Flame-retardant polylactic acid containing vanillin-based flame retardant and preparation method thereof

Abstract

The present invention belongs to the technical field of polymer materials, and specifically discloses a flame-retardant polylactic acid containing a vanillin-based flame retardant and a preparation method thereof. The flame-retardant polylactic acid is composed of 93.5 to 99 parts of polylactic acid, 0.5 to 6 parts of a vanillin-based flame retardant, and 0.5 parts of an antioxidant, in parts by weight. The bio-based flame retardant used in the present invention has a Schiff base structure and phosphorus elements, and has high flame retardant efficiency. The main raw material vanillin used in the synthesis of the vanillin-based flame retardant is renewable and easily available, and the production process is simple, which is in line with the sustainable development trend of materials. The prepared vanillin-based flame retardant not only has high flame retardant efficiency, but also can achieve the purpose of flame retardancy with a small amount of addition. In addition, the preparation process is non-toxic and environmentally friendly, which can effectively alleviate the burden of flame retardants on resources and the environment during synthesis and application.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials and specifically discloses a flame retardant polylactic acid containing a vanillin-based flame retardant and a preparation method thereof. Background Art

[0002] With increasing attention to environmental protection and energy issues, bio-based materials have garnered widespread attention. Furthermore, the development of bio-based polymers can reduce carbon emissions and contribute to the achievement of the "dual carbon goals." Polylactic acid (PLA), a key bio-based polymer, has been widely used in medicine, engineering, packaging, and other fields due to its excellent mechanical properties, biodegradability, and renewable raw material sources.

[0003] In recent years, PLA has seen increasing adoption in electronics, automotive, textiles, and other fields, placing higher demands on its flame retardancy. Directly adding flame retardants is one of the simplest and most effective methods for improving PLA's flame retardancy. However, traditional flame retardants for polymer materials are mostly halogenated and inorganic, which suffer from environmental concerns, require high dosages, and rely on petroleum resources. Therefore, bio-based phosphorus-containing flame retardants, known for their environmental friendliness and high efficiency, are currently a hot topic in flame retardant research.

[0004] Lignin is a natural polyphenol macromolecule, second only to cellulose in its storage in nature, and is considered to be the only biomass source with the potential to obtain phenolic compounds on a large scale. Industrial lignin mainly comes from wastewater from the paper and pulp industry and by-products of bioethanol production, most of which are used as fuel or directly discharged. The structural composition of lignin is complex and changes with changes in biomass sources, production areas, extraction processes, etc., making it difficult to ensure the stability of its composition and quality, which limits the effective utilization of lignin. However, due to the maturity and commercial use of the process for preparing vanillin from lignin, vanillin, as the only industrialized monophenol compound product derived from lignin, has received increasing attention in the field of bio-based flame-retardant polymer materials. However, vanillin itself lacks flame-retardant elements, and the flame-retardant effect of direct use is limited, making it difficult to meet the flame-retardant requirements of the material. At the same time, the thermal stability of vanillin is poor, and the initial degradation temperature (T 5％ ) Only 151℃ is difficult to meet the processing requirements of polymer materials, especially polylactic acid. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of traditional flame retardants' dependence on petrochemical resources, low flame retardant efficiency, environmental pollution, and harm to human health, and to make fuller use of vanillin, a commercial product derived from lignin. On this basis, a Schiff base structure and phosphorus element are introduced to obtain a vanillin-based flame retardant, which is effectively used to flame-retard polylactic acid, thereby obtaining a flame-retardant polylactic acid material containing a high-efficiency vanillin-based flame retardant, thereby realizing the full bio-based nature of the flame-retardant polylactic acid material.

[0006] In order to achieve the above purpose, the flame retardant polylactic acid material containing a high-efficiency vanillin-based flame retardant provided by the present invention has the following formula components by weight: 93.5 to 99 parts of polylactic acid, 0.5 to 6 parts of a high-efficiency vanillin-based flame retardant, and 0.5 part of an antioxidant.

[0007] The vanillin-based flame retardant used has the following structure as shown in the following formula:

[0008]

[0009] Where R is

[0010] n is 1, 3 or 5.

[0011] The preparation method of the vanillin-based flame retardant of the present invention comprises the following steps:

[0012] (1) Vanillin was added to a reactor containing anhydrous ethanol equipped with a reflux condenser and a stirrer, and magnetic stirring was applied until it was completely dissolved. Then, an aliphatic diamine was added and reacted at room temperature for 30 hours. The product was washed, filtered, and dried to obtain an intermediate product (VS) containing a Schiff base structure.

[0013] wherein the aliphatic diamine is ethylenediamine, hexamethylenediamine or decanediamine, and the molar ratio of vanillin to the diamine is 2.1:1;

[0014] (2) The intermediate product is then added to a reaction bottle containing N'N-dimethylformamide and magnetically stirred at room temperature until it is completely dissolved. Triethylamine is added, and then diphenoxyphosphoryl chloride or diphenylphosphoryl chloride is slowly added dropwise in an ice bath at 0-5°C. The addition is completed within 1 hour, and then the mixture is reacted at room temperature for 21 hours. The mixture is then filtered, rotary evaporated, washed, and dried to obtain a vanillin-based flame retardant containing a Schiff base structure and phosphorus element.

[0015] The molar ratio of the intermediate (VS), diphenoxyphosphoryl chloride or diphenylphosphoryl chloride and triethylamine is 1:2.1:2.2.

[0016] The present invention also provides a method for preparing a flame-retardant polylactic acid material containing a high-efficiency vanillin-based flame retardant: first, the vanillin-based flame retardant, antioxidant 1010 and polylactic acid are mixed in proportion, and then melt-blended in an internal mixer to obtain a flame-retardant polylactic acid material containing a high-efficiency vanillin-based flame retardant.

[0017] Compared with the existing technology, the present invention has the following advantages: the flame-retardant polylactic acid material containing a high-efficiency vanillin-based flame retardant prepared by the present invention has good flame retardant properties, the bio-based flame retardant used has a Schiff base structure and phosphorus element, and has high flame retardant efficiency, and the main raw material vanillin used to synthesize the vanillin-based flame retardant is renewable and easily available, the production process is simple, and it is easy to industrialize and produce, which is in line with the sustainable development trend of materials.

[0018] The vanillin-based flame retardant used in the present invention is derived from the commercial product vanillin derived from lignin. It is easily available and renewable, and can meet the sustainable development of materials. In addition, the bio-based monomer with a Schiff base structure on the flame retardant has little effect on the thermal stability of the base resin. When applied to polymers, it not only has very high flame retardant efficiency, but also can achieve the flame retardant purpose with a small amount of addition. In addition, the preparation process is non-toxic and environmentally friendly, which can effectively alleviate the burden of the flame retardant on resources and the environment during synthesis and application, and fully meets the conditions for processing and production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 IR spectra of vanillin, the flame retardant intermediate prepared in Example 1 of the present invention, and the vanillin-based flame retardant;

[0020] Figure 2 The thermogravimetric curves of vanillin, the flame retardant intermediate prepared in Example 1 of the present invention, and the vanillin-based flame retardant in a nitrogen atmosphere. DETAILED DESCRIPTION

[0021] The following examples further illustrate the present invention but do not limit its scope. The polylactic acid used in the following examples was Nature Works 4032D; antioxidant 1010 was purchased from Henan Wanshan New Materials Technology Co., Ltd.; vanillin and ethylenediamine, the main raw materials for the flame retardant, were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; diphenoxyphosphoryl chloride was purchased from Shanghai Lingfeng Chemical Reagent Co., Ltd.; hexanediamine was purchased from Shanghai Ruidong Chemical Co., Ltd.; decanediamine was purchased from Shanghai Gaoming Chemical Co., Ltd.; and triethylamine was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0022] Attachment Figure 1 The infrared spectra of vanillin, the flame retardant intermediate prepared in Example 1 of the present invention, and the vanillin-based flame retardant are shown in FIG. As shown in the figure, compared with vanillin, the flame retardant intermediate has a higher infrared spectroscopy value at 1667 cm -1 The characteristic absorption peak of C=O in the aldehyde group disappeared, while the peak at 1633cm -1 A new characteristic absorption peak appears at 3419 cm, which corresponds to the C=N stretching vibration peak. Compared with the flame retardant intermediate, the vanillin-based flame retardant has a peak at 3419 cm -1The characteristic absorption peak corresponding to phenolic hydroxyl group disappeared, and at the same time, the peaks at 1283m -1 and 1087cm -1 New characteristic absorption peaks appeared at 950cm -1 The characteristic absorption peak of POC also appeared, which shows that the vanillin-based flame retardant was successfully prepared.

[0023] Attachment Figure 2 Table 1 shows the thermal gravimetric loss curves of vanillin, the flame retardant intermediate prepared in Example 1 of the present invention, and the vanillin-based flame retardant in a nitrogen atmosphere. The relevant important thermal degradation parameters are shown in Table 1. As shown in Table 1, compared with vanillin, the vanillin-based flame retardant and the flame retardant intermediate have higher thermal stability and higher carbon residue, which can meet the processing requirements. At the same time, the temperature corresponding to the first maximum thermal degradation rate of the vanillin-based flame retardant (T max1 ) is significantly higher than that of vanillin and flame retardant intermediates, which is inseparable from its unique structural composition.

[0024] Table 1 Important thermal degradation parameter data of vanillin, flame retardant intermediates and vanillin-based flame retardants in nitrogen atmosphere

[0025]

[0026] Examples 1-5

[0027] According to the formula in Table 2, the vanillin-based flame retardant (VSEB or VSHB), antioxidant 1010, and polylactic acid (PLA) were first mixed uniformly in proportion, and then melt-blended in an internal mixer with the mixing temperature set to 180°C and the speed set to 30 r / min to obtain a flame-retardant polylactic acid material containing a high-efficiency vanillin-based flame retardant.

[0028] Among them, taking ethylenediamine as an example, the preparation method of vanillin-based flame retardant is:

[0029] First, 0.0210 mol of vanillin was added to a reactor equipped with a reflux condenser and a stirrer containing 25 mL of anhydrous ethanol and magnetically stirred until it was completely dissolved. Then, 0.0100 mol of ethylenediamine was added and reacted at room temperature for 30 hours. The product was washed, filtered and dried to obtain an intermediate product (VS) containing a Schiff base structure. Then, 0.00895 mol of the intermediate product was added to a reaction bottle containing 15 mL of N'N-dimethylformamide and magnetically stirred at room temperature until it was completely dissolved. 0.0199 mol of triethylamine was added, and then 0.0197 mol of diphenoxyphosphoryl chloride was slowly added dropwise in an ice bath at 0-5°C within 1 hour. The mixture was then reacted at room temperature for 21 hours. The mixture was then filtered, rotary evaporated, washed, and dried to obtain a vanillin-based flame retardant containing a Schiff base structure and phosphorus element.

[0030] The preparation method of the vanillin-based flame retardant (VSHB) obtained by using 0.0100 mol of hexamethylenediamine as the diamine is the same as above.

[0031] The flame retardant performance test results of the obtained flame retardant polylactic acid material containing vanillin-based flame retardant are shown in Table 2.

[0032] Comparative Example 1

[0033] According to the formula in Table 2, antioxidant 1010 and polylactic acid (PLA) were first mixed uniformly according to the proportion, and then melt-blended in an internal mixer to obtain pure polylactic acid material.

[0034] The flame retardant performance test results of the obtained pure polylactic acid material are shown in Table 2.

[0035] Comparative Example 2

[0036] According to the formula in Table 2, the lignin-based flame retardant, antioxidant 1010 and polylactic acid (PLA) were first mixed uniformly in proportion, and then melt-blended in an internal mixer to obtain a flame-retardant polylactic acid material containing a high-efficiency vanillin-based flame retardant.

[0037] The preparation method of the lignin-based flame retardant is as follows:

[0038] 18.0 g of hydroxymethylated lignin was dispersed in 150 mL of toluene solution in a 250 mL three-necked flask and ultrasonically dispersed for 1 hour. 36 mL of silane coupling agent KH540 was added, and the mixture was slowly heated to 110°C with mechanical stirring and refluxed for 16 hours. After the reaction, the mixture was cooled to room temperature, filtered, washed, and vacuum-dried to constant weight to obtain the intermediate Lig-NH2. Next, 18.0 g of Lig-NH2 was dispersed in 150 mL of toluene solution, and 3.8 g of 4-(diethylamino)salicylaldehyde was added. The mixture was ultrasonically dispersed for 1 hour, heated to 110°C, and refluxed for 16 hours. After the reaction, the mixture was washed and dried to obtain the intermediate NLig. Finally, 18.0 g of NLig and 3.5 g of DOPO were dispersed in 150 mL of anhydrous ethanol and refluxed at 50°C for 10 hours. After the reaction, the mixture was filtered, washed, and dried to obtain the target product, a lignin-based flame retardant.

[0039] The flame retardant performance test results of the obtained flame retardant polylactic acid material containing lignin-based flame retardant are shown in Table 2.

[0040] Comparative Example 3

[0041] According to the formula in Table 2, the lignin-based flame retardant, antioxidant 1010 and polylactic acid (PLA) were first mixed uniformly in proportion, and then melt-blended in an internal mixer to obtain a flame-retardant polylactic acid material containing a high-efficiency vanillin-based flame retardant.

[0042] The preparation method of the lignin-based flame retardant is the same as the preparation method of the flame retardant in Comparative Example 2.

[0043] The flame retardant performance test results of the obtained flame retardant polylactic acid material containing lignin-based flame retardant are shown in Table 2.

[0044] Table 2 Flame retardant polylactic acid formula and flame retardant performance test results

[0045]

[0046] Note: NR---No level

[0047] As can be seen from the flame retardant performance test results in Table 2, after the addition of vanillin-based flame retardants (VSEB, VSHB), that is, Examples 1 to 5, the flame retardant properties of the flame-retardant polylactic acid are significantly improved, and with the increase in the addition amount, the limiting oxygen index (LOI) value continues to increase. When the VSEB addition amount is 6%, the LOI value can reach 31.5%, and the U-94 vertical combustion reaches the V-0 level. In particular, the limiting oxygen index is significantly better than that of Comparative Example 3 (PLA / 20FRLig). In addition, when the VSEB addition amount is only 0.5%, the limiting oxygen index of the flame-retardant polylactic acid (PLA / 0.5VSEB) is increased by 6 values ​​compared with Comparative Example 1 (PLA0), and the UL-94 vertical combustion is increased from NR to V-2 level. At the same time, it is significantly higher than that of Comparative Example 2 (PLA / 10FRLig), which has an LOI value of only 23.0%.

[0048] It can be seen that the vanillin-based flame retardant prepared by the present invention can be effectively used for flame-retarding polylactic acid, and has good application prospects in the field of flame-retardant polylactic acid.

Claims

1. A flame-retardant polylactic acid containing a vanillin-based flame retardant, characterized in that: The flame retardant polylactic acid containing a vanillin-based flame retardant is composed of 93.5 to 99 parts of polylactic acid, 0.5 to 6 parts of a vanillin-based flame retardant, and 0.5 parts of an antioxidant in parts by weight. The vanillin-based flame retardant has a structure shown in the following formula: Where R is n is 1, 3 or 5.

2. The flame retardant polylactic acid containing a vanillin-based flame retardant according to claim 1, characterized in that: The preparation method of the vanillin-based flame retardant comprises the following steps: (1) Vanillin was added to a reactor containing anhydrous ethanol equipped with a reflux condenser and a stirrer, and magnetic stirring was applied until it was completely dissolved. Then, an aliphatic diamine was added and reacted at room temperature for 30 h. The product was washed, filtered, and dried to obtain an intermediate product VS containing a Schiff base structure; (2) The intermediate product is added to a reaction bottle containing N'N-dimethylformamide, and magnetic stirring is performed at room temperature until it is completely dissolved. Triethylamine is added, and then diphenoxyphosphoryl chloride or diphenylphosphoryl chloride is added dropwise in an ice bath at 0-5°C. The addition is completed within 1 hour, and then the mixture is reacted at room temperature for 21 hours. The mixture is then filtered, rotary evaporated, washed, and dried to obtain a vanillin-based flame retardant containing a Schiff base structure and phosphorus element.

3. The flame retardant polylactic acid containing a vanillin-based flame retardant according to claim 2, characterized in that: In step (1), the aliphatic diamine is ethylenediamine, hexamethylenediamine or decanediamine.

4. The flame retardant polylactic acid containing a vanillin-based flame retardant according to claim 2, characterized in that: In step (1), the molar ratio of vanillin to diamine is 2.1:

1.

5. The flame retardant polylactic acid containing a vanillin-based flame retardant according to claim 2, characterized in that: In step (2), the molar ratio of the intermediate (VS), diphenoxyphosphoryl chloride or diphenylphosphoryl chloride and triethylamine is 1:2.1:2.

2.

6. A method for preparing flame-retardant polylactic acid containing a vanillin-based flame retardant according to claim 1, characterized in that: The preparation method comprises the following steps: mixing a vanillin-based flame retardant, an antioxidant 1010 and polylactic acid according to parts by mass, and then melt-blending the mixture in an internal mixer to obtain flame-retardant polylactic acid containing the vanillin-based flame retardant.

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