Fire retardant properties of low density polymer foam are increased. Foam has pendant nitrile groups which form thermally-stable heterocyclic structures at temperature below degradation temperature of urethane linkages

Parker, J. A.

Riccitiello, S. R.

English

NASA Technical Reports Server

1972	 B72-10269 
NASA TECH BRIEF 
Ames Research Center
	 -4r 
NASA Tech Briefs announce now technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Fire Retardant Polyisocyanurate Foam 
The problem: 
To increase the fire retardant properties of low-
density polymer foams. 
The solution: 
A polyisocyanurate foam with pendant nitrile 
groups which form thermally-stable heterocyclic 
structures at a temperature below the degradation 
temperature of urethane linkages. 
How it's done: 
The nitrile groups are introduced as acrylonitrile 
grafted to a low-hydroxyl number polyol prepolymer 
which may be of the type typically derived from 
glycerin and propylene oxide. Because the modified 
poiyoi has a low hydroxyl number and low function-
ality, the resulting polyisocyanurate-polyurethane 
foam structure has mechanical flexibility, whereas 
the polyisocyanurate polymers do not. The polymeric 
structures containing nitrile groups cyclize at low 
temperatures to form nitrogen-containing heterocyclic 
ring structures; subsequent degradation of these struc-
tures and the polyisocyanurate-urethane structures 
at an elevated temperature provides a high char 
yield, implying a correspondingly lowered yield of 
the volatile flammable species which are formed in 
comparatively large quantities by state-of-the-art 
polyurethane polymer foams based on polyols such 
as sucrose and glucose. 
The new type of rigid foam is typically prepared 
by homogenizing in a ball mill a mixture of the polyol 
grafted with acrylonitrile, a tertiary amine catalyst, 
an inorganic base, a char stabilizer such as potassium 
fluoborate, and a blowing agent. Grinding is continued
until all dispersed solids are reduced at least to a 
diameter of 50 x 10 mm. It may be desirable to 
incorporate other polymeric materials (such as poly 
(vinyl chloride—vinyl acetate) copolymer) and inert 
refractories such as silica to increase density or to 
impart particular properties to the finished foam; 
other additives may be materials such as encapsulated 
flame retardants, cell stabilizers, colorants, etc. The 
premix formed by milling is then blended rapidly 
and thoroughly with a polymeric isocyanate, for ex-
ample, a polymethylene polyphenyl isocyanate, and 
immediately poured into a mold to cure for about 16 
to 24 hours. 
When exposed to a JP-4 fire at a heat flow rate of 
10-13 Btu/ft2
 sec (11.1 - 14.8 x 10 W/m 2 ), 5-cm 
thick state-of-the-art polyisocyanurate foams burn 
through in about 55 seconds; in contrast, the new 
type of polyisocyanurate foams withstand burn-
through for more than 600 seconds. 
Reference: 
Riccitiello, S. R.; Fish, R. H.; Parker, J
.
 A.; and 
Gustafson, E. C.: Development and Evaluation of 
Modified Polyisocyanurate Foams for Low-Heating-
Rate Thermal Protection. Journal of Cellular Plastics, 
vol. 7, no. 2, page 3, 1971. 
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B72-10269
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000269 2020-03-17T03:27:20+00:00Z
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to: 
Patent Counsel 
Mail Code 200-1A 
Ames Research Center 
Moffett Field, California 94035 
Source: Salvatore R. Riccitiello and 
John A. Parker
Ames Research Center 
(ARC-10280) 
B72-10269	 Category 04


Fire retardant polyisocyanurate foam

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