Protein bioplastic and preparation method and application thereof

Abstract

The application provides a protein biological plastic and a preparation method and application thereof. The protein biological plastic is prepared by using zein, natural silk micro-nano fiber and a small amount of plasticizer as raw materials to configure a composite slurry, and then using a film coating process. The application greatly improves the mechanical property of the zein film by compounding the natural silk micro-nano fiber with the zein film. In addition, the addition of the silk micro-nano fiber improves the film coating property of the zein composite slurry, so that the large-scale film coating preparation of the protein biological plastic is realized. The raw materials used in the application are all biodegradable, non-toxic and harmless materials, and the reaction process does not involve complex chemical reactions. The protein biological plastic has excellent mechanical property and can be used in the fields of packaging, special paper, coating finishing and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of biological plastics, and particularly relates to a protein biological plastic and a preparation method and application thereof. BACKGROUND

[0002] With the increasingly prominent environmental problems caused by non-degradable plastics and the reduction of traditional petroleum resources, the demand for renewable biodegradable plastics is increasing. Zein is a kind of food protein widely existing in plants, which is usually soluble in ethanol / water solution but insoluble in water. Zein has been prepared into films for food, medicine and chemical industries. However, the pure zein protein film is brittle and has poor impact resistance, which is difficult to be widely applied, especially in biological plastics.

[0003] Silk is a kind of natural protein fiber, which contains complex hierarchical nanostructure and has silk fibrils with a size of tens of nanometers to several microns. The natural silk micro-nano fiber has excellent mechanical properties, good biocompatibility and biodegradability. However, the pure silk micro-nano fiber film lacks water resistance, and it is difficult to prepare a water-resistant protein biological plastic by using pure silk micro-nano fiber alone.

[0004] In order to solve the above problems, a patent with the authorization announcement number CN104387604A discloses a kind of high moisture resistance degradable zein film material and its preparation method. Specifically, zein, water, ethanol, glycerol, polyethylene glycol-400 and glyceryl monostearate are blended and then dried in a tray made of polypropylene to obtain a zein composite film. On the one hand, the method mainly involves a casting evaporation method, which is difficult to mass-produce. On the other hand, the glycerol, polyethylene glycol-400 and glyceryl monostearate used in the method are plasticizers, and no reinforcing agent is involved. Therefore, the breaking strength of the zein film material prepared by the method needs to be improved.

[0005] In the prior art, gallic acid modified cellulose nanofilament, glycerol and zein are blended, and then a composite film that can be eaten is prepared by a casting method. When the ratio of gallic acid modified cellulose nanofilament to zein is 1:2, the composite film has the maximum tensile strength of 9.04 MPa, which is 1.89 times higher than that of the film without adding gallic acid modified cellulose nanofilament. However, the composite film is prepared by the casting method, which is difficult to mass-produce continuously. In addition, the gallic acid modified cellulose nanofilament used in the method involves complex chemical reactions, complicated process flow and high reagent cost, which limits its application.

[0006] Therefore, it is necessary to design an improved protein biological plastic and its preparation method and application to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide a protein bioplastic, its preparation method and application. The preparation process first involves pulping zein, silk micro / nano fibers, plasticizer, ethanol and water to obtain a uniformly dispersed composite slurry with moderate viscosity. Then, the composite slurry is uniformly coated onto a board using a scraper, followed by drying and peeling to obtain the protein bioplastic.

[0008] To achieve the above-mentioned objective, this invention provides a method for preparing protein bioplastics, comprising the following steps:

[0009] S1. Prepare an ethanol / water mixed solution, and then add zein, silk micro / nanofibers and plasticizer to the ethanol / water mixed solution in sequence and mix evenly to obtain a zein / silk micro / nanofiber / plasticizer composite slurry;

[0010] S2. Apply the zein / silk micro / nanofiber / plasticizer composite slurry obtained in step S1 onto the board using a scraper. After drying, a protein bioplastic is obtained.

[0011] Preferably, in the composite slurry of step S1, the mass fraction of zein is 1% to 30%, the mass of silk micro / nanofibers is 10% to 30% of the mass of zein, and the amount of plasticizer is 20% to 30% of the combined mass of zein and silk micro / nanofibers.

[0012] Preferably, the mass of the silk micro / nanofibers is 20% to 30% of the mass of zein.

[0013] Preferably, the mass fraction of the silk micro / nanofibers ranges from 0.5% to 5%. This gives the zein composite slurry good coating properties, thereby enabling large-scale coating preparation of protein bioplastics.

[0014] Preferably, in step S1, the volume fraction of ethanol in the ethanol / water mixture is 60% to 95%.

[0015] Preferably, in step S2, the coating speed of the scraper is 0.01 to 0.8 m / s, and the coating thickness is 50 to 10000 μm; the thickness of the protein bioplastic obtained after drying and peeling is 1 to 3000 μm.

[0016] Preferably, the silk micro / nanofibers are natural silk extracts with a diameter of 30–3000 nm.

[0017] Preferably, the plasticizer is glycerin, polyethylene glycol, sorbitol, etc. Glycerin is preferred.

[0018] To achieve the above-mentioned objectives, the present invention also provides a protein bioplastic, which is prepared by the protein bioplastic preparation method described in any of the foregoing technical solutions. The protein bioplastic has a thickness of 1-3000 μm, a tensile strength of 3-12 MPa, and an elongation at break of 10%-70%.

[0019] The protein bioplastics prepared by the aforementioned technical solution can be used in packaging, specialty paper, and coating finishing.

[0020] The beneficial effects of this invention are:

[0021] (1) The method for preparing protein bioplastics provided by this invention uses zein and silk micro / nanofibers, both of which are proteins and contain the same chemical component (alanine). They can be uniformly dispersed in an aqueous ethanol solution to form a uniform, coatable composite slurry. Except for the plasticizer, the raw materials used in this bioplastic are all proteins, so it can be called a protein bioplastic.

[0022] (2) The method for preparing protein bioplastics provided by this invention involves first preparing a certain proportion of ethanol / water mixed solution, then sequentially adding zein, silk micro / nanofibers, and a plasticizer, mixing them evenly to obtain a composite slurry; then using a coating applicator to coat the composite slurry onto a board, drying, and peeling to obtain the protein bioplastic. This invention controls the coating performance of the zein composite slurry by adding silk micro / nanofibers, thereby achieving large-scale coating preparation of protein bioplastics. Specifically, in this process, ethanol and water evaporate slowly, and silk micro / nanofibers and glycerol are uniformly dispersed in the zein membrane. Glycerol can improve the flexibility of the zein membrane by changing its supramolecular structure and reducing the interaction between zein chains. Silk micro / nanofibers form a uniform mechanical reinforcement network in the zein membrane, thereby increasing the tensile strength of the zein membrane.

[0023] (3) The method for preparing protein bioplastics provided by the present invention solves the problem of poor mechanical properties of pure corn glycol protein membranes, and also solves the problem of water intolerance of pure silk micro-nano fiber membranes.

[0024] (4) The preparation method of protein bioplastics provided by the present invention does not involve complex chemical reactions, the materials used are widely available, non-toxic and harmless, simple, low energy consumption, and can achieve large-scale and continuous production. At the same time, the protein bioplastics provided by the present invention have excellent mechanical properties and can be used in packaging, specialty paper, coating and finishing and other fields. Attached Figure Description

[0025] Figure 1The image shows the coating effect of the composite slurry prepared in Example 1 of the present invention.

[0026] Figure 2 The images shown are actual pictures of the protein bioplastic prepared in Example 1; where A is an actual picture of the upper surface and B is an actual picture of the lower surface.

[0027] Figure 3 The image shows an SEM image of the upper surface of the protein bioplastic prepared in Example 1, with a scale bar of 2 μm.

[0028] Figure 4 The image shows a cross-section of the protein bioplastic prepared in Example 1, with a scale bar of 100 μm.

[0029] Figure 5 The image shows the lower surface of the protein bioplastic prepared in Example 1, with a scale bar of 2 μm.

[0030] Figure 6 The results of the water resistance test are for the protein bioplastic prepared in Example 1.

[0031] Figure 7 The image shows the coating effect of the composite slurry in Comparative Example 1.

[0032] Figure 8 The image shows the coating effect of the composite slurry in Comparative Example 2.

[0033] Figure 9 The results show the water resistance test results of the protein bioplastic prepared in Comparative Example 3.

[0034] Figure 10 The images show actual photos of the protein bioplastic prepared in Comparative Example 4; where A is the upper surface image and B is the lower surface image.

[0035] Figure 11 The image shows the SEM image of the upper surface of the protein bioplastic prepared in Comparative Example 4, with a scale bar of 2 μm.

[0036] Figure 12 The image shows the lower surface of the protein bioplastic prepared in Comparative Example 4, with a scale bar of 2 μm.

[0037] Figure 13 The image shows the coating effect of the composite slurry in Comparative Example 5.

[0038] Figure 14 This is a photograph of the protein bioplastic prepared for Comparative Example 6.

[0039] Figure 15 This is a photograph of the protein bioplastic prepared for Comparative Example 7. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0042] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0043] This invention provides a method for preparing protein bioplastics, comprising the following steps: Zeat protein, silk micro / nanofibers, and a plasticizer are added to an ethanol / water mixture to prepare a composite slurry with uniform dispersion and suitable viscosity. The composite slurry is then coated onto a substrate using a coating applicator. After drying and peeling, the protein bioplastic is obtained.

[0044] S1. Preparation of composite slurry:

[0045] After degumming, the silk was placed in a swelling solution (a mixture of calcium nitrate, ethanol, and water, with a volume ratio of ethanol to water of 1:2 to 10 and a mass ratio of calcium nitrate to the total volume of ethanol and water of 1 to 10 g: 100 mL) and placed in an oven at 50 to 80°C for 60 to 80 hours to swell the silk and weaken the binding force between the nanofibers in the silk. After removal, the silk was washed three times with deionized water and placed in a crusher at a speed of 7000 to 9000 r / min with a bath ratio of 1 g: 100 to 200 mL (i.e., 1 g silk: 100 to 200 mL water) for 80 to 100 minutes to mechanically treat the silk fibers. The silk fibers were then mechanically peeled off, filtered three times with a filter screen, and freeze-dried to obtain silk micro-nano fibers.

[0046] Anhydrous ethanol and deionized water are mixed in a volume ratio to obtain an ethanol / water mixed solution with an ethanol volume fraction of 50-99%.

[0047] Next, zein, silk micro / nanofibers, and plasticizer are added to an ethanol / water mixture and mixed using a homogenizer at a speed of 50–50,000 rpm for 0.1–12 hours to obtain a composite slurry of the preset concentration. This process allows the silk micro / nanofibers and zein to form a uniformly dispersed network structure in the ethanol / water mixture, ensuring the composite slurry meets coating requirements.

[0048] Specifically, in the composite slurry, the mass fraction concentration of zein is 1%–30%, and the amount of silk micro / nanofibers is 10%–30% of the mass of zein, preferably 20%–30%; the amount of plasticizer is 20%–30% of the combined mass of zein and silk micro / nanofibers. To ensure the composite slurry meets the requirements for coating, the mass fraction concentration of silk micro / nanofibers is 0.5%–5%.

[0049] The plasticizer is glycerin, polyethylene glycol, sorbitol, etc., with glycerin being preferred.

[0050] Silk micro-nanofibers are natural silk extracts with a diameter of 30–3000 nm. Silk can be domesticated silkworm silk, tussah silkworm silk, or wild silkworm silk.

[0051] S2. Coating, drying, and peeling:

[0052] The composite slurry obtained in step S1 is applied to the board using a scraper, dried, and peeled off to obtain protein bioplastic.

[0053] Specifically, the coating speed of the scraper is 0.01 to 0.8 m / s, and the coating thickness is 50 to 10000 μm.

[0054] During this process, ethanol and water slowly evaporate, and silk micro / nanofibers and glycerol are uniformly dispersed within the zein membrane. Glycerol can improve the flexibility of the zein membrane by altering its supramolecular structure and reducing the interactions between zein chains. The silk micro / nanofibers form a uniform mechanically reinforcing network within the zein membrane, thereby increasing its tensile strength.

[0055] The present invention also provides a protein bioplastic, which is prepared by the above-described method for preparing protein bioplastics.

[0056] This invention also provides an application of protein bioplastics, which can be used to replace traditional petroleum-based plastics in fields such as product packaging, specialty paper, and coating finishing.

[0057] The present invention will now be described in detail through specific embodiments.

[0058] Example 1

[0059] A method for preparing a protein bioplastic includes the following steps:

[0060] S1. Preparation of composite slurry:

[0061] 5g of degummed silk was placed in a swelling solution (a mixture of calcium nitrate, ethanol, and water, with a volume ratio of ethanol to water of 1:3 and a calcium nitrate content of 5g:100mL) and placed in an oven at 60℃ for 72h. After removal, it was washed three times with deionized water and placed in a crusher with a blade speed of 8000r / min at a bath ratio of 1g:1200mL for 90min of mechanical treatment. After filtering three times with a filter screen, the silk micro-nano fibers were obtained by freeze drying.

[0062] Anhydrous ethanol and deionized water were mixed to prepare an ethanol solution with a volume fraction of 75%.

[0063] Next, 7g of zein, 1.4g of dry silk micro / nanofibers, 1.68g of glycerol, and 89.92g of 75% ethanol solution were mixed in a homogenizer at 800 rpm for 5 minutes to obtain a composite slurry. Then, the composite slurry was slowly stirred at 100 rpm to defoam for 12 hours.

[0064] At this point, in the composite slurry, the mass fraction of zein is 7%, the mass of silk micro-nanofibers is 20% of the mass of zein, and the mass of glycerol is 20% of the total mass of zein and silk micro-nanofibers.

[0065] Specifically, the mass fraction concentration of silk micro / nanofibers at this time is 1.4%.

[0066] The diameter of silk micro-nano fibers is mainly around 500 nm.

[0067] S2. Coating:

[0068] The composite slurry was coated onto an aluminum plate using a scraper with a coating thickness of 2500 μm at a coating speed of 0.02 m / s. The plate was then dried in a 37°C air box and peeled off to obtain the protein bioplastic.

[0069] The protein bioplastic prepared in Example 1 was subjected to tensile mechanical testing. The protein bioplastic prepared in Example 1 was cut into small strips, soaked in deionized water for three days, and then shaken.

[0070] Figure 1 The image shows the coating effect of the composite slurry prepared in Example 1. It can be seen that the addition of silk micro-nano fibers at this ratio can make the corn glycerin composite slurry coating uniform and the shape controllable.

[0071] Figure 2 A photograph of the protein bioplastic prepared in Example 1; Figures 3-5 The image shows a SEM image of the protein bioplastic prepared in Example 1. As can be seen, the protein bioplastic prepared in Example 1 has a smooth appearance, uniform microstructure, and a thickness of approximately 140 μm.

[0072] Figure 6 The results of the water resistance test for the protein bioplastic prepared in Example 1 are shown. It can be seen that the protein bioplastic prepared in Example 1 can still maintain a stable upright morphology in water after being soaked for 3 days, demonstrating a certain degree of water resistance.

[0073] Comparative Example 1

[0074] A method for preparing protein bioplastics differs from Example 1 in that no silk micro / nanofibers are added to the composite slurry. Otherwise, it is largely the same as Example 1 and will not be described in detail here.

[0075] Specifically, 7g of zein, 1.4g of glycerol, and 91.6g of 75% ethanol solution were mixed in a homogenizer at 800 rpm for 5 minutes to obtain a composite slurry. The composite slurry was then slowly stirred at 100 rpm to defoam for 12 hours. The resulting slurry was then coated onto an aluminum plate using a doctor blade with a coating thickness of 2500μm at a coating speed of 0.02m / s.

[0076] Figure 7 The image shows the coating effect of the composite slurry in Comparative Example 1. It is evident that the corn glycerin composite slurry lacking the addition of silk micro / nanofibers is difficult to coat evenly, and the shape of the coating is also difficult to control.

[0077] Comparative Example 2

[0078] A method for preparing a protein bioplastic differs from Comparative Example 1 in that the mass fraction concentration of zein in the composite slurry is increased to 40%. The rest is roughly the same as Comparative Example 1 and will not be described in detail here.

[0079] Specifically, 40g of zein, 8g of glycerol, and 52g of 75% ethanol solution were mixed in a homogenizer at 800 rpm for 5 minutes to obtain a composite slurry. The composite slurry was then slowly stirred at 100 rpm to defoam for 12 hours. The resulting slurry was then coated onto an aluminum plate using a doctor blade with a coating thickness of 2500 μm at a coating speed of 0.02 m / s.

[0080] Figure 8 The image shows the coating effect of the composite slurry in Comparative Example 2. It is evident that even a high-concentration zein-glycerol slurry without added silk micro / nanofibers is difficult to coat evenly, and the shape is uncontrollable.

[0081] Comparative Example 3

[0082] A method for preparing protein bioplastics differs from Comparative Example 1 in that the obtained composite slurry is cast into a mold using a casting method, allowed to dry naturally, and then demolded to obtain the protein bioplastic. Other aspects are largely the same as in Comparative Example 1 and will not be repeated here.

[0083] Figure 9 The results show the water resistance test of the protein bioplastic prepared in Comparative Example 3. It can be seen that although the protein bioplastic without the addition of silk micro / nanofibers has a certain degree of water resistance, it softens and collapses in water. This demonstrates that the wet mechanical properties of the protein bioplastic without the addition of silk micro / nanofibers are poor.

[0084] Example 2-3

[0085] A method for preparing a protein bioplastic differs from Example 1 in that the ratio of silk micro / nanofibers to corn alcohol-soluble protein and the mass fraction of silk micro / nanofibers in the composite slurry are changed, as shown in Table 1; the rest is largely the same as in Example 1 and will not be repeated here.

[0086] Example 4

[0087] A method for preparing a protein bioplastic differs from Example 1 in that the concentration of silk micro / nanofibers in the composite slurry is reduced to 0.5%, while the rest is largely the same as in Example 1 and will not be repeated here.

[0088] Specifically, 2.5g of zein, 0.5g of dry silk micro / nanofibers, 0.6g of glycerol, and 96.4g of 75% ethanol solution were mixed in a homogenizer at 800 rpm for 5 minutes to obtain a composite slurry; then the composite slurry was slowly stirred at 100 rpm on a force stirrer to defoam for 24 hours.

[0089] At this point, in the composite slurry, the mass of silk micro-nanofibers is 20% of the mass of zein, and the mass of glycerol is 20% of the total mass of zein and silk micro-nanofibers.

[0090] At this point, the concentration of silk micro / nanofibers is 0.5%.

[0091] Example 5

[0092] A method for preparing a protein bioplastic differs from Example 1 in that the concentration of silk micro / nanofibers in the composite slurry is increased to 5%, while the rest is largely the same as in Example 1 and will not be repeated here.

[0093] Specifically, 25g of zein, 5g of dried silk micro-nano fibers, 6g of glycerol, and 64g of 75% ethanol solution were mixed in a homogenizer at 800 rpm for 5 minutes to obtain a composite slurry; then the composite slurry was slowly stirred at 100 rpm on a force stirrer to defoam for 24 hours.

[0094] At this point, in the composite slurry, the mass of silk micro-nanofibers is 20% of the mass of zein, and the mass of glycerol is 20% of the total mass of zein and silk micro-nanofibers.

[0095] At this point, the concentration of silk micro-nano fibers is 5%.

[0096] Comparative Example 4

[0097] A method for preparing a protein bioplastic differs from Example 1 in that, in the composite slurry, silk micro-nano fibers account for 40% of the corn alcohol-soluble protein content; otherwise, it is largely the same as Example 1 and will not be repeated here.

[0098] Specifically, 3.5g of zein, 1.4g of dry silk micro / nanofibers, 0.98g of glycerol, and 94.12g of 75% ethanol solution were mixed in a homogenizer at 800 rpm for 5 minutes to obtain a composite slurry; then the composite slurry was slowly stirred at 100 rpm on a force stirrer to defoam for 24 hours.

[0099] At this point, in the composite slurry, the mass of silk micro-nanofibers is 40% of the mass of zein protein, and the mass of glycerol is 20% of the total mass of zein protein and silk micro-nanofibers.

[0100] Specifically, the concentration of silk micro / nanofibers at this time is 1.4%.

[0101] Figure 10 This is a photograph of the protein bioplastic prepared in Comparative Example 4. Figure 11 and Figure 12 SEM image of the protein bioplastic prepared in Comparative Example 4.

[0102] Depend on Figures 10-12 It was found that when the amount of silk micro / nanofiber exceeded 30% of the amount of zein, significant differences in appearance and structure appeared on the upper and lower surfaces of the protein bioplastic. This indicates that when the proportion of silk micro / nanofiber in this protein bioplastic is too high, it leads to significant phase separation and uneven dispersion between zein and silk micro / nanofiber. This will result in a decrease in the mechanical properties of the protein bioplastic.

[0103] Comparative Example 5

[0104] A method for preparing protein bioplastics differs from Example 1 in that the total concentration in the composite slurry remains unchanged, the amount of silk micro / nanofibers used is reduced, and the rest is largely the same as in Example 1, and will not be repeated here.

[0105] Specifically, 7.9g of zein, 0.5g of dry silk micro / nanofibers, 1.68g of glycerol, and 89.92g of 75% ethanol solution were mixed in a homogenizer at 800 rpm for 5 minutes to obtain a composite slurry; then the composite slurry was slowly stirred at 100 rpm on a force stirrer to defoam for 24 hours.

[0106] At this point, the concentration of silk micro-nanofibers is 0.5%, and the amount of silk micro-nanofibers used is approximately 6.3% of the corn alcohol-soluble protein content.

[0107] Figure 13 The image shows the coating effect of the composite slurry in Comparative Example 5. It can be seen that, under the condition of constant total concentration of the composite slurry, when the amount of silk micro / nanofibers is less than 10% of the corn alcohol-soluble protein content, the composite slurry is difficult to coat evenly, and the coating shape is difficult to control. This is because the viscosity of the composite slurry is mainly controlled by the amount of silk micro / nanofibers used. When the amount of silk micro / nanofibers is too low, the viscosity of the composite slurry is insufficient, making it difficult to coat evenly and control the coating shape.

[0108] Comparative Example 6

[0109] A method for preparing a protein bioplastic differs from Example 1 in that the concentration of silk micro / nanofibers in the composite slurry is increased to 8%, while the rest is largely the same as in Example 1 and will not be repeated here.

[0110] Specifically, 40g of zein, 8g of dried silk micro / nanofibers, 9.6g of glycerol, and 42.4g of 75% ethanol solution were mixed in a homogenizer at 800 rpm for 5 minutes to obtain a composite slurry; then the composite slurry was slowly stirred at 100 rpm on a force stirrer to defoam for 24 hours.

[0111] At this point, in the composite slurry, the mass of silk micro-nanofibers is 20% of the mass of zein, and the mass of glycerol is 20% of the total mass of zein and silk micro-nanofibers.

[0112] At this point, the concentration of silk micro / nanofibers is 8%.

[0113] Table 1

[0114]

[0115] The performance of the protein bioplastics prepared in Examples 1-5 and Comparative Examples 3-6 was tested, and the results are shown in Table 2:

[0116] Table 2

[0117]

[0118]

[0119] Table 1 shows that the addition of glycerol significantly improves the elongation at break of this protein bioplastic, but its tensile strength is severely insufficient. Glycerol can improve the flexibility of the zein membrane by altering its supramolecular structure, reducing the interactions between zein chains, or through other means. The addition of silk micro / nanofibers significantly improves the tensile strength of this protein bioplastic. This is because the silk micro / nanofibers form a uniform mechanical reinforcing network within the zein membrane, thereby increasing the tensile strength of the zein membrane.

[0120] However, when the mass ratio of silk micro-nanofibers to zein exceeds 30% (Comparative Example 4), the tensile strength and elongation at break of the protein bioplastic decrease significantly. The reason is that with the increase in silk micro-nanofibers, phase separation occurs between zein and silk micro-nanofibers, and weak points appear within the protein bioplastic, thus reducing the mechanical properties of Comparative Example 4.

[0121] When the mass ratio of silk micro / nanofibers to zein is less than 10% (Comparative Example 5), although the elongation at break increases, the breaking strength decreases significantly. The reason is that as the amount of silk micro / nanofibers decreases, their role as a reinforcing agent becomes less apparent.

[0122] Comparing Examples 1 and 4-6, it can be seen that when the concentration of silk micro-nano fibers in the composite slurry is significantly reduced, the viscosity of the composite slurry will decrease significantly, which will cause uneven coating and lead to a decrease in the mechanical properties of the protein bioplastic prepared in Example 4.

[0123] When the concentration of silk micro- and nanofibers in the composite slurry is too high (above 5%), the silk micro- and nanofibers in the composite slurry will agglomerate, which will create weak points inside the protein bioplastic, resulting in a decrease in the mechanical properties of the prepared bioplastic.

[0124] Comparative Example 7

[0125] A method for preparing a protein bioplastic differs from Comparative Example 3 in that glycerol is not added to the composite slurry; that is, silk micro / nanofibers and glycerol are not added. Otherwise, it is largely the same as Comparative Example 3 and will not be described in detail here.

[0126] Depend on Figure 14 It is known that pure corn protein membranes have a wrinkled appearance, which is not conducive to practical applications.

[0127] Comparative Example 8

[0128] A method for preparing a protein bioplastic differs from Example 1 in that the concentration of glycerol in the composite slurry is 10% of the total amount of corn alcohol-soluble protein. The other aspects are largely the same as in Example 1 and will not be repeated here.

[0129] Specifically, 7g of zein, 1.4g of dry silk micro / nanofibers, 0.84g of glycerol, and 90.76g of 75% ethanol solution were mixed in a homogenizer at 800 rpm for 5 minutes to obtain a composite slurry; then the composite slurry was slowly stirred at 100 rpm on a force stirrer to defoam for 12 hours.

[0130] The composite slurry was coated onto an aluminum plate using a scraper with a coating thickness of 2500 μm at a coating speed of 0.02 m / s. The plate was then dried in a 37°C air box and peeled off to obtain the protein bioplastic.

[0131] Depend on Figure 15 It is evident that the appearance of protein bioplastics with this glycerol content still suffers from wrinkling, which will affect practical applications.

[0132] Experiments show that when the concentration of glycerol accounts for less than 20% of the total mass of corn alcohol-soluble protein and silk micro / nanofiber, the problem of easy wrinkling in this protein bioplastic cannot be solved.

[0133] When the concentration of glycerol accounts for more than 30% of the total mass of zein and silk nanofibers, it will lead to a significant decrease in the tensile strength of the zein white film.

[0134] In summary, this invention provides a protein bioplastic, its preparation method, and its applications. The preparation method uses zein, natural silk micro / nanofibers, and a small amount of plasticizer as raw materials to formulate a composite slurry, which is then coated to prepare the protein bioplastic. This invention combines natural silk micro / nanofibers with a zein film, significantly improving the mechanical properties of the pure zein film. Furthermore, this invention controls the coating performance of the zein composite slurry by adding silk micro / nanofibers, thereby enabling large-scale coating preparation of protein bioplastics. Moreover, the raw materials used in this invention for preparing protein bioplastics are all biodegradable, non-toxic, and harmless. The reaction process does not involve complex chemical reactions, and the prepared protein bioplastics exhibit excellent mechanical properties, making them suitable for applications in packaging, specialty paper, coating finishing, and other fields.

[0135] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a protein bioplastic, characterized in that, Includes the following steps: S1. Prepare an ethanol / water mixed solution, then sequentially add zein, silk micro / nanofibers, and plasticizer to the ethanol / water mixed solution and mix thoroughly to obtain a zein / silk micro / nanofiber / plasticizer composite slurry; in the composite slurry, the mass fraction of zein is 1%~30%, the mass of silk micro / nanofibers is 10%~30% of the mass of zein, and the mass fraction of silk micro / nanofibers ranges from 0.5%~5%; S2. Apply the zein / silk micro / nanofiber / plasticizer composite slurry obtained in step S1 onto the board using a scraper. After drying, a protein bioplastic is obtained.

2. The method for preparing protein bioplastics according to claim 1, characterized in that, In the composite slurry of step S1, the amount of plasticizer is 20% to 30% of the combined mass of zein and silk micro / nanofibers.

3. The method for preparing protein bioplastics according to claim 2, characterized in that, In the composite slurry of step S1, the mass of the silk micro / nanofibers is 10% to 20% of the mass of zein.

4. The method for preparing protein bioplastics according to claim 1, characterized in that, In step S1, the volume fraction of ethanol in the ethanol / water mixed solution is 60%~95%.

5. The method for preparing protein bioplastics according to claim 1, characterized in that, In step S2, the coating speed of the scraper is 0.01~0.8m / s, and the coating thickness is 50~10000μm; the thickness of the protein bioplastic obtained after drying and peeling is 1~3000μm.

6. The method for preparing protein bioplastics according to claim 1, characterized in that, The silk micro-nano fibers are natural silk extracts with a diameter of 30~3000nm.

7. The method for preparing protein bioplastics according to claim 1, characterized in that, The plasticizer is glycerin, polyethylene glycol, or sorbitol.

8. A protein bioplastic, characterized in that, The protein bioplastic is prepared by the preparation method of any one of claims 1 to 7, wherein the thickness of the protein bioplastic is 1 to 3000 μm, the tensile strength of the protein bioplastic is 3 to 12 MPa, and the elongation at break is 10% to 70%.

9. The application of a protein bioplastic prepared by the method of any one of claims 1 to 7, or the protein bioplastic of claim 8, characterized in that, The protein bioplastics are used in packaging, specialty paper, and coating finishing.

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