light stabilization of flame retardant impact polystyrene

Light Stabilization of Flame Retardant Impact Polystyrene*

RICHARD BRADLEY

Betz Laboratories Trevose, Pennsylvania

and

JOSEPH FARRER and LAWRENCE TESTA

Ciba-Geigy Corporation Polymer Additives Department

Ardsley, New York 10502

This paper presents the results ofa study on the effectiveness of ultraviolet absorbers and light stabilizers in preventing the discoloration of flame retardant impact polystyrene. The de- leterious effect of certain flame retardants, i.e., aromatic or aliphatic halogenated compounds, on the light stability ofthis polymer is shown. Light stabilizer systems resulting i n substantially improved color stability during light exposure are presented. The beneficial effect of co-additives, including antioxidants, acid acceptors, epoxies, phosphites, and thiosynergists, on light stability is also discussed.

INTRODUCTION

nderwriters' Laboratories has issued manufacturing U specifications which require that all plastic enclo- sures used in television equipment manufactured after July 1, 1975 have a 94-V-2 ratingand a 94-V-1 rating by July, 1977 (1). As UL already requires that plastics used in electrical appliances enhibit low flammability, and comply with the 94 Horizontal Burning Test, the use of flame retardant additives in impact polystyrene (IPS) has become a matter of great interest to both polymer producers and appliance manufacturers.

I11 addition to low flammability, it is expected that the articles molded from these flame retardant grades of impact polystyrene retain all the other desirable proper- ties of the resin, e.g., impact strength, heat distortion temperature, and, especially in light colored articles, resistance to discoloration during light exposure. One method for providing this discoloration resistance has been to paint the molded part, an expensive operation (2) . The use ofan effective light stabilizer system would eliminate the need for this costly additional step, along with the environmental concerns of the paint systems, and provide an aesthetically more pleasing article.

EXPERIMENTAL

Sample Preparation and Test Procedure

The flame retardants and stabilizers were incorpo- rated into natural IPS by double pass extrusion in a one in., 24:l LID, extruder using a double flighted mixing

*Pre\eiited at the lrr ternational S?rnpuaiuni on Flammabili ty and Fire Retarclarits, Toronto, Canada, hla! 6-7, 1976

screw. The melt temperature was 210°C. In impact polystyrene, the halogenated flame retardants are commercially used at concentrations of 10 to 12 percent, while antimony oxide use levels range from 4 to 6 percent in order to achieve the 94-V-0 rating. A system containing 12 percent halogenated flame retardant and 4 percent antimony oxide was used in this study. Plaques, 4 x 4 x 0.060 in., were compression molded at 193°C. Light exposures were performed on 1 x 1 x 0.060 in. samples cut from the molded plaques.

Test samples were exposed in an Atlas Carbon Arc Fadeonieter (CAF) model FDA-R set to maintain 70 percent relative humidity and a temperature of 18°C.

Sample Evaluation and Materials

(I2-b) color measurements were obtained initially and at various exposure intervals with a Gardner XL 10 color meter. (L-b) values are calculated from measurements of L and b. In the Hunter color coordinate system, L iiidicates lightness, and b is a measure of blueness arid yellowness (3 ) . Higher (L-h) values indicate better color.

Listed below are the polymers and flame retardants used in this study:

Impact Polystryrene (IPS): High impact, high heat distortion, injection-molding grade.

FR-1 Primary flame retardant; decabromodiphenyl oxide, 83 percent aromatic bromine, 290-304" n1.p.

FR-2 Primary flame retardant; an alicyclic hydrocarbon (Citex BC-267, Cities Service), 69 percent aliphatic bromine plus chlorine, 200°C i n . p.

782 POLYMER ENGINEERING AND SCIENCE, NOVEMBER, 1977, Vol. 17, No. 7 1

Light Stabilization of Flame Retardant Impact Polystyrene

Sbz03 Antimony oxide (solid); 100 percent active ingre- dient, Thermoguard S, M & T Chemical.

RESULTS AND DISCUSSION

Effect of Flame Retardant on Color Stability of IPS The addition of halogenated flame retardant, either

FR-1 or FR-2, severely reduced the color stability of natural IPS during UV exposure.' I t was also observed that this reduction in color stability is due to both com- ponents of the flame retardant additive package, i.e., to the primary flame retardant and the antimony oxide synergist. Discoloration due to antimony oxide was grey, .while the halogenated flame retardants resulted in severe brown discoloration. These results are presented in Fig. I .

Stabilization of IPS Containing Aromatic Flame Retardant (12% FR-1 + 4% Sbz03)

Effect of Light Stabilizers and Blends. Several light stabilizers significantly improved the color stability of the flame retardant polymer during exposure i n the Carbon Arc Fadeometer. Among the light stabilizers evaluated, LS-1, a benzotriazole, and LS-2, a chlorinated henzotriazole, were the most effective in improving color stability at use levels between 0.5 and 1.0 percent (See Table 9 for identification of additives. ) Improved color stability was most apparent up to 100 hrs of exposure (Fig . 2). One other substituted beno- triazole, LS-6, was effective but less so than LS-1 or LS-2 (Table 1) . The nickel light stabilizer, LS-3, the benzoate, LS-7, the benzophenone, LS-5, and the

0 m 40 €4 80 100 110 140

Hours Exposure Carbon Arc Fadeometer

Fig. 1. Effect of f lame retardant on color stability of I P S ; no light stabilizer present.

--- -I 0 I 10 w 00 110 3 4 0 100

Hours Exposure -Carbon Arc Fadeometer

j---- - ~~~~

Fig. 2. Effect of light stabilizers on color stahilit!], 12% FR-I + 4% antimony oxide.

amine light stabilizer, LS-4, were relatively ineffective in improving color stability (Table 1 ).

No significant improvement in color stability relative to that with 0.5-1.0 percent of LS-2 was obtained with the light stabilizer blends evaluated. Evaluations in- cluded blends of the benzotriazole light stabilizers with a nickel light stabilizer and the ainine light stabilizer (Table 2).

Table 1. Effect of Light Stabilizer on Color Stability of Flame Retardant IPS Containing 12% FR-1 + 4% Sb,O::

Carbon arc fadeometer exposure Hunter (L-b) after indicated

exDosure time. hrs'

Unexposed 20 40 60 100 130 150

0.5 LS-1 1.0 LS-1 1.5 LS-1 0.25 LS-2 0.5 LS-2 1.0 LS-2 0.5 LS-3 1.0 LS-3 0.5 LS-4 1.0 LS-4 1.0 LS-5 1.0 LS-6 1.0 LS-7

No light stabilizer

No FR No LS

77 77 78 72 76 76 72 67 71 76 75 76 75

76

69

38 31 27 17 14 11 48 38 34 25 16 14 55 42 38 31 16 14 36 27 24 17 13 13 65 56 48 34 18 11 59 50 45 38 18 14 22 17 16 13 12 12 25 20 17 15 13 11 24 20 18 14 14 14 32 27 24 19 13 13 30 22 21 16 14 14 46 32 29 21 18 16 22 18 17 13 13 12

26 22 20 17 12 12

64 62 60 57 53 53

'Higher (I-b) values indicate better color.

POLYMER ENGlNEERlNG AND SCIENCE, NOVEMBER, 1977, VoJ. 17, No. 1 1 783

Richard Bradley, Joseph Farher and Lawreme Testa

Table 2. Effect of Light Stabilizer Blends on Color Stability of Flame Retardant IPS Containing 12% FR-1 + 4% Sb20:,


exposure time, hrs'

Unexposed 20 40 60 100 130 150

1.0% LS-1 + 1 .O% LS-4

0.5% LS-1 + 0.5% Ls-4

0.25% LS-I + 0.25% LS-4

1.0% LS-1 + 1 .O% LS-3

0.5% LS-I +

0.5% LS-3

0.25% LS-I + 0.25% LS-3

0.5% Ls-2 + 0.5% LS-4

0.25% LS-2 + 0.25% LS-4

0.5% LS-2 + 0.5% LS-3

0.25% LS-2 + 0.25% Ls-3

1.0% LS-4 t 1 .O% LS-3

0.5% Ls-4 + 0.5% LS-3

0.25% LS-4 + 0.25% Ls-3

76 65 47 41 37 24 26

79 59 50 42 33 15 16

77 60 41 27 16 16 13

65 56 40 37 34 21 17

61 56 47 47 41 20 20

73 29 23 21 16 14 13

76 36 35 42 31 26 18

75 33 31 24 16 15 14

73 48 35 30 24 18 16

74 34 25 22 15 13 15

69 31 22 21 20 15 13

73 27 23 22 20 17 19

77 29 25 22 21 20 18

'Higher (L-b) values indicate better color.

Effect of Co-Additives. Ofthe various light stabilizers evaluated, LS-2 was sclccted as the main candidate for additional evaluations. Co-additives at 0.25 percent were evaluated with 0.50 percent LS-2 in an attempt to further improve color stability of flame retardant IPS. Antioxidants were evaluated in order to determine their effectiveness in trapping any fi-ee radicals formed as a result of decomposition of the polymer or the flanic retardant. In addition, epoxies and other acid acceptors, such a s stearates and P\'C stabilizers, were evalrtated ;IS

co-additives for preventing the harmful effects due to acid forniation during the decomposition of thc flame retardant. Peroxide tlccomposers, i. e., thiosyngerists and phosphites, were also evaluated.

htioxidants provided substantially improved color stability in comliination with 0.50 percent IS-2. Of i l i a -

terials that are ciirren tly commercially available, 120-2 (Fig . 3 ) , '40-3, AO-4 and AO-8 were the most effective antioxidant5 eultiitted. AO-1, AO-5, '40-6, and AO-7 were found to have R detrimental effect on color staldit!. (Table 3 ) .

Ofthe three epoxy co-additives evaluated i n conjuiic- tion with 0.5 percent of the chloririated henzotriazole, LS-2, only EP-1, the epoxy cresol-iiovolac, sigtrificantly iniproved color stability (Tuble 4 and F i g . 3 ) .

Improved color stability was obtaincd with thc acid acceptors HX-1, zinc stcarate, and HX-2, tin inaleate, in coinliination with 0.5 percent LS-2 (Fig. 3) . N o significant itiiprovcirient wiis olitaiiicd with the other acid acceptors evalriated (Tahle 5).

In general, phosphites showed no activity in iniprov- ing the discoloration resistance already obtained with the light stabilizer. Thiosynergists, represented here by DLTDP (PO-l), also showed no improvcinent in light stability beyond that obtained with the light stabilizer alone. These results are shown in ?'cil?le 6.

Table 3. Effect of Antioxidants on Color Stability of Flame Retardant IPS Containing 12% FR-1 + 4% Sb,O,


exposure time, hrs*

Unexposed 20 40 60 100 130 150

0.5% LS-2 0.25% Antioxidant

AO-1 78 65 46 31 28 20 15 AO-2 78 57 55 44 40 44 27 AO-3 76 63 53 48 41 44 26 AO-8 75 64 42 40 43 40 17 AO-4 79 71 59 52 51 41 40 AO-7 75 44 31 26 17 14 14 AO-5 74 42 32 27 16 16 16 AO-6 74 43 31 28 18 16 16

No antioxidant 76 65 56 48 34 18 11

"Higher (L-b) values indicate better color.

784 POLYMER ENGINEERING AND SCIENCE, NOVEMBER, 1977, Vol. T7, No. 1 I

Light Stahilization of Flame Retardant Impact Polystyrene

Table 4. Effect of Epoxy on Color Stability of Flame Retardant IPS Containing 12% FR-1 and 4% Sb,O:)


exDosure time. hrs*

Unexposed 20 40 60 100 130 150

0.5% LS-2 + 0.25% EPOXY

EP-1 78 72 62 54 50 45 39 E P-2 77 42 33 28 16 16 14 E P-3 77 40 33 28 17 17 17

No epoxy 76 65 56 48 34 18 11

'Higher (L-b) values indicate better color

Table 5. Effect of AciU Acceptors on Color Stability of Flame Retardant IPS Containing 12% FR-1 + 4% SbyO.{


exposure time, hrs*

Unexposed 20 40 60 100 130 150

0.5% Ls-2 4- 0.25% Co-additive .l%HX-l

HX-1 HX-2 HX-3 HX-4 HX-5 HX-6 HX-7

No co-add itive

81 67 53 49 45 37 32 78 59 44 45 34 30 20

64 43 33 28 17 16 17 68 40 30 24 15 16 17 77 44 33 25 17 15 18 61 36 27 25 17 15 16 70 44 30 27 21 17 14 76 65 56 58 34 18 11

79 72 61 51 48 33 29

'Higher (L-b) values indicate better color.

Table 6. Effect of Thioester and Phosphites on Color Stability of Flame Retardant IPS Containing 12% FR-1 + 4% Sb,O,:


exDosure time. hrs*

4

................

b '

? so I 888.

a " \ -

I- .-. , ~ _ - -- r - - ~ - 7 p - 7

0 m 40 m LUI 1w 110 140

Hours Expowe - Carbon Arc Fademeter

Fig . 4 . Color sfabiZit!/ of I P S contuining cilii'/iutic.panict retnr- dotit, 12% FR-2 + 4% untitnoriy oxide.

Outstandirig color stability was obtained with 1:l blends of thc hindered amiiie (LS-4) with the henzotriazole (LS-1) or the chlorinated benzotriazole JLS-2) (Table 8 and Fig. 4 ) . These systems niaintained their initial white color through 150 hrs of Carbon Arc Fadcometer exposure, when the test was tei-ininated. Blends of the nickel light stabilizer (LS-3) with either the hindered aminc or the 1,enzotriazolr.s of€'crd no advantage over the henzotriazoles alone.

Unexposed 20 40 60 100 130 150 CONCLUSIONS

0.5% Ls-2 + 0.25% Co-add itive

The color stability of IPS containing halogellater1 flame retardant additives can be suljstantiallv iiririrovcd

PO-1 71 61 46 35 32 20 17 11y the addition of light stabilizers, light staLilizer PO-2 75 63 48 38 29 21 21

Table 7. Effect of Light Stabilizers on Color Stability of Fire PO-3 60 38 27 27 20 17 15

Retardant IPS Containing 12% FR-2 and 4% Sb,O, PO-4 11 44 33 29 21 17 16 No additive 76 65 56 48 34 18 11

'Higher (L-b) values indicate better coloi Carbon arc fadeometer exposure Hunter (L-b) after indicated

exDosure time. hrs'

Stabilization of IPS Containing Aliphatic Flame Unexposed 20 40 60 100 130 150 Retardant (12% FR-2 + 4% SbzOJ

The light stabilizing effectiveness of the benzo- triazoles was particularly apparent ill the IPS containing FR-2 (Tables 7 and 8 and Fig . 4 ) . IPS containing either LS-1, the benzotriazole, or LS-2, the chlorinated henzotriazole, at use levels from 0.5 to 1.5 percent showed minimal discoloration even after 100 hrs of exposure in a Carbon Arc Fadeometer and were essentially equiva- lent to the non-flame retardant IPS in UV resistance. Although each of the other light stabilizers evaluated offered improved color stability, they were inferior to I S 1 and LS-2 after longer Carbon Arc Fadeometer exposure (Table 7).

0.5% Ls-1 1 .O% LS-1 1.5% LS-1 0.50% LS-2 1 .O% LS-2

1.0% LS-3

1 .O% LS-4 1 .O% LS-5 1 .O% LS-6 1 .O% LS-7 No light stabilizer

0.5% Ls-3

0.5% Ls-4

77

75 72 77 70 65 73 76 71 63 62

77

78 75 71 69 61 37 41 78 76 74 69 49 46 74 73 70 64 42 38 74 72 69 65 64 69 77 70 73 71 65 67 71 43 41 27 19 20 65 63 56 25 19 17 73 67 62 34 31 32 70 64 62 38 18 17 72 61 59 39 26 27 55 48 42 29 26 25 27 21 20 16 14 14

46 32 24 20 13 13

'Higher (L-b) values indicate better color

POLYMER ENGlNEERING AND SCIENCE, NOVEMBER, 1977, VoI. 17, No. 7 1 785

Richard Bradley, Joseph Farber and Lawrence Testa

Table 8. Effect of Light Stabilizer Blends on Color Stability of 15-2 Fire Retardant IPS Containing 12% FR-2 + 4% Sb,O:< -. .


exposure time, hrs*

Unexposed 20 40 60 100 130 150 c1

1.0% LS-1 i 1.0% LS-4

0.5% Ls-1 t 0.5% LS-4

72 74 74 74 75 76 77

70 77 78 78 78 78 77

15-3 74 78 77 77 75 72 71 0.25% LS-1 +

0.25% LS-4

1.0% LS-1 + 1 .O% LS-3

0.5% Ls-1 + 0.5% Ls-3

0.25% LS-1 + 0.25% LS-3

60 60 61 61 61 60 50

65 67 67 66 64 62 64

70 71 69 67 60 57 59

+ 2-(3’,5’-di-tert-butyl-2’-hydroxyphenyl)-5~ chlorobenzotriazole; 154-158’C m.p.

T

1 oc, H5

74 77 77 78 78 78 78 0.5% Ls-2 + 0.5% Ls-4

Nickel bis[O-ethyl (3.5 di-tert-butyl-4-hydroxybenzyl)] phosphonate; 180°C m.p. (Min.) 72 77 78 77 76 74 76 0.25% LS-2 +

0.25% LS-4 15-4

Proprietary hindered amine light stabilizer 70 72 72 71 68 66 66 0.5% Ls-2 + 0.5% Ls-3

72 74 72 70 64 62 58

64 67 64 64 64 49 39 1.0% LS-4 + 1 .O% LS-3

68 71 67 54 28 29 26 0.5% Ls-4 + 0.5% Ls-3

15-5

71 73 60 29 25 22 22 2-hydroxy-4-n-octoxybenzophenone; 48-49°C rn.p. 0.25% LS-4 + 0.25% LS-3

‘Higher (L-b) values indicate bener color

15-6

blends, and light stabilizer/co-additive combinations. In systems containing the aromatic flame retardant,

the best color stability was obtained with 0.5-1.0 percent LS-2 in combination with 0.25 percent AO-2. In addition, results indicate that further iniprovements in color stability can be obtained with the epoxy cresol-novolac

Table 9. Additive Structures

LIGHT STABILIZERS

15-7

LS- 1

2(2’-hydroxy-5‘ rnethylphenyl) benzotriazole; 128-132°C rn.p.

C,H17

2(2-hydroxy-5-tert-octylphenyl) benzotriazole; 101-105°C rn.p.

2,4-di-tert-butylphenyl-3’,5‘-di-tert-butyl-4’- hydroxybenzoate; 190°C m.p. (Min.)

POLYMER ENGINEERING AND SCIENCE, NOVEMBER, 1977, Vol. 17, No. 1 1

Light Stabilization of Flame Retardant lmpact Polystyrene

AO-1

AO-2

AO-3

AO-4

AO-5

A 0 4

I. ANTIOXIDANTS

x

@- ,CH,CH,C-OCY, C It tetrakis [ methylene 3-(3',5'-di-tert-buty1-4'- hydroxyphenyl) propionate] methane; 1 10-1 25°C m.p.

% octadecyl 3-(3',5'-di-tert- butyl-4' hydroxyphenyl) propionate; 50-55'C m.p.

thiodiethylene bis-(3,5-di-tert-cutyl-4-hydroxy) hydrocinnamate; 63°C m.p. (Min.)

0.0-di-n-octadecyl-3.5 di-tert-butyl-4 hydroxybenzyl phosphonate; 50°C m.p. (Min.)

HO

N 4 <q SC, H,,

2.4 bis(n octylthio) 6 ~ ( 4 hydroxy~3.5di tert-butyl anlino)-l,3.5 triazine; 93-98°C

Y x

1.6-hexamethylene bis-(3,5-di-tert-buty1~4-hydroxydro cinnarnate): 103-108°C

AO-7

CH 1

2,6-di-tert-butyl p-cresol; 69°C m.p

AO-a

* % 0 0

CH, CH, -CNHNHC-CH, CH,

N,N'-bis[3(3',5'-di-tert-butyl-4'-hydroxvPh~~V~~ propionyl] hydrazine; 226°C m.P.

EPOXIES

EP-1 Epoxy Cresol Novolac

EP-2 triglycidyl isocyanurate (TGIC)

EP-3 Bisphenol epoxy

PHOSPHITES AND THIOSYNERGISTS

PO-1 DLTDP

PO-2 Distearyl pentaerythritol diphosphite

PO-3 tr ioxty l phosphite

PO-4 Experimental Phosphite

ACID ACCEPTORS

HX-1

HX-2

HX-3

HX-4

HX-5

HX-6

H X ~ 7

Zinc Stearate

Tin Maleate

Cyanoguanidine

Calcium Ricinoleate

Organo~tin Stabilizer

Phosphorous containing PVC stabilizer

Ea-Cd Stabilizer

(EP-1) and with zinc stearate (HX-1) or tin inaleate (HX-2)' (Fig . 3 ) .

In IPS containing the aliphatic flame retardant, good color stability was obtained with 0.5-1.0 percent of LS-1 or LS-2 alone. Outstanding color stability was obtained in blends of these light stabilizers with the amine light stabilizer, LS-4 (Fig. 4 ) .

ACKNOWLEDGMENTS We would like to express our sincerest thanks to Mr.

Harry Evers arid M r . John Windus, who performed most of the experimental work, and to 1413. Mary Trojak, whose help in preparing the manuscript was invalualde.

REFERENCES 1. A. S. Wood, Mod. Plust., (Sept. 1974). 2. R. B. Ludwig and S . Bergman, "Fire Retardancy in the Elec- trical and Electronics I n d i i s t ~ , " Fire Retardant Chemicals Association, New York, N.Y. (October 1975). 3. R. S. Huriter,J. Opt. SOC. Am., 48, 985 (1958).

POLYMER ENGINEERING AND SCIENCE, NOVEMBER, 1977, Vol. 17, No. 1 1 787

light stabilization of flame retardant impact polystyrene

Documents