Salicylate plasticizer as well as preparation method and application thereof

Abstract

The invention relates to a salicylate plasticizer and a preparation method and application thereof in the field of bio-based materials, according to the salicylate plasticizer, a flexible alkyl chain and multiple ester groups are introduced to a bio-based compound salicylic acid through esterification reaction and acylation reaction in sequence, salicylate is synthesized, the salicylate has good compatibility with polylactic acid, and the compatibility between the salicylate and polylactic acid is improved. When the salicylate plasticizer is used as a polylactic acid plasticizer, a good plasticizing effect can be generated, and an obtained polylactic acid product has good toughness, thermal stability and migration resistance, so that the salicylate plasticizer can be used as a plasticizer to be applied to 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 polymer material that is both bio-based and biodegradable. It has excellent biocompatibility, mechanical strength and processing properties, but its poor ductility and crystallization ability limit the use of its products. Therefore, a large number of researchers are currently focusing on toughening and modifying PLA to expand the application range of PLA. Blending with plasticizers is currently a relatively efficient modification method for PLA, which can greatly improve the ductility and impact resistance of PLA, thereby obtaining a PLA-based material with excellent toughness.

[0003] Plasticizer is a major additive in the plastic processing industry. Its main function is to add plastic to plastic to increase its plasticity. After adding plasticizer to polymer materials, it can reduce its melt viscosity, glass transition temperature and elastic modulus without changing the basic chemical properties of polymer materials, thereby improving its processability and improving the softness and tensile properties of products. For a long time, plasticizers have been mainly phthalate products, but due to their defects such as easy migration and physiological toxicity, they have been banned in many fields. Therefore, it has become a current trend to use biomass raw materials to develop new, efficient, environmentally friendly, and non-toxic bio-based plasticizers to replace phthalate plasticizers.

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

[0005]

[0006] Its molecular structure contains a hydroxyl group, a carboxyl group and an aromatic ring. The hydroxyl group and the carboxyl group are easy to modify and transform into esters. The ester structure can ensure that the plasticizer has good compatibility with the PLA resin. At the same time, its large benzene ring structure can also significantly improve the anti-migration ability of the plasticizer. Therefore, it is a worthy research direction to use salicylic acid to synthesize polylactic acid plasticizers with excellent comprehensive performance. At present, there is no related report on the modification of salicylic acid as a PLA plasticizer. Summary of the invention

[0007] The invention provides a salicylate plasticizer, a preparation method and use thereof. The salicylate plasticizer is obtained by modifying and optimizing the molecular structure of salicylic acid, thereby improving the plasticizing effect and enabling it to be used 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] Where R is -C4H9, -C6H 13 or -C8H 17 , its structural formula corresponds to the following:

[0011]

[0012] The 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 with a fatty alcohol through an esterification reaction to obtain a salicylate intermediate; and then reacts with acetoxyacetyl chloride through an acylation reaction to obtain a salicylate plasticizer.

[0013] The fatty alcohol used is isobutyl alcohol, 2-ethylbutyl alcohol 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, and then a water-carrying agent is added, and the temperature is raised to 150°C for reflux reaction for 10 to 15 hours. The water generated during the reaction is discharged from the system along with the water-carrying agent by azeotropy. When the reaction system no longer produces water, it is cooled to room temperature, and a solvent is added for extraction. The system is washed with alkali solution to a weak alkalinity, and then washed with water to neutrality, and distilled under reduced pressure to obtain a salicylate intermediate.

[0016] 2) Acylation reaction: Add the salicylate intermediate obtained in step 1) and acetoxyacetyl chloride into a reactor, and react at 0-40° C. for 1-3 hours under an inert atmosphere. After the reaction, add a solvent, wash with alkali solution to weak alkalinity, wash with water to neutrality, and distill 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 fatty alcohol undergo a dehydration esterification reaction under the action of a catalyst, and the generated byproduct water is discharged from the system with the water-carrying agent in an azeotropic manner, thereby promoting the reaction equilibrium to move in the positive direction, and finally obtaining 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 a byproduct of hydrogen chloride, and finally obtaining a salicylate plasticizer. The reaction order of the esterification reaction and the acylation reaction of the present invention cannot be interchanged, because: the acylation reaction is carried out first, which easily leads to a side reaction between the acyl chloride and the carboxylic acid to produce 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 has made the above-mentioned limitation on fatty alcohols, and the salicylic acid ester obtained by modifying the above-mentioned preferred fatty alcohols has a flexible alkyl chain of moderate length. If the alkyl chain is too long, on the one hand, it is not conducive to its compatibility with the polylactic acid resin, and on the other hand, during the synthesis process, the too long alkyl chain will cause greater steric hindrance, affecting the subsequent acylation reaction.

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

[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 salicylic acid ester environmentally friendly plasticizer with moderate viscosity through esterification reaction and acyl chloride reaction, thereby reducing the use of petroleum-based materials.

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

[0030] (3) The relatively large benzene ring structure can significantly improve the anti-migration ability of the plasticizer in polylactic acid resin. Salicylic acid ester 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 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 in conjunction with 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, add 10 g (72 mmol) of salicylic acid, 13.02 g (100 mmol) of 2-ethylhexanol, 0.86 g (7.2 mmol) of sodium hydrogen sulfate, add 250 ml of n-hexane as a water-carrying agent, heat to 100°C, and reflux to react until the system no longer generates new water. The reaction system is naturally cooled to room temperature, added with a solvent for extraction, washed with a sodium hydroxide solution to alkalinity, and then washed with deionized water to neutrality, and 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, salicylic acid intermediate, and salicylic acid ester in Example 1. In the spectra of salicylic acid and salicylic acid intermediate, 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 stretching vibration of OH, while the salicylic acid intermediate -1 The absorption peak at 1790cm is the stretching vibration of the methylene group, indicating that the carboxylic acid on salicylic acid was successfully esterified to synthesize the salicylic acid ester intermediate. In the spectrum of salicylic acid ester, the phenolic hydroxyl signal peak disappeared, and the peak at 1790cm -1 、1750cm -1 and 1720cm -1 There are three carbonyl stretching vibration peaks on the left and right, which indicates that the hydroxyl group has been successfully acylated, proving that salicylate plasticizer 1 has been 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, and 250 ml of n-hexane was added as a water-carrying agent. The temperature was raised to 100° C., and refluxed to react until no new water was generated in the system. The reaction system was naturally cooled to room temperature, and a solvent was added for extraction. The system was washed with a sodium hydroxide solution until alkaline, and 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, a condenser and a thermometer, add 10 g (72 mmol) of salicylic acid, 16 g (216 mmol) of isobutyl alcohol, 0.305 g (3.6 mmol) of phosphoric acid, add 250 ml of n-hexane as a water-carrying agent, heat to 100°C, and reflux to react until the system no longer generates new water. The reaction system is naturally cooled to room temperature, added with a solvent for extraction, washed with a sodium hydroxide solution to alkalinity, and then washed with deionized water to neutrality, 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 min, and the reaction was carried out at 25° C. for 2 h. 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 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 into an injection molding machine, and injection molding was performed at 200° C. and 60 MPa injection pressure, and the pressure was maintained for 2 min 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 into an injection molding machine for injection molding at 220°C and 60MPa 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 table 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 with the pure PLA sample of comparative example 1 which exhibits brittleness, the tensile properties of application examples 1 and 2 plasticized by salicylate plasticizer 1 have not been significantly improved. The reason is that the free volume between the PLA molecular chains cannot be expanded to the extent that its chain segments can move freely when the plasticizer content is low, while in application examples 3 and 4 samples with increased plasticizer content, the free volume of the PLA chain segments reaches the extent of free movement, so the elongation at break of the samples is significantly increased, and the plasticizing effect is better than comparative examples 4 and 5 of salicylic acid in the same proportion, which shows that the salicylate plasticizer 1 can not only produce a substantial good plasticizing effect on PLA, greatly improve the tensile properties of the PLA sample, but also has better compatibility with PLA than salicylic acid. Therefore, the preferred content of salicylate plasticizer in PLA is 15-20wt%.

[0087] Secondly, in Application Examples 4-6, the molecular weight and molecular volume of salicylate plasticizer 1 are greater than those of salicylate plasticizer 2 and salicylate plasticizer 3. Under the same proportion, salicylate plasticizer 1 can give the PLA molecular chain more free volume, and the effect of enhancing the mobility of the PLA molecular chain 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 is as follows Figure 3 As shown. Figure 3 It can be seen that when the samples were stored in an oven at 70°C for 24 hours and 48 hours, the mass loss rate of the PLA sample plasticized by salicylate plasticizer 1 was obviously lower than that of the PLA sample plasticized by salicylic acid, which shows that the salicylate plasticizer has strong volatility resistance and stability in PLA resin, and can maintain stability without exudation at higher temperatures, which is better than salicylic acid. Secondly, in application examples 4-6, the molecular weight of salicylate plasticizer 1 is greater than that of salicylate plasticizer 2 and salicylate plasticizer 3, and has higher thermal stability. Therefore, under the same proportion, the mass loss rate of application example 4 is lower than that of application examples 5 and 6, indicating that the volatility resistance and stability of salicylate plasticizer 1 in PLA resin are better than those of salicylate plasticizers 2 and 3.

[0089] The above shows and describes the basic principles and main features of the present invention and the 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 only for explaining the principles of the present invention. Without departing from the technical principles and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A salicylate plasticizer, characterized in that: The structural formula is as follows: Where 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, characterized in that: Salicylic acid is used as a raw material, and firstly reacts with fatty alcohol through esterification to obtain a salicylate intermediate; and then reacts with acetoxyacetyl chloride through acylation to obtain a salicylate plasticizer; the fatty alcohol is isobutyl alcohol, 2-ethylbutanol or 2-ethylhexanol.

3. The method for preparing a salicylate plasticizer according to claim 2, characterized in that The steps include: 1) Esterification reaction: salicylic acid, fatty alcohol, and catalyst are added to a reactor, and then a water-carrying agent is added, and the temperature is raised to 100-150° C. and refluxed for reaction for 10-15 hours. The water generated during the reaction is discharged from the system by azeotropy with the water-carrying agent. When the reaction system no longer generates water, it is cooled to room temperature, and a solvent is added for extraction. The system is washed with alkali solution until alkaline, and then washed with water until neutral, and distilled under reduced pressure to obtain a salicylate intermediate; 2) Acylation reaction: Add the salicylate intermediate obtained in step 1) and acetoxyacetyl chloride into a reactor, react at 0-40° C. for 1-3 hours under an inert atmosphere, add a solvent after the reaction, wash with alkali solution to weak alkalinity, wash with water to neutrality, and distill under reduced pressure to obtain a salicylate plasticizer.

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

9. The method for preparing a salicylate plasticizer according to claim 3, characterized in that: 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: 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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