Full-biomass-based soybean protein supramolecular material as well as solvent-free preparation method and application thereof

Abstract

The invention discloses a full-biomass-based soybean protein supramolecular material and a solvent-free preparation method and application thereof, after soybean protein powder, lipoic acid powder and phenolic compound powder are mixed by a physical dry method, the mixture is subjected to one-step melt blending and curing molding under a hot pressing condition, and no solvent is needed in the whole process. According to the invention, through in-situ phase behavior of a'macromolecule-micromolecule 'eutectic system under heating and pressurizing conditions, micromolecule melt is used as a reactive plasticizer to instantly permeate and plasticize a soybean protein matrix, and meanwhile, a supramolecular network is constructed through multiple crosslinking. The material has the advantages that the preparation process is solvent-free, one-step and extremely low in energy consumption, and a finished product has excellent mechanical property, optical transmittance, self-adhesion and antibacterial property and is applied to the field of fruit preservation. The method can be widely applied to the fields of sustainable packaging, hot melt adhesives, preservative films and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bio-based macromolecular materials, and particularly relates to a full-biomass-based soy protein supermolecular material and a solvent-free preparation method and application thereof. BACKGROUND

[0002] Among numerous biomass resources, soy protein is considered as one of the most potential candidates to replace petroleum-based plastics due to its wide source, low cost, complete biodegradability and good biocompatibility. However, in the industrialization process of transforming soy protein from "agricultural products" to "high-performance materials", there has been a long-standing "processing-performance" paradox that greatly limits its high-value application.

[0003] In terms of processability, soy protein has a fundamental defect. Soy protein (especially soy protein isolate) is a typical globular protein, and its native conformation is highly entangled and maintained by intramolecular and intermolecular hydrogen bonds, disulfide bonds, hydrophobic interactions and other complex interaction forces. This dense and random aggregate structure makes it lack true thermoplasticity, and its thermal decomposition temperature (about > 200°C) is much lower than the temperature required for its flow or melting. Therefore, soy protein cannot be molded by the most efficient and low-cost melt processing technology (such as hot pressing, injection molding, extrusion) in modern industry like traditional thermoplastic plastics such as polypropylene and polyethylene.

[0004] The existing processing approach relies heavily on "wet" process. The current mainstream technology adopts "solution casting method", which first needs to use a solvent (such as acid, alkali or organic solvent) to destroy the aggregate state of the protein, so that it is "denatured" and dissolved to form a flowable solution; then the solution is cast into a film, and then the solvent is removed by long-time baking or drying (usually taking 24-48 hours). This "wet" process not only has a complicated process and low efficiency, but also has a very high energy consumption in the drying process, and the volatilization of the solvent (such as the use of organic solvents) or the treatment (such as acid and alkali wastewater) will also cause secondary environmental pollution, which is completely inconsistent with the principles of green chemistry and economic benefits.

[0005] The material prepared by "wet" method has poor performance and is difficult to balance. The pure soy protein film obtained by solution volatilization has extremely low tensile strength (usually only 1-3 MPa) due to the disordered and fragile reconstruction of the molecular chain, and the texture is brittle and hard, which cannot meet the basic mechanical requirements of most applications. A large number of polar groups such as amino, carboxyl and hydroxyl groups are exposed on the soy protein molecular chain, resulting in strong hydrophilicity and water vapor sensitivity of the material, which will quickly absorb water and swell in a humid environment, leading to a catastrophic decline in mechanical properties.

[0006] To improve the above performance defects, the prior art mainly adopts two means, one is to add glycerol and other small molecule plasticizers, although it can increase the flexibility of the film (improve the elongation at break), but it is at the expense of the strength and modulus of the material. More importantly, glycerol itself has strong hygroscopicity, which will further exacerbate the water resistance of the material, and the plasticizer is easy to migrate and exude, resulting in unstable material performance over time. The other is to use glutaraldehyde, epoxy resin and other chemical crosslinking agents, although it can improve the strength and water resistance of the material by forming covalent bonds, but this strategy has two fatal defects: (1) Toxicity problem: these crosslinking agents are mostly biotoxic and derived from petroleum, which violates the green and safe intention of bio-based materials, making them unable to be used in food packaging or biomedical fields. (2) Thermosetting: the permanent chemical crosslinking network formed makes the material become a typical thermosetting material, completely losing thermoplasticity, that is, it cannot be reprocessed or recycled by heating and melting, and eventually becomes a "permanent" waste, which cannot be recycled.

[0007] In summary, the prior art route has always failed to solve the following fundamental technical problems: developing a technology that can completely get rid of solvent dependence, realize rapid, green, one-step thermoplastic processing of soy protein materials, and can simultaneously endow the material with high mechanical properties, optical transmittance, self-adhesion, and biological activity in the same system. Finding a new technical paradigm to replace "wet process" with "dry process" and "thermosetting" with "thermoplastic" is a key technical bottleneck that needs to be overcome but has not been solved in the field of soy protein and even the entire bio-based material. SUMMARY

[0008] The purpose of the application is to provide a full biomass-based soy protein supermolecular material which can overcome the fundamental defects of solvent dependence, poor processability and non-recyclability of the prior art, and has excellent comprehensive performance (high strength and toughness, high transparency and antibacterial property).

[0009] Technical scheme: The solvent-free preparation method of the full biomass-based soy protein supermolecular material of the application is characterized in that it comprises the following steps: (1) Dry mixing, 40-60 wt.% of soy protein and 40-60 wt.% of a eutectic mixture are placed in a high-speed mixer in the form of solid powders for physical dry mixing to obtain a uniform mixed powder; the eutectic mixture is composed of lipoic acid and at least one natural small molecule phenolic hydrogen bond donor; (2) Hot pressing, the mixed powder obtained in step (1) is placed in the mold of a hot press; (3) melt solidification, in-situ melting, blending and reacting the powder to form a homogeneous melt at a temperature of 100-120°C and a pressure of 5-10 MPa for 10-20 minutes; (4) after cooling the mold to room temperature, demolding, and the supermolecular material film or sheet can be obtained.

[0010] Preferably, the soybean protein is soybean protein isolate.

[0011] Preferably, the natural small molecule phenolic hydrogen bond donor is thymol or carvacrol or guaiacol or eugenol.

[0012] Preferably, in the eutectic mixture, the mass ratio of lipoic acid to the natural small molecule phenolic hydrogen bond donor is 2:1 to 1:2.

[0013] Preferably, the mass ratio of the soybean protein to the eutectic mixture is 1.5:1 or 1:1 or 1:1.5.

[0014] The full-biomass-based soybean protein supermolecular material prepared by the above-mentioned solvent-free preparation method of the full-biomass-based soybean protein supermolecular material.

[0015] The full-biomass-based soybean protein supermolecular material is prepared into a film, a sheet or a hot melt adhesive by a hot pressing or injection molding method.

[0016] The full-biomass-based soybean protein supermolecular material is recycled by a hot pressing method, and the mechanical properties of the material after recycling do not decrease significantly.

[0017] The full-biomass-based soybean protein supermolecular material is used as an active packaging material due to its antibacterial property.

[0018] The full-biomass-based soybean protein supermolecular material is used as a functional agricultural mulch due to its ultraviolet shielding property. The full-biomass-based soybean protein supermolecular material can be used as a full-biomass-based agricultural mulch to replace the existing petroleum-based plastic mulch.

[0019] Mechanism and innovation analysis: the core innovation of the present application is to propose and realize a new solvent-free strategy of "reactive thermoplastization", which completely overturns the traditional processing paradigm of protein materials. The key mechanism is that: (1) Formation and plasticization of in-situ eutectic melt: Under the conditions of heating and pressurization, small molecules such as thioctic acid and thymol in solid state first form a liquid eutectic mixture at a temperature much lower than their respective melting points. As an efficient, in-situ generated bio-based plasticizer, this liquid eutectic melt rapidly penetrates, swells and destroys the original dense aggregate structure of the soy protein powder particles under the synergistic action of pressure, releasing the movement ability of soy protein molecular chains, and realizing the transition from solid state to high-viscosity molten state.

[0020] (2) Rapid construction of multiple networks in the molten state: In this homogeneous, solvent-free melting system, all functional groups (-SH, -COOH, -NH2, -OH, benzene ring, etc.) have extremely high concentration and mobility. The heat pressing process (high temperature and high pressure) greatly accelerates the rate of chemical and physical action, and within a few minutes, it simultaneously promotes the rapid construction of disulfide bond exchange reactions of thioctic acid (forming covalent cross-linking with -SH of soy protein isolate) and dynamic hydrogen bond networks ( -COOH of thioctic acid, -OH of phenol and -NH2, -OH, -COOH of soy protein isolate) as well as hydrophobic interactions, forming a homogeneous supramolecular network cross-linked by covalent bonds and dynamic physical bonds.

[0021] (3) Reversible thermoplasticity from melt to solid: The supramolecular network rapidly solidifies after cooling to obtain high-performance materials. Since the network is mainly dominated by reversible dynamic physical bonds (hydrogen bonds), the material can break the hydrogen bond network when reheated and return to a flowable molten state, and can be reconstructed after cooling. This property endows the 100% bio-based material with excellent processing performance similar to traditional thermoplastic plastics, solving the problem of the inability of protein materials to be thermally processed.

[0022] Benefits: 1. The present application completely eliminates the dependence on any solvent such as water, acid, base, etc. The preparation process is shortened from the traditional wet method of several days (dissolution, stirring, drying) to 10 minutes of heat pressing, realizing one-step molding of "mixing and using", extremely low energy consumption, no "three wastes" emission, and fully meeting the green chemistry and carbon neutralization strategy; 2. The present application endows the full biomass-based soy protein material with melt processing performance similar to plastics; 3. The present application has high mechanical strength, high flexibility, excellent hydrophobicity (derived from the dense network and hydrophobic groups), broad-spectrum antibacterial property (derived from thymol, etc.) and ultraviolet shielding property, and is a high-performance multifunctional material; 4. Due to its thermoplasticity, the present material can not only be used for thin films, but also can be used as a high-performance bio-based hot melt adhesive, or can be prepared into devices with complex shapes through modern industrial technologies such as injection molding and extrusion, and has a much wider application prospect than traditional protein materials. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1Synthesis route map for preparing full-biomass-based soy protein supermolecular material of Example 1; Figure 2 Optical photos and UV-Vis transmittance curve atlas of low full-biomass-based soy protein supermolecular material of Example 1; Figure 3 Raman spectra of lipoic acid, lipoic acid / thymol eutectic mixture, Example 1 and pure soy protein isolate film; Figure 4 Differential scanning calorimetry scan curves of Example 1-Example 5; Figure 5 X-ray diffraction curves of pure soy protein isolate film and Example 1-Example 5; Figure 6 Optical photo of a 0.2g film of Example 2 lifting a 2Kg dumbbell; Figure 7 Stress-strain curves of Example 1-Example 5; Figure 8 Stress-strain curves of Example 2 after soaking in water for different times; Figure 9 Stress-strain curves of Example 3 after continuous 50 cycles of tensile stretching at 20% strain; Figure 10 Shear adhesion data map of Example 1-Example 5 used as hot melt adhesive on wood chips; Figure 11 Antibacterial comparison map of blank sample, pure soy protein isolate film and Example 4 in E. coli environment; Figure 12 Application display map of Example 5 used as blueberry preservation film; Figure 13 Mass retention rate column chart of Example 5; Figure 14 Stress-strain curves of Example 2 after recovery. DETAILED DESCRIPTION

[0024] Example 1 Step S1: Accurately weigh 1g of soy protein isolate powder, 0.33g of lipoic acid powder and 0.33g of thymol powder (mass ratio of soy protein isolate powder: (lipoic acid + thymol) = 1.5:1), and place them in a high-speed mixer for dry mixing for 5 minutes to obtain a uniform mixed powder.

[0025] Step S2: Take the above mixed powder and evenly spread it in a circular metal mold with a diameter of 100mm.

[0026] Step S3: Place the mold on a flatbed hot press and hot press it for 10 minutes at 100°C and 5 MPa. At this time, the powder will be completely melted into a transparent melt.

[0027] Step S4: Depressurize and demold to obtain a homogeneous, transparent, light yellow, high-toughness supramolecular material film.

[0028] like Figure 2 As shown, the prepared thin film material has an average optical transmittance of over 85% in the visible light range.

[0029] like Figure 3 As shown, pure lipoic acid has a concentration of 510 cm⁻¹ -1 A typical disulfide bond absorption peak was observed at 503 cm⁻¹; while in the formed lipoic acid / thymol eutectic mixture and in Example 1, the peak was at 503 cm⁻¹. -1 and 521 cm -1 An absorption peak for dynamic disulfide bonds was observed at [location], indicating that lipoic acid underwent a ring-opening reaction in all the corresponding systems. Furthermore, in the spectrum of Example 1, an absorption peak was also observed at 674 cm⁻¹. -1 and 1002 cm -1 Absorption peaks for CS and CC bonds were detected, indicating that lipoic acid underwent significant cross-linking and hardening in this system. In contrast, absorption peaks for CC bonds were only found in the spectrum of pure soy protein isolate membrane.

[0030] like Figure 4 As shown, the glass transition temperature of Example 1 is 53.41°C, which is higher than the glass transition temperature of room temperature.

[0031] like Figure 5 As shown, Example 1 exhibits a broad amorphous peak.

[0032] like Figure 7 As shown, Example 1 obtained a tensile strength of about 30 MPa and a tensile fracture length of about 30%.

[0033] like Figure 10 As shown, Example 1 achieved an adhesion strength of 1.33 MPa.

[0034] Example 2 Step S1: Accurately weigh 1g of soy protein isolate powder, 0.5g of lipoic acid powder and 0.5g of carvacrol (mass ratio of soy protein isolate powder: (lipoic acid + carvacrol) = 1:1), place them in a high-speed mixer and dry mix for 5 minutes to obtain a uniform mixed powder.

[0035] Step S2: Take the above mixed powder and spread it evenly in a circular metal mold with a diameter of 100mm.

[0036] Step S3: Place the mold on a flatbed hot press and hot press it for 20 minutes at 120°C and 10 MPa. At this time, the powder will be completely melted into a transparent melt.

[0037] Step S4: Depressurize and demold to obtain a homogeneous, transparent, light yellow, high-toughness supramolecular material film.

[0038] like Figure 4 As shown, the glass transition temperature of Example 2 is 51.89°C, which is higher than the glass transition temperature of room temperature.

[0039] like Figure 5 As shown, Example 2 exhibits a broad amorphous peak.

[0040] like Figure 6 As shown in the optical photograph, a 0.2g film from Example 2 lifts a 2kg dumbbell. It maintains its shape without breaking during the lifting of the heavy object, demonstrating superior mechanical properties.

[0041] like Figure 7 As shown, Example 2 obtained a tensile strength of ~17 MPa and a tensile fracture length of ~35%.

[0042] like Figure 8 As shown, even after prolonged underwater immersion, Example 2 exhibits a significant decrease in mechanical strength, but it still maintains the performance compared to current fully bio-based products.

[0043] like Figure 10 As shown, Example 2 achieved an adhesion strength of 1.37 MPa.

[0044] Example 3 Step S1: Accurately weigh 1g of soy protein isolate powder, 0.75g of lipoic acid powder and 0.75g of guaiacol (mass ratio of soy protein isolate powder: (lipoic acid + carvacrol) = 1:1.5), place them in a high-speed mixer and dry mix for 5 minutes to obtain a uniform mixed powder.

[0045] Step S2: Take the above mixed powder and spread it evenly in a circular metal mold with a diameter of 100mm.

[0046] Step S3: Place the mold on a flatbed hot press and hot press it for 15 minutes at 110°C and 8 MPa. At this time, the powder will be completely melted into a transparent melt.

[0047] Step S4: Depressurize and demold to obtain a homogeneous, transparent, light yellow, high-toughness supramolecular material film.

[0048] like Figure 4As shown, the glass transition temperature of Example 3 is 50.29°C, which is higher than the glass transition temperature of room temperature.

[0049] like Figure 5 As shown, Example 3 exhibits a broad amorphous peak.

[0050] like Figure 7 As shown, Example 3 obtained a tensile strength of ~14 MPa and a tensile fracture length of ~50%.

[0051] like Figure 9 As shown, in the initial few cycles, Example 3 exhibited a large hysteresis loop, indicating significant energy dissipation. Notably, the prepared Example 3 easily withstood 50 consecutive cycles of stretching without fracturing, demonstrating excellent flexibility.

[0052] like Figure 10 As shown, Example 3 achieved an adhesion strength of 1.40 MPa.

[0053] Example 4 Step S1: Accurately weigh 1g of soy protein isolate powder, 0.67g of lipoic acid powder and 0.33g of eugenol (mass ratio of soy protein isolate powder: (lipoic acid + carvacrol) = 1:1), place them in a high-speed mixer and dry mix for 5 minutes to obtain a uniform mixed powder.

[0054] Step S2: Take the above mixed powder and spread it evenly in a circular metal mold with a diameter of 100mm.

[0055] Step S3: Place the mold on a flatbed hot press and hot press it for 20 minutes at 120°C and 5 MPa. At this time, the powder will be completely melted into a transparent melt.

[0056] Step S4: Depressurize and demold to obtain a homogeneous, transparent, light yellow, high-toughness supramolecular material film.

[0057] like Figure 4 As shown, the glass transition temperature of Example 4 is 51.60°C, which is higher than the glass transition temperature of room temperature.

[0058] like Figure 5 Example 4 shown exhibits broad diffraction peaks and has an amorphous structure.

[0059] like Figure 7 As shown, Example 4 obtained a tensile strength of ~12 MPa and a tensile fracture length of ~42%.

[0060] like Figure 10 As shown, Example 4 achieved an adhesion strength of 1.38 MPa.

[0061] As shown in Figure 11 , the antibacterial effect of blank sample, pure soy protein isolate film and Example 4 in E. coli environment. It is found that Example 4 obtains a significant inhibition zone, showing excellent antibacterial performance.

[0062] Example 5 Step S1: accurately weigh 1 g of soy protein isolate powder, 0.33 g of lipoic acid powder and 0.67 g of thymol (mass ratio of soy protein isolate powder: (lipoic acid + thymol) = 1:1), and place in a high-speed mixer for dry mixing for 5 minutes to obtain a uniform mixed powder.

[0063] Step S2: take the above mixed powder and evenly spread it in a circular metal mold with a diameter of 100 mm.

[0064] Step S3: place the mold on a flat hot press and heat press at 100°C and 10 MPa for 10 minutes, at which time the powder completely melts into a transparent melt.

[0065] Step S4: release the pressure and demold to obtain a homogeneous, transparent, light yellow high-toughness supramolecular material film.

[0066] As shown in Figure 4 , the glass transition temperature of Example 5 is 48.52°C, showing a glass transition temperature higher than room temperature.

[0067] As shown in Figure 5 , Example 5 shows a wide diffraction peak, which is an amorphous structure.

[0068] As shown in Figure 7 , Example 5 obtains a tensile strength of ~7 MPa and a tensile fracture length of ~28%.

[0069] As shown in Figure 10 , Example 4 obtains an adhesion strength of 1.31 MPa.

[0070] Example 6 Application of full-biomass-based soy protein supramolecular material as an antibacterial preservative film.

[0071] Step S1: place fresh blueberries in a glass culture in a constant temperature (25°C) and constant humidity (40-60% relative humidity) environment.

[0072] Step S2: take the film prepared in Example 5 and tightly cover the surface of the petri dish containing the blueberries.

[0073] Step S3: accurately record the changes in the mass of the blueberries at different time periods.

[0074] As shown in Figure 12and Figure 13 As shown, the completely bare blank sample was significantly dehydrated after 14 days, showing wrinkles, and the mass was only 51.22% of the original mass. Under the same conditions, the pure soybean protein isolate film also performed poorly, with a blueberry mass retention rate of 56.34%. Compared with Example 5, it was found that the blueberry mass retention rate was as high as 87.96%, the appearance was well maintained, and excellent water retention capacity was exhibited.

Claims

1. A solvent-free preparation method for a fully biomass-based soybean protein supramolecular material, characterized in that, Includes the following steps: (1) 40-60 wt.% soybean protein and 40-60 wt.% eutectic mixture are physically mixed in the form of solid powder to obtain mixed powder; the eutectic mixture is composed of lipoic acid and at least one natural small molecule phenolic hydrogen bond donor; (2) Under heating and pressurization conditions, the mixed powder obtained in step (1) is melt-blended and solidified into shape.

2. The solvent-free preparation method of the all-biomass-based soybean protein supramolecular material according to claim 1, characterized in that, The soy protein is soy protein isolate powder; the natural small molecule phenolic hydrogen bond donor is thymol, carvacrol, guaiacol, or eugenol.

3. The solvent-free preparation method of the all-biomass-based soybean protein supramolecular material according to claim 1, characterized in that, In the eutectic mixture, the mass ratio of thioctic acid to the natural small molecule phenolic hydrogen bond donor is 2:1 to 1:

2.

4. The solvent-free preparation method of the all-biomass-based soybean protein supramolecular material according to claim 1, characterized in that, The mass ratio of the soybean protein to the eutectic mixture is 1.5:1, 1:1, or 1:1.

5.

5. The solvent-free preparation method of the all-biomass-based soybean protein supramolecular material according to claim 1, characterized in that, The heating temperature is 100-120 °C, the pressurization pressure is 5-10 MPa, and the heating and pressurization time is 10-20 minutes.

6. A fully biomass-based soybean protein supramolecular material prepared by the solvent-free preparation method of the fully biomass-based soybean protein supramolecular material according to any one of claims 1-5.

7. Application of the all-biomass-based soybean protein supramolecular material of claim 6, prepared into films, sheets or hot melt adhesives by hot pressing, injection molding or extrusion.

8. The method for recycling and reusing the all-biomass-based soybean protein supramolecular material according to claim 6, characterized in that, Includes the following steps: The biomass-based soybean protein supramolecular material is recycled and reused through hot pressing.

9. The application of the biomass-based soybean protein supramolecular material as described in claim 6 as an active packaging material.

10. The application of the all-biomass-based soybean protein supramolecular material of claim 6 as a functional agricultural mulch film.

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