21 Carbon Black Embrittlement of ABS
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RUDOLPH D. DEANIN and KALIDAS R. PATEL Plastics Department, University of Lowell, Lowell, Mass. 01854
The addition of carbon black to ABS resin improves its hardness, modulus of rigidity, heat deflection temperature, and ultraviolet stability but reduces its ultimate strength, particularly its impact strength. Fine particle size and high structure carbon blacks have the greatest effects.
/Commercial ABS generally combines the rigidity, strength, and heat ^ and chemical resistance of a continuous styrene/acrylonitrile (SAN) copolymer matrix with the impact resistance gained from small dispersed butadiene rubber particles (1). Carbon black reinforces the strength and the resistance of butadiene rubbers against tearing, abrasion, and chemical attack (2, 3); a similar reinforcement in plastics is rarely observed (4, 5). This study investigates if butadiene rubber in ABS makes it susceptible to carbon black reinforcement Experimental Two commercial grades of ABS were used: Goodrich Abson 89140 and 89110 (Table I) which represent "soft" and "hard" grades presumably made with high and low rubber contents (6). Four commercial grades of carbon black were used (Table II) which represent fine and coarse particle size and low and high "structure." ABS was blended with 0-20 phr (parts per hundred of resin) carbon black by masticating the blends for 10 min at 152 °C on 6 X 12 in. two-roll, differential-speed mills and by pressing for 10 min at 174° C to form % X 6 X 6 in. sheets. These were machined into standard % X % X 5 in. test bars, and properties were measured according to standard ASTM methods. Results are presented in Tables III-X. Discussion The addition of carbon black to ABS markedly increased its rigidity both at room temperature (Tables III-V) and at elevated temperature 256 Deanin and Crugnola; Toughness and Brittleness of Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
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Carbon Black in ABS
Table I.
Description of ABS
a
Goodrich Abson grade General type Shore D hardness Barcol hardness Flexural modulus, 10 psi Flexural strength, 10 psi Izod notched impact strength, fpi Heat deflection temperature, 264 psi, °C Melt flow, 250°C, 5000 g, g/10 min Burning rate, A S T M D635, inch/min
89140 "soft" 76 58 2.62 9.1 4.2 99 18.5 1.7
5
3
89110 "hard" 85 70 3.52 10.9 1.5 96 6.8 1.3
"Experimental data from present study
Table II.
Description of Carbon Blacks (7) Medium Color
Type
Black Sterling Black Pearls Pearls
Cabot Grade
Particle size Structure Av. particle diam.., nijtt D B P absorption, cc/100 g Density, lb/cu ft
Table III. Carbon Blacks Black Pearls 700
Black Pearls 800
Sterling SO
Regal SRF-S
Low Color Regal
700
800
SO
SRF-S
fine high 18 115 21
fine low 16 60 30
coarse high 41 120 22
coarse low 60 62 29
Shore Durometer (D) Hardness—ASTM D2240 Amount, phr 0 3 10 20 0 3 10 20 0 3 10 20 0 3 10 20
ABS-89140 76 79 81 84 76 78 79 84 76 79 81 82 76 79 81 82
ABS-89110 85 86 86 87 85 86 85 87 85 83 84 87 85 84 85 86
Deanin and Crugnola; Toughness and Brittleness of Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
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Table IV. Carbon Blacks Black Pearls 700
Black Pearls 800
Sterling SO
Regal SRF-S
Table V . Carbon Blacks Black Pearls 700
Black Pearls 800
Sterling SO
Regal SRF-S
Barcol Hardness—ASTM D2 5 8 3 Amount, phr
ABS-89140
0 3 10 20 0 3 10 20 0 3 10 20 0 3 10 20
58 58 62 66 58 57 62 70 58 58 62 67 58 61 63 65
ABS-89110 70 73 74 79 70 72 75 85 70 72 75 79 70 73 76 79
Flexural Modulus—- A S T M D790 (]psi) Amount, phr
ABS-89140
ABS-89110
0 3 10 20 0 3 10 20 0 3 10 20 0 3 10 20
262,000 277,000 293,000 372,000 262,000 294,000 344,000 427,000 262,000 278,000 300,000 346,000 262,000 274,000 298,000 350,000
352,000 379,000 410,000 458,000 352,000 374,000 392,000 451,000 352,000 373,000 432,000 467,000 352,000 397,000 417,000 468,000
(Table VIII). Fine particle carbon black was somewhat more effective than the coarse grade. Such "hardening" effects usually occur when inorganic fillers are added to organic polymers, particularly thermoplastics. In this study, the effects might be more pronounced for two reasons: (1). The carbon black probably concentrated in the rubber domains where it reached loadings as high as 200 parts carbon black per 100 parts polybutadiene; this greatly reduced the "softening" effect of the rubber on the SAN matrix. (2). The high surface area of the carbon
Deanin and Crugnola; Toughness and Brittleness of Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
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Carbon Black in ABS
blacks could immobilize more polymer molecules than the coarser inorganicfillerssuch as clay and calcium carbonate. Thus carbon black could increase the hardness, modulus, and heat deflection temperature of ABS in applications where the butadiene rubber had detracted too much from the inherent properties of SAN. However, the addition of carbon black reduced ultimate strength properties both in low-speed flexure (Table VI) and in high-speed impact (Table VII). Fine particle size carbon black had the greatest effect Table VI. Carbon Blacks Black Pearls 700
Black Pearls 800
Sterling SO
Regal SRF-S
Table VII. Carbon Blacks Black Pearls 700
Black Pearls 800
Sterling SO
Regal SRF-S
Flexural Strength—ASTM D790 (psi) Amount, phr 0 3 10 20 0 3 10 20 0 3 10 20 0 3 10 20
ABS-89140 9100 8900 7700 4500 9100 8600 8100 6900 9100 9000 8700 7900 9100 9100 8600 6700
ABS-89110 10,900 11,100 9400 6700 10,900 10,600 8800 6800 10,900 11,600 10,900 9700 10,900 11,600 10,500 9600
Izod Notched Impact Strength—ASTM D256 (fpi) Amount, phr
ABS-89140
0 3 10 20 0 3 10 20 0 3 10 20 0 3 10 20
4.2 1.9 1.0 0.8 4.2 1.4 1.0 0.7 4.2 2.8 1.2 1.0 4.2 2.7 1.4 1.0
ABS-89110 1.5 1.1 0.8 0.8 1.5 1.0 0.8 0.8 1.5 1.0 0.9 0.8 1.5 1.0 1.0 0.8
Deanin and Crugnola; Toughness and Brittleness of Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
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Table VIII. Carbon
Heat Deflection Temperature—ASTM D648 (264 psi), ( ° C )
Blacks
mt, phr
Black Pearls 700
0 3 10 20 0 3 10 20 0 3 10 20 0 3 10 20
Black Pearls 800
Sterling SO
Regal SRF-S
Table IX.
Black Pearls 700
Black Pearls 800
Regal SRF-S
99 101 103 106 99 101 103 106 99 100 102 103 99 100 102 102
ABS-89110
96 97 99 101 96 97 99 103 96 98 98 98 96 97 98 99
Melt Flow—ASTM D1238 ( 2 5 0 ° C , 5000 g, g/10 Min)
Carbon Blacks
Sterling SO
ABS-89140
A
lint, phr
0 3 10 20 0 3 10 20 0 3 10 20 0 3 10 20
ABS-89140
18.5 8.2 2.0 0.0 18.5 8.9 2.1 0.1 18.5 17.7 10.1 0.9 18.5 18.4 11.3 5.9
ABS-89110
6.8 5.2 3.9 0.6 6.8 4.4 3.1 0.7 6.8 7.8 3.1 2.7 6.8 5.5 5.0 4.1
on flexural strength. This probably arose from the carbon black acting as an impurity or flaw which initiated the failure in the SAN matrix. Also the carbon black in the rubber particles might reduce their ability to promote ductility and impact resistance. Thus carbon black may sacrifice much of the impact improvement which the rubber originally produced. Earlier studies show that even the small amounts of carbon black used for ultraviolet stabilization may produce some brittleness (8).
Deanin and Crugnola; Toughness and Brittleness of Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
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Note that in recent studies the embrittlement of ABS by fillers was alleviated by reducing interfacial adhesion (9). Also carbon black markedly reduced melt processability (Table IX), particularly when fine particle size was used in "soft" ABS. This might be caused by the bonding between carbon black surfaces and polymer molecules or by the adsorption of low molecular weight lubricants on the carbon black surface. This suggests that coarse carbon black, especially low structure grades, should be used for the least loss of processability. Finally, carbon black did reduce burning rate somewhat, especially when high structure grades were used (Table X ) , but not sufficiently to act as a sole flame-retardant—only as an assistant to more conventional flame-retardant additives. The importance of char and free radicals in burning mechanisms (JO) and the relationship of char and free radicals to carbon black should prompt further exploratory studies of this property—viz., carbon black's synergistic combination with conventional flame retardants. Table X. Carbon Blacks Black Pearls 700
Black Pearls 800
Sterling SO
Regal SRF-S
Burning Rate—ASTM D635 (Vs In., In./Min) Amount, phr
ABS-89140
ABS-89110
0 3 10 20 0 3 10 20 0 3 10 20 0 3 10 20
1.7 1.6 1.6 1.3 1.7 2.0 1.7 1.6 1.7 1.5 1.5 1.3 1.7 1.7 1.7 1.5
1.3 1.2 1.1 1.0 1.3 1.6 1.3 1.3 1.3 1.0 1.0 0.9 1.3 1.2 1.1 1.1
Conclusions The addition of carbon black to ABS improves its hardness, modulus of rigidity, heat deflection temperature, and ultraviolet stability but reduces its ultimate strength, particularly its impact strength; recent surface treatment techniques might alleviate this. Theoretically it could conribute to flame retardance, but this would require further studies of its synergism.
Deanin and Crugnola; Toughness and Brittleness of Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
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Literature Cited
1. Saxe, J. P., Pokigo, F. J., Mod. Plast. Encyc. (1973) 50 (10A), 16. 2. Kraus, G., "Reinforcement of Elastomers," Interscience, New York, 1965. 3. Boonstra, B. B., "Rubber Technology," M . Morton, Ed., Chap. 3, Van Nostrand Reinhold, New York, 1973. 4. Brydson, J. A., "Plastics Materials," pp. 118, 181, 390, 424, 442, 474, Van Nostrand, New York, 1966. 5. Boonstra, B. B., in "Reinforcement of Elastomers," G. Kraus, Ed., Chap. 16, Interscience, New York, 1965. 6. Goodrich Chemical Co., technical bulletins on Abson ABS. 7. Cabot Corp., technical bulletins on carbon blacks. 8. Deanin, R. D., Cebula, D. R. Soc. Plast. Eng. ANTEC. (1973) 19, 700. 9. Speri, W. M., Jenkins, C. F., Amer. Chem.Soc.,Div. Org. Coatings Plast. Chem., Preprints (1973) 33 (2), 152. 10. Lyons, J. W., "The Chemistry and Uses of Fire Retardants," pp. 14-20, Wiley, New York, 1970. RECEIVED
October 18, 1974. Taken from an MS thesis submitted by K. R. Patel.
Deanin and Crugnola; Toughness and Brittleness of Plastics Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
