Lignin-based expandable microspheres

Abstract

To provide alternative thermoplastic expandable microspheres whose thermoplastic polymeric shell is at least partially derived from a sustainable source, a method for preparing the microspheres, and use of the microspheres.SOLUTION: There are provided thermally expandable microspheres comprising a polymeric shell surrounding a hollow core, wherein the hollow core comprises a blowing agent, and the polymeric shell comprises isolated lignin. The isolated lignin preferably comprises Kraft lignin such as acetylated Kraft lignin. A method for preparing thermally expandable microspheres comprising a polymeric shell surrounding a hollow core comprises the steps of (i) preparing a mixture comprising the isolated lignin and the blowing agent in a solvent, and (ii) spray-drying the mixture obtained in step (i) to obtain thermally expandable microspheres.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to lignin-based thermally expandable microspheres and to a process for their production. [Background technology]

[0002] Thermally expandable microspheres are known in the art and are described, for example, in U.S. Pat. No. 3,615,972, International Patent Publication No. 00 / 37547, and International Patent Publication No. 2007 / 091960. Many examples are sold under the trade name Expancel®. They can be expanded to form extremely low-weight and low-density fillers and find use in applications such as foamed or low-density resins, paints and coatings, cements, inks, and crack fillers. Consumer products that often contain expandable microspheres include lightweight shoe soles (e.g., for running shoes), textured coverings such as wallpaper, solar-reflective and thermal insulation coatings, food packaging sealants, wine corks, artificial leather, foam for protective helmet liners, and automotive weatherstrips.

[0003] Thermally expandable polymer microspheres typically contain a thermoplastic polymer shell and a hollow core containing a blowing agent that expands upon heating. Examples of blowing agents include low-boiling hydrocarbons or halogenated hydrocarbons, which are liquid at room temperature but vaporize upon heating. To produce expanded microspheres, the expandable microspheres are heated so that the thermoplastic polymer shell softens, and the blowing agent vaporizes and expands, thereby expanding the microspheres. Typically, the diameter of the microspheres can increase 1.5 to 8 times during expansion. Expandable microspheres are commercially available in various forms, such as dry free-flowing particles, aqueous slurries, or partially dewatered wet cakes.

[0004] Expandable microspheres can be produced, for example, by polymerizing ethylenically unsaturated monomers in the presence of a blowing agent using a suspension polymerization process. Typical monomers include those based on acrylates, acrylonitrile, acrylamide, vinylidene dichloride, and styrene. The problem associated with these thermoplastic polymers is that they are typically derived from petrochemicals and not from sustainable sources. In addition, many polymers are non-biodegradable, or at least biodegrade very slowly, posing a risk of cumulative accumulation in the environment. However, simply replacing the monomer with a more sustainably derived alternative is not always straightforward, as it is necessary to ensure that acceptable expansion performance is maintained. For example, the polymer must have the appropriate surface energy to obtain core-shell particles in a suspension polymerization reaction so that the blowing agent can be encapsulated. In addition, the resulting polymer must have good gas barrier properties to retain the blowing agent. Furthermore, the polymer must have a glass transition temperature (T) that allows the shell to expand during expansion. g Therefore, it is not easy to replace conventional monomers with bio-based monomers.

[0005] Expandable microspheres have been described in which at least a portion of the monomers making up the thermoplastic shell are biobased and derived from renewable resources. For example, WO 2019 / 043235 describes polymers containing lactone monomers, WO 2019 / 101749 describes copolymers containing itaconic acid dialkyl ester monomers, and WO 2020 / 099440 and WO 2021 / 234010 disclose thermally expandable microspheres made from cellulosic biopolymers.

[0006] However, it has been found that these bio-based expandable microspheres may have some drawbacks from a commercial standpoint, such as the reduced commercial availability of the raw materials and the high cost of the raw materials compared to the petroleum-based raw materials. However, from the performance standpoint of the expandable microspheres, for example, the expansion characteristics may be inflexible or insufficient and may not always be precisely tunable for a specific desired application. Furthermore, there is always room for improvement regarding the biodegradability of the polymer shell. Furthermore, it has been found that such bio-based expandable microspheres tend to be flammable, which may pose complications for the use of such microspheres in applications with high requirements regarding fire safety.

[0007] Therefore, there remains a need for alternative thermoplastic expandable microspheres in which the thermoplastic polymer shell is at least partially derived from sustainable sources. Furthermore, there remains a further need to provide expandable microspheres in which the thermoplastic polymer shell is at least partially derived from sustainable sources, and in which the expandable microspheres have sufficient expansion properties, more preferably, can be tailored to meet needs. Such alternative thermally expandable microspheres would also be further desirable, especially if they have improved flammability resistance compared to known and commercially available thermally expandable microspheres. Accordingly, the present invention is directed to finding improved bio-based thermally expandable polymeric microspheres that have at least some of the aforementioned desirable properties. Summary of the Invention

[0008] The present invention is directed to thermally expandable microspheres comprising a polymeric shell surrounding a hollow core, the hollow core comprising a blowing agent, and the polymeric shell comprising isolated lignin. The thermally expandable microspheres described in this disclosure solve the above-mentioned problems.

[0009] The present invention is also directed to a method for preparing thermally expandable microspheres comprising a polymeric shell surrounding a hollow core, wherein the hollow core comprises a blowing agent and the polymeric shell comprises isolated lignin, the method comprising the steps of: (i) preparing a mixture comprising the isolated lignin and the blowing agent in a solvent; and (ii) spray-drying the mixture obtained in step (i) to obtain thermally expandable microspheres. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 illustrates the difference between single-core (FIG. 1A) and multi-core (FIG. 1B) microspheres. DETAILED DESCRIPTION OF THE INVENTION

[0011] One aspect of the present invention is a thermally expandable microsphere comprising a polymeric shell surrounding a hollow core, the hollow core comprising a blowing agent and the polymeric shell comprising isolated lignin.

[0012] The expandable microspheres are based on a polymer shell containing isolated lignin. Lignin is a class of complex organic polymers that form important structural materials in the support tissues of most plants, especially trees. In other words, lignin is embedded within and part of a complex natural matrix, often in the form of lignocellulose, where the lignin is bound to hemicellulose and / or cellulose. Lignin is particularly important in cell wall formation, especially in wood and bark, because it provides rigidity and does not easily rotate. From a chemical standpoint, lignin is a polymer made by crosslinking phenolic precursors. The expandable microspheres of the present invention contain isolated lignin. The term "isolated lignin" means that the lignin has been isolated from its natural matrix, such as from lignocellulose, by, for example, chemical and / or physical (e.g., mechanical) processes. In other words, as used herein, the term isolated lignin, when used in the expandable microspheres of the present invention, is used to distinguish isolated lignin from lignin still contained in its natural matrix.

[0013] Lignin can be isolated from its native matrix by a variety of physical and chemical processes to obtain the isolated lignin used in the present invention. These processes are commonly known to those skilled in the art, and isolated lignin obtained from any of these commonly known processes can be used in the present invention. Isolated lignin can be lignin that has simply been removed from its native matrix, or it can be chemically modified during or after removal from its native matrix.

[0014] In a preferred embodiment, the isolated lignin is a chemically modified lignin. Chemical modification of the lignin may involve derivatizing the lignin by adding functional groups to the lignin, such as sulfur-containing functional groups, or simply by cleaving bonds in the lignin to reduce its molecular weight.

[0015] Commonly known types of isolated lignin include clast lignin, sulfonated lignin, organic solvent-soluble lignin, hydrolyzed lignin, steam-exploded lignin, ground wood lignin, and soda lignin. Thus, in one embodiment, the lignin comprises a lignin selected from the group consisting of kraft lignin, sulfonated lignin, organic solvent-soluble lignin, hydrolyzed lignin, steam-exploded lignin, ground wood lignin, soda lignin, and any combination thereof. In a preferred embodiment, the isolated lignin comprises kraft lignin, sulfonated lignin, or a combination thereof. It is particularly preferred that the lignin comprises kraft lignin, such as acetylated kraft lignin. Isolated lignin can be purchased commercially.

[0016] The Kraft process (also known as Kraft pulping or sulfate process) involves treating lignin-containing organic material, such as wood, usually in the form of chips, with a high-temperature mixture of water, sodium hydroxide, and sodium sulfide, which breaks the bonds that bind the lignin, hemicellulose, and cellulose. The process involves several steps, both mechanical and chemical. The Kraft process results in so-called Kraft lignin. Kraft lignin can be further derivatized, for example, by acetylation, resulting in acetylated Kraft lignin.

[0017] So-called sulfonated lignin (or lignosulfonates) may be obtained by the sulfite process. In the sulfite process, lignin-containing organic material, such as wood, usually in the form of chips, is heated with a solution of sulfite and bisulfite ions. These chemicals break the bonds between the cellulose and lignin components of lignocellulose. During this process, the lignin is converted to lignosulfonates.

[0018] Organosolv pulping, a pulping technique that uses organic solvents to solubilize lignin and hemicellulose, can be used to obtain organic solvent-soluble lignin. Organosolv pulping involves contacting lignin containing organic material, such as wood, in the form of chips with an aqueous organic solvent at elevated temperatures, typically in the range of about 140 to about 220°C. This decomposes the lignin through hydrolytic cleavage of alpha-aryl ether links, resulting in fragments that are soluble in the solvent system. Suitable solvents for use in this process include acetone, methanol, ethanol, butanol, ethylene glycol, formic acid, and acetic acid.

[0019] Hydrolyzed lignin, steam exploded lignin, ground wood lignin, and soda lignin are further types of lignin that can be obtained from lignin containing organic material.

[0020] In embodiments, the number average molecular weight (M) of the isolated lignin used to form the microspheres n ) is in the range of 500 to 700,000, e.g., in the range of 1,000 to 500,000, and preferably in the range of 2,000 to 400,000. In embodiments, it is in the range of 1,000 to 100,000, e.g., in the range of 1,000 to 80,000, or in the range of 2,000 to 50,000. In some embodiments, the number average molecular weight (M) of the isolated lignin is n ) is 1,000 to 50,000, for example, 1,000 to 30,000, 1,000 to 10,000, 1,000 to 8,000, or 2,000 to 7,000.

[0021] The polymeric shell can include or consist of one or more polymeric components, with at least one component, more than one component, or all of the polymeric components being selected from such isolated lignins. In other words, in some embodiments, the polymeric shell includes two or more, such as two, three, or four different types of isolated lignin. When the shell includes polymers other than those described in this disclosure (i.e., isolated lignins), their content is typically 50% by weight or less, e.g., 30% by weight or less, or 10% by weight or less, e.g., 9% by weight or less, 5% by weight or less, or even 2% by weight or less. These percentages are based on the total polymer content of the shell. In some embodiments, the shell includes polymers other than isolated lignin in an amount of at least 0.1% by weight, at least 0.5% by weight, at least 1% by weight, at least 5% by weight, or at least 10% by weight. In some embodiments, the shell comprises a polymer other than isolated lignin in an amount of 0.1 to 50 wt%, e.g., 0.5 to 50 wt%, 1 to 45 wt%, or 5 to 40 wt%, However, in preferred embodiments, the shell consists solely of isolated lignin.

[0022] In some embodiments, the polymeric shell can comprise at least 5 wt%, e.g., at least 10 wt%, at least 20 wt%, or at least 30 wt%, preferably at least 50 wt%, e.g., at least 60 wt%, at least 70 wt%, or at least 80 wt%, more preferably at least 90 wt%, e.g., at least 95 wt%, or at least 98 wt%, of the isolated lignin, these percentages being based on the total polymer content of the shell.

[0023] Polymers other than those described in this disclosure are not limited, and therefore, if present, any polymeric component known to one of ordinary skill in the art can be used as the polymer other than those described in this disclosure (i.e., isolated lignin). Polymers other than those described in this disclosure are also further described herein as polymeric component(s). In some examples, the polymeric shell further comprises at least one additional polymeric component, i.e., a polymeric component that is not isolated lignin. In some embodiments, the polymeric shell further comprises at least one additional polymeric component selected from the group consisting of polysaccharides, polysaccharide derivatives, polyesters, polyethers, polyacids, polyols, polyalkenes, or any combination thereof. In some embodiments, the polysaccharides and polysaccharide derivatives may be selected from the group consisting of cellulose, cellulose derivatives, chitosan, hemicellulose, and alginates, and are preferably selected from cellulose, cellulose derivatives, and chitosan. In a preferred embodiment, the additional polymeric component is selected from alkyl cellulose, carboxy cellulose, vinyl acetate copolymer, polylactic acid, polyethylene glycol, polyvinyl alcohol, polyacid, polyacrylic acid, nanocrystalline cellulose, or a combination thereof, preferably alkyl cellulose, carboxy cellulose, vinyl acetate copolymer, polylactic acid, polyethylene glycol, polyacrylic acid, or a combination thereof, more preferably polyethylene glycol, polyacrylic acid, or a combination thereof. Any combination of the aforementioned additional polymeric components can be used. Such combinations also include copolymers of any of the aforementioned additional polymeric components.

[0024] Thermally expandable microspheres are hollow, with a shell consisting of isolated lignin and a hollow center or core consisting of one or more blowing agents. The isolated lignin used to prepare the microspheres typically has a density of 1.0-1.35 g / cm. 3 For expandable microspheres, the density is typically 1 g / cm 3 less than 0.005 to 0.8 g / cm3 , or 0.01 to 0.75 g / cm 3 In a preferred embodiment, the density of the expandable microspheres is in the range of 0.01 to 0.5 g / cm 3 Higher densities, especially 1 g / cm 3 Densities above this indicate that the microsphere sample is not suitable for use.

[0025] The temperature at which the thermally expandable microspheres start to expand, TStart, is preferably in the range of 100°C to 200°C. Start The temperature at which maximum expansion occurs is called T max It is called. start and T max may be determined using standard measurement techniques commonly known by those skilled in the art. For example, T start and T max can be determined in a temperature ramp experiment using a Mettler-Toledo thermomechanical analyzer, such as a Mettler-Toledo TMA / SDTA 841e, using a heating rate of 20°C / min and a net load of 0.06 N. In such a temperature ramp experiment, a sample of known weight of thermally expandable microspheres is heated at a constant heating rate of 20°C / min under a net load of 0.06 N. As the thermally expandable microspheres begin to expand, the volume of the sample increases and the load moves upward. From such measurements, an expansion thermogram is obtained, where the vertical axis represents the height to which the load is moved upward and the horizontal axis represents the temperature. T start and T max can be determined from this expansion thermogram using, for example, STARe software from Mettler-Toledo.

[0026] In embodiments, the thermally expandable microspheres have a Tstart in the range of 110°C to 190°C. The thermally expandable microspheres have a Tstart in the range of 120°C to 185°C, most preferably in the range of 125°C to 185°C. start It is even more preferred that

[0027] Many factors can contribute to high density, including poor expansion characteristics that can occur when there are too many microspheres and insufficient blowing agent to allow for proper expansion. This can result from a polymer shell that is too permeable to the blowing agent, or from the formation of so-called "multicore" microspheres, i.e., multiple blowing agent-containing cores within a shell (e.g., like a microspherical foam or sponge) instead of a single blowing agent-containing core. In such multicore microspheres, the blowing agent concentration is typically too low to adequately reduce density. Another cause is polymer aggregation or agglomeration, resulting in poorly produced microspheres and a denser material. Microspheres with too high a proportion of aggregated material or that do not expand sufficiently can also lead to large inhomogeneities in the expansion characteristics of the resulting microsphere product. This is particularly undesirable for surface-sensitive applications such as coatings where a smooth finish is desired.

[0028] Exemplary cross sections of single-core and multi-core microspheres are provided in Figures 1A and 1B, respectively, with polymeric regions 1 represented by crosshatched areas and blowing agent-containing regions 2 represented by blank areas.

[0029] In further embodiments, the polymer shell may include particles to improve the mechanical properties and gas barrier of the polymer shell, examples of such particles include various types of clays such as talc, montmorillonite, and bentonite.

[0030] The hollow core of the thermally expandable microspheres of the present invention comprises a blowing agent. The blowing agent can include one or more different blowing agents. The blowing agent(s) generally have a boiling point above 25°C at 5.0 bara or above 25°C at 3.0 bara, where "bara" stands for "bar-absolute." In some embodiments, they have a boiling point above 25°C at atmospheric pressure (1.013 bara). Typically, they have a boiling point below 250°C (e.g., below 220°C, or below 200°C) at atmospheric pressure. They are preferably inert and do not react with the isolated lignin shell. The boiling point at high pressure can be calculated using the Clausius-Clapeyron equation.

[0031] Examples of blowing agents include alcohols, dialkyl ethers, alkanes, and halocarbons (e.g., chlorocarbons, fluorocarbons, or chlorofluorocarbons). In embodiments, the alcohol comprises a C2-C8 alcohol, such as a C2-C6 alcohol or a C2-C4 alcohol. In embodiments, the dialkyl ether comprises two alkyl groups each selected from a C2-C5 alkyl group. In embodiments, the alkane comprises a C4-C 12 In some embodiments, the haloalkane is a C-C alkane. 10 The alkyl or haloalkane group in the alcohol, dialkyl ether, alkane, and haloalkane may be linear, branched, or cyclic. One or more blowing agents may be used singly or in combination.

[0032] In some embodiments, for environmental reasons, the one or more blowing agents are selected from alcohols, alkyl ethers, and alkanes, and in further embodiments, the one or more blowing agents are selected from alcohols and alkanes, preferably alcohols. Haloalkanes are preferably avoided due to their potential ozone depletion properties and also due to their generally higher global warming potential.

[0033] Examples of suitable blowing agents that can be used include ethanol, n-propanol, isopropanol, n-butanol, tert-butyl alcohol, n-pentanol, isopentanol, n-hexanol, isohexanol, heptanol, isoheptanol, octanol, isooctanol, tert-butyl acetate, butyl acetate, methyl tert-butyl ether, n-pentane, isopentane, neopentane, cyclopentane, cyclohexane, n-butane, isobutane, isohexane, neohexane, heptane, isoheptane, octane, isooctane, and isododecane. In a preferred embodiment, the blowing agent is selected from a C2-C8 alcohol, such as a C2-C6 alcohol or a C2-C4 alcohol. In a more preferred embodiment, the blowing agent comprises a blowing agent selected from isooctane, isohexane, tert-butyl acetate, butyl acetate, methyl tert-butyl ether, tert-butyl alcohol, and combinations thereof. In particularly preferred embodiments, the blowing agent comprises tert-butyl alcohol or isooctane, or a combination thereof.

[0034] In the expandable microspheres, the one or more blowing agents are typically present in an amount ranging from 5 to 50 wt. %, e.g., from 5 to 45 wt. %, or from 10 to 40 wt. %, based on the total weight of the isolated lignin and the blowing agent(s).

[0035] The expandable microspheres of the present invention can be obtained by a spray drying process comprising mixing isolated lignin, a solvent, and a blowing agent, and then spraying the mixture thus obtained into a drying apparatus to produce thermally expandable microspheres having a polymeric shell surrounding a hollow core, wherein the polymeric shell comprises isolated lignin and the hollow core comprises the blowing agent.

[0036] In principle, the spray drying apparatus for carrying out the spray drying process is not limited, and any conventional and commercially available spray drying apparatus can be used for the spray drying process. A typical spray drying apparatus suitable for the process described herein comprises a drying chamber equipped with a nozzle, a drying gas inlet, and an outlet connecting the drying chamber to a cyclone. The liquid to be atomized is usually combined with the atomizing gas and sprayed into the drying chamber through the nozzle, which is usually located at the top of the spray chamber (but may be located in any other part of the spray dryer). In the drying chamber, the atomized liquid is dried by the drying gas supplied into the spray chamber through the drying gas inlet. The drying gas inlet may be located, for example, immediately adjacent to the nozzle. The atomized liquid dries and forms particles. The resulting particles are then supplied to the cyclone together with the drying gas through the drying chamber outlet, which is usually located in the bottom area of ​​the drying chamber. In the cyclone, the particles are separated from the drying air. The drying air may be further filtered to remove any residual particles from the drying air.

[0037] A suitable spray drying apparatus for carrying out the spray drying process is a Büchi Mini Spray Dryer B-290, commercially available from Büchi / Switzerland.

[0038] The order in which the isolated lignin, solvent, blowing agent, and optionally further polymeric components are added is not limited and any order can be selected.

[0039] However, in a preferred embodiment, in the process of making expandable microspheres, isolated lignin is first mixed with a solvent and, optionally, an additional polymeric component, and then, in a further step, a blowing agent is added to the mixture.

[0040] The step of mixing the isolated lignin can also be carried out at ambient temperature, but temperatures in the range of 5 to 75° C. can be used. Mixing is typically carried out until the isolated lignin is completely dissolved in the solvent.

[0041] In embodiments, the mixture of isolated lignin, solvent, and optionally additional polymeric components can be allowed to stand or stirred for a period of time, such as from 1 to 100 hours, or from 2 to 50 hours, which can be carried out at a temperature ranging from 10 to 95°C, for example, from 20 to 90°C.

[0042] In a further step, a blowing agent is added to the mixture of isolated lignin, solvent, and optionally additional polymeric components. This mixing step can be carried out at ambient temperature, although temperatures ranging from 5 to 75°C can be used. This mixing step is typically carried out until the blowing agent is completely dissolved in the solvent.

[0043] After the foaming agent is added to the mixture of isolated lignin, solvent, and optionally further polymeric components, the resulting mixture may be further stirred for a period of time, for example, 1 to 100 hours, or 2 to 50 hours, at a temperature ranging from 10 to 95°C, for example, from 20 to 90°C.

[0044] The mixture containing the isolated lignin, solvent, blowing agent, and optionally additional polymeric components is then sprayed into a drying apparatus, which may be a spray drying apparatus as described above, to produce the thermally expandable microspheres described in this disclosure.

[0045] The optional propellant gas sprayed through the nozzle together with the liquid to be atomized is not particularly limited and may be any suitable propellant gas known to those skilled in the art.For example, the propellant gas may be selected from nitrogen, carbon dioxide, (pressurized) air, noble gas (argon, etc.).Preferably, in the method for fabricating expandable microspheres as described herein, a propellant gas is used, and more preferably, the propellant gas is nitrogen.

[0046] The dry gas is not particularly limited and may be any suitable dry gas known by those skilled in the art. For example, the dry gas may be selected from nitrogen, carbon dioxide, (pressurized) air, and noble gases (such as argon). The dry gas is preferably nitrogen.

[0047] Additional process parameters for operating the spray-drying apparatus, such as the atomizing gas flow rate, the inlet temperature of the drying gas as it enters the drying chamber, the feed rate of the liquid to be atomized, and the aspirator speed and atomizer speed for circulating the drying gas within the spray-drying apparatus, can be readily selected by one skilled in the art.

[0048] It has been found that the above-described method can provide expandable microspheres comprising a polymeric shell surrounding a hollow core, the hollow core comprising a blowing agent and the polymeric shell comprising isolated lignin.

[0049] The solvent can be selected from water or an organic solvent having one or more functional groups selected from esters, amides, aldehydes, ketones, alcohols (including glycols), and ethers, e.g., having 3 to 12 carbon atoms. In embodiments, the esters, ketones, and ethers may be part of a cyclic structure. Further examples include haloalkanes having 1 to 6 carbon atoms and halo-carboxylic acids having 1 to 6 carbon atoms, where the halogen is selected from fluorine, chlorine, bromine, and iodine. The solvent can also be a mixture of water and an organic solvent, e.g., any of the organic solvents described above.

[0050] Examples of organic solvents that can be used include ethyl acetate, ethyl formate, methyl acetate, n-propyl formate, isopropyl formate, n-propyl acetate, isopropyl acetate, isobutyl acetate, n-butyl acetate, n-pentyl formate, isopentyl formate, n-pentyl acetate, isopentyl acetate, ethyl propionate, isobutyl isobutyrate, n-butyl propionate, ethyl 3-ethoxypropionate, 2-ethylhexyl acetate, acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, methyl isoamyl ketone, methyl n-amyl ketone, mesityl oxide, acetophenone, cyclohexanone, diethyl phthalate, ethyl lactate, benzyl acetate, butyrolactone, acetylacetone, methylcyclohexanone, benzaldehyde, diisobutyl ketone, diacetone alcohol, ethylene glycol, glyceryl-α-monochlorohydrin, propylene glycol, glycol ethers (e.g., Examples of suitable solvents include propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, propylene glycol mono-tert-butyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether, glycol ether esters (e.g., ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, and ethylene glycol diacetate), n-propyl alcohol, isopropyl alcohol, n-butanol, sec-butanol, isobutanol, benzyl alcohol, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole, phenetole, and dimethylformamide. Other examples of solvents include dimethyl sulfoxide, toluene, xylene, n-methyl-2-pyrrolidone, methylene chloride, chloroform, carbon tetrachloride, trichloroacetic acid, methylene bromide, methylene iodide, trichloroethylene, and tetrachloroethylene. The organic solvent can be a mixture of two or more solvents. When the solvent is a mixture of two or more organic solvents, preferably one of the solvents is acetone.In embodiments, acetone is mixed with an alcohol, such as methanol or ethanol.

[0051] In some embodiments, the solvent is a mixture of water and an organic solvent. In such embodiments, the mixture preferably contains water in an amount of 50% by weight or less, e.g., 40% by weight or less, 30% by weight or less, or 20% by weight or less. In such embodiments, the mixture more preferably contains water in an amount of at least 1% by weight, such as at least 2% by weight or at least 5% by weight, based on the total weight of the solvent.

[0052] In particularly preferred embodiments, the solvent is selected from one or more of water, methanol, ethanol, and acetone. More preferably, the solvent comprises water, methanol, ethanol, or acetone. In certain preferred embodiments, the solvent comprises acetone. In some embodiments, the solvent comprises a mixture of at least two solvents, preferably selected from the group consisting of water, methanol, ethanol, acetone, and combinations thereof. In some embodiments, the solvent comprises acetone and water, or acetone and ethanol.

[0053] Typically, the content of isolated lignin in the spray-drying mixture is typically in the range of 0.1 to 50 wt. %. In embodiments, the amount can be in the range of 1 to 40 wt. %, for example, in the range of 5 to 35 wt. %, or even in the range of 10 to 30 wt. %. The wt. % is based on the total weight of the spray-drying mixture.

[0054] The amount of blowing agent(s) in the spray-drying mixture is typically in the range of 0.5 to 50% by weight. In embodiments, it can be in the range of 0.5 to 40% by weight, e.g., 1 to 30% by weight, 3 to 25% by weight, or even 5 to 25% by weight. In embodiments, the weight of the blowing agent in the spray-drying mixture is less than or equal to the weight of the isolated lignin; for example, the weight ratio of blowing agent to isolated lignin can be 1.5 or less, e.g., 1.3 or less, or even 1.1 or less. In embodiments, the minimum weight ratio is 0.1, or in further embodiments, 0.2. In embodiments, the weight ratio of blowing agent to isolated lignin in the organic phase is in the range of 0.1 to 1.5, e.g., 0.2 to 1.3, or even 0.3 to 1.1.

[0055] The amount of solvents totals 100% by weight. The amount of organic solvent is preferably at least 30% by weight, more preferably at least 40% by weight, and even more preferably at least 50% by weight. The weight percentages are based on the total weight of the spray-drying mixture.

[0056] The volume-average particle size (diameter) of the unexpanded microspheres, i.e., the D(0.5) value, is typically in the range of 1 to 500 μm (such as 5 to 200 μm), or in embodiments, in the range of 10 to 100 μm, or even in the range of 30 to 80 μm.

[0057] The diameter of the expanded microspheres is typically in the range of 1.5 to 8 times larger in diameter than the unexpanded microspheres, for example, 2 to 7 or 3 to 6 times their original diameter.

[0058] Particle sizes are suitably measured using light scattering techniques, e.g., laser diffraction, such as low angle laser light scattering (LALLS). They can also be measured by image analysis from photographic or electron micrograph images of the microspheres before or after expansion.

[0059] To expand the expandable microspheres, they are heated to a temperature above the boiling point of the blowing agent and the T gThe microspheres can be heated to a temperature above the T of the isolated lignin and below the melting point of the microspheres. g and / or may be cooled back down to below the boiling point of the blowing agent.

[0060] Methods of heating the expandable microspheres include direct or indirect contact with a heat transfer medium such as steam or pressurized steam, as described, for example, in International Publication Nos. 2004 / 056549, 2014 / 198532, and 2016 / 091847. In further embodiments, direct or indirect contact with other heated gases (e.g., air or nitrogen), optionally mixed with steam, can be used. In still further embodiments where indirect heating is used, a liquid heat transfer medium (e.g., heated oil) can be used. In another embodiment, IR radiation can be used to heat the microspheres.

[0061] The expansion properties of thermally expandable thermoplastic microspheres can be evaluated using a thermomechanical analyzer (e.g., Mettler TMA 841), and quantitative data can be obtained from images using suitable software, such as, for example, STARe software.

[0062] The expandable thermoplastic microspheres may be provided in an unexpanded form, for example, for local expansion to their point of use, or may be pre-expanded prior to shipment to the point of end use.

[0063] Microspheres can be used in numerous applications, for example, in the manufacture of paper (e.g., embossed paper, paper fillers, glues), inks, cork, cementitious compositions, adhesives, foams, insulating materials, coatings, rubber-based products, thermoplastics, thermosets, ceramics, nonwoven composites, fillers, etc. For example, they can find use to provide lightweight fillers in such applications.

[0064] Furthermore, the expansion of microspheres is typically irreversible, i.e., cooling the microspheres after thermal expansion does not result in their contraction back to their pre-expansion size.

[0065] Another aspect of the invention is a process for preparing thermally expandable microspheres, comprising mixing isolated lignin, an organic solvent, a blowing agent, and optionally, additional polymeric components, and then spraying the resulting mixture into a drying apparatus to produce thermally expandable microspheres having a polymeric shell surrounding a hollow core, the polymeric shell comprising the isolated lignin within the hollow core, and the hollow core comprising the blowing agent.

[0066] The process parameters, spray drying equipment, isolated lignin, solvent, blowing agent, further polymeric components as well as their amounts are the same as already described above and apply equally to the process according to the second aspect of the invention.

[0067] In a further aspect, the present invention is also directed to thermally expandable microspheres obtainable by the process for preparing thermally expandable microspheres as described above. [Example]

[0068] The following examples are intended to illustrate the present invention.

[0069] Microscopic evaluation of the expansion properties was carried out using a Linkam LTS420 heating stage in combination with a Leica DM1000 microscope. The heating rate was 40°C / min.

[0070] Expansion properties were evaluated using a Mettler TMA 841 thermomechanical analyzer interfaced to a PC running STARe software. The heating rate was 20°C / min using a load (net) of 0.06 N.

[0071] Gas chromatography-flame ionization detection (GC-FID) analysis was performed using an Agilent 7697A Headspace coupled with an Agilent 7890A GC.

[0072] General synthesis method: A solution of the isolated lignin, the blowing agent, and, if applicable, the further polymeric component in a suitable solvent was prepared by dissolving the polymer, the blowing agent, and, if applicable, the further polymeric component overnight with the use of a magnetic stirrer.

[0073] Additional polymeric components include PEG (polyethylene glycol; obtained from Merck, 807483), PAA (polyacrylic acid, MW 2,000, 63%, VWR, obtained from ACRO184992500), HC (hemicellulose; obtained from IRS Biotech, Xylan GBB1670); CMC (carboxymethylcellulose; MW 8,000-10,000 (GPC, pullulan standard); DS 0.7; obtained from Nuryon); CA (cellulose acetate; obtained from Easton, CA-398-3); chitosan (obtained from Chitolytic, CO-101211); and CAPh (cellulose acetate phthalate, obtained from Merck, 22192).

[0074] The mixture thus obtained was then spray-dried using a Büchi Mini Spray Dryer B-290. Nitrogen was used as the atomizing gas at a feed rate of 238 l / h. The feed rate of the mixture to be spray-dried was 4-13 ml / min (depending on the solvent). The temperature of the drying gas at the inlet was 70-120°C (depending on the solvent), and the aspirator speed was 38 m / s. 3 It was / o'clock.

[0075] The dried solids were collected from the bottom of the cyclone and analyzed.

[0076] Table 1 lists the isolated lignin polymers used to prepare the microspheres.

[0077] [Table 1]

[0078] Details of the prepared samples are shown in Table 2, and data on the resulting microspheres are shown in Table 3. In each of Examples 13-17, the weight ratio (w / w) of the polymer to the additional polymeric compound was 80 / 20. In Examples 6 and 9, the weight ratio (w / w) of the polymer to the additional polymeric compound was 90 / 10. In Example 18, the weight ratio (w / w) of the polymer to the additional polymeric compound was 97 / 3. In Examples 7 and 19, the weight ratio (w / w) of the polymer to the additional polymeric compound was 95 / 5.

[0079] [Table 2] (1) Weight percent based on the total weight of the mixture (2) Actn = acetone (3) t-BuOH = tert-butyl alcohol (4) PEG = polyethylene glycol (5) PAA = Polyacrylic acid (6) HC = Hemicellulose (7) CMC = carboxymethyl cellulose (8) CA = cellulose acetate (9) CAPh = cellulose acetate phthalate

[0080] [Table 3] (1) Blowing agent content of microspheres measured by GC-FID (2) The temperature at which the microspheres begin to expand (3) The temperature at which maximum microsphere expansion was observed (4) microscopic evaluation of the expansion properties of unexpanded microspheres; +=Good ++=Very Good +++=Excellent - = not measured

[0081] These data demonstrate that isolated lignin compositions can be used to create bio-based microspheres that have at least good expansion under microscopic evaluation and are highly versatile with respect to the tunable temperature at which expansion begins over a wide range. Furthermore, the microspheres of the present invention have suitable expanded densities for use in a wide range of applications, thus providing desirable expansion performance. Furthermore, it has been shown that expandable microspheres can be prepared based on mixtures of lignin polymers with a wide variety of additional polymeric compounds, including other bio-based polymeric compounds.

[0082] Flammability test: To test the flammability of the expandable microspheres, approximately 15 ml of expandable microspheres were collected in a long string approximately 10 cm long with an inclined surface. One end of the string was then placed over a fire, and the time it took for the flame to traverse the entire string (i.e., travel from one end of the string to the other) was recorded. Tests were performed on the microspheres of Examples 1-3 and 5. Commercially available microspheres available as Expancel FG41 and 920DU40 (obtained by suspension polymerization of Nakel-based ethylenically unsaturated monomers) were used as references. Strings formed from the kraft lignin and lignosulfonic acid microspheres of the present invention (Examples 1-3 and 5, respectively) almost immediately self-extinguished (i.e., the flame was extinguished by the microspheres and then given an opportunity to traverse the string to any significant extent, thus demonstrating the flame retardant properties of the microspheres), while the comparative microspheres Expancel FG41 and 920DU40 burned completely in 105 and 195 seconds, respectively (i.e., these microspheres did not have flame retardant properties).

Claims

1. 1. A thermally expandable microsphere comprising a polymeric shell surrounding a hollow core, the hollow core comprising a blowing agent, and the polymeric shell comprising isolated lignin.

2. 2. The thermally expandable microsphere of claim 1, wherein the isolated lignin comprises a chemically modified lignin.

3. 3. The thermally expandable microspheres of claim 1 or 2, wherein the isolated lignin comprises a lignin selected from the group consisting of kraft lignin, organic solvent soluble lignin, sulfonated lignin, hydrolyzed lignin, steam explosion lignin, comminuted wood lignin, soda lignin, and combinations thereof, and preferably sulfonated lignin, kraft lignin, or combinations thereof.

4. The thermally expandable microspheres according to any one of claims 1 to 3, wherein the isolated lignin comprises kraft lignin, such as acetylated kraft lignin.

5. The thermally expandable microsphere according to any one of claims 1 to 4, wherein the polymer shell comprises up to 50 wt%, preferably 1 to 45 wt%, more preferably 5 to 40 wt% of at least one further polymeric component, said wt% being based on the total weight of the polymer blend of the polymer shell.

6. The thermally expandable microsphere according to any one of claims 1 to 5, wherein the polymer shell further comprises an additional polymeric component selected from the group consisting of polysaccharides, polysaccharide derivatives, polyesters, polyethers, polyacids, polyols, polyalkenes, or combinations thereof.

7. 7. The thermally expandable microsphere of claim 6, wherein the additional polymeric component is selected from the group consisting of alkyl cellulose, carboxy cellulose, copolymers of vinyl acetate, polylactic acid, polyethylene glycol, polyacrylic acid, and combinations thereof.

8. 8. The thermally expandable microsphere according to claim 6 or 7, wherein the additional polymeric component is selected from the group consisting of polyethylene glycol, polyacrylic acid, and combinations thereof.

9. The thermally expandable microsphere according to any one of claims 1 to 8, wherein the blowing agent comprises an alcohol, an ether, an ester, or a hydrocarbon, preferably an alcohol or a hydrocarbon.

10. The thermally expandable microspheres according to any one of claims 1 to 9, wherein the blowing agent comprises a blowing agent selected from the group consisting of isooctane, isohexane, tert-butyl acetate, butyl acetate, methyl tert-butyl ether, tert-butyl alcohol, and combinations thereof, and preferably comprises tert-butyl alcohol or isooctane.

11. 1. A method for preparing thermally expandable microspheres comprising a polymeric shell surrounding a hollow core, wherein the hollow core comprises a blowing agent and the polymeric shell comprises isolated lignin, the method comprising: (i) preparing a mixture comprising the isolated lignin and the blowing agent in a solvent; (ii) spray drying the mixture obtained in step (i) to obtain heat-expandable microspheres.

12. 12. The method of claim 11, wherein the solvent is selected from the group consisting of water, alcohols, ketones, ethers, esters, and combinations thereof.

13. 13. The method of claim 11 or 12, wherein the solvent comprises a mixture of at least two solvents selected from the group consisting of water, methanol, ethanol, acetone, and combinations thereof.

14. Use of the thermally expandable microspheres according to any one of claims 1 to 10 as a flame retardant material.

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