A method for preparing a porous calcium alginate material with aerogel-like structure

Abstract

The present invention relates to the technical field of material synthesis, and discloses a method for preparing a porous calcium alginate material with a similar aerogel structure, comprising the following steps: (1) mixing: adding alginate and a stabilizer to pure water, stirring evenly, and obtaining a sol slurry; (2) homogenizing: homogenizing the sol slurry with a calcium chloride solution to obtain a gel slurry; (3) molding: expanding or decompressing the gel slurry to obtain a foamy wet aerogel; (4) shaping and drying: shaping the wet aerogel into a layered aerogel, and the layered aerogel enters a cold air dryer for drying to obtain a porous calcium alginate material. The calcium alginate aerogel material prepared by the present invention has a density of 0.3-0.6 g / cm 3 , with a surface area of ​​200-500m 2 / cm 3 , which can widely replace the application of aerogel. The preparation method of the present invention adopts cold air drying to replace the traditional supercritical drying and freeze drying, and the manufacturing cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of material synthesis, and in particular to a method for preparing a porous calcium alginate material with a structure similar to that of an aerogel. Background Art

[0002] During the drying process of existing aerogel materials, the capillary force generated by the shrinkage of the liquid surface in the pores will cause the structure to collapse. To avoid this problem, it is necessary to use drying conditions under critical conditions, such as freeze drying and supercritical drying.

[0003] Alginate is one of the important raw materials for preparing aerogel materials. Patents with application numbers CN202210604902.0 and CN201910892286.1 respectively disclose the preparation of sodium alginate aerogel with lignin and palm fiber as reinforcing materials; Patent with application number CN202110913415.8 discloses the preparation of alginate aerogel with shell structure; Patent with application number CN202110874627.X discloses the preparation of alginate aerogel beads, and the above patents all use freeze-drying technology. Patent with application number CN201810292061.8 discloses a hemostatic aerogel with chitosan modified with acetyl shanzhi glycoside methyl ester and sodium alginate as the main raw materials, using supercritical drying; Patent with application number CN201810047389.3 also discloses a method for preparing calcium alginate aerogel using supercritical drying.

[0004] The supercritical drying method is the most efficient and produces the best aerogel performance, but it is also the most expensive. Supercritical drying requires the use of special high-pressure containers, and the equipment manufacturing cost is 3-5 times that of ordinary containers. Its operation needs to be carried out under high pressure conditions, and the air compressor unit equipped with it consumes a lot of energy. According to industry estimates, the energy consumption for evaporating 1kg of water using supercritical drying is about 10-15Kw / h. This results in the use of supercritical drying to prepare aerogels, and its equipment depreciation and energy consumption costs are very high, and it does not have mass production capacity and application feasibility.

[0005] Although freeze drying is much cheaper than supercritical methods, it also has problems such as high energy consumption, long drying time and inability to produce continuously. According to industry estimates, the energy consumption for evaporating 1kg of water using freeze drying is about 1.5-2.0Kw / h, about 1.5 yuan. Because the equipment needs to be vacuumed, it can only be operated in batches, with manual assistance for mechanical loading and unloading, and cannot achieve continuous production.

[0006] In the laboratory, the research and development of aerogels is aimed at ultra-low density (0.1g / cm 3 Below) and ultra-large specific surface area (1000m 2 / cm 3Theoretical research and development regardless of cost is currently difficult to have practical application feasibility. In order to fully utilize the characteristics of aerogels and improve application feasibility, it is an urgent problem to develop a preparation method for aerogel-like structural materials that reduces production costs and maintains certain performance. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing a porous calcium alginate material with a structure similar to that of an aerogel.

[0008] In order to achieve the above object, the technical solution of the present invention is: a method for preparing a porous calcium alginate material with an aerogel-like structure, characterized in that it comprises the following steps:

[0009] (1) Mixing: Add alginate and stabilizer to pure water, and stir at high speed to obtain sol slurry;

[0010] (2) homogenizing: feeding the sol slurry prepared in step (1) and the calcium chloride solution into a high-pressure homogenizer for homogenization to obtain a gel slurry;

[0011] (3) molding: expanding or decompressing the gel slurry prepared in step (2) to obtain a foamy wet aerogel;

[0012] (4) Shaping and drying: The wet aerogel prepared in step (3) is shaped into a layered aerogel through a double-roll extruder, and the layered aerogel is dried in a cold air dryer to obtain a calcium alginate porous material.

[0013] Furthermore, in step (1), the mass ratio of pure water, alginate and stabilizer is 100:2-6:0.1-1.

[0014] Furthermore, the alginate in step (1) is a mixture of sodium alginate and sodium hydroxyalginate, the mass ratio of sodium alginate to sodium hydroxyalginate is 1-5:1, the content of guluronic acid in the sodium alginate is 65-70%, and the content of guluronic acid in the hydroxypropyl sodium alginate is 40-45%.

[0015] Furthermore, the stabilizer in step (1) is selected from one of carboxymethyl cellulose, polyvinyl pyrrolidone and lignin.

[0016] Furthermore, the rotation speed of the high-speed shear stirring in step (1) is 1200-1500 rpm, and the shear stirring time is 30-60 min.

[0017] Furthermore, the mass fraction of the calcium chloride solution in step (2) is 5%, and the mass ratio of calcium chloride to alginate in the calcium chloride solution is 1:50-100.

[0018] Furthermore; the homogenization pressure in step (2) is 10-20 MPa, and the homogenization time is 30 seconds.

[0019] Furthermore, in step (3), the gel slurry prepared in step (2) is input into a venturi tube installed at the outlet of the homogenizer, and is sprayed out through the venturi tube to obtain a foamy wet aerogel; or the gel slurry prepared in step (2) is input into a twin-screw extruder for extrusion and expansion to obtain a foamy wet aerogel.

[0020] Furthermore, in step (3), the inlet pressure of the venturi tube is 1.0-5.0 MPa, the outlet flow rate is 20-30 m / s, and the screw pressure (chamber pressure) of the twin-screw extruder is 20-30 MPa.

[0021] Furthermore, the cold air temperature during drying in step (4) is 0-10°C.

[0022] Beneficial effects of the present invention:

[0023] (1) The present invention has low cost and adopts a puffing method to prepare wet aerogel. The skeleton structure strength of the aerogel is higher than that of existing preparation methods such as mechanical shearing and stirring. The aerogel-like foam material can be obtained by subsequent cold air drying, thereby realizing continuous production and avoiding the problems of high energy consumption and inability to produce continuously of existing freeze drying and supercritical drying methods. It is estimated that the manufacturing cost of the aerogel by cold air drying of the present invention is 10-20% of that of the freeze drying of the prior art, which has good economic benefits.

[0024] (2) The wet aerogel prepared using alginate with a high guluronic acid content and hydroxypropyl-modified sodium alginate has higher structural strength and toughness than ordinary sodium alginate materials. Even under cold air drying conditions, the wet aerogel prepared by the present invention can maintain a small amount of collapse, thereby obtaining an aerogel-like material with a certain pore size and specific surface area.

[0025] (3) The materials used in the present invention are degradable and environmentally friendly materials, which are non-toxic and harmless. The prepared calcium alginate aerogel materials can be in direct contact with food and have a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a SEM image of the finished calcium alginate aerogel material prepared in Example 1;

[0027] Figure 2 is a schematic structural diagram of the preparation device of Example 1;

[0028] Figure 3 It is a schematic diagram of the structure of the preparation device of Example 3.

[0029] In the figure: 1. shear emulsification tank; 2. first delivery pump; 3. second delivery pump; 4. high-pressure homogenizer; 5. venturi tube; 6. twin-roll extruder; 7. fluidized bed cold air dryer; 8. twin-screw extruder. DETAILED DESCRIPTION

[0030] The sodium alginate and hydroxypropyl sodium alginate in the present invention are both purchased from Qingdao Mingyue Seaweed Group Co., Ltd.

[0031] Embodiment 1:

[0032] A method for preparing a porous calcium alginate material having an aerogel-like structure, comprising the following steps:

[0033] (1) Mixing: In a shear emulsification tank 1, 100 g of sodium alginate (guluronic acid content 65%) and 100 g of hydroxypropyl sodium alginate (guluronic acid content 40%) were added to 10 kg of pure water under stirring, and then 10 g of water-soluble lignin was added as a stabilizer. The mixture was sheared and stirred at 1500 rpm for 30 min to form a uniform sol slurry;

[0034] (2) Homogenization: The sol slurry prepared in step (1) and 80 g of a 5% calcium chloride solution are respectively delivered to a high-pressure homogenizer 4 through a first delivery pump 2 and a second delivery pump 3, with a homogenization pressure of 10 MPa and a material residence time of 30 seconds, to obtain a calcium alginate gel after homogenization;

[0035] (3) Forming: The homogenized calcium alginate gel directly enters the venturi tube 5 through the pipeline. The inlet pressure of the venturi tube 5 is 1.0 MPa. The outlet flow rate of the venturi tube 5 is adjusted to 20 m / s, so that the gel is sprayed out to form a foamy wet gel;

[0036] (4) Shaping and drying: The wet aerogel enters the twin-roll extruder 6 and is shaped into a 10 cm thick layered wet aerogel. It then enters the fluidized bed cold air dryer 7, where the cold air temperature is 10°C. After drying, the finished calcium alginate aerogel material is obtained. The SEM image of the finished aerogel is shown in FIG. Figure 1 shown.

[0037] like Figure 2 As shown, a preparation device of a porous calcium alginate material with an aerogel-like structure comprises a shear emulsification tank 1, a first delivery pump 2, a second delivery pump 3, a high-pressure homogenizer 4, a venturi tube 5, a double-roll extruder 6 and a fluidized bed cold air dryer 7, wherein the outlet of the shear emulsification tank 1 is connected to the inlet of the high-pressure homogenizer 4 through the first delivery pump 2, the inlet of the second delivery pump 3 is connected to the calcium chloride solution pipeline, the outlet of the second delivery pump 3 is connected to the inlet of the high-pressure homogenizer 4, the outlet of the high-pressure homogenizer 4 is connected to the inlet of the venturi tube 5 through a steel pipeline, the outlet of the venturi tube 5 is connected to the inlet of the double-roll extruder 6, and the outlet of the double-roll extruder 6 is connected to the fluidized bed cold air dryer 7.

[0038] Embodiment 2:

[0039] A method for preparing a porous calcium alginate material having an aerogel-like structure, comprising the following steps:

[0040] (1) Mixing: In a shear emulsification tank 1, 300 g of sodium alginate (guluronic acid content 65%) and 100 g of hydroxypropyl sodium alginate (guluronic acid content 40%) were added to 10 kg of pure water under stirring, and then 50 g of polyvinyl pyrrolidone (K30) was added as a stabilizer, and high-speed shear stirring was performed at 1200 rpm for 40 min to form a uniform sol slurry;

[0041] (2) Homogenization: The sol slurry prepared in step (1) and 100 g of a 5% calcium chloride solution are respectively delivered to a high-pressure homogenizer 4 through a first delivery pump 2 and a second delivery pump 3, with a homogenization pressure of 15 MPa and a material residence time of 30 seconds, to obtain a calcium alginate gel after homogenization;

[0042] (3) Forming: The homogenized calcium alginate gel directly enters the venturi tube 5 through the pipeline. The inlet pressure of the venturi tube 5 is 5.0 MPa. The outlet flow rate of the venturi tube 5 is adjusted to 30 m / s, so that the gel is sprayed out to form a foamy wet gel;

[0043] (4) Shaping and drying: The wet aerogel enters a twin-roll extruder 6 and is shaped into a 10 cm thick layered wet aerogel. The aerogel then enters a fluidized bed cold air dryer 7, where the cold air temperature is 5° C. The finished calcium alginate aerogel material is obtained after drying.

[0044] A preparation device for a porous calcium alginate material with an aerogel-like structure, same as that in Example 1.

[0045] Embodiment 3:

[0046] A method for preparing a porous calcium alginate material having an aerogel-like structure, comprising the following steps:

[0047] (1) Mixing: In a shear emulsification tank 1, 500 g of sodium alginate (guluronic acid content 70%) and 100 g of hydroxypropyl sodium alginate (guluronic acid content 45%) were added to 10 kg of pure water under stirring, and then 100 g of carboxymethyl cellulose was added as a stabilizer. The mixture was sheared and stirred at 1200 rpm for 60 min to form a uniform sol slurry.

[0048] (2) Homogenization: The sol slurry prepared in step (1) and 120 g of a 5% calcium chloride solution are respectively delivered to a high-pressure homogenizer 4 through a first delivery pump 2 and a second delivery pump 3, with a homogenization pressure of 20 MPa and a material residence time of 30 seconds, to obtain a calcium alginate gel after homogenization;

[0049] (3) Forming: The homogenized calcium alginate gel enters the twin-screw extruder 8 through a pipeline. The screw pressure of the twin-screw extruder 8 is 30 MPa, and the foamy wet aerogel is obtained by extrusion.

[0050] (4) Shaping and drying: The wet aerogel enters a twin-roll extruder 6 and is shaped into a 10 cm thick layered wet aerogel. The aerogel then enters a fluidized bed cold air dryer 7, where the cold air temperature is 0°C. After drying, the finished calcium alginate aerogel material is obtained.

[0051] like Figure 3 As shown, a preparation device of a porous calcium alginate material with an aerogel-like structure comprises a shear emulsification tank 1, a first delivery pump 2, a second delivery pump 3, a high-pressure homogenizer 4, a twin-screw extruder 8, a twin-roll extruder 6 and a fluidized bed cold air dryer 7, wherein the outlet of the shear emulsification tank 1 is connected to the inlet of the high-pressure homogenizer 4 through the first delivery pump 2, the inlet of the second delivery pump 3 is connected to the calcium chloride solution pipeline, the outlet of the second delivery pump 3 is connected to the inlet of the high-pressure homogenizer 4, the outlet of the high-pressure homogenizer 4 is connected to the inlet of the twin-screw extruder 8, the outlet of the twin-screw extruder 8 is connected to the inlet of the twin-roll extruder 6, and the outlet of the twin-roll extruder 6 is connected to the fluidized bed cold air dryer 7.

[0052] Comparative Example 1:

[0053] (1) In a shear emulsification tank, 3 g of sodium alginate (guluronic acid content 65%) and 1 g of hydroxypropyl sodium alginate (guluronic acid content 25%) were added to 100 g of pure water under stirring, and 1 g of carboxymethyl cellulose was added as a stabilizer. The mixture was sheared at 1200 rpm for 60 min, and 12 g of 0.5% calcium chloride solution was slowly dripped into the mixture to form a uniform gel.

[0054] (2) pressing the prepared gel into a 10 cm thick gel layer, and then freeze-drying it at a temperature of -20°C and a pressure of less than 1 KPa to obtain a finished calcium alginate aerogel material;

[0055] The aerogel-like materials prepared in Examples 1 to 3 and Comparative Example 1 were tested, as shown in Table 1:

[0056] Table 1

[0057]

[0058] It can be seen from Table 1 that the aerogel-like foam material prepared by the preparation method of the embodiment of the present invention has a cost of only 10-20% of that obtained by the traditional freeze-drying method, and has a certain specific surface area and aerogel characteristics.

[0059] The above-described embodiments are only preferred solutions of the present invention and are not intended to limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

[0060] In the description of the present invention, it is necessary to understand that the terms indicating orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

Claims

1. A method for preparing a porous calcium alginate material having an aerogel-like structure, characterized in that: The following steps are involved: (1) Mixing: adding alginate and a stabilizer to pure water, and stirring at high speed to obtain a sol slurry, wherein the alginate is a mixture of sodium alginate and hydroxypropyl sodium alginate, the mass ratio of the sodium alginate to the hydroxypropyl sodium alginate is 1-5:1, the content of guluronic acid in the sodium alginate is 65-70%, and the content of guluronic acid in the hydroxypropyl sodium alginate is 40-45%; (2) Homogenization: feeding the sol slurry prepared in step (1) and the calcium chloride solution into a high-pressure homogenizer for homogenization to obtain a gel slurry; (3) Molding: The gel slurry prepared in step (2) is transferred to a venturi tube installed at the outlet of a high-pressure homogenizer, and sprayed out through the venturi tube to obtain a foamy wet gel; Alternatively, the gel slurry prepared in step (2) is transported to a twin-screw extruder for extrusion and expansion to obtain a foamed wet aerogel; the inlet pressure of the venturi tube is 1.0-5.0 MPa, the outlet flow rate is 20-30 m / s, and the screw pressure of the twin-screw extruder is 20-30 MPa; (4) Shaping and drying: The wet aerogel prepared in step (3) is shaped into a layered aerogel through a double-roll extruder, and the layered aerogel enters a cold air dryer for drying to obtain a calcium alginate porous material.

2. The method for preparing the porous calcium alginate material with aerogel-like structure according to claim 1, characterized in that: The mass ratio of pure water, alginate and stabilizer in step (1) is 100:2~6:0.1~1.

3. The method for preparing the porous calcium alginate material with aerogel-like structure according to claim 1, characterized in that: The stabilizer in step (1) is selected from one of carboxymethyl cellulose, polyvinyl pyrrolidone and lignin.

4. The method for preparing the porous calcium alginate material with aerogel-like structure according to claim 1, characterized in that: The rotation speed of the high-speed shear stirring in step (1) is 1200-1500 rpm, and the shear stirring time is 30-60 min.

5. The method for preparing the porous calcium alginate material with aerogel-like structure according to claim 1, characterized in that: The mass fraction of the calcium chloride solution in step (2) is 5%, and the mass ratio of calcium chloride to alginate in the calcium chloride solution is 1:50-100.

6. The method for preparing a porous calcium alginate material having an aerogel-like structure according to claim 1, characterized in that: The homogenization pressure in step (2) is 10-20 MPa, and the homogenization time is 30 seconds.

7. The method for preparing a porous calcium alginate material having an aerogel-like structure according to claim 1, characterized in that: The cold air temperature during drying in step (4) is 0-10°C.

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