Note: Descriptions are shown in the official language in which they were submitted.
77
3-14119/CGC 998/-
Stabilization system for impact polystyrene
Impact polystyrenes in many different varieties are well known to
those skilled in the art. Such materials improve upon practical
toughness and overcome the brittleness and low impact strength of
general-purpose polystyrene by combining polystyrene with rubber,
generally of the polybutadiene type. The rubber ls dispersed iD the
polystyrene matrix in the form of discrete particles. Corresponding-
ly, most impact polystyrenes are graft copolymers or mechanical
mixtures of the components (polyblends). Processes for the prepara-
tions of these various impact polystyrenes are likewise well known
to those skilled in the art. Impact polystyrene exhibits most of the
advantages of polystyrene such as rigidity, ease of fabrication,
certain chemical resistance, variety of available shapes and colors.
In addition, it improves upon polystyrenes by exhibiting the prop-
erties noted hereinabove. As such, impact polystyrene is used in a
variety of applicatlons such as appliances, cabinets, packaging,
toys, housewares, industrial parts, decorative panels, and the like.
Impact polystyrene is fully described in numerous texts, for
example, Boundy ~ Boyer "Styrene - Its Polymers, Copolymers and
Derivatives", Reichhold Publishing Co., New York.
Since impact polystyrene is sub~ect to oxidatlve and tharmal
degradation and discoloration, a wide variety of light ~tabilizers
and antioxidants have been ~ecommended for use therein. The triazine
and cinnamate compounds noted herein are among such recommended
stabilizers and have shown good performance characte}istics in
impact polystyrene. These compounds have, howPver, exhibited
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lnadequate activity in the prevention of thermal degradation, a
property of signlficance in thermo-forming operations wherein
heat-softened fllm or sheet i8 forced against a cold mold.
It is, accordingly, the primary ob~ect of this invention to provide
a total stabilization system for impact polystyrene.
It is a further object to provide a combined system which improves
upon the stabilization performance of the individual components
thereof.
Various other objects and advantages of this inventlon will become
apparent from the following detailed description thereof.
It has now been found that by utilizing a combination of 2,4-bis(n-
octylthio)-6-(4-hydroxy-3,5-di-tert.butylanilino)-1,3,5-triazine and
octadecyl-3,5-di-tert.butyl-4-hydroxyhydrocinnamate in the propor-
tions noted hereinafter as a stabilizlng system for impact poly-
styrene, total stabilizing activity is achleved. Thus, thls blend
provides excellent stabilization against both oxidative and thermal
degradation. Of primary importance, the comblnation provides
significantly improved performance in the area where the individual
compounds are lacking, namely, in providing effective thermal
stability. In fact, a synergistlc effect i5 noted in that the
performance of the combination exceeds the sum of the performances
of the individ~al compounds at comparable concentrations. In
addition, the stabillzer system imparts minimal color to the impact
polystyrene and, after for~ulation, said polystyrene i9 character-
ized by ~ubstantial ability to retaln good color under processlng
conditions.
2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-dl-tert.butyl-anillno)-1,3,5-
triazlne ls commercially available under the trademar~ IRGANOX 565
from CIBA-GEIGY Corporation. The compound, methods ~or its prepsra-
tion and its antioxidant utility in a variety of substrate~,
including impact polystyrene, are well known.
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Octadecyl-3,5-di-tert.butyl-4-hydroxyhydrocinnamate is commercially
available under the trademark IRGANOX 1076 Erom CIBA-GEIGY Corpor-
ation. The compound, methods for its preparations and lts anti-
oxidant utility in a variety of substrates, including impact
polyYtyrene, are well known.
In order to exhibit the properties noted herein, the combination
contains the individual compounds in concentrations ranging from
0.01 to 0.04 % of triazine to 0.08 to 0.02 % of cinnamate, based on
the weight of the impact polystyrene. Preferred ranges include
0.01~S to 0.0375 % triazine and 0.075 to 0.025 % cinnamate.
Especially preferred is a combination of 0.0375 % triazine and
0.~25 % cinnamate.
All varieties of impact polystyrene are available for stabilization
by the synergistic combination of this invention. As previously
noted, the impact polystyrene may comprise polystyrene combined with
rubbers such as styrene - butadiene and polybutadiene.
The stabilizer combination may be incorporated into the impact
polystyrene by conventional techniques at any convenient stage.
Thus, it may be added prior to polymerization in conjunction with
the styrene monomer. Correspondingly, it may be added subsequent to
polymerization by being dissolved in a solvent such as methylene
chloride, hexane, cyclohexane, and the like, blending the solution
with the impact polystyrene and evaporation the solvent. In
addition, various secondary stabilizers may be included such as
ultraviolet absorbers, phosphitss, dialkyl thiodipropionates, and
the like.
The following example further illustrates the embodiments of this
invention.
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Example
This example illustrates the stabilizing effectiveness of the
instant stabili~er combination in impact polystyrene.
In the laboratory procedure utilized herein, a solution of eight
weight percent polybutadi~ne rubber (Firestone - DIENE 55) dissolved
in styrene monomer was prepared on a roller mill. The indicated
amount of stabilizer was also introduced at this point. 500 ppm of
zinc stearate were added to aid in removing the bottle after the
polymerization. The bottle was screwed into the polymerization
apparatus which was equipped with a double helical ribbon stirrer.
Since most commercial IPS bulk polymerizations are thermally
initiated processes, no initiator was used in the laboratory
process. A nitrogen atmosphere was established and then the rPactor
was heated to 121C within 1/2 hour. Heatlng continued at 121C with
efficient stirring until there was a 30 to 35 % monomer conversion
~~ 2-1/2 hours). The stirring rate was controlled to yield a two to
four ~m rubber particle size. The bottlss were removed from the
polymerization apparatus, blanketed with nitrogen, capped, and then
placed in a fluidized bed sand bath to complete the polymerizatlon.
The bottles were heated in the bath in the following fashion: one
hour at 100C to equilibrate the temperature, one hour to reach
140C and then an additional eight hours with the temperatur
increasing at the rate of 10C per hour to a maximum of 220C. After
the resin had cooled, the bottle was broken and the glass was
removed. The average weight of the polymer block was slightly over
600 grams. The block was placed into a vacuum oven at 200C and a
vacuum of 1 mm appl~ed as the polymer was heated for 45 ~inutes in
order to remove all volatiles. The block was removed fsom the oven,
immediately placed in a heated (205C) hydraulic press and then
pressed into a thick slab between two sheets of aluminium Poil
(three minutes heating, five minutes ln a cold press). The slab was
split with a band saw and the pieces were granulated.
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All the batches were extruded at 205C and then pelleti~ed. The
pellets were compression molded at 205C into 125 mil t2nsile bara.
The bars were then aged at 150C on glass plates placed on rotating
shelves in a forced air oven. Other tensile bars were aged at 80C
suspended from rotatlng shelves in a forced air oven. The specimen
yellowness index was determined on the bars at various intervals
according to ASTM D1925-63T. Correspondingly, the bars were
periodically measured for percent elongation in the Instron Tenaile
Testing Apparatus (Instron Engineering Corp., Mass.) at a pull rate
of 5 mm/minute according to ASTM D638.
The results of these tests are noted in Tables 1-4. Parts I and II
reflect experimental tests conducted at two different times.
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Table 1
Percent Elongation
Hours at 150C
-
Conc. (%) 0 1/2 1 1-1/2
Part I
IRGANOX 1076 0.1 56 38 10 7
IRGA~OX 565 0.05 66 45 22 7
0.035 63 38 19 7
0.025 39 31 9 7
IRGANOX 1076 0.05 53 36 22 8
IRGANOX 565 0.025
IRGANOX 1076 0.075 57 53 13 7
IRGANOX 565 0.0125
IRGANOX 1076 0.025 59 45 22 11
IRGANOX 565 0.0375
Part II
IRGANOX 1076 0.1 50 31 8 6
0.0875 43 29 8 6
0.~75 51 28 10 8
0.0625 61 16 11 8
IRGA~OX 1076 0.075 40 38 13 7
IRGANOX 565 0.0125
IRGANOX 1076 0.05 40 29 19 9
IRGANOX 565 0.025
IRGANOX 1076 0.025 47 34 22 7
IRGANOX 565 0.0375
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Table 2
Yellowness Index
_ Hours at 150C
Conc. (%) O 1/2 1 1-112 2 hrs.
Part I
IRGANOX 1076 0.1 -6 -1 7 13 ~-
IRGANOX 565 0.05 -3 4 5 8
0.035 -8 3 1 5
0.025 -8 4 ~2 5
IRGANOX 1076 0.05 -7 -1 1 3
IRGANOX 565 0.025
IRGANOX 1076 0.075 -6 -2 1 3
IRGANOX 565 0.0125
IRGANOX 1076 0.025 -6 -2 3 5
IRGA~OX 565 0.0375
Psrt II
IRGANOX 1076 0.1 -4 -3 -1 -1
0.0875 -6 -3 -2 -3 -1
0.075 -2 1 3 11 8
0.0625 -7 -5 -3 -3 -1
IRGANOX 1076 0.075 -3 -2 -1 0 -1
IRGANOX 565 0.0125
IRGANOX 1076 0.05 -3 -4 -2 -2
+
IRGANOX 565 0.025
IRGANOX 1076 0.025 -3 -2 -2 -2 -1
+ +
IRGANOX 565 0.0375
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Table 3
Percent Elon~ation
Hours at 80C __
-
Conc. (%) 0 300 600 900 1200
Part I
IRGANOX 1076 0.1 56 36 17 3 3
IRGANOX 565 0.05 66 23 14 7 3
0.035 63 26 9 7 3
0.025 39 14 4 3 3
IRGANOX 1076 0.05 53 33 32 15 8
IRGANOX 565 0.025
IRGANOX 1076 0.075 57 36 36 14 13
IRGANOX 565 0.0125
IRGANOX 1076 0.025 59 32 27 22 19
IRGANOX 565 0.0375
Part II
IRGANOX 1076 0.1 50 22 11 6
0.087543 14 9 4 7
0.075 51 26 20 10 7
0.062561 16 8 4 8
IRGANOX 1076 0.075 40 30 15 13 10
+ +
IRGANOX 565 0.0125
IRGANOX 1076 0.05 40 31 13 7 4
+ +
IRGANOX 565 0.02S
IRGANOX 1076 0.025 47 32 18 14 15
+ +
IRGANOX 565 0.0375
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Table 4
.
Yellowness Index
Hours at 80C
Conc. (%) O 300 600 900 1200
Part I
IRGANOX 1076 0.1 6 1 5 40 44
IRGANOX 565 0.05 -3 9 17 24 36
0.035 -8 -1 13 22 35
0.025 -8 2 17 38 43
IRGANOX 1076 0.05 -7 5 10 16 19
IRGA~OX 565 0.025
IRGANOX 1076 0.075 ~6 5 7 9 16
IRGANOX 565 0.0125
IRGANOX 1076 0.025 ~6 4 11 14 16
IRGANOX 565 0.0375
Part II
IRGANOX 1076 0.1 -4 -1 7
0.0875 -~ -1 12 33 48
0.075 -2 10 13 20 29
0.0625 -7 -2 6 22 46
IR~ANOX 1076 0.075 -3 9 14 - -
IRGANOX 565 0.0125
IRGANOX 1076 0.05 -3 1 8
IRGANOX 565 0.025
IRGANOX 1076 0.025 -3 5 16
IRGANOX 565 0.0375
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It i5 thus seen that the instant combination of antioxldants
provides significantly improved stabilization effectiveness in
impact polystyrene. This improvement is particularly seen in the
pattern of "total" stabilization, i.e., the combination provides
meaningful performance characteristics in each indicia of
stabilization as contrasted with the absence thereof in the
performance of the individual compounds.
In summary, this invention provides a synergistic system for
stabilizing impact polystyrene against oxidative and thermal degra-
dation. Variations may be made in various elements thereof without
departing from the scope of the invention as defined by th~ follow-
ing claims.
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