TECHNICAL FIELD

The invention relates to isoamyl ester rosin compound to be used as a biobased hardener in epoxy resin production, and its synthesis method. The invention can be applied in various fields such as the paper industry, adhesives, paint industry, printing inks, varnishes and adhesives in the furniture sector, adhesive production with water- repellent properties in the wood panel sector, different types of paint formulations that can be produced in the aerospace industry, and adhesive sector, among others.

BACKGROUND

An adhesive is any material or substance that holds or attracts other materials together through mechanical, chemical, adhesive cohesion. In other words, binders are liquid or paste-like substances that chemically or physically harden through a process, and are added into fibers, filler powders, and other particles. Examples of mechanical binders include stone-to-stone binding in masonry and beam-to-beam binding in wooden framing [1],

Natural-based or biobased adhesives are developed using organic materials, particularly natural-based polymers. Some of the most popular ones are derived from vegetable sources such as starch and dextrins, or from protein sources like soybean, casein, and milk albumin. Natural-based adhesives containing casein dry relatively slowly, form very strong bonds, and exhibit water resistance. Dextrins are commonly used in the paper industry and can create robust bonds with certain materials. However, these bonds are compromised when exposed to water. Natural-based or biobased adhesives are available in two forms: liquid solution or dry powder form; both are mixed with water before application. Adhesive strength occurs as a result of water evaporation or absorption by the substrate. Applications using permeable substrates are common, but there are other methods as well, such as a "rapid bonding" that involves a drying period before activating the adhesive, where two impermeable substrates are bonded. Most natural-based adhesives are biodegradable and not suitable for long-term storage [2],

Rosin, is used in adhesive production, is a transparent, yellow-colored, glassy substance formed through the distillation of natural resins. Natural resin is obtained from three sources for adhesive production: 1- Pine resin, obtained by making incisions in the trunks of living pine trees using various methods, 2- Extraction Resin from pine stumps and roots with resin content that has been left in the soil for an extended period after cutting, extracted after chipping, 3- Sulfate Resin, byproduct obtained from resinous pine chips during sulfate (kraft) paper pulp production. These sources yield rosin, which serves as a key ingredient in adhesive manufacturing. Rosin has a hydrophobic structure and is insoluble in water; however, it dissolves in ethers, alcohols, chlorinated hydrocarbons, and hydrocarbons. At room temperature, rosin is solid and varies in color from light yellow to brown. Resin naturally obtained from pine trees consists of approximately 80% rosin and 20% turpentine. The composition of rosin includes about 90% resin acids and 10% neutral materials. Rosin is widely used in various industries such as the paper industry, adhesives, and paint industry, as well as in printing inks. In Turkey, it is obtained from Turkish red pine (Pinus brutia) and maritime pine (Pinus maritima) [3]. Rosin is referred to as "white petroleum," indicating its versatility across multiple sectors, similar to petrochemical products. However, rosin's inherent properties might not always be suitable for its intended use. Hence, it is often modified to better suit its final application. Modified rosin derivatives, such as pentaerythritol- and glycerol-modified rosin, are the most commercially significant. These derivatives are applied using various solvents, depending on the specific application and usage area [4],

In the production of modified ester rosin derivatives, pentaerythritol and glycerol alcohols are among the most preferred alcohol groups worldwide. Generally, glycerol and pentaerythritol ester rosins, which are commonly produced and imported, have a rigid crystalline structure in the resulting products due to the high boiling points of the alcohols they contain during the esterification reaction. The acid number (acid value) of glycerol and pentaerythritol ester rosins falls within the range of 5-15 mg KOH and is completely esterified. The complete esterification of these rosins within the 5-15 mg KOH range indeed extends the processing times, consequently increasing production costs. The glycerol and pentaerythritol ester rosins mentioned exhibit hydrophobic (water-repellent) characteristics. This hydrophobic property displayed by modified rosin products provides an advantage only in applications where resistance to water is desired. The modified ester rosin derivatives typically exist in block or powdered form. Because these derivatives cannot be used as blocks or powders, they need to be dissolved in certain chemical solvents like toluene, petroleum ether, acetone, isopropyl alcohol, ethyl methyl ketone, to be used in liquid form. While this practice adds extra costs, it also poses limitations due to safety concerns. Especially in production processes requiring high temperatures, such as in industries like wood panel manufacturing, the use of these solvents can present occupational safety risks, which restricts their application. Especially in medium-density fiberboard (MDF) production lines, the risk of fire can arise due to the high press temperatures. Inhalation of solvent vapors by workers in inadequately ventilated areas can lead to respiratory issues. Modified ester rosin products produced from these alcohols find application in various industries such as thermoplastic paint formulations, rubber production, the cosmetic sector, and the paper industry.

The patent application CN110577799A, as known in the prior art, pertains to a resin modified particularly with an epoxy compound and its preparation method. In this method, 100 parts of resin, 0-8 parts of unsaturated acid, 0-10 parts of alcohol, 30-120 parts of epoxy compound, 0.1-0.5 parts of A catalyst, 0.1-0.5 parts of B catalyst, and 0.1-0.5 parts of an antioxidant are used. The mentioned A catalyst is an esterification catalyst, while the B catalyst is an epoxy-based ring-opening catalyst. Since the resin subject to the CN110577799A patent application is in solid form, it needs to be dissolved using expensive organic solvents for application. However, these organic solvents are toxic and harmful to human health.

In the current state of the art, the use of solid or high-viscosity rosin resins and derivatives as adhesives necessitates their dissolution in expensive organic solvents due to challenges related to their form. However, this approach has drawbacks including the toxicity and health risks associated with these solvents, their high cost, and the fact that the high acid numbers of these rosin resins result in prolonged esterification reactions. These issues highlight the need for advancements in the field to address these drawbacks and develop improved solutions.

AIM OF THE INVENTION

In this invention, a compound of isoamyl ester rosin represented by Formula I and the synthesis method of isoamyl ester rosin compound from pine resin rosin are described. The isoamyl ester rosin compound subject to the invention is suitable for use in various fields such as the paper industry, adhesives, paint industry, and printing inks. It finds application in the furniture sector as varnish and adhesive, in the wood panel sector for producing water-repellent adhesive, in the aerospace industry for producing paints with different properties, and in the adhesive sector. It is also suitable for use as a biobased hardener in epoxy resin production.

Formula I

The objective of the invention is to provide a fluid compound for the production of a biobased hardener used in epoxy resin production. This compound aims to find application in various fields such as the paper industry, adhesives, paint industry, and printing inks. It can be used in the furniture sector for varnish and adhesive production, in the wood panel sector for water-repellent adhesive production, and in the aerospace industry for creating paints with different properties. Furthermore, the invention targets the adhesive sector. The compound is designed to fulfill the role of a biobased hardener in epoxy resin production, offering versatility across multiple industries. In the invention, the synthesis of the isoamyl ester rosin compound represented by Formula I is carried out. The synthesis method of isoamyl ester rosin compound involves the use of isoamyl alcohol. The boiling point of isoamyl alcohol is 131 °C, and the melting point is -117.2 °C. The low boiling point of isoamyl alcohol enables the production of a fluid form of isoamyl ester rosin. By providing a fluid form of a rosin derivative, the use of organic solvents, which is necessary for the application of solid rosin derivatives in relevant industries in the current state of the art, is eliminated.

Another objective of the invention is to provide a method for synthesizing a short-term and cost-effective rosin derivative. This derivative aims to be used in various fields such as the paper industry, adhesives, paint industry, and printing inks. It can find application in the furniture sector for varnish and adhesive production, in the wood panel sector for water-repellent adhesive production, and in the aerospace industry for creating paints with different properties. The primary purpose is to produce a biobased hardener for epoxy resin production. The isoamyl ester rosin requires an acid value in the range of 25-30 mg KOH for complete esterification. This acidity level allows for a shorter reaction process. Additionally, the initial product is obtained from natural resin, and the isoamyl alcohol necessary for the esterification of the rosin is obtained from the fractionated distillation of fusel oil, which is derived as waste from the bioethanol production process using sugar cane molasses. This approach enables a short-term and cost-effective synthesis method.

Another objective of the invention is to facilitate the recycling of fusel oil obtained as waste in the process of bioethanol production from sugar cane molasses. In the invention, the isoamyl alcohol compound used in the synthesis of the rosin ester derivative is obtained from the fractionated distillation of fusel oil derived as waste from the bioethanol production process. By utilizing the waste fusel oil for the production of isoamyl alcohol, the recycling of fusel oil is achieved. This environmentally friendly approach contributes to the production of isoamyl ester rosin.

The invention provides a fluid form of isoamyl ester rosin compound and a shortterm, cost-effective synthesis method for this compound. This advancement is intended to have applications in various fields such as the paper industry, adhesives, paint industry, and printing inks. It can also be used in the furniture sector for varnish and adhesive production, in the wood panel sector for water-repellent adhesive production, and in the aerospace industry for creating paints with different properties. Furthermore, the invention aims to offer a biobased hardener for epoxy resin production.

LIST OF FIGURES

Figure 1 . FT-IR spectrum of pine resin rosin.

Figure 2. ¹ H-NMR (400 MHz) (CDCI3, 5 ppm) spectrum of pine resin rosin.

Figure 3. ¹³ C-NMR (100 MHz) (CDCI3, 5 ppm) spectrum of pine resin rosin.

Figure 4. Mass spectrum of pine resin rosin.

Figure 5. ¹ H-NMR (400 MHz) (CDCI3, 5 ppm) spectrum of isoamyl ester rosin.

Figure 6. ¹³ C-NMR (100 MHz) (CDCI3, 5 ppm) spectrum of isoamyl ester rosin.

Figure 7. Mass spectrum of isoamyl ester rosin.

Figure 8. FT-IR spectrum of isoamyl ester rosin. DETAILED DESCRIPTION OF THE INVENTION

The invention relates to the isoamyl ester rosin compound represented by Formula I and the synthesis method of this compound from pine resin rosin. The pine resin rosin subject to the invention is obtained from red pine (Pinus brutia) or maritime pine (Pinus maritima).

Formula I

Isoamyl ester rosin is obtained through the esterification reaction of pine resin rosin with isoamyl alcohol. In the synthesis method covered by the invention, a reaction accelerator catalyst is used to facilitate the reaction, high temperature and pressure conditions are employed to protect the isoamyl ester rosin product, an antioxidant is added to preserve the product, and an alcohol is used to esterify the carboxylic end of the rosin, which possesses nucleophilic characteristics.

In the synthesis method of isoamyl ester rosin compound, para-toluenesulfonic acid (P-TSA) is used as a catalyst at a ratio of 1.5%. P-TSA provides the necessary proton for the esterification reaction. The amount of acid catalyst added to the environment during the production of isoamyl ester rosin is crucial. An increase in the amount of acid catalyst can lead to resin degradation, while a lower amount than necessary can hinder the esterification of the rosin. However, due to the trace amount used in the invention (1.5%), there is no degradation in the isoamyl ester rosin compound.

In the method according to the invention, 2,4-bis(dodecylthiomethyl)-6- methylphenol compound is used as an antioxidant at a ratio of 0.15%. If the antioxidant amount is lower than necessary, the resin rosin cannot be adequately protected under environmental conditions, resulting in discoloration of the final product. On the other hand, excessive antioxidant content can overly protect the rosin, hindering the occurrence of the esterification reaction. Moreover, the compound 2,4- bis(dodecylthiomethyl)-6-methylphenol used as an antioxidant can also function as a catalyst due to its proton present in its structure. In the method of the invention, isoamyl alcohol is used for the esterification of the carboxylic end of the rosin, which possesses a nucleophilic character, to enable the esterification reaction. In the invention, isoamyl alcohol is obtained as a result of the fractional distillation of fusel oil, which is a byproduct generated as waste during the production of ethanol (bioethanol) from sugar cane molasses.

The synthesis scheme of the isoamyl ester rosin compound subject to the invention is as follows: (abietic

The synthesis method of the isoamyl ester rosin compound subject to the invention comprises the following steps: i. Producing transparent, yellow-colored, crystalline abietic acid-containing pine resin rosin by distilling 100 g of pine resin using a simple distillation apparatus with temperature control for 3 hours. ii. Producing isoamyl alcohol through fractional distillation of fusel oil in a separate location. iii. Placing 50 g (165 mmol) of the abietic acid-containing pine resin rosin obtained in step (i) and 36 ml of isoamyl alcohol (330 mmol) (1/2 n) obtained in step (ii), along with 0.75 g (1 .5% w/w) of P-TSA and 0.075 g (0.15% w/w) of antioxidant, in a 250 ml threenecked flask. Mixing the contents at the boiling temperature for 15 hours. iv. Obtaining isoamyl ester rosin after the 15-hour reaction.

The reaction time varies depending on the nature of the starting material. When reacting with pine resin rosin, the reaction time is approximately 15 hours. The reaction process involves placing the components in the flask at the specified temperature, under nitrogen, and progressing with reflux (boiling). The reaction process continues based on monitoring the acid value and IR spectrum. The reaction is terminated when complete esterification is achieved. Additionally, a sample was taken from the product obtained at the end of the 15- hour period and the acid value was determined according to ASTM D 465-05. The acid value was found to be 25.68 mg KOH/g. As the acid value approaches zero, the thermoplastic characteristics increase in modified rosin, and an acid value within the range of 25-30 mg KOH/g is considered adequate for the compound discussed in the invention. This is because as thermoplastic properties increase, hydrophobic characteristics also increase. The compound in question should not exhibit excessive hydrophobic characteristics as it will be used in the production of biobased hardeners.

In the method for synthesizing the isoamyl ester of rosin subject to the invention, step (ii) involves the production of isoamyl alcohol through fractional distillation of fusel oil comprising the following sub-steps: a) Passing the fusel oil through ordinary filter paper to remove impurities, b) Adding 400 g of Na2SC>4 per 1 liter of fusel oil to the filtered fusel oil to remove the water present in it and stirring the mixture using a magnetic stirrer without applying heat overnight to obtain a homogeneous solution, c) Passing the obtained solution through a molecular sieve to remove any remaining water, d) Passing the solution with removed water through a 125 mm filter paper to prepare the fusel oil solution for fractional distillation, e) Obtaining isoamyl alcohol through fractional distillation of the prepared fusel oil solution.

After conducting GC-MS analysis of the fusel oil, the fractional distillation process was initiated. The fractional distillation was carried out in three stages, during which the fusel oil was separated into its fractions using the fractional distillation method. The fractions at 90°C, 90-100°C, and 100°C were collected separately in bottles and preserved. Subsequently, the fractions stored in separate bottles were combined according to their respective boiling temperature ranges and subjected to another round of fractional distillation. In the second round of fractionation, the fractions at 78- 80°C, 80-97°C, 97-100°C, and 100°C were obtained. Despite the boiling point of isoamyl alcohol being 131 °C, the presence of various chemicals within the mixture created azeotropic environments, causing the reaction temperature to conclude in the range of 105-110°C. The term "molecular sieve" mentioned here refers to Molecular Sieve 3A. Molecular Sieve 3A is an alkali metal aluminosilicate. It is of Type A and exists in the crystalline structure as the potassium form. Molecular Sieve 3A has an effective pore diameter of approximately 3 angstroms (0.3 nm). The 3 angstrom (0.3 nm) pore size is suitable for the adsorption of moisture.

The characterization of rosin and isoamyl ester rosin compounds was carried out through mass spectrometry, FT-IR, ¹³ C-NMR, and ¹ H-NMR analyses. The ¹³ C- NMR and ¹ H-NMR data of these compounds were measured using a 400 MHz Nuclear Magnetic Resonance (NMR) instrument with deuterated chloroform (CDCh) solvent and tetramethylsilane (TMS) standard. The IR spectra were recorded using the attenuated total reflection (ATR) technique on a FT-IR spectrophotometer.

The mass of the isoamyl ester rosin (Formula I) compound is 372.80 g/mol. The FT-IR, ¹³ C-NMR, and ¹ H-NMR results of the compound with the chemical structure shown in Formula I are provided below:

Formula I

FT-IR (v _max , cm' ¹ ): 1723,39 cm’ ¹ (C=O)

¹³ C-NMR, APT (DMSO-de, 5 ppm): 185,18 (C=O)

The mass of the compound of pine resin rosin (Formula II) is 302.92 g/mol. The FT-IR, ¹³ C-NMR, and ¹ H-NMR results of the compound with the chemical structure shown in Formula II are provided below:

Formula II • FT-IR (v _max , cm' ¹ ): 1693,73 cm’ ¹ (C=0), 1274,33 cm’ ¹ (C-0)

• ¹ H-NMR (DMSO-de, 5 ppm): 11 (s, 1 H, OH)

• ¹³ C-NMR, APT (DMSO-de, 5 ppm): 185,48 (C=0)

As seen in Figure 1 , the FT-IR spectrum of the pine resin rosin compound exhibits peaks at 2927.50 cm ^-1 and 2867.54 cm ^-1 , indicating aliphatic C-H bonds. The peak observed at 1689.73 cm ^-1 corresponds to C=O stretching. The peak at 1274.36 cm ^-1 indicates the presence of C-0 stretching within the -COOH group. As shown in Figure 4, the mass spectrum of rosin reveals the highest abundance of abietic acid and its fragmentation products within the compound.

As shown in Figure 5, the ¹ H-NMR spectrum of isoamyl ester rosin does not exhibit specific peaks. The -OH band observed at 11 ppm in the FT-IR spectrum of the pine resin rosin compound has disappeared in the ¹ H-NMR spectrum of isoamyl ester rosin In Figure 6, the ¹³ C-NMR spectrum of the isoamyl ester rosin displays the ester group (C=O) stretching vibration at 185.18 ppm. In Figure 7, the mass spectrum of isoamyl ester rosin shows the compound at 372.80 m/z. As depicted in Figure 8, the FT-IR spectrum of isoamyl ester rosin features the carbonyl group (C=O) stretching vibration at 1723.39 cm ^-1 .

The isoamyl ester rosin compound, subject of the invention, is in a liquid form, and this fluid structure makes it suitable for use as a biobased hardener in epoxy resins. Additionally, due to its hydrophobic property, the isoamyl ester rosin compound is suitable as an alternative to paraffin for use in the production of medium-density fiberboard (MDF).

The isoamyl ester rosin compound described in the invention has been utilized in the production of Medium-Density Fiberboard (MDF). The MDF produced with the mentioned isoamyl ester rosin compound underwent analyses including moisture content, density, tensile strength, flexural modulus, bending strength, swelling, and water absorption. These analysis results were compared to those of MDF produced with paraffin. Four different MDF samples were prepared, containing 1% and 1.5% isoamyl ester rosin and paraffin, respectively. The analysis results are presented in Table 1 and Table 2.

Table 1. Comparison of MDF samples containing 1.5% paraffin and 1.5% isoamyl ester rosin As seen in Table 1 , the higher density of the panels produced with paraffin has resulted in higher resistance values. The decrease in resistance values of the panels produced using isoamyl ester rosin can be attributed to their lower density. The obtained results indicate that isoamyl ester rosin can be a sustainable and environmentally friendly alternative to petrochemical-derived paraffin, as it is biobased and eco-friendly.

Table 2. Comparison of MDF Samples Containing 1 % Paraffin and 1 % Isoamyl Ester

Rosin As seen in Table 2, the higher density of panels produced with paraffin has contributed to higher resistance values. The decrease in resistance values of panels produced using isoamyl ester rosin can be attributed to their lower density. The obtained results, along with this comparison, demonstrate that isoamyl ester rosin can be considered a sustainable, biobased, and environmentally friendly alternative to petrochemical- derived paraffin. The potential use of isoamyl ester rosin as an alternative material is highlighted by these findings.

The flexural modulus of elasticity of the mentioned MDFs was determined according to the standard TS EN 310 [181]. The flexural modulus of elasticity (E) was calculated using Equation I.

Equation I

Here;

Ae = Deflection (displacement) (cm)

F = Force causing deformation (kg)

L = Span between support points (cm) d = Sample thickness (cm) b = Sample width (cm).

Bending strength has been determined according to the relevant standard (TS EN 310 [181]). It is calculated using Equation II.

Equation II

Here:

F = Maximum force at the moment of fracture (kg)

L = Span between support points (cm) d = Sample thickness (cm) b = Sample width (cm) Swelling analysis; in accordance with the standard (TS EN 317 [180]), MDF samples of dimensions 50x50x10 mm were prepared, and the central parts of these samples were measured using a digital comparator gauge with a sensitivity of ±0.01 mm. The samples were kept in pure water at a temperature of 20±2°C, submerged 3 cm below the water surface. After 24 hours, the samples were removed from the water, excess water was removed with a dry cloth, and the thicknesses were measured again with the same precision. The swelling amount of the samples, or in other words, the increase in thickness, was calculated using Equation III. 100

Equation III

Here; ey = Thickness of the samples immersed in water (mm) ek = Thickness of the samples in conditioned state (mm).

The water absorption rate was determined according to the standard ASTM D1037 [179]. Specimens with dimensions of 50x50x10 mm were prepared and weighed on a precision balance with a sensitivity of ±0.01 grams. The specimens were immersed in distilled water at a temperature of 20±2°C for a period of 24 hours, with the water surface being 3 cm below the top of the specimens. After the designated time, the specimens were removed from the water and excess water was removed using a dry cloth, after which their weights were measured on a precision balance with a sensitivity of ±0.01 grams. The water absorption rate was calculated using Equation IV. 100

Equation IV

Here;

% SA = Water absorption rate (%)

M0 = Initial weight of the sample (g)

M = Weight of the sample after immersion in water (g). REFERENCES

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