Method for Producing Thermosetting Polymer Foams and Polymer Foams

Abstract

The present invention relates to a method for producing a thermosetting polymer foam, the method comprising the steps of subjecting a reaction mixture comprising a surfactant and a prepolymer to an agitation step, the prepolymer being obtained by polymerization of a combination of a polyol monomer and a polycarboxylic acid monomer, a combination of a plurality of hydroxycarboxylic acid monomers, or a combination of a polyol monomer, a polycarboxylic acid monomer and a hydroxycarboxylic acid monomer, the prepolymer having a degree of polymerization between 0.1 and 0.8, and subjecting the reaction mixture thus obtained to a curing step in the absence of agitation to obtain a thermosetting polymer foam. A thermosetting polymer foam is also claimed, the thermosetting polymer foam comprising a polymer obtained by polymerization of a combination of a polyol monomer and a polycarboxylic acid monomer, a combination of a plurality of hydroxycarboxylic acid monomers, or a combination of a polyol monomer, a polycarboxylic acid monomer, and a hydroxycarboxylic acid monomer, and an amphoteric surfactant, the total concentration of said surfactant being in the range of 0.1-6 wt.%, and the polymer having a degree of polymerization of at least 0.8 and a density of at most 850 grams / liter.

Description

[Technical field]

[0001] The present invention relates to a method for producing a thermosetting polymer foam, the method comprising using in the liquid phase a combination of a polyol monomer and a polycarboxylic acid monomer, a combination of multiple hydroxycarboxylic acid monomers, or a combination of a polyol monomer, a polycarboxylic acid monomer, and a hydroxycarboxylic acid monomer. [Background technology]

[0002] Thermoset polymer foams are known in the art.

[0003] International Publication No. WO2012052385 describes a process for producing glycerol tricarboxylic acid polyester foam, comprising the steps of combining glycerol and tricarboxylic acid in a liquid phase to provide a reaction mixture, and maintaining the reaction mixture at a temperature of 80° C. to 130° C. from the start of the reaction until at least 90% conversion is obtained.

[0004] International Publication No. WO2013121033 describes a method of making a glycerol tricarboxylic acid polyester foam, comprising combining glycerol and a tricarboxylic acid to provide a liquid reaction mixture, and contacting the reaction mixture with a substrate under polymerization conditions, wherein the substrate has a top layer comprising one or more of a metal, a metal oxide, and a metal halide.

[0005] International Publication WO2016207517 describes a method for producing polyester foam, in which a polyol component including at least one member selected from glycerol, diglycerol, and glycerol oligomers, a polyacid component, such as the above polyacid component including citric acid, a surfactant, and an esterification catalyst are combined, and the mixture is heated to a temperature of 135°C or less, preferably 175°C or less, to react the polyol component with the polyacid component to form a block of thermosetting polyester foam. It is stated that the surfactant is added to reduce cell size, narrow cell size distribution, and reduce the density of the resulting foam. In one embodiment, it is shown that the surfactant is a mixture of an anionic surfactant and a cationic surfactant. It is shown that a combination of sodium dodecyl sulfate (SDS) and tetradecyltrimethylammonium bromide (TTAB) is preferred. The use of non-ionic surfactants, such as alkyl polyglucosides, is also mentioned as an option.

[0006] International Publication No. WO2019122667 describes a method for producing a thermosetting polyester foam, comprising the steps of preparing a prepolymerized composition of polyol, polyacid, and catalyst, adding a surfactant to the composition, and heating the mixture to a temperature at least equal to 160° C. to form a thermosetting polyester foam. This document mentions the combination of TTAB / SDS and the alkyl polyglucosides mentioned above. This document further mentions the combination of cetyltrimethylammonium bromide (CTAB) and SDS. Summary of the Invention [Problem to be solved by the invention]

[0007] Although the methods described in these documents give interesting results, there is a need for methods that can use less surfactant while still obtaining foams with good properties. The present invention provides such a method. [Means for solving the problem]

[0008] The present invention relates to a method for producing a thermosetting polymer foam, the method comprising: subjecting a reaction mixture containing a surfactant and a prepolymer to a stirring step, wherein the prepolymer is obtained by polymerization of a combination of a polyol monomer and a polycarboxylic acid monomer, a combination of a plurality of hydroxycarboxylic acid monomers, or a combination of a polyol monomer, a polycarboxylic acid monomer, and a hydroxycarboxylic acid monomer, the prepolymer having a degree of polymerization of 0.1 to 0.8; The reaction mixture thus obtained is subjected to a curing step in the absence of stirring to obtain a thermoset polymer foam. Including, wherein the surfactant contains an amphoteric surfactant, and the total concentration of the surfactant is in the range of 0.1 to 6% by weight. Regarding the above method. Effect of the Invention

[0009] It has been found that by using amphoteric surfactants, it is possible to obtain foams with good properties with less surfactant than described in WO2016207517 or WO2019122667. The foamed polyester of the present invention is "green", biodegradable, non-toxic, and clean-burning. The foamed polyester of the present invention can be applied to packaging materials, heat insulating materials, materials with short life cycles, etc. [Brief description of the drawings]

[0010] [Figure 1] The resulting foam [Diagram 2] The resulting foam [Diagram 3] The resulting foam

[0011] Further advantages of the present invention and specific embodiments thereof will be described in more detail below. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] In the present invention, amphoteric surfactants are used, which in the present context are defined as surfactants which, under the conditions prevailing during polymerization and curing, carry a positive charge and a negative charge in the same molecule.

[0013] The amphoteric nature of the surfactant allows it to retain its positive and negative charges even when the pH in the reaction mixture changes. The surfactants described in the above cited documents do not exhibit this behavior. Without wishing to be bound by theory, it is believed that this property ensures that the surfactant has optimal effectiveness as a surfactant in the reaction medium during the polymerization reaction.

[0014] In one embodiment, the amphoteric surfactant comprises a positive charge on at least one nitrogen atom and a negative charge on at least one oxygen atom, e.g., in a group selected from amine oxides, carboxylates, sulfates, sulfonates, phosphates, and phosphonates.

[0015] More particularly, it is preferred that the amphoteric surfactant comprises at least one linear C8-C20 alkyl tail, at least one positively charged nitrogen atom, such as at least one positively charged nitrogen atom in a quaternary ammonium group, and at least one negative charge, such as at least one negative charge in a group selected from an amine oxide, carboxylate, sulfate, sulfonate, phosphate or phosphonate.

[0016] Examples of suitable amphoteric surfactants are as follows: Alkyl betaines of formula I Formula I:R1R2R3N + -CH2-COO - Alkyl sulfobetaines of formula II Formula II: R1R2R3N + -CH2-CH2-CH2-SOOO - Alkylhydroxysultaines of formula III Formula III: R1R2R3N + -CH2-C(OH)H-CH2-SOOO - An amine oxide of formula IV: Formula IV: R1R2R3N + O - Alkylamide betaines of formula V Formula V:R1-CO-NH-CH2-CH2-CH2-R2R3N + -CH2-COO - In the formula I, formula II, formula III, formula IV and formula V, R1 contains 8 to 20 carbon atoms, and R2 and R3 each contain 1 to 4 carbon atoms.

[0017] Further suitable surfactants include acylphosphocholine compounds, phosphatidylcholine compounds, phosphatidylethanolamine compounds, phosphatidylinositol compounds and lecithin, with lecithin being the preferred compound.

[0018] Examples of amphoteric surfactants which have been found to be attractive in the present invention include cocamidopropyl betaine, cocamidopropyl hydroxysultaine, coco-betaine, sodium lauroamphoacetate, lauryl sulfobetaine, lauryl hydroxysultaine and lecithin, such as soy lecithin.

[0019] Further suitable surfactants include amphiphilic polymeric surfactants. Polymeric surfactants include amphiphilic polymers, micellar polymers, hydrophobically modified water-soluble polymers, or associative polymers. When the hydrophilic part is charged, they may be classified into the category of polyelectrolyte or polyampholyte. Examples include amphiphilic copolymers (alternating or static), polymerizable surfactant homopolymers, amphiphilic diblock and multiblock polymers, and branched (graft, comb, star) polymers.

[0020] It has been found that attractive results can be obtained when the reaction mixture further comprises an anionic surfactant, in particular an anionic surfactant selected from the group of C8-C18 alkyl sulfate salts, C8-C18 alkyl ether sulfate salts, C8-C18 alkyl carboxylate salts, C8-C18 alkyl ether carboxylate salts, C8-C18 alkyl sulfonate salts, C8-C18 alkyl ether sulfonate salts, C8-C18 alkyl succinate salts and C8-C18 alkyl ether succinate salts. C8-C18 alkyl ether carboxylate salts, such as sodium or potassium laureth-4-carboxylate, are considered to be preferred.

[0021] When the combination of amphoteric surfactant and anionic surfactant is used, it may be preferable that the weight ratio of amphoteric surfactant to anionic surfactant is in the range of 5:1 to 1:5, especially in the range of 3:1 to 1:3.If the relative amount of amphoteric surfactant is too small, the advantages associated with the presence of this compound, especially the advantage that the total amount of surfactant can be kept relatively low, are not obtained.On the other hand, if the amount of anionic surfactant is too small, the benefit of adding this compound is small.

[0022] In the present invention, the total concentration of the surfactant in the reaction mixture directly subjected to the curing step without stirring is in the range of 0.1 to 6% by weight. The total concentration of the surfactant refers to the total of all surfactants in the system, i.e., amphoteric surfactants, anionic surfactants if present, and nonionic or cationic surfactants that may be present. As described later, the presence of an anionic surfactant in addition to the amphoteric surfactant is preferred, but the presence of a nonionic or cationic surfactant is not essential.

[0023] If less than 0.1 wt% of surfactant is used, the effect of the present invention is not obtained. If more than 6 wt% of surfactant is used, excessive foaming may occur, increasing costs and providing no additional benefits. The reaction mixture directly subjected to the curing process preferably has a total surfactant concentration of at least 0.5 wt%, particularly at least 1 wt%. In addition, it is preferred that the total surfactant concentration is 5 wt% or less, in some embodiments 4 wt% or less, and in particular embodiments 3 wt% or less. The surfactant concentration is calculated by the total weight of the composition without water.

[0024] The first step in the method according to the present invention is to subject a reaction mixture comprising a surfactant and a prepolymer to a stirring step, the prepolymer being obtained by polymerization of a combination of a polyol monomer and a polycarboxylic acid monomer, a combination of a hydroxycarboxylic acid monomer, or a combination of a polyol monomer, a polycarboxylic acid monomer, and a hydroxycarboxylic acid monomer, the prepolymer having a degree of polymerization of 0.1-0.8.

[0025] Suitable polyol monomers for use in the present invention include aliphatic polyhydric alcohols having 2 to 15 carbon atoms. The aliphatic polyhydric alcohols do not contain any aromatic moieties, nitrogen atoms, or sulfur atoms. In some embodiments, the aliphatic polyhydric alcohols essentially consist of carbon atoms, oxygen atoms, and hydrogen atoms. The aliphatic polyhydric alcohols contain at least two hydroxyl groups, preferably at least three hydroxyl groups. Generally, the number of hydroxyl groups is 10 or less, preferably 8 or less, more preferably 6 or less. The aliphatic polyhydric alcohols have 2 to 15 carbon atoms, preferably 3 to 10 carbon atoms. Examples of suitable aliphatic polyhydric alcohols are 1,2-propanediol, 1,3-propanediol, 1,2-ethanediol, 1,4-butanediol, glycerol, sorbitol, xylitol, and mannitol. Glycerol, sorbitol, xylitol, and mannitol are preferred examples of suitable aliphatic polyhydric alcohols. Glycerol is the most preferred example of a suitable aliphatic polyhydric alcohol. One reason for this is that glycerol has a melting point of 20°C, which allows for easy processing (e.g., compared to xylitol, sorbitol, and mannitol, which all have melting points above 90°C). Moreover, glycerol is readily available and results in polymers with desirable properties. Thus, in some embodiments, the aliphatic polyhydric alcohol consists essentially of glycerol. As used herein, "consists essentially of" means that other components (herein, other aliphatic polyhydric alcohols) may be present in amounts that do not adversely affect the properties of the material.

[0026] Mixtures of different aliphatic polyhydric alcohols may also be used. The aliphatic polyhydric alcohol may comprise at least 50 mol%, preferably at least 70 mol%, more preferably at least 90 mol% of glycerol, sorbitol, xylitol or mannitol. Preferably, the remainder is an aliphatic polyhydric alcohol having 3 to 10 carbon atoms. The polyhydric alcohol preferably comprises at least 70 mol% of glycerol, preferably at least 90 mol%, more preferably at least 95 mol%.

[0027] In some embodiments, the aliphatic polyhydric alcohol has a ratio of hydroxyl groups to the number of carbon atoms of 1:4 (i.e., one hydroxyl group per four carbon atoms) to 1:1 (i.e., one hydroxyl group per carbon atom). The ratio of hydroxyl groups to the number of carbon atoms is preferably 1:3 to 1:1, more preferably 1:2 to 1:1, and even more preferably 1:1.5 to 1:1, where a compound having a ratio of hydroxyl groups to the number of carbon atoms of 1:1 is considered to be particularly preferred.

[0028] Suitable polycarboxylic acid monomers for use in the present invention include aliphatic polycarboxylic acids having 3 to 15 carbon atoms, preferably 3 to 10 carbon atoms. The aliphatic polycarboxylic acids do not contain aromatic moieties, or nitrogen or sulfur atoms. In some embodiments, the aliphatic polycarboxylic acids consist of carbon, oxygen, and hydrogen atoms. The aliphatic polycarboxylic acids contain at least two carboxylic acid groups, preferably three carboxylic acid groups. Generally, the number of carboxylic acid groups will be 10 or less, preferably 8 or less, and more preferably 6 or less.

[0029] In one embodiment, the aliphatic polycarboxylic acid comprises at least 10% by weight of tricarboxylic acid, calculated based on the total amount of aliphatic polycarboxylic acid.The aliphatic polycarboxylic acid may comprise at least 30% by weight, preferably at least 50% by weight, more preferably at least 70% by weight, even more preferably at least 90% by weight, most preferably 95% by weight, calculated based on the total amount of acid.In some embodiments, the aliphatic polycarboxylic acid consists essentially of tricarboxylic acid, preferably essentially of citric acid.

[0030] The aliphatic polycarboxylic acid may be a mixture of acids, for example, one or more tricarboxylic acids and one or more dicarboxylic acids. In some embodiments, the aliphatic polycarboxylic acid comprises at least 2% by weight, preferably at least 5% by weight, more preferably at least 10% by weight, of dicarboxylic acid, and at least 10% by weight, preferably at least 30% by weight, more preferably at least 70% by weight, even more preferably at least 90% by weight, and most preferably at least 95% by weight, of tricarboxylic acid, calculated based on the total amount of aliphatic polycarboxylic acid.

[0031] When a dicarboxylic acid is used, the dicarboxylic acid can be any dicarboxylic acid having two carboxylic acid groups and generally up to 15 carbon atoms. Examples of suitable dicarboxylic acids include itaconic acid, malic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, oxalic acid, maleic acid, fumaric acid, muconic acid, suberic acid, and azelaic acid. Itaconic acid and succinic acid may be preferred. In one embodiment, a tricarboxylic acid is used. When a tricarboxylic acid is used, the tricarboxylic acid can be any tricarboxylic acid having three carboxylic acid groups and generally up to 15 carbon atoms. Examples include citric acid, isocitric acid, aconitic acid (both cis and trans), and 3-carboxy-cis,cis-muconic acid. The use of citric acid is considered to be preferred for both cost and availability reasons. In some cases, the acids may also be provided in the form of their anhydrides, such as anhydrous citric acid.

[0032] Suitable hydroxycarboxylic acid monomers suitable for use in the present invention include aliphatic hydroxycarboxylic acid monomers having 3 to 15 carbon atoms, particularly 3 to 10 carbon atoms. The hydroxycarboxylic acid monomer has at least one hydroxyl group, preferably 1 to 3 hydroxyl groups, and at least one, preferably 1 to 3, carboxyl groups. In one embodiment, at least one hydroxyl group is in the alpha position relative to at least one carboxylic acid group. Examples include tartaric acid, malic acid, lactic acid, and glycolic acid.

[0033] In a preferred embodiment of the invention, the prepolymer is derived from a combination of a polyol monomer and a polycarboxylic acid monomer; The polyol monomer is preferably selected from aliphatic polyols having 2 to 15 carbon atoms, in particular polyols having at least 3 hydroxy groups, such as glycerol, sorbitol, xylitol and mannitol, in particular glycerol. The polycarboxylic acid monomer is preferably selected from aliphatic polycarboxylic acids having 3 to 15 carbon atoms, especially polycarboxylic acids having at least three carboxylic acid groups, such as citric acid, isocitric acid, aconitic acid (both cis and trans), and 3-carboxy-cis,cis-muconic acid, especially citric acid.

[0034] The prepolymer used in the present invention is obtained by polymerization of a combination of a polyol monomer and a polycarboxylic acid monomer, a combination of a plurality of hydroxycarboxylic acid monomers, or a combination of a polyol monomer, a polycarboxylic acid monomer, and a hydroxycarboxylic acid monomer.

[0035] The prepolymer used as starting material in the present invention is obtained by polymerization of a combination of a polyol monomer and a polycarboxylic acid monomer, a combination of several hydroxycarboxylic acid monomers, or a combination of a polyol monomer, a polycarboxylic acid monomer, and a hydroxycarboxylic acid monomer. The polymerization can be carried out by bringing several monomers together to form a liquid phase. Depending on the nature of the compounds, this can be carried out, for example, by heating the mixture of components to a temperature at which the acid dissolves in the alcohol, in particular glycerol. Depending on the nature of the compounds, this can be carried out, for example, at a temperature in the range of 20 to 250°C, for example 40 to 200°C, for example 60 to 200°C, or 90 to 200°C. In one embodiment, the mixture can be heated and mixed at a temperature of 80 to 200°C, in particular 100 to 200°C, in some embodiments 120 to 180°C, for 1 minute to 2 hours, more in particular 5 minutes to 45 minutes. If desired, a suitable solvent, for example water, may be present. Preferably the amount of water will be limited since evaporation of water is energy consuming. It may be preferable to add up to 30% by weight water, especially 20% by weight water.

[0036] An advantage of the process of the present invention is that the polymer preparation and foaming steps can be separated, allowing for greater processing flexibility.

[0037] Optionally, a catalyst suitable for the preparation of polyesters can be used. Catalysts suitable for the production of polyesters are known in the art. Preferred catalysts are heavy metal-free catalysts. Useful catalysts include, but are not limited to, strong acids such as hydrochloric acid, hydroiodic acid (also referred to as hydroiodic acid) and hydrobromic acid, sulfuric acid (H2SO4), nitric acid (HNO3), chloric acid (HCIO3), boric acid, sodium hypophosphite, perchloric acid (HCIO4), trifluoroacetic acid, p-toluenesulfonic acid, sulfonic acid and trifluoromethanesulfonic acid. Catalysts such as Ti-butoxide, Sn-octanoate, Zn-acetate and Mn-acetate can also be used, but are less preferred.

[0038] The surfactant can be added to the prepolymer, to the monomer prior to polymerization, or during the polymerization process to form the prepolymer. The surfactant may be added in one or more steps, in batches, or continuously, in any order. The surfactant may optionally be premixed with a limited amount of the prepolymer.

[0039] The prepolymers used as starting materials in the present invention have a degree of polymerization of 0.1 to 0.8. In the context of this specification, the degree of polymerization is the ratio of reacted functional groups to the maximum number of functional groups that can react. The degree of polymerization can be determined by acid number (especially values ​​less than 0.5) or gravimetric method (especially values ​​greater than 0.5).

[0040] To determine the degree of polymerization of a polymer derived from an aliphatic polyol and an aliphatic polycarboxylic acid with an unknown degree of polymerization by gravimetric analysis, a sample of the polymer with an unknown degree of polymerization is cured at a temperature of 100 to 220°C until no water is released. It will be seen that the degree of polymerization of the polymer is 1, and it is possible to calculate the degree of polymerization of the sampled polymer using the water lost during curing.

[0041] The desired degree of polymerization will depend on many factors.

[0042] In particular, a higher degree of polymerization at this stage of the process has the advantage that less curing is required in further stages of the process.On the other hand, a higher degree of polymerization increases the viscosity of the prepolymer composition, which may adversely affect the effectiveness of the mixing step.The degree of polymerization of the prepolymer directly provided to the mixing step is preferably at least 0.2, particularly at least 0.3, particularly at least 0.4, more particularly at least 0.5.It is preferred that the degree of polymerization is 0.7 or less.

[0043] The reaction mixture containing the surfactant and the prepolymer is subjected to a stirring step. It has been found that the stirring step is necessary to obtain a foam with good properties. The purpose of the stirring step is to uniformly disperse the surfactant in the prepolymer. Any kind of stirring method known in the art can be used, including stirring, mixing and shaking. Static mixing may also be used. In one embodiment, the stirring is performed using a high shear mixer. High shear mixing equipment is known in the art and does not need to be further described here.

[0044] Depending on the degree of polymerization, it may be preferable to bring the composition to a high enough temperature to ensure that the mixture has a low enough viscosity to allow adequate mixing.

[0045] As long as the surfactant is uniformly dispersed throughout the prepolymer, the time for which the stirring step is carried out is not critical.

[0046] After the stirring step, the reaction mixture thus obtained is subjected to a curing step in the absence of stirring to obtain a thermosetting polymer foam. The curing step in the absence of stirring is generally carried out at least part of the time in the mold in which the stirred mixture was provided. The shape and size of the mold are not critical and depend on the shape and size of the foam to be formed. The shape and size of the mold should be selected to accommodate the increase in volume.

[0047] The curing step is generally carried out at an internal temperature of at least 80° C., in particular at least 100° C., more in particular at least 120° C., even more in particular at least 130° C. A very high internal temperature increases the number of side reactions. It is therefore preferred that the internal temperature does not exceed 250° C. It may be preferred that the internal temperature is in the range of 130-200° C. The internal temperature is measured during curing or immediately after the molded article has been removed from the means for curing, e.g. an oven or a press.

[0048] Curing can be carried out by heating techniques known in the art, for example in an oven with oven temperatures between 80°C and 450°C. Various types of ovens may be used, including but not limited to belt ovens, convection ovens, microwave ovens, infrared ovens, hot air ovens, conventional baking ovens, and combinations thereof. Vacuum ovens are also attractive. Curing can be done in a single step or in multiple steps. The curing time ranges from 5 seconds to 24 hours, depending on the size and shape of the object, the type of oven and the temperature used. The total curing time is preferably at least 10 minutes, especially at least 20 minutes, at most 12 hours, especially at most 6 hours. Longer curing times are not disadvantageous in themselves, but may be less attractive from an economic point of view. It is within the skill of the art to select the appropriate curing conditions.

[0049] The curing step is preferably carried out under a temperature regime where the oven temperature is slowly increased to allow for controlled foam formation.

[0050] Optionally, the curing step can be carried out in two stages, where a first curing step is carried out in a mould, then the cured foam is removed from the mould and the cured foam is subjected to a second curing step, also denoted as post-curing step. Optionally, after the cured foam is removed from the mould, a machining step can be carried out before and / or after the post-curing step.

[0051] After curing, the degree of polymerization is generally greater than 0.80, preferably greater than 0.90. Moreover, immediately after curing, the moisture content of the molded article is generally less than 10% by weight (calculated on the total weight of the molded article), preferably less than 5% by weight, more preferably less than 2% by weight, most preferably less than 1% by weight. Depending on the storage conditions, the moisture content of the molded article may increase after curing.

[0052] The process according to the invention may preferably be carried out under an inert atmosphere, for example under nitrogen or argon, to prevent reaction with atmospheric oxygen which may result in yellowing of the polymer.

[0053] The mixing and curing steps in the process according to the invention may be carried out under atmospheric pressure, under superatmospheric pressure and / or under reduced pressure, and optionally different pressure regimes are applied during different stages of the process. In one embodiment, the reaction mixture is kept at a pressure below atmospheric pressure during at least a part of the reaction time. It is believed that using subatmospheric pressure results in a product with a low density. In one embodiment, a pressure of at most 0.99 bar, in particular at most 0.8 bar, more in particular at most 0.5 bar, in particular at most 0.1 bar is applied. Lower pressures can also be used, for example a pressure of at most 50 mbar, or at most 10 mbar. A pressure of up to 1 mbar may be applied. When working under reduced pressure, the lower limit will generally be determined by the equipment used. In particular, it is attractive to carry out the curing step under reduced pressure.

[0054] In one embodiment, the curing rate may be increased by adding particulate material to the reaction mixture prior to curing, for example in an amount of 1-30% by weight, particularly 1-20% by weight. The use of seed particles has been found to result in a product having a lower density compared to the corresponding material produced in the absence of seeds. As one skilled in the art can easily determine, the particles should be large enough to be easily suspended in the reaction mixture, but large enough to act as seeds. A suitable maximum value for the average particle size may be 3 mm. A suitable minimum value for the average particle size may be 0.025 mm, although smaller particles may also be used. In one embodiment, the seeds may have an average particle size of less than 2 mm, particularly less than 1 mm, more particularly in the range of 0.1-0.7 mm. In view of the above, it is within the skill of the art to determine the suitable amount of particles and the suitable particle size. In one embodiment, the particles are polymer seed particles, particularly polyester seed particles. In one embodiment, the seeds are polymers as described herein. This has the advantage that the resulting material has a homogenous chemical composition.

[0055] The method of the present invention results in the formation of a thermoset polymer foam comprising a polymer obtained by polymerization of a combination of a polyol monomer and a polycarboxylic acid monomer, a combination of a plurality of hydroxycarboxylic acid monomers, or a combination of a polyol monomer, a polycarboxylic acid monomer, and a hydroxycarboxylic acid monomer, and an amphoteric surfactant, wherein the total concentration of the surfactant is in the range of 0.1-6 wt.%, and the polymer has a degree of polymerization of at least 0.8 and a density of at most 850 grams / liter.

[0056] The foams according to the present invention have a homogenous foam structure with small cells, and in some embodiments, they are rigid at room temperature.

[0057] The foams of the present invention have a density of less than 850 grams per liter. The density will generally be greater than 5 grams per liter.

[0058] In one embodiment, the density is 10-300 g / l, particularly 50-250 g / l. In another embodiment, the foam has a density of 300-700 g / l. In a further embodiment, the invention is directed to foams having a density of 500-850 g / l, particularly 550-700 g / l. Lower density materials may be attractive for packaging applications. Higher density materials may have better strength and better dimensional stability.

[0059] The polymer of interest is a reaction product obtained by polymerization of a combination of a polyol monomer and a polycarboxylic acid monomer, a combination of multiple hydroxycarboxylic acid monomers, or a combination of a polyol monomer, a polycarboxylic acid monomer, and a hydroxycarboxylic acid monomer. Other components may be present in the reaction medium, but only to the extent that they do not substantially interfere with the properties of the reaction product. In particular, they should not interfere with the formation of the foam. Suitable components that may be present include catalysts and colorants (dyes and pigments). Other components conventionally used in polymer processing that may be used in the foam of the present invention include inorganic fillers, antibacterial or antifungal agents, flame retardants, UV absorbers, and hydrophobizing agents.

[0060] Generally, less than 20% by weight of the reaction mixture should be composed of other components, preferably less than 15% by weight, more preferably less than 10% by weight. In some embodiments, it may be preferred that the mixture contains less than 5% by weight, or less than 2% by weight, of additional components. The above relates to the components contained in the final product. Water evaporated from the final product and other gaseous components that may be added, if any, are not included herein.

[0061] The actual size of the polymer object to be produced is not further limited and can be as large as necessary. If necessary, it can be divided into suitable sizes later. The shortest distance between the center of the object to be formed by polymerization and the outside of the object can be at least 2 mm, more particularly at least 4 mm, depending on the application. The reason for this preference is that the foaming process may be improved when the size of the object is large.

[0062] As will be apparent to one skilled in the art, different embodiments of the present invention may be combined unless they are mutually exclusive. All percentages used herein are by weight unless otherwise specified.

[0063] Where amounts, concentrations, dimensions, and other parameters are expressed in the form of ranges, preferred ranges, upper values, lower values, or preferred upper and lower values, it is to be understood that the range obtained by combining any upper value or preferred value with any lower value or preferred value is also specifically disclosed, regardless of whether the resulting range is expressly stated in the context.

[0064] The present invention is illustrated by the following examples, but is not limited thereto or by them.

[0065] Working Example

[0066] Prepolymer Masterbatch Manufacturing

[0067] A prepolymer masterbatch was prepared as follows: 1.0 kg of glycerol with a purity of >99% and 2.0 kg of citric acid (purity ≥99%) were placed in a stirred and heated reactor. 9 g of boric acid (0.5 m / m, purity >99%) was also added. The mixture was heated to 135°C in about 15 minutes and held at that temperature for 15 minutes, followed by dilution with tap water to a water content of 20% and further cooling. The resulting prepolymer had a degree of polymerization of 0.4. Dilution with tap water was performed to obtain a material with a suitable viscosity for downstream handling.

[0068] Example 1

[0069] General Description of Foam Production for This Example

[0070] The desired amount of the prepolymer masterbatch described above was stirred and heated to a temperature of 140°C until a degree of polymerization of 0.55 was reached. After the surfactant was added, the mixture was slowly stirred for 5 minutes at the same temperature for initial homogenization. Vigorous stirring was then applied to further homogenize the mixture. Vigorous mixing was performed for 4-10 minutes, depending on the batch size. Mixing was stopped when a homogenous mixture was obtained. The mixture was then transferred to a mold, placed in an oven, and subjected to the temperature profile specified in the examples. Upon completion of the cure profile described in the examples, the mold containing the foam was removed from the oven, removed from the mold, machined to the desired shape, and subjected to a post-cure step at the time and temperature indicated in the examples.

[0071] The following surfactants (combinations) were tested. Heating was performed as specified:

[0072] Experiment A (Comparative Example)

[0073] Cetyltrimethylammonium bromide (CTAB) + sodium dodecyl sulfate (SDS), total surfactant amount 2.5 wt%, weight ratio 2:1. Oven temperature sequence 150-160-170-180-190°C, time sequence 16-16-8-8-16 min. Post-curing was done at 180°C for 120 min.

[0074] Experiment B (Comparative Example)

[0075] Cetyltrimethylammonium bromide (CTAB) + sodium dodecyl sulfate (SDS), total surfactant amount 5 wt%, weight ratio 2:1. Oven temperature sequence 150-160-170-180-190°C, time sequence 16-16-8-8-16 min. Post-curing was done at 180°C for 120 min.

[0076] Example 1 (present invention)

[0077] Lauryl hydroxysultaine (LHS) + potassium laureth-4 carboxylate (PLC), total surfactant amount 2.5 wt%, weight ratio 1:1. Oven temperature sequence 140-150-160-170-180°C, time sequence 16-16-8-8-16 min. Post-curing was done at 180°C for 120 min.

[0078] The resulting foams are shown in Figures 1 to 3. As can be seen from these figures, the surfactant combination according to the invention results in the formation of a foam with small homogenous cells and a homogenous foam profile. This foam has better properties than the foam of Comparative Example A, which results in a non-uniform foam profile. It has a more homogenous appearance than the foam of Comparative Example B, which is obtained with a higher surfactant concentration. These examples therefore show that the use of the surfactants of the invention makes it possible to obtain foams with good properties while using less surfactant.

[0079] Example 2

[0080] 600 grams of the above described prepolymer masterbatch was mixed with 2.5 wt. % surfactant (total surfactant concentration) and mixed as described in Example 1.

[0081] After mixing, 300 grams of the mixture was poured into an aluminum mold and cured according to the following cure profile: 15 minutes at 140° C., 30 minutes at 150° C., 15 minutes at 160° C., and 60 minutes at 180° C. The sides of the mold were then cut open and a final cure was done at 180° C. for 120 minutes.

[0082] In this manufacturing method, in order to allow comparison with the use of a combination of cationic and anionic surfactants according to the prior art, a combination of (1-tetradecyl)trimethylammonium bromide (TTAB) + potassium laureth-4-carboxylate (PLC) was tested (total amount of surfactants 2.5% by weight, weight ratio 2:1). Furthermore, experiments were carried out with soy lecithin as a further example of an amphiphilic surfactant. The combination of hydroxysultaine (LHS) + potassium laureth-4 carboxylate (PLC) tested in Example 1 above was also tested in this manufacturing method (total amount of surfactants 2.5% by weight, weight ratio 2:1).

[0083] The table below gives the results of the experiments.

[0084] [Table 1]

[0085] Thus, it can be seen that foams produced according to the present invention containing either lecithin or LHS+PLC have lower density and better foam structure than foams prepared using a combination of cationic and anionic surfactants.

Claims

1. 1. A method for producing a thermoset polymer foam, the method comprising: subjecting a reaction mixture comprising a surfactant and a prepolymer to a stirring step, wherein the prepolymer is obtained by polymerization of a combination of a polyol monomer and a polycarboxylic acid monomer, a combination of a plurality of hydroxycarboxylic acid monomers, or a combination of a polyol monomer, a polycarboxylic acid monomer, and a hydroxycarboxylic acid monomer, the prepolymer having a degree of polymerization of 0.1 to 0.8; The reaction mixture thus obtained is subjected to a curing step in the absence of stirring to obtain a thermoset polymer foam. Including, wherein the surfactant comprises an amphoteric surfactant, and the total concentration of the surfactant is in the range of 0.1 to 6 wt.%; The method.

2. 2. The method of claim 1, wherein the amphoteric surfactant comprises a positive charge on at least one nitrogen atom and a negative charge on at least one oxygen atom, e.g., in a group selected from amine oxides, carboxylates, sulfates, sulfonates, phosphates, and phosphonates.

3. 2. The method of claim 1, wherein the amphoteric surfactant comprises at least one linear C8-C20 alkyl tail, at least one positively charged nitrogen atom, e.g., at least one positively charged nitrogen atom in a quaternary ammonium group, and at least one negative charge, e.g., at least one negative charge in a group selected from an amine oxide, carboxylate, sulfate, sulfonate, phosphate, or phosphonate.

4. The amphoteric surfactant is Alkyl betaines of formula I Formula I: R 1 R 2 R 3 N + -CH 2 -COO - Alkyl sulfobetaines of formula II Formula II: R 1 R 2 R 3 N + -CH 2 -CH 2 -CH 2 -SOOO - Alkylhydroxysultaines of formula III Formula III: R 1 R 2 R 3 N + -CH 2 -C(OH)H-CH 2 -SOOO - An amine oxide of formula IV: Formula IV: R 1 R 2 R 3 N + O - Alkylamide betaines of formula V Formula V: R 1 -CO-NH-CH 2 -CH 2 -CH 2 -R 2 R 3 N + -CH 2 -COO - In the formula I, formula II, formula III, formula IV and formula V, R 1 contains 8 to 20 carbon atoms, and R 2 and R 3 each contains 1 to 4 carbon atoms; The acylphosphocholine compound, the phosphatidylcholine compound, the phosphatidylethanolamine compound, the phosphatidylinositol compound, the polymer surfactant and the lecithin is selected from the group Here, lecithin is the preferred compound. The method of claim 1.

5. 2. The method of claim 1, wherein the reaction mixture comprising surfactant and prepolymer that is subjected to the stirring step further comprises an anionic surfactant, in particular an anionic surfactant selected from the group of C8 to C18 alkyl sulfate salts, C8 to C18 alkyl ether sulfate salts, C8 to C18 alkyl carboxylate salts, C8 to C18 alkyl ether carboxylate salts, C8 to C18 alkyl sulfonate salts, C8 to C18 alkyl ether sulfonate salts, C8 to C18 alkyl succinate salts, and C8 to C18 alkyl ether succinate salts.

6. 6. The method according to claim 5, wherein the weight ratio of amphoteric surfactant to anionic surfactant is in the range from 5:1 to 1:5, in particular in the range from 3:1 to 1:

3.

7. 2. The method according to claim 1, wherein the reaction mixture as it is brought to polymerization and curing conditions has a total surfactant concentration of 0.5 to 4% by weight, in particular 1 to 3% by weight.

8. the prepolymer is derived from a combination of a polyol monomer and a polycarboxylic acid monomer; The polyol monomer is preferably selected from aliphatic polyols having 2 to 15 carbon atoms, in particular polyols having at least 3 hydroxyl groups, such as glycerol, sorbitol, xylitol and mannitol, in particular glycerol; The polycarboxylic acid monomer is preferably selected from aliphatic polycarboxylic acids having 3 to 15 carbon atoms, in particular polycarboxylic acids having at least three carboxylic acid groups, such as citric acid, isocitric acid, aconitic acid (both cis and trans), and 3-carboxy-cis,cis-muconic acid, in particular citric acid. The method of claim 1.

9. 2. The process according to claim 1, wherein the prepolymer is obtained by subjecting a mixture of monomers in liquid phase to a reaction step at a temperature in the range of 20 to 250°C, such as 40 to 200°C, for example 60 to 200°C or 90 to 200°C.

10. 2. The process according to claim 1, wherein the degree of polymerization of the prepolymer as provided to the mixing step is at least 0.3, in particular at least 0.4, more in particular at least 0.5 and / or at most 0.

7.

11. The method of claim 1 , wherein the mixing step is carried out in a high shear mixer.

12. 2. The method according to claim 1, wherein the curing step in the absence of stirring is carried out at an internal temperature of at least 80°C, in particular at least 100°C, more in particular at least 120°C, even more in particular at least 130°C and / or up to 250°C, in particular in the range from 130 to 200°C.

13. The method of claim 1 , wherein the curing step is carried out at subatmospheric pressure.

14. 1. A thermosetting polymer foam comprising a polymer obtained by polymerization of a combination of a polyol monomer and a polycarboxylic acid monomer, a combination of a plurality of hydroxycarboxylic acid monomers, or a combination of a polyol monomer, a polycarboxylic acid monomer, and a hydroxycarboxylic acid monomer, and an amphoteric surfactant, wherein the total concentration of the surfactant is in the range of 0.1 to 6 wt. %, and the polymer has a degree of polymerization of at least 0.8 and a density of at most 850 grams per liter.

15. 15. The thermosetting polymer foam of claim 14 having a density of 10 to 300 g / l, or 300 to 700 g / l, or 500 to 850 g / l.

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