Method of starch degradation, greaseproof composite layer, and manufacturing method thereof

Abstract

°C, and a degradation reaction is carried out to form a first degraded starch solution. The pH value of the first degraded starch solution is increased by adding alkali to obtain a second degraded starch solution. A method of manufacturing a greaseproof composite layer includes the following operations. Acetylated distarch adipate with a weight-average molecular weight of

Description

Technical Field

[0001] The present disclosure relates to a starch degradation method, an oil-proof composite layer and a method for producing the same, and in particular to a method for degrading acetylated distarch adipate, an oil-proof composite layer containing the degraded starch and a method for producing the same. Prior Art

[0002] To prevent grease from seeping out of food containers, greaseproof paper is often used as the packaging material. Conventional greaseproof paper manufacturing methods, for example, involve coating a fluorocarbon resin onto a paper substrate to reduce its surface tension, making it relatively lower than grease. This allows the paper substrate to have a moderate grease-repelling ability, thereby achieving oil resistance or repellency. However, fluorocarbon resins tend to release perfluoroalkyl compounds during their decay process. Furthermore, the production of fluorocarbon resins requires the use of perfluoroalkyl compounds as additives, such as perfluorooctanesulfonic acid (PFOS), fluoroalcohols, or perfluorooctanoic acid (PFOA). However, these ingredients have been shown to be harmful to humans (e.g., carcinogenic) and may accumulate in the environment, causing damage. Consequently, they have been placed on the banned or watch lists of the United States and the European Union.

[0003] Another conventional method for manufacturing greaseproof paper involves laminating a plastic film, such as polyethylene (PE), onto a paper substrate to create a composite greaseproof paper. This composite paper offers high grease and oil resistance, excellent water resistance, and excellent airtightness. However, plastic materials are not heat-resistant and may release plastic particles, making them unsuitable for storing hot food. Furthermore, users may accidentally microwave the paper directly, unknowingly ingesting these harmful substances. Furthermore, composite greaseproof paper cannot be recycled like regular paper and must undergo special processing, such as high temperatures or the addition of alkaline solutions, to separate the plastic from the paper substrate. This not only makes recycling difficult but also increases environmental pollution and burden. Furthermore, due to the enactment of plastic reduction laws in many countries, the application of this composite greaseproof paper is limited. Summary of the Invention

[0004] The present disclosure provides a method for starch degradation, comprising the following steps: Acetylated distarch adipate, an acid, and a polar solvent are mixed to form a starch suspension. The starch suspension is then temperature adjusted to between -23°C and 47°C to allow a degradation reaction to occur, forming a first degraded starch solution. Alkali is added to increase the pH of the first degraded starch solution to obtain a second degraded starch solution.

[0005] In some embodiments, the degradation reaction is performed for a reaction time of 2 hours to 30 hours.

[0006] In some embodiments, the pH of the starch suspension is between 0.5 and 5.

[0007] In some embodiments, the pH of the second degraded starch solution is 6 to 8.

[0008] In some embodiments, the polar solvent comprises water, alcohol, or a combination thereof.

[0009] The present disclosure provides a method for producing an oil-repellent composite layer, comprising the following steps: Acetylated distarch adipate and a polar solvent are mixed to obtain a starch solution, wherein the acetylated distarch adipate has a weight-average molecular weight of 3.00×10⁶ to 5.50×10⁷. The starch solution is gelatinized to form a gelatinized starch solution. The gelatinized starch solution is adhered to a substrate by coating, impregnation, or wet-end addition. A drying process is performed to form the oil-repellent composite layer.

[0010] The present disclosure provides an oil-repellent composite layer comprising a substrate and an acetylated distarch adipate layer. The acetylated distarch adipate layer is attached to the substrate and comprises acetylated distarch adipate, wherein the acetylated distarch adipate has a weight-average molecular weight of 3.00×10⁶ to 5.50×10⁷.

[0011] In some embodiments, the oil repellency of the oil-repellent composite layer measured by the ISO 16532-2:2007 standard test method is 1 or greater.

[0012] In some embodiments, the acetylated distarch adipate has an acetyl content of less than 2.5 wt % and an adipyl content of less than 0.135 wt %.

[0013] In some embodiments, the weight of the acetylated distarch adipate layer is greater than or equal to 5 wt % of the substrate.

[0014] In some embodiments, the substrate comprises natural fibers, man-made fibers, or a combination thereof.

[0015] It is to be understood that both the foregoing general description and the following detailed description are exemplary only and are intended to provide further explanation of the disclosure as claimed. Simple diagram description

[0016] The present disclosure can be more fully understood by reading the following detailed description of the embodiments and referring to the accompanying drawings. FIG. 1 is a schematic flow diagram of a starch degradation method according to various embodiments of the present disclosure. FIG. 2 is a schematic flow chart of a method for manufacturing an oil-repellent composite layer according to various embodiments of the present disclosure. FIG. 3 is a schematic diagram of an oil-repellent composite layer according to various embodiments of the present disclosure. FIG4 shows viscosity test curves of the starch solutions of Comparative Example 1 and Examples 1-5 of the present disclosure. FIG5 shows the Fourier-transform infrared spectroscopy (FTIR) test results of the non-degraded starch of Comparative Example 1 and the degraded starches of Examples 1 to 5 of the present disclosure. Implementation Method

[0017] To provide a more detailed and complete description of the present disclosure, the following provides illustrative descriptions of implementations and specific embodiments of the present disclosure; however, these descriptions are not intended to be the only forms of implementing or utilizing the embodiments of the present disclosure. The embodiments disclosed below may be combined or substituted with one another where beneficial, and other embodiments may be added to some embodiments without further description or explanation.

[0018] Although the methods disclosed herein are described below using a series of operations or steps, the order in which these operations or steps are presented should not be construed as limiting the present disclosure. For example, certain operations or steps may be performed in a different order and / or concurrently with other steps. Furthermore, not all illustrated operations, steps, and / or features must be performed to implement the present disclosure. Furthermore, each operation or step described herein may include multiple sub-steps or actions.

[0019] This disclosure provides a method for starch degradation, a method for producing an oil-proof composite layer, and the oil-proof composite layer produced by this method. First, acetylated distarch adipate is degraded to form degraded starch, which is then coated on a substrate to produce an oil-proof composite layer with excellent oil-proof properties. The starch degradation method disclosed herein has the advantage of a simple process. Furthermore, since acetylated distarch adipate is a food additive and highly safe, the degraded starch disclosed herein can be used as a raw material for oil-proof layers and applied to various packaging containers requiring oil-proof isolation, particularly food packaging containers. For example, the oil-proof composite layer disclosed herein can be used to manufacture paper bags (such as fried food bags), paper plates, soup bowls, lunch boxes, instant food containers, pizza boxes, and the like, demonstrating its industrial applicability. The degraded starch disclosed herein is a fluorine-free modified starch and can be used as a non-fluorine-proofing agent, offering both low cost and environmental advantages. Various embodiments will be described below.

[0020] First, the present disclosure provides a method for starch degradation. Referring to FIG. 1 , FIG. 1 is a schematic flow diagram of a method 100 for starch degradation according to various embodiments of the present disclosure. Method 100 includes operations 110 , 120 , and 130 .

[0021] At operation 110, acetylated distarch adipate, an acid, and a polar solvent are mixed to form a starch suspension. In some embodiments, the pH of the starch suspension is between 0.5 and 5, for example, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5. In some embodiments, the acid includes any acid used in food additive manufacturing, such as, but not limited to, hydrochloric acid, sulfuric acid, orthophosphoric acid, acetic acid, or a combination thereof. If trace amounts of these acids remain in the starch degradation product and are ingested, they will not pose a hazard to the human body. In some embodiments, the polar solvent includes water, an alcohol, or a combination thereof. The alcohol may have, for example, 1, 2, 3, or 4 carbon atoms, and may be ethanol. In some embodiments, the starch suspension is prepared in a ratio of 350 mL to 450 mL of a polar solvent (e.g., an alcohol) for every 100 g of acetylated distarch adipate.

[0022] In operation 120, the temperature of the starch suspension is adjusted to -23°C to 47°C to perform a degradation reaction, forming a first degraded starch solution. In other words, operation 120 involves acid-alcohol degradation, hydrolyzing the starch in alcohol. In some embodiments, the temperature is -23, -21, -19, -17, -15, -13, -11, -9, -7, -5, -3, -1, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, or 47°C. Acid-alcohol degradation can be performed within the above temperature ranges and is effective in degrading starch. If the temperature is too high, gelatinization may occur. In some embodiments, the degradation reaction is performed for 2 to 30 hours. The reaction time is, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 hours. The present disclosure allows for starch degradation at low temperatures, has a simple operational process, and effectively degrades distarch acetylated adipate in a relatively short reaction time, producing a degraded starch suitable for manufacturing an oil-resistant composite layer having excellent oil-resistant properties.

[0023] At operation 130, alkali is added to increase the pH of the first degraded starch solution to obtain a second degraded starch solution. Alkali is added to make the second degraded starch solution substantially neutral, facilitating subsequent applications. In some embodiments, the second degraded starch solution comprises distarch acetylated adipate, i.e., degraded starch, having a weight-average molecular weight of 3.00×10⁶ to 5.50×10⁷. For example, the weight-average molecular weight is 3.00×10⁶, 5.00×10⁶, 10.00×10⁶, 15.00×10⁶, 20.00×10⁶, 25.00×10⁶, 30.00×10⁶, 35.00×10⁶, 40.00×10⁶, 45.00×10⁶, 50.00×10⁶, or 5.50×10⁷. In some embodiments, the degraded acetylated distarch adipate has an acetyl content of less than 2.5 wt% and an adipate content of less than 0.135 wt%, indicating that the degraded acetylated distarch adipate meets the requirements specified in the standard. In some embodiments, the second degraded starch solution is substantially neutral, that is, neutral, slightly acidic, or slightly alkaline. For example, the pH of the second degraded starch solution is between 6 and 8, such as 6, 6.5, 7, 7.5, or 8. In some embodiments, the base includes sodium bicarbonate, sodium hydroxide, potassium hydroxide, or a combination thereof. If a small amount of these remains in the starch degradation product, even if ingested, it will not cause harm to the human body. In some embodiments, operation 130 is performed at a temperature between -23°C and 47°C, for example, -23, -21, -19, -17, -15, -13, -11, -9, -7, -5, -3, -1, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, or 47°C. If the temperature is too high, gelatinization may occur. Subsequent experimental examples will verify that the second degraded starch solution includes degraded starch with a reduced degree of polymerization, and Fourier transform infrared spectroscopy (FTIR) testing will verify that the degraded starch still contains distarch acetylated adipate.

[0024] After operation 130, the method further includes filtering and washing the second degraded starch solution, and then drying and sieving to obtain degraded distarch acetylated adipate. In some embodiments, the filtered and washed second degraded starch solution is filtered and cooled to room temperature (e.g., 20° C. to 45° C.), and the resulting degraded starch is then dried and sieved to obtain the degraded starch.

[0025] Next, the present disclosure provides a method for fabricating an oil-repellent composite layer. Referring to FIG. 2 , FIG. 2 is a flow chart illustrating a method 200 for fabricating an oil-repellent composite layer according to various embodiments of the present disclosure. Method 200 includes operations 210 , 220 , 230 , and 240 .

[0026] In operation 210, acetylated distarch adipate and a polar solvent are mixed to obtain a starch solution, wherein the acetylated distarch adipate has a weight average molecular weight of 3.00×10 6 to 5.50×10 7 . The weight average molecular weight is, for example, 3.00×10 6 , 5.00×10 6 , 10.00×10 6 , 15.00×10 6 , 20.00×10 6 , 25.00×10 6 , 30.00×10 6 , 35.00×10 6 , 40.00×10 6 , 45.00×10 6 , 50.00×10 6 , or 5.50×10 7 . The acetylated distarch adipate can be obtained by the starch degradation method described in any of the aforementioned embodiments. In other embodiments, when the weight-average molecular weight of acetylated distarch adipate exceeds the aforementioned range, the weight-average molecular weight of the acetylated distarch adipate can be reduced to within the aforementioned range using an enzymatic method (α-amylase) or physical milling method (e.g., ball milling). Notably, when the weight-average molecular weight falls within the aforementioned range, the substrate to which the acetylated distarch adipate is attached can exhibit excellent oil repellency and low air permeability. When the weight-average molecular weight is below 3.00×10⁶, the oil repellency may be poor. When the weight-average molecular weight is above 5.50×10⁷, the starch layer containing the acetylated distarch adipate may be difficult to process during subsequent operations due to the high viscosity of the gelatinized starch solution. In some embodiments, the polar solvent includes water, an alcohol, or a combination thereof. The alcohol may have, for example, 1, 2, 3, or 4 carbon atoms, and an example of the alcohol is ethanol.

[0027] At operation 220, the starch solution is gelatinized to form a gelatinized starch solution. In some embodiments, the gelatinization is performed at a temperature above 95°C, for example, between 95°C and 100°C. In some embodiments, the starch solution is gelatinized in a boiling water bath.

[0028] In operation 230, the gelatinized starch solution is attached to the substrate by coating, impregnation, or wet-end addition. In some embodiments, the substrate comprises natural fibers, man-made fibers, or a combination thereof. More specifically, the gelatinized starch solution can be attached to the substrate by any of the following steps: directly coating the gelatinized starch solution on the surface of the substrate, soaking the substrate in the gelatinized starch solution, or adding the gelatinized starch solution to the raw materials used to make the substrate (e.g., paper). Wet-end addition can also be referred to as wet-end internal addition. In some embodiments, prior to operation 230, the gelatinized starch solution can be maintained at a temperature between 40°C and 65°C, for example, 40, 45, 50, 55, 60, or 65°C, to facilitate operation 230.

[0029] At operation 240, a drying process is performed to form the oil-repellent composite layer. After the drying process, the polar solvent may be substantially removed. In some embodiments, the drying process temperature is 40°C to 180°C, for example, 40, 60, 80, 100, 120, 140, 160, or 180°C.

[0030] An oil-proof composite layer can be produced by the above-described method 200. Please refer to Figure 3, which is a schematic diagram of an oil-proof composite layer 300 according to various embodiments of the present disclosure. The oil-proof composite layer 300 includes a substrate 310 and an acetylated distarch adipate layer 320. The acetylated distarch adipate layer 320 is attached to the substrate 310 and includes acetylated distarch adipate, wherein the acetylated distarch adipate has a weight-average molecular weight of 3.00×10⁶ to 5.50×10⁷. The oil-proof composite layer 300 can be produced by the method for producing an oil-proof composite layer described in any of the aforementioned embodiments. The substrate 310 can be a fiber layer. In some embodiments, the substrate 310 includes natural fibers, man-made fibers, or a combination thereof. For example, the substrate 310 includes paper, cloth, or a combination thereof. In some embodiments, the oil-proof composite layer 300 is oil-proof paper. In some embodiments, in the oil-repellent composite layer 300, the weight of the distarch acetylated adipate layer 320 is greater than or equal to 5 wt % of the substrate 310, such as 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 99 wt %. Manufacturers can adjust the weight of the distarch acetylated adipate layer 320 according to design requirements.

[0031] In some embodiments, the oil-repellent composite layer 300 has an oil repellency of 1 or greater as measured by the ISO 16532-2:2007 standard test method. In some embodiments, the oil repellency is from 1 to 9, for example, 1, 2, 3, 4, 5, 6, 7, 8, or 9. In some embodiments, the oil-repellent composite layer 300 has a tensile index of 50 N·m / g to 65 N·m / g as measured by the ISO 1924-2:2008 standard test method, for example, 50, 52, 54, 56, 58, 60, 62, 64, or 65 N·m / g. In some embodiments, the tear index of the oil-resistant composite layer 300, as measured by the ISO 1974:2012 standard test method, is between 5.0 mN·m 2 / g and 6.0 mN·m 2 / g, for example, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, or 6.0 mN·m 2 / g. In some embodiments, the burst index of the oil-resistant composite layer 300, as measured by the ISO 2758:2014 standard test method, is between 1 kPa·m 2 / g and 2 kPa·m 2 / g, for example, 1, 1.2, 1.4, 1.6, 1.8, or 2 kPa·m 2 / g. In some embodiments, the air permeability test is performed using the ISO 5636-5:2003 standard test method, based on the time required for 100 mL of air to pass through an area of 642 mm 2 of the oil-proof composite layer 300. The air permeability of the oil-proof composite layer 300 is greater than 900 seconds, for example, greater than 1200 seconds.

[0032] The following describes the features of the present disclosure in more detail with reference to Experimental Examples 1 to 5. While the following examples are provided, the materials used, their amounts and ratios, processing details, and process flow may be appropriately varied without departing from the scope of the present disclosure. Therefore, the present disclosure should not be construed as being limited by the examples described below.

[0033] Experimental Example 1: Degradation of Acetylated Distarch Adipate and Property Testing

[0034] Acetylated distarch adipate was added to a 95 vol% ethanol solution containing hydrochloric acid to form a starch suspension. The starch suspension was reacted in a thermostatic oscillator at 45°C for a predetermined degradation time, such as 5, 10, 15, 20, or 25 hours. After completion of the reaction, the starch suspension was neutralized with sodium bicarbonate solution until substantially neutral, cooled to room temperature, and vacuum filtered to obtain a starch filter cake. The starch filter cake was stirred evenly with 50 vol% ethanol and vacuum filtered again. The filtered starch was dried in a 40°C oven for 24 hours, pulverized, and sieved through a 100-mesh sieve to obtain degraded starch, i.e., degraded acetylated distarch adipate. Next, the weight-average molecular weight, acetyl content, and adipate content of the acetylated distarch adipate in the undegraded acetylated distarch adipate (Comparative Example 1) and the degraded starches obtained at different degradation times (Examples 1-5) were measured. The measurement results are shown in Table 1 below. The weight-average molecular weight of starch was measured by static light scattering (SLS), which includes the following steps. (1) Sample preparation: Using 1 mol / L NaOH as the solvent, at least five samples with different concentrations were prepared in the concentration range of 0.50 mg / mL to 2.10 mg / mL. The samples were stirred at room temperature for 18 hours using a magnetic stirrer. The stirred samples were then centrifuged at 3000 rpm for 30 minutes. Each sample was filtered through a nylon filter membrane with a pore size of 3 μm before measurement. (2) Instrument parameters: The sample was irradiated with light of a wavelength of 532 nm, with a light source output power of 60 mW and a measurement temperature of 20°C. Toluene was used as the standard sample. The scattering angle range was 40° to 140°, and the light scattering intensity was recorded every 10°. The specific refractive index increment (dn / dc) was 0.142 mL / g. The weight-average molecular weight of starch can be calculated from a Berry plot. The analytical methods for acetyl and adipic acid content can be found in the Joint FAO / WHO Expert Committee on Food Additives. 2018. Monograph 22. Modified starches. Compendium of Food Additive Specifications. Table 1 Starch degradation time (hours) Starch weight average molecular weight (Dalton) Acetyl content (wt%) Adipic acid content (wt%) Comparative Example 1 0 1.27×10 8 1.5 0.022 Example 1 5 5.08×10 7 1.2 0.022 Example 2 10 2.21×10 7 1.2 0.021 Example 3 15 1.91×10 7 1.0 0.020 Example 4 20 1.05×10 7 1.0 0.020 Example 5 25 3.81×10 6 0.9 0.019

[0035] As shown in Table 1, acetylated distarch adipate can be degraded with hydrochloric acid to produce the degraded starches of Examples 1-5. The longer the degradation time, the lower the molecular weight (degree of polymerization) of the degraded starch. Furthermore, the degraded starches of Examples 1-5 have an acetyl content of less than 2.5 wt% and an adipate content of less than 0.135 wt%, thus meeting the requirements of the standard.

[0036] Experimental Example 2: Starch Viscosity Analysis

[0037] The undegraded starch of Comparative Example 1 and the degraded starches of Examples 1-5 were each prepared with water to form starch solutions, wherein the concentration of these starch solutions was 6 wt%. The degradation time of the degraded starches of Examples 1-5 was 5, 10, 15, 20, or 25 hours, respectively. The degradation time of the degraded starch of Comparative Example 1 was 0 hours. Next, the changes in starch viscosity at different temperatures were observed using a Brabender viscometer, operating at an AACC of 22-10.0, a rotor speed of 75 rpm, and a torque of 700 cmg. The temperature increase step for measuring viscosity included: starting at 30°C, heating to 95°C at a rate of 1.5°C / min for gelatinization, holding at 95°C for 45 minutes, and then cooling to 50°C at a rate of 1.5°C / min and holding at 50°C for 45 minutes. Figure 4 shows the viscosity test curves of the starch solutions of Comparative Example 1 and Examples 1-5 of the present disclosure. The gelatinization temperature of the starch was assessed by observing the viscosity changes of a gelatinized starch solution of a fixed concentration under a continuously varying temperature environment. Curve BK represents the temperature change curve of the test environment. Curve 400 represents the viscosity change curve of the starch solution of Comparative Example 1, showing that the maximum viscosity temperature of this starch is approximately 65.0°C. Curves 410, 420, 430, 440, and 450 represent the viscosity change curves of the starch solutions of Examples 1, 2, 3, 4, and 5, respectively. The gelatinization temperature of the degraded starch of Example 1 is approximately 73.8°C. The gelatinization temperature of the degraded starch of Example 2 is approximately 74.4°C. The gelatinization temperature of the degraded starch of Example 3 is approximately 75.9°C. The gelatinization temperature of the degraded starch of Example 4 is approximately 73.5°C. The gelatinization temperature of the degraded starch of Example 5 is approximately 70.8°C. From this, we can see that when the degree of starch degradation is greater (that is, when the weight-average molecular weight of the degraded starch is smaller), the temperature of maximum viscosity of the starch solution will first increase and then decrease.

[0038] Experimental Example 3: Production of Greaseproof Paper and Property Testing

[0039] The undegraded acetylated distarch adipate from Comparative Example 1 and the degraded starches from Examples 1-5 were prepared with water to form starch solutions. The solutions were then gelatinized in a boiling water bath for 15 minutes. The concentration of each solution was 15 wt%. Using a wire-rod coating rod on a motorized coater (KCC 202), the different gelatinized starch solutions were applied to commercially available copy paper (paper ash content <10 wt%, tested according to ISO 1762:2001) with a coating speed of 6 cm / s. The coated copy paper was then dried to form greaseproof paper containing different starch layers. After drying, the starch coating weight on the copy paper was approximately 5.5 g / m2. The oil resistance (Kit value) of the paper was tested according to ISO 16532-2:2007. The air permeability of the paper was tested using the ISO 5636-5:2003 standard test method, with the evaluation method being the time required for 100 mL of air to pass through a 642 mm² test piece. The test results are shown in Table 2 below. Table 2 lists the test results for copy paper not coated with starch solution for comparison with Comparative Example 1 and Examples 1-5. Table 2 Starch degradation time (hours) Oil resistance Air permeability (seconds) Copy paper not coated with starch solution N / A 1 8.4±0.9 Comparative Example 1 0 1-3 >1200 Example 1 5 5-6 >1200 Example 2 10 7-9 >1200 Example 3 15 7 >1200 Example 4 20 3-5 >1200 Example 5 25 2 906.3±184

[0040] Table 2 shows that the degraded starches of Examples 1-5 can indeed improve the oil resistance of grease-proof paper. The degraded starch of Example 2 can achieve an oil resistance of up to 9. Different food packaging containers have different oil resistance requirements, but an oil resistance of approximately 5 or above generally meets the requirements of general food packaging. Comparative Example 1 and Examples 1-5 show that the degraded acetylated distarch adipate of Examples 1-5 is more effective in improving the oil resistance of grease-proof paper than undegraded acetylated distarch adipate. Furthermore, Examples 1-4 show that these grease-proof papers have low air permeability.

[0041] Experimental Example 4: Testing the Tensile Index, Tear Index, and Rupture Index of Paper

[0042] Tests were conducted on the starch-coated paper of Comparative Example 1 or Examples 1-5 in Experimental Example 3. The paper's tensile index was measured using the ISO 1924-2:2008 standard test method. The tear index was measured using the ISO 1974:2012 standard test method. The burst index was measured using the ISO 2758:2014 standard test method. The measurement results are shown in Table 3 below. Table 3 Starch degradation time (hours) Tensile index (N·m / g) Tear index (mN·m 2 / g) Rupture Index (KPa·m 2 / g) Copy paper not coated with starch solution N / A 58.7 5.88±0.28 1.20±0.27 Comparative Example 1 0 57.0 5.22±0.28 1.56±0.27 Example 1 5 56.0 5.32±0.37 1.51±0.30 Example 2 10 51.4 5.12±0.25 1.70±0.14 Example 3 15 62.7 4.78±0.37 1.65±0.30 Example 4 20 63.1 5.16±0.18 1.63±0.12 Example 5 25 61.5 5.28±0.51 1.60±0.20

[0043] The tensile index of the greaseproof paper coated with the degraded starch of Examples 1-5 ranged from 50 N·m / g to 65 N·m / g. The tear index of the greaseproof paper coated with the degraded starch of Examples 1-5 ranged from 5.0 mN·m² / g to 6.0 mN·m² / g. The burst index of the greaseproof paper coated with the degraded starch of Examples 1-5 ranged from 1 kPa·m² / g to 2 kPa·m² / g. These results indicate that the greaseproof paper of Examples 1-5 possesses excellent strength and is suitable for use as food packaging containers. The burst index of the greaseproof paper of Examples 1-5 is even higher than that of the uncoated copy paper of Comparative Example 1.

[0044] Experimental Example 5: FTIR test results of starch

[0045] Figure 5 shows the Fourier transform infrared spectroscopy (FTIR) test results for the undegraded starch (acetylated distarch adipate) of Comparative Example 1 and the degraded starches of Examples 1-5. Specifically, curve 500 represents the FTIR test result for the undegraded starch of Comparative Example 1, while curves 510, 530, 540, and 550 represent the FTIR test results for the degraded starches after degradation times of 5, 10, 15, 20, and 25 hours, respectively. As shown in Figure 5, the characteristic peaks of these infrared spectra remain largely consistent, confirming that after the degradation process of Experimental Example 1 of the present disclosure, the degraded starches of Examples 1-5 remain composed of acetylated distarch adipate. This demonstrates that the degradation process of Experimental Example 1 yields degraded starch with a reduced degree of polymerization, but it remains acetylated distarch adipate. Therefore, the degraded starch of the present disclosure is a highly safe food additive and is suitable as a raw material for oil-resistant coatings in food packaging containers.

[0046] In summary, the present disclosure provides a starch degradation method, a method for producing an oil-resistant composite layer, and the oil-resistant composite layer produced by such a method. This method, through a simple process and reaction conditions, degrades acetylated distarch adipate into degraded starch, which is then used as the raw material for the oil-resistant layer on the oil-resistant composite layer. This degraded starch is a non-fluorinated oil-resistant agent that is highly safe, inexpensive, and environmentally friendly, and can be used in the manufacturing of food packaging containers.

[0047] Although the present disclosure has been described in considerable detail with reference to certain embodiments, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.

[0048] It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the present disclosure. In view of the foregoing, the present disclosure is intended to cover modifications and variations of the present disclosure that fall within the scope of the appended claims.

[0049] 100, 200: Method 110, 120, 130, 210, 220, 230, 240: Operation 300: Oil-proof composite layer 310: Base material 320: Acetylated distarch adipate layer BK, 400, 410, 420, 430, 440, 450, 500, 510, 520, 530, 540, 550: curve

[0050] Domestic storage information (please note the order of storage institution, date, and number) none Overseas deposit information (please note the order of deposit country, institution, date, and number) none

Claims

1. A method for starch degradation, comprising: Mixing acetylated distarch adipate, acid and a polar solvent to form a starch suspension; The temperature of the starch suspension is adjusted to -23°C to 47°C, and a degradation reaction is performed to form a first degraded starch solution; and alkali is added to increase the pH value of the first degraded starch solution to obtain a second degraded starch solution.

2. The method of claim 1, wherein the degradation reaction is carried out for a reaction time of 2 to 30 hours.

3. The method of claim 1, wherein the pH value of the starch suspension is 0.5 to 5.

4. The method of claim 1, wherein the pH value of the second degraded starch solution is 6 to 8.

5. The method of claim 1, wherein the polar solvent comprises water, alcohol or a combination thereof.

6. A method for making an oil-proof composite layer, comprising: A starch solution is obtained by mixing acetylated distarch adipate and a polar solvent, wherein the acetylated distarch adipate has a weight average molecular weight of 3.00×10 6 to 5.50×10 7; the starch solution is gelatinized to form a gelatinized starch solution; the gelatinized starch solution is attached to a substrate by a coating process, an impregnation process or a wet end addition; and a drying process is performed to form the oil-proof composite layer.

7. An oil-proof composite layer comprising: a substrate; and an acetylated distarch adipate layer, attached to the substrate and comprising acetylated distarch adipate, wherein the acetylated distarch adipate has a weight average molecular weight of 3.00×10 6 to 5.50×10 7.

8. The oil-proof composite layer according to claim 7, wherein the oil-proof degree of the oil-proof composite layer measured by the ISO16532-2:2007 standard test method is 1 or more.

9. The oil-proof composite layer according to claim 7, wherein the acetylated distarch adipate has an acetyl content of less than 2.5 wt % and an adipic acid content of less than 0.135 wt %.

10. The oil-proof composite layer as claimed in claim 7, wherein the weight of the acetylated distarch adipate layer is greater than or equal to 5 wt % of the substrate.

11. The oil-proof composite layer according to claim 7, wherein the substrate comprises natural fibers, artificial fibers or a combination thereof.

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