Bio-based antibacterial polyester and preparation method thereof

Abstract

The invention discloses bio-based antibacterial polyester and a preparation method thereof, and belongs to the technical field of preparation of polyester materials, according to the preparation method, furandicarboxylic acid is used as a first monomer, dihydric alcohol is used as a second monomer, antibacterial amino acid Schiff base is used as a third monomer, and the bio-based antibacterial polyester is prepared through a melt polycondensation method; the high-barrier antibacterial material is obtained by introducing cinnamyl aldehyde-amino acid Schiff base with broad-spectrum antibacterial activity into a PEF material with high barrier property, and the problems that an added antibacterial agent has poor compatibility with the material and is easy to migrate into food to influence the taste are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyester material preparation, and particularly relates to a bio-based antibacterial polyester and a preparation method thereof. Background Art

[0002] As a furan derivative, 2,5-furandicarboxylic acid can be prepared from non-grain biomass. 2,5-furandicarboxylic acid has a structure similar to that of terephthalic acid and is an ideal raw material to replace terephthalic acid. It has been widely studied in the preparation of polyesters, polyamides, and polyurethanes. The polymerization product of 2,5-furandicarboxylic acid and ethylene glycol, polyethylene furanoate (PEF), has better water and oxygen barrier properties than polyethylene terephthalate (PET). Therefore, it has great application prospects in food packaging. At present, the application of PEF in packaging materials is mainly concentrated on food packaging films and beverage packaging bottles, which inhibit the growth of bacteria by high barrier to water and oxygen and extend the shelf life of food. However, most bacteria in food are anaerobic and facultative anaerobic, such as Escherichia coli, Staphylococcus aureus, anaerobic Clostridium, and yeasts. Therefore, to extend the shelf life of food through packaging materials, not only the oxygen barrier performance needs to be improved, but also certain antibacterial properties are required.

[0003] At present, most antibacterial materials are prepared by adding antibacterial agents such as nano-zinc oxide and nano-silver oxide to the materials. However, these nano-antibacterial agents have poor compatibility in some materials and are prone to agglomeration, resulting in defects in material processing. At the same time, they will migrate into food over time, affecting the taste of food.

[0004] Cinnamaldehyde is the main component of cinnamon essential oil, which widely exists in various parts of cinnamon trees. It is a natural antibacterial substance with broad-spectrum antibacterial activity and high safety. However, it is volatile and easily oxidized, so it is difficult to be used alone as an antibacterial substance. Amino acids are organic compounds with both amino and carboxyl groups, and their sources and types are rich. The amino group in amino acids can react with the aldehyde group of cinnamaldehyde to form cinnamaldehyde-amino acid Schiff base, which also has high antibacterial activity. Moreover, since some amino acids have two carboxyl groups and can undergo esterification reactions with mono- or polyhydric alcohols, there is a possibility of introducing cinnamaldehyde-amino acid Schiff base into polyester materials. However, there are few studies on introducing cinnamaldehyde-amino acid Schiff base into polyester materials at present. Summary of the Invention

[0005] The present invention provides a bio-based antibacterial polyester and a preparation method thereof, which introduce cinnamaldehyde-amino acid Schiff base with broad-spectrum antibacterial activity into PEF materials with high barrier properties, solving the problems of poor compatibility between the externally added antibacterial agent and the material and easy migration into food, affecting the taste.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of a bio-based antibacterial polyester, comprising the following steps:

[0008] S1: Prepare cinnamaldehyde-amino acid Schiff base;

[0009] S2: Stir and blend 2,5-furandicarboxylic acid, a catalyst, cinnamaldehyde-amino acid Schiff base and a diol in a reactor;

[0010] S3: Fill with an inert gas and then slowly release the gas. After repeating several times, introduce an inert gas into the kettle. After the temperature in the reactor rises to 150 °C, stir for 30 min;

[0011] S4: Slowly raise the temperature to 220 °C after stirring for esterification reaction. When the pressure in the reactor is greater than 4 atmospheres, release the pressure until water starts to come out, until normal pressure and no more water comes out, and the total amount of water out is more than 90% of the theoretical water out. The esterification ends;

[0012] S5: Add a polycondensation catalyst, a stabilizer and an antioxidant, wherein the stabilizer and the antioxidant are used to inhibit side reactions and thermal oxidative degradation of the polyester. Continue to stir for 30 min. The temperature in the reactor rises to 230 °C, slowly evacuate to below 150 Pa, and then raise the kettle temperature to 240 °C for polycondensation reaction for 3 - 4 hours to obtain the bio-based antibacterial polyester.

[0013] In the above steps, the structure of the cinnamaldehyde-amino acid Schiff base is:

[0014]

[0015] The preparation of cinnamaldehyde-amino acid Schiff base includes the following steps:

[0016] Ⅰ: Weigh 0.1 mol of glutamic acid or aspartic acid, add it to 300 ml of methanol solution, and then add potassium hydroxide in an equimolar amount to the carboxyl group in the amino acid. The mixed solution is stirred and refluxed in a water bath at 50 °C for 2 hours; after the reaction is completed, filter to remove the solid to obtain a clear filtrate;

[0017] Ⅱ: At room temperature, in a nitrogen atmosphere, add 0.14 mol of cinnamon oil to 200 ml of methanol solution, stir evenly and then slowly drop it into the clear filtrate obtained in step Ⅰ;

[0018] Ⅲ: Replace the air in the reactor with nitrogen. After reacting at room temperature for 4 hours, remove the excess solvent at 40 °C using a rotary evaporator. Wash the product 3 times with ether to remove the unreacted cinnamon oil, and dry it at 35 °C for 24 hours to obtain cinnamaldehyde-amino acid Schiff base potassium;

[0019] Ⅴ: Dissolve the obtained potassium cinnamaldehyde - amino acid Schiff base in pure water, add 300 ml of hydrochloric acid for acidification and then filter. Wash the filter residue with pure water 5 times and dry it at 70 °C for 24 hours to obtain cinnamaldehyde - amino acid Schiff base.

[0020] In S2, the addition amount of cinnamaldehyde - amino acid Schiff base is 5 - 20 mol% of the total amount of 2,5 - furandicarboxylic acid. The diol is one or two of ethylene glycol, 1,4 - butanediol, and 1,5 - pentanediol, and the molar ratio of alcohol to acid is 1.6 - 1.8.

[0021] In S2, the mass of the esterification catalyst is 0.02 - 0.04 wt% of the total mass of 2,5 - furandicarboxylic acid and cinnamaldehyde - amino acid Schiff base. The esterification catalyst is one or two of germanium oxide, zinc acetate, and zinc citrate.

[0022] In S5, the mass of the polycondensation catalyst is 0.03 - 0.05 wt% of the total mass of 2,5 - furandicarboxylic acid and cinnamaldehyde - amino acid Schiff base; the mass of the stabilizer is 0.02 - 0.03 wt% of the total mass of 2,5 - furandicarboxylic acid and cinnamaldehyde - amino acid Schiff base; the mass of the antioxidant is 0.02 - 0.03 wt% of the total mass of 2,5 - furandicarboxylic acid and cinnamaldehyde - amino acid Schiff base.

[0023] The polycondensation catalyst is one or two of dibutyltin oxide, titanium glycolate, aluminum acetylacetonate, germanium oxide, titanium(Ⅲ) citrate, titanium(Ⅲ) malate, and titanium(Ⅲ) tartrate.

[0024] The stabilizer is one or two of phosphoric acid, triphenyl phosphate, triethyl phosphate, triethyl phosphonoacetate, and trimethyl phosphate.

[0025] The antioxidant is one or two of sodium sulfite, antioxidant 1010, and antioxidant 168.

[0026] The bio - based antibacterial polyester prepared by the above method is:

[0027]

[0028] Among them, y = 0.05 - 0.2, x = 1 - y, z = 1 or 2, n = 50 - 200, R1 and R2 are alkyl chains with C2 - C6, and R1 and R2 can be the same structure or two different structures.

[0029] The above bio - based antibacterial polyester can be applied to the preparation of food preservative films, fresh - keeping bags, and fresh - keeping boxes.

[0030] Beneficial effects: The present invention provides a bio-based antibacterial polyester and a preparation method thereof. In the preparation method, furandicarboxylic acid is used as the first monomer, diol is used as the second monomer, and antibacterial amino acid Schiff base is used as the third monomer, and the bio-based antibacterial polyester is prepared by a melt polycondensation method; by introducing cinnamaldehyde-amino acid Schiff base with broad-spectrum antibacterial activity into the PEF material with high barrier properties, the problem of poor compatibility between the added antibacterial agent and the material is solved; and the imide bond in the Schiff base has strong stability, which can prevent cinnamaldehyde from being released into food, solving the problem of easy migration into food and affecting the taste, and at the same time, it can also ensure the long-term preservation performance of the material; a high-barrier antibacterial material is obtained, further broadening the application of PEF, and also providing a new idea for high-barrier antibacterial materials. Detailed implementation manners

[0031] The present invention will be described in detail below with reference to specific embodiments:

[0032] The preparation of cinnamaldehyde-amino acid Schiff base includes the following steps:

[0033] Ⅰ: Weigh 0.1 mol of glutamic acid or aspartic acid, add it to 300 ml of methanol solution, and then add potassium hydroxide with an equimolar amount of carboxyl group in the amino acid. The mixed solution is stirred and refluxed in a water bath at 50 °C for 2 hours; after the reaction is completed, the solid is filtered off to obtain a clear filtrate;

[0034] Ⅱ: At room temperature, in a nitrogen atmosphere, add 0.14 mol of cinnamon oil to 200 ml of methanol solution, stir evenly and slowly drop it into the clear filtrate obtained in step Ⅰ;

[0035] Ⅲ: Replace the air in the reactor with nitrogen, react at room temperature for 4 hours, then remove the excess solvent at 40 °C with a rotary evaporator. The product is washed 3 times with ether to remove the unreacted cinnamon oil, and dried at 35 °C for 24 hours to obtain cinnamaldehyde-amino acid Schiff base potassium;

[0036] Ⅴ: Dissolve the obtained cinnamaldehyde-amino acid Schiff base potassium in pure water, add 300 ml of hydrochloric acid for acidification and then filter. The filter residue is washed 5 times with pure water and dried at 70 °C for 24 hours to obtain cinnamaldehyde-amino acid Schiff base.

[0037] In the following examples, the cinnamaldehyde-amino acid Schiff base is selected from cinnamaldehyde-glutamic acid Schiff base or / and cinnamaldehyde-aspartic acid Schiff base, and the structure is shown in the following figure:

[0038]

[0039] Example 1

[0040] A preparation method of a bio-based antibacterial polyester specifically includes the following steps:

[0041] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, and high-purity nitrogen was charged to atmospheric pressure. The stirrer speed was set at 15 Hz. 780 g of 2,5-furandicarboxylic acid, 545.6 g of ethylene glycol, 130.5 g of cinnamaldehyde-glutamic acid Schiff base, and 0.182 g of zinc citrate were added to the reactor. After closing the valve and charging nitrogen at 1.2 bar, the gas was slowly released. After repeating this five times, nitrogen at 1.5 bar was introduced into the reactor. After the temperature in the reactor rose to 150 °C, stirring was carried out for 30 min. After stirring, the temperature was raised to 220 °C for esterification reaction. When the pressure in the reactor was greater than 4 bar, the pressure was slowly reduced to 3.5 bar. After repeating several times, esterification water began to be discharged until atmospheric pressure and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification was completed. Then, 0.27 g of titanium(III) citrate, 0.182 g of triethyl phosphonoacetate, and 0.182 g of antioxidant 1010 were mixed evenly in ethylene glycol and then added to the reactor. The reactor wall was rinsed with a small amount of ethylene glycol, nitrogen at 1 bar was introduced for protection, and stirring was continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and the vacuum was pumped to below 50 Pa in about 1 hour. Then, the temperature of the reactor was raised to 240 °C for polycondensation reaction. The polycondensation reaction was carried out for 3 - 4 hours. When the stirring power increased to a certain value, the stirring was stopped, the vacuum pump was closed, nitrogen was introduced to atmospheric pressure, and the mixture was allowed to stand for 5 min. After strand drawing through a water bath, pelletizing was carried out to obtain the bio-based antibacterial polyester.

[0042] Example 2

[0043] A preparation method of a bio-based antibacterial polyester specifically includes the following steps:

[0044] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, and high-purity nitrogen was charged to atmospheric pressure. The stirrer speed was set at 15 Hz. 780 g of 2,5-furandicarboxylic acid, 570.4 g of ethylene glycol, 195.7 g of cinnamaldehyde-glutamic acid Schiff base, and 0.195 g of zinc citrate were added to the reactor. The valve was closed, nitrogen was charged to 1.2 bar and then slowly vented. After repeating this five times, nitrogen was introduced into the reactor to 1.5 bar. After the temperature in the reactor rose to 150 °C, it was paddled for 30 min. After paddling, the temperature was raised to 220 °C for esterification reaction. When the pressure in the reactor was greater than 4 bar, it was slowly depressurized to 3.5 bar. After repeating several times, esterification water began to be discharged until atmospheric pressure and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification was completed. Then, 0.29 g of titanium(III) citrate, 0.195 g of triethyl phosphonoacetate, and 0.195 g of antioxidant 1010 were mixed in ethylene glycol and then added to the reactor. The reactor wall was rinsed with a small amount of ethylene glycol, nitrogen was introduced to protect it at 1 bar, and stirring continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and it was evacuated to below 50 Pa in about 1 hour. Then, the temperature of the reactor was raised to 240 °C for polycondensation reaction. The polycondensation was carried out for 3 - 4 hours. When the stirring power increased to a certain value, the stirring was stopped, the vacuum pump was closed, nitrogen was introduced to atmospheric pressure, and it was allowed to stand for 5 min. After strip-drawing through a water bath, it was pelletized to obtain the bio-based antibacterial polyester.

[0045] Example 3

[0046] A preparation method of a bio-based antibacterial polyester specifically comprises the following steps:

[0047] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, and high-purity nitrogen was filled to atmospheric pressure. The stirrer speed was set at 15 Hz. 780 g of 2,5-furandicarboxylic acid, 595.2 g of ethylene glycol, 261 g of cinnamaldehyde-glutamic acid Schiff base, and 0.21 g of zinc citrate were added to the reactor. After closing the valve, nitrogen was filled to 1.2 bar and then slowly vented. After repeating this five times, nitrogen was introduced into the reactor to 1.5 bar. After the temperature in the reactor rose to 150 °C, stirring was carried out for 30 min; after stirring, the temperature was raised to 220 °C for esterification reaction. When the pressure in the reactor was greater than 4 bar, the pressure was slowly reduced to 3.5 bar. After repeating several times, esterification water began to be discharged until atmospheric pressure and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification was completed; then 0.31 g of titanium(III) citrate, 0.21 g of triethyl phosphonoacetate, and 0.21 g of antioxidant 1010 were mixed in ethylene glycol and then added to the reactor. The reactor wall was rinsed with a small amount of ethylene glycol, nitrogen was introduced to protect at 1 bar, and stirring was continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and the vacuum was drawn to below 50 Pa in about 1 hour. Then the temperature of the reactor was raised to 240 °C for polycondensation reaction. The polycondensation was carried out for 3 - 4 hours. When the stirring power increased to a certain value, the stirring was stopped, the vacuum pump was closed, nitrogen was introduced to atmospheric pressure, and it was left standing for 5 min. After strip drawing through a water bath, pelletizing was carried out to obtain the bio-based antibacterial polyester.

[0048] Example 4

[0049] A preparation method of a bio-based antibacterial polyester specifically comprises the following steps:

[0050] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, and high-purity nitrogen was filled until atmospheric pressure. The stirrer speed was set to 15 Hz. 780 g of 2,5-furandicarboxylic acid, 545.6 g of ethylene glycol, 123.5 g of cinnamaldehyde-aspartic acid Schiff base, and 0.18 g of germanium oxide were put into the reactor. After closing the valve and filling with nitrogen at 1.2 bar, the gas was slowly released. After repeating this five times, nitrogen at 1.5 bar was introduced into the reactor. After the temperature in the reactor rose to 150 °C, stirring was carried out for 30 min. After stirring, the temperature was raised to 220 °C for esterification reaction. When the pressure in the reactor was greater than 4 bar, the pressure was slowly reduced to 3.5 bar. After repeating several times, esterification water began to be discharged until atmospheric pressure and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification was completed. Then, 0.26 g of titanium(III) tartrate, 0.18 g of triethyl phosphonoacetate, and 0.18 g of antioxidant 1010 were mixed in ethylene glycol and then added to the reactor. The reactor wall was rinsed with a small amount of ethylene glycol. Nitrogen at 1 bar was introduced for protection, and stirring was continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and the pressure was reduced to below 50 Pa in about 1 hour. Then, the temperature of the reactor was raised to 240 °C for polycondensation reaction. The polycondensation reaction was carried out for 3 - 4 hours. When the stirring power increased to a certain value, the stirring was stopped, the vacuum pump was closed, nitrogen was introduced until atmospheric pressure, and the mixture was allowed to stand for 5 min. After strip drawing through a water bath and pelletizing, a bio-based antibacterial polyester was obtained.

[0051] Example 5

[0052] A preparation method of a bio-based antibacterial polyester specifically includes the following steps:

[0053] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, and high-purity nitrogen was filled until atmospheric pressure. The stirrer speed was set at 15 Hz. 780 g of 2,5-furandicarboxylic acid, 570.4 g of ethylene glycol, 185.3 g of cinnamaldehyde-aspartic acid Schiff base, and 0.19 g of germanium oxide were added to the reactor. After closing the valve and filling with nitrogen at 1.2 bar, the gas was slowly released. After repeating this five times, nitrogen at 1.5 bar was introduced into the reactor. After the temperature in the reactor rose to 150 °C, stirring was carried out for 30 min. After stirring, the temperature was raised to 220 °C for esterification reaction. When the pressure in the reactor was greater than 4 bar, the pressure was slowly reduced to 3.5 bar. After repeating several times, esterification water began to be discharged until atmospheric pressure and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification ended. Then, 0.29 g of titanium(III) tartrate, 0.19 g of triethyl phosphonoacetate, and 0.19 g of antioxidant 1010 were mixed in ethylene glycol and then added to the reactor. The reactor wall was rinsed with a small amount of ethylene glycol. Nitrogen at 1 bar was introduced for protection, and stirring was continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and the vacuum was drawn to below 50 Pa in about 1 hour. Then, the temperature of the reactor was raised to 240 °C for polycondensation reaction. The polycondensation was carried out for 3 - 4 hours. When the stirring power increased to a certain value, the stirring was stopped, the vacuum pump was closed, nitrogen was introduced until atmospheric pressure, and it was allowed to stand for 5 min. After strand drawing through a water bath and pelletizing, a bio-based antibacterial polyester was obtained.

[0054] Example 6

[0055] A preparation method of a bio-based antibacterial polyester specifically includes the following steps:

[0056] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, and high-purity nitrogen was charged to atmospheric pressure. The stirrer speed was set at 15 Hz. 780 g of 2,5-furandicarboxylic acid, 595.2 g of ethylene glycol, 247 g of cinnamaldehyde-aspartic acid Schiff base, and 0.21 g of germanium oxide were added to the reactor. After closing the valve and charging nitrogen to 1.2 bar, the gas was slowly released. After repeating this five times, nitrogen was introduced into the reactor to 1.5 bar. After the temperature in the reactor rose to 150 °C, stirring was carried out for 30 min; after stirring, the temperature was raised to 220 °C for esterification reaction. When the pressure in the reactor was greater than 4 bar, the pressure was slowly reduced to 3.5 bar. After repeating several times, esterification water began to be discharged until atmospheric pressure was reached and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification was completed; then 0.31 g of titanium(III) tartrate, 0.21 g of triethyl phosphonoacetate, and 0.21 g of antioxidant 1010 were mixed in ethylene glycol and then added to the reactor, and the reactor wall was rinsed with a small amount of ethylene glycol. Nitrogen was introduced to protect, and stirring was continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and the vacuum was pumped to below 50 Pa in about 1 hour. Then the temperature of the reactor was raised to 240 °C for polycondensation reaction. Polycondensation was carried out for 3 - 4 hours. When the stirring power increased to a certain value, the stirring was stopped, the vacuum pump was closed, nitrogen was introduced to atmospheric pressure, and it was left standing for 5 min. After strip drawing through a water bath, granulation was carried out to obtain the bio-based antibacterial polyester.

[0057] Example 7

[0058] A preparation method of a bio-based antibacterial polyester specifically includes the following steps:

[0059] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, and high-purity nitrogen was filled until atmospheric pressure. The stirring speed of the stirrer was set to 15 Hz. 780 g of 2,5-furandicarboxylic acid, 792.8 g of 1,4-butanediol, 135 g of cinnamaldehyde-glutamic acid Schiff base, and 0.18 g of germanium oxide were put into the reactor. After closing the valve and filling with nitrogen at 1.2 bar, the gas was slowly released. After repeating this five times, nitrogen at 1.5 bar was introduced into the reactor. After the temperature in the reactor rose to 150 °C, it was paddled for 30 min; after paddling, the temperature was raised to 220 °C for esterification reaction. When the pressure in the reactor was greater than 4 bar, it was slowly depressurized to 3.5 bar. After repeating several times, esterification water began to be discharged until atmospheric pressure and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification was completed; then 0.26 g of germanium oxide, 0.18 g of triethyl phosphonoacetate, and 0.18 g of antioxidant 1010 were mixed in butanediol and then added to the reactor, and the reactor wall was rinsed with a small amount of butanediol. Nitrogen at 1 bar was introduced for protection, and stirring was continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and it was evacuated to below 50 Pa in about 1 hour. Then the temperature of the reactor was raised to 240 °C for polycondensation reaction. Polycondensation was carried out for 3 - 4 hours. When the stirring power increased to a certain value, the stirring was stopped, the vacuum pump was closed, nitrogen was introduced until atmospheric pressure, and it was left standing for 5 min. After strip drawing through a water bath, it was pelletized to obtain the bio-based antibacterial polyester.

[0060] Example 8

[0061] A preparation method of a bio-based antibacterial polyester specifically includes the following steps:

[0062] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, and high-purity nitrogen was charged to atmospheric pressure. The stirrer speed was set at 15 Hz. 780 g of 2,5-furandicarboxylic acid, 864.9 g of 1,4-butanediol, 261 g of cinnamaldehyde-glutamic acid Schiff base, and 0.21 g of germanium oxide were put into the reactor. After closing the valve and charging nitrogen at 1.2 bar, the gas was slowly released. After repeating this five times, nitrogen at 1.5 bar was introduced into the reactor. After the temperature in the reactor rose to 150 °C, it was stirred for 30 min; after stirring, the temperature was raised to 220 °C for esterification reaction. When the pressure in the reactor was greater than 4 bar, the pressure was slowly reduced to 3.5 bar. After repeating several times, esterification water began to be discharged until atmospheric pressure and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification ended; then 0.31 g of germanium oxide, 0.21 g of triethyl phosphonoacetate, and 0.21 g of antioxidant 1010 were mixed in butanediol and then added to the reactor, and the reactor wall was rinsed with a small amount of butanediol. Nitrogen at 1 bar was introduced for protection, and stirring continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and it was evacuated to below 50 Pa in about 1 hour. Then the temperature of the reactor was raised to 240 °C for polycondensation reaction. The polycondensation was carried out for 3 - 4 hours. When the stirring power increased to a certain value, the stirring was stopped, the vacuum pump was closed, nitrogen was introduced to atmospheric pressure, and it was allowed to stand for 5 min. After strip drawing through a water bath, it was pelletized to obtain the bio-based antibacterial polyester.

[0063] Example 9

[0064] A preparation method of a bio-based antibacterial polyester specifically includes the following steps:

[0065] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, and high-purity nitrogen was filled until atmospheric pressure. The stirring speed of the stirrer was set to 15 Hz. 780 g of 2,5-furandicarboxylic acid, 792.8 g of 1,4-butanediol, 123.5 g of cinnamaldehyde-glutamic acid Schiff base, and 0.17 g of zinc citrate were added into the reactor. After closing the valve and filling nitrogen to 1.2 bar, the gas was slowly released. After repeating this five times, nitrogen was introduced into the reactor to 1.5 bar. After the temperature in the reactor rose to 150 °C, stirring was carried out for 30 min; after stirring, the temperature was raised to 220 °C for esterification reaction. When the pressure in the reactor was greater than 4 bar, the pressure was slowly reduced to 3.5 bar. After repeating several times, esterification water began to be discharged until atmospheric pressure and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification was completed; then 0.25 g of germanium oxide, 0.17 g of triethyl phosphonoacetate, and 0.17 g of antioxidant 1010 were mixed in butanediol and then added to the reactor, and the reactor wall was rinsed with a small amount of butanediol. Nitrogen was introduced to protect, and stirring was continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and the vacuum was pumped to below 50 Pa in about 1 hour. Then the temperature of the reactor was raised to 240 °C for polycondensation reaction. Polycondensation was carried out for 3 - 4 hours. When the stirring power increased to a certain value, stirring was stopped, the vacuum pump was closed, nitrogen was introduced until atmospheric pressure, and it was left standing for 5 min. After strip drawing through a water bath, pelletizing was carried out to obtain the bio-based antibacterial polyester.

[0066] Example 10

[0067] A preparation method of a bio-based antibacterial polyester specifically includes the following steps:

[0068] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, high-purity nitrogen was charged to atmospheric pressure, the stirrer speed was set at 15 Hz, 780 g of 2,5-furandicarboxylic acid, 864.9 g of 1,4-butanediol, 247 g of cinnamaldehyde-glutamic acid Schiff base, and 0.26 g of zinc citrate were put into the reactor. After closing the valve, nitrogen was charged to 1.2 bar and then slowly vented. After repeating this five times, nitrogen was introduced into the reactor to 1.5 bar. After the temperature in the reactor rose to 150 °C, it was paddled for 30 min; after paddling, the temperature was raised to 220 °C for esterification reaction. When the pressure in the reactor was greater than 4 bar, it was slowly depressurized to 3.5 bar. After repeating several times, esterification water began to be discharged until atmospheric pressure and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification ended; then 0.3 g of germanium oxide, 0.21 g of triethyl phosphonoacetate, and 0.21 g of antioxidant 1010 were mixed in butanediol and then added to the reactor, and the reactor wall was rinsed with a small amount of butanediol. Nitrogen was introduced to protect it, and stirring continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and it was evacuated to below 50 Pa in about 1 hour. Then the temperature of the reactor was raised to 240 °C for polycondensation reaction. Polycondensation was carried out for 3 - 4 hours. When the stirring power increased to a certain value, stirring was stopped, the vacuum pump was closed, nitrogen was introduced to atmospheric pressure, and it was left standing for 5 min. After strip drawing through a water bath, it was pelletized to obtain bio-based antibacterial polyester.

[0069] Comparative Example 1

[0070] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, high-purity nitrogen was charged to atmospheric pressure, the stirrer speed was set at 15 Hz, 780 g of 2,5-furandicarboxylic acid, 496 g of ethylene glycol, and 0.16 g of germanium oxide were put into the reactor. After closing the valve, nitrogen was charged to 1.2 bar and then slowly vented. After repeating this five times, nitrogen was introduced into the reactor to 1.5 bar. After the temperature in the reactor rose to 150 °C, it was paddled for 30 min; after paddling, the temperature was raised to 220 °C for esterification reaction. When the pressure in the reactor was greater than 4 bar, it was slowly depressurized to 3.5 bar. After repeating several times, esterification water began to be discharged until atmospheric pressure and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification ended; then 0.2 g of germanium oxide, 0.16 g of triethyl phosphonoacetate, and 0.16 g of antioxidant 1010 were mixed in ethylene glycol and then added to the reactor, and the reactor wall was rinsed with a small amount of ethylene glycol. Nitrogen was introduced to protect it, and stirring continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and it was evacuated to below 50 Pa in about 1 hour. Then the temperature of the reactor was raised to 240 °C for polycondensation reaction. Polycondensation was carried out for 3 - 4 hours. When the stirring power increased to a certain value, stirring was stopped, the vacuum pump was closed, nitrogen was introduced to atmospheric pressure, and it was left standing for 5 min. After strip drawing through a water bath, it was pelletized to obtain bio-based antibacterial polyester.

[0071] Comparative Example 2

[0072] The 2.5 L reactor was evacuated to below 50 Pa, the vacuum pump was closed, high-purity nitrogen was charged to atmospheric pressure, the stirrer speed was set to 15 Hz, 780 g of 2,5-furandicarboxylic acid, 720 g of 1,4-butanediol, and 0.2 g of zinc citrate were put into the reactor. After closing the valve and charging nitrogen to 1.2 bar, the gas was slowly released. After repeating this five times, nitrogen was introduced into the reactor to 1.5 bar. After the temperature in the reactor rose to 150 °C, stirring was carried out for 30 min; after stirring, the temperature was raised to 220 °C for the esterification reaction. When the pressure in the reactor was greater than 4 bar, the pressure was slowly reduced to 3.5 bar. After repeating several times, the esterification water began to be discharged until atmospheric pressure and no more water was discharged, and the total amount of discharged water was more than 90% of the theoretical amount of discharged water, and the esterification was completed; then 0.3 g of germanium oxide, 0.16 g of triethyl phosphonoacetate, and 0.16 g of antioxidant 1010 were mixed in butanediol and then added to the reactor, and the reactor wall was rinsed with a small amount of butanediol. Nitrogen was introduced to protect, and stirring was continued for 30 min. The vacuum pump was turned on, the temperature of the reactor was raised to 230 °C, and the vacuum was pumped to below 50 Pa in about 1 hour. Then the temperature of the reactor was raised to 240 °C for the polycondensation reaction. The polycondensation was carried out for 3 - 4 hours. When the stirring power increased to a certain value, the stirring was stopped, the vacuum pump was closed, nitrogen was introduced to atmospheric pressure, and it was left standing for 5 min. After strand drawing through a water bath and then pelletizing, bio-based antibacterial polyester was obtained.

[0073] Comparative Example 3

[0074] PEF was synthesized with the same formulation as in Comparative Example 1. Zinc oxide powder with a particle size less than 100 nm was added to the PEF, and the mass ratio of ZnO:PEF was 20:80. After blending them, an antibacterial masterbatch was made through a twin-screw extruder. The antibacterial masterbatch and PEF chips were blended, and then pelletized through a twin-screw extruder. The mass ratio of the antibacterial masterbatch was 10%, and antibacterial PEF chips were obtained.

[0075] Performance Test

[0076] First, the antibacterial modified bio-based polyesters obtained in Examples 1 - 10 and Comparative Examples 1 - 3 above were pressed into sheets using a flat vulcanizer to obtain sheets with dimensions of 150×150×0.3 mm. Then the sheets were respectively cut into strips with dimensions of 25×150×0.3 mm and square sheets with dimensions of 40×40 mm for standby.

[0077] Mechanical Property Test

[0078] The test was carried out according to the experimental conditions in the third part of the national standard GB / T 1040.3 Determination of Tensile Properties of Plastics: Films and Sheets. The tensile rate was 50 mm / min, and the gauge length was 50 mm.

[0079] Oxygen and Water Vapor Barrier Property Test

[0080] The oxygen barrier property of the film was tested by the differential pressure method, and the detection was carried out in accordance with the national standard GB / T 1038-2000 Test Method for Gas Permeability of Plastic Films and Sheets. The water vapor transmission rate was tested by the infrared detection method in accordance with the national standard GB / T 26253-2010 Determination of Water Vapor Transmission Rate of Plastic Films and Sheets.

[0081] Antibacterial performance test

[0082] The test was carried out in accordance with the national standard GB / T 31402-2015 Experimental Method for Antibacterial Performance of Plastic Surfaces. The antibacterial performance was compared by measuring the viable bacteria count using the plate culture method. The bacteria were Escherichia coli and Staphylococcus aureus. The viable bacteria count was calculated according to the following formula:

[0083] N = (100 × C × D × V) / A

[0084] Where: N is the number of viable bacteria per square centimeter of each specimen; C is the average colony count of the two culture dishes; D is the dilution factor; V is the volume of SCDLP culture medium used for elution, in mL; A is the surface area of the covering film, in cm 2 ; The antibacterial performance was calculated by the following formula:

[0085] R = (U t - U0) - (A t - U0) = U t - A t

[0086] Where: R is the antibacterial performance value; U0 is the logarithmic average value of the number of bacteria immediately after inoculation of the specimen without antibacterial treatment, in CFU / cm 2 ); U t is the logarithmic average value of the number of bacteria 24 h after inoculation of the specimen without antibacterial treatment, in CFU / cm 2 ); A t is the logarithmic average value of the number of bacteria 24 h after inoculation of the specimen with antibacterial treatment, in CFU / cm 2 ).

[0087] The above performance test results are shown in Tables 1 - 3:

[0088] Table 1 Mechanical property test data of different antibacterial films

[0089]

[0090] Table 2 Oxygen and water vapor barrier property test data of different antibacterial films

[0091]

[0092] Table 3 Antibacterial performance data of different antibacterial films

[0093]

[0094]

[0095] It can be seen from Table 1 and Table 2 that with the addition of cinnamaldehyde amino acid Schiff base, the tensile strength and elongation at break of PEF and PBF-based antibacterial polyesters both decreased significantly, and the oxygen and water vapor barrier properties also decreased to some extent. Among them, cinnamaldehyde-aspartic acid has a more serious reduction in the mechanical properties and barrier properties of the material than cinnamaldehyde-glutamic acid. The introduction of glutamic acid has a certain increase in the elongation at break. The aspartic acid chain segment is longer, the elongation at break increases, and the strength decreases. After adding butanediol, the mechanical strength of the material is lower than that of ethylene glycol, and the elongation at break increases relatively. It can be seen from Table 3 that with the introduction of cinnamaldehyde-amino acid Schiff base, the bio-based polyester has obtained good antibacterial performance, and the antibacterial performance can reach the level of the PEF film added with nano-zinc oxide. Among them, the polyester with 20 mol% cinnamaldehyde-glutamic acid Schiff base added has the best antibacterial performance.

[0096] The above are only the preferred embodiments of the present invention, which will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements made all belong to the protection scope of the present invention.

Claims

1. A bio-based antibacterial polyester, characterized in that: The structural formula of the polyester is: ， Wherein, y=0.05-0.2; x=1-y; z=1 or 2; n=50-200; R1 is a C2-C6 alkyl chain, and R2 is a C2-C6 alkyl chain.

2. The method for preparing the bio-based antibacterial polyester according to claim 1, characterized in that: The following steps are involved: S1: Preparation of cinnamaldehyde-amino acid Schiff base; S2: stirring and blending 2,5-furandicarboxylic acid, an esterification catalyst, cinnamaldehyde-amino acid Schiff base and diol in a reactor; S3: After filling with inert gas, slowly release the gas, repeat several times, then introduce inert gas into the kettle, heat up and then beat the slurry; S4: After beating, continue to raise the temperature to carry out esterification reaction; S5: After the esterification reaction is completed, a polycondensation catalyst, a stabilizer and an antioxidant are added, stirring is continued, vacuum is evacuated, and the temperature is increased to carry out a polycondensation reaction to obtain a bio-based antibacterial polyester.

3. The method for preparing the bio-based antibacterial polyester according to claim 2, characterized in that: The cinnamaldehyde-amino acid Schiff base structure is: or .

4. The method for preparing the bio-based antibacterial polyester according to claim 2 or 3, characterized in that: The method for preparing cinnamaldehyde-amino acid Schiff base comprises the following steps: Ⅰ: Weigh 0.1 mol of glutamic acid or aspartic acid, add it to 300 ml of methanol solution, then add potassium hydroxide in an amount equal to the molar amount of the carboxyl group in the amino acid, and stir and reflux the mixed solution in a 50°C water bath for 2 hours; after the reaction is completed, filter out the solid to obtain a clear filtrate; II: At room temperature, in a nitrogen atmosphere, add 0.14 mol of cinnamon oil to 200 ml of methanol solution, stir evenly, and then slowly add dropwise to the clear filtrate obtained in step I; III: replacing the air in the reactor with nitrogen, reacting at room temperature for 4 hours, removing excess solvent with a rotary evaporator at 40°C, washing the product with ether three times, removing unreacted cinnamon oil, and drying at 35°C for 24 hours to obtain cinnamaldehyde-amino acid Schiff base potassium; V: The obtained cinnamaldehyde-amino acid Schiff base potassium was dissolved in pure water, 300 ml of hydrochloric acid was added to acidify and then filtered, the filter residue was washed with pure water 5 times, and dried at 70° C. for 24 hours to obtain cinnamaldehyde-amino acid Schiff base.

5. The method for preparing the bio-based antibacterial polyester according to claim 2, characterized in that: The amount of cinnamaldehyde-amino acid Schiff base added is 5-20 mol% of the total amount of 2,5-furandicarboxylic acid.

6. The method for preparing the bio-based antibacterial polyester according to claim 2 or 5, characterized in that: The amount of the esterification catalyst used is 0.02-0.04 wt % of the total mass of 2,5-furandicarboxylic acid and cinnamaldehyde-amino acid Schiff base.

7. The method for preparing the bio-based antibacterial polyester according to claim 2, characterized in that: The alkyd to acid ratio in S2 is 1.6-1.

8.

8. The method for preparing the bio-based antibacterial polyester according to claim 2 or 5, characterized in that: The mass of the polycondensation catalyst is 0.03-0.05wt% of the total mass of 2,5-furandicarboxylic acid and cinnamaldehyde-amino acid Schiff base.

9. The method for preparing the bio-based antibacterial polyester according to claim 2 or 5, characterized in that: The mass of the stabilizer is 0.02-0.03wt% of the total mass of 2,5-furandicarboxylic acid and cinnamaldehyde-amino acid Schiff base.

10. The method for preparing the bio-based antibacterial polyester according to claim 2 or 5, characterized in that: The weight of the antioxidant is 0.02-0.03 wt % of the total weight of 2,5-furandicarboxylic acid and cinnamaldehyde-amino acid Schiff base.

Images