Thermal and flammability analyses of poly(hydroxyamide) (PHA) and its derivatives
Huiqing Zhang, Phillip R. Westmoreland, Richard J. Farris University of Massachusetts, Amherst
CUMIRP Cluster F
Outline
• Introduction
• New microscale flammability tests--- PCFC*, STA*(TGA/DSC), Pyrolysis GC/MS
• Thermal decomposition and flammability--- Poly(hydroxyamide) (PHA)--- Halogenated PHAs--- PHAs with OMe groups--- PHAs with different phosphate groups
• Thermal decomposition mechanisms
• Conclusions
* PCFC: Pyrolysis-combustion flow calorimeter (FAA microcalorimeter)* STA: Simultaneous thermal analysis (TGA/DSC)
Fire --- A potential hazard for human life
• Annually account for more than 6,000 deaths and $10 billion in property damage.
• More stringent fire safety requirements in enclosed and inescapable applications, such as aircraft cabins, submarines, ships, subways, and high-rise buildings.
Los Angeles, 1991 Teibei, 2000 Austria, 2000
FAA long-term objectives: “eliminate burning cabin materials as a cause of death in aircraft accidents”
Aircraft interiors contain tons of combustible polymers
UMass CUMIRP Cluster F: “Fire-Safe Polymers and Polymer Composites”
• Create new tools and techniques for thermal decomposition and flammability characterization
• Establish the correlation between polymer structure, composition andmacroscopic flammability
• Understand polymer decomposition chemistry and fire-resistance mechanisms
• Develop a new generation of high-performance, environmental friendly fire-resistant polymers
Objectives:Reduce unwanted fires and extend polymer applications
How to make polymer more flame resistant?
• Reduce the generation of combustible gases• Increase char formation• Release chemical flame suppressants (Cl, Br, P)
Combustion cycle
Flame resistance
Gas-phase flame
Radiant heat transfer to
surface
Char
Pyrolysis gases
Unpyrolyzed polymer
Strategies for reducing polymer flammability• Inherent fire-resistant polymers
--- high thermal stability, low mass loss rate, low heat of combustion of pyrolysis gases, high char yield
Linear aromatic or heterocyclic polymers
Ladder polymers
Semi-organic polymers
• Structure and composition modificationCopolymers and blends
• Flame-retardant additivesB, Al, P, Cl, Br, Sb, Si, N
C6H5
NO
P Hn
C6H5
C6H5
Si O On
NN CO
CO
C
OC
O
n
NN n
PHA: High-performance fire-safe polymer
• High molecular weight, soluble and easy to process• Large endothermic cyclization heat sink• Simultaneous release of flame-quenching molecules• Low heat-release rate and high char yield• Precursor of polybenzoxazole (PBO) --- high-temperature
and flame-resistant polymer
Mars aerobot(PBO balloon)
H2O-
PHA PBO
O OCC
NN
n
OCC
O
OH
HN
HO
NH250 ~ 400C
O OCC
NN
n" Air Force " polybenzoxazole (PBO)
Standard flammability tests
• Ease of ignition• Flame spread ---- across a surface• Fire endurance ---- penetrate a wall or barrier• Rate of heat release• Ease of extinction• Smoke evolution ---- amount, rate and composition• Toxic gas evolution ----amount, rate and composition
Limiting oxygen index (LOI), UL-94 small flame test, cone calorimeter,Ohio State University (OSU) calorimeter, ASTM-E-84 Steiner Tunnel, NBS smoke chamber.
Tests most commonly used in USA:
Thermal decomposition and flammability tests
Cone calorimeter: 100g
PCFC (FAA): 1mg(Flammability)
Py-GC/MS: 50~300µg(pyrolysis gases)
STA (TGA/DSC): 10mg(Thermal decomposition)
Traditional: New:
UL-94
Pyrolysis-combustion flow calorimeter (PCFC)
High-throughput milligram-scale method for materials flammability research(based on oxygen consumption principle)
Lyon, R. E.; Walters, R.N. International SAMPE Symposium and Exhibition (Proceedings) 45th 2000, v45, p1721
Heat release capacity η c(J/g.K):
E=13.1± 0.7 kJ/g-O2
o
Occ m
mEh maxmax21 && ∆
==ββ
η
:maxch&
:β
Peak of heat release rate (w/g)
Heating rate (K/s)
Structures of PHA and its derivatives (1)
PHA
PHAs containing OMe group
Halogenated PHAs
PHA-1 (-OH)
PHA-3 (-OH, m-Br)
PHA-5 (-OH, -CF3, m-Br)
PHA-7 (-OMe)
PHA-8 (-OMe, -OH)
PHA-9 (-OMe, -OPO(OMe)2)
NH
HO
HN
OH
OC C
O
n
nBr Br
OCC
O
OH
HN
HO
NH
CF3
CF3NH
HO
HN
OH
OC C
O
BrBr n
MeO OMen
OCC
OHN NH
n
OCC
O
OH
HN
HO
NHNHHNOC C
O
OMeMeO
MeO-P=OOMe
O O
OMeO=P-OMe
MeO OMe
OCC
OHN NH NHHN
OC C
O
n
5
TGAs and derivative of TGAs (DTGs)
Two-stage
DSC curves
First stage: endothermicSecond stage: exothermic
Temp [°C]
Hea
t Fl
ow
[mW
]100 300 500 700 900
nR2
HO OH
R NHHNOC C
O
R2
PHA-1: R2= H; PHA-3: R2= Br; PHA-5: R2= Br, R= C(CF3)2
(10oC/min, N2)
0
2
4
6
8
10
12
Der
iv. W
eigh
t (%
/min
)
0
20
40
60
80
100
Wei
ght (
%)
100 300 500 700 900Temperature (°C) Universal V2.5H TA Instruments
1
3
5
3
3 115
Thermal decomposition of PHA and halogenated PHAs
TGAs and derivative of TGAs (DTGs) DSC curves
O O
NHHNOC C
O
R1 R1 n
Temp [°C]
Hea
t Fl
ow[m
W]
100 300 500 700
PHA-7: R1= Me; PHA-8: R1= H, Me; PHA-9: R1= Me, PO(OMe)2
(10oC/min, N2)
0
4
8
12
16
Der
iv. W
eigh
t (%
/min
)
0
20
40
60
80
100
Wei
ght (
%)
100 300 500 700Temperature (°C) Universal V2.5H TA Instruments
9
8
7
9
98
87
7
exo
Thermal decomposition of PHAs containing OMe groups
Samples H.R.capacity (a) Total heat (a) Peak mass loss rate (b) Char yield (b)
(J/g.K) (kJ/g) (x 103/s) (%)
PHA-7 (-OMe) 130 17 1.4 43
PHA-1 (-OH) (iso) 42 10 0.4 56
PHA-8 (-OMe,-OH) 33 11 0.5 55
PHA-9 (-OMe,-OPO(OMe)2) 18 9 0.2 60
PHA-3 (-OH, m-Br) 17 5 0.4 39
PHA-5 (-OH, -CF3, m-Br) 8 3 0.7 36
Flammability of PHAs (1)
(a) PCFC results. Pyrolyze at 4.3oC/s to 930oC. (b) TGA/DSC results. Heat at 10oC/min to 1000oC. Char yield is the solid residue left at 930oC.
0 200 400 600 800 1000 1200 1400 1600
PP
PE
PS
Nylon 66
PPO
PET
PC
PMMA
Kevlar
POM
PEEK
PHA-7
ULTEM
PHA-1
PHA-8
PI
PBZT
BPC-PC
PHA-9
PHA-3
PHA-5
Heat Release Capacity (J/g.K)
FAA threshold for fire-resistant polymers
The flammability of polymers
nOO
R RP P
R R
OO
COO
CNHNH
O OC2H5OCH3O
Cl
Cl
PHA-10 PHA-11 PHA-12 PHA-13 PHA-14
R:
PHAs containing phosphate groups
Structures of PHA and its derivatives (2)
Temperature (oC)
Wei
ght (
%)
100.0 200.0 300.0 400.0 500.0 600.0 700.0 800.00.0
8.0
16.0
24.0
32.0
40.0
Temperature (oC)
Hea
t flo
w
exo
TGA curves DSC curves
NH NH CO O
C
O O
RRPP
RR
O On
R OPh Ph OC2H5 OPh(Cl)2 OCH3
OCH3
OC2H5
OPh(Cl)2
OPh
Ph
20
40
60
80
100
100 300 500 700
OCH3
OC2H5
OPh(Cl)2
OPh
Ph
Thermal decomposition of phosphate PHAs
(10oC/min, N2)
Flammability of phosphate PHAs
Samples H.R.capacity (a) Total heat (a) Peak mass loss rate (b) Char yield (b)
(J/g.K) (kJ/g) (x 103/s) (%)
PHA-10 (-OPh) 340 15 3.3 36
PHA-11 (-Ph) 210 21 2.9 32
PHA-12 (-OC2H5) 73 9 0.4 41
PHA-13 (-OPh(Cl)2) 59 8 0.6 29
PHA-14 (-OCH3) 19 8 0.2 52
(a) PCFC results. Pyrolyze at 4.3oC/s to 930oC. (b) TGA/DSC results. Heat at 10oC/min to 1000oC. Char yield is the solid residue left at 930oC.
Thermal oxidative stability of PHAs
• Oxygen: No effect on initial thermal stability• Char: Easy to oxidize• Phosphorus: Enhance char formation
1 ( N2)
7 (N2)
7 (Air)1 (Air)
TGA curves (10oC/min)
0
20
40
60
80
100
120
Wei
ght (
%)
0 200 400 600 800 1000Temperature (°C)
PHA-1 (-OH)PHA-7 (-OMe)
Universal V2.5H TA Instruments
9 (N2)
12 (N2)9 (Air)
12 (Air)
0
20
40
60
80
100
120
Wei
ght (
%)
0 200 400 600 800Temperature (°C)
PHA-9 (-OMe, OPO(OMe)2)PHA-12 (--OPO(OC2H5)2)
Thermal cyclization of PHAs?
R2 = Br
R1 = H, CH3, PO(OPh)2, POPh2, PO(OCH3)2, PO(OC2H5)2, PO(OPhCl2)2
Cyclization
(Br and other flame-quenching molecules)
n
(H2O, CH3OH or phosphate)R1OH
+
PBO
NHHNOC C
O
R1O OR1 R2
?
R2
CNOO
NC
+
n
Elemental analysis of PHA-1
Temperature Measured (%) Calculated (%) Char
(oC) C H N O C H N O (%)
250 (PHA) 67.26 3.78 7.56 21.4 69.4 4.1 8.1 18.4 100
400 (PBO) 75.96 3.26 8.62 12.16 77.4 3.2 9 10.4 90
650 79.97 2.93 7.84 9.26 75
1000 87.07 0.44 3.78 8.71 50
Nominal formula of char at 1000oC : C 7.3 H 0.44 N 0.27 O 0.5
n
OCC
O
OH
HN
HO
NH
IR spectra of PHA-1 at different temperatures
υO-Hυ N-H δAr-H
υ N-H
υ N-H in --NH2
δAr-H
δAr-H
δAr-H
υ C=O
υ C=O
υ C=O+
υ C≡N
υ C=O
δN-H + υ C-N
δN-H + υ C-N
υC-O-C
υC-O-C
25 oC
250 oC
350 oC
400 oC
650 oC
N
OC
N
OC
N
OC
H2O (8%), CO2 (26%)CO (32%), HCN (10%)
* The numbers in the parentheses are the weight percents of each volatile
n
OCC
O
OH
HN
HO
NH
(10%)
(8%)
(2%)
(3%)
(1%)
4.3oC/s, 250oC ~ 930oC
Pyrolysis GC/MS (PHA-1)
PBO
CN
NC CN
N=C=O
CO
N
NHN
H2O (>90 wt%), CO2 (<10 wt%)
CO2,CO,HCN
First stage: 250 ~ 380 oC
Second stage: 380 ~ 930 oC
PHA-1 (-OH)
(Cyclization)
(Main chain scission)
CN
NC CNNH
N
CO
N
CO2 (29%), CO (25%)H2O (5%), CH3OH (1%)HCN (5%)
NHHNOC C
O
nOMeMeO
4.3oC/s, 250oC ~ 930oC
N
OC
(9%)
(5%)
(1%)
(1%)
(4%)
(6%)
(5%)
(4%)
Pyrolysis GC/MS (PHA-7)
CN
COOH
COOMeMeOOC
COOMe
COOHMeOOC
NC CN
CO2, CO, H2O, CH3OH
CO2, CO, H2O,
CH3OH, HCN
N
OC
Second stage: 465 ~ 930 oC
PHA-7 (--OMe)
First stage: 350 ~ 465 oC
(Backbone scission and cyclization)
(Random scission)
CN
COOMeMeOOC
COOHMeOOC
COOMeMeOOC
COOMe
COOH
NC CN
Pyrolysis GC/MS (PHA-10)
NH NH CO O
C
O O
RRPP
RR
O On
R= --OPh
H2O CO2 CO HCN
CN
OH
PO
PhPhF
PO
PhPhOPh
PO
OPhPhOOPh
4.3oC/s, 250oC ~ 930oC
PHA-10 (-OPh)
250 ~ 500oC
500 ~ 930oC
OH
PO
OPhPhOOPh
PO
PhPhOPh
OH
H2O CO2 CO HCN
CN
NC CN
COOH
PO
PhPhF
(Side group cleavage)
(Main chain scission)
CNNC CN
P OC2H5C2H5OO
OC2H5
P OC2H5C2H5OO
C2H5
Pyrolysis GC/MS (PHA-12)NH NH C
O OC
O O
RRPP
RR
O On
4.3oC/s, 250oC ~ 930oC
CO2, CO, H2O, HCNC2H5OH, CH3OH, C2H4
R= -OC2H5
P OC2H5C2H5OO
OC2H5
P OC2H5C2H5OO
OC2H5
NC CNCN
P OC2H5C2H5OO
C2H5
PHA-12 (-OC2H5)
200 ~ 400oC
(Side group cleavage)
400 ~ 930oC
(Main chain scission)
CO2, CO, H2O, HCNC2H5OH, CH3OH
C2H5OH, H2O, C2H4
Decomposition mechanisms of PHA and its derivatives
(a) Low temperature (< 500oC)
I: PHA and halogenated PHAs
II: PHAs with methoxy groups
NH
CO
CO
NH
OHHOO
NN
O
250 ~ 400oC- H2OCyclization
NH
CO
CO
NH
OOMeMe
CO
CO
OMeMeO
NH
CO
CO
NH
OHOMe
O
NHN
OCO
Me
- Me
350 ~ 500oC
CyclizationBackbone cleavage - H2O
Decomposition mechanisms of PHA and its derivatives
(III) PHAs with phosphate groups
(b) High temperature (>500oC)
NH
CO
CO
NH
OOPP
OR R
ORR RH
POR3 NH
CO
CO
NH
OHOP
OR R
O
NHN
OCO
PO RR
< 500oC
Cyclization
+Side group cleavage
R = -OPh, Ph, OPhCl2, OC2H5, OCH3
- H2O
O
NHN
R'OCO
O
NCN
CNNC
R'Main chain scission
CO2, CO, H2O, HCN
and other organic compounds
RecombinationAromatization
Calculated bond energies (kcal/mol)
Method: B3LYP/6-31G(d), Mean Error = 8kcal/mol
PHA-1
PHA-7
69109
95
76
106111
HO n
OCC
OHN
HO
N
H
93
50109
95
76
106111
O n
OCC
OHN
HO
N
H
93
Me
Weakest bonds: O-H (PHA-1), O-Me (PHA-7)
Conclusions
• PHA and its derivatives (except for some phosphate PHAs) are a series of new fire-safe polymers that have extremely low heat-release rates and very high char yields.
• PHA and halogenated PHAs decompose in two stages.First stage, water release to form PBO structure (endothermic). Second stage, random scission of PBO backbone (exothermic).
• Elemental analysis and IR prove that the first stage of decomposition of PHA-1 corresponds to cyclization into PBO.
• The major decomposition products of PHAs, except for PHA-7 and phosphate PHAs, are CO2, CO, H2O and HCN, which result in their low flammability.
• Substitution of hydroxyl groups with some other bigger groups such as methoxy or phosphate groups will lead to increase of the flammability due to the introduction of weak linkages between side groups andpolymer main chain.
• PCFC is a very rapid and quantitative screening tool for newly-synthesized fire-resistant materials.
UMass: Jungsoo Kim, Simon W. Kantor, Arthur Gavrin, Bryan CoughlinStanislav I. Stoliarov
FAA: Richard N. Walters, Richard E. Lyon
UMass CUMIRP Cluster F sponsors:Boeing - Commercial Airplane Group, BP-Amoco Polymers, Federal Aviation Administration, Foster - Miller, Inc., General Electric Co., NIST, US Army, Solutia Inc.,
Schneller Inc.
Acknowledgments