JPS5824448B2 - Spherical cellular beads made of organic polymer materials and their manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to spherical cellular beads made of organic polymeric materials that retain their original shape when carbonized in the solid state.

This bead consists of a plurality of closed cells and is characterized in that the walls of the cells on the outer periphery form a skin delimiting the outer surface.

Although the dimensions of the beads according to the invention may vary, the average diameter preferably ranges from a few tenths of a millimeter to several centimeters, with the skin thickness being a function of the bead dimensions. is preferably in the range of about 50 to 500 microns.

A particularly interesting form of bead according to the invention is one consisting of cells of approximately constant dimensions, with a central part surrounded by a peripheral part, and which It is as if the volume occupied by the cells gradually decreases from the inside of the bead to the outside.

The ratio of average cell diameter to average bead diameter is 0.001~
Preferably, it is in the range of 0.25.

Similarly, the ratio of the average cell wall thickness to the average cell diameter is 0
．． It is preferably in the range of 0.0016 to 0.25.

The beads according to the invention can be used as is or as a starting material for various industrial applications.

For example, layered beads may be exposed to chemical baths that are volatile, toxic, 1, flammable, flammable, or susceptible to adverse effects from direct contact with the atmosphere. It can be used to coat the surfaces of baths containing such chemicals to prevent contact of the chemicals with the atmosphere.

The beads according to the invention can also be used to create inert permeable beds for separating solids from liquids or gases.

Furthermore, these beads, with e.g. metal or synthetic resin matrices, have novel combinations of physicochemical and mechanical properties that can be highly modified, thereby making it possible to
It can be used to produce composite materials that allow for applications such as

In all of these applications, the spherical shape of beads made of these organic polymeric materials facilitates their use, and the cellular nature of these beads allows them to be This means that it has a low density that allows for the manufacture of mechanical components.

The presence of a surface layer (“skin”) surrounding the outer periphery as described above allows liquid substances to be absorbed into the closed molded material containing the beads according to the invention without these liquids being impregnated into the internal pores of the beads. By casting into objects, it is possible to manufacture composite materials.

The invention also relates to a method of manufacturing spherical carbon beads as described above.

This method involves preparing at least one hard organic polymer which retains its original shape when carbonized in the solid state.
A paste-like mixture is prepared containing a base material and at least one blowing agent, the mixture is divided into particles, the particles are separated from each other, and the separated particles are foamed into cells and cured. It is characterized by allowing

The organic polymeric material used, which can be carbonized in the solid state, is preferably such that it has a carbonization residue of at least 15% by weight of its original mass.

In particular, thermosetting resins such as phenolic resins, amino resins, unsaturated polyesters, alkyd resins, reticulated polyurethanes, frifuryl alcohol polymers, mixtures of the above two types of polymers, epoxide resins, aromatic polyamide resins, polysulfones, phenylene polysulfides, etc. It is possible to use

It is to be understood that precursors for such resins are monomers or prepolymers, optionally mixed with at least one polymerization catalyst for the resin.

The thermosetting resin precursor used is a resol stage phenol formaldehyde resin, i.e. preferably 0
．． It is the product of the first condensation step of phenol and formaldehyde in the presence of an alkaline polymerization catalyst and with slight heating in a molar ratio of 8:1 to 3:l.

It is likewise possible to use phenol-formaldehyde resins of the novolak type, ie the products of the first condensation step of phenol and formaldehyde in the presence of an acid catalyst.

Other phenolic resins, such as cresol-formol, phenol-furfural, phenol-acetaldehyde, phenol-hensaldehyde, phenol-acrolein, etc., or amine resins, such as urea-
It is also possible to use resins based on unsaturated polyesters crosslinked with formaldehyde, melamine formaldehyde, etc., or triallyl cyanurate, etc.

Similarly, as a precursor resin, at least one polyester or polyether polyol, at least one catalyst, at least Mixtures of one surfactant, water and/or at least one blowing agent and at least one organic diisocyanate can be used.

Blowing agents include, for example, fluorocarbon compounds such as trichlorofluoromethane, low molecular weight aliphatic alcohols, especially methanol and ethanol, volatile compounds such as petroleum ether (mixtures of some volatile compounds, or heated It is possible to use a mixture of substances that react together to generate a gas when heated, or a substance that decomposes and generates a gas when heated.

It is also preferred to introduce a surfactant into the mixture to prevent cells from coalescing during foaming of the beads while the mixture is not yet cured.

It is also preferred to add at least one curing catalyst for the resin to the mixture, for example an acid such as hydrochloric acid, sulfuric acid, phosphoric acid, para-toluenesulfone+t.

In addition to the components mentioned above, powdered inert substances, such as powdered silica, carbon black, etc., can also be added to the mixture to act as fillers.

According to a first treatment method, droplets of a pasty mixture are formed at the top of the column in a known manner, and these droplets are heated and foamed while falling down the column.

The rate of fall and the heating conditions are controlled to ensure that the resulting spherical beads are sufficiently cured without being deformed or poking each other when they reach the bottom of the column.

The rate of fall of the droplets may be controlled using an upward flow of gas, such as an air flow.

This airflow at least partially covers the surface of these beads during bead foaming while still viscous, to prevent the spherical beads from poking each other (and against the tower walls). Finely divided particles of material that can be coated, such as talcum powder, carbon black, etc., can be conveyed.

More generally, droplets of a pasty mixture are formed in a container of any suitable shape and these droplets are injected or, if necessary, particles of solid material are formed in this container. A relatively fast air flow, with or without airflow, can be used to impart appropriate downward, upward, lateral, etc. movement to the droplets.

This movement prevents the droplets from coming into contact with each other or with the walls of the container, or at least makes this contact time very short, and at the same time provides a suitable treatment for these droplets in order to foam them into spherical cellular beads. It provides heat treatment.

One way to carry out these operations is to use a so-called "cyclone" device in a container equipped with one or several stirring impellers, etc.

These particles can be expanded into cells under atmospheric pressure or under reduced pressure, for example under a pressure of 10 to 100 millimeters of mercury.

Heat treatment generally involves heating, polymerization of the resin,
or the termination of this polymerization and the evolution of gas inside the droplet and/or
Or it needs to be accompanied by an effect of causing expansion.

To carry out this heat treatment, all suitable methods can be used, for example radio frequency heating with microwave oscillators or radiation heating, or the air flow itself can be used to transfer the heat to the droplets.

Combining some of these heating methods, e.g., first at the point of initiation of the droplet in the container, the rapid heating of the droplet;
Microwave energy is used to heat the droplets to cause foaming into spherical cellular beads, e.g. within a few seconds, followed by heating using a stream of hot air to terminate polymerization of the resin and harden the beads. You can also do it.

According to a second method of operation, the particles of the mixture are dropped onto a bed containing at least one inert powder material (so that the particles do not come into contact with each other) and are then heat treated to foam into cellular beads; The resulting beads are hardened.

As inert powder substances minerals such as talcum, carbon black, graphite etc. or organic materials such as organic resins such as phenolic resins can be used.

This material is preferably in the form of fine particles, for example having a particle size on the order of 0.1 to 100 microns.

The bed of powder material is chosen as a function of the dimensions of the desired spherical beads and preferably has a thickness not exceeding a few millimeters, either a fixed bed or an "oscillating" bed, i.e. particles of powder material impart vibrations. A bed of powdered material, such as the one described above, can be used.

In the latter case, it may be vibrated by suitable means, e.g. a motor fixed to the dish by an eccentrically placed shaft, with an amplitude of a few millimeters and e.g.
A bed of powdered material placed in a dish that is given a circular vibrational motion at Hertzian frequencies can be used.

More generally, a bed of powdered material can be used that provides more vigorous agitation than simple vibration, such as a spirally stirred bed or a fluidized bed.

To form particles of the mixture, the mixture, which may be in liquid or pasty form, can be reduced into droplets or passed through a stage in which the mixture temporarily becomes solid.

In the first case, a device containing at least one nozzle of a size corresponding to the desired droplet size is used, through which the mixture can be flowed or extruded depending on its viscosity.

The device may be a container with a hollow needle-like nozzle or a bottom in the form of a plate, at least partially perforated.

The plate or other wall of the container may be vibrated, if necessary, at a frequency and amplitude suitable to provide liquid or glue droplets of the desired size.

It is likewise possible to use other devices, such as those for centrifuging the mixture, if necessary with heating devices, devices for the production of air currents that separate the droplets, etc.

In the latter case, use a liquid or paste-like case.

After extrusion through one or several nozzles to form a corresponding number of liquid or pasty threads, these threads are cooled, e.g. with a cold fluid, especially a liquid gas, especially liquid air or a liquid. The solid brittle filaments finally obtained are ground by immersion in nitrogen, and the particles obtained by this grinding are sieved, keeping the temperature sufficiently low during this cooling operation. A desired particle size can be achieved.

The latter method for forming droplets of mixture is capable of several variations.

For example, it is also possible to omit the initial pasty extrusion and to grind the mass of the mixture in various forms, which is hardened by cooling.

The method of droplet formation as described above facilitates the formation of uniformly sized particles with a narrow particle size range that can be easily varied, and when the viscosity of the pasty mixture is greater than a predetermined value. , which has the advantage of higher production rates than glue-like droplet formation.

It is clear that the two droplet formation methods as described above can be optionally combined by using a fixed bed of powdered material or by using a "vibrating" bed, respectively.

The use of a "vibrating" bed of powdered materials, compared to a fixed bed, is advantageous since the collapse of the particles in the paste before the resin hardens is prevented by the movement of these particles as imparted by the vibration of the bed.
Note that we have the advantage of being able to produce spherical beads with diameters up to the order of 1 crIl.

On the other hand, when a fixed bed is used, the dimensions of the final spherical beads are at a smaller upper limit, generally 5 to 6 mm, depending on the surface tension of the mixture and the individual masses. , has.

The use of such a vibrating bed also has the advantage of providing a greater production rate for a bed of powdered material of a given surface area compared to a fixed bed.

Additionally, in the case of a vibrating bed, the vibrations of the bed cause particles to move toward each other (
Placing the particles on a bed of powder material simplifies the operation, since it is not necessary to take special measures to prevent this and avoid contact between the particles.

If droplets of the mixture are formed in liquid or paste form and a fixed bed is used, the droplets will settle only slightly into the bed.

In contrast, when a vibrating bed is used, the droplets fall into the bed and immediately coat their entire surface with powder, so that they do not stick to the walls of the container containing the bed of powder material or are already in the bed. It does not stick to other droplets.

The heat treatment conditions for these particles, in particular the rate and duration of heating, depend on the viscosity of the mixture and the rate of increase in viscosity, mainly as manifested by polymerization of the resin, as well as on the production and/or expansion of the gas supplied by the blowing agent. Preferably, the speeds are chosen to be compatible with each other to produce spherical cellular beads with the desired properties.

For this purpose, the pasty mixture may be left for various lengths of time before foaming, before or after the formation of the droplets.

Thus, for example, in the second method of operation, a bed of powder material is used which is initially at a temperature lower than that required to foam the particles by the action of a blowing agent, and the temperature of this bed of powder material is adjusted to a suitable temperature. It may be increased at a speed.

Similarly, using beds of powdered material at various temperatures, the particles are transferred from one bed to another and successively progressed in the direction of increasing temperature to foam and form spherical beads. can also be hardened.

For example, bringing the particles of the first bed of powder material to a predetermined temperature sufficient to cause these particles to fully foam or to initiate foaming, and to fully harden the particles. After being held for a moderately long period of time, the particles are separated from the first bed, for example by sieving, and placed on another bed maintained at a higher temperature than the first bed. If necessary, these foams are completed and then cured.

Even if a fixed bed is used, it is preferred that one or more "oscillating" beds are used subsequently.

Of course, an operation in which these particles, during their foaming, are sequentially conveyed to different areas with different temperatures, e.g. temperatures that increase gradually depending on the thermal properties corresponding to the heat treatment to be carried out. It is also possible to use a single bed of elongated shape, vibrated at

The heat treatment of these particles is carried out in the same way whether the particles are formed from a solid or from a liquid or paste.

In the former case, the first stage of heating only softens these solid particles so that they become spherical under the action of surface tension and, if necessary, the vibratory action of the bed, before they begin to foam. It is.

All or part of the operations as described above may be performed in a discontinuous or continuous manner.

In the latter case, it is possible in particular to recirculate the bed of inert powder material following the second operating method.

The invention also relates to the use of spherical beads of organic polymeric material, as described above, for the production of spherical cellular beads with a high carbon content.

This use is characterized by heating these beads under a non-oxidizing atmosphere to a predetermined temperature for a time sufficient to cause their carbonization.

Preferably, the non-oxidizing atmosphere used is that of an inert gas, such as nitrogen or argon.

Heating is preferably carried out at a temperature in the range of 100 to 1200°C, with the temperature gradually increasing as carbonization progresses.

The heating time is preferably 1 to 24 hours.

If the spherical cellular beads of organic polymeric material are made of rigid polyurethane foam, it may be advantageous to subject these beads to an oxidation treatment before carbonization.

The heating conditions are such that, by carbonization, the total weight of carbon-rich beads with a carbon content of 90-100% by weight and a portion of the corresponding polymeric organic material from the starting spherical cellular beads is finally obtained. selected to provide spherical cellular beads in a partially carbonized state.

Such spherical cellular beads having a high carbon content can be used in conditions similar to those described above for spherical cellular beads made of organic polymeric materials.

However, for certain applications, this high carbon content cellular beads have advantages compared to cellular beads made of organic polymeric materials.

Particularly in applications such as insulating layers and inert filter materials for chemical baths, high carbon content beads are more inert than beads of polymeric materials.

Furthermore, the carbon-rich beads can be used in certain situations where it is not appropriate to use beads of polymeric material.

For example, spherical cellular beads with a high carbon content can be used to produce a composite material comprising a metal matrix containing high carbon spherical cellular beads according to the invention.

This application is described in Swiss Patent No. 515195.

Example 1 A mixture having the following composition was prepared.

"Resol" stage prepared by the condensation of approximately equimolar amounts of phenol and formaldehyde in the presence of a basic catalyst and having a specific gravity of 1.245 to 1.255 and a viscosity of 35 to 40 poise at 25°C. Phenolic resin 50g Anhydrous ethyl alcohol 4.25i35~7
Petroleum ether in the distillation range of 0°C 4.25i Valatoluenesulfonic acid 2.5L? The above ingredients were mixed by vigorous stirring for 1 minute using a spiral stirrer rotating at 1250 rpm.

Immediately after stirring, the mixture was poured into a syringe equipped with one part driven by an electric motor.

This syringe has a volume of 50i and an internal diameter Q, 3 mm
It was connected to a droplet making device with 24 openings in the form of a hollow needle.

The total flow rate of the extrusion speed of the motor 1 drive part is 0.3
It was adjusted to be crit/sec.

This resulted in the formation of 8 droplets of the viscous mixture per second, which were allowed to fall freely and were collected at room temperature onto a bed of talcum powder containing particles with a particle size on the order of 5-20 microns.

This bed had a thickness on the order of 1 cIrL, was placed approximately 20 crrl below the end of the needle contained in the droplet maker, and was subjected to horizontal circular vibrations of 1 cm amplitude.

The time required to drop the entire mixture was on the order of 2-3 minutes.

After all of the droplets were collected on the vibrated talcum bed, heating of the bed was started using an electrical resistor mounted in the support pan of the bed.

The heating rate is 40℃ in about 6 minutes in the center of the bed, 20~
The temperature was controlled to reach 80°C in 25 minutes.

It will be appreciated that when the temperature reaches about 40° C., droplets begin to expand into spherical shapes and float on the surface of the bed.

The bed was held at a maximum temperature of 80°C for 5-10 minutes, so the total heating time was on the order of 30 minutes.

The spherical beads thus obtained were then separated from the talcum bed by means of a sieve.

Thereby, the cell has an ideal spherical shape, a diameter on the order of 40 mm, and a thickness on the order of 100 microns surrounding an inner cellular part consisting of regular cells with dimensions on the order of 40 microns. Approximately 50 f fully cured pink beads with a continuous skin were obtained.

The volume occupied by these beads was on the order of 500- and the density of each bead was about 0.171/crit.

The obtained spherical beads were carbonized as follows.

That is, these spherical beads were heated from 100° C. to 1000° C. for 12 hours under a nitrogen atmosphere.

Spherical cellular beads of glassy carbon with a carbon content close to 100% are obtained, with an average diameter on the order of 32 mm and 0.18 mm. It had a density on the order of /crA.

The average cell size of such carbon-rich beads was on the order of 30 microns.

Example 2 The procedure of Example 1 was repeated using the same amount of mixture of the same composition.

However, in this case instead of collecting the droplets on a vibrated talcum bed, the droplets were collected on a fixed bed of talcum powder having a thickness of 51n11t and set 20 crIL below the droplet exit point.

The floor was spread over a fixed horizontal pan of steel sheet having an area of 0.1 m.

The droplet making device is moved in a horizontal plane, thus the floor 1cr
A constant free fall distance was maintained for the droplets of the mixture on the bed, giving one droplet per A.

Once the dish was completely loaded with droplets, it was heated from room temperature to 80° C. in 45 minutes with an approximately linear increase in temperature.

This yielded approximately 357 beads per meter of bed similar to those obtained in Example 1.

The obtained spherical beads were carbonized by the same operation as in Example 1.

Example 3 A mixture having the following composition was prepared.

It is obtained by condensation of phenol and formaldehyde in a molar ratio of 1:1.10 in the presence of sodium hydroxide and has a specific gravity of 1.2 and a viscosity of 100 poise at 25°C (containing 10% by weight of methanol). 1007 Surfactant (condensation product of monopalmitic anhydride sorbitate and ethylene oxide) 27 Oxalic acid 4.57 Distilled water
2d Petroleum ether with a distillation range of 35-70° C. 8i The above ingredients were mixed by vigorous stirring for 1 minute using a spiral stirrer rotating at 1250 rpm.

Next, 2 cIiL of methanol and 51
of para-toluenesulfonic acid was added and the whole was mixed for an additional minute using the same stirrer.

A pasty homogeneous mixture was obtained, which was then processed according to the same procedure as described in Example 1.

Example 4 A mixture having the following composition was prepared.

A "resol" stage phenol having a specific gravity of 1.245-1.255 and a viscosity of 35-40 poise at 25°C, obtained by condensing approximately equimolar amounts of phenol and formaldehyde in the presence of a basic catalyst. Resin 50735-70
A mixture of 142 parts by weight of an aqueous solution containing 92% of petroleum ether 4C111 acid catalyst H2SO4, 44 parts by weight of an aqueous solution containing 84-85% H3PO4 and 41.8 parts by weight of distilled water) 6 m before mixing the resin was vigorously stirred for 2 minutes using a spiral stirrer rotating at 1250 times/min to incorporate a predetermined amount of air.

After this, petroleum ether was added and the whole was stirred again for 1 minute using the same stirrer.

This mixture is then cooled to a temperature on the order of 1°C, after which
The catalyst was added and the mixture was stirred again for 30 seconds using the same stirrer.

The resulting viscous mixture was poured into a 50i capacity syringe equipped with an electric motor driven section.

The syringe was also equipped with a 1 mm diameter dispensing needle which extruded the viscous mixture into a thread approximately 1 mm in diameter.

As extrusion progressed, the thread was dropped into a container of liquid air.

The thread solidified spontaneously upon contact with liquid air.

The resulting solidified thread was cut into pieces of about 1 dragon length using a rotating cutter, which was also submerged in a liquid air container.

After cutting the entire mixture into solid particles as described above, these solid mixture particles were cut into solid particles having a lattice spacing of 1 mm;
Collected on a metal grid pre-cooled with solid carbon dioxide water.

These mixture particles were then transferred by shaking the grid onto a bed of carbon black having a thickness of approximately 5 mm and consisting of particles having an average size on the order of 0.1 microns.

This bed was contained in a metal pan.

After about 1 minute of this operation, the metalware was placed in an oven heated to a temperature of 80° C. and kept in this oven for 1 hour.

The above yielded 50 grams of spherical beads of hardened phenolic resin, pink in color and having a "skin" thickness on the order of 100 microns.

This amount of 507 corresponded to a capacity on the order of 500 d.

The particle size distribution of these beads in weight percent was approximately as follows:

Weight % Diameter range (mm) 20 1-3 30 3-4 40 4-5 10 5 or more These spherical beads were then subjected to the same carbonization treatment as described in Example 1.

Example 5 A polyurethane precursor mixture was prepared having the following composition (in parts by weight):

Condensation product of propylene oxide and sorbitol, having a density of 1.0947/d and a viscosity of 16.000 centistokes at 20°C, a hydroxyl number of 490 m9 of potash per gram and an acid number of potash of 0.1 to (commercially available from Union Carbide, "N1
ax Polyol LS-490") is a condensation product of 75.0 propylene oxide and glycerol with a density of 1.0223'iI/cA and a viscosity of 400 centistokes at 20°C. , a polyether with a hydroxyl number of 230-245 potassium per gram and a maximum acid number of 0.05 m9 potassium (a product marketed by Union Carbide and known under the trade name "N1ax Polyol LMT-240") 25.0 Foaming agent (CCl2F) 30.0 water
1.0 catalyst (N-N
-dimethylethanolamine) 2.2 Catalyst (N-N-N-N'-tetramethylbutanediamine-1.3) 1.0 Surfactant (Protect copolymer of ethylene oxide, propylene oxide and siloxene, , a silicone oil having a viscosity of 1000 centistokes at 25°C and a density of 1.053 P/i and a freezing point of 10°C: commercially available from Union Carbide and designated "5ilicone 5urfactant L-
1.5 diphenylmethane diisocyaner)
1
28.0 Mixture consists of the above ingredients in the order indicated, 1
This was done by rapidly charging into a container equipped with a helical stirrer rotating at 250 rpm and continuing stirring for 3 seconds after all ingredients had been added.

An equal amount of polymerized polyfurfuryl alcohol was then added to the creamy mixture with continued stirring.

The pasty mixture obtained was immediately subjected to the operation described in Example 1.

Carbonization of spherical beads of this resin was carried out in 17 hours.

These final spherical, carbon-rich beads had a mass and volume equal to 50% of the mass and volume of the starting spherical resin beads.

Example 6 A polyurethane precursor mixture having the same composition as shown in Example 5 was prepared as described in Example 5.

However, in this case, furfuryl alcohol polymer was not added.

Using this mixture, in the same manner as described in Example 1,
Cellular spherical polyurethane beads were produced.

These spherical cellular beads obtained according to Section 2 were then heated in air, first at 150° C. for 24 hours and then at 250° C.
℃ for 24 hours and subjected to carbonization treatment as described in Example 1.

These spherical, carbon-rich beads finally obtained are 4 times smaller than that of spherical polyurethane beads before being subjected to carbonization.
It had a mass equal to 5% and a volume equal to 40%.

Example 7 A mixture having the same composition as shown in Example 4 was prepared in Example 4.
Prepared by the same procedure as above.

Droplets were formed by flowing the mixture through holes of 0.57rL71 diameter drilled through the bottom of the container.

This container was installed at the tip of a tower consisting of a top section with a diameter of 30 CrrL and a height of 1 m, and a main bottom section with a diameter of 2 m and a height of 101 TL.

At the top of the tower, these droplets were heated using a microwave oscillator with a power of 3 KW and were almost completely expanded into spherical beads of droplets during their fall in this part of the tower.

In the main part of this column, a temperature of 150 °C and 2 ml
An ascending air flow with a speed of sec was circulated.

This warm air flow delayed the fall of the spherical beads, with a fall time on the order of 20 seconds, completing expansion of the spherical beads and curing the beads.

The spherical cellular beads obtained above were prepared in Example 1.
It was used to produce spherical beads with high carbon content by treatment and carbonization in the same manner as described in .

Example 8 Using a mixture having the same composition as in Example 1, Example 1
I repeated the same operation.

However, in this case, a pouring needle with an inner diameter of 1 mm was used.

Droplets of a viscous mixture with a mean diameter of the order of 61n11L were obtained and these droplets were expanded in the manner described above.

This resulted in spherical cellular beads with an average diameter of 18 mrn.

Claims (1)

[Scope of Claims] 1. A spherical cellular bead made of an organic polymer material that retains its original shape when carbonized in a solid state, which is composed of a plurality of closed cells, and the cells on the outer peripheral surface are The walls form a skin delimiting the external surface and have an average diameter ranging from a few tenths of a millimeter to a few centimeters and a diameter of 50 to 50 cm.
The ratio of the average cell diameter to the average bead diameter is in the range of 0.001 to 0.25, and the ratio of the average cell wall thickness to the average cell diameter is 0.00 microns.
A spherical cellular bead characterized in that the particle diameter is in the range of 0.0016 to 0.25. 2. A method for producing beads according to claim 1, comprising at least one type of hard organic polymer that retains its original shape when carbonized in a solid state. 1
A glue-like mixture is prepared containing a parent material and a small amount of a blowing agent, the mixture is divided into particles, the particles are separated from each other, and the particles are separated into cells. A method comprising the steps of foaming and curing.