A preparation method of polylactic acid antibacterial plastic

Abstract

The invention discloses a method for preparing a polylactic acid antibacterial plastic. The method comprises the following steps: in-situ reducing silver nitrate in a chitosan solution to prepare a silver-loaded chitosan antibacterial agent; taking PLA as a matrix material, adding chitosan, and carrying out solution blending, melt blending, tableting and injection molding to prepare the polylactic acid-chitosan antibacterial plastic; or taking PLA as a matrix material, adding the silver-loaded chitosan antibacterial agent, and carrying out solution blending, melt blending, tableting and injection molding to prepare the polylactic acid-silver-loaded chitosan antibacterial plastic.

Description

Technical Field

[0001] The invention relates to a method for preparing polylactic acid antibacterial plastic. Background Art

[0002] Polylactic acid (PLA) is a synthetic, microbially biodegradable thermoplastic aliphatic polyester, derived from the direct polymerization of lactic acid. Due to its excellent mechanical and physical properties, thermal stability, solvent resistance, and biocompatibility, it is widely used in food packaging, fast food lunch boxes, healthcare, 3D printing, and other fields.

[0003] Antimicrobial materials are materials with antibacterial or bactericidal activity, effectively preventing the growth of harmful microorganisms. Antimicrobial agents are a core component of these materials. They are primarily categorized into three main types: inorganic, organic, and composite. As early as World War II, antimicrobial materials were extensively used in soldiers' clothing. Subsequently, they gained widespread application in automotive, building materials, telecommunications, home appliances, and daily necessities, directly driving their rapid development. Currently, antimicrobial materials have become ubiquitous in everyday life, encompassing everything from clothing and food to housing and transportation.

[0004] Natural antimicrobial agents, derived from natural substances, offer numerous advantages. They exhibit excellent biocompatibility, pose no environmental pollution, and pose no harm to living things. Chitosan, a natural antimicrobial extracted from the shells of shrimp and crabs, boasts excellent antimicrobial properties, a wide range of applications, and is non-toxic to humans. Chitosan can also reduce wound inflammation, relieve pain, and promote wound healing.

[0005] Adding a certain amount of antimicrobial agent to plastic products can kill bacteria or inhibit their reproduction within a certain period of time. Antimicrobial agents are chemical components that are highly sensitive to some microorganisms such as bacteria, molds, fungi, yeasts, etc. The amount added to plastics is very small, but they can play a bactericidal role while maintaining the conventional properties and processing properties of the plastics. They play a very important role in the development of plastic products. Summary of the Invention

[0006] The present invention provides a method for preparing polylactic acid antibacterial plastic in order to solve the problems existing in the prior art.

[0007] The technical solutions adopted in the present invention are:

[0008] A method for preparing polylactic acid antibacterial plastic,

[0009] Silver nitrate was reduced in situ in chitosan solution to prepare silver-loaded chitosan antibacterial agent.

[0010] PLA was used as the matrix material, chitosan was added, and polylactic acid-chitosan antibacterial plastics were prepared through solution blending, melt blending, tableting and injection molding.

[0011] Alternatively, PLA is used as the matrix material, a silver-loaded chitosan antibacterial agent is added, and polylactic acid-silver-loaded chitosan antibacterial plastic is prepared by solution blending, melt blending, tableting and injection molding.

[0012] Furthermore, the preparation process of the silver-loaded chitosan antibacterial agent is as follows:

[0013] Take 1g of chitosan in a three-necked flask, add 100mL of 2wt% acetic acid solution, stir and dissolve in a 60℃ water bath for 1h, then add 10mL of 10mmol / L AgNO3 solution, stir in a 60℃ water bath for 1h, heat the chitosan solution to 80℃, and then slowly add 5mL of 35.2g / L ascorbic acid solution, one drop every 3 to 5s. After the addition is completed, stir in an 80℃ water bath for 4h. After the reaction is completed, the product is centrifuged and washed several times to obtain a silver-loaded chitosan antibacterial agent.

[0014] Furthermore, the amount of AgNO3 used was 0.1 mmol;

[0015] The concentration of chitosan solution is 1%;

[0016] The concentration of the ascorbic acid solution added dropwise was 35.2 g / L.

[0017] Furthermore, the preparation process of the polylactic acid-chitosan antibacterial plastic is as follows:

[0018] Weigh 10g of PLA, add 30mL of chloroform, and dissolve it at room temperature with stirring for 6h. After the PLA is completely dissolved, add 1g of chitosan, stir evenly, and pour into a glass dish. After the solvent evaporates, cut the product into pieces and put it into an oven at 60℃ to dry to constant weight to obtain a PLA / chitosan antibacterial masterbatch.

[0019] PLA / chitosan antibacterial masterbatch was added to 39 g of PLA for melt blending, tableting and injection molding to prepare a polylactic acid-chitosan antibacterial plastic with an antibacterial agent content of 2 wt%.

[0020] Furthermore, the preparation process of the polylactic acid-silver-loaded chitosan antibacterial plastic is as follows:

[0021] Weigh 10g of PLA, add 30mL of chloroform, and dissolve it at room temperature with stirring for 6h. After the PLA is completely dissolved, add 1g of silver-loaded chitosan, stir evenly, and pour into a glass dish. After the solvent evaporates, cut the product into pieces and put it into an oven, and dry it at 60℃ to constant weight to obtain PLA / silver-loaded chitosan antibacterial masterbatch.

[0022] PLA / silver-loaded chitosan antibacterial masterbatch was added to 39 g of PLA for melt blending, tableting and injection molding to prepare polylactic acid-silver-loaded chitosan antibacterial plastic with an antibacterial agent content of 2 wt%.

[0023] The present invention has the following beneficial effects:

[0024] 1) Chitosan and silver-loaded chitosan antibacterial agents can effectively improve the antibacterial properties of PLA.

[0025] 2) The addition of chitosan and silver-loaded chitosan antibacterial agents has no significant effect on the tensile properties of PLA and does not affect the thermal stability of polylactic acid.

[0026] 3) Chitosan and silver-loaded chitosan antibacterial agents can affect the crystallization temperature of PLA and regulate the crystallization process of PLA.

[0027] 4) Chitosan and silver-loaded chitosan antibacterial agents can increase the recovery flexibility of PLA.

[0028] 5) Silver-loaded chitosan antibacterial agent can increase the storage modulus, loss modulus and complex viscosity of PLA.

[0029] 6) The addition of chitosan and silver-loaded chitosan antibacterial agents can increase the hydrophobicity of the polylactic acid surface and reduce the wettability of the polylactic acid surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the infrared spectrum of chitosan.

[0031] Figure 2 This is the infrared spectrum of silver-loaded chitosan.

[0032] Figure 3 This is the UV spectrum of silver-loaded chitosan.

[0033] Figure 4 The DSC curves of Comparative Example, Example 1 and Example 2 are shown.

[0034] Figure 5 The relative crystallinity curves of the comparative example, embodiment 1 and embodiment 2 are shown.

[0035] Figure 6 The thermogravimetric curves of the comparative example, example 1 and example 2 are shown.

[0036] Figure 7 These are the tensile curves of the comparative example, example 1, and example 2.

[0037] Figure 8 The contact angles of the comparative example, example 1 and example 2 are shown.

[0038] Figure 9a 、 Figure 9b as well as Figure 9c They correspond to the creep and creep recovery curves of the comparative example, embodiment 1 and embodiment 2 respectively.

[0039] Figure 10a 、 Figure 10b as well as Figure 10c They correspond to the compliance and recovery compliance of the comparative example, embodiment 1, and embodiment 2, respectively.

[0040] Figure 11a 、 Figure 11b as well as Figure 11c They correspond to the storage modulus, loss modulus and complex viscosity of the comparative example, embodiment 1 and embodiment 2, respectively.

[0041] Figure 12 The antibacterial properties of the comparative example, embodiment 1 and embodiment 2 are shown. DETAILED DESCRIPTION

[0042] The following is combined with Figure 1-12 The present invention will be further described.

[0043] 1. Preparation of silver-loaded chitosan antibacterial agent

[0044] Take 1g of chitosan in a three-necked flask, add 100mL of 2wt% acetic acid solution, stir and dissolve in a 60℃ water bath for 1h, then add 10mL of 10mmol / L AgNO3 solution, stir in a 60℃ water bath for 1h, heat the chitosan solution to 80℃, and then slowly add 5mL of 35.2g / L ascorbic acid solution, one drop every 3 to 5s. After the addition is completed, stir in an 80℃ water bath for 4h. After the reaction is completed, the product is centrifuged and washed several times to obtain a silver-loaded chitosan antibacterial agent.

[0045] Figure 1 The infrared spectrum of chitosan is shown in Figure 2. The stretching vibration coupling of (NH) and intermolecular hydrogen bonds (OH) in chitosan is at 3300 cm -1 A broad absorption peak is formed at the position of 1652 cm. The deformation vibration absorption peak of (NH) in chitosan is located at 1652 cm -1 and 1595cm -1 The stretching vibration peak of (CN) in chitosan is located at 1377 cm -1 Place.

[0046] Figure 2 The infrared spectrum of silver-loaded chitosan is shown in Figure 2. After chitosan is combined with Ag particles, the chitosan has an infrared spectrum of 3300 cm -1 The absorption peak at 3234 cm shifts to the low frequency direction. -1 The peak shape changes slightly, indicating that -NH2 or -OH on chitosan participates in the coordination of Ag particles.

[0047] Figure 3 The UV spectrum of silver-loaded chitosan is shown in Figure 2. The characteristic peak of silver nanoparticles (around 429 nm) is visible in the figure, proving the successful preparation of silver-loaded chitosan.

[0048] 2. Preparation of polylactic acid-chitosan antibacterial plastic

[0049] Comparative Example

[0050] Pure PLA is melt blended, sheeted and injection molded to produce pure PLA plastic with the same thermal history as other materials.

[0051] Example 1

[0052] Weigh 10g of PLA, add 30mL of chloroform, stir and dissolve at room temperature for 6h. After the PLA is completely dissolved, add 1g of chitosan, stir evenly and pour into a glass dish. After the solvent evaporates, cut the product into pieces and put it into an oven, dry it at 60℃ to constant weight to obtain PLA / chitosan antibacterial masterbatch; add the PLA / chitosan antibacterial masterbatch to 39g of PLA for melt blending, tableting and injection molding to prepare polylactic acid-chitosan antibacterial plastic with an antibacterial agent content of 2wt%.

[0053] Example 2

[0054] Weigh 10g of PLA, add 30mL of chloroform, stir and dissolve at room temperature for 6h. After the PLA is completely dissolved, add 1g of silver-loaded chitosan, stir evenly and pour into a glass dish. After the solvent evaporates, cut the product into pieces and put it into an oven, dry it at 60℃ to constant weight to obtain PLA / silver-loaded chitosan antibacterial masterbatch; add the PLA / silver-loaded chitosan antibacterial masterbatch to 39g of PLA for melt blending, tableting and injection molding to prepare polylactic acid-silver-loaded chitosan antibacterial plastic with an antibacterial agent content of 2wt%.

[0055] Figure 4 The DSC curves for the comparative example, Example 1, and Example 2 are shown. As can be seen from the figure, the crystallization temperature of Example 1 is lower than that of the comparative example, indicating that the addition of chitosan inhibits the nucleation of PLA. The crystallization temperature of Example 2 is higher than that of the comparative example, indicating that the silver-loaded chitosan plays a heterogeneous nucleation role, promoting the nucleation process of PLA.

[0056] Figure 5 Figure 2 shows the relative crystallinity curves for the comparative example, Example 1, and Example 2. As can be seen from the figure, the half-crystallization time for the comparative example is 2.70 min, the half-crystallization time for Example 1 is 2.80 min, and the half-crystallization time for Example 2 is 2.55 min. This indicates that the addition of chitosan inhibits the crystallization process of PLA, while the addition of silver-loaded chitosan promotes the crystallization process of chitosan.

[0057] Figure 6The thermogravimetric curves of the comparative example, example 1, and example 2 are shown in FIG. As can be seen from the curves in the figure, the thermal decomposition temperatures of the comparative example, examples 1, and 2 are all around 300°C, indicating that the addition of chitosan and silver-loaded chitosan does not affect the thermal stability of polylactic acid, and the polylactic acid / chitosan antibacterial plastic still maintains good thermal stability.

[0058] Figure 7 The tensile curves are for the comparative example, example 1, and example 2. As can be seen from the curves in the figure, the tensile strengths of examples 1 and 2 are slightly lower than that of the comparative example, but both are higher than 50 MPa, indicating that the addition of a small amount of chitosan and silver-loaded chitosan does not cause significant loss in the mechanical properties of polylactic acid, and the polylactic acid / chitosan antibacterial plastic still maintains good mechanical properties.

[0059] Figure 8 : The contact angles of the comparative example, embodiment 1 and embodiment 2. From the data in the figure, it can be seen that the contact angles of embodiments 1 and 2 are greater than those of the comparative example, indicating that the addition of chitosan and silver-loaded chitosan improves the hydrophobicity of the polylactic acid surface and reduces the wettability of the polylactic acid surface.

[0060] Figure 9a 、 Figure 9b as well as Figure 9c The creep and creep recovery curves of the comparative example, Example 1, and Example 2 are shown. The creep recovery curves of the comparative example and the example show that the comparative example and Example 1 exhibit viscosity. The creep recovery curve of Example 2 tends to be constant after decreasing to a certain value, indicating viscoelasticity.

[0061] Figure 10a 、 Figure 10b as well as Figure 10c The compliance and recovery compliance of the comparative example, embodiment 1 and embodiment 2 are shown in FIG. As can be clearly seen from the curves in the figure, the recovery compliance of embodiment 1 and embodiment 2 is significantly higher than that of the comparative example.

[0062] Figure 11a 、 Figure 11b as well as Figure 11c The storage modulus, loss modulus and complex viscosity of the comparative example, embodiment 1 and embodiment 2 are shown in FIG. As can be seen from the curves in the figure, the storage modulus, loss modulus and complex viscosity of embodiment 2 are significantly higher than those of the comparative example.

[0063] Figure 12 The antibacterial (Staphylococcus aureus) performance of the comparative example, Example 1, and Example 2 is shown. Under the same experimental conditions, the colony count of the comparative example is 354, the colony count of Example 1 is 162, and the colony count of Example 2 is 42. This shows that the antibacterial performance of Examples 1 and 2 is better than that of the comparative example. The addition of chitosan and silver-loaded chitosan has a significant antibacterial effect on polylactic acid.

[0064] The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing polylactic acid antibacterial plastic, characterized in that: Silver nitrate was reduced in situ in chitosan solution to prepare silver-loaded chitosan antibacterial agent. PLA was used as the matrix material, silver-loaded chitosan antibacterial agent was added, and polylactic acid-silver-loaded chitosan antibacterial plastic was prepared through solution blending, melt blending, tableting and injection molding. The preparation process of silver-loaded chitosan antibacterial agent is as follows: Take 1g of chitosan in a three-necked flask, add 100mL of 2 wt% acetic acid solution, stir and dissolve in a 60℃ water bath for 1h, then add 10mL of 10 mmol / L AgNO3 solution, stir in a 60℃ water bath for 1h, heat the chitosan solution to 80℃, and then slowly add 5mL of 35.2g / L ascorbic acid solution dropwise, one drop every 3~5s. After the addition is completed, stir in an 80℃ water bath for 4h. After the reaction is completed, the product is centrifuged and washed several times to obtain a silver-loaded chitosan antibacterial agent; The preparation process of the polylactic acid-silver-loaded chitosan antibacterial plastic is as follows: Weigh 10 g of PLA, add 30 mL of chloroform, and dissolve it at room temperature with stirring for 6 h. After the PLA is completely dissolved, add 1 g of silver-loaded chitosan, stir evenly, and pour into a glass dish. After the solvent evaporates, cut the product into pieces and put it into an oven at 60°C to dry to constant weight to obtain a PLA / silver-loaded chitosan antibacterial masterbatch. PLA / silver-loaded chitosan antibacterial masterbatch was added to 39 g of PLA for melt blending, tableting and injection molding to prepare polylactic acid-silver-loaded chitosan antibacterial plastic with an antibacterial agent content of 2 wt%.

2. The method for preparing the polylactic acid antibacterial plastic according to claim 1, wherein: The amount of AgNO3 used is 0.1mmol; The concentration of chitosan solution was 1%; The concentration of the ascorbic acid solution added dropwise was 35.2 g / L.

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