Lignin-based charring agent containing silicon and nitrogen flame-retardant elements and imine structure for flame-retardant polylactic acid and preparation method of lignin-based charring agent

Abstract

The invention belongs to the technical field of high polymer materials, and particularly discloses a lignin-based charring agent containing silicon and nitrogen flame-retardant elements and an imine structure for flame-retardant polylactic acid and a preparation method of the lignin-based charring agent. The flame-retardant polylactic acid is prepared from the following components in parts by weight: 90 to 97 parts of polylactic acid, 1 to 3.33 parts of lignin-based charring agent and 2 to 6.67 parts of ammonium polyphosphate. The bio-based charring agent disclosed by the invention contains silicon and nitrogen flame-retardant elements and an imine structure, has remarkable charring and flame-retardant effects, is high in charring capacity, and can endow the PLA with relatively good flame-retardant property by compounding with ammonium polyphosphate and adding 1% of the lignin-based charring agent; the lignin and vanillin which are used as main raw materials for synthesizing the charring agent are bio-based sources and are easy to obtain, the production process is simple, industrial production is easy, the preparation process is non-toxic and environment-friendly, the dependence of charring agent synthesis on petroleum-based raw materials can be effectively relieved, and the sustainable development trend of materials is met.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and specifically discloses a lignin-based charring agent containing silicon and nitrogen flame-retardant elements and imine structures for flame-retardant polylactic acid and a preparation method thereof. BACKGROUND

[0002] With the continuous attention to environmental protection and energy problems of human beings, and the depletion of fossil resources, bio-based materials have received extensive attention. Among them, polylactic acid (PLA) as an important bio-based polymer, is gradually replacing traditional plastics due to its good biodegradability and environmental friendliness. However, the flammability of PLA and the dripping phenomenon during combustion seriously limit its application in the fields of electronic appliances, automobiles and the like. Therefore, it has important research value to modify PLA by flame retardation.

[0003] Directly adding flame retardants in PLA is a simple and effective method to solve the problem. However, most of the traditional flame retardants for high polymer materials are halogen-containing flame retardants and inorganic flame retardants. The former has high flame-retardant efficiency, but is not environmentally friendly. The latter is environmentally friendly and non-toxic, but requires a large amount of addition. Intumescent flame retardant (IFR) is widely used in the field of flame-retardant modification of high polymer materials due to its low toxicity and less smoke. As one of the important components of intumescent flame retardant, charring agent is crucial to the formation of carbon layer during the combustion of materials, and the quality of the carbon layer directly determines the flame-retardant performance of the materials. Among them, bio-based charring agent has a broad application prospect in the field of intumescent flame-retardant high polymer materials due to its renewability and wide source. Lignin, as the second largest biomass next to cellulose, contains a large amount of benzene rings and hydroxymethyl, alcohol hydroxyl and polyphenol hydroxyl functional groups, and has a high carbon content, and is regarded as an ideal natural polymer charring agent. However, lignin hardly chars in air, and a high amount of addition is often required to achieve or meet the flame-retardant requirements of the materials.

[0004] CN 114426678 B reports a lignin-based flame-retardant charring agent and its synthesis method and application. The lignin-based flame-retardant charring agent is prepared by a two-step method. The obtained lignin-based flame-retardant charring agent is compounded with ammonium polyphosphate (APP) for flame-retardant polypropylene. When the mass ratio of the charring agent to APP is 1:1.5, and the total amount of addition needs to reach 30%, the limiting oxygen index value of the obtained flame-retardant polypropylene is between 29.9 and 32%, and the UL-94 vertical combustion is over V-0 level.

[0005] In addition, CN 116715867 B reports a lignin flame retardant and its preparation method and flame-retardant composite material. The lignin flame retardant is prepared by a multi-step synthesis method. The obtained flame retardant can be effectively used for flame-retardant polylactic acid, but the synthesis process is relatively complex, a large amount of organic solvent is used, and a large amount of waste liquid is generated in the post-processing. SUMMARY

[0006] The present application aims to solve the problems of traditional flame retardants, such as dependence on petrochemical resources, environmental pollution, and harm to human health, and provides a preparation method of an environmentally friendly char-forming agent for flame retardant.

[0007] The lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structures has the following structure:

[0008] ,

[0009] The preparation method of the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structures comprises the following steps: adding vanillin and 3-aminopropyltrimethoxysilane into a beaker containing anhydrous ethanol, ultrasonic treatment for 10 min to obtain an intermediate product (VAN-KH540) containing a Schiff base structure, then adding deionized water, ultrasonic treatment for 5 min, then adding lignin and ultrasonic treatment for 1 h, and then placing it in a 105℃ air oven for 12 h to obtain the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structures.

[0010] The molar ratio of vanillin and 3-aminopropyltrimethoxysilane is 1:1, and the mass ratio of lignin and VAN-KH540 is 3:1~1:1.

[0011] The present application also provides a preparation method of flame-retardant polylactic acid containing the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structures, which comprises the following steps: first, uniformly mixing the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structures, ammonium polyphosphate and polylactic acid according to the proportion, and then preparing the flame-retardant polylactic acid containing the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structures through a banbury mixer melt blending.

[0012] The flame-retardant polylactic acid comprises the following components in parts by weight: polylactic acid 90~97 parts, the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structures 1~3.33 parts, and ammonium polyphosphate 2~6.67 parts.

[0013] Compared with the prior art, the present application has the following advantages:

[0014] The lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure prepared by the method has good flame-retardant performance, and the char-forming agent contains silicon, nitrogen flame-retardant elements and imine structure, has significant char-forming and flame-retardant effects, and has strong char-forming capacity. The lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure can be effectively used for preparing flame-retardant polylactic acid in combination with ammonium polyphosphate. The main raw materials lignin and vanillin used for synthesizing the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure are both biobased sources, are easy to obtain, and have simple production process and easy industrial production. The dependence of char-forming agent synthesis on petroleum-based raw materials can be effectively relieved, and the sustainable development trend of materials is met. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The infrared spectrum of the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure prepared in Example 1 of the present application and lignin.

[0016] Figure 2 The thermogravimetric curve of the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure prepared in Example 1 of the present application and lignin in a nitrogen atmosphere. DETAILED DESCRIPTION

[0017] The following examples are further illustrations of the present application and are not intended to limit the scope of the present application. The polylactic acid used in the following examples is 4032D from Nature Works, USA; alkali lignin from Jinan Yanghai Chemical Co., Ltd.; enzymatic lignin from Dalian Petroleum Chemical Research Institute; vanillin and 3-aminopropyltrimethoxysilane are both purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; anhydrous ethanol from Shanghai Lingfeng Chemical Reagent Co., Ltd.; deionized water is self-made in the laboratory; and ammonium polyphosphate is from Jiangmen High-end Chemical Technology Co., Ltd.

[0018] Examples 1-4

[0019] The preparation method of the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure is as follows: 4.61 g (0.0300 mol) of vanillin (VAN) and 5.60 g (0.0301 mol) of 3-aminopropyltrimethoxysilane are added into a 500 mL beaker containing 152 mL of anhydrous ethanol, and ultrasonic treatment is performed for 10 min to obtain an intermediate product (VAN-KH540) containing a Schiff base structure. Then, 8 mL of deionized water is added, and ultrasonic treatment is performed for 5 min. Subsequently, 10.21 g of alkali lignin is added, and ultrasonic treatment is performed for 1 h. The mixture is placed in a 105℃ air oven for 12 h to obtain the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure.

[0020] APPENDIX Figure 1The infrared spectrum of the lignin, the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure prepared in Example 1 of the present application. As can be seen from the figure, compared with the lignin, the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure has similar peaks, in addition, the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure has new characteristic absorption peaks at 1646 cm -1 , 1378 cm -1 and 467 cm -1 , which are respectively C=N stretching vibration absorption peak, C-N stretching vibration absorption peak and Si-O bending vibration absorption peak, and the silicon, nitrogen elements and imine structure are successfully introduced. As can be seen, the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure is successfully prepared.

[0021] The Figure 2 The thermogravimetric curve of the lignin, the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure prepared by the method of the present application in a nitrogen atmosphere, and the relevant important thermal degradation parameters are shown in Table 1. As can be seen from Table 1, compared with the lignin, the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure has higher thermal stability and higher carbon residue, which can meet the processing requirements; at the same time, the temperature (T max1 ) corresponding to the first maximum thermal degradation rate of the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure is lower than that of the lignin, which can degrade in advance to generate a carbon layer to protect the internal material in the flame-retardant polylactic acid.

[0022] Table 1 Important thermal degradation parameter data of lignin and lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure in a nitrogen atmosphere

[0023]

[0024] According to the formula of Table 2, first, the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure (MJL), ammonium polyphosphate (APP) and polylactic acid (PLA) are mixed in proportion and uniformly, and then the flame-retardant polylactic acid material of the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure is prepared by melt blending for 5 min through a banbury mixer (the temperature of the banbury mixer is 180°C, and the rotating speed is 30 r / min).

[0025] The flame-retardant performance test results of the obtained flame-retardant polylactic acid of the lignin-based char-forming agent containing silicon, nitrogen flame-retardant elements and imine structure are shown in Table 2.

[0026] Example 5

[0027] Into a 500 mL beaker containing 152 mL of anhydrous ethanol, 4.61 g (0.0300 mol) of vanillin (VAN) and 5.60 g (0.0301 mol) of 3-aminopropyltrimethoxysilane were added and sonicated for 10 min to obtain an intermediate product containing Schiff base structure (VAN-KH540), then 8 mL of deionized water was added and sonicated for 5 min, followed by the addition of 30.63 g of alkali lignin and sonicated for 1 h and placed in a 105 °C blast oven for 12 h to obtain a lignin-based charring agent containing silicon, nitrogen flame-retardant elements and imine structure.

[0028] Preparation of flame-retardant polylactic acid was the same as in Example 4.

[0029] Example 6

[0030] Into a 500 mL beaker containing 152 mL of anhydrous ethanol, 4.61 g (0.0300 mol) of vanillin (VAN) and 5.60 g (0.0301 mol) of 3-aminopropyltrimethoxysilane were added and sonicated for 10 min to obtain an intermediate product containing Schiff base structure (VAN-KH540), then 8 mL of deionized water was added and sonicated for 5 min, followed by the addition of 30.63 g of alkali lignin and sonicated for 1 h and placed in a 105 °C blast oven for 12 h to obtain a lignin-based charring agent containing silicon, nitrogen flame-retardant elements and imine structure.

[0031] Preparation of flame-retardant polylactic acid was the same as in Example 4.

[0032] Example 7

[0033] Compared with Example 4, the difference is that the type of lignin in Example 4 is changed to enzymatic hydrolysis lignin.

[0034] Comparative Example 1

[0035] According to the formula in Table 2, polylactic acid (PLA) was weighed and then melt blended by an internal mixer to obtain pure polylactic acid, and the flame-retardant performance test results of the obtained polylactic acid are shown in Table 2.

[0036] Comparative Example 2

[0037] According to the formula in Table 2, alkali lignin, ammonium polyphosphate and polylactic acid (PLA) were mixed in proportion and then melt blended by an internal mixer to obtain a lignin-containing flame-retardant polylactic acid material.

[0038] The flame-retardant performance test results of the obtained lignin-containing charring agent flame-retardant polylactic acid are shown in Table 2.

[0039] Comparative Example 3

[0040] According to the formulation in Table 2, first, the lignin-based charring agent, APP and polylactic acid (PLA) are mixed in proportion, and then the lignin-based charring agent-containing flame-retardant polylactic acid is prepared by melt blending through an internal mixer.

[0041] The preparation method of the lignin-based charring agent is as follows:

[0042] 0.8 g of γ-aminopropyltrimethoxysilane was weighed into an ethanol-water (95wt%:5wt%) system, and the solution was about 80 mL; then 8.0 g of dried alkali lignin (Lig) was added to the silane coupling agent solution, and ultrasonic dispersion was performed for 3 h, so that the γ-aminopropyltrimethoxysilane was uniformly coated on the surface of the lignin; the mixture after ultrasonic treatment was placed in a blast oven at 105°C for drying for 12 h. After the reaction was completed, the product was ground into powder and dried to constant weight in a vacuum oven at 80°C to obtain the target product Si-NLig.

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

[0044] Comparative Example 4

[0045] According to the formulation in Table 2, first, the lignin-based charring agent, APP and polylactic acid (PLA) are mixed in proportion, and then the lignin-based charring agent-containing flame-retardant polylactic acid is prepared by melt blending through an internal mixer.

[0046] The preparation method of the lignin-based charring agent is as follows:

[0047] (1) Activation of lignin

[0048] 42.0 g of alkali lignin and 1.8 g of sodium hydroxide solid were weighed, and 23.2 mL of formaldehyde solution was added to the hydrothermal reaction kettle, and after being mixed thoroughly, it was sealed and placed in a blast oven at 100°C for 2 h. After the reaction was completed, it was cooled to room temperature, and the crude product was washed with deionized water, centrifuged, and the above operation was repeated 4 times until the pH value of the upper clear liquid was neutral. The obtained precipitate was placed in a vacuum oven at 80°C and dried to constant weight, and then crushed, ground and sieved through a 100-mesh sieve for use.

[0049] (2) Modification of lignin

[0050] Take 0.8 g of dodecyl trimethoxysilane into an ethanol-water system (95wt%:5wt%) - configured into a silane coupling agent solution, then 8.0 g of activated lignin is added into the above configured silane coupling agent solution, and ultrasonic treatment is carried out in an ultrasonic instrument for 3 h; the mixed solution after ultrasonic treatment is placed in a blast oven at 105℃ for reaction for 12 h. After the reaction is completed, the product is ground into powder, and then placed in a vacuum oven at 60℃ for drying to constant weight to obtain the target product RLig.

[0051] The test results of the flame-retardant properties of the obtained flame-retardant polylactic acid containing the lignin-based charring agent are shown in Table 2.

[0052] Table 2 Formulation of flame-retardant polylactic acid and test results of its flame-retardant properties

[0053]

[0054] Note: NR - no rating

[0055] As can be seen from the test results of the flame-retardant properties in Table 2, after the addition of the lignin-based charring agent (MJL) containing silicon, nitrogen flame-retardant elements and imine structure and ammonium polyphosphate (APP), i.e. Examples 1-4, the flame-retardant properties of the flame-retardant polylactic acid are significantly improved, and with the increase of the addition amount, the limiting oxygen index (LOI) value is continuously increased, wherein when the total addition amount of MJL and APP is 10%, the LOI value can reach 29%, the UL-94 vertical burning reaches V-0 level, and the flame-retardant properties are obviously better than those of Comparative Examples 2, 3 and 4. In addition, under the condition that the total addition amount of MJL and APP is only 5%, the flame-retardant polylactic acid (PLA / 1.67MJL / 3.33APP) can reach the flame-retardant level, the limiting oxygen index value is increased by 6 values compared with Comparative Example 1 (PLA), and the UL-94 vertical burning is increased from NR to V-2 level.

[0056] Therefore, the lignin-based charring agent containing silicon, nitrogen flame-retardant elements and imine structure prepared by the present application can be effectively used for flame-retardant polylactic acid, and has good application prospect in the field of flame-retardant polylactic acid.

Claims

1. A lignin-based charring agent containing silicon, nitrogen flame retardant elements, and an imine structure, characterized in that, The lignin-based charring agent containing silicon, nitrogen flame retardant elements, and an imine structure has the structure shown in the following formula: 。 2. A method for preparing a lignin-based charring agent containing silicon, nitrogen flame retardant elements, and an imine structure according to claim 1, characterized in that, The preparation method is as follows: vanillin and 3-aminopropyltrimethoxysilane are added to a beaker containing anhydrous ethanol and ultrasonically treated for 10 min to obtain intermediate product VAN-KH540. Then deionized water is added and ultrasonicated for 5 min. After that, lignin is added and ultrasonicated for 1 h. Then it is placed in a 105℃ forced-air drying oven for 12 h to obtain lignin-based charring agent.

3. The method for preparing the lignin-based charring agent containing silicon, nitrogen flame retardant elements, and an imine structure according to claim 2, characterized in that, Lignin is either alkali lignin or enzymatically hydrolyzed lignin.

4. The method for preparing the lignin-based charring agent containing silicon, nitrogen flame retardant elements, and an imine structure according to claim 2, characterized in that, The molar ratio of vanillin to 3-aminopropyltrimethoxysilane is 1:

1.

5. The method for preparing the lignin-based charring agent containing silicon, nitrogen flame retardant elements, and an imine structure according to claim 2, characterized in that, The mass ratio of lignin to VAN-KH540 is 3:1 to 1:

1.

6. The application of a lignin-based charring agent containing silicon, nitrogen flame retardant elements, and an imine structure according to claim 1, characterized in that, The lignin-based charring agent is used to prepare flame-retardant polylactic acid.

7. The application of the lignin-based charring agent containing silicon, nitrogen flame retardant elements, and an imine structure according to claim 6, characterized in that, The flame-retardant polylactic acid is composed of the following components by weight: 90-97 parts polylactic acid, 1-3.33 parts lignin-based charring agent containing silicon, nitrogen flame-retardant elements and imine structure, and 2-6.67 parts ammonium polyphosphate.

8. The application of the lignin-based charring agent containing silicon, nitrogen flame retardant elements, and an imine structure according to claim 6, characterized in that, The method for preparing the flame-retardant polylactic acid is as follows: lignin-based charring agent containing silicon, nitrogen flame-retardant elements and imine structure, ammonium polyphosphate and polylactic acid are mixed in parts by mass, and then melt-blended in an internal mixer to obtain flame-retardant polylactic acid.

Images