1. “ NEW CHALLENGE for INCORPORATION of
EXPANDABLE GRAPHITE as FLAME-RETARDANT in
VARIOUS POLYMERS”
VIJAY J. BHAGAT
RESEARCH & DEVELOPMENT CENTRE
CLEANLINE PRODUCTS Pvt. Ltd. , PUNE, INDIA
PRESENTED AT
FIRE & MATERIALS 2003
8TH
INTERNATIONAL CONFERENCE & EXHIBITION
SAN FRANCISCO, USA.
ABSTRACT: Expandable Graphite is well accepted as a flame retardant in most of the
foam system. Incorporation of expandable graphite in foam system makes it easier due
to its lower operating temperature but it becomes difficult task to incorporate
expandable graphite into higher processing temperature of polymer.
This paper demonstrates about the incorporation of expandable graphite into high
processing temperature of polymer. It also helps to identify the growth areas of
expandable graphite to meet future demand of the market.
INTRODUCTION: For safety and environmental reasons, flame retardancy has
become a critical issue, particularly in the area of construction, transportation, and
electronic/electrical application. Although halogenated Flame-Retardants are highly
effective in reducing flammability at commodity products, their future use is not precisely
defined; this is due its potential unacceptable risk to the human health and the
environment. This is the driving force for the development of non-halogenated Flame-
Retardants.
2. R&D centre of Cleanline Products Pvt. Ltd., is constantly working on new technique and
future oriented NON HALOGENATED PRODUCTS. In last three years CPPL scientists
have studied the market demands and aggressively moved to broaden their product
range of Non Halogenated Flame Retardant - Expandable Graphite under the brand
name of “CARBOFOIL” which is : -
♦ ENVIRONMENT FRIENDLY.
♦ ECONOMICAL.
♦ MAINTAIN FLAME RETARDANT PERFORMANCE AT LOWER LOADING.
♦ IMPROVING & PRESERVING MECHANICAL PROPERTIES OF POLYMERS.
♦ COMPATIBLE WITH PROCESSING CONDITION OF VARIOUS POLYMERS.
CARBOFOIL – FLAME RETARDANT EXPANDABLE GRAPHITE
Expandable graphite consist of black flakes and characteristically exhibits expansion
along “C” axis of the crystal structure by about more than hundred times, when it rapidly
heated above 3000
C.
The mechanism of expansion lies in the vaporization of Intercalent present into the
layer of graphite flakes1
. Oxidation of graphite is necessary for expansion and flame
retardancy of expandable graphite. Expandable graphite is manufactured by oxidation
of graphite in sulfuric acid2
; oxidized graphite when exposed to heat it expands.
Expansion of graphite depends upon
1. Size of flake.
2. Purity of graphite.
3. Intercalent present into the layer of graphite flake.
Flame retardant properties of expandable graphite depends up on activation of
expandable graphite at temperature lower than the critical temperature (CT) where
polymer start to melt, decompose or ignite3
.
3. Expandable graphite is well accepted as a flame retardant in most of the foam system
(Ref. 4,5 & 6) and resins (Ref.7). The work reported into the paper seems to have
limitation to use E.G at higher processing temperature. Our work demonstrates that by
selection of Expansion Activation Temperature (E.A.T.) of E.G it is easier to incorporate
into various polymer during processing.
EXPANSION ACTIVATION TEMPERATURE OF DIFFERENT
EXPANDABLE GRAPHITE (CARBOFOIL GRADES)
0
20
40
60
80
100
120
140
160
180
200
220
240
TEMPERATURE IN DEGREE CENTIGRADE
EXPANSIONINCC/1GM/2MINUTES
EAT-150 0 5 12 32 38 55 80 220 80
EAT-170 0 1 7 20 25 30 110 60
EAT-180 1 18 26 36 44 200 40
EAT-220 0 2 5 13 55 30
EAT-240 0 6 12 80 45
EAT-270 0 5 23 30
150 170 185 223 245 270 300 500 1000
Figure of Expanded Graphite.
4. Selection of expandable graphite on the basis of E.A.T. with various polymers
processing temperature.
EXPANDABLE GRAPHITE
“CARBOFOIL”
PROCESSING TEMPERATURE OF POLYMER
Grade E.A.T < 150ºC < 220ºC < 240ºC < 270ºC
EAT – 150 150ºC X X X
EAT – 170 170ºC X X X
EAT – 180 180ºC X X X
EAT – 220 223ºC X X
EAT – 240 245ºC X
EAT – 270 270ºC
Easy incorporation X Expandable Graphite expands during processing
Work carried out by Fumio Okisaki shows that expandable graphite has limitation for
the flame-retardant properties and it works excellent in combination with other
chemical. However, our work revealed that by selecting the expansion of EG from
300ºC to 500ºC, limitation of expandable graphite for flame retardant properties can be
overcome. We have selected four grades of polymers (i.e. EVA, PP, LLDPE & PC.) for
the evolution of flame retardancy with the different expandable graphite grades.
6. Identified Growth Areas :
♦ To mask black colour of the graphite.
♦ To make smaller particle size of expandable graphite with higher expansion
for higher processing temperature of polymers.
♦ Lower loading to improve physical and mechanical properties of various
polymers.
CONCLUSION : Hereby it is demonstrated that expandable graphite grades
CARBOFOIL EAT – 220, CARBOFOIL EAT – 240 & CARBOFOIL EAT – 270 make
easy incorporation at processing temperature 220ºC, 240ºC & 270ºC respectively. By
selection of expansion properties at 300ºC to 500ºC improve the flame – retardancy
performance of polymer without addition of other flame retardant.
REFERENCES :
1. Carbon & graphite hand book by Charles L Mentel.
2. “Zhong” Patent cn85103917 A 29 October 1986.
3. “Vijay J. Bhagat”, Behavior of Expandable Graphite as a flame retardant in
flexible PU foam presented at Polyurethane Foam Association, Arlington
Virginia, USA, May 10, 2001.
4. “R.W.H Bell” Flexible polyurethane foam. UK patent application 2,168,706 A.
5. “MIKIO” Fire- Resistance styrene resin foam and their manufacture.
JP 03167236A219 July 1991.
6. “R.W.H Bell” Manufacture of Flame retardant rubber latex foam. EUR.PAL.APL
EP 245779A1. November 19, 2002.
7. “Daniel W Krassowski & Brain M Ford.” Expandable Graphite flake as an
intumescent flame retardant additive.
