A salicylate plasticizer, its preparation method and use

Abstract

The present invention relates to a salicylate plasticizer in the field of bio-based materials, a preparation method and use thereof. The salicylate plasticizer is synthesized by introducing a flexible alkyl chain and multiple ester groups into a bio-based compound salicylic acid through an esterification reaction and an acylation reaction. The salicylate plasticizer has good compatibility with polylactic acid and can be used as a polylactic acid plasticizer to produce a good plasticizing effect. The obtained polylactic acid product has good toughness, thermal stability and migration resistance, so that the salicylate plasticizer can be used as a plasticizer in the production of PLA plastic products.

Description

Technical Field

[0001] The present invention relates to the field of bio-based materials, and in particular to a salicylate plasticizer and a preparation method and application thereof. Background Art

[0002] Polylactic acid (PLA) is a biodegradable and biobased polymer with excellent biocompatibility, mechanical strength, and processability. However, its poor ductility and crystallization ability limit its use in products. Consequently, numerous researchers are currently focusing on toughening PLA to expand its applications. Blending with plasticizers is currently a relatively effective modification method for PLA, significantly improving its ductility and impact resistance, thereby yielding PLA-based materials with excellent toughness.

[0003] Plasticizers are a key additive in the plastics processing industry, primarily used to increase plasticity. When added to polymer materials, plasticizers can reduce their melt viscosity, glass transition temperature, and modulus of elasticity without altering the basic chemical properties of the polymer, thereby improving processability and enhancing the softness and tensile properties of the finished product. Phthalate esters have long been the primary plasticizer, but due to their inherent mobility and physiological toxicity, they have been banned in many applications. Therefore, the development of new, highly efficient, environmentally friendly, and non-toxic bio-based plasticizers using biomass feedstock to replace phthalate esters has become a trend.

[0004] Salicylic acid is an aromatic monomer found in willow bark, gaultheria sinensis leaves, and sweet birch trees. It is widely used in the pharmaceutical, pesticide, rubber, dye, food, and fragrance industries. It is one of the few renewable resources among aromatic compounds, which ensures the green and sustainable development of salicylic acid. The structural formula of salicylic acid is shown below:

[0005]

[0006] Its molecular structure consists of a hydroxyl group, a carboxyl group, and an aromatic ring. The hydroxyl and carboxyl groups are easily modified to form esters. The ester structure ensures good compatibility between the plasticizer and PLA resin. Furthermore, the larger benzene ring structure significantly enhances the plasticizer's anti-migration ability. Therefore, using salicylic acid to synthesize polylactic acid plasticizers with excellent overall properties is a worthy research direction. Currently, there are no reports on the modification of salicylic acid for use as a PLA plasticizer. Summary of the Invention

[0007] The present invention provides a salicylate plasticizer, a preparation method, and uses thereof. The salicylate plasticizer is obtained by modifying and optimizing the molecular structure of salicylic acid, thereby improving the plasticizing effect and enabling its application as a plasticizer in the production of PLA plastic products.

[0008] To this end, one of the objects of the present invention is to provide a salicylate plasticizer, the structural formula of which is as follows:

[0009]

[0010] Among them, R is -C4H9, -C6H 13 or -C8H 17 , its structural formula corresponds to the following:

[0011]

[0012] A second object of the present invention is to provide a method for preparing the above-mentioned salicylate plasticizer, which uses salicylic acid as a raw material, first reacts it with a fatty alcohol through an esterification reaction to obtain a salicylate intermediate; and then reacts it with acetoxyacetyl chloride through an acylation reaction to obtain the salicylate plasticizer.

[0013] The fatty alcohol used is isobutanol, 2-ethylbutanol or 2-ethylhexanol.

[0014] The specific steps are as follows:

[0015] 1) Esterification reaction: salicylic acid, fatty alcohol, and catalyst are added to a reactor, followed by a water-carrying agent. The temperature is raised to 150°C and refluxed for 10-15 hours. Water generated during the reaction is azeotropically discharged from the system along with the water-carrying agent. When the reaction system no longer produces water, the reaction is cooled to room temperature, extracted with a solvent, washed with alkali solution to a weak alkaline state, then washed with water to neutrality, and distilled under reduced pressure to obtain a salicylate intermediate.

[0016] 2) Acylation reaction: The salicylate intermediate obtained in step 1) and acetoxyacetyl chloride are added to a reactor, and reacted at 0-40° C. for 1-3 hours under an inert atmosphere. After the reaction, a solvent is added, and the mixture is washed with alkali solution to a weak alkaline state, washed with water to a neutral state, and distilled under reduced pressure to obtain a salicylate plasticizer.

[0017] The synthesis principle of the preparation method of the present invention is as follows: in the esterification reaction, the carboxyl group of salicylic acid and the hydroxyl group of a fatty alcohol undergo a dehydration esterification reaction under the action of a catalyst. The generated byproduct, water, is azeotropically discharged from the system along with the water-carrying agent, thereby promoting the reaction equilibrium to shift in the positive direction, ultimately producing a salicylate intermediate. In the acylation reaction, the phenolic hydroxyl group of the salicylate intermediate undergoes an acylation reaction with the acyl chloride group of acetoxyacetyl chloride to form an ester group and the byproduct, hydrogen chloride, ultimately producing a salicylate plasticizer. The order of the esterification and acylation reactions in the present invention cannot be reversed because performing the acylation reaction first tends to cause a side reaction between the acyl chloride and the carboxylic acid, resulting in the production of anhydride.

[0018] Preferably, in step 1), the molar ratio of salicylic acid, fatty alcohol and catalyst is 1:(1-3):(0.05-0.1).

[0019] Preferably, in step 2), the molar ratio of the salicylate intermediate to acetoxyacetyl chloride is 1:(1-2).

[0020] Preferably, in step 1), the water-carrying agent is one or more of benzene, toluene and n-hexane.

[0021] Preferably, in step 1), the amount of the water-carrying agent added is 10 to 15 times the total mass of salicylic acid, fatty alcohol and catalyst.

[0022] Preferably, in step 1), the catalyst is one or more of phosphoric acid, sulfuric acid, p-toluenesulfonic acid and sodium bisulfate.

[0023] Preferably, in step 1) and step 2), the alkali solution is one or more of sodium carbonate solution, sodium bicarbonate solution and sodium hydroxide solution.

[0024] Preferably, in step 2), the solvent is one or more of toluene, benzene, dichloromethane and ethyl acetate.

[0025] The present invention defines the fatty alcohols as defined above. The salicylate obtained by modifying the preferred fatty alcohols described above has a flexible alkyl chain of moderate length. Excessively long alkyl chains, on the one hand, compromise compatibility with the polylactic acid resin, and on the other hand, create significant steric hindrance during the synthesis process, hindering the subsequent acylation reaction.

[0026] The third object of the present invention is to provide the use of the above-mentioned salicylate plasticizer in the preparation of PLA plastic products, wherein the content of the salicylate plasticizer is preferably 15-20 wt%.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention uses the bio-based compound salicylic acid as the main raw material, and synthesizes a light yellow oily salicylate environmentally friendly plasticizer with moderate viscosity through esterification reaction and chlorination reaction, thereby reducing the use of petroleum-based materials.

[0029] (2) Multiple ester groups are introduced into the molecular structure of the salicylate, so it can have good compatibility with polylactic acid resin when used as a polylactic acid plasticizer.

[0030] (3) The larger benzene ring structure can significantly improve the anti-migration ability of the plasticizer in polylactic acid resin. Salicylate also has a flexible alkyl chain of moderate length, which can further improve its plasticizing properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the infrared spectrum of salicylic acid, salicylate intermediate and salicylate plasticizer in Example 1.

[0032] Figure 2 Graph of the tensile properties of PLA specimens after adding salicylic acid and salicylic acid plasticizer to PLA resin.

[0033] Figure 3 Mass loss curve of PLA sample when salicylic acid and salicylic acid plasticizer are added to PLA resin. DETAILED DESCRIPTION

[0034] In order to make the technical means, objectives and effects of the present invention easier to understand, the present invention is further described below with reference to embodiments.

[0035] Example 1

[0036] Preparation of salicylate plasticizer 1

[0037] (1) In a three-necked flask equipped with a water separator, a condenser, and a thermometer, 10 g (72 mmol) of salicylic acid, 13.02 g (100 mmol) of 2-ethylhexanol, and 0.86 g (7.2 mmol) of sodium bisulfate were added, and 250 ml of n-hexane was added as a water-carrying agent. The temperature was raised to 100°C and refluxed until no new water was generated. The reaction system was naturally cooled to room temperature, extracted with a solvent, washed with sodium hydroxide solution until alkaline, and then washed with deionized water until neutral. The mixture was distilled under reduced pressure to obtain a salicylate intermediate.

[0038] (2) The salicylate intermediate and acetoxyacetyl chloride were added to a reactor at a molar ratio of 1:2, nitrogen was introduced for 10 minutes, and the reaction was carried out at 25°C for 2 hours. After the reaction, toluene was added, and the solvent was washed with sodium hydroxide solution to a weak alkaline state, and then washed with deionized water to a neutral state, and then distilled under reduced pressure to obtain salicylate plasticizer 1.

[0039] Figure 1 The infrared spectra of salicylic acid, salicylate intermediate and salicylate in Example 1 are shown in FIG. In the spectra of salicylic acid and salicylic acid intermediate, the infrared spectra at 1670 cm -1 The absorption peak that appears is the stretching vibration of the carbonyl group (C=O), and the curve is at 3700-3100cm -1 The broad absorption peak at 722 cm represents the OH stretching vibration, while the salicylic acid intermediate -1 The absorption peak at 1790 cm is the stretching vibration of methylene, indicating that the carboxylic acid on salicylic acid has been successfully esterified to synthesize salicylate intermediate. In the spectrum of salicylate, the phenolic hydroxyl signal peak disappears, and the peak at 1790 cm -1 、1750cm -1 and 1720cm -1 Three carbonyl stretching vibration peaks appeared on the left and right, indicating that the hydroxyl group was successfully acylated, proving that salicylate plasticizer 1 was successfully synthesized.

[0040] Example 2

[0041] Preparation of salicylate plasticizer 2

[0042] (1) In a three-necked flask equipped with a water separator, a condenser, and a thermometer, 10 g (72 mmol) of salicylic acid, 7.36 g (72 mmol) of 2-ethylbutanol, and 0.71 g (7.2 mmol) of sulfuric acid were added, along with 250 ml of n-hexane as a water carrier. The temperature was raised to 100°C, and the mixture was refluxed to react until no new water was generated. The reaction system was naturally cooled to room temperature, extracted with a solvent, and washed with sodium hydroxide solution until alkaline, then washed with deionized water until neutral, and distilled under reduced pressure to obtain a salicylate intermediate.

[0043] (2) The salicylate intermediate and acetoxyacetyl chloride were added to a reactor at a molar ratio of 1:1.5, nitrogen was introduced for 10 minutes, and the reaction was carried out at 25°C for 2 hours. After the reaction, toluene was added, and the solvent was washed with sodium hydroxide solution to a weak alkaline state, and then washed with deionized water to a neutral state, and then distilled under reduced pressure to obtain salicylate plasticizer 2.

[0044] Example 3

[0045] Preparation of salicylate plasticizer 3

[0046] (1) In a three-necked flask equipped with a water separator, condenser, and thermometer, add 10 g (72 mmol) of salicylic acid, 16 g (216 mmol) of isobutanol, and 0.305 g (3.6 mmol) of phosphoric acid. Add 250 ml of n-hexane as a water carrier, heat to 100°C, and reflux until no new water is generated. The reaction system is cooled naturally to room temperature, extracted with a solvent, washed with sodium hydroxide solution until alkaline, then washed with deionized water until neutral, and distilled under reduced pressure to obtain a salicylate intermediate.

[0047] (2) The salicylate intermediate and acetoxyacetyl chloride were added to a reactor at a molar ratio of 1:1, nitrogen was introduced for 10 minutes, and the reaction was carried out at 25°C for 2 hours. After the reaction, toluene was added, and the solvent was washed with sodium hydroxide solution to a weak alkaline state, and then washed with deionized water to a neutral state. The mixture was distilled under reduced pressure to obtain salicylate plasticizer 3.

[0048] Application Example 1

[0049] (1) Salicylate plasticizer 1 was added to PLA resin at a ratio of 5 wt %, and the mixture was blended in an internal mixer at 180° C. and 60 rpm for 6 min to obtain a PLA blend, which was then used for volatility testing.

[0050] (2) The blend obtained in step (1) was added to an injection molding machine, and injection molding was performed at 200°C and an injection pressure of 60 MPa, and the pressure was maintained for 2 minutes to obtain a standard PLA specimen for performance testing.

[0051] Application Example 2

[0052] (1) Salicylate plasticizer 1 was added to PLA resin at a ratio of 10 wt %, and the mixture was blended in an internal mixer at 180° C. and 60 rpm for 6 min to obtain a PLA blend, which was then used for volatility testing.

[0053] (2) This step is the same as step (2) of Application Example 1.

[0054] Application Example 3

[0055] (1) Salicylate plasticizer 1 was added to PLA resin at a ratio of 15 wt %, and the mixture was blended in an internal mixer at 180° C. and 60 rpm for 6 min to obtain a PLA blend, which was then used for volatility testing.

[0056] (2) This step is the same as step (2) of Application Example 1.

[0057] Application Example 4

[0058] (1) Salicylate plasticizer 1 was added to PLA resin at a ratio of 20 wt %, and the mixture was blended in an internal mixer at 180° C. and 60 rpm for 6 min to obtain a PLA blend, which was then used for volatility testing.

[0059] (2) This step is the same as step (2) of Application Example 1.

[0060] Application Example 5

[0061] (1) Salicylate plasticizer 2 was added to PLA resin at a ratio of 20 wt %, and the mixture was blended in an internal mixer at 180° C. and 60 rpm for 6 min to obtain a PLA blend, which was then used for volatility testing.

[0062] (2) This step is the same as step (2) of Application Example 1.

[0063] Application Example 6

[0064] (1) Salicylate plasticizer 3 was added to PLA resin at a ratio of 20 wt %, and the mixture was blended in an internal mixer at 180° C. and 60 rpm for 6 min to obtain a PLA blend, which was then used for volatility testing.

[0065] (2) This step is the same as step (2) of Application Example 1.

[0066] Comparative Example 1

[0067] The pure PLA resin in the application example was used for thermal performance testing and added to an injection molding machine. Injection molding was performed at 220°C and 60 MPa injection pressure, and the pressure was maintained for 2 minutes to obtain a standard specimen for performance testing.

[0068] Comparative Example 2

[0069] (1) Salicylic acid was added to PLA resin at a ratio of 5 wt %, and the mixture was blended in an internal mixer at 180° C. and 60 rpm for 6 min to obtain a PLA blend, which was then used for volatility testing.

[0070] (2) This step is the same as step (2) of Application Example 1.

[0071] Comparative Example 3

[0072] (1) Salicylic acid was added to PLA resin at a ratio of 10 wt %, and the mixture was blended in an internal mixer at 180° C. and 60 rpm for 6 min to obtain a PLA blend, which was then used for volatility testing.

[0073] (2) This step is the same as step (2) of Application Example 1.

[0074] Comparative Example 4

[0075] (1) Salicylic acid was added to PLA resin at a ratio of 15 wt %, and the mixture was blended in an internal mixer at 180° C. and 60 rpm for 6 min to obtain a PLA blend, which was then used for volatility testing.

[0076] (2) This step is the same as step (2) of Application Example 1.

[0077] Comparative Example 5

[0078] (1) Salicylic acid was added to PLA resin at a ratio of 20 wt %, and the mixture was blended in an internal mixer at 180° C. and 60 rpm for 6 min to obtain a PLA blend, which was then used for volatility testing.

[0079] (2) This step is the same as step (2) of Application Example 1.

[0080] Performance Testing

[0081] Table 1: Group distribution ratio of each application example and comparative example

[0082]

[0083] Table 2: Test data of various application examples and comparative examples

[0084]

[0085] The mechanical properties of PLA samples are shown in Table 1 and Figure 2 shown.

[0086] First, compared to the brittle pure PLA sample of Comparative Example 1, the tensile properties of Examples 1 and 2 plasticized with salicylate plasticizer 1 did not show significant improvement. This is because the low plasticizer content prevented the free volume between PLA molecular chains from expanding to a level that allowed free movement of the segments. However, in Examples 3 and 4, where the plasticizer content was increased, the free volume of the PLA segments reached a level of free movement, resulting in a significant increase in the elongation at break of these samples. Furthermore, the plasticizing effect was superior to that of Comparative Examples 4 and 5, which used salicylic acid at the same ratio. This demonstrates that salicylate plasticizer 1 not only produces a substantial and positive plasticizing effect on PLA, significantly improving the tensile properties of the PLA samples, but also exhibits superior compatibility with PLA to salicylic acid. Therefore, the preferred content of salicylate plasticizer in PLA is 15-20 wt%.

[0087] Secondly, in Application Examples 4-6, the molecular weight and molecular volume of salicylate plasticizer 1 are both greater than those of salicylate plasticizers 2 and 3. At the same ratio, salicylate plasticizer 1 can provide more free volume to the PLA molecular chains, and the effect of enhancing the mobility of the PLA molecular segments is more significant. Therefore, the elongation at break of the sample in Application Example 4 is greater than that in Application Examples 5 and 6.

[0088] Finally, the volatility resistance test of PLA samples was as follows Figure 3 As shown. Figure 3 As can be seen, after 24 and 48 hours of storage in a 70°C oven, the mass loss rate of the PLA sample plasticized with salicylate plasticizer 1 was significantly lower than that of the PLA sample plasticized with salicylic acid. This demonstrates that this salicylate plasticizer exhibits superior volatility resistance and stability in PLA resin, maintaining stability without exudation at higher temperatures, surpassing salicylic acid. Furthermore, in Application Examples 4-6, salicylate plasticizer 1 has a higher molecular weight than salicylate plasticizers 2 and 3, indicating greater thermal stability. Therefore, under the same ratio, the mass loss rate in Application Example 4 was lower than in Application Examples 5 and 6, indicating that salicylate plasticizer 1 exhibits superior volatility resistance and stability in PLA resin than salicylate plasticizers 2 and 3.

[0089] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and improvements may be made to the present invention without departing from the technical principles and scope of the present invention. Such changes and improvements are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A salicylate plasticizer, characterized in that: The structural formula is as follows: Among them, R is -C4H9, -C6H 13 or -C8H 17 , its structural formula corresponds to the following:

2. The method for preparing a salicylate plasticizer according to claim 1, wherein: Salicylic acid is used as a raw material, and is first reacted with fatty alcohol through an esterification reaction to obtain a salicylate intermediate; then, the salicylate plasticizer is obtained through an acylation reaction with acetoxyacetyl chloride; the fatty alcohol is isobutanol, 2-ethylbutanol or 2-ethylhexanol.

3. The method for preparing a salicylate plasticizer according to claim 2, wherein The steps include: 1) Esterification reaction: salicylic acid, fatty alcohol, and catalyst are added to a reactor, followed by a water-carrying agent. The temperature is raised to 100-150° C. and refluxed for 10-15 hours. Water generated during the reaction is azeotropically discharged from the system along with the water-carrying agent. When the reaction system no longer generates water, the reaction is cooled to room temperature, solvent extraction is added, and the reaction mixture is washed with alkali solution until alkaline, then washed with water until neutral, and distilled under reduced pressure to obtain a salicylate intermediate. 2) Acylation reaction: The salicylate intermediate obtained in step 1) and acetoxyacetyl chloride are added to a reactor and reacted at 0-40° C. for 1-3 hours under an inert atmosphere. After the reaction, a solvent is added, and the mixture is washed with alkali solution to a weak alkaline state, washed with water to a neutral state, and distilled under reduced pressure to obtain a salicylate plasticizer.

4. The method for preparing a salicylate plasticizer according to claim 3, wherein: In step 1), the molar ratio of salicylic acid, fatty alcohol and catalyst is 1:(1-3):(0.05-0.1); In step 2), the molar ratio of the salicylate intermediate to acetoxyacetyl chloride is 1:(1-2).

5. The method for preparing a salicylate plasticizer according to claim 3, wherein: In step 1), the water-carrying agent is one or more of benzene, toluene and n-hexane.

6. The method for preparing a salicylate plasticizer according to claim 4, wherein: In step 1), the amount of the water-carrying agent added is 10 to 15 times the total mass of salicylic acid, fatty alcohol and catalyst.

7. The method for preparing a salicylate plasticizer according to claim 3, wherein: In step 1), the catalyst is one or more of phosphoric acid, sulfuric acid, p-toluenesulfonic acid and sodium bisulfate.

8. The method for preparing a salicylate plasticizer according to claim 3, wherein: In step 1) and step 2), the alkali solution is one or more of sodium carbonate solution, sodium bicarbonate solution and sodium hydroxide solution.

9. The method for preparing a salicylate plasticizer according to claim 3, wherein: In step 2), the solvent is one or more of toluene, benzene, dichloromethane and ethyl acetate.

10. The use of a salicylate plasticizer according to claim 1, characterized in that: When used as a plasticizer in the preparation of PLA plastic products, the content of salicylate plasticizer in PLA is 15-20wt%.

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