Thermal penetrometry is experimental technique for detecting temperature at which frozen prepolymer becomes soft enough to be pierced by weighted penetrometer needle; temperature at which this occurs is called penetration temperature. Apparatus used to obtain penetration temperatures can be set up largely from standard parts

Ashcraft, A. C.

Potts, J. E., Jr.

English

NASA Technical Reports Server

February 1973
	 B78-10036 
•	 NASA TECH BRIEF 
NASA Pasadena Office
	 -4r 
NASA Tech Briefs announce new technology derivedfromthe U..S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Glass Transition Temperatures of Liquid Prepolymers

Obtained by Thermal Penetrometry 
Thermal penetrometry is an experimental technique 
for detecting the temperature at which a frozen pre-
polymer becomes soft enough to be pierced by a 
weighted penetrometer needle; the temperature at 
which this occurs is called the penetration temper-
ature, T. In the vicinity of the glass transition tem-
perature there is a very large decrease in shear mod-
ulus; below the glass transition temperature, the 
sample is hard, often brittle, and resists deformation 
•
of any kind. Above the glass transition temperature, 
the sample is either ,
 soft and rubbery or else a viscous 
liquid which can be easily deformed. A weighted 
needle does not penetrate the glass formed by a liquid 
copolymer sample below the glass temperature, but it 
does so easily and rapidly at higher temperatures. 
The apparatus used to obtain penetration temper-
atures can be set up largely from standard parts; thus, 
the penetrometer needle is of the type specified by 
ASTM Method D-5, weight 2.5 g, and it is attached 
to a freely moving vertical rod conforming to the re-
quirements of the same standard method. The shaft 
has a weight of 47.5 g, and additional weights may be 
loaded on top of it; a weight of 150 g performs well 
with liquid copolymers. In order to detect and mea-
sure needle motion, a fixed collar on the vertical shaft 
holding the penetrometer needle can be made to bear 
on an arm which drives a pointer through a rack and 
pinion combination; the pointer scale should permit 
estimates of needle position to the nearest 0.02 mm. 
Alternatively, the collar on the vertical arm of the 
penetrometer can be rigged to cause rotation of a
stepless potentiometer used as a voltage divider, and 
its output can be monitored on a recorder. Moreover, 
the output of the potentiometer and a thermocouple 
can be recorded simultaneously to obtain accurate 
plots of needle motion vs temperature. 
A few drops of the polymer sample are placed in 
an aluminum foil cup and rapidly cooled in liquid 
nitrogen to give a small button of glassy polymer. 
The foil cup is placed in the bottom of a small beaker 
which is full of methanol at a temperature below the 
anticipated glass transition temperature. A thermo-
couple junction is placed on the polymer button 
and the penetrometer needle is allowed to come into 
contact with the button at a point near the thermo-
couple. The methanol bath is allowed to increase in 
temperature while continuous records of needle 
position and temperature are made. 
Below the penetration temperature, the record of 
the needle position is a straight line; when the pene-
tration temperature is at hand, the needle suddenly 
begins to sink into the sample and the record exhibits 
an abrupt and continuous change in position until the 
needle stops at the bottom of the polymer bead. Mean-
ingful values of penetration temperatures can be 
obtained only if the molecular weight of the prepoly-
mers are low enough. In general, the functional de-
pendence of penetration temperature and molecular 
weight is
T=A/M+B 
where Rn is the molecular weight and A and B are 
constants.
(continued overleaf) 
is document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000036 2020-03-17T06:36:43+00:00Z
Patent status: 
NASA has decided not to apply for a patent. 
Source: James E. Potts, Jr. and 00 
A. Clifford Ashcraft of 
Union Carbide Corp./Chemicals and Plastics 
under contract to 
NASA Pasadena Office 
(NPO-11730)
Note: 
Requests for further information may be directed 
to
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP 73-10036
. 
B73-10036	 Category 04


Glass transition temperatures of liquid prepolymers obtained by thermal penetrometry

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