Natural latex-based polyphenol nano-emulsion composite antibacterial biological adhesive and preparation method thereof

Abstract

The invention discloses a natural latex-based polyphenol nano-emulsion composite antibacterial biological adhesive and a preparation method thereof, and relates to the field of antibacterial adhesives. The method comprises the following steps: initiating a grafting reaction between natural latex and a pretreated lignin alkaline solution through a specific initiator to obtain a copolymer, preparing a nano-emulsion from cinnamyl aldehyde and tannic acid, adding the nano-emulsion into the copolymer, and uniformly stirring to obtain the bio-based antibacterial adhesive. The adhesive has the remarkable advantages that in the aspect of antibacterial property, the adhesive has a strong inhibiting and killing effect on various common bacteria and fungi by virtue of the antibacterial activity of lignin and the synergistic antibacterial effect of cinnamyl aldehyde and tannic acid; in the aspect of adhesive property, natural latex is used as a matrix, and lignin is grafted, so that the adhesive force and cohesive force to various materials are improved; the raw materials are natural sources, and few harmful chemicals are used in the preparation process; the stability is good, and layering and precipitation are not easily caused during storage. Experiments show that the inhibition rate of the adhesive on escherichia coli and staphylococcus aureus exceeds 98%, and the bonding strength is improved by 25% compared with that of the adhesive without the antibacterial agent. A good choice is provided for wood processing, packaging, medical treatment and other scenes needing antibacterial bonding.

Description

Technical Field

[0001] The invention belongs to the technical field of bio-based adhesives, and particularly relates to a natural rubber latex-based polyphenol nanoemulsion composite antibacterial bioadhesive and a preparation method thereof. Background Art

[0002] Traditional adhesives mostly rely on petroleum-based raw materials, and there are problems such as environmental pollution and non-renewable properties. Bio-based adhesives use natural renewable resources as raw materials, have the advantages of low carbon emissions, degradability, and environmental friendliness, and are in line with the concept of sustainable development. Natural latex and lignin, as two important natural polymer materials, have shown great potential in the development of bio-based adhesives, but their performance is limited when used alone. In addition, adhesives are susceptible to microbial contamination in humid environments, resulting in a decrease in the performance of the adhesive and even failure, which not only affects the service life of the adhesive, but may also damage the bonding material. Traditional antibacterial agents (such as silver nanoparticles) are costly and have biological toxicity, while natural antibacterial ingredients (such as plant extracts) are difficult to stably exert their efficacy due to poor dispersibility. Therefore, the present invention designs and introduces cinnamaldehyde-tannic acid nanoemulsion as an antibacterial functional unit, which can give the adhesive long-lasting antibacterial properties, effectively inhibit the growth of microorganisms, and extend the service life of the adhesive. Summary of the Invention

[0003] This invention aims to provide an innovative bio-based antimicrobial adhesive based on natural rubber latex and lignin, and its preparation method. This adhesive uses natural rubber latex and lignin as primary raw materials, ingeniously employing a nanoemulsion made from cinnamaldehyde and tannic acid as a functional reinforcing filler. This nanoemulsion is uniformly dispersed within the latex matrix, imparting the adhesive with excellent and long-lasting antimicrobial properties. This bio-based antimicrobial adhesive not only offers the advantages of being natural and environmentally friendly, but also effectively inhibits the growth of a wide range of bacteria, providing a highly effective and safe antimicrobial solution for related fields.

[0004] In order to achieve the above object, the present invention provides a natural rubber latex-based polyphenol nanoemulsion composite antibacterial bioadhesive and a preparation method thereof, characterized in that the method comprises the following steps:

[0005] Step 1: uniformly dispersing lignin in deionized water at room temperature, adding a pH buffer solution to obtain a pretreated lignin alkaline solution with a pH of 9;

[0006] Step 2: adding the alkaline lignin solution of step 1 to the natural rubber latex, and adding an initiator at the same time, stirring at a constant temperature to allow the lignin and the natural rubber latex to undergo a graft copolymerization reaction. After the reaction is completed, unreacted macromolecular impurities are removed by filtration or centrifugation to obtain a copolymer of natural rubber latex and lignin;

[0007] Step 3, dissolving tannic acid in water at room temperature to prepare an aqueous phase solution, and dissolving cinnamaldehyde essential oil in ethanol to prepare an oil phase solution;

[0008] Step 4: dispersing an emulsifier (such as Tween 80) in the tannic acid aqueous solution described in step 3 under high-speed stirring, then slowly adding the cinnamaldehyde ethanol solution dropwise, and after ultrasonic treatment, obtaining an oil-in-water (O / W) structured cinnamaldehyde-tannic acid nanoemulsion;

[0009] Step 5: adding the nanoemulsion described in step 4 to the copolymer described in step 2, and stirring the mixture at a constant temperature to obtain a nanoemulsion-enhanced natural rubber latex-based composite polyphenol antibacterial bioadhesive.

[0010] Preferably, the lignin in step 1 is one or more of alkali lignin, lignin sulfonate, and enzymatic lignin; the concentration of the lignin alkaline solution is 15 wt%, and the amount used is 15-50 wt% (based on the amount of natural rubber latex used in step 2).

[0011] Preferably, the initiator in step 2 is ammonium persulfate, potassium persulfate, etc.; the stirring speed is 300-400 rpm, the stirring temperature is 60±2° C., and the reaction time is 3 h.

[0012] Preferably, the concentration of the tannic acid aqueous solution in step 3 is 1-2 mg / mL, the concentration of the cinnamaldehyde ethanol solution is 10-40 mg / 100 μL, and the volume ratio of the cinnamaldehyde ethanol solution to the tannic acid aqueous solution is 1:9-10.

[0013] Preferably, the stirring speed for preparing the nanoemulsion in step 4 is 800-1000 rpm, and the time is 20-30 min; the power of the ultrasonic treatment is 200-300 W, and the time is 20-30 min.

[0014] Preferably, the cinnamaldehyde-tannic acid nanoemulsion can also be replaced by a combination of other naturally derived water-soluble polyphenols (such as gallic acid, chlorogenic acid, catechin, etc.) and oil-soluble aldehydes (such as vanillin, citral, furfural).

[0015] Preferably, in step 5, the cinnamaldehyde-tannic acid nanoemulsion accounts for 2-4 wt% of the dry weight of the natural rubber latex grafted lignin copolymer, the stirring speed is 800-1000 rpm, the stirring temperature is room temperature, and the stirring time is 20-30 min.

[0016] The present invention has at least the following beneficial effects:

[0017] The invention uses natural latex and lignin as raw materials, which are widely available, renewable, and degradable, and meet green environmental protection requirements.

[0018] The grafting reaction improves the compatibility of natural rubber latex and lignin, and enhances the bonding performance of the adhesive.

[0019] The introduction of cinnamaldehyde and tannic acid nanoemulsions gives the adhesive excellent antibacterial properties, which can effectively inhibit the growth of bacteria and fungi and extend the service life of the adhesive.

[0020] The preparation process of nanoemulsion is simple, the conditions are mild, and it is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of the preparation method of the natural rubber latex-based polyphenol nanoemulsion composite antibacterial bioadhesive of the present invention;

[0022] Figure 2 The diagram shows the antibacterial effects of the bio-based antibacterial adhesives of the comparative example, example 1, example 2, and example 3 of the present invention on Escherichia coli and Staphylococcus aureus. DETAILED DESCRIPTION

[0023] The present invention will be described in further detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0024] Step 1: uniformly dispersing lignin in deionized water at room temperature, adding a pH buffer solution to obtain a pretreated lignin alkaline solution with a pH of 9;

[0025] Step 2: adding the alkaline lignin solution of step 1 to the natural rubber latex, and adding an initiator at the same time, stirring at a constant temperature to allow the lignin and the natural rubber latex to undergo a graft copolymerization reaction. After the reaction is completed, unreacted macromolecular impurities are removed by filtration or centrifugation to obtain a copolymer of natural rubber latex and lignin;

[0026] Step 3, dissolving tannic acid in water at room temperature to prepare an aqueous phase solution, and dissolving cinnamaldehyde essential oil in ethanol to prepare an oil phase solution;

[0027] Step 4: dispersing an emulsifier (such as Tween 80) in the tannic acid aqueous solution described in step 3 under high-speed stirring, then slowly adding the cinnamaldehyde ethanol solution dropwise, and after ultrasonic treatment, obtaining an oil-in-water (O / W) structured cinnamaldehyde-tannic acid nanoemulsion;

[0028] Step 5: adding the nanoemulsion described in step 4 to the copolymer described in step 2, and stirring the mixture at a constant temperature to obtain a nanoemulsion-enhanced natural rubber latex-based composite polyphenol antibacterial bioadhesive.

[0029] The present invention is described in further detail below in conjunction with the embodiments:

[0030] Example 1

[0031] Step 1: dissolve 3 g of alkali lignin in 17 g of deionized water at room temperature, and add pH buffer solution to obtain a pretreated lignin alkaline solution with a pH of 9;

[0032] Step 2: Add the alkaline lignin solution described in step 1 to 100 g of natural rubber latex, add an initiator at the same time, and stir at 300-400 rpm and 60° C. for 3 hours to allow the alkaline lignin and natural rubber latex to undergo graft copolymerization. After the reaction is completed, remove unreacted macromolecular impurities by filtration or centrifugation to obtain a copolymer of natural rubber latex and lignin;

[0033] Step 3: Dissolve 0.1 g of catechin in 90 mL of water at room temperature, stir in a 60°C water bath (300 rpm) until completely dissolved, and cool to room temperature;

[0034] Step 4: Dissolve 4 g of cinnamaldehyde essential oil in 10 mL of ethanol;

[0035] Step 5: dispersing an emulsifier (such as Tween 80) in the catechin aqueous solution described in step 3 under high-speed stirring (800-1000 rpm), then slowly adding cinnamaldehyde ethanol solution dropwise, and ultrasonically treating for 30 minutes to obtain a catechin-tannic acid nanoemulsion;

[0036] Step 6: Take 2.7 g of the catechin-tannic acid nanoemulsion described in step 4 and add it to the copolymer described in step 2. After stirring at 800-850 rpm and room temperature for 20 minutes, a nanoemulsion-enhanced natural rubber latex-based composite polyphenol antibacterial bioadhesive is obtained.

[0037] The bio-based antibacterial adhesive prepared in this example exhibited excellent coating properties, with a bond strength of 0.8 MPa. After 14 days of bonding, the bond strength reached 1.2 MPa. The adhesive also exhibited an inhibition rate of 98.7% against Escherichia coli and 98.5% against Staphylococcus aureus, demonstrating excellent durability and antibacterial properties.

[0038] Example 2

[0039] Step 1: dissolve 3 g of alkali lignin in 17 g of deionized water at room temperature, and add pH buffer solution to obtain a pretreated lignin alkaline solution with a pH of 9;

[0040] Step 2: Add the alkaline lignin solution described in step 1 to 100 g of natural rubber latex, add an initiator at the same time, and stir at 300-400 rpm and 60° C. for 3 hours to allow the alkaline lignin and natural rubber latex to undergo graft copolymerization. After the reaction is completed, remove unreacted macromolecular impurities by filtration or centrifugation to obtain a copolymer of natural rubber latex and lignin;

[0041] Step 3: Dissolve Tween 80 in 90 mL of water and 4 g of cinnamaldehyde essential oil in 10 mL of ethanol under high-speed stirring (800-1000 rpm);

[0042] Step 4: slowly adding cinnamaldehyde ethanol solution dropwise under high-speed stirring, and ultrasonically treating for 30 minutes to obtain a cinnamaldehyde nanoemulsion with an oil-in-water (O / W) structure;

[0043] Step 5: taking 2.7 g of the cinnamaldehyde nanoemulsion described in step 4 and adding it to the copolymer described in step 2, stirring at 800-850 rpm and room temperature for 20 minutes to obtain a nanoemulsion-enhanced natural rubber latex-based composite polyphenol antibacterial bioadhesive.

[0044] The natural rubber latex-grafted lignin bioadhesive prepared in this example exhibited excellent coating properties, with a bond strength of 196.09 N. After bonding, after being placed in an environment of 28±2°C and 70±2% relative humidity for 4 hours, the bond strength remained at 170.44 N. After 14 days, the bond strength reached a high of 267.83 N, demonstrating excellent water resistance and durability.

[0045] Example 3

[0046] Step 1: dissolve 3 g of alkali lignin in 17 g of deionized water at room temperature, and add pH buffer solution to obtain a pretreated lignin alkaline solution with a pH of 9;

[0047] Step 2: Add the alkaline lignin solution described in step 1 to 100 g of natural rubber latex, add an initiator at the same time, and stir at 300-400 rpm and 60° C. for 3 hours to allow the alkaline lignin and natural rubber latex to undergo graft copolymerization. After the reaction is completed, remove unreacted macromolecular impurities by filtration or centrifugation to obtain a copolymer of natural rubber latex and lignin;

[0048] Step 3: dissolving 0.1 g of tannic acid in 90 mL of water at room temperature to prepare an aqueous solution, and dissolving 4 g of cinnamaldehyde essential oil in 10 mL of ethanol to prepare an oil solution;

[0049] Step 4: dispersing an emulsifier (such as Tween 80) in the tannic acid aqueous solution described in step 3 under high-speed stirring (800-1000 rpm), then slowly adding the cinnamaldehyde ethanol solution dropwise, and ultrasonically treating for 30 minutes to obtain an oil-in-water (O / W) structured cinnamaldehyde-tannic acid nanoemulsion;

[0050] Step 5: take 2.7 g of the cinnamaldehyde-tannic acid nanoemulsion described in step 4 and add it to the copolymer described in step 2, stirring at 800-850 rpm and room temperature for 20 minutes to obtain a nanoemulsion-enhanced natural rubber latex-based composite polyphenol antibacterial bioadhesive.

[0051] The bio-based antibacterial adhesive prepared in this example exhibited excellent coating properties, with a bond strength of 1.0 MPa. After 14 days of bonding, the bond strength reached 1.3 MPa. The adhesive also exhibited an inhibition rate of 99.2% against Escherichia coli and 99.1% against Staphylococcus aureus, demonstrating excellent durability and antibacterial properties.

[0052] Comparative Example

[0053] Step 1: dissolve 3 g of alkali lignin in 17 g of deionized water at room temperature, and add pH buffer solution to obtain a pretreated lignin alkaline solution with a pH of 9;

[0054] Step 2: Add the lignin alkaline solution described in step 1 to 100g of natural latex, add an initiator at the same time, and stir at 300-400rpm and 60°C for 3h to allow the alkaline lignin and natural latex to undergo graft copolymerization reaction. After the reaction is completed, remove unreacted macromolecular impurities by filtration or centrifugation to obtain a natural latex grafted lignin adhesive.

[0055] The bio-based adhesive prepared in this comparative example exhibited excellent coating properties, with a bond strength of 0.8 MPa. After 14 days of bonding, the bond strength reached 1.0 MPa. The inhibition rate against Escherichia coli was 51.9%, and against Staphylococcus aureus was 46.6%. This demonstrated excellent durability, but the inhibitory effect against pathogens was inferior to that of the adhesive containing the antimicrobial agent.

[0056] The methods for measuring the parameters in the above embodiments and comparative examples are as follows:

[0057] White cardboard (400g / m 2 ) was cut into dumbbell-shaped specimens, and then cut in the middle, and the adhesives prepared in the examples and comparative examples were mixed at a pressure of 250 g / m 2 The amount of glue and 250mm 2 The coating area was applied to a paper sample, and the two paper samples were adhered together. The sample was dried at room temperature for 20 minutes to obtain the desired sample. The adhesive strength of the paper sample was measured using a universal tensile testing machine at room temperature at a speed of 10 mm / min. The average value was calculated by three measurements.

[0058] In order to verify the effect of bonding time on the bonding performance of the adhesives prepared in the examples and comparative examples, the prepared bonded paper samples were placed in a normal temperature and humidity environment for 14 days to measure the bonding strength of the adhesive after 14 days.

[0059] 100 mg of the dry adhesive film was placed in 5 mL of nutrient broth containing 10 CFU / mL of Escherichia coli and Staphylococcus aureus and then incubated in a constant temperature shaking incubator at 37°C and 200 rpm for 24 hours. The antibacterial rate was calculated using the standard plate count method. Nutrient broth without the film was used as a control.

[0060] As described above, the present invention provides a natural latex-based polyphenol nanoemulsion composite antibacterial bioadhesive and a preparation method thereof. The core of the present invention is to combine the natural latex-lignin graft copolymer with the plant-derived nano-antibacterial agent through the synergistic effect of cinnamaldehyde and tannic acid nanoemulsion, thereby realizing the integration of the triple functions of "adhesion-antibacterial-environmental protection", giving the adhesive high-efficiency and long-lasting antibacterial properties, while also having excellent bonding strength and environmental protection characteristics. This adhesive not only adheres to the concept of green environmental protection, but also demonstrates extraordinary strength in bonding performance. Its antibacterial function is even more remarkable and unique, providing a strong guarantee for its application in various fields. Whether it is the packaging industry, the medical field, or many other fields such as wood processing, this bio-based antibacterial adhesive can play its unique advantages, show broad application prospects and huge market potential, and inject new vitality and motivation into the development of related industries.

[0061] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and exemplary embodiments. They can be applied to a variety of fields suitable for the present invention. Further modifications will be readily apparent to those skilled in the art. Therefore, the present invention is not limited to the specific details and illustrations shown and described herein without departing from the general concept defined by the claims and their equivalents.

Claims

1. A natural rubber latex-based polyphenol nanoemulsion composite antibacterial bioadhesive and a preparation method thereof, characterized in that: The method steps are: Step 1: uniformly dispersing lignin in deionized water at room temperature, adding a pH buffer solution to obtain a pretreated lignin alkaline solution with a pH of 9; Step 2: adding the alkaline lignin solution of step 1 to the natural rubber latex, and adding an initiator at the same time, stirring at a constant temperature to allow the lignin and the natural rubber latex to undergo a graft copolymerization reaction. After the reaction is completed, unreacted macromolecular impurities are removed by filtration or centrifugation to obtain a copolymer of natural rubber latex and lignin; Step 3, dissolving tannic acid in water at room temperature to prepare an aqueous phase solution, and dissolving cinnamaldehyde essential oil in ethanol to prepare an oil phase solution; Step 4: dispersing an emulsifier (such as Tween 80) in the tannic acid aqueous solution described in step 3 under high-speed stirring, then slowly adding the cinnamaldehyde ethanol solution dropwise, and after ultrasonic treatment, obtaining an oil-in-water (O / W) structured cinnamaldehyde-tannic acid nanoemulsion; Step 5: adding the nanoemulsion described in step 4 to the copolymer described in step 2, and stirring the mixture at a constant temperature to obtain a nanoemulsion-enhanced natural rubber latex-based composite polyphenol antibacterial bioadhesive.

2. A natural rubber latex-based polyphenol nanoemulsion composite antibacterial bioadhesive and a preparation method thereof according to claim 1, characterized in that: The lignin in step one is one or more of alkali lignin, lignin sulfonate, and enzymatic lignin; the concentration of the lignin alkaline solution is 15 wt %, and the amount used is 15-50 wt % (based on the amount of natural rubber latex used in step two).

3. The natural rubber latex-based polyphenol nanoemulsion composite antibacterial bioadhesive and its preparation method according to claim 1, characterized in that: The initiator in step 2 is ammonium persulfate, potassium persulfate, etc.; the stirring speed is 300-400 rpm, the stirring temperature is 60±2° C., and the reaction time is 3 h.

4. The natural rubber latex-based polyphenol nanoemulsion composite antibacterial bioadhesive and its preparation method according to claim 1, characterized in that: In the step 3, the concentration of the tannic acid aqueous solution is 1-2 mg / mL, the concentration of the cinnamaldehyde ethanol solution is 10-40 mg / 100 μL, and the volume ratio of the cinnamaldehyde ethanol solution to the tannic acid aqueous solution is 1:9-10.

5. The natural rubber latex-based polyphenol nanoemulsion composite antibacterial bioadhesive and its preparation method according to claim 1, characterized in that: The stirring speed for preparing the nanoemulsion in step 4 is 800-1000 rpm, and the time is 20-30 min; the power of the ultrasonic treatment is 200-300 W, and the time is 20-30 min.

6. The natural rubber latex-based polyphenol nanoemulsion composite antibacterial bioadhesive and its preparation method according to claim 1, characterized in that: The cinnamaldehyde-tannic acid nanoemulsion can also be replaced by a combination of other naturally derived water-soluble polyphenols (such as gallic acid, chlorogenic acid, catechin, etc.) and oil-soluble aldehydes (such as vanillin, citral, furfural).

7. The natural rubber latex-based polyphenol nanoemulsion composite antibacterial bioadhesive and its preparation method according to claim 1, characterized in that: In the step 5, the cinnamaldehyde-tannic acid nanoemulsion accounts for 2-4 wt% of the dry weight of the natural rubber latex grafted lignin copolymer, the stirring speed is 800-1000 rpm, the stirring temperature is room temperature, and the stirring time is 20-30 min.

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