Intrinsically flame retardant epoxy resin Fire performance and background Part II


Toldy, A.; Szabó, A.; Novák, C.S.; Madarász, J.; Tóth, A.; Marosi, G.Y.

Polymer Degradation and Stability 93(11): 2007-2013

2008


The flame retardant mechanism of a newly synthesized phosphorus-containing reactive amine, which can be used both as crosslinking agent in epoxy resins and as flame retardant, was investigated. The mode of action and degradation pathway were investigated by in situ analysis of the gases evolved during the degradation by thermogravimetric measurements coupled online with infrared (TG-EGA–FTIR) and mass spectroscopy (TG/DTα-EGA–MS) and by solid residue analysis by infrared (ATR) spectroscopic methods and X-ray photoelectron spectroscopy (XPS). It was observed that the main difference in the degradation of the reference and the flame retardant system is that the degradation of the latter begins at lower temperature mainly with the emission of degradation products of the phosphorus amine, which act as flame retardants in the gas phase slowing down the further degradation steps. At the high temperature degradation stage the solid phase effect of the phosphorus prevails: the formation of phosphorocarbonaceous intumescent char results in a mass residue of 23.4%. The ratio of phosphorus acting in gas phase and solid phase, respectively, was determined on the basis of thermogravimetric and XPS measurements.

Polymer
Degradation
and
Stability
93
(2008)
2007-2013
Contents
lists
available
at
ScienceDirect
Polymer
Degradation
and
Stability
crL
Polymer
Degradation
and
Stability
ELSEVT
FR
journal
homepage:
www.elsevier.com/locate/polydegstab
Intrinsically
flame
retardant
epoxy
resin
-
Fire
performance
and
background
-
Part
II
A.
Toldya'
b
'*,
A.
Szabo
a
,
Cs.
Novak`,
J.
Madardsz`,
A.
Toth
d
,
Gy.
Marosi
a
a
Department
of
Organic
Chemistry
and
Technology,
Budapest
University
of
Technology
and
Economics,
Miiegyetem
rkp.
3,
1111
Budapest,
Hungary
b
Department
of
Polymer
Engineering,
Budapest
University
of
Technology
and
Economics,
Miiegyetem
rkp.
3,
1111
Budapest,
Hungary
Department
of
Inorganic
and
Analytical
Chemistry,
Budapest
University
of
Technology
and
Economics,
Szt.
Gellert
ter
4,
1111
Budapest,
Hungary
d
Hungarian
Academy
of
Sciences,
Chemical
Research
Center,
Institute
of
Materials
and
Environmental
Chemistry,
1025
Budapest,
Pusztaszeri
at
59-67,
Hungary
ARTICLE INFO
ABSTRACT
Article
history:
Received
15
July
2007
Received
in
revised
form
29
January
2008
Accepted
13
February
2008
Available
online
19
July
2008
Keywords:
Epoxy
resin
organophosphorous
reactive
amine
flame
retardant
Flame
retardancy
Mode
of
action
Degradation
mechanism
by
TG-EGA-FTIR,
TG/DTA-EGA-MS,
ATR-IR,
XPS
The
flame
retardant
mechanism
of
a
newly
synthesized
phosphorus-containing
reactive
amine,
which
can
be
used
both
as
crosslinking
agent
in
epoxy
resins
and
as
flame
retardant,
was
investigated.
The
mode
of
action
and
degradation
pathway
were
investigated
by
in
situ
analysis
of
the
gases
evolved
during
the
degradation
by
thermogravimetric
measurements
coupled
online
with
infrared
(TG-EGA-FTIR)
and
mass
spectroscopy
(TG/DTA-EGA-MS)
and
by
solid
residue
analysis
by
infrared
(ATR)
spectroscopic
methods
and
X-ray
photoelectron
spectroscopy
(XPS).
It
was
observed
that
the
main
difference
in
the
degradation
of
the
reference
and
the
flame
retardant
system
is
that
the
degradation
of
the
latter
begins
at
lower
temperature
mainly
with
the
emission
of
degradation
products
of
the
phosphorus
amine,
which
act
as
flame
retardants
in
the
gas
phase
slowing
down
the
further
degradation
steps.
At
the
high
temperature
degradation
stage
the
solid
phase
effect
of
the
phosphorus
prevails:
the
formation
of
phosphorocarbonaceous
intumescent
char
results
in
a
mass residue
of
23.4%.
The
ratio
of
phosphorus
acting
in
gas
phase
and
solid
phase,
respectively,
was
determined
on
the
basis
of
thermogravimetric
and
XPS
measurements.
©
2008
Elsevier
Ltd.
All
rights
reserved.
1.
Introduction
Epoxy
resins
have
been
commercially
available
for
60
years
and
have
found
use
mainly
in
industrial
applications
where
their
exceptional
characteristics
such
as
good
adhesion
to
many
substrates;
moisture,
solvent
and
chemical
resistance;
low
shrinkage
on
cure;
outstanding
mechanical
and
electronic
resis-
tance
properties
justify
their
higher
costs
compared
to
other
ther-
mosets.
They
are
widely
used
as
adhesives,
surface
coatings,
laminates
and
matrix
materials
in
electronic,
transport
and
aero-
space
industries,
however
their
thermal
and
fire
resistance
needs
to
be
improved
in
many
applications.
Fire
retardancy,
as
an
outstanding
requirement
of
safety,
is
one
of
the
key
challenges
for
society
in
our
century.
The
increasing
focus
on
the
health
and
environmental
compatibility
of
flame
retardants
has
drawn
the
attention
to
the
organophosphorous
reactive
flame
retardants
[1
-
3].
The
new
European
Directive
2002/95/EC
[4],
requiring
the
*
Corresponding
author.
Department
of
Organic
Chemistry
and
Technology,
Budapest
University
of
Technology
and
Economics,
Miiegyetem
rkp.
3,
1111
Buda-
pest,
Hungary.
Tel.:
+36
1
463
3654;
fax:
+36
1
463
1150.
E-mail
address:
(A.
Toldy).
0141-3910/$
-
see
front
matter
©
2008
Elsevier
Ltd.
All
rights
reserved.
doi:10.1016/j.polymdegradstab.2008.02.011
substitution
of
some
widely
used
brominated
flame
retardants
(polybrominated
biphenyls
(PBB)
and
polybrominated
diphenyl
ethers
(PBDE))
in
new
electrical
and
electronic
equipment
put
in
the
market
from
1
July
2006,
also
facilitates
the
development
and
increased
use
of
phosphorus
flame
retardants.
In
the
case
of
epoxy
resins,
the
phosphorus-containing
chemical
unit
providing
the
flame
retardant
effect
can
be
incorporated
into
the
epoxy
compo-
nent,
the
crosslinking
agent
or
into
both
of
them.
From
the
many
possible
alternatives
the
combination
of
an
aliphatic
epoxy
component
-
more
difficult
to
flame
retard
than
the
aromatic
ones
-
and
a
simple
phosphorus-containing
crosslinking
agent
was
chosen.
In
the
current
literature
an
increasing
number
of
papers
deal
with
the
mode
of
action
of
reactive
organophosphorous
flame
retardants
in
an
epoxy
resin
matrix
[3,5,6],
however
there
are
no
references
dealing
with
the
degradation
of
aliphatic
epoxy
resin
systems.
Earlier
studies
focus
on
aromatic
epoxy
and
aromatic
phosphorus
compounds
such
as
DOPO
and
derivatives.
Concerning
the
mode
of
action
of
organophosphorous
flame
retardants
both
condensed
phase
and
gas
phase
actions
have
been
reported,
but
only
few
systematic
studies
are
available
taking
into
account
the
chemical
structure
of
the
phosphorus
compound,
the
chemical
environment,
and
the
interaction
with
the
polymer
matrix
during
2008
A.
Toldy
et
al.
/
Polymer
Degradation
and
Stability
93
(2008)
2007-2013
degradation.
Hergenrother
et
al.
[6]
found
that
with
increasing
oxidation
state
of
phosphorus
the
condensed
state
action
is
increasing.
Similarly,
Braun
et
al.
[3]
observed
that
decreasing
the
oxidation
state
of
phosphorus
resulted
in
an
increase
of
the
flame
retardancy,
which
was
supposed
to
be
explained
by
the
increasing
gas
phase
action.
Nevertheless,
no
reference
was
found
dealing
with
the
determination
of
the
ratio
of
phosphorus
acting
in
solid
phase
and
gas
phase,
respectively.
In
this
work
the
mode
of
action
and
degradation
pathway
of
an
aliphatic
epoxy
resin
system
was
investigated
by
analysis
of
the
gases
evolved
during
the
degradation
by
thermogravimetric
measurements
coupled
with
infrared
and
mass
spectroscopy
and
by
solid
residue
analysis
by
infrared
spectroscopic
methods
and
X-ray
photoelectron
spectroscopy.
The
ratio
of
phosphorus
acting
in
the
gas
phase
and
solid
phase,
respectively,
was
determined
on
the
basis
of
thermogravimetric
and
XPS
measurements.
The
better
understanding
of
the
degradation
mechanism
is
crucial
for
further
improving
the
fire
retardant
performance
of
epoxy
networks.
2.
Experimental
2.1.
Materials
The
polymer
matrix
was
ER
type
Eporezit
AH-16
(non-modified,
resin
like
reactive
dilutant,
epoxy
equivalent:
160-175;
viscosity
at
25
°C:
800-1800
mPa
s;
density
at
25
°C:
1.24
g/cm
3
,
hydrolysable
chlorine
content:
1.5
mass%)
used
with
Eporezit
T-58
curing
agent
(amine
number:
460-480
mg
KOH/g;
viscosity
at
20
°C:
100-200
mPa
s;
density
at
20
°C:
0.944
g/cm
3
;
curing
time:
2
days
at
25
°C)
supplied
by
P+M
Polimer
Kernia
Kft.,
Hungary.
Schemes
1
and
2
show
the
main
components
of
Eporezit
AH-16
and
Eporezit
T-58.
A
newly
synthesized
phosphorus-containing
reactive
amine,
TEDAP
(amine
number:
510-530
mg
KOH/g;
viscosity
at
20
°C:
400
mPa
s;
curing
time:
7
days
at
25
°C,
4
h
at
80
°C)
(Scheme
3)
was
used
as
flame
retardant
[7].
22.
Methods
Preparation
of
epoxy
resin
samples:
the
epoxy
and
curing
agent
amine
components
were
mixed
at
room
temperature
in
a
glass
beaker
in
order
to
obtain
a
homogenous
mixture.
A
silicone
mould
120
mm
long,
15
mm
wide
and
3
mm
thick
was
used
for
preparing
the
cured
samples.
The
fire
resistance
was
characterized
by
Limiting
Oxygen
Index
measurement
(LOI,
according
to
ASTMD
2863),
UL-94
test
(according
to
ASTM
1356-90
and
ANSI//ASTM
D-635/77),
Mass
Loss
Calorimeter
(according
to
ISO
13927,
Fire
Testing
Technology,
heat
flux
of
50
kW/m
2
),
and
Glow
Wire
Flammability
Index
test
(GWFI,
PTL
DR
GRABENHORST,
D-8652
Stadtsteinach,
10334
type
appa-
ratus,
according
to
IEC
60695-2-12).
The
thermal
treatment
of
the
cured
epoxy
resin
samples
was
done
in
the
furnace
of
a
TA
Instruments
AR2000
type
rheometer.
The
temperature
program
consisted
of
a
linear
part
with
a
heating
rate
of
10
°C/min
from
room
temperature
to
the
appropriate
CH2-
CH
-
CH2
-
0
-
CH2
CH2
-
0
-
CH2
-
CH
-
CH2
\
o
/
\/
\
o
/
/ \
CH2-
-
CH2
-
0
-
CH2
CH
2
-
0
-CH
2
-CH
-
CH2
\
o
/
Scheme
1.
Main
component
of
Eporezit
AH-16.
H3
NH
2
Scheme
2.
Main
component
of
Eporezit
T-58.
temperature
(in
the
temperature
range
of
200-400
°C)
and
a
subsequent
10
min
isotherm
part
at
the
final
temperature.
The
attenuated
total
reflection
infrared
(ATR-IR)
spectroscopic
measurement
of
the
epoxy
resin
samples
after
thermal
treatment
was
done
on
a
Labram
type
ATR-IR
apparatus
(Jobin
Yvon,
France).
The
IR
spectra
were
processed
using
LabSpec
4.02
software.
The
gases
evolved
during
thermal
degradation
of
the
epoxy
resin
were
analysed
using
coupled
techniques:
TG/DTA—MS:
A
TA
Instruments
SDT
2960
apparatus
was
coupled
with
Balzers
Instruments
Thermostar
GSD
300
T3
type
mass
spectrometer
(detector:
Quadrupole
CH-TRON,
operating
methods:
SCAN,
MID).
The
coupling
element
was
a
quartz
transfer
tube
heated
to
200
°C.
First,
mass
spectra
of
the
evolved
gaseous
mixtures
were
continuously
scanned
and
collected
between
m/z
=
1-200
(SCAN-mode),
then
64
mass/charge
numbers
were
selected
and
their
ion
currents
were
monitored
in
Multiple
Ion
Detection
(MID)
mode
with
the
measuring
time
of
0.5
s
for
each
channel.
Samples
with
initial
mass
of
7-11
mg
were
heated
in
an
open
Pt
crucible.
The
temperature
program
consisted
of
a
linear
part
with
a
heating
rate
of
10
°C/min
from
20
°C
to
600
°C
in
air.
TG—FTIR:
TGA
2050
type
thermogravimetric
analyzer
was
coupled
to
a
Bio-Rad
Excalibur
Series
FTS
3000
type
FTIR
spectrophotometer
with
external
gas
cell
heated
to
180
°C.
The
temperature
program
consisted
of
a
linear
part
with
a
heating
rate
of
10
°C/min
from
20
°C
to
600
°C
in
air.
Samples
with
initial
mass
of
42-110
mg
were
heated
in
open
Pt
crucible.
For
performing
an
elemental
analysis
of
the
pyrolysis
residues
X-ray
photoelectron
spectroscopy
(XPS)
analysis
was
carried
out
on
a
Kratos
XSAM
800
type
spectrometer
(15
kV,
15
mA)
using
1253,6
eV
energy
characteristic
X-ray
of
Mg
Kau
radiation.
It
was
focused
on
a
spot
having
a
diameter
of
—2
mm.
The
general
spectra
were
taken
with
an
energy
step
of
0.5
eV
steps
up
to
1250
eV,
while
the
detailed
spectra
were
taken
in
0.1
eV
steps.
3.
Results
The
flame
retardancy
of
the
AH-16—T-58
reference
epoxy
resin
and
the
flame
retarded
AH-16—TEDAP
system
was
compared
in
detail
in
the
previous
article
of
the
authors
[7].
In
this
paper,
after
a
short
summary
of
flame
retardancy
results,
we
compare
the
degradation
mechanisms
of
the
two
systems
and
investigate
the
mode
of
action
of
the
organophosphorous
flame
retardant.
The
synthesized
phosphorus-containing
amine,
TEDAP
is
suit-
able
for
substitution
in
place
of
the
traditional
epoxy
resin
curing
agents
additionally
providing
excellent
flame
retardancy:
the
epoxy
resins
flame
retarded
this
way
reach
960
°C
GWFI
value,
33
LOI
value
and
V-0
UL-94
rating
compared
to
the
550
°C
GWFI
value,
21
LOI
value
and
HB
UL-94
rating
of
the
reference
epoxy
/
NH
-C
H
2
C
H2
-
NH2
0=
P—NH
-CH
2
CH
2
-
NH2
NH
-
CH2CH2
-
NH2
Scheme
3.
Structure
of
the
synthesized
phosphorus-containing
reactive
amine,
TEDAP.
H2
N
C
H2
(0
)
50
100
80
70
60
40
20
90
30
10
0
0
98.4%
AH-16-TEDAP
92.
280
°
C
48.9%
36.6%
23.4%
mass
(%)
deriy.
mass
(%/min)
150-250
°
C
250-350
°
C
350-480
°
C
480-600
°
C
8
3
2
S
.
7
250-350
°
C
350-480
°
C
480-600
°
C
100
90
80
70
60
In
50
40
30
20
10
35
30
o.
25
20
3
15
10
3.
0
98.6%
AH-16-T-58
41.2%
mass
(%)
deriy.
mass
24.4%
(%/min)
1.6%
50
100 150
200
250
300 350
400
450
500 550
600
temperature
(°C)
0
0
1,00E-07
—18
-36
44
—55
58
miz
16
1,00E
08
44
36
1,00E-11
1,00E-12
0
55
58
50
100 150
200
250
300 350
400 450
temperature
(°C)
500
550
600
ion
current
(n
A)
1,00E-09
1,00E-10
A.
Toldy
et
al.
/
Polymer
Degradation
and
Stability
93
(2008)
2007-2013
2009
resin.
The
peak
of
heat
release
was
reduced
from
960
kW/m
2
to
110
kW/m
2
compared
to
the
non-flame
retarded
epoxy
resin,
furthermore
the
time
to
ignition
increased
from
49
s
to
98
s,
which
increases
the
time
to
escape
in
case
of
a
fire.
The
aim
of
this
study
was
to
find
a
reason
behind
the
excellent
flame
retardant
properties
of
the
synthesized
phosphorus-
containing
amine
in
an
aliphatic
resin
matrix
and
to
make
a
contribution
to
understanding
the
mode
of
action
of
organo-
phosphorous
flame
retardants
in
epoxy
resins
in
general
and
extending
the
knowledge
to
aliphatic
epoxy
resin
systems.
3.1.
TG/DTA-MS
and
TG-FTIR
in
situ
analysis
of
the
evolved
gases
(EGA)
during
thermal
degradation
The
gases
evolved
during
thermal
degradation
of
epoxy
resin
were
analysed
using
coupled
techniques.
The
chemical
structure
of
the
epoxy
resin
is
different
from
those
that
have
been
studied
earlier,
therefore
not
just
reference
data
but
also
new
information
was
expected
from
the
analysis
of
pristine
epoxy.
The
degradation
of
the
two
epoxy
resin
systems
studied
was
divided
into
temperature
regions
which
are
demonstrated
in
Figs.
1
and
2
showing
the
TG
and
dTG
curves
of
the
TG/DTA-MS
measurements.
According
to
these
results
the
degradation
of
the
TEDAP-con-
taining
epoxy
resin
begins
at
about
100
°C
lower
temperature
than
the
reference
system,
however
the
maximum
value
of
derivative
mass
loss
(dTG)
is
5x
lower
than
in
case
of
the
reference
system.
After
the
main
degradation
(250-350
°C)
step
there
is
a
plateau-
like
part
in
mass
loss
(350-480
°C),
especially
in
case
of
the
flame
retarded
system.
This
stage
is
followed
by
an
intensive,
high
temperature
degradation
(480-600
°C),
the
mass
residue
is
23.4%,
while
in
the
case
of
the
reference
system
amount
of
residue
is
almost
negligible.
According
to
the
TG/DTA-MS
spectra
of
the
gases
evolved
from
the
AH-16-T-58
reference
epoxy
resin
sample
(Fig.
3)
the
following
can
be
concluded:
-
emission
of
H
2
O
(m/z:
18)
due
to
the
dehydration
of
the
secondary
alcohol
in
epoxy
resin
is
detected
from
270
°C
and
has
a
maximum
intensity
at
295
°C,
-
formation
of
CO
2
(m/z:
44)
can
be
detected
from
230
°C
and
has
two
maxima
at
295
°C
and
535
°C,
-
the
formation
of
hydrocarbon
derivatives
(m/z:
55)
can
be
detected
from
260
°C
and
has
two
maxima
at
295
°C
and
320
°C,
-
emission
of
ketone
derivatives
(m/z:
58)
starts
at
220
°C
and
reaches
its
maximum
intensity
at
290
°C
(according
to
ATR-IR
0
50
100 150
200 250
300 350
400 450
500 550
600
temperature
(°C)
Fig.
2.
TG
and
dTG
results
of
AH-16-TEDAP
flame
retarded
epoxy
resin
system
in
air.
results
-
see
Section
3.2
-
the
intensity
of
the
C=0
signal
(—
1722
cm
-1
),
probably
due
to
ketene
formation
in
the
solid
phase,
diminishes
at
300
°C),
-
the
formation
of
HC1(m/z:
36)
can
be
detected
from
230
°C
and
has
two
maxima
at
295
°C
and
325
°C
(the
formation
of
HC1
is
due
to
the
1.5
mass%
hydrolysable
chloride
content
of
the
AH-16
epoxy
component
as
a
residue
of
its
synthesis
from
epichlorohydrin).
Compared
to
the
degradation
products
of
epoxy
resins
pub-
lished
in
the
literature
18]
in
this
case,
of
course,
no
phenolic
derivatives
were
found
and
not
even
their
aliphatic
analogues
(e.g.
ethanol)
were
detected,
instead,
formation
of
ketone
derivatives
was
proved.
This
difference
in
the
degradation
pathway
is
due
to
the
differences
in
the
epoxy
resin
matrix:
in
case
of
aromatic
systems
the
formation
of
phenolic
derivatives
results
in
an
increased
energy
gain
by
the
formation
of
a
more
stable aromatic
structure
than
in
case
of
the
aliphatic
system,
where
no
alcohol
formation
occurs.
The
degradation
of
aliphatic
phosphorus
segments
in
epoxy
resins
has
not
yet
been
studied,
thus
we
compared
the
TEDAP
cured
epoxy
resin
to
the
AH-16-T-58
reference.
According
to
the
TG/DTA-MS
spectra
of
the
gases
evolved
from
AH-16-TEDAP
flame
retarded
epoxy
resin
sample
(Fig.
4)
the
following
can
be
concluded:
-
emission
of
H
2
O
(m/z:
18)
due
to
the
dehydration
of
the
secondary
alcohol
in
epoxy
resin
is
detected
from
220
°C
and
has
a
maximum
intensity
at
280
°C,
Fig.
3.
TGIDTA-MS
spectra
of
the
gases
evolved
from
the
AH-16-T-58
reference
epoxy
Fig.
1.
TG
and
dTG
results
of
AH-16-T-58
reference
epoxy
resin
system
in
air.
resin
sample.
0
02
-
0.01
-
a)
C
0
DO
1111111111,14 11
,
1..
100
200
330
400
Temperature
('C)
000
F,
-25°C
200°C
250°C
300°C
350°C
400°C
2010
A.
Toldy
et
al.
/
Polymer
Degradation
and
Stability
93
(2008)
2007-2013
miz
—18
36
44
47
—55
-58
64
—74
18
_._._._......._
-
..........
:
„...r
.—_
44
64
7
=.-
-...,...
1,00E-12
0
50
100
150
200
250
300 350
400
450
500 550
600
temperature
(CC)
Fig.
4.
TGIDTA-MS
spectra
of
the
gases
evolved
from
AH-16-TEDAP
flame
retarded
epoxy
resin
sample.
-
formation
of
CO
2
(m/z:
44)
can
be
detected
from
220
°C
and
has
two
maxima
at
280
°C
and
530
°C,
-
the
formation
of
hydrocarbon
derivatives
(m/z:
55)
can
be
detected
from
150
°C
and
has
two
main
maxima
at
285
°C
at
390
°C,
-
at
300
°C,
the
emission
of
ketone
derivatives
(m/z:
58)
in
the
gas
phase
reaches
its
maximum
intensity
(according
to
ATR-IR
-
see
Section
3.2
-
results,
the
intensity
of
C=0
signals
1729
cm
-1
),
probably
due
to
ketene
formation
in
the
solid
phase,
diminishes
at
this
temperature),
-
the
formation
of
diethyl
ether
(m/z:
74)
was
detected
in
the
temperature
region
of
210-300
°C
and
has
a
maximum
at
260
°C,
-
phosphorus
is
not
only
active
in
the
solid
phase,
but
also
in
the
gas
phase:
the
P=0
fragment
(m/z:
47)
of
TEDAP
appears
already
at
160
°C
in
the
gas
phase
and
has
two
maxima
at
225
and
280
°C,
-
the
formation
of
HC1
(m/z:
36)
can
be
detected
from
185
°C
and
has
a
maximum
at
290
°C
(as
mentioned
before,
the
formation
of
HC1
is
due
to
the
1.5
mass%
hydrolysable
chloride
content
of
the
AH-16
epoxy
component).
Both
in
case
of
the
reference
and
the
flame
retarded
system,
the
shape
of
the
curves
describing
the
elimination
of
H
2
O
and
HC1
is
very
similar,
which
means
that
the
elimination
of
these
small
molecules
from
the
secondary
alcohol
containing
site
of
the
epoxy
matrix
occurs
at
the
same
temperature.
As
the
degradation
of
the
flame
retarded
system
occurs
at
lower
temperatures
than
in
case
of
the
reference
system,
the
formation
of
HC1
is
also
shifted
towards
lower
temperatures.
-
formation
of
ethyl
chloride
(m/z:
64)
can
be
detected
from
150
°C
and
reaches
its
maximum
intensity
at
225
°C
and
270
°C.
The
gases
evolved
during
thermal
degradation
of
epoxy
resin
were
also
analysed
by
the
FTIR
technique,
which
permits
rapid
0
015
-
4
0
0
1
0
-
a)
"4
0.005
-
0.000
-
100
200
300
400
600 600
Temperature
(DC)
Fig.
5.
Gram-Schmidt
thermogram
of
the
AH-16-T-58
epoxy
resin
system
determined
by
TG-FTIR
analysis.
Fig.
6.
Gram-Schmidt
thermogram
of
the
AH-16-TEDAP
epoxy
resin
system
determined
by
TG-FTIR
analysis.
and
simultaneous
measurement
of
high
resolution
IR
spectra
of
complex
gaseous
mixtures.
The
aim
of
TG-FTIR
measurements
was
to
determine
the
exact
amount
of
CO
and
detect
or
exclude
the
presence
of
some
low
molecular
weight
and
aromatic
compounds,
whose
unambiguous
detection
was
not
possible
by
other
means.
Gram-Schmidt
thermograms
indicate
the
overall
quantitative
distribution
of
the
evolved
gases
during
the
thermal
degradation
(Figs.
5
and
6).
Both
in
the
case
of
the
AH-16-T-58
reference
epoxy
resin
system
and
in
the
AH-16-TEDAP
epoxy
resin
system
evolved
gases
could
be
detected
from
200
°C,
however
in
the
reference
system
the
maximum
of
volatile
products
emission
occurred
at
520
°C,
while
in
the
flame
retarded
epoxy
resin
system
the
maximum
was
at
270
°C,
which
means
that
the
phosphorus-
containing
flame
retardant
promoted
the
evolution
of
gas
phase
degradation
products
in
the
early
stage
of
the
degradation.
Furthermore
the
TG-FTIR
technique
allowed
the
determination
of
the
quantitative
distribution
of
CO,
which
was
not
possible
by
the
TG/DTA-MS
technique
due
to
the
overlapping
of
key
ion
fragments
of
CO
with
other
compounds
and
also
the
formation
of
aromatic
compounds,
HCN
and
NH
3
could
be
excluded,
based
on
the
lack
of
the
appropriate
characteristic
signals.
32.
ATR-IR
analysis
of
the
solid
residue
during
thermal
degradation
Characterization
of
the
char
formed
in
various
stages
of
combustion
is
an
important
step
towards
complete
understanding
of
the
fire
retardancy
mechanism.
The
methodology
elaborated
for
analysing
charring
consists
of
a
heat
treatment
at
different
temperatures
and
a
subsequent
ATR-IR
analysis
of
the
surface
of
the
degraded
polymer.
4000
3500
3000
2500
2000
1500
1000
Raman
Shift
(cm
1
)
Fig.
7.
ATR-IR
spectra
of
the
AH-16-T-58
reference
epoxy
resin
system
after
heat
treatment
from
25
°C
to
400
°C.
1,00E-07
1,00E-08
S
1,00E-09
0
1,00E-10
1,00E-11
2.8
2.6
2.4
2.2
s;
2.0
O
1.8
3.,
1.6
'47)
1.4
1.2
.E
1.0
0.8
0.6
0.4
0.2
00
A.
Toldy
et
al.
/
Polymer
Degradation
and
Stability
93
(2008)
2007-2013
2011
bond
(
1043
cm
-1
)
is
collaterally
increasing;
above
300
°C
the
intensity
of
both
starts
to
decrease
and
diminishes
at
400
°C,
-
at
300
°C
the
signal
of
the
H-bonded
-OH
groups
(
—3371
cm
-1
)
disappears
and
the
signal
of
the
secondary
-NH
groups
at
—3270
cm
-1
replaces
it,
-
above
350
°C
the
double
bond
formation
(
2172
cm
-1
C=N,
N=N;
3075
cm
-1
C=C),
aromatization
processes
(3026
cm
-1
vinyl-benzene)
and
chain
splitting
of
the
aliphatic
chains
(
2955
cm
-1
)
-CH3
occur
in
the
solid
residue.
According
to
the
ATR-IR
spectra
of
the
AH-16-TEDAP
flame
retarded
epoxy
resin
sample
(Fig.
8)
the
following
can
be
concluded:
24
22
20
18
16
Ce
14
0
12
10
m
8
8
'1
1
55
d
-
25°C
-
180°C
-
190°C
-
200°C
-
210°C
-
220°C
-
230°C
-
240°C
-
250°C
-
260°C
-
280°C
-
300°C
-
350°C
6
4
2
0
-2
4000
3500
3000
2500 2000
1500
1000
Raman
Shift
(cm
1
)
Fig.
8.
ATR-IR
spectra
of
the
AH-16-TEDAP
epoxy
resin
system
after
heat
treatment
from
25
°C
to
350
°C.
According
to
the
ATR-IR
spectra
of
the
reference
epoxy
resin
AH-
16-1-58
(Fig.
7)
the
following
can
be
concluded:
-
the
thermal
decomposition
of
the
epoxy
resin
sample
begins
with
the
dehydration
of
the
secondary
alcohol
and
formation
of
C=C
double
bonds
at
200
°C
in
the
solid
phase
(
1651
cm
-1
)
(the
changes
in
the
solid
phase
could
be
detected
earlier
than
the
corresponding
gas
phase
change:
according
to
TG/DTA-MS
results
the
evolution
of
H
2
O
could
be
detected
only
from
270
°C,
whereas
the
maximum
intensity
of
the
C=C
double
bound
signal
in
the
solid
phase
is
at
250
°C),
-
the
intensity
of
C=0
signals
(
1722
cm
-1
)
starts
to
increase
at
200
°C,
most
probably
due
to
ketene
formation
in
the
solid
phase,
at
300
°C
this
signal
diminishes,
-
from
250
°C
the
intensity
of
out
of
plane
-CH
bond
(
744
cm
-1
)
is
gradually
decreasing,
probably
due
to
the
splitting
off
of
the
-CH
3
group
in
the
T-58
amine
hardener,
-
the
intensity
of
C-O-C
ether
signal
(
1093
cm
-1
)
is
decreasing
as
the
degradation
occurs,
while
the
signal
of
the
alcoholic
C-O
Table
'1
Summary
and
correlation
between
the
evolved
gas
and
solid
residue
analyses
-
the
thermal
decomposition
of
the
epoxy
resin
sample
begins
with
the
dehydration
of
the
secondary
alcohol
and
formation
of
C=C
double
bonds,
which
can
be
detected
at
180
°C
in
the
solid
phase
(
1658
cm
-1
)
(the
changes
in
the
solid
phase
could
be
detected
earlier
than
the
corresponding
gas
phase
change:
in
the
gas
phase
according
to
TG/DTA-MS
results
the
emission
of
H
2
O
is
detected
from
220
°C,
where
the
signal
of
C=C
double
bonds
has
a
maximum
intensity),
-
the
C=0
signal
(—
1729
cm
-1
)
can
be
detected
also
at
180
°C,
its
intensity
starts
to
increase
significantly
at
230
°C,
most
probably
due
to
ketene
formation
in
the
solid
phase,
at
the
300
°C
this
signal
diminishes,
-
the
intensity
of
the
C-O-C
signal
(—
1088
cm
-1
)
is
gradually
decreasing
until
240
°C,
then
the
intensity
starts
to
increase
again,
which
can
be
ascribed
to
the
splitting
of
the
C-O-C
bond
and
the
consequent
ether
formation,
-
there
is
an
interesting
phenomenon
at
240
°C:
instead
of
the
broad
signal
of
NH2
(
—3260
cm
-1
)
two
peaks
appear
at
3232
cm
-1
and
—3408
cm
-1
,
the
first
one
is
the
original
amine
peak,
while
the
latter
can
be
ascribed
to
the
formation
of
the
-OH
groups
when
the
C-O-C
bond
splits,
-
the
signal
of
P=0
is
shifted
from
1200
cm
-1
(N3P=O
in
TEDAP)
to
1215
cm
-1
,
which
can
be
ascribed
to
the
splitting
of
P-N
bonds
in
TEDAP
and
reaction
with
the
formed
alcohols
Evolved
gases,
detected
fragments
AH-16-T-58
gas
phase
AH-16-TEDAP
gas
phase
Change
in
solid
phase
AH-16-T-58
solid
phase
AH-16-TEDAP
solid
phase
Start
(°C)
Peaks
(°C)
Start
(°C)
Peaks
(°C)
Temperature
(°C)
Change
Temperature
(°C)
Change
H2O
270
295
220
280
C=C
200-
1
180-
OH
H-bonded
-300
1
240
CO
2
230
295,535
220
280,
530
CO
270
285
230
245,
510
Hydrocarbon
derivatives
260
295,320
150
285,390
-CH3
350-
1
300-
-CH
250-
P=0
from
TEDAP
160
225,
280
N-P=0
220-
C-P=0
220-
P-N-C
220-
Ketone
derivatives
220
290
190
300
C=0
200-300
180-300
it
C-O-C
250-400
—240
240-
C-O
250-300
11.
NH
sec
H-bonded
300-
C=N,
N=N
350
1
300
C6H5-CH=CH2
350
HCl
from
AH-16
230
295,325
185
290
Explanations:
1
increase,
1
decrease.
2012
A.
Toldy
et
al.
/
Polymer
Degradation
and
Stability
93
(2008)
2007-2013
Table
2
Summary
of
main
changes
during
the
degradation
steps
of
epoxy
resin
systems
Mass
loss
AH-16-T-58
AH-16-TEDAP
Temperature
region
Integrated
mass
variation
Gases
evolved
(°C)
(%)
Temperature
region
Integrated
mass
variation
Gases
evolved
(°C)
(%)
Initial
-250
-1.4
Negligible
effects
150-250
-7.5
P-containing
gases
Main
250-350
-58.8
-
H2O
-
CO2
-
CO
-
Ketone
deriv.
-
Hydrocarbon
derhy.
250-350
-51.1
-
H2O
-
CO2
-
CO
-
Ketone
deriv.
-
Hydrocarbon
deriv.
-
P-containing
gases
Subsequent
350-480
-75.6
Slow-up
of
volatile
350-480
-63.4
Slow-up
of
volatile
evolution
evolution
High
480-600
-98.4
-
CO2
480-600
-76.4
-
CO2
temperature
-
CO
-
CO
to
form
P-O
bonds
instead
of
P-N
bonds;
this
is
also
indicated
by
the
decreasing
intensity
of
the
P-N-C
bond
(
-
740
cm
-1
)
signal,
-
according
to
the
more
and
more
sharp
shape
of
the
C-O-C
(
-
1088
cm
-1
)
and
P-N-C
(
-
1040
cm
-1
)
signals,
it
can
be
concluded
that
after
220
°C
the
absorption
bands
differentiate,
which
means
that
the
degree
of
ordering
increases
and
more
regular
structure
is
formed
during
the
degradation
process
until
300
°C,
-
above
300
°C
double
bond
formation
(
-
2170
cm
-1
C=N,
N=N)
and
chain
splitting
of
the
aliphatic
chains
(
-
2950
cm
-1
-CH
3
)
occur
in
the
solid
residue.
33.
Discussion
On
the
basis
of
the
current
volatile
product,
solid
residue
and
mass
loss
result
studies,
models
are
postulated
and
summarized
for
the
degradation
of
the
AH-16-T-58
and
AH-16-TEDAP
epoxy
resin
systems.
First
correlation
was
established
between
the
results
of
the
evolved
gas
and
solid
phase
analyses,
then
the
main
changes
during
the
degradation
of
epoxy
resin
systems
were
summarized
according
to
degradation
temperature
regions.
The
correlation
between
the
changes
in
gas
phase
and
solid
phase
is
summarized
in
Table
1.
In
some
cases
there
is
a
shift
in
temperature
and
the
changes
are
detected
earlier
in
solid
phase
than
is
the
appropriate
gas
evolved
(e.g.
C=C
formation
in
solid
phase
-
H
2
O
evolved
in
the
gas
phase),
but
in
general
the
solid
phase
results
confirm
and
help
to
give
an
explanation
of
gas
phase
results.
The
degradations
of
the
reference
and
flame
retarded
epoxy
resins
are
compared
in
Table
2.
According
to
these
results
the
main
difference
in
the
degrada-
tion
of
the
reference
and
the
flame
retardant
system
is
that
the
degradation
of
the
TEDAP-containing
epoxy
resin
begins
about
100
°C
lower
mainly
with
the
emission
of
the
degradation
products
from
TEDAP:
the
TG/DTA-MS
results
indicate
the
presence
of
PO
radicals
in
the
gas
phase.
In
TEDAP
the
P
atom
in
the
P=0
fragment
is
chemically
bound
to
three
N
atoms
and
not
to
C
or
0
atoms
as
in
most
organophosphorous
flame
retardants.
Therefore
the
evolution
of
PO-containing
species
is
facilitated
because
the
binding
energy
of
C-N
bonds
is
lower
than
that
of
the
C-C
and
C-O
bonds
13].
The
mentioned
P-containing
species
act
as
flame
retardant
in
the
gas
phase
slowing
down
the
further
degradation
steps:
the
maximum
value
of
derivative
mass
loss
(dTG)
is
5
x
lower
than
in
case
of
the
reference
system.
After
the
main
degradation
step
the
mass
loss
curve
roughly
takes
the
form
of
a
plateau
(Figs.
3
and
4).
In
the
case
of
the
flame
retarded
system
this plateau
is
much
higher
and
has
a
lower
gradient,
because
the
mass
loss
is
significantly
lower
and
the
rate
of
mass
loss
is
slower
than
in
case
of
the
reference
system
due
to
the
solid
phase
action
of
phosphorus.
This
stage
is
followed
by
an
intensive,
high
temperature
degradation,
where
the
solid
phase
effect
of
the
phosphorus
is
prevailing:
the
amount
of
emitted
phosphorus-containing
gases
is
negligible,
and
the
formation
of
phosphorocarbonaceous
intumescent
char
results
in
a
mass
residue
of
23.4%
in
the
TG,
while
in
the
case
of
the
reference
system
the
amount
of
residue
is
negligible.
According
to
these
statements
it
can
be
concluded
that
the
outstanding
flame
retardancy
results
are
due
to
the
effect
of
phosphorus
in
both
gas
and
condensed
phase.
Initially
the
gas
phase
action
of
phosphorus
is
crucial
for
slowing
down
the
resin
degradation
before
ignition
and
thus
increasing
the
time
to
ignition
to
double
of
the
original
value.
During
high
temperature
degrada-
tion
the
solid
phase
action
of
phosphorus
results
in
reduction
in
the
rate
and
extent
of
char
oxidation.
As
a
result,
the
peak
of
heat
release
rate
decreased
to
1/10
of
the
original
value
and
mass
residue
is
significantly
increased.
In
order
to
determine
the
ratio
of
phosphorus
acting
in
gas
phase
and
solid
phase,
respectively,
supplementary
XPS
measure-
ments
of
the
char
residue
of
mass
loss
calorimeter
measurements
were
done
to
determine
the
elemental
composition
of
the
remaining
char
(Tables
3
and
4).
The
mass
residue
of
the
TG
Table
3
XPS
results
of
solid
residue
of
AH-16-T-58
sample
after
cone
heater
treatment
compared
to
the
original
mass
concentration
of
the
same
material
disregarding
H
Peak
Position
BE
(eV)
FWHM
(eV)
Raw
area
(CPS)
RSF
Atomic
mass
Atomic
conc.
(%)
Mass
conc.
(%)
Original
mass
conc.
a
disregarding
H
I
'
(%)
Relative
change
in
mass
conc.
(%)
O
is
5303
3.9
2930.2
0.7
16.0
13.22
16.68
28.91
-4231
N
is
396.4
3.2
1104.0
05
14.0
7.26
8.02
337
138.27
C
is
282.0
2.1
7615.6
03
12.0
79.52
7531
67.72
11.21
a
Calculated
according
to
the
sample
composition
determined
on
the
basis
of
epoxy
equivalent
and
amine
number.
b
H
was
disregarded
in
order
to
obtain
comparable
data
with
XPS
results.
A.
Toldy
et
al.
/
Polymer
Degradation
and
Stability
93
(2008)
2007-2013
2013
Table
4
XPS
results
of
solid
residue
after
cone
heater
treatment
of
AH-16-TEDAP
sample
compared
to
the
original
mass
concentration
disregarding
H
Peak
Position
BE
(eV)
FWHM
(eV)
Raw
area
(CPS)
RSF
Atomic
mass
Atomic
conc.
(%)
Mass
conc.
(%)
Original
mass
conc.
a
disregarding
H
I
'
(%)
Relative
change
in
mass
conc.
(%)
0
1
s
5323
3.0
6589.2
0.7
16.0
22.80
27.05
30.95
-1259
N
is
399.7
2.7
900.9
05
14.0
454
4.72
10.26
-54.01
C
is
284.6
2.0
87605
03
12.0
70.16
62.49
55.00
13.61
P
2p
134.2
2.0
519.9
05
31.0
250
5.74
3.79
5156
a
Calculated
according
to
the
sample
composition
determined
on
the
basis
of
epoxy
equivalent
and
amine
number.
b
H
was
disregarded
in
order
to
obtain
comparable
data
with
XPS
results.
measurements
was
not
sufficient
for
XPS
analysis,
therefore,
a
homogenized
sample
was
taken
from
the
broken
char
residue
from
the
mass
loss
calorimeter
measurements.
First
of
all,
it
has
to
be
mentioned
that
the
differences
between
the
two
epoxy
resin
systems
are
clearer
in
the
case
of
mass
loss
calorimeter
measurements
(sample
mass:
48
g),
where
the
condi-
tions
are
closer
to
real
fire
conditions,
than
in
the
case
of
TG
measurements
in
air
(sample
mass:
10
mg).
The
mass
residue
of
the
TEDAP-containing
system
increased
from
23.4%
to
50%
due
to
up-
scaling,
while
the
mass
residue
value
of
the
reference
remained
approximately
the
same
under
both
circumstances.
The
differences
in
the
original
elemental
compositions
are
well-
marked
(Tables
3
and
4):
the
flame
retarded
system
contains
10.26%
N,
acting
as
spumific
agent
and
3.79%
P
responsible
for
acid
formation
during
the
degradation,
both
are
essential
components
in
intumescent
flame
retardancy.
On
the
other
hand,
the
reference
epoxy
resin
only
contains
337%
N.
According
to
the
XPS
results
it
can
be
concluded
that
in
the
AH-16-T-58
sample
a
significant
enrichment
in
N
and
depletion
in
0
was
observed,
however
as
the
mass
residue
of
the
reference
is
negligible,
it
has
no
noteworthy
effect.
In
case
of
AH-16-TEDAP
sample,
depletion
in
both
N
and
0
was
observed.
Due
to
charring,
in
both
cases
enrichment
in
C
was
detected,
while
in
the
flame
retarded
system
the
P-content
also
increases
by
approximately
50%.
Considering
that
in
this
case
the
mass
loss
calorimeter
measure-
ment
residue
is
-50%
of
the
original
mass,
it
can
be
concluded
that
approximately
75%
of
the
originally
present
P
stays
in
the
solid
phase,
while
25%
of
it
acts
in
the
gas
phase,
which
is
in
accordance
with
the
IR
analysis
of
the
solid
residue
and
TG/DTA-MS
and
TG-IR
analysis
of
the
evolved
gases
during
thermal
degradation.
4.
Conclusions
This
study
aimed
at
making
a
contribution
towards
the
better
understanding
of
the
behaviour
of
reactive
phosphorus-containing
flame
retardants
in
aliphatic
epoxy
resins
by
determining
their
role
in
different
degradation
steps
and
the
exact
ratio
of
phosphorus
acting
in
the
gas
phase
to
that
in
the
solid
phase.
It
was
determined
that
the
main
difference
in
the
degradation
of
the
reference
and
the
flame
retardant
systems
is
that
the
degra-
dation
of
the
epoxy
resin
containing
the
synthesized
phosphorus-
containing
reactive
amine
(TEDAP)
begins
at
a
temperature
which
is
about
100
°C
lower
than
that
of
unmodified
one,
mainly
with
the
emission
of
degradation
products
of
TEDAP
(PO
radicals),
which
was
shown
by
the
TG-MS
coupled
technique.
The
evolved
phos-
phorus-containing
gases
act
as
flame
retardant
in
the
gas
phase
slowing
down
the
further
degradation
steps:
the
maximum
value
of
derivative
mass
loss
is
5
x
lower
than
in
case
of
the
reference
system.
It
was
stated
that
at
high
temperature
degradation
stage
the
solid
phase
effect
of
the
phosphorus
prevails:
the
amount
of
emitted
phosphorus-containing
gases
is
negligible,
while
the
formation
of
phosphorocarbonaceous
intumescent
char
results
in
a
mass
residue
of
23.4%
in
TG,
whereas
in
case
of
the
reference
system
the
amount
of
residue
is
basically
negligible.
The
enrich-
ment
of
the
intumescent
char
in
carbon
and
phosphorus
was
proved
by
XPS
measurements.
Based
on
the
mass
loss
and
XPS
results
of
the
solid
residue,
it
was
determined
that
25
mass%
of
the
originally
introduced
phosphorus
acts
in
gas
phase,
while
the
other
75
mass%
stays
in
the
solid
phase.
It
was
concluded
that
this
double
effect
of
phosphorus
is
the
reason
for
the
outstanding
flame
retardancy
of
the
AH-
16-TEDAP
system:
at
the
beginning
the
gas
phase
action
of
phos-
phorus
is
responsible
for
the
increase
in
the
time
to
ignition,
while
at
high
temperature
the
solid
phase
action
results
in
a
reduction
of
the
peak
of
heat
release
rate
and
an
increased
mass
residue.
Acknowledgement
The
authors
acknowledge
the
financial
support
received
through
the
EU-6
Framework
Program
(NMP3-CT-2004-505637),
Hungarian
Research
Fund
OTKA
T049121
and
Fund
of
the
European
Union
and
the
Hungarian
State
GVOP/3.1.1.-2004-0531/3.0.
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