RESISTANCE TO FREEZING AND GAS PERMEABILITY OF ELASTOMERS

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80-00809A000700250044-4
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 4
• Document Creation Date: December 22, 2016
• Document Release Date: July 8, 2011
• Sequence Number: 44
• Publication Date: February 27, 1956
• Content Type: REPORT

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STAT
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RESISTANCE TO FREEZING AND GAS PERMEABILITY OF ELASTOMERS
(Comment: The following article by G. Df. Bartenev, Doctor of
Chemical Sciences, Scientific Research Institute of the Rubber In-
dustry, was published in the September 1955 issue of the Moscow
periodical Khimicheskaya Promyshlennost'.
Numbers in parentheses refer to the author's bibliography ap_
pended. Table and figures are also appended.]
resistance to freezing is a desirables rocertrom the practical standpoint. Wh11e
able property in practical engineerlagpapplicati
an undeair-
wh
~e
hes
ons
Although t
two
ich have been mentioned are entirely different, there is a definite correlation
beiween them which is based on the fact +t,a+ +ti,. ,.
--~~~~u. - ----~-~=u ++~ one elastomer are iater-
The freezing resistance of elastomers is characterized by a conventional
temperature of vitrification
t
a
which the material changes from an elastic state
to a vitreous state. This resistance is determined by mechanical methods (static
and frequency methods) and thermal methods (b
h
d
y
eat capacity).(1)
etermining the heat expansion or
elastBrityimodulusaofothemelastomerhincreasestb eat is determined at which the
the coefficient of freezing resistance. It is numericallykequaletoathat frac-
tion of the high-elasticity deformation which has time to develop at lox temper-
atures during a set interval of time or a set period of multiple deformation.
Iri o?her words, the coefficient of resistance to freezing is numerically equal
to a ratio of the magnitude of deformation ~ at testing temperatures to the mag_
nitude of d=formation E oo at high temperatures (e. g., 250) at which the elasti-
city c*' the elastomer for all practical Purposes reaches a limit.
BY using thermal methods, the temperature T is determined below which the
rotational freedoms of the long-chain molecule o~ the elastomer are loot.
At k 0.01 the values of Tk for all practical purposes coincide with the
values of Tg.
The Bas Permeability of elastomers varies within wide limits depending of
the nature of the gas and the structure of the elastomer. In some cases the
values of the gas permeability differ by factors amounting to several hundred.
(3, 4) The highest gas permeability is exhibited by elastomers of normal
struc?ure which do not contain any polar groups in the molecule (NK S
According to G. Amerongen, the gas permeability of not a1 rubber amaunt~s~totc),
The4lowest gas3/sec cm a+, for hydrogen and to 8.3 X 10~ cm3/sec cm at for air.
permeability is possessed by polychloroprene and copolymers which
contain strong polar groups in the molecule (SKN_26, S~_40, etc).
In Table 1 the hydrogen and air permeabilities of elastomers at 25o accord-
~ng to Amerongen's da+,a (h) are Listed together with values of the resistance to
freezing TO.pl determined by us with the use of the static method on a Kargin
balance (time of observation 30 sec) and values of T taken from the literature.
(5) The gas permeabilities are given in percent of ~he permeability of natural
rubber,
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The dependence between the gas permeability P of the elastomers and their
temperature of vitrification (T0.01 and Tg) is shown in figures 1 s.nd 2.
It can be been from the data cited that ss the gas permeability drops, the
resistance of elastomers to freezing also drops. The reason for this is quite
obvious: as the intermolecular forces are reduced in the transition from polar
elastomers to nonpolar elastomers, both the rate of diffusion of gas molecules
and Y,he mobility of the links of elastomer molecules are increased. The first
condition brings about an increased gas permeability, chile the second results
in a preservation of the flexibility of the long-chain molecules of the elastomer
down to very low temperatures.
It follows from this that an elastomer cannot be expected to have both a
high resistance to freezing and a low gas permeability: these characteristics
are mutually incompatible.
Strictly speaking, this conclusion applies only to pure high-polymer sub-
stances and not to compounded rubbers. By compounding the elastomer with addi-
tives, one may obtain materials which possess both a high resistance to freezing
and a low gas permeability. If a dispersed filler which adsorbs gas is added,
the gas permeability will be lowered while the resistance to freezing ie pre-
served. To give another example, addition of a small quantity of plasticizer
may greatly improve the resistance to freezing while a low gas permeability is
preserved. Nevertheless, in working with material derived from elastomers it
is necessary to keep in mind the relationship which has been formulated.
Table 1. Resistance of Elastomers to Freezing and
Their Permeability to Hydrogen and Air
Temperature of
Vitrification in oC Perme
ability P at 25?C
in
Elaetomer
Te.ol ~ To Hy
drogen T
o A1:
Butadiene-styrene rubber
sxs-lo
-76
__
__
__
Natural rubber (NK)
-71
-73 1
00
100
Polybutadiene sty
_io
-66
86
81
Butadiene-styrene rubber
SKS-3o (Bona Es)
-61
-61
81
76
Butadiene-nitril rubber
SKN_18 (Perbunan-18)
=45
--
51
33
Polychloroprene (Neoprene) -38
-36
27
15
Butadiene-nitril rubber
SKN-26 (Hycar OR-25)
-26
-24
24
8.5
Butadiene-nitril rubber
SIIN-1~0 (Hycar OR-15)
-22
-20
15
3, 4
I
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 Sanitized Copy Approved for Release 2011/07/08: CIA-RDP80-00809A000700250044-4
3. S. A, Reytlinger, Uspekhi Khimii, Vol 20, p 213, 1951
4. 0. Amerongen, J. Polymer Sci., Vol 5, P 307, 1950
5. R. F. Boyer, R. S. Spencer, The Chemistry of Lsrge Molecules, No 2, Pub-
lishing Rouse of Foreign Literature, 1948; N. Bekkedahl, R. Scott, J, Res. Nat.
Bur, Stand., Vol 29, p 8j, 1942; N. Bekkedahl, J. Res. Nat. Bur. Stand., Vol 13,
p 411, 1934; N. Bekkedahl, H. Matheson, J. Res. Nat. Bur. Stand, Vol 15, p 503,
1935; K. Floyd, British J, Appl. Phys., Vol 3, P 373, 1952; R, Witte, il, Anthony,
J. Appl. Phys., Vol 22, p 689, 1851; L. Holroyd et al, J. App1. Phys., Vol 22,
p 696, 1951.
loo
P.at 25? C, in ~
50
-80 -60 -40 -20
Temperature of Vitrification in ?C
Fig 1. The Relationship Hetveen the Permeability oP Elsstomers To Hydrogen at
25oC mid Their temperature of Vitrification (points indicated by circles represent
values of Tg, those indicated by crosses values of T )
0.01
P at 25o C, in ~+
50
-80 -60 -40 -20
Temperature of Vitrification in oC
Fig 2. The Relationship Hetveen the Permeability of Elsstomers To Air at 25?C
and Their Temperature of Vitrification (points indicated by circles represent
values of Tg, those indicated by crosses values of T0.01)
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