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Asbestos-based plastic product molding compounds & mold release agents: this article describes the molding compounds & release agents used to produce asbestos-based or asbestos filled / reinforced plastic or molded products. This articles series about the manufacture & use of asbestos-containing products includes detailed information on the production methods, asbestos content, and the identity and use of asbestos-containing materials.
This article series about asbestos plastics & molded materials describes the history, manufacturing process & uses of asbestos plastics and molded materials.
Properties of Molding Compounds Containing Asbestos
The Military Specification MIL-M-14, "Molding Plastics
and Molded Plastic Parts, Thermosetting," lists twenty
types along with twelve types being mineral filled (asbestos).
This specification is considered one of the most
important and useful specifications for both military and
This specification lists requirements
that can be met by more than just one or two compounds
so that limited procurement does not exist. This
situation results in listing requirements which are lower
than some of the commercially available types.
The specification lists requirements on mineral filled phenolics,
melamine, alkyd, diallylphthalate, and silicone resins.
Table 9.8 lists some of the specification requirements.
TABLE 9.8. PROPERTY VALUES FOR BATCH-ACCEPTANCE TESTS OF
DIALLYLPUTHALATE, SILICONE, AND ALIYD RESIN
MOLDING COMPOUNDS ( MIL-M-14) [click to enlarge]
Other types of compounds include asbestos-tetrafluoroethylene
resins. Such combinations improve mechanical
properties of the base resin and permit compositions based
on the asbestos content to be tailored to such a wide variety
of chemical, mechanical, and electrical applications as resistance
to deformation under load, resistance to wear,
stiffness, thermal conductivity, compressive strength and
Originally, when molding compounds were manufactured
using phenolic resin as the basic component, expensive procedures
were use The ingredients were mixed with an
alcoholic resol solution and were thoroughly impregnated in
agitators. After this operation the solvents were evaporated
and the usual procedure of grinding the mixture on ball
The general procedure presently being used is to take the
phenol resin and grind it with other ingredients. The mixtures
can also be kneaded on heated rolls. For some mixtures,
premastication in a Banbury mixer is required prior
to the heated roll operation. During the roll operation, the
resin melts and thoroughly impregnates the fillers and other
After thorough mixing of ingredients has been
accomplished, the homogeneous sheet is ground in a mill.
In the case of novolacs, hexamethylene is added during
the rolling operation. When the hexamethylene is added a
quick reaction occurs where ammonia is liberated from the
hexa and acts as a catalyst. Immediately when this reaction
occurs, the mixture is removed from the rolls.
Various automatic techniques are used for mixing and
preparing phenolic molding compounds. The usual technique
is to take the rolled sheet and automatically convey it by
means of a conveyor belt to a grinder or a mixing screw.
When difficulty exists in obtaining proper treatment of
fiber fillers or other types of fillers, it is sometimes required that the fillers be impregnated with an alcohol solution of
the resin. Another method is to mix the ingredients in a
hollander to produce a pulp slurry. Generally, in this type
of operation the slurry is made into a preform. The preform
is made by vacuum suction on a sieve which produces a
shape approximately similar to the final article.
During the preparation of the molding compound, it is
important that the correct amount of condensation occurs.
If the condensation is too high, a poor flowing product is
produced, if insufficient condensation occurs, a free flowing
compound will be produced.
However, excess water of condensation
produced during the curing cycle in turn can result
in excessive sticking of the compound in the mold cavity,
producing blemished surface, poor electrical properties or
requiring the part to have a long curing cycle.
The heat conductivity of the compound also contributes
to the hardening velocity. Asbestos-filled mixtures heat up
quicker than wood flour filled mixtures, thus giving better
The time required for the compound to harden may not be
sufficient to harden the part completely, as in general, the
cure of a part takes place after the initial set. When thick
wall sections are to be cured, the heat conductivity of the
molding compound is indeed an important function. As the
thickness of the wall increases, the hardening time naturally
increases and this increase is in exponential relation to the
Premix Molding Compounds of Asbestos-Containing Plastics
These types of compounds have relatively low raw material
costs. Various types of mixes are prepared which are
dependent upon the specific applications. The end users of
these materials are largely in the automotive, electrical, electronics, home appliance, refrigeration, and industrial
equipment fields. Production runs are long.
A blend of reinforcing fibers (glass, asbestos, sisal, etc.)
fillers (asbestos, gypsum, talc, clay, etc.), polyester, or phenolic
resins, catalyst for polyester (benzoil peroxide) pigments,
and release agent (stearic acid, lecithin, silicone, etc.),
makes up a premix compound. It is important that the
blends are uniform and properly mixed. They are generally
prepared in a kneader, in a similar mixer such as the Banbury
mixer or special screw conveyors.
TABLE 9.9. HIGH STRENGTH REINFORCED ASBESTOS PREMIX COMPOUND *
[click to enlarge or clarify table contents]
During mixing of phenolic compounds, heat is required
to alter the chemical nature of the resin so that it is suitable
for molding (similar to preparing phenolic prepreg sheet).
Asbestos fibers are generally used which contribute to the
desirable properties in a premix compound. They will increase
flexural strength when they are used in the reinforcement. It is a highly absorbent material; it improves processing qualities of a mix by drying it to such a that stickiness does not occur. However, if too much
asbestos is added in certain compounds, there may tendency toward sticking and pregelation. A trend exists
toward the use of the longer fibers as reinforcements.
A typical formulation using asbestos as a reinforcement
is shown in Table 9.9 above.
Below iIn Table 9.10, asbestos is used filler.
TABLE 9.10. ASBESTOS PREMIX COMPOUND * [Click to enlarge]
* Wirsch, W. E., 'Polyester Premix Molding Compounds," Plastics Technology
* Interchemical Corporation, Bulletin 50-3
A vinyl toluene rigid type of asbestos-based resin compound for high strength and good flow properties is composed of:
A low cost asbestos plastic compound built around fibrous asbestos is composed
* Interchemical Corporation, Bulletin 50-3
Release Agents Used with Asbestos-Reinforced Plastic Products
In any molding operation, there is a tendency for the
molding compound to adhere to the mold surface. Release
agents are available in such various forms as sprays, liquids,
pastes, and powders.
This particular subject is so important
that recently the ASTM set up a new section on "Mold Release"
under Sub-Committee IX, Plastic Committee D-20.
Baking varnishes and enamels are available as mold release
agents which are generally phenolics or melamines. Fungicidals
can be incorporated in the release agent. There are
many different commercially available varnishes or enamels.
With phenolic-resin systems, glossy and attractive parts
can be made when using a methyl cellulose parting agent.
The usual procedure is to combine one pound of methyl
cellulose powder (Dow Chemical Company, Pharmaceutical
grade) with 15 lb of hot water (120 to 130°F) and to allow
the mixture to soak overnight.. After the soaking period,
approximately 10 lb of cold water is added. This mixture
an be added directly to the mold surface, or on the molding
compound if layers of laminated materials are used.
For general use with phenolic, furane and urea type resin
systems, carnauba wax directly on the mold surface is the
most desirable. Other types of compounds are Dow Corning's DC-20 or DC-200, Ram Chemical Corporation's
Garan 225 or Minnesota Mining and Manufacturing's compound
When using epoxy resin base systems, various parting
agents can be used, such as Dow Corning's DC-135A, cellophane
No. 600PT, "Teflon" sheet or sintered powder and
Garan mold release No. 225. In regard to polyester base
resin systems, du Pont's "Zelec" UN mold release agent is
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 Asbestos, its Industrial Applications, D.V. Roasato, engineering consultant, Newton MA, Reinhold Publishing Co., NY, 1959, Library of Congress Catalog No. 59-12535. We are in process of re-publishing this interesting text. Excerpts & adaptations are found in InspectApedia.com articles on asbestos history, production & visual identification in and on buildings.
 "Asbestos in Plastic Compositions", A.B. Cummins, Modern Plastics [un-dated, pre 1952]
 "Asbestos in Your Home," Spokane County Air Pollution Control Authority, Spokane WA 509-477-4727 www.scapa.org provides a one-page image, a .pdf file drawing of a house warning of some possible sources of asbestos in the home. The sources are not ranked according to actual risk of releasing hazardous levels of airborne asbestos fibers and the list is useful but incomplete.
 The US EPA provides a sample list of asbestos containing products epa.gov/earth1r6/6pd/asbestos/asbmatl.htm
 "Characterization of asbestos exposure among
automotive mechanics servicing and handling
asbestos-containing materials", Gary Scott Dotson, University of South Florida, 1 June 2006, web search 3/9/2012 original source: scholarcommons.usf.edu/cgi/viewcontent.cgi?article=3505&context=etd [copy on file as /hazmat/Automotive_Asbestos_Exposuret.pdf ].
 Asbestos Identification and Testing References
Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed
the basis for current work by asbestos identification laboratories.
Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151
Pott, F., Staub-Reinhalf Luft 38, 486-490 (1978) cited by McCrone
 Asbestos in Your Home U.S. EPA, Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
 Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on Asbestos, Its Industrial Applications, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print, text and images available at InspectAPedia.com).
 "Handling Asbestos-Containing roofing material - an update", Carl Good, NRCA Associate Executive Director, Professional Roofing, February 1992, p. 38-43
 EPA Guidance for Controlling Asbestos-Containing Materials in buildings, NIAST, National Institute on Abatement Sciences & Technology, [republishing EPA public documents] 1985 ed., Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460 Copy on file as - /hazmat/Asbestos_in_Your_Home_US_EPA.pdf - Asbestos in Your Home - U.S. EPA, Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
Basic Information about Asbestos, US EPA, web search 08/17/2010, original source: http://www.epa.gov/asbestos/pubs/help.html
"Handling Asbestos-Containing roofing material - an update", Carl Good, NRCA Associate Executive Director, Professional Roofing, February 1992, p. 38-43
EPA Guidance for Controlling Asbestos-Containing Materials in buildings, NIAST, National Institute on Abatement Sciences & Technology, [republishing EPA public documents] 1985 ed., Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
Copy on file as - /hazmat/Asbestos_in_Your_Home_US_EPA.pdf - Asbestos in Your Home - U.S. EPA, Exposure Evaluation Division, Office of Toxic Substances, Office of Pesticides and Toxic Substances, U.S. Environmental Protection Agency, Washington,D.C. 20460
[copy on file as /hazmat/Vermiculite_US_EPA.pdf/ Current Best Practices for Vermiculite Attic Insulation - May 2003, U.S. EPA
[copy on file as] /hazmat/Vermiculite_Health_Canada.pdf] Vermiculite Insulation Containing Amphibole Asbestos - September 2009, Health Canada
Managing Asbestos in Place, How to Develop and Maintain a Building Asbestos Operations and Maintenance (O&M) Program, U.S. EPA, web search 01/20/2011, original source: http://www.epa.gov/asbestos/pubs/management_in_place.html
Asbestos Strategies, Lessons Learned about Management and Use of Asbestos: Report of Findings and Recommendations on the Use and Management of Asbestos, 16 May 2003, US EPA, web search 01/20/2011, original source: http://www.epa.gov/asbestos/pubs/asbstrategiesrptgetf.pdf
prepared by the: Global Environment & Technology Foundation, 7010 Little River Turnpike, Suite. 460, Annandale VA 20003
Other US EPA Publications on asbestos: web search 01/20/2011, see http://www.epa.gov/asbestos/pubs/pubs.html
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