Recovery shoe based on biodegradable polymer composite

Abstract

A recovery shoe based on a biodegradable polymer composite according to the present invention is characterized by being made of a biodegradable polymer composite containing 50 to 70 parts by weight of a biodegradable polyurethane synthesized from seaweed oil-based epoxidized polyol and isocyanate, 10 to 20 parts by weight of a biodegradation accelerator derived from vegetable sugars, and 20 to 30 parts by weight of a fatigue-relieving agent including natural latex.

Description

Biodegradable polymer composite-based recovery shoes

[0001] The present invention relates to recovery shoes based on biodegradable polymer composites, and more specifically, to recovery shoes that maximize wearer comfort through shock absorption and fatigue relief, and are environmentally friendly and sustainable by utilizing biodegradable materials.

[0002] In modern society, functional shoes such as sneakers have gone beyond being mere everyday items to play an important role in various fields including exercise, health, and fashion. In particular, for shoes that are worn for long periods or must absorb repetitive impact, features that reduce user fatigue and provide comfort are essential.

[0003] These shoes must effectively absorb impact applied to the feet and disperse pressure, while simultaneously maintaining durability and physical stability. However, many existing shoes primarily use materials such as EVA (Ethylene Vinyl Acetate) or PU (Polyurethane) to meet these requirements.

[0004] EVA and PU are suitable in terms of lightweightness and shock absorption performance, but they have several limitations.

[0005] EVA lacks durability and is prone to deformation or wear during prolonged use, while PU has excellent durability but has a disadvantage in terms of weight reduction.

[0006] Moreover, these synthetic materials are difficult to meet environmental requirements due to their lack of biodegradability and significant environmental impact after use.

[0007] Recently, with the growing interest in eco-friendly materials, the demand for shoe designs utilizing biodegradable materials is increasing.

[0008] Korean Registered Patent No. 1223219, "Biodegradable Foam Composition for Shoe Midsoles Using Polylactic Acid and Method for Manufacturing the Same," relates to a biodegradable foam composition for shoe midsoles using polylactic acid and a method for manufacturing the same, characterized by mixing a large amount of polylactic acid into a mixed substrate composed of a mixture of polylactic acid and a copolymer, which is a biodegradable resin. It is disclosed that by mixing a large amount of polylactic acid, which is a biodegradable resin, into the mixed substrate, the biodegradability is high, and by using a mixture of ethylene vinyl acetate copolymer, styrene isoprene styrene copolymer, and ethylene methyl acrylate copolymer, the durability and hardness are excellent, making it suitable as a material for shoe midsoles.

[0009] However, the above technology has a problem in that, as it uses polylactic acid (PLA) as its main component, its shock absorption performance under repetitive loads is limited and it lacks flexibility, failing to provide sufficient comfort and fatigue relief effects when worn.

[0010] Therefore, there is a need to develop novel and advanced eco-friendly biodegradable recovery shoes that maintain biodegradability while simultaneously improving shock absorption and fatigue relief performance.

[0011]

[0012] The present invention was devised to overcome the problems of the above technology, and its main purpose is to provide a recovery shoe made of a biodegradable polymer composite that provides shock absorption and fatigue relief functions while realizing eco-friendly characteristics based on a biodegradable polymer composite.

[0013] Another objective of the present invention is to enhance durability and physical stability by adding a reinforcing agent to a biodegradable polymer composite and to maintain the structural performance of the biodegradable polymer composite even after repeated use.

[0014] Another objective of the present invention is to maximize the fatigue relief performance and shock absorption effect of shoes by adding a viscoelastic composite based on natural latex.

[0015]

[0016] To achieve the above objective, the recovery shoes based on a biodegradable polymer composite according to the present invention are characterized by being made of a biodegradable polymer composite comprising 50 to 70 parts by weight of a biodegradable polyurethane synthesized from an epoxidized polyol based on seaweed oil and an isocyanate, 10 to 20 parts by weight of a biodegradation accelerator derived from plant sugars, and 20 to 30 parts by weight of a fatigue reliever including natural latex.

[0017] In addition, the above-mentioned biodegradable polymer composite further comprises a reinforcing agent including cellulose nanofibers, characterized by comprising 50 to 55 parts by weight of biodegradable polyurethane, 10 to 20 parts by weight of a biodegradation accelerator, 20 to 25 parts by weight of a fatigue reliever, and 5 to 15 parts by weight of a reinforcing agent.

[0018] In addition, the fatigue reliever is characterized by comprising, based on 100 parts by weight of the fatigue reliever, 50 to 60 parts by weight of a base containing natural latex and 40 to 50 parts by weight of a viscoelastic composite containing polybutylene succinate (PBS) and caprolactam.

[0019]

[0020] According to the recovery shoes based on a biodegradable polymer composite according to the present invention,

[0021] 1) Including seaweed oil-based biodegradable polyurethane and natural latex, it has the advantage of simultaneously satisfying shock absorption performance and biodegradability while effectively relieving fatigue even during prolonged wear,

[0022] 2) Reinforcements containing cellulose nanofibers complement the physical strength and durability of the composite, maintaining stability and performance even during long-term use of the shoes, and

[0023] 3) The combination of natural latex and viscoelastic composite enhances shock absorption performance and flexibility, thereby reducing wearer fatigue and providing comfort.

[0024]

[0025] FIG. 1 is a conceptual diagram illustrating one embodiment of the recovery shoes of the present invention.

[0026] FIG. 2 is a conceptual diagram illustrating another embodiment of the recovery shoes of the present invention.

[0027] FIG. 3 is a conceptual diagram illustrating the basic composition of the biodegradable polymer composite of the present invention.

[0028] Figure 4 is a conceptual diagram illustrating the composition of a viscoelastic composite.

[0029]

[0030] The recovery shoes based on a biodegradable polymer composite according to the present invention are made of a biodegradable polymer composite comprising 50 to 70 parts by weight of a biodegradable polyurethane synthesized from an epoxidized polyol based on seaweed oil and an isocyanate, 10 to 20 parts by weight of a biodegradation accelerator derived from plant sugars, and 20 to 30 parts by weight of a fatigue reliever including natural latex, which is the best form for carrying out the invention.

[0031]

[0032] Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. The attached drawings are not drawn to scale, and the same reference numerals in each drawing refer to the same components.

[0033]

[0034] FIG. 1 is a conceptual diagram illustrating one embodiment of the recovery shoes of the present invention, and FIG. 2 is a conceptual diagram illustrating another embodiment of the recovery shoes of the present invention.

[0035] The recovery shoes of the present invention are designed with a focus on absorbing external shocks and alleviating user fatigue. In particular, they are manufactured based on biodegradable materials, specifically biodegradable polymer composites, and possess the fundamental characteristics of being eco-friendly and naturally decomposing even after long-term use, thereby minimizing the impact on the environment.

[0036] The embodiment illustrated in FIG. 1 illustrates a shoe designed with a focus on absorbing external shocks and relieving user fatigue, wherein the midsole is designed to properly absorb shocks by having a 3D, or porous, structure.

[0037] The embodiment illustrated in FIG. 2 illustrates a structure that maximizes breathability and flexibility by implementing a porous structure not only in the midsole but also in part of the upper. This porous structure further enhances the comfort and functionality of the shoe and provides sufficient support while naturally deforming according to the movement of the foot. This porous structure effectively disperses pressure applied to the foot and minimizes fatigue even when worn for a long time.

[0038] Porous structures can generally be fabricated using 3D printing technology or porous molding processes, which form tiny air holes by extruding or injecting polymer materials into a specific pattern. This allows each part of the shoe—namely the midsole, outsole, and upper—or selected parts thereof, to be designed to provide breathability and flexibility.

[0039] Of course, the shoes of the present invention are not necessarily limited to the porous structure attached in FIGS. 1 and 2, and can take the structure, function, and use of known shoes such as athletic shoes, slippers, and sandals that do not have a porous structure.

[0040] The recovery shoes of the present invention are made of a biodegradable polymer composite, thereby maintaining the durability and functionality of the shoes while maintaining environmentally friendly characteristics.

[0041] Biodegradable polymer composites are materials that can decompose in nature, offering a significant advantage in that they minimize the environmental impact after use, thereby enabling the creation of sustainable products.

[0042] As a result, the present invention can provide an innovative design and structure that is eco-friendly and simultaneously considers functionality and sustainability.

[0043] These biodegradable polymer composites can be applied to the entire shoe or selectively to specific parts such as the midsole, outsole, or upper, enabling a functionally optimized design according to the use and required physical properties of each part.

[0044] In particular, the biodegradable polymer composite of the present invention comprises an epoxidized polyol based on seaweed oil and an isocyanate, and since it provides excellent biodegradability and physical stability as well as shock absorption and fatigue relief effects, it is more desirable to apply it to the midsoles or outsoles of shoes, especially to midsoles (mainly athletic shoes, running shoes, etc.) where repetitive loads and impacts are concentrated.

[0045]

[0046] The following describes in detail the composition, physical properties, and manufacturing method of the biodegradable polymer composite applied to the recovery shoes of the present invention, explaining the role each component plays in contributing to shock absorption, fatigue relief, and environmentally friendly properties.

[0047]

[0048] FIG. 3 is a conceptual diagram illustrating the basic composition of the biodegradable polymer composite of the present invention.

[0049] As can be seen from FIG. 3, the biodegradable polymer composite of the present invention is based on comprising 50 to 70 parts by weight of biodegradable polyurethane, 10 to 20 parts by weight of a biodegradation accelerator, and 20 to 30 parts by weight of a fatigue reliever.

[0050] The biodegradable polyurethane of the present invention is synthesized from an epoxidized polyol based on seaweed oil and an isocyanate.

[0051] Seaweed oil-based epoxidized polyols are reaction products in which multiple hydroxyl groups (-OH) are introduced through an epoxidation reaction of fatty acids extracted from seaweed oil; they are highly biodegradable and are a major raw material used in the synthesis of polyurethane.

[0052] This material is manufactured by oxidizing the double bonds of fatty acids contained in seaweed oil to convert them into an epoxy structure, and then substituting them with hydroxyl groups. This allows for the enhancement of the physical properties and biodegradability of the final polymer while imparting the reactivity necessary for polyurethane synthesis.

[0053] Specifically, this seaweed oil-based epoxidized polyol combines a biodegradable function that minimizes environmental impact during the degradation process by including hydroxyl groups derived from natural fatty acids, a physical property enhancement function that improves shock absorption and durability by increasing the viscoelasticity and flexibility of the polymer structure, and an eco-friendly function that provides sustainability by using raw materials derived from natural resources.

[0054] This involves extracting fatty acids (e.g., linoleic acid, oleic acid, palmitic acid) contained in seaweed oil, then using a peroxide or acid catalyst to oxidize the double bonds of the fatty acids and introduce hydroxyl groups to the epoxidized fatty acids to convert them into polyfunctional polyols.

[0055] More specifically, seaweed oil-based epoxidized polyols may include detailed types such as epoxidized glyceryl linoleate, which contains multiple epoxy groups by epoxidizing the double bond of linoleic acid; epoxidized propyl alginate ester, which has increased reactivity by propyl esterifying alginate derived from brown algae and then epoxidizing it; epoxidized glyceryl oleate, which has epoxidized the single double bond of oleic acid and then glyceryl esterifying it; and epoxidized ethyl palmitate, which has reactivity imparted by epoxidizing palmitic acid and then ethyl esterifying it.

[0056] That is, the seaweed oil-based epoxidized polyol of the present invention is a type of bio-based polyol, can be manufactured in a manner similar to epoxidized soybean oil-based polyol, and has a reactive structure containing a plurality of hydroxyl groups.

[0057] Isocyanates are compounds with an -N=C=O structure and are essential reactive substances in polyurethane synthesis. Isocyanates react with the hydroxyl groups (-OH) of polyols to form urethane bonds (-NH-COO-), playing a role in determining the physical properties and durability of polyurethanes through the linkage and curing of polymer chains.

[0058] In the present invention, the isocyanate forms polymer chains through a chemical reaction with an epoxidized polyol to provide structural stability to the biodegradable polyurethane, and provides the function of enhancing high strength and shock absorption performance while imparting viscoelasticity and flexibility.

[0059] In other words, isocyanates play a key chemical role in determining the structure formation and physical performance of the biodegradable polyurethane of the present invention, thereby ensuring the functionality and sustainability of the recovery shoes based on the biodegradable polymer composite.

[0060] The synthesis process of biodegradable polyurethane synthesized with seaweed oil-based epoxidized polyols and isocyanates can proceed as follows.

[0061] In a state where fatty acids (linoleic acid, oleic acid, palmitic acid, etc.) extracted from seaweed oil are used as raw materials, an epoxy group is introduced by carrying out an epoxy reaction on the double bonds of the fatty acids using hydrogen peroxide or acetic peroxide.

[0062] Subsequently, an alcohol (glycerol, ethylene glycol, etc.) is added to the epoxidized fatty acid to convert it into an epoxidized polyol containing polyfunctional hydroxyl groups.

[0063] Next, the epoxidized polyol and isocyanate are prepared in an appropriate ratio (generally a molar ratio of 1:1 to 1:2), and a catalyst (e.g., dibutyltin dilaurate (DBTDL) or an amine-based catalyst) is added to prepare for the reaction.

[0064] When the hydroxyl group (-OH) of the epoxidized polyol and the isocyanate group (-NCO) of the isocyanate are mixed, the two components react to form a urethane bond (-NH-COO-). This mixing and reaction process is generally carried out at a temperature of 50 to 80°C and can be cured on its own for 1 to 3 hours or cured together with other components described later.

[0065]

[0066] More specifically, the aforementioned seaweed oil-based epoxidized polyol may be derived from at least one of an alginate ester extracted from brown algae, carrageenan extracted from red algae, and a linoleic acid derivative extracted from green algae.

[0067] Alginate ester is a compound produced by converting the carboxyl group of alginate, a natural polysaccharide derived from brown algae, through an esterification reaction.

[0068] At this time, brown algae are large, brown-colored seaweeds that inhabit the sea, such as kelp, wakame, and Sargassum.

[0069] Alginate is extracted from the cell walls of brown algae and is mainly composed of block copolymers of mannuronic acid and glucuronic acid. The esterification reaction is carried out by adding an alcohol (methanol or ethanol) to alginate, and through this process, alginate esters increase physical stability and reactivity.

[0070] Alginate esters exhibit excellent biodegradability, provide viscoelasticity and flexibility, and are used as useful raw materials in polymer synthesis. Furthermore, they can simultaneously enhance shock absorption and physical strength, making them suitable for high-performance composites such as footwear materials.

[0071] In particular, during the polyurethane synthesis process, the hydroxyl group (-OH) of the alginate ester reacts with the isocyanate to form a urethane bond.

[0072] Carrageenan is a sulfated polysaccharide extracted from red algae, mainly found in red algae such as *Chondrus crispus*, *Kappaphycus alvarezii*, and *Eucheuma denticulatum*.

[0073] Carrageenan is classified into three main forms: kappa, iota, and lambda, each of which differs in physical properties and uses.

[0074] Due to its structure with a high sulfate group, carrageenan binds well with water, possessing viscoelasticity and gel-forming ability, making it suitable for use as a reactive raw material in polymer synthesis. In polyurethane synthesis, the hydroxyl groups (-OH) of carrageenan react with isocyanates to form urethane bonds, thereby providing physical strength and biodegradability.

[0075] In addition, carrageenan enhances shock absorption and flexibility while complementing the physical stability of polymer composites. Thanks to its eco-friendly properties, it is utilized as a sustainable material and can be used as a suitable raw material for shoe midsoles or outsoles.

[0076] Linoleic acid derivatives are reactive substances produced through various chemical transformations based on linoleic acid extracted from green algae such as Chlorella spp., Spirulina spp., and Ulva spp.

[0077] Linoleic acid is a polyunsaturated fatty acid found primarily in the cell membrane lipids of green algae; it has a double bond structure, which is advantageous for enhancing chemical reactivity.

[0078] Linoleic acid derivatives are converted into polyols containing polyfunctional hydroxyl groups through epoxidation, esterification, or hydroxylation. These derivatives form polyurethanes through reaction with isocyanates, complementing the flexibility and shock absorption performance of the final material.

[0079] Furthermore, linoleic acid derivatives are gaining attention as eco-friendly materials due to their biodegradability, meaning they can decompose in the natural environment. Possessing properties that improve the viscoelasticity of polymer composites and enhance physical stability, they exhibit excellent functionality when utilized as footwear materials.

[0080] Hexamethylene diisocyanate (HDI), a type of isocyanate, is an organic compound having the chemical formula OCN-(CH₂)6-NCO and is a polyfunctional isocyanate containing a straight alkyl chain of six carbons and isocyanate groups (-NCO) at both ends.

[0081] Due to the highly reactive isocyanate group, it readily reacts with polyols to form urethane bonds (-NH-COO-).

[0082] Specifically, two isocyanate groups (-NCO) react with the hydroxyl groups (-OH) of the epoxidized polyol to form polymer chains of polyurethane, and the low toxicity and excellent reactivity of HDI make it suitable for the synthesis of environmentally friendly polyurethane.

[0083] In other words, compared to conventional toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI), it has higher biocompatibility and lower volatile organic compound (VOC) emissions.

[0084] In addition, hexamethylene diisocyanate improves the viscoelasticity and flexibility of polyurethane produced by its linear alkyl chain structure, and also provides a foundation for performing functions suitable for shock-absorbing parts such as the midsole or outsole of recovery shoes.

[0085] The synthesis process of the seaweed oil-based epoxidized polyol and hexamethylene diisocyanate described above is the same or similar to the synthesis process described above, so a separate explanation is omitted.

[0086] In summary, by utilizing various biodegradable polyols derived from brown algae, red algae, and green algae as materials for biodegradable polyurethane, it is possible to optimize shock absorption, flexibility, and physical strength in the recovery shoes of the present invention and provide an environmentally friendly and sustainable material.

[0087] This biodegradable polyurethane is set in an amount of 50 to 70 parts by weight based on 100 parts by weight of the biodegradable polymer composite to provide a foundation that enhances shock absorption and flexibility, as well as physical stability and durability.

[0088]

[0089] The biodegradation promoter of the present invention is derived from plant-based sugars and provides the function of increasing the decomposition rate of shoes made of the biodegradable polymer composite of the present invention by promoting microbial activation during the biodegradation process.

[0090] These biodegradation promoters have the characteristic of reducing environmental burden by efficiently decomposing in the natural environment while maintaining physical strength and viscoelasticity within the polymer structure.

[0091] This biodegradation accelerator is a naturally derived material that facilitates easy mixing during the polymer synthesis process and can maximize biodegradability and eco-friendly characteristics.

[0092] In this context, plant-based saccharides are carbohydrate compounds derived from plants, which are organic compounds composed of carbon (C), hydrogen (H), and oxygen (O).

[0093] These are classified into monosaccharides, disaccharides, and polysaccharides, and are eco-friendly raw materials that decompose easily in nature and can be utilized as biodegradable materials.

[0094] These plant sugars come in various types, such as glucose, sucrose, cellulose, and alginate.

[0095]

[0096] In particular, in the present invention, it is preferable to include alginate and maltodextrin as plant sugars.

[0097] Alginate is a natural polysaccharide derived from brown algae, and is mainly composed of copolymers of mannuronic acid and glucuronic acid.

[0098] Alginate is a water-soluble polymer with excellent properties of forming a gel by combining with water, and is utilized in various industrial and research fields. Its chemical formula is (C6H8O6)n, and it is an eco-friendly polymer that provides both physical stability and biodegradability.

[0099] Alginate promotes the activation of microorganisms during the biodegradation process to accelerate the degradation rate of polymer composites and enhances their flexibility and shock absorption performance by increasing viscoelasticity; furthermore, it can complement physical stability by interacting with the polyurethane structure.

[0100] In particular, among various plant-based sugars, it has the advantage of having excellent gel-forming ability and providing structural stability by combining with moisture, thereby strengthening the viscoelasticity of the polymer composite in the shoes of the present invention and minimizing physical deformation even with repeated use, which can extend the lifespan of the product.

[0101] Maltodextrin is a natural polysaccharide produced by enzymatic or acid hydrolysis of starch (corn, potatoes, rice, etc.), and it is biodegradable and easily broken down by microorganisms.

[0102] In the present invention, maltodextrin acts as a biodegradation promoter to increase the degradation rate of the polymer composite and enhance physical stability by supplementing viscoelasticity.

[0103] In particular, compared to other plant-based sugars, maltodextrin has the characteristics of being easily soluble in water and uniformly distributed within a complex, while possessing high reactivity relative to weight and excellent ease of processing.

[0104] Alginate and maltodextrin are preferably mixed in a 7:3 ratio to enhance the viscoelasticity of the polymer composite and maximize biodegradability while maintaining physical stability.

[0105] In addition, a biodegradation promoter may be included in an amount of 10 to 20 parts by weight in 100 parts by weight of the biodegradable polymer composite to accelerate the degradation rate of the polymer structure and maximize environmentally friendly properties.

[0106]

[0107] The fatigue reliever of the present invention is a material that effectively absorbs repetitive loads and impacts applied to the user's foot and evenly distributes pressure to reduce fatigue, thereby providing the main significance and justification for the shoes of the present invention to have the name 'Recovery'.

[0108] This fatigue reliever improves the fit of the shoe, minimizes foot discomfort caused by prolonged use, and provides the function of increasing the efficiency of physical activity. In other words, the main feature of this fatigue reliever is that it provides viscoelasticity and flexibility to cushion the impact between the foot and the ground and provides stable support.

[0109] Specifically, the fatigue reliever of the present invention is based on containing natural latex.

[0110] Natural latex is a natural polymer extracted from the sap of the rubber tree (Hevea brasiliensis), and its main component is polyisoprene, a material with excellent elasticity and flexibility.

[0111] Natural latex forms a fine pore structure, offering excellent shock absorption and energy dispersion capabilities. It evenly distributes the load applied to the feet, effectively relieving user fatigue.

[0112] Furthermore, natural latex provides viscoelasticity, delivering a stable cushioning effect at the contact surface between the foot and the shoe, and offers excellent resilience that minimizes deformation even under repetitive loads. These features can be fully understood as maximizing the shoe's comfort and supporting fatigue recovery capabilities that live up to the name 'Recovery'.

[0113] In addition, natural latex has excellent advantages in combination with other materials of the present invention.

[0114] For example, when mixed with the biodegradable polyurethane of the present invention, the physical bonding between polymers is strengthened to improve durability, and when used together with a biodegradation accelerator (alginate, maltodextrin), the eco-friendliness of the composite can be maximized.

[0115] Due to these characteristics, natural latex serves as a core material that satisfies the functional requirements of shock absorption, fatigue relief, and stability provided by the recovery shoes of the present invention, and possesses the property of maximizing performance through combination with other materials.

[0116] This fatigue reliever can be set in an amount of 20 to 30 parts by weight based on 100 parts by weight of the biodegradable polymer composite of the present invention, thereby preventing fatigue and discomfort of the feet caused by repetitive loading, while having the characteristics of enhancing shock absorption performance and stable support.

[0117] As mentioned earlier, the aforementioned biodegradable polymer composite is preferably used as a material for midsoles or outsoles in shoes. A brief explanation of the method for manufacturing the midsole is as follows.

[0118] Biodegradable polyurethane, a biodegradation accelerator, and a fatigue reliever are uniformly mixed according to a set weight ratio, and a catalyst or viscosity modifier is added during the mixing process to control viscoelasticity. The mixing temperature is maintained at 50 to 70°C, and a high-speed stirrer is used to ensure that the material is uniformly distributed.

[0119] The mixed polymer composite is injected into a pre-prepared mold. The mold is designed to fit the shape of the midsole, and pressure is applied after injection to ensure the mixture completely fills the mold.

[0120] The mixture injected into the mold is heat-cured at a temperature of 60 to 100°C for 30 minutes to 1 hour, and physical stability is ensured through a cooling process and separated from the mold.

[0121] The surface of the molded midsole is finished, and if necessary, additional heat treatment or coating processes are applied to enhance durability and water resistance, after which it is combined with an outsole and upper produced through other processes. Alternatively, they can be manufactured by molding them as a single unit using a 3D printer without using a mold.

[0122]

[0123] Below, the results of an experiment on the biodegradability of the recovery shoes of the present invention are presented.

[0124]

[0125] <Example 1>

[0126] 55 parts by weight of biodegradable polyurethane, 15 parts by weight of a biodegradation accelerator (a mixture of 10 parts by weight of alginate and 5 parts by weight of maltodextrin), and 25 parts by weight of natural latex, a fatigue reliever, were mixed at a mixing temperature of 60°C and injected into a pre-designed mold.

[0127] The mixture injected into the mold was heat-cured at 80°C for 45 minutes and then stabilized through a cooling process, and the surface of the molded product was smoothed to complete the midsole.

[0128]

[0129] [Experiment 1: Biodegradability Test]

[0130]

[0131] This experiment was conducted to evaluate biodegradability according to ASTM D5338 standards. First, the outsole was cut into 0.25 cm³ pieces to prepare a sample, and cellulose was used as a control.

[0132] The prepared sample was mixed with activated compost maintained for 24 months in a ratio of 1:3.

[0133] The compost was sieved to a particle size of 10 mm or less and uniformly mixed with the sample, and the mixture was maintained for 45 days at a temperature of 58°C and a relative humidity of 55%.

[0134] CO₂ emitted during the biodegradation process was measured daily, and the validity of the experiment was verified by confirming that the biodegradation rate of the control group (cellulose) was 70% or higher, as required by ASTM D5338 standards. After the experiment was completed, the amount of emitted CO₂ and the residue of the samples were analyzed to calculate the biodegradation rate.

[0135] The following Table 1 shows the experimental results.

[0136]

[0137] Measurement Item Example Control Group CO₂ Emission (mg / g, 45 days) 68.3 72.8 Biodegradation Rate (%) 88.5 98.0 Residue Status Fine particles Partial residue Complete decomposition experiment Validity Confirmation (Cellulose >70%) Effective Effective

[0138] As can be seen from the results above, the biodegradable polymer composite of the present invention met the biodegradation rate of 70% or more required by ASTM D5338 standards and recorded a biodegradation rate of 88.5% over 45 days, proving its eco-friendly characteristics.

[0139] It exhibited similar degradation characteristics when compared to the biodegradation rate (98.0%) of the control group (cellulose), and residue analysis indicated that further biodegradation is possible.

[0140] Through this, it was confirmed that the shoes made of the biodegradable polymer composite of the present invention are suitable as an environmentally friendly material.

[0141] In summary, the recovery shoes of the present invention maximize wearer comfort through shock absorption and fatigue relief, and provide environmentally friendly and sustainable characteristics by utilizing biodegradable materials.

[0142]

[0143] Furthermore, the biodegradable polymer composite may additionally include a reinforcing agent containing cellulose nanofibers.

[0144] At this time, the weight parts of each component are adjusted so that the biodegradable polymer composite comprises 50 to 55 parts by weight of biodegradable polyurethane, 10 to 20 parts by weight of a biodegradation accelerator, 20 to 25 parts by weight of a fatigue reliever, and 5 to 15 parts by weight of a reinforcing agent.

[0145] The strengthening agent of the present invention refers to a substance that complements physical strength and durability within a biodegradable polymer composite, minimizes deformation caused by external loads and repeated use, and maintains the physical stability of the shoe of the present invention. In other words, the strengthening agent reinforces the structure of the composite to maximize durability and impact resistance while maintaining the inherent flexibility and viscoelasticity of the biodegradable material.

[0146] In this invention, the reason a reinforcing agent is added to the biodegradable polymer composite is to satisfy the high durability and stability required for the midsole or outsole of a shoe while maintaining eco-friendly characteristics.

[0147] In other words, the reinforcing agent interacts with biodegradable polyurethane, fatigue relievers, and biodegradation accelerators to increase the bonding strength between polymers and improve physical strength and wear resistance, thereby enabling the shoe's performance to be stably maintained even during prolonged use.

[0148] The cellulose nanofibers fundamentally included in this reinforcing agent are high-strength nanomaterials manufactured by grinding natural cellulose to nano-sizes or chemically treating it, and they take the form of fibers with diameters ranging from several nanometers to tens of nanometers.

[0149] In the reinforcing agent of the present invention, cellulose nanofibers complement physical strength and durability within the biodegradable polymer composite through a high-strength fiber structure, and in particular, significantly enhance the structural stability of the composite by increasing the bonding strength between polymer chains.

[0150] Due to their nanometer-sized fibrous structure, these cellulose nanofibers are uniformly dispersed within the composite, helping to distribute external impact loads evenly rather than concentrating them on specific areas.

[0151] In addition, it maintains the viscoelasticity of the biodegradable polymer composite while minimizing deformation and wear caused by repetitive loads or external impacts, ensuring stable physical performance even during long-term use.

[0152] Due to these characteristics, cellulose nanofibers provide the ability to effectively enhance the durability and impact resistance of biodegradable polymer composites, as well as their resilience during prolonged use.

[0153] These reinforcing agents are configured to include 5 to 15 parts by weight based on 100 parts by weight of the biodegradable polymer composite, thereby improving the physical strength and durability of the composite and maximizing the impact dispersion effect while maintaining biodegradability.

[0154]

[0155] Additionally, the aforementioned reinforcing agent may further include lignin and natural silica.

[0156] Lignin is a natural polymer found in the cell walls of lignocellulosic biomass, composed primarily of irregular polymer chains of phenylpropane derivatives. Lignin provides stiffness and structural support in plant tissues and plays a role in increasing resistance to moisture and external physical stress.

[0157] In reinforcing agents, lignin enhances physical strength and durability by complementing the bonding forces between polymer chains within biodegradable polymer composites. When added to biodegradable polymer composites, lignin improves the physical stability of the composite by increasing shock absorption performance and minimizing deformation caused by repeated use or load.

[0158] In addition, lignin provides thermal stability and possesses eco-friendly characteristics that reduce the environmental impact during the biodegradation process.

[0159] Natural silica is silicon dioxide (SiO₂) derived from nature, existing mainly in the form of quartz, diatomite, or other minerals. This natural silica has a fine particle structure and a high surface area, which generally provides properties that complement physical strength and durability.

[0160] In the reinforcing agent of the present invention, natural silica plays a role in supplementing physical strength and improving shock absorption performance within the biodegradable polymer composite.

[0161] This natural silica enhances durability by strengthening the bonding forces between polymer chains within the composite and complements the physical stability of the product by effectively dispersing applied external loads.

[0162] In addition, the fine particle structure of natural silica can increase the wear resistance of the composite and minimize deformation caused by repeated use, while also ensuring the ability to maximize impact resistance and extend the lifespan of the product in areas requiring high durability and physical strength, such as the midsole and outsole of shoes.

[0163] The weight range of the reinforcing agent containing these three components can be adjusted according to the required characteristics and purpose of the biodegradable polymer composite. Based on 100 parts by weight of the reinforcing agent, cellulose nanofibers can be set to 50 to 60 parts by weight to ensure physical strength as the main component of the reinforcing agent, lignin can be set to 20 to 30 parts by weight to supplement shock absorption, physical strength, and stability, and natural silica can be set to 10 to 20 parts by weight to increase wear resistance and disperse external loads.

[0164] In summary, the physical strength and durability of the biodegradable polymer composite are maximized by reinforcing agents including cellulose nanofibers, lignin, and natural silica, and shock absorption and wear resistance are enhanced, thereby exhibiting characteristics that effectively improve the stability and lifespan of the shoes of the present invention.

[0165]

[0166] Natural latex, the main component of the fatigue reliever described earlier, offers the advantage of alleviating wearer fatigue and maximizing comfort by providing shock absorption and flexibility; however, there is a possibility that physical deformation or reduced durability may occur with repeated or long-term use. Therefore, to complement the durability of natural latex while enhancing the physical stability and viscoelasticity of the biodegradable polymer composite, the fatigue reliever additionally proposes a viscoelastic composite.

[0167] The viscoelastic composite of the present invention is a material having the characteristic of absorbing shock and dispersing energy by simultaneously exhibiting elasticity and viscosity in response to external loads, and plays a role in complementing shock absorption, flexibility, and physical stability within a biodegradable polymer composite.

[0168] The reason for reinforcing viscoelasticity is to minimize deformation under repetitive loads or impacts and maintain the structural stability of the composite, thereby maximizing the fit and comfort of the shoes and reinforcing the recovery function.

[0169] Specifically, the fatigue reliever of the present invention may comprise, based on 100 parts by weight of the fatigue reliever, 50 to 60 parts by weight of a base including natural latex and 40 to 50 parts by weight of a viscoelastic composite including polybutylene succinate (PBS) and caprolactam.

[0170] This weight range is designed to maintain a balance of each component within the fatigue reliever to maximize shock absorption and flexibility, while complementing the physical stability of the biodegradable polymer composite to minimize deformation even during prolonged use.

[0171] First, polybutylene succinate (PBS) is a biodegradable polymer produced by the condensation polymerization of butanediol (1,4-Butanediol) and succinic acid, and its chemical formula is (C8H12O4)n.

[0172] This material is a linear thermoplastic polyester containing ester bonds (-COO-), and is an eco-friendly material with excellent biodegradability, heat resistance, and flexibility.

[0173] Polybutylene succinate strengthens the bonding forces between polymer chains within viscoelastic composites and complements the flexibility and physical stability of the composite against external loads.

[0174] This provides a balanced combination of elasticity and viscosity to enhance shock absorption performance and minimize deformation even under repetitive loads. In particular, by providing flexibility while maintaining the durability and viscoelasticity of the viscoelastic composite, the wearing comfort of the shoe of the present invention is maximized, thereby enhancing the recovery function.

[0175] In addition, polybutylene succinate has excellent biodegradability, which not only enhances eco-friendly characteristics but also optimizes the physical properties of the viscoelastic composite through combination with other components of the viscoelastic composite (e.g., caprolactam).

[0176] Caprolactam is an organic compound represented by the chemical formula C6H11NO and is a lactam-based substance with a seven-membered ring structure.

[0177] Caprolactam is a material that is mainly used as a monomer for the synthesis of Nylon 6 and has reactivity with isocyanates and polyols, contributing to the linkage and curing of polymer chains, as well as providing high thermal stability and physical strength and thermoplastic properties.

[0178] Caprolactam plays a role in supplementing physical stability and durability by strengthening the bonding forces between polymer chains within viscoelastic composites.

[0179] In other words, it improves shock absorption performance by simultaneously providing elasticity and viscosity to respond to external loads.

[0180] In particular, caprolactam enhances the durability of viscoelastic composites by minimizing physical deformation even at high temperatures through thermal stability.

[0181] In addition, when combined with other components (polybutyrene succinate) within the viscoelastic composite, it can maximize the stability of the polymer structure while simultaneously maintaining flexibility and physical strength.

[0182] In addition, caprolactam combines the function of viscoelastic composites to alleviate fatigue caused by prolonged foot use. Specifically, within the viscoelastic composite, caprolactam combines flexibility and elasticity to help the midsole evenly distribute pressure on the soles of the feet. This is effective in absorbing the repetitive loads applied to the feet while standing or walking for long periods and preventing fatigue from concentrating on specific areas of the soles.

[0183] In addition, the viscoelastic properties of caprolactam support the natural movement of the foot and dynamically relieve the load transmitted to it, providing comfort even during prolonged wear.

[0184] Due to these characteristics, caprolactam not only provides the long-term use stability and repetitive load resistance required by viscoelastic composites but also alleviates foot fatigue, playing a key role in simultaneously enhancing the shock absorption and fatigue relief performance of the recovery shoes of the present invention.

[0185] The aforementioned viscoelastic composite is well mixed with a base containing natural latex, making it possible to maximize the shock absorption performance and flexibility of the shoe of the present invention while maintaining physical stability even under repetitive loads.

[0186] In summary, through a fatigue reliever composed of a combination of natural latex and a viscoelastic composite, it is possible to simultaneously satisfy fatigue relief and physical strength, as well as effectively enhance the durability and stability of the shoes of the present invention while maintaining biodegradability.

[0187]

[0188] Furthermore, the aforementioned viscoelastic composite can enhance a wider range of functions by including additional components other than the two components, which are explained in detail as follows.

[0189]

[0190] Figure 4 is a conceptual diagram illustrating the composition of a viscoelastic composite.

[0191] As can be seen from Figure 4, the viscoelastic composite may additionally include epoxidized castor oil, zirconia nanoparticles, and phytic acid.

[0192] At this time, the viscoelastic composite may comprise, based on 100 parts by weight, 40 to 50 parts by weight of polybutylene succinate, 20 to 30 parts by weight of caprolactam, 10 to 15 parts by weight of epoxidized castor oil, 5 to 10 parts by weight of zirconia nanoparticles, and 5 to 10 parts by weight of phytic acid.

[0193] Epoxidized castor oil is a compound prepared by introducing epoxy groups to the double bonds of fatty acids through an epoxidation reaction, using ricinoleic acid extracted from castor oil as the main component. Represented by the chemical formula (C57H104O9)n, it is an eco-friendly polymer material that contains an epoxy structure, exhibits high reactivity, and possesses excellent biodegradability and viscoelasticity.

[0194] Epoxidized castor oil provides physical stability by strengthening the bonding between polymers while complementing shock absorption and flexibility in viscoelastic composites.

[0195] The epoxy groups enhance the reactivity between polymer chains and improve the resilience of the composite against external loads while maintaining uniform viscoelasticity. Additionally, they serve to supplement physical strength while minimizing deformation even under repeated use or prolonged loading of the shoes of the present invention.

[0196] In addition, epoxidized castor oil possesses biodegradable properties, which enhances the eco-friendliness of viscoelastic composites and optimizes the performance of the composite through combination with other components (e.g., polybutylene succinate, caprolactam).

[0197] Through this, epoxidized castor oil combines the functions of shock absorption, flexibility, and durability in the recovery shoes of the present invention.

[0198] Zirconia nanoparticles are high-strength ceramic materials produced by processing zirconium oxide, represented by the chemical formula ZrO2, into nanometer sizes, characterized by high strength and heat resistance.

[0199] These nanoparticles possess various forms, such as monoclinic, orthorhombic, and tetragonal, depending on their crystal structure, and provide excellent chemical stability and physical strength. In other words, nano-sized zirconia has a high surface area and reactivity, performing a reinforcing function that enhances impact and wear resistance in polymer composites.

[0200] Zirconia nanoparticles play a role in enhancing physical strength and durability in viscoelastic composites and maximizing resistance to external impacts.

[0201] Nano-sized particles are uniformly dispersed within the composite, enhancing interactions between polymers and complementing the physical stability of the viscoelastic composite. Furthermore, the high hardness and wear resistance of zirconia significantly improve the wear resistance of the viscoelastic composite, enabling it to maintain stability even during prolonged use. Zirconia nanoparticles disperse impact loads and minimize deformation caused by external loads while maintaining the viscoelasticity of the viscoelastic composite.

[0202] Furthermore, this material provides thermal stability to viscoelastic composites, maintaining their physical properties even in high-temperature environments. Thanks to these characteristics, zirconia nanoparticles offer the ability to further enhance the durability and stability of viscoelastic composites.

[0203] Phytic acid is an organophosphate compound represented by the chemical formula C6H18O24P6, primarily found in the seeds of plants such as grains, legumes, and nuts. Phytic acid takes on a structure in which six phosphate groups are bonded to an inositol molecule, forming a polyvalent anion that acts as a chelating agent by readily binding to metal ions. Furthermore, it is evaluated as an eco-friendly material that is water-soluble and highly biodegradable.

[0204] Phytic acid enhances physical stability by strengthening the bonding forces between polymers in viscoelastic composites and provides a function that complements the dispersibility and viscoelasticity of the viscoelastic composites.

[0205] The polyfunctional phosphate structure of phytic acid interacts with polymer chains to increase impact resistance and the durability of the composite, and binds to metal ions to provide thermal stability of the composite as well as minimize deformation under repetitive loading.

[0206] In addition, phytic acid promotes biodegradability within the viscoelastic composite to maximize eco-friendly properties and works harmoniously with other components (zirconia nanoparticles, epoxidized castor oil) to optimize the physical properties of the viscoelastic composite.

[0207] Through this, phytic acid simultaneously provides shock absorption, durability, and environmental friendliness in the viscoelastic composite of the present invention.

[0208] In summary, by adding epoxidized castor oil, zirconia nanoparticles, and phytic acid to the viscoelastic composite, the shock absorption performance and durability of the viscoelastic composite are maximized, and biodegradability and physical stability are simultaneously enhanced, thereby providing the advantage of satisfying both the functionality and eco-friendliness of the shoes of the present invention.

[0209]

[0210] Below, experimental results are presented to demonstrate the superiority of the viscoelastic composite described above. In this case, Example 1 is the outsole described earlier, and a redundant description is omitted here.

[0211]

[0212] <Example 2>

[0213] 55 parts by weight of biodegradable polyurethane, 15 parts by weight of a biodegradation accelerator (a mixture of 10 parts by weight of alginate and 5 parts by weight of maltodextrin), and 25 parts by weight of a fatigue reliever (a mixture of 15 parts by weight of natural latex and 10 parts by weight of a viscoelastic composite) were mixed.

[0214] At this time, the viscoelastic composite was composed of 6 parts by weight of polybutylene succinate and 4 parts by weight of caprolactam.

[0215] The mixture was uniformly mixed with the mixing temperature adjusted to 60°C and then injected into a pre-designed mold. The mixture injected into the mold was heat-cured at 80°C for 45 minutes, stabilized through a cooling process, and the surface of the molded product was finished to complete the midsole.

[0216]

[0217] <Example 3>

[0218] 55 parts by weight of biodegradable polyurethane, 15 parts by weight of a biodegradation accelerator (a mixture of 10 parts by weight of alginate and 5 parts by weight of maltodextrin), and 30 parts by weight of a fatigue reliever (a mixture of 18 parts by weight of natural latex and 12 parts by weight of a viscoelastic composite) were mixed.

[0219] At this time, the viscoelastic composite was composed of 5 parts by weight of polybutylene succinate, 4 parts by weight of caprolactam, 1 part by weight of epoxidized castor oil, 1 part by weight of zirconia nanoparticles, and 1 part by weight of phytic acid.

[0220] The mixture was uniformly mixed with the mixing temperature adjusted to 60°C and then injected into a pre-designed mold. The mixture injected into the mold was heat-cured at 80°C for 45 minutes, stabilized through a cooling process, and the surface of the molded product was finished to complete the midsole.

[0221]

[0222] [Experiment 2: Evaluation of Shock Absorption and Pressure Dispersion Performance]

[0223]

[0224] This experiment was conducted according to ASTM F1614 (shoe shock absorption test) standards to evaluate the shock absorption and pressure dispersion performance of the shoe materials of Examples 1, 2, and 3.

[0225] First, the midsole samples of Examples 1, 2, and 3 were each cut to a size of 10 cm x 10 cm and placed on a test platform equipped with a pressure sensor.

[0226] A load of 75 kg was repeatedly applied to each sample 1,000 times, and the shock absorption rate and pressure dispersion data of the sample were measured after the load was applied.

[0227] Shock absorption rate was expressed as a percentage by calculating the difference in energy absorption before and after loading, and pressure dispersion was calculated based on the peak pressure measured on the sensor mat. The tests were conducted at room temperature, and all samples were evaluated under identical conditions.

[0228] Table 2 below shows the experimental results.

[0229] Measurement Item Example 1 Example 2 Example 3 Shock absorption rate (%) 67.27 2.87 9.3 Pressure dispersion rate (%) 62.16 8.77 4.9 Peak pressure reduction rate (%) 59.86 5.37 1.2

[0230]

[0231] Referring to the results above, Examples 2 and 3 containing viscoelastic composites, particularly Example 3, showed superior performance to Example 1 in terms of shock absorption rate and pressure dispersion rate.

[0232] Through this, it was confirmed that viscoelastic composites play an important role in the shock absorption and fatigue relief performance of shoes.

[0233]

[0234] [Experiment 3: Fatigue Recovery Performance Evaluation]

[0235]

[0236] The comfort and fatigue recovery performance of the midsoles of Examples 1, 2, and 3 were evaluated according to the ISO 20873 (shoe fatigue test) standard. This experiment was designed to demonstrate fatigue relief and improved fit of athletic shoes based on user-centered data.

[0237] At this time, the athletic shoe was manufactured using the midsoles of Examples 1, 2, and 3, and the upper was made of a mesh-type synthetic fiber material that provides breathability and lightness, while the outsole was made of rubber material to maintain the basic structure for the test. Through this, the effect of midsole performance on the overall fit of the athletic shoe was evaluated.

[0238] The experiment was conducted on 20 adults, and each subject performed walking and standing tests for 2 hours while wearing athletic shoes made with the midsoles of Examples 1, 2, and 3.

[0239] The subjects' muscle fatigue was analyzed by analyzing changes in muscle activity before and after walking using surface electromyography (sEMG), and subjective comfort was evaluated using a questionnaire designed with a 10-point scale.

[0240] All subjects underwent testing in the same environment, and data were collected before and after the experiment to calculate the average value.

[0241] Table 3 below shows the experimental results.

[0242] Measurement Item Example 1 Example 2 Example 3 Muscle Fatigue Reduction Rate (%) 12.3 18.7 24.2 Subjective Comfort Score (out of 10) 6.4 7.8 8.6

[0243]

[0244] Referring to the results above, Examples 2 and 3 containing viscoelastic composites showed superior performance compared to Example 1 in terms of muscle fatigue reduction rate and subjective comfort score.

[0245] Through this, it was confirmed that viscoelastic composites play an important role in fatigue recovery and improving the wearing comfort of shoes.

[0246]

[0247] As explained above, the composition and operation of the recovery shoes based on the biodegradable polymer composite according to the present invention have been described and illustrated in the above description and drawings; however, this is merely an example, and the concept of the present invention is not limited to the above description and drawings. It is understood that various changes and modifications are possible within the scope of the technical concept of the present invention.

[0248]

[0249] The recovery shoes according to the present invention can be widely applied throughout the high-performance shoe manufacturing industry, which has excellent shock absorption and fatigue relief performance.

[0250] In particular, this invention has very high industrial applicability as it possesses high market value and sustainable productivity in the eco-friendly footwear market and the healthcare-related sports goods industry based on biodegradable material technology.

Claims

1. As a recovery shoe based on a biodegradable polymer composite, 50 to 70 parts by weight of biodegradable polyurethane synthesized with seaweed oil-based epoxidized polyol and isocyanate, and 10 to 20 parts by weight of a biodegradation promoter derived from plant sugars and, Recovery shoes characterized by being made of a biodegradable polymer composite containing 20 to 30 parts by weight of a fatigue reliever including natural latex.

2. In Paragraph 1, The above seaweed oil-based epoxidized polyol is, Derived from at least one of an alginate ester extracted from brown algae, carrageenan extracted from red algae, and a linoleic acid derivative extracted from green algae, and The above isocyanate is, Recovery shoes characterized by being hexamethylene diisocyanate.

3. In Paragraph 1, The above biodegradation promoter is, Recovery shoes characterized by containing alginate and maltodextrin.

4. In Paragraph 1, The above-mentioned biodegradable polymer composite is, A reinforcing agent further comprising cellulose nanofiber, Recovery shoes characterized by comprising 50 to 55 parts by weight of biodegradable polyurethane, 10 to 20 parts by weight of a biodegradation accelerator, 20 to 25 parts by weight of a fatigue reliever, and 5 to 15 parts by weight of a reinforcing agent.

5. In Paragraph 4, The above reinforcing agent is, Recovery shoes characterized by additionally containing lignin and natural silica.

6. In Paragraph 1, The above fatigue reliever is, Based on 100 parts by weight of a fatigue reliever, 50 to 60 parts by weight of a base containing natural latex, and Recovery shoes characterized by comprising 40 to 50 parts by weight of a viscoelastic composite including polybutylene succinate (PBS) and caprolactam.

7. In Paragraph 6, The above viscoelastic composite is, Additionally comprising epoxidized castor oil, zirconia nanoparticles, and phytic acid, Based on 100 parts by weight of the above viscoelastic composite, Recovery shoes characterized by comprising 40 to 50 parts by weight of polybutylene succinate, 20 to 30 parts by weight of caprolactam, 10 to 15 parts by weight of epoxidized castor oil, 5 to 10 parts by weight of zirconia nanoparticles, and 5 to 10 parts by weight of phytic acid.

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