United States
                      Environmental Protection
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
                      Research and Development
EPA/600/SR-93/162    October 1993
&EPA       Project  Summary

                      Weatherability  of Enhanced
                      Degradable  Plastics
                      Anthony L. Andrady
                        The performance and the associated
                      variability of several selected enhanced
                      degradable plastic (EDP) materials was
                      assessed under a variety of different
                      exposure conditions. Several commer-
                      cially available materials, including both
                      photodegradable and biodeteriorable
                      plastics, were exposed to direct sun-
                      light, soil burial, and marine and fresh-
                      water exposure. Laboratory exposure
                      consisted of accelerated weathering by
                      Xenon Arc Weather- Ometer* and labo-
                      ratory-accelerated soil burial.
                        Results of this study showed  the
                      elongation at break and the energy to
                      break to be the tests  most sensitive to
                      weathering-induced changes.
                        This Project Summary was developed
                      by EPA's Risk Reduction Engineering
                      Laboratory, Cincinnati, OH, to announce
                      key findings of the  research  project
                      that is fully documented in a separate
                      report of the same  title (see  Project
                      Report ordering information at back).

                        The use of plastics in  packaging  and
                      other consumer  applications has led to a
                      growing fraction of post-consumer plastic
                      waste in the municipal solid waste stream.
                      The United States presently generates over
                      195 mil tons  of municipal  solid waste an-
                      nually; of this, about 8% by weight is plas-
                       Mention of trade names or commercial products does
                       not constitute endorsement or recommendation for
  Recently, scientific data have been gath-
ered to suggest that plastic waste may be
hazardous to wildlife, especially marine life,
e.g., sea lions and fur seals have been
entangled in  plastic debris and  marine
turtles and birds have eaten plastic litter.
  With EDPs, the intention is to accelerate
the breakdown of plastic material by chemi-
cally modifying the polymer, synthesizing
new environmentally degradable thermo-
plastics, and  incorporating additives into
commodity plastic materials to  achieve
faster breakdown.
  The goals of this study were to:
    study  the performance  and the
    associated variability of several  EDP
    materials under a variety of different
    geographic  exposure conditions,
    including air,  sea, and soil, as well as
    laboratory exposure conditions,
    better understand the underlying factors
    governing enhanced degradability in
    EDP systems including the effect of
    enhanced degradation on the water
    vapor and gas permeability of selected
    EDPs; also study activation spectra of
    the enhanced photodegradable plastics
    to identify the spectral regions most
    effective in bringing about light-induced
    study the major  products formed
    during enhanced degradation of EDP
    materials and assess  the toxicity of
    such products, and
    study the effects on  the quality of
    recycled  products when a  small
    fraction of partially degraded  EDP
    materials are included in a recycling
                                                                          Printed on Recycled Paper

  A  representative  set of sample types
was  selected from commercially available
materials by using several criteria such as
type  of resin and potential use of the ma-
     ethylene/carbon  monoxide (1%)
    copolymer (6P) selected because of
    its use as a beverage ring  holder in
    six-pack packaging,
    polystyrene blended with copolymer
    low-density polyethylene containing
    metal prooxidant compounds (PG) and
    low density  polyethylene/6% starch
    blends with  and  without metal
    prooxidant compounds (ADM) used in
    agricultural mulch films.
     linear,  low-density polyethylene/
    polycaprolactone (20%) blends (PCL),
    poly (hydroxybutyrate valeirate) film
    (BP) (limited testing).
  The materials were tested in sheet or
film form. Materials of low-density polyeth-
ylene as close in formulation as  possible
to the tested materials were used for con-
  The different types of exposure included:
    outdoor exposure at five locations
    direct weathering
    soil burial
    floating  and sediment exposure in marine
    and in fresh-water environments
    field soil burial
    laboratory  accelerated  weathering
   laboratory-accelerated burial in different
  In  general,  photodegradable samples
were exposed to direct weathering and to
marine  and freshwater  floating  environ-
ments, and biodegradable samples were
exposed to  marine sediment and soil burial.
Other testing included tests for tensile prop-
erties, yellowness index, tumbling friability,
gel  permeation chromatography for mo-
lecular weight measurements, water vapor
transmission rate, thermogravimetry to rap-
idly determine starch content of polyethyl-
ene/starch  blends,  gas transport  proper-
ties,  and toxicity.
  Basic methodologies  proposed in the
Quality Assurance  Project  Plan were
closely followed.
  Detailed findings of all tests are given in
the full report.

Results and Conclusions
  The study of the possible toxicity of deg-
radation products of the EDPs was limited
to selecting a toxicity screening test and to
determining if the leachate showed marked
toxicity. Data from  the modified standard
tests did not show  toxicity  at realistic lev-
els of leachate concentration.
  A limited study was done of the effect of
including a small fraction of partially de-
graded EDP in the composition of a  recy-
cling stream. The exposed degradable plas-
tics could not be tested before  entering
the stream because the films were too
brittle and thin to be tested. When some
unexposed films were used, both the
strength and flexibility of the extruded film
were enhanced by low concentrations of
degradable material.
  The rate of photodegradation of six-pack
ring material (6P) was not affected signifi-
cantly by temperature (65C to 85C), but
the degradation of both PG  and ADM ma-
terials was temperature dependent at the
same temperatures.
  A rapid thermogravimetric method to de-
termine  starch content  of a polyethylene/
starch blend material was developed and
found suitable to study partially degraded
films and to determine residual starch con-
tent in starch/polymer systems.
  The activation spectra for loss in tensile
elongation at  break  (the most  sensitive
tensile property to degradation) was  stud-
ied for certain materials. The region of the
sunlight  spectrum most likely to cause deg-
radation was found to be <340nm.
  In studying the effect of enhanced deg-
radation on gas permeability in PG and 6P
materials, where the photodegradation oc-
curred at an accelerated rate, carbon  diox-
ide transport rates changed  markedly with
duration of exposure. In 250  hr of Weather-
Ometer  exposure, 6P sample permeability
decreased 40% and PG sample perme-
ability increased about  275%. This is ex-
plained by increased crosslinking and gen-
eration of sol material in the PG material
during oxidation and/or crystallinity of the
6P material during oxidation.
  Water vapor transmission rate was af-
fected by enhanced photooxidative degra-
dation. A 10-day weathered sample of ADM
increased its water vapor transmission rate
30%. The increased rate for PG  samples
was measured as a function of time.  Forty
days of laboratory exposure to aerobic soil
did not,  however, change the water vapor
transmission rate of PCL film.
  When enhanced photodegradable  plas-
tics were exposed at outdoor locations:
   the  tensile test parameters  most
    sensitive to weathering  changes were
    elongation at break and  energy to
   the  rate  of breakdown markedly
    increased  as indicated  by loss in
    extensibility,  with the  ratio  between
    enhanced  degradable and control
    materials being called the "enhancement
   the geographic location influenced the
    photodegradability, with different
    degradation rates for different types
    of EDPs at the different sites;
   a moderate  correlation existed
    between loss of extensibility  and the
    amount of light received;
   the yellowness index increased with
    exposure;  and
   nearly all materials degraded faster in
    the Weather-Ometer studies but not
    at the same rates.
  When enhanced photodegradable plas-
tics were  exposed to marine  and fresh
   the loss of  extensibility was lower for
    the floating samples than  for  the
    terrestrial exposure (possibly because
    of lower temperatures and shielding
    from  light by  foulants), with  the
    breakdown of  the marine  control
    samples being,  in  some  instances,
    barely measurable;
   in Miami,  FL the degradation rates
    and enhancement factors were faster
    than they were in Seattle, WA;
   in  Miami, the breakdown  rate at  sea
    was 2-1/2 times that for land exposure
    of enhanced degradable polystyrene
    foam materials and, for the controls,
    it was about the same;
   BP samples  under sea sediment
    degraded at a rate more than 30 times
    that of the film exposed on land, and
    the fresh-water sediment degradation
    rate was about 85% of  that at sea;
   after 21  wk of marine sediment and 8
    wk of fresh-water sediment exposure,
    PCL  samples lost 50% of their
  When the EDP materials designed for
biologically mediated breakdown were ex-
posed outdoors under aerobic soil burial
conditions, the  time was too short to ob-
serve any significant  disintegration of the
PCL and ADM  materials, but under similar
conditions, BP  samples  degraded rapidly
and  were embrittled  by 29 days.  When
these materials were  exposed to  labora-
tory-accelerated soil burial, there was no
marked deterioration during the 10 wk ob-
servation time.
  Data are  needed from additional land
and marine locations and from exposures
at different seasons of the year to com-
plete this documentation of photodegrad-
able plastics. Longer observation periods
are needed  to establish limits of the per-
formance   of   biodegradable   and
biodeteriorable films, especially  the poly-

ethylene/starch  system.  Further  toxicity
studies are needed, as is a full-scale recy-
cling study that involves including  small
amounts of degraded post-consumer EDPs
in a recycling stream.
  The  full report was  submitted in  fulfill-
ment of Contract No. 68-02-4544 by Re-
search Triangle  Institute under the spon-
sorship of the U.S. Environmental Protec-
tion Agency.
                                                                      &U.S. GOVERNMENT PRINTING OFFICE: 1993 - 7SO-07I/8009S

Anthony L.  Andrady is  with Research  Triangle Institute,  Research Triangle
   Park, NC 27709.
Lynnann Hitchens is the EPA Project Officer (see  below).
The complete report, entitled "Weatherability of Enhanced Degradable Plastics"
   (Order No. PB93-229 789/AS; Cost: $44.50, 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:
        Risk Reduction  Engineering Laboratory
        U.S. Environmental Protection Agency
        Cincinnati, Ohio 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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