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Toxicity of decomposition products: polyvinyl chloride and wood
Sumi, K.; Tsuchiya, Y.
TOXICLTI OF
DECOMPOSITIONPRODUCTS
- POLYVINYLCHLORTDE AND
WOODby
K. Sumi and
Y.
TsuchiyaSeveral years ago, the a u t h o r s recognized t h e need f o r a
systematic study to o b t a i n quantitative data on t h e volatile decomposi- tion products [pyrolysis and combustion products] of a wide v a r i e t y of organic materials. l To accomplish this, a standardized method of
decomposition, s u i t a b l e for collection and subsequent analysis of products, i s required. A method used earlier
in
t h e DBR Fire Researchlaboratory f o r t h e study of combustion products of polymeric materials
c o n t a i n i n g nitrogen i s not s u i t a b l e for subsequent a n a l y s i s o f
i m p o r t a n t components such as hydrogen chloride [ H C t ) . The problem is
a t t ~ i b u t e d t o the exposed heating element which comes in contact with
the decomposition products. Because of the w i d e use o f halogen compounds to impart f i r e r e t a r d a n c e , h a l o g e n acids are produced by many materials.
Any standardized method of decomgasition, theyefore, muss not ha-crc an exposed h e a t i n g element.
The purpose o f t h i s paper i s to describe a new flow method
f o r thermal decomposition that has been developed, and to present
experimental results obtained from the combustion [or pyrolysis) o f PVC and wood (white pine]. The toxicity indices "obtained from t h e decom-
p o s i t i o n products of t h e two materials, based on these results, a r e a l s o presented.
MATERIALS
Specimens were made
in
t h e form o f pellets from PVC generalpurpose resin and w h i t e p i n e sawdust. THERMAL DECOMPOSITION
The experimental s e t u p for the decomposition
of
PVC is shown in Figure 1. Samples were decomposed in a horizontal quartz tube t h r o u g h which air was metered. The i n s i d e diameter o f t h e furnace tube was 57 mrn.The sample was weighed in a q u a r t z b o a t and moved to t h e hot
zone of t h e furnace by a magnetic sample insertion d e v i c e . Glass.wool was placed at the outlet end of t h e furnace t u b e to t r a p s o l i d particles, and a h e a t i n g tape was wound around t h e same area to prevent condensation of volatile products. The sample w e i g h t was v a r i e d from 400 m g to 2 g ,
air was metered a t various rates r a n g i n g from 500 to 4000 cm3min-l, and thc f u r n a c e t u b e was m a i n t a i n e d a t temperatures ranging from 400 t o 8 0 0 ' ~
.
Hydrogen c h l o r i d e was collected In liquid traps containing 2 per
cent
NaOH and analyzed u s i n g a specific i o n e l e c t r o d e f o r c h l o r i d e i o n . Thegaseous sample was collected in a p l a s t i c bag and analyzed for CO and
CO u s i n g gas chromatography. 2
The experimental setup for t h e decomposition of white pine was similar except t h a t t h e glass wool filter and t h e heating tape were not
used. Experiments with white pine were conducted in a i r , nitrogen and mixtures of both. CO and CQ2 were analyzed.
RESULTS
AND
DISCUSSION1. P o l v i n y l c h l o r i d e
When PVC is heated to temperatures above 250"~, it decomposes and produces H C X . The removal o f f K R
leaves
a residue having a polyene structure which breaks down f u r t h e rt o
yield benzene and other aronatics.When PVC is heated in an o x i d i z i n g atmosphere, some of the volatile
components burn to produce oxidation products such as CO, C02 and H2Q.
Quantitative data on the main decomposition products of PVC a r e
presented as a function of a i r flow sate (Figure 23 and a s a function of sample weight $Figure 3 ) . The yield of HCR was ap~rsximately equal to
t h e theoretical amount expected f r o m complete conversion of C k atoms t o
HGR. Variation in a i r flow rate or sample weight had very little
influence.
Quantitative data on decomposition products of PVC at d i f f e r e n t temperatures are presented in Table I . The variation of temperature from
400 to 8 0 0 ~ ~ had little effect on t h e HCR y i e l d which was again
approximately equal t o t h e theoretical amount f o r complete conversion t o
HCR. The authors believe t h a t the C02 results were lower than those actually produced by decomposition of PVC i n the oxidizing atmosphere because o f absorption of some of this gas in the NaOH t r a p . Separate
experiments f o r CO determination were
not
conducted to correct t h i s d i ~ c r e p -ancy because the
3
i f f e r e n c e in results would not make a s i g n i f i c a n t difference to t h e over-all toxicity d u e to the combincd e f f e c t of IICR,CO and COZ.
The quantitative r e s u l t s for G O , C02 and HCK reported in Tablc!
1 were used to determine the toxicity index (which is a measure of c
v
t o x i c i t y ] from t h e equation T =
- -
Cf
where T = toxicity index
c = c o n c e n t r a t i o n of a gaseous compound
cf = concentration of t h e same compound t h a t is fatal to man
in 30 minutes
V
= volume i n t o which t h e decomposition psaducts a r e d i f f u s e d W = weight of sampleFor convenience Tn calculation, c is expressed in volume ratio, that is
v
c = v/V where Y i s the volume of the gaseous compound, t h e n ,
T
=-
.
ccw I
The t o x i c i t y i n d i c e s f o r the study are r e p o r t e d in litres per g . , and
were obtained
by
u s i n g cf = 4x
10-3 ( i . e . . 4000 ppm) f o r CO 4,85 x f o r CU2 and 1 x 10-3 f o r HCL
'.
The t o x i c i t y index data for PVC, presented in Table 2 , v i v i d l y
illustrate t h a t t h e t o x i c i t y of t h e decomposition products was primarily due to t h e h i g h yield of HCR. The a d d i t i o n a l e f f e c t of CO was very small.
2 . Wood (White Pine)
\"hen wood i s decomposed by heat, a large v a r i e t y of combustible
vapours are produced along with carbon, CO, C02 and water vapour. Some
pyrolysis products a c t as irritants t o t h e eyes and r e s p i r a t o r y t r a c t . ICI~enwood
is subjected to flaming combustion, some o f t h e s e combustible vapours are consumed by the
fire.
Because large amounts of CO andCO
a r e producedin comparison with other harmful compounds, t h e toxicity ue to CO and C 0 2 only were considered in this study.
2
Quantitative data on CO and CO produced by combustion o f white pine are presented as a function o
I
decomposition temperature in F i g u r e 4 . Experimental data showing the influence of varying t h e sample weight and the atmosphere a r e presented in Table 3 . Toxicity i n d e x d a t abased on these r e s u l t s are presented in Table 4 . In combustion
experiments, generation of
CO
increased w i t h increase in temperature[Figure 4) and was greatest with t h e larger sample weights. Experiments
in n i t r o g e n and mixtures of n i t r o g e n and a i r gave h i g h e r y i e l d of CO
than experiments in a i r .
CONCLUSIONS
1 . A standardized method of decomposition for o b t a i n i n g quantitative
data of decomposition products o f d i f f e r e n t materials has been developed.
2 . The maximum toxicity index obtained f o r PVC u s i n g the new flaw method was about 360 L g-l. The maximum toxlcity index f o r white p i n e
was about 50 P, g-l.
3 . The higher value f o r FVC i n d i c a t e s that it has a substantially
g r e a t e r propensity f o r g e n e r a t i n g t o x i c decomposition products than
white pine.
ACKNOWLEDGEMENT
?he authors wish to thank D.W. Morwick f o r a s s i s t a n c e i n
REFERENCES
1 . Tsuchiya Y. and K . Sumi. Thermal decomposition products
of
polyvinyl c h l o r i d e . J. App. Chem. 17, 364-
€19671.2. Sumi K. and Y. Tsuchiya. Combustion products of polymeric materials containing n i t r o g e n
in
their chemical structure. J . Fire and F l m . - 4 ,15 (1973).
3 . Sumi K. and Y. Tsuchiya. Toxicity of Decomposition Products. To be submitted for publication.
4 . Henderson Y. and H.W. Haggard. Noxious Gases and t h e Principles of
Respiration I n f l u e n c i n g t h e i r Action. Chem. C a t a l o g C a . , New York, p . 110 and p . 127 ( 1 9 2 7 ) -
5. Documentation of the Threshold L i m i t Values. American Conference of Governmental Industrial Hygienists, Cincinnati, p. 39 (1971)
TABLE I
DECOMPOSITION PRODUCTS OF PVC
Air
flow r a t e = 2 , 0 0 0 cm3min' 1TABLE 2
DECOMPOSITION PRODUCT OF
WHITE
PINE Temperature = 8,0Q°C Atmosphere Air I T t 1 I T 11 t f I t T I L1 ? l 25%N2, 75% a i r II 50%N2, 50% air l r 75"N2' 25% air I I Nitrogen 1 t 3 - 1 F l o w r a t e = 1000 cm min Sample Weight mg 250 250 500 500 800 800 12100 1200 11600 E600 500 500 500 5 00 5 00 500 500 Products, g J g sample CO Residue 0.08I
0.217 0.032 0 0 0 0 0 0 < O . 0 1 4 . 0 1 <O. 0 1a.
0 1 < D m 01 <O. 01 0.02 0 . 0 3 0.05 0.04 0.08 0.076 0.073 0.146 0,152 0.167 0 . 1 6 6 0.185 0 . 7 4 4 0 . 7 5 5 0.507 0.507 0.376 0 . 3 6 7 0 . 2 6 8 0.181 0.171 0 . 1 6 0 1). 272 0.209 0.197 0 . 2 3 6 0 . 2 3 6 0.432 0.451 0 . 2 1 3 0.227 10.217 0.248 0.226 0 . 2 4 6 0.257 0.110 0,118 0.032TABLE 4
TOXICIR INDEX
FROM
DECOMPOSITION PRODUCTS OF WHITE PINE Atmosphere Sample Weight mg Toxicity,
CO A i r I t I F H 11 I T I 7 TI I ? I I ZS%N2, 75% air ? I 505N2, 50% air I ! 7S%N2, 25% a i r t l Nitrogen 11 1 5 . 2 14.6 29.2 30.4 3 3 . 4 33.2 37.0 36.2 34.2 3 2 . 0 4 7 . 2 47.2 4 2 . 6 4 5 . 4 4 3 . 4 4 9 # 6 45.2 4 3 . 4 I I 250 2 5 0 5 0 0 500 800 8 00 1 2 00 1 2 0 0 , 1600 1600Son
5100 500 500 5 00 SO0 500 500 Index, Il.g - 1 SUM 4.5 4.5 3.0 3 - 0 2 . 3 2 . 2 1.6 \ 1.6 1.3 1.2 2 . 6 2.7 1 . 5 1.5 0.7 0.7 0.2 0.2 TO 19 32 32 36 35 39 38 36 3 3 5 0 5 0 4 4 47 4 4 5 0 45 44D TO E X H A U S T
-
A-
M A G N E T B - S T E E L C - S A M P L E B O A T I L D - F U R N A C E T U B E E - F U R N A C E F-
G L A S S W O O L , G - H E A T I N G T A P E M - L l Q U l D T R A P S I - 3 - W A Y S T O P C O C K J - P L A S T I C BAG FIGURE I T H E R M A L D E C O M P O S I T I O N A P P A R A T U ST E M P E R A T U R E f 8 0 0 ° C S A M P L E W T = 8 0 0 m g k i R FLOW R A T E , c r n 3 r n i n - ' F I G U R E 2 D E C O M P O S I T I O N P R O D U C T S OF PYC V 4 A I R FLOW LLL 2 " 0.6 z
