Investigation determines structural potential of asbestos fibrils. Methods are developed for dispersing macrofibers of the asbestos into colloidal-sized ultimate fibrils and incorporating these fibrils in matrices without causing reagglomeration

Rader, C. A.

Schwartz, A. M.

English

NASA Technical Reports Server

Rh. 1313 
June1970	 KSC FIQS.	 Brief 70-10020 
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Reinforcement of Polymeric Structures with Asbestos Fibrils 
An experimental intiestigation was conducted to 
determine the structural potential of chrysotile as-
bestos fibrils, which have found wide use as reinforce-
ments in various plastic matrixes; and to develop 
methods for dispersing macrofibers of the asbestos 
into colloidal-sized (200 to 500 A) ultimate fibrils 
(abbreviated UAF) and for incorporating the UAF 
in matrixes without causing reagglomeration. At-
tempts to develop methods for producing UAF were 
undertaken because it was found that the tensile 
strength of conventional macroscopic asbestos fibers 
(abbreviated MF) increases as fiber diameter de-
creases. Fine-diameter MF, in the range of 10 to 20 
(10 to 2 x 10 A), have tensile strengths which have 
been reported to be as high as 824,000 psi (U.S. Pat. 
2,626,213). It is therefore reasonable to assume that 
0.02i (200 A) UAF could have strengths greater than 
1,000,000 psi. A commercial method of producing 
asbestos fibrils (based on U.S. Pat. 2,626,213) for 
use as reinforcements in plastics composites yields a 
mixture of UAF and MF. In that method, the UAF-
MF fibrils are produced by slow-speed stirring of a 
suspension of MF in a water solution of a suitable 
surfactant. 
One of the results of the investigation was the de-
velopment of an improved method for producing 
colloidal dispersions of asbestos in a water solution 
of any one of several commercially available sur-
factants (phosphate esters, for example). In this 
method, 100% UAF dispersions are obtained by high-
speed shear-mixing of AY grade asbestos in aqueous 
surfactant solutions (in a commercial household 
blender, for example) for about 1-1/2 hours. The re-
covery of UAF, or UAF-MF, from the dispersing 
medium is accomplished by either one of two tech-
niques. In the first technique, the dispersion is filtered
to remove the larger fibers, and the filtrate containing 
the colloidal UAF is coagulated by adding water (or 
alcohol). The supernatant water is removed by filtra-
tion and the resultant mat or paper of UAF is dried. 
These papers were found to contain a high percentage 
of adsorbed surfactant. In the second technique, the 
UAF is recovered by evaporation of the water. In 
this case, the percentage of surfactant retained by 
the UAF is even higher. To provide for the prepara-
tion of solid, void-free*composites of high densities, 
the dried paper obtained by either technique is pressed 
at 400 to 1000 psi. The densified paper may then be 
vacuum-impregnated with any one of a variety of 
resins. It was found that the surfactant adsorbed on 
the asbestos fibrils affects the ultimate bonding of the 
asbestos to the matrix in the composites prepared. 
In general, high proportions of residual surfactant 
tend to reduce the strength of asbestos/phenolic and 
asbestos /polyester composites. The papers containing 
33% or more surfactant are remarkably strong (tensile 
strengths range from 820 to 6100 psi) compared to 
papers with lower surfactant content (tensile strength 
of approximately 100 psi), before phenolic resin im-
pregnation. In these papers, the surfactant may be 
acting as a lubricant, preventing the asbestos fibrils 
from cutting each other when placed under tension. 
When these papers containing 33% surfactant are im-
pregnated with phenolic resin, the tensile strengths 
range from 4600 to 5200 psi depending on the com-
position of the surfactant used. However, the sur-
factant apparently interferes with resin/asbestos 
bonding. As expected, by orienting the asbestos re-
inforcement, an increase in strength (over isotropic 
reinforcement) was obtained in the direction of orien-
tation. Partially oriented arrays of UAF were pre-
pared by slowly drawing filaments of UAF from a 
(continued overleaf) 
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water-diluted dispersion of UAF in an aqueous sur-
factant solution. When impregnated with phenolic 
resin, the arrays had tensile strengths up to 100,000 
psi. UAF was thus found to be at least as strong as 
MF, although anticipated strength advantage over 
M  was not demonstrated. 
In the second and improved method the UAF dis-
persions are prepared simply by mixing macrosized 
asbestos fibers with any one of several organic liquids 
in the same type of high-speed blender used for the 
water-surfactant dispersions. The following are 
among the organic liquids which were found to serve 
as effective dispersants for the asbestos: ethylene 
glycol, mono-, di-, and tri-ethanolamine, glycerol, 
polyethylene glycol, polypropylene glycol, undecylenic 
acid, lauric 'diethanolamide, mineral oil, and linoleic 
acid. This method of producing UAF offers the fol-
lowing advantages: 
(1) The colloidal asbestos fibrils can be readily 
recovered free of adsorbed contaminants by 
evaporation of volatile dispersing media. 
(2) Selected dispersing liquids can serve as solvents 
for a matrix resin, thus allowing intimate mixing 
of the resin with UAF in the stage before the 
solvent is removed to produce an asbestos-
reinforced resin. 
(3) Certain dispersin liquids can serve either as 
precursors of a matrix resin or as one of the 
components of a matrix resin, thus obviating 
the need to evaporate a solvent.
This method of producing colloidal asbestos dis-
persions in organic media should be particularly use-
ful in the preparation of asbestos-reinforced plastics 
and elastomers; special lubricants; solvent-carried 
paints, varnishes, and adhesives; and in paper, film, 
and foil coatings where the fibrils must be free of 
surface contaminants. 
Note: 
The following documentation may be obtained 
from:
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.65) 
References: 
NASA-CR-893 (N67-36014), Colloidal 
Asbestos Fibrils As Reinforcements for 
Polymeric Structures 
NASA-CR-77225 (N66-34670), The Rein-
forcement of Polymeric Structures by 
Asbestos Fibrils 
Patent status: 
No patent action is contemplated by NASA. 
Source: A. M. Schwartz and C. A. Rader of 
Harris Research Laboratories, Inc. 
under contract to 
NASA Headquarters 
(HQN-09954 and -09955) 
Brief 70-10020	 Category 03


Reinforcement of polymeric structures with asbestos fibrils

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