Thermosetting resins

Abstract

The present disclosure relates to a thermosetting resin that can be obtained by carrying out a reaction between 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and a mixture of divanillic alcohol ethers. The present disclosure also provides a thermoset resin obtained from said thermosetting resin.

Description

[0001] Thermosetting resins

[0002] Technical field of the invention

[0003] The present disclosure relates to a thermosetting resin obtained by reaction between 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and a mixture of divanillic alcohol ethers. The present disclosure also relates to a thermosetting resin obtained from said thermosetting resin.

[0004] State of the art

[0005] Epoxy resins are often the matrix of choice for high-performance composites, due to their exceptional mechanical properties, low density, ease of handling, and processability. However, epoxy resins have undeniable drawbacks in aerospace applications, as their flammability and poor compatibility with liquid oxygen can limit their applicability. Many studies have addressed this problem, and proposed solutions involve simply incorporating a flame retardant into the epoxy precursors to increase the flame resistance and self-extinguishing properties of the resins. The most widely used epoxy precursor in many applications, including aerospace, is DGEBA (diglycidyl ether of bisphenol A).The flame retardant commonly used in combination with DGEBA (due to its low cost and high efficacy) is tetrabromobisphenol A (TBBPA). However, this compound contains bromine, which raises many concerns regarding its toxicity potential, persistence, and bioaccumulation capacity. As a result, the production and use of halogenated flame retardants have been regulated and restricted.

[0006] Organic phosphorus-based flame retardants have been considered as an alternative to halogenated flame retardants. Although the former are less harmful to the environment than the latter, they still have a potential negative impact on the environment, particularly due to the difficulty of processing materials or substances containing them.

[0007] Furthermore, the use of DGEBA in carbon fiber-reinforced composites, in addition to the problems of high flammability and poor compatibility with liquid oxygen, can also pose environmental and health concerns. As a derivative of bisphenol A, which is a fuel-based reprotoxic substance subject to strict regulations, this epoxy precursor now has an uncertain future, as a growing body of research is devoted to finding healthier and more environmentally friendly alternatives. Among potential renewable sources for DGEBA substitutes, vegetable oils stand out for their abundant availability and relatively low price, but their derivatives can be disappointing in terms of performance due to their aliphatic structure.Epoxy thermosets with a more rigid backbone can be obtained from building blocks, such as rosin, glucose derivatives, cardanol, and others, as recently reported, but they are generally not comparable to conventional DGEBA-based epoxy networks in terms of thermal and thermomechanical properties. Tannins and lignin could be promising sources of aromatic building blocks, but their variable and complex structure, as well as their poor processability, reduce their potential as substitutes for bisphenol A.

[0008] Recently, biphenyl pluriepoxide compounds have been described as potential substitutes for DGEBA (see WO 2019 / 092359 and WO 2019 / 155169). Many of these compounds can be obtained from vanillin, a natural product. They are non-hazardous, biomass-derived aromatic compounds available on an industrial scale. Representative bio-based pluriepoxide compounds have demonstrated good thermomechanical properties, particularly in terms of glass transition temperature and coke content.

[0009] In this context, the inventors set themselves the specification of developing epoxy resin precursors (thermosets) with thermomechanical properties compatible with use in the aerospace sector in particular.

[0010] Summary of the invention

[0011] The present disclosure relates to a thermosetting resin obtainable by reaction between 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and a mixture of divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether.

[0012] In some embodiments, divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether are present in said mixture in a weight ratio of about 10:90 to about 30:70.

[0013] In some embodiments, the mass ratio between DOPO and said mixture is from about 1:1 to about 1:20. The present disclosure also relates to a thermoset resin obtained by heat treatment, in the presence of a hardener, of a thermosetting resin as defined above.

[0014] The present disclosure also relates to a composite material comprising such a thermoset resin.

[0015] Description of figures

[0016] Figures 1, 3, 4 and 5 each represent an FTIR spectrum (acronym for Fourier Transform Infra Red spectroscopy) of a thermosetting resin in accordance with the invention.

[0017] Figure 2 represents the NMR spectrum of a thermosetting resin in accordance with the invention.

[0018] Figure 6 shows the TGA (ThermoGradient Metric Analysis) curves of thermoset resins in accordance with the invention and outside the invention; from left to right, over the temperature range 600-800°C: DGEBA-DDS, GEDVA-DDS, P-GEDVA-DDS (5:1) and P-GEDVA-DDS (1:1) resins.

[0019] Description of the invention

[0020] The present disclosure relates to a thermosetting resin obtainable by reaction between 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and a mixture of divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether.

[0021] In the context of this disclosure, "GEDVA" means a mixture of divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether, and "P-GEDVA" means the reaction product between GEDVA and DOPO.

[0022] DOPO (CAS: 35948-25-5), represented by the formula below, is commercially available:

[0023] Divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether are respectively represented by the following formulas:

[0024] These compounds can be prepared for example as described in WO 2019 / 155169.

[0025] In some embodiments, divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether are present in said mixture in a weight ratio of about 10:90 to about 30:70. In some embodiments, divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether are present in said mixture in a weight ratio of about 15:85 to about 25:75. In some embodiments, the weight ratio of DOPO to said mixture is about 1:1 to about 1:20. In some embodiments, the weight ratio of DOPO to said mixture is about 1:2 to about 1:10.

[0026] In some embodiments, the reaction between DOPO and the mixture of divanillic alcohol triglycidyl ethers is carried out at a temperature ranging from about 80°C to about 200°C, for example at a temperature ranging from about 100°C to about 180°C. In some embodiments, said reaction is carried out for a time ranging from about 30 min to about 10 h, for example for a time ranging from about 1 h to about 5 h. The reaction is carried out under inert conditions, typically under argon.

[0027] The present disclosure also relates to a thermoset resin obtained by heat treatment, in the presence of a hardener, of a thermosetting resin as defined above.

[0028] In some embodiments, the weight ratio of thermosetting resin to hardener is from about 2:1 to about 15:1. In some embodiments, the weight ratio of thermosetting resin to hardener is from about 3:1 to about 10:1.

[0029] In some embodiments, the hardener is selected from diaminodiphenyl sulfone, diaminodiphenylmethane (or methylene dianiline), isophorone diamine, dicyandiamide, 4,4-methylene-bis(2-isopropyl-6-methylaniline) and 4,4'-methylene-bis(2,6-diisopropylamineaniline). In some advantageous embodiments, the hardener is diaminodiphenyl sulfone.

[0030] The present disclosure also relates to a thermoset resin obtained by reaction between 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a mixture of divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether, and a hardener.

[0031] In some embodiments, the mass ratio of said mixture of divanillic alcohol ethers, DOPO and hardener is from about 3:1:1 to about 15:1:5.

[0032] In some embodiments, divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether are present in said mixture in a weight ratio of about 10:90 to about 30:70. In some embodiments, divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether are present in said mixture in a weight ratio of about 15:85 to about 25:75.

[0033] In some embodiments, the hardener is selected from diaminodiphenyl sulfone, diaminodiphenylmethane (or methylene dianiline), isophorone diamine, dicyandiamide, 4,4-methylene-bis(2-isopropyl-6-methylaniline) and 4,4'-methylene-bis(2,6-diisopropylamineaniline). In some advantageous embodiments, the hardener is diaminodiphenyl sulfone.

[0034] This disclosure is illustrated by the following examples.

[0035] Example 1

[0036] 2.76 g of a mixture of divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether, in a mass ratio of 20:80, were placed in a round-bottomed flask equipped with an argon inlet and a vacuum system, and then the flask was placed in an oil bath and heated to 80°C. The mixture was stirred and evacuated for 15 minutes, and then argon was introduced into the flask until atmospheric pressure was reached. 0.29 g of DOPO was added, and the mixture was again stirred and evacuated at 80°C to remove traces of water. Argon was introduced into the flask until atmospheric pressure was reached, and the reaction mixture was gradually heated to 100°C and maintained at this temperature for 5 h.

[0037] The reaction product was analyzed by Fourier transform infrared spectroscopy (Figure 1) and NMR (Figure 2). The epoxy equivalent weight (EEW) of the reaction product was 253. The value of "EEW" can be determined by methods well known to those skilled in the art, for example by chemical titration with HBr.

[0038] Example 2

[0039] The procedure of Example 1 was repeated (mass ratio of ether mixture to DOPO of approximately 10:1), but the reaction mixture was kept at 100°C for 1 h. The reaction product was analyzed by Fourier transform infrared spectroscopy (Figure 3). The epoxy equivalent mass of the reaction product was 233.

[0040] Example 3

[0041] The procedure of Example 1 was repeated, but using 1.34 g of divanillic alcohol ether mixture and 0.69 g of DOPO (mass ratio of approximately 2:1) and maintaining the reaction mixture at 100°C for 5 h. The reaction product was analyzed by Fourier transform infrared spectroscopy (Figure 4). The epoxy equivalent mass of the reaction product was 272.

[0042] Example 4

[0043] The protocol of Example 3 was repeated (mass ratio between ether mixture and DOPO of approximately 2:1) but the reaction mixture was maintained at 160°C for 5 h. The reaction product was analyzed by Fourier transform infrared spectroscopy (Figure 5). The epoxy equivalent mass of the reaction product was 430.

[0044] Example 5

[0045] 2.37 g of resin obtained in Example 2 were placed in a flask which was heated to 80°C, then 0.65 g of diaminodiphenyl sulfone (DDS) was added, and the mixture was heated, under vacuum, to 140°C for complete dissolution of the DDS. The mixture was cooled as soon as it became clear.

[0046] The mixture was then transferred into 5 cm diameter aluminum molds to make 1-2 mm thick resin plates, or into larger aluminum molds to make 175x150x5 mm resin plates. The plates were then cured in an oven with circulating air at 130°C for 1 hour, then post-cured at 170°C for 2 hours. A sample of resin plate was analyzed by thermogravimetry under air atmosphere (Figure 6), and the residual coke content of the resin after degradation at 800°C was determined. The result is shown in Table 1 below.

[0047] Example 6

[0048] 5.04 g of a mixture of divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether, in a mass ratio of 20:80, were placed in a round-bottomed flask equipped with an argon inlet and a vacuum system, then the flask was placed in an oil bath and heated to 80°C. The mixture was stirred and evacuated for 15 minutes, then argon was introduced into the flask until atmospheric pressure was reached. 1.01 g of DOPO and then 1.1 g of DSS were added, and the mixture was again stirred and evacuated to 80°C to remove traces of water. Argon was introduced into the flask until atmospheric pressure was reached. The mixture was heated, under vacuum, to 140°C to obtain a clear mixture which was then cooled.

[0049] The mixture was then transferred into 5 cm diameter aluminum molds to make 1-2 mm thick resin plates, or into larger aluminum molds to make 175x150x5 mm resin plates. The plates were then cured in an oven with air circulation at 130°C for 1 hour, then post-cured at 170°C for 2 hours. A sample of resin plate was analyzed by thermogravimetry under air atmosphere (Figure 6), and the residual coke content of the resin after degradation at 800°C (R800) was determined. The result is shown in Table 1 below.

[0050] Example 7

[0051] 1.34 g of a mixture of divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether, in a mass ratio of 20:80, were placed in a round-bottomed flask equipped with an argon inlet and a vacuum system, and then the flask was placed in an oil bath and heated to 80°C. The mixture was stirred and evacuated for 15 minutes, and then argon was introduced into the flask until atmospheric pressure was reached. 0.69 g of DOPO was added, and the mixture was again stirred and evacuated at 80°C to remove traces of water. Argon was introduced into the flask until atmospheric pressure was reached, and the reaction mixture was gradually heated to 100°C and maintained at this temperature for 5 h.

[0052] 0.50 g of this resin was placed in a flask which was heated to 80°C, then 0.05 g of diaminodiphenyl sulfone (DDS) was added, and the mixture was heated, under vacuum, to 140°C for complete dissolution of the DDS. The mixture was cooled as soon as it became clear.

[0053] The mixture was then transferred into 5 cm diameter aluminum molds to make 1-2 mm thick resin plates, or into larger aluminum molds to make 175x150x5 mm resin plates. The plates were then cured in an oven with circulating air at 130°C for 1 hour, then post-cured at 170°C for 2 hours. A sample of resin plate was analyzed by thermogravimetry under air atmosphere (Figure 6), and the residual coke content of the resin after degradation at 800°C was determined. The result is shown in Table 1 below.

[0054] Comparative example

[0055] 1.64 g of a mixture of divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether, in a mass ratio of 20:80, was placed in a flask which was heated to 80°C, then 0.66 g of diaminodiphenyl sulfone (DDS) was added, and the mixture was heated, under vacuum, to 140°C for complete dissolution of the DDS. The mixture was cooled as soon as it became clear.

[0056] The mixture was then transferred into 5 cm diameter aluminum molds to make 1-2 mm thick resin plates, or into larger aluminum molds to make 175x150x5 mm resin plates. The plates were then cured in an oven with circulating air at 130°C for 1 hour, then post-cured at 170°C for 2 hours. A sample of resin plate was analyzed by thermogravimetry under nitrogen atmosphere and air atmosphere (Figure 6), and the residual coke content of the resin after degradation at 800°C (R800) was determined. The result is shown in Table 1 below.

[0057] Table 1

[0058] As can be seen from Table 1, the residual mass at 800°C of the thermoset resins in accordance with the invention is at least 40% higher than that obtained without the use of DOPO. This is very interesting since the higher the residual coke content, the better the flame retardancy properties of the materials considered.

[0059] The thermosetting resins described in the present disclosure, in addition to the advantage of being bio-sourced, have, once cured, increased thermal resistance.

Claims

CLAIMS 1. Thermosetting resin obtainable by reaction between 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and a mixture of divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether.

2. Thermosetting resin according to claim 1, wherein divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether are present in said mixture in a mass ratio of 10:90 to 30:

70.

3. Thermosetting resin according to claim 2, wherein divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether are present in said mixture in a mass ratio of 15:85 to 25:

75.

4. Thermosetting resin according to one of the preceding claims, in which the mass ratio between DOPO and said mixture is from 1:1 to 1:

20.

5. Thermosetting resin according to claim 2, wherein the mass ratio between DOPO and said mixture is 1:2 to 1:

10.

6. Thermoset resin obtained by heat treatment, in the presence of a hardener, of a thermosetting resin according to one of claims 1 to 5.

7. Thermoset resin according to claim 6, wherein the hardener is selected from diaminodiphenyl sulfone, diaminodiphenylmethane, isophorone diamine, dicyandiamide, 4,4-methylene-bis(2-isopropyl-6-methylaniline) and 4,4'-methylene-bis(2,6-diisopropylamineaniline).

8. Thermoset resin obtainable by reaction between 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, a mixture of divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether, and a hardener.

9. A thermoset resin according to claim 8, wherein divanillic alcohol triglycidyl ether and divanillic alcohol tetraglycidyl ether are present in said mixture in a mass ratio of 10:90 to 30:

70.

10. A thermoset resin according to claim 8 or claim 9, wherein the hardener is selected from diaminodiphenyl sulfone, diaminodiphenylmethane, isophorone diamine, dicyandiamide, 4,4-methylene-bis(2-isopropyl-6-methylaniline) and 4,4'-methylene-bis(2,6-diisopropylamineaniline).

11. A composite material comprising a thermoset resin according to any one of claims 6 to 10.

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