Spore recovery form cured silicone potting compounds using amine solvents to degrade the cured polymers was investigated. A complete list of solvents and a description of the effect of each on two different silicone polymers is provided

Hill, L. W.

Hsiao, Y. C.

Pappas, S. P.

English

NASA Technical Reports Server

QUANTITATION OF BURIED CONTAMINATION
BY USE OF SOLVENTS
Semiannual Progress Report
January - June, 1974
;,.- ^
Supported by
NASA Grant NCR 35-001-012
Supplement No. 3
Submitted to the
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
by the
Department of Polymers and Coatings
North Dakota State University
Fargo, North Dakota 58102
Investigators: S. Peter Pappas and Yu-Chuan ( Paul) Hsia
Principal Investigator: Loren W. Hill
/
https://ntrs.nasa.gov/search.jsp?R=19740021363 2020-03-23T06:16:48+00:00Z
INTRODUCTION
This report for January through June 1974 describes experiments directed
at determining the potential of reclaimed silicone polymers for reuse. The dis-
covery that amines can dissolve cured silicone resins ' ^ has been recognized
as potentially providing two "spinoffs". These are (1) recovery of silicone
resins from used silicone furniture molds and (2) silicone coating of heat sensi-
tive materials. Both of these processes could be of some importance to the
national interest. The former involves recycling of products prepared from
raw materials that are in short supply. The latter may lead to new coating
technology that would broaden the scope of silicone use. Silicone polymers are,
to a large extent, derived from sources other than petroleum (currently the
methyl and phenyl side groups are incorporated from petroleum derived raw
^—._
materials, however); thus, increased use of silicones would ameliorate petroleum
raw material shortages, and in the long run may provide an alternative raw ma-
terial to the petrochemicals used currently in nearly all other coatings.
The Inventions and Contributions Board of NASA has been informed of the
discovery described above, and attempts to prepare a patent application have
been reported. A request for waiver of NASA patent rights is currently being
held in abeyance pending determination of our intent to submit a patent applica-
tion. North Dakota State University has one of the typical patent application
agreements frequently negotiated between universities and Research Corporation,
405 Lexington Avenue, N. Y. City, N. Y. 10017. At our request, Research
Corporation reviewed a report submitted for consideration of a patent applica-
tion and, after a long delay, reported that they would not submit an application
because (a) the solvents used in the reclaiming process were so common that
2it would be difficult to prove a violation should one occur and ( b) the specifics
of reuse of the reclaimed material had not been adequately worked out. Subse-
quently to this decision, we obtained permission from the Inventions and Contri-
butions Board to allow private companies the opportunity of considering product
development research related to (b) above. At present, a large paint company
is considering the feasibility of development of processes using the amine solu-
bilization technology. If the technology is used commercially, a delay in dis-
closure or a sharing of patent rights will be negotiated.
RESULTS AND DISCUSSION
Reuse of reclaimed silicone polymer solutions would be greatly facilitated
if crosslinks were regenerated during solvent evaporation. Based on the
mechanism as presented previously, ' it was anticipated that a significant
number of crosslinks would reform on evaporation of the amine solvent. One
approximate measure of the extent of crosslinking is the weight fraction that
cannot be extracted; the greater the nonextractable fraction, the greater the
number of crosslinks. The extraction in this case was carried out in refluxing
acetone for 48 hours using a Soxhlet extractor. Free films of both the original
and reclaimed polymer were weighed before and after extraction with the results
presented in Table I . If the arnine solvent was not removed, the whole sample
was essentially extractable. Thus, the results presented for the reclaimed
samples indicate that crosslinks are reformed and that conditions during solvent
removal affect the extent of recrosslinking. Contrary to the trend suggested in
Table I, the extent of recrosslinking did not continue to increase indefinitely as
the temperature of drying increased as indicated by lower levels of % nonex-
tractable when films were dried at 230°C. It is difficult to predict optimum
recrosslinking conditions because the reaction may depend on a complex set of
reaction rate constants and evaporation rates. It is felt that the DC840 silicone'
considered in Table I is typical of oven cure resins of the poly( methylphenyl-silox-
ane) type. The structure of DC840 has been studied thoroughly**.
Silicone rubber as well as cured silicone resins were subjected to tests of
"recovery of properties after evaporation of solvent following dissolution in amines.
Results of tensile property determinations for a silicone rubber consisting of
lightly crosslinked poly(methylsiloxane) are given in Table II. It is clear that
some of the "rubbery" properties are recovered indicating that crosslinks are
reformed. However, extended storage periods in the dissolved state clearly
alter the structure as indicated by reductions in both tensile strength and percent
elongation. Tensile properties- were determined on an Instron instrument using
widely accepted procedures that are described in detail elsewhere".
A number of tests that are common in the coatings industry (but little known
elsewhere) were carried out on dried films of DC840 and on reclaimed samples
of DC840. Reclaimed samples were cast as films from a number of different
amines and air dried for ten days. The control, film samples were baked at
240° C for one hour; such samples dissolved in the desired amine were designated
as the reclaimed material. With regard to solvent and chemical resistance tests,
reclaimed samples were equal to the controls with the exception of samples dis-
solved in 1, 2-diaminopropane. This diamine may have persisted in the air
dried films due to its lower volatility. Reclaimed samples were also equal to
controls in tests designed to measure hardness, again with the exception of films
cast from 1, 2-diaminopropane. As expected for a highly crosslinked silicone,
flexibility was poor for both controls and reclaimed samples.
Although tests cannot be considered conclusive, it is encouraging to note
that reclaimed films have properties that approach acceptable levels for com-
mercial coatings. Further study appears to be worthwhile, and since product
development research is not an objective of this project or of NDSU, private
industry has been apprised of the possibilities^ The high curing temperatures
and long cure periods required for silicones have created problems with silicone
coatings for a long period. The possibility of forming silicone coatings by solvent
evaporation is, therefore, an attractive alternative.
PLANS FOR ADDITIONAL WORK
During the next six month period, efforts will be directed at:
1) Determination of the toxicity of epoxy prepolymers to spores. (Some
initial results suggest a significant level of sporicidal activity. )
2) Investigation of sporicidal effects of high temperatures reached during
epoxy cure due to exothermic chemical reactions.
3) Completion and submission of publications.
4) Use of silicone compounds in uv curable coatings that contain epoxy
resins.
5) Assessment of patent possibilities with an input from private industry
concerning product development research.
PERSONNEL
Ronald Just, a second year graduate student in the Polymers and Coatings
Department, is now receiving financial support on this project in connection
with (4) above. Mr. Just received his B. S. degree in 1973 from Minot State
College, Minot, North Dakota; he is a native of Mandan, North Dakota.
Joseph Helm is continuing the viability study with epoxy systems as related to
( 1) and ( 2) above. Yu-Chuan ( Paul) Hsiao has completed his Ph. D. degree and
moved to South Bend, Indiana to join O'Brien Corporation.
Table I. The Degreeof Crjjsslinking of Cured and Reclaimed
DC 840 by Acetone^ Extraction
% Nonextractability
Sam pie %_ Nonext rac table recovered
Control sample* 86. 5 ( 100)
Reclaimed sample**
1) dried at room temp.
for 48 hrs 66. 6 77. 0
2) baked at 60° C for
24 hrs 65.2 75.4
3) baked at 100° C
for 2 hrs 77. 3 89. 4
*Cured at 240° C for 1 hour.
** Prepared by dissolving the control sample in n-butylamine and
removing solvent under specified conditions.
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REFERENCES
1. S. P. Pappas, Y. P. Hsiao, and L. W. Hill, "Quantitation of Buried Contam-
ination by Use of Solvents, " Semiannual Progress Report, July-December,
1973, NASA Grant No. NGR35-001-012.
2. ibid, Semiannual Progress Report, January-June, 1973.
3. ibid. Semiannual Progress Report, July-December, 1972.
4. ibid. Semiannual Progress Report, January-June, 1972.
5. Y. P. Hsiao and L. W. Hill, "Solubilization of Cured Silicone Resins in
Amine Solvents; A Report Submitted for Consideration of a Patent Applica-
tion," May 1973, NASA Grant NGR35-001-012.
6. A. E. Rheineck and R. A. Heskin, "Quantitation of Buried Contamination by
Use of Solvents; Solvent Degradation of Amine Cured Epoxy Resins";
First Interim Report, prepared by L. W. Hill, February 1972, NASA Grant
NGR35-001-012.
7. R. A. Heskin, "Solvent Degradation and Exotherm Studies of Amine-Cured
Epoxy Resins, " Ph. D. Thesis, North Dakota State University ( 1971).
8. Y. P. Hsiao, "Solubilization and Spore Recovery from Silicone Polymers, "
Ph. D. Thesis, North Dakota State University, in press.


Quantitation of buried contamination by use of solvents

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