Using ethylene oxide in preparation of sterilized solid rocket propellants and encapsulating material

Montgomery, L. C.

Morelli, F. A.

English

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3,305,415 United States Patent O&ce Patented Feb. 21, 1967 
1 2 
In the case of solid propellants, the ethylene oxide may 
3,305,415 be added to a polymeric solid propellant at the same time 
PROCESS FOR PREPARING STERILE SOLID 
PROPELLANTS wring agent is added to the propellant. For example, 
James E. Webb, Administrator of NationaI Aeronau- it has been found that when ethyllene oxide is added to 
tics and respect to an 5 polyurethane propellants at the same time the curing 
invention of L~~~~~~~ C. Montgomery and Frank A. agent suoh as toluene diisocyanate is added, a highly 
Morelli sterile propellant results. 
No Drawing Filed M a .  15, 1965, See. No. 440,033 The ethylene oxide may be added to the propellant as 
4 Claims. (CI. 149-109) a gas or as a liquid. Regardless of the method of addi- 
tion, the physical and ballistic characteristics of the pro- 
The invention described herein was made in the Per- pe,llants are not degraded. Furthermore, the in~rease in 
formance of work under a NASA contract and is sub- fluidity obtained by adding liquid ethylene oxide sub- ject to the provisions of Section 305 of the National stantially facilitates the mixing process and is considered 
Aeronautics and Space Act of 1958, Public Law 85-568 suitable for such processes as continuous propellant mix- (72 Stat. 435; 42 U.S.C. 2457). 15 ing for continuous casting of large motors. The fluidity 
The present invention re!ates to a method of sterilizing is proportional to the amount of ethylene oxide added. 
certain cormpositions, the products so p~odumd, and the The major portion of the ethylene oxide is removed 
use of these products. More particularly, the present from the propellant during vacuum casting. Under the 
invention relates to a process for preparing a sterilized vacuum, the ethylene oxide bubbles up through the pro- 
solid ~ropellant and to a process for preparing sterilized 20 pellant and purges other gases from the propellant thereby 
encapsulating materials which are suitable for encaps~lat- giving it a greater homogeneity. While the pmsent in- 
ing medical inst~uments or other objects which it is de- vention is not to be considered t o  be limited a.0 any par- 
sired to preserve in a sterile condition. ticular theory, it would appear that no significant reaction 
It  has long been recognized that it is highly desirable occurs between the propellant and the ethylene oxide. 
to maintain, to the greatest extent vossible, space crafts 25 The practice of the present invention to produce steri- 
of all types as sterile as possible. This sterility is desired lized encapsula+ing materials is quite similar to the 
to prevent bacteria or other living organisms of any type sterilization of solid propellants. Etheylend oxide in 
from contaminating other planets or other bodies in Sipace either the gaseous or liquid slate is mixed with an un- 
upon which a space craft might land. Such contamina- cured polymeric material which does not chemically re- 
tion would be undesirable both because the transfer of 30 act with the ethylene oxide. Medical or other instruments 
such bacteria O r  living organisms from the Space craft are then dipped in a solution of the mixture to form a thin 
to the body in space upon which it lands would make it coating of the mixture thereon. The adherent film is then 
difficult for future investigators to determine whether any cured on the instrument. Sterilization of the instrument 
life existed on the body prior to the arrival of the space ocaurs during the degasing and curing process. in 
craft and because of the danger that some living things on 35 the case of the solid propellant, most of the ethylene 
the body might be attacked and destroyed by the bacteria oxide and other residual gases are liberated from the mix- 
or other living organisms carried by the space craft. It  ture and all surfaces of the instrument are exposed to the 
has been ~ r o ~ o s e d  that solid p~opellants might be steri- sterilizing action of the generated ethylene oxide gas. A 
lized by exposing them to heat. However, if bhe Wes- residual quantity of this sterilizing gas is believed to re- 
ently avaiiable solid propellants are subjected to the beat 40 main diffused within the tightly adherent solid polymer 
conditions necessary to kill all micro-organisms which film which encapsulates the instrument. The instrument 
might be Present, e.g.9 275" F+ for 24 hours, they suffer is thus sterilized and preserved in a sterile condition by 
degradation and the characteristics and reliability thereof the enc~psu~ating material. m e  encapsulating material 
are adversely affected. may be easily removed when it is desired to use the in- 
Similarly, the desirability of maintaining medical and 45 strument. 
other instlluments in a sterile condition is well known. In the case of the sterilized propellant of the present 
The Present invention provides a Process for sterilizing invention, it has been found that the ethylene oxide should 
such instruments in an encapsulating material whiclh will be present in an alnount of at least about 3% by weight, 
Preserve them in a sterile condition for indefinite periods. based on the weight of the polymeric binder. I n  the case 
This Process does not require autoclaving with steam and 50 of the encapsulating material, the ethylene oxrde should 
the encapsulating materid may be readily remmed when he present in an amount of at least about 3% by weight 
the instruments are needed for use. based on the weight of the polymer. In each case, the 
The basic principle of the present invention is applicable preferred proportion range is about 6% to 14% based 
both of the above arhodiments and, broadly, corn- on the weight of the polymer. In the case of the propel- 
prises the use of ethylene oxide as a sterilizing material. 55 lant, it would appear that a maximum proportion of 
I t  is an object of the Present invention to provide a ethylene oxide is about 50% by weight, but. this may vary 
Process f0h sterilizing solid propellants and the resulting depending upon the of the propellant. 
product. Polyurethanes and silicone resins are preferred for use 
It  is another object of bhe lyresent invention to provide both as binders and encapsulating materials in the present 
a Process for sterilizing medical and other instruments 60 invention. However, any polymeric material which is 
in an encapsulting material which will1 preserve the in- substantially inert to ethylene oxide and which is prepared 
stwments in a sterile condition for an indefinite period by a curing procedure, e.g., with catalyst, heat and/or 
of time and the product so produced. light, to form a film or other shaped article may be used. 
It is a further object of the !?=Sent invention to sterilize In the encapsulation embodiment, jt is desirable that the 
solid propellants and encapsulating materials by com- 65 resin be transparent. 
bining ethylene oxide therewith. It has also been found that the encapsulation procedure 
Other objects and advantages of the present invention, of the present invention is useful as a preliminary to heat 
it is believed, will he apparent from the following de- sterilization of articles, e.g., electrical components for 
scription of specific embodiments thereof. space craft. In other words, the present invention tends 
Broadly, the present invention comprises combining 70 to improve the efficiency of heat sterilization. 
ethylene oxide with sdid propellants oh encapsulating ma- The present invention is further illustrated by the 
terials in such a manner as to accomplish sterilization. following examples of specific embodiments thercof. 
3,305,415 
3 4 
EXAMPLE I Both of the formulations set forth in this example 
Liquid oxide in an amount of parts by formed transparent encapulations. Thus, the need for 
tagging the instruments was ,obviated. 
weight was added to a propellant comprising a mixture 
of 18.8 parts by weight of polyurethane, 16 parts by Having fully described the present invention, it is to 
weight aluminum and 64 parts by weight of ammonium 5 be understood that it is not to be limited to the specific 
details set forth, but is of the full scope of the appended perchiorate. This mixture was then molded into a propel- 
lant at a temperature of 140" F. for 72 hours. What is claimed is: Prior to casting, a particularly hardy bacteria, Bacillus A process for preparing a sterile solid propellant 
subtilis, was added to the propellant. After casting, the 
propellant was tested for the presence of this bacteria lo comprising adding ethylene oxide to an uncured propel- 
and it was found that the bacteria had been completely lant oomposition and curing said composition to form 
killed. Whcn a propellant having the same composition a sterile solid propellant. 2. A process for preparing a sterile solid propellant 
with the exception of ethylene oxide was cast under the 
comprising adding ethylene oxide to an poly- same conditions, it was found that the bacteria remained 15 urethane propellant composition and 
said composi- in vigorous health after the casting had been oompleted. tioll to form a sterile solid propellant. 
EXAMPLE I1 3. A process for preparing a sterile solid propellant 
Two mixes were prepared as follows: comprising adding a sterilizing amount of ethylene oxide 
( 1 )  General Electric's LTV-602 is used to an uncured propellant composition comprising ~ 0 1 ~ -  
as a polymer with 0.1% S R G 0 5  catalyst and 6% ethylene 20 urethane and ammonium perchlorate and curing said corn- 
oxide. (This formulation cures at room temperature position produce a propellant. 
in about 20 minutes, is clear and will peel off after cure.) 4. The process of claim 3 wherein said uncured com- 
(2) ~o~ corning 182 Sylgard is u& as a pdymer position contains toluene diisocyanate. 
with 10% 128 catalyst and 6% ethylene oxide. 
The first forn~ulation had somewhat shorter pot life 25 References Cited by the Examiner 
than the second, the second having a minimum pot life UNITED STATES PATENTS 
of 24 hours. 3,157,990 11/1964 Ward ------------ 149-109 X Both of these formulations will cure in short periods 3,236,046 2,1966 Wellman --------- 149-109 
of time under high temperature environments such as heat 
lamps. It  is not necessary to have a vacuum curing in this 30 
packaging process because any bubbles left will also be References Cited by the Applicant 
sterilized. UNITED STATES PATENTS 
Medical instruments were dipped into each of the above 2,167,537 711939 Tobis. 
formulations and were allowed to cure at a temperature 2,890,191 6/1959 Edmon&. 
of about 108" F. They were then encapsulated, but 35 2,901,467 8/1959 Croco. 
ethylene oxide continued to cliffuse through and Out of 2,922,773 1/1960 Goler. 
the encapsulating material. Thus, they were allowed to 2,958,677 11/1960 Kleinschmidt. 
stand in a curing room until diffusion was complete. 3,102,875 9/1963 Heiss. 
Neither encapsulating material showed any tendency 
to adhere to the medical instruments. Upon removal of 40 BENJAMIN R. PADGETT, Primary Examirzer. 
the encapsulating material the medical instruments were 
found to be sterile. S, J. LECHERT, JR., Assistaizt Examiner. 


Process for preparing sterile solid propellants Patent

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