A11101 111707 H PUBLICATIONS

NBSIR 79-1766

Studies on the Photodegradation

of Poly (Methyl Methacrylate)

Mohamed Abouelezz

Structures and Materials Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

and

P. F. Waters

Chemistry Department

American University

Washington, D.C. 20016

June 1979

U S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

CC — 1

100

, U56

7 j- 17 oo

C.2

SEP 2 0 1

NBSIR 79-1766

STUDIES ON THE PHOTODEGRADATION

OF POLY (METHYL METHACRYLATE)

Mohamed Abouelezz

Structures and Materials Division

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

and

P. F. Waters

Chemistry Department

American University

Washington, D.C. 20016

June 1 979

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

CO
-
I

ABSTRACT

When poly (methyl methacrylate), PMMA, is exposed to sunlight, it

gradually degrades and, after long-term exposures, may be unable to

perform its intended functions. While the photodegradation of PMMA has

been studied extensively using radiation sources below 300 run, natural

sunlight at the earth's surface does not extend below 292 nm. This study

was performed in order to examine the effect of the radiation from the

upper part of the ultraviolet, UV, and the visible regions on PMMA and

to identify the mechanism(s) of degradation induced by the radiation.

Thin films of PMMA were irradiated in air with upper UV, upper UVvisible, upper UV-visible-near infrared and 436 and 546 nm radiation.

Exposure to either the upper UV or visible radiation caused degradation

of the polymer. The data show that both random scission and unzipping of

the polymer chain are operative in the degradation. Unzipping becomes

increasingly important with incident radiation of increasing wavelength.

Keywords: Degradation, IR; photodegradation; poly (methyl methacrylate)

UV; visible.

iii
ACKNOWLEDGMENT

The authors wish to acknowledge the contributions of the staff at NBS

and others who contributed to the success of this publication. In particular, substantial contributions were made by members of the Building Materials and Building Composities Programs of the Structures and Materials

Division. The authors thank Dr. P. Campbell and Mr. L. Masters for their

valuable contributions and Dr. G. Frohnsdorff, Dr. G. Thom, and Dr. R. Steihler

for their editorial review. The authors wish to acknowledge the Research

Laboratory Division of the Rohm and Hass Co. for supplying the polymer samples.

iv
CONTENTS

Page

1 . INTRODUCTION 1

2. EXPERIMENTAL 3

2.1 Test Samples 3

2.2 Light Sources 3

2.2.1 Mercury lamps 3

2.2. 1.1 Photochemical reactor 3

2. 2. 1.2 Flood lamp 3

2.2.2 Xenon-Arc Lamp 4

2.3 Polymer Irradiation 4

2.4 Experimental Methods 4

3. RESULTS AND DISCUSSION 5

4. CONCLUSION 8

5. REFERENCES 9

6. TABLES 10

7. FIGURES 27

v

1. INTRODUCTION

Poly (methyl methacrylate), PMMA, is an • important polymer in the building

industry as well as other industries [1]. However, despite its long history

of use, little information is available from controlled tests about the stability

of the polymer to long-term exposure to sunlight.

Studies of the degradation of PMMA when exposed to the 253.7 nm mercury

line have been carried out [2-7]. The photolysis of PMMA under these conditions

has been assumed to result in a random scission of the polymer backbone by a

free radical process [1,6,8]. The main volatile products of the photolysis in

air are methyl methacrylate, methyl formate, methanol, carbon monoxide, carbon

dioxide and hydrogen. In contrast, the dominant product of thermal degradation

is monomer which is liberated in high yield at 250°C. The mechanism of monomer

formation is assumed to be the reverse of free radical polymerization [9].

After the initial chain homolytic scission generates radicals, the latter

unzip to produce monomer [1,9].

Earlier [1] we reported the irradiation of PMMA with 253.7 and 300 nm

mercury lamps and found that this radiation caused a rapid decrease in the

molecular mass accompanied by a small amount of volatile products, characteristic of random scission degradation. Molecular mass and glass transition

temperature data further showed that, while the intensity of 300 nm lamps

at the 253.7 nm wavelength was about one tenth of that of the 253.7 nm

lamps, the quantum yield was about one fourth [1]. That led us to conclude

that ultraviolet (UV) radiation greater than 253.7 nm plays a role in the

degradation. We also noted [1] that the mass loss data showed that exposure

to 300 nm lamps resulted in a greater mass loss than exposure to 253.7 nm

lamps. Finally we suggested that the longer wavelength radiation results

1
in a different degradation mechanism than for 253.7 nm. We noted that the

mechanism might be, at least in part, a thermal degradation.

When PMMA is exposed to sunlight for a long period of time it degrades.

Since no 253.7 nm irradiation reaches the earth's surface, degradation studies

above 300 nm were carried out in order to begin building a data base for

understanding how the polymer degrades at longer wavelengths so that methods

of stabilizing it might be developed.

For these reasons we proposed to study the effect of the following

additional radiation sources on the degradation of PMMA:

a. Irradiation from 300 nm lamps filtered with a pyrex filter to eliminate

the band at 253.7 nm.

b. Irradiation from 350 nm lamps, in which the spectrum is almost entirely

between 300 and 400 nm.

c. Irradiation in the upper UV (300-400 nm) and the visible spectrum

using a flood lamp and an infrared (IR) filtered Xenon arc lamp.

d. Irradiation with two different bands in the visible, 436 nm (blue)

and 546 nm (green).

e. Irradiation from a Xenon arc lamp with borosilicate filters, simulating

outdoor weathering and sunlight which contain the upper UV, visible

and IR light.

Such studies, combined with earlier studies [1] were needed to characterize more fully the mechanisms of degradation under these different conditions. Once the degradation mechanisms are characterized, the feasibility

of utilizing accelerated aging tests to predict the long-term performance

of the polymer can be determined.

2
2 . EXPERIMENTAL

2.1 Test Samples

Test samples of PMMA of two different mass average molecular masses

(190,000 and 240,000) were provided by the Rohm and Haas Company*, these were

identified as PMMA I and II, respectively. The polymer was purified and

cast into thin films (20 + 5 y). For a detailed description of this

method see [1].

2.2 Light Sources

2.2.1 Mercury lamps

2.2. 1.1 Photochemical reactor

The photochemical reactor has been described previously [1]. The lamps

used in the irradiation of samples were the 300 nm and 350 ram lamps, the

radiation from the former being filtered through pyrex. The spectral distribution of these two sets of lamps are shown in Figure 1 and 2, respectively.

2.2. 1.2 Flood lamp

A high intensity mercury lamp with pyrex filters, operating at a

constant power of 400 watts, was used to irradiate the sample. Exposures

were performed with and without bandpass optical filters. Two different

filters were used, one transmitted a band at 436 nm (blue) while the

other transmitted a band at 546 nm (green). The spectral distribution

* DISCLAIMER: Certain trade names and company products are identified in

order to adequately specify the experimental procedure. In no case does

such identification imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the products are necessarily

the best available for the purpose.

3
of the flood lamp alone and of the blue and green light are shown in

Figures 3, 4 and 5, respectively.

2.2.2 Xenon-Arc Lamp

An Atlas Electric Weatherometer (Model M65) was used in irradiating the

polymer. The Xenon arc lamp was operated at 650 watts and monitored at three

different wavelengths 340, 420 and 580 nm. Infrared and borosilicate filters

were used with this lamp. The spectral distributions of the Xenon arc lamp

with these filters in the light path are shown in Figures 6 and 7. The temperature inside the weatherometer was monitored and did not exceed 50°C.

2.3 Polymer Irradiation

For the irradiations with the 300 and 350 nm lamps (Rayonet) see [1]

When the flood lamp was used for irradiation, the PMMA samples were clipped

to glass slides and placed 200 mm from the lamp. While in the case of

the Xenon arc lamp the samples were mounted on an aluminum holder which

was held vertically facing the lamp at a distance of 480 mm (see Figure 8).

Samples of PMMA I and II were exposed to all of the different light sources for 1000,

2000, 3000 and 4000 hours respectively. In addition PMMA I and II samples were

respectively exposed for 500 and 1500 hours to the flood and the Xenon lamp.

Additional exposures of 4500, 6000 and 8000 hours were made with the Xenon lamp

and borosilicate filters.

2.4 Experimental Methods

The molecular masses were measured using the gel permeation chromatography

technique. The glass transition temperature (T ) was measured by thermal

O

mechanical analysis (TMA). The UV, IR spectra and the prcent mass loss

4
were measured according to the normal technique. For a complete description

of these methods see [1].

3. RESULTS AND DISCUSSION

The data obtained from the various experiments are shown in Table 1

through 14. The mass average molecular mass, Rw, of PMMA I and II decreased

by 22.8 and 23.4 percent, respectively, after irradiation with the 300 nm lamps

with pvrex filter for 4000 hours (Tables 1 and 2). While irradiation of

the 350 nm lamps for 4000 hours, the Rw of PMMA I and II decrease by 11.6 and

12.9 percent, respectively (Tables 3 and 4). The flood lamp with a pyrex filter

was intense, and irradiated samples showed bigger decreases in Rw of 33.9 and

33.1 percent respectively when each were irradiated for the the same number

of hours. (Tables 5 and 6). When the polymer was irradiated for 4000 hours

with the blue (436 nm) light the degradation was slow and Rw respectively

decreased by 7.9 and 8.1 percent for PMMA I and II (Tables 7 and 8), while

with a 4000 hours exposure to the green (546 nm) light the Rw decreased

by 6.9 percent for both PMMA I and II (Tables 9 and 10).

In the case of the Xenon lamp with IR filters the exposure time was also

4000 hours and the Rw decreased by 22.2 and 21.8 for PMMA I and II, respectively (Tables 11 and 12). While with borosilicate filters, PMMA I and II was

exposed for 8000 hours and Rw decreased by 34.9 and 37.5 percent, respectively

(Tables 13 and 14).

From these data, the percent degradation was calculated as the mass average

molecular mass as percent of the original for PMMA I and II when irradiated

with different light sources. The data are summarized in Table 15 and

Figures 9 and 10. An examination of the data shows that irradiation with

the upper part of the UV region (300-400 nm) from the 350 nm lamps causes

degradation of PMMA. Similarly degradation was caused by irradiation of PMMA

5
with 436 nm (blue) light and 546 nm (green) light. As shown in Figures 9

and 10, the rates of degradation caused by the optical bands are much slower

than that by the higher-energy light sources.

Percent mass loss and changes in the T of PMMA I and II caused by

o irradiation with different light sources are summarized in Tables 16 and 17,

respectively. The percent mass loss and the T are plotted vs. percent

O

—

degradation for PMMA I and II in Figures 11, 12, 13 and 14 and 15, 16, 17

and 18, respectively.

The percent mass loss was the highest when PMMA I and II were irradiated

with the Xenon lamp with borosilicate filters: 2.83 and 2.97, respectively

(Tables 13 and 14). The smallest percent mass loss (0.49 and 0.51 percent)

was due to the green (546 nm) light. The rest of irradiation caused a mass

loss in between these extremes.

By examining Figures 11 and 12 we observe that for the same percent

degradation, the percent mass loss is higher for PMMA exposed to the Xenon

lamp with borosilicate filters than all other light sources. Figures 13 and

14 show the percent degradation vs . percent mass loss for PMMA I and II,

respectively, irradiated with 253.7 nm, 300 nm [1], 300 nm with pyrex filter

and 350 nm lamps as well as the Xenon arc lamp with borosilicate filters.

We can see clearly that for the same percent degradation the irradiation with

253.7 nm lamps caused the lowest mass loss, followed by the 300 nm lamps without a filter. As noted before (Figures 11 and 12), irradiation with the Xenon

lamp with borosilicate filters shows the highest mass loss, while all of the

other sources causes losses between the extreme values.

The irradiation of PMMA causes an increase in the UV absorption of the

thin film, as shown in Figures 19 and 20. Increase in the absorption between

6
260 and 320 nm previously observed [1] was also observed here. This absorption is in the region usually associated with carbonyl chromphores and is

believed to result from carbonyl groups in the polymer chain itself rather

than in the low molecular mass photolysis products.

The only changes in the IR spectrum of PMMA during the irradiation

were a broadening of the carbonyl band at 5.71 ym (1750 cm~^) and the

appearance of small new bands at 6.19-6.10 ym (1610-1640 cm

-

*). The latter

bands are attributed to olefinic unsaturation produced during the photolytic

chain scission. It should be noted that substantial degradation has to

occur in order to form enough fragments with unsaturated groups, or

containing carbonyl chromophore to cause changes in the UV and IR spectra.

It is interesting to note that the Xenon lamp with the borosilicate

filters is the only light source with a substantial portion of radiation

in the IR regions (Figure 7). While most of the other light sources emit

radiation which falls in the upper part of UV (300-400 nm) and the visible

(400-700 nm), (Figures 1-6), only the 253.7 nm and the 300 nm lamps without

a filter, emit primarily in the UV region [1].

It is known that with random scission the amount of volatile products are

very small, while with unzipping, is much larger. From the percent mass loss

vs . percent degradation and the information about the light sources one can

conclude that in addition to the random scission mechanism proposed for the

photodegradation of PMMA at 253.7, unzipping of the polymer chain is also

occurring. Moreover, the unzipping increases with increasing incident wavelength, which is seen by the increase of the percent mass loss in this direction.

7
Although the percent mass loss as a result of Irradiation with IRcomponent lamps was relatively small In the case of the high molecular mass

polymers used In this study, the IR-induced mass loss may become significant

In polymers of lower molecular masses.

From Figures 15-18 one can see that for the same percent degradation

there Is good aggreement in the change In the glass transition temperature

with irradiation, no matter what the light source is. One can also notice

that the initial rate of decrease in the glass transition temperature is

high compared to the rate at later stage of degradation which it does agree

with the general relationship between molecular mass and glas transition

temperature (Figures 17 and 18).

4. CONCLUSIONS

The test data show that the irradiation of PMMA with visible light causes

degradation of the polymer. This has not been reported before. Also, the

irradiation of PMMA with UV radiation above 300 nm wavelength alone causes

the polymer to degrade.

The data also reveal that the percent mass loss for the same percent

degradation increases with increasing incident wavelength up to and including

the IR region. This leads to the conclusion that in addition to the random

scission mechanism proposed for the photodegradation of PMMA, unzipping of

the polymer chain plays an important role in the degradation. This role

increases with increasing wavelength of Incident radiation.

8
6 . REFERENCES

[1] M. Abouelezz and P. F. Waters, "Studies on the Photodegradation

of Poly (methyl methacrylate)," NBSIR 78-1463 (1978).

[2] P.R.E.J. Cowley and H. W. Melville, Proc. Roy. Soc. A210, 461 (1952).

[3] A. Shultz, J. Phys. Chem, 65, 967 (1961).

[4] D. G. Gardner, J. Chem. Phys., 34, 1653 (1961).

[5] A. Charlesby and D. K. Thomas, Proc. Roy Soc. A 269 (1962).

[6] R. B. Fox, L. G. Isaacs and S. Stokes, J. Polym. Sci. , Al, 1,1979 (1963).

[7] V. Ya. Shlyapintokh and V. I. Goldenberg, EUROP. Polym. J. , 10,

679 (1974).

[8] B. Ranby and J. F. Rabek, "Photodegradation, Photo-oxidation and Photo

stablization of Polymers," John Wiley & Sons (1975).

[9] N. Grassie, Polymer Science [Ed. A.D. Jenkins, American Elsevier,

(1972)].

9
Table 1. PMMA I Exposed to 300 nm Lamps, with Pyrex Filter, in Air

Exposure - a *

^ - a*

-a Mw as b*

Time in Hrs. Mw x 10“J Mn x 10~J % of Original t °r % Mass Loss

0 189 152 100 115 0

1000 176 139 93.1 113 .32

2000 165 129 87.3 111 .71

3000 156 121 82.5 110 1.02

4000 146 112 77.2 109 1.24

The molecular mass averages were determined by gel permeation

chromatograhy

The glass transition temperatures were determined by thermal mechanical

ana lysis.

10
( Table 2. PMMA II Exposed to 300 nm Lamps, with Pyrex Filter, in Air

Exposure

Time in Hrs. Mw x 10"3 Mn x 10" 3

Mw as

% of Original Tg°C % Mass Loss

0 248 197 100 115 0

1000 230 181 92.7 114 .39

2000 214 166 86.3 112 .87

3000 204 156 82.3 111 1.12

4000 190 144 76.6 110 1.46

11
Table 3. PMMA I Exposed to 300 nm Lamps, in Air

Exposure

Time in Hrs. Mw x 10"3 Mn x 10 3

Mw as

% of Original Yc % Mass Loss

0 189 152 100 115 0

1000 183 147 96.8 115 .22

2000 177 141 93.7 114 .40

3000 172 137 91.0 113 .57

4000 167 132 88.4 112 .75

12
Table 4. PMMA II Exposed to 300 nm Lamps, in Air

Exposure

Time in Hrs. Mw x 10~3 Mn x 10 3

Mw as

% of Original Yc % Mass Loss

0 248 197 100 116 0

1000 239 189 96.4 116 .24

2000 231 182 93.1 115 .42

3000 223 175 89.9 114 .61

4000 216 169 87.1 114 .78
Table 5. PMMA I Exposed to the Flood Lamp with Pyrex Filter, in Air

Exposure

Time in Hrs. Mw x 10

-3

Mn x 1 0

3

Mw as

% of Original Yc % Mass Loss

0 189 152 100 115 0

500 176 139 93.1 114 .43

1000 167 131 88.4 112 .71

1500 159 123 84.1 111 .98

2000 148 115 78.3 110 1.29

3000 136 104 72.0 108 1.72

4000 125 93 66.1 106 2.20

14
Table 6. PMMA II Exposed to the Flood Lamp with Pyrex Filter , in Air

Exposure

Time in Hrs . Mw x 10 ^ Mn x 10

Mw as

% of Original T °C % o Mass Loss

0 248 197 100 115 0

500 233 181 94.0 115 .42

1000 224 170 90.3 113 .65

1500 213 159 85.9 112 .97

2000 204 150 82.3 111 1.32

3000 186 133 73.4 109 1.71

4000 166 120 66.9 107 2.22

15
Table 7. PMMA I Exposed to 436 nm Light From the Flood Lamp, in Air

Exposure

Time in Hrs. Hw x 10 ^ Mn x 10 ^ Mw as

% of Original Yc % Mass Loss

0 189 152 100 115 0

1000 185 149 97.9 115 j'O

2000 182 146 96.3 114 .22

3000 178 142 94.2 114 .39

4000 174 137 92.1 113 .53

16
Table 8. PMMA II Exposed to 436 nm Light From the Flood Lamp, in Air

Exposure

Time in Hrs. Mw x 10'3 Mn x 10"3

Mw as

% of Original Tg°c % Mass Loss

0 248 197 100 116 0

1000 243 193 98.0 116 v^0

2000 239 189 96.4 115 .24

3000 234 184 94.4 114 .41

4000 228 178 91.9 114 .55

17
Table 9. PMMA I Exposed to 546 nin Light From the Flood Lamp, in Air

Exposure

Time in Hrs. Mw x 10

-3

Mn x 10 3

Mw as

% of Original T °C %

©

Mass Loss

0 189 152 100 115 0

1000 186 150 98.4 115 v^O

2000 183 147 96.8 114 .20

3000 179 143 94.7 113 .36

4000 176 140 93.1 113 .49

18
Table 10. PMMA II Exposed toi 546 nm Light From the Flood Lamp , in Air

Exposure

Time in Hrs . Mw x 10 3 Mn x 10~3

Mw as

% of Original T

g

°C % Mass Loss

0 248 197 100 116 0

1000 244 194 98.4 115 ^0

2000 240 190 96.8 115 .21

3000 236 186 95.2 114 .38

4000

' 231 181 93.1 114 .51

19
Table 11. PMMA I Exposed to Xenon Lamp with IR Filters, in Air

Exposure

Time in Hrs. Mw x 10"3 Mn x 10 3

Mw as

% of Original Yc % Mass Loss

0 189 152 100 115 0

500 184 147 97.4 114 .19

1000 178 141 94.2 114 .35

1500 172 135 91.0 113 .55

2000 168 130 88.9 113 .78

3000 159 123 84.1 112 1.09

4000 147 111 77.8 110 1.41

20
Table 12. PMMA II Exposed to Xenon Lamp with IR Filters, in Air

Exposure

Time in Hrs. Mw x 10“ 3 Mn x 10~3

Mw as

% of Original Yc % Mass Loss

0 248 197 100 116 0

500 243 191 98.0 116 .18

1000 236 184 95.2 115 .32

1500 230 177 92.7 114 .51

2000 223 170 89.9 114 .73

3000 209 157 84.3 113 1.15

4000 194 143 78.2 111 1.49

21
Table 13. PMMA I Exposed to Xenon Lamp with Borosilicate Filters,

in Air

Exposure

Time in Hrs. Mw x 10 ^ Mn x 10 ^ Mw as

% of Original Yc % Mass Loss

0 189 152 100 115 0

500 182 146 96.3 114 .24

1000 178 141 94.2 113 .47

1500 175 138 92.6 113 .62

2000 165 130 87.3 112 1.08

3000 156 122 82.5 110 1.42

4500 144 111 76.2 109 1.84

6000 132 100 69.8 108 2.48

8000 123 92 65.1 107 2.83

22
Table 14. PMMA II Exposed to Xenon Lamp with Borosilicate Filters,

in Air

Exposure

Tine in Hrs. Mw x 10 3 Mn x 10~3

Mw as

% of Original Yc % Mass Loss

0 248 197 100 116 0

300 242 191 96.3 115 .22

1000 235 182 94.8 114 .49

1500 228 176 92.6 113 .77

2000 219 167 88.3 112 1.05

3000 206 156 83.1 111 1.61

4500 192 143 77.4 110 1.93

6000 176 129 71.0 109 2.45

8000 155 113 62.5 108 2.97

23
*Exposure

for

4500

hours

00 O' u> Ni t—

o o o o O cn o cn o o o o O O o O o o o o o O o o

00 00 vO 1 1 Ni 1 CO 1 M 1 1 • . . 1 • 1 N) cn CO I—*

CD 00 VO 1 1 O' Ni O' 1 Ni 1 hf 1 1 • • . 1 • 1 l-f O' u> CO

00 vO VO vO 1 1 1 00 1—

CO 1 O' 1 hf 1 1 • . * 1 • o '-J 00

00 00 VO vO l-f 1 1 vO CO 1 O' 1 M 1 1 • • . 1 • 1 H— VO 1—> -P>

O' 00 00 vO |—

1 1 O' Ni 00 4> 00 co 1 1 • • . . « •

1—* o CO I—

t- t—

ON 00 00 VO VO

M 1 1 O' u> Ni cn o 4>* M 1 1 • • • . • • VO .p- co VO co o

VO vO vO VO 1 1 ho .p- O' 1 1 l-f 1 1 • . . 1 . 1 >— Ni co vO

vO VO vO VO l-f 1 1 -O' O' 00 1 M 1 1 • . . 1 • 1 VO -t- P- o

vO vO vO vO ff 1 1 to -O O' 1 00 1 1 • . . 1 . 1 t—

00 S'

vO VO VO VO 1 1 to Cn O' 1 00 1 l-f 1 1 • . . 1 . 1 M

*—

Ni 00 -O'

00 00 VO VO vO l-f 1 1 P- 00 .o 1 1 • • • • . . 00 1—

vO o Ni Poo 00 VO vO VO 1 1 00 -p> vO NO Cn 00 hf 1 1 • . . . . * l-f ho co vO Ni O

O' O' "^1 00 00 VO vO VO

Cn VO O' N> "0 Ni -> O' l-f • • • . . . . • — 00 ho Cn CO O' Ni co *

O' 00 00 VO VO vO l-f K5 —

co 00 Ni -F> O' rf • • • . . • . • tn o CO O' 00 to * nx H ~aO 3 CA

n> c

it

n>

13 CO X O f

(I)

€

X H- 3

rf 3

Tl ZT

h- r*

I-1 3

rf 3 3 T3

if ca e

-1 Co

Pi Cn 3 o T)

CA 33

T> T) X I-*

i-l

O

CD S O X H- Qrf ti zx c

H* Pi t- 3

rf T3

CDr1 H- CO

TO O'

=r

rf 33 t

-1 cn

H- TO O'

3*

rf 3B

?on* X

I-* CD rf 3

rt>

O f 3

CA >fO

00o r1 if 3 O 3

(-*• cn -a

(-* H*

rf I-1 3 (-*• f O

CA 3

rf3

24

Table

15.

Mass

Average

Molecular

Masses

as

Percent

of

Original

of

PMMA I

and

II

During

Irradiation

with

Different

Light

Sources

in

Air
Exposure

for

4500

hours.

00 O' -P* LJ ro t—

o O o O o Ln o Ln o O o o o o o O o o o o o o o O — X-* • • • • • 1 1 hO o 1 lo 1 M 1 1 > hO X-* 1 N3 1

X- x- • • • . 1 1 •P* t—* 00 1 U> 1 M 1 1 O' hO 1 vO 1 M • • • . 1 1 Ln 1 fO ! M 1 1 Ln o 1 ro • • • . M 1 1 O' 1 ro *“• 1 1 00 X-* ho 1 -OhO X-* X- • • • « . • M 1 1 ro ho vO 'O 1 1 o hO VO oo LO

ISO X- X-* • • • • • • r-c 1 1 hO U> O' O M 1 1 hO — ro '-J Ln ro • • • 1 1 Ln LJ hO 1 s 1 M 1 1 LJ vO ho 1 o 1 • • • S i-i 1 1 Ln hO 1 o 1 r-1 1 1 O' X- .p* 1 1 • • • s 1 W 1 1 U) ho 1 o 1 1 1 vO ON O 1 • • • 1 1 Ln u> ho 1 s 1 M 1 1 H- 00 X- 1 o 1 M

X- X- • • • • . • 1 1 O Ln LO X- XH 1 1 X- vO 00 Ln Ln VO

X-* X— • • • • . • 1 1 X- Ln LO x- XH 1 1 vo Ln LO X- ro 00 XH

ro N5 X- X— • • • • • • • • 00 00 O ON hO XH Lo 00 -> hO 00 hO •P* *

N) fo X- X- • • • • • • • • XH

v£> .C- vO 0s o ^1 hO XH -O Ln U) X— vO VO N> *

H* PI 3 X H ~0

33 H*O 0 3 3 c 3 c p i-i CO 3 $ s p o 3 t, X P- 3

rr 3

nj g*

P- f

I-* 3

rr 3

(0 TJ

r» CO f U) 3 Ln a o T33 35

P3 •<

r|3 £ X Prt PI 3“

PIP*OO

Cu

r*3§

r* -o

P»

W 00 O'

3*

rt 3B C

-1 Ln

t* -O

00 O'

3“

rr 33

50

CP3P3

03O

>-» PI O

P- 3

I-1 P>

rt I— 3 P- P O 3 3

rr3 X33O3>PO

t-1 3s

XJ

25

Table

16.

Percent

Mass

Loss

for

PMMA I

and

II

Exposed

to

Different

Light

Sources

in

Air
Exposure

for

4500

hours. * 00 O' u> ho

p

— o o o o O cn o Ln o o o o O O o O o o o o O O o O

H—H-* t— H-* 1 1 o t—

1 — 1 P^ 1 1 vO o H—

1 U) 1

»— H-

H—

1 1 H—

t—H— 1 H— 1 M 1 1 o H—

ho 1 -O 1 M

H—

t—H-H—

1 1 H- 1—

—

1 —1 PH 1 1 ro LO 1 Ln 1

h— H—

—

M 1 1 >—

»—

H— 1 —

1 PH 1 1 -O Ln 1 1

h— h—H-i—| , p o o H— p H-* P P 11 11 O' 00 o p hO JP

i—H-*p »— P P o o — p »—

p P 11 11 VO H-

N5 LO Cn

h-h—

t—

H—

1 1 1—

—

H-* 1 ph 1 1 u> 4> 11 U1 1 —

»—1

1 H-* 1 P-* 1 1 — H- »— >—

1 P 1 1 K) -O Ui 11 ON

H— H—

t—

»— 1 1 t—

H- H—K- 1 PH 1 1 u> U> 11 Ln 1

1—

t—

—

1 1 H—

h- H— i— 1 PH 1 1 U1 11 Ln 1 PH P

H- H-

—

p P P 1 1 >—• H— H- p P- 1 1 o ro U> U> 1—

—

t—

p h- P 1 1 •—

—

H-

p P P 1 1 H— LO -> -CP Ln O' P p H-* —

h— P —*

p o o o H-* >—

P H— p

00 vO o ro U> U) JP

p * p p — — —

p H— p o o H— — H- P p p

00 VO o —

N) u> Ui

p *

26

w

H-S P O 3 cn a> cp

id

ti uj x o 1-1 o fD £ X P 3

rf 3

ti 3* P f P 3 £ 3

fD -a

i-i cn r1 33

TD

cn

Lno33

TJ Tl X P

p(

O

(D £ O X H* CL

rr Tl f P 3 P 3

rr

a

fD

P!

IT1 P> P U>

05 O'

3*

rr 33 r1 Cn

p- -CP 00 O'

3“

rt 33

po

TI

PX

P* fD rr 3 3 O T 3

CO >pn

too r*

if CD PI O 3

p- cn -a

fD P p o

cn id3 |

jt

Table

17.

Glass

Transition

Temperatures

of

PMMA I

and

II

During

Irradiation

with

Different

Light

Sources

in

Air
Figure

1.

Spectral

distribution

of

the

300

nm

lamps

with

Pyrex

filter

used

in

the

test

reactor.

RELATIVE INTENSITY

Nd

ro
Figure

2.

Spectral

distribution

of

the

350

nm

lamps

used

in

the

test

reactor.

28
Figure

3.

Spectral

distribution

of

the

flood

lamp

with

Pyrex

filter.

RELATIVE INTENSITY

29
620 570 520 470 420 370

WAVELENGTH (nm)

Figure 4. Spectral distribution of the 436 nm (blue) light

band (from flood lamp with special filter).

30
WAVELENGTH (nm)

Figure 5. Spectral distribution of the 546 nm (green)

light band (from flood lamp with special filter).

31
WAVELENGTH

(nmj

Figure

6.

Spectral

distribution

of

natural

sunlight,

noon

June (

)

and

6500

watt

xenon

lamp

with

IR

filter (

).

RELATIVE INTENSITY

32
300

400

500

600

700

800

900

1000

1100

1200

WAVELENGTH

(nm)

Figure

7.

Spectral

distribution

of

natural

sunlight,

noon

June (

)

and

6500

watt

xenon

lamp

with

borosilicate

filter (

).

RELATIVE INTENSITY

05

33
Figure 8. Inside view of the Xenon Arc Weatherometer

34
MASS

AVERAGE

MOLECULAR

MASS

(M

w

)

AS

PERCENT

OF

ORIGINAL

EXPOSURE TIME IN HOURS

Figure 9. Percent degradation vs. exposure time for

PMMA I exposed to different radiation sources

in air.

35
MASS

AVERAGE

MOLECULAR

MASS

(M

w

j

AS

PERCENT

OF

ORIGINAL

Figure 10. Percent degradation vs. exposure time for

PMMA II exposed to different radiation

sources in air.

36
MASS

AVERAGE

MOLECULAR

MASS

(M

w

)

AS

PERCENT

OF

ORIGINAL

% MASS LOSS

Figure 1 1. Percent degradation vs. percent mass loss for

PMMA I exposed to different light sources in

air.

37
MASS

AVERAGE

MOLECULAR

MASS

(M

w

)

AS

PERCENT

OF

ORIGINAL

% MASS LOSS

Figure 12. Percent degradation vs. percent mass loss for

PMMA II exposed to different light sources in

air.

38
100

96

88

80

72

64

56

48

40

32

24

16

8

0

nm tamps

lamps

lamps w/ Pyrex filter

350 nm lamps

Xenon arc lamp w/

borosilicate filter

1 1 1 1 I 1 1 1

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

% MASS LOSS

re 13. Percent degradation vs. percent mass loss for

PMMA I exposed to different light sources in

air.

39
96

88

80

72

64

56

48

40

32

24

16

8

0

• 253.7 nm lamps

o 300 nm lamps

0 300 nm lamps w/ Pyrex filtered 350 nm lamps

Xenon arc lamp w/

borosilicate filter

i 1 1 1 1 1 1

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

% MASS LOSS

e 14. Percent degradation vs. percent mass loss for

PMMA II exposed to different light sources in

air.

40
GLASS TRANSITION TEMPERATURE (T

g

) °C

Figure 15. Percent degradation vs. Tg for PMMA I exposed to different light sources in air.

41
MASS

AVERAGE

MOLECULAR

MASS

(M

w

)

AS

PERCENT

OF

ORIGINAL

Figure 16. Percent degradation vs. Tg for PMMA II exposed to different light sources in air.

42
100

96

88

80

72

64

56

48

40

32

24

16

8

0

i r i r

• 253.7 nm lamps

o 300 nm lamps

o 300 nm lamps w/ Pyrex filter

a 350 nm lamps

I l i i i l l l 94 98 102 106 110 114 118 122 126

GLASS TRANSITION TEMPERATURE (T

g

) °C

17. Percent degradation vs. Tg for PMMA I exposed to different light sources in air.

43
Figure 18. Percent degradation vs. Tg °C for PMMA II exposed to different light sources in air.

44
90

80

70

60

50

40

30

20

10

2

}.

10

WAVELENGTH (nm)

Changes in the ultraviolet spectrum of

>MMA II during irradiation with flood lamp

H33-FY400, with Pyrex filter) in air.

45
WAVELENGTH (nm)

Figure 20. Changes in the ultraviolet spectrum of

PMMA II during irradiation with xenon

lamp (borosilicate filters) in air.

46
NBS-114A (REV. »-7*i

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR 79-1766

3. Recipient's Accession No.

4. title and subtitle

Studies on the Photodegradation of

Poly (Methyl Methacrylate)

5. Publication Date JUNE 1979 —4

7. AUTHOR(S)

Mohamed Abouelezz, P. F. Waters

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

NO. ,1

11. Contract/Grant No.

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, city, state, zip)

same as 9 above

13. Type of Report & Period Covers

15. SUPPLEMENTARY NOTES

{ Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or leaa factual summary of moat significant information. If document includes a significant bibliography or

literature survey, mention it here.) When poly (methyl methacrylate), PMMA, is exposed to sunlight, it gradually degrades

and, after long-term exposures, may be unable to perform its intended functions.

While the photodegradation of PMMA has been studied extensively using radiation

sources below 300 nm, natural sunlight at the earth's surface does not extend below

292 nm. This study was performed in order to examine the effect of the radiation

from the upper part of the ultraviolet, UV, and the visible regions on PMMA and to

identify the mechanism(s) of degradation induced by the radiation.

Thin films of PMMA were irradiated in air with upper UV, upper UV-visible, upper UVvisible-near infrared and 436 and 546 nm radiation. Exposure to either the upper UV or visible radiation caused degradation of the polymer. The data show that both

random scission and unzipping of the polymer chain are operative in the degradation.

Unzipping becomes increasingly important with incident radiation of increasing wave1 ength.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons)

Degradation; IR; photodegradation; poly (methyl methacrylate); UV; visible.

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