The preparation method according to claim 1, characterized in that: The hydrated calcium salt includes one or more of hydrated calcium chloride, hydrated calcium bromide and hydrated calcium acetate.

3. The preparation method according to claim 1, characterized in that: The organic carboxylic acid includes one or more of formic acid, acetic acid and propionic acid.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The mass ratio of the hydrated calcium salt to the organic carboxylic acid is 1:1.8-2.

5. The preparation method according to claim 4, characterized in that: The temperature of the heating reaction is ≥70°C and the time is 15 to 30 minutes.

6. The preparation method according to claim 1, characterized in that: The mass ratio of the cellulose to the esterification system is 7.5-13.7:

100.

7. The preparation method according to claim 1 or 6, characterized in that: The temperature of the esterification reaction is room temperature to 60°C.

8. The preparation method according to claim 1, characterized in that: The coagulation bath includes methanol or ethanol.

9. The preparation method according to claim 1, characterized in that: After the coagulation and forming, the fibers obtained by spinning are washed and dried to obtain the cellulose regenerated fibers and washing liquid; The washing liquid and the used coagulation bath are mixed and separated to obtain a recovered esterification system, recovered water and recovered coagulation bath respectively. The recovered esterification system is returned to the esterification reaction for recycling, the recovered water is returned to the water washing process for recycling, and the recovered coagulation bath is returned to the coagulation molding process for recycling.

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