Controlled degradation starch film based on Schiff base cross-linking reaction and preparation and application thereof

Abstract

The invention discloses a controlled degradation starch film based on Schiff base cross-linking reaction as well as preparation and application thereof, and belongs to the technical field of degradable materials. Sodium carboxymethyl starch and chitosan are subjected to a reaction to form Schiff base cross-linking, then a cross-linked solution and an oxidized starch solution are mixed, a plasticizer is added, and then the controlled degradation starch film based on the Schiff base cross-linking reaction is prepared. The method disclosed by the invention is simple, green, pollution-free and low in energy consumption; the starch film disclosed by the invention is controllable in degradation, waterproof, oil-proof, good in air permeability, good in permeability and the like.

Description

Technical Field

[0001] The invention relates to a controlled degradation starch film based on a Schiff base cross-linking reaction and its preparation and application, belonging to the technical field of degradable materials. Background Art

[0002] Biodegradable materials are materials that degrade thermodynamically and kinetically over a period of time. Currently, there are two sources of biodegradable materials: starch, polylactic acid (PLA), polyhydroxyalkanoates (PHAs), and other biodegradable materials derived from biomass or biomass fermentation; and polybutylene succinate (PBS), polybutylene terephthalate adipate (PBAT), and their copolyesters, which are derived from fossil resources. However, the degradation process of biodegradable materials is prone to uncontrolled degradation and the materials have poor oil and water resistance, which has limited their further development.

[0003] To address these issues with biodegradable materials, existing technologies add perfluorinated and polyfluorinated chemicals (PFASs) to some biodegradable materials to enhance their oil and water repellency. However, there remains no universal solution for the controlled degradation of starch-based biodegradable materials. However, these methods are not only limited in effectiveness, but also chemicals (such as PFASs) can accumulate in the human body, potentially impacting human health. They fail to simultaneously address both the uncontrolled degradation of biodegradable materials and their poor oil and water repellency.

[0004] Starch is a type of degradable natural polymer material with the advantages of wide availability, low price, and easy biodegradation. Blending starch with other biodegradable materials with excellent performance improves its processing and usage performance, allowing starch-based plastics to be used in more fields while maintaining their green and degradable properties.

[0005] Therefore, there is an urgent need to develop a starch film that can simultaneously solve the problems of controlled degradation of degradable materials and oil and water resistance. Summary of the Invention

[0006] [Technical Issues]

[0007] Degradable materials have the problems of uncontrolled degradation and poor oil and water resistance.

[0008] [Technical solution]

[0009] To address the above-mentioned issues, the present invention provides a controlled-degradation starch film based on a Schiff base crosslinking reaction, as well as its preparation and application. Specifically, the present invention uses sodium carboxymethyl starch to react with chitosan to form Schiff base crosslinks. The crosslinked solution is then mixed with an oxidized starch solution and a plasticizer is added to produce a controlled-degradation starch film based on the Schiff base crosslinking reaction. The method is simple, environmentally friendly, pollution-free, and energy-efficient. The starch film exhibits controllable degradation, is water- and oil-resistant, and exhibits excellent air permeability and permeability.

[0010] The first object of the present invention is to provide a method for preparing a controlled degradation starch film based on a Schiff base crosslinking reaction, comprising the following steps:

[0011] (1) Starch gelatinization treatment:

[0012] heating the sodium carboxymethyl starch emulsion at 90-100° C. for 20-60 minutes for gelatinization, and cooling the emulsion to obtain a gelatinized sodium carboxymethyl starch solution;

[0013] Heating the oxidized starch emulsion at 90-100° C. for 20-60 minutes for gelatinization, and cooling to obtain a gelatinized oxidized starch solution;

[0014] (2) Preparation of film-forming solution:

[0015] The gelatinized sodium carboxymethyl starch solution and chitosan solution are mixed and shaken to mix evenly; then the gelatinized oxidized starch solution and plasticizer are added and mixed evenly to obtain a film-forming solution;

[0016] (3) Preparation of starch film:

[0017] The film-forming solution is cast into a film and dried to obtain a controlled degradation starch film based on a Schiff base cross-linking reaction.

[0018] In one embodiment of the present invention, the mass ratio of sodium carboxymethyl starch to water in the sodium carboxymethyl starch emulsion of step (1) is 1:20-40, more preferably 1:25-35.

[0019] In one embodiment of the present invention, the mass ratio of oxidized starch to water in the oxidized starch milk of step (1) is 1:20-40, more preferably 1:25-35.

[0020] In one embodiment of the present invention, the temperature is cooled to 40-60°C in step (1).

[0021] In one embodiment of the present invention, the chitosan solution in step (2) is obtained by uniformly mixing chitosan and an acetic acid aqueous solution with a volume fraction of 1-5%, and the amount ratio of chitosan to acetic acid solution is 1g:40-80mL, which can be 1g:45mL, 1g:50mL, 1g:60mL, or 1g:70mL.

[0022] In one embodiment of the present invention, the plasticizer in step (2) is one or more of glycerol, sorbitol, PEG400, ethylene glycol, triethanolamine, diammonium hydrogen citrate, etc.

[0023] In one embodiment of the present invention, the volume ratio of the gelatinized sodium carboxymethyl starch solution, the chitosan solution, and the gelatinized oxidized starch solution in step (2) is 1:(1-3):(0.1-2); more preferably 1:(1.5-2.5):(0.5-2); more preferably 1:2:(0.5-1.5); more preferably 1:2:1.

[0024] In one embodiment of the present invention, the plasticizer in step (2) is 0.5-1.5% of the mass of the entire liquid solution (the sum of the mass of the gelatinized sodium carboxymethyl starch solution, chitosan solution, and gelatinized oxidized starch solution).

[0025] In one embodiment of the present invention, the film-casting in step (3) is obtained by pouring the film-forming solution into a flat plate and drying it in a horizontal state.

[0026] The second object of the present invention is a controlled degradation starch film based on Schiff base cross-linking reaction prepared by the method of the present invention.

[0027] In one embodiment of the present invention, controlled degradation is to control the pH to achieve different degradation degrees.

[0028] The third object of the present invention is to use the controlled degradation starch film based on Schiff base cross-linking reaction in the production of agricultural mulch films, packaging films, shopping bags, and garbage bags.

[0029] The fourth object of the present invention is to provide a food packaging film, which uses the controlled degradation starch film based on Schiff base cross-linking reaction described in the present invention.

[0030] A fifth object of the present invention is to provide a method for simultaneously improving the controlled degradation and oil and water repellency of a starch film, comprising the following steps:

[0031] (1) Starch gelatinization treatment:

[0032] heating the sodium carboxymethyl starch emulsion at 90-100° C. for 30-60 minutes for gelatinization, and cooling the emulsion to obtain a gelatinized sodium carboxymethyl starch solution;

[0033] Heating the oxidized starch emulsion at 90-100° C. for 30-60 minutes for gelatinization, and cooling to obtain a gelatinized oxidized starch solution;

[0034] (2) Preparation of film-forming solution:

[0035] The gelatinized sodium carboxymethyl starch solution and chitosan solution are mixed and shaken to mix evenly; then the gelatinized oxidized starch solution and plasticizer are added and mixed evenly to obtain a film-forming solution;

[0036] (3) Preparation of starch film:

[0037] The film-forming solution is cast into a film and dried to obtain a starch film.

[0038] [Beneficial Effects]

[0039] (1) The starch film of the present invention can not only achieve controlled degradation through the unique pH-responsive mechanism of Schiff base crosslinking, but also enhance the tensile strength of the starch film. This has important significance and economic value for the development of starch-based biodegradable materials.

[0040] (2) The present invention is based on the Schiff base cross-linking reaction, in which chitosan as an amino donor and sodium carboxymethyl starch as a carbonyl donor undergo an imine exchange reaction, and can also undergo a dissociation and regeneration reaction, in which interactions occur between starch molecules to cause Schiff base cross-linking, thereby making the starch film have controlled degradability at a specific pH and improving the mechanical properties; the oxidized starch hot paste has low viscosity and enhanced thermal stability, and has good film-forming properties, making the starch film easier to process and shape.

[0041] (3) The method of the present invention is simple, green, pollution-free and low in energy consumption.

[0042] (4) The starch film of the present invention is controllably degradable, waterproof and oil-proof, has good air permeability and permeability, etc.

[0043] (5) The starch film of the present invention has excellent mechanical properties at room temperature, which can broaden the application scenarios; the Schiff base cross-linking switch technology can achieve controlled degradation at a specific pH value; the oxidized starch hot paste has low viscosity and enhanced thermal stability, and has good film-forming properties, making the starch film easier to process and shape. DETAILED DESCRIPTION

[0044] The following describes preferred embodiments of the present invention. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0045] Test method:

[0046] 1. Mechanical properties test

[0047] The mechanical properties of the films were characterized using a texture analyzer (TA, TA-XT Plus, Stable Microsystems, UK).

[0048] The films were cut into rectangular pieces of 4 cm x 1 cm and conditioned in a desiccator controlled at a relative humidity of 53 ± 2% for 24 hours. The initial gripping interval was set to 2 cm, and the pre-test, test, and post-test speeds were set to 1, 1, and 10 cm / min, respectively. The tensile strength (TS) was determined by dividing the maximum strength (before entering the plastic region) by the cross-sectional area (width × thickness) of the film. The elongation at break (EAB) was calculated by dividing the elongation at break by the initial gauge length of the specimen (2 cm) and multiplying by 100.

[0049] 2. Controlled degradation performance test:

[0050] The starch film was treated with solutions of different pH values and the degradation was observed.

[0051] 3. Waterproof and oilproof test:

[0052] Tested by water contact angle and oil contact angle.

[0053] 4. Air permeability and permeability test:

[0054] Refer to the conventional test method of starch film for testing.

[0055] The raw materials used in the embodiment are:

[0056] Sodium carboxymethyl starch: CAS number: 9063-38-1;

[0057] Oxidized starch: CAS number: 65996-62-5; purity 99%;

[0058] Chitosan: CAS number: 9012-76-4, purity 98%.

[0059] Example 1

[0060] A method for preparing a controlled degradation starch film based on a Schiff base cross-linking reaction comprises the following steps:

[0061] (1) Starch gelatinization treatment:

[0062] 2 g of sodium carboxymethyl starch and 50 g of water were mixed evenly to obtain sodium carboxymethyl starch emulsion; the sodium carboxymethyl starch emulsion was heated at 90° C. for 30 min for gelatinization, and cooled to 50° C. to obtain a gelatinized sodium carboxymethyl starch solution;

[0063] 2 g of oxidized starch and 50 g of water were mixed evenly to obtain an oxidized starch milk; the oxidized starch milk was heated at 90° C. for 30 min for gelatinization, and then cooled to 50° C. to obtain a gelatinized oxidized starch solution;

[0064] (2) Preparation of film-forming solution:

[0065] 2 g of chitosan was added to 100 mL of 1 wt% acetic acid aqueous solution and stirred at 60 °C and 500 rpm for 2 h to obtain a chitosan solution;

[0066] The gelatinized sodium carboxymethyl starch solution and chitosan solution are mixed and shaken to mix evenly; then the gelatinized oxidized starch solution and glycerol are added and mixed evenly to obtain a film-forming solution;

[0067] The volume ratio of the gelatinized sodium carboxymethyl starch solution, chitosan solution, and gelatinized oxidized starch solution is 1:2:1; the amount of glycerol added is 1% of the mass of the entire liquid solution (the sum of the mass of the gelatinized sodium carboxymethyl starch solution, chitosan solution, and gelatinized oxidized starch solution);

[0068] (3) Preparation of starch film:

[0069] The film-forming solution is poured onto a polystyrene plate by a casting method and dried in a horizontal drying oven to obtain a controlled degradation starch film based on a Schiff base cross-linking reaction.

[0070] Example 2

[0071] The volume ratio of the gelatinized sodium carboxymethyl starch solution, chitosan solution, and gelatinized oxidized starch solution in step (2) of Example 1 was adjusted to 1:2:1.5, while other aspects remained the same as in Example 1 to obtain a starch film.

[0072] Example 3

[0073] The volume ratio of the gelatinized sodium carboxymethyl starch solution, chitosan solution, and gelatinized oxidized starch solution in step (2) of Example 1 was adjusted to 1:2:0.5, while other ratios remained the same as in Example 1 to obtain a starch film.

[0074] Comparative Example 1

[0075] The gelatinized oxidized starch solution in step (2) of Example 1 was omitted, and the other steps were the same as in Example 1 to obtain a starch film.

[0076] Comparative Example 2

[0077] The glycerol in step (2) of Example 1 was omitted, and the other steps were the same as in Example 1 to obtain a starch film.

[0078] Comparative Example 3

[0079] The gelatinized sodium carboxymethyl starch solution in step (2) of Example 1 was omitted, and the other steps were the same as in Example 1 to obtain a starch film.

[0080] The obtained starch film was subjected to performance testing, and the test results are as follows:

[0081] Table 1

[0082] example <![CDATA[Toughness / KJ·m -3 > Tensile strength / MPa Example 1 2991.83 54.22 Example 2 2746.04 56.98 Example 3 2840.01 58.14 Comparative Example 1 1273.23 43.78 Comparative Example 2 1316.78 48.44 Comparative Example 3 1610.59 42.60

[0083] It can be seen from Table 1 that the toughness and tensile strength of the starch films prepared in Examples 1-3 are significantly increased under room temperature storage environment, and the tensile strength of the starch films is the largest when the volume ratio of sodium carboxymethyl starch, chitosan and oxidized starch is 1:2:1, thus giving them excellent mechanical properties; the toughness and tensile strength of the starch films prepared in Comparative Examples 1-3 are relatively small, and their mechanical properties under room temperature storage environment are poor.

[0084] At the same time, the starch films prepared in Examples 1-3 have controllable pH degradation, are waterproof and oil-proof, have good air permeability and permeability, etc.

[0085] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing a controlled degradation starch film based on a Schiff base cross-linking reaction, characterized in that: The steps include: (1) Starch gelatinization treatment: heating the sodium carboxymethyl starch emulsion at 90-100° C. for 20-60 minutes for gelatinization, and cooling the emulsion to obtain a gelatinized sodium carboxymethyl starch solution; Heating the oxidized starch emulsion at 90-100° C. for 20-60 minutes for gelatinization, and cooling to obtain a gelatinized oxidized starch solution; (2) Preparation of film-forming solution: The gelatinized sodium carboxymethyl starch solution and chitosan solution are mixed and shaken to mix evenly; then the gelatinized oxidized starch solution and plasticizer are added and mixed evenly to obtain a film-forming solution; (3) Preparation of starch film: The film-forming solution is cast into a film and dried to obtain a controlled degradation starch film based on a Schiff base cross-linking reaction.

2. The method according to claim 1, characterized in that In step (2), the volume ratio of the gelatinized sodium carboxymethyl starch solution, the chitosan solution, and the gelatinized oxidized starch solution is 1:(1-3):(0.1-2); more preferably 1: (1.5-2.5):(0.5-2); more preferably 1:2:(0.5-1.5); more preferably 1:2:

1.

3. The method according to claim 1, characterized in that In step (2), the plasticizer accounts for 0.5-1.5% of the mass of the entire liquid solution (the sum of the mass of the gelatinized sodium carboxymethyl starch solution, the chitosan solution, and the gelatinized oxidized starch solution).

4. The method according to claim 1, wherein The plasticizer in step (2) is one or more of glycerol, sorbitol, PEG400, ethylene glycol, triethanolamine, diammonium hydrogen citrate, etc.

5. The method according to claim 1, wherein The mass ratio of sodium carboxymethyl starch to water in the sodium carboxymethyl starch emulsion of step (1) is 1:20-40, more preferably 1:25-35; the mass ratio of oxidized starch to water in the oxidized starch emulsion is 1:20-40, more preferably 1:25-35.

6. The method according to claim 1, characterized in that The chitosan solution in step (2) is obtained by uniformly mixing chitosan and an acetic acid aqueous solution with a volume fraction of 1-5%. The dosage ratio of chitosan to acetic acid solution is 1g:40-80mL, which can be 1g:45mL, 1g:50mL, 1g:60mL, or 1g:70mL.

7. A controlled degradation starch film based on Schiff base cross-linking reaction prepared by the method according to any one of claims 1 to 6.

8. Use of the controlled degradation starch film based on Schiff base cross-linking reaction according to claim 7 in the production of agricultural mulch films, packaging films, shopping bags, and garbage bags.

9. A food packaging film, characterized in that The controlled degradation starch film based on Schiff base cross-linking reaction as described in claim 7 is used.

10. A method for simultaneously improving the controlled degradation and oil and water resistance of starch films, characterized in that: The steps include: (1) Starch gelatinization treatment: heating the sodium carboxymethyl starch emulsion at 90-100° C. for 20-60 minutes for gelatinization, and cooling the emulsion to obtain a gelatinized sodium carboxymethyl starch solution; Heating the oxidized starch emulsion at 90-100° C. for 20-60 minutes for gelatinization, and cooling to obtain a gelatinized oxidized starch solution; (2) Preparation of film-forming solution: The gelatinized sodium carboxymethyl starch solution and chitosan solution are mixed and shaken to mix evenly; then the gelatinized oxidized starch solution and plasticizer are added and mixed evenly to obtain a film-forming solution; (3) Preparation of starch film: The film-forming solution is cast into a film and dried to obtain a controlled degradation starch film based on a Schiff base cross-linking reaction.