&EPA
United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-139 Aug. 1981
Project Summary
Securing Containerized
Hazardous Wastes with
Welded Polyethylene
Encapsulates
H. R. Lubowitz, R. W. Telles, S. L linger, and R. R. Phillips
Full-scale encapsulation of 208-L
(55-gal) drums was studied as a
means for managing corroding con-
tainers of hazardous wastes in the
field and rendering them suitable for
transport and safe deposit within a
final disposal site such as a landfill.
Polyethylene (PE) receivers with 6.35-
mm-thick (1/4 in.) walls and wide
mouths were used for fabricating
encapsulates. After insertion of drums.
the receivers were weld-sealed with
6.35-mm (1 /4-in.) sheet PE. A proto-
type apparatus was designed and
constructed to fabricate the PE en-
capsulates by welding. The apparatus,
which was light weight and trans-
portable, was analogous to that used
in the commercial butt welding of PE
pipe. Precision alignment of pieces
and high regularity of surfaces to be
joined were found to be unnecessary.
Furthermore, only minimal mechanical
pressures were needed to form the
welded joints. Results indicated plas-
tics welding to be an effective method
for encapsulating corroding drums of
hazardous wastes.
This report is a companion to two
other documents investigating the use
of plastics for the encapsulation of
corroding containers of hazardous
wastes: "Securing Containerized
Hazardous Wastes with Polyethylene
and Fiberglass Encapsulates" (EPA-
600/2-81-138) and "Securing Con-
tainerized Hazardous Wastes by En-
capsulation with Spray-on/Brush-on
Resins" (EPA-600/2-81-140).
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
Corroding containers of hazardous
wastes exist throughout the United
States, constituting a hazard to man and
his environment. Clearing these loca-
tions involves transporting the wastes
in ensembles that conform to Depart-
ment of Transportation (DOT) regulations
governing transportation of container-
ized hazardous wastes. Should the
waste be placed in a final disposal site,
the containers must be constituted to
resist degradation by the physical and
chemical stresses of the disposal
environment.
This report investigates full-scale
encapsulation of 208-L (55-gal) drums
with welded polyethylene (PE) as a
means for managing corroding con-
tainers of hazardous wastes in the field
and rendering them suitable for trans-
port and safe deposit within a final
disposal site such as a landfill. Materials
are described along with the design and
-------
construction of the encapsulate welding
apparatus, the technique used for
encapsulate fabrication, and an evalua-
tion of encapsulates. A preliminary
economic analysis of the encapsulation
process is also presented.
The work performed here continues
earlier work carried out for the U.S.
Environmental Protection Agency (EPA)
to develop encapsulates to secure
corroding, 208-L (55-gal) steel drums
holding hazardous wastes. This study
aimed to provide another option for
encapsulating drums in addition to the
one developed previously.1 The estab-
lishment of two viable options broadened
the base for studying the feasibility of a
commercial operation.
The process options were restricted to
those that would produce seam-free
containers for use as encapsulates. This
approach distinguished the work from
current developments in container
technology and yielded encapsulates
with advanced performance qualities.
The costs for seamed and unseamed
containers were estimated to be compa-
rable. The similar costs were plausible
because the resins used were mass
produced and of the same type as those
used in commercial containers; further-
more, the encapsulate fabrication
apparatus was simple enough to coun-
terbalance production advantages
associated with expensive commercial
apparatuses.
Earlier work had developed laboratory-
scale encapsulates characterized by
6.35-mm (1/4-in.) PE outer walls
reinforced by fiberglass casings. These
encapsulates featured homogeneous,
seam-free outer walls and high com-
pressive strengths. Encapsulates of
drums, therefore, would not be en-
cumbered by ancillary closure devices
associated with conventional contain-
ers such as lids, threads, gaskets,
hoops, etc.
In this study, the container walls were
not reinforced. The resulting encapsu-
lates, though seam-free, exhibited less
mechanical strength than the fiberglass-
reinforced models; but they were
expected to be sufficiently strong for
securing drums. (Additional strength, if
required, was obtainable by placing
filler material such as foam in the free
space between the walls of the inserted
drums and the containers.)
Use of unreinforced polyethylene
containers permitted greater utilization
of commercially available materials and
techniques, and it allowed a more direct
application of current technology to
securing 208-L (55-gal) drums in the
field. Such advantages counterbalanced
the probable losses of mechanical
performance.
Though commercial plastic containers
were not available for securing 208-L
(55-gal) steel drums, the rotomolding
industry did fabricate PE receivers large
enough to accommodate these drums.
Such receivers were successfully used
as free-standing tanks for holding
corrosive chemicals and for carrying out
chemical reactions. The PE resins used
in their fabrication were mass produced
and were well characterized by their
producers. Rotomolded PE receivers
were, according to our estimate, the
commercially available materials best
suited for securing drums. Extruded PE
flat stock was selected for sealing the
receivers.
Plastic welding was the commercial
technique selected for sealing the
receivers. Welding is a widely used,
high performance technique for joining
materials, both metals and plastics. Its
structural and sealant performance
characteristics are well known, and its
wide acceptance attests to its merit. In
the field of plastics, welding has been
used successfully to join PE pipe, and
commercial apparatuses are available
for this purpose. Unfortunately, the
equipment was not suitable for fabrica-
tion of PE encapsulates. To utilize the
proven advantages that PE welding
offers to encapsulate fabrication, a
novel plastic-welding apparatus was
designed and built to seal PE covers to
PE receivers.
Materials and Equipment
Particular emphasis was placed on
using PE receivers fabricated by com-
mercial rotomolding. Equipment was
designed and constructed to seal the
receivers with PE flat stock by plastics
welding. PE pipe welding art was
applied to determining equipment
requirements and selecting processing
conditions.
Materials
Polyolefins, particularly PE (but not
excluding high-impact polypropylene
and polybutylene), were selected for
fabricating encapsulates because such
materials were well characterized,
mass-produced and low in cost. They
also provided a unique combination of
properties: excellent chemical stability,
flexibility, and mechanical toughness.
Earlier laboratory studies showed PE*
encapsulates to have high retention of
heavy metal contaminants when sub-
jected to aggressive leaching solutions.2
Commercial PE containers were not
available in the proper size and con-
struction for encapsulating 208-L (55-
gal) metal drums. The largest plastic
vessels that may be transported in
compliance with DOT regulations were
208-L (55-gal) drums fitted with bung
holes. Wide-mouth drums did not
qualify, and other PE vessels were not
fitted with the means to effect secure
closure. They were used mainly as
liners of steel and fiberglass-reinforced
vessels, or as free-standing receivers
and holding tanks. Their value was
particularly noteworthy in process and
storage operations involving corrosive
chemicals. Plastics fabricators displayed
great interest in rotomolding large, free-
standing PE tanks to replace plastic-
coated or glass-lined steel tanks,
stainless steel tanks, and fiberglass-
reinforced plastic tanks. These PE tanks
were selected as receivers for 208-L
(55-gal) drums.
After commercial container art and
the mechanics of encapsulate fabrica-
tion were considered, rotomolded,!
wide-mouth PE receivers and PE flat
sheet were selected for making en-
capsulates. Though on-the-shelf re-
ceivers were longer than desired, they
were capable of being readily con-
structed to specifications when needed
in significant numbers.
The height and diameter of receptacles
readily accommodated the 208-L (55-
gal) drums. Any free space between
receptacle and inserted drum can be
filled, if required, with low-cost fillers
such as foam to minimize drum move-
ment during handling. Furthermore, the
free space allows encapsulation of
distorted drums.
Equipment
A new plastic-welding apparatus was
designed and built to fabricate PE
encapsulates (Figure 1). This apparatus
was capable of welding flat PE covers
onto the rim of wide-mouth receivers.
The welding apparatus for encapsulate
fabrication was viewed as a container
heat-sealing device comparable with
commercially used PE pipe welding
devices. This encapsulation apparatus
was designed as a prototype experi-
mental device that allowed alteration o1
various parameters affecting the prop
erties of the welded joint (i.e., heatinj
-------
and cooling times, temperature, welding
pressure, etc.). As with commercially
used pipe-welding apparatuses, the
prototype was designed to be easily
transported and sturdy so that it could
be used in the field encapsulation of
drums.
Procedure
PE encapsulates were fabricated by
plastics welding procedures. A 208-L
(55-gal) drum was first inserted into a
wide-mouth PE receiver with a re-
leasable wire harness. The receiver was
then positioned under the H-frame of
the apparatus, and the cover fashioned
from PE flatstock was clamped to the
platen. The cover was then welded to
the receiver by means of heat and
pressure. After the weld was cooled
under pressure, the clamps were
removed from the cover and the platen
was raised to remove the encapsulated
drum.
Results
Welded encapsulates were found to
be watertight overpacks for 208-L (55-
gal) drums. They were expected to
preclude effectively the contact of
hazardous waste consignments with
aggressive environmental waters even
though the drums within might continue
to corrode. Performance estimates were
obtained by inspection and testing of the
welded joints of PE covers and receivers.
Nature of Welded Joints
To investigate the nature of the
welded bond, the top portion of a welded
plastic encapsulate was removed. Close
visual inspection of the weld showed
the formation of a continuous, solid,
resinous bead surrounding the welded
interface. To investigate the water-
tightness of the welded bond, the
specimen was charged with water
containing a high-visibility dye de-
tectable at 1 ppm. Over a period of 4
months, no leakage was observed.
Several PE receiver-cover welds were
inspected by optical microscopy to
determine -the quality of the welded
bonds. The optical micrographs showed
that the welds were continuous, void-
free structures that should exhibit the
high strength properties expected of
high-density PE.
To investigate further the microstruc-
tural characteristics of the weld, a thin
cross section was mounted in a trans-
parent medium, and transmission
optical micrographs were obtained.
Cylinder
Figure 1. Apparatus for encapsulating 208-liter (55-gal) drums holding hazardous
wastes.
These micrographs showed the welds to
be continuous, void-free regions in
which good wet out and mixing of
receiver-cover materials occurred.
Strength of Welded Joints
The mechanical performance of en-
capsulates was characterized by noting
the behavior of welded specimens in
tension. These tests snowed that
encapsulate welded joints are capable
of withstanding high mechanical loads
and will undergo appreciable elongation
before rupture.
Preliminary Cost Estimates
Costs associated with the process
were investigated to compare the plas-
tic welding encapsulation process with
other hazardous waste management
options. Major costs were due to
consumable materials (i.e., PE flat stock
and receivers), which accounted for
some $4.8 million per year to encapsu-
late 80,000 drums. Labor and capital
equipment costs were negligible by
comparison—$228,000 and $45,000
per year, respectively. Other costs such
as utilities were also estimated to be
minor, even when including the con-
tingency factors.
Conclusions
Full-scale encapsulation of 208-L
(55-gal) drums can be carried out by
inserting drums into wide-mouth poly-
ethylene (PE) receivers with 6.35-mm-
thick (1 /4 in.) walls and sealing them by
welding with PE flat sheet 6.35-mm-
thick (1 /4 in.). Characterizations of the
> US. GOVERNMENT PHNTwa OFFICE 1M1 -757-OU/7290
-------
welded joints indicate that the encapsu-
lates will perform satisfactorily (that is,
they will comply with DOT regulations
concerning the transport of containerized
hazardous wastes and their long-term,
safe deposit in a landfill).
The apparatus designed and used in
this work for making prototype encapsu-
lates was simple compared with com-
mercial plastics fabricating devices, and
it was also readily transportable. An
apparatus for use in the field need not
be more complex than the one used
here for making encapsulates. Improve-
ments such as semiautomating can be
accomplished at moderate costs.
Important features of the apparatus
were its use of a flat ring heater and PE
flat stock. These items allowed sealing
of PE receivers with flat stock without
the need for precise alignment. Further-
more, the surfaces to be joined did not
need to be smooth. These features were
expected to facilitate management of
drums.
Compatibility of PE encapsulates and
their contents can be determined from
data supplied by vendors of PE resin.
Extensive material compatibility data
are available for PE, a fact that contrib-
utes greatly to the usefulness of this
material in waste management. These
data should be examined when selecting
drums for encapsulation, but it is
unlikely that materials deleterious to PE
would remain with corroding drums
after long-term exposure to the atmo-
sphere.
The cost of the encapsulation process
was mainly attributable to the cost of
receivers and flat stock. Equipment and
labor costs were negligible. Cost reduc-
tions will thus depend on making less
expensive receivers and flat stock.
DuPont has indicated that it will receive
unusable 208-L (55-gal) drums, pulverize
them, and sell the powder for about one-
third the price of commercial PE. This
material in turn would be usable for
making receivers. Flat stock used for
making ice skating rinks (a popular,
energy-saving alternative to conven-
tionally maintained ice) must be replaced
periodically because of scarring, but it is
still usable for weld-sealing receivers.
Recommendations
More intensive investigation of the
formation and nature of the welded joint
between PE receivers and PE sheet
stock should be carried out. This
investigation should follow the guide-
lines presented in the art of PE pipe butt
welding. The applied stresses would be
appreciably less severe on the encapsu-
late joints than the pipe joints, thereby
lessening the performance requirements
of serviceable joints. This advantage is
due mainly to the absence of dynamic
and cyclical mechanical stresses on
encapsulates.
Investigations are needed both to
determine how to produce high-per-
formance welded joints and to maximize^
welding apparatus performance in the
field. Various equipment and labor
scenarios should be examined for
making drum-populated areas safe at a
reasonable cost.
The full report was submitted in
fulfillment of Contract No. 68-03-2483
by the Environmental Protection
Polymers, Inc., under sponsorship of the
U.S. Environmental Protection Agency.
References
1. Lubowitz, H.R., and R.W. Telles.
Study of Encapsulate Formation with
Polyethylene Resin and Fiberglass
for Use in Stabilizing Containerized
Hazardous Wastes. In: Fortieth
Monthly Report under EPA Contract
No. 68-03-2483, draft of final report,
U.S. Environmental Protection
Agency, Cincinnati, OH, May 1980.
2. Lubowitz, H.R., et al. Development of
a Polymeric Cementing and Encap-
sulating Process for Managing
Hazardous Wastes. EPA-600/2-77-
045, U.S. Environmental Protection
Agency, Cincinnati, OH, 1977.
H. R. Lubowitz, R. W. Telles, S. L Linger, and R. R. Phillips are with Environ-
mental Protection Polymers, Inc., Hawthorne, CA 90250.
Carlton C. Wiles is the EPA Project Officer (see below).
The complete report, entitled "Securing Containerized Hazardous Wastes with
Welded Polyethylene Encapsulates," (Order No. PB 81-231 292; Cost: $9.50,
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
------- |