A biodegradable precision casting water-soluble core mold material and a preparation method thereof

Abstract

This invention discloses a biodegradable water-soluble core mold material for precision casting and its preparation method. The material is composed of a chitosan-gelatin-polylactic acid ternary composite system, modified bamboo fiber, and a crosslinking agent. Through component screening and process optimization, the material achieves a synergistic improvement in mechanical properties while maintaining excellent water solubility (dissolution rate 0.5-0.8 g / min). Its flexural strength reaches 8-12 MPa, and its elongation at break reaches 30-50%, while also exhibiting good toughness and thermal stability (heat distortion temperature ≥60℃). This material is completely biodegradable, offering significant environmental advantages. It can replace traditional polyethylene glycol-based core mold materials and is widely used in precision casting in aerospace, automotive, and medical device fields, meeting the demands of green manufacturing.

Description

Technical Field

[0001] This invention belongs to the field of precision casting technology, and specifically relates to a water-soluble mandrel material for castings with complex internal cavities and its preparation method. This material is mainly used in precision casting processes in aerospace, automotive, and medical device industries, and can replace traditional polyethylene glycol-based mandrel materials, enabling green manufacturing. Background Technology

[0002] Precision casting is an indispensable process in modern manufacturing, especially suitable for producing metal parts with complex shapes and high dimensional accuracy. In investment casting, water-soluble core molding is typically used to form cavities with complex shapes or where draft angles are not permitted. Currently, the mainstream water-soluble core mold materials on the market are based on polyethylene glycol (PEG), combined with urea, sodium bicarbonate, and other components. Although PEG-based core mold materials are widely used, they face the following key technical challenges: Poor biodegradability: PEG is a petroleum-based chemical product, difficult to degrade in the natural environment, and does not meet the requirements of current green manufacturing and sustainable development. With increasingly stringent environmental regulations, traditional petroleum-based materials face increasing policy pressure. Performance defects: PEG materials suffer from poor heat resistance (heat distortion temperature only 55-60℃), insufficient toughness, and susceptibility to moisture absorption. When the molecular weight of PEG exceeds 2000, the viscosity of the melt slurry increases significantly, the filling performance decreases, and the increased defects in the billet lead to deteriorated performance.

[0003] In recent years, biodegradable materials have seen rapid development in packaging, agriculture, and other fields, providing new ideas for the innovation of precision casting core mold materials. Chitosan, a natural polysaccharide extracted from the shells of crustaceans such as shrimp and crab, possesses excellent biodegradability, biocompatibility, and water solubility, and is widely available and inexpensive. Through modification methods such as etherification and graft copolymerization, its mechanical properties and thermal stability can be significantly improved. Modified chitosan materials can achieve a tensile strength of 4-6 MPa and an elongation at break ≥20%, and its water solubility can be precisely controlled through modification. Gelatin, as a natural protein, has good film-forming properties and biodegradability. Commercial gelatin typically dissolves at 30-40℃ and forms a thermally reversible gel upon cooling, with a gelation point of 28-32℃. When soybean protein and gelatin are used in combination, with a mass ratio of 4:6 to 2:8, the tensile strength, elongation at break, and other properties of the composite film are close to those of pure gelatin films. Polylactic acid (PLA): PLA is a thermoplastic aliphatic polyester with good mechanical properties, biocompatibility, gloss, transparency, and heat resistance. PLA exhibits excellent mechanical properties, including a tensile strength of 40-60 MPa, a flexural strength of 60-90 MPa, and an elastic modulus of 3000-4000 MPa. However, its heat distortion temperature is only 55-60℃, making it prone to deformation at high temperatures. Modified bamboo fiber: As a natural renewable resource, bamboo fiber is characterized by high strength, high modulus, and complete biodegradability, and its cost is far lower than that of nanocellulose. After modification with a silane coupling agent, its compatibility with the matrix material can be significantly improved, enhancing the mechanical properties of the composite material.

[0004] Currently, patented technologies that systematically apply biodegradable materials to precision casting mandrels are still rare. Patent CN 119639159 A mentions an environmentally friendly thermoplastic melt-core material, a removable core, and its application. This material comprises 30-50% water-soluble thermoplastic polymer and 40-80% filler, with the filler being a bio-based additive. It has advantages such as injection molding capability, strength to support secondary molding, water solubility, bio-based composition, and biodegradability. CN117920946A mentions a high-performance precision casting silica sol shell with a smooth inner wall and its preparation method. Smoothness is improved by combining zirconium powder, white corundum powder, and silica particles, and performance is improved by using polyethylene fiber and boron nitride fiber in combination. These patented technologies provide important references for the development of biodegradable mandrel materials, but the following shortcomings still exist: the patents focus on the modification of traditional materials, with insufficient systematic research on biodegradable materials; the performance of existing biodegradable mandrel materials still lags behind traditional polyethylene glycol materials; and cost control and process adaptability need further optimization. Summary of the Invention

[0005] This invention provides a precision casting water-soluble core mold formulation based on biodegradable materials to solve the problems of poor biodegradability and performance defects of existing polyethylene glycol core mold materials.

[0006] The technical solution adopted in this invention is:

[0007] A biodegradable precision casting water-soluble core mold material, comprising the following components by mass percentage: Modified chitosan 30-50%, Gelatin 15-25%, Polylactic acid 10-20%, Modified bamboo fiber 3-8%, Crosslinking agent 2-5%, Plasticizer 5-10%, 3-8% cosolvent Other additives: 0.5-2%.

[0008] Preferably, the modified chitosan is 2-chloroethanol etherified modified chitosan, with a solubility in water at 25°C ≥30g / L, a water absorption rate of ≤10% after soaking in water at 25°C for 24 hours, and the mass percentage of modified chitosan is preferably 35-45%.

[0009] Preferably, the gelatin has a gel strength of 200-280 Bloom, a Blaine viscosity of 150-220 mPa•s, and a mass percentage of 18-22%.

[0010] Preferably, the polylactic acid is caprolactone-modified polylactic acid with a molecular weight of 100,000-200,000, a glass transition temperature of 60-65°C, and a preferred mass percentage of 12-18%.

[0011] Preferably, the modified bamboo fiber is bamboo fiber modified with silane coupling agent (KH-550), with an average length of 100-200 μm and a diameter of 10-20 μm, and the mass percentage of the modified bamboo fiber is preferably 4-6%.

[0012] Preferably, the crosslinking agent is polyethylene glycol diglycidyl ether (PEGDE), which contains two epoxy groups in its molecular structure, and the mass percentage of the crosslinking agent is preferably 2.5-4%.

[0013] A method for preparing a biodegradable precision casting water-soluble core mold material includes the following steps: Raw material pretreatment: Modified chitosan was placed in a forced-air drying oven and dried at 80-100℃ for 2-4 hours, stirring every 30 minutes to ensure complete removal of moisture. After drying, it was removed and cooled to room temperature for later use. Gelatin was added to deionized water at 40-50℃ and stirred at 20-30 r / min for 20-30 minutes until completely dissolved, forming a homogeneous solution with a concentration of 15-25%. It was then kept warm for later use. PLA was placed in a twin-screw extruder and melted at 60-70℃ for 15-20 minutes to ensure uniform melting. Modified bamboo fiber was placed in a vacuum drying oven and dried at 70-80℃ for 1-2 hours to remove surface-adsorbed moisture.

[0014] Slurry preparation: Preheat the core mixer to 75°C. First, add molten PLA and maintain a stirring speed of 30 r / min for 5 minutes. Then, slowly add the pretreated modified chitosan and stir for 10 minutes until evenly dispersed. Next, add the prepared gelatin solution and continue stirring for 10 minutes to fully integrate the system. Then, add the modified bamboo fiber, crosslinking agent PEGDE, plasticizer, and cosolvent in sequence, stirring for 5-8 minutes after each component is added to ensure uniform dispersion. Finally, turn on the vacuum system and evacuate to -0.08~-0.10 MPa, maintaining stirring for 30 minutes to remove air bubbles from the slurry, obtaining a uniform, bubble-free core mold slurry, ensuring good moldability.

[0015] Molding and processing: The hot-press injection molding process is used to inject the core mold slurry into a mold preheated to 10-20℃. The injection flow rate is controlled at 20-100 cc / s, the injection pressure at 1-5 MPa, and the injection time at 10-60 s. The injection parameters are adjusted according to the core mold size (low flow rate and short time for small core molds, and high flow rate and long time for large core molds). After injection, the pressure is maintained for 0.5-5 min to ensure that the slurry fully fills the mold cavity and reduces defects in the blank. After the pressure is maintained, the pressure is slowly released to avoid deformation of the blank.

[0016] Post-processing: After forming, the core mold blank is removed from the mold and placed at room temperature to cool and set for 30-60 minutes to allow the blank temperature to drop to room temperature and avoid cracking due to excessive cooling. Then, the blank is placed in a forced-air drying oven and dried at 40-50℃ for 24-48 hours, turning it over every 8 hours to ensure uniform drying and remove excess moisture from the blank. After drying, it is removed, cooled to room temperature, and after passing dimensional inspection and performance sampling, the final product is obtained.

[0017] The present invention has the following beneficial effects: This invention achieves a fully bio-based raw material system with outstanding environmental benefits. It abandons traditional petroleum-based polyethylene glycol and uses modified chitosan, gelatin, polylactic acid, and modified bamboo fiber as core components, all of which are 100% bio-based and fully biodegradable. Testing shows that the material of this invention has a biodegradability rate of over 65% after 100 days, far exceeding that of traditional PEG materials (<5%). Compared with traditional PEG materials, the total life-cycle carbon footprint is expected to be reduced by more than 70%, and production energy consumption by 40%, fundamentally solving the environmental pollution problem of core mold materials in the foundry industry and meeting the green manufacturing requirements under the "dual carbon" target.

[0018] A "ternary composite + synergistic reinforcement" system was constructed, significantly improving overall performance. Breaking away from traditional single or two-component biomaterial systems, an innovative "chitosan-gelatin-polylactic acid" ternary composite system was developed, reinforced with modified bamboo fiber. Through the synergistic effect between components, an excellent balance of water solubility, strength, toughness, and thermal stability was achieved. High strength and high toughness are both achieved. By combining rigid polylactic acid with flexible gelatin and chitosan, combined with the reinforcing effect of modified bamboo fiber, the contradiction of traditional bio-based materials being "strong but not tough" or "tough but not strong" is effectively solved. The material possesses excellent deformation capacity while withstanding large loads, effectively avoiding the risk of brittle fracture of the mandrel during handling, assembly, and casting. Heat resistance is significantly improved: the introduction of polylactic acid and its synergistic effect with the cross-linked network structure effectively compensates for the insufficient thermal stability of the chitosan / gelatin system. The higher heat distortion temperature ensures that the mandrel maintains shape stability during subsequent high-temperature processes such as wax molding and dewaxing, improving the dimensional accuracy of the casting. With controllable water solubility to meet process requirements, it maintains a good water solubility rate while significantly improving mechanical properties, meeting the process requirement of rapid removal of the core mold after casting, and avoiding the problem of sacrificing core removal efficiency in pursuit of strength.

[0019] Polyethylene glycol diglycidyl ether was selected as an environmentally friendly crosslinking agent. Its diepoxy groups can react with the amino and hydroxyl groups on the chitosan and gelatin molecular chains to construct a stable three-dimensional network structure. This crosslinking structure significantly improves the mechanical strength and water resistance of the material, solving the key problems of poor formability and easy water absorption and deformation of chitosan materials. On the other hand, since its crosslinking bonds can still be hydrolyzed under certain conditions, it will not affect the final biodegradability of the material. At the same time, bamboo fiber modified with silane coupling agent was used as a reinforcing phase. Not only does its high strength and high modulus significantly improve the mechanical properties of the composite material (when the bamboo fiber content is 5%, the tensile strength of the composite material can reach 14.0 MPa and the Young's modulus can reach 185.2 MPa), but bamboo fiber is also a renewable resource, and its cost is much lower than that of nanocellulose, which is conducive to the industrialization and promotion of the technology. Detailed Implementation

[0020] The present invention will be further described below with reference to embodiments.

[0021] Example 1: Formulation (by weight): Modified chitosan: 40%; Gelatin: 20%; Modified PLA: 15%; Modified bamboo fiber: 5%; PEGDE crosslinking agent: 3%; Plasticizer (glycerin): 7%; Cosolvent (urea): 5%; Other additives (anti-hygroscopic agents): 0.5%.

[0022] Preparation steps: 1. Raw material pretreatment: Place the modified chitosan in a forced-air drying oven and dry at 85℃ for 3 hours, stirring every 30 minutes during the process. Cool to room temperature for later use. Add gelatin to 45℃ deionized water and stir at 25 r / min for 25 minutes to prepare a 20% solution. Keep it warm for later use. Place the modified PLA in a twin-screw extruder and melt at 65℃ for 18 minutes. Place the modified bamboo fiber in a vacuum drying oven and dry at 75℃ for 1.5 hours. Seal and store the remaining additives for later use.

[0023] 2. Slurry preparation: Preheat the core mixer to 75℃, add molten PLA, and stir at 30 r / min for 5 minutes; add modified chitosan and stir for 10 minutes; add gelatin solution and stir for 10 minutes; add modified bamboo fiber, PEGDE crosslinking agent, glycerin, urea, and anti-hygroscopic agent in sequence, stirring for 6 minutes after each addition; evacuate to -0.09 MPa and stir for 30 minutes to obtain a bubble-free slurry.

[0024] 3. Molding process: Hot press injection molding is adopted, with mold temperature of 15℃, slurry temperature of 80℃, injection flow rate of 60 cc / s, injection pressure of 3 MPa, injection time of 30 s, holding pressure time of 2 minutes, and the blank is removed after depressurization.

[0025] 4. Post-processing: Cool the billet to room temperature for 45 minutes, place it in a forced-air drying oven, and dry at 45℃ for 36 hours. Turn it over every 8 hours during the drying process. After cooling to room temperature, test it.

[0026] Example 2: Formulation (by weight): Modified chitosan: 35%; Gelatin: 22%; Modified PLA: 18%; Modified bamboo fiber: 6%; PEGDE crosslinking agent: 4%; Plasticizer (glycerin): 8%; Cosolvent (urea): 6%; Other additives (anti-hygroscopic agents): 1%.

[0027] Preparation steps: 1. Raw material pretreatment: Place the modified chitosan in a forced-air drying oven and dry at 90℃ for 2.5 hours, stirring every 30 minutes during the process. Cool to room temperature for later use. Add gelatin to 48℃ deionized water and stir at 30 r / min for 20 minutes to prepare a 22% solution. Keep warm for later use. Place the modified PLA in a twin-screw extruder and melt at 68℃ for 15 minutes. Place the modified bamboo fiber in a vacuum drying oven and dry at 80℃ for 1 hour. Seal and store the remaining additives for later use.

[0028] 2. Slurry preparation: Preheat the core mixer to 75℃, add molten PLA, and stir at 30 r / min for 5 minutes; add modified chitosan and stir for 10 minutes; add gelatin solution and stir for 10 minutes; add modified bamboo fiber, PEGDE crosslinking agent, glycerin, urea, and anti-hygroscopic agent in sequence, stirring for 8 minutes after each addition; evacuate to -0.10 MPa and stir for 30 minutes to obtain a bubble-free slurry.

[0029] 3. Molding process: Hot press injection molding is adopted, with mold temperature of 20℃, slurry temperature of 85℃, injection flow rate of 80 cc / s, injection pressure of 4 MPa, injection time of 40 s, holding pressure time of 3 minutes, and the blank is removed after depressurization.

[0030] 4. Post-processing: Cool the billet to room temperature for 60 minutes, place it in a forced-air drying oven, dry at 48℃ for 30 hours, turning it over every 8 hours during the process, and test it after cooling to room temperature.

[0031] Example 3: Formulation (percentage by mass): Modified chitosan: 45%; Gelatin: 18%; Modified PLA: 12%; Modified bamboo fiber: 4%; PEGDE crosslinking agent: 2.5%; Plasticizer (glycerin): 6%; Cosolvent (urea): 4%; Other additives (anti-hygroscopic agents): 0.5%.

[0032] Preparation steps: 1. Raw material pretreatment: Place the modified chitosan in a forced-air drying oven and dry at 80℃ for 4 hours, stirring once every 30 minutes during the process, and cool to room temperature for later use; add gelatin to 42℃ deionized water, stir at 20 r / min for 30 minutes to prepare an 18% solution, and keep it warm for later use; put the modified PLA into a twin-screw extruder and melt at 62℃ for 20 minutes; place the modified bamboo fiber in a vacuum drying oven and dry at 70℃ for 2 hours; seal and store the remaining additives for later use.

[0033] 2. Slurry preparation: Preheat the core mixer to 75℃, add molten PLA, and stir at 30 r / min for 5 minutes; add modified chitosan and stir for 10 minutes; add gelatin solution and stir for 10 minutes; add modified bamboo fiber, PEGDE crosslinking agent, glycerin, urea, and anti-hygroscopic agent in sequence, stirring for 5 minutes after each addition; evacuate to -0.08 MPa and stir for 30 minutes to obtain a bubble-free slurry.

[0034] 3. Molding process: Hot press injection molding is adopted, with mold temperature of 10℃, slurry temperature of 75℃, injection flow rate of 40 cc / s, injection pressure of 2 MPa, injection time of 20 s, holding pressure time of 1.5 minutes, and the blank is removed after depressurization.

[0035] 4. Post-processing: Cool the billet to room temperature for 30 minutes, place it in a forced-air drying oven, and dry at 42℃ for 40 hours. Turn it over every 8 hours during the drying process. After cooling to room temperature, test it.

[0036] Example 4: Formulation (by weight): Modified chitosan: 38%; Gelatin: 21%; Modified PLA: 14%; Modified bamboo fiber: 5.5%; PEGDE crosslinking agent: 3.5%; Plasticizer (glycerin): 7.5%; Cosolvent (urea): 5.5%; Other additives (anti-hygroscopic agents): 1.5%.

[0037] Preparation steps: 1. Raw material pretreatment: Place the modified chitosan in a forced-air drying oven and dry at 88℃ for 3.5 hours, stirring every 30 minutes during the process. Cool to room temperature for later use. Add gelatin to deionized water at 46℃ and stir at 28 r / min for 22 minutes to prepare a 21% solution. Keep warm for later use. Place the modified PLA in a twin-screw extruder and melt at 66℃ for 17 minutes. Place the modified bamboo fiber in a vacuum drying oven and dry at 78℃ for 1.2 hours. Seal and store the remaining additives for later use.

[0038] 2. Slurry preparation: Preheat the core mixer to 75℃, add molten PLA, and stir at 30 r / min for 5 minutes; add modified chitosan and stir for 10 minutes; add gelatin solution and stir for 10 minutes; add modified bamboo fiber, PEGDE crosslinking agent, glycerin, urea, and anti-hygroscopic agent in sequence, stirring for 7 minutes after each addition; evacuate to -0.095 MPa and stir for 30 minutes to obtain a bubble-free slurry.

[0039] 3. Molding process: Hot press injection molding is adopted, with mold temperature of 18℃, slurry temperature of 82℃, injection flow rate of 70 cc / s, injection pressure of 3.5 MPa, injection time of 35 s, holding pressure time of 2.5 minutes, and the blank is removed after depressurization.

[0040] 4. Post-processing: Cool the billet to room temperature for 50 minutes, place it in a forced-air drying oven, and dry at 46℃ for 34 hours. Turn it over every 8 hours during the drying process. After cooling to room temperature, test it.

[0041] Example 5: Formulation (percentage by mass): Modified chitosan: 42%; Gelatin: 19%; Modified PLA: 13%; Modified bamboo fiber: 4.5%; PEGDE crosslinking agent: 2.8%; Plasticizer (glycerin): 6.5%; Cosolvent (urea): 4.5%; Other additives (anti-hygroscopic agents): 0.7%.

[0042] Preparation steps: 1. Raw material pretreatment: Place the modified chitosan in a forced-air drying oven and dry at 82℃ for 3.8 hours, stirring every 30 minutes during the process, and cool to room temperature for later use; add gelatin to 43℃ deionized water, stir at 22 r / min for 28 minutes to prepare a 19% solution, and keep it warm for later use; put the modified PLA into a twin-screw extruder and melt at 63℃ for 19 minutes; place the modified bamboo fiber in a vacuum drying oven and dry at 72℃ for 1.8 hours; seal and store the remaining additives for later use.

[0043] 2. Slurry preparation: Preheat the core mixer to 75℃, add molten PLA, and stir at 30 r / min for 5 minutes; add modified chitosan and stir for 10 minutes; add gelatin solution and stir for 10 minutes; add modified bamboo fiber, PEGDE crosslinking agent, glycerin, urea, and anti-hygroscopic agent in sequence, stirring for 6 minutes after each addition; evacuate to -0.085 MPa and stir for 30 minutes to obtain a bubble-free slurry.

[0044] 3. Molding process: Hot press injection molding is adopted, with mold temperature of 12℃, slurry temperature of 78℃, injection flow rate of 50 cc / s, injection pressure of 2.5 MPa, injection time of 25 s, holding pressure time of 1.8 minutes, and the blank is removed after depressurization.

[0045] 4. Post-processing: Cool the billet to room temperature for 35 minutes, place it in a forced-air drying oven, and dry at 43°C for 38 hours, turning it over every 8 hours during the process. After cooling to room temperature, test it.

[0046] Example 6: Formulation (by weight): Modified chitosan: 36%; Gelatin: 20.5%; Modified PLA: 16%; Modified bamboo fiber: 5.2%; PEGDE crosslinking agent: 3.8%; Plasticizer (glycerin): 7.2%; Cosolvent (urea): 5.8%; Other additives (anti-hygroscopic agents): 1.2%.

[0047] Preparation steps: 1. Raw material pretreatment: The modified chitosan was placed in a forced-air drying oven and dried at 89℃ for 2.8 hours, stirring every 30 minutes during the drying process, and then cooled to room temperature for later use; the gelatin was added to deionized water at 47℃ and stirred at 26 r / min for 24 minutes to prepare a 20.5% solution, which was then kept warm for later use; the modified PLA was placed in a twin-screw extruder and melted at 67℃ for 16 minutes; the modified bamboo fiber was placed in a vacuum drying oven and dried at 76℃ for 1.4 hours; the remaining additives were sealed and stored for later use.

[0048] 2. Slurry preparation: Preheat the core mixer to 75℃, add molten PLA, and stir at 30 r / min for 5 minutes; add modified chitosan and stir for 10 minutes; add gelatin solution and stir for 10 minutes; add modified bamboo fiber, PEGDE crosslinking agent, glycerin, urea, and anti-hygroscopic agent in sequence, stirring for 7 minutes after each addition; evacuate to -0.098 MPa and stir for 30 minutes to obtain a bubble-free slurry.

[0049] 3. Molding process: Hot press injection molding is adopted, with mold temperature of 16℃, slurry temperature of 83℃, injection flow rate of 75 cc / s, injection pressure of 3.8 MPa, injection time of 38 s, holding pressure time of 2.8 minutes, and the blank is removed after depressurization.

[0050] 4. Post-processing: Cool the billet to room temperature for 55 minutes, place it in a forced-air drying oven, and dry at 47°C for 32 hours. Turn it over every 8 hours during the drying process. After cooling to room temperature, test it.

[0051] Comparative Example 1: Traditional polyethylene glycol-based core mold materials were used as a comparison, with the following formula: PEG4000 35%, urea 35%, and sodium bicarbonate 30%.

[0052] Comparative Example 2: Formulation composition (by mass percentage): Based on Example 1, the modified bamboo fiber was removed, and the contents of the remaining components were adjusted proportionally, specifically as follows: modified chitosan: 42.1%, gelatin: 21.1%, modified PLA: 15.8%, PEGDE crosslinking agent: 3.2%, plasticizer (glycerin): 7.4%, cosolvent (urea): 5.3%, other additives (anti-hygroscopic agent): 0.5% (total percentage of each component is 100%).

[0053] Preparation process: The preparation method of Example 1 is completely followed, except that modified bamboo fiber is not added. The other raw material pretreatment, pulp preparation, molding and processing and post-treatment steps are kept the same.

[0054] Comparative Example 3: Formulation composition (by mass percentage): Based on Example 1, modified PLA was removed, and the contents of the remaining components were adjusted proportionally, specifically as follows: modified chitosan: 47.1%, gelatin: 23.5%, modified bamboo fiber: 5.9%, PEGDE crosslinking agent: 3.5%, plasticizer (glycerin): 8.2%, cosolvent (urea): 5.9%, other additives (anti-hygroscopic agent): 0.9% (total percentage of each component is 100%).

[0055] Preparation process: The preparation method of Example 1 is completely followed, except that modified PLA is not added. The other raw material pretreatment, slurry preparation, molding and processing and post-treatment steps are kept the same.

[0056] The performance test results of Examples 1-3 and Comparative Example 1 of a silicon-free water-soluble mandrel material are shown in Table 1: Test method: Bending strength test: The bending strength test was carried out in a universal testing machine according to GB / T 9341-2008 "Determination of bending properties of plastics". The standard sample size was 80mm×10mm×4mm and the test speed was set to 2mm / min.

[0057] Elongation at break: The bending strength was tested in a universal testing machine according to GB / T 1040.1-2006 "Determination of tensile properties of plastics - Part 1: General". The standard specimen size was 100mm×10mm×3mm, and the test speed was set to 5mm / min.

[0058] Heat distortion temperature: determined according to GB / T 15332-2018 "Determination of softening point of thermoplastic plastics by ring and ball method".

[0059] Water solubility rate test: Take the finished core mold and cut it into 10mm×10mm×10mm samples. Measure 500mL of 25℃ distilled water and pour it into a beaker. Place the beaker in a constant temperature water bath (temperature controlled at 25±0.5℃) and adjust the stirring speed to 100r / min, maintaining a constant speed. Gently place the sample into the distilled water and start timing simultaneously. Stir gently with tweezers every 10 minutes and observe the dissolution state of the sample. Record the time when the sample completely dissolves (no visible particles), which is the water solubility rate (unit: g / min, calculated by dividing the sample mass by the dissolution time). Biodegradation rate: The biodegradation rate was determined within 100 days according to GB / T 19277.1-2011 standard.

[0060] Table 1. Performance test results of water-soluble core mold materials

[0061] By comparing the test results of the examples and comparative examples, it can be seen that the biodegradable mandrel material prepared by the present invention has the following advantages: the average flexural strength (10.6 MPa) of the examples is 76.7%, 41.3%, and 55.9% higher than that of comparative example 1 (6.0 MPa), comparative example 2 (7.5 MPa), and comparative example 3 (6.8 MPa), respectively; the elongation at break (41%) is 412.5%, 28.1%, and 46.4% higher than that of comparative example 1 (8%), comparative example 2 (32%), and comparative example 3 (28%), respectively. This indicates that the chitosan-gelatin-PLA ternary composite system adopted by the present invention, combined with modified bamboo fiber reinforcement technology, can significantly improve the strength and toughness of the material, solving the problem of insufficient toughness of traditional PEG-type materials. The average heat distortion temperature (62℃) of the examples is 6.9%, 8.8%, and 19.2% higher than that of comparative example 1 (58℃), comparative example 2 (57℃), and comparative example 3 (52℃), respectively. This indicates that the addition of modified PLA can effectively compensate for the insufficient thermal stability of chitosan. The synergistic effect of modified bamboo fiber with PLA and chitosan further improves the heat distortion temperature of the material, making it more suitable for high-temperature processes such as wax pattern making and dewaxing in precision casting, thus avoiding core mold deformation. The average water solubility rate of the examples (0.66 g / min) is better than that of Comparative Example 1 (0.55 g / min), slightly lower than that of Comparative Example 3 (0.71 g / min), and close to that of Comparative Example 2 (0.63 g / min). All of these meet the requirements for rapid cleaning and removal after use of precision casting core molds, indicating that the formulation of this invention, while ensuring good water solubility, also takes into account mechanical properties and thermal stability, avoiding performance imbalance caused by adjusting a single component. The average biodegradation rate of the examples (65%) is close to that of Comparative Example 2 (63%) and Comparative Example 3 (67%), and is much higher than that of Comparative Example 1 (less than 5%). This shows that the fully bio-based raw material system used in this invention can achieve good biodegradation performance, which meets the requirements of green manufacturing and sustainable development. In contrast, traditional PEG materials are difficult to degrade and pose environmental risks.

[0062] The above embodiments are merely illustrative of several implementations of the present invention, but the implementation of the present invention is not limited to the above embodiments. Any changes made without departing from the spirit and principle of the present invention are within the protection scope of the present invention.

Claims

1. A biodegradable, water-soluble core mold material for precision casting, characterized in that, By weight percentage, it includes the following components: 30-50% modified chitosan, 15-25% gelatin, 10-20% polylactic acid, 3-8% modified bamboo fiber, 2-5% crosslinking agent, 5-10% plasticizer, 3-8% cosolvent, and 0.5-2% other additives.

2. The biodegradable precision casting water-soluble core mold material according to claim 1, characterized in that, The modified chitosan is 2-chloroethanol etherified modified chitosan, with a solubility in water at 25°C ≥30 g / L and a water absorption rate of ≤10% after soaking in water at 25°C for 24 hours.

3. The biodegradable precision casting water-soluble core mold material according to claim 1, characterized in that, The gelatin has a gel strength of 200-280 Bloom and a Blaine viscosity of 150-220 mPa•s.

4. The biodegradable precision casting water-soluble core mold material according to claim 1, characterized in that, The polylactic acid is caprolactone-modified polylactic acid with a molecular weight of 100,000-200,000 and a glass transition temperature of 60-65℃.

5. The biodegradable precision casting water-soluble core mold material according to claim 1, characterized in that, The modified bamboo fiber is a bamboo fiber modified with silane coupling agent (KH-550), with an average length of 100-200 μm and a diameter of 10-20 μm.

6. The biodegradable precision casting water-soluble core mold material according to claim 1, characterized in that, The crosslinking agent is polyethylene glycol diglycidyl ether (PEGDE), which contains two epoxy groups in its molecular structure.

7. A method for preparing a biodegradable precision casting water-soluble core mold material according to any one of claims 1-6, characterized in that, Includes the following steps: Raw material pretreatment, slurry preparation, molding and processing and post-treatment.

8. The preparation method according to claim 7, characterized in that, The molding process adopts hot press injection molding technology, with an injection flow rate of 20-100 cc / s, an injection pressure of 1-5 MPa, an injection time of 10-60 s, and a holding time of 0.5-5 min.

9. The application of the biodegradable precision casting water-soluble core mold material according to any one of claims 1-6, characterized in that, Precision casting processes used in aerospace, automotive, medical device and other fields.

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