A bio-based oligomeric lactate plasticizer and its preparation method and application

Abstract

The present invention discloses a bio-based oligomeric lactate plasticizer and its preparation method and application. The structural formula of the plasticizer is as follows. Its preparation method is: diethylene glycol monomethyl ether, lactic acid and a catalyst are added to a reactor, and heated to react; after the reaction is completed, a crude product is extracted, cleaned to neutrality, and the solvent is removed by rotary evaporation to obtain diethylene glycol monomethyl ether-oligomeric lactate; diethylene glycol monomethyl ether-oligomeric lactate, cinnamic acid and a catalyst are added to a reactor, and heated to react; after the reaction is completed, a crude product is extracted, cleaned to neutrality, and then rotary evaporation to remove the solvent to obtain diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate. The present invention prepares an environmentally friendly oligomeric lactate plasticizer by a two-step esterification method, has low viscosity, good compatibility with PHA, and has more excellent thermal stability, tensile properties, migration resistance, etc. It can reduce the melting point Tm and glass transition temperature Tg of PHA and improve the elongation at break of PHA.

Description

Technical Field

[0001] The present invention relates to a plasticizer and a preparation method and application thereof, and in particular to an oligolactic acid ester bio-based plasticizer and a preparation method and application thereof. Background Art

[0002] Polyhydroxyalkanoates (PHAs) are natural polyesters obtained through microbial fermentation. Due to their excellent biodegradability and biocompatibility, they have become a hot research topic in the field of biomaterials. Furthermore, PHAs possess unique materials properties, such as nonlinear optical activity, piezoelectricity, and odor barrier properties. Poly (3-hydroxybutyrate) (PHB), the most common form of PHA, is a candidate for replacing non-biodegradable plastics in high-value-added sectors such as food service, biopharmaceuticals, and product packaging. However, numerous challenges currently limit the commercial application of PHB, such as the polymer's melting temperature being close to its decomposition temperature, resulting in a narrow processing window; high crystallinity, low toughness and impact strength; and poor thermal stability. Marketization requires extensive research. Currently, traditional petroleum-based plasticizers are banned in the food and medical sectors and can, to a certain extent, affect the biodegradability of PHB. This necessitates the development of bio-based, environmentally friendly plasticizers with versatile properties.

[0003] Bio-based plasticizers are chemicals based on renewable resources and are widely used in the production of materials such as plastics and rubber to improve their flexibility and processing properties. As an environmentally friendly alternative to traditional plasticizers, they hold broad application prospects. However, in practical applications, they face challenges with insufficient physical and chemical properties, such as poor fluidity at low temperatures and poor thermal stability at high temperatures. Furthermore, the raw materials for bio-based plasticizers, which typically come from biomass resources such as vegetable oils, starch, and corn stalks, are relatively expensive and involve complex processes, resulting in insufficient market competitiveness of the final products. Therefore, continuous technological innovation and optimized production processes are necessary. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a bio-based oligomeric lactate plasticizer with excellent plasticizing properties; the second purpose of the present invention is to provide a method for preparing the above-mentioned bio-based oligomeric lactate plasticizer; the third purpose of the present invention is to provide an application of the above-mentioned bio-based oligomeric lactate plasticizer.

[0005] Technical solution: The oligomeric lactate bio-based plasticizer of the present invention has the following structural formula:

[0006]

[0007] Wherein, n is the number of lactic acid repeating units.

[0008] The preparation method of the above-mentioned oligomeric lactate bio-based plasticizer comprises the following steps:

[0009] (1) adding diethylene glycol monomethyl ether, lactic acid and a catalyst into a reactor and heating the reactor for reaction; after the reaction is completed, extracting the crude product, washing it to neutrality, and removing the solvent by rotary evaporation to obtain diethylene glycol monomethyl ether-oligomeric lactate;

[0010] (2) adding diethylene glycol monomethyl ether-oligomeric lactic acid ester, cinnamic acid and a catalyst into a reactor and heating the reactor for reaction; after the reaction is completed, extracting the crude product, washing it to neutrality, and then removing the solvent by rotary evaporation to obtain diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamic acid ester.

[0011] Wherein, in step (1), the catalyst is p-toluenesulfonic acid, and the mass of the catalyst is 0.4% to 0.6% of the total mass of the raw materials.

[0012] Wherein, in step (1), the molar ratio of diethylene glycol monomethyl ether to lactic acid is 1:2-3.

[0013] In step (1), the temperature is heated to 120-160° C. and the reaction is carried out for 2-4 hours. Under such heating conditions, the catalyst has the best activity and the highest catalytic efficiency.

[0014] Wherein, in step (1), the vacuum degree of rotary evaporation is -0.1 MPa, and the distillation temperature is 70-90° C. for 0.5-2 h. Under these rotary evaporation parameters, the solvent can be evaporated quickly.

[0015] Wherein, in step (2), the catalyst is a strongly acidic cation exchange resin, and the mass of the catalyst is 20-30% of the molar mass of cinnamic acid.

[0016] Wherein, in step (2), the molar ratio of diethylene glycol monomethyl ether-oligomeric lactate to cinnamic acid is 1:2-3.

[0017] In step (2), the temperature is heated to 160-200° C. and the reaction is carried out for 12-16 hours. Under such heating conditions, the catalyst has the best activity and the highest catalytic efficiency.

[0018] In step (2), the vacuum degree of rotary distillation is -0.1 MPa, and the distillation temperature is 70-90° C. for 0.5-2 h. Under these rotary distillation parameters, the solvent can be evaporated quickly.

[0019] The oligomeric lactate bio-based plasticizer prepared by the above method is used in the preparation of polyhydroxyalkanoate PHA and poly 3-hydroxybutyrate PHB.

[0020] Principle of the invention: The present invention improves PHB by adding low molecular weight compounds. The addition of plasticizers can reduce the glass transition temperature (T g ) and average melting temperature (Tm ), which is beneficial to the thermal processing of materials and reduces thermal degradation. At the same time, plasticizers are inserted between polymer segments, expanding the distance between polymers, improving processing performance, and making the material more tough and flexible.

[0021] Beneficial effects: Compared with the prior art, the present invention has achieved the following significant effects: (1) The present invention uses lactic acid, diethylene glycol monomethyl ether and cinnamic acid as main raw materials, and chemically modifies lactic acid through a two-step esterification reaction. The diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate plasticizer prepared by this method has low viscosity, light yellow and transparent color, and good compatibility with PHA; compared with DOP and ATBC used in PHA, the plasticizer of the present invention has better plasticizing ability and can reduce the melting point T of PHA. m and glass transition temperature T g (2) The addition of the plasticizer of the present invention can increase the elongation at break of PHA and broaden its application scenarios. (3) The diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate plasticizers are all made of biomass raw materials and have good biocompatibility and biodegradability. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The infrared spectra of the raw materials and products of Example 1 are shown below:

[0023] Figure 2 This is a thermogravimetric test diagram of three plasticizer samples in Example 1;

[0024] Figure 3 1. Thermogravimetric test diagram of three plasticized PHB samples and pure PHB for application implementation. DETAILED DESCRIPTION

[0025] The present invention is described in further detail below.

[0026] Example 1

[0027] (1) First step esterification reaction: lactic acid, diethylene glycol monomethyl ether and catalyst p-toluenesulfonic acid are added to a reactor and heated to react; the molar ratio of the raw materials lactic acid and diethylene glycol monomethyl ether is 1:2, the mass of the catalyst is 0.5% of the total mass of the raw materials, heated to 120°C, and reacted for 2 hours; after the reaction is completed, washed with deionized water to neutrality, and then vacuum distilled at -0.1 MPa and 70°C for 2 hours to remove residual water and ethyl acetate to obtain diethylene glycol monomethyl ether-oligomeric lactate;

[0028] (2) Second step esterification reaction: add the diethylene glycol monomethyl ether-oligomeric lactate, cinnamic acid and catalyst strong acid cation exchange resin prepared in step (1) into a reactor and conduct heating reaction, wherein the molar ratio of diethylene glycol monomethyl ether-oligomeric lactate and cinnamic acid is 1:2, the mass of the catalyst is 20 parts of the molar mass of cinnamic acid, the model of the strong acid cation exchange resin is 001X 7 (732), manufacturer: Fuchen Chemical; the heating reaction temperature is 160°C, and the reaction is carried out for 12 hours; after the reaction is completed, the crude product is first extracted with ethyl acetate, washed with saturated sodium bicarbonate solution and deionized water to neutrality, and then vacuum distilled at -0.1 MPa and 70°C for 2 hours to remove residual water and ethyl acetate to obtain diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamic ester.

[0029] Example 2

[0030] (1) First step esterification reaction: lactic acid, diethylene glycol monomethyl ether and catalyst p-toluenesulfonic acid are added to a reactor and heated to react; the molar ratio of raw materials lactic acid and diethylene glycol monomethyl ether is 1:2.5, the mass of the catalyst is 0.5% of the total mass of the raw materials, heated to 130°C, and reacted for 3 hours; after the reaction is completed, washed with deionized water to neutrality, and then vacuum distilled at -0.1 MPa and 80°C for 2 hours to remove residual water and ethyl acetate to obtain diethylene glycol monomethyl ether-oligomeric lactate;

[0031] (2) Second step esterification reaction: add the diethylene glycol monomethyl ether-oligomeric lactate prepared in step (1), cinnamic acid and catalyst strong acidic cation exchange resin into a reactor and carry out heating reaction; the molar ratio of diethylene glycol monomethyl ether-oligomeric lactate to cinnamic acid is 1:2.5, the mass of the catalyst is 25 parts of the molar mass of cinnamic acid, heat to 170°C, and react for 14 hours; after the reaction is completed, the crude reaction product is first extracted with ethyl acetate, washed with saturated sodium bicarbonate solution and deionized water until neutral, and then vacuum distilled at -0.1 MPa and 80°C for 2 hours to remove residual water and ethyl acetate to obtain diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamic acid.

[0032] Example 3

[0033] (1) First step esterification reaction: lactic acid, diethylene glycol monomethyl ether and catalyst p-toluenesulfonic acid are added to a reactor and heated to react; the molar ratio of raw materials lactic acid and diethylene glycol monomethyl ether is 1:3, the mass of the catalyst is 0.5% of the total mass of the raw materials, heated to 140°C, and reacted for 3 hours; after the reaction is completed, washed with deionized water to neutrality, and then vacuum distilled at -0.1 MPa and 80°C for 2 hours to remove residual water and ethyl acetate to obtain diethylene glycol monomethyl ether-oligomeric lactate;

[0034] (2) Second step esterification reaction: add the diethylene glycol monomethyl ether-oligomeric lactate prepared in step (1), cinnamic acid and catalyst strong acidic cation exchange resin into a reactor and carry out heating reaction; the molar ratio of diethylene glycol monomethyl ether-oligomeric lactate and cinnamic acid is 1:3, the mass of the catalyst is 30 parts of the molar mass of cinnamic acid, heat to 180°C, and react for 16 hours; after the reaction, extract the crude product with ethyl acetate, wash it with saturated sodium bicarbonate solution and deionized water until it is neutral, and then vacuum distill at -0.1 MPa and 80°C for 2 hours to remove residual water and ethyl acetate to obtain diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamic acid.

[0035] Example 4

[0036] The first step of the esterification reaction is as follows: lactic acid, diethylene glycol monomethyl ether and a catalyst, p-toluenesulfonic acid, are added to a reactor for a heating reaction; the molar ratio of the raw materials, lactic acid and diethylene glycol monomethyl ether, is 1:2, the mass of the catalyst is 0.5% of the total mass of the raw materials, the reaction is heated to 100° C., and the reaction is carried out for 2 hours; after the reaction is completed, the mixture is washed with deionized water until neutral, and then vacuum distilled at -0.1 MPa and 70° C. for 2 hours to remove residual water and ethyl acetate to obtain diethylene glycol monomethyl ether-oligomeric lactate; the obtained diethylene glycol monomethyl ether-oligomeric lactate is tested for an acid value, and the acid value is too high, which will affect the second step of the esterification reaction and the final product, so the second step reaction is no longer carried out.

[0037] The raw materials lactic acid, cinnamic acid and product diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate in Example 1 were subjected to infrared spectrum test. The test results are as follows: Figure 1 shown.

[0038] Figure 1 From the top to the bottom, 1, 2, 3 and 4 are lactic acid, cinnamic acid, diethylene glycol monomethyl ether and the product diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate. From the infrared results, it can be seen that after the two-step esterification reaction, the product diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate CLDE is at 3100-3010cm -1 -C=CH stretching vibration peaks appeared in the range of 1641 and 1575 cm -1 The stretching vibration of -C=C- skeleton on benzene ring and 769cm -1 The deformation vibration peak of the single-substituted CH on the benzene ring is at 3421 cm. -1 No peak was detected at , indicating that there were no hydroxyl-containing substances in the product, and further indicating that the hydroxyl groups of lactic acid had been completely reacted. In summary, it can be considered that the final product, diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate, was successfully synthesized.

[0039] The thermogravimetric test was performed on the diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate CLDE and the comparative plasticizers ATBC and DOP in Example 1. The specific thermogravimetric results are as follows: Figure 2 As shown;

[0040] Figure 2 In the figure, curves 1, 2, and 3 are the thermogravimetric curves of plasticizers DOP, ATBC, and CLDE, respectively. As can be seen from the figure, compared with plasticizers DOP and ATBC, the initial decomposition temperature T i The highest temperature was approximately 247.5°C, indicating that the diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate CLDE prepared by the present invention possesses excellent thermal stability. The thermal stability of a plasticizer is related to its molecular structure and molecular weight. The CLDE prepared by the present invention is a small-molecule oligomer with a molecular weight much higher than that of the comparative plasticizers DOP and ATBC, thus exhibiting excellent thermal stability during the programmed temperature rise process.

[0041] Application Example 1

[0042] 3 g of PHB and 0.45 g of diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate prepared in Example 1 were dissolved in 100 mL of water, refluxed for 1 hour, cooled, and cast into a glass dish. After chloroform evaporation, the sample was dried for 2 days to prepare the sample. The obtained PHB sample was subjected to thermogravimetric and tensile tests.

[0043] Comparative Example 1

[0044] The DOP plasticizer in the prior art was used in the same steps as in Application Example 1 to prepare PHB comparative sample 1.

[0045] Comparative Example 2

[0046] The ATBC plasticizer in the prior art was prepared using the same steps as in Application Example 1 to obtain PHB comparative sample 2.

[0047] The PHB sample prepared by the product of the present invention in Application Example 1 and the two PHB comparative samples obtained were subjected to thermogravimetric testing. The specific thermogravimetric results are as follows: Figure 3 As shown in the figure, curves 1, 2, 3 and 4 are the thermogravimetric curves of ATBC plasticization, DOP plasticization, pure PHB and diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate CLDE plasticization respectively. As can be seen from the figure, after adding 10 parts (0.45g) of plasticizer DOP and ATBC to PHB, the initial decomposition temperature T iOn the contrary, it decreased. This may be due to the poor stability of the plasticizer itself, which causes the plasticized PHB sample to decompose at relatively low temperatures. However, the diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamate CLDE prepared by the product of the present invention has good thermal stability and can play a certain role in delaying the thermal degradation of PHB. It can also increase the decomposition temperature of the plasticized PHB material to a certain extent, expanding the processing temperature range of the plasticized material.

Claims

1. A bio-based oligomeric lactate plasticizer, characterized in that: Its structural formula is shown below: Wherein, n is the number of lactic acid repeating units.

2. A method for preparing the oligomeric lactate bio-based plasticizer according to claim 1, characterized in that: The following steps are involved: (1) adding diethylene glycol monomethyl ether, lactic acid and a catalyst into a reactor and heating the reactor for reaction; after the reaction is completed, extracting the crude product, washing it to neutrality, and removing the solvent by rotary evaporation to obtain diethylene glycol monomethyl ether-oligomeric lactate; (2) adding diethylene glycol monomethyl ether-oligomeric lactic acid ester, cinnamic acid and a catalyst into a reactor and heating the reactor for reaction; after the reaction is completed, extracting the crude product, washing it to neutrality, and then removing the solvent by rotary evaporation to obtain diethylene glycol monomethyl ether-oligomeric lactic acid-cinnamic acid ester.

3. The method for preparing the oligomeric lactate bio-based plasticizer according to claim 2, characterized in that: In step (1), the catalyst is p-toluenesulfonic acid, and the mass of the catalyst is 0.4% to 0.6% of the total mass of the raw materials.

4. The method for preparing the oligomeric lactate bio-based plasticizer according to claim 2, characterized in that: In step (1), the molar ratio of diethylene glycol monomethyl ether to lactic acid is 1:2-3.

5. The method for preparing the oligomeric lactate bio-based plasticizer according to claim 2, characterized in that: In step (2), the catalyst is a strongly acidic cation exchange resin, and the mass of the catalyst is 20-30% of the molar mass of cinnamic acid.

6. The method for preparing the oligomeric lactate bio-based plasticizer according to claim 2, characterized in that: In step (2), the molar ratio of diethylene glycol monomethyl ether-oligomeric lactate to cinnamic acid is 1:2-3.

7. The method for preparing the oligomeric lactate bio-based plasticizer according to claim 2, characterized in that: In step (1), the mixture is heated to 120-160° C. and reacted for 2-4 hours.

8. The method for preparing the oligomeric lactate bio-based plasticizer according to claim 2, characterized in that: In step (2), the mixture is heated to 160-200° C. and reacted for 12-16 hours.

9. The method for preparing the oligomeric lactate bio-based plasticizer according to claim 2, characterized in that: The vacuum degree of the rotary evaporation in step (1) is -0.1 MPa, and the distillation is carried out at 70-90° C. for 0.5-2 h; the vacuum degree of the rotary evaporation in step (2) is -0.1 MPa, and the distillation is carried out at 70-90° C. for 0.5-2 h.

10. Use of the oligomeric lactate bio-based plasticizer according to claim 1 in the preparation of polyhydroxyalkanoate (PHA) and poly 3-hydroxybutyrate (PHB).

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