Preparation method of antibacterial thermoplastic starch plastic

Abstract

The invention relates to a preparation method of antibacterial thermoplastic starch plastic, and belongs to the field of antibacterial materials and biodegradable materials. The preparation method comprises the following steps: firstly, preparing maleopimaric acid with higher reaction activity from maleated rosin, then modifying polyethyleneimine 300 (PEI300) by using maleopimaric acid, further uniformly mixing the maleopimaric acid modified polyethyleneimine 300 (PEI300) with starch and glycerol, and extruding by using a single (or double) screw extruder to obtain the antibacterial thermoplastic starch plastic. According to the method, under the condition that a small amount (0.9-1.2 parts) of maleopimaric acid modified PEI300 is added, the thermoplastic starch plastic can have obvious antibacterial property, and especially has an obvious inhibition zone phenomenon on escherichia coli (E.coli) and staphylococcus aureus (S.aureus). Besides, the strength and the fracture toughness of the maleopimaric acid modified PEI300 enhanced thermoplastic starch are also improved at the same time, the tensile strength is improved by 77-99.5%, the elongation at break is improved by 38-53%, and the novel thermoplastic starch plastic has wide application prospects in the fields of food packaging, disposable articles or medical supplies and the like.

Description

Technical Field

[0001] The invention belongs to the field of antibacterial plastics and biodegradable plastics, and relates to a preparation method of antibacterial thermoplastic starch plastics. Background Art

[0002] With global concern about plastic pollution and the implementation of plastic bans, the development of biodegradable materials has become an urgent need. Starch, as a natural polymer, offers advantages such as renewability, low cost, and biodegradability, making it an ideal alternative to petroleum-based plastics. However, natural starch's strong hydrophilicity, poor thermal stability, and susceptibility to bacterial growth limit its application in areas with high hygiene requirements, such as food packaging and medical applications.

[0003] Starch-based materials can easily become a breeding ground for microorganisms in humid environments, leading to material degradation and causing health and safety issues. For example, unmodified starch films have extremely low antibacterial rates against Escherichia coli and Staphylococcus aureus, which cannot meet the needs of plastic wrap or medical packaging. Therefore, imparting antibacterial properties to thermoplastic starch through physical or chemical means has become a key direction for enhancing its application value. Antibacterial properties can be improved by introducing hydrophobic monomers (such as acrylates) or antibacterial groups (such as quaternary ammonium salts). However, traditional methods require the use of strong oxidants or solvents, and the process is complex and costly. For example, the preparation of dialdehyde starch involves toxic reagents, which poses environmental problems: electron beam irradiation can trigger grafting reactions, but high-dose irradiation can easily lead to breakage of starch molecular chains, reducing material strength (such as tensile strength less than 5MPa); chitosan is widely used due to its good antibacterial properties, but it has poor compatibility with starch and needs to be improved through electric field-assisted film formation or composite nanofillers (such as titanium dioxide). However, the addition of chitosan may reduce the mechanical properties of the material, and the dispersibility of nanofillers is difficult to control; nano-titanium dioxide (TiO2) has photocatalytic antibacterial properties, but its interfacial bonding with starch is weak and needs to be enhanced by coupling agents (such as silanes), which is a complex process; existing studies mostly use a single modification method, such as only irradiation or adding antibacterial agents, which makes it difficult to achieve a balance among antibacterial properties, mechanical properties and processing stability. For example, patent CN116082715B improves heat resistance by adding plasticizers, but does not solve the antibacterial problem; patent CN115536996B adds natural fibers to improve heat resistance, but the fibers may aggravate microbial attachment. Summary of the Invention

[0004] To address the existing technical problem of reducing the tensile strength and elongation at break of thermoplastic starch plastics while imparting antibacterial properties, the inventors unexpectedly discovered that using maleopimaric acid-modified polyethyleneimine 300 (PEI300) as an additive can achieve a significant antibacterial effect while simultaneously increasing the tensile strength and elongation at break of thermoplastic starch plastics. Based on these findings, the present invention was completed.

[0005] Therefore, the present invention first provides a method for preparing maleopimaric acid-modified polyethyleneimine 300 (PEI300).

[0006] The present invention also provides the use of the maleopimaric acid-modified polyethyleneimine 300 (PEI300) of the present invention as a thermoplastic starch plastic additive.

[0007] Specifically, the maleopimaric acid-modified polyethyleneimine 300 (PEI300) of the present invention is used to prepare an antibacterial thermoplastic starch plastic, which is composed of the following components by weight:

[0008] 100 parts starch

[0009] 30-40 parts of glycerin

[0010] Maleopimaric acid modified PEI300 0.3~1.2 parts

[0011] The specific method adopted by the present invention is:

[0012] 1) Preparation of maleopimaric acid and maleopimaric acid-modified PEI300

[0013] Weigh 15 to 20 parts of maleic rosin, dissolve it in about 50 parts of anhydrous ethanol, add a saturated sodium hydroxide ethanol solution, control the pH of the solution to about 9 to 11, heat at 65 to 70°C for 2 to 3 hours, and after the solution cools, filter it to obtain a precipitate, wash it with anhydrous ethanol, dissolve the washed precipitate in a small amount of ultrapure water, add dilute hydrochloric acid dropwise, and adjust the pH of the solution to about 2 to 4 to obtain a precipitate, filter the precipitate, wash it with ultrapure water, and place the washed precipitate in a vacuum drying oven at 40 to 50°C for 10 to 14 hours to obtain maleopimaric acid;

[0014] 2-4 parts of the maleopimaric acid prepared above and 8-10 parts of polyethyleneimine 300 (PEI300) were weighed and added to a round-bottom flask. 0.5-1 part of 4-dimethylaminopyridine (DMAP) as a catalyst and 0.5-1 part of 1,3-dicyclohexylcarbodiimide (DCC) as a water absorbent were added. The mixture was stirred and heated at 110-120°C for 3-4 hours to obtain a brownish-red viscous liquid, which is maleopimaric acid-modified polyethyleneimine 300 (PEI300).

[0015] 2) Preparation of maleopimaric acid modified polyethyleneimine (PEI300) antibacterial thermoplastic starch plastic

[0016] Take 100 parts of starch, add 30-40 parts of glycerol and 0.9-1.2 parts of maleopimaric acid-modified PEI300, mix well, extrude strips in a single-screw extruder with a barrel temperature of 115-125°C, a die temperature of 105-115°C, and a rotation speed of 40-50 r / min, and hot press at 110-120°C using a hot press to obtain a thermoplastic starch plastic with antibacterial properties.

[0017] The advantages of the present invention are:

[0018] 1) Natural rosin is a renewable forest chemical with a wide source and low cost. After modification, it can be added to thermoplastic starch plastics. The addition amount is small and will not significantly increase the cost of thermoplastic starch plastics. It has good market application prospects.

[0019] 2) PEI300 is a low molecular weight oligomer with relatively low cost, and a small amount of additives will not significantly affect the degradation of thermoplastic starch plastics;

[0020] 3) Thermoplastic starch plastics prepared from maleopimaric acid-modified PEI300 have certain antibacterial properties and can be used in fields such as food packaging or medical supplies.

[0021] 4) Thermoplastic starch plastics prepared by maleopimaric acid-modified PEI300 have antibacterial properties and significantly improved tensile strength and elongation at break. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Preparation mechanism of maleopimaric acid and maleopimaric acid-modified PEI300

[0023] Figure 2 Infrared spectra of maleopimaric acid, PEI300 and maleopimaric acid-modified PEI300

[0024] As attached Figure 2 As shown in Figure 2, maleopimaric acid modified PEI300 has a peak at 3264 cm -1 A new broad absorption peak appeared at 2918 cm, which may correspond to the stretching vibration absorption peak of amino NH in PEI300; -1 The absorption peak at 1592 cm-1 may correspond to the stretching vibration absorption peak of -CH3 in the maleopimaric acid structure according to the structural characteristics of maleopimaric acid; -1 The absorption peak at 1685 cm may correspond to the bending vibration absorption peak of amino NH in the PEI300 molecular structure; -1The absorption peaks at these positions may correspond to the stretching vibration absorption peaks of the NH in the amide group formed by the reaction of maleopimaric acid and PEI300. The absorption peaks at these positions indicate that maleopimaric acid and PEI300 are likely to undergo an amidation reaction.

[0025] Figure 3 H NMR spectra of maleopimaric acid and maleopimaric acid-modified PEI300

[0026] As attached Figure 3 The chemical shift of hydrogen at the indicated position of maleopimaric acid modified PEI300, the chemical shift at 5.33 corresponds to the chemical shift of hydrogen on the carbon-carbon double bond (i.e. Figure 3 The chemical shift at 2.68 corresponds to the chemical shift of hydrogen on -CH2- in the long chain of PEI300 molecules (i.e., the attached Figure 3 The hollow circle corresponds to the chemical shift of hydrogen); the chemical shift at 1.46 corresponds to the chemical shift of hydrogen on -NH- and -NH2- in the long chain of PEI300 molecules (i.e., the attached Figure 3 The chemical shifts of the three positions above indicate that maleopimaric acid and PEI300 exist in maleopimaric acid-modified PEI300. The chemical shift at 7.23 corresponds to the chemical shift of hydrogen on the amide group (i.e., the attached Figure 3 The chemical shift of hydrogen at the corresponding position of the hollow triangle indicates that maleopimaric acid undergoes an amidation reaction with PEI300, which is consistent with the results of infrared absorption spectrum analysis.

[0027] Figure 4 Scanning electron microscope images of the cross-section of the thermoplastic starch plastic film prepared in Examples 1, 2, 3, 4 and Comparative Example 1

[0028] Figure 5 Characterization of antibacterial properties of TPS and TPS modified with different amounts of MPA-PEI300

[0029] As attached Figure 5 , Figure 5 (a) Characterization of the antibacterial activity of TPS and modified TPS against Escherichia coli. Figure 5 (b) is the characterization of the antibacterial activity of TPS and modified TPS against Staphylococcus aureus. Figure 5(a) It can be seen that the TPS membrane has essentially zero inhibitory effect on E. coli and Staphylococcus aureus. When the addition amount of maleopimaric acid-modified PEI300 exceeds 0.6 phr, the TPS-modified membrane begins to show an inhibition zone. The inhibitory effect becomes increasingly pronounced as the addition amount of maleopimaric acid-modified PEI300 increases. This indicates that the addition of maleopimaric acid-modified PEI300 results in a certain degree of inhibitory effect on E. coli and Staphylococcus aureus. This is because the TPS membrane prepared with maleopimaric acid-modified PEI300 introduces a large number of amino groups from the PEI300 structure, which have certain antibacterial activity, giving the modified TPS membrane antibacterial properties.

[0030] Note: The test was performed using an MTS\SANS CMT4000 universal testing machine from MTS Industrial Systems (China) Co., Ltd. The film size was 40×10×0.7 mm and the tensile rate was 50 mm / min. DETAILED DESCRIPTION

[0031] The present invention will be further understood from the following illustrative examples. It should be noted that the following examples do not limit the scope of protection claimed in the present invention.

[0032] Example 1:

[0033] 1) Preparation of maleopimaric acid and maleopimaric acid-modified PEI300

[0034] Weigh 16g of maleic rosin and dissolve it in approximately 50ml of anhydrous ethanol. Add saturated sodium hydroxide ethanol solution, adjust the solution's pH to 10, and heat with stirring at 68°C for 2.5 hours. After the solution cools, filter the resulting precipitate and wash it with anhydrous ethanol. Dissolve the washed precipitate in a small amount of ultrapure water, add dilute hydrochloric acid dropwise, and adjust the solution's pH to 3 to obtain a precipitate. Filter the precipitate and wash it with ultrapure water. Place the washed precipitate in a vacuum drying oven at 45°C and dry it for 12 hours to obtain maleopimaric acid.

[0035] 3 g of the maleopimaric acid prepared above and 9 g of polyethyleneimine 300 (PEI300) were weighed and added to a round-bottom flask. 0.5 g of 4-dimethylaminopyridine (DMAP) as a catalyst and 0.5 g of 1,3-dicyclohexylcarbodiimide (DCC) as a water absorbent were added. The mixture was stirred and heated at 110°C for 3 h to obtain a brownish-red viscous liquid, which is maleopimaric acid-modified polyethyleneimine (PEI300).

[0036] 2) Preparation of antibacterial thermoplastic starch plastics obtained by modifying PEI300 with maleopimaric acid

[0037] 100 g of starch was weighed, 35 g of glycerol, and 0.3 g of maleopimaric acid-modified PEI300 were added, and the mixture was uniformly mixed. The mixture was extruded into strips using a single-screw extruder at a barrel temperature of 120°C, a die temperature of 115°C, and a rotation speed of 40 r / min. The mixture was then hot-pressed at 110°C using a hot press to obtain a maleopimaric acid-modified PEI300-reinforced thermoplastic starch plastic film.

[0038] Example 2:

[0039] 1) Preparation of maleopimaric acid and maleopimaric acid-modified PEI300

[0040] Preparation of maleopimaric acid and maleopimaric acid-modified PEI300 Reference preparation method in step (1) of Example 1

[0041] 2) Preparation of antibacterial thermoplastic starch plastics obtained by modifying PEI300 with maleopimaric acid

[0042] 100 g of starch was weighed, 35 g of glycerol, and 0.6 g of maleopimaric acid-modified PEI300 were added, and the mixture was uniformly mixed. The mixture was extruded into strips using a single-screw extruder at a barrel temperature of 120°C, a die temperature of 115°C, and a rotation speed of 40 r / min. The mixture was then hot-pressed at 110°C using a hot press to obtain a maleopimaric acid-modified PEI300-reinforced thermoplastic starch plastic film.

[0043] Example 3:

[0044] 1) Preparation of maleopimaric acid and maleopimaric acid-modified PEI300

[0045] Preparation of maleopimaric acid and maleopimaric acid-modified PEI300 Reference preparation method in step (1) of Example 1

[0046] 2) Preparation of antibacterial thermoplastic starch plastics obtained by modifying PEI300 with maleopimaric acid

[0047] 100 g of starch was weighed, 35 g of glycerol, and 0.9 g of maleopimaric acid-modified PEI300 were added, and the mixture was uniformly mixed. The mixture was extruded into strips using a single-screw extruder at a barrel temperature of 120°C, a die temperature of 115°C, and a rotation speed of 40 r / min. The mixture was then hot-pressed at 110°C using a hot press to obtain a maleopimaric acid-modified PEI300-reinforced thermoplastic starch plastic film.

[0048] Example 4:

[0049] 1) Preparation of maleopimaric acid and maleopimaric acid-modified PEI300

[0050] Preparation of maleopimaric acid and maleopimaric acid-modified PEI300 Reference preparation method in step (1) of Example 1

[0051] 2) Preparation of antibacterial thermoplastic starch plastics obtained by modifying PEI300 with maleopimaric acid

[0052] 100 g of starch was weighed, 35 g of glycerol, and 1.2 g of maleopimaric acid-modified PEI300 were added, and the mixture was uniformly mixed. The mixture was extruded into strips using a single-screw extruder at a barrel temperature of 120°C, a die temperature of 115°C, and a rotation speed of 40 r / min. The mixture was then hot-pressed at 110°C using a hot press to obtain a maleopimaric acid-modified PEI300-reinforced thermoplastic starch plastic film.

[0053] Comparative Example 1: (No maleopimaric acid-modified PEI300 was added, and only the thermoplastic starch plastic was plasticized with glycerol)

[0054] Weigh 100 g of starch and 35 g of glycerol and mix them evenly; extrude the mixture into strips using a single-screw extruder with a barrel temperature of 120° C., a die temperature of 115° C., and a rotation speed of 40 r / min; and hot-press the strips at 110° C. using a hot press to obtain a glycerol-plasticized thermoplastic starch plastic film.

[0055] Table 1

[0056]

[0057]

[0058] Table 1 shows the dosage of each component and the test data of strength (tensile strength) and toughness (elongation at break) of each embodiment and comparative example sample. The results show that the strength and toughness of the modified thermoplastic starch plastic prepared by using 0.3 to 1.2 parts of maleopimaric acid-modified PEI300 are improved by about 18 to 100% in tensile strength and about 40 to 94% in elongation at break compared with the comparative example (no maleopimaric acid-modified PEI300). In addition, the attached Figure 4 Scanning electron micrographs of the fracture surfaces of thermoplastic starch films further support this finding, demonstrating that 0.3 to 1.2 phr of maleopimaric acid-modified PEI300 can form a uniform and stable interaction with the thermoplastic starch matrix. Furthermore, as the amount of maleopimaric acid-modified PEI300 added increases, the fracture surface becomes increasingly rough and uneven, consistent with the changes in elongation at break shown in Table 1. Of all the examples, Example 3 exhibits the highest combination of strength and toughness.

Claims

1. This invention is a method for preparing antibacterial thermoplastic starch plastic, characterized by: The antibacterial thermoplastic starch plastic is made according to the following steps: Weigh 15 to 20 parts of maleic rosin, dissolve it in about 50 parts of anhydrous ethanol, add a saturated sodium hydroxide ethanol solution, control the pH of the solution to about 9 to 11, heat at 65 to 70° C. for 2 to 3 hours, and after the solution cools, filter it to obtain a precipitate, wash it with anhydrous ethanol, dissolve the washed precipitate in a small amount of ultrapure water, add dilute hydrochloric acid dropwise, and adjust the pH of the solution to about 2 to 4 to obtain a precipitate, filter the precipitate, wash it with ultrapure water, and place the washed precipitate in a vacuum drying oven at 40 to 50° C. and dry it for 10 to 14 hours to obtain maleopimaric acid; Weigh 2-4 parts of the maleopimaric acid prepared above and 8-10 parts of polyethyleneimine 300 (PEI300) into a round-bottom flask. Add 0.5-1 part of 4-dimethylaminopyridine (DMAP) as a catalyst and 0.5-1 part of 1,3-dicyclohexylcarbodiimide (DCC) as a water absorbent. Stir and heat at 110-120°C for 3-4 hours to obtain a brownish-red viscous liquid, which is maleopimaric acid-modified polyethyleneimine 300 (PEI300). Take 100 parts of starch, add 30-40 parts of glycerol and 0.9-1.2 parts of maleopimaric acid-modified PEI300, mix well, extrude strips in a single-screw extruder with a barrel temperature of 115-125°C, a die temperature of 105-115°C, and a rotation speed of 40-50 r / min, and hot press at 110-120°C using a hot press to obtain a thermoplastic starch plastic with antibacterial properties.

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