Note: Descriptions are shown in the official language in which they were submitted.
10~
The pr~sent invention relates to degradable poly-
mers of ~ -olefins, hereinafter referred to as poly- ~ -
ole~ins. More particularly, the present invention pertains
to novel compositions which promote the degradation of poly-
~-olefins when incorporated therein. By this invention, it
has been ~ound that compositions comprising a lower carbon
number para-alkanoylaminophenol and a higher carbon number
para-alkanoylaminophenol will promote the deterioratlon, par-
ticularly biodegradation, of ~C-olefln polymers when inti-
mately contained therein. The biodegradation of ~ -olefin
polymers containing the composition of this invention may
occur even in the absence of light, thereby enabling the
polymer to be, for example, buried as a means of disposal and
still be degraded.
The disposal of articles made with ~ -olefin poly-
mers in an ecologically safe manner has been the subject of
much concern. Generally, ~ -olefin polymers are relatively
inert to the mechanisms which cause deterioration of articles,
which may be constructed of, for instance, paper, wood, etc.,
to decomposed forms which are not harmful to ecology. Arti-
cles made from ~ -olefin polymers when disposed of may re-
main undegraded since they are resistant to assimilation by
micro-organisms or deterioration from exposure to radiation
energy, particularly ultraviolet light, even for considerable
periods of time. As society continues to employ ~ -olefin
polymers for a great number of commercial uses due to their
inexpensiveness, ease of handling and consumer appeal, their
efficient and inexpensive disposal without pollution is re-
quired and is becoming more critical as time passes.
3~0'~
Many proposals for the disposal of ~-olerin poly-
mers have been infeasible or have met with limited success.
For instance, front end separation in solid waste disposal
systems has been suggested for the removal of non-biodegrad-
able polymeric materials from refuse prior to using the re-
fuse in land fill. The polymeric materials could be used as
fuel for power plants or for recyclin~ lowever, separation
of polymeric materials entails considerable additional costs
in waste disposal as well as being an unpleasant task. Due
to the e~pense involved, most likely only large metropolitan
areas having a unified sanitary system could adopt front end
separation, if at all. Such separation would, therefore, be
unavoidable to a large segment of the population living in
smaller cities, suburbs, and in rural areas. Moreover, as
the use of ~ -olefin polymers increases for disposable wrap-
pers or containers for high sales volume consumer items, the
tendency of these items to comprise a significant portion of
litter along highways, in forests and fields, and in bodies
of water is noted. These littered items may remain intact
for even centuries, creating an essentially permanent eyesore.
An advantageous use of ~ -olefin polymer films is for agri-
culture mulches to prevent growth of weeds while promoting
growth of the plant crop by maintaining the soil warm and
moist. However, a serious economic disadvantage exists in
that the mulch films must be lifted from the field and dis-
posed of by the farmer when their use is terminated. To
avoid this type of economic hardship, degradable films are
desirable which need not require special handling for their
disposal.
b~
Investi~ations have been con~ucte~ to provide ~ _
olefin polymers which are photodegradable. Photodegradable
polymers have, however, met with little success. The expense
of ultraviolet light sensitizers or degradation catalysts
often raises the cost of the polymer composition to a level
where it cannot compete with alternative materials which are
degradable suchas paper and the like. Moreover, photode-
gradable polymers usually only degrade in the presence of
strong sunlight. Thus, any polymer which is buried or is not
exposed to sunlight will remain undeteriorated. A]so, the
amount of ultraviolet light sensitizers or degradation cata-
lysts employed with the polymer will depend upon the location
in which it is used. Hence, a polymer composition designed
for degradation at the conditions in, for instance, Florida
may take an excessive period of time to degrade in Minnesota.
Conversely, a polymer composition designed for Minnesota may
degrade before it can be used or before its use is completed
in Florida, rendering its commercial value nearly nil. The
high mobility of society may prove a photo degradation system
to be infeasible for many consumer applications.
Heretofore, acyl-p-aminophenols have been suggested
as effective oxidation inhibitors and stabilizers for solid
organic materials which usually degrade in the presence of
air and/or heat. See Young et al., United States Patent No.
2,654,723. The use of N-acyl-p-aminophenols in a composition
to stabilize most formaldehyde polymers is disclosed by Green,
et al., in United States Patent No. 3,288,885. Conventional
slip additives for the production of polyethylene and poly-
isobutylene sheeting, such as stearic acid, are disclosed in,
for instance, Koehnlein, et al., United States Patent No.
3,558,762.
In accordance with this invention a composition
containing a lower carbon atom para-alkanoylaminophenol and
a higher carbon atom para-alkanoylaminophenol has been found
to promote degradation, particularly biodegradation, of ~ -
olefin polymers. Para-alkanoylaminophenols may be illus-
trated by the formula:
~H
H -~-R
wherein, for the lower carbon atom para-alkanoylaminophenol,
hereinafter referred to as the lower para-alkanoylaminophenol,
R is an alkyl group of from 1 to about 3 carbon atoms, i.e.,
the alkanoyl group has from 2 to about 4 carbon atoms, and
for the higher carbon atom para-alkanoylaminophenol, herein-
after referred to as the higher para-alkanoylaminophenyl, R
is an alkyl group of from 2 to about 20 carbon atoms, i.e.,
the alkanoyl group has from 3 to about 21 carbon atoms,
preferably R is 2 to about 8, with the proviso that the
higher para-alkanoylaminophenol has an alkanoyl group with a
greater number of carbon atoms than that of the lower para-
alkanoylaminophenol. Each of the lower and the higher para-
alkanoylaminophenols is present as a minor amount in the
polymer composition and is in an amount sufficient that the
overall amount of alkanoylaminophenol promotes the desired
rate of degradation of the polymer. The lower alkanoylamino-
phenol may hasten the degradation of the polymer to a greater
degree than the same amount of the higher alkanoylamino-
phenol. Thus, the rate of degradation of the polymer may
primarily depend upon the amount of lower alkanoylaminophenol.
Of course, the higher alkanoylaminophenol may contribute with
h~
the lower alkanoylaminophenol to provide the enhanced degra-
dation of the polymer. The higher alkanoylaminophenol is
present in an amount sufficient to prevent unduly excessive
loss of the lower alkanoylaminophenol from the polymer, which
loss is apparently due to the lesser degree of compatibility
of the lower alkanolyaminophenol with the polymer than the
higher alkanolyaminophenol. Generally, the weight ratio of
the higher to the lower alkanoylaminophenol is from about 1:10
to 2:1, preferably about 1:3 to 1.5:1. The particular ratio
of the alkanoylaminophenols employed in a selected instance
may be dependent on several variables. For instance, the
selection of the ratio and relative molecular weights of the
alkanoylaminophenols may depend on the particular ~ -olefin
polymer into which they are incorporated to promote the de-
sired degradation. The solubility of the alkanoylaminophenols
may be yet another factor. Generally, lower alkanoylamino-
phenol will be less stable in ~ -olefin polymers than higher
alkanoylaminophenol. Thus, the higher alkanoylaminophenols
may serve as a common solvent to enhance dispersion and re-
tention of the lower alkanoylaminophenol within the polymer.Also, since the biodegradation of the ~ -olefin polymer may
be hastened to a greater degree by the lower alkanoylamino-
phenol than by the higher alkanoylaminophenol, the number of
carbon atoms in the alkanoyl group of the lower and higher
alkanoylaminophenol and by varying their relative amounts, an
additive can be designed to enhance biodegradation of a de-
sired polymer in a given general period of time. For certain
applications, it may be desirable to employ three or more
alkanoylaminophenols having varying numbers of carbon atoms
in the alkanoyl group to enhance a particular rate of degra-
--6--
'
dation or to enhance compatibility of the alkanoylaminophenolsin the polymer.
The ~ -olefin polymers which may be suitably em-
ployed in the present invention are those which are normally
solid at room temperature and are represented by the repeating
unit:
~ CH - CH2 ~
wherein R' is hydrogen or a hydrocarbon radical containing 1
to about 6 carbon atoms and preferably R~ is alkyl when it is
not hydrogen. Illustrative of such ~ -olefin polymers are
polyethylene, polypropylene, poly(butene-l), poly(pentene-l),
poly(4-methylpentene-1), poly(hexene-l), and the like. De-
composition of interpolymers as well as block copolymers of
~ -olefins with other olefins and vinyl monomers, including
vinyl monomers substituted with, for instance, halogen, e.g.,
chlorine, fluorine and bromine; aryl and aralkyl substituents
of about 5 to 8 carbon atoms, e.g., phenyl; heterocyclic sub-
stituents of about 5 to 8 carbon atoms, e.g. pyrrolidonyl,
and the like may also be promoted by the composition of this
invention. The ~ -olefins in said copolymers are preferably
present in the amount of at least about 25 or 50, preferably
at least about 80, weight percent of the total polymer.
Thus, the term ~ -olefin polymer as used herein includes
homopolymers and interpolymers and block copolymers of ~ -
olefin polymers. The polymer may be high density, for in-
stance having a specific gravity of about 0.95 for polyethyl-
ene, or low density, for instance having a specific gravity
of about 0.92 for polyethylene, and in the case of, for
instance, polypropylene, it may be isotactic or atactic.
--7--
Advantageously, the polymer may have an average molecular
weight of about 2,000 to 3,000,000; preferably about 5,000 to
1,500,000. The molecular weight may advanta~eously be deter-
mined employing the infrared spectral method disclosed by
Rugg et al. in the Journal of Polymer Science, Volume XI,
No. 1, pages 1 to 20. Other suitable methods of molecular
weight determinations, as disclosed by Rugg et al., may also
be employed if desired. The polymer or resin compositions
can also include conventional additives such as colorants,
stabilizers, lubricants, dispersing agents, plasticizers,
fillers, and the like, and can be physically admixed with
other polymeric materials either compatible or incompatible
therewith.
In one aspect of this invention, the polymer may
include ultraviolet light absorbers such as octadecyl-3,5-
di-tertiary-butyl-4-hydroxy-hydrocinnamate, 2-(3',5'-di-ter-
tiary-butyl-2'-hydroxyphenyl)-5-chlorobenzotriazole, and the
like. The polymer may also contain pro-oxidants including
the carboxylates, alkanoylacetonates, alkyl alkanoylacetates,
and the alkylbenzoyl acetates of copper, vanadium, chromium,
cobalt, manganese, iron, nickel, and zinc. Exemplary of pro-
oxidants are manganous stearate, manganous oleate, manganous
acetate, manganous dodecyl acetoacetate, cobalt acetyl ace-
tonate, cobaltous acetate, cobaltous naphthalenate, cobaltous
acetyl acetonate, cobaltous oleate, cobaltous stearate, co-
baltous dodecyl acetoacetate, cupric stearate, cupric oleate,
ferric acetate, and the like. The pro-oxidant serves as an
oxidation catalyst to promote the oxidative deterioration of
the polymer at a controlled rate. The amount of pro-oxidant
will depend on its activity; however, a minor amount of pro-
.
iO~4~3~
oxidant based on the polymer is generally employed, for exam-
ple total amounts of one, or mixtures Or two or more of the
pro-oxidants, equally from about 0.01 to about 1.5 weight
percent based on the polymer may find utility. A more detail-
ed discussion of the use of pro-oxidants may be found in U.S.
Patent No. 3,592,792, issued to Newland et al.
The polymer may also contain pigments and dyes to
render the polymer opaque to substantially all or selected
wavelengths. Carbon black pigments, 4-Cp-bis(2-hydroxyethyl)-
amlnophenylazo-p-phenyleneazo]-3-hydroxy-2-naphthoic acid
black dye, and the like may beneficially be employed. Gener-
ally minor amounts, for instance, about 0.05 to one or two
weight percent or more based on polymer, of pigments or dyes
may conveniently be employed. Other pigments are disclosed
by Newland et al. in U.S. Patent No. 3,592,792 and 3,454,510.
Conventional stabilizers or antioxidants are often employed
in the polymer to inhibit oxidation or inhibit reactions pro-
moted by oxygen or peroxides to protect the polymer against
deterioration during processing, or protection against deter-
ioration during the useful life of the polymer. When employ-
ing the polymer as, for instance, a mulch sheet, it may be
highly desirable to provide significant amounts of stabilizer
to prevent excessively quick deterioration of the polymer due
to exposure to sunlight and weathering. The stabilizer or
antioxidant employed in the polymer composition is prefer-
ably compatible with the polymer. A summary of conventional
antloxidants which may find application in polymers is found
in the Kirk-Othmer~ Encyclopedia of Chemical Technology, Second
Edition, Volume 2, pages 588 to 604, particularly pages 603 to
601. The stabilizers may be employed in minor amounts, e.g., from
about 0.0001 to about 5 or more weight percent based on the
polymer.
The amount of total alkanoylaminophenol incorporated
into the ~ -olefin polymer in this invention may vary depend-
ing upon the particular polymer employed, the desired rate of
degradation, the amount and nature of other conventional addi-
tives, and the like. Generally, the total lower and higher
alkanoylaminophenol is in a minor amount which is sufficient
to promote the desired rate of degradation of the polymer, for
instance, an amount of about 0.03 to 4, preferably about 0.07
to 2 weight percent based on the weight of the polymer. The
amount of total alkanoylaminophenol will generally depend, in
part, on the portion of lower alkanolyaminophenol therein and
its number of carbon atoms in the alkanoyl group. Often, with
amounts of alkanoylaminophenol in excess of about 4 weight
percent based on the polymer, insubstantial increases in the
rate of biodegradation are noted. Although such larger
amounts may be employed, the rate of deterioration of the
polymer is sufficiently rapid employing lesser amounts of
alkanoylaminophenol, for instance, about 0.15 to 1 weight
percent, that additional amounts of alkanoylaminophenol will
often be unnecessary in most applications. Frequently, a
greater amount of alkanoylaminophenol will be employed to pro-
mote degradation of higher molecular weight polymers or of
more highly branched polymers than of lower molecular weight
and less branched polymers in order to obtain similar degra- s
dation characteristics. The amount of alkanoylaminophenol
employed will also depend in part on the ratio of the lower
to high molecular weight component. A polymer may tend to
biodegrade more rapidly when a higher weight ratio~ rather
--10--
than lower o~ the lower to higher alkanoylaminophenol is
present for a similar amount of total alkanoylaminophenol.
On the other hand, the lower alkanoylaminophenols are gener-
ally less soluble in ~ -olefin polymers than the higher molec-
cular weight alkanoylaminophenols, and hence,their incorpora-
tion into the polymer may therefore be limited. The determin-
ation of the amount of alkanoylaminophenol in a specific ole-
fin polymer to provide a satisfactory rate of biodegradation
may be determined realizing the operation of the present in-
vention. ~ften, the lower alkanoylaminophenol will comprise
about 0.01 to 3, preferably about 0.03 to 2, weight percent
based on the polymer.
The alkanoylaminophenols may be incorporated into
the polymer separately or as a mixture. It is preferred that
each of the alkanoylaminophenols be well dispersed throughout
the polymer in order that the degradation of the polymer will
not become localized due to higher concentrations of say
the lower alkanoylaminophenol or the lower and higher alkan-
oylaminophenols in certain portions of the polymer. When the
lower and higher alkanoylaminophenols are added separately to
the polymer, it is preferred that the polymer be passed
through a molten form to enhance dispersion of the alkanoyl-
aminophenols. It may be possible, ~or instance, to achieve
the enhanced degradation provided by this invention by mixing
the alkanoylaminophenols with particles of polymer and then
cold milling the mixture, to produce, for instance a low
density sheet, to provide distribution of the alkanoyls.
Another method of incorporating the alkanoylaminophenols into
the polymer is by adding the higher and/or lower alkanoyl-
aminophenol to a polymer in a higher concentration than may
--11--
t,~
:~v~
be desired in a finished polymer product and then adding the
polymer havlng the higher and/or lower alkanoylaminophenol
therein to polymer not having the alkanoylaminophenols there-
in, or having one of the alkanoylaminophenols therein, to ob-
tain a product having the desired concentration of alkanoyl-
aminophenols. The polymer containing the alkanoylaminophenol
may, for instance, have about 0.3 to 15 or more, preferably
about 0.5 to 5, weight percent alkanoylaminophenols therein.
Since the polymer containing the alkanoylaminophenols may
have good storage stability, the higher concentration Or
alkanoylaminophenols in such a polymer for addition, will
have little, if any, effect on the polymer product.
A dispersant may be added to the polymer to assist
in the dispersion of the alkanoylaminophenols in the polymer
mass. The dispersant may also reduce the melting temperature
of the alkanoylaminophenol mixture. When, for instance, the
alkanoylaminophenols are mixed and subsequently added to the
polymer it is often beneficial to have the melting point of
their mixture in a range compatible with the melt polymer
during processing. For instance, polyethylene may be sub;ect
to degradation under excessive temperatures, e.g., in excess
of about 170C. and, therefore, is commonly extruded at tem-
peratures of about 125 to 155C. A high melting alkanoyl-
aminophenol may, however, remain in the solid phase during
processing of the polyethylene and, thus, not be advantageous-
ly diffused throughout the resultant, fused polymeric body.
The presence of non-melted, larger particles of alkanoylamino-
phenol may detract from the appearance and physical properties
of the polymer. Dispersants may reduce the melting point of
alkanoylaminophenols and thereby assist in the dispersion of
'}~
the alkanoylaminophenols throughout the ~ -olefin polymer at
convenient temperatures for polymer processing.
Particularly advantageous dispersants are monocar-
boxylic and dicarboxylic acids of about 10 to 30, preferably
about 12 to 22 carbon atoms. The carboxylic acid may be
saturated or contain one or more unsaturated carbon-carbon
bonds, and may be a hydroxy acid. Exemplary of these advan-
tageous dispersants are stearic acid, oleic acid, palmitic
acid, lauric acid, myristoleic acid, myristic acid, linoleic
acid, margaric acid, arachidic acid, elaidic acid, dodecane-
dioic acid, tetradecanedioic acid, and the like. Stearic acid
is preferred due to its availability and compatible properties
with the composition of this invention and ~ -olefin polymers.
The carboxylic acid dispersants may additionally serve as per-
oxidation catalysts to assist the degradation of the ~ -ole-
fin polymer.
Other dispersants which may be beneficially employed
in accordance with this invention include paraffin waxes, hav-
ing, for instance, about 14 to 20 to 40 or more carbon atoms,
microcrystalline paraffin waxes of about 30 to 50 or more car-
bon atoms slightly oxidized paraffin and microcrystalline
waxes, Hoeschst waxes, mildly oxidized Fischer-Tropsch waxes
which are highly tertiary in structure and other synthetic
waxes, and the like.
The amount of dispersant employed with the alkanoyl-
aminophenols, if employed, is frequently in a weight ratio of
dispersant to total alkanoylaminophenol of about 1:9 to 5:1,
preferably about 1:6 to 1:1. Advantageously, in polyethylene
compositions the dispersant is in a minor amount based on the
polymer and is preferably in an amount sufficient to provide
-13-
a mixture of total alkanoylaminophenol and dispersant which
has a melting point in the range of fusing temperatures of
the polymer, for instance, about 125 to 160C., preferably
130 to 150C. for polyethylene. This mixture is thus com-
patible in melting point to the temperatures which the poly-
mer is subjected during physical processing of the polymer,
for instance, extruding, calendering, molding, casting, and
the like. The alkanoylaminophenols and the dispersant may
be admixed prior to their incorporation into the polymer.
Desirably, this mixture is obtained by intimately admixing
finely-divided particles of the alltanoylaminophenols and dis-
persant. The finely-divided mixture of alkanoylaminophenols
and dispersant is then well dispersed in the ~ -olefin
polymer.
It has been found that biodegradability of ~ -ole-
fin polymers may be enhanced when the alkanoylaminophenol
components are dispersed in the polymer by mechanically mill-
ing. Examples of mechanical milling are cold milling, ball
milling, and the like. Alternatively, the alkanoylamino-
phenol and dispersant mixture may be stirred or tumbled withthe polymer, and then the resultant composition is heated to
obtain a fused mass with the alkanoylaminophenol and dispers-
ant distributed essentially uniformly throughout the polymer
mass.
The polymer containing the alkanoylaminophenols may
be processed and employed in any manner in which such polymer
without the composition of this invention is commonly pro- ~ -
cessed and used. It is realized that the ability of the ~
polymer compositions of the present invention to biodegrade ~ -
will widen commercial acceptance of the use of ~ -olefin
-14-
polymers due to their ecological compatibility. For instance,
the polymer compositions of this invention may be employed as
agriculture mulch films. Heretofore, such rilms have had to
be removed by the farmer at the end Or the growing season and
disposed Or, often by merely removing the used mulch film to
a remote section of the farm for storage or burning. Recent
proposals to eliminate labor in removing agriculture mulch
films have included photodegradable films; however, the com-
position of these films must be dependent not onl~y on the
weather conditions at the farming location to prevent prema-
ture or excessively late decomposition, but also, on the
length of the growing season for a particular crop. With
mulch films of the polymer of the present invention, the far-
mer need only turn under the film when it has served its use-
ful purpose. The polymer composition need not be designed
for the particular growing season and environmental area in
which it is to be used as the degradation is promoted by a
biological process.
Since alkanoylaminophenols are relatively non-toxic,
~ -olefin polymers containing the composition of this inven-
tion may advantageously be employed as wrappings and contain-
ers for foodstuffs, pharmaceuticals, feeds and the like as
well as other consumer items. Advantageously, disposable
sandwich and food bags, grocery bags, and the like which are
often used only one time, may be made in accordance with the
present invention and will biograde upon disposal after such
use. The composition of this invention does not adversely
affect the strength of ~ -olefin polymers, and hence, garbage
bags and other containers which may hold refuse may benefi-
cially be comprised of ~ -olefin polymer containing the
-15-
h~
co~n~osition Or this lnvention. ~nother ben~rit of th~ pres-
ent invention may be realized when it is considered that
plastic garbage bags are normally sealed with a tie when
filled with refuse and disposed of in for example land
fllls. Since the bag is sealed, normal biodegradation of the
refuse is hindered. Plastic garbage bags containing the com-
position of this invention may biode~rade thereby allowing
entry of oxygen and microorganisms to degrade the contents of
the bag. The polymer containinp the composition of the pres-
ent invention may also advantageously be employed as a coat-
ing, for instance, coatings for paper, cardboard, and the
like.
Another embodiment of the use of ~-olefin polymers
containing the composition of the present invention is in
polymer emulsions. Polymer emulsions either aqueous or in
organic liquid may comprise finely-divided, ~-olefin poly-
mer. Frequently the polymer particles are of regular shape
for instance, essentially spherical, and have an average par-
ticle size in the range of about 8 to 30 microns. The emul-
sion may be employed in a wide variety of applications such
as coatings, binders, additives, fillers, dispersing agents,
carriers, and the like. Aqueous emulsions may be prepared
from such finely-divided ~-olefin polymer which contain, say
about 2 to 70 weight percent solids. To provide stability
the normally hydrophobic polymer may be treated with a non-
ionic, anionic, or cationic surfactant. Particularly prefer-
red surfactants are non-ionic surfactants, especially biode- ~ -
gradable non-ionic surfactants such as alkylphenoxypoly(oxy-
ethylene)ethanols. Exemplary of biodegradable non-ionic sur-
factants are for example, Igepal ~ CA, CO DM and RC series
-16-
~o~
surfactants, obtainable from General Aniline & ~ilm Corpora-
tion. Generally, minor amounts which are su~ricient to
stabilize the emulsion, frequently, about 0.1 to 2 weight
percent of the emulsion, is surfactant. Water-soluble resins
may also be employed in the aqueous polymer dispersion as
thickening and emulsion stabilizing agents. Exemplary of
water-soluble resins are methyl carboxycellulose, polyvinyl
alcohol, polyvinyl pyrrolidone, polypeptldes, and the like.
The thickening agent may comprise a minor amount of the poly-
mer to provide the desired viscosity, for instance, about 0.01to 2 weight percent of the emulsion. Further information re-
garding polyolefin emulsions may be found in, for instance,
"Dispersing MICROTHENF. O F Polyolefin Powders in Liquids",
National Distillers and Chemical Corporation, 1965.
A particularly advantageous use of aqueous emulsions
containing ~ -olefin polymers is as an agriculture spray to
protect fruit and the like from frost, insects, and the like.
The emulsions generally contain a minor amount, for example,
about 5 to 15 weight percent polyolefin and about 2 to 30
weight percent of water-soluble polymer such as carboxymethyl
cellulose, methyl cellulose, other cellulose ethers, polyvinyl
alcohol, polyvinyl pyrrolidone, polypeptides, modified star-
ches, ethylene oxide polymers, polyethyleneimine, and the
like. The selection and amount of the water-soluble polymer
and the ratio of the water-soluble polymer to polyolefin will
depend in part upon the desired effect of the coating, the
period of time which is desired for the coating to remain
intact, and the environmental conditions. The aqueous emul-
sion may, for instance, be employed to spray fruit trees
under threat of impending frost, and the coating may be
-17-
'}
adapted to deteriorate, through the effect Or rain, agricul~
ture watering or other moisture, and possibly sunlight, in
about 12 hours to two days. The polyolefin will be carried
by rain or agriculture watering or fall by gravity to the
ground. Since the polyolefin is bicdegradable due to the
presence of the composition Or the present invention, it may
be degraded by micro-organisms into an ecologically harmless
~orm. The biodegradation of the polyole~in may occur not
only in the soil but also in streams, rivers, and other bod-
ies of water. Thus, polyolefin which may be carried by run-
of~ water ~rom the orchard may be desirably degraded.
The following examples are provided to further il-
lustrate the present invention. All parts and percentages
are by weight unless otherwise indicated.
EXAMPLE I "
.
A mixture of 50 weight percent para-acetylamino-
phenol, 25 weight percent of para-butyroylaminophenol, and 25 --
weight percent stearic acid are ball-mixed until dispersed.
This mixture, hereinafter referred to as Additive A, is ana-
lyzed to contain 6 ~ 51% of nitrogen and has a bulk weight den-
sity, loose pack, of 0. 43 grams per cubic centimeter and a
bulk weight density, settled, of o.63 grams per cubic centi-
meter. Upon being slowly heated, Additive A becomes sticky
at about 57C. and this property increases with rising tem-
perature. The material stiffens at about 114C. At about
135C. the material is partially molten and is completely
molten at about 143C. The molten material is of a reddish
color. The molten material is cooled and forms a solid at
about 121C. The cooled material is a grey, brittle solid.
-18-
.
EXAMPLE II
A high surface area, low density polyethylene sheet
is prepared in the following manner. Commercially available
pellets of low density polyethylene (obtained from the
Northern Petrochemical Company) having a melt index Or about
2.0 (British Standards Institute, B.S. 2782) are placed into
a glass jar. A desired amount of Additive A is then added to
the pellets and tumbled until a uniform distribution of Addi-
tive A through the polymer has been achieved. Polymer sheets
containing 0.25, 0.50, 1.0, and 2.0 weight percent Additive A
are prepared. Generally, to obtain a uniform mixture of
polymer particles and the above prepared mixture, the tumbl-
ing is continued for about 30 to 40 minutes. The thusly pre-
pared polymer containing the additive is placed in a two-roll
mill which serves to reduce the size of the polymer particles
and further the incorporation of Additive A in the polymer.
After the polymer-containing mixture is roll-milled, it is
cold milled at room temperature into a polymer sheet having a
high surface area. The cold milling does not continue beyond
a point at which sufficient mechanical strength is present to
hold the film together. The polymer-containing mixture is
generally passed through the cold mill from about 10 to 15
times with continual shaping in order to provide the desired
weak, low density sheet of polyethylene having a high surface
area. The polymer sheet is not fused.
Thus high surface area polymer film can be advan-
tageously employed in polymer degradation tests since the bi-
odegradation will be accelerated due to its high surface area
and since the mechanical degradation of the polymer during
forming the sheet by cold milling is minimal, enabling a
-19-
better evaluation of the biodegradation achieved employing the
present invention. The polymer sheet is of an average thick-
ness o~ about 7 to 11 mils. The exact thickness of the poly-
mer sheet is not of significant importance since the degrada-
tion examples are intended primarily ~o demonstrate degrada-
tion of the polymer and not physical properties of a sheet
made therefrom.
EXAMPLE III
Low density, polyethylene film containing 0.25
weight percent Additive A is prepared under commercial condi-
tions employing a conventional extruder such as is described
in "Polyethylene Film Extrusion...an operating manual",
National Distillers & Chemical Corp., 1960. Unmodified poly-
ethylene pellets having a density of about 0.922 grams per
cubic centimeter and a melt index of about 2.0 (B.S. 2782), `
obtained from the Union Carbide Corporation, is admixed with
0 25 weight percent Additive A based on the mixture in a hop-
per at a temperature of about 250 to 270F. The polymer is
then extruded at about 300 to 320F. and calendered to pro-
vide a film of 1.5 mil in thickness. The mixing, pelletizing,
extruding and calendering to form the polyethylene sheet is
easily accomplished, and no difficulties arise either in poly-
mer sheet quality or manufacture due to the incorporation of
Additive A. No cross-linking of the polymer in the film is
observed, and the film cannot be visually distinguished from
polyethylene film which is similarly processed. The nitrogen
content of the polymer without Additive A is about 69 ppm (by
weight), and with 0.25 weight percent Additive A, about 208
ppm (by weight).
-20-
lU~
EXAMPLE IV
Cast films of low density polyethylene havlng a melt
index of 2.0 grams per 10 minutes (ASTM D-1238-65T) and a ten-
sile strength at brealc of 1680 pounds per square inch at 20
inches per minute (ASTM D-638-68) and 0.05, 0.10, 0.15, 0.20,
0~25, 0.35, 0.40, and 0.50 weight percent of Additive A are
prepared as follows. To a mixture of the polymer and Additive
A is added about 5 weight percent of hot hydrocarbon solvent
containing about eight to twelve carbon atoms per molecule,
and a flowable mixture results. The mixture is cast on glass
which has been previously coated with a layer of castor oil
to form a lubricating layer which enables easy removal of the
cast film from the glass. The thickness of the film ranges
from about 1.1 to 1.2 mils, and the film exhibits essentially
the same physical properties as similarly cast polyethylene
film without Additive A.
The biodegradability of polyolefins containing Addi-
tive A may be determined by employing laboratory tests or by
actually subjecting the polymer to the natural environment.
The tests conducted under laboratory conditions may be gener-
ally more severe than those expected in nature and quickly
provide an indication of susceptibility of the polymer to
biodegradation. Typically, select microorganisms which are
frequently encountered in soil or water and which have affin-
ity towards organic matter, such as Cladesporium resinae,
Aspergillus terrus, Aspergillus niger, Aspergillus flarus,
Aspergillus versicolor, Penicillum funiculosum, Trichoderma,
Pullaria pullans, and the like, are employed in such tests.
Usually, an indication of degradation will occur in several
3o days to three weeks. Under natural conditions, reliable
-21-
4~
indications Or biodegradation Or the polymer may be obtained
in about one month. The following examples illustrate the
promotion of biodegradation of polyolef~ns by the composition
of this invention in both laboratory tests and natural tests.
E~AMPLE V
In this example the biodegradability of low density
sheets of polyethylene by the microorganism Cladesporium
resinae is determined using fifty, 3-inch by 4-inch sheets of
high surface area, low density polyethylene containing 0.25 .
weight percent of Additive A as is described in Example II.
The polyethylene obtained from Northern Petrochemical Company -
has a melt index of 2.0, a molecular weight of about 32,000,
and a tensile strength of about 1800 pounds per square inch
(British Standards Institute, B.S. 903).
An agar solution is prepared as follows to coat the
polyethylene film to promote development of the microorganism
and thus hasten biodegradation. D.I.F.C.O. Laboratories
Sabourand Maltose agar-dehydrate having a pH of about 5 to 6
at 25C. is melted at 100C. and put in sufficient distilled
water to make a 5 weight percent solution at about 32C. The
agar is innoculated with microorganisms from a culture of
Cladesporium resinae. Cladesporium resinae is commonly found
in the soil and adaptable to utilize hydrocarbon materials for
its sustenance and is described in Simmons, Quartermaster
Corp., Natick Publication #7998 and in Development in Indus-
trial Microbiology, Chapter 27, Garamond Pridemark, p. 247.
The agar and microorganism mixture are coated on one side of
each of the polymer sheets. The coated films are placed in
petri dishes and 5 cc. of sterile water added thereto. The
petrl dishes are covered and placed in a cool, dark room at
-22-
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about 20C. The absence of light sources to better enable the
realiza~ion Or biodegradation since ultrav~olet radiation is
removed as a possible promoter of polymer degradation.
Visual checks are made of the treated polyethylene
films during the test. After five days, brown circles Or the
microorganism can be detected on the plastic film. After six
weeks the film is washed with water and is milled slightly
with a rubber tipped stirring rod to assist in removing the
growth of brown-yellow Cladesporium resinae. The film is held
for two days at 21C. and at 65~ relative humidity. The film
is then cut into small pieces with a knife and molded at 300F.
to make melt flow for the samples to be used in the test.
This product is held for two days at 25C. before the tests
are conducted. The sheets of polymer are analyzed to have a
melt index of 5.8, a molecular weight of 28,000, and a tensile
strength of 1440 pounds per square inch.
A low density polyethylene sheet containing 0.25
weight percent Additive A made in accordance with the proce-
dure of Example II but using polyethylene obtained from the
Union Carbide Corporation having a melt index of about 2.0 and
a density of 0.922, is also employed in this example. Con-
trols employing both the polyethylene sheet produced from the
Northern Petrochemical Company and Union Carbide Corporation
polyethylene which are made in accordance with Example II but
not containing Additive A, are used. The results are pro-
vided in Table I.
Table I
Northern Petrochemi- Union Carbide Corp.
cal Co. Polyethylene Polyethylene wlth
with 0.25 wt.% 0.25 wt.%
Additive A Additive A
Visual Surface
Area
Mold Growth %
After 5 Days20 tcontrol:trace)20 (control:2)
Visual Surface
Area
Mold Growth %
After 6 Weeks 80 (control:3) 85 (control:5)
Tensile Strength
Loss ~
After 6 Weeks13.5 (control:3)25 (control:2)
This accelerated laboratory screening shows that the
addition of this invention promotes the biodegradation of
polyethylene whereas control samples without the additive
showed negligible deterioration.
Other screening tests employing fungi such as
Aspergellus niger, Aspergellus flavus, Aspergellus versicolor,
Penicillium funiculosum, Trichoderma sp., and Pullaria pullans
may also be employed to demonstrate biodegradation of poly-
olefins. Generally, positive results are obtained within
about 40 to 50 days. A particularly useful procedure in the
evaluation of polymers for susceptability to deterioration by -
microorganisms is the American Society for Testing and - -
Materials test D 1924-61T. A more recent test is set out in
ASTM D1924-70 and also illustrates the biodegradability of
polymer containing the composition of this invention.
-24- -
.
, ~
.
Another test which may be employed to determine
whether or not a polymer may biodegrade is to disperse the
polymer in finely-divided rorm in samples of, ror instance,
ordinary river, pond, or lake water and subsequently determine
the deterioration by measuring weight loss of polymer. This
test may be convenient to conduct and may provide good indica-
tions of biodegradation in relatively short periods Or time,
for instance, two or three days. Further, this test may ap-
proximate conditions to which the polymer may be exposed in
that, for example, polymer film may be disposed of in a body
of water or, especially, polyolefin which may be employed in
an emulsion in agricultural use to coat fruit to prevent frost
damage or in industrial or commercial use may be washed into
streams and rivers. Commonly, this test is referred to as
the river die-away test.
EXAMPLE VI
A high surface area polyethylene sheet as described
in Example II and having 0.25 weight percent Additive A is
rubbed gently against itself to produce finely-divided poly-
ethylene particles. To five grams of the finely-divided
polyethylene is added 500 grams of Kankakee River water taken
at the Kankakee State Park in Illinois. The sample is agi-
tated slowly for 12 hours at 25C. in a Waring blender. The
sample is then agitated rapidly at 25C. for 48 hours.
Fresh river water is added to keep the volume constant, and
the sample is shaded from any source of excessive ultraviolet
radiation which may also promote polymer degradation. A sam-
ple is drawn from the blender after 72 hours and evaporated
in a low-vacuum oven. The weight of the residue is determined.
This is compared with a blank containing only the river water.
-25-
The difference between the residue of the sample containing
polymer and the blank is the weight of polymer remaining.
This is compared with the polymer originally charged to ob-
tain a weight percent of polymer lost or decomposed. The
sample is analyzed to have a 37.8 weight percent decomposition
after 72 hours.
As a comparison, 5 grams of polyethylene prepared as
in Exan~ple II except containing no Additive A is added to 500
grams of Kankakee River water procured at the same time and
location as above~ The test procedure is repeated with the
result that 4.4 weight percent of polymer is lost or decom-
posed after 72 hours.
EXAMPLE VII
This example demonstrates biodegradability of low
density polyethylene of the present invention in the presence
of raw sewage sludge.
A polyethylene sheet (Northern Petrochemical Company
low density polyethylene) is prepared in essentially the same
manner as set forth in Example II having 0.25 weight percent
Additive A. The polyethylene sheet is rubbed gently against
itself to produce finely-divided polyethylene particles. Ac-
tive raw sewage sludge is obtained from the municipal sewerage
system of Hazel Crest, Illinois, and is placed in the amount
of about two liters in a gyrotory shaking machine which agi-
tates the sewage and thus serves to aerate the sewage and to
prevent agglomeration of solid materials in the sewage. To
the sewage is added 100 milligrams per liter of finely-divided
particles of polyethylene containing Additive A, and the mix-
ture is agitated for 100 hours at room temperature.
-26-
The slud~e containing the polyethylene is then
washed with hot hexane to extract the polymer therefrom. The
hexane is evaporated, and the weight of the residue is com-
pared with the amount of polyethylene charged to the shaking
machine after determining the amount of residual matter which
exists in the sludge which will concurrently be extracted
with hot hexane by running a blank. Approximately 31 weight
percent of the polyethylene is found to be decomposed.
As a comparison, this Example is repeated except em-
ploying no Additive A in the polyethylene~ The polyethyleneis extracted from the sludge after 100 hours at room tempera-
ture and is analyzed to have only a 5.3 weight percent loss
of polyethylene.
The above procedure is repeated except using a low
density polyethylene obtained from Union Carbide Corporation
which has a melt index of about 2.0 and a density of 0.922.
With 0.25 weight percent Additive A, a 25.8 weight percent
loss is experienced after 100 hours. A control employing the
same type polymer but without any Additive A shows only a 2.6
weight percent loss after 100 hours.
It is realized that the decomposition rates demon-
strated in this example will not probably remove the problem
heretofore experienced in municipal sewage systems with poly-
olefin materials due to the normally short retention time in
the system. However, the ability of microorganisms which are `
normally found in waste disposal systems to degrade polyole- ~
fins with the composition of this invention is clearly shown. ~ -
Often, polyolefin materials such as bags, film,
moldings, agriculture mulch films and the like are buried as
a means of disposal. Thus, one of the significant indications
Or operability of a biodegradable polymer system is its per-
formance in contact with soil.
EXAMPLE VIII
Low density polyethylene sheets (Northern Petro-
chemical Company polyethylene) containin~ 0.25, 0.50, l.0,
and 2.0 weight percent Additive A are prepared in accordance
with the procedure set ~orth in Example II. The strips are
tested for microbial deterioration by soil burial in a proce-
dure which is slightly modified from that disclosed by Wendt,
et al., Int. _iodetn, Bull., 6(4), p. 139-43, (1970). The
sheets are cut into strips of l inch by 8 inches and are sta-
bilized for two days at room temperature and about 60 to 70
percent relative humidity. Each strip is placed in 1750
grams of moist, typical sandy soil obtained from Crawford
County, Illinois, in a 2 liter flask. The strips are re-
covered at four or twenty weeks and are weighed to determine
the deterioration of the polyethylene. As a comparison, a
polyethylene strip made in accordance with Example II but
without Additive A is tested in the same manner. Table II
sets forth the results of the results of this example.
Table II
~,
Amount of Time Percent
Additive A, in Soil, weight
wt. % weeks loss
.. .. _ _
0.25 4 3.9
0.25 20 37.7 `
0.50 4 14.7
l.0 4 19.8
2.0 4 22.3
0 4 0.03
0 20 1.6
-28-
.
~u~
To illustrate the abillty to employ the system Or
this invention without substantial concern ror particular lo-
cation or soil condition, soil samples are obtained from
Alachua, Florida; Anaheim, California; Lake Sardis,
Mississippi; and Crawford County and Homewood, Illinois, and
the above procedure is employed. Union Carbide low density
polyethylene having a melt index of about 2.0 and density of
0.922 grams per cubic centimeter is employed. The results
are provided in Table III.
Table III
Weight % Loss
Weeks inWith 0.25%
Location Soil Additive A No Additive A
Alachua 4 3.7 0.15
24.4 1.97
Lake Sardis 4 2.7 0.55
37.3 2.30 ~f
Anaheim 4 1.9 0.33
22.8 1.70
Homewood 4 2.7 0.79
31.9 2.96
Crawford 4 2.7 0.27 ~-
31.4 0.98
EXAMPLE IX
Example VIII is repeated except employing a blown
polyethylene (obtained from Union Carbide Corporation and
having a melt index of 2.02 and a density of 0.922 grams per
cubic centimeter) film of about 1. 5 mils in thickness. Table
IV provides the results.
- 29 -
Table IV
_Weight % Loss
Weeks in With 0.25%
Location Soil Additive A No Additive A
Lake Sardis 4 0.92 0.1
13.95 1.0
Anaheim 4 1.7 0.1
10.3 1.0
Crawford 4 2.1 0.0
14.0 1.11
The tensile strength at yield at 20 inches per minute
(ASTM D-638-68) of the films containing Additive A drops from
about 1880 pounds per square inch to about 1300 to 1700 pounds
per square inch after 20 weeks in soil immersion.
On the other hand, samples of polyethylene contain-
ing 0.25 weight percent Additive A which are stored under
laboratory conditions of 75F. and 55 percent relative humidi-
ty in an opaque bag for 10 months do not show any appreciable
degradation.
.
EXAMPLE X
A milled film about 1.3 mils in thickness is pre-
pared from polybutene-l obtained from the Petro-Tex Corp. and
having a melt index of 0.5 and 0.25 weight percent Additive A.
The film is fused and is employed as a mulch for strawberry
plants in Anaheim, California. The film is spread in early
December. By the following May, there are visual signs of
degradation of the film such as brittleness and cracking. The
film can be easily tilled into the soil by conventional cul-
tivating equipment in the summer. Examination of the surface
and subsoil reveals small particles of decomposing polybutene
film ranging in size from approximately 1 inch squares to
pinheads.
-30-
A similar polybutene-l film, except havlng an Addi-
tive A, is placed in the same strawberry field at the same
time as above. After nine months, no signs Or significant
deterioration could be detected. The film could not be tilled
into the soil usin~ conventional cultivating equipment, and
the film had to be rolled up and trucked away in order to
commence cultivating.
The mixture of the composition of this invention
and a commercially available, unmodified poly-~-olefin is
not overly sensitive to degradation promoted by ultraviolet
light. However, it may be desirable for certain commercial
applications to modify the polymer with promoters for ultra-
violet radiation degradation or to use a polymer which does
not contain ultraviolet radiation degradation stabilizers
which are normally present in commercially obtainable polymer.
The following examples illustrate the effect of ultraviolet
radiation on polyethylene film containing various amounts of
the composition of this invention.
EXAMPLE XI
A cast polyethylene film of about 1 to 1.5 mils in
thickness is obtained using essentially the same procedure as
set forth in Example IV. The film contains low density poly-
ethylene obtained from Northern Petrochemical Company having
a melt index of about 2.0 and a density of about 0.924 grams
per cubic centimeter and 0.25 weight percent of Additive A.
The film is exposed to southern Florida sun and crazing
occurs within 5 to 6 months whereas similar films without
Additive A, which are identically exposed, craze in 9 to 12
months.
31
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~XA~'lPI ~[1
Cast fil~s are pr~parcd as in EY~amples IV and XI
and are ag-ed ror two l.~eel;s, then placed in a Model Xl~l, Atlas
Electric ~leatherometer em~loyin~ a Xenon arc lamp, and the
time to photode,radation, that is, where the polymer loses
its useful properties is determined. Table V presents the
results. As a compar:ison, thls example is repeated except
when the polyethylene is heated to 135C., no Additive A is
admixed therewith.
Table V
Amount of Film Time to
Additive A, Thickness, Degradation,
wt. % mils hours
0.05 1.2 1590
0.10 1.1 740
0.15 1.1 610
0.20 1.2 500
0.25 1.1 .410
0.35 1.1 315
0.40 1.1 300
0.50 1.2 280
(control) 1.1 1200
EXAMPLE XIII
Four groups of film are prepared in accordance with
a procedure such as set forth in Example III. Group I is
made from low density polyethylene obtained from the Union
Carbide Corporation and has a density of 0.922 grams per cu- -
bic centimeter and has incorporated therein 0.25 weight per-
cent of Additive A based on the polymer. Group II is essen-
30 tially the same as Group I except no Additive A is incorpor-
--32--
... ..
*Trade Mark
4~
ated therein. 5roup III is made from low density polyethyl-
ene obtained from U.S. Industrial Chemicals Company, a divi-
sion of National Distillers & Chemical Corp. and contains 0.25
weight percent of Additive A based on the polymer. Group IV
is essentially the same as Group III except no Additive A is
incorporated therein. The film for each group is portioned
into five 8-inch by 12-inch samples and framed with flexible
material around its outer perimeter. Two of the five samples
from each group are further stapled onto a fiberglass screen
as a backing. All the samples are then exposed in Miami,
Florida, on a 45 angle ~acing south to normal weathering
conditions for approximately 180 days, beginning in mid July.
After about 4 months, the strength of the films decreased
sufficiently that tears occurred due to wind, with the panels
with the fiberglass backing being the first to show signs of
ripping. There is no readily ascertainable difference be-
tween the Groups having Additive A therein and those not hav-
ing Additive A with respect to the time in which sufficient
deterioration of the films occurred to permit physical damage
by the wind. Thus, it is seen that the resistance to weather-
ing of film of polyethylene containing Additive A is essen-
tially the same as conventional polyethylene film.
