United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-140 Aug. 1981
Project Summary
Securing Containerized
Hazardous Wastes by
Encapsulation with
Spray-On/Brush-On Resins
H. R. Lubowitz and R. W. Telles
Methods were investigated for
securing containerized hazardous
wastes in the field with spray-on or
brush-on resins at ambient tempera-
tures. Laboratory-scale, cylindrical
specimens of containerized sodium
chloride (which simulated soluble
salts containing heavy metals) were
fabricated 63.5 mm in diameter by
88.9 mm high (2.5 by 3.5 in.). The salt
was confined in fiberglass-reinforced,
thermosetting resin casings and then
sealed with a water-based polyurethane
to provide a tough exterior jacket that
would protect the contents from
leaching and mechanical stress.
The specimens exhibited functional
stiffness and kept their contents
stable when subject to leaching
stresses. The exterior jackets did not
fail when specimens were compressed
to about 80% of their original heights.
Under heavy compression, however,
the jackets ruptured where they were
thinnest. Several coatings were needed
to produce sufficiently thick, tough
jackets.
This report is a companion to two
other documents on the use of plastics
to encapsulate corroding hazardous
waste containers: "Securing Container-
ized Hazardous Wastes with Poly-
ethylene and Fiberglass Encapsulates"
(EPA-600/2-81-138) and "Securing
Containerized Hazardous Wastes with
Welded Polyethylene Encapsulates"
(EPA-600/2-81-139).
This Project Summary was devel-
oped by EPA's Municipal Environmen-
tal Research Laboratory, Cincinnati,
OH, to announce key findings of the
research project that is fully docu-
mented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Contaminants leaking from corroding
208-L (55-gal) drums of hazardous
wastes may harm man and his environ-
ment. This laboratory-scale, study
investigates methods for reinforcing
such containers in the field by spraying
or brushing onto their surfaces atmo-
spheric-curing, water-based resins.
This simple procedure reinforces drums
at their disposal site using commercially
available, low-cost, commonly used
equipment. The use of water-based
resins eliminates the hazards and
contamination associated with solvents,
and processing at atmospheric temper-
atures has obvious advantages.
Methods and Materials
Cylindrical specimens of containerized
sodium chloride (which simulated
soluble salts containing heavy metals)
were fabricated 63.5 mm in diameter by
88.9 mm high (2.5 by 3.5 in.). The
specimens were then encapsulated by
spraying first with fiberglass-reinforced
thermosetting resins to provide func-
tional stiffness, and then with a water-
-------
based polyurethane to provide a tough
exterior jacket that would protect the
contents from leaching and mechanical
stress.
Performance Requirements
Performance requirements for encap-
sulated specimens were to prevent
leaching of their sodium chloride con-
signments by water and to withstand
heavy compression without rupture of
their jackets. Retention of the highly
soluble sodium chloride was assumed
to indicate similar encapsulate per-
formance for soluble heavy-metal-
containing salts. We also assumed that
specimens compressed heavily without
jacket rupture would be able to with-
stand severe impact. (Although the
jacketing resin per se was expected to
withstand impact because of its rubber-
like qualities, it was subject to additional
stresses from distortion of the specimens
under compression and fragmentation
of the stiff materials.)
The coating materials were required
to spread and cure on the container
surfaces and, with further processing
(e.g., post heating), to give rise to
monolithic, tough, chemically stable
encapsulates. The encapsulates were
expected to hold the hazardous con-
signments securely when subjected to
mechanical and chemical stresses
associated with sequestering them in
disposal sites. Such stresses could
include (1) impact and compression
during transit, (2) tear and overburden
resulting from depositing and processing
at the ultimate disposal sites, (3)
disposal site leachates, and (4)corrosive
action of hazardous consignments.
Structuring encapsulates to withstand
impact and compression stresses was
particularly difficult. According to DOT
guidelines, containers geared for trans-
porting hazardous wastes must with-
stand the test of dropping on edge
without rupture. Since a 208-L (55-gal)
drum and its contents weigh about
226.8 kg (500 Ib), such a test would
inflict severe tensile and flexural
stresses on the encapsulates, thus
requiring the use of tough, flexible
materials for container fabrication.
Furthermore, encapsulates must be
composed of stiff materials to withstand
compression stresses resulting from
the stacking of heavy objects. Other
stresses were less difficult to deal with.
Pressures exerted by landfill over-
burdens were not particularly severe
when encapsulates were deposited
deeply enough for the soil to act as a
fluid. Encapsulate resistance to chemi-
cal degradation did not need to be
characterized in detail because it could
be estimated by data from resin vendors
and performance data provided in the
chemical literature. Permeability resist-
ance data were not readily available for
resins that were not mass produced,
and thus some determinations were
required.
Materials
No material was currently available
for encapsulate fabrication that could
provide impact and compression resist-
ance as well as chemical stability with
spray-on and brush-on techniques.
Metals and ceramics were obviously
ruled out. Resins, on the other hand,
gave rise to difficult problems: impact
resistance was usually gained at the
expense of stiffness, and toughness
was related to processing parameters.
Unfortunately, state-of-the-art resins
used in spray-on and brush-on applica-
tions were, as a class, weak materials.
Production of stronger materials required
the use of newly developed resins.
A literature review subsequently
disclosed a promising and novel genera-
tion of atmospheric-temperature-curing
polyurethanes free of the deficiencies of
those considered earlier. Four coating
formulations were subsequently selected
as potential candidates for jacket
studies. The coating finally chosen for
detailed studies was Neorez R-960*
cross-linked with CX-100. This coating
had strong mechanical and chemical
properties, was workable, and was
generally easy to process.
Although the water-based polyure-
thanes exhibited appropriate toughness
and flexibility to withstand impact
stresses, they did not possess the stiff-
ness required for container encapsu-
lates. Toughness and stiffness were
realized by fabrication of composite
structures that provided properties not
found in a single material. In this work,
fiberglass-reinforced epoxides were
used to provide encapsulates with
required functional stiffness. Further-
more, they could be sprayed onto
substrates using commercial techniques.
Procedures
During the encapsulation of contain-
ers, the stiff materials were first sprayed
Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use by the U.S. Environmental Protection.
Agency.
onto the container walls. Becaus
stiffness only was required, there wa
no need to realize the watertight
structures that are sought in plastics
fabricating. Sealing of the fiberglass-
treated containers would be effected by
spraying water-based polyurethane
resin onto the stiff materials. The
essential features of the spray-up
procedure and the encapsulate are
illustrated in Figure 1.
In addition to sealing the encapsu-
lates, the polyurethane resin was
expected to provide them with impact
resistance. (Structuring stiff materials
per se to withstand severe impact
stresses, without fracture would be
prohibitive in terms of material and
processing costs. Consequently, the
stiff materials would provide functional
stiffness and impact resistance only
under normal handling conditions; but
under severe stresses, they were
expected to fracture.) The hazardous
contents were expected to remain
secure as a result of the presence of the
tough sealing resin. Even with fracture,
the encapsulates were expected to
exhibit sufficient residual stiffness to
allow manipulation to and deposition
within a direct disposal site.
Results and Discussion
The criteria for estimating suitable
performance of encapsulates under
field conditions was the satisfactory
performance of the test specimens
under heavy compression. The sealing
resin had to exhibit the property of
withstanding the stresses without
rupture stemming from the fracture of
the stiff materials. Such performance
would indicate that the sealing resin
would secure the hazardous consign-
ments in the event that the encapsulates
were subjected to severe impact
stresses.
The specimens exhibited functional
stiffness and kept their contents stable
when subjected to leaching stresses.
The exterior jackets did not fail when
specimens were compressed to about
80% of their original heights. Under
heavy compression, however, the outer
polyurethane jackets ruptured where
they were thinnest.
The results of this work led to the
realization of several attractive features
and disadvantages of the process.
The principal advantages of the
process are:
No need exists for applied thermal
energy, as with thermoplastics and
thermosets.
-------
State-of-the-art spray-on equip-
ment may be used for resin appli-
cation.
The process offers a method for
managing distorted 208-L (55-gal)
drums. This advantage may ad-
versely affect subsequent handling
techniques, however.
No need exists for heavy-duty or
high-tolerance equipment.
The technique is generally appli-
cable without tailoring the process
to waste type (wet or dry).
The main disadvantages of the
process are:
Use of a special, higher-priced,
marginally characterized resin is
required.
Special safety equipment must be
used by personnel during formula-
tion/fabrication because of the
toxicity of the cross-linker.
Formation of thick coatings requires
multiple applications.
Coatings require longer curing
times at lower atmospheric tem-
peratures.
Of the disadvantages listed, the
overriding limitation affecting feasibility
is the inability to achieve sufficiently
thick, tough coatings with one or a few
applications. A minimal number of
applications is desirable to reduce man-
ho\jr requirements.
Mitigation of this .deficiency would
require modification of the advanced
resin formulation, which would inher-
ently define several new areas of
concern:
Identification of one or more
additives (possibly thixotropic) that
would enhance thicker coatings
and not hinder curing.
Identification of a compatible
pigmentation system (thixotropic
agent and pigment might be a
single component).
Demonstration that the altered
formulation is manageable with
state-of-the-art spray-on equip-
ment.
Demonstration that the altered
formulation does not degrade
coating properties or encapsulate
performance.
Conclusions
Encapsulates of containers holding
hazardous wastes can be fabricated
under atmospheric conditions using the
resins tested here and of brushing or
spraying materials onto the surfaces of
containers. The watertight encapsulate
Fiberglass
Casing
Resin
Jacket
Filler
Figure 1.
55 Gallon Drum
Management of containerized wastes by spray-up with organic resins.
(Note: Fiberglass and resin thicknesses not to scale.)
materials studied here are considered to
be unique because they are stiff but
retain their watertight properties when
distorted by compression. Generally,
only metals and thermoplastics yield
such properties. But metals are prone to
corrosion, and thermoplastics lack
comparable stiffness unless thickly
applied.
The use of fiberglass-reinforced
resins (epoxides) and water-based
polyurethane resins gives rise to room-
temperature-cured encapsulates that
keep their water-soluble salt consign-
ments stable under aqueous leaching
conditions. The application of the
polyurethanes to the surfaces of fiber-
glass/epoxide substrates effectively
seals porosity existing in the substrates.
Consequently, watertight, double-
walled composites are obtained, with
the outer wall acting as a jacket for the
encapsulates.
The polyurethane resins that exhibit
best performance are those containing
chemical cross-linking agents. The
curing of the polyurethane resins on
surfaces of preformed glass/epoxides
yield double-wall composites showing
excellent resistance to hydrolysis.
Thereby the sealing effect of the
polyurethane jackets is assured. Since
the polyurethane resin per se was not
expected to transpire salt, this work
showed that the high retention per-
formance of encapsulates with double-
walled composites is because of wetting
and sealing by water-based polyure-
thane resin in fiberglass/epoxide sub-
strates and the forming of hydrolytically
stable bonds between the applied resins
and the substrates.
The fiberglass/epoxide substrates
give expected stiffness to encapsulates.
With compression of the encapsulates,
the substrates yield, as expected, by
fracture. The encapsulate load-bearing
properties under heavy compression
were because of residual strengths of
the fractured substrates and the exis-
tence of the polyurethane jackets.
The jackets do not show satisfactory
performance under heavy encapsulate
compression (i.e., greater than 20%).
Rupture of the jackets was the observed
mode of jacket failure. To be sure that
full-scale encapsulates would satisfy
DOT guidelines concerning transporta-
tion of containerized hazardous wastes,
it was assumed that the jackets should
remain functional under very heavy (at
least 80%) encapsulate compression.
Thus the present development of this
work does not assure realization of full-
it U.S GOVERNMENT PRINTING OFFICE: «61 -757-012/7289
-------
scale encapsulates that would comply
with DOT regulations.
This study does, however, provide
means for securing the contents of
hazardous-waste-containing, corroding
containers at the site of their disposition.
Containers threatening to lose their
contents can be reinforced on the spot
by simple means. The entire container
or the greatly corroded areas can be
effectively treated by applying fiber-
glass/epoxide to the surface (glass mat
applied to container, then wetted by
epoxide spray would be desirable)
followed by application of water-based
polyurethane resin.
The conclusions reached by this study
are as follows:
Encapsulate fabrication is readily
realized under atmospheric condi-
tions using simple means (e.g.,
spraying and/or brushing on resins
and using fiberglass, possibly
either as mat or as sprayable,
chopped fibers).
High performance retention of
heavy metal salts can be expected
based on results of water leaching
of encapsulates holding sodium
chloride as a waste simulant.
Thicker jackets must be realized for
assucing compliance with DOT
guidelines.
Recommendations
Advancement of this work requires
bench-scale development to achieve
thick coatings with one or two applica-
tions at most. This additional work
would be necessary to fabricate encap-
sulates of 208-L (55-gal) drums of
hazardous wastes that can meet DOT
guidelines for containers used to trans-
port hazardous materials.
The present status of the work
permits ready refinement for application
to the sealing of 208-L (55-gal) drums of
hazardous materials that have under-
gone appreciable corrosion. This opera-
tion would secure the contaminants
until provision is made for their final
disposition.
The full report was submitted in
fulfillment of Contract No. 68-03-2483
by the Environmental Protection Poly-
mers, Inc., under sponsorship of the
U.S. Environmental Protection Agency.
H. R, Lubowitz and R. W. Telles are with Environmental Protection Polymers,
Inc., Hawthorne. CA 90250.
Carlton C. Wiles is the EPA Project Officer (see below).
The complete report, entitled "Securing Containerized Hazardous Wastes by
Encapsulation with Spray-On/'Brush-On Resins,"(Order No. PB 81-231 284;
Cost: $8.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
RETURN POSTAGE GUARANTEED
------- |