A starch-based foamed material and a method for preparing the same

Abstract

The application discloses a starch-based foaming material and a preparation method thereof. The method comprises the following steps: mixing starch, polylactic acid, chitosan, a nucleating agent and an additive to obtain a first mixture; adding a plasticizer and water into the first mixture to obtain a second mixture; plasticizing the second mixture to form a continuous melt; adding an isocyanate chain extender into the melt to form a high-viscosity melt; and foaming the high-viscosity melt to obtain the starch-based foaming material. The method fundamentally eliminates the uneven gelation and crystal point defects commonly seen in traditional processes, and ensures the stability and uniformity of the quality of the final material.

Description

Technical Field

[0001] This application relates to the field of foaming materials technology, specifically to a starch-based foaming material and its preparation method. Background Technology

[0002] Starch, as a natural polymer material, has advantages such as wide availability, renewability, and biodegradability, and has broad application prospects in packaging materials, cushioning materials, and other fields. Starch foam materials, by introducing a bubble structure into the starch matrix, can achieve lightweighting and functionalization of materials, and represent an important direction for replacing traditional petroleum-based foam materials.

[0003] Due to the short molecular chains and weak intermolecular forces of starch, the melt strength of pure starch matrix is ​​low, making it difficult to maintain a stable cell structure during foaming. Specifically, in the molten state, the viscoelasticity of starch melt is insufficient to effectively encapsulate and support the bubbles generated during foaming, leading to easy bubble rupture or coalescence and ultimately a low foaming ratio. Furthermore, the molded starch foam material suffers from insufficient internal cell wall strength, making it prone to cell collapse during cooling. This results in poor dimensional stability and decreased mechanical properties, limiting its widespread application.

[0004] To improve the performance of starch foaming materials, existing technologies typically employ chemical modification methods to enhance the melt strength of the starch matrix. One common method is to use isocyanate chain extenders (NCO chain extenders) to modify starch. NCO chain extenders react with the hydroxyl groups on starch molecular chains, forming cross-linked or extended chain structures between molecular chains, thereby increasing melt strength. However, NCO chain extenders have high reactivity. When mixed with starch, if the dispersion is uneven or the reaction conditions are not properly controlled, high-concentration areas can easily form locally, triggering explosive cross-linking reactions. This leads to a sudden surge in melt torque and the formation of difficult-to-eliminate crystal points, lumps, and gel particles in the product, severely damaging the uniformity of the foam cells.

[0005] Currently, research on chain extender modification of starch-based materials mainly focuses on the selection of chain extenders and optimization of their addition amounts. However, effective technical solutions for achieving uniform dispersion and controllable release of chain extenders are still lacking. In existing technologies, chain extenders are usually added directly to the melt in liquid or powder form, which inevitably leads to explosive crosslinking caused by excessively high local concentrations. Although some studies have attempted to use layered graphene as a carrier to load isocyanate chain extenders to improve their dispersibility, or to prepare chain extenders in masterbatch form using polymer carriers, these technical solutions are mainly aimed at thermoplastic polymer systems such as polyester and polylactic acid, and there are no reports of their application to starch foaming material systems. Due to the significant differences between starch and the aforementioned polymers in terms of molecular structure, rheological behavior, and reaction characteristics, the above solutions are difficult to directly apply to starch foaming materials.

[0006] Therefore, there is an urgent need in this field to develop a technical solution that can achieve uniform dispersion and controllable release of NCO chain extenders in starch matrix, so as to solve the technical problem of explosive cross-linking caused by excessively high local concentration of chain extenders in the existing technology, thereby obtaining starch foaming materials with uniform cell structure, high foaming ratio and excellent mechanical properties. Summary of the Invention

[0007] To address the aforementioned deficiencies in this field, this application aims to provide a starch-based foaming material and its preparation method.

[0008] According to one aspect of this application, a method for preparing a starch-based foaming material is provided, comprising: Starch, polylactic acid, chitosan, nucleating agent and additives are mixed to obtain the first mixture; The plasticizer is premixed with water and then added to the first mixture to obtain the second mixture; The second mixture is plasticized to form a continuous melt; Adding isocyanate chain extenders to the melt creates a high-viscosity melt. The starch-based foamed material is prepared by foaming a high-viscosity melt.

[0009] According to some embodiments of this application, starch, polylactic acid, chitosan, nucleating agent, and additives are mixed to obtain a first mixture, comprising: Starch, polylactic acid, chitosan with a degree of deacetylation of 85% to 95%, nucleating agent, lubricant and antioxidant are mixed to obtain the first mixture.

[0010] According to some embodiments of this application, after premixing the plasticizer with water, it is added to the first mixture to obtain a second mixture, comprising: The plasticizer is premixed with water and then evenly sprayed into the first mixture through a spraying device. The mixing temperature is controlled at 80~100℃ and the mixing time is 8~12 minutes until the water is completely coated by the plasticizer, and the material is loose flocculent or granular with no free water precipitated.

[0011] According to some embodiments of this application, an isocyanate chain extender is added to the melt to form a high-viscosity melt, including: Asymmetric isocyanate chain extenders are added to the melt, and the chain extension reaction is completed by shearing and dispersing the asymmetric isocyanate chain extenders within 10 to 30 seconds to form a high-viscosity melt.

[0012] According to some embodiments of this application, plasticizing the second mixture to form a continuous melt includes: The second mixture is plasticized at 90~130°C to form a continuous melt.

[0013] According to some embodiments of this application, a starch-based foamed material is prepared by foaming a high-viscosity melt, including: High-viscosity melt is foamed at 140~150℃ and 10~15MPa; after depressurization, the temperature is controlled at 130~140℃ to obtain starch-based foamed material.

[0014] According to another aspect of this application, a starch-based foaming material prepared by the above preparation method is also provided, which is prepared from raw materials comprising the following parts by weight: 50-70 parts starch; Polylactic acid 10-25 parts; 3-10 parts chitosan; Plasticizer 15-30 parts; 10-25 parts water; 2-6 parts of isocyanate chain extender; Nucleating agent 0.5-3 parts; Additives: 1-3 parts.

[0015] According to some embodiments of this application, the isocyanate chain extender is an asymmetric isocyanate chain extender.

[0016] According to some embodiments of this application, the isocyanate chain extender is hydrogenated toluene diisocyanate.

[0017] According to some embodiments of this application, the plasticizer includes glycerin.

[0018] According to some embodiments of this application, the starch is selected from tapioca starch or corn starch.

[0019] According to some embodiments of this application, the nucleating agent is selected from: talc powder or nano-calcium carbonate.

[0020] According to some embodiments of this application, the additives include lubricants and antioxidants.

[0021] Compared with the prior art, this application has at least the following beneficial effects: This application provides a starch-based foaming material. By introducing chitosan and pre-dispersing it in a starch matrix, the highly active amino groups on the chitosan molecular chain serve as preferential reaction sites for isocyanate chain extenders (NCO chain extenders), effectively guiding the chain extension reaction to occur uniformly at the microscale. This strategy successfully avoids the local enrichment and explosive reaction of NCO groups in the starch system, fundamentally eliminating the uneven gelation and crystal point defects common in traditional processes, ensuring the stability and uniformity of the final material quality. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the preparation process of starch-based foaming material according to an example embodiment of this application.

[0023] Figure 2 This is a process flow diagram for preparing a starch-based foaming material according to another embodiment of this application. Detailed Implementation

[0024] The technical solution of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] It should be particularly noted that similar substitutions and modifications made to this application are obvious to those skilled in the art, and they are all considered to be included in this application. Those skilled in the art can obviously make modifications or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this application to implement and apply the technology of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0026] Unless otherwise specified, this application is conducted under standard conditions or conditions recommended by the manufacturer. The raw materials or excipients used, as well as the reagents or instruments used, whose manufacturers are not specified, are all conventional products that can be obtained commercially.

[0027] The following is a detailed description of this application.

[0028] Currently, to improve the performance of starch foaming materials, existing technologies typically employ chemical modification methods to enhance the melt strength of the starch matrix. For example, one approach uses a blocked isocyanate chain extender to address the rapid gelation problem by 'masking' the active groups. However, this approach requires the introduction of additional blocking and deblocking chemical reactions to control the reaction rate, resulting in an extremely complex preparation process; furthermore, the blocking agents used (such as oximes or pyrazole derivatives with specific structures) are expensive, significantly increasing the overall cost of the additives.

[0029] This application finds that the prior art has the following main drawbacks: Uneven dispersion of chain extenders can easily lead to the formation of localized high-concentration areas in the starch matrix, resulting in explosive cross-linking and the formation of gel agglomerates, which seriously affects the cell uniformity and mechanical properties of foamed products.

[0030] The processing window is narrow, the chain extension reaction rate is difficult to control, excessive cross-linking occurs when the temperature is slightly high, and insufficient chain extension occurs when the temperature is too low, so the melt strength cannot be effectively improved.

[0031] Foamed products have uneven cell size distribution, with cell diameter variation coefficient (CV) typically exceeding 30%, poor density control accuracy, and low product quality stability.

[0032] This application aims to solve the technical problems existing in the chain extension modification process of starch-based foaming materials, such as the easy local aggregation of NCO chain extenders, which leads to uneven gelation and crystal point defects in the material, as well as the resulting insufficient melt strength, low foaming ratio, uneven cell structure and poor dimensional stability.

[0033] In some examples, such as Figure 1 As shown, the preparation method of the starch-based foaming material of this application includes: Step S110: Mix starch, polylactic acid, chitosan, nucleating agent and additives to obtain a first mixture; Step S120: After premixing the plasticizer with water, add it to the first mixture to obtain the second mixture; Step S130: Plasticize the second mixture to form a continuous melt; Step S140: Add isocyanate chain extenders to the melt to form a high-viscosity melt; Step S150: Prepare the starch-based foamed material from the high-viscosity melt.

[0034] In some optional embodiments, starch, polylactic acid, chitosan, a nucleating agent, and an additive are mixed to obtain a first mixture comprising: Starch, polylactic acid, chitosan with a degree of deacetylation of 85% to 95%, nucleating agent, lubricant and antioxidant are mixed to obtain the first mixture.

[0035] In some optional embodiments, the plasticizer is premixed with water and then added to the first mixture to obtain a second mixture, comprising: The plasticizer is premixed with water and then evenly sprayed into a mixer containing the first mixture through a spraying device. The temperature inside the mixer is controlled at 80~100℃ and the mixing time is 8~12 minutes until the water is completely coated by the plasticizer, and the material is loose flocculent or granular with no free water precipitated.

[0036] In some optional embodiments, isocyanate chain extenders are added to the melt to form a high-viscosity melt, including: Asymmetric isocyanate chain extenders are added to the melt, and the chain extension reaction is completed by shearing and dispersing the asymmetric isocyanate chain extenders within 10 to 30 seconds to form a high-viscosity melt.

[0037] In some alternative embodiments, a high-viscosity melt is foamed to obtain a starch-based foam material, comprising: High-viscosity melt is foamed at 140~150℃ and 10~15MPa; after depressurization, the temperature is controlled at 130~140℃ to obtain starch-based foamed material.

[0038] Further optional, such as Figure 2 As shown, the preparation method of the starch-based foaming material of this application includes the following steps: Step S1 Premixing and Water Locking: Starch, PLA, chitosan, nucleating agent, and processing aids are added to a high-speed mixer to obtain the first mixture. Plasticizer and water are premixed and evenly sprayed into the mixer using a spray device. The temperature inside the mixer is controlled at 80~100℃, and the mixing time is 8~12 minutes, until the water is completely coated by the plasticizer, the material is loose and flocculent or granular, and no free water is released, thus obtaining the second mixture (premix).

[0039] Step S2: Low-Temperature Chain Extension: Add the second mixture to the main feed port of the twin-screw extruder, and control the temperature of zones 1 to 5 (low-temperature chain extension section) of the extruder to be 90~130℃. After the material is completely plasticized to form a continuous melt, inject HTDI into the melt through the side feed port. The injection port is located in zone 5 of the extruder (rear end of the melting section), and a strong shear kneading block must be installed downstream of the injection port to ensure that HTDI is sheared and dispersed within 10~30 seconds and completes the chain extension reaction to form a high melt strength network.

[0040] Step S3 High-Temperature Foaming: The high-viscosity melt after chain extension is conveyed forward to the high-temperature zone. The temperature in zones 6 to 10 of the extruder (high-temperature foaming section) is controlled at 140~150℃, while maintaining the melt pressure inside the barrel at 10~15 MPa to prevent premature boiling of water inside the barrel. At this time, the high-strength melt network wraps around the water like a balloon skin, and the water vaporizes upon heating, forming a large number of micronuclei on the surface of the nucleating agent.

[0041] Step S4 Extrusion and Shaping: The high-pressure melt is instantly depressurized through a specific flow channel die. The temperature of zone 11 and the die head is controlled at 130~140℃. Water vapor expands rapidly, forming a high foaming ratio material. After extrusion, it is immediately shaped by air cooling or water cooling, with the traction speed matched to the extrusion speed, and finally pelletized or wound.

[0042] In some examples, the starch-based foaming material of this application is prepared from raw materials comprising the following parts by weight: 50-70 parts starch; Polylactic acid 10-25 parts; 3-10 parts chitosan; Plasticizer 15-30 parts; 10-25 parts water; 2-6 parts of isocyanate chain extender; Nucleating agent 0.5-3 parts; Additives: 1-3 parts.

[0043] In some optional embodiments, the degree of deacetylation of the chitosan in this application is 85% to 95%. As a core additive, chitosan not only utilizes the preferential reaction of amino groups with HTDI to guide the chain extension process and prevent the premature reaction of NCO groups with water, but also acts as an organic nucleating agent to refine the pores and improve the toughness and barrier properties of the material.

[0044] In some alternative embodiments, water is used as the sole physical foaming agent in this application, and foaming is achieved using the latent heat of vaporization; high water content is the key to this application's breakthrough of traditional limitations.

[0045] In some optional embodiments, the isocyanate chain extender is hydrogenated toluene diisocyanate (HTDI), which contains asymmetric NCO groups in its molecular structure. The para-position NCO has higher activity and preferentially reacts with NH, while the ortho-position NCO has lower activity due to steric hindrance and reacts with OH. It is used to connect starch, PLA and chitosan to build a three-dimensional network and significantly improve melt strength.

[0046] In some alternative embodiments, the starch is selected from tapioca starch or corn starch, serving as a continuous phase matrix to provide a foaming framework.

[0047] In some alternative embodiments, polylactic acid (PLA) is used as a reinforcing phase to provide rigidity and heat resistance, forming an interpenetrating network with starch to improve mechanical properties.

[0048] In some alternative embodiments, the plasticizer, preferably glycerol, is used as a processing aid; its function is to lower the glass transition temperature of starch to plasticize it and to physically encapsulate moisture to prevent premature evaporation.

[0049] In some alternative embodiments, the nucleating agent, selected from talc or nano-calcium carbonate, serves as a pore regulator to provide heterogeneous nucleation sites.

[0050] In some alternative embodiments, the additives serve as stabilizers, including lubricants (such as calcium stearate) and antioxidants, to prevent thermal degradation during processing.

[0051] The technical solution of this application will be further described below with reference to specific embodiments.

[0052] Example 1 This embodiment provides a high-performance starch-based foaming material and its preparation method.

[0053] Formula composition (parts by weight): 60 parts tapioca starch, 10 parts polylactic acid (PLA), 10 parts chitosan (90% degree of deacetylation), 20 parts glycerol, 20 parts deionized water, 4 parts hydrogenated toluene diisocyanate (HTDI), 1.5 parts nano talc, and 1 part calcium stearate.

[0054] Preparation process: Tapioca starch, PLA, chitosan, and nano talc are added to a high-speed mixer and heated to 90°C. Glycerin and water are mixed and then added to the mixer through an atomizing spray device. The mixture is mixed for 8 minutes to obtain a premix without free water, which is then sealed for later use.

[0055] A twin-screw extruder with a length-to-diameter ratio of 48:1 is used. The premixed material is fed into the self-feeding port. In zone 5 (temperature set at 130°C), HTDI preheated to 55°C is injected through the side feed port, and three sets of strong shear kneading blocks downstream are used to enhance dispersion and reaction. The temperature in zones 6 to 10 of the barrel is controlled between 140°C and 146°C, and the die head temperature is set at 135°C. The melt pressure is maintained at approximately 12 MPa throughout the process. The high-pressure melt is instantly depressurized and foamed through the die head, and then pelletized after being shaped and cooled by three rollers.

[0056] Performance test results: The material prepared in this embodiment exhibits excellent overall performance. The melt strength reaches 19.2 N, and the foaming ratio reaches 41 times. Microstructurally, the cells are uniform and dense, with diameters ranging from 100 to 200 micrometers. The material is flexible to the touch, and its dimensional change rate after 7 days of constant temperature and humidity aging is less than 3%.

[0057] Example 2: Low Chitosan Scheme Formula composition (parts by weight): 65 parts tapioca starch, 10 parts PLA, 5 parts chitosan (90% deacetylation), 20 parts glycerol, 20 parts deionized water, 4 parts HTDI, 1.5 parts nano talc, and 1 part calcium stearate.

[0058] The preparation process is the same as in Example 1.

[0059] Performance test results: Performance tests show that the melt strength of this scheme is 10.5 N, and the foaming ratio is 28 times. The cell diameter is distributed between 150 and 300 micrometers, and the 7-day size change rate is 4.2%. Although the performance data are lower than those of Example 1, they are still significantly better than the traditional chemical-free chain extender technology.

[0060] Example 3: Low Starch Content Scheme Formula composition (parts by weight): 50 parts tapioca starch, 20 parts PLA, 10 parts chitosan (90% deacetylation), 20 parts glycerol, 10 parts deionized water, 4 parts HTDI, 1.5 parts nano talc, and 1 part calcium stearate.

[0061] The preparation process is the same as in Example 1.

[0062] Performance test results: The melt strength of this solution is 16.8 N, and the foaming ratio is 28 times. The cell diameter is distributed between 80 and 150 micrometers, and the 7-day dimensional change rate is 7.6%.

[0063] Example 4: CHDI chain extender scheme Formulation composition: The chain extender is replaced with cyclohexane-1,4-diisocyanate (CHDI), and the rest of the formulation and process are the same as in Example 1.

[0064] Performance test results: Due to differences in the activity of chain extenders, although chitosan was introduced, its function was not fully realized. The final melt strength was measured to be 13.3 N, and the foaming ratio was 20 times.

[0065] Comparative Example 1: Traditional chain extension scheme without chitosan This comparative example removed the chitosan component and increased the amount of HTDI to 8 parts in an attempt to compensate for the loss of strength. The rest of the formulation and process were the same as in Example 1.

[0066] Performance test results: Due to the lack of chitosan's dispersing and guiding effect on the chain extension reaction, HTDI underwent localized explosive crosslinking in the system. Test results showed that the melt strength was only 2.8N, and obvious crystal points and gel particles appeared on the surface of the product. The foaming ratio was only 3.5 times, with severe cell rupture and merging. After 7 days, the dimensional change rate was as high as 18.7%, and cooling collapse was obvious.

[0067] Comparative Example 2: No Premixing Scheme The formulation composition is the same as in Example 1, but the chitosan and starch are not completely mixed in the preparation process.

[0068] Performance test results: Due to uneven mixing, although chitosan was introduced, its function was not fully realized. The coefficient of variation of cell diameter exceeded 35%, the distribution was extremely uneven, the cross-section was rough, and a small amount of gel particles were still present.

[0069] Comparative Example 3: Pure physical foaming scheme without chain extenders This comparative example omits the HTDI chain extender, while the rest of the formulation is the same as in Example 1. The difference in the preparation process is that only simple melt blending and extrusion foaming are performed.

[0070] Performance test results: Due to the lack of a chemically extended chain network, the starch melt strength is extremely low, only 1.5N, and cannot encapsulate air bubbles. Moisture vaporizes and escapes directly inside the barrel, resulting in a foaming ratio of only 2 times, and failing to form an effective cell structure.

[0071] Comparative Example 4: Epoxy Chain Extender Scheme Formula composition (parts by weight): 60 parts tapioca starch, 10 parts polylactic acid (PLA), 10 parts chitosan (90% deacetylation), 20 parts glycerol, 20 parts deionized water, 4 parts epoxy chain extender (ADR-4370S), 1.5 parts nano talc, and 1 part calcium stearate.

[0072] The preparation process is the same as in Example 1.

[0073] Performance test results: The melt strength of this solution is 3.2 N, and the foaming ratio is 6.5 times. The comparative example has poor melt strength, a rough extruded surface with obvious "orange peel" texture, and some areas show broken and fused bubbles. The cell sizes are inconsistent, with some cells exceeding 500 μm in diameter and extremely thin walls, resulting in multiple ruptures. Under high temperature and high water content conditions, the melt strength increase rate of this comparative example is lower than the water vaporization rate, leading to bubble wall rupture and gas escape.

[0074] Comparative Example 5: Low Water Content Scheme In this comparative formulation, the amount of water added is 5 parts, and the other formulations and preparation processes are the same as in Example 1.

[0075] Performance test results: melt strength 18.8 N, foaming ratio 8.5 times. However, due to a severe deficiency in the amount of foaming agent (water), the generated steam pressure was insufficient, resulting in dense and hard extruded samples with extremely small and few cells in the cross-section, making them more like solid plastics.

[0076] Comparative Example 6: The amount of chitosan added was lower than the limit specified in this application. The formulation and process of this comparative example are the same as those of Example 1, except that the amount of chitosan added is 2 parts.

[0077] Performance test results: melt strength 10.5 N, foaming ratio 12 times. Due to insufficient chitosan content to cover all HTDI reaction sites, slight gelation still occurred in some areas, and the chain extension guiding effect failed.

[0078] Comparative Example 7: The amount of chitosan added exceeded the limits specified in this application. The formulation and process of this comparative example are the same as those of Example 1, except that the amount of chitosan added is 15 parts.

[0079] Performance test results: Melt strength 19.5 N, foaming ratio 32 times. Extruded sample surface smooth, without crystal points or gel. Excess chitosan increases melt rigidity and reduces melt elongation.

[0080] Comparative Example 8: Different order of chitosan addition The formulation is the same as in Example 1.

[0081] The difference in the preparation process is that chitosan is added after the chain extender.

[0082] Performance test results: Melt strength 7.2 N, foaming ratio 9.2 times. Cell size is extremely uneven, with a large number of fused cells (bubble merging).

[0083] Based on the above embodiments and comparative data, it can be seen that the beneficial effects of the starch-based foaming material and its preparation method of this application include at least one of the following: Excellent material homogeneity, completely eliminating processing defects: This application introduces chitosan and pre-disperses it in a starch matrix, utilizing the highly active amino groups on the chitosan molecular chain as preferential reaction sites for NCO chain extenders, effectively guiding the chain extension reaction to occur uniformly at the microscale. This strategy successfully avoids the local enrichment and explosive reaction of NCO groups in the starch system, fundamentally eliminating the uneven gelation and crystal point defects common in traditional processes, ensuring the stability and uniformity of the final material quality.

[0084] Significantly improved melt strength and broadened thermal processing window: This application utilizes the characteristic that the reactivity of chitosan amino groups with NCO groups is much higher than that of starch hydroxyl groups to construct a stable chain-extended network of "starch-chitosan-NCO" with high reactivity selectivity. Compared with the control group without chitosan (melt strength <3 N), the material prepared in this application has a melt strength of over 5 N, an increase of more than 70%. This significant enhancement greatly improves the rheological properties of starch melt, making it more suitable for thermal processing processes such as high-temperature foaming and extrusion.

[0085] Excellent foaming performance and controllable cell structure: The dense extended chain network significantly increases the entanglement density and interaction force between starch molecular chains, significantly improving the melt's ability to encapsulate bubbles and resist gas escape during the foaming process. This allows the material's foaming ratio to jump from less than 5 times in existing technologies to 10-30 times, while the average cell diameter is controlled within the range of 100-300 μm and is uniformly distributed, achieving a balance between high foaming capacity and microporous structure.

[0086] Excellent dimensional stability and strong anti-collapse performance: The stable chemical chain-extended structure endows the cell walls with sufficient structural strength, enabling them to support the internal gas pressure of the cells for a long time, effectively inhibiting cell collapse and shrinkage during material cooling and shaping and subsequent storage. Testing showed that the dimensional change rate of the material after 7 days of constant temperature and humidity aging was reduced from >15% in the prior art to <5%, significantly improving the dimensional accuracy and reliability of the product.

[0087] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of this application. It should be noted that, for those skilled in the art, several improvements and modifications can be made to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A method for preparing a starch-based foaming material, characterized in that, include: Starch, polylactic acid, chitosan, nucleating agent and additives are mixed to obtain the first mixture; The plasticizer is premixed with water and then added to the first mixture to obtain the second mixture; The second mixture is plasticized to form a continuous melt; Add isocyanate chain extenders to the melt to form a high-viscosity melt; The starch-based foamed material is obtained by foaming the high-viscosity melt.

2. The preparation method according to claim 1, characterized in that, Starch, polylactic acid, chitosan, nucleating agent, and additives are mixed to obtain a first mixture, comprising: Starch, polylactic acid, chitosan with a deacetylation degree of 85%–95%, nucleating agent, lubricant, and antioxidant are mixed to obtain a first mixture; and / or After premixing the plasticizer with water, it is added to the first mixture to obtain a second mixture, comprising: The plasticizer is premixed with water and then evenly sprayed into the first mixture through a spraying device. The mixing temperature is controlled at 80~100℃ and the mixing time is 8~12 minutes until the water is completely coated by the plasticizer, and the material is loose flocculent or granular with no free water precipitated.

3. The preparation method according to claim 2, characterized in that, Adding isocyanate chain extenders to the melt to form a high-viscosity melt includes: An asymmetric isocyanate chain extender is added to the melt, and the asymmetric isocyanate chain extender is sheared and dispersed within 10 to 30 seconds to complete the chain extension reaction, forming a high-viscosity melt.

4. The preparation method according to claim 3, characterized in that, Plasticizing the second mixture to form a continuous melt includes: The second mixture is plasticized at 90~130°C to form a continuous melt.

5. The preparation method according to claim 4, characterized in that, The starch-based foamed material is prepared by foaming the high-viscosity melt, comprising: The high-viscosity melt is foamed at 140-150°C and 10-15 MPa; after depressurization, the temperature is controlled at 130-140°C to obtain the starch-based foamed material.

6. A starch-based foaming material prepared by any one of the preparation methods according to claims 1-5, characterized in that, Prepared from raw materials comprising the following parts by weight: 50-70 parts starch; Polylactic acid 10-25 parts; 3-10 parts chitosan; Plasticizer 15-30 parts; 10-25 parts water; 2-6 parts of isocyanate chain extender; Nucleating agent 0.5-3 parts; Additives: 1-3 parts.

7. The starch-based foaming material according to claim 6, characterized in that, The isocyanate chain extender is an asymmetric isocyanate chain extender; The isocyanate chain extender is hydrogenated toluene diisocyanate.

8. The starch-based foaming material according to claim 7, characterized in that, The starch is selected from: tapioca starch or corn starch; The plasticizer includes glycerin.

9. The starch-based foaming material according to claim 8, characterized in that, The nucleating agent is selected from talc or nano-calcium carbonate.

10. The starch-based foaming material according to claim 9, characterized in that, The additives include: lubricants and antioxidants.

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