Thermal decomposition and fire behavior of glass fiber-reinforced polyester resin composites containing phosphate-based fire-retardant additives


Ricciardi, M. R.; Antonucci, V.; Giordano, M.; Zarrelli, M.

Journal of Fire Sciences 30(4): 318-330

2012


The thermal degradation and the fire behavior of a polyester resin containing phosphate-based fire-retardant additives and its corresponding glass fiber composites were investigated. An unsaturated commercial polyester resin was modified by the addition of three phosphate-based fire retardants: ammonium polyphosphate, silane-coated ammonium polyphosphate, and melamine pyrophosphate, at 35% w/w. The effects of the fire retardants on resin thermal decomposition and small-scale fire behavior were studied using dynamic thermogravimetric tests at different heating rates and microcalorimetric measurements according to ASTM D7309-07. Different modes of degradation with different activation energy levels for the neat resin and the phosphate-loaded resins were identified by analyzing the thermogravimetric data through the Kissinger method. Since the ammonium polyphosphate-containing resin showed greater thermal and fire performance than the other systems, it was used to manufacture unidirectional glass fiber composites by a vacuum infusion process. The oxidative pyrolysis and fire behavior of the composites produced were studied using thermogravimetric and cone calorimeter tests that demonstrated improvement of their thermal stability and fire performance.

JOURNAL
OF
FIRE
SCIENCES
Article
Thermal
decomposition
and
fire
behavior
of
glass
fiber—
reinforced
polyester
resin
composites
containing
phosphate-based
fire-retardant
additives
Journal
of
Fire
Sciences
30(4)
318-330
CO
The
Author(s)
2012
Reprints
and
permissions:
sagepub.co.uk/journalsPermissions.nav
DOI:
10.11
77/073490411
2439293
jfs.sagepub.com
()SAGE
Maria
R
Ricciardi,
Vincenza
Antonucci,
Michele
Giordano
and
Mauro
Zarrelli
Date
received:
22
July
2011;
accepted:
26
January
2012
Abstract
The
thermal
degradation
and
the
fire
behavior
of
a
polyester
resin
containing
phosphate-based
fire-retardant
additives
and
its
corresponding
glass
fiber
composites
were
investigated.
An
unsatu-
rated
commercial
polyester
resin
was
modified
by
the
addition
of
three
phosphate-based
fire
retardants:
ammonium
polyphosphate,
silane-coated
ammonium
polyphosphate,
and
melamine
pyrophosphate,
at
35%
w/w.
The
effects
of
the
fire
retardants
on
resin
thermal
decomposition
and
small-scale
fire
behavior
were
studied
using
dynamic
thermogravimetric
tests
at
different
heating
rates
and
microcalorimetric
measurements
according
to
ASTM
D7309-07.
Different
modes
of
degradation
with
different
activation
energy
levels
for
the
neat
resin
and
the
phosphate-loaded
resins
were
identified
by
analyzing
the
thermogravimetric
data
through
the
Kissinger
method.
Since
the
ammonium
polyphosphate-containing
resin
showed
greater
thermal
and
fire
perfor-
mance
than
the
other
systems,
it
was
used
to
manufacture
unidirectional
glass
fiber
composites
by
a
vacuum
infusion
process.
The
oxidative
pyrolysis
and
fire
behavior
of
the
composites
produced
were
studied
using
thermogravimetric
and
cone
calorimeter
tests
that
demonstrated
improve-
ment
of
their
thermal
stability
and
fire
performance.
Institute
for
Composite
and
Biomedical
Materials,
National
Research
Council
(CNR),
Piazzale
Enrico
Fermi,
Portici,
Italy
Corresponding
author:
Vincenza
Antonucci,
Institute
for
Composite
and
Biomedical
Materials,
National
Research
Council
(CNR),
Piazzale
Enrico
Fermi
I,
80055
Portici,
Italy.
Email:
Ricciardi
et
al.
319
Keywords
Polymer
composites,
fire
behavior,
ammonium
polyphosphate
Introduction
Unsaturated
polyester
resins
are
widely
used
as
matrices
of
composites
for
several
industrial
sectors,
for
example,
building,
electrical,
and
transportation,
due
to
their
low
cost,
easy
pro-
cessing,
low
density,
and
good
corrosion
resistance.
However,
the
typical
polyester
resin
is
highly
flammable
and
produces
a
large
amount
of
smoke
and
toxic
gases
during
burning.'
Therefore,
their
increasing
commercial
use
points
out
the
development
of
flame-retardant
systems
to
reduce
fire
risks.
Currently,
the
most
effective
and
advantageous
method
to
enhance
the
thermal
decompo-
sition
and
reduce
the
fire
hazard
of
polymers
is
the
incorporation
of
flame
retardants
that
act
by
interfering
with
the
radical
flame
reaction,
changing
the
solid-state
decomposition
mechanism
of
the
polymer
and
producing
a
barrier
layer
(char
or
glass)
to
the
heat
feedback.
2
The
range
of
such
additives
is
large,
and
the
choice
must
take
into
account
several
factors
such
as
self-ignition
temperature
of
the
polymer,
the
decomposition
of
the
fire
retardant,
the
influence
on
the
physical
properties
of
the
polymer,
effects
on
human
health,
and
recycling.
In
general,
the
phosphorus-based
flame
retardants
are
the
most
effective
nonhalogen
flame
retardants
for
unsaturated
polyester
resin.
3
They
can
act
in
the
condensed
phase
and
in
the
gas
phase.
Their
efficiency
depends
on
the
chemical
nature
of
the
polymer,
being
more
effective
with
polymers
having
a
high
oxygen
content,
such
as
polyesters,
polyurethanes,
and
epoxy.
The
phosphorus
flame
retardant
is
converted
by
thermal
decomposition
to
phos-
phoric
acid
and,
subsequently,
to
polyphosphoric
acid
that
esterifies
and
dehydrates
the
polymer
with
formation
of
a
carbonaceous
layer
having
a
glassy
coating.
4
'
5
This
protective
layer
shields
the
polymer
from
the
radiant
heat
and
prevents
its
decomposition.
The
most
efficient
phosphorous
flame
retardants
for
unsaturated
polyester
resin
are
ammonium
polyphosphate
(APP)
6
and
melamine
pyrophosphate
(MPP).
7
These
additives
have
been
used
alone
or
in
synergy
with
other
fillers
to
investigate
the
thermal
decomposi-
tion
and
the
fire
performance
both
of
the
resin
and,
in
some
cases,
of
the
corresponding
composites.
Shih
et
al.
8
investigated
the
synergistic
effect
of
expandable
graphite
(EG)
and
phosphorus-based
flame
retardants
such
as
APP
and
triphenyl
phosphate
(TPP)
on
the
ther-
mal
properties
and
the
flammability
of
an
unsaturated
polyester
resin.
Their
results
indi-
cated
that
APP
both
alone
and
in
combination
with
EG
is
more
efficient
than
TPP
to
prevent
the
thermal degradation
and
reduce
the
combustion
of
the
investigated
polyester
resin
due
to
greater
char
yield
and
the
similar
values
of
the
decomposition
temperatures
to
the
resin.
In
fact,
to
be
effective,
a
flame
retardant
should
decompose
in
a
range
of
tempera-
tures
where
the
polymer
decomposes
simultaneously.
Furthermore,
Nazare
et
al.
9
'
16
investi-
gated
the
flammability
properties
of
unsaturated
polyester
resins
modified
by
the
addition
of
nanoclay
and
different
condensed-phase
flame
retardants,
such
as
APP
and
MPP.
They
observed
that
APP
formulations
showed
the
best
results
compared
to
the
other
flame
retar-
dants
(MPP
and
ATH)
since
the
peak
heat
release
rate
(PHRR)
of
the
APP
formulation
was
reduced
by
around
70%
with
respect
to
the
pure
resin.
In
addition,
in
well-ventilated
fire
conditions,
APP
itself
proved
to
be
a
good
smoke
suppressor.
Furthermore,
in
a
320
Journal
of
Fire
Sciences
30(4)
previous
study,
]]
the
authors
have
demonstrated
by
cone
calorimetric
tests
that
APP
is
more
effective
than
silane-coated
APP
(S-APP)
and
MPP
both
as
fire
retardant
and
smoke
sup-
pressor
for
an
unsaturated
polyester
resin.
In
fact,
the
composites
with
the
APP
at
35%
(w/
w)
were
characterized
by
the
highest
reductions
of
PHRR
(70%)
and
smoke
release
para-
meters:
total
smoke
released
(TSR;
50%),
smoke
parameter
(SP;
78%),
and
smoke
factor
(SF;
85%).
The
effect
of
phosphate
flame
retardants
on
the
properties
of
polymer
fiber—reinforced
composites
has
been
investigated
more
recently.
In
fact,
Zhao
et
a1.
12
studied
the
thermal
sta-
bility
and
the
burning
behavior
of
glass
fiber
(GF)—reinforced
polyamide
6
composites
con-
taining
aluminum
hypophosphite.
The
addition
of
the
aluminum
hypophosphite
enhanced
the
thermal
decomposition
behavior
by
decreasing
the
onset
decomposition
temperature,
the
maximum
mass
loss
rate,
and
the
maximum
rate
of
degradation
and
by
increasing
the
char
formation.
These
benefits
were
also
confirmed
for
the
fire
resistance
properties,
finding
a
reduction
of
the
main
cone
calorimeter
parameters,
such
as
PHRR
and
total
heat
released
(THR)
due
to
the
formation
of
a
compact
residual
char.
Furthermore,
Perret
et
al.
13
investi-
gated
the
effect
on
the
pyrolysis
and
fire
behavior
of
a
novel
phosphorus
compound
(DOPI)
incorporated
in
two
different
epoxy
resins
(DGEBA/DMC
and
RTM6),
adopted
as
matrices
to
manufacture
carbon
fibers
composites.
The
action
of
the
flame
retardant
was
different
for
the
two
resins,
finding
just
a
flame
inhibition
in
the
gas
phase
for
the
DGEBA/DMC
compo-
site,
while
flame
inhibition
and
a
condensed-phase
interaction
increasing
charring
for
the
RTM6
composites.
In
the
first
part
of
this
study,
a
commercial
unsaturated
polyester
resin
has
been
modified
by
three
different
phosphorus-based
flame
retardants:
APP,
S-APP,
and
MPP
at
35%
by
weight
with
respect
to
the
pure
resin.
The
thermal
degradation
and
the
combustion
proper-
ties
of
the
produced
fire-retarded
resin
have
been
investigated
by
performing
thermogravi-
metric
(TGA)
and
microscale
combustion
calorimeter
tests,
respectively.
The
TGA
data
have
been
analyzed
by
modeling
the
kinetic
decomposition
with
the
Kissinger
approach
in
order
to
understand
the
effect
of
the
fire
retardants
on
the
thermal
decomposition
stages
of
the
resin
and
on
the
respective
activation
energy.
The
results
of
these
analyses
evidenced
the
best
performance
of
the
APP-based
resin
in
terms
of
both
burning
behavior
and
thermal
decomposition.
Therefore,
both
the
neat
and
the
APP
resin
have
been
used
to
manufacture
GF-reinforced
composites
that
have
been
experimentally
tested
by
TGA
and
cone
calori-
meter
experiments.
Materials
The
investigated
commercial
resin
is
the
unsaturated
low-viscosity
prepromoted
polyester
Arotran
Q6530,
formulated
for
light
RTM
processes
and
transportation
applications.
It
cures
at
ambient
temperature
in
few
hours
by
adding
methyl
ethyl
ketone
peroxide
(MEKP)
catalyst
(1%-2%).
The
resin
composition by
weight
from
the
safety
data
sheet
is
50.0%-
54.0%
for
the
polymer,
42.7%
of
styrene,
3.4%
methyl
methacrylate,
and
0.2%
cobalt
com-
pounds.
In
this
study,
after
the
addition
of
MEKP
at
1%
wt/wt,
the
neat
resin
has
been
cured
at
85°C
for
45
min.
The
polyester
resin
has
been
modified
by
adding
three
different
phosphorus-based
flame
retardants
at
35%
wt/wt:
an
intumescent
APP,
Exolit
AP740
by
Clariant;
a
S-APP,
FR
CROS
486
by
Budenheim;
and
an
MPP,
BUDIT
311
by
Budenheim.
11
The
fire-retarded
Ricciardi
et
al.
321
resins
have
been
prepared
by
mechanical
mixing
using
an
homogenizer
ULTRA-TURRAX
18
Basic
for
30
min
and
then
degassing
for
30
min
to
eliminate
entrapped
air.
MEKP
at
1%
w/w
was
added
to
the
mixture
as
cure
initiator.
The
mixtures
were
stirred
again
by
mechani-
cal
agitation.
Cure
was
performed
for
90
min
at
isothermal
temperatures."
Fiber-reinforced
composites
were
manufactured
by
a
vacuum
infusion
process
(VIP),
an
alternative
cost-effective
technology
to
the
more
conventional
resin
transfer
molding
requiring
only
one
tool
side
being
the
other
a
polymeric
flexible
bag,
and
adopting
the
vacuum
to
infil-
trate
the
resin
through
the
dry
fibers.
14
The
fibrous
reinforcement
was
laid
onto
an
open-faced
heating
plate,
where
a
liquid
mold
release
agent
had
been
spread
(Loctite
Frewax
Frekote).
Then,
a
release
film
(Release
Ease
234TFP)
was
placed
on
top
of
the
preform
up
to
the
vacuum
tube,
followed
by
the
bleeder
material
(Compoflex
150)
that
absorbs
the
resin
exceeding
during
the
infusion,
assuring
a
good
vacuum
distribution.
In
the
case
of
the
fire-retarded
resin,
the
bleeder
material
(Compoflex
150)
was
placed
not
on
the
whole
reinforcement
as
for
the
neat
resin
but
just
as
a
frame
of
the
plies
in
order
to
avoid
absorption
of
the
fire-retardant
material.
Then,
a
resin
distribution
medium
(Green
Flow)
was
placed
on
the
top
and
partially
in
contact
with
the
heating
plate,
useful
for
helping
the
resin
to
impregnate
all
the
plies.
Finally,
after
pla-
cing
a
peel
ply,
a
nylon
vacuum
bag
was
put
on
the
layers
to
cover
the
entire
plate
and
stitched
to
the
plate
by
means
of
a
high-temperature
resistant
adhesive,
the
tacky
tape.
Two
different
composite
panels
(200
mm
x
350
mm)
were
produced
using
the
neat
resin
and
the
APP
(35%wt/w0-based
resin
and
six
plies
of
unidirectional
fiberglass
(weight
=
600
g/m
2
).
Experimental
TGA
tests
were
performed
on
all
the
analyzed
materials
by
using
TA-Q5000
equipment
in
air
from
30°C
up
to
800°C
under
dynamic
conditions
at
different
heating
rates,
5°C/min,
10°C/min, 15°C/min,
and
20°C/min.
Microscale
combustion
calorimetry
(MCC)
tests
were
carried
out
on
the
neat
resin
and
all
fire-retarded
resin
systems
according
to
the
standard
method
ASTM
D7309-07
by
using
a
Federal
Aviation
Administration
(FAA)
microcalorimeter
supplied
by
Fire
Testing
and
Technology
Ltd.
In
the
MCC
test,
a
3-
to
5-mg
specimen
was
heated
in
the
pyrolysis
zone
at
constant
rate
of
1°C/s-800°C/s
under
an
0
2
/N
2
mixture
flow
at
ratio
of
20/80
cc/min.
The
combustion
furnace
was
set
at
900°C.
Reported
values
are
the
average
data
resulting
from
three
measurements
on
each
sample.
The
cone
calorimeter
experiments
were
carried
out
on
the
fiber-reinforced
composite
materi-
als
by
using
a
Fire
Testing
Technology
Ltd
instrument
according
to
ISO
5650
procedure.
Samples,
with
nominal
dimensions
of
100
X
100
X
3
mm
3
,
were
tested
horizontally
under
an
incident
flux
of
50
kW/m
2
.
Three
samples
were
tested,
and
the
results
were
averaged.
Results
and
discussion
Neat
resin
and
fire-retarded
resins
TGA
data
analysis
and
modeling.
The
thermal
decomposition
behavior
of
the
neat
resin
and
all
fire-retarded
resin
systems
was
investigated
by
carrying
out
the
TGA
test
at
different
heating
rates
(5°C/min,
10°C/min,
15°C/min,
and
20°C/min)
from
environmental
temperature
up
to
800°C.
Figure
1
shows
the
TGA
data
for
all
samples
obtained
at
10°C/min.
322
Journal
of
Fire
Sciences
30(4)
100
80
80
40
20
Resin
+APP
3NN.
0
Resin
+NW
35%
Resin
SAPP
WM
0
Neat
Resin
200
400
600
800
Temperature
("C)
Figure
I.
TGA
data
of
neat
resin
and
fire-retarded
matrices.
TGA:
thermogravimetric;
APP:
ammonium
polyphosphate;
S-APP:
silane-coated
APP;
MPP:
melamine
pyrophosphate.
It
can
be
noticed
that
the
neat
resin
decomposition
is
a
two-stage
process
characterized
by
a
first
step
in
the
temperature
range
150°C-450°C
with
a
mass
loss
of
86
wt%,
followed
by
a
second
decomposition
step
located
in
the
range
450°C-750°C
and
characterized
by
a
mass
loss
of
13
wt%.
The
final
residue
of
the
neat
resin
is
0.08
wt%.
This
behavior
is
deter-
mined
in
the
initial
stages
by
scission
of
highly
strained
portion
of
polystyrene
crosslink
with
consequent
formation
of
free
radicals
that
promote
further
decomposition
and
scission
of
the
polyester
backbone.
As
a
result,
a
large
amount
of
low-molecular-weight
volatiles
(CO,
CO
2
,
methane,
ethylene)
are
released
rather
than
char.
15
In
the
case
of
the
fire-retarded
resins,
a
slight
shift
of
the
degradation
onset
and
a
clear
evident
reduction
of
the
mass
loss
can
be
noticed.
In
fact,
in
the
temperature
range
of
150°C-
450°C,
the
mass
loss
is
reduced
by
29
wt%,
45
wt%,
and
29
wt%
for
APP-,
S-APP-,
and
MPP-based
resin
as
compared
with
the
neat
resin,
respectively,
and
the
final
residue
at
800°C
for
all
modified
resins
is
about
3
wt%.
Furthermore,
it
is
possible
to
observe
more
degradation
steps
for
the
APP
resin
than
for
the
S-APP
and
MPP
resins.
To
better
evidence
the
different
decomposition
steps
and
understand
the
effect
of
the
addi-
tives
on
the
polyester
resin
thermal
behavior,
it
is
useful
to
plot
the
differential
thermogravi-
metric
(DTG)
thermograms
and
identify
the
peaks
in
DTG
curves
as
corresponding
to
the
different
thermal
decomposition
stages.
Furthermore,
the
DTG
curves
can
be
analyzed
by
using
the
Kissinger
method
to
evaluate
the
energy
activation
of
each
decomposition
steps.
Among
the
various
methods
to
analyze
the
TGA
data,
the
Kissinger
procedure
is
generally
used,
as
previous
knowledge
of
the
decomposition
mechanisms
is
not
required
to
evaluate
the
degradation
energy
activation.'
6
In
fact,
it
analyzes
the
variations
in
the
dynamic
TGA
data
through
the
changes
of
run
heating
rate,
0,
as
a
function
of
the
maximum
peak
tem-
peratures,
T
ina
„,
in
the
DTG
curves.
The
activation
energy
can
be
calculated
from
the
plot
of
the
logarithm
of
the
heating
rate
versus
the
inverse
of
the
temperature
at
the
maximum
reac-
tion
rate
by
the
equation
6-
Neat
ResinyeAmin
0-
Neat
Resin
10sedmin
4-
Neat
Resin:15
.
0min
0-
Neat
Resin
20sChnin
CD
el]
600
800
200
400
Temperature
(
C
C)
Ricciardi
et
al.
323
Figure
2.
DTG
data
for
the
neat
resin
at
different
heating
rates.
DTG:
differential
thermogravimetric.
d(ln
/3)
=
Ea
d
(
1
)
RTmax
where
p
is
the
heating
rate,
T
max
is
the absolute
temperature
(K),
E
a
is
the
activation
energy,
and
R
is
the
gas
constant
(8314
J/kmol).
Hence,
the
activation
energy
E
a
can
be
calculated
by
the
curve
slope
of
the
In
(
—)
plot
versus
1/T
max
.
Figures
2
to
5
show
the
differential
weight
loss
(DTG)
curves
for
the
different
resin
systems.
In
general,
a
right
shift
of
all
curves
at
increasing
rates
was
observed.
In
Figure
2,
report-
ing
the
DTG
curves
of
the
neat
resin,
it
is
possible
to
clearly
notice
three
peaks.
The
first
two
peaks
are
very
close
corresponding
to
the
scission
of
the
polystyrene
bonds
and
to
the
oxidation
and
the
breakage
of
the
secondary
bonds.
Thus,
these
two
peaks
have
been
con-
sidered
as
one
large
degradation
step
(150°C-450°C),
and
the
intermediate
reaction
stages
have
been
neglected
in
the
kinetic
analysis
by
the
Kissinger
model.
The
activation
energy
associated
to
the
identified
decomposition
stages
for
the
neat
resin
and
the
fire-retarded
resins
as
a
result
of
the
Kissinger
analysis
is
shown
in
Table
1.
The
addition
of
the
APP
to
the
polyester
resin
causes
a
different
decomposition
evolution
in
the
temperature
range
of
150°C-450°C
(see
Table
1
and
Figure
3)
where
different
phenomena
relating
to
both
the
additive
and
resin
degradation
occur
and
have
to
be
considered
in
the
kinetic
modeling.
In
fact,
as
already
explained
by
the
authors,"
in
the
temperature
range
of
150°C-300°C,
APP
decomposes
by
the
production
of
phosphoric
acid
that
converts
to
the
polyphosphoric
acid,
which
enhances
cross-linking
of
polymer
fragments
to
form
a
stable
char
and
exhibits
its
intumescence
behavior
at
temperatures
lower
than
the
resin
degradation
temperature.
Therefore,
APP
interacts
with
the
polyester
resin
and
decreases
the
mass
lost,
that
is,
61
wt%
mass
loss
for
the
APP-based
resin
and
86
wt%
mass
loss
for
the
neat
resin.
The
effect
of
the
APP
addition
is
also
noticeable
by
the
right
shift
of
the
other
decomposition
peak
that
occurs
at
higher
temperature
range
than
those
of
the
neat
resin.
Furthermore,
the
activation
Der
iv.
INe
ig
ht
(
%f
C)
4—
10844
5
.P.54,20
.
0
.
min
lies44
5
.P.596
10°C/min
Reein+APP35%5T/min
0—
Flesin.APP396:15
.
0
.
min
12
10
08
06
04
02
00
e—
Resin.SAPP354._Mmin
10sin..APP354210Tdmin
4—
10sin..APP354._15Tdmin
0--
Resin+4APP35%
20,rnin
200
400
600
800
Temperature
(°C)
t
324
Journal
of
Fire
Sciences
30(4)
200
400
600
800
Temperature
(°C)
Figure
3.
DTG
data
for
the
APP
resin
at
different
heating
rates.
DTG:
differential
thermogravimetric;
APP:
ammonium
polyphosphate.
Figure
4.
DTG
data
for
the
S
-
APP
resin
at
different
heating
rates.
DTG:
differential
thermogravimetric;
S-APP:
silane-coated
ammonium
polyphosphate.
energy
(155
kJ/mol)
of
APP
for
the
final
range
(450°C-750°C)
was
higher
than
the
activa-
tion
energy
found
for
the
neat
resin
(122
kJ/mol),
demonstrating
that
APP
is
effective
in
the
char
formation
and
subsequent
oxidation.
In
the
case
of
the
S-APP
and
MPP,
the
DTG
dia-
gram
of
Figures
4
and
5
show
that
S-APP
and
MPP
do
not
affect
the
decomposition
mechanisms
of
the
polyester
resin
since
the
number
of
peaks
are
similar
to
those
of
the
neat
resin.
As
for
the
neat
resin,
for
the
kinetic
analysis,
the
first
two
peaks
have
been
considered
as
one
degradation
step
in
the
temperature
range
of
150°C-450°C,
and
a
double
U
0—
Realn+MPP
-
35%5°C
ResIn+MPP35%
IOC
4—•
ResIn+MPP3516:15C
0---
ResIn+MPP35%
20°C
lb
/
200
400
sbo
800
Temperature
(CC)
Ricciardi
et
al.
325
0.8
U
0.4
Figure
5.
DTG
data
for
the
MPP
resin
at
different
heating
rates.
DTG:
differential
thermogravimetric;
MPP:
melamine
pyrophosphate.
Table
I.
Thermogravimetric
data
of
resin
systems
Material
Stage
I
(150°C-450°C)
E
a
(kJ/mol);
mass
lost
(%)
Stage!!
(450°C-750°C)
E
a
(kymol);
mass
lost
(%)
Neat
resin
145;
86
122;
13
Resin
+
APP
89;
11
(150°C-300°C)
155;
36
123;
50
(300°C-450°C)
Resin
+
S-APP
131;
47
88;
47
Resin
+
MPP
83;
61
113;
33
APP:
ammonium
polyphosphate;
S-APP:
silane-coated
ammonium
polyphosphate;
MPP:
melamine
pyrophosphate.
Table
2.
Microcalorimeter
results
Material
PHRR
(VV/g)
T
(°C)
THR
(kyg)
HRC
(J/g
K)
Residue
(wt%)
Neat
Resin
418.5
390
23.6
414.3
8.2
Resin
+
APP
270.2
384
13.3
265.6
42
Resin
+
S-APP
311.25
383
15.4
306.5
23
Resin
+
MPP
277.8
384
13.6
273.3
28
PHRR:
peak
heat
release
rate;
T:
temperature;
THR:
total
heat
released;
HRC:
heat
release
capacity;
APP:
ammonium
polyphosphate;
S-APP:
silane-coated
ammonium
polyphosphate;
MPP:
melamine
pyrophosphate.
decomposition
stage
in
the
whole
temperature
range
has
been
considered
for
the
evaluation
of
the
activation
energy
(see
Table
1)
that
was
lower
in
both
stages
and
for
both
additives.
The
action
of
the
additives
is
more
evident
for
the
mass
lost
in
the
first
decomposition
stage,
326
Journal
of
Fire
Sciences
30(4)
where
the
level
of
the
mass
losses
for
the
S-APP
and
MPP
systems
was
reduced
by
45
wt%
and
29
wt%,
respectively,
with
respect
to
the
neat
resin.
On
the
basis
of
these
results,
it
is
possible
to
conclude
that
the
S-APP
system
is
character-
ized
by
an
higher
thermal
stability
in
the
first
part
of
the
thermal
cycle
(150°C-450°C),
where
S-APP
provides
a
minor
loss
of
mass
and
an
higher
activation
energy
than
APP.
However,
at
higher
temperatures,
APP
is
more
effective
as
its
activation
energy
(155
kJ/mol)
of
the
last
decomposition
stage
is
higher
than
that
of
S-APP
(88
kJ/mol).
This
indicates
that
the
ther-
mal
decomposition
of
APP
resin
is
slower
than
the
decomposition
of
S-APP
resin
due
to
the
capability
of
APP
to
form
a
good-quality
char.
MCC
results.
The
heat
release
data
and
char
yields
for
the
unsaturated
polyester
system
tested
with
the
MCC
are
shown
in
Table
2.
Char
yield
was
measured
by
weighting
the
sample
cru-
cible
before
and
after
testing
according
to
the
ASTM
D7309-7
method.
The
heat
release
measurements
collected
were
heat
release
capacity
(HRC),
THR,
PHRR,
and
maximum
temperature
at
peak.
THR
is
the
area
under
the
curve,
while
the
HRC
peak
values
were
the
peaks
observed
in
each
heat
release
curve
for
each
tested
sample.
The
heat
of
complete
com-
bustion
(THR)
was
calculated
with
the
following
equation:
heat
of
complete
combustion
=
THR/(1
char
yield).
From
the
data
in
Table
2,
it
can
be
seen
that
the
addition
of
all
fire
retardants
is
effective
at
lowering
the
heat
release
of
the
material
and
increasing
the
char
residue,
while
leaving
the
PHRR
almost
unchanged
at
T
max
=
384°C.
In
general,
it
is
possible
to
observe
that
the
resin
modified
with
APP
is
characterized
by
lower
values
of
PHRR
and
heat
of
complete
combus-
tion
while
providing
a
higher
char
yield
(42
wt%).
Therefore,
due
to
the
best
performance
of
the
APP-based
resin
in
terms
of
thermal
degra-
dation
and
combustion
behavior,
the
resin
including
APP
at
35
wt%
has
been
adopted
to
manufacture
fiber-reinforced
composites.
Fiber
-
reinforced
composites
After
curing,
the
produced
composites
have
been
experimentally
tested
by
TGA
and
cone
calorimeter
experiments.
TGA.
Figure
6
and
Table
3
show
the
DTG
thermogram
versus
temperature
and
the
mass
loss
for
the
neat
and
the
fire-retarded
composites.
It
is
possible
to
observe
similar
decomposition
behavior
for
the
fiber-reinforced
compo-
sites,
that
is,
characterized
by
two
DTG
peaks
in
the
temperature
ranges
150°C-450°C
and
450°C-750°C.
The
addition
of
APP
to
the
polyester
resin
induces
a
right
shift
and
a
reduc-
tion
of
both
peaks
and
a
decrease
(8
wt%)
of
the
mass
loss
during
the
first
decomposition
stage.
Cone
calorimeter.
Both
manufactured
composite
samples
have
been
tested
by
cone
calorimeter
to
get
information
on
the
combustion
behavior
and
the
effect
of
the
addition
of
the
APP
to
the
polyester
resin.
Before
testing,
the
composite panels
have
been
cut
to
comply
with
the
standard
size
(100
mm
X
100
mm)
of
the
ISO5650
for
the
cone
calorimeter
tests
and
condi-
tioned
for
24
h
under
vacuum
at
room
temperature.
Ricciardi
et
al.
327
06
Composite Neat
a
0.2
200
400
800
800
Temperature
('C)
Figure
6.
TGA
data
of
fiber-reinforced
composites.
TGA:
thermogravimetric;
GF:
glass
fiber.
Table
3.
Thermogravimetric
data
of
fiber-reinforced
composites
Material
Stage
I
(I
50°C-450°C)
Stage
II
(450°C-750°C)
Mass
lost
(%)
Mass
lost
(%)
Neat
resin
composite
Resin
+
APP
35%
composite
26
3
18
3
00
0
APP:
ammonium
polyphosphate.
Figure
7
shows
the
heat
release
rate
(HRR)
versus
time
for
the
neat
composite
and
the
fire-retarded
composite.
Table
3
reports
the
derived
data
from
the
cone
calorimeter
test:
time
to
ignition
(TTI),
flame
out
(FO),
PHRR,
the
fire
growth
rate
(FIGRA),
and
the
total
heat
evolved
(THE).
It
is
possible
to
observe
that
the
neat
resin
GF
composite
burned
quickly
after
ignition
with
a
peak
of
293
kW/m
2
,
followed
by
a
second
lower
peak
of
255
kW/m
2
.
The
occur-
rence
of
two
distinct
peaks
should
be
related
to
the
initial
burning
of
the
composite
surface
and
its
propagation
through
the
thickness
that
take
place
with
different
HRRs
for
the
dif-
ferent
distribution
of
the
resin
between
the
plies
and
within
the
plies.
This
phenomenon
should
be
more
evident
in
the
case
of
woven
fabric
composites
that
have
distinct
layered
construction
with
resin-rich
region
between
the
ply
layers
15
and,
hence,
are
characterized
by
a
series
of
peaks
in
the
HRR
evolution
over
time.
When
the
APP
is
added
to
the
resin,
a
slight
delay
in
the
ignition
time
is
observed,
and
both
PHRR
values
are
reduced
by
18%
and
19%,
respectively.
In
addition,
due
to
the
action
of
the
fire
retardant,
the
second
peak
of
the
HRR
is
less
pronounced,
and
the
total
burning
time
is
increased
indicating
that
the
fire-retarded
composite
burned
for
a
longer
time
with
a
weaker
flame
than
that
of
neat
composite.
The
PHRR
reduction
determined
also
the
decrease
of
FIGRA
by
21%
for
the
fire-retarded
composite.
FIGRA
is
an
important
parameter
to
understand
the
reaction
of
a
material
when
exposed
to
heat
and
represents
the
burning
propensity
of
a
material,
328
Journal
of
Fire
Sciences
30(4)
2
)
\
.
Neat
Resin-GF
Composite
Resin+APP-GF
composite
:
k
50
100 150
200 250
300 350
400 450
500
Tune,
see
Figure
7.
Heat
release
rate
as
a
function
of
time
for
the
GF-reinforced
composites.
GF:
glass
fiber.
Table
4.
Cone
calorimeter
results
for
fiber-reinforced
composites
Material
TT1
(s)
FO
(s)
PHRR
TTP
(s)
FIGRA
THE
Residue
THE/ML
(kW/m
2
)
(kW/s)
(MJ/m
2
)
(wt%)
(MJ/m
2
g)
Neat
resin
54
369
292.68
78
3.75
42.56
67.44
2.39
composite
Resin
+
APP
35%
59
413
239.64
81
2.96
25.93
72.27
1.73
composite
300
250
5
200
150
1'4
100
50
0
TTI:
time
to
ignition;
FO:
flame
out;
PHRR:
peak
of
heat
release
rate;
FIGRA:
fire
growth
rate;
THE:
the
total
heat
evolved;
APP:
ammonium
polyphosphate.
being
the
ratio
of
PHRR
and
the
time
to
reach
the
PHRR:
a
higher
value
of
FIGRA
indi-
cates
faster
flame
propagation.
The
flame-retarding
effect
of
APP
for
the
investigated
GF
composite
can
be
noticed
also
by
the
significant
reduction
of
the
THE
that
was
decreased
from
42.56
MJ/m
2
for
the
neat
composite
to
25.93
MJ/m
2
for
the
APP-based
composite.
The
reduction
of
THE
and
the
enhanced
residue
formation
(see
Table
4)
indicate
that
APP
decomposition
reduced
the
composite
burning
by
decreasing
the
total
heat
produc-
tion
due
to
the
char
formation
in
the
condensed
phase.
The
char
formation
and
the
APP
intumescent
behavior
was
clearly
noticed
during
and
after
the
cone
calorimeter
test
for
the
APP-based
composite.
Figures
8
and
9
show
pictures
of
the
burned
neat
and
fire-retarded
samples,
respectively.
It
is
possible
to
observe
that
the
residue
of
the
neat
composite
is
represented
by
the
GFs
surrounded
by
soot,
while
a
black
swelled
char
characterizes
the
final
fire-retarded
compo-
site,
confirming
the
efficiency
of
APP
in
foaming
and
expanding
the
composite
surface
and,
hence,
in
insulating
and
protecting
the
underlying
material.
Conclusions
The
thermal
decomposition
and
the
combustion
behavior
of
an
unsaturated
polyester
resin
and
the
corresponding
GF
composite
were
investigated.
In
particular,
to
improve
the
fire
behavior
of
the
polyester
resin,
different
phosphate
fire
retardants,
APP,
S-APP,
and
MPP
Ricciardi
et
al.
329
Of,
Figure
8. 8.
Residue
of
neat-reinforced
composite
after
burning.
Figure
9.
Residue
of
fire
retarded—reinforced
composite
after
burning.
were
dispersed
within
the
resin.
The
microcalorimeter
results
and
the
Kissinger
analysis
of
TGA
dynamic
data
evidenced
a
more
effective
action
of
the
APP
fire
retardant
by
reducing
the
mass
lost
during
burning,
by
modifying
the
decomposition
evolution
and
enhancing
the
char
formation.
GF
composites,
manufactured
using
the
neat
resin
and
the
APP-based
resin,
were
characterized
by
TGA
and
cone
calorimeter
tests
demonstrating
the
efficiency
of
APP
to
shift
the
decomposition
stages
to
higher
temperatures
and
to
enhance
the
combustion
behavior.
A
reduction
of
PHRR
(21%)
and
THE
(39%)
for
the
fire-retarded
composite
were
measured,
indicating
that
APP
is
efficient
as
a
fire
retardant
of
polyester-based
GF-rein-
forced
composites
due
to
the
capability
to
form
a
good-quality
char.
Funding
This
research
received
no
specific
grant
from
any
funding
agency
in
the
public,
commercial,
or
not-for-
profit
sectors.
330
Journal
of
Fire
Sciences
30(4)
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Author
biographies
Maria
Rosaria
Ricciardi
has
a
short-term
research
position
at
Institute
for
Composite
and
Biomedical
Material
of
CNR,
working
on
polymer
composite
manufacturing
processes.
Vincenza
Antonucci,
graduated
cum
laude
in
Chemical
Engineering
(January
1996)
at
University
of
Naples
"Federico
II",
attained
the
Materials
Engineering
Phd
(February
2000)
on
"Polymer
infiltra-
tion
processes
for
the
production
of
Composite
Materials".
From
2001,
she
is
researcher
at
Institute
for
Composite
and
Biomedical
Material
of
CNR.
Mauro
Zarrelli
received
his
Master
degree
cum
Laude
in
Chemical
Engineering
at
the
University
of
Naples
Federico
II
in
1998.
He
attained
the
Ph.
Doctor
in
Advanced
Material
in
2004.
Actually,
he
is
researcher
at
Institute
for
Composite
and
Biomedical
Material
of
CNR.
Michele
Giordano
received
his
Master
degree
cum
Laude
in
Chemical
Engineering
at
the
University
of
Naples
Federico
II
in
1992.
In
the
same
year
he
started
a
Ph.
D.
course
in
Materials
Engineering.
Ph.
Doctor
in
1995.
Actually,
he
is
leading
researcher
at
Institute
for
Composite
and
Biomedical
Material
of
CNR.