Thermally expandable cellulose microspheres

Abstract

The present invention relates to a thermally expandable microsphere comprising a polymeric shell surrounding a hollow core, the hollow core comprising a blowing agent, the polymeric shell comprising acetate-functionalized cellulose having a glass transition temperature in the range of 150-250°C, and a hydrogen bond donor selected from the group of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid. The present invention further relates to a process for preparing the expandable microspheres, as well as to the thermally expandable microspheres obtained by such a process, the process comprising mixing acetate-functionalized cellulose, an organic solvent, a blowing agent, and a hydrogen bond donor selected from the group of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, followed by spraying the mixture thus obtained into a drying device to produce thermally expandable microspheres having a polymeric shell surrounding a hollow core, the polymeric shell comprising acetate-functionalized cellulose, the hollow core comprising acetate-functionalized cellulose, and the hollow core comprising a blowing agent.

Description

[Technical Field]

[0001] The present invention relates to thermally expandable microspheres made from cellulosic biopolymers that have low expansion temperatures, and also to processes for their manufacture. [Background technology]

[0002] Thermally expandable microspheres are known in the art and are described, for example, in U.S. Pat. No. 3,615,972, WO 00 / 37547, and WO 2007 / 091960. Some 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 are described in which at least a portion of the monomers making up the thermoplastic shell are bio-based and derived from renewable resources.

[0006] WO 2019 / 043235 describes polymers comprising lactone monomers having the general formula: [ka] In the formula, R1 to R4 each independently represent H and C 1~4 alkyl.

[0007] WO 2019 / 101749 describes copolymers comprising itaconic acid dialkyl ester monomers having the following general formula: [ka] wherein each of R1 and R2 is independently selected from alkyl groups.

[0008] Published patent application WO 2020 / 099440 (PCT / EP2019 / 081076) discloses thermally expandable microspheres made from cellulosic biopolymers. The polymeric shell of these microspheres has a glass transition temperature (T) of at least 125°C. g In WO 2020 / 099440, microspheres are prepared by solvent evaporation or solvent extraction. However, these techniques have drawbacks, such as limited scalability and therefore limited production capacity, the need for an additional drying step for the product, and the need to handle large amounts of contaminated water. It would be desirable to be able to produce microspheres using a method that does not have these drawbacks.

[0009] Therefore, there remains a need for alternative thermoplastic expandable microspheres in which the thermoplastic polymer shell is at least partially derived from a sustainable source. Furthermore, there remains a need to provide expandable microspheres in which the thermoplastic polymer shell is at least partially derived from a sustainable source, and in which the expandable microspheres have desirable expansion properties, such as, for example, desirably low density expanded microspheres. Furthermore, when such expandable microspheres are derived from a sustainable source, it would be desirable for them to have sufficient or even improved storage stability. Furthermore, it would be desirable if these microspheres could be produced by a method that allows for efficient production scale-up and does not require additional product drying steps or the handling of large amounts of contaminated water. Therefore, the present invention is directed to finding thermally expandable polymer microspheres, for example, by using bio-based polymers, that have desirable expansion properties, such as desirably low density of the expanded microspheres, and at the same time, that preferably have sufficient or even improved storage stability. Furthermore, it has been found that these microspheres can be efficiently produced using a spray drying process that can be easily and efficiently scaled up and does not require additional product drying steps or the handling of large amounts of contaminated water. Summary of the Invention

[0010] The present invention relates to thermally expandable microspheres comprising a hollow core surrounded by a polymeric shell, the hollow core containing a blowing agent, and the polymeric shell having a glass transition temperature (T) in the range of 150-250°C. g ) and a hydrogen bond donor selected from the group of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid.

[0011] The present invention is directed not only to a process for preparing expandable microspheres, but also to the thermally expandable microspheres obtained by such a process, which process provides a microsphere having a glass transition temperature (T) in the range of 150-250°C. g), an organic solvent, a blowing agent, and a hydrogen bond donor selected from the group consisting of alcohol, urea, and carboxylic acid, preferably the hydrogen bond donor in the form of a carboxylic acid; and subsequently spraying the mixture thus obtained into a drying apparatus to produce the thermally expandable microspheres having a polymeric shell surrounding a hollow core, wherein the polymeric shell comprises the acetate-functionalized cellulose and the hollow core comprises the blowing agent. [Brief explanation of the drawings]

[0012] [Figure 1] Figure 1 illustrates the difference between single-core (Figure 1A) and multi-core (Figure 1B) microspheres. [Figure 2] FIG. 2 illustrates the determination of Tstart, Tmax, and Lmax by thermomechanical analysis (TMA). DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention discloses thermally expandable microspheres comprising a polymeric shell surrounding a hollow core, wherein the hollow core comprises a blowing agent, and the polymeric shell has a glass transition temperature (T) in the range of 150-250°C. g ), and a hydrogen bond donor selected from the group of alcohols, ureas, carboxylic acids, preferably in the form of a carboxylic acid such as a dicarboxylic acid, tricarboxylic acid, or tetracarboxylic acid.

[0014] The expandable microspheres are based on a polymeric shell made of acetate-functionalized cellulose. The functional group can be one acetate group or multiple acetate groups. Therefore, the term "acetate-functionalized cellulose" means that the cellulose contains at least one acetate group. The acetate moiety forms part of the link between the acetate functional group and the cellulose; that is, the cellulose is attached to the acetate functional group via an ester bond.

[0015] The polymeric shell can comprise or consist of one or more polymeric components, with at least one, one or more, or all polymeric components being selected from these acetate-functionalized celluloses. When the shell comprises polymers other than those described herein (i.e., acetate-functionalized celluloses), their content is typically less than 50% by weight, for example, less than 30% by weight, or less than 10% by weight, for example, 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.

[0016] In certain embodiments, the polymeric shell is an acetate-functionalized cellulose, more specifically, a polymer having a glass transition temperature T in the range of 150° C. to 250° C. g The composition contains only one polymer component, which is cellulose acetate having the formula:

[0017] Acetate-functionalized cellulose may contain one or more additional carboxylate functional groups different from acetic acid.When acetate-functionalized cellulose contains one or more carboxylate functional groups different from acetic acid, these carboxylate functional groups are different from each other.For example, in embodiments, acetate-functionalized cellulose may contain one additional carboxylate functional group different from acetic acid.However, it is preferred that acetate-functionalized cellulose does not contain any additional carboxylate functional group different from acetic acid.

[0018] In embodiments, when the acetate-functionalized cellulose includes an additional carboxylate functionality other than acetic acid, the additional carboxylate functionality on the acetate-functionalized cellulose can be represented by formula (1): [ka]

[0019] In formula (1), A is -H, -OH, -OR b , -C(O)OH, and -C(O)OR bIn embodiments, A is selected from -H and -C(O)OH.

[0020] R a may be absent, i.e., A may be attached directly to the C=O group. However, if present, R a can be selected from saturated or unsaturated aliphatic groups having 1 to 11 carbon atoms and can be linear, branched, or cyclic.

[0021] R a may also be selected from five- and six-membered aromatic rings.

[0022] R a -OH, halide, C 1~4 Alkyl, and C 1~4 alkoxy, wherein C 1~4 Alkyl and C 1~4 The alkoxy group is optionally substituted with one or more groups selected from halide and -OH.

[0023] In embodiments, R a contains 1 to 7 carbon atoms, for example, 1 to 5, or 1 to 3 carbon atoms.

[0024] In each occurrence R b independently, C 1~4 Alkyl groups (e.g., C 1~2 alkyl groups), optionally bearing one or more substituents selected from halide and —OH groups. 1~4 Alkyl group or C 1~2 The alkyl group is unsubstituted.

[0025] In embodiments, R a is a saturated linear or branched chain [ka] v is an integer ranging from 1 to 11, for example, from 1 to 8 (such as from 1 to 6 or from 1 to 4), and w is an integer ranging from 3 to 11, for example, from 4 to 6.

[0026] In each occurrence R c are independently H, -OH, halide, C 1~4 Alkyl, and C 1~4 alkoxy, C 1~4 Alkyl and C 1~4 The alkoxy group is optionally substituted with one or more groups selected from halide and -OH.

[0027] In other embodiments, R a is an unsaturated, linear or branched chain containing a "y" double bond. [ka] x is an integer ranging from 2 to 11, for example, from 2 to 6 or from 2 to 4. y represents the number of double bonds and is typically 1 or 2.

[0028] In a further embodiment, R a contains the "y" double bond [ka] where y is typically 1 or 2.

[0029] In still further embodiments, R a teeth, [ka] z is an integer selected from 5 and 6.

[0030] In still further embodiments, R a can be a linear or branched aliphatic group containing a cycloaliphatic or aromatic ring. a has 11 or fewer carbon atoms [ka] where E is as defined above. [ka] p and r are each independently an integer from 0 to 8, and p + r is at least 1. q and s are each the number of double bonds in each acyclic aliphatic moiety. In an embodiment, q and s are each independently selected from 0, 1, and 2.

[0031] The halide is typically selected from F and Cl. However, in embodiments, the functional group does not include a halide, thereby reducing the functionality of the groups A, R a , R b and R c No halides are present in the

[0032] In embodiments, at least one R c The group is H. In other embodiments, no more than two R c groups other than H, and in further embodiments, not more than one R c groups are other than H. In still further embodiments, all R c The group is H.

[0033] R a , R b , and R c In the above definition of, when there are two or more -OH substituents, there is typically no more than one -OH substituent per carbon atom.

[0034] In certain embodiments, R a is an optionally substituted C1-C8 aliphatic (alkylene) group. In other embodiments, R a is an optionally substituted C aromatic ring. In a further embodiment, R a is unsubstituted.

[0035] In embodiments, the carboxylate functional groups on the cellulose substituent are selected from acetate, propionate, butyrate, pentanoate, hexanoate, heptanoate, octanoate, and phthalate. In further embodiments, they are selected from propionate and butyrate.

[0036] The degree of substitution (DS) of the hydroxyl groups of the cellulose with acetate and, if present, one or more additional carboxylate functional groups can be in the range of 0.9 to 4.0, preferably in the range of 0.9 to 3.5, and in embodiments in the range of 1.5 to 3.5, for example in the range of 2.0 to 3.0.

[0037] When acetate-functionalized cellulose contains one or more additional carboxylate functional groups, the degree of substitution (DS) of acetate is higher than the degree of substitution (DS) of one or more additional carboxylate functional groups.In other words, acetate-functionalized cellulose according to the present invention contains more acetate groups (i.e., acetate functional groups) than one or more additional carboxylate functional groups (i.e., functional groups).In embodiments, the degree of substitution (DS) of one or more additional carboxylate functional groups is preferably 1.0 or less, for example, 0.5 or less, 0.2 or less, or even 0.1 or less.

[0038] In an embodiment, in the acetate-functionalized cellulose, the degree of substitution (DS) with acetate is in the range of 0, 0.9 to 3.5, e.g., 1.5 to 3.5 or 2.0 to 3.0, and the degree of substitution (DS) with one or more additional carboxylate functional groups is 1.0 or less, e.g., 0.5 or less, or 0.2 or less, or even 0.1 or less, provided that the degree of substitution (DS) with acetate is higher than the degree of substitution (DS) with one or more additional carboxylate functional groups.

[0039] In a preferred embodiment, the acetate-functionalized cellulose has a degree of substitution (DS) with acetate in the range of 2.0 to 3.0 and a degree of substitution (DS) with one or more additional carboxylate functional groups of 1.0 or less, e.g., 0.5 or less, 0.2 or less, or even 0.1 or less.

[0040] The degree of substitution (DS) is a measure of the average number of hydroxyl groups per glucose unit of cellulose that are substituted with other groups, such as carboxylic acid groups and especially acetate groups. Therefore, the degree of substitution (DS) of cellulose should not exceed 4.0. The degree of substitution (DS) can be determined by the ASTM D817-12 method.

[0041] Optionally, other functional groups other than carboxylate functional groups may be present in the acetate-functionalized cellulose. For example, -OH groups on the cellulose molecule not already substituted with carboxylate functional groups can be substituted with one or more alkoxy groups, e.g., C1-C6 alkoxy groups. In other, less preferred, -OH groups can be replaced with halide groups, e.g., F or Cl. If such other functional groups are present, their molar amount is lower than that of the one or more carboxylate groups.

[0042] In embodiments, the degree of substitution of cellulose with other functional groups (i.e., functional groups other than acetate or other carboxylate functional groups) is 1.0 or less, for example, 0.5 or less, or 0.2 or less. In further embodiments, the degree of substitution with groups other than carboxylate groups is 0.1 or less. However, the degree of substitution of cellulose with other functional groups is lower than the degree of substitution with acetate.

[0043] In certain embodiments, the acetate-functionalized cellulose is a cellulose acetate having a degree of substitution (DS) with acetic acid ranging from 0.9 to 4.0, e.g., 0.9 to 3.5, particularly 1.5 to 3.5, and more particularly 2.0 to 3.0. As used herein, the term "cellulose acetate" means that no other functional groups other than acetate and hydroxyl groups are present in the cellulose.

[0044] The glass transition temperature (T) of the acetate-functionalized cellulose forming the shell of the microspheres or at least a portion of the shell of the microspheresg ) is in the range of 150°C to 250°C, for example, 150°C to 190°C. In a preferred embodiment, the polymeric shell comprises acetate-functionalized cellulose having a glass transition temperature in the range of 150°C to 190°C. T g can be measured using differential scanning calorimetry (DSC), for example, using the method described by Nishio et al.; Cellulose, 2006(13), 245-259, where a 5 mg sample is first heated from ambient temperature (25°C) to 240°C at a rate of 20°C / min under a nitrogen atmosphere, then immediately quenched to -50°C, and then heated a second time from -50°C to 240°C at a rate of 20°C / min under a nitrogen atmosphere, and T g The calculation is based on the second heating cycle.

[0045] In a further embodiment, the T of acetate functionalized cellulose g is in the range of 160 to 220°C, for example, 160 to 200°C, 160 to 190°C, 170 to 185°C, or 175 to 185°C.

[0046] The melting point of acetate-functionalized cellulose is typically T g The melting point is equal to or greater than 200° C., in embodiments greater than 220° C. The melting point is typically equal to or less than 270° C., for example, equal to or less than 260° C. or equal to or less than 250° C.

[0047] T of acetate-functionalized cellulose g The melting point can be modified or controlled by varying the functional groups on the acetate-functionalized cellulose, by varying the molecular weight, or by varying the degree of substitution.

[0048] Thermally expandable microspheres are hollow, with a shell made of acetate-functionalized cellulose and a hollow center or core made of one or more blowing agents. The acetate-functionalized cellulose used to prepare the microspheres typically has a density of 1.1-1.35 g / cm. 3For expanded microspheres, the density is typically 1 g / cm 3 Less than 0.005 to 0.8 g / cm 3 , or 0.01 to 0.6 g / cm 3 In a further embodiment, the density of the expanded microspheres is in the range of 0.01 to 0.4 g / cm. 3 For example, the range is 0.01 to 0.2 g / cm 3 in the range of 0.01 to 0.15 g / cm 3 Higher densities, especially in the 1 g / cm range, 3 A density above this generally means that the microsphere sample is not suitable for use.

[0049] In embodiments, the number average molecular weight (M n ) is in the range of 1,000 to 700,000, for example, 2,000 to 500,000, 2,000 to 100,000, 2,000 to 80,000, or 2,000 to 50,000 Da. In an embodiment, it is in the range of 5,000 to 50,000, for example, 10,000 to 50,000.

[0050] Examples of suitable acetate-functionalized celluloses include those having a number average molecular weight (M) in the range of 1,000 to 700,000, e.g., in the range of 2,000 to 500,000, 2,000 to 100,000, 2,000 to 80,000, or 2,000 to 50,000 Da, preferably in the range of 5,000 to 50,000, and more preferably in the range of 10,000 to 50,000. n ) is an example of a cellulose acetate having the formula:

[0051] In certain embodiments, the acetate-functionalized cellulose has a degree of substitution (DS) with acetate in the range of 0.9 to 4.0, such as in the range of 0.9 to 3.5, particularly in the range of 1.5 to 3.5, and more particularly in the range of 2.0 to 3.0, and a number average molecular weight (M) in the range of 1,000 to 700,000, such as in the range of 2,000 to 500,000, such as in the range of 2,000 to 100,000, such as in the range of 2,000 to 80,000, or such as in the range of 2,000 to 50,000 Da, preferably in the range of 5,000 to 50,000, and more preferably in the range of 10,000 to 50,000. n ) is cellulose acetate.

[0052] Thermally expandable microspheres begin to expand at a temperature T Start The expansion starting temperature T 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 (an exemplary thermogram is shown in Figure 2) 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.

[0053] In embodiments, the thermally expandable microspheres have a T in the range of 155°C to 220°C, for example, 160°C to less than 200°C. Start Preferably, the thermally expandable microspheres have a T in the range of 160°C to 190°C, preferably 165°C to 185°C, more preferably 165°C to 180°C. Start Even more preferably, the thermally expandable microspheres have a T in the range of 165°C to 175°C. Start It has.

[0054] To further enhance the properties of the polymeric shell, the polymeric shell of the thermally expandable microspheres contains a hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid. The hydrogen bond donor can interact with groups on the acetate-functionalized cellulose via hydrogen bonds. The addition of a hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, can further improve the barrier properties of the polymeric shell, enhance the mechanical properties of the polymeric shell, and ultimately the expansion properties of the microspheres. The hydrogen bond donor thus functions as a polymeric shell enhancer. Furthermore, it can also improve the density, for example, after four weeks of storage.

[0055] The hydrogen bond donor may be a polymer having an average molecular weight of, for example, 10,000 g / mol, for example, an average molecular weight of 1,000 to 5,000 g / mol, for example, an average molecular weight of 1,500 to 3,000 g / mol. The hydrogen bond donor may also be a low-molecular-weight compound having, for example, a molecular weight of less than 2,000 g / mol, preferably less than 1,500 g / mol, more preferably less than 1,000 g / mol, and even more preferably less than 500 g / mol; the hydrogen bond donor is typically and preferably a low-molecular-weight compound. For example, the hydrogen bond donor may have a molecular weight in the range of 20 to 500 g / mol, preferably 30 to 400 g / mol, and more preferably 40 to 300 g / mol.

[0056] The hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids is a compound having a hydrogen atom covalently bonded to a more electronegative atom, i.e., oxygen (when the hydrogen bond donor is an alcohol or a carboxylic acid) or nitrogen (when the hydrogen bond donor is a urea), where these hydrogen atoms form intermolecular hydrogen bonds with functional groups (hydrogen bond acceptors) of the acetate-functionalized cellulose, such as acetate groups, one or more additional carboxylate functional groups, hydroxyl groups, and ether groups, particularly acetate groups and, if present, one or more additional carboxylate functional groups.

[0057] The hydrogen bond donor is selected from the group of alcohols, ureas, and carboxylic acids. Preferably, the hydrogen bond donor is selected from the group of alcohols and carboxylic acids. In a more preferred embodiment, the hydrogen bond donor is a carboxylic acid. In another more preferred embodiment, the hydrogen bond donor is an alcohol.

[0058] The hydrogen bond donor selected from the group of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, may have a molecular weight in the range of 20 to 2000 g / mol, preferably in the range of 20 to 500 g / mol, more preferably in the range of 30 to 400 g / mol, even more preferably in the range of 40 to 300 g / mol.

[0059] When the hydrogen bond donor is an alcohol, it can be selected from compounds containing at least one alcohol group, for example, 1, 2, 3, 4, 5, or 6 alcohol groups, and preferably has a molecular weight in the range of 20 to 2000 g / mol.When the hydrogen bond donor is an alcohol, it is preferably a diol, triol, tetraol, pentaol, or hexaol.

[0060] Suitable diols are, for example, 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 2,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, preferably 1,3-butanediol.

[0061] Suitable triols are, for example, glycerol, 1,2,3-butanetriol, 1,2,4-butanetriol, 1,1,1-tris(hydroxymethyl)propane, pentanetriol, and hexanetriol. A preferred triol is glycerol.

[0062] Suitable tetraols are, for example, ascorbic acid (vitamin C), erythritol, threitol, or pentaerythritol. Preferred tetraols are ascorbic acid (vitamin C) and pentaerythritol.

[0063] Suitable pentaols are xylitol, arabitol, ribitol, glucose, fructose, galactose, and mannose.

[0064] Suitable hexaols are, for example, sorbitol, mannitol, and cyclohexanehexol. A preferred hexaol is sorbitol.

[0065] When the hydrogen bond donor is an alcohol, it is preferably selected from 1,3-butanediol, glycerol, ascorbic acid (vitamin C), or sorbitol.

[0066] The hydrogen bond donor is particularly preferably a carboxylic acid, i.e., a compound containing at least one carboxylic acid group, such as a monocarboxylic acid, dicarboxylic acid, tricarboxylic acid, tetracarboxylic acid, or polycarboxylic acid (e.g., a polycarboxylic acid polymer). More specifically, the hydrogen bond donor is a carboxylic acid having a molecular weight in the range of 20 to 2000 g / mol. Preferably, the hydrogen bond donor is a carboxylic acid containing at least two carboxylic acid groups (—COOH), particularly a dicarboxylic acid, tricarboxylic acid, or tetracarboxylic acid.

[0067] Examples of monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, and lactic acid.

[0068] Examples of dicarboxylic acids include adipic acid, maleic acid, succinic acid, tartaric acid, and aldaric acid.

[0069] Examples of tricarboxylic acids include citric acid and isocitric acid.

[0070] Examples of tetracarboxylic acids include pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), ethylenediaminetetraacetic acid (EDTA), and butanetetracarboxylic acids such as 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0071] Preferred examples of suitable hydrogen bond donors in the form of a carboxylic acid include citric acid, maleic acid, succinic acid, pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), lactic acid, tartaric acid, ethylenediaminetetraacetic acid (EDTA), and butanetetracarboxylic acids such as 1,2,3,4-butanetetracarboxylic acid (BTCA). More preferred examples of suitable hydrogen bond donors in the form of a carboxylic acid include pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), citric acid, tartaric acid, 1,2,3,4-butanetetracarboxylic acid (BTCA), and maleic acid.

[0072] In particular, when the hydrogen bond donor is in the form of a carboxylic acid according to preferred embodiments, it is selected from the group consisting of pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), citric acid, tartaric acid, 1,2,3,4-butanetetracarboxylic acid (BTCA), and maleic acid.

[0073] More specifically, when the hydrogen bond donor is in the form of a carboxylic acid according to a preferred embodiment, it is selected from the group consisting of pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), citric acid, tartaric acid, and 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0074] Preferably, when the hydrogen bond donor is in the form of a carboxylic acid according to a preferred embodiment, it is a tricarboxylic or tetracarboxylic acid such as citric acid, pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), or 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0075] In certain embodiments, when the hydrogen bond donor is in the form of a carboxylic acid according to preferred embodiments, it is a tetracarboxylic acid such as pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid) or 1,2,3,4-butanetetracarboxylic acid (BTCA). Most preferably, the hydrogen bond donor is in the form of a carboxylic acid, which is 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0076] The amount of hydrogen bond donor selected from the group of alcohol, urea, and carboxylic acid, preferably the amount of hydrogen bond donor in the form of carboxylic acid, used to prepare the expandable microspheres of the present invention is not particularly limited.

[0077] However, the amount of hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, can be 0.01 to 50 wt % based on the total weight of the hydrogen bond donor and acetate-functionalized cellulose. In embodiments, the amount can be in the range of 0.01 to 40 wt %, e.g., 0.05 to 30 wt %, 0.1 to 20 wt %, or 0.5 to 15 wt %, e.g., 0.5 to 10 wt %, 1.0 to 5.0 wt %, 1.2 to 5 wt %, or even 1.5 to 5 wt %, where the weight percentage is based on the total weight of the hydrogen bond donor and acetate-functionalized cellulose.

[0078] In further embodiments, the polymeric shell can include particles to improve the mechanical properties and gas barrier of the polymer shell, thus also acting as a polymer shell enhancer. Examples of such particles are talc, montmorillonite, nanocrystalline cellulose, and various types of clay (such as bentonite).

[0079] A number of factors can result in high density. For example, high density can result from low microsphere yield, i.e., the proportion of microspheres in the polymeric material is too low to reduce the overall density to an acceptable level. Another problem is poor expansion characteristics, which can occur when there are too many microspheres and insufficient blowing agent to allow for adequate 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 the 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 poor microsphere production and a higher density material. Microspheres with too high a proportion of aggregated material or that do not expand sufficiently can also lead to significant heterogeneity 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.

[0080] 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.

[0081] The one or more blowing agents 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 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 functionalized cellulose shell. The boiling point at high pressure can be calculated using the Clausius-Clapeyron equation.

[0082] Examples of blowing agents include dialkyl ethers, alkanes, and halocarbons (e.g., chlorocarbons, fluorocarbons, or chlorofluorocarbons). In embodiments, the dialkyl ethers include two alkyl groups each selected from C2 to C5 alkyl groups. In embodiments, the alkanes include C4 to C6 alkyl groups. 12 In an embodiment, the haloalkane is a C-C 10 The dialkyl ether, the alkane, and the haloalkane may contain one or more halogen atoms selected from chlorine and fluorine. The alkyl or haloalkyl groups in the dialkyl ether, the alkane, and the haloalkane may be linear, branched, or cyclic. One or more blowing agents may be used singly or in combination.

[0083] In embodiments, for environmental reasons, the one or more blowing agents are selected from alkyl ethers and alkanes, and in further embodiments, the one or more blowing agents are selected from alkanes. Haloalkanes are preferably avoided due to their potential ozone depletion properties and also due to their generally higher global warming potential.

[0084] Examples of suitable blowing agents that can be used include n-pentane, isopentane, neopentane, cyclopentane, cyclohexane, n-butane, isobutane, isohexane, neohexane, heptane, isoheptane, octane, isooctane, isodecane, and isododecane. In a preferred embodiment, the blowing agent is a C4-C6 12 isoalkanes.

[0085] In expandable microspheres, the one or more blowing agents are typically present in an amount ranging from 5 to 50% by weight, for example, from 5 to 45% by weight, or from 10 to 40% by weight, based on the total weight of the functionalized cellulose and the blowing agent(s).

[0086] Acetate-functionalized cellulose materials can be purchased commercially or can be prepared by known means, for example, by mixing cellulose with a suitable carboxylic acid in the presence of a strong acid such as sulfuric acid, or by the base-catalyzed reaction of cellulose with an acyl chloride, as described, for example, in Nishio et al; Cellulose, 2006(13), 245-259.

[0087] Examples of suitable acetate-functionalized celluloses include cellulose acetate (CA) (i.e., acetate-functionalized celluloses that do not contain additional carboxylate functional groups other than acetic acid), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB), particularly those having molecular weights (M) in the range of 2,000 to 100,000 Da, e.g., 2,000 to 80,000 Da, 10,000 to 50,000 Da, or 20,000 to 50,000 Da. n ) are cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB).

[0088] Preferred acetate-functionalized celluloses have a number average molecular weight (M) in the range of 10,000 to 100,000 Da, for example in the range of 10,000 to 80,000 Da, preferably in the range of 10,000 to 50,000 Da, more preferably in the range of 20,000 to 50,000 Da. n ) (i.e., acetate-functionalized cellulose that does not contain additional carboxylate functional groups different from acetic acid).

[0089] For example, when the polymeric shell is composed of cellulose acetate propionate (CAP) or cellulose acetate butyrate (CAB), the amount of hydrogen bond donor in the form of a carboxylic acid used can be 0.01 to 50 wt %, based on the total weight of the hydrogen bond donor and acetate-functionalized cellulose. In embodiments, the amount can be in the range of 0.01 to 40 wt %, e.g., 0.05 to 30 wt %, 0.1 to 20 wt %, or even 0.5 to 15 wt %, such as 0.5 to 10 wt %, or 1.0 to 5.0 wt %, based on the total weight of the hydrogen bond donor and acetate-functionalized cellulose.

[0090] For example, when the polymeric shell is comprised of cellulose acetate (CA) (i.e., acetate-functionalized cellulose without additional carboxylate functional groups other than acetic acid), the amount of hydrogen bond donor in the form of a carboxylic acid used can be 0.01 to 50 wt %, based on the total weight of the hydrogen bond donor and acetate-functionalized cellulose. In embodiments, the amount can be in the range of 0.01 to 40 wt %, e.g., 0.05 to 30 wt %, 0.1 to 20 wt %, or 0.5 to 15 wt %, such as 0.5 to 10 wt %, or 1.0 to 5.0 wt %, based on the total weight of the hydrogen bond donor and acetate-functionalized cellulose.

[0091] The expandable microspheres of the present invention can be obtained by a spray-drying process that involves mixing acetate-functionalized cellulose, an organic solvent, a blowing agent, and a hydrogen bond donor selected from the group consisting of alcohol, urea, and carboxylic acid, preferably in the form of a carboxylic acid, and then spraying the mixture thus obtained into a drying apparatus to produce thermally expandable microspheres having a polymeric shell surrounding a hollow core, the polymeric shell consisting of acetate-functionalized cellulose, and the hollow core consisting of a blowing agent.

[0092] 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.

[0093] A suitable spray drying apparatus for carrying out the spray drying process is a Buchi Mini Spray Dryer B-290 available from Buchi / Switzerland.

[0094] The order in which the acetate-functionalized cellulose, the organic solvent, the blowing agent, and the hydrogen bond donor selected from the group of alcohol, urea, and carboxylic acid, preferably the hydrogen bond donor in the form of a carboxylic acid, are added for mixing is not limited, and any order can be selected.

[0095] However, in a preferred embodiment, in the process of fabricating expandable microspheres, the acetate-functionalized cellulose is first mixed with an organic solvent, and then in a further step, a blowing agent and a hydrogen bond donor selected from the group of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, are added to the mixture.

[0096] Mixing of the acetate-functionalized cellulose may be carried out at ambient temperature, although temperatures ranging from 5 to 75° C. may also be used. Mixing is typically carried out until the acetate-functionalized cellulose is completely dissolved in the organic solvent.

[0097] In embodiments, the mixture of acetate-functionalized cellulose and organic solvent can be allowed to stand or stirred for a period of time, such as 1 to 100 hours, or 2 to 50 hours, which can be carried out at a temperature ranging from 10 to 95°C, such as 20 to 90°C.

[0098] In a further step, a blowing agent and a hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, are added to the mixture of acetate-functionalized cellulose and an organic solvent. The order in which the blowing agent and the hydrogen bond donor are added is not important; thus, the blowing agent may be added first, followed by the hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid. Alternatively, the hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, may be added first, followed by the blowing agent. This mixing step can also be carried out at ambient temperature, although temperatures ranging from 5 to 75°C can be used. This mixing step is also typically carried out until the blowing agent and the hydrogen bond donor selected from the group of alcohol, urea, and carboxylic acid, preferably in the form of a carboxylic acid, are completely dissolved in the organic solvent.

[0099] After adding the blowing agent and the hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, to the mixture of acetate-functionalized cellulose and organic solvent, the resulting mixture may be further stirred, for example, for 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.

[0100] The mixture of acetate-functionalized cellulose, organic solvent, blowing agent, and hydrogen bond donor selected from the group of alcohol, urea, and carboxylic acid, preferably in the form of a carboxylic acid, is then sprayed into a drying apparatus, which may be a spray drying apparatus as described above, to produce the thermally expandable microspheres described herein.

[0101] 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.

[0102] In addition, the drying gas is not particularly limited and may be any suitable drying gas known by those skilled in the art. For example, the spraying gas may also be selected from nitrogen, carbon dioxide, (pressurized) air, and noble gases (such as argon). The drying gas is preferably nitrogen.

[0103] 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.

[0104] The above-described method can provide thermally expandable microspheres consisting of a hollow core surrounded by a polymeric shell, the hollow core containing a foaming agent, the polymeric shell containing acetate-functionalized cellulose, and the thermally expandable microspheres having an expansion onset temperature T Start It has been found that the temperature is 140° C. or higher, for example 150° C. to 250° C. Furthermore, it has been found that this method is particularly suitable for obtaining such thermally expandable microspheres, wherein the polymeric shell further comprises a hydrogen bond donor selected from the group of alcohols, ureas, and carboxylic acids, preferably a hydrogen bond donor in the form of a carboxylic acid.

[0105] The organic solvent can be selected from organic solvents having one or more functional groups selected from, for example, esters, amides, aldehydes, ketones, alcohols (including glycols), and ethers 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.

[0106] Examples of organic solvents that can be used include ethyl acetate, ethyl formate, methyl acetate, n-propyl formate, iso-propyl formate, n-propyl acetate, iso-propyl acetate, iso-butyl acetate, n-butyl acetate, n-pentyl formate, iso-pentyl formate, n-pentyl acetate, iso-pentyl acetate, ethyl propionate, iso-butyl 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 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, methyl chloride, chloroform, carbon tetrachloride, trichloroacetic acid, methyl bromide, methyl iodide, trichloroethylene, and tetrachloroethylene. The organic solvent can be a mixture of two or more solvents.The organic solvent may contain water, but typically the water content of the organic solvent(s) is less than 5% by weight, ie 0-5% by weight water, for example 0-1% by weight water.

[0107] In embodiments, the solvent is selected from one or more of ethyl acetate, methyl acetate, ethyl formate, and acetone. It is particularly preferred that the solvent is acetone.

[0108] Typically, the acetate-functionalized cellulose content in the spray-drying mixture is typically in the range of 0.1 to 50 wt. %. In embodiments, it can be in the range of 1 to 40 wt. %, such as 2 to 35 wt. % or even 5 to 10 wt. %. The wt. % is based on the total weight of the spray-drying mixture.

[0109] 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, or even 3 to 25% by weight. In embodiments, the weight of the blowing agent in the spray-drying mixture is equal to or less than the weight of the acetate-functionalized cellulose; for example, the weight ratio of blowing agent to acetate-functionalized cellulose 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 acetate-functionalized cellulose 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.

[0110] The amount of hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, in the spray-drying mixture is typically in the range of 0.01 to 15 wt %, e.g., 0.05 to 10 wt %, 0.1 to 5 wt %, or 0.1 to 3.0 wt %, e.g., 0.1 to 1.0 wt %, based on the total weight of the acetate-functionalized cellulose, the blowing agent, the hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, and the solvent in the spray-drying mixture.

[0111] For example, when cellulose acetate propionate (CAP) or cellulose acetate butyrate (CAB) is used as the polymer, the amount of hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, used can be 0.01 to 15 wt %. In embodiments, it can be in the range of 0.05 to 10 wt %, 0.1 to 5 wt %, or even 0.1 to 3.0 wt %, for example, 0.1 to 1.0 wt %. The weight percentage is based on the total weight of the acetate-functionalized cellulose, the blowing agent, the hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, and the solvent in the spray-drying mixture.

[0112] For example, in a preferred embodiment, when cellulose acetate (CA) (i.e., acetate-functionalized cellulose that does not further contain carboxylic acid functional groups different from acetic acid) is used as the polymer, the amount of hydrogen bond donor selected from the group of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, can range from 0.01 to 15 wt %, e.g., 0.05 to 10 wt %, 0.1 to 5 wt %, or even 0.1 to 1.0 wt %, where the weight percent is based on the total weight of the acetate-functionalized cellulose, the blowing agent, the hydrogen bond donor selected from the group of alcohols, ureas, and carboxylic acids, preferably in the form of a carboxylic acid, and the solvent in the spray-drying mixture.

[0113] The amount of organic solvent adds up to 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.

[0114] The amount of the hydrogen bond donor, preferably in the form of a carboxylic acid, selected from the group consisting of alcohols, ureas, and carboxylic acids in the spray-drying mixture may be 0.01 to 50 wt % based on the total weight of the hydrogen bond donor, preferably in the form of a carboxylic acid, selected from the group consisting of alcohols, ureas, and carboxylic acids, and the acetate-functionalized cellulose in the spray-drying mixture. In embodiments, the amount may be in the range of 0.1 to 40 wt %, e.g., 0.5 to 35 wt %, 1 to 30 wt %, or even 2 to 25 wt %, where the wt % is based on the total weight of the hydrogen bond donor, preferably in the form of a carboxylic acid, selected from the group consisting of alcohols, ureas, and carboxylic acids, and the acetate-functionalized cellulose in the spray-drying mixture.

[0115] Unexpanded microspheres typically have a volume average particle size (diameter) 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 15 to 80 μm, i.e., a D(0.5) value.

[0116] The diameter of an expanded microsphere is typically in the range of 1.5 to 8 times larger in diameter than an unexpanded microsphere, for example, 2 to 7 or 3 to 6 times its original diameter.

[0117] 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.

[0118] To expand the expandable microspheres, they are heated to a temperature between the boiling point of the blowing agent and the T g The microspheres can be heated to a temperature above the T of the functionalized cellulose 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.

[0119] 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.

[0120] 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.

[0121] The expandable or expanded 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 end-use location.

[0122] Microspheres may find use 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, to provide lightweight fillers in such applications.

[0123] The thermally expandable microspheres described herein can be thermally expandable when dry, wet, or in a slurry. They can also withstand blowing agents for extended periods of time, such as at least one week, at least one month, or at least four months. Furthermore, their expansion is typically irreversible, i.e., cooling the microspheres after thermal expansion does not result in their shrinkage back to their pre-expansion size.

[0124] A second aspect of the present invention is a process for preparing thermally expandable microspheres, the process comprising mixing an acetate-functionalized cellulose having a glass transition temperature in the range of 150-250°C, an organic solvent, a blowing agent, and a hydrogen bond donor selected from the group consisting of alcohol, urea, and carboxylic acid, preferably the hydrogen bond donor in the form of a carboxylic acid, 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 the acetate-functionalized cellulose and the hollow core comprises the blowing agent.

[0125] The process parameters, spray drying equipment, acetate-functionalized cellulose, organic solvent, blowing agent, and hydrogen bond donor selected from the group of alcohols, ureas, and carboxylic acids, preferably in the form of carboxylic acids, as well as the amounts thereof, are the same as those already described above and apply analogously to the process according to the second aspect of the invention.

[0126] In a further embodiment, the process for preparing thermally expandable microspheres further comprises storing the prepared thermally expandable microspheres for at least two weeks, preferably at least four weeks, after preparation before expanding the thermally expandable microspheres. Surprisingly, it has been found that storing the prepared thermally expandable microspheres can improve the expanded density of the thermally expandable microspheres. The expanded density represents the density of the microspheres at their maximum expansion. The expanded density can be determined using standard measurement techniques commonly known by those skilled in the art. For example, the expanded density can be determined by measuring the T Start The density can also be determined by the heating experiments described above for the determination of the density, i.e., using a Mettler-Toledo thermomechanical analyzer, such as a Mettler-Toledo TMA / SDTA 841e, and by analysis of the resulting expansion thermograms, for example, by using STARe software from Mettler-Toledo. The typical value determined for density using such an instrument is called TMA density. The TMA density is calculated by dividing the weight of the sample [g] by the volume increase of the sample at maximum expansion [dm 3 ]. Lower TMA densities generally indicate more desirable expansion properties. 3 A TMA density of less than or equal to 0.15 g / cm is considered desirable and at least 3 The following TMA densities are considered particularly desirable:

[0127] 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]

[0128] The following examples are intended to illustrate the present invention.

[0129] Expansion properties were evaluated using a Mettler TMA / SDTA 841e thermomechanical analyzer interfaced to a PC running STARe software. The samples to be analyzed were prepared from 0.5 mg (+ / - 0.02 mg) of thermally expandable microspheres contained in an aluminum oxide crucible with a diameter of 6.8 mm and a depth of 4.0 mm. The crucible was sealed using an aluminum oxide lid with a diameter of 6.1 mm. Using a TMA expansion probe type, the temperature of the sample was increased from approximately 30°C to 240°C at a heating rate of 20°C / min while applying a net load of 0.06 N on the probe. The expansion properties were analyzed by measuring the vertical displacement of the probe. The initial temperature of expansion (T start ): The temperature (°C) when the probe began to displace. ·Maximum expansion temperature (T max ): The temperature (°C) at which the probe reaches its maximum displacement. Maximum displacement (L max ): Probe displacement (μm) when the probe displacement reaches its maximum. TMA density: When the probe displacement reaches its maximum value, the sample weight (d) is multiplied by the sample volume increase (dm 3 ) divided by .

[0130] The parameters were determined as illustrated by the exemplary embodiment shown in FIG.

[0131] The volatile content in the microspheres was determined using a Mettler Toledo TGA / DSC1 TGA instrument.

[0132] Gas chromatography-flame ionization detection (GC-FID) analysis was performed using an Agilent 7697A Headspace coupled with an Agilent 7890A GC.

[0133] Differential scanning calorimetry (DSC) was obtained using a Mettler Toledo DSC 822e device.

[0134] General synthesis method:

[0135] In the experiments of Examples 1-2, all components (solvent, polymer, hydrogen bond donor and blowing agent) were mixed and stirred overnight using a magnetic stirrer.

[0136] The mixture thus obtained was then spray dried using a Buchi 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 measured to be about 12-13 ml / min. The temperature of the drying gas at the inlet was 105°C, and the suction speed was 38 m / s. 3 / h, the temperature at the outlet was approximately 78-80°C, and the spraying time was approximately 4 minutes.

[0137] The dry solids were collected from the bottom of the cyclone and analyzed within a few days or after storage.

[0138] Table 1 lists the acetate-functionalized cellulose polymer (cellulose acetate (CA1)) used in the preparation of microspheres and its properties. Table 1 also lists a more suitable acetate-functionalized cellulose polymer, i.e., cellulose (CAB1) with acetate and butyrate functional groups, having a degree of substitution (DS) of 2.0-3.0 and a degree of substitution (DS) of 1 or less.

[0139] [Table 1]

[0140] (1) DS = degree of substitution. Total DS = sum of DS of individual substituents. (2) Number average molecular weight (unit: Da) provided by the supplier (3) Glass transition temperature provided by supplier (Eastman) (4) Melting point provided by supplier - Not applicable

[0141] Example 1: CA1 was used as the polymer for the polymer shell, and T start , T max, and the effect of the amount of various hydrogen bond donors added on the TMA density was investigated.

[0142] The mixtures for all experiments in Example 1 contained 2.25 g of CA1, 26.5 g of acetone, and 1.2 g of isooctane. Various hydrogen bond donors were added at various dosages ranging from 1 to 10 wt% (based on the total weight of the hydrogen bond donor and CA1), as shown in Table 2. (PMA = pyromellitic acid, BTCA = 1,2,3,4-butanetetracarboxylic acid, PAA(2000) = polyacrylic acid with a weight average molecular weight of 2000 g / mol)

[0143] [Table 2A]

[0144] [Table 2B]

[0145] (1) Based on the combined weight of the hydrogen bond donor and CA1 (2) Volatile content of microspheres measured by TGA, based on total weight of microspheres ‡ Measured by GC-FID (Gas Chromatography-Flame Ionization Detection)

[0146] From the data obtained in Example 1, it can be seen that the acetate-functionalized cellulose composition has a desirably low TMA density and an expansion onset temperature T start It was revealed that the cellulose acetate polymer can be used to produce bio-based microspheres with a glass transition temperature (Tg) in the range of 158 to 175°C. This result indicates that the addition of hydrogen bond donors can increase the Tg of cellulose acetate, which has a glass transition temperature of 180°C. start The data presented in Table 3 of Example 2 below show that storage of the microspheres for 4 weeks does not significantly change the swelling properties, demonstrating the desirable storage stability of the microspheres of the present invention.

[0147] Example 2: A storage test was conducted to evaluate the storage stability of the microspheres of the present invention after storage for 4 weeks. Table 3 shows the T of the microspheres from the experiment in Example 1 above after 4 weeks of storage. start , T max , and TMA density characteristics. For example, the data shown in Table 2 above for Experiment 2 of Example 1 are for freshly prepared microspheres, while the data shown in Table 3 below for the corresponding Experiment 2 (4w) are for the exact same microspheres, except that the microspheres were measured after 4 weeks of storage. The results are summarized in Table 3.

[0148] [Table 3A]

[0149] [Table 3B]

[0150] (1) Based on the combined weight of the hydrogen bond donor and CA1 (2) Volatile content of microspheres measured by TGA, based on total weight of microspheres (3) Percent change in TMA density of microspheres after 4 weeks of storage compared to the TMA density of the same microspheres immediately after fabrication. Negative values ​​indicate that the TMA density of the microspheres was lower after 4 weeks of storage than immediately after fabrication. ‡ Measured by GC-FID (Gas Chromatography-Flame Ionization Detection)

[0151] From this data, it can be seen that during the four-week storage period, the microspheres slightly loosen the blowing agent, but surprisingly, the expansion properties T start , T max and TMA density were found to be unchanged and even improved in most cases, demonstrating the desirable storage stability of the microspheres of the present invention. The present specification includes the following inventions. Section 1. A thermally expandable microsphere comprising a polymeric shell surrounding a hollow core, wherein the hollow core comprises a blowing agent, and the polymeric shell comprises an acetate-functionalized cellulose having a glass transition temperature in the range of 150 to 250°C, and a hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids. Section 2. Item 1, wherein the hydrogen bond donor is a hydrogen bond donor in the form of a carboxylic acid, preferably selected from the group consisting of pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), citric acid, tartaric acid, butanetetracarboxylic acid, succinic acid, lactic acid, maleic acid, and any combination thereof. Section 3. Item 1 or 2, wherein the hydrogen bond donor is selected from the group consisting of citric acid, pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), and 1,2,3,4-butanetetracarboxylic acid (BTCA), preferably 1,2,3,4-butanetetracarboxylic acid (BTCA). Thermally expandable microspheres according to item 1 or 2. Section 4. Item 1. The thermally expandable microspheres according to item 1, wherein the hydrogen bond donor is an alcohol, preferably selected from the group consisting of 1,3-butanediol, glycerol, pentaerythritol, sorbitol, and ascorbic acid. Section 5. T Start Item 5. The thermally expandable microsphere according to any one of Items 1 to 4, wherein the temperature is 150°C to 250°C, for example, 155°C to 220°C, preferably 160°C to 190°C, and more preferably 165°C to 180°C. Section 6. Item 6. The thermally expandable microsphere according to any one of items 1 to 5, wherein the amount of the hydrogen bond donor, preferably the hydrogen bond donor in the form of a carboxylic acid, is 0.01 to 50% by weight, preferably in the range of 0.01 to 30% by weight, more preferably in the range of 0.1 to 20% by weight, even more preferably in the range of 0.2 to 15% by weight, or in the range of 0.5 to 10% by weight, and most preferably in the range of 1 to 5% by weight, wherein the weight percentage is based on the total weight of the hydrogen bond donor, preferably the hydrogen bond donor in the form of a carboxylic acid, and the acetate-functionalized cellulose. Section 7. Item 7. The thermally expandable microspheres according to any one of items 1 to 6, wherein the acetate-functionalized cellulose comprises one or more additional carboxylate functional groups different from acetic acid, and the one or more other carboxylate functional groups are selected from optionally substituted C1-C8 aliphatic carboxylic acid groups and carboxylic acid groups containing an optionally substituted C6 aromatic ring, and the degree of substitution of the acetate-functionalized cellulose with the one or more other carboxylate functional groups different from acetic acid is 1.0 or less. Section 8. Item 8. The thermally expandable microspheres according to item 7, wherein the one or more additional carboxylate functional groups are selected from propionate, butyrate, pentanoic acid, hexanoate, heptanoic acid, octanoic acid, and phthalate, preferably selected from propionic acid groups and butyrate groups. Section 9. Item 7. The thermally expandable microsphere according to any one of items 1 to 6, wherein the acetate-functionalized cellulose does not contain any additional carboxylate functional groups other than acetic acid. Section 10. Item 10. The thermally expandable microsphere according to any one of items 1 to 9, wherein the polymer shell comprises an acetate-functionalized cellulose having a glass transition temperature in the range of 150°C to 190°C. Section 11. The acetate-functionalized cellulose has a number average molecular weight (M) in the range of 2,000 to 100,000 Da, and preferably in the range of 10,000 to 50,000 Da. n Item 11. The thermally expandable microsphere according to any one of items 1 to 10, having a molecular weight of 1.001 or more. Section 12. Item 12. The thermally expandable microsphere according to any one of items 1 to 11, which can be obtained by a spray drying process comprising mixing the acetate-functionalized cellulose, an organic solvent, the blowing agent, and a hydrogen bond donor selected from the group consisting of alcohols, urea, and carboxylic acids, preferably a hydrogen bond donor in the form of a carboxylic acid, 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 the acetate-functionalized cellulose and the hollow core comprises the blowing agent. Section 13. 1. A process for preparing thermally expandable microspheres, the process comprising mixing an acetate-functionalized cellulose having a glass transition temperature in the range of 150-250°C, an organic solvent, a blowing agent, and a hydrogen bond donor selected from the group consisting of alcohols, urea, and carboxylic acids, preferably in the form of a carboxylic acid, and subsequently spraying the mixture thus obtained into a drying apparatus to produce the thermally expandable microspheres having a polymeric shell surrounding a hollow core, wherein the polymeric shell comprises the acetate-functionalized cellulose and the hollow core comprises the blowing agent. Section 14. Item 14. The process according to item 13, wherein the hydrogen bond donor selected from the group consisting of alcohols, ureas, and carboxylic acids, preferably the hydrogen bond donor in the form of a carboxylic acid, is added in an amount ranging from 0.01 to 15 wt %, preferably in the range of 0.05 to 10 wt %, more preferably in the range of 0.1 to 5 wt %, and most preferably in the range of 0.1 to 3.0 wt %, for example, in the range of 0.1 to 1.0 wt %, wherein the weight % is based on the total weight of the acetate-functionalized cellulose, the blowing agent, the hydrogen bond donor, preferably the hydrogen bond donor in the form of a carboxylic acid, and the solvent in the mixture. Section 15. Item 15. The process according to item 13 or 14, further comprising storing the prepared thermally expandable microspheres for at least 2 weeks, and preferably at least 4 weeks, after preparation before expanding the thermally expandable microspheres.

Claims

1. 1. A thermally expandable microsphere comprising a polymeric shell surrounding a hollow core, wherein the hollow core comprises a blowing agent, and the polymeric shell comprises an acetate-functionalized cellulose having a glass transition temperature in the range of 150 to 250°C, and a hydrogen bond donor selected from the group consisting of an alcohol, a urea, and a carboxylic acid, wherein the alcohol is a diol, a triol, a tetraol, a pentaol, or a hexaol, and the amount of the hydrogen bond donor is 0.5 to 15 wt%, wherein the wt% is based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose.

2. 2. The thermally expandable microsphere of claim 1, wherein the hydrogen bond donor is a hydrogen bond donor in the form of a carboxylic acid.

3. 2. The thermally expandable microsphere according to claim 1, wherein the hydrogen bond donor is selected from the group consisting of pyromellic acid (1,2,4,5-benzenetetracarboxylic acid), citric acid, tartaric acid, butanetetracarboxylic acid, succinic acid, lactic acid, maleic acid, and any combination thereof.

4. 2. The thermally expandable microsphere according to claim 1, wherein the hydrogen bond donor is selected from the group consisting of citric acid, pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), and 1,2,3,4-butanetetracarboxylic acid (BTCA).

5. 2. The thermally expandable microsphere according to claim 1, wherein the hydrogen bond donor is selected from the group consisting of 1,3-butanediol, glycerol, pentaerythritol, sorbitol, and ascorbic acid.

6. T Ｓｔａｒｔ The thermally expandable microsphere according to any one of claims 1 to 5, wherein the temperature is 150°C to 250°C.

7. The acetate-functionalized cellulose comprises one or more additional carboxylate functional groups different from acetic acid, and the one or more other carboxylate functional groups are optionally substituted C １ -C ８ aliphatic carboxylic acid groups, and optionally substituted C ６ The thermally expandable microsphere according to any one of claims 1 to 5, wherein the degree of substitution of the acetate-functionalized cellulose with the one or more other carboxylate functional groups selected from carboxylic acid groups containing aromatic rings and different from the acetic acid is 1.0 or less.

8. 8. The thermally expandable microsphere of claim 7, wherein the one or more additional carboxylate functional groups are selected from propionate, butyrate, pentanoate, hexanoate, heptanoate, octanoate, and phthalate.

9. The thermally expandable microsphere according to any one of claims 1 to 5, wherein the acetate-functionalized cellulose does not contain any additional carboxylate functional groups different from acetic acid.

10. The thermally expandable microsphere according to any one of claims 1 to 5, wherein the polymeric shell comprises an acetate-functionalized cellulose having a glass transition temperature in the range of 150°C to 190°C.

11. The acetate-functionalized cellulose has a number average molecular weight (M ｎ The thermally expandable microsphere according to any one of claims 1 to 5, having a molecular weight of 1000 or more.

12. A process for preparing thermally expandable microspheres, comprising: mixing an acetate-functionalized cellulose having a glass transition temperature in the range of 150-250°C, an organic solvent, a blowing agent, and a hydrogen bond donor selected from the group of alcohols, ureas, and carboxylic acids; and subsequently spraying the resulting mixture into a drying apparatus to produce the thermally expandable microspheres having a polymeric shell surrounding a hollow core; the alcohol is a diol, triol, tetraol, pentaol, or hexaol; the amount of the hydrogen bond donor is 0.5 to 15 wt %, said wt % being based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose; the polymeric shell comprises acetate-functionalized cellulose; The hollow core comprises the blowing agent.

13. The process of claim 12 , wherein the hydrogen bond donor is a carboxylic acid.

14. 14. The process of claim 12 or 13, further comprising storing the prepared thermally expandable microspheres for at least two weeks after preparation before expanding the thermally expandable microspheres.

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