Expanded microspheres

Abstract

To provide a method for preparing expanded microspheres, expanded microspheres, and uses of expanded microspheres without the need to use a solid suspending agent.SOLUTION: A method for preparing expanded microspheres comprising a) obtaining a composition comprising a polymer dissolved in a solvent, wherein the polymer has a glass transition temperature (Tg, °C), and b) spray-drying the composition of step a) in a spray dryer, the spray dryer comprising an inlet drying gas having an inlet temperature (Tinlet, °C), wherein a minimum inlet temperature of the drying gas (Tinlet,min, °C) is Tinlet,min=Tg*0.75, wherein a maximum inlet temperature of the drying gas (Tinlet,max, °C) is Tinlet,max=Tg*2.2, and wherein Tinlet,max≥Tinlet≥Tinlet,min.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to expanded microspheres and methods for their production. [Background technology]

[0002] Thermally expandable microspheres are known in the art and are described, for example, in U.S. Pat. No. 3,615,972, International Patent Publication No. 00 / 37547, International Patent Publication No. 2007 / 091960, International Patent Publication No. 2021 / 234010, U.S. Patent Application Publication No. 2020 / 216631, and U.S. Patent Application Publication No. 2024 / 149236. Many examples are sold under the trade name Expancel®. They can be expanded to form extremely low-weight and low-density fillers and may find use in applications such as foamed or low-density resins, paints and coatings, cements, inks, and crack fillers. Consumer products that often contain expandable microspheres include lightweight shoe soles (e.g., for running shoes), textured coverings such as wallpaper, solar reflective and thermal insulation coatings, food package sealants, wine corks, artificial leather, foam for protective helmet liners, and automotive weatherstrips, genuine leather, pre-decorated clothing, personal care applications, thermostat and block materials, thermoplastic packaging, paint, automotive putty, and terrazzo. Most of these applications require the expanded microspheres to be substantially white.

[0003] Typically, one or more solid suspending agents (e.g., colloidal silica, alumina sol, magnesium hydroxide, etc.) must be added to prevent coalescence during the preparation of unexpanded microspheres and to prevent agglomeration of the unexpanded microspheres, particularly during the subsequent expansion process. While the use of solid suspending agents has proven to be a highly successful approach to solving these agglomeration problems, a drawback of using such additives is that they coat the outer surface of the expanded microspheres (this can be seen in Figure 2, an SEM image of a prior art expanded microsphere; the distant dark patches / bumps coating the outer surface of the expanded microsphere are particles of the solid suspending agent). In fact, because solid suspending agents are inorganic, placing the suspending agent on the outer surface of the microspheres substantially increases the ash content of the microspheres. Inorganic agents also generally add weight to the microspheres, thereby increasing their particle density.

[0004] However, there are many applications where a high ash content is undesirable and / or harmful to the intended application. Expanded microspheres are commonly used as lightweight fillers (e.g., in acrylic coatings), and therefore reducing the ash content and density of expanded microspheres has clear benefits in this regard. Additional applications that would benefit from low ash content expanded microspheres include: · Use of expanded microspheres with low ash content as sacrificial molds in the production of porous ceramic products (filters, high-temperature insulation, membrane reactors, and catalyst supports, etc.); Use of the low ash content expanded microspheres in polishing pads for Si wafers, where the absence of inorganic deposits is beneficial; Use of said low ash content expanded microspheres in mortars, such as dry mix mortars, etc., includes, but is not limited to:

[0005] Also notable in this regard is the pharmaceutical sector, which has long shown interest in microspheres as drug delivery vehicles. However, obtaining microspheres with suitable properties for use in such applications has proven quite challenging, and most reported methods in the pharmaceutical sector rely on laborious and expensive freeze-thaw or freeze-drying processes (i.e., non-expanded microspheres). Therefore, expanded microspheres with little or no ash content would show great potential for use in such low-ash applications, especially when combined with pharmaceutically acceptable polymers such as poly(lactic acid) (PLA), carboxymethylcellulose (CMC), and polyvinyl alcohol (PVA).

[0006] Therefore, a primary objective of the present disclosure was to find a method for preparing expanded microspheres without requiring the use of solid suspending agents. Summary of the Invention

[0007] An unexpected discovery was that this objective could be fully realized by directly spray-drying a polymer solution at high temperature. This technical solution was surprisingly effective, since it was found that the method not only allows the preparation of expanded microspheres without the use of solid suspending agents, but also works with polymers that could not be used in the prior art techniques for preparing expanded microspheres, most notably polyvinyl alcohol and carboxymethyl cellulose. It was found that expanded microspheres can be obtained by the method without necessarily requiring the use of a blowing agent, although a blowing agent can also be used in the method. Thus, in a first aspect, the present disclosure relates to a method for preparing expanded microspheres, the method comprising: a) obtaining a composition comprising a polymer dissolved in a solvent, wherein the polymer has a glass transition temperature (T g , °C), b) spray drying the composition of step a) in a spray dryer, wherein the spray dryer has an inlet temperature (T inlet, °C), and inlet,min , °C) is T inlet,min =(T g *0.75), The maximum inlet temperature of the drying gas (T inlet,max , °C) is T inlet,max =(T g *2.2) In the formula, T inlet,max ≧T inlet ≧T inlet,min This includes the step of:

[0008] For the avoidance of doubt, “T g *0.75" is the glass transition temperature (T g , °C) multiplied by 0.75. For example, T at 100 °C g Polystyrene with T inlet,min 75°C, and T inlet,max Requires 220°C.

[0009] Minimum inlet temperature (T inlet,min It has been found that the inlet temperature (T inlet It has been found that the boiling point of the expanded microspheres cannot be substantially higher (i.e., >20°C) than 0.5°C, otherwise expansion will fail (i.e., no expanded microspheres will be obtained). Thus, in a second aspect, the present disclosure relates to a method for preparing expanded microspheres, the method comprising: a) obtaining a composition comprising a polymer dissolved in a solvent, wherein the polymer has a glass transition temperature (T g、 °C), wherein the composition further comprises a blowing agent; b) spray drying the composition of step a) in a spray dryer, wherein the spray dryer has an inlet temperature (T inlet、 °C), and inlet,min、 °C), T inlet,min =(T g*0.60), The maximum inlet temperature of the drying gas (T inlet,max , °C) is T inlet,max =(T g *2.2), In the formula, T inlet,max ≧T inlet ≧T inlet,min and The boiling point of the blowing agent (T BABP , °C) is T BABP ≦(T inlet +20°C).

[0010] For the avoidance of doubt, “T g *0.60" is the glass transition temperature (T g , °C) multiplied by 0.60. For example, T at 100 °C g Polystyrene having 、 If a blowing agent is used in step a), a T of 60°C inlet,min and T of 220°C inlet,max requires.

[0011] For the avoidance of doubt, T BABP ≦(T inlet +20℃) means that the boiling point of the blowing agent must be at or below the inlet temperature +20℃. For example, inlet is 70°C, the blowing agent must have a boiling point of ≦90°C.

[0012] An additional advantage of these methods is that the density of the expanded microspheres increases with the inlet temperature, T inlet Furthermore, the inlet temperature can be adjusted to a specified maximum and minimum temperature (i.e. 、 T inlet,max ≧T inlet ≧T inlet,min), the method results in expanded microspheres that are non-agglomerated and are substantially white having an ISO brightness value of at least 70 (with the caveat that, for obvious reasons, substantially white microspheres cannot be obtained when using inherently non-white polymers such as lignin).

[0013] These methods produce expanded microspheres without the need for the use of solid suspending agents. Thus, in a third aspect, the present disclosure relates to expanded microspheres comprising a polymeric shell surrounding a hollow core, the outer surface of which is free of particulate deposits from the solid suspending agent. As can be seen from Figure 3, these expanded microspheres are of excellent quality and free of solid suspending agent particles on the outer surface of the polymeric shell. The only apparent "discoloration" on the outer surface of the polymeric shell is actually a small number of very small microspheres that are statistically unavoidable as a result of the Gaussian size distribution (these are less apparent in Figure 2 due to the solid suspending agent coating the outer surface). Thus, the expanded microspheres disclosed herein are particularly suitable for use as low-ash, low-density filler materials. Thus, in a fourth aspect, the present disclosure relates to the use of the expanded microspheres disclosed herein as a filler material, for example, as a sacrificial mold in the manufacture of porous ceramic products (such as filters, high temperature insulation, membrane reactors, and catalyst supports), in polishing pads for Si wafers, or in mortars, such as dry mix mortars.

[0014] As mentioned above, low ash content microspheres show great promise in the pharmaceutical sector, especially when combined with pharmaceutically acceptable polymers.

[0015] Thus, in a fifth aspect, the present disclosure relates to the use of the expanded microspheres disclosed herein as drug delivery vehicles (i.e., substances used as a vehicle for administering pharmaceuticals, typically serving to improve the selectivity, efficacy, and / or safety of pharmaceutical administration). Preferably, the expanded microspheres comprise a polymer shell formed from a pharmaceutically acceptable polymer, preferably a biodegradable pharmaceutically acceptable polymer, such as (but not limited to) homopolymers and copolymers of lactic acid, carboxymethylcellulose (CMC), and polyvinyl alcohol (PVA). The expanded microspheres can be used as is (e.g., drug molecules (commonly referred to as active pharmaceutical ingredients) can be dispersed in the solvent of step a) and thus encapsulated or embedded in the resulting expanded microspheres), or the expanded microspheres can undergo further chemical modification so that drug molecules can be covalently attached to the outer surface of the microspheres (e.g., PVA-expanded microspheres can be further functionalized via chemical reaction with free alcohol (OH) groups on the polymer backbone). Related to the fifth aspect are the PVA and CMC expanded microspheres disclosed herein. To the inventors' knowledge, this is the first disclosure of expanded microspheres having a polyvinyl alcohol or carboxymethylcellulose polymer shell surrounding a hollow core (i.e., single-core expanded microspheres having a polyvinyl alcohol or carboxymethylcellulose shell). While U.S. Pat. No. 3,960,583 at first glance appears to disclose PVA microspheres, the inventors discovered that the PVA microspheres obtained by the method of U.S. Pat. No. 3,960,583 were of such poor quality that they would be unusable from a real-world practical standpoint (see Examples 37-38 below). This, combined with an essentially zero weight percent ash content, makes these expanded microspheres particularly promising candidates for use in the pharmaceutical sector, such as drug delivery vehicles (e.g., PVA is known to be a biocompatible polymer with low toxicity and excellent biodegradation properties).Thus, in a sixth aspect, the present disclosure relates to expanded microspheres comprising a polymeric shell surrounding a hollow core, the polymeric shell comprising or consisting of a polymer selected from polyvinyl alcohol or carboxymethyl cellulose, and the expanded microspheres having an ISO brightness value of at least 70 (ISO 2470-1:2016). This concept of drug delivery can be extended beyond the pharmaceutical sector to any technical field in which delivery of an active ingredient is desired, such as the agrochemical field (e.g., pesticides, plant nutrients [fertilizers], etc.), the cosmetic field (e.g., cosmetic actives, fragrances, etc.), and the household care field (e.g., antibacterial agents, air fresheners, fabric softeners, etc.). Thus, it is contemplated that the expanded microspheres of the present disclosure may further comprise an active ingredient encapsulated in the hollow core and / or embedded in the polymeric shell. Thus, in a seventh aspect, the present disclosure relates to the use of the expanded microspheres disclosed herein as an active ingredient delivery vehicle. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 illustrates the difference between hollow (single-core) expanded microspheres according to the present disclosure (A, polymer shell 1 and single core 2) and multicore microspheres not according to the present disclosure (B, polymer shell 1 and multiple cores 2). [Figure 2] FIG. 2 is an SEM image (103x magnification) of a prior art expanded microsphere having solid suspension particles on the outer surface of the microsphere (for comparison). [Figure 3] FIG. 3 is an SEM image (103x magnification) of expanded microspheres according to the present disclosure (present invention). [Figure 4] FIG. 4 shows microscopic images (10x magnification) of expanded microspheres (A) and non-expanded microspheres (B). DETAILED DESCRIPTION OF THE INVENTION

[0017] The term "expanded microsphere" has its well-established meaning in the art, i.e., a microsphere that has been thermally expanded to yield a single-core microsphere with a low density, uniform shape, polymer shell, and a single hollow core (as illustrated in FIG. 1A and shown in microscopy image FIG. 4A). For the avoidance of doubt, the term expanded microsphere does not encompass microspheres prepared by freeze-thaw or freeze-drying methods (which typically yield multi-core porous microspheres as illustrated in FIG. 1B, which resemble microspherical foams or sponges).

[0018] Glass transition temperature (T g The term ) has its usual technical meaning and can be estimated in advance using the Fox formula (Fox TG, Bull. Am. Phys. Soc. 1, p. 123 (1956)).

[0019]

number

[0020] In the formula, X N represents the mass fraction of each monomer N (wt% / 100), and Tg N is the glass transition temperature of the homopolymer of monomer N in Kelvin. Tg values ​​for homopolymers are listed, for example, in Ullmann's Encyclopedia of Industrial Chemistry, VCH, Weinheim, Vol. A21 (1992), p. 169. The glass transition temperature Tg of (co-)polymers and / or polymer blends can further be determined experimentally by differential scanning calorimetry (DSC), for example, by measuring the Tg (midpoint) of the copolymer according to ASTM D3418-82 (1988) e1. DSC is a well-established technique in the art for determining Tg and is the preferred method for measuring the Tg of polymers used in the methods of the present disclosure.

[0021] As used in this disclosure, "ISO brightness value" means the brightness value obtained for expanded microspheres when evaluated using the ISO standard ISO 2470-1:2016.

[0022] As used in this disclosure, "CIELAB value" means the CIELAB whiteness value (L, a, b) obtained for the expanded microspheres when evaluated using ISO standard ISO 11475:2017.

[0023] As used in this disclosure, the minimum inlet temperature of the drying gas (T inlet,min The term ) refers to the minimum temperature of the drying gas at the inlet of the spray dryer required to obtain expanded microspheres from the spray expansion process disclosed in this disclosure.

[0024] As used in this disclosure, the maximum inlet temperature of the drying gas (T inlet,max The term ) refers to the maximum temperature of the drying gas at the inlet of the spray dryer required to obtain expanded microspheres from the spray expansion method disclosed in this disclosure.

[0025] As used in this disclosure, the inlet temperature (T inlet The term ) refers to the temperature of the drying gas at the inlet of the spray dryer.

[0026] For the avoidance of doubt, "T inlet,max ≧T inlet ≧T inlet,min " means that the temperature of the drying gas at the inlet of the spray dryer must be equal to or greater than the calculated minimum temperature of the drying gas required to obtain expanded microspheres from the spray expansion method disclosed in this disclosure, and must be equal to or less than the calculated maximum temperature of the drying gas required to obtain expanded microspheres from the spray expansion method disclosed in this disclosure (i.e., T inlet is T inlet,max and T inlet,min (The temperature must be set between 0 and 100°C.)

[0027] For the avoidance of doubt, all temperatures referred to in this disclosure are in °C.

[0028] As used in this disclosure, the term "external surface of the polymeric shell" is used in its ordinary sense, i.e., to refer to the surface of the polymeric shell that is exposed to the surrounding external environment. For the avoidance of doubt, the surface of the polymeric shell 1 that is the "external surface" is indicated by arrow 3 in FIG. 1A. Arrow 4 in FIG. 1A indicates the internal surface of the polymeric shell 1 that is exposed to the hollow core 2.

[0029] As used in this disclosure, the term "free of particulate deposits from solid suspending agents" has its ordinary meaning, i.e., that particulate material from solid suspending agents is not disposed on the outer surface of the polymer shell of the expanded microspheres. The presence or absence of such particulate material on the outer surface of the polymer shell is determined by the presence or absence of particulate material from the solid suspending agents. 3 This can be easily determined by scanning electron microscopy at 5x magnification (e.g., 5.54kx magnification, field of view 100 µm; SEM HV 2 kV), and particles originating from solid suspensions can be easily identified by their characteristic "furry" appearance on the outer surface of the polymer shell (as shown in Figure 2), which is not observed when the expanded microspheres are free of such particles (as shown in Figure 3).

[0030] The term "solid suspending agent" is a well-known term in the art, widely used in the field of expandable microspheres, e.g., U.S. Pat. No. 3,615,972, European Patent No. 0,486,080, International Publication Nos. 2007,091,960, 2013,178,561, and 2019,043,235. In the field of expandable microspheres, the term "solid suspending agent" is synonymous with the term "dispersion stabilizer" and its equivalents, as used, for example, in International Publication No. 2019,124,233. For the avoidance of doubt, "solid suspending agent," as used in this disclosure, refers to the solid particulate stabilizer used in "Pickering emulsions." Examples of such "solid suspending agents" include salts, oxides and hydroxides of metals such as Ca, Mg, Ba, Zn, Ni and Mn (e.g., one or more of calcium phosphate, calcium pyrophosphate, magnesium pyrophosphate, calcium carbonate, magnesium hydroxide, magnesium oxide, barium sulfate, calcium oxalate, and hydroxide of zinc, nickel or manganese), starch, methylcellulose, hydroxypropylmethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, gum agar, silica, colloidal clay, oxides and hydroxides of aluminum or iron, etc. Colloidal silica is the primary solid suspending agent in the art of expandable microspheres.

[0031] The term "active ingredient" is a term well understood in the chemical arts used to refer to any ingredient that provides a desired effect. "Active ingredients" include, but are not limited to, active pharmaceutical ingredients, food chemical active ingredients (e.g., insecticides, phytonutrients, etc.), cosmetic active ingredients (e.g., fragrances, topical cosmetics, sunscreen UV actives, etc.), and household care active ingredients (e.g., antibacterial agents, antiviral agents, antimicrobial agents, air and / or fabric fresheners (e.g., flavor oils), fabric softeners, etc.).

[0032] The expanded microspheres of the present disclosure can be obtained by a spray drying method in which a polymer is dissolved in a suitable solvent (i.e., a solvent in which the polymer is soluble), optionally adding a blowing agent, and then spraying the resulting mixture into a drying apparatus to produce thermally expanded microspheres having a polymer shell surrounding a hollow core. Thus, a first aspect of the present disclosure relates to a method for preparing expanded microspheres, the method comprising: a) obtaining a composition comprising a polymer dissolved in a solvent, wherein the polymer has a glass transition temperature (T g ) b) spray drying the composition of step a) in a spray dryer, wherein the spray dryer has an inlet temperature (T inlet ) and wherein the inlet drying gas has a minimum inlet temperature (T inlet,min )but, T inlet,min =(T g *0.75), where the maximum inlet temperature of the drying gas (T inlet,max , °C) is T inlet,max =(T g *2.2) In the formula, T inlet,max ≧T inlet ≧T inlet,min and step b) wherein

[0033] For the avoidance of doubt, T g , T inlet , T inlet,min , and T inlet,max The unit is °C.

[0034] In this first embodiment, the minimum temperature of the drying gas at the spray dryer inlet (T inlet,min ) is preferably T inlet,min =(T g *0.80), more preferably T inlet,min =(T g *0.85), most preferably T inlet,min =(T g *0.90).

[0035] In this first embodiment, the maximum temperature of the drying gas at the spray dryer inlet (T inlet,max ) is preferably T inlet,max =(T g *2.1), more preferably T inlet,max =(T g *2).

[0036] In a second aspect, the method of the present disclosure uses a foaming agent, and thus the second aspect relates to a method for preparing expanded microspheres, the method comprising: a) obtaining a composition comprising a polymer dissolved in a solvent, wherein the polymer has a glass transition temperature (T g ), wherein the composition further comprises a blowing agent; b) spray drying the composition of step a) in a spray dryer, wherein the spray dryer has an inlet temperature (T inlet ) and wherein the inlet drying gas has a minimum inlet temperature (T inlet,min )but, T inlet,min =(T g *0.60), The maximum inlet temperature of the drying gas (T inlet,max , °C) is T inlet,max =(T g *2.2), In the formula, T inlet,max ≧T inlet ≧T inlet,min and The boiling point of the blowing agent (T BABP )but, T BABP ≦(T inlet and step b) wherein the temperature is +20°C.

[0037] In this second embodiment, the minimum temperature of the drying gas at the spray dryer inlet (T inlet,min ) is preferably T inlet,min =(T g *0.65), more preferably T inlet,min =(T g *0.75).

[0038] In this second embodiment, the maximum temperature of the drying gas at the spray dryer inlet (T inlet,max ) is preferably T inlet,max =(T g *2.1), more preferably T inlet,max =(T g *2).

[0039] T BABP≦ (T inlet +10℃), and T BABP ≦T inlet It is more preferable that:

[0040] In principle, the spray drying apparatus for carrying out the spray drying method is not limited, and any conventional and commercially available spray drying apparatus can be used for the spray drying method. A typical spray drying apparatus suitable for the method described herein comprises a drying chamber equipped with a nozzle, a drying gas inlet, and an outlet connecting the drying chamber to a cyclone. The liquid to be atomized is sprayed into the drying chamber, usually in combination with the atomizing gas, through the nozzle, which is usually located at the top of the atomizing chamber (but may be located in any other part of the spray dryer). In the drying chamber, the atomized liquid is dried by the drying gas supplied into the atomizing chamber through the drying gas inlet. The drying gas inlet may be located, for example, immediately adjacent to the nozzle. The atomized liquid dries and forms particles. The resulting particles are then supplied to the cyclone together with the drying gas through the drying chamber outlet, which is usually located in the bottom area of ​​the drying chamber. In the cyclone, the particles are separated from the drying air. The drying air may be further filtered to remove any residual particles from the drying air.

[0041] One suitable spray drying apparatus for carrying out the spray drying process is a Büchi Mini Spray Dryer B-290, available from Büchi / Switzerland.

[0042] In step a), the order in which the polymer, solvent, and optional blowing agent are added is not limited and any order can be selected.

[0043] However, in a preferred embodiment, in the method for producing expanded microspheres, the polymer is first mixed with a solvent and, optionally, a blowing agent is added to the mixture.

[0044] Mixing of the polymers can be carried out at ambient temperature, although temperatures ranging from 5 to 75° C. can be used. Mixing is carried out until the polymer is completely dissolved in the solvent.

[0045] In embodiments, the mixture of polymer and solvent can be allowed to stand or stirred for a period of time, such as 1 to 100 hours, or 2 to 50 hours, which can be carried out at a temperature ranging from 10 to 95°C, such as 20 to 90°C.

[0046] In a further step, an optional blowing agent is added to the polymer and solvent mixture, and this mixing step can be carried out at ambient temperature, although temperatures in the range of 5 to 75°C can be used.

[0047] After adding the blowing agent to the mixture of polymer and solvent, the mixture thus obtained may be further stirred for a period of time, for example, 1 to 100 hours, or 2 to 50 hours, at a temperature ranging from 10 to 95°C, for example, from 20 to 90°C.

[0048] The mixture containing the polymer, solvent, and optional blowing agent is then sprayed into a drying apparatus to produce the thermally expandable microspheres described in this disclosure.

[0049] The optional propellant gas sprayed through the nozzle together with the liquid to be atomized is not particularly limited and may be any suitable propellant gas known to those skilled in the art. For example, the propellant gas may be selected from nitrogen, carbon dioxide, (pressurized) air, and noble gases (such as argon). Preferably, in the method for fabricating expanded microspheres as described in the present disclosure, a propellant gas is used, and more preferably, the propellant gas is nitrogen.

[0050] The dry gas is not particularly limited and may be any suitable dry gas known by those skilled in the art. For example, the dry gas may be selected from nitrogen, carbon dioxide, (pressurized) air, and noble gases (such as argon). The dry gas is preferably nitrogen.

[0051] Further process parameters for operating the spray drying apparatus, such as the atomizing gas flow rate, the inlet temperature of the drying gas as it enters the drying chamber, the feed rate of the liquid to be atomized, and the aspirator speed and atomizer speed for circulating the drying gas within the spray drying apparatus, can be readily selected by one skilled in the art.

[0052] It has been unexpectedly discovered that using the methods disclosed in the present disclosure, expanded microspheres can be successfully prepared using a wide variety of polymer types, ranging from entirely synthetic polymers (e.g., polystyrene, polyvinyl alcohol) to entirely bio-derived polymers (e.g., polylactic acid). As such, the polymer is not considered to limit the scope of the method, and thus, it is contemplated that any polymer component known to those skilled in the art can be used as the polymer in the methods described herein. Polymer blends are also contemplated, and thus, as used in this disclosure, the term "polymer" encompasses a single polymer as well as a blend of two or more polymers. When a polymer blend is used, T inlet T used to calculate g , the minimum is the T of each polymer g Rather than calculating the T individually, the experimentally measured T of the blend is used. gSuitable polymers for use in the present disclosure include, but are not necessarily limited to, one or more polymers selected from the group consisting of polymers obtained by polymerizing one or more vinyl monomers, lignin, polysaccharides, polysaccharide derivatives, polyesters, polyethers, polyacids, polyols, polyalkenes, polyanhydrides, or any combination thereof. In some embodiments, the one or more vinyl monomers are selected from the group consisting of vinylidene chloride, acrylonitrile, methyl methacrylate, methyl acrylate, methacrylonitrile, methacrylic acid, acrylic acid, styrene, vinyl alcohol, vinyl acetate, and combinations thereof. In some embodiments, the lignin is selected from the group consisting of kraft lignin, lignosulfonates, lignin / hemicellulose blends, and lignosulfonate / hemicellulose blends. In some embodiments, the polysaccharides and polysaccharide derivatives may be selected from the group consisting of cellulose, cellulose derivatives, chitosan, hemicellulose, and alginates. Preferred cellulose derivatives include cellulose esters and cellulose ethers. In some embodiments, the polymer is selected from kraft lignin, lignosulfonate, lignosulfonate / hemicellulose blends, cellulose acetate, cellulose acetate propionate, carboxymethylcellulose, homopolymers or copolymers of styrene, vinyl acetate, lactic acid, glycolic acid, vinyl alcohol, polyacid, acrylic acid, or combinations thereof. In some embodiments, the polymer is polyvinyl alcohol obtained by hydrolysis of polyvinyl acetate. While the degree of hydrolysis is not considered a limiting factor, in preferred embodiments, the polyvinyl alcohol has a degree of hydrolysis of at least 50%, preferably at least 70%, preferably at least 80%, e.g., 50-100%, 70-100%, or 80-100%. Any combination of the aforementioned polymer components can be used. Such combinations also include copolymers of any of the aforementioned polymer components.

[0053] To facilitate the spray expansion methods disclosed herein, the one or more polymers preferably have a number average molecular weight (Mn) in the range of 500 to 700,000, e.g., 1,000 to 500,000, and preferably 2,000 to 400,000. In some embodiments, it is, for example, 1,000 to 100,000, e.g., 1,000 to 80,000, or 2,000 to 50,000. For the avoidance of doubt, Mn is measured by gel permeation chromatography (GPC) using polystyrene standards.

[0054] Determining an appropriate solvent for dissolving a given polymer can be accomplished using routine solvent screening and / or simple predictive models, such as comparing the Hildebrand solubility parameters (δ) of the polymer and solvent (e.g., polystyrene has a solubility parameter (δ) of 9.1 cal). 1 / 2 cm -3 / 2 and ethyl acetate also has a δ value of 9.1 cal 1 / 2 cm -3 / 2 Therefore, using the Hildebrand solubility parameter, (One can predict that ethylenediaminetetraacetic acid (ETA) is likely to be a good solvent for polystyrene, and indeed it is.) Determining the appropriate solvent for dissolving a given polymer is well within the routine capabilities of one skilled in the art. The term "solvent" should be understood to include aqueous and organic solvents, as well as mixtures thereof (e.g., water / alcohol mixtures).

[0055] The solvent may be, for example, water or an organic solvent, such as one selected from organic solvents having one or more functional groups selected from, for example, esters, amides, aldehydes, ketones, alcohols (including glycols), and ethers, e.g., having 3 to 12 carbon atoms. In embodiments, the esters, ketones, and ethers may be part of a cyclic structure. Further examples include haloalkanes having 1 to 6 carbon atoms and halo-carboxylic acids having 1 to 6 carbon atoms, where the halogen is selected from fluorine, chlorine, bromine, and iodine. The solvent may also be a mixture of water and an organic solvent, e.g., any of the organic solvents described above.

[0056] Examples of organic solvents that can be used include ethyl acetate, methyl formate, ethyl formate, methyl acetate, n-propyl formate, isopropyl formate, n-propyl acetate, isopropyl acetate, isobutyl acetate, n-butyl acetate, n-pentyl formate, isopentyl formate, n-pentyl acetate, isopentyl acetate, ethyl propionate, isobutyl isobutyrate, n-butyl propionate, ethyl 3-ethoxypropionate, 2-ethylhexyl acetate, acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, methyl isoamyl ketone, methyl n-amyl ketone, mesityl oxide, acetophenone, cyclohexanone, diethyl phthalate, ethyl lactate, benzyl acetate, butyrolactone, acetylacetone, methylcyclohexanone, benzaldehyde, diisobutyl ketone, diacetone alcohol, ethylene glycol, glyceryl-α-monochlorohydrin, propylene glycol, glycol ethers (e.g., Examples of suitable solvents include propylene glycol monomethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono-n-butyl ether, propylene glycol mono-tert-butyl ether, propylene glycol monopropyl ether, and propylene glycol monobutyl ether, glycol ether esters (e.g., ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, and ethylene glycol diacetate), n-propyl alcohol, isopropyl alcohol, n-butanol, sec-butanol, isobutanol, benzyl alcohol, diisopropyl ether, dimethoxymethane, dimethoxyethane, 1,4-dioxane, 1,3-dioxolane, tetrahydrofuran, anisole, phenetole, and dimethylformamide. Other examples of suitable solvents include dimethyl sulfoxide, toluene, xylene, n-methyl-2-pyrrolidone, methylene chloride, chloroform, carbon tetrachloride, trichloroacetic acid, methylene bromide, methylene iodide, trichloroethylene, and tetrachloroethylene. The organic solvent may be a mixture of two or more solvents.When the solvent is a mixture of two or more organic solvents, one of the solvents is preferably acetone, hi embodiments, the acetone is mixed with an alcohol, such as methanol or ethanol.

[0057] In some embodiments, the solvent is a mixture of water and an organic solvent. In such embodiments, the mixture preferably contains water in an amount of 50% by weight or less, e.g., 40% by weight or less, 30% by weight or less, or 20% by weight or less. In such embodiments, the mixture more preferably contains water in an amount of at least 1% by weight, such as at least 2% by weight or at least 5% by weight, based on the total weight of the solvent.

[0058] In particularly preferred embodiments, the solvent is selected from one or more of water, methanol, ethanol, ethyl acetate, and acetone. More preferably, the solvent comprises water, methanol, ethanol, ethyl acetate, or acetone. In certain preferred embodiments, the solvent comprises acetone. In some embodiments, the solvent comprises a mixture of at least two solvents, preferably selected from the group consisting of water, methanol, ethanol, ethyl acetate, acetone, and combinations thereof. In some embodiments, the solvent comprises acetone and water, or acetone and ethanol.

[0059] Typically, the polymer content in the spray-drying mixture is typically in the range of 0.1 to 50 wt. %. In some embodiments, it can be in the range of 1 to 40 wt. %, for example, in the range of 5 to 35 wt. %. The wt. % is based on the total weight of the spray-drying mixture.

[0060] The amount of optional blowing agent(s) in the spray-drying mixture typically ranges from 0.5 to 50% by weight, and in embodiments can range from 0.5 to 40% by weight, such as from 1 to 30% by weight, from 3 to 25% by weight, or even from 5 to 25% by weight.

[0061] The amount of solvents totals 100% by weight. The amount of organic solvent is preferably at least 30% by weight, more preferably at least 40% by weight, and even more preferably at least 50% by weight. The weight percentages are based on the total weight of the spray-drying mixture.

[0062] When a blowing agent is used in the method, the blowing agent is preferably one or more low-boiling hydrocarbons or halogenated hydrocarbons that are liquid at room temperature but vaporize upon heating. For the avoidance of doubt, the blowing agent is different from the solvent used to dissolve the polymer. In this regard, the blowing agent(s) generally have a boiling point above 25°C at 5.0 bara or above 25°C at 3.0 bara, where "bara" stands for "bar-absolute." In some embodiments, they have a boiling point above 25°C at atmospheric pressure (1.013 bara). Typically, they have a boiling point below 250°C (e.g., below 220°C or below 200°C) at atmospheric pressure. They are preferably inert and do not react with the polymer. Boiling points at elevated pressures can be calculated using the Clausius-Clapeyron equation.

[0063] Examples of blowing agents include alcohols, dialkyl ethers, alkanes, and halocarbons (e.g., chlorocarbons, fluorocarbons, or chlorofluorocarbons). In embodiments, the alcohol comprises a C2-C8 alcohol, such as a C2-C6 alcohol or a C2-C4 alcohol. In embodiments, the dialkyl ether comprises two alkyl groups each selected from a C2-C5 alkyl group. In embodiments, the alkane comprises a C4-C 12 In some embodiments, the haloalkane is a C-C alkane. 10The alkyl or haloalkane group in the alcohol, dialkyl ether, alkane, and haloalkane may be linear, branched, or cyclic. One or more blowing agents may be used singly or in combination.

[0064] In some embodiments, for environmental reasons, the one or more blowing agents are selected from alcohols, alkyl ethers, and alkanes, and in further embodiments, the one or more blowing agents are selected from alcohols and alkanes, preferably alcohols. Haloalkanes are preferably avoided due to their potential ozone depletion properties and also due to their generally higher global warming potential.

[0065] Examples of suitable blowing agents that can be used include methanol, ethanol, n-propanol, isopropanol, n-butanol, tert-butyl alcohol, n-pentanol, isopentanol, n-hexanol, isohexanol, heptanol, isoheptanol, octanol, isooctanol, n-pentane, isopentane, neopentane, cyclopentane, cyclohexane, n-butane, isobutane, isohexane, neohexane, heptane, isoheptane, octane, isodecane, and isododecane. In a preferred embodiment, the blowing agent is selected from a C2-C8 alcohol, such as a C2-C6 alcohol or a C2-C4 alcohol. In a more preferred embodiment, the blowing agent comprises a blowing agent selected from isooctane, isohexane, isopentane, tert-butyl acetate, butyl acetate, methyl tert-butyl ether, tert-butyl alcohol, and combinations thereof.

[0066] It has been found that the above-described method can produce expanded microspheres comprising a polymer shell surrounding a hollow core, the outer surface of which is free of particulate deposits derived from solid suspending agents. In other words, the present disclosure provides expanded microspheres obtainable by a method that does not use a solid suspending agent, wherein the expanded microspheres comprise a polymer shell surrounding a hollow core. Furthermore, it has been found that when using a polymer that is essentially white (i.e., an essentially uncolored polymer, such as, but not limited to, PVA, PLA, CMC, cellulose acetate, cellulose acetate propionate, polymethyl methacrylate, polystyrene, etc.), substantially white expanded microspheres can be obtained in a cyclone. In this regard, the obtained expanded microspheres have an ISO brightness value of at least 70 (ISO 2470-1:2016). Preferably, the expanded microspheres have an ISO brightness value of at least 80 (ISO 2470-1:2016). Preferably, the expanded microspheres have a CIELAB whiteness index, where the "L" value is at least 90, the "a" value is less than ±5, preferably less than ±2, and the "b" value is less than ±5, preferably less than ±2. Thus, preferred embodiments of expanded microspheres comprise a polymeric shell surrounding a hollow core, the outer surface of the polymeric shell being free of particulate deposits from solid suspending agents, and the expanded microspheres have an ISO brightness value of at least 70 (ISO 2470-1:2016). Another preferred embodiment of an expanded microsphere comprises a polymeric shell surrounding a hollow core, the exterior surface of the polymeric shell being free of particulate deposits from a solid suspending agent, the expanded microsphere having an ISO luminance value (ISO 2470-1:2016) of at least 70, the expanded microsphere having a CIELAB "L" value of at least 90, the expanded microsphere having a CIELAB "a" value of less than 5, and the expanded microsphere having a CIELAB "b" value of less than 5 (ISO 11475:2017).

[0067] Preferably, the polymer shell of the expanded microspheres comprises one or more polymers selected from the group consisting of kraft lignin, lignosulfonates, lignin / hemicellulose blends, lignosulfonate / hemicellulose blends, cellulose acetate, cellulose acetate propionate, carboxymethyl cellulose, a homopolymer or copolymer of styrene, a homopolymer or copolymer of vinyl acetate, a homopolymer or copolymer of acrylic acid, a homopolymer or copolymer of methacrylic acid, a homopolymer or copolymer of methyl acrylate, a homopolymer or copolymer of methyl methacrylate, a homopolymer or copolymer of lactic acid and a homopolymer or copolymer of glycolic acid, a homopolymer or copolymer of vinyl alcohol, or a combination thereof.

[0068] Expanded microspheres obtained by the methods disclosed in this disclosure have been found to consistently have particle densities less than 325 g / L. Low particle density is beneficial because it reduces weight in end use applications compared to heavy fillers such as calcium carbonate glass microspheres.

[0069] Furthermore, the expanded microspheres consistently had a bulk density of less than 100 g / L. Preferred expanded microspheres of the present disclosure have a bulk density of less than 80 g / L.

[0070] Thus, the expanded microspheres of the present disclosure represent an excellent low-density filler material for applications such as paints and coatings, cultured marble, UCC (automotive underbody coatings), polyester putty, porous ceramics, mining explosives, sealants, and adhesives.

[0071] The volume average particle size (diameter) of the expanded microspheres, i.e., the D(0.5) value, is typically in the range of 1 to 500 μm, e.g., in the range of 5 to 400 μm, or in embodiments, in the range of 10 to 300 μm, or even in the range of 20 to 200 μm. The volume average particle size can be measured by any suitable means, such as laser diffraction.

[0072] Preferred expanded microspheres of the present disclosure have an ash content of less than 1 wt%, preferably less than 0.5 wt%, preferably less than 0.1 wt%, preferably less than 0.01 wt%, and most preferably less than 0.001 wt%, e.g., 0 wt%. Measuring ash content is routine in the art and, for the present disclosure, can be measured by thermogravimetric analysis of the expanded microspheres.

[0073] As previously mentioned, the present disclosure also provides expanded microspheres comprising a polymeric shell surrounding a hollow core, the polymeric shell being formed from polyvinyl alcohol. This, combined with the essentially zero ash content, makes these expanded microspheres particularly promising candidates for use in the pharmaceutical sector, such as as drug delivery vehicles (PVA is known to be a biocompatible polymer with low toxicity and excellent biodegradability properties). The inventors already have a general proof-of-concept for this application, having found through initial research that active ingredients can be successfully incorporated into microspheres by including them in the polymer solution of step a) (successfully incorporated into microspheres comprising a eucalyptol-fragrance-cellulose acetate polymeric shell). This proof-of-concept finding indicates that the expanded microspheres disclosed in this disclosure can be used as delivery vehicles for a wide range of active ingredients across a wide range of technical fields, including, but not limited to, the pharmaceutical, agricultural, cosmetic, and home care sectors.

[0074] It should be noted that various elements of the present disclosure, including but not limited to the preferred ranges of various parameters, can be combined unless they are mutually exclusive. [Example]

[0075] The present disclosure is illustrated by, but not limited to, the following examples.

[0076] General synthesis method: Polymer solutions were prepared by dissolving the polymer in a suitable solvent by stirring overnight at room temperature using a magnetic stirrer. In examples using a blowing agent, the blowing agent was added to the polymer / solvent mixture and stirred overnight at room temperature using a magnetic stirrer. Each component and its relative amount (in weight percent, provided in parentheses) is shown in Table 1.

[0077] The mixture thus obtained was then spray-dried using a Büchimini Spray Dryer B-290. Nitrogen was used as the atomizing gas at a feed rate of 238-397 L / h (depending on the solvent). The feed rate of the mixture to be spray-dried was 4-13 ml / min (depending on the solvent). The temperature of the drying gas at the inlet is shown in Table 1. The aspirator speed was 38 m / s. 3 It was / o'clock.

[0078] The dried solids were collected from the bottom of the cyclone and analyzed.

[0079] Microscopic evaluation of the microspheres collected from the bottom of the cyclone was performed using a Leica DM1000 microscope (10x magnification). When viewed under the microscope, expanded microspheres are large, uniformly shaped (i.e., essentially perfectly spherical), substantially transparent (with an occluding polymer shell), and generally well-dispersed (as shown in Figure 4A). Unexpanded microspheres, viewed under the microscope, are essentially the opposite: small, irregularly shaped, substantially opaque, and generally clumped together (opacity is a function of clumping, as shown in Figure 4B). This qualitative analysis is more than sufficient to determine whether the microspheres collected from the bottom of the cyclone are expanded. That said, experimental studies have found that expanded microspheres can be distinguished from unexpanded microspheres by measured particle density. Microspheres confirmed as expanded by microscopic evaluation consistently had measured particle densities below 325 g / L.

[0080] Density was measured by adding the sample to a vial of known volume up to 50% by volume. The weight of the sample was recorded and, combined with the known volume of the vial, the bulk density could be calculated. An inert medium with a known density (usually isooctane) was then added without affecting the sample in any way, and the vial was completely filled, ensuring that the mixture was carefully mixed and no air bubbles were present. By measuring the weight of the added inert medium, the particle density of the product could be calculated using the following formula:

[0081]

number

[0082] [Table 1-1]

[0083] [Table 1-2]

[0084] [Table 1-3]

[0085] Shaded examples in Table 1 are not according to the present disclosure. CA = cellulose acetate, Mn 30,000 g / mol CAP = cellulose acetate propionate, Mn 25,000 g / mol PS = recycled polystyrene PLA = Polylactic acid, Mn 8,826g / mol PVA = Polyvinyl alcohol, Mn 13,000-23,000g / mol, degree of hydrolysis = 87-89% CMC = carboxymethyl cellulose PMMA = Polymethyl methacrylate, Mn 35,000 g / mol LS = lignosulfonate IB = isobutane, bp -12°C IP = isopentane, bp 28°C IO = isooctane, bp 99°C IH = Isohexane, bp 60°C t-BuOH = tert-butanol, bp 82℃ Acetone / water = 94 / 6 acetone / water

[0086] A commonly observed trend was that when no blowing agent was used, T was used to ensure that the expanded microspheres were obtained from the bottom of the cyclone. inlet T g In other words, the minimum gas inlet temperature when no blowing agent is used must be at least 75% of the 、 T inlet,min is T g *0.75. inlet T -inlet,min If it is less than 、 The microspheres obtained from the bottom of the cyclone were dense, small, non-uniformly shaped unexpanded microspheres that showed a tendency to clump together (Figure 4B: Microscopic image of unexpanded microspheres obtained from the bottom of the cyclone in Example 8. Reference Figure 4A: Microscopic image of less dense, larger, more uniformly dispersed, uniformly shaped (spherical) expanded microspheres obtained from the bottom of the cyclone in Example 13 with no significant tendency to clump).

[0087] If a foaming agent is used, ensure that the expanded microspheres are obtained from the bottom of the cyclone (i.e., T inlet,min =T g *0.60), T inlet T g The exceptions were Examples 17 and 22, where the inlet gas temperature 、 T inlet is the calculated T inlet,min (T g*0.60), no expanded microspheres were obtained. inlet (T BABP 99℃, T inlet This is due to the blowing agent isooctane, which has a boiling point substantially higher than 70° C. (Example 17) and 50° C. (Example 22). By increasing the temperature (e.g., Example 18) or switching to a blowing agent with a lower boiling point (isopentane, Examples 22-23; isopentane + isobutane, Examples 24-25), expanded microspheres could be obtained from the bottom of the cyclone under the same spray dryer settings as in Examples 17 and 22, respectively.

[0088] An unexpected result was that a wide variety of polymer types could be successfully used with this method, ranging from fully synthetic polymers (polystyrene, polyvinyl alcohol, PMMA) to bio-derived polymers (CA, CAP, PLA, CMC). It was also discovered that blends of polymers could be successfully used (Examples 35-36; 4:1 blend (wt / wt) lignosulfonate:polyvinyl alcohol).

[0089] A further unexpected result was the ability to prepare expanded polyvinyl alcohol microspheres. To the inventors' knowledge, this is the first example of expanded microspheres with a polyvinyl alcohol polymer shell surrounding a hollow core (i.e., single-core expanded microspheres with a polyvinyl alcohol shell). This, combined with the essentially zero ash content, makes these expanded microspheres particularly promising candidates for use in the pharmaceutical sector, such as as drug delivery vehicles (PVA is known to be a biocompatible polymer with low toxicity and excellent biodegradation properties).

[0090] Thermal Limit While attempting to further develop the range of particle and bulk density profiles of expanded microspheres obtainable by the methods of the present disclosure, it was discovered that there is an upper limit to the inlet temperature of the inlet drying gas, at which point the inlet drying gas temperature should be approximately 2.2*T gAbove this temperature, the quality of the expanded microsphere product obtained in the cyclone deteriorates rapidly and significantly, and in some cases, can even clog / plug the spray drying equipment, resulting in no product in the cyclone and rendering the equipment unusable until it undergoes intensive cleaning methods (clearly problematic from a productivity standpoint, and the need to avoid unnecessary equipment downtime). Thus, the maximum inlet temperature of the drying gas (T inlet,max , °C) is approximately T g *2.2, preferably about T g *2.1, more preferably about T g *2. This specific example includes >2.2*T g These include repeats of Examples 27-29 (PVA) and Examples 23-24 (PLA) carried out at an inlet gas temperature of 1000 rpm, the results of which are shown in Table 2.

[0091] [Table 2]

[0092] T inlet,max ≧T inlet ≧T inlet,min The product obtained in the cyclone in this case was substantially white, low density expanded microspheres, i.e., excellent quality expanded microspheres suitable for many applications where substantially white expanded microspheres are required. (Note: Examples using inherently colored polymers, i.e., lignosulfonates, yield otherwise excellent microspheres that are not white due to the inherent coloration of the polymer, i.e., the coloration is not caused by the process. These off-white microspheres are useful for other purposes.)

[0093] Table 3 illustrates the differences between expanded microspheres according to the present disclosure and expanded microspheres not according to the present disclosure.

[0094] [Table 3]

[0095] Expanded PVA microspheres of the present disclosure (Example 29, T inlet =T g *2) has ISO brightness and CIELAB values ​​close to perfect white, while expanded PVA microspheres (Example 37; T inlet =T g *2.35) had ISO brightness and CIELAB values ​​that clearly indicated significant yellowing (the combination of a low ISO brightness of 44.22, a relatively low L [whiteness] value of 83.32, and a positive (+) "b" value of 20.32 indicated significant yellowing, which was confirmed by visual inspection of the microspheres).

[0096] As used herein, unless expressly indicated otherwise, the word "or" is used to mean an operator that returns a true value when either or both stated conditions are met, as opposed to the operator "exclusive or," which requires that only one of the stated conditions be met. The word "comprising" is used in the sense of "including," not "consisting of." All prior teachings acknowledged above are incorporated herein by reference. Acknowledgment herein of any previously published document should not be construed as an admission or representation that the teaching was general knowledge in Europe or elsewhere as of the date hereof.

Claims

1. 1. A method for preparing expanded microspheres, comprising: a) obtaining a composition comprising a polymer dissolved in a solvent, said polymer having a glass transition temperature (T ｇ , °C); b) spray drying the composition of step a) in a spray dryer, wherein the spray dryer has an inlet temperature (T ｉｎｌｅｔ , °C), and ｉｎｌｅｔ，ｍｉｎ , °C), T ｉｎｌｅｔ，ｍｉｎ =(T ｇ *0.75)、 The maximum inlet temperature of the drying gas (T ｉｎｌｅｔ，ｍａｘ , °C), T ｉｎｌｅｔ，ｍａｘ =(T ｇ *2.2) In the ceremony, T ｉｎｌｅｔ，ｍａｘ ≧T ｉｎｌｅｔ ≧T ｉｎｌｅｔ，ｍｉｎ and

2. The minimum temperature (T ｉｎｌｅｔ--，ｍｉｎ )but, T ｉｎｌｅｔ，ｍｉｎ ≧(T ｇ *0.90) and / or the maximum inlet temperature of the drying gas (T ｉｎｌｅｔ，ｍａｘ , °C), T ｉｎｌｅｔ，ｍａｘ = (T ｇ *2) The method according to claim 1.

3. 1. A method for preparing expanded microspheres, comprising: a) obtaining a composition comprising a polymer dissolved in a solvent, said polymer having a glass transition temperature (T ｇ , °C), wherein the composition further comprises a blowing agent; b) spray drying the composition of step a) in a spray dryer, wherein the spray dryer has an inlet temperature (T ｉｎｌｅｔ , °C), and ｉｎｌｅｔ，ｍｉｎ , °C), T ｉｎｌｅｔ，ｍｉｎ =(T ｇ *0.60)、 The maximum inlet temperature of the drying gas (T ｉｎｌｅｔ，ｍａｘ , °C), T ｉｎｌｅｔ，ｍａｘ =(T ｇ *2.2) In the formula, Ｔｉｎｌｅｔ，ｍａｘ ≧T ｉｎｌｅｔ≧ T ｉｎｌｅｔ，ｍｉｎ , The blowing agent boiling point temperature (T ＢＡＢＰ、 °C), T ＢＡＢＰ ≦(T ｉｎｌｅｔ +20°C).

4. The minimum temperature (T ｉｎｌｅｔ--、最小 )but, T ｉｎｌｅｔ，ｍｉｎ =(T ｇ *0.75) and / or the maximum inlet temperature of the drying gas (T ｉｎｌｅｔ，ｍａｘ , °C), T ｉｎｌｅｔ，ｍａｘ = (T ｇ *2) The method according to claim 3.

5. The method according to any one of claims 1 to 4, wherein the polymer is a polymer obtained by polymerizing one or more vinyl monomers, lignin, ・Polysaccharides, ・Polysaccharide derivatives, ·polyester, polyether, Polyacids, polyols, - polyalkenes, Polyhydric anhydrides, - and any combination thereof.

6. 6. The method of any one of claims 1 to 5, wherein the polymer is selected from the group consisting of lignosulfonates, lignin / hemicellulose blends, lignosulfonate / hemicellulose blends, cellulose acetate, cellulose acetate propionate, carboxymethyl cellulose, a homopolymer or copolymer of styrene, a homopolymer or copolymer of vinyl acetate, a homopolymer or copolymer of acrylic acid, a homopolymer or copolymer of methacrylic acid, a homopolymer or copolymer of methyl acrylate, a homopolymer or copolymer of methyl methacrylate, a homopolymer or copolymer of lactic acid, a homopolymer or copolymer of glycolic acid, a homopolymer or copolymer of vinyl alcohol, or a combination thereof.

7. The polymer is from about 500 to about 700,000 g 7. The method according to claim 1, wherein the polymer has a number average molecular weight of 1 / mol (measured by GPC, polystyrene standard).

8. 8. The method of any one of claims 3 to 7, wherein the blowing agent is one or more hydrocarbons or halogenated hydrocarbons having a boiling point above 25°C at atmospheric pressure.

9. 1. An expanded microsphere comprising a polymeric shell surrounding a hollow core, wherein the exterior surface of the polymeric shell is free of particulate deposits from a solid suspending agent, and wherein the expanded microsphere has an ISO brightness value (ISO 2470-1:2016) of at least 70.

10. 10. The expanded microsphere of claim 9, wherein the polymer shell comprises: a polymer obtained by polymerizing one or more vinyl monomers, ・Polysaccharide ・Polysaccharide derivatives, Polyhydric anhydrides, ·polyester, polyether, Polyacids, polyols, - polyalkenes, Expanded microspheres comprising or consisting of a polymer selected from the group consisting of: and any combination thereof.

11. 1. An expanded microsphere comprising a polymeric shell surrounding a hollow core, wherein the outer surface of the polymeric shell is free of particulate deposits from a solid suspending agent, and wherein the polymeric shell comprises or consists of a polymer selected from lignin or a lignin derivative.

12. 12. The expanded microsphere of claim 11, wherein the lignin derivative is a lignosulfonate.

13. 1. An expanded microsphere comprising a polymeric shell surrounding a hollow core, the polymeric shell comprising or consisting of a polymer selected from polyvinyl alcohol or carboxymethyl cellulose, the expanded microsphere having an ISO brightness value (ISO 2470-1:2016) of at least 70.

14. The expanded microsphere of any one of claims 9 to 13, further comprising an active ingredient encapsulated in the hollow core and / or embedded in the polymeric shell.

15. 15. The expanded microsphere of any one of claims 9 to 14, wherein the expanded microsphere has a particle density of less than 325 g / L.

16. The expanded microspheres of any one of claims 9 to 15, wherein the expanded microspheres have a bulk density of less than 100 g / L.

17. Use of expanded microspheres obtainable by the method according to any one of claims 1 to 8 or by the method according to any one of claims 9 to 16 as an active ingredient delivery vehicle.

18. Use of expanded microspheres obtainable by the method according to any one of claims 1 to 8 or by the method according to any one of claims 9 to 16 in the manufacture of porous ceramic products, in polishing polishing pads for Si wafers or as sacrificial moulds in mortars, such as dry mix mortars.

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