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SS * MILS- 4 0 -2 0 0 2 0 4 0 6 0 8 0 100 120 140 160 160 2 0 0 2 2 0 TEMPERATURE - °F.
F ig u re 8. E ffect o f T em p e ra tu re o n D ielectric C o n sta n t and Pow er F a cto r o f P o ly th en e
F igu re 9. R e la tio n o f D ielectric S tr e n g th o f P o ly th en e to T h ick n ess
SHEET THICKNESS ( INCHES x 1000)
F igure 10. R e la tio n o f M o istu re P er m ea b ility o f P o ly th e n e t o T h ic k n e s s o f S h ee t
COM PATIBI LITY AND COM POUNDING
The com patibility of polythene w ith certain m aterials follows:
I n All Pr o p o r t io n s
Raw natural rubber Gutta-percha Butyl rubber (GR-I) Buna S (GR-S) Polyisobutylene
I n Lim it e d Pr o p o r t io n s
Neoprene GN
Butadiene-acrylonitrile rubbers Thiokol FA organic polysulfide Paraffins
Coumarone-indene resins
Compatibility in general was determ ined b y m illing th e ingredi
ents together to a homogeneous m ixture, m olding a te s t slab
M illin g T im e, H o u rs
F igu re 11. E ffect o f M illin g T im e o f P o ly th en e on Pow er F actor
from th e product, and bending th e slab. T he developm ent of a w hite m ark a t th e bend indicates separation of th e ingredients and, thus, incom patibility. E xudation from th e test slab also is evidence of incom patibility.
As would be expected from its structure, polythene blends w ith aliphatic hydrocarbons of large molecular weight. T he com pati
bility is sometimes improved by th e presence of combined chlorine in th e latter. Com patibilities vary som ewhat w ith th e source and ty p e of polythene. Paraffin and, to a lesser extent, m ineral oil have lim ited com patibility w ith polythene; they exude when present beyond certain proportions. T he paraffins of larger m olecular weight are th e more compatible. T he solubility lim its for paraffin w a x (m elting a t 56-58° C.) and m ineral oil w ith one particular polythene tested are approxim ately 15 and 3.5% , respectively, and beyond these lim its they exude (Figure 12).
M any additives, even though compatible, lower th e tensile strength. Nevertheless, for specific uses (e.g., where greater flexibility is required) modification w ith these additives m ay be advantageous. Figure 13 gives a general indication of the effect of certain modifiers on th e rigidity of polythene. This property was measured by a m ethod developed in this laboratory, which
532 I N D U S T R I A L Ä N D E N G I N E E R I N G C H E i n s T R Y VoL 37, No. 6
% MODIFIER
F ig u re 12. E ffect o f M odifiers o n T e n s ile S tr e n g th a n d E lo n g a tio n o f P o ly th e n e
comprises reading, in h u n d red th s of a millimeter, th e deflection of th e center of a disk 4 inches in diam eter, placed o n supports 1.62 inches a p a rt a n d loaded w ith 700 gram s for 5 seconds.
Ta b l e V I. Ba s i c G R -I a n d G R -S Fo r m u l a s (i n Pa r t s b t We i g h t)
G R -I ZnO Sulfur
Tuads (tetram ethylthiuram disulfide) R otax (mercaptobenaothiasole) Stearic acid
ClayCuinar M H l l/ j (cumarone-indene resin) Polythene
GR-S '
Neoione A (antioxidant) ZnOCumar M H V / t Paraffin (m.p. 55-57° C.) Heliosone
Kalvan (calcium carbonate) Stearic acid
Sulfur
Thionex (accelerator) 2-M T (accelerator) Polythene
In th e case of w hite G R -I an d G R -S ru b b er form ulations (T able V I), ad ap tab le to electrical use an d having relatively low tensile strengths, th e ad d itio n of polythene im proves bo th electrical and tensile properties (Figures 14, 15, a n d 16). T he addition of polythene to m ixtures containing carbon blacks and having higher tensile stren g th s generally lowers th e tensile stren g th b u t im proves th e electrical properties.
a p p l i c a t i o n s
Polythene can be handled b y ap p ro p riate a d ap ta tio n of any of th e techniques norm ally used for therm oplastics. I t can be form ed in to films (17), sheets, tubes, rods, tap es, a n d filam ents (16), or applied as an insulating m aterial on wire, b y th e fam iliar m ethods of extrusion. Sheeting can read ily be m ad e also by calendering, eith er u n supported or up o n fabric, or b y th e block pressing technique. Polythene can b e easily m olded b y compres
sion or b y injection in any of th e sta n d a rd com m ercial m achines
<M).
C oatings of polythene can be applied from solution or emulsion (1, 11), b y th e m elt m ethod, or b y th e flam e spraying m ethod which has been used previously for applying coatings of m etals.
I n general, th e solution m eth o d is applicable only to relatively th in coatings, u p to ab o u t 3 mils. F o r heavier coatings, u p to
«
£o oK t-ottl 100.0
5 .0 1 . 6 0 .51.0 3.0 50.010.0 As required
100.0 2.0 5.0 2 0 . 0
2. 0 2 .0 60.0
0 .5 2 .5 0 .6 1.25 As required
PARTS POLYTHENE PER 100 PARTS GR-I
F ig u re 14. E ffect o f A d d itio n o f P o ly th e n e u p o n P o w er F a c to r a n d D ie le c tr ic C o n s ta n t o f G R -I
10 2 0 3 0 4 0 SO
% MODIFIER
F ig u re 13. E ffect o f M odifiers o n R ig id ity o f P o ly th e n e R63 ream is a prod u ct e f R erinou» Product* an d C hem ical C om -
p m n j i PR1 is an exp erim en tal eth er resin .
I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 533
F igu re 15. E ffect o f A d d itio n o f P o ly th e n e u p o n T e n sile S tren g th a n d E lo n g a tio n o f G R -I
about 20 mils, th e flame spraying technique can be used, and even thicker coatings can be applied by th e m elt m ethod. The latter requires a m aterial having extrem ely low m elt-viscosity.
In coating by flame spraying, particles of finely ground m a
terial are passing through a flame, and are either softened on the surface or completely m elted before th ey impinge on th e article to be coated. Successive particles impinge on those previously deposited before either is solidified, and th u s continuous coatings are obtained which are so free from microscopic holes th a t a Tesla coil shows a coating on m etal to be entirely nonporous.
Such coatings have been deposited on m etals, and m ay be de
posited also on wood, glass, brick, plastics, and even paper.
They are extrem ely resistant to corrosion. While pure polythene is quite adherent, it has been found desirable, for service of some types, to add a more adhesive resin to th e polythene. F or ex
ample, the adm ixture of polyvinyl b u ty ral causes a m arked im
provement in adhesion, even though th e two m aterials do n ot possess characteristics which w ould lead one to believe th a t they are compatible.
Coatings of polythene compositions applied to steel by flame spraying exhibit good protective action against corrosion by brines and chemicals. F o r example, coatings on steel test speci
mens showed excellent adhesion a fter 9-m onth immersion in brine, and there was sub stan tially no corrosion of th e m etal.
F igu re 16. E ffect o f A d d itio n o f P o ly th e n e u p o n T en sile S tren g th a n d E lo n g a tio n o f G R -S
T he m ilitary applications of polythene arc chiefly in th e insulation of cable and high-fre
quency accessories {22). E ven before th e war its uses in com m unication and television ap
plications were progressing from th e experi
m ental to th e commercial stage, and the m aterial will be widely utilized in th e post
w ar developm ent of high-frequency communica
tion systems.
Since polythene is extrem ely resistant to m any chemicals and solvents, it should find use in the field of chemical equipm ent as a protective coat
ing on piping, reaction vessels, and containers, and as a gasketing m aterial in contact with various acids, alkalies, and other chemicals. In this laboratory hydrofluoric acid has been stored in bottles m ade of polythene. Sim ilarly, it is suitable for caps and cap liners (6) for containers of corrosive m aterials.
T he low m oisture perm eability and good water resistance of polythene indicate its suitability for th e coating of cloth, paper, wood, brick, and concrete, for th e fabrication of containers (for m ilk and other liquids), and for packaging in general. F or the la tte r purposes th e plastic can be employed either as sheeting or as an im pregnant for paper (7, 8, I t ) .
T he use of polythene as a modifying agent m ay be expected to contribute useful improvem ents in th e properties of various rubbers, waxes, etc.
T he commercial production of polythene in this country was a w artim e developm ent for m ilitary purposes, and th e product is under allocation by th e W ar Production Board. However, small quantities can be obtained for experim ental purposes.
ACKNOW LEDGM ENT
T he authors wish to acknowledge th e invaluable assistance of inform ation m ade available by Im perial Chemical Industries L td. and by th e Chemical D epartm ent, the Ammonia D ep art
m ent, and th e R ayon D epartm ent of du P ont. W. M. D . B ry
a n t of th e Ammonia D epartm ent m ade m any of th e determ ina
tions of refractive index and coefficient of expansion presented here.
LITERATURE C ITED
(1) Alvarado, A. M., et al., U. S. Patent 2,290,794 (July 21, 1942).
(2) Bamberger, E., and Tsohirner, F., Ber., 33, 965 (1900).
(3) Bunn, C. W., Tran». Faraday Soc., 35, 482 (1939).
(4) Carothers, W. H„ et al., J . Am. Chem. Soc., 52, 6279 (1930).
(4A) Charch and Soroggie, Paper Trade J., Oct. 3, 1936.
(6) Crafton, H. C., Jr., and Slade, H. B., Modern Plastics, 21, No. 11, 90 (1944).
(6) Dorough, G. L„ U. S. Patent 2,238,681 (AprU 15, 1941).
(7) Dunbar, C„ Ibid., 2,299,807 (Oct. 27, 1942).
(8) Evans, J. G., et al., Ibid., 2,237,344 (April 8, 1941).
(9) Fawcett, E. W., et al., Ibid., 2,153,553 (April 11, 1939) Brit.
Patent 471,590.
(10) Fawcett, E. W., and Gibson, R. O., J. Chem. Soc., 1934, 386.
(11) Gomm, A. S., U. S. Patent 2,313,144 (Maroh 9, 1943).
(12) Habgood, B. J., et al.. Ibid., 2,292,441 (Aug. 11, 1942^.
(13) Hengstenberg, Z. Krist., 67, 589 (1928).
(14) Imperial Chem. Ind. Ltd., Tech. Bull. Plastics, 5 (Nov., 1943).
(15) Mark, H., and Raff, R„ “High Polymeric Reactions", pp. 233-62, New York, Interscience Publishers, 1941.
(16) Perrin, M. W., et al., U. S. Patent 2,210,774 (Aug. 6, 1940).
(17) Ibid., 2,219,700 (Oct. 29, 1940).
(18) Renfrew, A., et al., Ibid., 2,232,475 (Feb. 18, 1941).
(19) Rice, F. G., Can. Chem. Process Inds., 28, 459 (1944).
(20) Shackleton, J. W., Modern Plastics, 21, No. 6, 99 (1944).
(21) Swallow, J. C., Endeavour (London), 3, No. 9, 26 (1944).
(22) Swallow, J. C.,etal., U. S. Patent 2,204,737 (June 18,1940).
P r e s e n t e d before the Division of P ain t, Varnish, and Plastics Chemistry a t the 108th M eetinf of the Am e r i c a n Ch e u i o a l So c i e t yin New York, N . T.