CN111607106A - Dissolution of cellulose and preparation method of regenerated cellulose - Google Patents

Abstract

The invention proposes a method for dissolving cellulose and preparing regenerated cellulose. The key point is to prepare a high-concentration inorganic salt solution, add 0.5-18wt% of cellulose raw materials under stirring conditions of 20-150°C, and cellulose The cellulose solution is gradually dissolved to form a solution with a certain viscosity, and the cellulose solution is extruded and solidified in different ways, and finally a cellophane film or fiber is obtained. The prepared cellophane film or fiber is easy to add functional materials in the preparation process to prepare a high-performance composite regenerated cellulose material. Inorganic salts are abundant in reserves, low in price, and have no pollution to the environment. The present invention conforms to the concept of "green development", and at the same time greatly reduces production costs, so the present invention has huge market potential.

Description

Dissolution of cellulose and preparation method of regenerated cellulose

technical field

The invention relates to a method for dissolving cellulose, in particular to a method for dissolving cellulose and a method for preparing regenerated cellulose, and belongs to the field of dissolving methods for cellulose.

technical background

As an inexhaustible renewable resource in nature, cellulose is one of the oldest and most abundant natural macromolecules on earth, mainly derived from wood, grass, bamboo and bast. As well as seed hairs and other plants, they have the advantages of short regeneration cycle, abundant reserves and easy availability, environmental friendliness, good biocompatibility, low price, and good biodegradability. The efficient utilization of biomass resources is conducive to alleviating the increasing depletion of non-renewable resources such as oil and the increasingly severe environmental pollution in the world today. However, due to the high crystallinity of cellulose and its strong intramolecular and intermolecular hydrogen bonding, it is insoluble and infusible, and thus difficult to be used directly, so it needs to be further processed. At present, the dissolving methods of cellulose can be divided into two categories. The derivatization method is to attach certain functional groups to the cellulose molecular chain through chemical reactions during the dissolving process, so that it becomes a soluble cellulose derivative and dissolves. Including sodium hydroxide/carbon disulfide (NaOH/CS ₂ ) system, urethane, paraformaldehyde/dimethyl sulfoxide (PF/DMSO) and protonic acid, etc.; and the direct dissolution method is to directly destroy the fiber through small solvent molecules Intermolecular and intramolecular hydrogen bonds are used to achieve dissolution, including cuprammonium solution, N-methylmorpholine-N-oxide (NMMO), lithium chloride/N,N-dimethylacetamide (LiCl/DMAc ), ionic liquids, and alkali/urea and NaOH/thiourea systems, etc.

The efficient dissolution of cellulose depends on the continuous development of solvent systems. The research and utilization of green and efficient solvent systems has always been a hot spot in the development of cellulose. In the patent with publication number of CN 102432892A, the aqueous solution of urea/thiourea, polyethylene glycol and sodium hydroxide/hydroxide is selected as the dissolving solvent of cellulose, and for the natural cellulose with a degree of polymerization of 250, fiber can be obtained Homogeneous and stable solutions with a concentration of up to 15 wt%.

In the present invention, a high-concentration inorganic salt solution is used to dissolve the cellulose raw material to obtain a cellulose solution of 0.5-18 wt %. The high-concentration inorganic salt solution is a good solvent for cellulose, the dissolution process is simple, the conditions are mild, and the inorganic salt is cheap and easy to obtain, easy to recycle, and the use process will not cause environmental pollution. A series of regenerated cellulose products, including gels, fibers and films, can be prepared from cellulose solutions through coagulation and regeneration in a coagulation bath, washing and desalination, and drying. The addition of functional materials enables regenerated cellulose composite fibers or composite membranes to obtain high added value, which can meet market demands in various fields.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for dissolving cellulose and preparing regenerated cellulose, and preparing regenerated cellulose fibers or films by wet spinning or coating into a film from a cellulose solution, and adding functional Materials Preparation of regenerated cellulose composites with versatility, optimized properties to respond to changing market demands.

In the cellulose dissolving process of the invention, the conditions are mild, the inorganic salt is cheap and easy to obtain, easy to recycle, and the use process will not cause environmental pollution.

A method for dissolving cellulose, comprising the steps of:

1) Prepare high-concentration single or compound inorganic salt solution;

2) A certain amount of cellulose raw material is added to the inorganic salt solution obtained in step 1), and a homogeneous cellulose solution is obtained by stirring and dissolving at a certain temperature.

In the described step 1), the inorganic salt is a metal salt, and the metal ions are respectively Li ⁺ , Mg ²⁺ , Al ³⁺ , Ca ²⁺ , Ti ⁴⁺ , Mn ²⁺ , Fe ³⁺ , Co ²⁺ , Cu ^{2 +} , Zn ²⁺ , the anion is one of Clˉ and Brˉ.

In the step 1), the concentration of the inorganic salt solution is that the molar ratio of inorganic salt:water is 1:10～1:2.

The amount of cellulose raw material added in the step 2) is 0.5-18 wt%.

In the step 2), the stirring temperature is 20-150°C.

A preparation method of regenerated cellulose, which is suitable for the dissolving method of a kind of cellulose, is characterized in that, comprises the following steps:

1) cooling a cellulose solution prepared by a cellulose dissolving method to obtain a high-strength and high-toughness gel;

2) Treat the gel obtained in step 1) with a certain method, cool and solidify in a coagulation bath, wash to remove salt, and dry to obtain a regenerated cellulose product.

The processing method of the gel in the step 2) is one of wet spinning and coating to form a film, so as to obtain a regenerated cellulose product in two forms of fiber and film.

In the described step 2), the coagulation bath is one of an organic solvent, a mixed solution of an organic solvent and water, and a dilute acid solution.

Further, by adding functional materials to the cellulose solution obtained by the cellulose dissolving method disclosed in the present invention, or adding functional materials to the coagulation bath, high-performance multi-functional fibers can be prepared; the functional materials can be zinc oxide, etc. Antibacterial materials, conductive polymer materials such as polyaniline, and high-strength conductive materials such as carbon nanotubes have rich and diverse sources, which endow regenerated cellulose composite fibers or composite films with extremely high added value, and are used in various fields.

The inorganic salt solution used in the present invention belongs to the non-derivatized solvent of cellulose, and the direct action of metal ions and their complexes with cellulose molecules can realize rapid and efficient dissolution of cellulose. The solution of cellulose is translucent and cools After that, gel can be formed, cellulose gel obtained by dissolving cellulose in inorganic salt solution, regenerated cellulose fiber, regenerated cellulose film, especially the regenerated cellulose composite material with functional materials has multi-functional characteristics, which can meet different applications The performance requirements of the field have huge market potential.

A microscope was used to characterize the microscopic changes of the cellulose gradually dissolved; X-ray diffraction (XRD) was used to characterize the crystallinity and crystal form changes of the obtained cellulose before and after dissolution. The result is as follows:

(1) Microscopic change diagram of complete dissolution of cellulose, see Figure 3;

(2) XRD patterns of the regenerated cellulose membrane and the cellulose raw material, see FIG. 4 .

The innovation of the present invention is:

(1) the inorganic salt solution of the present invention has mild conditions for dissolving cellulose raw materials, and the inorganic salt is cheap and easy to obtain, easy to recycle, and the use process will not cause environmental pollution;

(2) The emerging solvent-dissolved cellulose to prepare regenerated cellulose materials has a simple process and can be applied in large-scale production. In particular, the regenerated cellulose composite fiber and composite membrane products have multi-functional characteristics, high added value, and adapt to various market demands.

Description of drawings

FIG. 1 is a schematic diagram of the dissolving of cellulose and the preparation process for preparing regenerated cellulose.

Figure 2 is a physical diagram of the dissolving of cellulose to form a homogeneous solution in Example 1.

Figure 3 shows the microscopic changes of the complete dissolution of cellulose in Example 2.

FIG. 4 is the XRD pattern of the regenerated cellulose membrane and the cellulose raw material in Example 2. FIG.

Specific implementation cases

The present invention will be further described below in conjunction with specific examples. These examples are only intended to illustrate the present invention and not to limit the scope of the present invention. In addition, after reading the teaching content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Example 1

The solution was prepared with ZnCl ₂ : H ₂ O as 1:3, stirred at 70°C under normal pressure, and dissolved by adding 3wt% wood pulp; as shown in Figure 2, it was seen that the cellulose raw material was dissolved in the inorganic salt solution to form a phase solution; a clear gel can be obtained after cooling.

Example 2

Prepare a solution with ZnCl ₂ : H ₂ O as 1:3, stir at 80°C under normal pressure, add 3.5wt% wood pulp to dissolve; observe the dissolution of cellulose under a microscope, as shown in Figure 3, it can be seen that Cellulose is completely dissolved.

The dissolved cellulose solution was coated at 50 °C to form a film, solidified in anhydrous ethanol to form a film, washed with water for several times to remove inorganic salts, and dried to obtain a transparent regenerated cellulose film; The crystallinity of the cellulose film is reduced because the original crystalline region of the fiber is completely destroyed during the dissolution process, and although the crystals are regenerated through intermolecular rearrangement, the crystallinity is still not as high as that of the fibril. In addition, the crystalline form of cellulose changes before and after the dissolution of the zinc chloride solution, and the position of the corresponding characteristic peak changes.

Example 3

A solution was prepared with FeCl ₃ : H ₂ O as 1:6, stirred at 95°C under normal pressure, and dissolved by adding 3wt% absorbent cotton; the dissolved cellulose solution was wet-spun at 50°C, and spun in anhydrous methanol. It is solidified into fibers, washed with water to remove inorganic salts, and dried to obtain regenerated cellulose fibers.

Example 4

A solution was prepared with LiBr:H ₂ O as 1:2, stirred at 150°C, and dissolved by adding 18wt% microcrystalline cellulose;

The dissolved cellulose solution was wet-spun at 50°C, solidified into fibers in dilute hydrochloric acid, washed with water to remove inorganic salts, and dried to obtain a transparent regenerated cellulose film.

Example 5

Prepare a solution with CoCl ₂ : H ₂ O as 1:10 and CaCl ₂ : H ₂ O as 1:4, the mixing mass ratio is 1:1, stir at 120°C, add 0.5wt% pulp to dissolve; dissolve the dissolved fibers The cellulose solution was coated at 50 °C to form a film, and dipped in absolute ethanol for several times; then dipped in 10wt% polyvinyl alcohol (PVA) solution, and dried to obtain a high-strength and high-modulus regenerated cellulose composite film .

Example 6

Prepare a solution with TiCl ₄ : H ₂ O as 1: 4 and ZnCl ₂ : H ₂ O as 1: 3, the mixing mass ratio is 2: 8, and under stirring at 20°C, add 3wt% of cellulose powder to dissolve; The cellulose solution was coated at 60 °C to form a film, and immersed in absolute ethanol for many times; then dissolved in 1wt% sodium hydroxide (NaOH) solution and immersed, and dried to obtain regenerated cellulose with antibacterial function Composite film; this is because the zinc ions remaining in the regenerated cellulose film react with sodium hydroxide to obtain zinc hydroxide precipitation; the zinc hydroxide is dried in the regenerated cellulose film to obtain zinc oxide, which is the characteristic of the regenerated cellulose composite film. Anti-mildew and antibacterial function, can be used for a long time.

Claims (8)

1. A method for dissolving cellulose, comprising the steps of:

1) preparing a high-concentration single or compound inorganic salt solution;

2) adding a certain amount of cellulose raw materials into the inorganic salt solution obtained in the step 1), and stirring and dissolving at a certain temperature to obtain a homogeneous cellulose solution.

2. The method according to claim 1, wherein the inorganic salt in step 1) is a metal salt, and the metal ions are each Li⁺、Mg²⁺、Al³⁺、Ca²⁺、Ti⁴⁺、Mn²⁺、Fe³⁺、Co²⁺、Cu²⁺、Zn²⁺The anion is one of Cl-and Br-.

3. The method for dissolving cellulose according to claim 1, wherein the concentration of the inorganic salt solution in the step 1) is inorganic salt: the molar ratio of water is 1: 10-1: 2.

4. The method for dissolving cellulose according to claim 1, wherein the cellulose raw material is added in an amount of 0.5 to 18wt% in the step 2).

5. The method for dissolving cellulose according to claim 1, wherein the stirring temperature in the step 2) is 20 to 150 ℃.

6. A method for producing regenerated cellulose suitable for the method for dissolving cellulose according to claim 1, comprising the steps of:

1) cooling the cellulose solution prepared in claim 1 to obtain a high strength and high toughness gel;

2) treating the gel obtained in the step 1) by a certain method, cooling and solidifying in a coagulating bath, washing to remove salt, and drying to obtain a regenerated cellulose product.

7. The method for preparing regenerated cellulose according to claim 6, wherein the gel in step 2) is processed by one of wet spinning and coating to form a film, so as to obtain regenerated cellulose products in both fiber and film forms.

8. The method of claim 6, wherein the coagulating bath in step 2) is one of an organic solvent, a mixture of an organic solvent and water, and a dilute acid solution.

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