Thermal Characteristics of Some Rigid Urethane Foams Page: 4 of 14
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THERMAL CHARACTERISTICS OF SOME RIGID URETHANE FOAMS
Clifford H. Smith
The Bendix Corporation
Kansas City Division
The use of rigid urethane foams as insulative materials and structural mem-
bers is rapidly increasing as their unusually low thermal conductivities and
good strength-to-weight ratio become better established. Service tempera-
tures for these applications, as well as others, range from cryogenic to
somewhat above normal room conditions.
The utility of rigid urethane foams in higher temperature applications has
been limited, to a certain degree, by the lack of significant information
concerning the thermal stability of these materials. However, thermal
characteristics of urethanes themselves have long been known, for Hofmann
in 1870 showed that an aromatic urethane dissociates into an isocyanate and
an alcohol between 1700 to 1800C (5). Another investigator has also made
an extensive quantitative study of the kinetics of the urethane dissociation
and is in good agreement with this early work (10). Additional kinetic
studies of this decomposition in several solvents indicate that the reaction
proceeds at an appreciable rate even at 1500C (6) (8).
Some data on the thermal stability properties of urethane elastomers and low
density fluorocarbon blown foams have been published (1) (4) (9). Com-
pressive strength data at elevated temperatures has also been determined on
a rigid urethane foam system at various densities (3). Still there exists a
considerable absence of detailed information concerning the thermal service
limitations for rigid urethane foams.
The work reported in this paper is directed toward both a theoretical and
practical aspect for the determination of some of the thermal characteristics
for rigid urethane foams. The methods used to measure the parameters
inclie.:- compressive strength properties at elevated temperatures, thermos
-gravimetric analysis, differential thermal analysis, heat aging (somewhat
of a static thermal stability test), and elemental chemical analysis. A
possible correlation between physical and thermal properties is suggested
as a guide for determining the elevated service temperatures for these ma-
Materials. The Jthree rigid urethane foam formulations chosen for this
study show a wide range of molecular structure. A brief description of
each is listed below.
Foam 1 - An aromatic dibasic acid-based polyester/toluene
diisocyanate (TDI) prepolymer foam.
Foam 2 - An E-caprolactone - pentaerythritol polyester/toluene
diisocyanate (TDI) prepolymer (20%) - polymethylene
polyphenylisocyanate (PAPI) (80%) material.
Foam 3 - A commercial high temperature rigid urethane foam
based on a polyester and polymethylene
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Smith, C. H. Thermal Characteristics of Some Rigid Urethane Foams, report, April 1, 1965; Kansas City, Missouri. (digital.library.unt.edu/ark:/67531/metadc1034922/m1/4/: accessed November 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.