Note: Descriptions are shown in the official language in which they were submitted.
- 1118~
077168~
LIGHT-STABLE POLYPROPYLENE CO~OSITIONS
.
Description
The invention of this application relates, as
indicated, to polypropylene compositions. I~lore parti-
cularly, it relates to such compositions which are
stabilized against deterioration that ordinarily results
from prolonged exposure to sunlight. Still more parti-
cularly, it relates to the stabilization of polypropylene
compositions by means of the combination of small pro-
portions of additives.
Ultraviolet light has a degradative effect uponolefin polymers, the severity of which is dependent
- primarily on the degree of exposure. The effect is es-
pecially se~ere on polypropylene, probably because of the
high concentration of tertiary carbon atoms which are
peculiarly susceptible to oxidative attack.
Ordinarily, polypropylene is characterized by high
tensile strength, i.e., higher than that of other olefin
polymers, as well as by high abrasion resistance and a
lustrous surface which is resistant to acid, alkali, solvent
and other chemical attack. It is also very light in weight,
i.e., it has a specific gravity of about 0.90. All of these
physical properties, plus the fact that, as a fiber, it
can be oriented so as to significantly increase its tensile
strength, are highly desirable and, as expected, it finds
wide usage in many applications.
Unfortunately, these desirable qualities are
accompanied by a tendency of the polypropylene to deteriorate
rapidly by means of photooxidation upon exposure to sunlight.
The result is discoloration, reduced molecular weight and
embrittlement. It is accordingly necessary to stabilize
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077168~ 2 -
the polymer against such deterioration, and this is done
by the addition of small amounts of chemical agents which
are effective for this purpose. Hydroxybenzophenones,
hydroxyphenylbenzotriazoles and phenylsalicylates are
thus effective and are used in this manner. They operate
by absorbing harmful ultraviolet energy and reemitting it
at a different energy level which does not adversely affect
the polymer.
The relative instability of polypropylene is due
to the presence of tertiary carbon atoms in the polymer
chain; these are subject to oxidative attack which is
catalyzed by heat and light. In the case of fiber compo-
sitions, for example, light is an especially important
factor because of the relatively large amount of surface
area of the polypropylene.
Japanese Patent Publication No. 66551/77
shows the stabilization of
certain synthetic resins, including polypropylene, by the
combination of a substituted piperidine, a triorganophosphite
and a secondary organophosphite. The secondary organophosphite
is an essential component of the stabilizer combination.
U.S. 3,640,928 (Murayama et al), which deals with
the stabilization of a wide variety of synthetic polymers,
shows the use of certain piperidine derivatives for that
purpose. Included among such piperidine derivatives is
bis(2,2,6,6-tetramethyl-4-piperidyl)adipate. It is stated
that these compounds can be used alone or in co~bination
with other known stabilizers, fillers, pigments and the like.
U.S. 3,840,494 (Murayama et al) shows much the same thing.
West German Patent Publication No. ~5 00 314 deals
with the stabilization of pigmented polyolefin compositions.
Stabilization is accomplished by means of cyclic di-tert-
alkylamines; these are defined very broadly and illustrated
profusely, and include bis-(2,2,6,6-tetramethyl-4-piperidinyl-
l-oxyl)-sebacate (see page 15). It is also stated that
07716S~ 3 ~
these cyclic di-tert-amines can be used for their intended
purpose in combination with other known additives.
The invention of this application is a light-stable
polypropylene composition comprising polypropylene and
minor proportions sufficient to improve the light stability
of said polypropylene of each of a piperidinyl compound
having the formula
r CH
7 ~ A
CHX--
~ 3 CH3
i_ Y
where R is alkyl of 1-4 carbon atoms or hydrogen, y is 1-4
and A is an organic radical or a phosphorus acid residue,
and a pentaerythritol polyphosphite. The organic radical
or phosphorous acid residue may be an ester, carbonate,
ether, thiocarbonate, sulfinate, sulfonate, phosphite or
phosphate radical, as shown more particularly in U.S.
3,640,928.
~ore narrowly, the invention comprises polypropylene
compositions containing a piperidinyl compound having the
formula
- CH3/
Rl~ O--CO . (CH2)h~--~ Nn
CH3 CH3
_ x
where R is alkyl of 1-4 carbon atoms or hydrogen, m is 1-4,
x i~ 2-3 and n is 0 or 1, and a pentaerythritol polyphosphite.
077168~ 4 _
It will be noted that the above piperidinyl compound
may comprise three substituted piperidinyl groups bound to
one another through a nitrogen atom, as well as one where
two substituted piperidinyl groups are bound to one
another through the residue of an aliphatic dicarboxylic
acid. In the first instance, such a compound may be
prepared by the reaction of a lower alkyl ester of a
tricarboxylic acid having the formula
N [ (CH2)mCOOH~
where m is 1-4, with 4-hydroxy-2,2,6,6-tetramethylpiperidine.
In the other instance, the piperidinyl compound
of the invention may be prepared by reaction of a di-
(lower)alkyl dicarboxylate with the 4-hydroxy-2,2,6,6-
tetramethylpiperidine. Illustrative di-(lower)alkyl di-
carboxylates include dimethyl and diethyl, glutarates,
suberates, sebacates, adipates and pimelates. The methods
of preparation shown in the above Murayama et al patents
are suitable here.
The pentaerythritol polyphosphite preferably is
a dialkyl pentasrythritol diphosphite. It may be prepared
by the reaction of pentaerythritol and two mols of triphenyl
phosphite, followed by transesterification of the resulting
diphenyl pentaerythritol diphosphite with a relatively non-
volatile alcohol such as stearyl alcohol. Other suitable
pentaerythritol polyphosphites may be prepared by reacting
various proportions of pentaerythritol and triphenyl
phosphite with one another. Thus, the reaction of three
mols of pentaerythritol and four mols of triphenyl phosphite
results in tripentaerythritol tetraphosphite, i.e., a product
wherein all of the phosphorus valences are attached through
oxygen to a pentaerythritol residue. It will be understood
3g
077168-~ - 5 -
that products of this type, being derived from two
polyfunctional reactants, are necessarily a mixture of
several products and that the term "product" is used
herein to designate the product obtained in principal
amounts.
Other proportions of the above two reactants may
be employed to obtain, on the one hand, products having
free hydroxyl groups attached to the pentaerythritol
residue and, on the other hand, products having un-
reacted phenyl ester groups; these phenyl ester groupscan, of course, be transesterified with relatively non-
volatile alcohols such as stearyl alcohol, dodecyl alcohol,
decyl alcohol and the like.
The details of method of preparation of these
pentaerythritol polyphosphites may be gleaned from the
disclosures of U.S. 3,205,250; U.S. 3,281,381;
U.S. 3,310,609; and U.S. 3,928,505.
The piperidinyl compound of the invention should
be used in concentrations ranging from about 0.03% to about
1.0% based on the polypropylene content. The pentaerythritol
polyphosphite should be used in concentrations ranging from
about 0.05% to about 1.0% on the same basis.
The piperidinyl compounds herein are known to impart
good ultraviolet stability to polymer compositions. Un-
fortunately, they are expensive because of the number ofprocessing steps required in their manufacture. The
invention of this application permits substitution of a
much less expensive additive, viz., the pentaerythritol
polyphosphite, for a large proportion, i.e., up to about
75%, of the piperidinyl compound, without loss of ultraviolet
stabilizing activity. ~s a matter of fact, in many instances
there is a considerable increase in such activity upon
1118~3~
077168-.~l - 6 -
addition of ,he pentaerythritol polyphosphite.
Other stabilizing agents can be added to the
polypropylene compositions herein. These include
neutralizers such as metal oxides and metal salts of higher
molecular weight carboxylic acids such as calcium stearate,
barium laurate, etc.; phenolic oxidation inhibitors such
as those described in U.S. 3,285,855; U.S. 3,644,482;
and U.S. 3,531,483; and various fillers, pigments, etc.
The efficacy of the polypropylene compositions of
the invention is shown by data collected from tests carried
out on 200/16 denier natural polypropylene multifilament.
The fiber compositions are prepared by dry blending the
various components and then extruding the mixture at
475F. Fibers are spun at 540 F, drawn at a ratio of
7:1 and given one twist per inch. The test consists of
exposure of the test fiber to conditions of ordinary
weather in the Caribbean. The tensile strength of the
fiber is measured at periodic intervals and the percent
retention of the original tensile strength after 140
kilolangleys ("KL") is taken as a measure of the resistance
of the fiber to deterioration. Test data for various
polypropylene fibers are shown in the following table.
Each fiber composition contains 100 parts of poly-
propylene, 0.05 phr (parts per hundred parts of resin)
of calcium stearate, 0.15 phr of octadecyl 3-(4-hydroxy-3,
5-ditertiarybutylphenyl)propionate and the indicated amounts
(phr) of toher additives.
Table
% Retention of
A B C D Tensile Strength after 140 KL
1. 0.2 43
2. 0.4 ~6
3. 0.2 0 (at 44 KL)
4. 0.2 0.2 74
077168~
~ Retention of
A B C D Tensile Strength after 40 KL
5. 0.3 0.1 64
6. 0.3 0.3 90
7. 0.2 0 (at 96 KL)*
8. 0.3 0 (at 48 KL)*
9. 0.6 64
A: bis-(2,2,6,6-tetramethyl-4-piperidyl)sebacate
B: tris-(2,2,6,6-tetramethyl-4-piperidyl)nitriloacetate
C: distearyl pentaerythritol diphosphite
D: tripentaerythritol tetraphosphite
* extrapolated values
It will be seen that test fiber samples Nos. 4, 5
and 6, representing the combination of the claims, are
rated quite high. ~oreover, No. 5 is rated as high (64)
as No. 9 (64), although it has a lower overall additive
content. Likewise, No. 4 is rated higher (74) than
No. 2 (56), with which it is directly comparable. So also,
No. 5 is rated higher (64) than No. 2 (56).
All parts and percentages herein, unless otherwise
expressly stated, are by weight.
