The very best landfill liners today are made of a tough plastic film
called high density polyethylene (HDPE). HDPE has only been in use in
this country for this purpose since the early 1980s, so we have little
actual experience to go on. However, landfill designers assure us that
HDPE resists attack by nearly all chemicals.
Resistance to chemical attack is important because the theory of
landfill design says that the landfill liner must maintain its
integrity for the duration of the hazard it is supposed to contain. If
the garbage in the landfill will remain toxic for thousands of years,
the landfill liner must maintain its integrity for thousands of years;
if the liner fails before the hazard has gone away, the failed liner
will allow the hazard to escape, and we will have simply passed today's
problem onto our children and grandchildren.
There are other plastic liners besides HDPE in use today, and we will
discuss their characteristics in future issues of RHWN. But HDPE is the
liner of choice, if you can afford it, so let's start there.
When we looked up HDPE in a standard reference source (the KIRK-OTHMER
ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, 3rd edition), we learned that HDPE
"is not attacked by most inorganic chemicals and is insoluble in most
organic solvents at room temperature. In a study of linear
polyethylenes, only 14 of 270 chemicals and materials were rated as
capable of causing, upon prolonged exposure at room temperature,
softening, embrittlement, or a significant loss of strength." The study
cited by KIRK-OTHMER was conducted by the Phillips Petroleum Company in
Bartlesville, OK, so we phoned Phillips to learn more.
Phillips has been in the plastic business for 30 years, and they are
proud of their HDPE product. They sent us a very informative booklet
describing the chemical properties of HDPE. The booklet described the
use of HDPE for packaging. Thus the information is very relevent,
because that's what a landfill liner is: a huge plastic baggie for
packaging wastes; like a plastic bottle or drum, a landfill liner is
intended to contain wastes, to prevent them from escaping. The booklet
gave us confidence that Phillips has done its homework, but it did not
give us confidence in HDPE as a landfill liner.
According to Phillips, there are many household chemicals that will
degrade HDPE, permeating it (passing through it), making it lose its
strength, softening it, or making it become brittle and crack. If
you've ever held a thick (100 mil, or 1/10 of an inch) piece of HDPE
landfill liner in your hand, you know it's about as stiff as a linoleum
tile. If chemicals make it even stiffer and it cracks under the massive
weight of the garbage heaped above it, that's all she wrote for the
safety of the local environment.
In addition to many individual chemicals (mentioned below), Phillips
lists two major classes of chemicals that are not compatible with HDPE:
aromatic hydrocarbons, and halogenated hydrocarbons. The basic aromatic
hydrocarbon is benzene (a major component of gasoline); others are
toluene (also called methylbenzene), and the three xylenes (o-, m-and
p-xylene). Others include naphthalene (moth balls), and
pdichlorobenzene (also moth balls). These aromatic hydrocarbons
"permeate excessively and cause package deformation," says Phillips.
Another class of compounds incompatible with HDPE is halogenated
hydrocarbons. The most familiar names here are carbon tetrachloride,
chloroform, DDT, aldrin, dieldrin, lindane, 2,4-D, 2,4,5-T,
trichloroethylene, trichloroethane, perchloroethylene, and so forth.
The full list is very long and growing all the time as chemists find
new ways to attach chlorine, fluorine, bromine and iodine atoms to
carbon and hydrogen.
The Phillips booklet lists many individual household chemicals as
incompatible with HDPE.
Appendix I of the Phillips booklet lists the following chemicals under
the heading "can cause stress cracks" in HDPE:
Acids: acetic acid (1% to 10% solution); aqua regia.
Foods & food products: cider, lard, margarine, vinegar, vanilla
Household toiletries and pharmaceutical products: detergents
(standard); detergents (heavy duty); dry cleaners; hair oil; hair
shampoo; hair wave lotions; hand creams; iodine (tincture)
("embrittlement may occur after prolonged exposure"); lighter fluid;
nail polish; shaving lotion; shoe polish (liquid); shoe polish (paste);
soap; wax (liquid and paste); amyl alcohol 100%; carbon tetrachloride;
chlorobenzene ("softening and part deformation will occur"); chloroform
("softening and part deformation will occur"); cyclohexanol; ethyl
alcohol (also known as booze); methyl alcohol (a component of shellac);
Oils: castor; mineral; peppermint; vegetable; pine.
Industrial chemicals: amyl alcohol 100%; chlorobenzene; chloroform;
cyclohexanol; ethyl alcohol; methyl alcohol; propyl alcohol.
So much for stress cracks. What about common chemicals that can
permeate through HDPE? Phillips says "permeation is considered a
physical migration of a product through the container walls." Chemicals
that will permeate a plastic film will often also physically damage it.
Appendix I of the Philips booklet lists the following chemicals (giving
the permeation in parentheses):
Household toiletries and pharmaceutical products: lighter fluid
("high"); nail polish ("4% loss per year"); shoe polish (liquid)
("high"); turpentine ("8.5% loss per year").
Industrial chemicals: acetone ("3.4% loss per year"); amyl acetate ("4%
loss per year"); amyl chloride ("high"); benzene ("high"); carbon
tetrachloride ("80% loss per year"); chlorobenzene ("high; softening
and part deformation will occur"); chloroform ("high"); ethylene
chloride ("high; softening and part deformation will occur"); gasoline
("high"); toluene ("high; softening, swelling, and part deformation
will occur"); trichloroethylene ("high; softening, swelling, and part
deformation will occur").
Oils: orange ("high"); peppermint ("high"); pine ("high").
So much for chemicals that pass through HDPE, weakening it as they go.
Appendix II of the Phillips booklet lists the following chemicals as
"unsatisfactory" or causing "some attack" on HDPE at room temperature:
bromine liquid; butyl acetate; chlorine liquid; chlorosulfonic acid
100%; cyclohexanone; ethyl chloride; methyl ethyl ketone; methyl
bromide; methylene chloride 100%; nitrobenzene 100%; oleum
concentrated; petroleum ether; tetralin; tetrahydrofuran; xylene.
So long as your municipality's garbage contains none of the items
listed above (assuming the information from Phillips is complete), HDPE
will perhaps do a good job for you. However, if your garbage is free of
these items, you're probably from another planet anyway and therefore
you won't need to rely on America's best available landfill liners for
solving your resource management problems.
Get MARLEX POLYETHYLENE TIB 2 PACKAGING PROPERTIES free from: Mrs.
Frances L. Campbell, Plastics Technical Center, Plastics Division,
Phillips 66 Company, Bartlesville, OK 74004. Phone (918) 661-6600.
Additional technical information available from: Phillips 66 Company,
P.O. Box 792, Pasadena, TX 77501; phone 1-800-231-1212.
Descriptor terms: high density polyethylene; landfilling; landfill
liners; failure mechanisms; leaks; toluene; methylbenzene; carbon
tetrachloride; chloroform; ddt; aldrin; dieldrin; halogenated