Photodegradable polyethylene or polystyrene compositions of copolymers thereof containing up to 500 ppm of iron in the form of a ferrous carboxylic acid salt having a substituted alkyl chain of at least 6 carbon atoms.

The present invention relates to photodegradable polymer compositions 
containing a ferrous salt of a carboxylic acid. 
With the every increasing attention being paid to environmental pollution 
problems there has become a critical need for film forming polymer 
compositions that can be used as durable packaging materials, but that 
will quickly degrade in the outdoor environment and particularly under the 
influence of ultraviolet light or sunlight. 
Many different additives, such as metal salts or complezes, have been 
proposed in the past for use with polymers such as polyethylene and 
polystyrene in an attempt to improve their degradation properties without 
affecting their durability as packaging materials. None of the additives, 
however, have been able to provide the proper balance between the 
properties desired in the final product. For example, ferric iron salts of 
carboxylic acids have been proposed for use in the past as photodegradable 
additives for polyethylene films, but and as more fully shown in the 
accompanying examples, these additives have not proven entirely 
satisfactory in achieving an acceptable rate of outdoor degradation while 
retaining durability for packaging purposes. 
The present invention therefore relates to the use of certain new and novel 
additives having advantageous properties compared to those additives 
previously proposed. More particularly, the present invention relates to 
photodegradable polymer compositions comprising at least one polymer 
selected from the group consisting of polyethylene and polystyrene and 
copolymers thereof and from 1 to 500 ppm relative to the polymer of 
(iron-II) in the form of a salt from a carboxylic acid having an alkyl 
chain containing at least 6 carbon atoms and being substituted in 
positions 2, 3, 4 or 5 relative to the acid group in position 1, with at 
least one radical selected from the group consisting of carboxylic acid, 
sulphonic acid, alcohol and amide radicals. Preferably the ferrous iron is 
used in an amount of from 10 to 150 ppm based on the amount of the 
polymer. 
It is to be understood that both the foregoing general description and the 
following detailed description are exemplary and explanatory but are not 
restrictive of the invention. 
Exemplary of polymers which can be used in the present invention are 
polyethylene, polystyrene, and copolymers based on ethylene or styrene, 
such as, for example, copolymers of ethylene with vinyl acetate, vinyl 
chloride, methyl vinyl ether, ethyl vinyl ether, acrylonitrile, acrylic 
esters, carbon monoxide and sulphur dioxide or copolymers of styrene with 
acrylonitrile-butadiene, and mixtures of the polymers and copolymers 
defined above. 
Conventionally, the polymer can also contain other additives such as 
antioxidants, slip agents and the like. 
Exemplary of the ferrous iron salts that can be used in the present 
invention are iron-(II) dodecylsuccinate, iron-(II) 
O-palmitoyl-1-ascorbate, iron-(II) monolaurylethanolamide sulphosuccinate, 
iron-(II) monostearylsulphosuccinate, iron-(II) N-palmitoyl-glutamate, 
iron-(II) N lauroylaspartate, iron-(II) 2-sulphopalmitate and iron-(II) 
O-palmitoylgluconate. 
The ferrous salts can be prepared, for instance, by the action of the 
corresponding acid on freshly prepared ferrous carbonate in the absence of 
air, or by double decomposition, in air, of a salt of the acid (for 
example the potassium salt) with ferrous alum. If necessary, the acids can 
be prepared by the action of an acid chloride on an alcohol-acid or on an 
amino-acid in a pyridine medium. 
These ferrous salts have been found to have particularly valuable 
properties when used as additives with the polymers of the present 
invention because they are compatible with, and easily dispersible in, the 
polymers, particularly because of the long alkyl chain in the acid salts. 
They do not have a heat-degrading action on the plastics during the 
production of the polymer compositions or during the thermoplastic 
processing of these compositions. This property is probably due to the 
presence of at least one of the defined substituents in positions 2, 3, 4, 
or 5 on the alkyl chain, which substituent is believed to have a 
complexing action on iron-(II) and is also responsible for the storage 
stability of the additive. For example, in the presence of a 100 ppm of 
ferrous iron according to the present invention, a degradation of a 40.mu. 
thick polyethylene film exposed to outdoor sunlight was completed within 
about 100 days. 
These ferrous iron salts are particularly active in inducing the 
photo-chemical degradation of the polymers to which they are added, while 
at the same time are non-toxic which allows the compositions to be used 
with foodstuffs and they are also not water-extractable. 
Of course it is possible, according to the invention, to regulate the 
photo-chemical degradability of the polymers by regulating the amount of 
the additive introduced into the polymer compositions. Experiments have 
established that the photo-chemical degradability of the polymers 
increases progressively with the concentration of the additive until the 
latter reaches an optimal value depending on the molecular absorption 
coefficient of the additive and the thickness of the irridated object. 
Beyond this value, the increase in degradability tends to decline 
markedly. 
Preferably sulphur, in the form of sulphur or polysulphide, is used in the 
compositions of the present invention with the ferrous additive to delay 
initial photodegradation of the polymer compositions. The sulphur content 
is generally between 1 and 250 ppm and preferably between 10 and 100 ppm 
relative to the polymer. 
The compositions may be prepared by hot mixing the polymer with the 
additive or additives until a homogeneous mixture is obtained by 
conventional techniques. 
To illustrate the invention more specifically, reference is made to the 
following examples. These examples illustrate the preparation of polymer 
compositions containing various ferrous iron carboxylic acid salts 
according to the present invention, their photodegradability, as well as 
their comparison with control samples containing no additive and some 
control samples containing additives of the prior art. 
The examples are merely illustrative and are to be understood as not 
limiting the scope and underlying principles of the invention in any way.

EXAMPLE 1 
A polymer composition is prepared by intimate hot mixing of virgin 
polyethylene having a density of 0.92 and a melt index of 1.9 with 100 ppm 
of iron-(II) in the form of dodecylsuccinate as the ferrous additive. 
The composition obtained is then converted to a film of about 500 microns 
thickness and samples of the film are irradiated for varying periods in a 
"Weather-O-meter" of the ATLAS 600 type, which is a well-known apparatus 
making it possible to carry out accelerated aging under ultraviolet 
radiation. 
The action of the additive is assessed by subjecting the product obtained 
to a tensile test which makes it possible to determine the decrease (in %) 
of the elongation at break of the sample relative to the sample before 
irradiation. 
A control sample film is also prepared using the same polymer, but without 
any additive. After 208 hours, it was found that the control film sample 
had only decreased by 4% in elongation at break, whereas the film 
containing the ferrous additive had achieved a decrease of 22% after 100 
hours; 55% after 200 hours, and 95% or practically complete degradation 
after 300 hours. The results are repeated below in Table I. 
EXAMPLES 2-15 
The procedure of Example 1 is repeated in each of Examples 2-15 in all 
respects except that varying amounts of the same and different ferrous 
carboxylic acid salts are used and sometimes together with varying amounts 
of sulphur. 
The same test as described in Example 1 is conducted on each of the films. 
The compositions of the films and the results of the tests in each example 
are reported below in Table 1. 
TABLE I 
__________________________________________________________________________ 
decrease, in %, in 
Example ppm of ppm of 
duration of 
the elongation at 
No. Ferrous Additive 
iron II Sulphur 
irradiation 
break 
__________________________________________________________________________ 
CONTROL 
NONE 0 0 208 hrs. 
- 4% 
1 Iron-(II) dodecylsuccinate 
100 0 100 hrs. 
-22% 
200 hrs. 
-55% 
300hrs. 
-95% 
2 Iron-(II) dodecylsuccinate 
100 10 100 hrs. 
+ 5% 
200 hrs. 
- 5% 
300 hrs. 
-82% 
400 hrs. 
-85% 
3 Iron-(II) dodecylsuccinate 
100 50 100 hrs. 
-15% 
200 hrs. 
-12% 
300 hrs. 
-65% 
400 hrs. 
-80% 
4 Iron-(II) dodecyulsuccinate 
100 100 100 hrs. 
-24% 
200 hrs. 
-47% 
300 hrs. 
-80% 
5 Iron-(II) - O-palmitoyl-1 
100 0 100hrs. 
-30% 
ascorbate 200 hrs. 
-82% 
300 hrs. 
-92% 
6 Iron-(II) O-palmitoyl-1- 
200 0 100 hrs. 
-21% 
ascorbate 200 hrs. 
-87% 
7 Iron-(II) O-palmitoyl-1- 
10 0 100 hrs. 
-10% 
ascorbate 200 hrs. 
-20% 
8 Iron-(II) O-palmitoyl-1- 
100 10 100 hrs. 
+12% 
ascorbate 200 hrs. 
+ 3% 
300 hrs. 
-11% 
400 hrs. 
-15% 
9 Iron-(II) O-palmitoyl-1- 
100 50 100 hrs. 
+ 5% 
ascorbate 200 hrs. 
-10% 
300 hrs. 
-12% 
400 hrs. 
-24% 
10 Iron-(II) O-palmitoyl-1- 
100 100 200 hrs. 
-20% 
ascorbate 300 hrs. 
-80% 
11 Iron-(II) O-palmitoyl- 
100 0 204 hrs. 
-91% 
gluconate 
12 Iron-(II) N-palmitoyldiimino- 
100 0 100 hrs. 
-65% 
acetate 192 hrs. 
-88% 
431 hrs. 
-94% 
13 Iron N-palmitoyl-glutamate 
100 0 204 hrs. 
-90% 
14 Iron-(II) monostearyl- 
100 0 189 hrs. 
-25% 
succinate 
15 Iron-(II) monolaurylethanol- 
100 0 189 hrs. 
-68% 
amide sulphosuccinate 
__________________________________________________________________________ 
EXAMPLE 16 
A comparative example is carried out to illustrate the influence of the 
alkyl chain having more than 6 carbon atoms with respect to a similar 
ferrous compound containing an alkyl chain of 6 or less carbon atoms. In 
this example, the ferrous compound is 100 ppm of iron-(II) in the form of 
gluconate which is added to the same polyethylene as that used in Example 
1. 
The film product obtained is irradiated and the decrease, in %, of the 
elongation at break, is measured by the same test as shown in Example 1. 
The film was irradiated for 213 hours and the decrease was only 13%. 
The example is repeated using iron-(II) succinate as the ferrous additive 
and after being irradiated for 196 hours, the decrease was only 10%. 
EXAMPLE 17 
This example is carried out to demonstrate the effect of the valency of the 
iron in the additive. The example is similar to Example 1 except ferric 
iron compounds are used as the additive. 
In this example, otherwise similar to Example 1, 100 ppm of iron-(III) in 
the form of glycerophosphate is used as the additive. After 200 hours of 
irradiation, the film product had a decrease in elongation of 16%. 
The example is repeated using sodium ferricitrate and sodium ferritartrate 
as the additive. The elongation at break was 2% and 3%, respectively. 
EXAMPLE 18 
The good stability to thermal oxidation of polyethylene containing the 
additives of the present invention is demonstrated by this example. The 
property is demonstrated by studying the variation, as a function of time 
in minutes by calendering the sample at 180.degree. C., of the melt index 
of the polyethylene having an initial melt index of about 2. 
In this example, like in example 1, the polyethylene composition contained 
100 ppm of iron-(II) in the form of dodecylsuccinate. 
A control sample was also prepared using the same polyethylene, but without 
any additive. 
The results of the study of the decrease in melt index as a function of 
time are reported below in Table II. 
EXAMPLES 19-22 
The procedure of Example 18 is repeated, using in Example 19, 100 ppm of 
iron-(II) in the form of O-palmitoyl-1-ascorbate; in Example 20, 100 ppm 
of iron-(II) in the form of dodecylsuccinate and 100 ppm of sulphur; in 
Example 21, 100 ppm of iron-(II) in the form of O-palmitoyl-1-ascorbate 
and 100 ppm of sulphur; and in Example 22, 100 ppm of iron-(III) in the 
form of tristearate. 
In each example, the same polyethylene was used as that used in the control 
of Example 18. 
The variation in the melt index as a function of time is reported below in 
Table II. 
TABLE II 
__________________________________________________________________________ 
Time (minutes) 
Example No. 
0 5 10 20 30 40 50 
__________________________________________________________________________ 
18 1.9 1.85 1.78 1.55 1 0.5 crosslinked 
(Control) 
18 1.85 1.89 1.90 1.79 1.40 0.88 0.5 
19 1.8 1.91 1.94 1.80 1.56 1.18 0.8 
20 1.9 1.85 
21 1.9 1.7 1.65 
22 1.95 1.89 1.65 1.01 0.60 0.35 0.20 
__________________________________________________________________________ 
EXAMPLES 23 and 24 
The aging experiment as described in Example 1 is repeated in these two 
examples, using as the polymer a vinyl acetate-ethylene copolymer 
containing 6.5% of vinyl acetate and having a melt index of 1.5. The 
copolymer did not contain any antioxidant. The ferrous iron additive was 
iron-(II) O-palmitoyl-ascorbate. 
A control sample film was also prepared using the same copolymer 
composition but without any additive. The results of the aging tests are 
reported below in Table III. 
TABLE III 
__________________________________________________________________________ 
decrease in 
Example ppm of 
ppm of 
duration of 
elongation at 
No. Additive iron 
sulphur 
irradiation 
break,-% 
__________________________________________________________________________ 
CONTROL 
NONE 0 0 196 hrs. 
-28% 
23 Iron-(II) O-palmitoyl- 
100 0 180 hrs. 
-86% 
ascorbate 412 hrs. 
-97% 
24 Iron-(II) O-palmitoyl- 
50 0 180 hrs. 
-48% 
ascorbate 412 hrs. 
-93% 
__________________________________________________________________________ 
EXAMPLE 25 
This example is submitted to show the difference in action between a 
product according to the invention as demonstrated in Examples 5 and 10, 
and a product according to the prior art containing 100 ppm iron-(III) in 
the form of tripalmitate and 100 ppm sulphur. The decrease in the 
elongation at break, the oxygen content, and the weight content of 
CHCl.sub.3 extractable substances (at 20.degree. C.) of molded plates of 
500.mu. thickness and of a polyethylene having a melt index of 2 and 
containing one of these additives is compared as a function of the 
duration of irradiation according to the aging test of Example 1. 
The results obtained are listed below in Table IV. 
TABLE IV 
__________________________________________________________________________ 
Duration of irradiation in the Weather-O-meter 
Variables examined 
Example 
0 100 hrs. 
200 hrs. 
300 hrs. 
400 hrs. 
__________________________________________________________________________ 
Loss in elonga- 
tion at break, % 
10 0 40 81 96 
25 0 77 97 
Oxygen content 
5 0.05 0.14 0.2 0.24 0.33 
mol/liter 25 
0.1 0.34 0.44 0.51 0.57 
Content of extrac- 
5 1.0 0.76 0.8 1.1 1.5 
tables, % by 
weight 25 1.55 1.1 1.2 1.44 1.7 
__________________________________________________________________________ 
The invention in its broad aspects is not limited to the specific details 
shown and described and departures may be made from such details without 
departing from the principles of the invention and without sacrificing its 
chief advantages.