Properties
(Typical values for 100 gauge film)
PHYSICAL
Specific gravity 1:38
Area factor:
sq. in./lb. 20,000
sq. m./kg. 27:7
Water absorption after prolonged immersion by weight) 0:6
Swelling due to water absorption 0:06
Water vapour permeability (24 h. at 38°C. (100°F.) and
90%/0% r.h.) (g./sq. m.) 21
Oxygen permeability (c.c./sq. cm. per sec. per cm. Hg at
25°C. (77°F.) 4:2 x 10-
Tensile strength:
lb./sq. in. 25,000
kg./sq. cm. 1,750
Elongation at break 70
Yield strength:
lb./sq. in. 13,000
kg./sq. cm. 910
Elongation at yield 5
Elastic modulus:
lb./sq. in. 500,000
kg./sq. cm. 35,000
Tear propagation strength (Elmendorf test) (g. cm/cm. tear) 40
Fold endurance (M.I.T. test: 1000 lb./sq. in. (70 kg./sq. cm.)
at 20°C. (68°F.)) (cycles) 230,000
ELECTRICAL
Dielectric constant (25°C. (77°F.), 1 kc.) 2:95
Dielectric strength (25°C. (77°F.)) (volts) 4,000
Power factor (25°C. (77°F.), 1 kc.) 0:006
Volume resistivity (25°C. (77°F.)) (ohmcm., approx.) 1019
THERMAL
Melting temperature:
°C. (approx.) 260
°F. (approx.) 500
Heat sealing temperature (to give a surface blocking seal):
°C. (approx.) 230
°F. (approx.) 446
110]
Low-temperature flexibility
Coefficient of expansion per °C.
Inflammability
Coefficient of thermal conductivity
Excellent at 70°C.
94°F.); some flexi
bility retained at
200°C. 328°F.)
27 x 10-r>
Burns with difficulty;
passes B.S. 850 1939
4 x 10-4 cal. cm./sq.
cm per sec. per °C.
OPTICAL
Refractive index (mean of refractive indices in the three
principal directions)
Light transmission:
Visible spectrum
U.V. spectrum
Resistance to sunlight:
Visible spectrum
U.V. spectrum
1:6
90%
Cuts off sharply at
3150 A.U.
Good
Moderate
CHEMICAL
Resistance to dilute acids and alkalis Good
Resistance to concentrated alkalis Poor
Resistance to concentrated hydrochloric acid Good
Resistance to fuming nitric acid Poor
Resistance to concentrated sulphuric acid Poor
Resistance to greases, oils and fats Good
Resistance to organic solvents, alcohols and hydrocarbons Good
Resistance to ketones, esters and chlorinated compounds Fairly good
Resistance to phenols, cresols and chlorinated phenols Embrittles
Resistance to mould growth Good
[111]
