Method for Producing Filler-Containing Compositions Having Particular Curing Regimens - Patent application

Abstract

The present invention provides a method for producing a filled composite object, comprising the steps of: providing a composition comprising a filler and a polymer, wherein the polymer is a polyester obtained from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, the polyester having a degree of polymerization in the range of 0.1 to 0.8, the degree of polymerization being the ratio of a portion of reacted functional groups to a maximum of functional groups capable of reacting; and subjecting said composition to a curing step, wherein in said step said composition is 6 and subjecting the mixture to high frequency heating at a pressure of up to 10 bar for a period of 10 seconds to 30 minutes, resulting in the formation of a composite object. The present invention relates to the above method, which comprises the steps of: Surprisingly, it has been found that a manufacturing method comprising a specific curing regimen in combination with the specific polymer used herein leads to particularly attractive results. In particular, fast heating rates are observed, which allows the curing time to be reduced. In addition, a homogeneous heating profile is obtained, which is surprising, even when relatively thick objects are produced. Finally, and this is particularly surprising, it has been found that the curing pressure can be reduced while obtaining objects with an attractive high density and good shape stability. This allows filler-containing composites to be produced in a cost-effective manner.

Description

[Technical field]

[0001] The present invention relates to a method for making a composition comprising a filler and certain polyesters, particularly bio-based polyesters. [Background technology]

[0002] International Publication No. WO 2012 / 140237 describes a method for producing a composite material comprising 10-98% by weight of a bio-based particulate or fibrous filler and at least 2% by weight of a bio-based polyester, the method comprising combining the filler with the polyester (or a precursor thereof) and dissolving the combination in a solution of at least 1×10 6 It is described that the process comprises subjecting the polyester to a curing step under pressure at 120°C for 12 hours at a pressure of 10 bar (100 psi). The polyester is the reaction product of an aliphatic polyalcohol having 2 to 15 carbon atoms, preferably glycerol, with an aliphatic polyacid having 3 to 15 carbon atoms, in particular a triacid, such as citric acid.

[0003] WO 2012 / 140239 describes the preparation of composite materials containing synthetic fillers, such as glass fiber fillers, using the same polyesters as used in WO 2012 / 140237. In the examples, curing is carried out for, for example, 12 hours.

[0004] It has been found that when commercial applications of filled composites using certain polyesters are desired, high temperatures, pressures and long cure times are necessary to obtain a material with the desired high density and degree of polymerization to obtain a product with good stability. Long cure times at relatively high temperatures and pressures are associated with relatively high costs. Summary of the Invention [Problem to be solved by the invention]

[0005] There is a need in the art for a method of making certain polyester-based compositions that overcomes these problems, and the present invention provides such a method. [Means for solving the problem]

[0006] The present invention therefore provides a method for producing a filler-containing composite object, comprising the steps of: providing a composition comprising a filler and a polymer, the polymer being a polyester obtained from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, the polyester having a degree of polymerization in the range of 0.1 to 0.8, the degree of polymerization being the ratio of the fraction of reacted functional groups to the maximum functional groups that can react; subjecting said composition to a curing step, wherein in said step said composition is 6 and subjecting the mixture to high frequency heating at a pressure of up to 10 bar for a period of 10 seconds to 30 minutes, resulting in the formation of a composite object. The present invention relates to the above method, which comprises the steps of: Effect of the Invention

[0007] Surprisingly, it has been found that a manufacturing method comprising a specific curing regimen in combination with the specific polymer used herein leads to particularly attractive results. In particular, fast heating rates are observed, which allows the curing time to be reduced. In addition, a homogeneous heating profile is obtained, which is surprising, even when relatively thick objects are produced. Finally, and this is particularly surprising, it has been found that the curing pressure can be reduced while obtaining objects with an attractive high density and good shape stability. This allows filler-containing composites to be produced in a cost-effective manner.

[0008] Without wishing to be bound by theory, it is believed that the advantageous effects of the present invention may be related in part to the nature of the monomers, particularly when monomers having a relatively low number of carbon atoms compared to the number of oxygen-containing reactive groups are used. This is true, for example, when the aliphatic polyol contains a substantial amount of a polyol having at least three hydroxyl groups and the aliphatic polycarboxylic acid contains a substantial amount of a tricarboxylic acid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The invention will be explained in more detail below.

[0010] In the process of the present invention, a curing step is carried out in which a composition comprising a filler and a specific polyester having a degree of polymerization in the range of 0.1 to 0.8 is subjected to high frequency heating for a period of 10 seconds to 30 minutes.

[0011] In the context of the present investigation, high-frequency heating (herein also indicated as HF heating) consists in subjecting an object to an alternating electromagnetic field of a frequency in the range of 3 to 100 MHz, in particular 10 to 50 MHz. Frequencies used for industrial purposes are 13.56 MHz, 27.12 MHz and 40.68 MHz, in particular 27.12 MHz is used.

[0012] The energy provided for the curing process depends on the field strength of the electromagnetic field. The desired energy input depends on the size of the object to be cured and on the nature of the equipment. As a general guideline values ​​in the range of 1000-20,000 V can be mentioned, but it is within the skill of the art to select a suitable voltage.

[0013] Depending on the size and shape of the object to be cured and the power supplied, the HF heating step may be carried out for a period of 10 seconds to 30 minutes. Periods of less than 10 seconds are generally insufficient to achieve the desired temperature in the center of the object. Periods of more than 30 minutes are generally not necessary. It may be preferred that the heating is carried out for a period of 10 seconds to 20 minutes, in particular 20 seconds to 10 minutes, more in particular 20 seconds to 5 minutes or even 20 seconds to 3 minutes.

[0014] Hardening can be carried out in a single step or in multiple steps. In one embodiment, two hardening steps are carried out. If desired, the object to be hardened can be machined between the two hardening steps, where the machining can include any step that changes the shape or surface properties of the object. However, generally, one hardening step is sufficient.

[0015] Suitable equipment for carrying out the HF heating is commercially available.

[0016] The curing process is 1×10 6 The reaction can be carried out at pressures of up to 8×10 Pa (10 bar). However, in general, such high pressures are not necessary. 5 Pa (8 bar) or less, especially 6×10 5 Pa (6 bar) or less, or 4 x 10 5 Pa (4 bar) or less, in some embodiments, 3×10 5 The minimum level is 1.1×10 Pa (3 bar) or less. 5 Pa (1.1 bar), specifically 1.5×10 5 Pa (1.5 bar) may be mentioned.

[0017] It may be attractive to carry out two or more curing steps, where the pressure in the first curing step is lower than the pressure in the second curing step. In this case, the first curing step is mainly a heating step, which results in the softening of the polymer. The softened polymer can exhibit better flowability under pressure. This allows the redistribution of the polymer in the heating step under pressure, which results in a composite with better properties.

[0018] To prevent the heat generated by the RF heating from escaping into the environment, it can be attractive for the parts of the HF heating device in contact with the composition to be cured to be heatable or insulated.

[0019] The above polymer

[0020] The polymer used in the present invention is a polyester obtained from an aliphatic polyol having 2-15 carbon atoms and an aliphatic polycarboxylic acid having 3-15 carbon atoms, wherein the polyester has a degree of polymerization in the range of 0.1-0.8, the degree of polymerization being the ratio of the portion of reacted functional groups to the maximum number of functional groups that can react.

[0021] Suitable polyol monomers for use in the present invention include aliphatic polyalcohols having 2 to 15 carbon atoms. The aliphatic polyalcohols do not contain aromatic moieties, nitrogen atoms, or sulfur atoms. In some embodiments, the aliphatic polyalcohols consist of carbon atoms, oxygen atoms, and hydrogen atoms. The aliphatic polyalcohols 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 polyalcohols have 2 to 15 carbon atoms, preferably 3 to 10 carbon atoms. Examples of suitable aliphatic polyalcohols 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 polyalcohols. Glycerol is the most preferred example of suitable aliphatic polyalcohols. One reason for this is that glycerol has a melting point of 20°C, thereby allowing for easy processing (e.g., compared to xylitol, sorbitol, and mannitol, all of which have melting points above 90°C). Moreover, glycerol is readily available and results in polymers with desirable properties. Thus, in some embodiments, the aliphatic polyalcohol consists essentially of glycerol. As used herein, "consists essentially of" means that other components (here, other aliphatic polyalcohols) may be present in amounts that do not adversely affect the properties of the material.

[0022] The aliphatic polyol may comprise at least 30% by weight, particularly at least 50% by weight, more preferably at least 70% by weight, even more preferably at least 90% by weight, and most preferably 95% by weight, of a polyol having at least three hydroxyl groups. In some embodiments, the aliphatic polyol consists essentially of a polyol having at least three hydroxyl groups.

[0023] Mixtures of different aliphatic polyalcohols may also be used. The aliphatic polyalcohols may comprise at least 50 mol %, preferably at least 70 mol %, preferably at least 90 mol % of glycerol, sorbitol, xylitol or mannitol. Preferably, the remainder is an aliphatic polyalcohol having 3 to 10 carbon atoms. The polyalcohol preferably comprises at least 70 mol % of glycerol, preferably at least 90 mol %, more preferably at least 95 mol %.

[0024] In some embodiments, the aliphatic polyalcohol has a ratio of hydroxyl groups to the number of carbon atoms of 1:4 (i.e., 1 hydroxyl group per 4 carbon atoms) to 1:1 (i.e., 1 hydroxyl group per 1 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. Compounds with a ratio of hydroxyl groups to the number of carbon atoms of 1:1 are considered to be particularly preferred.

[0025] 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, and in some embodiments, 3 to 6 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 is 10 or less, preferably 8 or less, and more preferably 6 or less.

[0026] In one embodiment, the aliphatic polycarboxylic acid comprises at least 10% by weight of tricarboxylic acid calculated 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, of tricarboxylic acid calculated on the total amount of acid. In some embodiments, the aliphatic polycarboxylic acid consists essentially of tricarboxylic acid, preferably essentially of citric acid.

[0027] The aliphatic polycarboxylic acid may be a mixture of acids, for example, a mixture of 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, calculated on the total amount of aliphatic polycarboxylic acid, in combination with 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.

[0028] When a dicarboxylic acid is used, it may be any dicarboxylic acid having two carboxylic acid groups and generally not more than 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, it may be any tricarboxylic acid having three carboxylic acid groups and generally not more than 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.

[0029] In one embodiment, the polymer is a polyester obtained from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, wherein the aliphatic polyol comprises at least 30% by weight, in particular 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, of a polyol having at least three hydroxyl groups, wherein the aliphatic polyol having at least three hydroxyl groups is preferably glycerol, and the aliphatic polycarboxylic acid consists of 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, of a polyol having at least three hydroxyl groups, calculated on the total amount of acid, in particular 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, and the tricarboxylic acid is preferably citric acid.

[0030] In one embodiment of the invention, the polymer is derived from a combination of polyol monomers and polycarboxylic acid monomers, The polyol monomer is preferably selected from aliphatic polyols having 2 to 15 carbon atoms and having at least 3 hydroxy groups, such as glycerol, sorbitol, xylitol, and mannitol, in particular glycerol; Here, the polycarboxylic acid monomer is selected from aliphatic polycarboxylic acids having 3 to 15 carbon atoms and 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.

[0031] A polymer having a degree of polymerization in the range of 0.1 to 0.8 is obtained by polymerization of a combination of polyol monomers and polycarboxylic acid monomers. The polymerization can be carried out by bringing the 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 the components to a temperature at which the acid dissolves in the alcohol, in particular in 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 may 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. Optionally, a suitable solvent, for example water, may be present. Preferably, the amount of water is limited, since evaporation of water is energy consuming. It may be preferred to add up to 30% by weight water, especially up to 20% by weight water.

[0032] Optionally, a suitable catalyst for the preparation of the polyester can be used. Suitable catalysts for the production of polyesters are known in the art. Preferred catalysts are heavy metal-free catalysts. Useful catalysts include strong acids such as hydrochloric acid, hydroiodic acid (also referred to as hydroiodic acid) and hydrobromic acid, sulfuric acid (H 2 SO 4 ), nitric acid (HNO 3 ), chloric acid (HCIO 3 ), boric acid, sodium hypophosphite, perchloric acid (HCIO 4 ) trifluoroacetic acid, p-toluenesulfonic acid, sulfonic acid and trifluoromethanesulfonic acid, but are not limited to these. Catalysts such as Ti-butoxide, Sn-octanoate, Zn-acetate and Mn-acetate can also be used, but are less preferred.

[0033] The polymers used as starting materials in the present invention have a degree of polymerization between 0.1 and 0.8. In the context of this specification, the degree of polymerization is the ratio of the portion 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).

[0034] It is clear that in order to determine the degree of polymerization of a polymer obtained from an aliphatic polyol and an aliphatic polycarboxylic acid with an unknown degree of polymerization using gravimetric analysis, a sample of the polymer with an unknown degree of polymerization needs to be cured at a temperature of 100-220° C. until no water is lost. Since the degree of polymerization of the polymer is 1, the water lost during the curing can be used to back-calculate the degree of polymerization of the sample polymer.

[0035] As will be apparent to those skilled in the art, determining the degree of polymerization, for example by acid value titration with KOH, can be carried out as follows: a certain amount of polymer is dissolved in a solvent, after which the acid value can be determined, for example by titration with KOH. By comparing the measured acid value with the theoretical acid value of the amount of polymer dissolved, the conversion can be calculated. Depending on the available information, the degree of polymerization can also be determined by comparing the acid value of the reaction mixture with the theoretical acid value of the sum of the monomers.

[0036] As will be appreciated by those skilled in the art, the degree of polymerization can also be determined by ester value (EV). This method is suitable for both liquid and non-liquid samples. Here, a certain amount of polymer is hydrolyzed, for example with KOH. The uptake of KOH is measured using back titration, which gives the ester value. By comparing the measured ester value with the theoretical ester value of the certain amount of polymer, the conversion can be calculated.

[0037] The desired degree of polymerization of the composition to be applied to the curing step will depend on many factors. 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 may make it more difficult to mold the object to be applied to the curing step. This will be explained in more detail below. It may be preferred that the degree of polymerization of the polymer of the composition to be applied to the curing step is at least 0.2, in particular at least 0.3, in particular at least 0.4, more particularly at least 0.5. It is preferred that the degree of polymerization is 0.7 or less.

[0038] The composition fed to the curing step preferably has a water content of at least 2% by weight, in particular at least 4% by weight. This is because water improves the effectiveness of RF heating. During the curing step, water is generated by the polymerization reaction. The presence of this water makes the HF heating more effective, thereby increasing the reaction rate of the polymerization reaction. Therefore, a limited amount of water will generally be sufficient. Thus, the composition fed to the curing step preferably has a water content of 50% by weight or less, in particular 20% by weight or less, in particular 15% by weight or less, more particularly 11% by weight or less. The water content can be determined gravimetrically by comparing the weight of the composition with the weight of the same composition after all the water has been removed by drying. As will be clear to the skilled person, drying should be carried out under conditions such that polymerization is prevented.

[0039] As will be clear to those skilled in the art, the polyesters specified above can be the only polymers present in the composition.The presence of additional polymers is not intended, desired or required.Nevertheless, if desired, the composition can contain additional polymers in an amount of 20% by weight or less, preferably 15% by weight or less, more preferably 10% by weight or less, particularly preferably 5% by weight or less, and particularly preferably 2% by weight or less.

[0040] The polymers used in the present invention are polyesters obtained from aliphatic polyols having 2 to 15 carbon atoms and aliphatic polycarboxylic acids having 3 to 15 carbon atoms. The presence of additional monomers is not intended, desired or required. Nevertheless, if desired, the polymers may contain additional monomers in an amount of up to 15 mol%, preferably up to 10 mol%, more particularly up to 5 mol%, specifically up to 2 mol%.

[0041] The above filler

[0042] As indicated above, the composition provided for the curing step comprises a filler. Various types of fillers may be envisaged. Particulate, fibrous and / or layered fillers of natural or synthetic origin may generally be used. Combinations of different fillers may be used. The filler may be present in an amount of 10-95% by weight, in particular in an amount of 20-80% by weight, more in particular in an amount of 40-70% by weight, calculated relative to the total weight of the composite object.

[0043] An example of a suitable filler is a particulate material. Within the context of this specification, a particulate material is a material having an aspect ratio in the range of 10:1 to 1:1, preferably in the range of 8:1 to 1:1, more preferably in the range of 6:1 to 11:1. As used herein, "aspect ratio" is defined as the length of a particle determined along its longest axis to the maximum diameter of the particle determined along its longest axis.

[0044] The particulate matter in the core layer may have a maximum length, determined along the longest axis of the particles in the matter, of less than 20 mm, more preferably 15 mm or less, more preferably 10 mm or less, particularly 5 mm or less, especially 2 mm or less. As a minimum value, an average length of the particles of 0.001 mm may be mentioned. In some embodiments, the average length of the particles is at least 0.05 mm, particularly at least 0.1 mm, more particularly at least 0.5 mm. In some embodiments, the average length of the particles is in the range of 0.5 to 5 mm, especially 0.5 to 2 mm.

[0045] Suitable particulate materials may be in the form of, for example, powder, dust, pulp, broken fibers, flakes, or chips. Examples include wood chips, wood flakes, sawdust, flax, (dried) grass, and pulp, such as (recycled) paper pulp or other fiber pulps from sugar beet, fruits and vegetables, etc. Examples of plant-derived materials that may be used as particulate materials are cotton, flax, hemp, grass, reed, bamboo, coconut, miscanthus, coffee grounds, seed husks (e.g. from rice), burlap, kenaf, ramie, sisal, etc., and materials derived therefrom. In general, plant materials that have been ground to a suitable particle size and, if necessary, dried to an appropriate moisture content, may be used.

[0046] The particulate material may include natural materials, such as materials obtained from plants or animals. Examples of plant-based materials include cellulose-based materials, such as fresh or used paper, fresh or used cardboard, any form of wood or other plant material, and combinations thereof. The cellulose-based material may be obtained from so-called virgin pulp, which is obtained directly from a wood pulping process. This pulp can be obtained from any plant material, but is mostly obtained from wood. Wood pulp is obtained from softwood trees, such as spruce, pine, fir, larch and hemlock, and hardwood trees, such as eucalyptus, popular, aspen and birch. Additionally or alternatively, the cellulose-based material may include cellulose materials obtained from recycled paper, for example cellulose pulp obtained from recycled books, papers, newspapers and periodicals, egg cartons, and other recycled paper or cardboard products. A combination of cellulose sources may also be used. Other attractive sources of cellulose-based materials are rejected paper fibers (paper fibers that are too short to be used in paper production) and recycled materials (mechanically and / or chemically) from any (composite) material, for example recycled furniture made from cellulose-based materials. In particular, (composite) materials made with the polymers described herein as binders are attractive sources of cellulose-based materials. The use of these (recycled) materials is highly sustainable and low cost, so they can be widely used, for example, in furniture manufacturing.

[0047] Examples of animal-derived materials include feathers, down, hair and their derivatives such as wool, but also bone meal.

[0048] Further examples of suitable particulate materials include ceramic materials, including oxides such as alumina, beryllia, ceria, zirconia, silica, titania, and mixtures and combinations thereof, and non-oxides such as carbides, borides, nitrides, silicides, and mixtures and combinations thereof, such as silicon carbide. For the purposes of this specification, glass is considered a ceramic material. Glass can be used in the form of, for example, short fibers, glass beads, whether solid or hollow, and crushed glass particles. Suitable particulate materials further include micaceous fillers, calcium carbonate, and minerals such as phyllosilicates. Clay, sand, talcum, gypsum, and the like can also be used.

[0049] Suitable particulate materials also include polymer fillers, such as polyethylene, polypropylene, polystyrene, polyester (e.g., polyethylene terephthalate), polyvinyl chloride, polyamide (e.g., nylon-6, nylon 6.6, etc.), polyacrylamide, and arylamide (e.g., aramid) polymers. Suitable particulate materials also include carbon fibers and carbon particulate materials. Ground cured polyester resins as used in the present invention can also be used as particulate materials. Ground cured polyester resins containing fillers can also be used. The addition of carbon particulate materials can be attractive to improve the RF heating properties of the object. Therefore, in one embodiment, a filler is used that contains at least 0.1% by weight of carbon particulate material, calculated on the total amount of filler used. Depending on the composition of interest, a combination of fillers may be used that contains 0.1 to 10% by weight, specifically 0.1 to 5% by weight, for example 0.1 to 2% by weight, of carbon particulate material, calculated on the total amount of filler.

[0050] In some embodiments, particulate matter is used that includes one or more organic particulate matter, such as one or more organic particulate matter selected from the group consisting of shives, wood dust, wood chips, and recycled paper, In other embodiments, the particulate matter (also) includes one or more inorganic particulate matter, such as one or more inorganic particulate matter selected from the group consisting of (recycled) glass, stone, ceramic, mineral, and metal.

[0051] Suitable fillers also include fibrous materials, which in the context of this specification are materials having an aspect ratio of greater than 10:1.

[0052] In the context of this specification, the term "fiber" refers to monofilaments, multifilament monofilaments, threads, tapes, strips, and other elongated objects having a regular or irregular cross-section and a length substantially greater than its width and thickness.

[0053] Suitable fibrous materials may, for example, have a fiber length determined across their longest axis of at least 1 cm, preferably at least 3 cm, preferably at least 4 cm. For example, the fibrous material has a fiber length determined across its longest axis of 1-20 cm. Preferably, the fibrous material has a fiber length of 1-10 cm. Long (longer) long fibers are preferred because they provide strength to the composition.

[0054] The fibrous material may comprise fibers having a diameter of 0.001 to 10 mm, preferably 0.01 to 1 mm, more preferably 10 to 500 μm. Thinner fibers are advantageous in many applications because they smooth the surface of the panel object. For example, when manufacturing kitchen cupboards, a smooth surface is of course desirable.

[0055] The fibers may, for example, have an aspect ratio in the range of 20:1 to 200,000:1, preferably in the range of 200:1 to 20,000:1, and more preferably in the range of 250:1 to 5000:1. The use of fibers with a relatively large aspect ratio allows for a combination of high strength and a smooth surface.

[0056] The fibers that may be used as fillers in the present invention may be oriented in a random (e.g., nonwoven sheet) or non-random manner. The fibrous material is preferably a nonwoven sheet.

[0057] In the context of this specification, "oriented in a non-random manner" refers to any structure in which the fibers are oriented relative to one another in an essentially regular manner. Examples of layers containing fibers oriented in a non-random manner include woven layers, knitted layers, layers in which the fibers are oriented parallel, and any other layer in which the fibers are connected to one another in a repeating pattern.

[0058] The orientation of fibers in a fibrous material can affect, for example, the strength of the final product. Therefore, in some cases, it may be preferable to orient the fibers in a manner that maximizes the strength of the article. In some embodiments, at least 50% of the fibers are oriented parallel, preferably at least 60% of the fibers are oriented parallel, and more preferably at least 70% of the fibers are oriented parallel. In other cases, more anisotropic properties or bi-directional resistance may be required.

[0059] The fibrous material that can be used in the present invention can include plant-derived fibers, preferably cellulosic and / or lignocellulosic fibers. The fibrous material can also consist essentially of plant-derived fibers. Examples of fibers based on plant-derived fibers include flax, hemp, kenaf, jute, ramie, sisal, coconut, bamboo, and cotton. The fibrous material can also include animal-derived fibers. Animal-derived fibers can be fibers derived from wool, hair, silk, and feathers (e.g., chicken feathers). Other parts of internal organs can also be used. The fibrous material can include synthetic fibers. Examples of suitable synthetic fibers are fibers obtained from viscose, glass, polyester, carbon, aramid, nylon, acrylic, polyolefins, etc. The fibrous material can also be a mixture of fibers of different origins, such as a mixture of plant-derived fibers and synthetic fibers.

[0060] The fibrous material used in the present invention preferably comprises plant-derived fibers, preferably cellulosic and / or lignocellulosic fibers, and it may be particularly preferred that the fibrous material essentially consists of plant-derived fibers. As indicated above, examples of fibers based on plant-derived fibers include flax, hemp, kenaf, jute, ramie, sisal, coconut, bamboo, and cotton, with hemp being particularly attractive.

[0061] In the context of this specification, a composition of filler and polymer also includes a composition in which the filler is provided in the form of a thin layer, alternating with layers of polymer. Suitable layered materials generally comprise at least 2, in particular at least 4, and up to 50, in particular up to 20, filler layers. The individual filler layers generally have a thickness of 0.1 to 10 mm, in particular 0.1 to 5 mm, more in particular 0.2 to 2 mm. The total thickness of the object is, for example, 0.5 to 200 mm. The polymer layers may have a thickness of, for example, 10 to 4000 microns, in particular 10 to 2000 microns, more in particular 10 to 500 microns. A suitable filler is, for example, wood (also indicated as wood veneer). Plywood is an example of this embodiment. Other layered fillers, such as paper or cardboard, may also be applied.

[0062] As will be appreciated by those skilled in the art, different types and combinations of materials may also be used as fillers.

[0063] In one embodiment, the composite object comprises a particulate filler and a polymer, particularly the particulate filler in an amount of 10 to 95% by weight, particularly 20 to 80% by weight, more particularly 40 to 70% by weight, calculated on the entire composite.

[0064] In another embodiment, the composite object comprises a fibrous filler and a polymer, in particular the fibrous filler in an amount of 10 to 95% by weight, in particular 20 to 80% by weight, more in particular 40 to 70% by weight, calculated on the entire composite.

[0065] In addition to the polymer and filler, the composition may contain further ingredients, such as colorants and stabilizers, generally in minor amounts. Suitable further ingredients will be apparent to those skilled in the art.

[0066] In one embodiment, the composition comprising a polymer and a filler further comprises an inorganic salt. The presence of an inorganic salt has been found to increase the effectiveness of the heating process used herein.

[0067] Salts, when used, are generally present in an amount of 10% by weight or less calculated on the amount of the polymer. Inorganic salts may be preferred to be present in an amount of 5% by weight or less, in particular 2% by weight or less, more particularly 1% by weight or less. This upper limit is governed by many considerations. Too much salt may affect the properties of the formed composite object (including its recyclability) while not providing additional benefits. If salt is added, the minimum value may be at least 0.01% by weight, in particular at least 0.05% by weight, more particularly at least 0.1% by weight, calculated on the amount of the polymer. Adding too little salt will not achieve the intended effect of increasing the effectiveness of the heating process.

[0068] The nature of the inorganic salt is not critical to the present invention, and it is within the skill of the art to select a suitable salt. Examples include inorganic salts of alkali metals (e.g., K, Na), or alkaline earth metals (e.g., Ca, Mg), and ammonium salts. As counterions, conventional counterions can be envisaged, such as halides (e.g., chlorides), nitrates, carbonates, phosphates. Particular examples are NaCl, KCl, CaCl 2 , MgCl 2 , FeCl 3 , sodium phosphate, and ammonium salts (e.g., ammonium chloride, ammonium nitrate). The salts may be added to the composition in any suitable manner. For example, the salts may be blended with a polymer or incorporated within the filler, for example, through impregnation.

[0069] By adjusting the method of supplying the salt, the distribution of the salt in the composite before curing can be influenced. The salt may be supplied homogeneously throughout the composite object. However, it may be attractive to supply the salt specifically near the outer surface of the composite object to be cured, where an improvement in the curing effect may be particularly required. Thus, in one embodiment, the concentration of salt in the outer 10% by volume of the composite object is higher than the concentration of salt in the core of the object, the core of the object being defined as the innermost 10% by volume of the object.

[0070] One way to provide salt near the surface of the composite object is to provide an impregnating material, for example in the form of an impregnated sheet, at or near the surface of the composite object before curing. Other embodiments are also possible that provide a non-uniform salt distribution in the composite object, such as providing polymer and salt in the outer layer of the composite object (e.g., 0.1-10 wt %) while providing polymer with low or no salt in the core of the composite object (e.g., 0-5 wt % or less in the outer layer).

[0071] In one embodiment, the composite object comprises at least two layers having the same or different compositions.

[0072] In one embodiment, the composite object comprises at least two layers having different compositions, where one layer comprises a fibrous filler and the other layer comprises a particulate filler.

[0073] In one embodiment, the composite object is a panel comprising a core layer and at least one surface layer connected to the core layer, where the core layer comprises particulate material connected by a polymer and the surface layer comprises fibrous material connected by a polymer, and the ratio of the polymer content (wt%) of the core layer to the total polymer content (wt%) of the one or more surface layers is in the range of 1:1.5 to 1:15. In this embodiment, a relatively core layer comprising particulate filler and having a relatively low polymer content is combined with at least one relatively dense surface layer having a higher polymer content and having good strength and surface properties as a result of the presence of fibrous filler.

[0074] Preferably, the core layer is sandwiched between two surface layers.

[0075] In one embodiment, the core layer has a thickness of at least 1.5 mm, particularly at least 2 mm, more particularly at least 4 mm and / or no more than 50 cm, particularly no more than 20 cm, more particularly no more than 10 cm, more particularly no more than 5 cm, even more particularly no more than 3 cm; and / or one or more of the surface layers has a thickness of at least 0.3 mm, particularly at least 0.5 mm, more particularly more than 1 mm, even more particularly at least 1.1 mm and / or no more than 20 mm, more particularly no more than 10 mm, even more particularly no more than 5 mm, even more particularly less than 5 mm.

[0076] Preferably, the ratio of the thickness of the core layer to the total thickness of the one or more surface layers is in the range of 1:1 to 150:1, more preferably in the range of 1:1 to 50:1, more preferably 1:1 to 25:1, more preferably 2:1 to 25:1, more preferably 3:1 to 25:1, more preferably 5:1 to 20:1.

[0077] In one embodiment, the composite object is a panel, the polymer content of the panel being in the range of 10-60% by weight, preferably 15-50% by weight, more preferably 15-40% by weight, calculated based on the total weight of the panel. The polymer content of the core layer is preferably in the range of 1-40% by weight, preferably 2-30% by weight, more preferably 5-20% by weight. The polymer content of the surface layer is preferably 10-90% by weight, preferably 20-80% by weight, more preferably 30-70% by weight, even more preferably 40-60% by weight, calculated based on the total weight of the particulate material and the polymer, based on the total weight of the fibrous material and the polymer.

[0078] Preferably, the ratio of the polymer content (wt %) of the core layer to the polymer content (wt %) of one or more surface layers is from 1:1.5 to 1:10, more particularly from 1:2 to 1:8.

[0079] In a first step of the method of the present invention, a composition is provided comprising a filler and a polyester polymer as described above, wherein the polyester has a degree of polymerization in the range of 0.1 to 0.8, the degree of polymerization being the ratio of the portion of reacted functional groups to the maximum number of functional groups that can react.

[0080] There are many ways in which this composition can be provided. In its simplest form, the filler is combined with the polymer when the polymer is in liquid phase, optionally in the form of an aqueous solution. Depending on the nature of the filler, this can be done by mixing, impregnation, injection, rolling, or any other method that ensures intimate contact between the filler and the polymer.

[0081] If the composite object consists of two or more layers, the compositions constituting the various layers may be prepared separately and then combined and subsequently cured. It is also possible to prepare different layers one on top of the other.

[0082] When the polymer is provided as a liquid, it may have a relatively low degree of polymerization, for example 0.1 to 0.5, and / or the liquid may contain a relatively large amount of water. When a relatively large amount of water is present, it may be preferable to subject the composition comprising the filler and the polymer to a drying step before the curing step under pressure. The drying step may be carried out through HF heating, although other methods are also envisaged. The drying step is generally intended to remove water, not necessarily to cure (polymerize) the polymer. The drying step may or may not be a HF heating step. Drying by HF heating may be preferred for reasons of efficiency.

[0083] If the degree of polymerization of the polymer is relatively low, a pre-curing step can be carried out, with or without pressure. The pre-curing step may or may not be an HF heating step. Pre-curing by HF heating may be preferred for reasons of efficiency.

[0084] In the method according to the invention, a forming process may be performed. In the context of this specification, a forming process is any process that gives the composite object a predetermined shape. Predetermined shapes include flat plates, curved plates, and any other desired shapes. Examples of suitable forming processes include pressing between flat or curved surfaces, bending, and forming using a die.

[0085] The molding step can be carried out at various times in the process. For example, the molding step can be combined with the curing step, for example by carrying out the curing step on a composition present in a mold or provided on a surface. It is also possible to carry out the molding step at an earlier stage in the process, for example when the polymer is provided in a liquid phase, for example by using a mold. Filament winding is an example of this method. Other methods, such as free-forming or vacuum molding, can also be considered.

[0086] After curing, the degree of polymerization is generally greater than 0.80, preferably greater than 0.90, more preferably at least 0.95, and most preferably at least 0.98. Moreover, immediately after curing, the moisture content of the object is generally less than 10% by weight (calculated relative to the total weight of the object), preferably less than 5% by weight, and in some embodiments, less than 2% by weight, or even less than 1% by weight. Depending on storage conditions, the moisture content of the article may increase after curing.

[0087] Preferably, the thickness of the object obtained by the method ranges from 0.5 mm to 50 cm, preferably from 3 mm to 20 cm, in the main embodiment from 3 mm to 10 cm, or from 3 mm to 5 cm. HF heating has been found to be particularly advantageous for relatively thick materials compared to conventional heating in an oven, because the temperature across the cross-section of the article is more uniform and heating of the core of the object can be performed faster. Thus, in some embodiments, the thickness across the smallest cross-section of the object is at least 4 mm, in particular at least 6 mm. In some embodiments, the thickness may be at least 8 mm, or at least 10 mm, or at least 15 mm, or even at least 20 mm.

[0088] In some embodiments, the object produced by the method according to the invention has a flexural strength of more than 20 MPa, for example as determined using ASTM D 7264. Depending on the intended use, it may be preferred that the flexural strength is at least 40 MPa, in particular at least 60 MPa. Values ​​within this range have been obtained using the present invention.

[0089] As will be apparent to one skilled in the art, different embodiments of the present invention can be combined unless they are mutually exclusive. All percentages used herein are by weight unless otherwise specified.

[0090] When 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 any range that can be 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.

[0091] The present invention will now be illustrated with reference to the following examples, without being limited thereto or by them.

[0092] Example 1: Preparation of a solution of a polyester polymer

[0093] Glycerol (1.0 kg, >99% purity) and citric acid (2.0 kg, >99% purity) were combined in a reaction vessel and heated with stirring. Boric acid (9 g, 0.5 m / m, >99% purity) was added. Within approximately 15 minutes, the mixture was heated to 135°C and held at that temperature for 15 minutes. The mixture was then diluted using tap water, after which the water content was 20-50% by weight, depending on the batch. The mixture was allowed to cool. The compositions prepared herein are referred to as resin compositions.

[0094] Example 2: Manufacturing of sandwich panels in a single step

[0095] Step 1: Preparation of hemp mats

[0096] Hemp roll (15x1m, thickness 10mm, 1100g / m 2 Two hemp mats (35x35cm) were cut out from a 100% polyester fiberglass (Hempflax). The hemp mats were each impregnated with the resin composition obtained in Example 1. The diluted resin composition was evenly poured onto one side of the hemp mats and evenly distributed in the hemp mats using a rolling pin. The impregnation of the resin composition was carried out at room temperature. After these steps, the total amount of polymer impregnated into the mats was 48-55% by weight. The impregnated hemp mats were pre-cured (dried) in an oven at 90°C for 2 hours. Then, they were cooled to room temperature.

[0097] Step 2: Preparation of the core layer base

[0098] A particulate material was prepared from 900 g of hemp flakes. 150 g of the resin composition of Example 1 was added to the particulate material, and the resulting particulate mixture was stirred. The particulate mixture had a polymer content of 10 wt.%.

[0099] Step 3: Forming a layered structure

[0100] The first hemp mat was made of Teflon (登録商標) Sheet (Teflon (登録商標) The granulated mixture was placed on a 100% polyester sheet, and a square wooden mould (30 x 30 cm) was placed on top of it. The granulated mixture was spread on the first hemp mat (in the mould). The mould was covered and pressure was manually applied on the mould to pre-compress the loose hemp granules. The mould was removed and a second hemp mat was applied on top of the granulated mixture and a second Teflon (登録商標) The sheet was applied, taking care to avoid the structure sticking to the press plate.

[0101] Step 4: Curing the layered structure to obtain a panel

[0102] The loose sandwich structure obtained in step 3 was placed in a high-frequency press. At that time, the moisture content was 6-7%. It was heated to 5×10 5 The panels were pressed for a total of 3-5 minutes at a pressure of 100 Pa (5 bar). The pressed panels were cooled under pressure for 2 minutes and then removed from the press. The temperature reached at the core was 130° C. The sandwich panels thus obtained had a smooth and homogenous surface as determined by touch and visual inspection.

[0103] The panels were then subjected to a post-curing step as follows: the panels were placed in a conventional heating oven, preheated to 120° C. and cured at that temperature for 30 minutes, followed by curing for 105 minutes at 160° C. Longer exposure times in the radio frequency press should eliminate the post-curing step.

[0104] The final panel has a density of 0.65g / cm 3 The thickness was 17 mm. The flexural strength was about 30 to 40 MPa.

[0105] Example 3: 4-layered hemp panel

[0106] Four hemp mats (45x45cm) were cut from a hemp roll (15x1m, 10mm thick, Hempflax). The hemp mats were impregnated with the resin composition obtained in Example 1 in the manner described in Example 2. After these steps, the total amount of polymer impregnated into the mats was 48-55% by weight. The impregnated hemp mats were pre-cured (dried) in a conventional oven at 90°C for 2 hours. Then, they were cooled to room temperature.

[0107] Four layers of impregnated hemp mats were stacked on top of each other on a high-frequency press plate, where the fiber direction was the same in all mats. To prevent the hemp from sticking to the plate, a Teflon (登録商標) Sheets were placed under and on top of the hemp structure. 1.5×10 5 Pa or 2.8 x 10 5 A pressure of 1.5 or 2.8 bar (1.5 or 2.8 bar) was applied to the structure. HF heating was then performed at 6000 V for 3-4 minutes. The structure was then cooled for 2 minutes. The core temperature of the hemp plates was 125°C.

[0108] The article so obtained has a smooth and uniform surface and a density of 0.95 to 1 g / cm 3 The panels had a density in the range of 0.01 mm to 0.05 mm. The cross section of the panels was homogenous and there was no delamination between the layers. The panels were 8 mm thick.

[0109] The panels were then subjected to a post-cure step as follows: the panels were placed in an oven, pre-heated to 120° C. and cured at that temperature for 30 minutes, followed by a 105 minute cure at 160° C. The post-cure step was not considered necessary, but was performed to ensure comparability with other samples.

[0110] The linen panels from this example and the linen panels of Examples 4 to 6 below all had flexural strengths in the range of 40 to 80 MPa.

[0111] Example 4: Fabrication of four layered panels - 6300V energy input

[0112] Example 3 was repeated, except that the power during the HF heating step was 6300 V instead of 6000 V. This resulted in a sample core temperature of 140° C. This example shows that energy input can be used to control the core temperature.

[0113] The resulting article has a smooth and uniform surface and a density of 0.95 to 1 g / cm 3The panels had a density in the range of 0.01 mm to 0.05 mm. The cross section of the panels was homogenous and there was no delamination between the layers. The panels were 8 mm thick.

[0114] Example 5: Manufacturing of four layered hemp panels - 6600V energy input

[0115] Example 3 was repeated, except that the power during the HF heating step was 6600V instead of 6000V and the cure was for 2 minutes instead of 3 minutes. The sample core temperature was 140°C, the same as in Example 4. This example shows that a higher energy input can be used to shorten the cure time.

[0116] The resulting article has a smooth and uniform surface and a density of 0.95 to 1 g / cm 3 The panels had a density in the range of 0.01 mm to 0.05 mm. The cross section of the panels was homogenous and there was no delamination between the layers. The panels were 8 mm thick.

[0117] Example 6: Manufacturing of eight layered hemp panels

[0118] The sample preparation process was carried out in the same manner as in Example 3. Instead of four layers, eight layers of impregnated hemp mats were stacked on top of each other. Pressing was carried out in two steps at a power level of 6300V. The first pressing step was carried out at a pressure of 0.2×10 5 The second pressing was performed at 0.2 bar (0.02 Pa) for 1 min to preheat the material and soften the polymer. This step served to ensure a more homogeneous compression during the second pressing step. The core temperature after the first pressing step was not measured to avoid cooling of the material. The second pressing was performed at the same power level, at 2×10 5 Pa~4×10 5 The process was carried out at a pressure of 2-4 bar for 3 minutes. The temperature at the core and surface of the structure was 145-150°C.

[0119] The article has a smooth and uniform surface and a density of 1 g / cm 3 The panels had a density in the range of 0.01 to 0.05 mm. The cross section of the panels was homogenous and there was no delamination between the layers. The panels were 16 mm thick.

[0120] A post-cure step was performed similar to that in Example 3. The post-cure step was not considered necessary, but was performed to ensure comparability with other samples.

[0121] Example 7: Manufacturing panels from porous materials based on recycled cardboard

[0122] A 30 cm x 30 cm cellulosic (recycled carboard / paper) insulation panel (8x50x120 cm) with a void fraction of 0.92 and a density of 90 grams per liter, commercially available from EverUse, was used as the starting material. It was contacted with the resin composition from Example 1 to obtain a fully impregnated material. The final polymer content was 30 wt%.

[0123] The panel was heated by HF at a frequency of 27.12 Hz, with an estimated pressure of about 5×10 5 The mixture was cured in the press for a total of 2 minutes at less than 5 bar. After 2 minutes cooling, the internal temperature was 160°C.

[0124] The resulting article was a panel with a thickness of 20 mm and a smooth and uniform surface.

[0125] Example 8: Chipboard Production

[0126] A 30cm x 30cm cardboard panel was constructed as follows: Two mixtures of resin composition and birchwood chips were prepared. The mixtures differed in the particle size of the chips. The particulate mixtures had a polymer content of 15 wt. % calculated based on the dry weight of polymer and filler. The particulate mixtures were then dried at 120° C. for 1 hour.

[0127] A 30 cm x 30 cm wooden mould was filled with three layers in succession: 50% of the mixture with fine chips, all of the mixture with coarse chips and the remainder of the mixture with coarse chips.

[0128] The panel was heated by HF at a frequency of 27.12 Hz, with an estimated pressure of about 5×10 5 The mixture was cured in the press for a total of 5 minutes at less than 5 bar. After 2 minutes cooling, the internal temperature was 160°C.

[0129] The resulting article was a panel with a thickness of 20 mm and a smooth and uniform surface.

[0130] Example 9: Plywood Production

[0131] Plywood samples were produced by laminating layers of wood veneer with an intermediate layer of the resin composition of Example 1. The thickness of the veneer layers was 1-1.5 mm. Five layers were used. The total polymer content was about 15 wt. %. The total thickness of the laminate was 7 mm.

[0132] The laminate of multiple layers is pressed in a press for 5 minutes at a pressure of 5×10 5 The plywood was heated with HF at 5 bar and a frequency of 27.12 Hz. The adhesive properties of the plywood were found to be very good under both wet and dry conditions.

Claims

1. A method for producing a filler-containing composite object, A composition comprising a filler and a polymer, wherein the polymer is a polyester obtained from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, the polyester having a degree of polymerization in the range of 0.1 to 0.8, and the degree of polymerization is the ratio of the portion of reacted functional groups to the maximum number of reactable functional groups, and The composition is subjected to a curing process, wherein in this process, the composition is 1 × 10 6 The composition is subjected to high-frequency heating at a pressure of 10 bar or less for a period of 10 seconds to 30 minutes, resulting in the formation of a composite object, where the high-frequency heating is performed by subjecting the composition to an alternating current electromagnetic field having a frequency in the range of 3 to 100 MHz. The method comprising the step of

2. The method according to claim 1, wherein high-frequency heating is performed by applying the composition to an alternating electromagnetic field having a frequency in the range of 10 to 50 MHz, more particularly 13.56 MHz, 27.12 MHz, or 40.68 MHz, and more particularly 27.12 MHz.

3. The method according to claim 1, wherein high-frequency heating is performed for a period of 10 seconds to 20 minutes, particularly 20 seconds to 10 minutes, more particularly 20 seconds to 5 minutes, or even more specifically 20 seconds to 3 minutes.

4. The aforementioned curing process is 8 × 10 5 Below Pa (8 bar), especially 6 x 10 5 Pa (6 bar) or less, or 4 x 10 5 Pa (4 bar) or less, in several embodiments, 3 × 10 5 Pa (3 bar) or less, and at least 1.1 × 10⁻⁶ 5 Pa (1.1 bar), especially at least 1.5 × 10⁻⁶ 5 The method according to claim 1, performed at a pressure of Pa (1.5 bar).

5. The method according to claim 1, wherein the composition subjected to the high-frequency curing step has a water content of at least 2% by weight, particularly at least 4% by weight, and 50% by weight or less, particularly 20% by weight or less, more particularly 15% by weight or less, and even more particularly 11% by weight or less.

6. The method according to claim 1, wherein the polymer is a polyester obtained from an aliphatic polyol having 2 to 15 carbon atoms and an aliphatic polycarboxylic acid having 3 to 15 carbon atoms, the aliphatic polyol contains at least 30% by weight, particularly at least 50% by weight, more preferably at least 70% by weight, even more preferably at least 90% by weight, and most preferably 95% by weight, of a polyol having at least 3 hydroxyl groups, the aliphatic polyol having at least 3 hydroxyl groups is preferably glycerol, and the aliphatic polycarboxylic acid contains 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, and most preferably 95% by weight, of tricarboxylic acid calculated relative to the total amount of acid, and the tricarboxylic acid is preferably citric acid.

7. The method according to claim 1, wherein the polymer having a degree of polymerization in the range of 0.1 to 0.8 is obtained by subjecting the mixture of the polyol and polycarboxylic acid in the liquid phase to a reaction step 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.

8. The method according to claim 1, wherein the filler is present in an amount calculated as 10 to 95% by weight, particularly 20 to 80% by weight, and more particularly 40 to 70% by weight, relative to the total weight of the composite object.

9. The method according to claim 1, wherein the composite object comprises at least two layers having the same or different compositions.

10. The method according to claim 1, wherein the polymer is optionally in the form of an aqueous solution in the liquid phase, the composition comprising a filler and a polyester combines the filler with the polymer, and optionally performs one or more of the following steps: drying, molding, or pre-curing.

11. The method according to claim 1, wherein the method includes a molding step.

12. The method according to claim 1, wherein, after curing, the degree of polymerization of the polymer is greater than 0.80, preferably greater than 0.90, more preferably at least 0.95, most preferably at least 0.98, and the water content of the filler-containing composite object is less than 10% by weight (calculated relative to the total weight of the object), preferably less than 5% by weight, less than 2% by weight in some embodiments, or less than 1% by weight.

13. The method according to claim 1, wherein the composite subjected to the curing step has a thickness of at least 4 mm, particularly at least 6 mm, over the minimum cross-section of the object, and in some embodiments, the thickness may be at least 8 mm, or at least 10 mm, or at least 15 mm, or even further at least 20 mm.

14. The method according to claim 1, wherein the composition comprising a filler and a polymer further comprises an inorganic salt.