Patent Description:
Lignin is rich in hydroxyl (OH), phenolic and aliphatic groups and is considered a polyol of renewable origin with great potential to partially replace petrochemical polyols used in the polyurethane industry.

Lignin can be used directly as a crosslinking agent in the synthesis of polyurethanes, through the condensation reaction of lignin's OH groups with isocyanate groups [<NUM>]. However, since lignin is a polymer with a high average molecular weight and aromatic structure, crosslinking reactions between lignin's OH groups (especially phenolic OH groups) and isocyanate groups is a challenge due to the steric hindrance inherent to lignin's structure.

Another complementary strategy is the addition of lignin in the solid state without any chemical modification (lignin powder) to the polyol of petrochemical origin for subsequent reaction with isocyanate in the synthesis of polyurethane. The addition of lignin to conventional polyol allowed an increase in the biomass incorporation rate of up to <NUM> % (w/w), but in this case the polyol became extremely viscous or almost solid [<NUM>-<NUM>]. In addition, the solid lignin dissolved in the petroleum-based polyol acted as a filler, i.e., it did not allow the formation of a homogeneous liquid product due to its low solubility with these polyols.

One way of increasing the reactivity of lignin with isocyanates is to liquefy the lignin using alkylene oxides (propylene oxide and ethylene), which makes it possible to produce renewable polyether-based polyols with up to <NUM> % (w/w) lignin [<NUM>-<NUM>]. Propylene oxide is the most widely used reagent in the lignin oxyalkylation reaction. However, due to the characteristics of this reagent, which is flammable, the reaction requires the use of special reactors (pressurized systems), and the transport of propylene oxide within the member countries of the European Union must follow special rules defined by the "European Agreement concerning the International Carriage of Dangerous Goods by Road (ADR)". In addition, the reaction of propylene oxide with lignin leads to the formation of a considerable amount of homopolymer which can negatively affect the final polyurethane product, for example the rigidity of polyurethane foams [<NUM>].

An alternative to propylene oxide is to liquefy the lignin using cyclic carbonates (propylene carbonate, ethylene carbonate, glycerol carbonate), which are considered safe reagents that allow the oxyalkylation reaction to be carried out under atmospheric pressure. However, the incorporation of lignin into the final polyol does not exceed <NUM> % (w/w) [<NUM>-<NUM>].

Patent <CIT> describes the incorporation of lignin in polyurethane products, namely in polyisocyanate compositions which involves dispersing lignin in the polyisocyanate with specific average sizes. Smaller lignin particle sizes lead to better interaction/reaction of the lignin with the isocyanate, more stable lignin dispersions (no sedimentation, even after a longer period of time), and higher viscosity. The amount of dispersed lignin does not exceed <NUM> % by weight.

Patent application <CIT> discloses a composition resulting from the addition of dispersants, with a polyol or a mixture of polyols, to a lignin, preferably an alkaline lignin. The lignin has an average particle size of about <NUM> to about <NUM> and the dispersants have a solubility parameter of about <NUM> to about <NUM> MPa and a viscosity of about <NUM> mPas to about <NUM> mPas. These particle sizes allow these dispersions to be incorporated into thermosetting and thermoplastic industrial products, where lignin can form part of the polymer structure of different products. The lignin content does not exceed <NUM> % by weight.

Patent application <CIT> relates to a method for producing a binding composition consisting of forming an aqueous composition made up of lignin molecules, a polymerizable substance and a cross-linking agent in the presence of a catalyst, where the polymerizable substance may be a phenol, cresol, resorcinol and combinations thereof, and where the cross-linking agent is an aldehyde.

Patent application <CIT> discloses a method of preparing polyurethane materials consisting of the reaction of a polyol with isocyanate in which lignin is added to at least one component of the reaction. The powdered lignin particles are reduced to the size of nanometers and micrometers and are simultaneously dispersed without the use of solvents in a prepolymer containing reactive isocyanate groups.

<CIT> relates to alkoxylated lignin for the preparation of rigid polurethane foams.

The processes for incorporating lignin into liquid polyols are therefore limited by the low percentage of lignin incorporated and/or the generation of highly viscous and heterogeneous products.

The present invention relates to a process for incorporating lignin into polyols, comprising the following steps:.

According to a preferred embodiment, in step ii) the lignin is selected from the group consisting of Kraft lignin, organosolv lignin, soda lignin, hydrolysis lignin, lignosulphonates and combinations thereof.

According to a preferred embodiment, in step i) the cyclic carbonate is selected from the group consisting of propylene carbonate, ethylene carbonate, glycerol carbonate and combinations thereof.

According to a preferred embodiment, the heating of step iii) is carried out over a period of time from <NUM> to <NUM> hours.

A process for incorporating lignin into renewable-based liquid polyols is described here, as described in this patent application and claim <NUM>, which makes it possible to obtain a homogeneous liquid product which, due to the compatibility of lignin with this type of bio-based polyol, allows for a chemical incorporation of total lignin of more than <NUM> % by weight. The product resulting from this incorporation is still liquid and homogeneous. The reaction takes place in ordinary reactors, without the need for pressurized systems, for example.

Also described is a process for producing polyurethanes from renewable-based polyols with an increased amount of lignin incorporated, in which the reaction between the aliphatic hydroxyl groups of the lignin and the isocyanate groups that have not reacted with the polyol allows for the formation of a more cross-linked polyurethane structure with a higher lignin content in its composition.

In the case of polyurethane foam formulations, this more cross-linked structure results in a foam with better mechanical properties. In addition, increasing the lignin content reduces the number of free isocyanate groups, which translates into a higher level of chemical and thermal stability, as well as in terms of hygiene and safety.

In the context of the present invention, LignoBoost lignin refers to a lignin obtained from the black liquor of the Kraft process using the LignoBoost process in which the lignin is precipitated from the black liquor with the addition of CO<NUM> with subsequent washing with acidified water and hot water up to pH <NUM>-<NUM>.

Kraft refers to Kraft cooking, or sulfate cooking. This chemical process consists of cooking the wood in a cooking liquor usually made up of sodium hydroxide and sodium sulfide, at temperatures of around <NUM> to <NUM>, in pressurized reactors.

In the context of the present invention, organosolv lignin refers to a lignin obtained from the organosolv process in which the lignin is precipitated with the elimination of solvents or by water precipitation.

In the context of the present invention, soda lignin relates to a lignin obtained from the soda cooking process in which the lignin is precipitated with acidification of the liquor.

In the context of the present invention, hydrolysis lignin refers to lignin obtained during the acid hydrolysis of wood.

In the context of the present invention, lignosulphonates refer to a lignin obtained from the acid sulfite or bisulfite cooking process with different bases.

In the context of the present invention, a polyether polyol refers to polymers with multiple hydroxyl groups formed from cyclic ethers. When produced from lignins, these are also called lignin-based and renewable-based.

In the context of the present invention, any type of technical lignin can be used, for example, but not limited to Kraft lignin, organosolv lignin, soda lignin, hydrolysis lignin. Lignosulphonates can also be used. Isolated lignin is preferably presented in the form of a powder and dried (residual moisture less than <NUM> %).

The renewable-based polyether polyol is obtained by the oxyalkylation of a lignin with a cyclic carbonate such as, but not limited to, propylene carbonate, ethylene carbonate and glycerol carbonate.

In the present invention, a minimum of <NUM>% by weight of lignin is dissolved in a liquid polyol obtained by the oxyalkylation of a lignin with a cyclic carbonate, followed by the heating of the resulting solution under constant stirring until a homogeneous solution is obtained.

Any suitable reaction vessels can be used, such as, but not limited to, a batch reactor, a continuous reactor or a semi-continuous reactor with mechanical stirrers.

The lignin-based polyol with the dissolved lignin is mixed with a polyisocyanate to produce the polyurethane. Polyisocyanates such as, but not limited to, polymeric diphenylmethane diisocyanate (p-MDI), <NUM>,<NUM> hexamethylene diisocyanate (HDI), <NUM>,<NUM>' methylene diphenyl isocyanate, <NUM>,<NUM>-toluene isocyanate, <NUM>,<NUM>-toluene diisocyanate, can be used.

Depending on the type of polyurethane and its application (foams, adhesives and elastomers), catalysts and other chemical reagents are first added to the lignin-based polyol with the dissolved lignin. These reagents include: surfactants such as different types of silicones, flame retardants, which include organophosphorus and chlorinated halogen compounds, blowing agents such as water and hydrocarbons, biocides such as quaternary ammonium compounds, among others.

The polyisocyanate is then added to the resulting mixture under constant stirring and cured at room temperature, considered in this invention to be between <NUM> and <NUM>. Curing consists of the formation of crosslinks within the polymeric material resulting from the bonds between isocyanate and hydroxyl groups of different chains.

The technical lignin used was isolated from the black liquor of the Kraft cooking process of Eucalyptus globulus wood using the LignoBoost process.

<NUM> of a liquid lignin-based polyether polyol was weighed into a beaker, to which <NUM> of dry LignoBoost lignin was added.

The lignin-based polyether polyol used had a number of hydroxyl groups of <NUM> KOH/g, a viscosity of <NUM> Pa. s and a lignin content of <NUM>% by weight.

The beaker with the mixture was heated on a hotplate under constant magnetic stirring. The mixture was heated to a temperature of <NUM> for <NUM> minutes at <NUM> rpm. The final product consisted of a viscous, homogeneous liquid, resulting in the dissolution of <NUM> % by weight of lignin in the polyol.

The same procedure was carried out for the incorporation of <NUM> %, <NUM> %, <NUM> % and <NUM> % by weight of lignin, i.e., <NUM>, <NUM>, <NUM> and <NUM> of the liquid polyether polyol based on lignin were weighed into a beaker, to which <NUM> of dry LignoBoost lignin was added. The resulting mixtures were heated on a hotplate under constant magnetic stirring. The mixtures were heated to a temperature of <NUM> for <NUM> minutes at <NUM> rpm. The final products consisted of viscous, homogeneous liquids.

Rigid polyurethane foams were prepared using the formulations shown in Table <NUM>, with the isocyanate index (NCO/OH) equal to <NUM> for both. Formulations were prepared, one with the lignin-based polyol, but without additional incorporation of lignin in it (Reference Foam) and others with lignin-based polyol with <NUM> %, <NUM> % and <NUM> % dissolved lignin (Foam with extra lignin). For the foam formulations using the lignin-based polyol with increased amounts of dissolved lignin, the amount of isocyanate in the formulation was calculated solely on the basis of the amount of hydroxyl groups (OH) in the lignin-based polyol and the blowing agent (water); the OH groups in the lignin are ignored in this calculation.

In a beaker, the catalyst N,N-dimethylcyclohexylamine (DMCHA) and a polyether-modified polysiloxane surfactant were added to the lignin-based polyol and the components were mixed using a mechanical mixer (<NUM> rpm) for <NUM> seconds. Next, the blowing agent (water and n-pentane) was added and stirred for a further <NUM> seconds at <NUM> rpm, the resulting mixture being labelled "component A". Immediately afterwards, the polymeric MDI isocyanate was added to component A and the mixture was subjected to a further <NUM> seconds of mechanical stirring (<NUM> rpm). The foams expanded/formed by free growth in the beaker (free-rise).

The foams prepared using a lignin-based polyol with a greater amount of renewable raw material were characterised according to the procedure illustrated in <FIG>. Confirmation that the dissolved lignin was incorporated into the polyol and consequently reacted with the isocyanate was carried out using solid-state carbon-<NUM> nuclear magnetic resonance analyses (<FIG>), infrared spectroscopy (<FIG>) and by comparing the final weight of the solid fraction of the reference foam and the foam with extra lignin, the results of which are shown in Table <NUM>.

The reaction between the aliphatic OH groups of lignin and the isocyanate groups that did not react with the polyol allows the formation of a more cross-linked polyurethane structure with a higher lignin content in its composition. Additionally, the increase in lignin content allowed the number of free isocyanate groups to be reduced, which translates into a higher level of thermal stability, as can be seen in <FIG>, which relates the loss of mass to the increase in temperature, for the foam produced with the lignin-based polyol with <NUM>% dissolved lignin (foam with extra lignin) and for a reference foam, this is produced from the lignin-based polyol but without additional incorporation of lignin. For the results presented in <FIG>, a thermogravimetric analysis (TGA) was carried out to evaluate the thermal stability of the foams using a SET-SYS Evolution <NUM> thermogravimetric analyzer, from room temperature to <NUM>, with a heating rate at <NUM>/min and under oxygen flow (<NUM>/min).

It is possible to verify that the mass of the foam produced with the lignin-based polyol with <NUM>% of lignin dissolved with the increase in temperature occurs at higher temperatures, thus conferring a thermal stability slightly higher than that of the reference foam. Additionally, the behavior of the reference foams and those with extra lignin was evaluated using the cone calorimeter test. Samples with a size of <NUM> × <NUM> × <NUM> were tested with a heat flux of <NUM> kW. Before testing, the specimens were conditioned for a period of <NUM> hours at <NUM> ± <NUM> and <NUM> ± <NUM>% relative humidity, meeting the constant mass criteria. The specimens were wrapped in a single layer of aluminum foil, with the shiny side facing the test body. The average heat release rate (TLC) and the maximum heat release rate (TMLC)) were determined according to ISO <NUM> and are shown in Table <NUM>. Three measurements were taken for each sample. TLC is one of the most important variables in the flammability of materials, corresponding to the amount of heat generated per unit area and time. It was observed that the TLC and TMLC values of the foam with extra lignin are lower when compared to the reference foam, thus confirming the flame retardant effect of lignin due to its aromatic structure which may be able to produce a certain amount of char residue by heating at a high temperature, reducing the heat of combustion. Finally, the time to ignition, which corresponds to the minimum time needed to cause a combustible material to ignite and burn continuously when exposed to a certain heat flux, could not be determined due to the speed at which ignition occurs and the relative errors associated with it. However, it was clearly observed that the foam with lignin burns more slowly, with a layer of charcoal forming around the sample, which is not the case with the reference foam.

Claim 1:
A process for incorporating lignin into polyols, comprising the following steps:
i) oxyalkylating a lignin with a cyclic carbonate for producing a polyether polyol;
ii) dissolving between <NUM> % and <NUM>% by weight of lignin in the liquid polyol obtained in step i) ;
iii) heating the mixture resulting from step ii) at a temperature of <NUM> to <NUM>, preferably <NUM> to <NUM>, under constant stirring and for a period of time of <NUM> to <NUM> hours until a homogeneous solution is obtained;
iv) cooling the solution resulting from point iii) to room temperature and obtaining a lignin-based polyether polyol with at least <NUM>% by weight of dissolved lignin.