Nitrogen-containing compound plasticized biodegradable thermoplastic starch composition and preparation method thereof

Abstract

The invention provides a novel biodegradable thermoplastic starch composition and a preparation method thereof. The thermoplastic starch composition of the present invention has excellent mechanical strength, improved stability and retrogradation resistance compared to conventional thermoplastic starch materials, and can maintain its biodegradability because it does not need to be mixed with fossil-based plastics.

Description

Technical Field

[0001] This invention relates to the field of biodegradable materials, specifically to a marine biodegradable thermoplastic starch composition and its preparation method. Background Technology

[0002] To achieve environmental sustainability and reduce carbon emissions from human activities, the use of bio-based polymers is highly advantageous. Thermoplastic starch is the most widely used bioplastic due to its abundant sources, renewability, low production costs, low biological and ecotoxicity, and high compatibility with existing plastics processing techniques such as extrusion, injection molding, and thermoforming.

[0003] Conventional bio-based plastics are generally non-biodegradable (similar to fossil-based plastics) or require specific conditions (such as high temperatures and specific microorganisms) to degrade. Thermoplastic starch, on the other hand, can rapidly biodegrade in natural environments such as soil or oceans, a feat difficult to achieve with other bio-based plastics.

[0004] The conversion of starch into thermoplastic starch is achieved through plasticization (sometimes also called gelatinization), during which plasticizers are introduced to break down the intermolecular and intramolecular hydrogen bonds of starch molecules. To date, most thermoplastic starch formulations use polyols as plasticizers because the hydroxyl groups in polyols can participate in the starch hydrogen bond network. Typical polyol plasticizers include glycerol, sugar alcohols, ethylene glycol, and related derivatives. For example, US20130158169A1 discloses the use of polyols as plasticizers in thermoplastic starch compositions, where the addition of other thermoplastic polymers such as polyolefins reduces the biodegradability and biomass content of the composition. US4900361A and US5405564A disclose thermoplastic starch compositions containing plasticizers such as glycerol, propylene glycol, sorbitol, and triethyl citrate. US5449708A discloses the use of polyols such as glycerol, sorbitol, or ethylene glycol as plasticizers in thermoplastic starch compositions. CN1063699A discloses the use of polyols (such as glycerol, sorbitol and related derivatives) as plasticizers in thermoplastic starch compositions.

[0005] Despite the numerous advantages of thermoplastic starch, its relatively low mechanical strength and poor water resistance are major obstacles to its widespread application. The relatively weak and limited hydrogen bond network between polyols and starch leads to low mechanical strength and regression (due to plasticizer migration and loss) in thermoplastic starch after long-term storage. Therefore, thermoplastic starch is often used in the form of polymer blends, incorporating other components such as low-density polyethylene, high-density polyethylene, and polypropylene to improve mechanical strength and stability, while sacrificing biodegradability.

[0006] Therefore, there is a need in the art for a thermoplastic starch composition with improved mechanical strength and stability. Summary of the Invention

[0007] The present invention aims to overcome the shortcomings of existing thermoplastic starch compositions. The inventors have screened a nitrogen-containing compound and deep eutectic system that can provide higher mechanical strength, stability and hydrophobicity to thermoplastic starch compositions as a plasticizer, thereby realizing the present invention.

[0008] In a first aspect of the invention, a thermoplastic starch composition is provided, comprising:

[0009] -100 parts by weight of at least one starch-based material; and

[0010] -1-30 parts by weight of at least one nitrogen-containing plasticizer, wherein the nitrogen-containing plasticizer is a compound or deep eutectic system having at least three nitrogen atoms.

[0011] In a second aspect of the invention, a thermoplastic composite material is provided, which is formed by combining the thermoplastic starch composition described in the first aspect with a fossil-based plastic.

[0012] In a third aspect of the invention, a food contact article is provided, which is made of the thermoplastic starch composition described in the first aspect or the thermoplastic composite material described in the second aspect.

[0013] This application utilizes stronger and more extensive hydrogen bonds formed between at least three nitrogen atoms in a nitrogen-containing compound or deep eutectic system and the hydroxyl groups of starch to construct novel thermoplastic starch compositions. The thermoplastic starch compositions of this invention achieve higher mechanical strength, better hydrophobicity, improved resistance to retrogradation, and enhanced stability without mixing with fossil-based plastics.

[0014] Because it does not use fossil-based plastics, the thermoplastic starch composition of the present invention retains its biodegradability, particularly in marine environments, water, soil, and compost, making it environmentally friendly. Not wishing to be bound by theory, the thermoplastic starch composition of the present invention can be further compounded with fossil-based plastics as needed, thereby obtaining thermoplastic composite materials with higher mechanical strength, ductility, thermodynamic stability, and water resistance, thus enabling a wider range of applications.

[0015] When selecting a plasticizer that can directly contact food as defined in this invention, the thermoplastic starch composition of this invention can be manufactured into food contact articles conforming to standards GB / T 41220, GB / T 10457, GB / T18006 or GB / T 10004, such as, but not limited to, food packaging boxes, tableware, food packaging lids, food preservation films, and plastic composite films for packaging. Attached Figure Description

[0016] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated herein by reference and constitute a part of this specification, are provided. The drawings described herein are for illustrative purposes only and are not intended to limit the scope of disclosure in any way.

[0017] Figure 1 The formation process of a urea-choline chloride deep eutectic solvent (DES) according to one embodiment of the present invention is shown.

[0018] Figure 2 The stress / strain curve of a thermoplastic starch composition according to one embodiment of the present invention is shown.

[0019] Figure 3 The appearance of comparative example C1 of the thermoplastic starch composition before and after 60 days of storage is shown.

[0020] Figure 4 The appearance of thermoplastic starch composition N3 before and after 7 months of storage is shown according to one embodiment of the present invention.

[0021] Figure 5 The water contact angles of thermoplastic starch compositions (A) C1, (B) C2, (C) N5 and (D) N6 according to one embodiment of the present invention are shown. Detailed Implementation

[0022] The following detailed description is merely exemplary and is by no means intended to limit the scope of the invention or its application or use.

[0023] Although the numerical ranges and parameters given for the broad scope of this invention are approximations, the values ​​in specific examples are made as precisely as possible. However, any numerical value inherently contains a certain degree of error, which is necessarily caused by variations in the standards used in the respective test measurements.

[0024] Furthermore, it should be understood that any numerical range described herein is intended to include all subranges contained therein. For example, the range “1 to 10” is intended to include (and include) all subranges between the minimum value of 1 and the maximum value of 10, i.e., the minimum value is equal to or greater than 1 and the maximum value is equal to or less than 10.

[0025] The terminology used in this document is for the purpose of describing specific example implementations only and is not restrictive.

[0026] As used herein, “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably to indicate the presence of at least one specified element, material, component, or method step, unless the context clearly indicates otherwise.

[0027] The terms “first,” “second,” or “third” used in this article are used for distinction purposes only and are not intended to define order, priority, or hierarchy.

[0028] As used herein, the terms “about,” “primarily,” and “essentially” refer to the measurable value and range due to expected variations known to those skilled in the art (such as limitations and variability in measurement). The term “about” also implies that the numerical value is allowed some slight imprecision (the value is somewhat close to precision; approximately or reasonably close to the value; close). If the imprecision provided by the term “about” is not understood in this ordinary sense in the art, then the term “about” as used herein at least indicates variations that may arise from ordinary methods of measuring and using such parameters. Furthermore, the scope of disclosure includes all disclosed values ​​and further subdivisions throughout the range.

[0029] The terms “comprising,” “containing,” and similar terms as used herein, together with their grammatical variations, are synonymous with the term “including” and its grammatical variations. The term “comprising” and its grammatical variations are open-ended and, in the context of this invention, should be understood to include not only the specified elements, materials, components, or method steps, but also other unspecified elements, materials, components, or method steps.

[0030] As used herein, the term "composed of" and its grammatical variations should be understood in the context of this invention to exclude any unspecified elements, ingredients, or method steps. As used herein, the terms "substantially composed of" or "mainly composed of" and their grammatical variations should be understood in the context of this invention to include specified elements, materials, ingredients, or method steps, as well as those elements, materials, ingredients, or method steps that do not substantially affect the described essential and novel features. It should be understood that when using the term "comprising" and its grammatical variations, if other elements, materials, ingredients, or method steps that may substantially affect the "essential and novel features" of the content are not included, the terms "composed of" or "mainly composed of" and their grammatical variations may be used instead of the term "comprising".

[0031] In describing the specific aspects of this invention in detail, those skilled in the art will recognize that various modifications and substitutions can be made to these details based on the general teachings of this invention. Therefore, the specific embodiments disclosed are for illustrative purposes only and are not intended to limit the scope of disclosure, which should include the full scope of the appended claims and any and all their equivalents.

[0032] As previously stated, the present invention aims to provide a thermoplastic starch composition that has excellent mechanical strength, stability and hydrophobicity, and is able to maintain biodegradability, especially in marine environments, soil and compost.

[0033] thermoplastic starch composition

[0034] In the context of this invention, the term "thermoplastic starch composition" should be understood as a starch-based composition that reversibly softens under heat and hardens by cooling. It has at least one glass transition temperature (Tg) below which the amorphous portion of the composition is in a brittle glassy state, and above which the composition may undergo reversible plastic deformation. The thermoplastic starch compositions of this invention can be formed by methods conventionally used in plastics processing, such as extrusion, injection molding, molding, blow molding, calendering, etc.

[0035] In a first aspect of the invention, a thermoplastic starch composition is provided, comprising:

[0036] -100 parts by weight of at least one starch-based material; and

[0037] -1-30 parts by weight of at least one nitrogen-containing plasticizer, wherein the nitrogen-containing plasticizer is a compound or deep eutectic system having at least three nitrogen atoms.

[0038] In one specific embodiment, the thermoplastic starch composition of the present invention contains more than 60% bio-based carbon content according to standards ASTM D6866 and EN16640.

[0039] In a further specific embodiment, the thermoplastic starch composition of the present invention contains 100% bio-based carbon content according to standards ASTM D6866 and EN 16640.

[0040] In yet another specific embodiment, the thermoplastic starch composition of the present invention contains more than 60% bio-based components according to standard EN 16785-1.

[0041] In one specific embodiment, the thermoplastic starch composition of the present invention is biodegradable, particularly in marine, water, soil, or compost environments. As previously stated, the thermoplastic starch composition of the present invention has improved stability, which slows down the degradation rate of the thermoplastic starch composition, but those skilled in the art will understand that this does not fundamentally alter the biodegradability of the starch composition.

[0042] The thermoplastic starch composition of the present invention can be prepared using methods well known to those skilled in the art. For example, a mixture comprising starch and a nitrogen-containing plasticizer is fed into an extruder and passed through the extruder at a temperature of 80°C to 200°C, preferably 100°C to 140°C, with the screw speed of the extruder set to 20 rpm to 60 rpm, to extrude the mixture through a die to obtain a biodegradable thermoplastic starch composition.

[0043] Nitrogen-containing plasticizers

[0044] In the context of this invention, a "nitrogen-containing plasticizer" is an organic compound or deep eutectic system having at least three nitrogen atoms. Nitrogen atoms exist in the organic compound or deep eutectic system in the form of amino groups, amine groups, amides, etc. The inventors have discovered that, on the one hand, the hydrogen bonds formed between nitrogen atoms in the nitrogen-containing plasticizer and the hydroxyl groups of starch have larger bond energies than those formed between oxygen atoms (in water and polyols) and the hydroxyl groups of starch, approximately 29 kJ / mol OH-:N and 2921 kJ / mol OH-:O, respectively; on the other hand, multiple nitrogen atoms in the compound or deep eutectic system having at least three nitrogen atoms can form multiple hydrogen bonds, thereby forming a wider hydrogen bond network. Therefore, the compound or deep eutectic system having at least three nitrogen atoms of this invention, as a plasticizer, can give thermoplastic starch compositions higher mechanical strength and stability while maintaining biodegradability without mixing with fossil-based plastics.

[0045] In one specific implementation, the nitrogen-containing plasticizer may be 5-25 parts by weight relative to 100 parts by weight of starch-based material, for example, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, 20 parts by weight, 21 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, or 25 parts by weight, or a range consisting of any two of these values.

[0046] In one specific embodiment, the compound having at least three nitrogen atoms may be selected from one or more of arginine, guanidine, diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), 2-cyanoguanidine, diurea, melamine, tri(2-aminoethyl)amine (TREN), poly(allylamine) hydrochloride, polyetheramine, and polyamide.

[0047] In yet another specific implementation, the deep eutectic system having at least three nitrogen atoms is a urea-based deep eutectic system.

[0048] It is worth noting that the nitrogen-containing compounds or deep eutectic systems of the present invention do not include carboxylic acid compounds with a pH below 5 that can hydrolyze starch, such as lactic acid or citric acid, in order to avoid affecting the properties of the obtained thermoplastic starch composition.

[0049] In yet another specific embodiment, when the thermoplastic starch composition of the present invention is intended for use in food contact applications, the nitrogen-containing plasticizer is selected from one or more of arginine, guanidine, diethylenetriamine, and urea-based deep eutectic systems. The thermoplastic starch composition of the present invention thus prepared can comply with the relevant food laws and regulations of many countries and regions, including but not limited to REACH, RoHHS, U.S. Federal Regulations 21 (parts 170-199), the Chinese Food Safety Standards issued by the National Health Commission of China, and the European Union Food Contact Materials Regulation (EC) 1935 / 2004.

[0050] It is understood that, when selecting plasticizers that can directly contact food as defined in this invention, the thermoplastic starch composition of this invention can be manufactured into biodegradable articles that can directly contact food, such as food contact articles conforming to standards GB / T41220, GB / T 10457, GB / T 18006 or GB / T10004, such as food packaging boxes, tableware, food packaging lids, food preservation films, packaging plastic composite films, etc., but not limited thereto.

[0051] Similarly, it can be understood that when the thermoplastic starch composition of the present invention is not intended for use as a food contact material, other nitrogen-containing plasticizers, such as triethylenetetramine, tetraethylenepentamine, 2-cyanoguanidine, diurea, melamine, tri(2-aminoethyl)amine, poly(allylamine) hydrochloride, polyetheramine, polyamide, etc., can be added to the thermoplastic starch composition.

[0052] Deep eutectic system

[0053] In the context of this invention, "deep eutectic system" is also known as deep eutectic solvent (DES) or eutectic solvent. It has similar properties to ionic liquids, is liquid at room temperature, and is a eutectic solvent of binary and ternary systems mainly composed of hydrogen bond donors (such as polyols, urea and carboxylic acids) and hydrogen bond acceptors (quaternary ammonium salts, such as choline chloride).

[0054] In one specific implementation, the urea-based deep eutectic system may be a binary system that also includes a second compound.

[0055] In a further specific embodiment, the second compound in the binary system can be a quaternary ammonium compound or a salt thereof, such as choline chloride or betaine. Therefore, the binary urea-based deep eutectic system of the present invention can be urea-choline chloride DES, urea-betaine DES, etc., but is not limited thereto.

[0056] Depending on the specific choice of the second compound, those skilled in the art can adjust the molar ratio of urea to the second compound to allow the binary system to form a eutectic. In one specific embodiment, the molar ratio of urea to the second compound in the binary system is in the range of 4:1 to 1:4. In a preferred embodiment, the molar ratio of urea to the second compound in the binary system is in the range of 2:1 to 1:2.

[0057] In yet another specific embodiment, the urea-based deep eutectic system may be a ternary system comprising a second compound and a third compound.

[0058] In one specific implementation, the second compound of the ternary system may be a quaternary ammonium compound or its salt, such as choline chloride, betaine, etc., but not limited thereto; or an amino acid, such as proline.

[0059] In another specific embodiment, the third compound of the ternary system can be a polyol, such as sorbitol, glycerol, sucrose, glucose, etc., but is not limited thereto. Therefore, the ternary urea-based deep eutectic system of the present invention can be urea-choline chloride-glycerol DES, urea-choline chloride-sucrose DES, urea-choline chloride-glucose DES, urea-betaine-glycerol DES, urea-sorbitol-proline DES, etc., but is not limited thereto.

[0060] Depending on the specific selection of the second and third compounds, those skilled in the art can adjust the molar ratio of urea to the second and third compounds to achieve a eutectic formation in the ternary system. In one specific embodiment, the molar ratio of urea, the second compound, and the third compound in the ternary system is in the range of 4:1:1 to 1:1:1. In a preferred embodiment, the molar ratio of urea, the second compound, and the third compound in the ternary system is in the range of 3:1:1 to 1:1:1.

[0061] The inventors have discovered that by using a urea-based DES system in the thermoplastic starch composition of the present invention, the extensive hydrogen bond network of DES can be further utilized to effectively plasticize starch molecules.

[0062] The urea-based deep eutectic system of the present invention can be prepared by methods well known to those skilled in the art, such as simply mixing urea, a second compound (and a third compound) in a specific molar ratio and heating to a temperature of 50°C-80°C until the mixture becomes a homogeneous liquid.

[0063] Starch-based materials

[0064] In one specific embodiment, the starch-based material used in this invention is natural starch, modified starch, or any combination thereof.

[0065] In a preferred embodiment, the starch-based material is natural starch.

[0066] In a further specific embodiment, the natural starch can be of any plant origin, such as cereals like wheat, barley, corn, sorghum; tubers like potatoes or cassava; or legumes like peas or soybeans, but is not limited thereto. The thermoplastic starch composition of the present invention has proven applicable to various types of natural starches, such as wheat starch and corn starch.

[0067] In yet another specific embodiment, the modified starch is a starch with a chemical structure different from its native form, and the modification methods include, but are not limited to, hydrolysis, crosslinking, esterification, etherification, substitution, redox reactions, or any combination thereof. The thermoplastic starch composition of the present invention has proven applicable to various types of modified starch. An exemplary modified starch may be hydroxypropyl distarch phosphate (TS-HPDSP), but is not limited thereto.

[0068] Oxygen plasticizer

[0069] In the context of this invention, in addition to the nitrogen-containing plasticizers described above, the thermoplastic starch compositions of this invention may also include 1-20 parts by weight of an oxygen-containing plasticizer, which is a C4-C8 oxygen-containing organic compound, such as an oxygen-containing compound having at least one of acetal, acyl, hydroxyl, aldehyde, alkoxy, carboxyl, ester, ether, ketone or any combination thereof.

[0070] In a preferred embodiment, relative to 100 parts by weight of starch-based material, the oxygen-containing plasticizer may be present in the thermoplastic starch composition in a range consisting of any two of the following values: 1 part by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, or 20 parts by weight.

[0071] In one specific embodiment, the oxygen-containing plasticizer is a polyol, such as glycerol, sorbitol, sugar alcohol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, or any combination thereof.

[0072] The inventors have discovered that the use of oxygen-containing plasticizers can further expand the extensive hydrogen bond network, thereby increasing the tensile stress and strain of thermoplastic starch compositions.

[0073] Functional additives

[0074] In the context of this invention, the thermoplastic starch composition of this invention may also include 1-20 parts by weight of functional additives, such as waterproofing agents, antioxidants, fillers, release agents, etc., but is not limited thereto.

[0075] In a preferred embodiment, the functional additive can be a range consisting of any two of the following values: 1 part by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight, or 20 parts by weight, relative to 100 parts by weight of starch-based material.

[0076] In one specific embodiment, the waterproofing agent may be selected from beeswax, chitin, modified cellulose, lipids, palm wax, rice bran wax, soybean wax, candle wax, fatty acids, Japanese wax, paraffin wax, microcrystalline wax, shellac, dimethyl polysiloxane, cetearyl alcohol, lanolin, petroleum wax, polyethylene wax, or any combination thereof, but is not limited thereto.

[0077] The inventors have discovered that adding a waterproofing agent to a thermoplastic starch composition can significantly improve the hydrophobicity of the thermoplastic starch, making its water contact angle reach about 115°. This is advantageous for starch-based articles made from the thermoplastic starch composition of the present invention, for example, it can reduce the adsorption of liquids by starch-based articles, such as water absorption, thereby minimizing the negative impact of liquids on the mechanical properties of starch-based articles.

[0078] In yet another specific embodiment, the antioxidant may be selected from carvacrol, ascorbic acid, tocopherol, tocotrienol, or any combination thereof, but is not limited thereto. The inventors have discovered that adding an antioxidant to a thermoplastic starch composition can reduce the damage to the polymer chains in the thermoplastic starch caused by the heating and pressurizing steps during processing, thereby improving the stability of the thermoplastic starch.

[0079] In another specific embodiment, the filler can be an inorganic filler, such as selected from calcium carbonate, silica, bentonite, kaolin, mica, talc, or any combination thereof, but not limited thereto. The inventors have discovered that adding a filler to a thermoplastic starch composition can reduce starch agglomeration during processing and prevent starch or starch composition from clogging the feed inlet during feeding.

[0080] In yet another specific embodiment, the release agent may be selected from dimethylpolysiloxane, linoleamide, oleamide, palmitamide, stearamide, or any combination thereof, but is not limited thereto. The inventors have discovered that adding a release agent to a thermoplastic starch composition can lubricate the extruder barrel, reduce friction between the plastic and the barrel, which can reduce pyrolysis caused by the additional heating due to friction and reduce machine back pressure, thereby reducing energy consumption.

[0081] In a second aspect of the invention, a thermoplastic composite material is provided, which is formed by combining the thermoplastic starch composition described in the first aspect with a fossil-based plastic.

[0082] In one specific implementation, the fossil-based plastic may be selected from LDPE, PP, PBAT and PBS, but is not limited thereto.

[0083] In a preferred embodiment, the fossil-based plastic may be LDPE.

[0084] In yet another specific embodiment, the thermoplastic starch composition and fossil-based plastic in the thermoplastic composite material have a ratio range of not less than 1:1, so that the resulting thermoplastic composite material retains a high starch content while having enhanced mechanical properties, such as higher mechanical strength, extensibility, thermodynamic stability and water resistance, thereby enabling a wider range of applications.

[0085] In a further specific embodiment, the ratio of the thermoplastic starch composition to the fossil-based plastic in the thermoplastic composite material ranges from 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1, or a range consisting of any two of these values.

[0086] In the thermoplastic composite material of the present invention, the ratio of the thermoplastic starch composition to the fossil-based plastic can be determined according to the specific selection of the thermoplastic starch composition and the fossil-based plastic. For example, when the fossil-based plastic is LDPE or PBAT, the ratio of the thermoplastic starch composition to LDPE or PBAT can be in the range of 1:1 to 2:1, for example, 50:50 to 65:35 or 60:40 to 65:35.

[0087] In the context of this invention, the preparation of thermoplastic composite materials can be carried out using techniques well known to those skilled in the art, such as blown film. The specific steps can be as follows: adding a thermoplastic starch composition and fossil-based plastic masterbatch into a twin-screw extruder and heating it to 120°C-180°C at a rotation speed of 30rpm-60rpm, and then blowing, stretching, and winding it into a film through a die.

[0088] In a third aspect of the invention, a food contact article is provided, which is made of the thermoplastic starch composition described in the first aspect or the thermoplastic composite material described in the second aspect.

[0089] In one specific implementation, the food contact article conforms to standards GB / T41220, GB / T 10457, GB / T 18006 or GB / T 10004.

[0090] As previously described, when using the plasticizers that can directly contact food as defined in this invention, the thermoplastic starch composition of this invention can be manufactured into biodegradable products that come into direct contact with food, such as food packaging boxes, tableware, etc. Therefore, in one specific embodiment, the food contact products are food packaging boxes, tableware, food packaging lids, food preservation films, packaging plastic composite films, etc., but are not limited thereto.

[0091] Example

[0092] The following examples illustrate the preparation of the thermoplastic starch compositions of the present invention and the characterization of their related properties. Unless otherwise specified, all test methods used are conventional methods, and all test materials used in the following examples were purchased from conventional chemical reagent stores. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0093] Example 1: Preparation of urea-choline chloride deep eutectic solvent

[0094] A urea-choline chloride deep eutectic solvent is prepared by mixing urea and choline chloride in a molar ratio of 3:1 and heating the mixture to approximately 80°C, stirring until the mixture becomes a homogeneous liquid with no visible solids. Its formation is as follows: Figure 1 As shown.

[0095] Example 2: Preparation of thermoplastic starch composition

[0096] The general steps for preparing the thermoplastic starch composition of the present invention are as follows: starch, nitrogen-containing plasticizer, oxygen-containing plasticizer, functional additives, etc. are stirred in a mixer at room temperature until a homogeneous solid mixture is obtained; the mixture containing starch and nitrogen-containing plasticizer is fed through an extruder, the screw speed of the extruder is set to 20 rpm to 60 rpm, the temperature is about 100°C to 140°C, and the mixture is extruded through a die to obtain a biodegradable thermoplastic starch composition.

[0097] The thermoplastic starch compositions of the present invention and comparative examples were prepared according to the above procedure and the components shown in Tables 1 and 2 below. Urea-based DES was prepared using the method of Example 1.

[0098]

[0099] Table 2: Comparative Examples of Starch Compositions (Components by Weight)

[0100] Components Comparative Example C1 Comparative Example C2 Comparative example C3 Comparative Example C4 serial number NBM005 NBM023 NBM003 NBM006 corn starch 100 100 100 100 Urea 15 Lysine 15 glycerin 15 25 15 15 Sorbitol 30 Stress (megapascals) 4.89 4.25 2.42 5.57 strain(%) 60 67 270 70 WCA(°) 70.3 68.5

[0101] Example 3: Performance testing of thermoplastic starch compositions

[0102] After preparing the thermoplastic starch composition according to the steps of Example 2, various performance tests were conducted on the composition, as follows:

[0103] Mechanical performance testing: Mechanical properties of the thermoplastic starch composition, including tensile stress and strain, were tested according to standard GB / T 1040.2-2022 (type 5A specimen). The results are shown in Tables 1 and 2. Figure 2 As shown.

[0104] According to Table 1, Table 2 and Figure 2The results show that, compared with comparative examples C1 and C2 based solely on polyol plasticizers, and C3 and C4 also based on nitrogen-containing plasticizers, the thermoplastic starch compositions of the present invention exhibit higher tensile stress and / or strain. In particular, thermoplastic starch compositions N1, N6, and N8, using guanidine, arginine, and urea-based DES as nitrogen-containing plasticizers respectively, exhibited significant tensile stress, while thermoplastic starch compositions N1, N11, and N12, using diethylenetriamine (DETA), triethylenetetramine (TETA), and tetraethylenepentamine (TEPA) as nitrogen-containing plasticizers respectively, exhibited significant strain. Thermoplastic starch compositions N3-N5, N7, and N9, using urea-based DES as a nitrogen-containing plasticizer, showed a balanced improvement in both tensile stress and strain.

[0105] Anti-regeneration test: The thermoplastic starch composition C1 was placed at room temperature (15℃-25℃) for 60 days, and the appearance changes of the thermoplastic starch composition were observed by the naked eye. The results are as follows. Figure 3 As shown. The thermoplastic starch composition N3 of the present invention was placed at room temperature (15℃-25℃) for 7 months, and the appearance changes of the thermoplastic starch composition were observed by the naked eye. The results are as follows. Figure 4 As shown.

[0106] according to Figure 3 and Figure 4 The results showed that after 60 days of storage, the thermoplastic starch composition C1 exhibited surface plasticizer release, indicating retrogradation. This demonstrates that starch compositions based solely on polyol plasticizers have low resistance to retrogradation. In contrast, the surface of the thermoplastic starch composition N3 of this invention showed no significant appearance change after 7 months of storage (the sample was cut for other tests), demonstrating the significant resistance to retrogradation of the thermoplastic starch composition of this invention.

[0107] Hydrophobicity test: Water contact angle tests were performed on compositions C1, C2, N3, and N4 according to the method shown in ASTM D5946-17. The results are shown in Table 1 and... Figure 5 As shown.

[0108] From Table 1 and Figure 5 The results show that, compared with comparative examples C1 and C2 which are based solely on polyol plasticizers, the thermoplastic starch compositions N3 and N4 of the present invention both exhibit larger water contact angles, i.e., higher hydrophobicity. Furthermore, due to the addition of the waterproofing agent beeswax, the hydrophobicity of composition N4 is significantly improved, with a water contact angle reaching approximately 115°.

[0109] Bio-based carbon content test:According to standard EN 16640, the bio-based carbon content in thermoplastic starch samples N1-N14 was determined by radiocarbon dating using an accelerated mass spectrometer (AMS). The results are shown in Table 1. The N1-N14 samples of this invention all have a bio-based carbon content of >90%, and even N2-N10 and N13 have a bio-based carbon content of 100%.

[0110] Example 4: Biodegradability Test

[0111] The marine environmental biodegradability of the thermoplastic starch composition of the present invention was tested according to standard ISO 23977-1:2020, and the specific steps are as follows:

[0112] 1) Use seawater and sediment collected from the same location as the seawater collection site. Before use, remove coarse particles from the seawater and, as appropriate, remove coarse particles from the sediment;

[0113] 2) Immerse a sample of thermoplastic starch composition N1-N14 in seawater containing sediment and place it in a test beaker, ensuring that the concentration of the tested N1-N14 sample in each liter of seawater is at least 100 mg (preferably 150 mg to 300 mg) and the carbon content of the N1-N14 sample is approximately 60 mg / L.

[0114] 3) Tests should be conducted in darkness or under diffused light, ensuring the absence of vapors that inhibit marine microorganisms and maintaining a constant acidophilic temperature. The temperature should be controlled between 15°C and 25°C, but not exceeding 28°C, with an accuracy of ±1°C.

[0115] 4) The carbon dioxide volatilization of the sample was measured, and the theoretical carbon dioxide volatilization (ThCO2) of the sample was calculated using the molecular formula. The level of biodegradation in the marine environment was determined by comparing the amount of carbon dioxide volatilized with the theoretical carbon dioxide volatilization (ThCO2), and expressed as a percentage.

[0116] Using the above method, it was determined that the biodegradation rate of the N1-N14 samples of the present invention exceeded 90% after immersion in the marine environment for 53 days.

[0117] Based on the disclosure of this invention, those skilled in the art will understand that many changes can be made to the specific embodiments disclosed herein, and the same or similar results can still be obtained without departing from or exceeding the spirit or scope of this disclosure. Those skilled in the art will further understand that any property reported herein represents a property that is conventionally measured and can be obtained by a variety of different methods. The methods described herein represent one such method, and other methods can be used without departing from the scope of this disclosure.

[0118] The above description of various forms of the invention is for illustrative and descriptive purposes only. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications or variations are possible in accordance with the foregoing teachings. The forms discussed have been chosen and described to provide the best illustration of the principles of the invention and its practical application, thereby enabling those skilled in the art to utilize the invention in various forms and make various modifications to suit the particular intended use. All such modifications and variations are within the scope of the invention as defined by the appended claims when interpreted according to the fair, legal, and just right right to enjoy it.

Claims

1. A thermoplastic starch composition comprising: - 100 parts by weight of at least one starch-based material; and - 1-30 parts by weight, preferably 5-25 parts by weight of at least one nitrogen-containing plasticizer, said nitrogen-containing plasticizer being a compound having at least three nitrogen atoms or a deep eutectic system.

2. The thermoplastic starch composition according to claim 1, wherein, said compound having at least three nitrogen atoms is selected from one or more of arginine, guanidine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 2-cyanoguanidine, biuret, melamine, tris(2-aminoethyl)amine, poly(allylamine) hydrochloride, polyetheramine, polyamide.

3. Thermoplastic starch composition according to claim 1 or 2, wherein said deep eutectic system having at least three nitrogen atoms is a urea-based deep eutectic system; for example, said urea-based deep eutectic system is a binary system comprising a second compound, said second compound being for example a quaternary amine compound or a salt thereof, such as choline chloride, betaine; preferably, the molar ratio of urea to second compound in said binary system is in the range of 4:1 to 1:4, preferably in the range of 2:1 to 1:2; for another example, said urea-based deep eutectic system is a ternary system comprising a second compound and a third compound, said second compound being for example a quaternary amine compound or a salt thereof (such as choline chloride, betaine) or an amino acid (such as proline), said third compound being for example a polyol, such as sorbitol, glycerol, sucrose, glucose; preferably, the molar ratio of urea, second compound and third compound in said ternary system is in the range of 4:1:1 to 1:1:1, preferably in the range of 3:1:1 to 1:1:

1.

4. Thermoplastic starch composition according to any one of claims 1-3, wherein, when said thermoplastic starch composition is used for food contact applications, said nitrogen-containing plasticizer is selected from one or more of arginine, guanidine, diethylenetriamine and a urea-based deep eutectic system.

5. Thermoplastic starch composition according to any one of claims 1-4, wherein, said starch-based material is a native starch such as corn starch, wheat starch, a modified starch or any combination thereof.

6. Thermoplastic starch composition according to any one of claims 1-5, wherein, said composition further comprises: - 1-20 parts by weight of an oxygen-containing plasticizer, which is a C4-C8 oxygen-containing organic compound, for example an oxygen-containing compound having at least one of an acetal, acyl, hydroxyl, aldehyde, alkoxy, carboxyl, ester, ether, ketone or any combination thereof; preferably, said oxygen-containing plasticizer is a polyol, for example glycerol, sorbitol, a sugar alcohol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol or any combination thereof; - 1-20 parts by weight of one or more functional additives selected from a water repellent agent, an antioxidant, a filler, a release agent or any combination thereof.

7. Thermoplastic starch composition according to any one of claims 1-6, wherein, said thermoplastic starch composition comprises a bio-based carbon content higher than 60%, even 100% according to standard ASTM D6866 or EN 16640.

8. Thermoplastic starch composition according to any one of claims 1-7, wherein, said thermoplastic starch composition comprises a bio-based content of 60% or more according to standard EN 16785-1.

9. A thermoplastic composite formed by compounding the thermoplastic starch composition of any one of claims 1-8 and a fossil-based plastic (such as LDPE, PP, PBS and PBAT); preferably, said thermoplastic starch composition and fossil-based plastic have a ratio range of not less than 1:1, for example 1:1-2:

1.

10. A food contact article made from the thermoplastic starch composition of any one of claims 1-8 or the thermoplastic composite of claim 9, such as those complying with standards GB / T 41220, GB / T 10457, GB / T 18006 or GB / T 10004, such as food packaging boxes, tableware, lidding films for food packaging, food preservation films, plastic composite films for packaging.

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