Preparation method of sugarcane fiber composite thermal insulation material based on controllable ice crystal growth

Abstract

The invention relates to the technical field of environment-friendly composite thermal insulation materials, in particular to a preparation method of a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth. Comprising the steps of sugarcane fiber pretreatment, suspension preparation, high-speed homogenization, single-direction freezing, vacuum drying and heat treatment shaping. According to the method, agricultural waste bagasse is used as a reinforcing framework, a nucleation guiding agent and bacterial cellulose hydrogel are used as a matrix, and after mixing and homogenizing treatment, a directional freezing process is adopted to prepare the composite thermal insulation material with an ordered structure and synergistically optimized thermal performance. The prepared material has low thermal conductivity, high compressive strength and environmental friendliness, and has wide application prospects in the fields of low-temperature cold-chain transportation, green building energy conservation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of environmentally friendly composite thermal insulation materials, and in particular to a method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth. Background Art

[0002] In recent years, as the global energy market has accelerated its transformation, people are actively looking for more efficient insulation materials to improve energy efficiency.

[0003] Traditional bacterial cellulose aerogels suffer from low compressive strength and poor durability, making them prone to structural collapse under external forces. Their complex preparation process further hinders their large-scale application. Furthermore, traditional disposal methods for agricultural waste products containing cellulose skeletons, such as sugarcane bagasse (sacking and incineration), result in pollution and resource waste. Therefore, it is necessary to utilize this material as a base skeleton for the production of environmentally friendly materials.

[0004] In the prior art, patents with publication numbers CN111073026A and CN111635640B disclose a method for preparing a bamboo cellulose aerogel insulation material and a composite material based on agricultural waste, as well as its preparation method and application. The insulation material of the former patent method has a certain strength and good thermal insulation effect, which can effectively improve the utilization rate and industrial added value of bamboo product waste and expand the path of waste recycling. However, this method uses chemical treatment, and the structural strength and thermal conductivity coefficient cannot be adjusted, and it cannot provide corresponding products for scenarios with different usage requirements; the latter patent achieves the reuse of agricultural waste by multifunctionally regulating the composite material through the mass percentage concentration of agricultural waste. However, this method dissolves the agricultural waste and regenerates it in a coagulation bath. There is no directional control process and it cannot form a directional structure, which leads to the inability to coordinately optimize the thermal insulation performance and material strength.

[0005] To this end, it is urgent to develop a composite environmentally friendly thermal insulation material with agricultural waste fibers as the reinforcing skeleton and bacterial cellulose as the matrix, so as to achieve the unity of low thermal conductivity, high mechanical stability and environmental friendliness through coordinated regulation. Summary of the Invention

[0006] In response to the above problems, the purpose of the present invention is to provide a method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth. The prepared sugarcane fiber composite thermal insulation material has the advantages of controllable thermal properties and simple preparation method.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth. Under different sugarcane fiber mass ratios, the prepared composite thermal insulation material has different microscopic pore structures and corresponding thermal and mechanical properties; through a hierarchical orderly arrangement design, an anisotropic composite thermal insulation material is prepared.

[0009] A method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth comprises the following steps:

[0010] S1. Grinding, screening, removing impurities and drying sugarcane waste to obtain sugarcane fiber raw materials;

[0011] S2. dispersing 0-3% by weight of sugarcane fiber in the bacterial cellulose hydrogel to obtain multiple groups of sugarcane fiber bacterial cellulose gel suspensions;

[0012] S3, homogenizing the sugarcane fiber bacterial cellulose gel suspensions with different mass proportions to obtain multiple groups of homogenized sugarcane fiber bacterial cellulose gel suspensions;

[0013] S4, arranging different groups of sugarcane fiber bacterial cellulose gel suspensions in a preset spatial configuration and directionally freezing them, so that ice crystals grow independently with the assistance of the sugarcane fibers, forming a sugarcane fiber bacterial cellulose gel with a continuous gradient;

[0014] S5, vacuum drying the frozen multiple groups of sugarcane fiber bacterial cellulose gel suspensions to form multiple groups of sugarcane fiber bacterial cellulose gel freeze-dried materials;

[0015] S6. heat-setting the multiple groups of sugarcane fiber bacterial cellulose gel freeze-dried materials.

[0016] Preferably, in step S1, the sugarcane fiber serves as an ice crystal nucleating agent and a reinforcing skeleton.

[0017] Preferably, in step S2, the bacterial cellulose hydrogel has a cellulose content of 1% and a diameter of 15 nm.

[0018] Preferably, in step S3, the homogenizing speed is 8000-12000 r / min, and the stirring time is 5-10 min.

[0019] Preferably, in step S4, directional freezing is performed in a temperature-controlled mold, and the mold comprises a heat-conducting base in a single direction and heat-insulating in other directions.

[0020] Preferably, in step S4, directional freezing means that the sugarcane fiber bacterial cellulose gel suspension is frozen under controlled conditions so that ice crystals grow in a single direction, and the freezing direction is optional, the freezing temperature is -80 to -60°C, and the freezing rate is 0.6 to 1°C / min.

[0021] Preferably, in step S5, the vacuum drying temperature is -45°C and the time is 48-72 hours.

[0022] Preferably, in step S6, the heat setting is performed by drying the freeze-dried material in a drying oven at a temperature of 100° C. for 24 hours.

[0023] Preferably, the sugarcane fiber is added to promote ice crystal nucleation and improve the compressive strength of the overall material. The comprehensive performance of thermal conductivity and compressive strength of the composite thermal insulation material is coordinated and regulated by adjusting the process formula according to the target requirements. To achieve this goal, fiber materials such as bamboo and wood can also be used to replace sugarcane fiber to prepare composite thermal insulation materials.

[0024] Preferably, the mass percentage of the sugarcane fiber is based on a range between 0 and 3, excluding 0 and 3. When the sugarcane fiber concentration exceeds 3, directional freezing will not produce corresponding single-directional channels, thereby losing control of the rapid increase in thermal conductivity. Only when the mass percentage is between 0 and 3 will single-directional channels be formed, achieving dual control of mechanics and thermodynamics.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention utilizes sugarcane fiber as a reinforcing skeleton to enhance the compressive strength of bacterial cellulose aerogel.

[0027] 2. The present invention uses sugarcane fiber as a nucleating agent, so that long-range ordered channels can be formed around the sugarcane fiber during the growth of ice crystals, generating anisotropic thermal insulation materials, which improves the thermal insulation performance compared with materials with disordered ice crystal growth.

[0028] 3. The present invention uses bio-based raw materials to make high-value use of agricultural waste sugarcane bagasse.

[0029] 4. The present invention has no high-temperature sintering or chemical reaction in the entire preparation process, and the production energy consumption is much lower than that of traditional materials and the performance is stable.

[0030] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following is a detailed description in combination with the preferred embodiments and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments are briefly introduced below.

[0032] Figure 1 It is a process flow chart of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of the sugarcane fiber composite thermal insulation material of the present invention, wherein the gray part is bacterial cellulose aerogel and the yellow strips are sugarcane fibers;

[0034] Figure 3 These are the morphology SEM images and ice crystal growth trend diagrams of the sugarcane fiber composite thermal insulation material and the pure bacterial cellulose aerogel comparison sample of the present invention, a is the SEM image of the pure bacterial cellulose aerogel; b is the SEM image of the composite thermal insulation material with a mass ratio of sugarcane fiber of 2; c is the ice crystal growth trend diagram during the formation process of Figure a; d is the ice crystal growth trend diagram during the formation process of Figure b. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0036] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0037] The present invention discloses a method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth, comprising the following steps:

[0038] S1. Grinding, screening, removing impurities and drying sugarcane waste to obtain sugarcane fiber raw materials;

[0039] S2. dispersing 0-3% by weight of sugarcane fiber in the bacterial cellulose hydrogel to obtain multiple groups of sugarcane fiber bacterial cellulose gel suspensions;

[0040] S3, homogenizing the sugarcane fiber bacterial cellulose gel suspensions with different mass proportions to obtain multiple groups of homogenized sugarcane fiber bacterial cellulose gel suspensions;

[0041] S4, arranging different groups of sugarcane fiber bacterial cellulose gel suspensions in a preset spatial configuration and directionally freezing them, so that ice crystals grow independently with the assistance of the sugarcane fibers, forming a sugarcane fiber bacterial cellulose gel with a continuous gradient;

[0042] S5, vacuum drying the frozen multiple groups of sugarcane fiber bacterial cellulose gel suspensions to form multiple groups of sugarcane fiber bacterial cellulose gel freeze-dried materials;

[0043] S6. heat-setting the multiple groups of sugarcane fiber bacterial cellulose gel freeze-dried materials.

[0044] The raw materials used in the present invention are all purchased from the market. For example, bacterial cellulose comes from Shansi Technology, and bagasse comes from a bamboo cane planting base.

[0045] The technical solution of the present invention is further illustrated by the following examples.

[0046] Example 1

[0047] A method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth comprises the following steps:

[0048] Weigh 1 part of sugarcane fiber and 99 parts of bacterial cellulose hydrogel (cellulose content: 1%, diameter: 15 nm), and mix the two to form a sugarcane fiber bacterial cellulose gel suspension;

[0049] Use a homogenizer to mix the two thoroughly at a stirring speed of 10,000 r / min for 8 minutes;

[0050] The homogenized sugarcane fiber bacterial cellulose gel suspension is transferred into a cylindrical mold for directionally freezing. The bottom opening of the selected mold is directly in contact with the cold source and the material is polytetrafluoroethylene.

[0051] The directional freezing temperature was -60°C and the freezing rate was 0.7°C / min, and a frozen material of sugarcane fiber bacterial cellulose gel with ice crystals was obtained, which was placed in a vacuum dryer at a temperature of -45°C for 48 hours to obtain a freeze-dried material of sugarcane fiber bacterial cellulose gel;

[0052] The freeze-dried sugarcane fiber bacterial cellulose gel freeze-dried material is placed in an oven for drying at a temperature of 100° C. for 24 hours to obtain a sugarcane fiber composite thermal insulation material.

[0053] Example 2

[0054] A method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth comprises the following steps:

[0055] Weigh 2 parts of sugarcane fiber and 98 parts of bacterial cellulose hydrogel (cellulose content: 1%, diameter: 15 nm), and mix the two to form a sugarcane fiber bacterial cellulose gel suspension;

[0056] Use a homogenizer to mix the two thoroughly at a stirring speed of 10,000 r / min for 8 minutes;

[0057] The homogenized sugarcane fiber bacterial cellulose gel suspension is directionally frozen at a freezing temperature of -60°C to obtain a sugarcane fiber bacterial cellulose gel frozen material with ice crystals, which is then placed in a vacuum dryer at a temperature of -45°C for 48 hours to obtain a sugarcane fiber bacterial cellulose gel freeze-dried material;

[0058] The freeze-dried sugarcane fiber bacterial cellulose gel freeze-dried material is placed in an oven for drying at a temperature of 100° C. for 24 hours to obtain a sugarcane fiber composite thermal insulation material.

[0059] Example 3

[0060] A method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth comprises the following steps:

[0061] Weigh 3 parts of sugarcane fiber and 97 parts of bacterial cellulose hydrogel (cellulose content: 1%, diameter: 15 nm), and mix the two to form a sugarcane fiber bacterial cellulose gel suspension;

[0062] Use a homogenizer to mix the two thoroughly at a stirring speed of 10,000 r / min for 8 minutes;

[0063] The homogenized sugarcane fiber bacterial cellulose gel suspension is transferred into a cylindrical mold for directionally freezing. The bottom opening of the selected mold is directly in contact with the cold source and the material is polytetrafluoroethylene.

[0064] The directional freezing temperature was -60°C and the freezing rate was 0.7°C / min, and a frozen material of sugarcane fiber bacterial cellulose gel with ice crystals was obtained, which was placed in a vacuum dryer at a temperature of -45°C for 48 hours to obtain a freeze-dried material of sugarcane fiber bacterial cellulose gel;

[0065] The freeze-dried sugarcane fiber bacterial cellulose gel freeze-dried material is placed in an oven for drying at a temperature of 100° C. for 24 hours to obtain a sugarcane fiber composite thermal insulation material.

[0066] Comparative Example 1

[0067] The difference from Examples 1 to 3 is that sugarcane fiber is not used, and the bacterial cellulose aerogel is prepared by directional freezing.

[0068] The parts mentioned above are all parts by mass.

[0069] The thermal conductivity and compressive strength data of the sugarcane fiber composite thermal insulation materials in Examples 1 to 3 and the bacterial cellulose aerogel in Comparative Example 1 are shown in Table 1.

[0070] Table 1 Thermal conductivity and compressive strength data of composite insulation materials and aerogels

[0071] Serial number Thermal conductivity (W / (m·K)) Compressive strength (MPa) Material diameter (m) Example 1 0.033 0.37 0.03 Example 2 0.036 0.41 0.03 Example 3 0.048 0.51 0.03 Comparative Example 1 0.029 0.21 0.03

[0072] Comparative analysis of experimental results shows that the addition of sugarcane fiber to the materials of Examples 1-3 significantly increases the compressive strength at a 20% compression deformation. The compressive strength of Examples 1-3 increases by 76%, 75%, and 143%, respectively, compared to Comparative Example 1. Simultaneously, the thermal conductivity of the materials does not increase significantly. At room temperature (20°C), the thermal conductivity of Examples 1-3 increases by 13%, 24%, and 65%, respectively, compared to Comparative Example 1. This demonstrates that by modifying the preset spatial configuration and then performing directional freezing, ice crystals grow independently with the assistance of sugarcane fiber, achieving synergistic regulation of thermal performance within a given mass range. This demonstrates the competitive thermal performance mechanism of sugarcane fiber composite insulation materials. When the sugarcane fiber mass fraction is increased from 2 to 3, the thermal conductivity differs significantly from that when the sugarcane fiber mass fraction is increased from 1 to 2. Despite the directional freezing technique, the aerogel no longer forms ordered pores, and its anisotropic structure is destroyed.

[0073] In summary, the present invention uses waste sugarcane bagasse as raw material, has a simple preparation process, solves the problems of poor durability and complex process of traditional bacterial cellulose aerogel, and provides high-performance thermal insulation materials for low-temperature storage and transportation, building energy conservation and other fields.

[0074] The above description is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principles of the present invention. These improvements and changes are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth, characterized in that: The following steps are included: S1. Grinding, screening, removing impurities and drying sugarcane waste to obtain sugarcane fiber raw materials; S2. dispersing 0-3% by weight of sugarcane fiber in the bacterial cellulose hydrogel to obtain multiple groups of sugarcane fiber bacterial cellulose gel suspensions; S3, homogenizing the sugarcane fiber bacterial cellulose gel suspensions with different mass proportions to obtain multiple groups of homogenized sugarcane fiber bacterial cellulose gel suspensions; S4, arranging different groups of sugarcane fiber bacterial cellulose gel suspensions in a preset spatial configuration and directionally freezing them, so that ice crystals grow independently with the assistance of the sugarcane fibers, forming a sugarcane fiber bacterial cellulose gel with a continuous gradient; S5, vacuum drying the frozen multiple groups of sugarcane fiber bacterial cellulose gel suspensions to form multiple groups of sugarcane fiber bacterial cellulose gel freeze-dried materials; S6. heat-setting the multiple groups of sugarcane fiber bacterial cellulose gel freeze-dried materials.

2. The method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth according to claim 1, characterized in that: In the step S1, the sugarcane fiber serves as an ice crystal nucleating agent and a reinforcing skeleton.

3. The method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth according to claim 1, characterized in that: In step S2, the bacterial cellulose hydrogel has a cellulose content of 1% and a diameter of 15 nm.

4. The method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth according to claim 1, characterized in that: In step S3, the speed of the homogenization treatment is 8000-12000 r / min, and the stirring time is 5-10 minutes.

5. The method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth according to claim 1, characterized in that: In step S4, directional freezing is performed in a temperature-controlled mold, and the mold includes a single-directional heat-conducting substrate.

6. The method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth according to claim 1, characterized in that: In step S4, directional freezing means freezing the sugarcane fiber bacterial cellulose gel suspension under controlled conditions so that ice crystals grow in a single direction, with a freezing temperature of -80 to -60°C and a freezing rate of 0.6 to 1°C / min.

7. The method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth according to claim 2, characterized in that: In step S5, the vacuum drying temperature is -45°C and the time is 48 to 72 hours.

8. The method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth according to claim 1, characterized in that: In step S6, the freeze-dried material is heat-set by drying it in a drying oven at a temperature of 100° C. for 24 hours.

9. The method for preparing a sugarcane fiber composite thermal insulation material based on controllable ice crystal growth according to claim 1, characterized in that: The sugarcane fiber in the sugarcane fiber composite thermal insulation material can be made of bamboo or wood fiber materials.

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