Post-heating of cellulose-based expandable microspheres

Abstract

The present invention relates to storage stable thermally expandable microspheres comprising a polymeric shell surrounding a hollow core wherein the hollow core comprises a blowing agent and the polymeric shell comprises a carboxylic acid ester functionalized cellulose wherein the microspheres retain at least 80% of the initial weight of the blowing agent encapsulated in the microspheres after six months of storage under ambient conditions. The invention also relates to a process for the preparation of storage-stable thermally expandable microspheres comprising a polymeric shell surrounding a hollow core wherein the hollow core comprises a blowing agent and the polymeric shell comprises a carboxylic acid ester functionalized cellulose, the process comprising the steps of: (i) preparing thermally expandable microspheres, the microspheres comprise a polymeric shell surrounding a hollow core wherein the hollow core comprises a blowing agent and the polymeric shell comprises a carboxylic acid ester functionalized cellulose; and (ii) subjecting the thermally expandable microspheres obtained in step (i) to a post-heat treatment by heating the thermally expandable microspheres to a temperature of at least 40 DEG C.

Description

TECHNICAL FIELD

[0001] The present invention relates to thermally expandable microspheres made of cellulosic biopolymers, which retain at least 80% of the initial weight of the blowing agent encapsulated in the microspheres after storage for six months under ambient conditions; the present invention also relates to a method for producing such expandable microspheres. BACKGROUND OF THE INVENTION

[0002] Thermally expandable microspheres are known in the art and are described, for example, in US3615972, WO 00 / 37547 and WO 2007 / 091960. Many examples are sold under the trade name They can expand to form fillers of extremely low weight and low density and can be used in applications such as foamed or low-density resins, paints and coatings, cement, inks and crack fillers. Consumer products that typically contain expandable microspheres include lightweight shoe soles (such as for running shoes), textured overlays (such as wallpaper), solar reflective and insulating coatings, food packaging sealants, wine corks, artificial leather, foams for protective helmet linings, and automotive weatherstripping.

[0003] Thermally expandable polymer microspheres generally comprise 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 liquids at room temperature but evaporate upon heating. To produce expanded microspheres, the expandable microspheres are heated so that the thermoplastic polymer shell softens, the blowing agent evaporates and expands, causing the microspheres to expand. Typically, during expansion the diameter of the microspheres can increase by a factor of 1.5 to 8. Expandable microspheres are sold in various forms, such as as dry free-flowing granules, as aqueous slurries or as partially dehydrated wet cakes.

[0004] Expandable microspheres can be produced by polymerizing ethylenically unsaturated monomers in the presence of a blowing agent, for example using a suspension polymerization process. Typical monomers include those based on acrylates, acrylonitrile, acrylamides, vinylidene chloride and styrene. Problems associated with such thermoplastic polymers are that they are generally derived from petrochemicals rather than from sustainable sources. In addition, many polymers are non-biodegradable or at least biodegrade very slowly so that they risk accumulating in the environment. Thus, expandable microspheres have been described in which at least a portion of the monomers constituting the thermoplastic shell are bio-based and can be derived from renewable resources. For example, WO2019 / 043235 describes polymers containing lactone monomers, WO2019 / 101749 describes copolymers containing itaconic acid dialkyl ester monomers, and WO2020 / 099440 and WO2021 / 234010A1 disclose thermally expandable microspheres made of cellulosic biopolymers.

[0005] Due to the biodegradability of expandable microspheres made of cellulose-based biopolymers, the availability of monomers from sustainable sources, and the swelling and performance characteristics, these expandable microspheres have been found to be particularly desirable. However, there are still some problems with the long-term storage of unexpanded cellulose-based microspheres, as it has been found that the swelling performance of unexpanded microspheres will decline to a certain extent over time, because the encapsulated blowing agent in the unexpanded microspheres will be lost over time, presumably by diffusion through the polymer network of the microsphere shell. This situation is undesirable because unexpanded microspheres are usually produced at the manufacturer and then shipped to customers in large batches, and the customers expand them step by step in small amounts as needed. However, this means that a portion of the initially shipped large batch of unexpanded microspheres will be stored at the customer's location for an unforeseeable period of time, often up to several months, such as up to three months, or up to six months, or even longer.

[0006] Therefore, there is still a need for expandable microspheres made of cellulose-based biopolymers with improved storage stability. For example, it would be desirable if expandable microspheres made of cellulose-based biopolymers could be stored for up to three months, preferably even up to six months, or even longer and their swelling performance is not significantly impaired. It would be even more desirable if expandable microspheres made of cellulose-based biopolymers could be stored for up to three months, preferably even up to six months, or even longer and retain at least 80% of the initial weight of the blowing agent encapsulated in the microspheres. It would be even more desirable if the cellulose-based biopolymers retain at least 85%, such as at least 90%, at least 95%, or even at least 98% of the initial weight of the blowing agent encapsulated in the microspheres when stored for six months or longer under environmental conditions.

[0007] Therefore, the present invention aims to find such expandable polymer microspheres made of cellulose-based biopolymers and their preparation methods, which retain at least 80% of the initial weight of the blowing agent encapsulated in the microspheres after being stored for six months under environmental conditions. It has been found that such microspheres can be efficiently produced by post-heating treatment of expandable microspheres made of cellulose-based biopolymers after their production. Summary of the Invention

[0008] In a first aspect, the present invention relates to a storage-stable thermally expandable microsphere, which comprises a polymer shell surrounding a hollow core, wherein the hollow core contains a blowing agent, and the polymer shell contains carboxylate-functionalized cellulose, and wherein after being stored for six months under environmental conditions, the microsphere retains at least 80% of the initial weight of the blowing agent encapsulated in the microsphere.

[0009] The present invention also relates to a method for preparing storage-stable thermally expandable microspheres, said microspheres comprising a polymer shell surrounding a hollow core, wherein said hollow core contains a blowing agent and said polymer shell contains a carboxylate-functionalized cellulose, said method comprising the steps of: (i) preparing thermally expandable microspheres, said microspheres comprising a polymer shell surrounding a hollow core, wherein said hollow core contains a blowing agent and said polymer shell contains a carboxylate-functionalized cellulose; and (ii) post-heating the thermally expandable microspheres obtained in step (i) by heating the thermally expandable microspheres to a temperature of at least 40 °C.

[0010] The present invention also relates to storage-stable thermally expandable microspheres obtained by the above method. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 illustrates the difference between mononuclear ( Figure 1A ) and multinuclear ( Figure 1B ) microspheres.

[0012] Figure 2 illustrates the effect of pyromellitic dianhydride (PMDA) or pyromellitic acid (PMA) on the storage stability after post-heating treatment.

[0013] Figure 3 shows an exemplary thermogram for determining the amount of blowing agent encapsulated in exemplary microspheres. DETAILED DESCRIPTION

[0014] The present invention discloses storage-stable thermally expandable microspheres, which comprise a polymer shell surrounding a hollow core, wherein said hollow core contains a blowing agent and said polymer shell contains a carboxylate-functionalized cellulose, and wherein after storage for six months under ambient conditions, said microspheres retain at least 80% of the initial weight of the blowing agent encapsulated in the microspheres.

[0015] The expandable microspheres are based on a polymer shell containing a carboxylate-functionalized cellulose. The functional group is one carboxylate group or more than one carboxylate group, usually selected from C1 to C 12 carboxylate. Thus, the term "carboxylate-functionalized cellulose" means that cellulose contains at least one carboxylate group. The carboxylate moiety forms part of the linkage between the carboxylate functional group and cellulose, i.e., cellulose is linked to the carboxylate functional group via an ester bond.

[0016] The polymer shell can comprise or consist of one or more polymer components, where at least one component, more than one component or all polymer components are selected from such carboxylate-functionalized celluloses. When the shell comprises other polymers in addition to the polymers described herein (i.e., carboxylate-functionalized celluloses), their content is generally less than 50% by weight, such as less than 30% by weight, or less than 10% by weight, such as 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.

[0017] In an embodiment, the carboxylate functional group on the carboxylate-functionalized cellulose can be represented by formula (1):

[0018]

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

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

[0021] R a can also be selected from 5- and 6-membered aromatic rings.

[0022] R a can optionally contain one or more substituents selected from -OH, halogen, C 1-4 alkyl and C 1-4 alkoxy, where the C 1-4 alkyl and C 1-4 alkoxy are optionally substituted with one or more groups selected from halogen and -OH.

[0023] In an embodiment, R a contains 1 to 7 carbon atoms, such as 1 to 5 or 1 to 3 carbon atoms.

[0024] R b is independently selected, each occurrence, from C 1-4 alkyl, such as C 1-2 alkyl, which is optionally substituted with one or more groups selected from halogen and -OH groups. In an embodiment, C 1-4 alkyl or C 1-2 alkyl is unsubstituted.

[0025] In an embodiment, R aIt can be saturated linear or branched aliphatic groups or cyclic aliphatic groups. v is an integer in the range of 1 to 11, for example in the range of 1 to 8, such as 1 to 6 or 1 to 4. w is an integer in the range of 3 to 11, for example 4 to 6.

[0026] R c is independently selected from H, -OH, halogen, C 1-4 alkyl and C 1-4 alkoxy each time it appears, wherein the C 1-4 alkyl and C 1-4 alkoxy are optionally substituted by one or more groups selected from halogen and -OH.

[0027] In other embodiments, R a can be an unsaturated linear or branched aliphatic group containing "y" double bonds x is an integer in the range of 2 to 11, for example 2 to 6 or 2 to 4. y represents the number of double bonds, usually 1 or 2.

[0028] In further embodiments, R a can be an unsaturated cyclic aliphatic group containing "y" double bonds wherein y is usually 1 or 2.

[0029] In still further embodiments, R a can be an aromatic group. 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 cyclic aliphatic ring or an aromatic ring. Thus, R a can be a group having no more than 11 carbon atoms where E is as defined above or p and r are each independently an integer from 0 to 8, where p + r is at least 1. q and s are each the number of double bonds in the corresponding acyclic aliphatic component. In embodiments, q and s are each independently selected from 0, 1, and 2.

[0031] Halogen is usually selected from F and Cl. However, in embodiments, the functional group does not contain halogen, so the groups A, R a , R b and R c do not contain halogen.

[0032] In embodiments, at least one R c group is H. In other embodiments, no more than two R cThe group is not H, and in a further embodiment, no more than one R c group is not H. In an even further embodiment, all R c groups are H.

[0033] In the above definitions of R a , R b and R c , in the case where there are more than one -OH substituents, each carbon atom generally has no more than one -OH substituent.

[0034] In certain embodiments, R a is an optionally substituted C1-C8 aliphatic (alkylene) group. In other embodiments, R a is an optionally substituted C6 aromatic ring. In a further embodiment, R a is unsubstituted.

[0035] In an embodiment, the functional groups on the cellulose substituent are selected from acetate, propionate, butyrate, valerate, caproate, heptanoate, octanoate, and phthalate. In a further embodiment, the functional groups on the cellulose substituent are selected from acetate, propionate, and butyrate, preferably acetate. Thus, the carboxylate-functionalized cellulose is preferably acetate-functionalized cellulose, propionate-functionalized cellulose, or butyrate-functionalized cellulose, more preferably acetate-functionalized cellulose.

[0036] The degree of substitution (DS) of the hydroxyl groups of the cellulose substituted by the one or more carboxylate groups can range from 0.9 to 3.5, and in an embodiment, ranges from 1.5 to 3.5, for example, ranges from 2.0 to 3.3.

[0037] Optionally, other functional groups may be present in the functionalized cellulose. For example, the -OH groups on the cellulose molecule that have not been substituted by the carboxylate functional groups can be replaced by one or more alkoxy groups (e.g., selected from C1 to C6 alkoxy groups). In other embodiments, although less preferred, the -OH groups can also be replaced by halogen groups (e.g., F or Cl). When such other functional groups are present, the molar amounts of these functional groups are lower than those of the one or more carboxylate groups. In an embodiment, the degree of substitution of the cellulose substituted by other functional groups does not exceed 1, for example, does not exceed 0.5 or does not exceed 0.2. In a further embodiment, the degree of substitution by groups other than carboxylate groups does not exceed 0.1.

[0038] In an embodiment, the carboxylate-functionalized cellulose contains acetate, propionate, or butyrate groups, preferably acetate groups.

[0039] In an embodiment, cellulose can be functionalized with two or more different carboxylic acid ester groups. In some embodiments, the carboxylic acid ester-functionalized cellulose is functionalized with at least two (such as exactly two) different carboxylic acid ester functional groups, which are the carboxylic acid ester functional groups as described above. For example, the carboxylic acid ester-functionalized cellulose can be functionalized with at least one acetate group and at least one additional group selected from propionate groups, butyrate groups, valerate groups, hexanoate groups, heptanoate groups, octanoate groups, and phthalate groups. In some embodiments, the carboxylic acid ester-functionalized cellulose is functionalized with at least one acetate group and at least one additional group selected from butyrate groups and propionate groups (i.e., among the additional carboxylic acid ester groups, R a is an aliphatic and unsubstituted C2 or C3 group, and A is H). For example, the carboxylic acid ester-functionalized cellulose can be functionalized with acetate groups and butyrate groups, or the carboxylic acid ester-functionalized cellulose can be functionalized with acetate groups and propionate groups.

[0040] In an embodiment, the glass transition temperature (T g ) of the functionalized cellulose forming the microsphere shell or at least part of the microsphere shell is at least 80 °C. T g can be determined using differential scanning calorimetry (DSC), for example, using the method described by Nishio et al. in Cellulose, 2006(13), 245 - 259, where a 5 mg sample is first heated from the ambient temperature (25 °C) to 240 °C at a rate of 20 °C / minute in a nitrogen atmosphere, then immediately quenched to -50 °C, and then heated from -50 °C to 240 °C at a rate of 20 °C / minute in a nitrogen atmosphere for the second time, and T g is calculated based on the second heating cycle.

[0041] In a further embodiment, the T g of the carboxylic acid ester-functionalized cellulose is at least 90 °C, such as at least 100 °C, at least 110 °C, or at least 120 °C. In an embodiment, the T g of the carboxylic acid ester-functionalized cellulose does not exceed 250 °C, such as does not exceed 220 °C, or does not exceed 200 °C, or does not exceed 190 °C, such as being about 180 °C. In an embodiment, T g is in the range of 80 to 250 °C, such as in the range of 90 to 220 °C, 100 to 200 °C, or 110 to 190 °C. In a further embodiment, T g is in the range of 120 to 190 °C, such as in the range of 150 to 190 °C or 170 to 190 °C.

[0042] The melting point of the functionalized cellulose is generally higher than T ga value and, in embodiments, is above 125 °C. In further embodiments, the melting point is above 150 °C. The melting point generally does not exceed 270 °C, such as not exceeding 250 °C.

[0043] The T of the carboxylate-functionalized cellulose g and the melting point can be altered or controlled by varying the functional groups on the carboxylate-functionalized cellulose or by varying the molecular weight.

[0044] The thermally expandable microspheres are hollow, wherein the shell comprises carboxylate-functionalized cellulose and the hollow center or core comprises one or more blowing agents. The density of the carboxylate-functionalized cellulose used to prepare the microspheres is generally 1.1 to 1.35 g / cm 3 . In the expanded microspheres, the density is generally less than 1 g / cm 3 , suitably in the range of 0.005 to 0.8 g / cm 3 , or 0.01 to 0.6 g / cm 3 range. In further embodiments, the density of the expanded microspheres is in the range of 0.01 to 0.4 g / cm 3 range. Higher densities, especially 1 g / cm 3 or higher densities generally mean that the microsphere sample is not suitable.

[0045] In embodiments, the number average molecular weight (M n ) of the functionalized cellulose used to form the microspheres is in the range of 1000 to 700000 Da, such as in the range of 2000 to 500000 Da or in the range of 2000 to 100000 Da. In embodiments, it is in the range of 10000 to 100000 Da, such as in the range of 10000 to 50000 Da.

[0046] The expansion start temperature T 开始 of the thermally expandable microspheres can be 80 °C to below 250 °C. The expansion start temperature is referred to as T 开始 , and the temperature at which maximum expansion is reached is referred to as T max . T 开始 and T max can be determined using standard measurement techniques well known to those skilled in the art. For example, T 开始 and T maxIt can be determined by a heating experiment, for example, using a Mettler-Toledo Thermomechanical Analyser (such as Mettler-Toledo TMA / SDTA841e), with a heating rate of 20 °C / minute and a net load of 0.06 N. In such a heating experiment, a sample of thermally expandable microspheres of known weight is heated at a constant heating rate of 20 °C / minute under a net load of 0.06 N. When the thermally expandable microspheres start to expand, the sample volume increases and causes the load to move upward. An expansion thermogram is obtained through this measurement, where the ordinate represents the height of the upward movement of the load and the abscissa represents the temperature. T 开始 and T max can be determined from this expansion thermogram, for example, by using the STARe software from Mettler-Toledo.

[0047] In an embodiment, the T of the thermally expandable microspheres 开始 can be in the range of 90 to 220 °C, such as 100 to 210 °C, 110 to 200 °C, or 115 to 190 °C. In a preferred embodiment, the T of the thermally expandable microspheres 开始 can be in the range of 120 to 185 °C.

[0048] To further enhance the performance of the polymer shell, the polymer shell of the thermally expandable microspheres can contain an acid anhydride compound or a hydrogen bond donor selected from alcohols, ureas, and carboxylic acids, preferably an acid anhydride compound or a hydrogen bond donor in the form of a carboxylic acid. For example, the hydrogen bond donor can interact with the groups on the carboxylate-functionalized cellulose via hydrogen bonds. By adding an acid anhydride compound or a hydrogen bond donor selected from alcohols, ureas, and carboxylic acids, preferably an acid anhydride compound or a hydrogen bond donor in the form of a carboxylic acid, the barrier properties of the polymer shell can be further improved and the mechanical properties of the polymer shell can be improved, thus improving the expansion properties of the microspheres. Therefore, the hydrogen bond donor serves as a polymer shell enhancer.

[0049] The acid anhydride compound or the hydrogen bond donor can be, for example, a polymer with a maximum average molecular weight of 10,000 g / mol, such as 1,000 g / mol to 5,000 g / mol, or 1,500 g / mol to 3,000 g / mol. The acid anhydride compound or the hydrogen bond donor can be and the acid anhydride compound or the hydrogen bond donor is generally and preferably a low molecular weight compound with a molecular weight 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. For example, the molecular weight of the acid anhydride compound or the hydrogen bond donor can be in the range of 20 to 500 g / mol, preferably between 30 and 400 g / mol, and even more preferably between 40 and 300 g / mol.

[0050] The acid anhydride compound is a compound containing at least one acid anhydride group, such as at least two acid anhydride groups or at least three acid anhydride groups. However, a compound containing exactly two acid anhydride groups ("dianhydride") is preferred.

[0051] In an embodiment, the acid anhydride compound is preferably selected from 1,2,4,5-benzenetetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, ethylene tetraacetic dianhydride, butane tetracarboxylic dianhydride, ethylenediamine tetraacetic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, cyclobutane-1,2,3,4-tetracarboxylic dianhydride, 4,4'-oxybisphthalic anhydride, and tetrahydrofuran-2,3,4,5-tetracarboxylic dianhydride. More preferably, the acid anhydride compound is selected from 1,2,4,5-benzenetetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, and ethylene tetraacetic dianhydride, and even more preferably is 1,2,4,5-benzenetetracarboxylic dianhydride or benzophenone tetracarboxylic dianhydride. A particularly preferred acid anhydride compound is pyromellitic dianhydride (1,2,4,5-benzenetetracarboxylic dianhydride). 1,2,4,5-benzenetetracarboxylic dianhydride is also referred to as and herein called pyromellitic dianhydride.

[0052] A hydrogen bond donor selected from an alcohol, a urea, and a carboxylic acid is a compound having a hydrogen atom covalently bonded to a more electronegative atom, namely oxygen (if the hydrogen bond donor is an alcohol or a carboxylic acid) or nitrogen (if the hydrogen bond donor is a urea), wherein these hydrogen atoms form an intermolecular hydrogen bond with the functional groups (hydrogen bond acceptors) of the carboxylic acid ester-functionalized cellulose, such as carboxylic acid ester functional groups, or, if present, the one or more other optional hydroxyl and ether groups.

[0053] The hydrogen bond donor is selected from an alcohol, a urea, and a carboxylic acid. Preferably, the hydrogen bond donor is selected from an alcohol and a carboxylic acid. 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.

[0054] The hydrogen bond donor is selected from an alcohol, a urea, and a carboxylic acid, preferably the hydrogen bond donor in the form of a carboxylic acid, and its molecular weight can be in the range of 20 to 2000 g / mol, preferably the molecular weight is 20 to 500 g / mol, more preferably 30 to 400 g / mol, and even more preferably 40 to 300 g / mol.

[0055] If the hydrogen bond donor is an alcohol, it can be selected from any compound containing at least one alcohol group, such as one, two, three, four, five, or six alcohol groups, preferably with a molecular weight in the range of 20 to 2000 g / mol. If the hydrogen bond donor is an alcohol, it is preferably a diol, triol, tetrol, pentol, or hexol.

[0056] Suitable diols are, for example, selected from 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 and 1,4-cyclohexanediol, preferably 1,3-butanediol.

[0057] Suitable triols are, for example, glycerol, 1,2,3-butanetriol, 1,2,4-butanetriol, 1,1,1-tris(hydroxymethyl)propane, pentaerythritol and hexanetriol. The preferred triol is glycerol.

[0058] Suitable tetraols are, for example, ascorbic acid (vitamin C), erythritol, threitol or pentaerythritol. The preferred tetraols are ascorbic acid (vitamin C) and pentaerythritol.

[0059] Suitable pentaols are xylitol, arabitol, ribitol, glucose, fructose, galactose and mannose.

[0060] Suitable hexitols are, for example, sorbitol, mannitol and cyclohexanehexol. The preferred hexitol is sorbitol.

[0061] If the hydrogen bond donor is an alcohol, it is preferably selected from 1,3-butanediol, glycerol, ascorbic acid (vitamin C) or sorbitol.

[0062] 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, a dicarboxylic acid, a tricarboxylic acid, a tetracarboxylic acid or a polycarboxylic acid (such as 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), especially a dicarboxylic acid, a tricarboxylic acid or a tetracarboxylic acid.

[0063] Examples of monocarboxylic acids are formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, benzoic acid and lactic acid.

[0064] Examples of dicarboxylic acids are adipic acid, maleic acid, succinic acid, tartaric acid and aldaric acid.

[0065] Examples of tricarboxylic acids are citric acid and isocitric acid.

[0066] Examples of tetracarboxylic acids are pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), ethylenediaminetetraacetic acid (EDTA) and butanetetracarboxylic acid, such as 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0067] Preferred examples of suitable hydrogen bond donors in the form of carboxylic acids are citric acid, maleic acid, succinic acid, pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), lactic acid, tartaric acid, ethylenediaminetetraacetic acid (EDTA), butanetetracarboxylic acid, such as 1,2,3,4-butanetetracarboxylic acid (BTCA). Even more preferred examples of suitable hydrogen bond donors in the form of carboxylic acids are pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), citric acid, tartaric acid, 1,2,3,4-butanetetracarboxylic acid (BTCA) and maleic acid.

[0068] In particular, according to a preferred embodiment, if the hydrogen bond donor is in the form of a carboxylic acid, it is selected from pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), citric acid, tartaric acid, 1,2,3,4-butanetetracarboxylic acid (BTCA) and maleic acid.

[0069] Even more particularly, according to a preferred embodiment, if the hydrogen bond donor is in the form of a carboxylic acid, it is selected from pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), citric acid, tartaric acid and 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0070] Preferably, according to a preferred embodiment, if the hydrogen bond donor is in the form of a carboxylic acid, it is a tricarboxylic acid or a tetracarboxylic acid, such as citric acid, pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid) or 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0071] In a specific embodiment, according to a preferred embodiment, if the hydrogen bond donor is in the form of a carboxylic acid, 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 and is pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid).

[0072] The amount of the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas and carboxylic acids, preferably the acid anhydride compound or the hydrogen bond donor in the form of a carboxylic acid, which can be used to prepare the expandable microspheres of the present invention is not particularly limited.

[0073] However, based on the total weight of the acid anhydride compound or hydrogen bond donor and the carboxylic acid ester functionalized cellulose, the amount of the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas, and carboxylic acids (preferably the acid anhydride compound or the hydrogen bond donor in the form of a carboxylic acid) can be 0.01 to 50 wt%. In an embodiment, it can be in the range of 0.01 to 40 wt%, such as in the range of 0.05 to 35 wt%, in the range of 0.1 to 30 wt%, or even in the range of 0.5 to 25 wt%, such as in the range of 0.5 to 20 wt%, 1.0 to 20 wt%, or even 1.2 to 17 wt% or 1.5 to 15 wt%, wt% based on the total weight of the corresponding acid anhydride compound or hydrogen bond donor and the carboxylic acid ester functionalized cellulose.

[0074] In some embodiments, if the carboxylic acid ester functionalized cellulose is acetate functionalized cellulose, the amount of the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas, and carboxylic acids (preferably the acid anhydride compound or the hydrogen bond donor in the form of a carboxylic acid) can be 0.01 to 50 wt%, such as in the range of 0.01 to 40 wt%, in the range of 0.05 to 30 wt%, in the range of 0.1 to 20 wt%, or even in the range of 0.5 to 15 wt%, such as in the range of 0.5 to 10 wt%, 1.0 to 5.0 wt%, or even 1.2 to 5 wt% or 1.5 to 5 wt%, wt% based on the total weight of the corresponding acid anhydride compound or hydrogen bond donor and the acetate functionalized cellulose.

[0075] In some embodiments, if the carboxylic acid ester functionalized cellulose is butyrate functionalized cellulose or propionate functionalized cellulose, such as preferably cellulose acetate butyrate (CAB) or cellulose acetate propionate (CAP) respectively, the amount of the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas, and carboxylic acids (preferably the acid anhydride compound or the hydrogen bond donor in the form of a carboxylic acid) can be 0.01 to 50 wt%, such as in the range of 0.01 to 40 wt%, in the range of 0.05 to 35 wt%, in the range of 0.1 to 30 wt%, or even in the range of 0.5 to 25 wt%, such as in the range of 1.0 to 20 wt%, 3.0 to 20 wt%, or even 5.0 to 18 wt% or 10 to 15 wt%, wt% based on the total weight of the corresponding acid anhydride compound or hydrogen bond donor and the butyrate functionalized cellulose or propionate functionalized cellulose.

[0076] In a further embodiment, the polymer shell can contain particles to improve the mechanical properties and gas barrier properties of the polymer shell, and thus also act as a polymer shell enhancer. Examples of such particles are talc, montmorillonite, nanocrystalline cellulose, and various types of clays, such as bentonite.

[0077] Many factors can lead to high density. For example, high density can be caused by poor microsphere yield, i.e., the percentage of microspheres in the polymer material is too low to reduce the total density to an acceptable level. Another problem is poor expansion characteristics, which occurs when too many microspheres contain insufficient blowing agent to achieve sufficient expansion. This can be due to the polymer shell being too permeable to the blowing agent or due to the formation of so-called "multicore" microspheres, in which there are multiple blowing agent-containing (e.g., microspherical foam or sponge) nuclei in the shell of the "multicore" microsphere rather than a single blowing agent nucleus. In such multicore microspheres, the blowing agent concentration is usually too low to adequately reduce the density. Another cause is the aggregation or agglomeration of the polymer, resulting in poor microsphere production and a denser material. A too-high proportion of aggregated material or poor microsphere expansion also leads to significant non-uniformity in the expansion characteristics of the resulting microsphere product. This is particularly disadvantageous for surface-sensitive applications (such as coatings) that require a smooth finish.

[0078] Schematic cross-sections of single-core and multicore microspheres are provided in Figure 1A and 1B respectively, where the region 1 of the polymer is represented by the hatched area and the blowing agent-containing region 2 is represented by the blank area.

[0079] The thermally expandable microspheres contain at least one blowing agent. The one or more blowing agents typically have a boiling point above 25 °C at a pressure of 5.0 bar or above 25 °C at a pressure of 3.0 bar, where "bar" represents absolute barometric pressure. In an embodiment, they have a boiling point above 25 °C at atmospheric pressure (1.013 bar). Generally, they have a boiling point of 250 °C or lower at atmospheric pressure, such as 220 °C or lower, or 200 °C or lower. They are preferably inert and do not react with the functionalized cellulose shell. The Clausius-Clapeyron equation can be used to calculate the boiling point at high pressure.

[0080] Examples of blowing agents include dialkyl ethers, alkanes, and halogenated hydrocarbons, such as chlorohydrocarbons, fluorohydrocarbons, or chlorofluorocarbons. In an embodiment, the dialkyl ether contains two alkyl groups, each alkyl group selected from C2 to C5 alkyl groups. In an embodiment, the alkane is a C4 to C 12 alkane. In an embodiment, the halogenated alkane is selected from C2 to C 10 halogenated alkanes. The halogenated alkane can contain one or more halogen atoms selected from chlorine and fluorine. The alkyl or haloalkyl groups in the dialkyl ether, alkane, and halogenated alkane can be linear, branched, or cyclic. A mixture of one or more blowing agents can be used.

[0081] In an embodiment, for environmental reasons, the one or more blowing agents are selected from alkyl ethers and alkanes, and in a further embodiment, the one or more blowing agents are selected from alkanes. Halogenated alkanes are preferably avoided because they have potential ozone-depleting properties and also because they generally have a higher global warming potential.

[0082] 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 selected from C4 to C 12 isoalkanes.

[0083] In the expandable microspheres, based on the total weight of the functionalized cellulose, the blowing agent, and optional additives such as acid anhydride compounds or hydrogen bond donors selected from alcohols, ureas, and carboxylic acids, the one or more blowing agents are generally present in an amount of 5 to 50% by weight, such as 5 to 45% by weight or 10 to 40% by weight.

[0084] Carboxylate-functionalized cellulose materials can be commercially available or can be prepared by known methods, for example, by mixing cellulose with a suitable carboxylic acid (such as acetic acid, propionic acid, or butyric acid, and optionally additional carboxylic acids) in the presence of a strong acid such as sulfuric acid, or by base-catalyzed reaction of cellulose with an acyl chloride, for example, as described by Nishio et al. in Cellulose, 2006(13), 245-259.

[0085] Examples of suitable carboxylate-functionalized celluloses are cellulose acetate (CA) (i.e., acetate-functionalized cellulose without other carboxylate functional groups different from acetate), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB), especially those having a number average molecular weight (M n ) in the range of 2,000 to 100,000 Da, such as in the range of 2,000 to 80,000 Da, in the range of 10,000 to 50,000 Da, or in the range of 20,000 to 50,000 Da for cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB).

[0086] Preferred acetate-functionalized celluloses are cellulose acetate (CA) (i.e., acetate-functionalized cellulose without other carboxylate functional groups different from acetate) and cellulose acetate butyrate (CAB), having a number average molecular weight (M n ) in the range of 10,000 to 100,000 Da, such as 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. Even more preferred is the number average molecular weight (Mn ) Cellulose acetate (CA) in the range of 10,000 to 100,000 Da, such as in the range of 10,000 to 80,000 Da, preferably in the range of 10,000 to 50,000 Da and more preferably in the range of 20,000 to 50,000 Da.

[0087] For example, if the polymer shell contains cellulose acetate propionate (CAP) or cellulose acetate butyrate (CAB), the amount of the hydrogen bond donor in the form of a carboxylic acid can be 0.01 to 50% by weight, based on the total weight of the hydrogen bond donor and the carboxylic acid ester functionalized cellulose. In an embodiment, it can be in the range of 0.01 to 40% by weight, such as in the range of 0.05 to 35% by weight, in the range of 0.1 to 30% by weight or even in the range of 0.5 to 25% by weight, such as in the range of 1.0 to 20% by weight, 3.0 to 20% by weight or even 5.0 to 18% by weight or 10 to 15% by weight, % by weight based on the total weight of the hydrogen bond donor and the carboxylic acid ester functionalized cellulose.

[0088] For example, if the polymer shell contains cellulose acetate (CA) (i.e., acetate functionalized cellulose without other carboxylic acid ester functional groups different from acetate), the amount of the hydrogen bond donor in the form of a carboxylic acid can be 0.01 to 50% by weight, based on the total weight of the hydrogen bond donor and the carboxylic acid ester functionalized cellulose. In an embodiment, it can be in the range of 0.01 to 40% by weight, such as in the range of 0.05 to 30% by weight, in the range of 0.1 to 20% by weight or even in the range of 0.5 to 15% by weight, such as in the range of 0.5 to 10% by weight, 1.0 to 5.0% by weight or even 1.2 to 5% by weight or 1.5 to 5% by weight, % by weight based on the total weight of the hydrogen bond donor and the carboxylic acid ester functionalized cellulose.

[0089] After storage for six months under ambient conditions, the storage-stable thermally expandable microspheres of the present invention retain at least 80% of the initial weight of the blowing agent encapsulated in the microspheres.

[0090] Preferably, after storage for six months under ambient conditions, the storage-stable thermally expandable microspheres of the present invention retain at least 85%, preferably at least 90%, even more preferably at least 95% and most preferably at least 98% of the initial weight of the blowing agent encapsulated in the microspheres.

[0091] The weight of the blowing agent in the microspheres can be determined by measuring the volatile content of the microspheres (i.e., the weight of the volatile encapsulated in the microspheres). Therefore, the terms "weight of the blowing agent" or "weight percentage of the blowing agent" used herein in the context of microspheres shall be considered equivalent to and interchangeable with "volatile content". The determination of the volatile content of microspheres is well-known to those skilled in the art and in principle any suitable method can be used to determine the volatile content of the microspheres.

[0092] For example, a Mettler Toledo TGA / DSC1 TGA instrument can be used to determine the volatile content. In an exemplary and preferred experimental setup, the volatile content of the microspheres according to the present invention is determined as follows: A sample to be analyzed is prepared from 1.7 mg (+ / - 0.2 mg) of thermally expandable microspheres contained in an alumina crucible with a volume of 600 μl. The sample temperature is raised from 30 °C to 650 °C at a heating rate of 20 °C / minute in a nitrogen atmosphere. The sample is held at 650 °C for an additional two minutes in a nitrogen atmosphere, after which the nitrogen is replaced with air and the sample is held at 650 °C for an additional 15 minutes. The weight of the sample is continuously monitored during the heating program. Figure 3 An exemplary thermogram obtained thereby is shown, with the ordinate being the sample weight (in mg) and the abscissa being the heating temperature (in °C, related to the heating time (t), up to 650 °C). The volatile content (VC, %) of the microspheres can be obtained from such a thermogram by subtracting the sample weight measured at the second inflection point (IP2) of the thermogram curve (i.e., here, after the blowing agent has evaporated and the sample weight reaches the first substantially stable plateau, which is typically between 170 °C and 300 °C, depending on the actual blowing agent and polymer used) from the starting weight of the sample (SW; 30 °C and t = 0), then dividing the difference by the starting weight of the sample and multiplying the result by 100 (see also Equation (2) below).

[0093] VC 样品 = ((weight 样品@ t =0 – weight 样品@ IP2 ) / weight 样品@ t =0) * 100 Equation (2)

[0094] The percentage of the blowing agent retained in the microspheres after storage (VC 储存后保留 ; %) can be calculated by dividing the volatile content after storage (VC 储存后 ) by the volatile content before storage (VC0) and multiplying by 100 (see also Equation (3) below).

[0095] VC 储存后保留 = (VC储存后 / VC0) * 100 Formula (3)

[0096] As used herein, the term "environmental conditions" refers to standard room temperature within the range of 20 - 25 °C (such as 22.5 ± 2.5 °C, or 22 ± 2 °C, or 22 ± 1 °C), and normal shelf storage conditions at atmospheric pressure (i.e., 1013 ± 50 mbar, such as 1013 ± 20 mbar or 1013 ± 10 mbar).

[0097] The expandable microspheres of the present invention can be prepared according to the following method, that is, the expandable microspheres of the present invention can be obtained according to the following method. Thus, in another aspect, the present invention relates to a method for preparing storage - stable thermally expandable microspheres, the microspheres comprising a polymer shell surrounding a hollow core, wherein the hollow core contains a blowing agent, and the polymer shell contains carboxylate - functionalized cellulose, that is, such as the expandable microspheres described above, wherein the method comprises the following steps:

[0098] (i) Prepare thermally expandable microspheres, the microspheres comprising a polymer shell surrounding a hollow core, wherein the hollow core contains a blowing agent, and the polymer shell contains carboxylate - functionalized cellulose; and

[0099] (ii) Post - heat the thermally expandable microspheres obtained in step (i) by heating the thermally expandable microspheres to a temperature of at least 40 °C.

[0100] Since the method according to the other aspect of the present invention provides the expandable microspheres as described above, that is, the microspheres retain at least 80% of the initial weight of the blowing agent encapsulated in the microspheres after being stored for six months under environmental conditions, all the characteristics of the polymer shell of the expandable microspheres and the components used for preparing the microspheres (including optional other components, such as acid anhydride - containing compounds or hydrogen - bond donors selected from alcohols, ureas, and carboxylic acids) as well as the blowing agent and any other optional components can be the same as those described above for the expandable microspheres according to the first aspect of the present invention.

[0101] In the first step (i) of the method according to the other aspect of the present invention, thermally expandable microspheres comprising a polymer shell surrounding a hollow core are prepared, wherein the hollow core contains a blowing agent, and the polymer shell contains carboxylate - functionalized cellulose.

[0102] In principle, any known method for preparing such expandable microspheres can be used. Suitable methods include, for example, the solvent extraction method, or the spray - drying method, preferably the spray - drying method.

[0103] The solvent extraction method can be used to prepare expandable microspheres by dissolving a component including an optional anhydride-containing compound or a hydrogen bond donor selected from alcohols, ureas, and carboxylic acids in a suitable organic solvent or solvent mixture, adding the one or more blowing agents, and mixing with an aqueous phase optionally containing one or more emulsifiers. After a period of time (e.g., from 1 minute to 20 hours, such as 5 minutes to 10 hours), unexpanded microspheres are optionally formed under active mixing (e.g., by stirring) and can be separated in solid form, for example, using conventional techniques such as decantation or filtration.

[0104] Mixing can be carried out at ambient temperature, but temperatures in the range of 5 to 75 °C can be used.

[0105] In an embodiment, the aqueous phase can be pre-saturated with one or more organic solvents that can dissolve carboxylate-functionalized cellulose and then mixed with the organic phase containing carboxylate-functionalized cellulose. In a further embodiment, the mixture can be left to stand or stirred for a period of time, e.g., from 1 to 100 hours, or 2 to 50 hours, to allow at least partial evaporation of the solvent / water mixture. This operation can be carried out at a temperature of 10 to 95 °C, e.g., at 20 to 90 °C.

[0106] The emulsifier helps to stabilize the droplets of the organic phase containing carboxylate-functionalized cellulose in the aqueous phase and, in an embodiment, helps to form an emulsion of the organic phase in the aqueous phase (i.e., an oil-in-water emulsion).

[0107] For various reasons, stabilization of the droplets or emulsion droplets is preferred. If stabilization is not carried out, the droplets containing carboxylate-modified cellulose and the blowing agent may coalesce. Coalescence can have negative effects such as non-uniform droplet size, poor microsphere yield, and also increased aggregation of the microspheres.

[0108] The emulsifier is generally present in the aqueous phase in an amount of 0 to 20% by weight, e.g., 0.01 to 20% by weight, 0.05 to 10% by weight, or 0.1 to 5% by weight. In a further embodiment, the emulsifier is present in the aqueous phase in an amount of 0.1 to 1% by weight.

[0109] The choice of emulsifier is not particularly limited and can be selected from inorganic or organic emulsifiers.

[0110] Examples of inorganic materials that can be used as emulsifiers include silica, especially colloidal silica, which can be used in its unmodified "naked" form or can optionally be surface-modified to fine-tune its hydrophobic / hydrophilic properties, e.g., using organosilane-modified silica or colloidal silica.

[0111] In an embodiment, the "organic" group in the organosilane can be selected from C 1-20 alkyl, C 1-20 alkenyl, C5-6 Aryl and C 5-6 Heteroaryl, wherein one or more (e.g., 1 to 3) heteroatoms are selected from O, S, and N. Each of these groups may optionally be substituted with one or more groups selected from the following: halogen, hydroxyl, epoxy, thiol, amino, C 1-20 Alkylamino, di-C 1-20 Alkylamino, hydroxyamino, hydroxy-C 1-20 Alkylamino, (hydroxy-C 1-20 Alkyl)(C 1-20 Alkyl)amino, bis(hydroxy-C 1-20 Alkyl)amino C 1-20 Alkoxy, C 1-20 Amido, C 1-20 Ureido, C 1-20 Mercapto, C 3-20 Epoxyalkoxy, C 1-20 Alkyl acrylate, ethylene glycol or its oligomers containing 1 to 20 ethylene glycol groups, and propylene glycol or its oligomers containing 1 to 20 propylene glycol groups. Any aliphatic group can be linear, branched, or cyclic.

[0112] Organosilane-modified silica or colloidal silica can be prepared by reacting silica (or colloidal silica) with an organosilane compound generally having the formula R n SiX 4-n wherein R is one of the above organic groups, X is halogen, hydroxyl, or C 1-6 Alkoxy, and n is an integer from 1 to 3, usually 1 or 2.

[0113] Suitable silane compounds include tris(trimethoxy)silane, octyltriethoxysilane, methyltriethoxysilane, methyltrimethoxysilane; γ-mercaptopropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; silanes containing epoxy groups (epoxysilanes), silanes containing glycidyl and / or glycidylpropyl groups, such as γ-glycidylpropyltrimethoxysilane, γ-glycidylpropylmethyldiethoxysilane, (3-glycidylpropyl)trimethoxysilane, (3-glycidylpropyl)hexyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane; silanes containing vinyl groups, such as vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, vinylmethyldimethoxysilane, vinyltriisopropoxysilane; γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriisopropoxysilane, γ-methacryloxypropyltriethoxysilane, octyltrimethoxysilane, ethyltrimethoxysilane, propyltriethoxysilane, phenyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, dimethyldiethoxysilane, 3-chloropropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, isobutyltriethoxysilane, trimethylethoxysilane, phenyldimethylethoxysilane, hexamethyldisiloxane, trimethylsilyl chloride, vinyltriethoxysilane, hexamethyldisilazane and mixtures thereof. US4927749 discloses other suitable silanes that can be used.

[0114] Examples of silica that can be used include those sold under the trade names Levasil TM , Bindzil TM and Ludox TM that are related to colloidal silica. Solid forms of silica include fumed silica, and precipitated silica can also be used, where it can be dispersed in water to form a fine suspension. Sources of fumed silica include those sold under the trade names Cab-o-Sil TM and Aerosil TM .

[0115] Other inorganic emulsifiers include colloidal clays (such as chalk and bentonite) and salts, oxides and hydroxides of Al, Ca, Mg, Ba, Fe, Zn, Ti, Ni and Mn (such as calcium phosphate, calcium carbonate, magnesium hydroxide, barium sulfate, calcium oxalate, titanium dioxide; and hydroxides of aluminum, iron, zinc, nickel or manganese).

[0116] When solid inorganic emulsifiers are used, they can produce so-called "Pickering" emulsions, where the solid inorganic particles are located at the interface between the aqueous and organic phases.

[0117] Organic emulsifiers include the commonly known and commercially available anionic, cationic, amphoteric, zwitterionic, and nonionic surfactants.

[0118] Examples include sorbitan esters (such as those sold under the trade name Span TM ), for example, sorbitan monolaurate (e.g., Span TM 20) and sorbitan monooleate (e.g., Span TM 80). Further examples include polyethoxylated sorbitan esters (such as those sold under the trade name Tween TM ), such as PEG-20 sorbitan monolaurate (Tween TM 20), PEG-20 sorbitan monooleate (Tween TM 80), and polyoxyethylene sorbitan trioleate (Tween TM 85). Other examples include C6-C 22 alkyl sulfates, such as sodium dodecyl sulfate; sulfates of anions having the formula C n H 2n+1 (OC m H 2m ) p -OSO3 - where n is from 6 to 22, m is from 2 to 3, and p is from 2 to 4, such as sodium lauryl ether sulfate and C 12-14 alkanol polyether 3 sulfate (C 12-14 pareth-3sulfate); C 6-22 alkyl glucosides, such as lauryl glucoside; glucamides of the formula C n H 2n+1 C(O)N(X)CH2(C4H4[OH]4)CH2OH, where n is from 6 to 22 and X is H or C 1-4 alkyl, for example, octyl methyl glucamide, lauryl methyl glucamide, and dodecyl glucamide; amino acids and their salts substituted with C 2-16 carboxylate groups, such as sodium cocoyl glutamate or disodium and sodium lauroyl sarcosinate; C 6-22 fatty acids and their salts, such as sodium oleate and potassium oleate; phenols substituted with polyethylene glycol having 5 to 25 glycol units, for example, polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (available as Triton TM X-100); C 6-22Alkylamine oxides such as lauramine oxide and C 6-22 alkyl alcohols such as cetyl alcohol and stearyl alcohol. Further examples include polymeric emulsifiers such as (meth)acrylate and (meth)acrylic acid polymers (e.g., polymethyl methacrylate) and polymers based on organic ammonium salts having at least one C 3-10 alkenyl and at least one C 1-4 alkyl, such as polydiallyldimethylammonium chloride (polyDADMAC).

[0119] Consumer wash liquids can be used as a source of emulsifiers, e.g., those sold under the trade names and which contain sodium lauryl sulfate, C 12-14 alkanol polyether-3-sulfate and lauramine oxide.

[0120] Other examples of emulsifiers include polyvinyl alcohol, optionally partially or fully saponified. In embodiments, the degree of hydrolysis of the polyvinyl alcohol is in the range of 70 to 100 mol%, e.g., in the range of 80 to 100 mol% or 80 to 98 mol%. The Hoppler viscosity in a 4% aqueous solution can be 1 to 70 mPas, or in other embodiments in the range of 3 to 40 mPa·s (measured at 20 °C according to DIN 53015).

[0121] One or more emulsifiers can be used. A mixture of organic and inorganic emulsifiers can also be used.

[0122] Organic solvents can be selected from those having one or more functional groups selected from esters, amides, aldehydes, ketones, alcohols (including diols) and ethers, e.g., those having 3 to 12 carbon atoms. In embodiments, the esters, ketones and ethers can be part of a cyclic structure. Other examples include haloalkanes having 1 to 6 carbon atoms and haloacids having 1 to 6 carbon atoms, where the halogen is selected from fluorine, chlorine, bromine and iodine. In embodiments, any alcohol used is a diol.

[0123] 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, glycerol-α-monochloroethanol, propylene glycol, glycol ethers (such as propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monon-butyl ether, propylene glycol monoter-butyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether), glycol ether esters (such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol diacetate), n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, benzyl alcohol, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole, phenol, and dimethylformamide. Other examples of solvents include dimethyl sulfoxide, toluene, xylene, N-methyl-2-pyrrolidone, chloromethane, 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 can contain water, but the water content of the organic solvent is usually less than 5% by weight, i.e., 0 to 5% by weight of water, such as 0 to 1% by weight of water, before mixing with the aqueous phase.

[0124] In an embodiment, the solvent is selected from one or more of ethyl acetate, methyl acetate, ethyl formate, and acetone.

[0125] Generally, the carboxylic acid ester-functionalized cellulose content in the organic phase ranges from 0.1 to 50% by weight. In an embodiment, it can range from 0.5 to 25% by weight, such as from 1 to 15% by weight.

[0126] The amount of the foaming agent in the organic phase generally ranges from 0.5 to 20% by weight, such as from 1 to 15% by weight. In an embodiment, the weight of the foaming agent in the organic phase is equal to or less than the weight of the carboxylic acid ester-functionalized cellulose. For example, the weight ratio of the foaming agent to the carboxylic acid ester-functionalized cellulose can be 1.0 or less, such as 0.8 or less. In an embodiment, the minimum weight ratio is 0.1, or in a further embodiment, the minimum weight ratio is 0.2. In an embodiment, the weight ratio of the foaming agent to the carboxylic acid ester-functionalized cellulose in the organic phase ranges from 0.1 to 1.0, such as from 0.2 to 0.8.

[0127] Based on the total weight of the water / organic phase emulsion, the weight percentage of the organic phase in the total water / organic phase emulsion can range from 0.1 to 45 wt%, for example, from 1 to 30 wt%, or from 3 to 25 wt% or from 4 to 15 wt%.

[0128] If substances and / or particles that react with the groups on the carboxylate-functionalized cellulose are added to further improve the properties of the polymer shell, these substances and / or particles are typically added to the organic phase (i.e., the phase containing carboxylate-functionalized cellulose, solvent, and foaming agent).

[0129] Alternatively and preferably, the expandable microspheres are prepared by a spray drying method, which includes mixing carboxylate-functionalized cellulose, an organic solvent, a foaming agent, and optionally an acid anhydride compound or a hydrogen bond donor selected from alcohols, ureas, and carboxylic acids, and then spraying the resulting mixture into a drying device to produce thermally expandable microspheres having a polymer shell surrounding a hollow core, wherein the polymer shell contains carboxylate-functionalized cellulose and the hollow core contains the foaming agent.

[0130] In principle, the spray drying device used for carrying out the spray drying process is not limited, and any conventional and commercially available spray drying device can be used for the spray drying process. Typical spray drying devices suitable for the process described herein include a drying chamber equipped with a nozzle, a drying gas inlet, and an outlet connecting the drying chamber to a cyclone separator. The liquid to be atomized is typically sprayed into the drying chamber together with a spray gas through a nozzle usually located at the top of the spray chamber (but can also be located in any other part of the spray dryer). In the drying chamber, the atomized liquid is dried by the drying gas fed into the spray chamber through the drying gas inlet. The drying gas inlet can be located, for example, beside the nozzle. The atomized liquid dries and forms particles. Then the resulting particles are fed into the cyclone separator together with the drying gas through the drying chamber outlet usually located in the bottom region of the drying chamber. In the cyclone separator, the particles are separated from the dry air. The dry air can be further filtered to remove any residual particles in the dry air.

[0131] A spray drying device suitable for carrying out the spray drying process is the Büchi Mini Spray Dryer B-290 available from Büchi of Switzerland.

[0132] The order of adding carboxylate-functionalized cellulose, organic solvent, foaming agent, and optionally an acid anhydride compound or a hydrogen bond donor selected from alcohols, ureas, and carboxylic acids for mixing is not limited and any order can be chosen.

[0133] However, in a preferred embodiment, in the method for producing expandable microspheres, the carboxylate-functionalized cellulose is first mixed with the organic solvent, and then in a further step, the foaming agent and optionally an acid anhydride compound or a hydrogen bond donor selected from alcohols, ureas, and carboxylic acids are added to the mixture.

[0134] The mixing of the carboxylate-functionalized cellulose can be carried out at ambient temperature, but temperatures in the range of 5 to 75 °C can also be employed. The mixing is generally carried out until the carboxylate-functionalized cellulose is completely dissolved in the organic solvent.

[0135] In an embodiment, the mixture of the carboxylate-functionalized cellulose and the organic solvent can be left standing or stirred for a period of time, such as 1 to 100 hours, or 2 to 50 hours, to allow at least partial evaporation of the solvent. This operation can be carried out at a temperature in the range of 10 to 95 °C, for example at a temperature of 20 to 90 °C.

[0136] In a further step, a blowing agent and optionally an acid anhydride compound or a hydrogen bond donor selected from alcohols, ureas, and carboxylic acids are added to the mixture of the carboxylate-functionalized cellulose and the organic solvent. In the case where an acid anhydride compound or a hydrogen bond donor selected from alcohols, ureas, and carboxylic acids is added to the mixture of the carboxylate-functionalized cellulose and the organic solvent, the order of addition of the blowing agent and the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas, and carboxylic acids is not important. Thus, the blowing agent can be added first, followed by the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas, and carboxylic acids; or alternatively, the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas, and carboxylic acids can be added first, followed by the blowing agent. This mixing step can also be carried out at ambient temperature, but temperatures in the range of 5 to 75 °C can also be employed. And this mixing step is generally carried out until the blowing agent and optionally the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas, and carboxylic acids are completely dissolved in the organic solvent.

[0137] After adding the blowing agent and optionally the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas, and carboxylic acids to the mixture of the carboxylate-functionalized cellulose and the organic solvent, the mixture thus obtained can be stirred for a further period of time, such as 1 minute to 100 hours, such as 10 minutes to 80 hours or 1 to 50 hours. And this stirring is carried out at a temperature in the range of 10 to 95 °C, for example at a temperature of 20 to 90 °C.

[0138] The mixture comprising the carboxylate-functionalized cellulose, the organic solvent, the blowing agent, and optionally the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas, and carboxylic acids is sprayed into a drying device to produce the thermally expandable microspheres as described herein. The drying device can be the spray drying device as described above.

[0139] The optional spray gas ejected through the nozzle together with the liquid to be atomized is not particularly limited and can be any suitable spray gas known to those skilled in the art. For example, the spray gas can be selected from nitrogen, carbon dioxide, (pressurized) air, inert gases (such as argon), etc. Preferably, a spray gas is used in the method for producing expandable microspheres as described herein, and more preferably, the spray gas is nitrogen.

[0140] The drying gas is not particularly limited and can be any suitable drying gas known to those skilled in the art. For example, the spraying gas can also be selected from nitrogen, carbon dioxide, (pressurized) air, inert gases (such as argon), etc. Preferably, the drying gas is nitrogen.

[0141] Those skilled in the art can easily select other process parameters for operating the spray drying equipment, such as the spraying gas flow rate, the inlet temperature of the drying gas when entering the drying chamber, the feeding rate of the liquid to be atomized, and the aspirator speed at which the drying gas circulates in the spray drying equipment.

[0142] It has been found that expandable microspheres comprising a polymer shell surrounding a hollow core can be obtained by the above method, wherein the hollow core contains a blowing agent and the polymer shell contains a carboxylate-functionalized cellulose. It has also been found that the method is particularly suitable for obtaining such expandable microspheres, wherein the polymer shell further contains an acid anhydride-containing compound or a hydrogen bond donor selected from alcohols, ureas, and carboxylic acids.

[0143] The organic solvent can be selected from the same solvents as those described above in the context of the solvent extraction method for preparing expandable microspheres.

[0144] Generally, the content of the carboxylate-functionalized cellulose in the mixture for spray drying is usually in the range of 0.1 to 50% by weight. In some embodiments, it can be in the range of 1 to 40% by weight, such as in the range of 5 to 35% by weight or even in the range of 7.5 to 30% by weight. The % by weight is based on the total weight of the mixture for spray drying.

[0145] The amount of the blowing agent in the mixture for spray drying is usually in the range of 0.5 to 50% by weight. In an embodiment, it can be in the range of 0.5 to 40% by weight, such as in the range of 1 to 30% by weight or even 3 to 25% by weight. In an embodiment, the weight of the blowing agent in the mixture for spray drying is equal to or less than the weight of the carboxylate-functionalized cellulose. For example, the weight ratio of the blowing agent to the carboxylate-functionalized cellulose can be 1.5 or lower, such as 1.3 or lower, or even 1.1 or lower. In an embodiment, the minimum weight ratio is 0.1, or in a further embodiment is 0.2. In an embodiment, the weight ratio of the blowing agent to the carboxylate-functionalized cellulose in the organic phase is in the range of 0.1 to 1.5, such as in the range of 0.2 to 1.3 or even in the range of 0.3 to 1.1.

[0146] The amount of the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas and carboxylic acids in the mixture for spray drying is generally in the range of 0 to 15% by weight. In an embodiment, it can be in the range of 0.01 to 15% by weight, such as in the range of 0.05 to 10% by weight, in the range of 0.1 to 5% by weight or even in the range of 0.2 to 5% by weight. The % by weight is based on the total weight of the mixture for spray drying.

[0147] The amount of the organic solvent can be up to 100% by weight. Preferably, the amount of the organic solvent is at least 30% by weight, more preferably at least 40% by weight, even more preferably at least 50% by weight. The % by weight is based on the total weight of the mixture for spray drying.

[0148] The volume average particle size (diameter), i.e., the D(0.5) value, of the unexpanded microspheres obtained by the solvent extraction method or the spray drying method is generally in the range of 1 to 500 μm, such as 5 to 200 μm, or in an embodiment, 10 to 100 μm or even 30 to 80 μm.

[0149] In the second step (ii) of the method according to another aspect of the present invention, the thermally expandable microspheres obtained in step (i) are post-heated by heating the thermally expandable microspheres to a temperature of at least 40 °C.

[0150] Surprisingly, it has been found that the expandable microspheres post-heated in the second step (ii) of the method according to another aspect of the present invention have significantly improved storage stability, i.e., such post-heated expandable microspheres retain at least 80%, such as at least 85%, at least 90%, at least 95%, or even at least 98% of the initial weight of the blowing agent encapsulated in the microspheres after being stored for six months under ambient conditions.

[0151] Heating can be carried out by any known method for heating substances, for example, by placing the expandable microspheres in a heating chamber or drying oven set at an appropriate temperature. Heating can also be carried out by tumbling the material in a stirring container, where the heating is achieved by introducing a heating gas into the container or by heating the jacketed container wall. Tumbling can be achieved in any way, such as using a belt blender device or stirring with a rotating paddle.

[0152] There is no specific upper limit to the temperature used for the post-heating treatment. However, any such temperature must be lower than the expansion temperature of the corresponding expandable microspheres, otherwise the expandable microspheres will have already started to expand. Therefore, in an embodiment, the post-heating treatment can be carried out at a temperature between 50 °C and 150 °C, preferably between 60 °C and 140 °C, even more preferably between 70 °C and 130 °C, and most preferably between 75 °C and 125 °C.

[0153] There is no specific requirement for the duration of the post-heating treatment. However, in some embodiments, the post-heating treatment is carried out for at least 5 minutes, preferably at least 10 minutes, more preferably at least 30 minutes, and even more preferably at least 50 minutes. In an embodiment, the post-heating treatment is carried out for no more than 10 hours, such as no more than 5 hours, no more than 2 hours or no more than 1 hour. However, the temperature of the post-heating treatment and the duration of the post-heating treatment may be interdependent, and those skilled in the art can adjust the appropriate duration of the post-heating treatment according to the specific treatment temperature, and vice versa. For example, a preferred method according to another aspect of the present invention involves heating the expandable microspheres obtained in step (i) at 75 °C to 125 °C (such as 100 °C) for 5 minutes to 2 hours (such as 10 minutes to 1 hour, for example 1 hour).

[0154] In a preferred embodiment, the post-heating treatment is carried out at a temperature between 70 °C and 130 °C, such as between 75 °C and 125 °C or between 80 °C and 120 °C, for at least 20 minutes, such as at least 30 minutes or at least 50 minutes.

[0155] In a particularly preferred embodiment, the temperature during the post-heating treatment is maintained at a discrete temperature for at least 1 minute, such as at least 2 minutes, at least 3 minutes, at least 5 minutes, at least 10 minutes, at least 20 minutes, at least 30 minutes or at least 50 minutes. The term "maintaining the temperature at a discrete temperature" as used herein means that the temperature does not change significantly within a certain period of time, that is, the temperature remains constant. If the change in the given temperature (such as those temperatures described above for the post-heating treatment) within the specified period does not exceed ±5 °C, such as not exceeding ±3 °C, not exceeding ±2 °C or even not exceeding ±1 °C, the temperature is considered constant. In other words, "maintaining the temperature at a discrete temperature" as used herein means that the temperature does not rise continuously, that is, the temperature does not continuously increase, but rather the temperature is maintained at a discrete temperature for at least some periods.

[0156] The post-heating treatment of step (ii) can be assisted by using ventilation and / or tumbling during the treatment. This ensures uniform post-heating treatment of all the thermally expandable microspheres within the microsphere batch. If the post-heating treatment is carried out, ventilation is preferably carried out using air. In some embodiments, ventilation is not carried out in an inert gas atmosphere (such as a nitrogen atmosphere).

[0157] In some embodiments, the post-heating treatment of step (ii) is carried out at standard atmospheric pressure, such as 101.3 kPa ± 5 kPa (1013 ± 50 mbar). In other words, in some embodiments, no additional external pressure other than standard atmospheric pressure is applied during the post-heating treatment of step (ii).

[0158] The post-heating treatment of the thermally expandable microspheres has the effect of improving the storage stability of the expandable microspheres. Thus, in some embodiments, after the first step (i) and the second step (ii), in a further step (iv), the thermally expandable microspheres obtained in step (ii) are stored for at least 5 minutes, such as at least 10 minutes, at least 30 minutes, at least 1 hour, at least 12 hours, at least 1 day, preferably at least 10 days, such as at least 20 days, at least 1 month, at least 2 months, at least 3 months or even at least 6 months. In principle, the storage conditions are not restricted and can be, for example, at any temperature at which the expandable microspheres have not expanded, but usually at a temperature lower than the temperature used for the post-heating treatment in step (ii), and in particular at ambient temperature, such as 25 °C ± 5 °C, or even 22.5 °C ± 2.5 °C, and / or at standard atmospheric pressure, such as 101.3 kPa ± 5 kPa (1013 ± 50 mbar).

[0159] Thus, in a preferred embodiment, the method of the present invention may further comprise the following further step:

[0160] (iv) storing the thermally expandable microspheres obtained in step (ii) or, if carried out, in step (iii) (described below) for at least 10 minutes, preferably at least 30 minutes, more preferably at least 1 hour, most preferably at least 1 day, such as at least 10 days, at least 20 days or at least 1 month.

[0161] In a further embodiment, the thermally expandable microspheres obtained in step (ii) are cooled in step (iii). The cooling in step (iii) means reducing the temperature of the thermally expandable microspheres to below the temperature used for the post-heating treatment in step (ii). In step (iii), the microspheres that are still in a thermally expandable state (i.e., unexpanded microspheres) are cooled. If step (iv) is employed, step (iii) can be carried out before this step (iv). For step (iii), any type of cooling device (such as a refrigerator) can be used for active cooling. However, it is preferred to carry out the cooling only by allowing the post-heated thermally expandable microspheres to cool at ambient temperature, i.e., without using any specific cooling device. Thus, in a preferred embodiment, in step (iii), the thermally expandable microspheres obtained from step (ii) are cooled to below 40 °C, such as below 30 °C, and preferably cooled to ambient temperature, such as 25 °C ± 5 °C, or even 22.5 °C ± 2.5 °C.

[0162] Thus, in a further preferred embodiment, the method of the present invention may comprise the following further steps

[0163] (iii) Cool the thermally expandable microspheres obtained in step (ii) to a temperature below the temperature used in step (ii), preferably to ambient temperature.

[0164] In a particularly preferred embodiment, the process of the invention comprises further steps (iii) and (iv).

[0165] The invention also relates to storage-stable expandable microspheres obtainable by a process comprising a post-heating treatment as described above.

[0166] Examples

[0167] The following examples are intended to illustrate the invention.

[0168] The volatile content in the microspheres was determined using a Mettler Toledo TGA / DSC1 TGA instrument with the following procedure: A sample for analysis was prepared from 1.7 mg (+ / - 0.2 mg) of thermally expandable microspheres contained in an alumina crucible with a volume of 600 μl. The sample temperature was raised from 30 °C to 650 °C at a heating rate of 20 °C / minute in a nitrogen atmosphere. The sample was held at 650 °C for a further two minutes in a nitrogen atmosphere, then the nitrogen was replaced with air and the sample was held at 650 °C for a further 15 minutes. The sample weight was continuously monitored during the heating program to obtain a thermogram, with the ordinate being the sample weight (in mg) and the abscissa being the heating temperature (in °C, related to the heating time (t), up to 650 °C). The volatile content (VC, %) of the microspheres was obtained from such a thermogram by subtracting the sample weight measured at the second inflection point (IP2) of the thermogram curve (i.e., here, after the blowing agent had evaporated and the sample weight had reached a first substantially stable plateau, which was between 170 °C and 300 °C, depending on the blowing agent and polymer actually used) from the starting weight of the sample (SW; 30 °C and t = 0), then dividing this difference by the starting weight of the sample and multiplying the result by 100 (see also equation (2) as defined above). The percentage of blowing agent retained in the microspheres after storage (VC 储存后保留 ; %) was calculated by dividing the volatile content after storage (VC 储存后 ) by the volatile content before storage (VC0) and multiplying by 100 (see also equation (3) as defined above).

[0169] The expansion properties were evaluated on a Mettler TMA / SDTA 841e thermomechanical analyzer connected to a PC running STARe software. The sample to be analyzed was prepared from 0.5 mg (+ / - 0.02 mg) of thermally expandable microspheres contained in an alumina crucible with a diameter of 6.8 mm and a depth of 4.0 mm. The crucible was sealed with an alumina lid with a diameter of 6.1 mm. Using a TMA ExpansionProbe type probe, the sample temperature was raised from approximately 30 °C to 240 °C at a heating rate of 20 °C / minute, while applying a (net) load of 0.06 N with the probe. The displacement of the probe was measured in the vertical direction to analyze the expansion properties. The initial expansion temperature (T 开始 ) is the temperature (°C) at which the probe displacement starts. The maximum expansion temperature (T max ) is the temperature (°C) at which the probe displacement reaches its maximum value. The TMA density is the sample weight (d) divided by the increase in the volume of the sample (dm 3 ) when the probe displacement reaches its maximum value.

[0170] General synthesis method:

[0171] Prepare a solution of the carboxylic acid ester functionalized cellulose polymer in a suitable organic solvent by dissolving the polymer overnight using a magnetic stirrer.

[0172] Add a blowing agent to the solution and stir the mixture for five minutes to redissolve any precipitated polymer.

[0173] If appropriate, further add an acid anhydride compound or a hydrogen bond donor selected from alcohols, ureas, and carboxylic acids to the solution and stir the mixture for an additional ten minutes to dissolve the acid anhydride compound or the hydrogen bond donor selected from alcohols, ureas, and carboxylic acids.

[0174] Then spray dry the mixture thus obtained using a Büchi Mini Spray Dryer B-290. Nitrogen is used as the spray gas, with a feed rate of 238 liters / hour for the examples containing cellulose acetate butyrate (CAB); and a feed rate of 307 liters / hour for the examples containing cellulose acetate (CA). The feed rate of the mixture to be spray dried is 13 ml / minute. The temperature of the drying gas at the inlet is 105 °C (for all examples using cellulose acetate 1 (CA1)) or 70 °C (for all examples using cellulose acetate butyrate 1 (CAB1)), and the aspirator rate is 38 m 3 / hour.

[0175] Collect the dried solid from the bottom of the cyclone separator, analyze it, and if appropriate, perform further post-heating treatment.

[0176] Table 1 lists the carboxylate-functionalized cellulose polymers used to prepare the microspheres. They are either cellulose acetate (CA) or cellulose acetate butyrate (CAB).

[0177] Table 1 - Details of Carboxylate-Functionalized Cellulose

[0178]

[0179] (1) DS = degree of substitution. Total DS = sum of DS of individual substituents

[0180] (2) Number-average molecular weight, provided by the supplier

[0181] (3) Glass transition temperature, provided by the supplier (Eastman)

[0182] (4) Melting point, provided by the supplier

[0183] - Not specified / determined

[0184] Example 1

[0185] Determine the effect of post-heat treatment at 125 °C for 1 hour on the expandable microspheres made from CA1.

[0186] Prepare a mixture containing 13.5 g of CA1, 159.0 g of acetone, and 7.2 g of isooctane as described above and spray-dry to prepare expandable microspheres. Determine the T 开始 、T max 、TMA density, and volatile content of the resulting expandable microspheres, and the results are shown in Table 2.

[0187] Table 2: Microsphere Properties

[0188]

[0189] (1) Volatile content of the microspheres, determined by TGA; based on the total weight of the microspheres

[0190] - Not added

[0191] Divide the resulting microsphere material into two equal portions. Subject one portion to post-heat treatment at 125 °C for 1 hour by placing approximately 1 g of microspheres in an oven set at 125 °C, and leave the other portion untreated and just leave it as it is. Then cool the portion that has undergone post-heat treatment to ambient temperature (22.5 ± 2.5 °C). Store these two portions of expandable microspheres at 22.5 ± 2.5 °C and standard pressure (1013 ± 50 mbar), and measure their volatile content after 1 month, 2 months, and 6 months. In addition, measure the volatile content of the expandable microspheres that have undergone post-heat treatment immediately after post-heat treatment. The results are shown in Table 3.

[0192] Table 3: Volatile Content of Expandable Microspheres after Storage

[0193]

[0194]

[0195] (1) For expandable microspheres subjected to post-heating treatment, this value represents the volatile content after post-heating treatment; for expandable microspheres not subjected to post-heating treatment, this value represents the volatile content after microsphere preparation.

[0196] (2) The retention percentage indicates how much of the volatile content remains after 6 months compared to the volatile content before storage.

[0197] As can be seen from Table 3, post-heating treatment significantly increases the volatile content of expandable microspheres. In the case of post-heating treatment, even after 6 months of storage, 97.3 wt% of the volatiles can still be retained, while the same untreated expandable microspheres only retain 22.8 wt% of the volatiles.

[0198] Example 2

[0199] Determine the effect of post-heating treatment at 100 °C for 1 hour on expandable microspheres made from CAB1 and pyromellitic dianhydride (pyromellitic dianhydride; PMDA) or pyromellitic acid (pyromellitic acid; PMA).

[0200] Prepare a mixture containing CAB1, acetone, isooctane, and PMA or PMDA in the amounts specified in Table 4 as described above and perform spray drying to prepare expandable microspheres. Measure the T 开始 、T max 、TMA density, and volatile content of the resulting expandable microspheres, and the results are shown in Table 5.

[0201] Table 4: Components and Dosages for Preparing Expandable Microspheres

[0202]

[0203] Table 5: Microsphere Properties

[0204]

[0205] (1) The volatile content of the microspheres, determined by TGA; based on the total weight of the microspheres.

[0206] The obtained microsphere material was divided into two equal parts. For each experiment, one part was post-heated at 100 °C for 1 hour by placing approximately 1 g of microspheres in an oven set at 100 °C, and the other part was not post-heated but simply left as it was. Then the part that had been post-heated was cooled at the ambient temperature (22.5 ± 2.5 °C). All portions of the expandable microspheres were then stored at 22.5 ± 2.5 °C and standard pressure (1013 ± 50 mbar), and their volatile content was determined after 1 month, 3 months, and 6 months. In addition, the volatile content of the expandable microspheres that had been post-heated was also determined immediately after the post-heating treatment. The results are shown in Table 6.

[0207] Table 6: Volatile content of expandable microspheres after storage

[0208]

[0209] (1) For the expandable microspheres that had been post-heated, this value represents the volatile content after the post-heating treatment; for the expandable microspheres that had not been post-heated, this value represents the volatile content after microsphere preparation.

[0210] (2) The retention percentage indicates how much of the volatile content was retained after 6 months compared to the volatile content before storage.

[0211] As can be seen from Table 6, the post-heating treatment significantly increased the volatile content of the expandable microspheres. In the case of the post-heating treatment, even after 6 months of storage, up to 93.5 wt% of the volatile matter could still be retained, while the same untreated expandable microspheres retained less than 80 wt% of the volatile matter.

[0212] Example 3

[0213] The effect of post-heating treatment at different temperatures was determined using expandable microspheres prepared from CA1 and 1,2,4,5-benzenetetracarboxylic dianhydride (pyromellitic dianhydride; PMDA).

[0214] A mixture containing 13.5 g of CA1, 159.0 g of acetone, 7.2 g of isooctane, and 0.36 g of PMDA was prepared as described above and spray-dried to prepare expandable microspheres. The T 开始 、T max 、TMA density, and volatile content of the obtained expandable microspheres were determined, and the results are shown in Table 7.

[0215] Table 7: Microsphere properties

[0216]

[0217] (1) The volatile content of the microspheres, determined by TGA; based on the total weight of the microspheres.

[0218] The obtained microsphere material was divided into four equal parts. Three parts were subjected to post-heating treatment at 75 °C, 100 °C or 125 °C for 1 hour. This was done by placing approximately 1 g of microspheres in an oven set to the corresponding temperature. One part was not subjected to post-heating treatment and was just left as it was. Then, those parts that had undergone post-heating treatment were cooled at the ambient temperature (22.5 ± 2.5 °C). All parts of the expandable microspheres were stored at 22.5 ± 2.5 °C and standard pressure (1013 ± 50 mbar), and their volatile content was measured after 1 month, 2 months and 6 months. In addition, the volatile content of the expandable microspheres after post-heating treatment was measured immediately after the post-heating treatment. The results are shown in Table 8.

[0219] Table 8: Volatile content of expandable microspheres after storage

[0220]

[0221] (1) For the expandable microspheres after post-heating treatment, this value represents the volatile content after post-heating treatment; for the expandable microspheres without post-heating treatment, this value represents the volatile content after microsphere preparation.

[0222] (2) The retention percentage indicates how much of the volatile content is retained after 6 months compared to the volatile content before storage.

[0223] As can be seen from Table 8, the post-heating treatment can be carried out within a wide temperature range and still significantly increase the volatile content of the expandable microspheres.

[0224] Example 4

[0225] The influence of different durations of post-heating treatment was determined using expandable microspheres prepared from CA1 and 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid; PMA).

[0226] A mixture containing 13.5 g of CA1, 159.0 g of acetone, 7.2 g of isooctane and 0.42 g of PMDA was prepared and spray-dried to prepare expandable microspheres as described above. The T 开始 、T max 、TMA density and volatile content of the obtained expandable microspheres were determined, and the results are shown in Table 9.

[0227] Table 9: Microsphere properties

[0228]

[0229] (1) The volatile content of the microspheres, determined by TGA; based on the total weight of the microspheres.

[0230] The obtained microsphere material was divided into six equal portions. Five portions were subjected to post-heating treatment at 100 °C for 5 minutes, 15 minutes, 30 minutes, 1 hour, or 2 hours, respectively, by placing approximately 1 g of microspheres in an oven set at 100 °C. One portion was not subjected to post-heating treatment and was just left as it was. Then, those portions that had undergone post-heating treatment were cooled at the ambient temperature (22.5 ± 2.5 °C). All portions of the expandable microspheres were stored at 22.5 ± 2.5 °C and standard pressure (1013 ± 50 mbar), and the volatile content of the expandable microspheres was measured after 1 month, 2 months, and 3 months. In addition, the volatile content of the expandable microspheres after post-heating treatment was measured immediately after the post-heating treatment. The results are shown in Table 10.

[0231] Table 10: Volatile content of expandable microspheres after storage

[0232]

[0233] (1) For the expandable microspheres after post-heating treatment, this value represents the volatile content after post-heating treatment; for the expandable microspheres without post-heating treatment, this value represents the volatile content after microsphere preparation.

[0234] (2) The retention percentage indicates how much of the volatile content is retained after 3 months compared to the volatile content before storage.

[0235] As can be seen from Table 10, the post-heating treatment can be carried out within a wide time range and still significantly increase the volatile content of the expandable microspheres.

[0236] Example 5

[0237] Determine the effect of adding an acid anhydride compound (i.e., pyromellitic dianhydride; PMDA) or a hydrogen bond donor (i.e., pyromellitic acid; PMA) on the storage stability after post-heating treatment.

[0238] Prepare a mixture containing CA1, acetone, isooctane, and (if applicable) PMDA or PMA in the amounts specified in Table 11 as described above and perform spray drying to prepare expandable microspheres. Determine the T 开始 、T max 、TMA density, and volatile content of the obtained expandable microspheres, and the results are shown in Table 12.

[0239] Table 11: Components and amounts for preparing expandable microspheres

[0240]

[0241] - Without addition

[0242] Table 12: Microsphere properties

[0243]

[0244] (1) The volatile content of the microspheres was determined by TGA; based on the total weight of the microspheres.

[0245] - Without addition

[0246] For each experiment, the microsphere material obtained each time was divided into two equal parts. For each experiment, one part was post-heated at 100 °C for 1 hour by placing approximately 1 g of microspheres in an oven set at 100 °C, and the other part was not post-heated but just left as it was. Then the part that had been post-heated was cooled at the ambient temperature (22.5 ± 2.5 °C). Subsequently, all parts of the expandable microspheres were stored at 22.5 ± 2.5 °C and standard pressure (1013 ± 50 mbar), and their volatile content was measured after 1 month, 3 months, and 6 months. In addition, the volatile content of the expandable microspheres after post-heating was also measured immediately after the post-heating treatment. The results are shown in Table 13.

[0247] Table 13: Volatile content of expandable microspheres after storage

[0248]

[0249] (1) For the expandable microspheres after post-heating treatment, this value represents the volatile content after the post-heating treatment; for the expandable microspheres without post-heating treatment, this value represents the volatile content after the microsphere preparation.

[0250] (2) The retention percentage indicates how much of the volatile content is retained after 6 months compared to the volatile content before storage.

[0251] As can be seen from Table 13, the post-heating treatment significantly increased the volatile content of the expandable microspheres. In the case of post-heating treatment, even after 6 months of storage, the retention rate of the volatile matter can reach basically 100 wt%, while the remaining volatile content of the same untreated expandable microspheres is significantly lower than 80 wt%. The results are also shown in Figure 2 . In Figure 2 , (Δ) indicates that the corresponding sample has undergone post-heating treatment. For each experiment, the first column represents the volatile content before storage, the second column represents the volatile content after 1 month (1m) of storage, the third column represents the volatile content after 3 months (3m) of storage, and the fourth column represents the volatile content after 6 months (6m) of storage.

Claims

1. A storage-stable thermally expandable microsphere, which comprises a polymer shell surrounding a hollow core, wherein the hollow core contains a blowing agent and the polymer shell contains a carboxylate-functionalized cellulose, and wherein after storage for six months under ambient conditions, the microsphere retains at least 80% of the initial weight of the blowing agent encapsulated in the microsphere.

2. The storage-stable thermally expandable microsphere according to claim 1, wherein after storage for six months under ambient conditions, the microsphere retains at least 85%, preferably at least 90%, even more preferably at least 95%, and most preferably at least 98% of the initial weight of the blowing agent encapsulated in the microsphere.

3. The storage-stable thermally expandable microsphere according to claim 1 or 2, wherein the polymer shell further contains an acid anhydride-containing compound or a hydrogen bond donor selected from alcohols, ureas, and carboxylic acids, preferably an acid anhydride-containing compound or a carboxylic acid.

4. The storage-stable thermally expandable microsphere according to claim 3, wherein the hydrogen bond donor is selected from pyromellitic dianhydride, i.e., 1,2,4,5-benzenetetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, pyromellitic acid, i.e., 1,2,4,5-benzenetetracarboxylic acid, citric acid, tartaric acid, butanetetracarboxylic acid, succinic acid, lactic acid, maleic acid, and any combination thereof, preferably selected from pyromellitic dianhydride, i.e., 1,2,4,5-benzenetetracarboxylic dianhydride, citric acid, pyromellitic acid, i.e., 1,2,4,5-benzenetetracarboxylic acid, and 1,2,3,4-butanetetracarboxylic acid.

5. The storage-stable thermally expandable microsphere according to any one of claims 1-4, wherein the carboxylate-functionalized cellulose contains a carboxylate group of formula (1) wherein: A is selected from -H, -OH, -OR b , -C(O)OH and -C(O)OR b ; R a does not exist such that A is directly connected to the C=O group; or R a is selected from saturated or unsaturated aliphatic groups having 1 to 11 carbon atoms, which may be linear, branched or cyclic; and selected from 5- and 6-membered aromatic rings; wherein R a is optionally substituted by one or more substituents selected from -OH, halogen, C 1-4 alkyl and C 1-4 alkoxy, wherein the C 1-4 alkyl and C 1-4 alkoxy is optionally substituted by one or more groups selected from halogen and -OH; and R b independently selected from C at each occurrence 1-4 alkyl, optionally having one or more substituents selected from halogen and -OH groups.

6. The storage-stable thermally expandable microsphere according to any one of claims 1-5, wherein one or more of the following conditions apply: (a) A is selected from H and C(O)OH; (b) R a contains 1 to 7 carbon atoms; (c) R a is selected from (i) saturated linear or branched aliphatic groups; (ii) cyclic aliphatic groups, (iii) unsaturated linear or branched aliphatic groups containing "y" double bonds; (iv) unsaturated cyclic aliphatic groups containing "y" double bonds; and (v) aromatic groups Wherein: v is an integer in the range from 1 to 11; w is an integer in the range from 3 to 11; x is an integer in the range from 2 to 11; y is 1 or 2; z is 5 or 6, and R c independently selected from H, -OH, halogen, C 1-4 alkyl and C 1-4 alkoxy each time it appears, wherein said C 1-4 alkyl and C 1-4 alkoxy is optionally substituted by one or more groups selected from halogen and -OH; (d)R a selected from groups having no more than 11 carbon atoms wherein: E is as defined in (c) above or 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 the respective acyclic aliphatic component, each independently selected from 0, 1, and 2.

7. The storage-stable thermally expandable microspheres according to any one of claims 1 to 6, wherein the carboxylate-functionalized cellulose comprises carboxylate functional groups selected from optionally substituted C1-C8 aliphatic carboxylate groups and carboxylate groups comprising an optionally substituted C6 aromatic ring, and is preferably selected from acetate, propionate, butyrate, valerate, hexanoate, heptanoate, octanoate and phthalate.

8. The storage-stable thermally expandable microspheres according to any one of claims 1 to 7, wherein the carboxylate-functionalized cellulose is acetate-functionalized cellulose, propionate-functionalized cellulose or butyrate-functionalized cellulose, preferably acetate-functionalized cellulose or butyrate-functionalized cellulose, and most preferably acetate-functionalized cellulose.

9. The storage-stable thermally expandable microspheres according to claim 8, wherein the number average molecular weight (M n ) of the carboxylate-functionalized cellulose is in the range of 2,000 to 100,000 Da and preferably in the range of 10,000 to 50,000 Da.

10. A method for preparing storage-stable thermally expandable microspheres, the microspheres comprising a polymer shell surrounding a hollow core, wherein the hollow core contains a blowing agent and the polymer shell contains carboxylate-functionalized cellulose, the method comprising the following steps: (i) Preparing thermally expandable microspheres comprising a polymer shell surrounding a hollow core, wherein the hollow core contains a blowing agent and the polymer shell contains carboxylate-functionalized cellulose; and (ii) Post-heating the thermally expandable microspheres obtained in step (i) by heating the thermally expandable microspheres to a temperature of at least 40 °C.

11. The method according to claim 10, wherein the post-heat treatment is carried out at a temperature between 50 °C and 150 °C, preferably between 60 °C and 140 °C, even more preferably between 70 °C and 130 °C and most preferably between 75 °C and 125 °C.

12. The method according to claim 10 or 11, wherein the post-heat treatment is carried out for at least 5 minutes, preferably at least 10 minutes, more preferably at least 30 minutes and even more preferably at least 50 minutes.

13. The method according to any one of claims 10 to 12, which comprises the following further step (iii) cooling the thermally expandable microspheres obtained in step (ii) to a temperature below the temperature used in step (ii), preferably to ambient temperature.

14. The method according to any one of claims 10 to 13, which comprises the following further step (iv) storing the thermally expandable microspheres obtained in step (ii) or step (iii) (if carried out) for at least 10 minutes, preferably at least 30 minutes, more preferably at least 1 hour and most preferably at least 1 day.

15. Storage-stable thermally expandable microspheres obtained by the method according to any one of claims 10 to 14.

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