Environment-friendly biodegradable and renewable refrigerator and manufacturing method thereof

Abstract

The present invention relates to a biodegradable and renewable eco-friendly refrigerator and a manufacturing method thereof, which is a technology of biodegrading and recycling a waste refrigerator and combining it with a natural insulation material to achieve superior performance. The manufacturing method of the present invention includes: (a) biodegrading a waste refrigerator by treating it with yellow mealworm and brown mealworm degradation strains, (b) preparing a natural insulation material composed of jute fiber, bamboo fiber, silica aerogel, etc., and compounding it with the biodegraded material, (c) adding a strength enhancer and molding the refrigerator body through vacuum molding, and (d) forming a functional protective layer of a multi-layer structure using rice bran wax, propolis, etc. The refrigerator manufactured by the present invention has excellent heat insulation performance and durability, and is biodegradable, contributing to the reduction of environmental pollution.

Description

Technical Field

[0001] The following examples illustrate biodegradable, renewable, and environmentally friendly refrigerators, as well as their manufacturing methods and technologies. Background Technology

[0002] In the modern world, refrigerators are essential for the distribution of fresh food and the transportation of medicines, and they are primarily made of expanded polystyrene (EPS). EPS is widely used as a main material for refrigerators due to its excellent insulation, light weight, and economic feasibility, but it causes serious environmental problems.

[0003] The biggest problem with traditional refrigerators is that they are not biodegradable. When discarded refrigerators are landfilled, they accumulate in the soil for hundreds of years without decomposing, eventually breaking down into microplastics that pollute the soil and water. Furthermore, incineration releases harmful substances such as dioxins, causing air pollution and adversely affecting human health. In particular, the recent surge in refrigerator use, driven by the rapid increase in fresh food and pharmaceutical delivery, has exacerbated these environmental problems.

[0004] To address this issue, researchers have attempted to develop environmentally friendly refrigerators using biodegradable polymers. However, traditional biodegradable refrigerators have several significant limitations. First, their insulation performance is significantly lower than existing expanded polystyrene foam products, making them difficult to use as a practical alternative. Second, they are susceptible to moisture and external impacts, resulting in poor durability. Third, their production costs are 2-3 times higher than ordinary refrigerators, making it difficult to ensure market competitiveness.

[0005] Recently, researchers at Stanford University discovered that mealworms (the larvae of the brown mealworm) can biodegrade polystyrene. The mealworms' gut microbiota can convert polystyrene into carbon dioxide and biomass, a discovery that opens new possibilities for waste plastic treatment. However, the technology to utilize this biodegradation mechanism in the industrial production of refrigerators has not yet been developed.

[0006] Furthermore, existing research and development of environmentally friendly insulation materials largely relies on single materials or simple mixing methods, which limits the ability to simultaneously meet insulation and mechanical performance requirements. In particular, the low thermal stability and weak mechanical properties of biodegradable polymers remain significant technical challenges that need to be overcome when manufacturing insulated containers such as refrigerators.

[0007] Therefore, there is an urgent need to develop environmentally friendly and practical refrigerator manufacturing technology by combining the biodegradation technology of discarded refrigerators with the manufacturing technology of high-performance environmentally friendly insulation materials.

[0008] Previous documents

[0009] [Patent Documents]

[0010] (Patent Document 1) Korean Patent 10-1397853

[0011] (Patent Document 2) Korean Patent Registration 10-1822577

[0012] (Patent Document 3) Korean Patent No. 10-2015-0120983

[0013] (Patent Document 4) Korean Patent Registration 10-2114185 Summary of the Invention

[0014] Given the lack of effective biodegradation technologies for existing discarded freezers, this invention aims to develop a technology for industrially utilizing the biodegradation capabilities of mealworms and brown mealworms. To this end, we propose a technical solution that precisely controls the optimal input rate of the decomposing organisms, environmental conditions, and decomposition time.

[0015] Furthermore, this invention seeks to derive optimal mixing ratios and processing conditions with natural insulating materials to overcome the physical property limitations of biodegradable polymer materials. In particular, our goal is to develop composite material technologies utilizing natural materials such as jute fiber, bamboo fiber, and silica aerogel, while ensuring excellent thermal insulation and mechanical strength.

[0016] Furthermore, this invention aims to establish a technology for forming a multi-layered functional protective layer using naturally derived materials (such as rice bran wax, pine oil, and propolis) to compensate for the water resistance and durability of biodegradable materials. In this way, our goal is to provide a technological solution that maintains the necessary properties throughout the product's entire lifespan and ultimately makes it fully biodegradable.

[0017] Furthermore, this invention aims to develop an energy-saving and environmentally friendly process technology that emits no harmful substances, thereby minimizing the environmental impact of the entire manufacturing process. In particular, by achieving optimal conditions in processes such as vacuum forming, electrostatic spraying, and UV curing, our goal is to simultaneously ensure product quality and environmental performance.

[0018] Furthermore, this invention aims to design a manufacturing process that is both continuous and economically feasible, ensuring the industrial viability of the developed technology. To this end, our goal is to optimize the key variables at each process step and develop process control technologies that can simultaneously ensure quality stability and productivity.

[0019] The present invention solves the technical problem by adopting the following technical solution:

[0020] This invention provides a method for manufacturing a biodegradable and renewable environmentally friendly refrigerator. The method first involves implanting a biodegradable organism into a biodegradable polymer substrate, promoting the substrate's decomposition. Then, through a thermoforming process, the decomposed material is processed into a composite material that is thoroughly mixed with natural insulation materials. Finally, a functional protective layer is constructed on the surface of this composite material. The resulting refrigerator not only possesses environmentally friendly properties, enabling biodegradation and material regeneration, but also exhibits excellent insulation performance.

[0021] In this case, (a) organic biodegradable organisms are introduced into a biodegradable polymer substrate and the substrate is decomposed; (b) natural insulating materials and biodegradable catalysts are mixed in the decomposed material to prepare a composite material; (c) functional additives are added to the composite material and the refrigerator body is thermoformed; (d) a multi-layered functional protective layer is constructed on the surface of the refrigerator body.

[0022] At this point, (a) the waste refrigerator is crushed, treated with a combination of mealworm and brown mealworm decomposing strains, and then microalgae biomass and enzyme complexes are added sequentially for biodecomposition. Then it is dried, finely ground and mixed with biodegradable polymers until melt-mixed. (b) a biodegradable catalyst is prepared from wild vegetable by-products. Jute fiber and bamboo fiber are mixed with silica aerogel and alkalized to prepare natural heat-insulating material. Then a thermal stability enhancer is prepared with oyster shell and persimmon extract and melt-mixed with the substrate. (c) a strength enhancer composed of cellulose nanofibers and chitosan nanofibers is added to the composite material for melt mixing and defoaming treatment. Then the refrigerator body is shaped by vacuum forming after extrusion and preheating, and gradually cooled in a nitrogen atmosphere to impart dimensional stability. (d) a waterproof coating is prepared with rice bran wax and pine essential oil. An antibacterial composition prepared with propolis, Coptis chinensis and Houttuynia cordata extracts and nanoliposomes is mixed and applied by electrostatic spraying. This is a stage of UV curing and drying and forming a final protective layer with honeycomb propolis and brown algae extracts.

[0023] At this point, step (a) involves crushing the (a1) waste refrigerator into 1-3 mm pieces, then preparing a degrading bacterial composition, which is mixed with larvae and brown mealworms at a ratio of 2:1; (a2) mixing the crushed waste refrigerator and the degrading bacterial composition at a weight ratio of 3:1, and then adding 5% by weight of Chlorella microalgae biomass to prepare the first composition; (a3) ​​subjecting the first composition to primary biodegradation for 15 days at 26-28℃ and 65-70% relative humidity, and then adding an enzyme complex of lipase, protease, and cellulase at 3% by weight. (a4) Mix the biodegradable first composition at 3% of the total weight and then perform a second biodegradation for 7 days; (a5) Dry the biodegradable first composition at 55°C for 36 hours and then prepare biodegradable powder by fine grinding to make the particle size 50 μm or smaller; (a6) Mix the biodegradable powder with a biodegradable polymer mixed with polylactic acid, polybutylene succinate and polycaprolactone at a weight ratio of 2:2:1 and 3:7, and then melt mix at 175±5°C and a screw speed of 180 rpm for 30 minutes, and prepare the granular form of the substrate using a twin-screw extruder.

[0024] At this point, step (b) involves mixing fern stems, duck skin, and bellflower root with supercritical carbon dioxide at a weight ratio of 2:1:1, and extracting the prepared wild vegetable byproducts at a temperature of 45°C and a pressure of 250 bar to prepare a biodegradable catalyst; (b2) mixing jute fiber and bamboo fiber at a weight ratio of 2:1 and alkalizing them in a 3-wt% sodium hydroxide aqueous solution at a temperature of 60°C for 2 hours; (b3) mixing the alkali-treated jute fiber and bamboo fiber mixture with silica aerogel at a weight ratio of 1:1, and then vacuum drying it at a temperature of -40°C for 48 hours to produce... (b4) A porous natural thermal insulation material with a porosity of over 80% is produced; (b5) Calcium oxide powder obtained by firing oyster shells at 900°C for 2 hours and persimmon extract are mixed in a weight ratio of 2:1 to prepare a thermal stability enhancer with a heat resistance temperature of 200°C or higher; (b6) The substrate, biodegradable catalyst, natural insulating material and thermal stability enhancer prepared in step (A5) above are mixed in a weight ratio of 70:10:15:5, and then the composite material is prepared by melt mixing for 30 minutes in a twin-screw extruder at a temperature of 170±3°C and a screw speed of 200 rpm.

[0025] At this point, step (c) is (c1) adding a mixed cellulose nanofiber and chitosan nanofiber strength reinforcing material to the composite material at a weight ratio of 3:1, representing 5% of the total weight; (c2) after melting and mixing the composite material in a twin-screw extruder at 165±2℃ and a screw speed of 150rpm, maintaining a vacuum of -700mmHg for 30 minutes to remove air bubbles; (c3) extruding to a thickness of ±303mm using a T-die extruder at 30±2℃, preheating the surface temperature to 85±2℃ for 30 minutes using an infrared heater, and then transferring it to a vacuum forming machine while maintaining the vacuum forming preheating temperature; (c4) in the vacuum forming of step (c3) above, the die temperature difference is controlled at 160±2℃ at the top and 150±2℃ at the bottom, and the vacuum temperature is maintained at -700±10mmHg. 15 minutes to form the refrigerator body; (c5) Cool the formed refrigerator body in a nitrogen atmosphere to keep the oxygen concentration in the cavity at 0.5% or lower, cooling to 40°C for the first 2 hours and to 25°C for the next 4 hours to impart dimensional stability so that the dimensional change rate measured at 23°C is less than 0.5%.

[0026] At this point, step (d) involves mixing (d1) rice bran wax and pine essential oil in a 3:1 weight ratio, dissolving them at 80°C, and then treating them with ultrasound at a frequency of 40kHz and an output of 300W for 30 minutes to prepare the basic components of the waterproof coating; (d2) mixing propolis extract, coptis extract, and houttuynia cordata extract in a 2:2:1 weight ratio, and then preparing nanoliposomes with an average particle size of 50-100nm to prepare an antibacterial composition; (d3) mixing the basic components of the waterproof coating agent with the antibacterial composition in a 4:1 weight ratio, then homogenizing at 10,000rpm for 30 minutes, and treating them with ultrasound at a frequency of 35kHz for 15 minutes to prepare a primary coating solution; (d4) applying the primary coating solution to the surface of the refrigerator body using electrostatic spraying, applying a voltage of 25kV, a spraying distance of 20cm, and using an irradiation intensity of 500mW / cm at a wavelength of 365nm. 2 The primary protective layer was cured with ultraviolet light for 10 minutes and then dried with far-infrared light at 60°C for 30 minutes to form a primary protective layer with a thickness of 50±5μm. (d5) The honeycomb propolis and brown algae extract were mixed on the plasma-treated primary protective layer at a weight ratio of 2:1. The mixture was prepared in an oxygen atmosphere at a pressure of 0.1 Torr and an output of 100W for 2 minutes and then dried at 45°C for 4 hours to form the final protective layer.

[0027] According to one embodiment, the device can be controlled by a computer program stored on a medium in combination with hardware to perform any of the methods described above.

[0028] The present invention has the following beneficial effects:

[0029] This invention effectively treats discarded refrigerators using the biodegradation process of yellow mealworms and brown yellow mealworms. When treated using the method of this invention, more than 90% of the discarded refrigerators are biodegraded within 21 days, and the yellow mealworm biomass produced in this process can serve as a high-quality feed resource with a protein content of 60% or more.

[0030] Furthermore, this invention ensures excellent thermal insulation and mechanical properties through an optimal combination of natural insulating materials and biodegradable polymers. The refrigerator manufactured using this invention has a thermal conductivity of 0.030 W / mK or lower and a compressive strength of 250 kPa or higher, providing quality equal to or exceeding that of existing products.

[0031] Furthermore, this invention significantly improves the product's usability by using naturally sourced materials to form a multi-layered functional protective layer. The developed protective layer exhibits a water absorption rate of less than 1% and antibacterial activity of over 99% after 24 hours of immersion, and its physical properties remain unchanged for more than 6 months under actual use conditions.

[0032] Furthermore, this invention minimizes the environmental impact of the entire manufacturing process by applying environmentally friendly technologies. In particular, no harmful substances are emitted during this process, and energy consumption can be reduced by more than 30% compared to existing processes.

[0033] Furthermore, this invention ensures excellent economic feasibility through a precisely controlled continuous production process. Production capacity exceeds 100 pieces per hour, with a quality pass rate of over 95%, making it suitable for industrial production. Moreover, through raw material recycling and process optimization, production costs can be reduced by more than 20% compared to existing products.

[0034] Furthermore, when this invention is disposed of in landfills after use, it minimizes the environmental impact by biodegrading over 90% of its products within six months. Compared to existing products, the carbon emissions throughout the process are reduced by over 60%, contributing to carbon neutrality. This approach allows for a proactive response to increasingly stringent environmental regulations and a competitive advantage in the environmental protection market. Detailed Implementation

[0035] The embodiments are described in detail below with reference to the accompanying drawings. However, various modifications can be made to the embodiments, and therefore the scope of the patent application is not limited to or restricted by these embodiments. Any changes, equivalents, or substitutions to the embodiments should be understood to be included within the scope of the claims.

[0036] The specific structural or functional descriptions of the embodiments are provided for illustrative purposes only and may be modified and implemented in various forms. Therefore, the embodiments are not limited to a particular form of disclosure, and the scope of this specification includes changes, uniformities, or substitutions incorporated into the descriptive concepts.

[0037] Terms such as "first" or "second" can be used to describe various components, but the interpretation of these terms should only be used to distinguish one component from another. For example, the first component can be named the second component, and similarly, the second component can be named the first component.

[0038] When a component is said to be "connected" to another component, it should be understood that it may be directly connected to or connected to another component, but there may be another component between them.

[0039] The terminology used in the embodiments is for illustrative purposes only and should not be construed as intended to be limiting. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to indicate the presence of a feature, number, step, action, component, part, or combination thereof described in the specification, rather than one or more other features or numbers, steps, actions, or components, and should be understood to not exclude the possibility of the presence or addition of parts or combinations thereof.

[0040] Unless otherwise defined, all terms used herein, including technical or scientific terms, shall have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments pertain. Terms such as those defined in common dictionaries shall be interpreted as having the meaning consistent with their meaning in the relevant descriptive context and shall not be interpreted in an idealistic or overly formal sense unless expressly defined in this application.

[0041] The advantages and features of the present invention, as well as methods for implementing them, will be described with reference to the embodiments described in detail below and the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be practiced in various different forms. The embodiments are provided only to ensure that the disclosure of the invention is complete and to fully provide the scope of the invention to those skilled in the art to which it pertains, and the invention is defined only by the class of the claims.

[0042] [Comparative Example 1]

[0043] Except for the biodegradation process, only pure biodegradable polymers were used to manufacture the refrigerator. Polylactic acid, polybutylene succinate, and polycaprolactone were mixed in a weight ratio of 2:2:1 and melted in a twin-screw extruder at 175±5°C and a screw speed of 180 rpm for 30 minutes. Then, the same natural insulating material and thermal stability enhancer as in Example 1 were added, and the refrigerator was manufactured using the same molding conditions and protective layer formation process.

[0044] [Comparative Example 2]

[0045] Except for the brown mealworm degrading strain, only yellow mealworms were used for biodegradation. Waste refrigerator waste was pulverized into 1-3 mm pieces and mixed with yellow mealworms at a 3:1 weight ratio, with 5% Chlorella microalgae biomass added by weight. After biodegradation for 20 days at 26-28°C and 65-70% relative humidity, it was dried and ground in the same manner as in Example 1. Subsequent biodegradable polymer mixing, composite material manufacturing, molding, and protective layer formation were carried out under the same conditions as in Example 1.

[0046] [Comparative Example 3]

[0047] Commercially available expanded polystyrene powder (average particle size 100 μm) was used instead of natural insulation material. The biodegradation of waste refrigerators and the preparation of the biodegradable polymer were carried out in the same manner as in Example 1, except that expanded polystyrene powder was added at the same weight ratio instead of natural insulation in the manufacture of the composite material. Molding conditions and the formation of the protective layer were the same as in Example 1.

[0048] [Comparative Example 4]

[0049] It does not form a functional protective layer, but only manufactures it to the main body of the refrigerator. The biodegradation of the discarded refrigerator, the mixing with biodegradable polymers, the preparation of natural insulating materials, the manufacture of composite materials, and the molding of the refrigerator body by vacuum forming were carried out under the same conditions as in Example 1. However, the process of forming a protective layer using a waterproof coating and antibacterial composition was not performed.

[0050] [Comparative Example 5]

[0051] A common commercially available expanded polystyrene refrigerator was purchased and used as a control. The product specifications were the same as in Example 1, with a density of 0.025 g / cm³ according to the specifications. 3 It has a thermal conductivity of 0.036 W / mK and a compressive strength of 200 kPa. This product represents the typical physical properties of the most commonly used refrigerators on the market today.

[0052] [Evaluation of Physical Properties]

[0053] According to the present invention, the following tests were conducted to evaluate the physical properties of the refrigerator. The compressive strength of 100mm × 100mm and 100mm × 50mm specimens was measured using a universal testing machine (UTM) at a speed of 10mm / min. Bending strength was evaluated by a three-point bending test using 200mm × 50mm and 30mm specimens, with the distance between the points set to 160mm and the test speed set to 2mm / min. For impact strength, cantilever beam impact tests were performed on 80mm × 10mm × 4mm specimens. Dimensional stability, width, and thickness were measured after storage in a thermostat at 23°C and 50% relative humidity for 168 hours. All tests were repeated five times to calculate the average value.

[0054] [Table 1]

[0055]

[0056]

[0057] Example 1 demonstrates the best results across all physical property evaluations. Specifically, the compressive strength is 245 ± 12 kPa, which is 22.5% higher than that of the existing commercial comparative example 5 (200 ± 10 kPa). This is attributed to the optimal blending of the microparticles and biodegradable polymer obtained through the biodegradation process, as well as the effective reinforcing effect of the nanofiber strength modifier. In Example 1, the flexural strength and impact strength are also the highest, at 4.8 ± 0.2 MPa and 12.5 ± 0.6 kJ / m, respectively. 2 This is interpreted as meaning that the synergistic effect of the uniform degradation caused by the degrading strains of yellow mealworm and brown yellow mealworm, as well as the effective dispersion of the natural insulating material, contributes to the improvement of the mechanical properties of the composite material. In particular, in the case of Comparative Example 2, due to the use of only yellow mealworm for biodegradation, the flexural strength was 14.6% lower and the impact strength was 18.4% lower than that of Example 1.

[0058] Regarding dimensional stability, Example 1 achieved an excellent dimensional change rate of 0.3 ± 0.1%. This is due to the dimensional stabilizing effect of the stepwise cooling process in a nitrogen atmosphere and the multilayer protective layer, showing a significant difference compared to Comparative Example 4 (1.5 ± 0.3%), which lacks a functional protective layer. Comparative Example 1, using only a pure biodegradable polymer, exhibits the lowest overall physical properties, which is interpreted as demonstrating the importance of structural control and improved physical properties through biodegradation processes.

[0059] [Insulation Performance Evaluation Methods]

[0060] To evaluate the insulation performance of this invention in a refrigerator, thermal conductivity measurements, insulation performance tests, and thermal imaging analysis were conducted. Thermal conductivity was measured using a heat flow system with sample sizes of 300mm × 300mm, 300mm, and 30mm, under conditions of 23±2℃ and 50±5% relative humidity. For the cold insulation performance test, 10 kg of 0℃ ice was filled into a prepared refrigerator, and the internal temperature change was measured for 24 hours under constant temperature and humidity of 40±1℃ and relative humidity of 65±5%. Temperature was measured using a platinum thermistor (PT-100) installed in the center of the refrigerator, and recorded every hour. For thermal imaging analysis, an infrared thermal imaging camera (resolution: 320×240 pixels, temperature resolution: 0.05℃) was used to observe the heat distribution on the outer wall of the refrigerator.

[0061] [Table 2]

[0062]

[0063] As a result of the evaluation of thermal insulation performance, Example 1 of the present invention showed the best thermal insulation performance with a thermal conductivity of 0.031 W / mK. This is an improvement of 8.3-22.6% compared to the comparative example and was determined to be the effect of the natural insulating material of jute fiber and bamboo fiber mixed in the optimal ratio and combined with silica aerogel. In particular, the analysis showed that the excellent thermal insulation performance was expressed due to the uniform formation of the porous structure and the effect of the thermal stability enhancer. In the cold insulation performance test, Example 1 showed the longest time (18.5 hours) for the internal temperature to reach 10°C, and the internal temperature was also maintained at 12.3°C after 24 hours. This is an improvement of 10.1-21.7% and 14.2-28.5% respectively compared to the comparative example. In particular, the performance was improved by 16.4% compared to Comparative Example 4 without a functional protective layer, and confirmed the contribution of the multilayer protective layer to the thermal insulation performance.

[0064] When assessing the uniformity of heat distribution through thermal imaging analysis, Example 1 exhibited a high uniformity of 95.8%, demonstrating superior results compared to the comparative examples (88.5-93.4%). This translates to uniform dispersion of the composite material and optimized process conditions during vacuum forming, thereby minimizing non-uniformity in the heat transfer path. In particular, it was determined that the gradual cooling process in a nitrogen atmosphere effectively controlled internal stress, contributing to improved uniformity of heat transfer performance.

[0065] In summary, Example 1 of the present invention demonstrates that, while possessing biodegradability, it achieves superior thermal insulation performance compared to existing expanded polystyrene refrigerators (Comparative Example 5). This performance improvement is attributed to the synergistic effect of optimal design of natural insulating materials, application of multi-layered protective layers, and precise process control.

[0066] [Durability Assessment Methods]

[0067] To evaluate the durability of the refrigerator manufactured according to this invention, water resistance, chemical resistance, and weather resistance tests were conducted as follows. For the water resistance test, the water absorption rate was measured after immersing the sample in water at 23±2°C for 168 hours. For the chemical resistance test, considering the food contact environment, the sample was immersed in an aqueous acetic acid solution with a pH of 4.0 and an aqueous sodium hydroxide solution with a pH of 10.0 for 72 hours, and the rate of weight change and surface condition changes were observed. An accelerated aging test was conducted using an accelerated aging tester to measure the effect of ultraviolet radiation (irradiance: 60±2W / m²). 2 The color difference (ΔE) and performance degradation rate after 1,000 hours of exposure under water spray conditions were measured. Each test was repeated 5 times to calculate the average value.

[0068] Table 3

[0069]

[0070] Example 1 of the present invention demonstrates the best results in all durability evaluation items. In terms of water absorption, Example 1 shows a water resistance improvement of over 35% compared to 0.42% in Example 5 (0.65%), and approximately 85% or more better than Comparative Example 4 (2.85%) without a protective layer. This result indicates that the multilayer functional protective layer based on rice bran wax and pine oil effectively blocks moisture penetration. In the chemical resistance evaluation, Example 1 shows weight changes of 0.38% and 0.45% in acidic and alkaline solutions, respectively, demonstrating the most stable chemical resistance compared to other comparative examples. In particular, chemical resistance is improved by approximately 75% or more compared to Comparative Example 1 (acid: 1.45%, alkali: 1.68%) which uses only biodegradable polymers. These results demonstrate that the propolis and the natural extract-based protective layer used in the present invention act as an effective barrier against chemical corrosion.

[0071] As a result of the aging test, Example 1 showed very low discoloration after 1,000 hours of accelerated aging, with a color difference of 1.8 and a tensile strength degradation rate of only 8.5%. Compared with Comparative Example 5, this represents an improvement of over 65% and 54%, respectively, in terms of color difference (5.2) and tensile strength degradation rate (18.5%). In particular, Comparative Example 4, without the protective layer, exhibited the greatest physical property degradation, with a color difference of 6.8 and a tensile strength decrease rate of 28.5%, demonstrating the effectiveness of the multilayer protective layer system of the present invention in preventing the deterioration of physical properties caused by ultraviolet radiation and moisture.

[0072] In a comprehensive analysis of the above durability evaluation results, it has been proven that the biodegradable and reproducible environmentally friendly refrigerator of the present invention exhibits excellent water resistance, chemical resistance and weather resistance, and can be used stably for a long time in actual use environments.

[0073] [Biodegradability Evaluation Methods]

[0074] In this invention, biodegradability was evaluated under soil, marine, and composting conditions. Soil biodegradability was tested using forest soil under laboratory conditions, measuring weight loss and carbon dioxide production for 28 days. Marine biodegradability was tested after preparing artificial seawater and inoculating it with microorganisms, evaluating biodegradability for 56 days. Biodegradability was tested under composting conditions using active compost at 58±2℃ and 60% relative humidity for 180 days. Biodegradability was calculated based on the amount of carbon dioxide produced. All tests were repeated three times using 20mm × 20mm and 20mm × 10mm samples.

[0075] Table 4

[0076]

[0077] *Measurements are expressed as mean ± standard deviation (n=3)

[0078] Example 1 demonstrated good biodegradability under all environmental conditions. In particular, a high biodegradability of 98.7% was achieved after 180 days under composting conditions, which was determined by the synergistic effect of the degrading strains of yellow mealworm and brown mealworm and the influence of the biodegradation catalyst. It also showed biodegradability of 92.5% and 85.3% in soil and marine environments, respectively, confirming efficient decomposition in natural environments.

[0079] Comparative Example 1, which uses only a pure biodegradable polymer without a biodegradation process, showed approximately 25% lower biodegradability than Example 1. This indicates that the biological pretreatment process plays a crucial role in improving the biodegradability of the final product. In the case of Comparative Example 2, the synergistic effect of using only a brown mealworm degrading strain of mealworm showed lower biodegradability than Example 1, but still demonstrated better results than Comparative Example 1.

[0080] Comparative Example 3 uses expanded polystyrene as the insulation material, resulting in significantly reduced biodegradability. This is interpreted as limiting the overall biodegradability of the product due to the fire-resistant properties of expanded polystyrene. Comparative Example 4, without a protective layer, shows a similar level of biodegradability to Example 1, but with slightly lower values. This demonstrates that the protective layer used in this invention does not impair the biodegradability of the product.

[0081] The control group, Comparative Example 5 (ordinary EPS refrigerator), showed very low biodegradability, below 10%, under all environmental conditions, even during the 6-month trial. These results demonstrate that this invention significantly improves biodegradability compared to existing products, making it a valuable environmentally friendly alternative material.

[0082] [Antibacterial Evaluation]

[0083] The following tests were performed to evaluate the antimicrobial properties of the refrigerator of the present invention. Samples were prepared by cutting them into 5cm × 5cm pieces in the refrigerators of Example 1 and Comparative Examples 1-5. Antimicrobial activity against Staphylococcus aureus and Escherichia coli was evaluated. The test strains were incubated at 37°C for 18 h, then diluted with physiological saline and adjusted to a concentration of 1.0–3.0 × 10⁵ CFU / mL. After inoculating the surface of the prepared sample with 0.2 mL of bacterial solution, it was incubated at 35 ± 1°C and 90% or higher relative humidity for 24 h. The number of viable bacteria was measured after incubation and immediately after 24 hours to calculate the inhibition rate. To evaluate antifungal properties, Aspergillus niger was incubated at 28 ± 1°C and 85% or higher relative humidity for 28 days, and the degree of mycelial growth was observed.

[0084] [Table 5]

[0085]

[0086]

[0087] As a result of the antibacterial performance evaluation, Example 1 of the present invention showed excellent inhibition rates of 99.9% and 99.8% against Staphylococcus aureus and Escherichia coli, respectively. This is attributed to the synergistic effect of the antibacterial composition made from propolis, Coptis chinensis, and Houttuynia cordata extracts as nanoliposomes and the multilayer protective layer composed of honeycomb propolis and brown algae extracts. In particular, Example 1 showed more than twice the antibacterial activity compared to Comparative Examples 1-5, demonstrating the effectiveness of the electrostatic spraying process used in the present invention in terms of uniform distribution and stable fixation of the antibacterial substance. In the fungal resistance assessment, Example 1 recorded grade 0, where no hyphal growth was observed during the 28-day incubation period. On the other hand, Comparative Example 4 without a protective layer and Comparative Example 5 with a conventional EPS refrigerator showed severe mold growth (grade 3). These results indicate that the multilayer protective layer system of the present invention not only effectively inhibits the growth of microorganisms but also maintains a stable antibacterial effect even under long-term use. Furthermore, it has been confirmed that the use of antibacterial substances derived from nature ensures safety for humans and the environment.

Claims

1. A biodegradable and renewable environmentally friendly refrigerator and its manufacturing method, characterized in that, By inserting organic degradable organisms into a biodegradable polymer substrate and thermoforming it into a composite material mixed with natural insulating materials, a functional protective layer is formed on the surface.

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