Extensible preparation method of polysaccharide oriented foam

Abstract

The invention relates to the field of cellulose foam materials, in particular to an extensible preparation method of polysaccharide oriented foam. The extensible preparation method of the polysaccharide oriented foam comprises the following steps: dissolving cellulose in a urea solution, and pre-cooling to obtain a solution A; mixing a sodium hydroxide solution with the solution A to obtain a cellulose solution; adding a template agent into the cellulose solution, uniformly mixing, carrying out gel forming, sequentially regenerating, washing, freezing, unfreezing, and naturally drying, so as to obtain the polysaccharide oriented foam. The method is low in energy consumption and high in production efficiency, the polysaccharide oriented foam prepared through the method has high strength, the preparation process and materials are natural, green, non-toxic and harmless, and the polysaccharide oriented foam has practical value in the fields of buildings, cold chains, packaging materials and the like.

Description

Technical Field

[0001] The invention relates to the field of cellulose foam materials, in particular to an expandable preparation method of polysaccharide oriented foam. Background Art

[0002] The traditional preparation methods of cellulose foam materials are freeze drying and supercritical drying. Although the above methods can produce high-quality foam, the equipment is expensive, the drying conditions are complicated, and the drying time is long. The normal pressure and normal temperature drying method has the advantages of simple operation and low energy consumption, but the preparation of porous foams with oriented channel structures is still challenging. At present, oriented channel foams are mainly constructed by directional freezing and freeze drying of solutions, but the mechanical properties of foams prepared by this method are relatively weak. Therefore, it is of great significance to the field of cellulose foam materials to provide a cellulose foam with an oriented channel structure that can be dried under normal temperature and normal pressure conditions and has good mechanical properties. Summary of the Invention

[0003] Based on the above content, the present invention provides an expandable preparation method of polysaccharide oriented foam.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] The present invention provides an expandable preparation method of polysaccharide oriented foam, comprising the following steps:

[0006] Dissolve cellulose in a pre-cooled urea solution to obtain solution A;

[0007] Mixing sodium hydroxide solution with solution A to obtain a cellulose solution;

[0008] A template is added to the cellulose solution and mixed to form a gel, which is then regenerated, washed, frozen, thawed and dried in sequence to obtain the polysaccharide oriented foam.

[0009] The present invention also provides a polysaccharide oriented foam prepared by utilizing the above-mentioned expandable preparation method of the polysaccharide oriented foam.

[0010] The present invention discloses the following technical effects:

[0011] The method of the present invention has low energy consumption and high production efficiency. The polysaccharide oriented foam prepared by the method of the present invention has high strength. The preparation process and materials are natural, green, non-toxic and harmless, and have practical value in the fields of construction, cold chain, packaging materials, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0013] Figure 1 This is a process flow chart of the expandable preparation method of the polysaccharide oriented foam of the present invention.

[0014] Figure 2 These are optical photographs of the cellulose foam precursor and the cellulose foam in Example 1; wherein (a) is the cellulose foam precursor, and (b) is the cellulose foam.

[0015] Figure 3 This is the compressive stress-strain curve of the cellulose foam in Example 1.

[0016] Figure 4 These are optical microscope images and scanning electron microscope images of the cellulose foam in Example 1; (a) is an optical microscope image, and (b) is a scanning electron microscope image.

[0017] Figure 5 These are optical photographs of the cellulose foam precursor and the cellulose foam in Example 2; wherein (a) is the cellulose foam precursor, and (b) is the cellulose foam.

[0018] Figure 6 This is the compressive stress-strain curve of the cellulose foam in Example 2.

[0019] Figure 7 These are optical microscope images and scanning electron microscope images of the cellulose foam in Example 2; (a) is an optical microscope image, and (b) is a scanning electron microscope image.

[0020] Figure 8 These are optical photographs of the cellulose foam precursor and the cellulose foam in Example 3; wherein (a) is the cellulose foam precursor, and (b) is the cellulose foam.

[0021] Figure 9 This is the compressive stress-strain curve of the cellulose foam in Example 3.

[0022] Figure 10 These are optical microscope images and scanning electron microscope images of the cellulose foam in Example 3; (a) is an optical microscope image, and (b) is a scanning electron microscope image.

[0023] Figure 11These are optical photographs of the cellulose foam precursor and the cellulose foam in Comparative Example 1; wherein (a) is the cellulose foam precursor, and (b) is the cellulose foam.

[0024] Figure 12 These are optical microscope images and scanning electron microscope images of the cellulose foam in Comparative Example 1; wherein (a) is an optical microscope image, and (b) is a scanning electron microscope image.

[0025] Figure 13 These are optical microscope images of different positions of the cellulose foam in Comparative Example 2.

[0026] Figure 14 These are optical microscope images of different positions of the cellulose foam in Comparative Example 3. DETAILED DESCRIPTION

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0029] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0030] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0031] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0032] The "room temperature" and "normal temperature" mentioned in the present invention, unless otherwise specified, refer to 20-30°C.

[0033] The present invention uses a salt-templated method to improve the dense pore structure of regenerated cellulose gel. Furthermore, through directional freezing and thawing, followed by drying at room temperature and pressure, a cellulose foam material with highly oriented pore channels and high strength is successfully prepared. The atmospheric pressure drying method reduces energy consumption and improves production efficiency. This foam material exhibits high strength, and the preparation process and materials are naturally green, non-toxic, and harmless, making it useful in fields such as construction, cold chain manufacturing, and packaging materials.

[0034] The present invention provides an expandable preparation method of polysaccharide oriented foam, comprising the following steps:

[0035] Dissolve cellulose in a pre-cooled urea solution to obtain solution A;

[0036] Mixing sodium hydroxide solution with solution A to obtain a cellulose solution;

[0037] A template is added to the cellulose solution and mixed to form a gel, which is then regenerated, washed, frozen, thawed and dried in sequence to obtain the polysaccharide oriented foam.

[0038] In the present invention, the cellulose can be selected from natural cellulose materials such as cotton pulp, wood pulp, and bamboo pulp. The degree of polymerization of the cellulose is 550.

[0039] In a preferred embodiment of the present invention, the temperature of the solution A is -5°C to 0°C; the mass concentration of the urea solution is 8% to 12%; and the mass concentration of cellulose in the solution A is 2-8 wt%.

[0040] The urea solution is prepared by dissolving urea in deionized water. The cellulose and urea solution are mixed and placed in a low-temperature freezing device and pre-cooled to -5°C to 0°C.

[0041] In a preferred embodiment of the present invention, the temperature of the sodium hydroxide solution is -18°C to -16°C; and the concentration of the sodium hydroxide solution is 7% to 9%.

[0042] The sodium hydroxide solution is prepared by dissolving sodium hydroxide in deionized water; the sodium hydroxide solution is placed in a low-temperature freezing device and pre-cooled to -18°C to -16°C.

[0043] The sodium hydroxide solution was mixed with solution A and stirred at a speed of 1000-1300 rpm for 3-5 minutes to form a uniform cellulose solution.

[0044] Compared with the prior art method of dissolving cellulose in a urea / alkaline solution, the present invention prepares a cellulose solution through a two-step method. First, the cellulose is dissolved in a urea solution and precooled to -5°C to 0°C, and then mixed with a sodium hydroxide solution precooled to -18°C to -16°C. This can improve the solubility and dispersion uniformity of the cellulose, thereby improving the void uniformity and mechanical properties of the prepared polysaccharide oriented foam.

[0045] The present invention has been found through repeated experiments that the pre-cooling temperature affects the dispersion uniformity of cellulose in the cellulose solution, and the dispersion uniformity of cellulose is best only within the above-mentioned pre-cooling temperature range.

[0046] In a preferred embodiment of the present invention, the volume ratio of the sodium hydroxide solution to the solution A is 1:1.

[0047] In a preferred embodiment of the present invention, the template is sodium carbonate; and the concentration of the template in the cellulose solution is 5-20 wt%.

[0048] The template is slowly added to the cellulose solution while stirring at a speed of 1000-1300 rpm for 3-5 minutes to ensure that the sodium carbonate and the cellulose solution are evenly mixed.

[0049] In a preferred embodiment of the present invention, the gel forming temperature is 40° C. to 80° C., and the time is 1 hour to 3 hours.

[0050] The mold material used in the gel molding is polytetrafluoroethylene (PTFE) or a silicone mold.

[0051] In a preferred embodiment of the present invention, the regeneration is specifically as follows: placing the hot sol obtained by gel formation in a regeneration solution and regenerating it at room temperature for 2 to 4 hours to obtain a cellulose gel; the regeneration solution is a sodium bicarbonate solution with a concentration of 80 to 100 g / L.

[0052] The hot melt obtained by gel molding is taken out from the mold, placed in a sodium bicarbonate solution, and soaked at room temperature for 2 to 4 hours to regenerate the cellulose gel in the sodium bicarbonate solution to form a stable cellulose gel structure.

[0053] The regeneration solution used in the present invention is a sodium bicarbonate solution. Compared with the situation that "ethanol solution is highly volatile and the temperature and time of the regeneration process need to be strictly controlled", the present invention has lower requirements on the temperature and time of the regeneration process.

[0054] In a preferred embodiment of the present invention, the washing is specifically washing with deionized water; the freezing temperature is -40°C to -20°C, and the time is 2 to 4 hours; the thawing is specifically natural thawing at room temperature for 2h to 3h; and the drying is specifically drying at room temperature to 60°C and normal pressure for 24h to 72h.

[0055] The washing specifically involves taking the regenerated cellulose gel out of the sodium bicarbonate solution and repeatedly washing it with deionized water to ensure that the residual solvent and salt (sodium bicarbonate, sodium carbonate) are removed.

[0056] Place the washed cellulose gel in a freezer at -40°C to -20°C for 2 to 4 hours to allow the cellulose gel to form a unidirectional frozen structure. Remove the frozen cellulose gel from the freezer and allow it to thaw naturally at room temperature for 2 to 3 hours.

[0057] The thawed cellulose gel is placed in a room temperature environment or in a drying oven at room temperature to 60° C. for 12 to 72 hours until the cellulose gel is completely dry to obtain the final polysaccharide oriented foam (cellulose foam material).

[0058] Compared with traditional freeze-drying and supercritical drying methods, the method of the present invention can be dried under normal temperature and pressure conditions, and has the advantages of simple operation, low cost, low energy consumption and high production efficiency.

[0059] The present invention utilizes the above-described preparation method to produce a polysaccharide oriented foam with high orientation and a uniform pore structure. The process parameters of each step are carefully designed to ensure that the cellulose is fully dissolved, uniformly mixed, and stably formed, and that an ideal foam structure is formed during the regeneration, washing, freezing, thawing, and drying processes. This method offers the advantages of simple operation and low energy consumption. It also produces a high-strength, naturally green, and non-toxic cellulose foam material suitable for a variety of applications, including construction, cold chain manufacturing, and packaging materials.

[0060] The present invention also provides a polysaccharide oriented foam prepared by utilizing the above-mentioned expandable preparation method of the polysaccharide oriented foam.

[0061] The density of the polysaccharide oriented foam is 120 to 300 mg·cm -3 .

[0062] The technical solutions described in the present invention, unless otherwise specified, are all conventional solutions in the art, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or are publicly available.

[0063] The cellulose used in the embodiments of the present invention was purchased from Qingshan Paper Industry and was bamboo cellulose with a main parameter of polymerization degree of 550.

[0064] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0065] Example 1

[0066] Step (1), add 4 g of cellulose to 50 mL of 8 wt% urea solution (solvent is water) and precool to -5°C (-5°C to 0°C);

[0067] Step (2), prepare 7 wt% sodium hydroxide solution (solvent is water) and pre-cool to -18°C (-18°C to -16°C);

[0068] Step (3), mixing the mixture of step (1) and the solution of step (2) in a volume ratio of 1:1 and stirring for 5 minutes (3 minutes to 5 minutes) at a stirring rate of 1300 r / min to obtain a cellulose solution;

[0069] Step (4) adds 10 g of anhydrous sodium carbonate to 100 mL of the cellulose solution obtained in step (3) and stirs for 2 minutes (2 minutes to 3 minutes is acceptable) at a stirring rate of 1000 r / min to uniformly mix to form a salt-templated cellulose suspension. The solution is then poured into a square silica gel mold and gelled at 60° C. for 2 hours. The solution is then removed from the mold and placed in a 100 g / L sodium bicarbonate solution for regeneration for 3 hours to obtain a cellulose gel. The residual solvent and sodium carbonate are washed with deionized water to obtain a neutral cellulose gel. Finally, the solution is subjected to unidirectional freeze casting at -40° C. for 2 hours and naturally thawed at room temperature for 2 hours to obtain a cellulose foam precursor. The cellulose foam precursor is dried at room temperature and pressure for 12 hours to obtain an expandable cellulose foam (i.e., polysaccharide oriented foam, abbreviated as cellulose foam).

[0070] The density of the cellulose foam prepared in Example 1 is 135.73 mg·cm -3 , the porosity is 91%. Figure 2 After drying, the cellulose foam showed relatively uniform shrinkage, with a shrinkage rate of 40-45%. The obtained cellulose foam was subjected to mechanical property testing. The cellulose foam was compressed using a tensile compression material testing machine at a compression rate of 5 mm / min and a compression strain of 50%. The obtained compressive strength was 1296.89 kPa ( Figure 3 ). Observed by optical microscope and scanning electron microscope (SEM) ( Figure 4 ) The pore structure of cellulose foam is relatively uniform and has an oriented structure.

[0071] Example 2

[0072] The only difference from Example 1 is that the amount of anhydrous sodium carbonate added in step (4) is 20 g; the remaining steps and parameters are the same as those in Example 1.

[0073] The density of the cellulose foam prepared in Example 2 is 167.15 mg·cm -3 , the porosity is 89%. Figure 5After drying, the cellulose foam showed relatively uniform shrinkage, with a shrinkage rate of 45% to 50%. The obtained cellulose foam was subjected to mechanical property testing. The cellulose foam was compressed using a tensile compression material testing machine at a compression rate of 5 mm / min and a compression strain of 50%. The compressive strength was 661.11 kPa ( Figure 6 ). Observed by optical microscope and scanning electron microscope (SEM) ( Figure 7 ) The pore structure of cellulose foam is relatively uniform and has an oriented structure.

[0074] Example 3

[0075] The only difference from Example 1 is that, before adding 10 g of anhydrous sodium carbonate to the cellulose solution in step (4), 3 mL of 1,4-butanediol diglycidyl ether is added and stirred for 3 min (2 min to 3 min); the remaining steps and parameters are the same as those in Example 1.

[0076] The density of the cellulose foam prepared in Example 3 is 115.53 mg·cm -3 The porosity is 92%. Figure 8 After drying, the cellulose foam showed relatively uniform shrinkage, with a shrinkage rate of 38% to 45%. The obtained cellulose foam was subjected to mechanical property testing. The cellulose foam was compressed using a tensile compression material testing machine at a compression rate of 5 mm / min and a compression strain of 50%. The compressive strength was 475.85 kPa ( Figure 9 ). Observed by optical microscope and scanning electron microscope (SEM) ( Figure 10 ) The pore structure of cellulose foam is relatively uniform and has an oriented structure.

[0077] Comparative Example 1

[0078] The only difference from Example 1 is that the addition of 10 g of anhydrous sodium carbonate is omitted in step (4); the remaining steps and parameters are the same as those in Example 1.

[0079] The density of the cellulose foam prepared in Comparative Example 1 is 270.77 mg·cm -3 , the porosity is 82%. Figure 11 After drying, the cellulose foam showed uneven shrinkage, with a large shrinkage degree and a shrinkage rate of 66% to 70%. Figure 12 ) The pore structure of cellulose foam is uneven and the pores are relatively large.

[0080] Comparative Example 2

[0081] The only difference from Example 1 is that the temperature of gel formation in step (4) is adjusted from 60°C to 5°C; the remaining steps and parameters are the same as those in Example 1.

[0082] The cellulose foam prepared in Comparative Example 2 was observed by optical microscopy ( Figure 13 ), the pore distribution of cellulose foam is uneven, the pore size is large, and it does not have an oriented structure.

[0083] Comparative Example 3

[0084] The only difference from Example 1 is that the temperature of gel formation in step (4) is adjusted from 60°C to 25°C; the remaining steps and parameters are the same as those in Example 1.

[0085] The cellulose foam prepared in Comparative Example 3 was observed by optical microscopy ( Figure 14 ), the pore distribution of cellulose foam is uneven and does not have an oriented structure.

[0086] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing an expandable polysaccharide oriented foam, characterized in that: The following steps are involved: Dissolve cellulose in a pre-cooled urea solution to obtain solution A; Mixing sodium hydroxide solution with solution A to obtain a cellulose solution; A template is added to the cellulose solution and mixed to form a gel, which is then regenerated, washed, frozen, thawed and dried in sequence to obtain the polysaccharide oriented foam.

2. The expandable preparation method of polysaccharide oriented foam according to claim 1, characterized in that: The temperature of the solution A is -5°C to 0°C; the mass concentration of the urea solution is 8% to 12%; and the mass concentration of cellulose in the solution A is 2-8 wt%.

3. The expandable preparation method of polysaccharide oriented foam according to claim 1, characterized in that: The temperature of the sodium hydroxide solution is -18°C to -16°C; the concentration of the sodium hydroxide solution is 7% to 9%.

4. The expandable preparation method of polysaccharide oriented foam according to claim 1, characterized in that: The volume ratio of the sodium hydroxide solution to the solution A is 1:

1.

5. The expandable preparation method of polysaccharide oriented foam according to claim 1, characterized in that: The template agent is sodium carbonate; the concentration of the template agent in the cellulose solution is 5-20 wt%.

6. The expandable preparation method of polysaccharide oriented foam according to claim 1, characterized in that: The temperature for gel formation is 40° C. to 80° C., and the time is 1 hour to 3 hours.

7. The expandable preparation method of polysaccharide oriented foam according to claim 1, characterized in that: The regeneration is specifically as follows: placing the hot sol obtained by gel molding in a regeneration solution and regenerating it at room temperature for 2 to 4 hours to obtain cellulose gel; the regeneration solution is a sodium bicarbonate solution with a concentration of 80 to 100 g / L.

8. The expandable preparation method of polysaccharide oriented foam according to claim 1, characterized in that: The washing is specifically washing with deionized water; the freezing temperature is -40°C to -20°C, and the time is 2 to 4 hours; the thawing is specifically natural thawing at room temperature for 2h to 3h; the drying is specifically drying at room temperature to 60°C and normal pressure for 12h to 72h.

9. The oriented polysaccharide foam prepared by the expandable preparation method of the oriented polysaccharide foam according to any one of claims 1 to 8.

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