MXPA01002731A - Process for the preparation of expanded polyvinylarene particles - Google Patents

Abstract

Process for the preparation of expanded polyvinylarene particles in which polyvinylarene particles pre-expanded to an apparent density do ranging between 600 and 200 kg/m3 are impregnated by an inorganic gas, and the impregnated particles thus obtained are expanded to an apparent density of at least three times lower than do.

Description

PROCESS FOR THE PREPARATION OF EXPANDED PARTICLES OF POLYVINYLARENE Description of the invention. The present invention relates to a process for the preparation of expanded particles of polyvinylarene and to a process for the preparation of foamed articles from these expanded particles. It has been known for several years that the particles of the polyvinylarene, such as polystyrene, can be made expandable, and that the particles thus obtained can be used in the preparation of foamed articles. In this regard reference is made to, for example, the U.S. Patent. No. 2,681,321 which describes a process in which the polystyrene particles are exposed to liquid hydrocarbons and are subjected to treatment in such a way that the liquid hydrocarbon is dispersed in the polystyrene particles. The particles that are prepared in this way generally contain from 4 to 8% by weight of this liquid hydrocarbon, such as butane, n-pentane, or mixtures thereof.

Ref: 127628 pentanes. Halogenated hydrocarbons have also been used for this purpose. These particles can then be expanded to particles with a reduced density. The apparent densities for the encapsulation particles are typically between 20 to 60 g / 1. Once they expand, the particles are fused in a steam heated mold to produce a foamed article of the desired shape. One of the factors influencing the expansion of the polystyrene particles is the amount of the hydrocarbon blowing agent. From Kirk Othmer, Encyclopedia of Chemical Technology, third edition, volume 21, page 838, it can be seen that the density of the particles containing b. 1% weight of n-pentane, are typically 1080 kg / m3, compared to a value of 1050 kg / m3 for pure polystyrene beads compared to a calculated density of 1020 kg / m3 for a simple mixture wherein the n-pentane dissolves in polystyrene. If all the pentane were in the empty spaces, the calculated density would be 1120 kg / m3. Therefore it has been suggested that part of the hydrocarbon blowing agent is present in small empty spaces of polystyrene. The skilled technician appreciates that the above densities are particle densities, which can be recalculated at apparent densities. A particle density of 1080 kg / m3 corresponds to a bulk density of approximately 720 kg / m3. A drawback of current practice is that during transport and storage of the unexpanded particles, the hydrocarbons can evaporate from the particles, in particular, from the voids. When the particles are transported and / or stored at various temperatures and / or times of duration, the amounts of, for example, the pentane that is retained can vary significantly. Apart from the additional precautionary measures that must be taken during transport, such as a gas-tight container, it is to be appreciated that such variation may have an effect on the resulting foam that is obtained after expansion. Moreover, the expansion process itself also causes the hydrocarbons that are originally present in the unexpanded particles, are issued in the environment. In order to reduce emissions, complicated equipment has been developed to collect the hydrocarbons emitted for later handling, for example, combustion. This equipment has to be installed in the end-user complexes of the particles, that is, the customer that produces the foamed articles. This requires additional investment experience with these clients. The present invention aims to eradicate the above drawbacks by providing a process for the preparation of expanded particles of polyvinylarene, wherein the preexpanded polyvinylarene particles at a bulk density of d0 ranging between 600 and 200 kg / m3 are impregnated with an inorganic gas, and the impregnated particles thus obtained, expand to an apparent density of at least three times less than d0. The advantages of the present invention are enormous. In the polyvinylarene manufacturer's facilities, the non-expanded polymer particles of the polyvinylarene containing a blowing agent are prepared and the subsequent particles are preexpanded to a reduced bulk density in the range from 600 to 200 g / 1. If this density reduction is obtained by the use of a hydrocarbon blowing agent, the blowing agent that is emitted can be collected and subsequently handled, (for example, reused) in the polyvinylarene manufacturer's facility. Second, the manufacturer of polyvinyl anery has absolute control over the quality of the product in the period of time between production and use by the customer. By using the process of the present invention, the manufacturer of polyvinylarene is in a position to extract at least the blowing agent from the empty spaces. If you have done so, there will be no loss of the blowing agent during transport and / or storage of the pre-expanded particles. This ensures that the customer always obtains the pre-expanded particles with a consistent cellular structure and with consistent foaming properties. Because the pre-expansion has been carried out in such a way that the apparent density dQ encompasses 600 to 200 kg / m3, the increase in volume compared to the volume of the original unexpanded particle is from about 1.5 to less than 3 times. This increase is so small that transport costs are not such that they outweigh the advantages. On the other hand, the increase in volume, if it ensures that the pores are present in the pre-expanded particle and have a size with which the customer can impregnate a reasonable amount of inorganic gas in them, in order to make the particles are sufficiently expansible. The preexpanded polyvinylarene particles of the present invention have a bulk density d0 of 600-200 kg / m3. Preferably, the bulk density d0 ranges from 530 to 250 kg / m3, more preferably from 500 to 300 kg / m3 and more preferably from 450 to 350 kg / m3.

The pre-expanded particles can be obtained by pre-expanding any unexpanded polyvinylarene particle containing a sufficient amount of blowing agent to achieve apparent densities as defined. The non-expanded particles of polyvinylarene can be prepared by various methods, which include solution polymerization, bulk polymerization, suspension polymerization or mixtures of these methods. The blowing agent can be added after the polymerization, as described in the patent of E.U.A. No. 2,681,321. It is also possible to add the blowing agent during the polymerization of the vinylarene monomers or to add it to the monomers before the polymerization. Preferably, the blowing agent is added during the polymerization of the vinylarene monomers, the polymerization is advantageously carried out in the form of a suspension. The unexpanded particles of the polyvinylarene suitably have an average particle size of 0.2-3 mm. The particles suitable for use in the present invention are, for example, as described in the patent of E.U.A. No. 3,973,884, which describes polymer particles with a relatively high density. These high density polymer particles are obtained by preexpanding unexpanded polymer particles containing 5.8-7.01 by weight of pentane. From GB Patent No. 1 106 143 and from PCT Application No. WO 98/01489 it is known that water can also be used as a blowing agent. Apart from hydrocarbons, it is also possible to use, for example, C2-C6 hydrocarbons or halogenated hydrocarbons, or water, or other blowing agents. Examples are inorganic blowing agents (carbon dioxide) or so-called chemical blowing agents, that is, compounds that release gaseous components at the time of heating. The latest compounds are usually solids and are particularly used in bulk polymerization techniques. Examples of chemical blowing agents are solid dioxide or nitrogen releasing compounds such as azodicarbonamide. The document US 3, 973,884, mentioned in the previous paragraph, specifically describes that for the production of the particles for applications of higher density, it is possible to use smaller amount of pentane or other blowing agents than that which has been used in the particles for low applications. density. However, it is still said that the difference is small and that in the particles for low density applications, the pentane content can be 6-7.2% weight, which is just more than 5.8-7.01 by weight of the pentane content of the particles for high density applications . It has now been discovered that lower amounts of the hydrocarbon blowing agent also allow a density reduction at a level between 600 and 200 kg / m3. The resulting "pre-expanded particles are more advantageous in view of environmental and safety concerns during transport and storage." Therefore, it is preferred to prepare the pre-expanded particles in an invention, by using a process in which the expandable polyvinylarene particles that contain from 0.5 to 4% by weight of the volatile organic blowing agent, based on the polyvinylarene, are pre-expanded at a bulk density of 600 to 200 kg / m 3 A more preferred particle to be used in the present invention, is the porous particle as described in applicant's co-pending application No. 98203099.1 This particle contains 2.0% by weight or less of a volatile organic agent of blowing, based on the weight of the polyvinylarene, which preferably is less than 1.5% by weight. This particle can be obtained, for example, by preexpanding a non-expanded polyvinylarene particle, which is prepared by an aqueous suspension polymerization of the vinylarene monomers in the presence of a nucleating agent and from 0.1 to 1% by weight of a free radical initiator, wherein a C2-6 hydrocarbon blowing agent is added before, during or after polymerization, wherein the amount of the blowing agent ranges from 0.5 to 4% by weight, based on the amount of vinylarene. Alternatively, they may be prepared by pre-expanding the particles that are obtained by a process as described in co-pending application of Applicant No. 98203098.3. Here, the compact polymer particles of the polyvinylarene, are impregnated with an inorganic gas containing N2- and / or 02- at a temperature below 95 ° C and at a pressure of 100 to 2,000 kPa in the indicator, to produce expandable particles of polyvinylarene.

The preexpansion of a non-expanded particle of polyvinylarene into a pre-expanded particle can be carried out in any suitable manner. Suitable methods that are well known are the use of hot air, a hot oil bath, infrared radiation, microwave radiation or steam. The vapor can be used at temperatures of 100 to 168 ° C at pressures of 0 to 600 kPa, in the indicator, depending on the presence of additives and / or other polymers in the polyvinylarene particle. In the case of polystyrene, it is preferred to use a saturated steam at a temperature of 100 -125 ° C at pressures of 0 to 230 kPa in the indicator. The unexpanded polyvinylarene particles can also be pre-expanded when exposed to warm water. This method is preferred. In this mode, the water suitably has a temperature ranging from 60 to 100 ° C and the exposure lasts from 5 to 120 minutes. The most preferred method for pre-expanding the non-expanded particles of polyvinylarene in the present invention is the use of hot air, which has a temperature which ranges from 90-200 ° C, preferably from 95-160 ° C and more preferably from 100-140 ° C. Preferably the exposure lasts up to 3 hours. Another preferred particle for use in the present invention is a particle that has been pre-expanded "in-itself". For this purpose, the styrene is polymerized in bulk in an extruder in the presence of a blowing agent. When the molten mixture of the hot polymer exits the extruder, the blowing agent is released to effect pre-expansion at a density of 600-200 kg / m3. The slightly expanded strands of the polymer are then cut to obtain the particles for use in the present invention. In this technique, it is preferred to use carbon dioxide or chemical blowing agents. The vinylarene monomer, comprised within the polymer of the present process consists preferably and mainly of styrene. The polyvinylarene can contain up to 10% moles of another monomer containing a vinyl group, such as acrylonitrile, acrylic or methacrylic acid or esters, substituted styrene, such as chlorostyrene, or α-methylstyrene or divinylbenzene. However, preferably the vinylarene in the polyvinylarene consists of more than 99% moles of styrene. More preferably the polyvinylarene is polystyrene. Polymerization per se is well known in the art. It can be initiated thermally, by means of polymerization of free radicals or by means of anionic polymerization. Although both methods are equally possible, preference is given to free radical polymerization. Suitable initiators of free radicals can be selected from conventional initiators for free radical polymerization. They include, in particular, peroxy organic compounds, such as peroxides, peroxycarbonates and peresters. Typical examples of these peroxy compounds are C6-20 acyl peroxides such as decanoyl peroxide, benzoyl peroxide, octanoyl peroxide, stearyl peroxide, peresters, such as t-butyl benzoate, t-butyl peracetate. , t-butyl perisobutyrate, t-butylperoxy- (2- ethylhexyl) carbonate, hydroperoxides and dihydrocarbyl peroxides, such as those containing C3-10 hydrocarbyl moieties, including di-isopropylbenzene hydroperoxide, di-t-butyl peroxide, dicumyl peroxide or combinations thereof. Other initiators other than the peroxy compounds are also possible, for example, a, a'-azobisisobutyronitrile. The suspension polymerization is suitably carried out in the presence of suspension stabilizers. Suitable suspension stabilizers are known in the art and comprise polyvinyl alcohol, gelatin, agar, polyvinyl pyrrolidone, polyacrylamide, inorganic stabilizers such as alumina, bentonite, magnesium silicate or phosphates, such as tricalciiophosphate and / or disodiohydrogen. phosphate, optionally in combination with any of the stabilizer compounds mentioned above. The amount of the stabilizing agent can suitably vary from 0.1 to 0.9% weight, based on the weight of the aqueous phase.

The suspension polymerization is carried out suitably in two temperature stages, wherein the temperature in the first stage ranges from 85 to 110 ° C and in the second stage from 115 to 140 ° C. It may be advantageous to polymerize the vinylarene monomers in the presence of other polymers such as polyphenylene oxide or elastomeric polymers. Suitable polyphenylene oxides have been described in EP-A-350137, EP-A-403023 and EP-A-391499. The polyphenylene oxide is preferably present in an amount ranging between 1 and 30% by weight, based on the amount of the vinylarene monomers, and can improve the rigidity of the polyvinylarene polymer. Examples of suitable elastomeric polymers have also been described in EP-A-350137 and comprise (block) copolymers of vinyl-substituted aromatic monomers and a conjugated diene monomer. These elastomeric polymers are preferably present in an amount ranging from 0.5 to 10% by weight, based on the amount of the vinylarene monomers, and can improve the impact strength of the polyvinylarene polymer.

The non-expanded and / or pre-expanded particles of the polyvinylarene can contain various conventional additives. These additives include chain transfer agents, crosslinking agents and nucleating agents. Suitable examples of the chain transfer agents are the C2-C15 alkyl mercaptans, such as n-dodecyl mercaptan, t-dodecyl mercaptan, t-butyl mercaptan and n-butyl mercaptan. Other agents are pentaphenyl ethane and dimer of -methylstyrene. Examples of the crosslinking agents are butadiene and divinylbenzene. Nucleating agents are agents that promote cell formation and are suitable for use in an amount ranging from 0.01 to 3% by weight, based on vinylarene, preferably in an amount of 0.05 to 2% by weight. Examples of nucleating agents are finely dispersed inorganic compounds, polymeric particles and organic solids. Examples are carbonated compounds, such as calcium carbonate, sulphated compounds such as barium sulfate and calcium sulfate, silicate compounds such as talc, clay, magnesium silicate, amorphous silica particles, zeolites, diatomaceous earth, oxides such as magnesium oxide, and titanium oxide, mixtures of sodium bicarbonate with citric acid, organic compounds containing bromine, naphthalene compounds, polycyclic aromatic hydrocarbons, carbon black, coke, charcoal, graphite and diamond powder, paraffin and fatty acid derivatives such as stearate and palmitate compounds. Examples of suitable polymer particles are polyvinyl chloride, polypropylene, polyethylene, styrene rubber of acrylonitrile butadiene, styrene-butadiene rubber, anhydrous styrene / maleic copolymer and cellulose. Other examples include polar polymers as described, for example, in WO 98/01501 comprising, for example, starch and starch modified by esterification or etherification, emulsifiers as described, for example, in WO 98/01488 and WO 98/01489 comprising bisalkylsulfosuccinates, sorbitol-carboxylates-Cs-C2o, and sulfonates of Cs-C2o alkylxylene. Particularly suitable nucleating agents are polyethylene waxes having an average molecular weight of from 500 to 5,000, which are typically finely divided through the polymer matrix in an amount of 0.01-1.0% by weight, based on the amount of vinylarene, preferably from 0.1 to 0.5% by weight. The particles may also contain antistatic additives, flame retardants, such as hexabromocyclododecane, dyes, filler, stabilizing agents, plasticizing agents, such as white oil, and lubricants. These particles are suitably coated with coating compositions comprising silicones, silicates, metal carboxylates or glycerol. Suitable carboxylates are glycerol mono-, di- and tri-stearates, zinc stearate, and mixtures thereof. Examples of these compositions have been described in GB Patent No. 1, 409, 285. In place of the stearate, citrate or palmitate can also be used. The coating compositions have been applied to the particles by means of a dry coating, in a mixer of tape or by means of a watered paste or solution of a liquid easily vaporizable. The pre-expanded particles are impregnated with an inorganic gas to produce the impregnated particles. The pores in the pre-expanded particle are of such size that a reasonable amount of inorganic gas can permeate into the pores of the particle. By the term "inorganic" gas it is implied that the impregnated gases according to the present invention may contain mostly 1% by volume, based on the volume of the gas, of organic compounds, preferably mostly at 0.5% by volume . More preferably, the gases according to the present invention do not contain any organic compound. An example of a suitable inorganic gas is carbon dioxide. However, this interferes with the polyvinylarene matrix. Like many commercial blowing agents, it dissolves to a certain degree in the polymer matrix. This means that for some applications it has to be removed with effort in view of the potentially negative effects, for example, in the field of safety, health or toxicology. The dioxide carbon, also known as a well-known greenhouse gas, is therefore not preferred. Inorganic gases which do not have this negative effect and which show less interaction with the polymer matrix are preferred. Examples of these gases are the inorganic gases containing N2- and / or 02-, helium, neon and argon. More preferably, the inorganic gas which is used for the impregnation is selected from inorganic gases containing N2- and / or 02-. These gases adequately contain more than 90% by volume, based on the volume of the gas, of N2 and / or 02, more suitably more than 95% by volume. More preferably, the gas is nitrogen or air. Not only do these gases barely interfere with the polymer matrix, but they are also effective and cheap, and have no negative effect on the environmental or health impact. Impregnation can be carried out in several ways. However, it is preferred to impregnate the pre-expanded particles with an inorganic gas by exposing the particles to the gas at temperatures ranging from 0 to 95 ° C. The preferred temperature ranges are found between 0 to 50 ° C, more preferably between 10 to 30 ° C. More preferably, the temperature used is the room temperature. In this way, the empty spaces in the particles are filled with the gas without the polyvinylbenzene being heated, in such a way that it can be deformed. This deformation can have a negative effect on the structure and property of the empty spaces and therefore can have a negative impact on the expansion capacity of the resulting impregnated particles. Moreover, the low temperatures ensure that the particles remain in a free fluid and do not stick with each other, which can occur if the impregnation is carried out at higher temperatures. The impregnation is such that, in the pores of the porous particle, a pressure of 100 to 1,500 kPa in the indicator can be canceled. Preferred pressures of the pores are between 200 and 1,000 kPa in the indicator, more preferably between 300 and 800 kPa in the indicator. Pressures less than 100 kPa in the indicator mean that the empty spaces are barely filled with gas, example, nitrogen or air, at approximately atmospheric pressure. This replacement will result from insufficient expansion, if any. Pressures greater than 1,500 kPa in the indicator are possible, but are undesirable due to economic and safety reasons. The external pressure applied, necessary to establish the desired pressure in the pores, is preferably between 100 to 2,000 kPa. Although it is possible to use higher external pressures, this requires better equipped pressure containers and would make sampling more difficult. Preferably, the maximum external pressure employed is 1,500 kPa. Suitably, the external pressure applied is the same to the desired pressure in the pores of the porous particle. After impregnation, the impregnated particles can be taken to a conventional expansion unit and further expanded by at least 3 times the volume of the pre-expanded particle. There is no need to take any specific precautions when carrying the particles to the expansion unit. However, it can be useful to do this by means of a pressure lock.

Within the expansion unit, the impregnated particles expand to a bulk density that is at least 3 times lower than the original bulk density. Preferably, the impregnated particles are expanded to a bulk density of at least 5 times less than ds. Although the expansion can be carried out at any desired bulk density, it is practical to carry out the expansion at a bulk density that is up to 20 times, more preferably up to 40 times less than d0. It can be advantageous to carry out the expansion process in stages. To this, the expanded polyvinylarene particles which are obtained after the expansion are advantageously impregnated again ("reimpregnar") with an inorganic gas and in this way the reimpregnated particles expand again. The reimpregnation process can be repeated up to a certain number of times. However, the right-handed technician must seek a balance between the duration of the impregnation in order to maximize the amount of impregnated gas on one side, and a low number of impregnation repeats and expansion sequences on the other. Properly, this leads to a process where the impregnation and expansion stages are repeated between 1 and 4 times. As already indicated, the expansion can be carried out in any conventional expansion unit. The proper methods are the same to the methods that are well known and as described for pre-expansion. The use of steam as an expansion method is preferred. As already indicated in the above description, the expanded particles are suitably placed in a mold and heated so that the expanded particles are fused together to produce foamed and molded articles. Therefore, the invention also provides a process for preparing a foamed article in which the expanded polyvinylarene particles that are obtained by a process according to this invention are heated in a mold until the polyvinylarene particles soften and adhere to each other. , and the heated mold thus obtained, is cooled to form a foamed article. Heating in the mold is conventional and Typically it is in the range from 110 to 125 ° C. The invention is to be illustrated by means of the following Examples.

Examples All apparent densities are quantified in accordance with the following method: A cylindrical crucible of 1000 cm3 +/- 2 cm3 capacity, which has an internal diameter of 66 mm and a height of 293 mm is weighed to the nearest 0.1 gram (pressure atmospheric, room temperature). Subsequently, the crucible is filled with polyvinylarene particles. A perfectly flat metal scraper is used to strike three times against the side of the crucible and subsequently scrape the excess material in the top of the crucible, without stirring the crucible. The material inside the crucible is weighed to the nearest 0.1 gram and the weight of the polyvinylarene particles in grams of 1 cm3 is calculated and converted to kg / m3.

The pentane contents are quantified with gas chromatography using N-hexane in the manner of the internal standard.

Examples 1-2 The polystyrene particles are prepared by a suspension polymerization process. Here, 4,000 grams of demineralized water (4 liters), 3,680 grams of styrene (4 liters), conventional suspension stabilizers, 0.25% weight, based on the weight of styrene, of a polyethylene wax, and 0.25% weight of white oil , they are mixed at a stirring speed of 475 rpm. Polymerization begins by raising the temperature to 86 ° C and by adding the peroxide initiators (0.65% weight). In addition, it adds 0. 05% weight of the dimer of α-methylstyrene. After about a period of 6 hours, 81 grams of pentane (mixture of 75% weight of n-pentane and 25% weight isopentane) are added and the temperature rises to about 120 ° C where it is kept for 2 hours . After finishing the polymerization, the reaction mixture is cooled.

The resulting polystyrene particles contain 2.1% by weight of pentane, based on the weight of the polystyrene, and have a particle size in the range of 0.4-0.7 mm. The polystyrene particles are pre-expanded by placing them in a water bath at 100 ° C for a period of 15 minutes or by placing them in a batch steam pre-expander KURTZ KV450 using a vapor pressure of 80 kPa in the indicator a temperature of 117 ° C for a period of time of 30 seconds (KURTZ is the trade name). The apparent density ds of the resulting pre-expanded particles is quantified. Then, the pre-expanded particles are impregnated with nitrogen gas by storing them in a pressurized container under a pressure of 600 kPa in the nitrogen gas gauge at room temperature. After a period of 3 hours, the pressure is released and the pre-expanded and impregnated particles are removed. After a half-hour period, they are placed in a KURTZ KV450 batch steam expander, where the particles are allowed to expand even further under a pressure of, respectively, 80 and 60 kPa in the indicator and at a temperature of, 117 ° C and 11 ° C, respectively for 30 seconds. From the particles obtained thus, the bulk density d is quantified. In addition, the proportion of ds / d is calculated. The results are indicated in Table I.

Examples 3-4 The procedure of Examples 1-2 is repeated, except that the polystyrene particles are preexpanded by placing them in a KURTZ KV450 batch steam pre-expander under a pressure of 80 kPa in the indicator at a temperature of 117. ° C for a period of time of 15, respectively 45 seconds, and the resulting pre-expanded particles are impregnated with air instead of nitrogen. The results are indicated in Table I. Example 5 The procedure of Examples 1-2 is repeated, with the exception that the polystyrene particles are preexpanded by subjecting them to hot air at 110 ° C for 50 minutes, and in that the particles The resulting pre-expanded products are impregnated with air instead of nitrogen. The particles are further expanded by using a POLYTECH steam batch expander under a pressure of 90 kPa in the steam gauge and at a temperature of 118.5 ° C for 30 seconds (POLYTECH is the trade name). The results are shown in Table I.

Table I steam Expansion under 60 kPa in the steam pressure gauge 3 Expansion under 90 kPa in the steam pressure gauge Comparative experiments 5-6 The procedure of Example 2 and 4 is repeated except that the pre-expanded polystyrene particles are not impregnated respectively with nitrogen gas or air. The results are indicated in Table II. In both cases, a significantly smaller expansion is observed than in Examples 2 and 4.

Table II 1 Expansion under 60 kPa in the steam pressure gauge, It is noted that in relation to this date, the best known method for the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers.

Claims (10)

R E I V I N D I C A C I O N S Having described the invention as above, the content of the following claims is claimed as property:

1. A process for the preparation of expanded particles of polyvinylarene characterized by the fact that the polyvinylarene particles of preexpanded at an apparent density d0 ranging between 600 and 200 kg / m3 are impregnated with an inorganic gas, and the impregnated particles obtained in this way, they expand to an apparent density of at least three times less than ds.

2. The process according to claim 1, characterized in that the polyvinylarene particles are polystyrene particles.

3. The process according to claim 1 or 2, characterized in that the bulk density d0 ranges from 530 to 250 kg / m3.

4. The process according to any one of claims 1 to 3, characterized in that the polyvinylarene particles are impregnated by the inorganic gas when the particles are exposed to the gas at temperatures ranging from 0 to 95 ° C, in such a way that in the pores of the porous particle a pressure of 100 to 1,500 kPa is achieved in the indicator.

5. The process according to any of claims 1 to 4, characterized in that the inorganic gas is selected from gases containing N2- and / or 02-.

6. The process according to claim 5, characterized in that the inorganic gas is nitrogen or air.

7. The process according to any one of claims 1 to 6, characterized in that the impregnated particles are expanded to a bulk density of at least 5 times less than dQ.

8. The process according to any of claims 1 to 7, characterized in that the impregnated particles are expanded to a bulk density of up to 40 times less than ds.

9. The process according to any one of claims 1 to 8, characterized in that the impregnated particles are expanded by exposing them to steam at temperatures of 100 to 168 ° C and at pressures ranging from 0 to 600 kPa of indicator.

10. The process for preparing a foamed article characterized in that the expanded polyvinylarene particles that are obtained by the process according to any of Claims 1 to 9, are heated in a mold until the polyvinylarene particles soften and adhere to each other , and the heated mold thus obtained is cooled to form a foamed article.