Preparation and application of a rigid cinnamaldehyde bio-based flame retardant

Abstract

The present invention discloses a rigid cinnamaldehyde bio-based flame retardant and its preparation method and application, using bio-based material cinnamaldehyde and p-aminobenzonitrile to react, and then introducing DOPO to synthesize a rigid cinnamaldehyde bio-based flame retardant PPABCA rich in aromatic ring structure, and applied to the preparation of flame-retardant epoxy resin composite materials. The advantages of the present invention are: compared with the current commercial flame retardant, which has a high addition amount and deteriorates the mechanical properties of epoxy resin composite materials, PPABCA only needs to add 1wt% to make the epoxy resin composite material have a limiting oxygen index of 29.2%; only 3wt% needs to be added to make it reach the UL‑94V‑0 level vertical combustion rating and 31.4% limiting oxygen index, while obtaining 11.2% and 13.8% tensile and bending strength improvement; and when PPABCA is further added to reach 5wt%, its flame retardant performance and mechanical properties will be further improved. The flame retardant provided by the present invention is based on bio-based materials, is green and environmentally friendly, has a low addition amount, is highly flame-retardant and can improve the mechanical properties of epoxy resin composite materials.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant polymers, and specifically relates to a rigid cinnamaldehyde bio-based flame retardant and a preparation method and application thereof. Background Art

[0002] Epoxy resin (EP) is one of the most widely used thermosetting resins. Due to its excellent physical, mechanical and electrical insulation properties, adhesion to various materials, and flexibility in its use process, it has been widely used in coatings, composite materials, castings, adhesives, electronic packaging, and aerospace. However, the flammability of epoxy resin limits its further application, so improving the flame retardant properties of epoxy resin has become a research hotspot.

[0003] With the massive consumption of coal and oil resources, as well as the emission of polluting waste gas, global resource shortage and environmental pollution have become the bottleneck of sustainable development. Developing clean energy and reducing environmental pollution has become a global consensus, and the international community has begun to vigorously promote the use of renewable resources. Therefore, the research on flame retardant epoxy resins tends to be halogen-free, highly flame retardant, environmentally friendly and renewable. Many researchers have begun to pay attention to green and environmental issues throughout the life cycle of flame retardant epoxy resins, such as the use of renewable bio-based raw materials, environmentally friendly methods in the manufacturing process, and the degradability or reusability of products.

[0004] The patent document with application publication number CN115594714A discloses "a green preparation method and application of bio-based flame retardants based on phytic acid", in which a type of biomass material containing flame retardant elements such as phosphorus and nitrogen is prepared using phytic acid as raw material, overcoming the defects of halogen flame retardants in terms of greenness and environmental protection. However, its preparation process is relatively complicated and risky, and it is not suitable for expanded production. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0007] One of the purposes of the present invention is to provide a method for preparing a rigid cinnamaldehyde bio-based flame retardant. The rigid cinnamaldehyde bio-based flame retardant of the present invention is a flame retardant rich in phosphorus and nitrogen elements based on bio-based materials, has excellent flame retardant effect, and the preparation process is relatively simple and environmentally friendly.

[0008] In order to solve the above technical problems, the present invention provides the following technical solution: a rigid cinnamaldehyde bio-based flame retardant PPABCA, whose chemical structure is shown in Formula I:

[0009]

[0010] Another object of the present invention is to provide a method for preparing an epoxy resin composite material containing the rigid cinnamaldehyde bio-based flame retardant PPABCA, comprising:

[0011] (1) First, cinnamaldehyde is dissolved in anhydrous ethanol under a nitrogen atmosphere, and then p-aminobenzonitrile is added and stirred under a nitrogen atmosphere for reaction at a stirring temperature of 75 to 85° C. for a stirring time of 2 to 3 h;

[0012] (2) adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to the above solution under a nitrogen atmosphere and continuing to stir the reaction at a temperature of 80 to 90° C. for 2 to 3 h, then vacuum filtering, washing and drying to obtain an intermediate product;

[0013] (3) dissolving the intermediate product obtained in step (2) in glacial acetic acid, then adding DOPO and stirring the reaction at a stirring temperature of 105 to 115° C. for 4 to 6 hours;

[0014] (4) using a solvent precipitation method to precipitate and centrifuge the solution after the reaction in step (3) to obtain a crude product;

[0015] (5) The crude product in step (4) is added into ethanol for purification, and then vacuum filtered, washed and dried to obtain the final product, rigid cinnamaldehyde bio-based flame retardant PPABCA.

[0016] Preferably, in the step (1), the mass volume ratio of cinnamaldehyde to anhydrous ethanol is 1.4-2.8 g:100-150 mL; the mass volume ratio of p-aminobenzonitrile to cinnamaldehyde is 1.2-2.4:1.3-2.6.

[0017] Preferably, in step (2), the mass ratio of DOPO to cinnamaldehyde is 2.2-4.4:1.3-2.6.

[0018] Preferably, in step (3), the mass volume ratio of the intermediate product to glacial acetic acid is 4.5-8.9 g:150-200 mL; the mass ratio of DOPO to the intermediate product is 4.3-8.6:4.5-8.9.

[0019] Preferably, the precipitant used in step (4) is deionized water and the volume ratio of the precipitant to the solution after the reaction is 100-150:100-150.

[0020] (6) Grind and sieve the rigid cinnamaldehyde bio-based flame retardant PPABCA, add it to the epoxy resin and stir it evenly, then add the curing agent and stir it until it is evenly mixed, and cure it to obtain a flame-retardant epoxy resin composite material.

[0021] Preferably, the curing agent in step (6) includes one of 4,4-diaminodiphenylmethane, 4,4-diaminodiphenyl ether, ethylenediamine, dicyandiamide, and diaminodiphenyl sulfone.

[0022] Preferably, the mass ratio of the epoxy resin, the curing agent and the rigid cinnamaldehyde bio-based flame retardant PPABCA in step (6) is 90-110:24-26:5-7.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention provides a rigid cinnamaldehyde bio-based flame retardant PPABCA, the structural formula of which is shown in Formula I, and the structure contains a DOPO structure and a nitrogen element, and the synergistic flame retardant effect of phosphorus and nitrogen during combustion makes it have an excellent flame retardant effect. In addition, the raw material of the rigid cinnamaldehyde bio-based flame retardant of the present invention is renewable, halogen-free, non-toxic, green and environmentally friendly. Compared with pure epoxy resin, the epoxy resin composite material prepared by using the rigid cinnamaldehyde bio-based flame retardant PPABCA synthesized by the present invention has stronger mechanical properties due to the rich rigid aromatic ring structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the following briefly introduces the drawings required for describing the embodiment, wherein:

[0026] Figure 1 This is a reaction flow chart of the rigid cinnamaldehyde bio-based flame retardant PPABCA prepared in Example 1 of the present invention.

[0027] Figure 2 This is a Fourier transform infrared spectrum of the rigid cinnamaldehyde bio-based flame retardant PPABCA prepared in Example 1 of the present invention; wherein, sample 1 is cinnamaldehyde; sample 2 is p-aminobenzonitrile; sample 3 is 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; sample 4 is the intermediate product prepared in Example 1; sample 5 is the rigid cinnamaldehyde bio-based flame retardant PPABCA prepared in Example 1.

[0028] Figure 3 This is a comparison chart of the mechanical property test results of the epoxy resin composite material prepared with the rigid cinnamaldehyde bio-based flame retardant PPABCA obtained in Examples 2 to 5 of the present invention and the pure epoxy resin obtained in Comparative Example 1. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0031] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0032] Unless otherwise specified, the raw materials used in the examples were purchased commercially.

[0033] The technical solution adopted by the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0034] Example 1

[0035] The preparation of rigid cinnamaldehyde bio-based flame retardant PPABCA specifically includes the following steps:

[0036] (1) dissolving 2.64 g of cinnamaldehyde in 200 mL of anhydrous ethanol to obtain solution A;

[0037] (2) Subsequently, 2.36 g of p-aminobenzonitrile was added to solution A in a nitrogen atmosphere under mechanical stirring at 85° C. for 3 h to obtain solution B;

[0038] (3) Add 4.32 g of DOPO to solution B and stir at 80° C. for 3 h to obtain solution C;

[0039] (4) Filtering and washing the solution C to obtain powder D;

[0040] (5) Powder D was dried at 75°C for 5 h to obtain 7.28 g of an intermediate product with a yield of 81.3%;

[0041] (6) Dissolve 3.24 g of DOPO in 200 mL of glacial acetic acid to obtain solution E;

[0042] (7) 4.48 g of the intermediate product was added to solution E and stirred at 110° C. for 3 h to obtain solution F;

[0043] (8) After solution F is cooled to room temperature, 100 mL of deionized water is added as a precipitant to solution F for stirring and precipitation. The stirring time is 10 min to obtain solution G;

[0044] (9) Centrifuging, washing, and filtering the solution G to obtain powder H;

[0045] (10) drying the powder H at 75 °C for 5 h to obtain 5.72 g of rigid cinnamaldehyde bio-based flame retardant PPABCA with a yield of 86.1%;

[0046] The chemical structural formula of the rigid cinnamaldehyde bio-based flame retardant PPABCA obtained in Example 1 is:

[0047]

[0048] Figure 2 The infrared spectra of cinnamaldehyde, p-aminobenzonitrile, DOPO, intermediates and rigid cinnamaldehyde bio-based flame retardant PPABCA, 2212 cm -1 The characteristic peaks at 3477 and 3371 cm are the stretching vibrations of the C≡N bond of p-aminobenzonitrile and the rigid cinnamaldehyde bio-based flame retardant PPABCA. -1 The characteristic peak at 1681 cm is the stretching vibration of -NH2. -1 The characteristic peak at 3270 cm is the stretching vibration of C=O, while the intermediate product and the rigid cinnamaldehyde bio-based flame retardant PPABCA have a peak at 3270 cm -1 The shallow absorption band at 1681cm is the stretching vibration of NH, indicating that -CHO and -NH2 are involved in the reaction. -1 The characteristic peaks at 1232 and 905 cm-1 are the stretching vibrations of the C=C bond of the intermediate product. The intermediate product and the rigid cinnamaldehyde bio-based flame retardant PPABCA have the peaks at 1232 and 905 cm-1. -1 The peaks at 2815cm correspond to the stretching vibrations of P=O and POC respectively. The biggest feature of the infrared spectrum of flame retardant rigid cinnamaldehyde bio-based flame retardant PPABCA is that the C=CH bond corresponds to 2815cm -1 and C=C corresponding bond 905cm -1 The disappearance of the characteristic peak at 2428 cm indicates that the intermediate product is completely converted into the rigid cinnamaldehyde bio-based flame retardant PPABCA. -1 The characteristic peak at 786 cm-1 disappears and corresponds to the PC bond -1 The appearance of the characteristic peak at indicates that the reaction with DOPO is successful. The above results show that the rigid cinnamaldehyde bio-based flame retardant PPABCA is successfully synthesized in the present invention.

[0049] Example 2

[0050] This embodiment provides a preparation process of an epoxy resin composite material containing a rigid cinnamaldehyde bio-based flame retardant PPABCA, which specifically includes the following steps:

[0051] 5.0 g of the rigid cinnamaldehyde bio-based flame retardant PPABCA in Example 1 after passing through a 200-mesh sieve was added to 76.0 g of epoxy resin, and the mixture was stirred for 20 min in a 70° C. water bath, and then 19.0 g of 4,4-diaminodiphenylmethane was added. The mixture was stirred for 10 min, and then vacuum degassed. Finally, the mixture was poured into a standard-sized polytetrafluoroethylene mold coated with silicone oil, placed in an oven at 120° C. for curing for 4 h, and then cooled and demolded to obtain an epoxy resin composite material containing a rigid cinnamaldehyde bio-based flame retardant PPABCA, which was marked as 5PPABCA / EP.

[0052] Example 3

[0053] This embodiment provides a preparation process of an epoxy resin composite material containing a rigid cinnamaldehyde bio-based flame retardant PPABCA, which specifically includes the following steps:

[0054] 1.0 g of the rigid cinnamaldehyde bio-based flame retardant PPABCA in Example 1 after passing through a 200-mesh sieve was added to 79.2 g of epoxy resin, and the mixture was stirred for 20 min in a 70° C. water bath, and then 19.8 g of 4,4-diaminodiphenylmethane was added. The mixture was stirred for 10 min, and then vacuum degassed. Finally, the mixture was poured into a standard-sized polytetrafluoroethylene mold coated with silicone oil, placed in an oven at 120° C. for curing for 4 h, and then cooled and demolded to obtain an epoxy resin composite material containing a rigid cinnamaldehyde bio-based flame retardant PPABCA, which was marked as 1PPABCA / EP.

[0055] Example 4

[0056] This embodiment provides a preparation process of an epoxy resin composite material containing a rigid cinnamaldehyde bio-based flame retardant PPABCA, which specifically includes the following steps:

[0057] 3.0 g of the rigid cinnamaldehyde bio-based flame retardant PPABCA in Example 1 after passing through a 200-mesh sieve was added to 77.6 g of epoxy resin, and the mixture was stirred for 20 min in a 70° C. water bath, and then 19.4 g of 4,4-diaminodiphenylmethane was added. The mixture was stirred for 10 min, and then vacuum degassed. Finally, the mixture was poured into a standard-sized polytetrafluoroethylene mold coated with silicone oil, placed in an oven at 120° C. for curing for 4 h, and then cooled and demolded to obtain an epoxy resin composite material containing a rigid cinnamaldehyde bio-based flame retardant PPABCA, which was marked as 3PPABCA / EP.

[0058] Example 5

[0059] This embodiment provides a preparation process of a composite material of epoxy resin containing a rigid cinnamaldehyde bio-based flame retardant PPABCA, which specifically includes the following steps:

[0060] 10.0 g of the rigid cinnamaldehyde bio-based flame retardant PPABCA in Example 1 after passing through a 200-mesh sieve was added to 72.0 g of epoxy resin, and the mixture was stirred for 20 min in a 70° C. water bath, and then 18.0 g of 4,4-diaminodiphenylmethane was added. The mixture was stirred for 10 min, and then vacuum degassed. Finally, the mixture was poured into a standard-sized polytetrafluoroethylene mold coated with silicone oil, placed in an oven at 120° C. for curing for 4 h, and then cooled and demolded to obtain an epoxy resin composite material containing a rigid cinnamaldehyde bio-based flame retardant PPABCA, which was marked as 10PPABCA / EP.

[0061] Comparative Example 1

[0062] For comparison, pure epoxy resin without rigid cinnamaldehyde bio-based flame retardant PPABCA was prepared, and the specific steps are as follows:

[0063] Add 20.0 g of 4,4-diaminodiphenylmethane to 80.0 g of epoxy resin, stir under heating in a 70°C water bath for 10 min, then pour the mixture into a standard-sized polytetrafluoroethylene mold coated with silicone oil, put it into an oven at 120°C for curing for 4 h, cool and demold, and obtain pure epoxy resin, marked as EP.

[0064] Comparative Example 2

[0065] The epoxy resin composite material prepared according to the method disclosed in the literature (DOI: 10.19491 / j.issn.1001-9278.2022.12.005) is marked as CS-ZIF-67 / EP.

[0066] Comparative Example 3

[0067] The epoxy resin composite material prepared according to the method disclosed in the literature (DOI: 10.19491 / j.issn.1001-9278.2023.03.013) is marked as PPAP / Ni-MOF / EP.

[0068] Comparative Example 4

[0069] The epoxy resin composite material prepared according to the method disclosed in the literature (DOI: 10.13650 / j.cnki.rgxsz.2023.02.006) is marked as 6% TAP / EP.

[0070] Comparative Example 5

[0071] The epoxy resin composite material prepared according to the method disclosed in the literature (DOI: 10.13637 / j.issn.1009-6094.2021.0321) is marked as 2PSiCN-8APP / EP.

[0072] Comparative Example 6

[0073] An integrated phytic acid and arginine flame-retardant epoxy resin composite material prepared according to the method disclosed in patent CN110643148A is marked as integrated phytic acid and arginine / EP.

[0074] Comparative Example 7

[0075] The epoxy resin composite material prepared according to the method disclosed in the literature (DOI: 10.16865 / j.cnki.1000-7555.2023.0114) is marked as 15% DOPS-HQ / EP.

[0076] Comparative Example 8

[0077] The epoxy resin composite material prepared according to the method disclosed in the literature (DOI: 10.13759 / j.cnki.dlxb.2023.06.022) is marked as (lignin+piperazine pyrophosphate) composite intumescent flame retardant / EP.

[0078] The flame retardant properties of the epoxy resin composite materials obtained in Examples 2 to 5 and Comparative Example 1 were tested, and compared with the flame retardant properties of the epoxy resin composite materials in Comparative Examples 2 to 8. The limiting oxygen index test method refers to the GB / T2406.2-2009 standard; the UL-94 grade test method refers to the GB / T2408-2021 standard. The oxygen index test specimen size is 120×10×4mm 3 , UL-94 test specimen size is 130×13×3mm 3 The test results are shown in Table 1.

[0079] Table 1 Comparison of limiting oxygen index and UL-94 grade of epoxy resin composite materials in each embodiment and comparison

[0080]

[0081] The present invention uses the synthesized rigid cinnamaldehyde bio-based flame retardant PPABCA to prepare an epoxy resin composite material. Compared with pure epoxy resin (limiting oxygen index of 25.6%), the epoxy resin composite material obtained by the preparation method only needs 1wt% of the addition amount to reach a limiting oxygen index of 29.2%, reaching the flame retardant level, especially when the addition amount is 10wt%, the limiting oxygen index is as high as 35.0%, and the flame retardant performance is the best; the epoxy resin composite material prepared by the method only needs 3wt% of the addition amount to reach the UL-94V-0 vertical combustion level, indicating that the epoxy resin containing the rigid cinnamaldehyde bio-based flame retardant PPABCA prepared by the present invention has excellent flame retardant effect.

[0082] Mechanical properties of the epoxy resin composite materials containing rigid cinnamaldehyde bio-based flame retardant PPABCA obtained in Examples 2 to 5 and the pure epoxy resin obtained in Comparative Example 1 were tested. The bending performance test method was based on the GB / T9341-2008 standard, and the tensile performance test was based on the GB / T 1040-2006 standard. The test results are shown in Figure 2. Figure 3 shown.

[0083] Depend on Figure 3 It can be seen that adding a small amount of rigid cinnamaldehyde bio-based flame retardant PPABCA can improve the mechanical properties of the composite material due to the π-π conjugation effect of the rigid aromatic ring structure and the participation of the cyano and amino groups with micro-reactivity in curing. In particular, when the addition amount is 5wt%, the flexural strength and tensile strength are increased to 132.3 and 74.2MPa, respectively, which are 20.5% and 16.5% higher than those of pure epoxy resin, respectively, and the mechanical properties are the best. However, when the addition amount of rigid cinnamaldehyde bio-based flame retardant PPABCA reaches 10wt%, due to the π-π conjugation and micro-reactive cyano and amino groups have become saturated, excessive addition will reduce the compatibility of the flame retardant in the epoxy resin matrix, resulting in a decrease in mechanical properties.

[0084] Based on the above test results, the preferred addition amount of rigid cinnamaldehyde bio-based flame retardant PPABCA is 3wt%. At this time, the addition amount of flame retardant is low, which can increase the limiting oxygen index of epoxy resin composite material to 31.4%, reaching the flame retardant grade, and obtain the UL-94V-0 vertical burning grade. In addition, the 3wt% addition of PPABCA increases the tensile and flexural strength of epoxy resin composite material by 11.2% and 13.8% respectively, which has both cost-effectiveness and flame retardant efficiency. And according to the actual situation, the addition amount of PPABCA can be further increased to meet the requirements of product performance.

[0085] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A rigid cinnamaldehyde bio-based flame retardant PPABCA, characterized in that: Its chemical structure is shown in Formula I:

2. The method for preparing the rigid cinnamaldehyde bio-based flame retardant according to claim 1, characterized in that: include: (1) firstly dissolving cinnamaldehyde in anhydrous ethanol under a nitrogen atmosphere, then adding p-aminobenzonitrile and stirring to react under a nitrogen atmosphere, the stirring temperature is 75-85° C., the stirring time is 2-3 h, wherein the mass volume ratio of cinnamaldehyde to anhydrous ethanol is 1.4-2.8 g:100-150 mL, and the mass volume ratio of p-aminobenzonitrile to cinnamaldehyde is 1.2-2.4:1.3-2.6; (2) adding 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO to the above solution under nitrogen atmosphere and continuing stirring the reaction at a temperature of 80 to 90° C. for 2 to 3 hours, and then vacuum filtering, washing and drying to obtain an intermediate product, wherein the mass ratio of DOPO to cinnamaldehyde is 2.2 to 4.4:1.3 to 2.6; (3) dissolving the intermediate product obtained in step (2) in glacial acetic acid, then adding DOPO and stirring the reaction, the stirring temperature is 105-115° C., the stirring time is 4-6 hours, wherein the mass volume ratio of the intermediate product to glacial acetic acid is 4.5-8.9 g:150-200 mL, and the mass ratio of DOPO to the intermediate product is 4.3-8.6:4.5-8.9; (4) using a solvent precipitation method to precipitate and centrifuge the solution after the reaction in step (3) to obtain a crude product, wherein the precipitant used is deionized water and the volume ratio of the precipitant to the solution after the reaction is 100-150:100-150; (5) The crude product in step (4) is added into ethanol for purification, and then vacuum filtered, washed and dried to obtain the final product, rigid cinnamaldehyde bio-based flame retardant PPABCA.

3. The use of the rigid cinnamaldehyde bio-based flame retardant PPABCA in the preparation of epoxy resin composite materials according to claim 1, characterized in that: The rigid cinnamaldehyde bio-based flame retardant PPABCA is ground and sieved, added to the epoxy resin and stirred evenly, and then a curing agent is added and stirred evenly, and cured to obtain a flame-retardant epoxy resin composite material.

4. The use according to claim 3, characterized in that: The curing agent is one or more of 4,4-diaminodiphenylmethane, 4,4-diaminodiphenyl ether, ethylenediamine, dicyandiamide, and diaminodiphenyl sulfone, and the mass ratio of the epoxy resin, the curing agent, and the rigid cinnamaldehyde bio-based flame retardant is 90-110:24-26:5-7.

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