The photooxidation process was modelled with input data consisting of Arrhenius parameters A (the preexponential factor) and E (the activation energy)

Guillet, J. E.

Somersall, A. C.

English

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https://ntrs.nasa.gov/search.jsp?R=19830025056 2020-03-21T02:57:11+00:00Z
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DR L. No. 119	 DOE,/JPL 955591-83/3
DRL Line Item No. 5
DR  No. SE-5
	 Distribution Category UC-63
(NASA-cR --172971) MUDELL.ING OF POLYMER 	 N83 -33327
PLUTUDEGRADAT.ION FOU SOLAR CELL MODULES	 I
vuarterly T'eclinical Progress Report, 1
Apr. - 'n Jun. 1983 (Toronto Univ.) 7 p	 Unclas
HC A 0 2/rir A10 1 	 CSCL 10A 03/44 28571
Modelling of Polymer Photodegradation
for Solar Cell Modules
A Quarterly Technical Progress Report
^2^ ^^ 5 6 ti ^ Covering the Period April 1 - June 30, 1983i
^ uJ^
a^ ^Gk^\^QO^1•
S
CP^SQGG^ ^	 ' •
A. C. Somersall and J. E. Guillet*
* Principal Investigator
d9
t
JPL 955591 -- 2
Contract Goals and Objectives
As part of the Encapsulation Task, this research program is Intended
to model the photodegradation of synthetic polymers used as pottants and/or
cover sheets in the LSA solar cell module designs. It involves the develop-
ment of a computer simulation of the chemical processes that t<zke place
under weathering conditions which could, in principle, relate directly to the
performance of these materials and afford some !jasis for predicting and/or
controlling their useful lifetimes.
The program can be divided into three main parts:
I. The development of a computer program to model the weathering/
photooxidation of an ethylene-vinyl acetate copolymer as 0. typical
candidate for LSA applications.
u. The development of new analytical procedures for the determination
of photoosidation and photodegradation at early stages in solid poly-
nzer samples.
3.	 The development of weathering tests suitable for use with a computer
kinetic model to provide a basis for extrapolated predictions.
JPL 955591
Summary
We have already shown that many of the experimental observations in
the photooxidation of hydrocarbon polymers can be accounted for with a computer
simulation using a mechanistic model with corresponding rate constants for
each elementary reaction. However, it is obvious that in outdoor applications,
such as with photovoltaic modules, the variation of temperature will have im-
portant effects on the useful lifetimes of such materials.
In the last quarter we have eventually managed to model the photooxida-
tion process with input data consisting of Arrhenius parameters A (the pre-
exponentia.l factor) and E (the activation energy) . This naturally multiplied the
mathemat;.cal complexity in the program but moreso, the different magnitudes
Oil., the activation energy caused various changes in the relative importance of
the various key processes of propagation and termination with changes in tem-
perature.
We have also now included the thermal reactions of hydroperoxide decom-
position:
ROOH	 RO • + OH
This increased the reaction basis set from 51 to 56 reactions. The complete
and revised data base is summarised in Table I.
Figure 1 shows the variation of time to failure (5% oxidation, as before)
with temperature. The decrease in	 lifetime (no stabiliser) is, more
or less, as expected. The change in tempera tore from 280 K (45 °F, a cool
tropical day) to 310K (100 °F, a hot tropical day) shortens the time to failure
from 20 months to three months. An attempt at a typical Arrhenius plot (Fib;. 2)
shows an "apparent net activation energy" of 10 kcal/mole.
a
yi
3
2 yr
1 yr
ti
00
o .
C
l
0 3.2	 3.3	 3.4	 3.5	 3.6
1/T x 103
FIGURE 2. A rrhenius plot of the rate
of oxidation (k vs. 1/T) .
f
r
4
m 0.6
00
a
^C
c
° 0.4
ni
0
v 0 .2
0
280	 290	 300	 310
T (K)
FIGURE 1. Time to failure (5% oxidation)
as a function of temperature.
E
A	 kcal/mal
0.70 x 10~9
0.59 x 109
0.80 x 1017
0.56 x 108
0.70 x 10-9
0.32 x 1013
0.56 x 109
0.13 x 109
0.10 x 1010
0.10 x 10' 0
0.13 x 10-9
0.16 x 1010
0.16 x 1010
0.32 x 1016
0.25 x 1010
0.25 x 1010
0.80 x 1014
0.10 x 1010
0.10 x 1010
0.13 x 10 -9
0.10 x 1015
0
4.8
15
2.0
0
8.5
2.0
0
17.0
17.0
0
6.2
6.2
17.4
11.6
11.6
9.6
7.3
17.0
0
6.6
n
ORIGQS AL PAGE 9S
TABLE I. Data Set: Photooxidation Reaction Scheme and OF POOR QUALrty
Activation Parameters
2.
1. Ke tone > KE T*
2. KE T * > SMRO 2 + SI M CO
; 3. SMft CO > SMR02 + CO
4. KET* > Alkene + SiYlKetonL-
5. SMKetone > SlYIKET*
6. SMKE T * > SMRO2 + CH  CO
r
7. SIYMKET* > Alkeae + Acetone
8 • ROOH > RO + OH
9. RO2 + RH > ROOH + RO2r
10. SNI MO 2 + RH SMROOH + RO2
11. SMROOH > SZ R0 + OH
12 STLVLRO + P,H > S1^IROH + RO2r
13. RO + RH > R 0 H + RO2
14. RO > S-LYLR0 2 + A ldehyder
15. KET`	 ROOH > Ketone + RO + OH
a . 113.
 
Sti1KET^` + ROOH > S1HSe cone + RO + OH
17. SiYM CO + O 2 > SM:R COOO
18. SMRCO + RH RO2 + Aldehyde
r
19. SMRCOOO + RH > S1^LR000OH + RO Z
20 . COOOH > NSl	 COO + OH
21.
6S
SNrR COO > Sl[R02 + CO Z
OF
22. SNIMCOO + RH Acid + RO 2 0 .10 x 10 10
17.0
23. OH + RH > RO 2 + Water 0 .10 x 10 10 0.5
24. CH 3 CO + RH RO 2 + CH 3 CHO
0.10 x 10 10 7.3
25. CH 3 CO + 02 CH 3 C000
0.89 x 101`1
26. CH COOO + RH CH COOOH + RO 0.10 x 10 10 17.03 3	 2
27. CH 3 COOOH CH 3 COO + OH 0.13 x 10
-9 0
28. CH 3 COO + ',RH CH 3 COOH + RO 2
0.10 x 10 15 6.6
29. KET* Ketone 0.10 x 10 9 0
30. SMIXE T SNTlXe tone 0.10 x 10 9 0
31. KET* + 02 Ketone + SO 2 0.89 x 10 14 9.6
32. SZ,,IXET*	 0 2 a tone
	
+ 150SMK	 .; 2 .09 x 1	 140	 u	 A.0 9.6
33. RO 2 + RO 2 ROH + Ketone + SO 2 0.25 x 10 10 11.6
34. RO 2 + ROH ROOH + Ketone + HOO 0 .10 x 10 10 15.3
35. HOO + RH HOOH + RO 2 0.32 x 10 9 15.0
36. HOO + RO C ROOH + SO 2 0.32 x 109 2.1
37. R,00
	
+ Ketone ROOH + PeroxyCO 0.13 x 10 5 8.9
38. PeroxyCO J- RH PER OOH + RO 2 0.10  x 10 10 17.0 A,"
39. PER OOH PER 0 + OH 0.13 x 10 -9 0
40. PERO + RO2 DIXecone + ROOH
100.25 x 10 11.6
41. RO 2 + ROOH ROOH + Ketone + OH 0.25 x 10 8 11.6
42. R02 + SINMOH ROOH + Aldehyde + HOO 0.10 x 10 10 15.3
43. RO 2 + Aldehyde ROOH + SNI LRCO 0.25 x 10 10 11.6
44. RO 2 + RO 2 ROOR + SO2 120.38 x 10 16.0
0.63 x 105
0 .20 x 1014
0.16 x 109
0.16 x 109
0.16 x 108
0.80 x 1013
0.80 x 1013
0.63 x 1015
r
0.63 x 10 5
0.63 x "915
r
0.63 x 1015
0.13 x 1015
0
10.0
11.6
11.6
5.2
9.5
9.5
35
35
35
35
35
ORIGWAL PAGE 13
45. S02 > 02 
OF POOR QUALITY
46. S02 + A Ike ne > ROOH
47. R02 + Alkene > Branch
48. SMR0 2 + Al:kene > ROOH
49. R02 + QH --> ROOH + Q
50. KET* + Q1 > Ketone + Heat
51. ROOH + QD > PRODS
52. ROOH RO • + OH
53. SMROOH SMRO + OH
54. SMRCOOOH SIVIRCOO + OH
55. CH3COOOH > C113 COO+ OH
56. PEROOH - PERO + OH


Modelling of polymer photodegradation for solar cell modules

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