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