EP2885344A1

EP2885344A1 - A particulate, expandable polymer, a method for the production thereof and applications thereof

Info

Publication number: EP2885344A1
Application number: EP13756731.9A
Authority: EP
Inventors: Jan Noordegraaf; Franciscus Petrus Antonius Kuijstermans; Matthijs Gebraad
Original assignee: Synbra Technology BV
Current assignee: Synbra Technology BV
Priority date: 2012-08-14
Filing date: 2013-08-14
Publication date: 2015-06-24
Also published as: JP6309007B2; CN104520364A; JP2015524874A; WO2014027888A1; NL2009320C2

Abstract

The present invention relates to a particulate, expandable polymer that can be processed into a foam with a fine cellular structure and a low density and that contains a carbon-based material increasing the thermal insulation value to increase the thermal insulation value thereof. The present invention further relates to a method for producing a particulate, expandable polymer, and to a foam material obtained with it.

Description

A particulate, expandable polymer, a method for the production thereof and applications thereof.

The present invention relates to a particulate, expandable polymer that can be processed into a flame-retardant foam with a fine cellular structure and a low density, which contains a carbon-based material that increases the thermal insulation value to improve the thermal insulation value thereof. The present invention also relates to a method for producing a particulate, expandable polymer, and to a foam material obtained with it.

Known from International application WO 2008/1 19059 is a composition for producing a thermoplastic polymer foam comprising a foamable polymer material, 1 , 1 ,2,2-tetrafluoroethane as the only desired blowing agent and nanographite in concentrations ranging between 80 and 99%, 3.0 and 12% and 0.05 and 5.0%, respectively, said percentages being based on dry weight. The employed nanographite is to be regarded as a multilayer nanographite, at least one dimension of which has a thickness of less than 100 nm and is preferably contained in a carrier, viz. a polyethylene methyl acrylate copolymer. The addition of the nanographite is claimed to improve the thermal, mechanical and flame-retardant properties of the ultimate foamed product.

International application WO 2007058736 relates to a thermally stable brominated copolymer, said copolymer, herein polymerised, containing a butadiene part and a vinyl aromatic part. Such a copolymer is added to polystyrene in a flame-retardant quantity, the mixture ultimately obtained having a bromine content in the range of 0.1 -25 wt.%, based on the mixture's weight.

US 2002/01 17769 relates to foamed cellular polymer particles to which additives, such as carbon black, titanium dioxide, aluminum and graphite, can be added to lower the thermal conductivity.

US 2012/0123007 relates to a styrene polymer composition to which a brominated flame retardant has been added.

Known from European patent EP 1 486 530 (corresponding to

NL 1023638) in the name of the present applicant is an expandable polystyrene (EPS) whose polystyrene particles contain active carbon as the material increasing the thermal insulation value. The relevant active carbon has a particle size of ≤ 12 micrometres. A foam obtained with such a material increasing the thermal insulation value meets the fire resistance requirements according to the B2 test, viz. DI N 4102, part 2.

Known from WO 2010/041936 in the name of the present applicant is an expandable polystyrene (EPS) in which active carbon with a specific particle distribution is used as the means for increasing the thermal insulation value.

Known from U.S. patent No. 6, 130,265 is a method for producing graphite containing EPS, in which an amount of 0.05-25 wt.% graphite, based on styrene polymer, is added.

Known from U .S. patent No. 6,340,713 is a particulate, expandable polystyrene, which styrene polymer contains 0.05 to 8 wt.% homogeneously distributed graphite particles with an average particle size of 1 to 50 μm.

A method for increasing the thermal insulation of EPS is also known per se from International patent application WO 00/43442, in which styrene polymer is melted in an extruder and is mixed with at least a blowing agent and aluminium particles, which are predominantly in the form of plates, and are jointly extruded, the employed concentration of aluminium particles being at most 6 wt.%, after which the extrudate is cooled and reduced to particles. Such polymers contain at least aluminium in the form of particles to improve their thermal-insulation properties, the aluminium particles being homogeneously distributed and incorporated as a material reflecting infrared radiation. The aluminium particles have a plate-like shape of a size varying from 1 to 15 pm.

The raw material that is used to produce expandable polystyrene (EPS) can be obtained not only via the extrusion process known from the aforementioned international patent application, but also via suspension polymerisation. The EPS granulate thus obtained is generally used as a raw material in the packaging industry and in construction. The method for further processing comprises prefoaming, in which an amount of steam is passed through a layer of EPS granules in an expansion vessel, causing the blowing agent contained in the EPS granules, usually pentane, to evaporate and the foaming of the granules to take place. After a storage period of about 4-48 hours, also referred to as curing, the granule thus prefoamed is introduced into a mould in which the granules are further expanded under the influence of steam. The employed mould has small openings allowing the blowing agent still present during the expansion to escape while the granules fuse into the desired shape. The size of this shape is in principle not limited, with it being possible to obtain both blocks for the building industry and packaging material for the food and non-food industries. The aforementioned method differs substantially from the method known from WO20081 19059, which relates to a continuously foamed foam in a single-step process in a continuous extruder.

A flame retardant is often added to the production of a foam. Such foam materials are further processed into products and objects whose fire or flame retardancy must meet a requirement stipulated by the national authorities. It is assumed that such flame retardants have an unacceptable chemical impact on humans and the environment. Because of this, certain flame retardants are being phased out.

One object of the present invention is to prove a particulate, expandable polymer granule with which, after further processing, a flame-retardant foam is obtained that has a practically desired, sufficiently low thermal conductivity coefficient to make it suitable for use for the intended thermal insulation properties.

Another aspect of the present invention is the provision of a method for producing expandable polymer granules in which styrene polymers can, in the presence of one or more additional components, be converted into a material that has an increased thermal insulation value after foaming and moulding.

Another aspect of the present invention is the provision of a method for producing expandable polymer granules in which use is made of a flame retardant showing little biotoxicity, which is safe for humans and animals and meets the safety requirements prevailing in the building industry.

The invention as referred to in the preamble is characterised in that the polymer particles contain carbon with a particle size of < 1 μm as the material increasing the thermal insulation value and a brominated SBS (styrene-butadiene- styrene) as the flame retardant.

One or more aspects of the present invention is/are met by using such a type of carbon as the material increasing the thermal insulation value. The aforementioned flame retardant may moreover be regarded as a means for meeting the safety requirements prevailing in the building industry and also has little impact on humans and the environment.

A preferred value of 0.1 μm is specified as a lower limit for the particle size. The present invention excludes in particular the use of carbon black as the source of carbon.

It is particularly desirable for the particle size D50 to be at most 1 μηι, more specifically the particle size D₅₀ to be at most 0.8 μm.

The D₉₀ value and D₅₀ value are understood to be the 90^th and 50^th percentile, respectively, being the particle sizes below which fall 90% and 50% of the population, respectively. The D10 (the size below which falls 10% of the population), D50 (the size below which falls half of the population) and D90 (the size below which falls 90% of the population) can be easily inferred from a cumulative distribution curve obtained by Malvern Instruments using the products Mastersizer and Lazersizer, and these three values (D10, D50 and D90) can be used to characterise the particle size distribution in powder. In particular, the (D90- D10)/D50 ratio (also referred to as particle size distribution) provides a good indication of the spread of sizes contained in the powder.

In other words, the 10^th percentile is the particle size for which 10% of the particles are smaller than or equal to this value, and therefore 90% of the particles are larger than said value.

In other words, the 50^th percentile is the particle size for which 50% of the particles are smaller than or equal to this value, and therefore 50% of the particles are larger than said value. The D50 is preferably at most 1 .0 μm, in particular at most 0.8 μm.

In other words, the 90^th percentile is the particle size for which 90% of the particles are smaller than or equal to this value, and therefore 10% of the particles are larger than said value.

It is preferable for a block copolymer of polystyrene and brominated polybutadiene to be used as the brominated SBS (styrene-butadiene-styrene) in the present particulate, expandable polymer.

The weight percent of bromine preferably ranges between 60 and 70 wt.%, based on the brominated SBS (styrene-butadiene-styrene). A preferred range of 30-50 wt.%, based on the brominated SBS (styrene-butadiene-styrene), is specified for the weight percent of styrene. In a special embodiment the molecular weight of the brominated SBS (styrene-butadiene-styrene) preferably ranges between 60,000 and 150,000.

The amount of brominated SBS (styrene-butadiene-styrene) preferably ranges between 0.7 and 2.2 wt. %, based on the total weight of the particulate, expandable polymer.

In a special embodiment, the amount of hexabromocyclododecane (H BCD) is less than 1 .0 wt.%, in particular less than 0.6 wt.%, more specifically less than 0.2 wt.%, and preferably less than 0.05 wt.%, calculated on the basis of the total weight of the particulate, expandable polymer.

The aforementioned values were found to be particularly favourable from the viewpoint of compatibility with the polymer, the required flame-retardant properties, biotoxicity, thermal stability and sustainability.

The polymer used in the present invention is selected from the group comprising polystyrene, expanded polypropylene (EPP), expanded cellular polyethylene (EPE), polyphenylene oxide (PPO), polypropylene oxide and polylactic acid, or a combination thereof.

Polylactic acid (PLA) is a collective noun for polymers based on lactic acid monomers, with it being possible for the structure of the polylactic acid to vary from completely amorphous to semi-crystalline or crystalline, depending on its composition. Polylactic acid can be produced for example from milk products, starch, flour and maize. Lactic acid is the monomer of which polylactic acid is composed, and this monomer occurs in two stereoisomers, viz. L-lactic acid and D- lactic acid. Polylactic acid therefore contains a certain proportion of L-lactic acid monomers and a certain proportion of D-lactic acid monomers. The ratio of the L- and D-lactic acid monomers in polylactic acid determines its properties. The terms "D-value" and "D-content" (percentage of D-lactic acid-monomers) are also used. The polylactic acid that is currently commercially available has an L: D ratio of between 100:0 and 75:25; in other words, a D-content of between 0 and 25%, or between 0 and 0.25.

An example of the further processing of PLA granulate is as follows. After impregnation with for example 6-8 % CO₂, PLA granulate is foamed at a pressure of for example 20 bar. Then the PLA is once again as a foam impregnated with for example 6 % CO₂ and shaped in a mould at a steam pressure of between 0.2 and 0.5 bar. This way the moulded part is obtained in the same way as discussed for EPS granules above. PLA granules are produced using a die plate in an extrusion device. Solid PLA is to this end introduced into an extrusion device and melted. Then the melted PLA is pressed through a mould, for example a so-called underwater granulator, and the PLA granules are cut via a die plate. It is also possible for liquid PLA to be supplied directly to the extrusion device in an in-line polymerisation process, so without having to be melted first. Preferably a twin-screw extruder is used as the extrusion device. In an extrusion device the polylactic acid or the mixture of polylactic acid and optionally one or more other biodegradable polymers with optionally one or more chain extenders, nucleating agents and lubricants can be processed into particles. Such particulate polylactic acid is also described in PCT/N L2008/000109 of the present inventors.

After the extrusion of the polylactic acid a blowing agent is added by impregnating the PLA granules to obtain expandable PLA (EPLA). Examples of blowing agents that may be used are CO₂, MTBE, nitrogen, air, (iso)pentane, propane, butane and the like or one or more combinations thereof. The first way is for the polylactic acid to be shaped into particles, for example by means of extrusion, which particles are subsequently made expandable through impregnation with a blowing agent. The second way is for the polylactic acid to be mixed with a blowing agent, which is subsequently directly shaped into expandable particles, for example by means of extrusion.

The present inventors assume that in particular graphene or exfoliated graphite, which former material is to be conceived as a single-atom-thick flat layer of sp2-bound carbon atoms, which carbon atoms are arranged in a honeycomb-like flat crystal grid, can be used to obtain a certain thermal insulation value in a smaller amount than the usual state-of-the-art materials for increasing the thermal insulation value, in particular in comparison with other carbon sources, such as graphite or active carbon. Supplementary experiments have shown that the material here referred to as "graphene" may also be regarded as exfoliated graphite with a particle size of 0.1-0.8 μm. In the description, "graphene" is therefore to be understood to be exfoliated graphite with a particle size of 0.1-0.8 μm. Such a lowering of the amount of added material increasing the thermal insulation value has a favourable effect on the ultimate colour of EPS, which material is originally white. The aforementioned additives contribute towards a somewhat grey "discolouration" of the originally white EPS. In particular, the present invention therefore focuses on the use of a special carbon source, in particular exfoliated graphite, which material may in small amounts have a remarkable effect, which surprising result is assumed to be attributable to the special geometric design of exfoliated graphite combined with a specific flame retardant to meet both the insulation requirements and the fire- retardant requirements. The aforementioned combination of a special carbon source and a specific flame retardant is to be considered the essence of the present invention.

The term "exfoliated graphite" as used herein is not to be confused with the term "nanographite" as known from WO20081 19059, in particular as far as their dimensions and dimensional structure are concerned.

In a special embodiment it is in particular desirable to use exfoliated graphite with an aspect ratio of ≥ 10: 1 , more specifically≥ 100: 1 . Such a layered structure has an especially good influence on increasing the thermal insulation value.

It is in particular desirable for the amount of carbon to be 1 -15 wt.%, based on polymer, preferably 2-8 wt.%, based on polymer.

It must be clear that it is in certain embodiments desirable for one or more other agents for increasing the thermal insulation value to be additionally present in the particulate expandable polymer, selected from the group comprising graphite, carbon black, aluminium powder, AI(OH)₃, Mg(OH)₂ and Al₂O₃, iron, zinc, copper and alloys thereof.

In the past, hexabromocyclododecane (HBCD) was used as a fire retardant to obtain a good fire-retardant effect. The present invention focuses in particular on the use of a replacement for HBCD that results in an end product that is comparable with a polymer product containing HBCD, in particular in terms of fire requirements. In particular, the object of the present invention is to minimise the amount of HBCD, more specifically to reduce the amount of HBCD to zero.

If the product obtained must meet strict fire safety requirements it is desirable to additionally supply one or more fire retardants selected from the group comprising dicumyl peroxide, brominated polymer compounds, in particular polystyrene compounds, and 2,3-dimethyl-2,3-diphenylbutane, in an amount of between 1 .0 and 8 wt.%, based on the amount of polymer. It is also possible to add as an auxiliary a phosphorus compound selected from the group comprising polyphosphonates, diphenylphosphonate, bisphenol A-bis(diphenyl phosphate) and resorcinol aromatic polyphosphate compounds, or a combination thereof.

The exfoliated graphite referred to in the present application can be obtained by subjecting a carbon source to mechanical shearing forces, in particular by subjecting graphite to such a treatment. An example of such a treatment is the extrusion process in which graphite is in the extruder subjected to substantial shearing forces causing the graphite to be converted into flat carbon plates, in particular exfoliated graphite. The present inventors assume of the aforementioned flat carbon plates that such plates are responsible for reflection through a mirror effect of the thermal radiation. This makes it desirable for the employed carbon to have a somewhat flat dimension or a geometric shape to realise the intended mirror effect. In certain embodiments the carbon source may be dosed as a masterbatch or directly as a powdery material, which powdery material has been pretreated to obtain the desired particle size as specified in the claims.

The present invention also relates to a method for producing a particulate, expandable polymer in which polymer is supplied to an extruder and is mixed with at least a blowing agent, brominated SBS (styrene-butadiene-styrene), a carbon source and one or more other auxiliaries as referred to in the enclosed subclaims, and is subsequently extruded, cooled and further reduced to particles.

In a special embodiment the present invention further relates to a method for producing a particulate, expandable polymer in which a monomer, brominated SBS (styrene-butadiene-styrene), a blowing agent, an agent for increasing the thermal insulation value and one or more other auxiliaries as referred to in the enclosed subclaims are subjected to a polymerisation reaction in a reactor. In particular, it is desirable for the density of EPS, as a preferable polymer, to range between 850 and 1050 kg/m³. A preferable blowing agent is (iso)pentane. It is desirable to exclude hydrocarbon compounds containing fluorine as a blowing agent. It is therefore preferable to produce a particulate expandable polymer in which the amount of hydrocarbon compounds containing fluorine is minimised, preferably less than 2.0 wt.%, in particular less than 1 .0 wt.%, more specifically less than 0.5 wt.%, based on the amount of particulate expandable polymer. On account of minimising the aforementioned hydrocarbon compounds containing fluorine in the particulate expandable polymer, the foamed product ultimately obtained is essentially free of hydrocarbon compounds containing fluorine. The present invention further relates to a polymer foam material based on a particulate, expandable polymer as described above, the polymer foam material preferably being used for thermal insulation purposes, for example in the building industry, but also as packaging material in the food and non-food industries.

The present invention will now be elucidated with reference to some examples, to which it must be added that the present invention is by no means limited to such examples.

Figure 1 shows the measurement results of various carbon sources. Figure 2 is a graphical representation of the density vs the lambda value of various EPS materials.

The particle size distribution of various products was determined, as shown in the following table.

It is in particular desirable for the D50 value to be at most 1 μm, more specifically at most 0.8 μm.

A number of mechanical properties were determined of a number of commercially available products, and a flammability test was carried out. It can be clearly inferred from the measurement results that the addition of graphene or exfoliated graphite has a favourable effect on the thermal conductivity of the ultimate foamed moulded part based on EPS.

The figures in the table included below have the following meanings:

1 = H BCD as a flame retardant

2= no flame retardant

3= resorcinol as a flame retardant 4= Emerald 3000 (commercially introduced by Chemtura) as a flame retardant

5= FR122P (commercially introduced by ICI) as a flame retardant 6=XP-7720 FR122P (commercially introduced by Albemarle) as a flame retardant.

The table successively shows the columns of type of starting material, wt.% flame retardant, wt.% dicumyl peroxide, density (g/l), lambda (W/mK), density (g/l), compression strength (kPa), density (g/l), tensile strength at break (kPa) and finally the flammability test DI N 4102-1 B2, in which nt= not measured and pass=passed.

The material EPS 710F 0.7-1.0 mm particle size Synbra Technology with 5.5 % pentane was melted in a twin-screw extruder with a capacity of 125 kg/hour with the addition of P1000 polyethylene (Baker Huigjes) 0.1 % and graphene masterbatch and a graphene concentrate that effectively introduced 4% graphene into the polystyrene. The extruder's temperature is preferably between 150°C and 230°C; in this embodiment 0.8% extra pentane was also added as a blowing agent. The mixture was fed to a cooling extruder with temperatures between 60°C and 150°C, with which a grey XPS plate was produced.

The obtained foam had a density of 35 kg/m3. The foam's insulation value was found to be 31 .1 mW/mK in the case of the master batch and 30.9 mw/mK in the case of the concentrate, and both products passed the flammability test DI N4102 B2.

The enclosed figure 2 is a graphic representation of a number of measurements, with the horizontal axis representing the density and the vertical axis the lambda (W/mK). From this representation it can be clearly inferred that a higher lambda value is obtained for the commercially available Neopor, containing 4 wt.% graphite (predominantly with a particle size of > 1 μm, in particular 1-50 μm), at the same density as for EPS to which exfoliated graphite (particle size between 0.1 and 0.8 μm) has been added in a certain weight percentage.

Determination of the particle size of exfoliated graphite

An amount of 10 g of grey foamed EPS was dissolved in 28 ml of toluene. The slurry was subjected to analysis. The residue was ultrasonically dispersed with the addition of more toluene and analysed using an ALV instrument. The particle size was determined by a Malvern Zetasizer. Further dilution with toluene was carried out where necessary. Zetasizer GMA is a so-called Dynamic Light Scattering instrument with the following specifications: Correlator: ALV5000/60X0 External Goniometer Correlator: ALV-125 Detector: ALV / SO SIPD Single Photon Detector with Static and Dynamic Enhancer ALV Laser Fiber optics: Cobolt Samba 300 DPSS Laser, Wavelength: 532 nm, 300 mW Power Temperature Control: Static Thermal Bath: Haake F8-C35. No special standards were used; the instrument measures the Brownian motion of the particles and the measured values are converted into particle sizes via the Einstein-Stokes equation under the assumptions that the solvent is water and that the particles are approximately spherical. The radius was measured.

It is clear that the graphite reference material has a larger particle size and agglomerates, which was also visually observable. The exfoliated graphite contained in EPS shows much finer particles, on average 3 to 5 times smaller than the particle size of graphite. Although some agglomeration of small particles occurred, the agglomerates were less dominant than in the case of graphite. The results are graphically represented in the enclosed figure 1 .

Claims

1 . A particulate, expandable polymer that can be processed into a flame-retardant foam with a fine cellular structure and a low density and that contains a carbon-based material increasing the thermal insulation value to improve the thermal insulation value thereof, characterised in that the polymer particles contain carbon with a particle size of < 1 μm as the material increasing the thermal insulation value, and comprises a brominated SBS (styrene-butadiene-styrene) as the flame retardant.

2. A particulate, expandable polymer according to claim 1 , characterised in that the D50 particle size is at most 1 μm.

3. A particulate, expandable polymer according to either one or both of the preceding claims, characterised in that the D50 particle size is at most 0,8 μm.

4. A particulate, expandable polymer according to one or more of the preceding claims, characterised in that the polymer is selected from the group comprising polystyrene, expanded polypropylene (EPP), expanded cellular polyethylene (EPE), polyphenylene oxide (PPO), polypropylene oxide and polylactic acid, of a combination thereof.

5. A particulate, expandable polymer according to one or more of the preceding claims, characterised in that exfoliated graphite, in particular with a particle size ranging between 0.1 and 0.8 μm, is used as the carbon, the aspect ratio of the exfoliated graphite being≥ 10: 1 , which exfoliated graphite in particular has a structure of flat carbon plates.

6. A particulate, expandable polymer according to claim 5, characterised in that the aspect ratio of exfoliated graphite is≥ 100: 1 .

7. A particulate, expandable polymer according to one or more of the preceding claims, characterised in that the amount of carbon is 1 -15 wt.%, based on the amount of particulate, expandable polymer.

8. A particulate, expandable polymer according to claim 7, characterised in that the amount of carbon is 2-8 wt.%.

9. A particulate, expandable polymer according to one or more of claims 5-8, characterised in that the exfoliated graphite, in particular with a particle size ranging between 0.1 and 0.8 μιη, is obtained through mechanical shearing of a carbon source, in particular graphite.

10. A particulate, expandable polymer according to one or more of the preceding claims, characterised in that the lower limit of the particle size of the carbon is > 0.1 μm.

1 1. A particulate, expandable polymer according to one or more of the preceding claims, characterised in that the brominated SBS (styrene-butadiene- styrene) is a block copolymer of polystyrene and brominated polybutadiene.

12. A particulate, expandable polymer according to claim 1 1 , characterised in that the weight percentage of bromine ranges between 60 and 70 wt.%, based on the brominated SBS (styrene-butadiene-styrene).

13. A particulate, expandable polymer according to either one or both of claims 1 1 -12, characterised in that the weight percentage of styrene ranges between 30 and 50 wt.%, based on the brominated SBS (styrene-butadiene- styrene).

14. A particulate, expandable polymer according to one or more of claims 1 1-13, characterised in that the molecular weight of the brominated SBS (styrene-butadiene-styrene) ranges between 60,000 and 150,000.

15. A particulate, expandable polymer according to one or more of the preceding claims, characterised in that the amount of brominated SBS (styrene- butadiene-styrene) ranges between 0.7 and 2.2 wt.%, based on the total weight of the particulate, expandable polymer.

16. A particulate, expandable polymer according to one or more of the preceding claims, characterised in that the amount of hexabromocyclododecane (H BCD) is less than 1 .0 wt.%, in particular less than 0.6 wt.%, more specifically less than 0.2 wt.%, preferably less than 0.05 wt.%, based on the total weight of the particulate, expandable polymer.

17. A method for producing a particulate, expandable polymer according to one or more of the preceding claims 1 -16, characterised in that polymer is supplied to an extruder and is mixed with at least a blowing agent, brominated SBS (styrene-butadiene-styrene), carbon with a particle size of < 1 μm and one or more other desired auxiliaries and is subsequently extruded, cooled and further reduced to particles.

18. A method for producing a particulate, expandable polymer according to one or more of the preceding claims 1-16, characterised in that a monomer, a blowing agent, brominated SBS (styrene-butadiene-styrene) and carbon with a particle size of < 1 μm and one or more other desired auxiliaries are subjected to polymerisation in a reactor and are optionally cooled and reduced further to particles in a subsequent step.

19. A method according to either one or both of claims 17-18, characterised in that one or more agents increasing the thermal insulation value selected from the group comprising graphite, carbon black, aluminium powder, AI(OH)₃, Mg(OH)₂, Al₂O₃, iron, zinc, copper and alloys thereof is/are added as the auxiliary/auxiliaries.

20. A method according to claims 17-19, characterised in that a phosphorus compound selected from the group comprising polyphosphonates, diphenyl phosphonate, bisphenol A-bis(diphenyl phosphate) and resorcinol aromatic polyphosphate compounds, or a combination thereof, is added as the auxiliary.

21. A polymer foam material based on a particulate, expandable polymer according to one or more of claims 1 -16.

22. Use of carbon with a particle size of < 1 μm in a flame-retardant foam material comprising a brominated SBS (styrene-butadiene-styrene) as the flame retardant based on a particulate, expandable polymer for increasing the thermal insulation value thereof.

23. Use according to claim 22 in the building industry.

24. Use according to claim 22 in the packaging industry.