WO2024239083A1 - Method for obtaining lignin dispersion, lignin dispersion, use of the lignin dispersion, phenolic resin composition with lignin, and use of the phenolic resin composition with lignin - Google Patents

Abstract

The present invention aims to provide a method for obtaining lignin dispersion, which directly replaces phenolic resins with lignin in a phenolic resin mixture, while also providing phenolic resin compositions with lignin having suitable physical and chemical properties for application as an adhesive in the bonding of different wood substrates or as a binder.

Description

PROCESS OF OBTAINING LIGNIN DISPERSION, LIGNIN DISPERSION, USE OF LIGNIN DISPERSION, COMPOSITION OF PHENOLIC RESIN WITH LIGNIN AND USE OF COMPOSITION OF PHENOLIC RESIN WITH LIGNIN

TECHNICAL FIELD

[0001] The present invention belongs to the field of renewable materials and relates to a process for obtaining lignin dispersion, to said lignin dispersion and its respective use, to a composition of phenolic resin with lignin and its respective use.

[0002] Specifically, the process of the present invention is related to the preparation of lignin dispersion, which directly replaces phenolic resins (resol) with lignin in up to 50% of the resin, while obtaining compositions of phenolic resins with lignin with suitable characteristics of physical-chemical properties for application in the gluing of different wood substrates (for example, plywood, MDF (medium density fiberboard), MDP (medium density particleboard) and OSB (oriented strand board)).

FUNDAMENTALS OF THE INVENTION

[0003] In the current context in which sustainability has gained increasing relevance, the search for high-quality materials from renewable sources has been intensified, in which the replacement of fossil components with natural components is particularly advantageous.

[0004] In the search for renewable materials, biomass from lignocellulosic sources has always offered different alternatives, given its wide availability and variety, with the following primary constituents: cellulose, hemicellulose and lignin.

[0005] Lignin should be highlighted, since it can be considered the most abundant aromatic macromolecule from a renewable source in nature, formed from phenylpropane units (basically by random bonds of three monolignol precursors: coniferyl alcohol (guaiacyl), p-coumaryl alcohol (hydroxyphenyl) and sinapyl alcohol (syringyl)).

[0006] Lignin is generally present in the residual fractions generated as secondary streams in carbohydrate-based conversion processes, such as the cellulose and bioethanol industries, and is generally burned to obtain energy. Instead, lignin can be used to manufacture new high-value-added products, improving the sustainability and competitiveness of these lignocellulosic transformation processes (BORRERO-LÓPEZ, 2020).

[0007] One of the most discussed applications for the use of lignin refers to the use of this material in phenolic synthesis (KALAMI, 2018; CETIN, 2002). Specifically, its nature phenolic allows this material to be a potential substitute for phenolic products, with greater emphasis in the literature for partial replacement of phenol in the synthesis of phenol-formaldehyde resins.

[0008] However, it has been extensively reported about the lower reactivity of lignin towards formaldehyde, caused by the greater steric hindrance of macromolecules, lower accessibility of the free positions of the reactive ring in relation to formaldehyde, lower availability of available reactive aromatic sites, which are some factors that must be considered in the development and limit the total replacement of phenol by lignin. Many researchers have used different modification techniques to improve the low reactivity of lignin towards formaldehyde, such as: demethylation, phenolation and methylolation (GORBHANI, 2018).

[0009] It is worth noting that there are other technological routes for incorporating lignin into phenolic resins. Since lignin is basically formed by aromatic macromolecules, instead of using it as a derivative of phenol synthesis, it can also be used as a substitute for phenol-formaldehyde resins in various applications.

[0010] Phenolic resins are considered prepolymers that need to be cured during the application process in order to become thermosets with adhesive properties. This process for conversion into highly crosslinked products can be promoted without the addition of a curing agent. This is possible due to the presence of hydroxymethylated groups linked to the ring. Thus, only through thermal action does the phenolic system initiate the characteristic curing reactions, and the temperature used varies according to the process in which the resin is being used, as well as the composition of the resole (BORGES, 2004).

[001 1 ] In macromolecular chemistry, crosslinking refers to reactions in which a large number of individual molecules are linked together to form a three-dimensional network. The linking can be achieved by direct configuration of macromolecules or by reaction to existing polymers. This can be easily measured by means of differential scanning calorimetry (DSC).

[0012] It is important to highlight that the chemical structure of the phenolic resin varies according to the different synthesis conditions and the proportions of the reagents, and this diversity in its chemical structure determines the complexity of the phenolic resin curing process. At the same time, the diversity of phenolic resin species also leads to completely different curing reaction mechanisms (PILATO, 2010). [0013] Thus, when lignin is mixed with a phenolic resin for substrate bonding, the curing and adhesion mechanisms of the mixed system are expected to be different from the resin alone.

[0014] When using lignin as a substitute for phenolic resins, for example as an adhesive for wood panels, the efficiency may not be the same, as lignin is a polymer with few positions to promote crosslinking, so this limits the percentage of substitution.

[0015] In fact, the lower reactivity of lignin in relation to formaldehyde, as mentioned above, prevents and discourages its use as a substitute for the fossil component of phenolic resin.

[0016] Furthermore, the use of a material in powder form, such as Kraft lignin, as a substitute for liquid phenolic resin, becomes an obstacle, as it causes inconvenience or impacts for the end user who is accustomed to and has infrastructure designed for liquid dosing.

[0017] Furthermore, the known technique of solubilizing lignin in caustic soda (NaOH) as a way of enabling its use in liquid form results in a mixture with high viscosity and a lower content of active solids, so that it becomes a solid paste and not a liquid that can be added or transported in the product.

[0018] For example, the paper by Yang, M. et al, “Preparation and properties of adhesives based on phenolic resin containing lignin micro and nanoparticles: A comparative study”, Materials and Design, 161, 55-63, 2019 reveals a complex process of physicochemical modification of lignin for its use in a mixture of resin and lignin in an ice bath.

[0019] The document by Wang, G. et al, “Carbohydrate elimination of alkaline-extracted lignin liquor by steam explosion and its methylolation for substitution of phenolic adhesive", Industrial Crops and Products, 53, 93-101 , 2014 describes a process of activating lignin so that it can participate in the resole curing process, in which activation is achieved through a hydroxymethylation treatment of lignin with formaldehyde, a toxic reagent.

[0020] However, none of the prior art documents were able to provide a lignin solubilization process that enables its use in phenolic resin composition, that is, in which the lignin dispersion obtained presents good viscosity, solids content and residual enthalpy characteristics. These characteristics will ensure that lignin can replace resole in a phenolic resin mixture, allowing the curing of said mixture to obtain a thermosetting polymer with adhesive properties. [0021] Thus, considering that there are a series of challenges related to the replacement of phenolic resins with renewable materials, mainly with regard to compatibility with other components and the workability of the final product, obtaining an environmentally friendly product with adequate physical-chemical and mechanical properties to be applied as an adhesive in the gluing of different wood substrates or as a binder is still a challenge and a necessity in the technique.

[0022] Therefore, the present invention provides a technical solution to this need through a process for obtaining lignin dispersion and its use in a phenolic resin composition with lignin for application as an adhesive on wood substrates, for example, plywood, MDF, MDP and OSB, in which the phenolic resin compositions with lignin present physicochemical and mechanical properties similar to phenolic resins without lignin.

[0023] Specifically, the present invention relates to the replacement of a petrochemical adhesive (fossil component) by a renewable and environmentally friendly material as obtained by the process of the present invention. Said replacement will consequently provide the technical advantage of reducing the content of free formaldehyde and phenol in the final composition of the phenolic resin material, while maintaining the applicability characteristics of phenolic resins without said replacement.

SUMMARY OF THE INVENTION

[0024] The present invention discloses a process for obtaining lignin dispersion, in which said dispersion is produced under alkaline catalysis for application in a phenolic resin composition that will be used as an adhesive in wood substrates or as a binder.

[0025] Specifically, lignin dispersion directly replaces phenolic resins with lignin.

[0026] Furthermore, the present invention also provides the advantage that the lignin dispersion already has a solids content close to that of the phenolic resin, thus providing greater ease of processing the product, as well as the possibility of a higher level of incorporation of lignin into the resin.

[0027] One embodiment of the invention relates to a process for obtaining lignin dispersion comprising the following steps: a) loading water at room temperature into the reactor; b) adding lignin under stirring; c) adding an alkalizing agent and checking the resulting pH; d) adjusting the pH; e) heat the mixture and let it react; f) carry out distillation under vacuum and at temperature; eg) monitor the viscosity of the mixture.

[0028] Another embodiment of the invention describes a lignin dispersion.

[0029] In another embodiment of the invention, the use of lignin dispersion to partially replace phenolic resin (resole) with lignin in a mixture of phenolic resin with lignin is described.

[0030] In yet another embodiment of the invention, a phenolic resin composition with lignin is described with suitable viscosity, solids content and residual enthalpy characteristics to be applied in the gluing of different wood substrates (e.g. plywood, MDF, MDP and OSB).

[0031] In another embodiment of the invention, the use of the phenolic resin composition with lignin as an adhesive or binder is described.

BRIEF DESCRIPTION OF THE FIGURES

[0032] To assist in identifying the main features of the present invention, some figures are presented to which reference is made, as follows:

[0033] FIG. 1 illustrates a graph of the viscosity of the acidic lignin dispersion after its production over a period of 30 days.

[0034] FIGS. 2 to 3 illustrate graphs of the viscosity monitoring of phenolic resin mixtures with lignin dispersions produced in different ways, as a function of shelf time at ambient conditions.

[0035] FIG. 4 is a differential scanning calorimetry (DSC) analysis of samples with different levels of phenolic resin substitution by lignin compared to the reference phenolic resin, i.e., without lignin.

[0036] FIG. 5 is a comparative graph of the residual enthalpy of samples with different levels of substitution of phenolic resin by lignin in comparison with the reference phenolic resin, in cold tests or under lignin cooking conditions.

[0037] FIG. 6 is a Fourier Transform Infrared Spectroscopy (FTIR spectra) image of samples with different levels of Kraft lignin incorporation with commercial phenolic resin without curing process. [0038] FIG. 7 is a Fourier Transform Infrared Spectroscopy (FTIR spectra) image of samples with different levels of Kraft lignin incorporation with commercial phenolic resin after curing process at 154°C.

DETAILED DESCRIPTION OF THE INVENTION

[0039] The invention relates to a process for obtaining a lignin-based adhesive dispersion for application in a phenolic resin composition, in which the reference phenolic resin is partially replaced in said composition by lignin in a proportion of up to 50%.

[0040] The term “dispersion” should be understood as a mixture of substances, of a solid finely distributed in a liquid.

[0041] The terms “phenolic resin composition with lignin”, “phenolic resin composition with lignin dispersion”, “phenol-formaldehyde resin mixture with lignin dispersion”, “phenolic resin mixture” and “phenolic resin mixture with lignin” are interchangeable with each other and should be understood as the product resulting from the partial replacement of phenolic resin with a lignin dispersion.

[0042] Specifically, the phenolic resin composition with lignin dispersion of the present invention is used for application as an adhesive on wood substrates or as a binder (“binder ¹ '), in which an activated lignin dispersion directly replaces phenolic resins (resol), while maintaining suitable viscosity, solids content and residual enthalpy characteristics to be applied in the gluing of different wood substrates (e.g. plywood, MDF, MDP and OSB).

[0043] Lignin is originally less crosslinkable than resole, mainly due to its few positions where molecules can be linked to form a three-dimensional network, so that this limits the percentage of substitution. Thus, the Kraft pulping process provides a more reactive lignin (Kraft lignin), to be added to the process for obtaining lignin dispersion of the present invention.

[0044] Despite the known difficulty related to the increase in viscosity in the process of solubilizing lignin in sodium hydroxide (NaOH), the inventors of the present invention were unexpectedly able to obtain a method that combines the application of vacuum (pressure) and temperature during the preparation of a lignin dispersion for application in a mixture of phenolic resin with lignin, in which the properties of the final product are positively impacted, allowing greater flexibility in the application due to the control of viscosity and a high solids content. [0045] When the technical solution described in this application is used, involving a whole sequence of steps and use of temperature with vacuum, this lignin dispersion can be mixed with phenolic resin without presenting problems of increased viscosity, which would make its application unfeasible, since the increase in viscosity would transform the product into a solid paste and not a liquid that can be transported or added to the phenolic resin mixture.

[0046] That is, the technical solution described in the present invention is related to the use of the combined strategy of temperature and distillation under reduced pressure to obtain a lignin dispersion that, when replacing the resole, allows the phenolic resin composition with lignin to be applicable as an adhesive with mechanical and physicochemical properties similar to phenolic resins without said lignin, but with the advantage of comprising a sustainable component partially replacing a fossil component.

[0047] Surprisingly, the inventors of the present invention have demonstrated that by distilling and heating the lignin dispersion, the residual curing enthalpy decreases, which provides the technical advantage of applying the phenolic resin and lignin composition as an adhesive in bonding wooden substrates.

[0048] In fact, the reduction of residual enthalpy as a result of the process of the present invention complements the crosslinking process (curing process) for transforming the mixture of phenolic resin with lignin described herein into a thermosetting material for application as an adhesive.

[0049] In a first embodiment, a process for obtaining lignin dispersion in an aqueous and basic medium is disclosed, comprising the following steps: a) loading water at room temperature into the reactor; b) adding lignin under stirring; c) adding an alkalizing agent and checking the resulting pH; d) adjusting the pH; e) heating the mixture and allowing it to react; f) performing distillation under vacuum and temperature; and g) monitoring the viscosity of the mixture.

[0050] Optionally, the process of obtaining lignin dispersion further comprises the following steps: h) cooling the reaction; and i) unload and screen the resulting material.

[0051] In some embodiments, the amount of water loaded in step a) is in the range of 800 to 2,000 g, preferably in the range of 1,000 to 1,900 g, more preferably in the range of 1,100 to 1,800 g.

[0052] In some embodiments, the lignin of step b) is selected from the group consisting of powdered lignin, acidic lignin cake, and unwashed lignin cake (alkaline lignin).

[0053] When the lignin is in the form of powdered lignin, step b) of adding said lignin is carried out under vigorous stirring and homogenization is maintained at room temperature. In addition, the heating of step e) is maintained by complete dissolution of the lignin.

[0054] In some embodiments the amount of powdered lignin added in step b) is in the range of 800 to 1,100 g, preferably in the range of 900 to 1,000 g, more preferably 966 g.

[0055] When the lignin is in the form of acid lignin cake or unwashed cake, step b) of adding said lignin is through dispersion under agitation until a homogeneous paste (“slurry”) is obtained.

[0056] In some embodiments, the acidic lignin cake is dispersed in step b) in an amount in the range of 1,300 to 1,700 g, preferably in the range of 1,500 to 1,600 g, more preferably 1,548 g.

[0057] In some embodiments, the acid lignin cake has a solids content in the range of 50% to 80%, preferably in the range of 55% to 65%, more preferably 59%.

[0058] In some embodiments, the agitation to obtain the homogeneous paste (“slurr”) in step b) is carried out in the range of 1 to 3 hours, preferably 2 hours.

[0059] In some embodiments, the agitation of step b) is in the range of 250 to 450 rpm, preferably in the range of 300 to 400 rpm, more preferably 350 rpm.

[0060] In some embodiments, homogenization is performed in the range of 20 to 60 minutes, preferably in the range of 25 to 45 minutes, more preferably 30 minutes.

[0061] In some embodiments, the alkalizing agent added in step c) is a strong base to adjust the pH to a range of 12.5 to 13.5. Preferably, the strong base is caustic soda (NaOH). In embodiments where the addition of NaOH is not sufficient to bring the pH into the range of 13.0 +/- 0.5, the pH is adjusted to 13.5 by adding an additional amount of NaOH. [0062] Optionally, caustic soda can also be added together with the initial process water.

[0063] In some embodiments, caustic soda (NaOH) is used in concentrations of 50% (50% NaOH) or 33% (33% NaOH), or in pellet form. Preferably, 50% NaOH is used.

[0064] In some embodiments, heating the mixture in step e) is carried out at a temperature in the range of 40 to 95 ^° C, preferably 50 to 85 ^° C, more preferably 55 to 80 ^° C. The reaction time of the mixture after heating is 1 to 3 hours, preferably 2 hours.

[0065] In some embodiments, the vacuum distillation step is carried out at a pressure in the range of 150 to 500 mmHg (2.00 x 10 ⁴ to 6.66 x 10 ⁴ Pa), preferably 200 mmHg (2.67 x 10 ⁴ Pa). In turn, the temperature used in the distillation step is in the range of 60 to 95 ^° C, preferably in the range of 65 to 85 ^° C, more preferably in the range of 70 to 75 ^° C.

[0066] In some embodiments, the vacuum and temperature distillation step is carried out until the viscosity of the system is in the range of 100 to 2,500 cP (0.1 to 2.5 Pa.s), preferably in the range of 400 to 1,600 cP (0.4 to 1.6 Pa.s), more preferably in the range of 700 to 1,000 cP (0.7 to 1.0 Pa.s), even more preferably 915 cP (0.915 Pa.s).

[0067] In some embodiments, the cooling step is performed to a temperature between 50 and 60 ^s C.

[0068] In some embodiments, the sieving step is performed with a sieve having a mesh size in the range of 60 to 120 mesh. Preferably, a 66, 80 or 100 mesh sieve is used. Most preferably, a 66 mesh sieve is used.

[0069] After carrying out the process, the final dispersion has a solids content in the range of 40% to 55%, preferably 45% to 48%.

[0070] A second embodiment of the invention describes a lignin dispersion obtained by the process according to the first embodiment of the invention. In a particularly preferred embodiment, the lignin dispersion comprises a solids content in the range of 45 to 50%, pH in the range of 13.0 to 14.0 and viscosity in the range of 900 to 1600 cP (0.9 to 1.6 Pa.s).

[0071] In a third embodiment of the invention, the use of lignin dispersion to partially replace phenolic resin (resole) with lignin in a phenolic resin-lignin mixture is described. [0072] A fourth embodiment of the present invention relates to a composition of phenolic resin with lignin produced under alkaline catalysis according to the process of the present invention for application as an adhesive on wood substrates, in which said lignin directly replaces phenolic resins (resole) with lignin, in up to 50% of the resin.

[0073] Optionally, the replacement of phenolic resins by lignin is in the range of up to 30% of the resin, or in the range of up to 20% of the resin.

[0074] In some embodiments, the lignin is a Kraft lignin, preferably from hardwood.

[0075] A fifth embodiment of the present invention relates to the use of the phenolic resin composition with lignin as an adhesive or binder.

EXAMPLES

[0076] The following examples, described in detail, serve to illustrate embodiments of the present invention without, however, having a limiting character to the scope of protection thereof.

Example 1 - Process for preparing hot dispersion of lignin in aqueous and basic medium

[0077] The process consists of preparing a lignin dispersion in an aqueous and basic medium, which comprises the following steps: a) loading 1,142 g of water at room temperature into the reactor; b) gradually dispersing 1,548 g of acidic lignin cake with a solids content of 59% under stirring for 2 hours, until obtaining a “homogeneous slurry”, which was homogenized for 30 minutes; c) adding 368 g of 50% sodium hydroxide (NaOH) and checking the resulting pH; d) adjusting the pH to 13.5 by adding 100 g of 50% sodium hydroxide (NaOH); e) heating the mixture to a temperature between 50 and 60 ^s C and allowing it to react for 2 hours; f) carry out distillation under vacuum at a pressure of 200 mmHg (2.67 x 10 ⁴ Pa) and a temperature of 70 ^sC ; g) monitor the process until the viscosity of the system is between 700 and 1,600 cP (0.7 to 1.6 Pa.s).

Example 2 - Process for preparing a powdered lignin dispersion activated by reaction in an aqueous and alkaline medium at temperature [0078] The process consists of preparing an alkaline dispersion of acidic lignin, which comprises the following steps: a) adding 1,725 g of water at room temperature to the reactor; b) adding 966 g of lignin within two hours, with vigorous stirring at 350 rpm; c) maintaining homogenization for 30 minutes at room temperature; d) adding 367 g of caustic soda (NaOH) 50%; e) measuring the pH of the solution and adjusting it with further addition of caustic soda so that the pH is between 13.0 and 13.5; f) heating the reaction to a temperature between 55 and 80°C; g) maintaining heating for complete dissolution of the lignin for 2 hours; h) apply a vacuum to 200 mmHg (2.67 x 10 ⁴ Pa) and distill the solution at a temperature between 70 and 85°C until it reaches a viscosity between 100 and 2,500 cP (from 0.1 to 2.5 Pa.s); i) cool the reaction to a temperature between 50 and 60°C; j) discharge and sieve the resulting material with a 66 mesh sieve; and k) perform analyses of the material.

[0079] In this example, the distillate volume from step h) was measured at a value of 600 ml_.

[0080] Table 1 illustrates the components of the lignin dispersion of example 2:

Table 1 - components of lignin dispersion

[0081] Table 2 illustrates the properties of the lignin dispersion from example 2:

[0082] A Figura 1 ilustra o acompanhamento de viscosidade do produto após sua produção por um período de 30 dias. Table 2 - lignin dispersion properties

[0082] Figure 1 illustrates the viscosity monitoring of the product after its production for a period of 30 days.

[0083] The graph in Figure 1 shows that the product of the present invention is stable over time, that is, it does not have a very short shelf-life. Specifically, said graph indicates that the product can be stored and used after some time.

[0084] Furthermore, the viscosity of the product does not increase exponentially, which would make the use of the product unfeasible, and no precipitate formation was observed.

Example 3 - Process for preparing a lignin dispersion in an aqueous and alkaline medium at a temperature

[0085] The process consists of preparing an alkaline dispersion of acidic lignin, which comprises the following steps: a) adding 1,725 g of water at room temperature to the reactor; b) adding 966 g of lignin within two hours, with vigorous stirring at 350 rpm; c) maintaining homogenization for 30 minutes at room temperature; d) adding 367 g of caustic soda (NaOH) 50%; e) measuring the pH of the solution and adjusting it with further addition of caustic soda so that the pH is between 13.0 and 13.5; f) heating the reaction to a temperature between 55 and 80°C; g) maintaining heating for complete dissolution of the lignin for 2 hours; h) apply a vacuum to 200 mmHg (2.67 x 10 ⁴ Pa) and distill the solution at a temperature between 70 and 85°C until it reaches a viscosity between 50 and 1,000 cP (from 0.05 to 1.0 Pa.s); i) cool the reaction to a temperature between 50 and 60°C; j) discharge and sieve the resulting material with a 66 mesh sieve; and k) perform analyses of the material.

[0086] In this example, the distillate volume from step h) was measured at a value of 300 ml_.

[0087] Table 3 illustrates the components of the lignin dispersion of example 3:

Table 3 - components of lignin dispersion

[0088] Table 4 illustrates the properties of the lignin dispersion from example 3:

Table 4 - lignin dispersion properties

[0089] In other words, two distinct specifications of lignin dispersion modified by the process described were produced from the same quantity of raw materials.

Example 4 - Process for preparing a lignin dispersion using lignin cake activated by reaction in an alkaline medium at a temperature

[0090] The process consists of preparing an alkaline dispersion of acidic lignin, which comprises the following steps: a) adding 1,725 g of water at room temperature to the reactor; b) adding 966 g of acidic lignin cake within two hours, with vigorous stirring at 350 rpm; c) maintaining homogenization for 30 minutes at room temperature; d) adding 367 g of caustic soda (NaOH) 50%; e) measuring the pH of the solution and adjusting it with further addition of caustic soda so that the pH is between 13.0 and 13.5; f) heating the reaction to a temperature between 55 and 80°C; g) maintaining heating for complete dissolution of the lignin for 2 hours; h) apply a vacuum to 200 mmHg (2.67 x 10 ⁴ Pa) and distill the solution at a temperature between 70 and 85°C until it reaches a viscosity between 400 and 1,600 cP (from 0.4 to 1.6 Pa.s); i) cool the reaction to a temperature between 50 and 60°C; j) discharge and sieve the resulting material with a 66 mesh sieve; and k) perform analyses of the material.

[0091] Table 5 indicates the properties of the acid lignin cake from example 4:

Table 5 - Properties of acid lignin cake

[0092] Table 6 illustrates the components of the acidic lignin cake dispersion from Example 4:

Table 6 - Components of acidic lignin cake dispersion

[0093] Table 7 illustrates the properties of the acidic lignin cake dispersion from example 4: Table 7 - Properties of the acidic lignin cake dispersion

Example 5 - Partial replacement of the reference phenolic resin by lignin dispersion according to Example 2

[0094] For the partial replacement of the reference phenolic resin by the lignin dispersion, a phenol-formaldehyde resin (reference resin) was used with the following properties indicated in Table 8.

Table 8 - properties of phenol-formaldehyde resin

[0095] Specifically, the following levels of resin replacement by lignin were used: 7.5%, 10% and 20% as replacement of active solids.

[0096] The results of the properties of the reference resin and the resins carrying the solids replacement contents are shown in Table 9 below.

Table 9 - properties of the reference resin and resins with lignin substitution

[0097] With the increase in the replacement of lignin adhesive in place of phenolic resin, it is possible to see some differences in relation to the reference resin, such as an increase in pH, a drop in solids content and an increase in gel time.

Example 6 - Phenol-formaldehyde resin mixture with lignin dispersion

[0098] In order to prove that two materials can replace phenol-formaldehyde resins, resole type, mixtures were prepared by replacing phenolic resin with lignin in the following proportions: 10, 20, 30, 40 and 50% (mass of active solid, i.e. dry base resin per lignin dispersion, also in dry mass).

[0099] The shelf-life of the resin and lignin mixture was monitored over time with periodic viscosity measurements.

[0100] Figure 2 illustrates the evolution of the viscosity of the mixture of phenolic resin with lignin dispersion produced in example 2 as a function of shelf time under ambient conditions. [0101] The results of the properties of the mixture of phenolic resin with lignin dispersion produced in example 2 are shown in table 10 below:

Table 10 - properties of the phenol-formaldehyde resin mixture with lignin produced according to example 2

[0102] Figure 3 illustrates the evolution of the viscosity of the mixture of phenolic resin with lignin dispersion produced in example 3 as a function of shelf time under ambient conditions.

[0103] The results of the properties of the mixture of phenolic resin with lignin dispersion produced in example 3 are shown in table 11 below: Table 11 - properties of the mixture of phenol-formaldehyde resin with lignin produced according to example 3

[0104] The most important parameters for applying a resin are viscosity and gel time. In order to verify the stability of the generated product, the material produced in examples 2 and 3 was subjected to aging under ambient conditions and these parameters were analyzed 40 and 70 days after its production, as shown in table 12:

Table 12 - Gel time measured in minutes of the phenol-formaldehyde resin mixtures with lignin according to examples 2 and 3 as a function of the aging time under ambient conditions

[0105] According to the National Wood Quality Program (PNQM), established by the Brazilian Association of the Mechanically Processed Wood Industry, the curing time of a phenolic adhesive must be between 6 and 12 minutes according to the methodology used in this document. Therefore, even after 70 days, despite the reduction in gel time, the material is still within the phenolic resin specification for application.

[0106] This change in gel time is expected and comes from condensation reactions of the phenol formaldehyde resin with lignin that occur as a function of production time.

[0107] Resol-type phenolic resins applied to wood panels can have a gel time of 6 to 11 minutes. Thus, the results obtained by replacing resin with lignin are within the range for the desired application for this material. Table 13 - Brookfield viscosity measured in centipoise (cP) of phenol-formaldehyde resin mixtures with lignin dispersion according to examples 2 and 3 as a function of aging time under ambient conditions

[0108] The viscosity of the mixtures shows an increasing tendency, which also occurs with the phenol-formaldehyde resin as the aging time progresses.

[0109] With the data reported in table 13, up to 40 days, the mixtures are still suitable as they have a plausible application viscosity.

[01 10] It is found that phenol-formaldehyde resin formulations with partial replacement by a lignin-containing dispersion are within the gel time and viscosity requirements adopted by most users of phenolic resin for the manufacture of plywood.

[01 1 1] The process allows the generation of distinct products with different behaviors in relation to the viscosity of the mixture, since the product generated in example 3 forms mixtures with lower viscosities than the product generated in example 2, even at higher lignin substitution levels. In turn, the solids contents of the mixture in example 2 and the mixture in example 3 are similar.

[01 12] Specifically, the resins were applied in the production of composite phenolic plywood panels with 5 industrial Pinus spp. veneers, with dimensions of 500 mm x 500 mm x 3.0 mm (length, width and thickness, respectively), generating a panel with a nominal thickness of 15 mm. In the formulation, in addition to the resin, extender (common wheat flour) and water were used, generating a glue mix with a solids content of around 30%.

[01 13] According to the national wood quality program (PNQM), a newly produced resin must have a viscosity of approximately 400 to 800 cP (0.4 to 0.8 Pa.s). [01 14] This adjustment ensures that the amount of resin applied is the same, since the samples have different solids contents. The parameters used to produce the panels are listed in table 14 below.

Table 14 - parameters used for the production of phenolic plywood panels

[01 15] To evaluate the mechanical properties, 12.5% of resin was applied by mass, relative to the mass of the pine veneer.

[01 16] After pressing, the panels were conditioned until stabilization. After conditioning, test specimens were prepared to evaluate the bonding quality by measuring the glue line's resistance to shearing, in accordance with European standards (CEN - European Committee for Standardization).

- EN 314-1 (2004) - Plywood- Bonding quality- Test methods

- EN 314-2 (2002) - Plywood- Bonding quality- Requirements

[01 17] The pre-treatments performed on the test specimens of the different treatments were:

- Dry (air-conditioned);

- Immersion in cold water for 24 hours (20±3°C);

- Boiling 6h (Boiling for 6 hours and cooling for 1 hour in water at 20±3°C); and

- Boiling cycle (4 hours of boiling; 16-20 hours of drying at 60±3°C; 4 hours of boiling; cooling for 1 hour in water at 20±3°C).

[01 18] After pretreatments, the shear bond strength of the glue line was determined as requested by the methodology for each of the samples (reference resin and resins with lignin at 7.5%, 10% and 20%). The average results are detailed in Table 15 below. Table 15 - Shear stress results on wood panels under different test conditions (dry, cold water and boiling cycle)

[01 19] The results obtained were subjected to statistical analysis, using tests for: outliers, homogeneity of variances, analysis of variance and comparison of Tukey means, at 95% confidence.

[0120] From the results, it can be seen that the levels of replacement of phenolic resin by alkaline lignin dispersion present the same bonding quality as the reference resin in the different treatments to which they were subjected.

[0121] In the boiling cycle test, it is important to note that in the comparison with the reference resin, the average values of the resins with lignin are equal and greater than 1 MPa. Thus, the wood panel with different contents of the lignin-based adhesive is approved according to evaluations of the EN 314-2 standard.

Example 7 - Evaluation of residual cure of phenolic resin mixture with lignin dispersions

[0122] From the powdered lignin, two alkaline mixtures were prepared, one made only from the dissolution of lignin in water/soda 50% (solids content = 43.5%) and the other following the procedure described in the present invention (solids content = 47%).

[0123] Mixtures of a phenol formaldehyde resin for gluing wood were prepared, with replacement of said resin with lignin dispersions in increasing amounts (5-20%), in percentage.

[0124] The resin/lignin mixtures were cured, that is, subjected to heat to transform into a thermosetting polymer (thermosetting resin) on a plate at 154 ^° C, in a manner analogous to ASTM D4040-6, defining the time (expressed in seconds) required for the resin kept under a hot surface (at a certain temperature) and under the movement of a spatula, polymerize and adhere to the surface and no longer to the sheet.

[0125] After the curing process, the mixtures were subjected to differential scanning calorimetry (DSC) analysis to check whether all the material had cured. This can be seen in the endothermic peak in the thermogram illustrated in Figure 4.

[0126] The results obtained, which are summarized in Figure 4, demonstrate that after the material curing process, the mixtures with levels of resin replacement by Kraft lignin adhesive maintain properties similar to the reference resin and, therefore, do not impact the curing process of a resin without lignin.

[0127] Figure 5 illustrates the results for the analysis of residual enthalpy in J/g of a phenol formaldehyde resin without lignin and of resin mixtures with replacement of said resin with lignin dispersions in increasing amounts (from 5 to 20%) in cold and baking tests.

[0128] Analyzing the residual enthalpy values illustrated in Figure 5, it can be seen that at the temperature used for curing, the reference phenolic resin (i.e., without lignin) did not cure completely, exhibiting a residual enthalpy of 269 J/g.

[0129] However, when the resin is replaced by a dispersion of cold-dispersed lignin in an alkaline medium, the residual enthalpy is higher, that is, the mixture cured less than the reference resin during the heating process on the plate, so that the material is more difficult to crosslink.

[0130] In turn, when the process described in the present patent application is carried out, that is, replacing resin with a dispersion of lignin dispersed under cooking in an alkaline medium, it is found that the residual enthalpy is in the same range of values as the reference resin, even when 20% of the resin was replaced by the lignin dispersion.

[0131] Thus, the conclusion obtained from this experiment is that the process developed in this patent application is capable of replacing phenol formaldehyde resin without disrupting the curing process for use as a thermosetting resin component, which can lead to better adhesion of the material, as this characteristic is also linked to the degree of crosslinking.

Example 8 - Evaluation of Fourier transform infrared spectroscopy (FTIR spectra) of the incorporations of lignin adhesive with commercial phenolic resin with different resin replacement levels without curing process [0132] Figure 6 illustrates the FTIR spectra of the samples of the reference phenolic resin without lignin and of the resin mixtures with lignin at resin replacement levels of 7.5%, 10% and 20%, but without a curing process.

[0133] When comparing the infrared spectra of the reference resin and the resins in which lignin was incorporated, it is noted that the spectra basically overlap, so that no distinct bands are observed with the incorporation of the new component. This indicates that the product has no structural differences and has similarities to the resins up to the percentage of 20% replacement of resin by lignin.

[0134] Specifically, the IR spectrum of the resin in the initial state has the most intense band. The maximum is recorded at the wavelength close to 3400 cm ^-1 .

Example 9 - Evaluation of Fourier transform infrared spectroscopy (FTIR spectra) of the incorporations of lignin adhesive with commercial phenolic resin with different resin substitution levels after curing process at 154 ^° C

[0135] Figure 7 illustrates the FTIR spectra of the samples of the reference phenolic resin without lignin and of the resin mixtures with lignin at resin replacement levels of 7.5%, 10% and 20%, but with the curing process carried out at 154 ^° C.

[0136] After the material curing process, the infrared spectrum profiles are still very similar, demonstrating, therefore, that replacing the reference resin with lignin also does not affect the curing process, molecular structure and adhesive capacity of the thermosetting product.

[0137] Thus, it is observed that the 3400 cm ^-1 band is drastically reduced in all cases in Figure 7, showing similar cures.

[0138] It is understood that when a range of parameters is given, all integers and ranges within that range, and tenths and hundredths, are also given by the embodiments. For example, “5-10%” includes 5%, 6%, 7%, 8%, 9%, and 10%; 5.0%, 5.1%, 5.2%....9.8%, 9.9%, and 10.0%; and 5.00%, 5.01%, 5.02%....9.98%, 9.99%, and 10.00%, as well as, for example, 6-9%, 5.1%-9.9%, and 5.01%-9.99%. Likewise, when a list is given, unless otherwise indicated, it is to be understood that each individual element of that list, and each combination of components of that list, is a separate embodiment. For example, “1, 2, 3, 4 and 5” includes, among numerous modalities, 1; 2; 3; 1 and 2; 3 and 5; 1, 3 and 5; and 1, 2, 4 and 5. [0139] It should be understood that the embodiments described above are merely illustrative and that various modifications may be made by a person skilled in the art to them without departing from the scope of the present invention. Consequently, the present invention should not be considered limited to the exemplary embodiments described in the present application. Furthermore, the present disclosure may include subject matter not currently claimed, but which may be claimed in the future in combination with or separately from the features now claimed.

References:

- Antonio M. Borrero-López, Raquel Martín-Sampedro, David Ibarra, Concepcion Valencia, Maria E.

Eugenio, José M. Franco, “Evaluation of lignin-enriched side-streams from different biomass conversion processes as thickeners in bio-lubricant formulations”, International Journal of Biological Macromolecules, Volume 162, 2020, pages 1398-1413, ISSN 0141 -8130 , https://doi.Org/10.1016/j.ijbiomac.2020.07.292.

- Kalami, S.; Chen, N.; Borazjani, H.; Nejad, M., “Comparative Analysis of Different Lignins as Phenol Replacement in Phenolic Adhesive Formulations”, Ind. Crop. Prod. 125, 520-528, 2018.

- Cetin, N.S.; Ozmen, N., “Use of Organosolv Lignin in Phenol-Formaldehyde Resins for Particleboard Production — I. Organosolv Lignin Modified Resins,” Int. J. Adhes. Addhes. 22, 477-480, 2002.

- Ghorbani, M.; Mahendran, A.; Hendrikus van Herwijnen, W.; Liebner, F., “Paper-based laminates produced with kraft lignin-rich phenolformaldehyde resoles meet requirements for outdoor usage", European Journal of Wood and Wood Products 76:481-487, 2018.

- Borges, S. G., “Synthesis and characterization of novolac-type liquid phenolic resins applicable in the pultrusion process”, Master's dissertation, Universidade Federal do Rio Grande do Sul - UFRGS.

- Pilato L, “Resin chemistr, In: Pilato L (ed) Phenolic Resins: A Century of Progress[M], Berlin, Heidelberg: Springer-Verlag; 2010, pp. 41-91.

- Lee, Y., Kim, H., Rafailovich, M., Sokolov, J., “Curing monitoring of phenolic resol resins via atomic force microscope and contact angle”, International Journal of Adhesion and Adhesives, Volume 22, Issue 5, 2002, pages 375-384, ISSN 0143-7496.

Claims

1. Process for obtaining lignin dispersion characterized by the fact that it comprises the following steps: a) loading water at room temperature into the reactor; b) adding lignin under stirring; c) adding an alkalizing agent and checking the resulting pH; d) adjusting the pH; e) heating the mixture and allowing it to react; f) carrying out distillation under vacuum and at temperature; and g) monitoring the viscosity of the mixture. 2. Process according to claim 1, characterized in that it further comprises the following steps: h) cooling the reaction; and i) discharging and screening the resulting material. 3. Process according to claim 1 or 2, characterized in that the lignin of step b) is selected from the group consisting of powdered lignin, acidic lignin cake and unwashed lignin cake (alkaline lignin). 4. Process according to claim 3, characterized in that: a) when the lignin is in the form of powdered lignin, step b) of adding said lignin is under vigorous stirring and homogenization is maintained at room temperature; or b) when the lignin is in the form of acid lignin cake or unwashed cake, step b) of adding said lignin is through dispersion under stirring until a homogeneous paste (“slurry”) is obtained. 5. Process according to claim 3, characterized in that: a) when the lignin is in the form of powdered lignin, the heating of step e) is maintained for complete dissolution of the lignin. 6. Process according to any one of claims 1 to 5, characterized in that the lignin is Kraft lignin, preferably from short-fiber woods (“hardwood”). 7. Process according to any one of claims 1 to 6, characterized in that the alkalizing agent is a strong base, preferably sodium hydroxide (NaOH). 8. Lignin dispersion characterized by the fact that it is obtained by the process as defined in any one of claims 1 to 7. 9. Lignin dispersion characterized by the fact that it comprises a solids content in the range of 45 to 50%, pH in the range of 13.0 to 14.0 and viscosity in the range of 100 to 2,500 cP (from 0.1 to 2.5 Pa.s). 10. Lignin dispersion according to claim 9, characterized in that the viscosity is in the range of 400 to 2,000 cP (0.4 to 2.0 Pa.s), preferably in the range of 900 to 1,600 cP (0.9 to 1.6 Pa.s). 1 1. Use of the lignin dispersion as defined in any one of claims 8 to 10 characterized in that it is to partially replace phenolic resin (resole) with lignin in a mixture of phenolic resin with lignin. 12. Composition of phenolic resin with lignin characterized by the fact that said lignin partially replaces phenolic resin (resole) with lignin dispersion. 13. Phenolic resin composition with lignin according to claim 12, characterized in that the lignin replaces phenolic resin in the range of up to 50% of the resin. 14. Phenolic resin composition with lignin according to claim 12 or 13, characterized in that it presents suitable physical-chemical properties to be applied as an adhesive in the gluing of different wood substrates or as a binder. 15. Phenolic resin composition with lignin according to claim 14, characterized in that the wood substrate is selected from the group consisting of plywood, MDF (“medium density fiberboard”), MDP (“medium density particleboard”) and OSB (“oriented strand board”). 16. Phenolic resin composition with lignin according to claim 14 or 15 characterized by the fact that the physicochemical properties are selected from the group consisting of viscosity, solids content and residual enthalpy. 17. Use of the phenolic resin composition with lignin as defined in any one of claims 12 to 16 characterized by the fact that it is as an adhesive or binder.