Z-HFO-1336mzz blowing agents for foaming thermoplastic polymers comprising polystyrene

Abstract

The present application relates to a Z-HFO-1336 mzz blowing agent for foaming a thermoplastic polymer comprising polystyrene. The present invention provides a method comprising extruding a molten composition comprising a thermoplastic polymer comprising polystyrene and a blowing agent comprising Z-1, 1, 1, 4, 4, 4-hexafluoro-2-butene (Z-HFO-1336 mzz) under the following conditions: (a) forming the molten composition by melt mixing at a temperature of at least 180 DEG C, (b) the melt mixing is carried out at a pressure of at least 1500 psi (103 bar), (c) the extrusion is carried out at a temperature of at least 120 DEG C, and (d) the extrusion is carried out at a pressure of at least 1000 psi (69 bar) under conditions effective to produce a closed-cell, smooth-skin, low-density polystyrene-containing thermoplastic polymer in the absence of any co-blowing agent.

Description

[0001] This application is a divisional application of an invention patent application, the application date of the parent application is May 2, 2017, the application number is 201780027495.9 (PCT / US2017 / 030587), and the invention name is "Z-HFO-1336mzz foaming agent for foaming thermoplastic polymers containing polystyrene". Background Art Technical Field

[0002] The present invention relates to the use of Z-HFO-1336mzz as a blowing agent for thermoplastic polymers comprising polystyrene.

[0003] Related technical description

[0004] WO 2008 / 118627 (assigned to Dow Global Technologies) discloses the discovery of blowing agents having zero ODP and a GWP of less than 50, and solubility in olefinic polymers (notably polystyrene) such that these blowing agents, when present at over 50% by weight of the total blowing agent, are capable of producing high quality foam. Table 2 discloses HFO-1336mzz (CF3-CH=CH-CF3), which has intermediate solubility compared to the compounds of Table 1. It also discloses that while the olefins of Table 2 may comprise over 50% by weight of the blowing agent composition, additional blowing agents that are more soluble in the polymer are necessary to achieve high quality foam (page 15, columns 9-12). The high quality foam is described as having an average cell size of 0.02 to 5 mm, closed cells, and a density of 64 kg / m 3 Or smaller foam. The indicators of low quality are small average cell size, greater than 64kg / m 3 High density, high open porosity, and pores (page 2, columns 9-13). High-quality foams are also essentially free of pores, which are described as having multiple pore sizes and can rupture at the foam surface to produce an irregular surface (page 2, columns 15-20). Unruptured pores can be referred to as macropores, and the irregular surface caused by ruptured pores is contrasted with a smooth surface (skin). Summary of the Invention

[0005] The present invention relates to the discovery of foaming conditions different from those disclosed in the practice invention of WO 2008 / 118627, which allow Z-CF3-CH=CH-CF3 (Z-HFO-1336mzz, Z-1,1,1,4,4,4-hexafluoro-2-butene) to be used to foam thermoplastic polymers containing polystyrene, wherein the foam product of the present invention does not contain the indicators of non-high-quality foam, i.e., has a smooth skin and is free of macrovoids and / or air holes.

[0006] One embodiment of the present invention is a method comprising extruding a molten composition comprising a thermoplastic polymer comprising polystyrene and a blowing agent comprising Z-1,1,1,4,4,4-hexafluoro-2-butene (Z-HFO-1336mzz), and a foam prepared by the method under the following conditions:

[0007] (a) forming the molten composition by melt mixing at a temperature of at least 180° C.,

[0008] (b) conducting said melt mixing at a pressure of at least 1500 psi (103 bar),

[0009] (c) carrying out said extrusion at a temperature of at least 120°C, and

[0010] (d) conducting said extruding at a pressure of at least 1000 psi (69 bar), said conditions being effective to produce a closed-cell, smooth-skin, low-density foamed thermoplastic polymer comprising polystyrene in the absence of any co-blowing agent.

[0011] In another embodiment of the present invention, the method, and the foam prepared by the method, comprises extruding a molten composition comprising a thermoplastic polymer comprising polystyrene and a blowing agent consisting essentially of Z-1,1,1,4,4,4-hexafluoro-2-butene (Z-HFO-1336mzz) under the following conditions:

[0012] (a) forming the molten composition by melt mixing at a temperature of at least 180° C.,

[0013] (b) conducting said melt mixing at a pressure of at least 1500 psi (103 bar),

[0014] (c) carrying out said extrusion at a temperature of at least 120°C, and

[0015] (d) conducting said extruding at a pressure of at least 1000 psi (69 bar), said conditions being effective to produce a closed-cell, smooth-skin, low-density foamed thermoplastic polymer comprising polystyrene in the absence of any co-blowing agent.

[0016] A smooth skin indicates the absence of macropores and pores. Blowholes are macropores that break through the skin. The size of the closed cells is uniform and has an average cell size of 0.02 to 5 mm, indicating the absence of internal macropores. Low density is preferably not more than 48 kg / m 3 These results were obtained using Z-HFO-1336mzz as the sole blowing agent in the molten composition.

[0017] The thermoplastic polymer comprising polystyrene is preferably of high molecular weight as indicated by it exhibiting a melt flow rate (sometimes referred to as MFR or MFI) of no greater than 25 g / 10 minutes as measured on the molten polymer at 200°C using a 5 kg weight according to the procedure of ASTM D 1238.

[0018] This preferred combination of high molecular weight and conditions (a)-(d) enables Z-HFO-1336mzz to act by itself as the sole blowing agent to produce the aforementioned foam products even when the melt composition does not contain any co-blowing agent.

[0019] According to another embodiment of the present invention, a co-blowing agent may be present in the molten composition in a trace amount relative to the amount of Z-HFO-1336mzz foaming agent present in the molten composition to advantageously contribute to the density and / or closed cell size of the foam product. When the co-blowing agent is present, the extrusion process remains stable even when the density of the foam product is not greater than 48 kg / m 3 The method for obtaining the foam product described above can also be performed using Z-HFO-1336mzz as the sole blowing agent. The same applies to the preferred molecular weight of the thermoplastic polymer comprising polystyrene. In other words, when a co-blowing agent is present, operating conditions (a)-(d) allow the foam product of the present invention described above to be obtained even in the absence of the co-blowing agent. The presence of a co-blowing agent is unnecessary for obtaining the foam product. According to this embodiment, the amount of Z-HFO-1336mzz is increased to replace the amount of the co-blowing agent, thereby obtaining a foam product having a total blowing agent content of 100% by weight Z-HFO-1336mzz.

[0020] This embodiment of the present invention can be described as a method comprising extruding a molten composition comprising a thermoplastic polymer comprising polystyrene and a blowing agent comprising Z-HFO-1336mzz (Z-1,1,1,4,4,4-hexafluoro-2-butene) and a co-blowing agent under the following conditions:

[0021] (a) forming the composition by melt mixing at a temperature of at least 180° C.,

[0022] (b) conducting said melt mixing at a pressure of at least 1500 psi (103 bar),

[0023] (c) carrying out said extrusion at a temperature of at least 120°C, and

[0024] (d) performing said extrusion at a pressure of at least 1000 psi (69 bar), and

[0025] Thus, a closed-cell, smooth-skin, low-density foamed thermoplastic polymer containing polystyrene is obtained, and the co-blowing agent is effective for the Z-HFO-1336mzz (E-1,1,1,4,4,4-hexafluoro-2-butene) under the conditions to obtain the closed-cell, smooth-skin, low-density (preferably not more than 48 kg / m 3 ) is not necessary. Z-HFO-1336mzz achieves this result by itself, ie in the absence of a co-blowing agent. DETAILED DESCRIPTION

[0026] The foamed thermoplastic polymer according to the present invention comprises polystyrene.

[0027] The polystyrene may be a styrene homopolymer or may contain a comonomer other than styrene, i.e., a polystyrene copolymer. The thermoplastic polymer may also be a blend of polystyrene with another thermoplastic polymer. The other thermoplastic polymer may also be a copolymer of styrene with a monomer other than styrene. A preferred monomer other than styrene is acrylonitrile.

[0028] Whether the foamed thermoplastic polymer is polystyrene or a blend of polystyrene and other thermoplastic polymers, styrene is preferably the main polymerized monomer (unit) in the foamed thermoplastic polymer. More preferably, the polymerized units of styrene account for at least 70 mol%, at least 80 mol%, at least 90 mol%, or at least 100 mol% of the polymerized monomer units constituting the foamed thermoplastic polymer.

[0029] When the thermoplastic polymer comprises a styrene copolymer, the amount of the other monomers copolymerized with the styrene is such that the styrene content of the copolymer is at least 60 mol %, preferably at least 70 mol %, or at least 80 mol % or at least 90 mol % of the copolymer, based on the total moles comprising the copolymer (100%). This applies whether the styrene copolymer is the only styrene-containing polymer in the thermoplastic polymer or is a blend with other thermoplastic polymers such as a styrene homopolymer or other styrene copolymers.

[0030] Preferably, the expanded thermoplastic polymer is entirely polystyrene, notably a styrene homopolymer. When the expanded thermoplastic polymer foam is a blend of polystyrene and other thermoplastic polymers as described above, the polystyrene component of the blend is preferably a styrene homopolymer that constitutes at least 80% by weight of the combined weight of the polystyrene and other thermoplastic polymers.

[0031] The molecular weight of the thermoplastic polymer containing polystyrene being foamed must be sufficiently high to provide the necessary strength for the foam application. This strength requirement determines the minimum density of the foam product. The high molecular weight of the thermoplastic polymer containing polystyrene also contributes to the strength of the foam product. Molecular weight is an indicator of the rate at which a molten polymer flows through a defined orifice under a defined load. The lower the flow rate, the higher the molecular weight. Melt flow rate is measured according to ASTM D 1238 at 200°C using a 5 kg weight on a molten polymer. The weight of the molten polymer flowing through the orifice in a defined amount of time allows the melt flow rate to be reported in g / 10 minutes. Preferably, the melt flow rate of the thermoplastic polymer containing polystyrene is no greater than 20 g / 10 minutes, more preferably no greater than 15 g / 10 minutes, and most preferably no greater than 10 g / 10 minutes. Surprisingly, the higher the molecular weight (the lower the melt flow rate), the better the foaming results, particularly with respect to the availability of low-density foam products, while still achieving a smooth skin on the foam product. Preferably, the minimum melt flow rate of all melt flow rates disclosed herein is at least 1 g / 10 min, thus the melt flow rate ranges disclosed herein are 1 to 25, 1 to 20, 1 to 15, and 1 to 10, all values ​​being in g / 10 min. These molecular weights apply to thermoplastic polymers comprising polystyrene in the molten composition, whether Z-HFO-1336mzz is the only blowing agent present in the composition or a co-blowing agent is also present.

[0032] References to thermoplastic polymers comprising polystyrene also apply to polystyrene itself. Thus, for example, the thermoplastic polymers comprising polystyrene disclosed in the preceding paragraphs may be replaced by the disclosed polystyrene.

[0033] Another embodiment of the present invention is a foam product comprising a polymer matrix comprising a thermoplastic material selected from the group consisting of polystyrene, polystyrene copolymers, and blends of polystyrene with other thermoplastic polymers, and a blowing agent comprising Z-HFO-1336mzz (Z-1,1,1,4,4,4-hexafluoro-2-butene), the foam product defining a plurality of cells having an average cell size of 0.02 to 5 mm, and having a mass fraction of less than 65 kg / m 2 The thermoplastic polymer has a melt flow rate of less than 25 g / 10 minutes.

[0034] In other embodiments, the foamed molten composition may contain additives other than the foamed polymer and Z-HFO-1336mzz blowing agent, such as co-blowing agents, nucleating agents, flame retardants, cell stabilizers, surfactants, preservatives, colorants, antioxidants, reinforcing agents, fillers, antistatic agents, infrared attenuating agents, extrusion aids, plasticizers, viscosity modifiers, and other known additives, all present in amounts to achieve the desired effect. Unless otherwise indicated in any of the appended claims, the present invention is not limited to any specific additives.

[0035] For some of these additives mentioned, the co-blowing agent is preferably an additive with negligible ODP and low GWP, for example no greater than 150. If a co-blowing agent is used, it may be selected from the group consisting of: HFC-152a, XO2, DME, HFO-1234ze(E), HFO-1234ze(Z), HCFO-1233zd(E), HCFO-1233zd(Z), HCFO-1224yd(E), HCFO-1224yd(Z) and HFO-1234yf.

[0036] If a co-blowing agent is used, Z-HFO-1336mzz can comprise the majority of the total blowing agent. Thus, Z-HFO-1336mzz can comprise at least 60% by weight of the total blowing agent, preferably at least 70% by weight, with the co-blowing agent present in amounts of 40% and 30% by weight, respectively. If a co-blowing agent is used, its minimum amount will be as little as 5% or 10% by weight, whereby Z-HFO-1336mzz will be present in amounts of 95% and 90% by weight, respectively. When a co-blowing agent is present, a preferred blowing agent composition is 90 to 75% by weight Z-HFO-1336mzz and 10 to 25% by weight of the co-blowing agent, based on the combined weight of the blowing agents totaling 100% by weight.

[0037] Preferred examples of the nucleating agent are talc, graphite and magnesium silicate.

[0038] Examples of preferred flame retardants include tetrabromobisphenol A and polymer flame retardants.

[0039] The molten composition is actually a foamable composition. The amount of blowing agent in the molten composition will depend on the amount of additives other than the blowing agent and the desired density of the foam product. Generally speaking, the blowing agent (whether Z-HFO-1336mzz is the only blowing agent or Z-HFO-1336mzz blowing agent plus a co-blowing agent) will be 5% to 25% by weight based on the weight of the molten composition.

[0040] Use extruder to carry out method of the present invention, to form molten composite and extrude it to form foam product.Step (a)-(d) is in extruder and is implemented using extruder.Thermoplastic polymer comprising polystyrene forms the feed for extruder.Preferably one or more foaming agents are fed to the feed in the extruder and the position in the middle of the extrusion section of the extruder, usually fed into the molten composite, which is formed when the extrusion screw advances the feed to the extruder along its length.Other additives for the molten composite are added when convenient, and can be determined by the state of the additive.For example, solid additives can be conveniently added to the feed end of the extruder, can be used as a mixture form with the polymer feed in the form of particles and added to the extruder.The molten composite in the extruder is extruded through a die head, thereby making the foamable composite expand into a foam product.Then the foam product that can be in the form of a sheet, plate, rod or pipe is cooled.

[0041] The present invention resides in the conditions under which the extruder is operated that are unique to the extrusion of thermoplastic polymers, including polystyrene.

[0042] The area in the extruder where the composition is melted to form a molten composition, the melting being carried out by inputting heat and generating heat during the mixing process to form the melt, is considered the melt mixing zone. The preferred temperature is at least 185°C, more preferably at least 190°C or at least 200°C or at least 210°C. The preferred maximum temperature of all melt mixing temperatures disclosed herein is 230°C. The melt mixing temperatures disclosed herein are the temperatures of the melt in the mixing zone during mixing. The preferred pressure at which melt mixing is carried out is at least 3000 psi (207 bar), more preferably at least 3500 psi (241 bar), more preferably at least 4000 psi (276 bar). The preferred maximum of all disclosed minimum pressures at which melt mixing is carried out is no more than 5000 psi (345 bar). The pressures disclosed herein are gauge pressures.

[0043] In the zone of the extruder where the molten composition is extruded, the molten composition is cooled so that the temperature at which extrusion is performed is preferably at least 125° C., more preferably at least 130° C. The maximum of all minimum extrusion temperatures disclosed herein is preferably no greater than 140° C. The extrusion temperatures disclosed herein are the temperatures of the melt at the time of extrusion.

[0044] Extrusion is preferably carried out at a pressure of at least 1500 psi (103 bar), more preferably at least 1600 psi (110 bar). The maximum of the minimum extrusion pressure disclosed herein is preferably no greater than 2000 psi (138 bar). The extrusion pressure is the pressure inside the extrusion die.

[0045] The various ranges disclosed above for melt flow rate, temperature, and pressure can be used in any combination in the practice of the present invention to achieve the desired specific foam structure. For example, to achieve low foam density for a foam product, a melt mixing pressure of 3000 to 5000 psi (207 to 345 bar) is preferred, and this temperature range can be used with any of the melt mixing and extrusion temperature ranges to form any of the smooth skin, closed cell foam product densities disclosed herein. The same is true for a melt extrusion pressure range of 1500 to 2000 psi (103 to 138 bar) pressure range along with a 3000 to 5000 psi (207 to 345 bar) pressure range for melt mixing. Most preferably, the two preferred pressure ranges for melt mixing (207 to 345 bar) and extrusion (103 to 138 bar) are used together. Melt flow rates of the foamed polymer of no greater than 25, 20, 15, and 10, and as little as at least 1 (all values ​​in g / 10 minutes) can be used with any of these combinations of pressure and temperature, depending on the desired foam product results.

[0046] Conditions (a)-(d) may be used in any combination with any of the polymer melt flow rates and compositions and blowing agent compositions disclosed above.

[0047] Preferably, the thermoplastic polymer comprising polystyrene and the polystyrene itself exhibit the following foam product attributes:

[0048] Closed cells - at least 80%, preferably at least 90% and most preferably at least 95%, and having an average cell size of 0.02 to 5 mm,

[0049] Density, not more than 40g / m 3 And more preferably not more than 35g / m 3 or 30kg / m 3 ,and

[0050] Smooth epidermis as described above.

[0051] The minimum required strength (compression) of the foam product will dictate a density of at least 16 kg / m 3 .

[0052] As used herein, the terms "comprises," "includes," "has," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0053] The transitional phrase "consisting of excludes any unspecified element, step, or ingredient. If in a claim, protection for materials other than those recited would be excluded, except for impurities normally associated therewith. When the phrase "consisting of" appears in a clause in the body of a claim, rather than immediately following the preamble, it limits only the elements specified in that clause; other elements are not excluded from the claim as a whole. The transitional phrase "consisting essentially of" is used to define a composition or method that includes materials, steps, features, components, or elements in addition to those disclosed in the literature, provided that those additionally included materials, steps, features, components, or elements do not significantly affect the basic and novel characteristics of the claimed invention, particularly the mode of action for achieving any desired result of the claimed method. The term "consisting essentially of" occupies an intermediate position between "comprising" and "consisting of."

[0054] Where the applicant has defined an invention or a portion thereof using open-ended terms such as "comprising," it should be readily understood that (unless otherwise indicated) the description should be interpreted as also including such inventions using the terms "consisting essentially of" or "consisting of."

[0055] Example 1 :

[0056] Polystyrene foam extrusion using pure Z-HFO-1336mzz as a blowing agent using a slot die

[0057] This embodiment demonstrates the use of Z-HFO-1336mzz blowing agent to prepare polystyrene foam insulation material, which shows uniform closed cells, smooth skin and low density. Macropores and pores are not present in the foam insulation material. The polystyrene used in this embodiment is a styrene homopolymer purchased with Nova 1600 polystyrene, which has a melt flow rate (MFR) of 6g / 10 minute. Nucleating agent (nucleating agent), i.e. magnesium silicate, is present in the molten composite formed in the extruder together with polystyrene and blowing agent.

[0058] For this example, a 30 mm twin screw laboratory extruder was used, which had 8 individually controlled electric heating zones and a water-cooled barrel. slot die .

[0059] Table 1 - Extruder operating parameters and achieved foam density

[0060] Extruder speed (rpm) 101 Extrusion rate (lb / hr) 7 (3.2 kg / hr) Foaming agent rate (lb / hr) 1.8 (0.8 kg / hr) Foaming agent concentration (weight %) 20.5 Nucleating agent concentration (weight %) 0.5 Melt mixing temperature (℃) 200 Melt mixing pressure (psi) 3000 (207 bar) Extrusion temperature (℃) 131 Extrusion pressure (psi) 1500 (103 bar) <![CDATA[Foam density (kg / m 3 )]]> 45.3 Cell size range (μM) 20-140

[0061] Example 2 :

[0062] Polystyrene foam extrusion using pure Z-HFO-1336mzz as a blowing agent using a circular die

[0063] This embodiment demonstrates the use of Z-HFO-1336mzz blowing agent to prepare polystyrene foam insulation material, which shows uniform closed cells, smooth skin and low density. Macropores and pores are not present in the foam insulation material. The polystyrene used in this embodiment is a styrene homopolymer purchased with Nova 1600 polystyrene, which has a melt flow rate (MFR) of 6g / 10 minute. Nucleating agent (nucleating agent), i.e. magnesium silicate, is present in the molten composite formed in the extruder together with polystyrene and blowing agent.

[0064] For this example, a 30 mm twin-screw laboratory extruder was used, which had 8 individually controlled electrically heated zones and a water-cooled barrel. A circular die was used for extrusion.

[0065] Table 2 - Extruder operating parameters and achieved foam density

[0066] Extruder speed (rpm) 100 Extrusion rate (lb / hr) 7 (3.2 kg / hr) Foaming agent rate (lb / hr) 1.44 (0.65 kg / hr) Foaming agent concentration (weight %) 17.1 Nucleating agent concentration (weight %) 0.5 Melt mixing temperature (℃) 209 Melt mixing pressure (psi) 1400 (96.5 bar) Extrusion temperature (℃) 115 Extrusion pressure (psi) 1245 (85.8 bar) <![CDATA[Foam density (kg / m 3 )]]> 46.8 Cell size range (μM) 50-500

[0067] Example 3 :

[0068] Polystyrene foam extrusion using a 77 / 23 wt% Z-HFO-1336mzz / HFC-152a blend as a blowing agent out

[0069] This example demonstrates the preparation of a polystyrene foam insulation material using a Z-HFO-1336mzz / HFC-152a blend containing 77 wt% Z-HFO-1336mzz as a blowing agent, which exhibits uniform closed cells, a smooth skin, and low density. Macropores and air holes are absent from the foam insulation. The polystyrene used in this example is a styrene homopolymer available from Total Petrochemicals under the trade name PS 535B, having a melt flow rate of 4 g / 10 min. A nucleating agent, i.e., talc, is present in the molten composite formed in the extruder along with the polystyrene and blowing agent.

[0070] For this example, a 50 mm twin-screw laboratory extruder with nine individually controlled electrically heated zones was used. The first four zones of the extruder were used to heat and soften the polymer. The remaining barrel section, from the blowing agent injection point to the end of the extruder, was set to the selected lower temperature. When extruding the foam stick samples, an annular die with a 3 mm opening was used.

[0071] Table 3 - Extruder operating parameters and achieved foam density

[0072] Extruder speed (rpm) 40 Polystyrene flow rate (kg / hr) 20 Nucleating agent flow rate (kg / hr) 0.07 Nucleating agent ratio in solid (polystyrene + nucleating agent) feed (wt%) 0.35 Foaming agent flow rate (kg / hr) 1.99 Proportion of foaming agent in foamable composition (polystyrene + nucleating agent + foaming agent) (weight %) 9.06 Extrusion temperature (℃) 135 Extrusion pressure (psi) 1320 <![CDATA[Foam density (kg / m 3 )]]> 46

Claims

1. A method comprising extruding a molten composition comprising a thermoplastic polymer comprising polystyrene and a blowing agent comprising cis-1,1,1,4,4,4-hexafluoro-2-butene (Z-HFO-1336mzz) under the following conditions: (a) forming the molten composition by melt mixing at a temperature of at least 180° C., (b) conducting said melt mixing at a pressure of at least 1500 psi (103 bar), (c) carrying out said extrusion at a temperature of at least 120°C, and (d) carrying out said extruding at a pressure of at least 1000 psi (69 bar), The conditions are effective to produce a closed-cell, smooth-skin, low-density foamed thermoplastic polymer containing polystyrene in the absence of any co-blowing agent, wherein the polystyrene-containing thermoplastic polymer has a melt flow index of no greater than 25 g / 10 seconds.

2. The method according to claim 1, wherein the low density is not greater than 48 kg / m 3 .

3. The method of claim 1, wherein the melt mixing temperature is 185°C to 230°C, and / or the melt mixing is carried out at a pressure of 1500 psi (103 Bar) to 5000 psi (345 Bar), or 3000 psi (207 Bar) to 5000 psi (345 Bar).

4. The method of claim 1, wherein the extruding is performed at a temperature of 125°C to 140°C, and / or the extruding is performed at a pressure of 1500 psi (103 bar) to 2000 psi (138 bar).

5. The method of claim 1, wherein the thermoplastic polymer comprising polystyrene has a melt flow index of 1 g / 10 sec to 20 g / 10 sec, preferably 1 g / 10 sec to 10 g / 10 sec.

6. The method according to claim 1, wherein The polymerized units of styrene account for at least 70 mol %, or at least 80 mol %, or at least 90 mol %, or at least 100 mol % of the polymerized monomer units constituting the foamed thermoplastic polymer. Preferably, the thermoplastic polymer comprising polystyrene is polystyrene.

7. The method of claim 1, wherein the foamed thermoplastic polymer comprising polystyrene has at least 80%, preferably at least 90%, and more preferably at least 95% closed cells.

8. The method of claim 1, wherein the foamed thermoplastic polymer has an average cell size of 0.02 μM to 500 μM, preferably 50 μM to 500 μM or 20 μM to 140 μM.

9. The method of claim 1, wherein the molten composition comprises a nucleating agent, preferably graphite.

10. The method of claim 1, wherein the molten composition further comprises a flame retardant, preferably a polymeric flame retardant.