Materials Sciences and Application, 2011, 2, 1134-1138 
doi:10.4236/msa.2011.28153 Published Online August 2011 (
Copyright © 2011 SciRes.                                                                             MSA
Flame Retardancy Enhancement of Hybrid
Composit e Materia l by Using Inorganic
Mohammed Al-Maamori1, A. Al-Mosawi2, Abbass Hashim3*
1Faculty of Material Engineering, University of Babylon, Babylon, Iraq; 2Department of Mechanical Engineering, Technical Institute,
Babylon, Iraq; 3 Materials and Engineering Research Institute, Sheffield Hallam University, Sheffield, S1 1WB, UK
Email: a.hashim@sh
Received January 18th, 2011; r evised March 22nd , 2011; accept ed May 24th, 2011
This study aims to investigate the possibility of improving the flame Retardancy for the hybrid composite material con-
sisting arald ite resin (CY223). The hybrid composite was reinforced by hybrid fibers from carbon and Kevlar fibe rs on
woven roving form (0˚ - 45˚), by using a surface layer of 4 mm thick of Zinc Borate flame retardant. Afterward, the
structure was exposed directly to gas flame of 2000˚C due to 10 mm and 20 mm exposure interval. The retardant layer
thermal resistance and protection capability were determined. The study was continued to improve the performance of
Zinc Borate layer mixed by 10%, 20% and 30% of Antimony Trioxide. To determine the heat transfer of the compo site
material the opposite surface temperature method was used. Zinc Borate with (30%) Antimony Trioxide gives the opti-
mized result of the experiment.
Keywords: Hybrid Composite Material, Flame Retardant Material, Inorganic Retardant
1. Introduction
Fire safety is an integral part of precautions having an
objective to minimize the damage from measuring hin-
dering their initiation, limiting their propagation and the
possibility of excluding flash-over. Preventing fires or
delaying them makes escape possible over a longer pe-
riod of time. As a result, life, health, and property are
efficiently protected [1].
Plastics are synthetic organic materials with carbon
and high hydrogen contents, they are most likely com-
bustible. For various applications in the building, elec-
trical, transpo rtation a nd other ind ustries, plast ics have to
fulfill flame retardancy requirements laid down in man-
datory regulatio n and voluntary spec ification. The obj ec-
tive of flame retarding polymers is to increase ignition
resistance and reduce rate of flame spread [2].
One of the ways for better protect combustible mate-
rials against initiati ng fires is the use of flame retard ants.
This substance can be chemically inserted into the poly-
mer molecule or physically blended in polymers after
polymerization. This will suppress, reduce, delay or
modify the propagation of the flame through plastic ma-
There are several classes of flame retardants; haloge-
nated hydrocarbons (chlorine and bromine containing
compounds and reactive flame retardants), inorganic
flame retardants (boron compounds, antimony oxides,
aluminum hydroxide, etc) and phosphorus compounds
flame retardants containing ni trogen. Depending on their
nature, flame retardants can act physically or chemically
2. Flame Retardant Materials
Flame retardants are substances used in plastics, textiles,
electronic circuitry and other materials to prevent fires.
There are several types of flame retardants as mentioned
above, one of these types is inorganic flame retardants.
Few inorganic compounds are suitable for use as flame
retardants in plastics, since such compounds must be
effective in the range of decomposition temperature of
the plastic, mainly (150˚C - 400˚C). Inorganic flame re-
tardants don’t evaporate under the influence of heat ra-
ther they decompose giving o f f non-flammable gase s li ke
water, carbon dioxide, sulphur dioxide and hydrogen
chloride. Endothermic reaction in the gas phase acts by
Flame Retardancy Enhancement of Hybrid Composite Material by Using Inorganic Retardants
Copyright © 2011 SciRes.                                                                               MSA
dilut ing the mixtur e of fla mma ble gase s and b y shield ing
the surface of the polymer against oxygen at tack [4 ].
The inorganic flame retardants are performed simulta-
neously on the surface of the solid phase by cooling the
polymer via endothermic breakdown process and reduc-
ing the formation of pyrolysis products. In addition as in
the case of inorganic boron compounds, a glassy protec-
tive la yer can for m on t he s ub stra te fe ndin g o ff the effect
of oxygen and heat [5]. As example to inorganic flame
retardants is zinc borate, aluminum hydroxide, magne-
sium hydroxide and antimony oxides.
Zinc borate is an effective inorganic flame retardant
possessing the characteristic properties of smoke sup-
pression and promoting charring which is particularly
important according to new fire standards. Zinc borate is
commonly used as multifunctional flame retardant in
combination with other halogenated or halogen free
flame retardant systems to boost FR properties. Its effi-
cacy depends upon the type of halogen source (aliphatic
versus aromatic) and the used polymer. The zinc borate
can generally display synergistic effects with antimony
oxide in fire retardancy [6]. Table 1 shows the characte-
rizations and properties of zinc borate.
Antimony trioxide (ATO) has white color or colorless
depended on its structure. ATO dissolved slightly in wa-
ter and dissolved in potassium hydroxide, dilute hy-
drochloric acid and with many organic acids [4]. Table 2
shows the properties of ATO. Figure 1 sho ws the c hem-
ical structure of ATO .
3. Composite Materials
Composite material is a material consisting of two or
more physically and (or) chemically distinct phase suita-
bly arranged or distributed. The composite material
usually has characteristics that are not dep icted by any of
its components in isolation [6]. Generally, the composite
material contains two elements:
1) Material matrix: it i s the co nti nuous p hase o f metal,
ceramic or polymer. The polymer matrix is considered
the best because of its mechanical and thermal properties
and also it can reinforce by a large fiber volume fraction
compared with metal and ceramic matrix. The polymer
matrix is low cost and easy fabrication, e.g. araldite resin,
polyester, and epoxy resin. Araldite resin belongs to
epoxy group which has excellent thermal and physical
properties and usually used in composite materials for
different applications. Epoxy group distinct by excellent
adhesive capability especially to fibers and retains con-
stant dimensions after dryness [7].
2) Material reinforce: the distributed phase is called
reinforcement; many reinforcement materials are availa-
ble in a variety of forms, e.g. continuous fibers, short
fibers, whiskers, particles...etc. Reinforcements include
organic fibers such as carbon and Kevlar fibers, metallic
fibers, ceramic fibers and particles [8].
High strength and high modulus carbon fibers are of
about (7-8µm) in diameter and consist of small crystal-
lites of Turbostratic graphite, one of the allotropic forms
of carbon [9].
Kevlar is an organic Aramid fiber with (3100 MPa)
tensile strength and (131,000 MPa) elastic modulus.
Kevlar density is approximately one-half of aluminum
and good toughness [10].
4. Experimental Work
5. Material s
There are three types of materials implemented in this
1) Flame retardant material:
a) Zinc Borate 2335 (2ZnO.3B2O3.5H2O) was used as
a flame retardant supplied by C-Tech corporation. Table
3 shows the chemical composition of Zinc Borate.
Antimony Trioxide (Sb2O3) supplied by BDH Chemi-
cal Ltd Pool England) with particle siz e 2 µ.
2) Matrix material; Araldite resin (CY223) with den-
sity of (1.15 - 1.2 g/cm3) belong to epoxies group was
used i n thi s st udy. Figure 2 shows t he che mica l str uct ure
of Araldite resin.
3) Reinforce fibers: two types of fibers were used as
consec utive layers in sa me matrix:
a) Carbon fibers, woven roving fibers (0˚ - 45˚), with
density of (1.75 g/cm3).
b) Kevlar fibers, woven roving fibers (0˚ - 45˚), with
density of (1.45 g/cm3).
Figure 3 shows the chemical structure of Kevlar fi-
Table 1. Characterizations and properties of zinc borate [3].
Mo l Wt PH Density g/cm3 Melting Poin t ˚C Appearance Property
434.62 7.6 3.64 980 White Crystalline Value
Table 2. properties of antimony trioxide [4].
Density(g/cm3) Boiling Point(˚C) Melting Point(˚C) Property
5.67 1425 656 Value
Flame Retardancy Enhancement of Hybrid Composite Material by Using Inorganic Retardants
Copyright © 2011 SciRes.                                                                             MSA
Figure 1 . Chemical structure of ATO.
5.1. Samples Preparation
The samples of thermal erosion test are squared shape
with dimensions of 100 × 100 mm2 and 10 mm thic k con-
sisting two layers as shown in Figure 4.
a- Flame retardant Zinc Borate layer with 4 mm thick.
Composite of carbon and Kevlar fiber layer of 6mm
thick used as consecutive layers in ara ldite resin.
5.2. Thermal Erosion Test
Flame generated from butane-propane gas (C3H8-C4H10)
with temperature of 2000˚C was used. The structure
contains flame retardant material and composite material
exposed to this temperature with exposure intervals of 10
Table 3. Chemical composition of zinc borate.
Compound Zinc Oxide Boric Anhydride Water of Hydration Impurities
mm and 20 mm. Figure 5 shows the experimental setup
of thermal erosion test, surface temperature method used
to determine heat transferred through flame retardant /
composite structure. Temperature was monitored, ob-
served, measured and recorded using PC transformation
card (AD) connected to K-type thermocouple.
6. Results and Discussion
Figure (6) represents the thermal erosion test for compo-
site material with retardant surface layer at exposed dis-
Figure 2 . Che mica l structure of Araldite resin.
-O- -C- -O-CH
-O- -C- -O-CH
CO - - CO – NH - - NH
Figure 3 . chemical structure of Kevlar fibe rs.
Figure 4 . Sample of thermal erosion test.
Composite material layer
Flame retardant material layer
Flame Retardancy Enhancement of Hybrid Composite Material by Using Inorganic Retardants
Copyright © 2011 SciRes.                                                                             MSA
010 20 30 40 50 60
Surface Tem perature
Time (sec)
Zinc Borate Only
Zinc Borate + 10%Sb2O3
Zinc Borate + 20%Sb2O3
Zinc Borate + 30%Sb2O3
Zinc Borate + 40%Sb2O3
Figure 6 . Flame retardancy results with exposure interval of 10 mm.
020 40 60 80100
Surface Tem perature
Time (sec)
Zinc Borate Only
Zinc Borate + 10 % Sb2O3
Zinc Borate + 20 % Sb2O3
Zinc Borate + 30 % Sb2O3
Zinc Borate + 40 % Sb2O3
Figure 7 . Flame retardancy results with exposure interval of 20mm.
Sliding Slot
Fl ame
Thermocouple type -K
Figure 5 . thermal erosion test setup.
Flame Retardancy Enhancement of Hybrid Composite Material by Using Inorganic Retardants
Copyright © 2011 SciRes.                                                                             MSA
tance of 10 mm. The temperature of the opposite surface
to the torch begins to increase with increasing of the ex-
posure time. During this stage zinc borate has a water of
hydration in its chemical structure therefore water is re-
lease d to exti nguish the fire thro ugh cool ing. Zinc b orate
will formed glassy coating layer which protect the sub-
strate (composite material) and the fire spreading will
Zinc borate flame retardancy is increased by adding
few percentage of antimony trioxide. Through the fire
exposure internal structure of the antimony trioxide will
be changed causing phase transformation in Zinc borate
enhancing flame retardancy of composite materials as a
result. This retardant action increased with the increasing
of antimony trioxide percentage from 10% to 30 %.
Figure 7 shows the thermal erosion test for the com-
posite material of retardant surface layer with exposure
interval of 20mm. As a result the time required to break
down the composite of flame retardant layer will increase
and the combustion gaseous will reduced. There will be a
less plastic to burn due to water of hydration and pro-
tected glassy coating layer comes from zinc borate and
this protection will improve with addition of antimony
trioxide. The mixing ratio of 3:1 (zinc borate: antimony
trioxide) is o btaining the best r e sult.
It is quite obvious from Figure 6 and 7, that the opti-
mum mixing ratio is 3:1, gives the best flame retardant
and shows standard layers structure stability. The oppo-
site surface temperature reached 135˚C after 85 sec.
The flame retardant is reduced when the mixing ratio
is increased to 4:1. The opposite surface temperature
reached 180oC within 85 sec.
This retardant action decreased with the increasing of
antimony trioxide percentage of 40% and expecting to
decrease rapidly with the increasing of antimony trioxide
percentage. The 40% test shows that the surface layer
was starting to decomposed and fractured after exposed
to 2000˚C flam temper ature within less than one minute.
7. Conclusions
From this study we c oncluded t hat:
1) Using Zinc borate improved the flame retardancy of
2) Adding Antimony trioxide to Zinc borate improved
the layer Durab ility and structure.
3) The mixing ratio of 3:1 (zinc borate: antimony tri-
oxide) is the op timum mixing ra tio which is obtainin g th e
best result.
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