Solvent system dissolves the solid curing agents used with polyurethane resins in adhesive systems. The system developed yields bond strengths comparable to 100 percent solid formulations. The optimum solvent chosen was a 55.5 percent solution in anhydrous tetrahydrofuran

St. Cyr, M. C.

English

NASA Technical Reports Server

December 1967	 Brief 67-10593 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Solvent Permits Solid Curing Agents to be Used at Room Temperatures 
The problem: 
To determine the feasibility of using a solvent 
system for dissolving the solid curing agents used with 
polyurethane resins in adhesive systems. The bonds 
formed must be as strong, or nearly as strong, as in 
the prior method which used melted solid curing 
agents. This process was difficult to use in assembly 
line operations because of the necessity of melting the 
curing agent before it could be mixed with the . base 
resin.	 I 
The solution: 
Two polyurethane two-component adhesive pastes 
used in cryogenic bonding, each consisting of a 
solid adhesive curing agent and a resin were tested. 
The solid curing agents are normally melted at 250° F 
prior to mixing with the polyurethane resins. 
The various solvents evaluated included: tetrahydro-
furan, acetone, dimethyl formamide, and mesityl 
oxide. Iii the case of each solvent, the solid curing 
agent was stirred in until a saturation solution was 
formed. The resulting dispersed solvent was mixed 
with the applicable polyurethane resin until the 
mixture was homogeneous. Entrapped air and as much 
solvent as possible were then removed. 
The various resin mixtures were applied to alumi-
num panels, which were then assembled for bond 
testing. The panels were allowed to cure for a 
minimum of 3 days at 2 to 3 psi pressure. The 
assembled panels were shear tested in a tensile test-
ing machine at various temperatures between —4231F 
and 2501 F. The bonds were also tested for thermal 
shock cycling and sustained exposure in liquid hydro-
gen.
A solvent dispersion system was developed which 
yielded bond strengths comparable to 100 percent 
solid formulations. The optimum solvent chosen was 
a 55.5 percent solution in anhydrous tetrahydro-
furan. A saturated solution containing the curing 
agent was mixed in the ratio of 11:100 with the 
applicable base resin. 
Notes: 
I. The solvents used were mainly nonreactive 
diluents and as such extended pot life without 
appreciably increasing the set time. Tetrahydro-
furan had the least detrimental effect on the 
mechanical properties of the cured adhesive. 
2. The maximum amount of solvent must be removed 
from the resin mixture before the parts are 
assembled, making degassing and an extended 
open time essential. 
3. Inquiries concerning this invention may be di-
rected to:
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B67-10593 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code 
GP, Washington, D.C. 20546.
Source: M. C. St. Cyr
of Douglas Aircraft Company
under contract to

Marshall Space Flight Center 
(M FS- 13434) 
Category 03 
This 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.
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Solvent permits solid curing agents to be used at room temperatures

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