A method for the synthesis of lignin-based semi-biobased epoxy resin

Abstract

The present invention relates to a method for the synthesis of lignin-based semi-biobased epoxy resin which is sensitive to worker health and to the environment. With the inventive method, a synthesis method that eliminates the need for high temperature and reduces energy consumption is provided by using Bisguaiacol F (BGF). Risks to worker health are minimized by using environmentally harmless organic solvents. The invention provides an environmentally friendly, energy efficient and sustainable synthesis method.

Description

[0001] A METHOD FOR THE SYNTHESIS OF LIGNIN-BASED SEMIBIOBASED EPOXY RESIN

[0002] Technical Field

[0003] The present invention relates to a method for the synthesis of lignin-based semibiobased epoxy resin which is sensitive to worker health and to the environment.

[0004] Background of the Invention

[0005] Epoxy resins are thermosetting polymers which are used in coatings, paints, adhesives and composite materials and have high mechanical and chemical resistance after curing. Epoxy resins are produced with a system that comprises 1,2-epoxy groups and usually consists of two components, an epoxy monomer or oligomer (component A) and a hardener or catalyst (component B). When these components are mixed, the crosslinking reaction starts and a hard, durable polymer structure is obtained.

[0006] Lignin-based aromatic monophenols and their derivatives play an important role in epoxy resin production. These monophenols have the capacity to improve the mechanical and chemical properties of epoxy resins and increase the hardness, thermal stability and chemical resistance of the resin. Furthermore, lignin-based monophenols offer significant advantages in terms of sustainability as they are environmentally friendly and biodegradable. Epoxy resins modified with monophenols are used in many industrial fields such as automotive, construction, electronics and aerospace. These resins are preferred in composite materials and structural applications due to their low weight and high strength. The addition of monophenols to epoxy resins also enables materials that last longer in outdoor conditions to be obtained by increasing their ultraviolet (UV) resistance. These resins offer processability and ease of application by means of their low viscosity. They also show high performance in the curing process and increase productivity by accelerating production processes. As a result, the use of epoxy resin with monophenols provides significant advantages in terms of both performance and environmental sustainability and has the potential for wide use in future industrial applications [1],

[0007] One of the compounds commonly used in epoxy resins is bisphenol A (BP A). However, the adverse effects of BPA on the endocrine and reproductive systems and the risk of triggering certain types of cancer have raised concerns about its use. Therefore, it is of great importance to develop safer and environmentally friendly compounds as alternatives to BPA. Bisguaiacol F (BGF), a lignin derivative synthesized from guaiacol and vanillyl alcohol derived from lignin, has lower toxicity compared to BPA and offers a significant advantage in terms of environment and human health in epoxy resin production. BGF is considered as a structural analog of BPA, however, unlike BPA, it does not have adverse effects for human health. Furthermore, the fact that the raw materials used in the production of BGF (such as lignin) are derived from renewable resources makes it an environmentally friendly option. Moreover, the inclusion of BGF in epoxy resin compositions creates a more sustainable alternative in terms of health and safety while maintaining the mechanical and chemical properties of the resin [2],

[0008] In the article titled “Replacing Bisphenol-A with Bisguaiacol-F to synthesize polybenzoxazines for a Pollution- free Environment”, which relates to the synthesis of a compound called Bisguaiacol F (BGF) as an environmentally friendly alternative to bisphenol A (BPA) and the development of benzoxazine monomers based on this compound, it is stated that BGF and the benzoxazines derived from this compound were synthesized by a solvent-free method and the structure of these compounds was confirmed by methods such as FT-IR, NMR, MS and GC. Furthermore, it is emphasized that these monomers were polymerized via ring opening polymerization, and the thermal properties and flame-retardant performance of the obtained polymers were examined. In the method described in this article, a high temperature of 150°C is used and the reaction time is 24 hours. The use of a high temperature of 150°C and a reaction time of 24 hours increases production costs by increasing energy consumption. Moreover, the long reaction time reduces efficiency and makes the processes less environmentally friendly.

[0009] The United States patent document no. US20170210689A1, an application included in the state of the art, relates to the synthesis of compounds called blocks and the use of these compounds as sustainable and less toxic alternatives to industrially important bisphenols. These phenolic blocks comprise one or more phenolic units and these units are linked by substituted or unsubstituted methylene groups. The patent application covers the synthesis of these phenolic blocks, with controlled regioselectivity, from hydroxymethyl phenols and optionally from substituted phenols that do not comprise hydroxymethyl groups. Dichloromethane was used here for organic phase separation. Dichloromethane is a solvent used for organic phase separation. However, dichloromethane is a toxic and volatile compound, which poses health and safety risks. It also has properties that can harm the environment. For this reason, the use of dichloromethane is a major drawback, especially for developing environmentally friendly and sustainable processes.

[0010] The disadvantages and limitations of existing methods such as high temperature, long reaction times and use of toxic solvents necessitate the development of alternative methods for synthesizing biobased epoxy resins at lower temperatures, in a shorter time and more sensitive to the environment.

[0011] Summary of the Invention The invention aims to develop a method for synthesizing, at low temperature, lignin-based semi-biobased epoxy resin which is environmentally friendly and efficient by eliminating the disadvantages of existing methods such as high temperature, long reaction time and use of toxic solvents.

[0012] The most important object of the invention is to provide an optimized method for synthesizing semi-biobased epoxy resin which does not require energy-intensive conditions such as high temperature and pressure. The inventive method reduces energy consumption by lowering the reaction temperature and at the same time increases efficiency.

[0013] Another object of the invention is to provide an environmentally friendly and safe method for synthesizing semi-biobased epoxy resins by eliminating the use of organic solvents that are harmful to the environment and human health. Within this scope, semi-biobased epoxy resins with physicochemical properties such as desired epoxy value and viscosity are obtained without the use of toxic solvents.

[0014] A further object of the invention is to provide an alternative method which is sustainable for synthesizing semi-biobased epoxy resin and safe in terms of toxicity.

[0015] By means of the invention, an environmentally friendly and efficient method which eliminates the use of high temperatures, long reaction times and toxic solvents is provided.

[0016] Detailed Description of the Invention

[0017] The present invention relates to a method for synthesizing lignin-based semibiobased epoxy resin in order to achieve all of the aforementioned objects which will become apparent from the detailed description below. The method for the synthesis of lignin-based semi-biobased epoxy resin comprises the process steps of: i. selecting at least two lignin-derived aromatic monophenols that will react; ii. adding at least two selected lignin-derived aromatic monophenols and organic solvent to the reactor; iii. initiating the reaction by adding 2-10 ml of catalyst to the obtained solution with the aim of accelerating the reaction and increasing the yield; iv. synthesizing the bisphenol derivative by stirring it in the reactor at 350- 700 rpm for 10-20 hours in the range of 50-80 °C with reflux system; v. loading the synthesized bisphenol derivative with bisphenol A (BPA) and epichlorohydrin into the reactor and stirring these in the range of 50-70°C in order to obtain a homogeneous mixture; vi. dosing the homogeneous mixture with sodium hydroxide (NaOH) in a period of 1-3 hours; vii. removing the salt formed after dosing, by adding water; viii. dosing the homogeneous mixture with sodium hydroxide (NaOH) in a period of 25-55 minutes after salt is removed; ix. removing the formed salt by adding water; x. purifying the product taken from the reactor, by filtering it under vacuum and placing it in the evaporator; and xi. obtaining a lignin-based semi -biobased epoxy resin as a result of the reaction continuing for 2-7 hours.

[0018] The mentioned at least two lignin-derived aromatic monophenols are selected from vanillin, guaiacol, cresol, syringol, catechol, eugenol, methylguaiacol and vanillyl alcohol. In the preferred embodiment of the invention, vanillyl alcohol and guaiacol are selected in order to form diphenol. Here, the vanillyl alcohol: guaiacol ratio is 1 : 1-1,5 and preferably 1 : 1-1,2 by mole. According to the yield analysis carried out in Gas Chromatography-Mass Spectrometry (GC-MS) device, the highest yield is obtained at a ratio of 1 : 1-1,2. The bisphenol derivative obtained in the case of selecting vanillyl alcohol and guaiacol is bisguaiacol F (BGF). BGF synthesis reaction mechanism is shown below (Reaction I):

[0019] Guaiacol Vanillyl alcohol Bisguaiacol F

[0020] Reaction I

[0021] The organic solvent mentioned in the inventive method is selected from acetone, methanol, ethanol, chloroform, acetic acid, xylol, toluene and methylene chloride. In the preferred embodiment of the invention, the organic solvent is ethanol. Ethanol is a solvent that exhibits both polar and apolar properties and provides a wide solubility range. This property facilitates the dissolution of various organic and inorganic substances and offers lower toxicity and flammability risk than other organic solvents. The usage ratio of ethanol to total input amount is in the range of 70%-90% by weight.

[0022] The catalyst mentioned in the inventive method is p-toluene sulfonic acid, sulfuric acid, methanesulfonic acid or trifluoroacetic acid. The catalyst accelerates the reaction and increases the yield. In one embodiment of the invention, 0,5-1 N, preferably 0,5-0, 8 N of sulfuric acid is used as the catalyst. The amount of catalyst is preferably kept between 3-7 ml with the aim of ensuring the best yield. While insufficient amount of acid causes the reaction to be incomplete or the yield to decrease, excessive amount of acid increases the formation of unwanted products by stimulating side reactions. This leads to a decrease in the yield of the desired product. In addition, high acid concentrations reduce the yield by affecting the solubility properties of the reactant. In the inventive method, the ratio of BPA to sodium hydroxide (NaOH) (BPA:NaOH) is in the range of 1 : 1,9 to 1 :2,3 by mole. In the preferred embodiment of the invention, the ratio of BPA to sodium hydroxide (NaOH) (BPA:NaOH) is 2, 0:2, 2. In the inventive method, the ratio of BGF to sodium hydroxide (NaOH) (BGF:NaOH) is in the range of 1 : 1,9 to 1 :2,3 by mole. In the preferred embodiment of the invention, the ratio of BGF to sodium hydroxide (NaOH) (BGF:NaOH) is 2, 0:2, 2 for the reaction to be carried out stoichiometrically in full yield. The said ratios are determined by taking into consideration the hydroxyl numbers of the components. Since the amounts of BPA and BGF entering the reaction are calculated stoichiometrically, there is no increased BPA or BGF as a result of the reaction.

[0023] In the preferred embodiment of the invention, the reaction temperature for synthesizing bisguaiacol F (BGF) is 60-70°C and the reaction time is 15-20 hours. The FT-IR peaks of bisguaiacol F (BGF) obtained at the said time and temperature are clearly visible and high yield is obtained.

[0024] In the preferred embodiment of the invention, lignin-based semi-biobased epoxy resin is obtained by reacting synthesized BGF with bisphenol A (BPA) and epichlorohydrin in the presence of sodium hydroxide (NaOH) solution for 2-5 hours.

[0025] In the inventive method, the ratio of synthesized BGF to BPA (BGF:BPA) is 20:80, 40:60, 50:50, 60:40 or 80:20 by weight. In one embodiment of the invention, the ratio of BGF to BPA (BGF:BPA) is 40:60, 50:50 or 60:40. In the preferred embodiment of the invention, the ratio of BGF to BPA (BGF:BPA) is 50:50. The product obtained by synthesis of BPA and epichlorohydrin (Formula I) and the product obtained by synthesis of BGF and epichlorohydrin (Formula II) are shown below:

[0026] Formula II

[0027] The thermal and mechanical properties of the resin obtained by reacting the synthesized BGF with BPA and epichlorohydrin are shown in Table 1. According to the data in Table 1, the thermal and mechanical properties of the lignin-based semi-biobased epoxy resins synthesized by the inventive method differ depending on the change in BGF (Bisguaiacol F) and BPA (Bisphenol A) ratios. As the BGF:BPA ratio increases, the epoxy equivalent weight (EEW) values also increase. For example, EEW, which is 195 g / eq at the 20:80 ratio, increases to 210 g / eq at the 50:50 ratio and to 250 g / eq at the 80:20 ratio. This shows that with the increase in the amount of BGF, more epoxy groups are included in the molecular structure of the epoxy resin. However, the EEW value of 210 g / eq obtained in the 50:50 ratio offers the closest value to the optimal EEW range used in applications such as coatings and paints. The color of the resin darkens as the amount of BGF increases. While a color close to transparent is obtained at the 20:80 ratio, a yellow color is observed at the 50:50 ratio and a brownish color is observed at the 80:20 ratio. This is caused by the fact that BGF is naturally a darker colored component due to being a lignin derivative. Viscosity values increase significantly as the BGF ratio increases. For example, while the viscosity is 25,000 cP at the 20:80 ratio, it reaches 93,000 cP at the 50:50 ratio and 120,000 cP at the 80:20 ratio. This increase shows that the density and viscosity resistance of the resin increases depending on the amount of BGF. Again, the resin obtained in the 50:50 ratio offers the closest value to the medium viscosity range (11,000-15,000 cP) used in applications such as coatings and paints. The 50:50 BGF-BPA ratio provides the most ideal results for coating and paint applications by offering both a favorable EEW value and a medium viscosity value. Since other ratios offer higher EEW and viscosity values, they can be considered for different applications. However, the 50:50 ratio supports the use of the bio-based epoxy resin synthesized by the inventive method in common applications such as coatings and paints.

[0028] Table 1. Thermal and mechanical properties of lignin-based semi-biobased epoxy resin synthesized by the inventive method

[0029] BGF-BPA 20:80 40:60 50:50 60:40 80:20

[0030] Resin

[0031] EEW (g / eq) 195 205 210 225 250

[0032] Color Close to Transparent Light Yellow Yellow Dark Yellow Brownish

[0033] Viscosity 25000 58000 93000 105000 120000

[0034] In the present invention, when synthesizing BGF, the best synthesis yield obtained by using sulfuric acid catalyst was 81% and 84% with p-toluene sulfonic acid catalyst.

[0035] In one embodiment of the invention, BGF was synthesized by placing vanillyl alcohol in the range of 1-1,2 mole, 1 mole of guaiacol, ethanol and H2SO4 in a 250 ml reactor and reacting with a magnetic stirrer at 80-100°C with a reflux system at 350-700 rpm stirrer speed for 14-18 hours and with 81% yield. In another embodiment of the invention, BGF was synthesized by placing 1-1,2 mole of vanillyl alcohol, 1 mole of guaiacol, ethanol and p-toluene sulfonic acid (PTS A) in a 250 ml reactor and reacting with a magnetic stirrer at 80-100°C with a reflux system at 350-700 rpm stirrer speed for 14-18 hours and with 84% yield.

[0036] In a further embodiment of the invention, epoxy resin was obtained by reacting the synthesized BGF and BPA with epichlorohydrin at a temperature range of 60- 70°C for 2-5 hours. The epoxy equivalent weight (EEW) of the resin obtained is 210 g / eq.

[0037] References

[0038] [1] Van De Velde, N., Javornik, S., Sever, T., Stular, D., Sobak, M., Stirn, Z.,

[0039] Likozar, B., & Jerman, I. (2021). Bio-Based Epoxy Adhesives with Lignin-Based Aromatic Monophenols Replacing Bisphenol

[0040] A. Polymers, 13(22), 3879. https: / / doi.org / 10.3390 / polyml3223879

[0041] [2] Manzoor, M. F., Tariq, T., Fatima, B., Sahar, A., Tariq, F., Munir, S., Khan, S.,

[0042] Ranjha, M. M. a. N., Sameen, A., Zeng, X., & Ibrahim, S. A. (2022). An insight into bisphenol A, food exposure and its adverse effects on health: A review. Frontiers in Nutrition, 9. https: / / doi.org / 10.3389 / fnut.2022.1047827

Claims

CLAIMS1. The method for the synthesis of environmentally friendly, high-yield ligninbased semi-biobased epoxy resin; characterized in that it comprises the process steps of:

1. selecting at least two lignin-derived aromatic monophenols that will react; ii. adding at least two selected lignin-derived aromatic monophenols and organic solvent to the reactor; iii. initiating the reaction by adding 2-10 ml of catalyst to the obtained solution with the aim of accelerating the reaction and increasing the yield; iv. synthesizing the bisphenol derivative by stirring it in the reactor at 350- 700 rpm for 10-20 hours in the range of 50-80 °C with reflux system; v. loading the synthesized bisphenol derivative with bisphenol A (BPA) and epichlorohydrin into the reactor and stirring these in the range of 50-70°C in order to obtain a homogeneous mixture; vi. dosing the homogeneous mixture with sodium hydroxide (NaOH) in a period of 1-3 hours; vii. removing the salt formed after dosing, by adding water; viii. dosing the homogeneous mixture with sodium hydroxide (NaOH) in a period of 25-55 minutes after salt is removed; ix. removing the formed salt by adding water; x. purifying the product taken from the reactor, by filtering it under vacuum and placing it in the evaporator; and xi. obtaining a lignin-based semi -biobased epoxy resin as a result of the reaction continuing for 2-7 hours.

2. A method according to Claim 1; characterized in that at least two lignin- derived aromatic monophenols are selected from vanillin, guaiacol, cresol, syringol, catechol, eugenol, methylguaiacol and vanillyl alcohol.

3. A method according to Claim 2; characterized in that the at least two lignin- derived aromatic monophenols are vanillyl alcohol and guaiacol.

4. A method according to Claim 3; characterized in that the vanillyl alcohol: guaiacol ratio is 1 : 1-1,5 by mole.

5. A method according to Claim 4; characterized in that the vanillyl alcohol: guaiacol ratio is 1 : 1-1,2 by mole.

6. A method according to any one of the preceding claims; characterized in that the organic solvent is acetone, methanol, ethanol, chloroform, acetic acid, xylol, toluene or methylene chloride.

7. A method according to Claim 6; characterized in that the organic solvent is ethanol.

8. A method according to Claim 7; characterized in that the ratio of ethanol to total input is 70-90% by weight.

9. A method according to any one of the preceding claims; characterized in that the catalyst is p-toluene sulfonic acid, sulfuric acid, methanesulfonic acid or trifluoroacetic acid.

10. A method according to Claim 9; characterized in that the catalyst is sulfuric acid.

11. A method according to Claim 10; characterized in that the catalyst is 0,5-1 N of sulfuric acid.

12. A method according to Claim 11; characterized in that the catalyst is 0,5-0, 8 N of sulfuric acid.

13. A method according to any one of the preceding claims; characterized in that the amount of catalyst is 3-7 ml.

14. A method according to any one of the preceding claims; characterized in that the reaction temperature for synthesizing the bisphenol derivative is 60-70°C.

15. A method according to any one of the preceding claims; characterized in that the ratio of BPA to sodium hydroxide (NaOH) (BPA:NaOH) is between 1:1,9 to 1:2,3.

16. A method according to Claim 15; characterized in that the ratio of BPA to sodium hydroxide (NaOH) (BPA:NaOH) is 2, 0:2, 2.

17. A method according to any one of the preceding claims; characterized in that the bisphenol derivative is bisguaiacol F (BGF).

18. A method according to Claim 17; characterized in that the ratio of BGF to BPA (BGF:BPA) is 20:80, 40:60, 50:50, 60:40 or 80:20 by weight.

19. A method according to Claim 18; characterized in that the ratio of BGF to BPA (BGF:BPA) is 40:60, 50:50 or 60:40 by weight.

20. A method according to Claim 19; characterized in that the ratio of BGF to BPA (BGF:BPA) is 50:50 by weight.

21. A method according to any one of Claims 17-20; characterized in that the ratio of BGF to sodium hydroxide (NaOH) (BGF: NaOH) is between 1:1,9 to 1:2,3.

22. A method according to Claim 21; characterized in that the ratio of BGF to sodium hydroxide (NaOH) (BGF:NaOH) is 2, 0:2, 2.

Images