Cellulose-based heat-expandable microspheres

Abstract

The present invention relates to heat-expandable microspheres comprising a polymeric shell surrounding a hollow core, wherein the hollow core comprises a blowing agent, and the polymeric shell comprises an acetate-functionalized cellulose having a glass transition temperature in the range of 150 to 250 °C and a hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably a hydrogen bond donor in the form of a carboxylic acid. The present invention further relates to a process for the preparation of heat-expandable microspheres and heat-expandable microspheres obtained by such a process, the process comprising mixing an acetate-functionalized cellulose, an organic solvent, a blowing agent, with a hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably a hydrogen bond donor in the form of a carboxylic acid, and then spraying the mixture thus obtained into a drying device to produce heat-expandable microspheres having a polymeric shell surrounding a hollow core, wherein the polymeric shell comprises an acetate-functionalized cellulose, and the hollow core comprises a blowing agent.

Description

TECHNICAL FIELD

[0001] The present invention relates to heat-expandable microspheres made from cellulose-based biopolymers, and also to a method for their production. BACKGROUND

[0002] and in the applications of coatings, cements, inks and crack fillers. Consumer products that often contain expandable microspheres include lightweight shoe soles (e.g. for running shoes), textured coverings such as wallpaper, solar reflective and insulating coatings, food packaging sealants, wine bottle stoppers, artificial leather, foam for protective helmet liners and automotive weather stripping.

[0003] Heat-expandable polymeric microspheres generally comprise a thermoplastic polymer shell having a hollow core, which contains a blowing agent that expands upon heating. Examples of blowing agents include low-boiling hydrocarbons or halocarbons that are liquid at room temperature but vaporize upon heating. To produce expanded microspheres, the expandable microspheres are heated so that the thermoplastic polymer shell softens and the blowing agent vaporizes and expands, thereby expanding the microspheres. Typically, the microspheres can increase in diameter by a factor of 1.5 to 8 during expansion. Expandable microspheres are sold in various forms, for example as dry, free-flowing particles, aqueous slurry or partially dewatered wet cake.

[0004] Expandable microspheres can be prepared 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, acrylamide, vinylidene chloride and styrene. One problem associated with such thermoplastic polymers is that they are typically derived from petrochemicals rather than from sustainable sources. Furthermore, many of the polymers are not biodegradable, or at least biodegrade so slowly that they risk accumulating in the environment. However, it is not necessarily straightforward to replace these monomers with more sustainably derived alternatives, because it is necessary to ensure that acceptable expansion properties are maintained. For example, the polymer must have a suitable surface energy to form core-shell particles in a suspension polymerization reaction, so as to encapsulate the blowing agent. Furthermore, the polymer must have good gas barrier properties to retain the blowing agent. Furthermore, the polymer must have a suitable viscoelasticity above the glass transition temperature Tgso that the shell can stretch during expansion. Thus, it is not straightforward to replace conventional monomers with bio-based monomers. g

[0005] Expandable microspheres have been described in which at least a proportion of the monomers making up the thermoplastic shell are bio-based monomers that can be derived from renewable resources.

[0006] WO2019 / 043235 describes polymers comprising lactone monomers having the general formula:

[0007] ​

[0008] wherein R1-R4 are each independently selected from H and C 1-4 alkyl.

[0009] WO2019 / 101749 describes copolymers comprising itaconic acid dialkyl ester monomers having the general formula:

[0010]

[0011] wherein each of R1and R2is independently selected from alkyl.

[0012] Published patent application WO2020 / 099440 (PCT / EP2019 / 081076) discloses heat-expandable microspheres made from cellulose-based biopolymers. The polymeric shell of these microspheres comprises a carboxylate-functionalized cellulose having a glass transition temperature (T g ) of at least 125 °C. In WO 2020 / 099440, the microspheres are prepared by solvent evaporation or solvent extraction. However, these techniques have certain drawbacks such as limited possibility to scale up, thus limited production capacity, the need for an additional product drying step and the handling of large amounts of contaminated water. It would be desirable if the microspheres could be produced by a method that does not have these drawbacks.

[0013] Therefore, there is still a need for alternative thermoplastic expandable microspheres wherein the thermoplastic polymeric shell is at least partially derived from a sustainable source. Furthermore, there is also a need to provide expandable microspheres wherein the thermoplastic polymeric shell is at least partially derived from a sustainable source and wherein the expandable microspheres have desirable expansion properties such as a desirable low density of the expanded microspheres. In addition, it would be desirable if such expandable microspheres derived from a sustainable source have sufficient or even improved storage stability. Furthermore, it would be desirable if these microspheres can be produced by a method that allows efficient scaling up of their production and that does not require an additional product drying step and the handling of large amounts of contaminated water. Therefore, the present invention is directed to finding heat-expandable polymeric microspheres with desirable expansion properties such as a desirable low density of the expanded microspheres and at the same time preferably with sufficient or even improved storage stability by using biologically derived polymers. It was further found that these microspheres can be efficiently produced using a spray-drying process that can easily and efficiently be scaled up and that does not require an additional product drying step and the handling of large amounts of contaminated water. SUMMARY

[0014] The present invention relates to heat-expandable microspheres comprising a polymeric shell surrounding a hollow core, wherein the hollow core comprises a blowing agent and the polymeric shell comprises an acetoate-functionalized cellulose having a glass transition temperature (Tg) in the range of 150 to 250 °C and a hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably a hydrogen bond donor in the form of a carboxylic acid.

[0015] The present invention also relates to a process for the preparation of heat-expandable microspheres and heat-expandable microspheres obtained by such process, the process comprising mixing an acetoate-functionalized cellulose having a glass transition temperature (Tg) in the range of 150 to 250 °C, an organic solvent, a blowing agent, a hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably a hydrogen bond donor in the form of a carboxylic acid, and then spraying the mixture thus obtained into a drying device to produce heat-expandable microspheres having a polymeric shell surrounding a hollow core, wherein the polymeric shell comprises an acetoate-functionalized cellulose and the hollow core comprises a blowing agent. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 shows the difference between single-core Figure 1A ) and multi-core Figure 1B ) microspheres.

[0017] Figure 2 TMA-determined T 开始 , T max and L max are shown. DETAILED DESCRIPTION

[0018] The present invention discloses heat-expandable microspheres comprising a polymeric shell surrounding a hollow core, wherein the hollow core comprises a blowing agent and the polymeric shell comprises an acetoate-functionalized cellulose having a glass transition temperature (Tg) in the range of 150 to 250 °C and a hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably a hydrogen bond donor in the form of a carboxylic acid, such as a di- or tetracarboxylic acid.

[0019] The expandable microspheres are based on a polymeric shell comprising an acetoate-functionalized cellulose. The functional group is one acetoate group or more than one acetoate group. Thus, the term “acetoate-functionalized cellulose” means that the cellulose comprises at least one acetoate group. The acetoate moiety forms part of the linkage between the acetoate functional group and the cellulose, i.e. the cellulose is linked to the acetoate functional group via an ester bond.

[0020] The polymer shell can comprise or consist of one or more polymer components, wherein at least one component, more than one component, or all polymer components are selected from such acetate-functionalized celluloses. In case the shell comprises polymers other than those described herein, i.e. acetate-functionalized celluloses, their content is typically less than 50 wt.%, for example less than 30 wt.%, or less than 10 wt.%, such as 9 wt.% or less, 5 wt.% or less, or even 2 wt.% or less. These percentages are based on the total polymer content of the shell.

[0021] In a particular embodiment, the polymer shell comprises only one polymer component, which is an acetate-functionalized cellulose, more particularly cellulose acetate having a glass transition temperature Tgin the range of 150 °C to 250 °C.

[0022] The acetate-functionalized cellulose can comprise one or more additional carboxylate functional groups different from acetate. If the acetate-functionalized cellulose comprises more than one additional carboxylate functional group different from acetate, these additional carboxylate functional groups are different from each other. For example, in embodiments, the acetate-functionalized cellulose can comprise one additional carboxylate functional group different from acetate. However, it is preferred that the acetate-functionalized cellulose is free of additional carboxylate functional groups different from acetate.

[0023] In embodiments, if the acetate-functionalized cellulose comprises an additional carboxylate functional group different from acetate, said additional carboxylate functional group on the acetate-functionalized cellulose can be represented by formula (1):

[0024]

[0025] In formula (1), A is selected from -H, -OH, -OR b , -C(O)OH and -C(O)OR b . In embodiments, A is selected from -H and -C(O)OH.

[0026] R a may be absent, i.e. A can be directly connected to the C=O group. However, in case it is present, R a may be selected from saturated or unsaturated aliphatic groups having 1 to 11 carbon atoms, and it can be linear, branched or cyclic.

[0027] R a may also be selected from 5- and 6-membered aromatic rings.

[0028] R a may optionally comprise one or more groups selected from -OH, halogen, C 1-4 alkyl and C 1-4alkyl and C 1-4 alkyl and C 1-4 alkyl is optionally substituted with one or more groups selected from halo and -OH.

[0029] In embodiments, R a comprising 1 to 7 carbon atoms, for example 1 to 5 or 1 to 3 carbon atoms.

[0030] R b is independently at each occurrence selected from H, -OH, halo, C 1-4 alkyl, for example C 1-2 alkyl, optionally having one or more substituents selected from halo and -OH groups. In embodiments, C 1-4 alkyl or C 1-2 alkyl is unsubstituted.

[0031] In embodiments, R a may be a saturated linear or branched aliphatic group or a cyclic aliphatic group. v is an integer in the range of 1 to 11, for example 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.

[0032] R c is independently at each occurrence selected from H, -OH, halo, C 1-4 alkyl and C 1-4 alkyl, wherein the C 1-4 alkyl and C 1-4 alkyl is optionally substituted with one or more groups selected from halo and -OH.

[0033] In other embodiments, R a may be an unsaturated linear or branched aliphatic group comprising "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 and is typically 1 or 2.

[0034] In further embodiments, R a may be an unsaturated cyclic aliphatic group comprising "y" double bonds, wherein y is typically 1 or 2.

[0035] In still further embodiments, R a may be an aromatic group. z is an integer selected from 5 and 6.

[0036] In still further embodiments, R a may be a linear or branched aliphatic group comprising a cyclic aliphatic or aromatic ring. Thus, Ra may be selected from the group consisting of wherein E is as defined above or p and r are each independently an integer from 0 to 8, wherein p+r is at least 1. q and s are each the number of double bonds in the respective acyclic aliphatic component. In embodiments, each of q and s is independently selected from 0, 1, and 2.

[0037] Halogen is typically selected from F and CI. However, in embodiments, the functional group is halogen-free, such that there is no halogen in groups A, R a , R b , and R c .

[0038] In embodiments, at least one R c group is H. In other embodiments, no more than two R c groups are different from H; and in further embodiments, no more than one R c group is different from H. In still further embodiments, all R c groups are H.

[0039] In the above definitions of R a , R b , and R c , in cases where there is more than one -OH substituent, typically there is no more than one -OH substituent per carbon atom.

[0040] 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 further embodiments, R a is unsubstituted.

[0041] In embodiments, the additional carboxylate functional group on the cellulose substituent is selected from propionate, butyrate, valerate, hexanoate, heptanoate, octanoate, and phthalate. In further embodiments, it is selected from propionate and butyrate.

[0042] The degree of substitution (DS) of the hydroxyl groups of the cellulose that are replaced by acetate and, if present, the one or more additional carboxylate functional groups can be in the range of 0.9 to 4.0, preferably 0.9 to 3.5, and in embodiments, in the range of 1.5 to 3.5, for example in the range of 2.0 to 3.0.

[0043] If the acetate-functionalized cellulose comprises one or more additional carboxylate functional groups, the degree of substitution (DS) of the acetate groups is higher than the degree of substitution (DS) of the one or more additional carboxylate functional groups. In other words, the acetate-functionalized cellulose according to the present application contains more acetate groups (i.e. acetate functional groups) than groups (i.e. functional groups) having the one or more additional carboxylate functional groups. In embodiments, it is preferred that the degree of substitution (DS) of the one or more additional carboxylate functional groups is not greater than 1.0, for example not greater than 0.5 or not greater than 0.2, or even not greater than 0.1.

[0044] In embodiments, in the acetate-functionalized cellulose, the degree of substitution (DS) of the acetate groups is in the range of 0.9 to 3.5, for example 1.5 to 3.5 or 2.0 to 3.0, and the degree of substitution (DS) of the one or more additional carboxylate functional groups is not greater than 1.0, for example not greater than 0.5 or not greater than 0.2, or even not greater than 0.1, provided that the degree of substitution (DS) of the acetate groups is higher than the degree of substitution (DS) of the one or more additional carboxylate functional groups.

[0045] In preferred embodiments, in the acetate-functionalized cellulose, the degree of substitution (DS) of the acetate groups is in the range of 2.0 to 3.0, and the degree of substitution (DS) of the one or more additional carboxylate functional groups is not greater than 1.0, for example not greater than 0.5 or not greater than 0.2, or even not greater than 0.1.

[0046] The degree of substitution (DS) is a measure of the average number of hydroxyl groups per glucose unit of cellulose that are substituted with other groups, such as carboxylic acid groups and in particular acetate groups. Thus, the degree of substitution (DS) of cellulose cannot be greater than 4.0. The degree of substitution (DS) can be determined by method ASTM D817-12.

[0047] Optionally, other functional groups than carboxylate functional groups can be present in the acetate-functionalized cellulose. For example, -OH groups on the cellulose molecule that have not been replaced by carboxylate functional groups can be replaced by one alkoxy group or more than one alkoxy group, for example selected from Ci to C6 alkoxy groups. In other embodiments, although less preferred, the -OH groups can be replaced by halogen groups, for example F or CI. In case such other functional groups are present, their molar amount is lower than the molar amount of the one or more carboxylate groups.

[0048] In embodiments, the degree to which the cellulose is substituted by other functional groups (i.e. functional groups other than acetate or additional carboxylate functional groups) is not greater than 1.0, for example not greater than 0.5 or not greater than 0.2. In further embodiments, the degree of substitution of groups of non-carboxylate groups is not greater than 0.1. However, the degree to which the cellulose is substituted by other functional groups is less than the degree to which it is substituted by acetate.

[0049] In particular embodiments, the acetate functionalized cellulose is cellulose acetate having an acetate degree of substitution (DS) in the range of 0.9 to 4.0, such as 0.9 to 3.5, in particular 1.5 to 3.5, more in particular 2.0 to 3.0. As used herein, reference to "cellulose acetate" means that no other functional groups than acetate groups and hydroxyl groups are present in the cellulose.

[0050] The glass transition temperature (Tg) of the acetate functionalized cellulose forming the shell of the microsphere or at least a part of the shell of the microsphere is in the range of 150 to 250 °C, such as 150 to 190 °C. In a preferred embodiment, the polymeric shell comprises acetate functionalized cellulose having a glass transition temperature in the range of 150 to 190 °C. The T g The glass transition temperature (Tg) of the acetate functionalized cellulose forming the shell of the microsphere or at least a part of the shell of the microsphere is in the range of 150 to 250 °C, such as 150 to 190 °C. In a preferred embodiment, the polymeric shell comprises acetate functionalized cellulose having a glass transition temperature in the range of 150 to 190 °C. The T g The calculation is based on the second heating cycle.

[0051] In further embodiments, the Tg of the acetate functionalized cellulose is in the range of 160 to 220 °C, such as in the range of 160 to 200 °C, 160 to 190 °C, 170 to 185 °C or 175 to 185 °C.

[0052] The melting point of the acetate functionalized cellulose is typically higher than the Tg value and in embodiments higher than 200 °C. In embodiments, the melting point is higher than 220 °C. The melting point is typically not more than 270 °C, such as not more than 260 °C or not more than 250 °C.

[0053] The Tg and melting point of the acetate functionalized cellulose can be varied or controlled by varying the functional groups on the acetate functionalized cellulose or by varying the molecular weight or by varying the degree of substitution.

[0054] The heat-expandable microspheres are hollow, wherein the shell comprises acetate functionalized cellulose and the hollow center or core comprises one or more blowing agents. The density of the acetate functionalized cellulose used to make the microspheres is typically in the range of 1.1-1.35 g / cm 3 In the expanded microspheres, the density is typically less than 1 g / cm 3 and suitably in the range of 0.005 to 0.8 g / cm 3 or 0.01 to 0.6 g / cm 30.4 g / cm3, for example in the range of 0.01 to 0.2 g / cm3, preferably in the range of 0.01 to 0.15 g / cm3. A higher density, in particular a density of 1 g / cm3or more, generally means that the sample of microspheres is not suitable for use. 3 0.4 g / cm3, for example in the range of 0.01 to 0.2 g / cm3, preferably in the range of 0.01 to 0.15 g / cm3. A higher density, in particular a density of 1 g / cm3or more, generally means that the sample of microspheres is not suitable for use. 3 0.4 g / cm3, for example in the range of 0.01 to 0.2 g / cm3, preferably in the range of 0.01 to 0.15 g / cm3. A higher density, in particular a density of 1 g / cm3or more, generally means that the sample of microspheres is not suitable for use. 3 0.4 g / cm3, for example in the range of 0.01 to 0.2 g / cm3, preferably in the range of 0.01 to 0.15 g / cm3. A higher density, in particular a density of 1 g / cm3or more, generally means that the sample of microspheres is not suitable for use. 3 0.4 g / cm3, for example in the range of 0.01 to 0.2 g / cm3, preferably in the range of 0.01 to 0.15 g / cm3. A higher density, in particular a density of 1 g / cm3or more, generally means that the sample of microspheres is not suitable for use.

[0055] In embodiments, the acetoate functionalized cellulose used to form the microspheres has a number average molecular weight (Mn) in the range of 1,000 to 700,000 Dalton, for example in the range of 2,000 to 500,000, 2,000 to 100,000, 2,000 to 80,000 or 2,000 to 50,000 Dalton. In embodiments, the number average molecular weight is in the range of 5,000 to 50,000, for example 10,000 to 50,000 Dalton.

[0056] Examples of suitable acetoate functionalized cellulose are cellulose acetate having a number average molecular weight (Mn) in the range of 1,000 to 700,000 Dalton, for example in the range of 2,000 to 500,000, 2,000 to 100,000, 2,000 to 80,000 or 2,000 to 50,000 Dalton, preferably in the range of 5,000 to 50,000, more preferably in the range of 10,000 to 50,000 Dalton.

[0057] In particular embodiments, the acetoate functionalized cellulose is cellulose acetate having an acetoate degree of substitution (DS) in the range of 0.9 to 4.0, such as 0.9 to 3.5, in particular 1.5 to 3.5, more in particular 2.0 to 3.0, and a number average molecular weight (Mn) in the range of 1,000 to 700,000, for example in the range of 2,000 to 500,000, 2,000 to 100,000, 2,000 to 80,000 or 2,000 to 50,000 Dalton, preferably in the range of 5,000 to 50,000 Dalton, and more preferably in the range of 10,000 to 50,000 Dalton.

[0058] The temperature T 开始 may be higher than 140 °C, such as 150 °C to less than 250 °C. The temperature at which the heat-expandable microspheres start to expand is referred to as T 开始 , while the temperature at which maximum expansion is reached is referred to as T max . T 开始 and T Max may be determined using standard measurement techniques known to the skilled person. For example, T 开始 and TMax The temperature of the onset of expansion of the heat-expandable microspheres can be determined in a temperature ramp experiment by using for example a Mettler-Toledo thermo-mechanical analyzer such as a Mettler-Toledo TMA / SDTA 841 e by using a heating rate of 20 °C / min and a (net) load of 0.06 N. In such a temperature ramp experiment, a known weight of a sample of heat-expandable microspheres is heated at a constant heating rate of 20 °C / min under a (net) load of 0.06 N. When the heat-expandable microspheres start to expand, the sample volume increases and the load is moved upwards. From this measurement an expansion thermogram (exemplary thermogram is shown in Fig. 2) is obtained, wherein the ordinate represents the height of the load moved upwards and the abscissa represents the temperature. Figure 2 The temperature of the onset of expansion of the heat-expandable microspheres can be determined in a temperature ramp experiment by using for example a Mettler-Toledo thermo-mechanical analyzer such as a Mettler-Toledo TMA / SDTA 841 e by using a heating rate of 20 °C / min and a (net) load of 0.06 N. In such a temperature ramp experiment, a known weight of a sample of heat-expandable microspheres is heated at a constant heating rate of 20 °C / min under a (net) load of 0.06 N. When the heat-expandable microspheres start to expand, the sample volume increases and the load is moved upwards. From this measurement an expansion thermogram (exemplary thermogram is shown in Fig. 2) is obtained, wherein the ordinate represents the height of the load moved upwards and the abscissa represents the temperature. 开始 The temperature of the onset of expansion of the heat-expandable microspheres can be determined in a temperature ramp experiment by using for example a Mettler-Toledo thermo-mechanical analyzer such as a Mettler-Toledo TMA / SDTA 841 e by using a heating rate of 20 °C / min and a (net) load of 0.06 N. In such a temperature ramp experiment, a known weight of a sample of heat-expandable microspheres is heated at a constant heating rate of 20 °C / min under a (net) load of 0.06 N. When the heat-expandable microspheres start to expand, the sample volume increases and the load is moved upwards. From this measurement an expansion thermogram (exemplary thermogram is shown in Fig. 2) is obtained, wherein the ordinate represents the height of the load moved upwards and the abscissa represents the temperature. Max The temperature of the onset of expansion of the heat-expandable microspheres can be determined in a temperature ramp experiment by using for example a Mettler-Toledo thermo-mechanical analyzer such as a Mettler-Toledo TMA / SDTA 841 e by using a heating rate of 20 °C / min and a (net) load of 0.06 N. In such a temperature ramp experiment, a known weight of a sample of heat-expandable microspheres is heated at a constant heating rate of 20 °C / min under a (net) load of 0.06 N. When the heat-expandable microspheres start to expand, the sample volume increases and the load is moved upwards. From this measurement an expansion thermogram (exemplary thermogram is shown in Fig. 2) is obtained, wherein the ordinate represents the height of the load moved upwards and the abscissa represents the temperature.

[0059] In embodiments, the heat-expandable microspheres have a T 开始 The heat-expandable microspheres have a T 开始 . Even more preferably, the heat-expandable microspheres have a T 开始 .

[0060] To further enhance the performance of the polymer shell, the polymer shell of the heat-expandable microspheres comprises a hydrogen bond donor selected from the group consisting of an alcohol, a urea and a carboxylic acid, preferably a hydrogen bond donor in the form of a carboxylic acid. The hydrogen bond donor can interact via hydrogen bonds with the groups on the acetoxy-functionalized cellulose. By adding a hydrogen bond donor selected from the group consisting of an alcohol, a urea and a carboxylic acid, preferably 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 and thus the expansion properties of the microspheres can be improved. Thus, the hydrogen bond donor acts as a polymer shell enhancer. Furthermore, the density after storage, for example for 4 weeks, can be improved.

[0061] The hydrogen bond donor can be a polymer having an average molecular weight of at most 1000 g / mol, such as 1000 g / mol up to 5000 g / mol or 1500 g / mol up to 3000 g / mol. The hydrogen bond donor can also be, and the hydrogen bond donor is typically and preferably a low molecular weight compound having a molecular weight of for example less than 2000 g / mol, preferably less than 1500 g / mol, more preferably less than 1000 g / mol and even more preferably less than 500 g / mol. For example, the hydrogen bond donor can have a molecular weight in the range of 20 to 500 g / mol, preferably 30 to 400 g / mol and even more preferably 40 to 300 g / mol.

[0062] The hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid is a compound having hydrogen atoms covalently bound to an atom with a higher electronegativity, i.e. oxygen if the hydrogen bond donor is an alcohol or carboxylic acid or nitrogen if the hydrogen bond donor is a urea, which form intermolecular hydrogen bonds with functional groups of the acetate functionalized cellulose, such as the acetate groups, the one or more further carboxylate functional groups, the hydroxyl groups and the ether groups, in particular the acetate groups and the one or more further carboxylate functional groups, if present.

[0063] 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.

[0064] 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 can have a molecular weight in the range of 20 to 2000 g / mol and preferably has a molecular weight in the range of 20 to 500 g / mol, more preferably between 30 and 400 g / mol and even more preferably between 40 and 300 g / mol.

[0065] If the hydrogen bond donor is an alcohol, it can be selected from any compound containing at least one alcohol group, such as 1, 2, 3, 4, 5 or 6 alcohol groups, preferably having a molecular weight in the range of 20 to 2000 g / mol. If the hydrogen bond donor is an alcohol, a diol, a triol, a tetraol, a pentaol or a hexaol is preferred.

[0066] Suitable diols are for example selected from the group consisting of 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.

[0067] Suitable triols are for example glycerol, 1,2,3-butanetriol, 1,2,4-butantriol, 1,1,1 -tris(hydroxymethyl)propane, pentanetriol and hexanetriol. A preferred triol is glycerol.

[0068] Suitable tetraols are for example ascorbic acid (vitamin C), erythritol, threitol or pentaerythritol. Preferred tetraols are ascorbic acid (vitamin C) and pentaerythritol.

[0069] Suitable five-membered alcohols are xylitol, arabinol, ribitol, glucose, fructose, galactose and mannose.

[0070] Suitable six-membered alcohols are, for example, sorbitol, mannitol and cyclohexanehexanol. Preferred six-membered alcohols are sorbitol.

[0071] If the hydrogen bond donor is an alcohol, it is preferably selected from 1,3-butanediol, glycerol, ascorbic acid (vitamin C) or sorbitol.

[0072] The hydrogen bond donor is particularly preferably a carboxylic acid, i.e. a compound containing at least one carboxylic acid group, such as a mono-, di-, tri-, tetra- or polycarboxylic acid, such as a polycarboxylic acid polymer. More particularly, the hydrogen bond donor is a carboxylic acid having a molecular weight in the range from 20 to 2000 g / mol. Preferably, the hydrogen bond donor is a carboxylic acid containing at least two carboxylic acid groups (-COOH), in particular a di-, tri- or tetra-carboxylic acid.

[0073] Examples of mono-carboxylic acids are formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, benzoic acid and lactic acid.

[0074] Examples of di-carboxylic acids are adipic acid, maleic acid, succinic acid, tartaric acid and aldonic di-acids.

[0075] Examples of tri-carboxylic acids are citric acid and isocitric acid.

[0076] Examples of tetra-carboxylic acids are pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), ethylenediaminetetraacetic acid (EDTA) and butane tetracarboxylic acid, such as 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0077] Preferred examples of suitable hydrogen bond donors in carboxylic acid form are citric acid, maleic acid, succinic acid, pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), lactic acid, tartaric acid, ethylenediaminetetraacetic acid (EDTA), butane tetracarboxylic acid, such as 1,2,3,4-butanetetracarboxylic acid (BTCA). Even more preferred examples of suitable hydrogen bond donors in carboxylic acid form are pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), citric acid, tartaric acid, 1,2,3,4-butanetetracarboxylic acid (BTCA) and maleic acid.

[0078] In particular, according to one preferred embodiment, if the hydrogen bond donor is in carboxylic acid form, 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.

[0079] More particularly, according to one preferred embodiment, if the hydrogen bond donor is in carboxylic acid form, it is selected from pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), citric acid, tartaric acid and 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0080] Preferably, according to one preferred embodiment, if the hydrogen bond donor is in carboxylic acid form, it is a tri- or tetra-carboxylic acid, such as citric acid, pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid) or 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0081] In a particular embodiment, according to one preferred embodiment, if the hydrogen bond donor is in carboxylic acid form, it is a tetra-carboxylic 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 carboxylic acid form and is 1,2,3,4-butanetetracarboxylic acid (BTCA).

[0082] The amount of hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably the hydrogen bond donor in carboxylic acid form, used to prepare the expandable microspheres of the present application is not particularly limited.

[0083] However, the amount of hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably the hydrogen bond donor in carboxylic acid form, can be in the range of 0.01 to 50 wt.-%, based on the total weight of the hydrogen bond donor and the acetoate-functionalized cellulose. In embodiments, it can be in the range of 0.01 to 40 wt.-%, for example 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 wt.-% to 5.0 wt.-% or even in the range of 1.2 wt.-% to 5 wt.-% or 1.5 wt.-% to 5 wt.-%, the wt.-% being based on the total weight of the hydrogen bond donor and the acetoate-functionalized cellulose.

[0084] In further embodiments, the polymeric shell can comprise particles to improve the mechanical properties and the gas barrier of the polymeric shell and thus also act as a polymeric shell reinforcing agent. Examples of such particles are talc, montmorillonite, nanocrystalline cellulose and various types of clay such as bentonite.

[0085] Many factors can contribute to high density. For example, high density can be due to low microsphere yield, i.e. too low a percentage of microspheres in the polymer material to reduce the overall density to an acceptable level. Another problem is poor expansion properties, which occurs when too many microspheres contain insufficient blowing agent to achieve full expansion. This can be due to too high a permeability of the polymer shell to the blowing agent, or due to the formation of so-called “multi-core” microspheres, in which there are multiple blowing agent-containing cores inside the shell (e.g. like a microsphere foam or sponge) rather than a single blowing agent-containing core. In such multi-core microspheres, the blowing agent concentration is typically too low to reduce the density sufficiently. Another cause is aggregation or agglomeration of the polymer, leading to poor microsphere production and denser material. A high proportion of aggregated material or poorly expanded microspheres can also lead to large variability in the expansion properties of the resulting microsphere product. This is particularly disadvantageous for surface sensitive applications such as paints, which require a smooth finish.

[0086] Figure 1A and 1B Illustrative cross-sections of single-core and multi-core microspheres are provided, respectively, in which the polymer region 1 is represented by the cross-hatched region and the blowing agent-containing region 2 is represented by the blank region.

[0087] Typically, the one or more blowing agents have a boiling point above 25 °C at 5.0 bara pressure or a boiling point above 25 °C at 3.0 bara pressure, where “bara” means bar (absolute pressure). In embodiments, they have a boiling point above 25 °C at atmospheric pressure (1.013 bara). Typically, they have a boiling point of 250 °C or less at atmospheric pressure, for example 220 °C or less, or 200 °C or less. They are preferably inert and do not react with the functionalised cellulose shell. The boiling point at high pressure can be calculated using the Clausius Clapeyron equation.

[0088] Examples of blowing agents include dialkyl ethers, alkanes and haloalkanes, e.g. chloroalkanes, fluoroalkanes or chlorofluoroalkanes. In embodiments, the dialkyl ether comprises two alkyl groups each selected from C2 to C5 alkyl groups. In embodiments, the alkane is a C4 to C 12 alkane. In embodiments, the haloalkane is selected from C2 to C 10 haloalkanes. The haloalkanes can comprise one or more halogen atoms selected from chlorine and fluorine. The alkyl or haloalkyl groups in the dialkyl ether, alkane and haloalkane can be linear, branched or cyclic. One blowing agent or a mixture of one or more blowing agents can be used.

[0089] In embodiments, the one or more blowing agents are selected from alkyl ethers and alkanes for environmental reasons, and in further embodiments, the one or more blowing agents are selected from alkanes. The use of halogenated alkanes is preferably avoided because of their potential ozone depletion properties and also because they generally have a higher global warming potential.

[0090] Examples of suitable blowing agents that can be used include n-pentane, isopentane, neopentane, cyclopentane, cyclohexane, n-butane, isobutane, isohexane, neohexane, heptane, isohexane, octane, isooctane, isodecane, and isododecane. In preferred embodiments, the blowing agent is selected from C4to C 12 isoparaffins.

[0091] In the expandable microspheres, the one or more blowing agents are typically present in an amount of 5 to 50 wt.%, for example in the range of 5 to 45 wt.% or 10 to 40 wt.%, based on the total weight of the functionalized cellulose and the blowing agent.

[0092] Acetate functionalized cellulose materials can be commercially purchased or can be prepared by known means, for example by mixing cellulose with a suitable carboxylic acid (i.e. acetic 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 acid chloride, for example as described by Nishio et al.; Cellulose, 2006 (13), 245-259.

[0093] Examples of suitable acetate functionalized celluloses are cellulose acetate (CA) (i.e. acetate functionalized cellulose that does not contain additional carboxylate functional groups different from acetate esters), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB), in particular cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) having a number average molecular weight (Mn) in the range of 2,000 to 100,000 Dalton, such as in the range of 2,000 to 80,000 Dalton, in the range of 10,000 to 50,000 Dalton or in the range of 20,000 to 50,000 Dalton.

[0094] Preferred acetate functionalized celluloses are cellulose acetate (CA) (i.e. acetate functionalized cellulose that does not contain additional carboxylate functional groups different from acetate esters) having a number average molecular weight (Mn) in the range of 10,000 to 100,000 Dalton, such as in the range of 10,000 to 80,000 Dalton, preferably in the range of 10,000 to 50,000 Dalton and more preferably in the range of 20,000 to 50,000 Dalton.

[0095] For example, if the polymeric shell comprises cellulose acetate propionate (CAP) or cellulose acetate butyrate (CAB), the amount of hydrogen bond donor used in carboxylic acid form can be 0.01 to 50 wt.%, based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose. In embodiments, it can be in the range of 0.01 to 40 wt.%, for example 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.% or in the range of 1.0 to 5.0 wt.%, the wt.% based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose.

[0096] For example, if the polymeric shell comprises cellulose acetate propionate (CAP) or cellulose acetate butyrate (CAB), the amount of hydrogen bond donor used in carboxylic acid form can be 0.01 to 50 wt.%, based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose. In embodiments, it can be in the range of 0.01 to 40 wt.%, for example 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.% or in the range of 1.0 to 5.0 wt.%, the wt.% based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose.

[0097] The expandable microspheres of the present application can be obtained by a spray drying process, the method comprising mixing an acetate-functionalized cellulose, an organic solvent, a blowing agent and a hydrogen bond donor selected from an alcohol, urea and a carboxylic acid, preferably a hydrogen bond donor in carboxylic acid form, and then spraying the mixture thus obtained into a drying device to produce heat-expandable microspheres having a polymeric shell surrounding a hollow core, wherein the polymeric shell comprises an acetate-functionalized cellulose and the hollow core comprises a blowing agent.

[0098] In principle, the spray-drying apparatus used to carry out the spray-drying process is not limited and any conventional and commercially available spray-drying apparatus can be used for the spray-drying process. A typical spray-drying apparatus suitable for the process described herein comprises a drying chamber equipped with a spray nozzle, an inlet for drying gas and an outlet connecting the drying chamber with a cyclone. The liquid to be atomized is sprayed together with a spray gas through the spray nozzle, which is usually located at the top of the spray chamber, but can also be located on any other part of the spray dryer, into the drying chamber. In the drying chamber, the atomized liquid is dried with drying gas which is fed into the spray chamber through the drying gas inlet. The inlet for the drying gas can be located, for example, next to the spray nozzle. The atomized liquid is dried and forms particles. The particles thus obtained are then fed together with the drying gas through the drying chamber outlet, which is usually located in the bottom region of the drying chamber, into the cyclone. In the cyclone, the particles are separated from the drying air. The drying air can be further filtered to remove any remaining particles from the drying air.

[0099] A suitable spray-drying apparatus for carrying out the spray-drying process is the Bϋchi Mini Spray Dryer B-290, which is commercially available from Bϋchi, Switzerland.

[0100] The order in which the acetate-functionalized cellulose, the organic solvent, the blowing agent and the hydrogen bond donor selected from the group consisting of alcohols, ureas and carboxylic acids, preferably the hydrogen bond donor in the form of a carboxylic acid, are added for mixing is not limited and any order can be chosen.

[0101] However, in a preferred embodiment, in the process for producing expandable microspheres, the acetate-functionalized cellulose is first mixed with the organic solvent and then, in a further step, the blowing agent and the hydrogen bond donor selected from the group consisting of alcohols, ureas and carboxylic acids, preferably the hydrogen bond donor in the form of a carboxylic acid, are added to the mixture.

[0102] Mixing of the acetate-functionalized cellulose can be carried out at ambient temperature, although temperatures in the range of 5 to 75 °C can be used. Mixing is usually carried out until the acetate-functionalized cellulose has completely dissolved in the organic solvent.

[0103] In embodiments, the mixture of the acetate-functionalized cellulose and the organic solvent can be left or stirred for a period of time, for example 1 to 100 hours, or 2 to 50 hours. This 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.

[0104] In a further step, a blowing agent and a hydrogen bond donor selected from an alcohol, urea and a carboxylic acid, preferably in the form of a carboxylic acid, are added to the mixture of the acetate-functionalized cellulose and the organic solvent. The order of addition of the blowing agent and the hydrogen bond donor selected from an alcohol, urea and a carboxylic acid, preferably in the form of a carboxylic acid, is not critical, thus, the blowing agent can be added first, followed by the hydrogen bond donor selected from an alcohol, urea and a carboxylic acid, preferably in the form of a carboxylic acid, or, alternatively, the hydrogen bond donor selected from an alcohol, urea and a carboxylic acid, preferably in the form of a carboxylic acid, can be added first, followed by the blowing agent. This mixing step can also be carried out at ambient temperature, although temperatures in the range of 5 to 75 °C can be used. Furthermore, this mixing step is typically carried out until the blowing agent and the hydrogen bond donor selected from an alcohol, urea and a carboxylic acid, preferably in the form of a carboxylic acid, have completely dissolved in the organic solvent.

[0105] After the blowing agent and the hydrogen bond donor selected from an alcohol, urea and a carboxylic acid, preferably in the form of a carboxylic acid, have been added to the mixture of the acetate-functionalized cellulose and the organic solvent, the mixture thus obtained can be stirred for a further period of time, e.g. for 1 to 100 hours, or for 2 to 50 hours. This can also be carried out at a temperature in the range of 10 to 95 °C, e.g. at a temperature of 20 to 90 °C.

[0106] The mixture comprising the acetate-functionalized cellulose, the organic solvent, the blowing agent and the hydrogen bond donor selected from an alcohol, urea and a carboxylic acid, preferably in the form of a carboxylic acid, is sprayed into a drying device to produce the heat-expandable microspheres described herein. The drying device can be a spray drying device as described above.

[0107] The optional spray gas which is ejected through the nozzle together with the liquid to be atomized is not particularly limited and can be any suitable spray gas known to the skilled person. For example, the spray gas can be selected from the group consisting of nitrogen, carbon dioxide, (pressurized) air, a noble gas such as argon, and the like. Preferably, in the process for producing the expandable microspheres as described herein, a spray gas is used, more preferably the spray gas is nitrogen.

[0108] The drying gas is also not particularly limited and can be any suitable drying gas known to the skilled person. For example, the spray gas can also be selected from the group consisting of nitrogen, carbon dioxide, (pressurized) air, an inert gas such as argon, and the like. Preferably, the drying gas is nitrogen.

[0109] The skilled person can readily select further process parameters for operating the spray drying device, such as the spray gas flow, the inlet temperature of the drying gas when entering the drying chamber, the feed speed of the liquid to be atomized, and the aspirator speed for circulating the drying gas in the spray drying device.

[0110] It has been found that with the above method expandable microspheres comprising a polymer shell around a hollow core can be obtained, wherein the hollow core comprises a blowing agent and the polymer shell comprises an acetate-functionalized cellulose, wherein the thermally expandable microspheres have an expansion onset temperature T 开始 It has further been found that this method is particularly suitable for obtaining such expandable microspheres, wherein the polymer shell further comprises a hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably a hydrogen bond donor in the form of a carboxylic acid.

[0111] The organic solvent can be selected from those having one or more functional groups selected from esters, amides, aldehydes, ketones, alcohols (including diols), and ethers, for example those having 3 to 12 carbon atoms. In embodiments, the esters, ketones and ethers can be part of a cyclic structure. Other examples include halogenated alkanes having 1 to 6 carbon atoms and halogenated carboxylic acids having 1 to 6 carbon atoms, wherein the halogen is selected from fluorine, chlorine, bromine and iodine.

[0112] 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, iso-pentyl formate, n-pentyl acetate, iso-pentyl 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, isopropylidene acetone, phenyl ethyl ketone, cyclohexanone, diethyl phthalate, ethyl lactate, benzyl acetate, butyrolactone, acetylacetone, methylcyclohexanone, benzaldehyde, diisobutyl ketone, dimethyl ketone alcohol, ethylene glycol, glycerol-a-monochloroethanol, propylene glycol, glycol ethers (e.g. propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol mono-tert-butyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether), glycol ether esters (e.g. 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, dimethoxy methane, dimethoxy ethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole, phenetole, 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 comprise water, but the water content of the organic solvent is typically less than 5 wt%, i.e. 0 to 5 wt% water, for example 0 to 1 wt% water.

[0113] In embodiments, the solvent is selected from one or more of ethyl acetate, methyl acetate, ethyl formate and acetone. It is particularly preferred that the solvent is acetone.

[0114] Typically, the content of acetoate-functionalized cellulose in the mixture for spray drying is typically in the range of 0.1 to 50 wt.%. In embodiments, it can be in the range of 1 to 40 wt.%, for example in the range of 2 to 35 wt.% or even 5 to 10 wt.%. The wt.% is based on the total weight of the mixture for spray drying.

[0115] The amount of blowing agent in the mixture for spray drying is typically in the range of 0.5 to 50 wt.%. In embodiments, it can be in the range of 0.5 to 40 wt.%, for example in the range of 1 to 30 wt.% or even 3 to 25 wt.%. In embodiments, the weight of blowing agent in the mixture for spray drying is equal to or less than the weight of acetoate-functionalized cellulose, for example the weight ratio of blowing agent to acetoate-functionalized cellulose can be 1.5 or less, for example 1.3 or less or even 1.1 or less. In embodiments, the minimum weight ratio is 0.1, or in further embodiments 0.2. In embodiments, the weight ratio of blowing agent to acetoate-functionalized cellulose in the organic phase is in the range of 0.1 to 1.5, for example in the range of 0.2 to 1.3 or even 0.3 to 1.1.

[0116] The amount of hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably in the form of a carboxylic acid, in the mixture for spray drying is typically in the range of 0.01 to 15 wt.%, for example in the range of 0.05 to 10 wt.%, in the range of 0.1 to 5 wt.% or even in the range of 0.1 to 3.0 wt.%, such as 0.1 to 1.0 wt.%. The wt.% is based on the total weight of acetoate-functionalized cellulose, blowing agent, hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably in the form of a carboxylic acid, and solvent in the mixture for spray drying.

[0117] For example, if cellulose acetate propionate (CAP) or cellulose acetate butyrate (CAB) is used as the polymer, the amount of hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably in the form of a carboxylic acid, used can be in the range of 0.01 to 15 wt.%. In embodiments, it can be in the range of 0.05 to 10 wt.%, in the range of 0.1 to 5 wt.% or even in the range of 0.1 to 3.0 wt.%, such as 0.1 to 1.0 wt.%. The wt.% is based on the total weight of acetoate-functionalized cellulose, blowing agent, hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably in the form of a carboxylic acid, and solvent in the mixture for spray drying.

[0118] For example, if in a preferred embodiment cellulose acetate (CA) (i.e. acetate-functionalized cellulose not containing additional carboxylic acid ester functional groups different from acetate) is used as the polymer, the amount of hydrogen bond donor selected from the group consisting of alcohols, ureas and carboxylic acids (preferably hydrogen bond donor in form of carboxylic acid) used can be in the range of 0.01 to 15 wt.-%, such as in the range of 0.05 to 10 wt.-%, in the range of 0.1 to 5 wt.-% or even in the range of 0.1 to 1.0 wt.-%. The wt.-% is based on the total weight of acetate-functionalized cellulose, blowing agent, hydrogen bond donor selected from the group consisting of alcohols, ureas and carboxylic acids (preferably hydrogen bond donor in form of carboxylic acid) and solvent in the mixture used for spray drying.

[0119] The amount of organic solvent amounts to 100 wt.-%. Preferably, the amount of organic solvent is at least 30 wt.-%, more preferably at least 40 wt.-% and even more preferably at least 50 wt.-%. The wt.-% is based on the total weight of the mixture used for spray drying.

[0120] The amount of hydrogen bond donor selected from the group consisting of alcohols, ureas and carboxylic acids (preferably hydrogen bond donor in form of carboxylic acid) in the mixture used for spray drying can also be in the range of 0.01 to 50 wt.-%, based on the total weight of hydrogen bond donor selected from the group consisting of alcohols, ureas and carboxylic acids (preferably hydrogen bond donor in form of carboxylic acid) and acetate-functionalized cellulose in the mixture used for spray drying. In embodiments, it can be in the range of 0.1 to 40 wt.-%, such as in the range of 0.5 to 35 wt.-%, in the range of 1 to 30 wt.-% or even in the range of 2 to 25 wt.-%, based on the total weight of hydrogen bond donor selected from the group consisting of alcohols, ureas and carboxylic acids (preferably hydrogen bond donor in form of carboxylic acid) and acetate-functionalized cellulose in the mixture used for spray drying.

[0121] The volume average particle size (diameter), i.e. the D(0.5) value, of the generally unexpanded microspheres is in the range of 1 to 500 pm, such as 5 to 200 pm, or in embodiments, 10 to 100 pm or even 15 pm to 80 pm.

[0122] The diameter of the expanded microspheres is generally 1.5 to 8 times the diameter of the unexpanded microspheres, such as 2 to 7 times or 3 to 6 times their initial diameter.

[0123] The particle size is suitably measured using light scattering techniques, such as laser diffraction, such as low angle laser light scattering (LALLS). They can also be measured by image analysis from photographs or electron micrographs of the microspheres before or after expansion.

[0124] To expand the expandable microspheres, they can be heated to a temperature above the boiling point of the blowing agent and the T gthe temperature of the higher of the two, and a temperature below the microsphere melting point. To stop the expansion, the microspheres can be cooled back to a temperature below the Tg of the functionalized cellulose g and / or the boiling point of the blowing agent.

[0125] The manner in which the heat-expandable microspheres are heated includes direct or indirect contact with a heat transfer medium such as steam or pressurized steam, for example as described in WO2004 / 056549, WO2014 / 198532 and WO2016 / 091847. In further embodiments, direct or indirect contact with other heating gases (e.g. air or nitrogen) optionally mixed with steam can be used. In still further embodiments, where indirect heating is used, a liquid heat transfer medium such as a heating oil can be used. In another embodiment, IR radiation can be used to heat the microspheres.

[0126] The expansion properties of the heat-expandable thermoplastic microspheres can be assessed using a thermal mechanical analyzer (e.g. Mettler TMA 841) and quantitative data can be obtained from the images using suitable software (e.g. STARe software).

[0127] The heat-expandable or expanded thermoplastic microspheres can be provided in unexpanded form, for example for in situ expansion at the location of their use, or they can be pre-expanded before being sent to the final location of use.

[0128] The microspheres can be used in many applications, for example for the manufacture of paper (e.g. embossed paper, paper fillers, sizing agents), inks, softwood, cement-based compositions, adhesives, foams, insulation materials, paints, rubber-based products, thermoplastics, thermosets, ceramics, non-woven composites, fillers, etc. to provide, for example, lightweight fillers in these applications.

[0129] The heat-expandable microspheres described herein can be heat-expanded when dry, when wet or in slurry. They are also able to retain the blowing agent for a long time, for example at least 1 week, such as at least 1 month or at least 4 months. Furthermore, their expansion is generally irreversible, i.e. cooling the microspheres after heat expansion does not cause them to shrink back to their pre-expansion size.

[0130] A further second aspect of the present invention is a process for the preparation of heat-expandable microspheres, the process comprising mixing an acetate-functionalized cellulose having a glass transition temperature in the range of 150 to 250 °C, an organic solvent, a blowing agent and a hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, preferably the hydrogen bond donor in the form of a carboxylic acid, and then spraying the mixture thus obtained into a drying device to produce heat-expandable microspheres having a polymeric shell surrounding a hollow core, wherein the polymeric shell comprises the acetate-functionalized cellulose and the hollow core comprises the blowing agent.

[0131] The process parameters, spray drying apparatus, acetic acid ester functionalized cellulose, organic solvent, blowing agent, hydrogen bond donor selected from the group consisting of alcohols, ureas and carboxylic acids, preferably the hydrogen bond donor in the form of a carboxylic acid, and the amounts thereof are the same as already described above and are equally applicable to the process according to the second aspect of the present invention.

[0132] In a still further embodiment, the process for preparing heat-expandable microspheres then further comprises the step of storing the prepared heat-expandable microspheres for at least two weeks, preferably at least four weeks, after preparation before the heat-expandable microspheres are expanded. Surprisingly, it has been found that storing the prepared heat-expandable microspheres can improve the expansion density of the heat-expandable microspheres. The expansion density represents the density of the microspheres at maximum expansion of the heat-expandable microspheres. The expansion density can be determined using standard measurement techniques known to the skilled person. For example, the expansion density can also be determined in a temperature ramp experiment as described above for determining T 开始 . The density determined using such equipment is typically referred to as TMA density. The TMA density is calculated using the following equation: sample weight [g] divided by the volume increase of the sample at maximum expansion [dm 3 ]. A smaller TMA density generally indicates more desirable expansion properties. A TMA density of 0.2 g / cm 3 or less is considered desirable, and a TMA density of at least 0.15 g / cm 3 or less is considered particularly desirable.

[0133] In another aspect, the present invention also relates to heat-expandable microspheres obtained by the process for preparing heat-expandable microspheres as described above.

[0134] Embodiments

[0135] The following examples are intended to illustrate the present invention.

[0136] - The expansion properties are evaluated using a Mettler TMA / SDTA 841 e thermo-mechanical analyzer connected to a PC running the STARe software. The sample to be analyzed is prepared from 0.5 mg (± 0.02 mg) of heat-expandable microspheres packed in an alumina crucible with a diameter of 6.8 mm and a depth of 4.0 mm. The crucible is sealed using an alumina lid with a diameter of 6.1 mm. Using a TMA-type expansion probe, the temperature of the sample is raised from about 30 °C to 240 °C at a heating rate of 20 °C / min, while a (net) load of 0.06 N is applied with the probe. The vertical displacement of the probe is measured to analyze the expansion properties. The initial expansion temperature (T 开始) : Temperature at the start of probe displacement (°C).

[0137] - Maximum expansion temperature (T max ) : Temperature at the maximum probe displacement (°C).

[0138] - Maximum displacement (L max ) : Displacement of the probe (pm) when the probe displacement reaches a maximum.

[0139] - TMA density: The weight of the sample (d) divided by the volume increase of the sample (dm 3 ) when the probe displacement reaches a maximum.

[0140] Each parameter was determined according to the illustrative examples shown in Figure 2

[0141] The volatile content in the microspheres was determined using a Mettler Toledo TGA / DSC1 TGA instrument.

[0142] An Agilent 7697A Headspace coupled with an Agilent 7890A GC was used to perform gas chromatography - flame ionization detection (GC-FID) analysis.

[0143] Differential Scanning Calorimetery (DSC) measurements were obtained using a Mettler Toledo DSC 822e apparatus.

[0144] General synthesis method:

[0145] For the experiments of Examples 1 and 2, all components (solvents, polymers, hydrogen bond donors and blowing agents) were mixed and stirred overnight using a magnetic stirrer.

[0146] The mixture thus obtained was spray dried using a Buchi mini spray dryer B-290. Nitrogen was used as the spray gas and the feed rate was 238 liters / hour. The feed rate of the mixture to be spray dried was measured to be about 12-13 ml / minute. The drying gas temperature at the inlet was 105°C, the aspirator rate was 38 m 3 / hour, the temperature at the outlet was around 78-80°C and the spray time was around 4 minutes.

[0147] The dried solids were collected from the bottom of the cyclone and analyzed after a few days or after storage.

[0148] ​Table 1 lists the acetoate-functionalized cellulose polymer used to prepare the microspheres (cellulose acetate (CA1)) and its properties. Table 1 also lists another suitable acetoate-functionalized cellulose polymer, i.e. cellulose with acetoate and butyrate functional groups having an acetoate degree of substitution (DS) in the range of 2.0 to 3.0 and a butyrate degree of substitution (DS) of not more than 1 (CAB1).

[0149] Table 1 - Details of acetoate-functionalized cellulose

[0150]

[0151] (1) DS = degree of substitution. Total DS = sum of DS of individual substituents

[0152] (2) Number average molecular weight (in Dalton), provided by supplier

[0153] (3) Glass transition temperature, provided by supplier (Eastman)

[0154] (4) Melting point, provided by supplier

[0155] - not applicable

[0156] Example 1

[0157] Using CA1 as the polymer for the polymer shell, the effect of various doses of different hydrogen bond donors on T 开始 , T max and TMA density was investigated.

[0158] The mixture for all experiments of Example 1 contained 2.25 g CA1, 26.5 g acetone and 1.2 g isooctane. Various hydrogen bond donors were added in different doses of 1 to 10 wt% (based on the total weight of hydrogen bond donor and CA1) as indicated in Table 2. (PMA = pyromellitic acid; BTCA = 1,2,3,4-butanetetracarboxylic acid; PAA(2000) = polyacrylic acid with a weight average molecular weight of 2000 g / mol)

[0159] Table 2: Microsphere properties

[0160]

[0161]

[0162] (1) based on the total weight of hydrogen bond donor and CA1

[0163] (2) volatile content of the microspheres, measured by TGA; based on the total weight of the microspheres

[0164] measured by GC-FID (gas chromatography - flame ionization detection)

[0165] The data obtained in Example 1 indicate that the acetate functionalized cellulose compositions can be used to make biobased microspheres having a desired low TMA density and having an expansion onset temperature T 开始 of in the range of 158°C to 175°C 开始 The results indicate that the expansion onset temperature T 开始 of cellulose acetate having a glass transition temperature of 180°C is reduced by the addition of the hydrogen bond donor and the data given in Table 3 of Example 2 indicate that the expansion performance does not change significantly after 4 weeks of microsphere storage. This indicates that the microspheres of the present invention have a desired storage stability.

[0166] Example 2:

[0167] Storage tests were performed to evaluate the storage stability of the microspheres of the present invention after 4 weeks of storage. Table 3 shows the performance T max , T 开始 and TMA density of the microspheres from the experiments of Example 1 after 4 weeks of storage. For example, the data provided in Table 2 above for Experiment 2 from Example 1 is for freshly prepared microspheres, while the data provided in Table 3 below for the corresponding Experiment 2 (4 weeks) is for the exact same microspheres, the only difference being that the measurements were taken after 4 weeks of microsphere storage. The results are summarized in Table 3.

[0168] Table 3: Microsphere performance of the microspheres of Example 1 after 4 weeks of storage

[0169]

[0170]

[0171]

[0172] (1) based on the total weight of the hydrogen bond donor and CA1

[0173] (2) volatile content of the microspheres, measured by TGA; based on the total weight of the microspheres

[0174] (3) percent change in TMA density of the microspheres after 4 weeks of storage compared to the TMA density of the same microspheres immediately after production. A negative value indicates that the TMA density of the microspheres after 4 weeks of storage is lower than the density immediately after production

[0175] measured by GC-FID (gas chromatography - flame ionization detection)

[0176] The data indicate that while there is a slight loss of blowing agent after 4 weeks of microsphere storage, surprisingly the expansion performance T 开始 , T maxThere were no significant changes in TMA density, and in most cases there was even an improvement. This indicates that the microspheres of the present invention have the desired storage stability.

Claims

1. Heat-expandable microspheres comprising a polymeric shell surrounding a hollow core, wherein the hollow core comprises a blowing agent, and the polymeric shell comprises an acetate-functionalized cellulose having a glass transition temperature in the range of 150 to 250 °C and a hydrogen bond donor selected from an alcohol, a urea, and a carboxylic acid, wherein the amount of the hydrogen bond donor is in the range of 0.01 to 50 wt.%, the wt.% being based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose.

2. The heat-expandable microspheres according to claim 1, wherein the hydrogen bond donor is a hydrogen bond donor in the form of a carboxylic acid and is selected from pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), citric acid, tartaric acid, butane tetracarboxylic acid, succinic acid, lactic acid, maleic acid, and any combination thereof.

3. The heat-expandable microspheres according to claim 2, wherein the hydrogen bond donor is selected from citric acid, pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid), and 1,2,3,4- butane tetracarboxylic acid (BTCA).

4. The heat-expandable microspheres according to claim 1, wherein the hydrogen bond donor is an alcohol.

5. The heat-expandable microspheres according to claim 1, wherein the hydrogen bond donor is selected from 1,3-butanediol, glycerol, pentaerythritol, sorbitol, and ascorbic acid.

6. The heat-expandable microspheres according to any one of claims 1 to 5, wherein T 开始 is from 150 °C to 250 °C.

7. The heat-expandable microspheres according to claim 6, wherein T 开始 is from 155 °C to 220 °C.

8. The heat-expandable microspheres according to claim 6, wherein T 开始 is from 160°C to 190°C.

9. The heat-expandable microspheres according to claim 6, wherein T 开始 is from 165°C to 180°C.

10. The heat-expandable microspheres according to any one of claims 1 to 5, wherein the amount of the hydrogen bond donor is in the range of 0.01 to 30 wt.%, the wt.% being based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose.

11. The heat-expandable microspheres according to claim 10, wherein the hydrogen bond donor is a hydrogen bond donor in the form of a carboxylic acid.

12. The heat-expandable microspheres according to claim 10, wherein the amount of the hydrogen bond donor is in the range of 0.1 to 20 wt.%, the wt.% being based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose.

13. The heat-expandable microspheres according to claim 10, wherein the amount of the hydrogen bond donor is in the range of 0.2 to 15 wt.%, the wt.% being based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose.

14. The heat-expandable microspheres according to claim 10, wherein the amount of the hydrogen bond donor is in the range of 0.5 to 10 wt.%, the wt.% being based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose.

15. The heat-expandable microspheres according to claim 10, wherein the amount of the hydrogen bond donor is in the range of 1 to 5 wt.%, the wt.% being based on the total weight of the hydrogen bond donor and the acetate-functionalized cellulose.

16. The heat-expandable microspheres according to any one of claims 1 to 5, wherein the acetate-functionalized cellulose comprises one or more additional carboxylate functional groups different from acetate, wherein the one or more additional carboxylate functional groups are selected from an optionally substituted C1-C8 aliphatic carboxylate group and a carboxylate group comprising an optionally substituted C6 aromatic ring, wherein the degree of substitution of the one or more additional carboxylate functional groups different from acetate on the acetate-functionalized cellulose is not greater than 1.

0.

17. The heat-expandable microspheres according to claim 16, wherein the one or more additional carboxylate functional groups are selected from propionate, butyrate, valerate, hexanoate, heptanoate, octanoate and phthalate groups.

18. The heat-expandable microspheres according to claim 16, wherein the one or more additional carboxylate functional groups are selected from propionate groups and butyrate groups.

19. The heat-expandable microspheres according to any one of claims 1 to 5, wherein the acetate functionalized cellulose is free of additional carboxylate functional groups different from acetate.

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

21. The heat-expandable microspheres according to any one of claims 1 to 5, wherein the acetate functionalized cellulose has a number average molecular weight (Mn) in the range of 2,000 to 100,000 Dalton.

22. The heat-expandable microspheres according to claim 21, wherein the acetate functionalized cellulose has a number average molecular weight (Mn) in the range of 10,000 to 50,000 Dalton.

23. The heat-expandable microspheres according to any one of claims 1 to 5, obtainable by a spray-drying process comprising mixing an acetate functionalized cellulose, an organic solvent, a blowing agent, with a hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, and then spraying the mixture thus obtained into a drying device to produce heat-expandable microspheres having a polymeric shell surrounding a hollow core, wherein the polymeric shell comprises an acetate functionalized cellulose and the hollow core comprises a blowing agent.

24. The heat-expandable microspheres according to claim 23, wherein the hydrogen bond donor is a hydrogen bond donor in the form of a carboxylic acid.

25. A process for the preparation of heat-expandable microspheres, the process comprising mixing an acetate functionalized cellulose having a glass transition temperature in the range of 150-250 °C, an organic solvent, a blowing agent, with a hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid, and then spraying the mixture thus obtained into a drying device to produce heat-expandable microspheres having a polymeric shell surrounding a hollow core, wherein the polymeric shell comprises an acetate functionalized cellulose and the hollow core comprises a blowing agent, wherein the hydrogen bond donor is added in an amount in the range of 0.01 to 15 wt.%, the wt.% being based on the total weight of acetate functionalized cellulose, blowing agent, hydrogen bond donor and solvent in the mixture used for spray-drying.

26. The process according to claim 25, wherein the hydrogen bond donor selected from an alcohol, a urea and a carboxylic acid is added in an amount in the range of 0.05 to 10 wt.%, the wt.% being based on the total weight of acetate functionalized cellulose, blowing agent, hydrogen bond donor and solvent in the mixture used for spray-drying.

27. The method of claim 26, wherein the hydrogen bond donor is added in an amount in the range of 0.1 to 5 weight %, the weight % based on the total weight of acetate functionalized cellulose, blowing agent, hydrogen bond donor, and solvent in the mixture used for spray drying.

28. The method of claim 26, wherein the hydrogen bond donor is added in an amount in the range of 0.1 to 3.0 weight %, the weight % based on the total weight of acetate functionalized cellulose, blowing agent, hydrogen bond donor, and solvent in the mixture used for spray drying.

29. The method of claim 26, wherein the hydrogen bond donor is added in an amount in the range of 0.1 to 1.0 weight %, the weight % based on the total weight of acetate functionalized cellulose, blowing agent, hydrogen bond donor, and solvent in the mixture used for spray drying.

30. The method of any one of claims 25 to 29, wherein the hydrogen bond donor is a hydrogen bond donor in carboxylic acid form.

31. The method of any one of claims 25 to 29, further comprising the step of storing the prepared heat-expandable microspheres for at least two weeks after preparation, prior to expanding the heat-expandable microspheres.

32. The method of claim 31, wherein the step of storing the prepared heat-expandable microspheres for at least four weeks after preparation, prior to expanding the heat-expandable microspheres.

33. The method of claim 31, wherein the hydrogen bond donor is a hydrogen bond donor in carboxylic acid form.

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