| Expandable Graphite |
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| Expandable Graphite |
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Expandable graphite is a graphite intercalation compound (GIC). Compare with other pure carbon material like diamond and C60, the special layer lattice structure of flake graphite makes it possible to be intercalated by other chemicals.
With flake graphite, the expandable graphite can be made through intercalate acid (sulphuric acid, nitric acid, and acetic acid are the commonly used acids) into the crystal layer of the graphite. To introduce such acid into the graphite layer, oxidants like H2O2, HNO3 or KMnO4 is necessary to be used. Or we can use electrochemical method to prepare GIC. After reaction, neutralizing, washing and drying are necessary.
For very long time, expandable graphite was mainly used as an intermediate. After expansion at 1000¡ÆC in oven, we get expanded graphite which could be used to make graphite sheet and graphite packing -- an important sealing material in industry. As an intermediate product, expandable graphite had only a few specifications. Most important items were particle size, expansion volume, carbon content and volatiles. In some area, low sulphur content was also very important. The storage time was only guaranteed for 6 months. The pH value was lower than 4.
Applications
During the recent ten years, great progress had been achieved regarding the application of expandable graphite in flame retardant materials. Some main applications are listed below.
Foam Products
Due to its easy ignition and rapid fire spread rate, reducing fire risk for polymeric foam products had always been considered as a top priority. Now expandable graphite had been used in PU foam. Such flame retarded PU foam had been used as seat material in aircraft and other traffic tools. It was also used as heat and sound insulation sheet for car after special treatment.
In building industry, such flame retarded PU foam has been used as sealing tape in windows and doors. Besides used in PU foam, expandable graphite was also used at EVA foam and now is of interest to be used in EPS foam.
Coating
Expandable graphite had been found its application in intumescent flame retarded coatings. Fine particle size expandable graphite had been used in steel structure flame retarded coatings in many countries.
Polyolefins
Expandable graphite had already been used in PE, PP and other POs when halogenated flame retardant was forbidden use, although up to know after using expandable graphite the mechanical property would be reduced more or less. Expandable graphite was mainly used in Plastics /Metal (Al) composite board at the moment.
Bitumen Roof Sheets
Recently expandable graphite had been used in bitumen roof sheets. For this application the black colour was not a barrier for use. Expandable graphite has very good flame retardancy to bitumen roof material.
Other applications
In China, using steel pipes as waste water pipes in buildings are not allowed now. Plastics pipes now are commonly used for rain water pipes and waste water pipes. Anti-fire ring then is forced to be used by regulation when the pipes pass through floors. Expandable graphite had been used in such rings by large amount. Together with resin and other additives, expandable graphite expanded during fire and then sealed the space caused by its melting or burning of the plastics pipes.
In other applications like fire-stop putties, fire-stop pillows, expandable graphite had replaced other intumescent agents and used widely.
In the back adhesives of carpets, we could also find the existing of expandable graphite. |
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Expandable graphite is a graphite intercalation compound (GIC). Compare with other pure carbon material like diamond and C60, the special layer lattice structure of flake graphite makes it possible to be intercalated by other chemicals.
With flake graphite, the expandable graphite can be made through intercalate acid (sulphuric acid, nitric acid, and acetic acid are the commonly used acids) into the crystal layer of the graphite. To introduce such acid into the graphite layer, oxidants like H2O2, HNO3 or KMnO4 is necessary to be used. Or we can use electrochemical method to prepare GIC. After reaction, neutralizing, washing and drying are necessary.
For very long time, expandable graphite was mainly used as an intermediate. After expansion at 1000¡ÆC in oven, we get expanded graphite which could be used to make graphite sheet and graphite packing -- an important sealing material in industry. As an intermediate product, expandable graphite had only a few specifications. Most important items were particle size, expansion volume, carbon content and volatiles. In some area, low sulphur content was also very important. The storage time was only guaranteed for 6 months. The pH value was lower than 4.
Applications
During the recent ten years, great progress had been achieved regarding the application of expandable graphite in flame retardant materials. Some main applications are listed below.
Foam Products
Due to its easy ignition and rapid fire spread rate, reducing fire risk for polymeric foam products had always been considered as a top priority. Now expandable graphite had been used in PU foam. Such flame retarded PU foam had been used as seat material in aircraft and other traffic tools. It was also used as heat and sound insulation sheet for car after special treatment.
In building industry, such flame retarded PU foam has been used as sealing tape in windows and doors. Besides used in PU foam, expandable graphite was also used at EVA foam and now is of interest to be used in EPS foam.
Coating
Expandable graphite had been found its application in intumescent flame retarded coatings. Fine particle size expandable graphite had been used in steel structure flame retarded coatings in many countries.
Polyolefins
Expandable graphite had already been used in PE, PP and other POs when halogenated flame retardant was forbidden use, although up to know after using expandable graphite the mechanical property would be reduced more or less. Expandable graphite was mainly used in Plastics /Metal (Al) composite board at the moment.
Bitumen Roof Sheets
Recently expandable graphite had been used in bitumen roof sheets. For this application the black colour was not a barrier for use. Expandable graphite has very good flame retardancy to bitumen roof material.
Other applications
In China, using steel pipes as waste water pipes in buildings are not allowed now. Plastics pipes now are commonly used for rain water pipes and waste water pipes. Anti-fire ring then is forced to be used by regulation when the pipes pass through floors. Expandable graphite had been used in such rings by large amount. Together with resin and other additives, expandable graphite expanded during fire and then sealed the space caused by its melting or burning of the plastics pipes.
In other applications like fire-stop putties, fire-stop pillows, expandable graphite had replaced other intumescent agents and used widely.
In the back adhesives of carpets, we could also find the existing of expandable graphite. |
| Industrial field |
additive, adhesive & sealant, others, paper & pulp additive, rubber & additives, solvents, waste & water treatment |
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