prinziples and history of chemiluminescence · prinziples and history of chemiluminescence...

Research & ProductDevelopment Polymer AdditivesDivision Pigments & Additives

Prinziples and History of Chemiluminescence

Christoph KröhnkeClariant Huningue, Division Pigments & Additives Research & Product Development and Technical Service Polymer AdditivesF-68331 Huningue, France

Folie 214.11.2006Dr.C.Kröhnke, Research & Product Development Polymer Additives

Overview

IntroductionDefinition of CLApplications to the screening of specific polymer samples, discussionConclusion


Classification of luminescence

Type of excitation Name

Absorption of light Photo luminescence

High energy particles Radio luminescence

Cathode rays / electron beams Cathodo luminescence

Electric fields Electro luminescence

Thermally activated ion recombination Thermo luminescence

Chemical reaction (oxidation) Chemi (oxy) luminescence

Biological process (enzymatic) Bio luminescence

Friction / mechanical forces Tribo luminescence

Sound / ultrasound Sono luminescence


Origin of Chemiluminescence

Emission of radiation resulting from a chemicalreaction. The emitting species may be a reaction product or a species excited by energytransfer from an excited reaction product.

The excitation may be electronic, vibrational or rotational


History of ChemiluminescenceOrganic low molecular weight compounds– Callaud, J. Pharm. 7 (1821) 579-580

quinine sulfate

– Bronislaus Radziszewski, Ber. d. Dtsch. Chem. Ges., 10 (1877) 70-75 & 321-3222,4,5-triphenylimidazole

Polymers– G.E. Ashby, J. Polymer Sci.,50 (1961) 90– “...A rapid method for screening chemicals for

antioxidant action follows from these experiments...”

Discovery that the phenomenon is associated with a simple organic reaction


Simplified Autoxidation Mechanisms of Polymers

R

ROOHRH

R

2 RHROO

O2

Quantum yieldΦ = 10-9

ROH + 1O2 + 3R=O*RH ROOROOH{ }

∆

∆

R + ROH + H2O

• “Russell Mechanism”: bi-molecular termination of alkyl-peroxy radicals


Alternative attempts to interpret the mechanism:

Chemically Initiated ElectronExchange Luminescence (CIEEL)

A type of luminescence resulting from a thermal electron-transfer reaction, also called catalyzedchemiluminescence

IUPAC Compendium of Chemical Terminology 2nd Edition (1997)and G.B. Schuster, Acc. Chem. Res., 12, 366 (1997)


Characteristics of emission

spectral range: 380-450 nm

I = G x Φ X R

I is the intensity of the CLG is a geometrical factorR is the reaction rateΦ is the quantum efficiency

surface phenomenon

Quantum yieldΦ = 10−9


Spectral Photon Irradiance

Object photon / s (cm2)(µm)*

full moon

bright star

oxidizing Polypropylene @ 150 °C under O2

6 1011

5 106

1 105

* centered @ 500 nm


Light detectionPhotomultipliers (PM) used in photon counting modeSlow Scan Charge Coupled Devices (CCD)

Detector type– UV-coated, back illuminated CCD 512 X 512 pixels (pixel

size 24 mm)– N2 cooled (-130 °C)

Characteristics– Quantum efficiency > 60%– wide spectral response (190-1100 nm)– low noise, 5-7 counts (standard deviation)– high dynamic range, saturation insensitive

Intensified CCD’s (ICCD)


CL ApparatusCL Apparatus

Rapid heatingGood temperature stabilityGas exchange facilityLight tightness

PMTSlow scan CCDsMicro channel plate (MCP)

Light sensitive Light sensitive detectordetector

1. CCD sensor2. Objective3. Sample heater4. Sample height

adjuster

+Oven


Detection range and sensitivity

Wavelength (nm)

0

10

20

30

40

50

60

70

200 300 400 500 600 700 800 900 1000 1100 1200

Qua

ntum

Effi

cien

cy (%

)

0

0.05

0.1

0.15

0.2

0.25

Num

ber o

f "de

tect

able

" ph

oton

s(c

ount

s / p

ixel

/ se

c / n

m)

CL-emissionCCD

PMT

heaterradiation


Photomultiplier vs. Slow Scan CCDquantum efficiency CCDspectral response curve CCDnoise level PM = CCDdynamic range CCDlight collection PM


Photomultiplier vs. Slow Scan CCDquantum efficiency CCDspectral response curve CCDnoise level PM = CCDdynamic range CCDlight collection PM

Picture taken with Slow Scan CCD:

dark room

light source 1 matchaperture f/16

exposure time 1/10 s


Typical Chemiluminescence Curve

Heating time

Ligh

t em

issi

on

N2 O2

∫ = f [ROOH]OIT


Arrhenius plots from OITsln

(OIT

)

2.34 2.36 2.38 2.40 2.42 2.44 2.46 2.48 2.503

4

5

6

7

103 1/ T (k)

Stabilized PP samples (250 ppm Hostanox® O 10)

DSCCL

Data: courtesy Prof. Dr. N. C. Billingham (Sussex University)


OIT measured by CL and DSCPolypropylene film250 ppm phenolic antioxidant1 bar O2 flow 50 ml/min

-0.685

-0.635

-0.585

-0.535

0 200 400 600 800 1000Time (min)

Hea

t Flo

w (m

W)

0

5000

10000

15000

20000

25000 Photons/sec

130°C

Hea

t Flo

w (m

W)

-0.57

-0.07

0.43

0.93

1.43

0 20 40 60 800

20000

40000

60000

80000

100000

120000 Photons/sec

150°C

Time (min)


Advantages of CL over DSC

Higher sensitivitymeasurement at lower temperaturesmall samples

CL signal related to only one reactionsharp OITs excellent baseline stability

Imaging capacitiesmultiple sample analysisheterogeneity of oxidation


Temperature dependent OIT‘sstudied on Polybutadiene rubber film stabilized with 0.3% phenolic antioxidant

100200300400500600700800900

0 500 1000 1500 2000 2500

140 °C

130 °C

120 °C

110 °C100 °C 90 °C

0100200300400500600700800900

1000

Oven time [min]

Cou

nts/

pixe

l/15m

in


CL curves of stabilized individual Polypropylene particles

300300

0 60 120 180 240 300 3600

50

100

150

200

250

300

batch concentration: 0.0075% Hostanox® O 10

Residence Time / min.

CL

Inte

nsity T=150ºC


Acceleration of oxidation withpressure

stabilized Polypropylene film / 250 ppm AO

0

10000

20000

30000

40000

50000

0 200 400 600 800 1000

1 bar5 bar

15 bar

10 bar30 bar

25 barT=130 °C

Phot

ons/

sec

Time (min)



Acceleration of oxidation withpressure

stabilized PP film / 250 ppm AO

250000

1 bar

5-25 barT=150 °C

Phot

ons/

sec 200000

150000

100000

50000

00 20 40

Time (min)60 80



Limitations of Chemiluminescence(CL) Measurements

Materials– Difference in CL intensity depending on the polymer

PA>PU>PAN>PP≈NR>PVC≈PE>PSSample to sample contaminationOptical artefacts– Light guiding– Sensitive to surface changes

CL is emitted from the polymer surface !

Modification of surface will increase or decrease the signal.CL-intensity is primarily dependent on the sample surface not sample thickness or weight.

cracksLight-pipe

d


Examples – Screening of Antioxidants

Conventional Method: Forced draft air oven for accelerated thermal ageing of polymer samples


Acceleration factors

Oven ageing

– air (turbulent)

– 100 °C < T < 150 °C

– sample thickness1-2 mm

CL-test

– O2 (slow flow)

– T = 150 °C

– sample thickness100 mm

– pressure


Experimental Setup

Al sampletray

PP films~13 mm

imaged surface


Visual Information

Camera Screen

counts/pixel

65’535

0

255

0

>1000grey levels

false colors

0

1000


Chemiluminescene Images

0

> 500

250

45 min. 1.25 h

counts/pixel/15min


2.5 h 3.75 h

5 h 6.25 h


22.5 h

8.75 h

12.5 h


Data Analysis

pixelarray

1) Define a pixelarray over each sample

2) Read the average pixel intensity in each arrayof each picture

3) Plot intensities vs. time


Chemiluminescence Data Curves

0 5 10 15 20 25 30oven time [hours]

0

100

200

300

400

500

Cou

nts/

pixe

l/15 m

in

100 ppm

0 ppm

250 ppm

500 ppm

750 ppm

1000 ppm


Efficiency of phenolic Antioxidantsin Polypropylene

0 200 400 600 800 10000

500

1000

1500

2000

2500

6

AO Concentration /ppm

CL

OIT

/ m

in.

Hostanox® O 10

Hostanox® O 13

Hostanox® O 16

HO CH2CH2 CO

O CH2 C

4

OH

CH2R

CH3

CH3

CH2RRCH2

CH3

R =

HO CH2CH2 CO

OC18H37


Correlation with Oven Aging Test (I)

7

0 10 20 30 40 500

1

2

3

4

5

6

CL Oxidation Induction Time / hours

Tim

e to

em

britt

lem

ent/

day

s

Hostanox® O 13 Hostanox® O 10


Correlation with Oven Aging Test (II)

0.5 days

10 min

Hostanox O 16

0 2 4 6 8 10CL induction time [hours]

0

1

2

3

4

5

time

toe m

b ritt

lem

ent[

days

]


Advantages of Chemiluminescencefor Polymer / Additive testing

• early detection of sample defects• small sample sizes are sufficient• low volatilization of additives• discrimination of low stabilizer concentrations• discrimination of various sample geometry's• acceleration versus oven aging: 10- 20 x• automation


Dynamic oxidation test

Additive responsein “real time”Perturbation

sample


Experimental Setup

Al sampletray unstabilized

Polypropylenefilm

stabilized Polypropylene

film


Dynamic Oxidation at T=150ºC

20 min 40 min 60 min

counts/pixel/10 min

0

40080 min 100 min


120 min

coun

ts/p

ixel

/10

min

0

400

140 min

180 min160 min


Spreading of Oxidation in Polypropylene

0 100 200 300 400 500Minutes@150°C inOxygen

0

4

8

Oxida

tionf

rontp

osit io

n(mm

)

Hostanox® O 16Hostanox® O 10

Hostanox® O 13


Summary

Assess the thermally induced degradation of polymers– quick and easy (30 min )– automatation– small samples– early detection of sample defects– measure on real samples (Al-panels)– visual information (imaging)– simultaneous multiple sample testing– lower volatilization of antioxidants– discrimination already at low antioxidant concentrations– acceleration

10-20 x vers. conventional methods (oven aging)


Acknowledgements

University of Sussex at Brighton, UK– Prof. N. Billingham– Dr. D. Lacey

Swiss Federal Office of Public Health– Dr. V.Dudler

University of Basel– Dr.D.Kohler

prinziples and history of chemiluminescence · prinziples and history of chemiluminescence...

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