A Flame Resistant ABS-Type Polymer from Terpolymerization with a

35 A Flame Resistant ABS-Type Polymer from Terpolymerization with a Novel Bromine-

Downloaded by CORNELL UNIV on August 4, 2016 | http://pubs.acs.org Publication Date: June 1, 1969 | doi: 10.1021/ba-1969-0091.ch035

Containing Monomer WILLIAM CUMMINGS and RONALD E. STARK Uniroyal Chemical, Naugatuck, Conn.

Bis(2,3-dibromopropyl) fumarate has been used as a fourth monomer in nitrile rubber- and graft-type ABS materials giving flame-resistant polymers. At least 10% bromine incorporation is required to pass the Underwriter's Laboratories Subject 94 test. The graft-type materials fail at 7-10% bromine only because of dripping. Both types pass the ASTM D-635 test with 7% or more bromine. For the impact strength to be equivalent to that of conventional ABS, the fourth monomer must be present in both the rubber and resin phases. Thermal stability is marginal but can be improved with typical PVC stabilizers.

T h e ABS polymers ( acrylonitrile-butadiene-styrene ) have unusual properties which combine toughness with high strength, easy flow in processing, and good surface appearance (2). The rapid growth in the use of these polymers during their 19-year history is testimony to the usefulness of this combination of properties in a variety of applications.

/

1

In common with most thermoplastics, ABS polymers are not flame resistant. In principle, aflame-resistantABS could be made by incorpo rating halogen- and/or phosphorus-containing structures either by (a) copolymerization of appropriate monomers or (b) addition of small molecules containing these structures as plasticizers. Recognizing that the second approach can involve a serious loss in heat deflection tem perature, hardness, and occasionally impact strength (4), we have favored the copolymerization approach in the work described here. 536

Platzer; Addition and Condensation Polymerization Processes Advances in Chemistry; American Chemical Society: Washington, DC, 1969.

35.

cuMMiNGs

537

Ffome-Resistant Polymer

A N D STARK

The development of bis(2,3-dibromopropyl) fumarate (DBPF) in these laboratories by Amidon and Bill ( 1 ) :

(I)

HC—COOCH CHBrCH Br 2

2

BrCH CHBrCH OOC—CH I 2

2


provided a monomer which seemed to offer interesting possibilities as a fourth monomer in ABS-type polymers. Experimental DBPF was prepared using either the procedure of Amidon and Bill (I) or of Cummings (3). The product was recrystallized from benzene-methanol, m.p., 6 7 ° - 6 8 ° C . (uncorrected). Terpolymer Resins. DBPF was dissolved in a mixture of styrene, acrylonitrile, and mercaptan (Table I). About one-tenth of this solution was added to a solution of sodium alkylbenzene sulfonate emulsifier (Nacconal NRSF, 2 parts) in deionized water (180 parts) at 60°C. Potassium persulfate (0.3 part) was added, followed by the remaining monomer mixture at a rate consistent with temperature control ( 6 0 ° C . ) Gentle agitation and a nitrogen atmosphere were maintained throughout the polymerization. The latex was maintained at 60 °C. until a solids determination indicated no further conversion ( 6-8 hours total polymeri zation time). Nitrile Rubbers. Mixtures of butadiene, acrylonitrile, and DBPF were polymerized in bottles at 35°C. using the following recipe: Parts

Monomers Water Mixed tertiary mercaptans (C , C , C ) Oleic acid Sodium hydroxide Sodium salt of alkylbenzene sulfonate (Nacconal NRSF) Potassium persulfate Divinylbenzene ( commercial 42% solution) 12

1 4

1(5

100 180 1.3 1.16 0.1 2.85 0.26 1.5

Table II gives the feed ratios and the composition of the finished rubbers. Graft Polymers. The procedure used was described by Cummings (3). To a quantity of commercially available polybutadiene latex (52.3% solids) containing 50 parts of rubber was added sufficient deionized water to increase the water content to 180 parts. The diluted latex was heated to 60°C. Potassium persulfate (0.3 part) and mono mers ( styrene, acrylonitrile, DBPF; 50 parts) were added, and poly-



538

ADDITION

A N D CONDENSATION

P O L Y M E R I Z A T I O N

PROCESSES

merization was carried out with gentle stirring under a nitrogen blanket for five hours at 60°C. Preparation of Resin-Rubber Blends. To a mixture of appropriate quantities of the resin and rubber latices was added sufficient quan tities of an emulsion of 2,6-di-tert-butyl-p-cresol to furnish 1 p.p.h. of antioxidant. This mixture was flucculated by pouring it into a stirred 2% aqueous solution of calcium chloride held at 9 5 ° - 9 8 ° C . After cooling to 6 0 ° - 7 0 ° C . , the resulting slurry was filtered. The polymeric crumb was washed with water and dried 16-24 hours at 60 °C. Zinc stéarate and tribasic lead silicate (1 p.p.h. each) were added during mixing on a mill at 149°-160°C. The Izod impact strength (ASTM D256-56), Rockwell R hardness (ASTM D785-51), and flame resistance (Underwriter's Subject 94 ) were measured on 1/4-inch compression molded test pieces. Table I.

Styrene-Acrylonitrile—DBPF Terpolymers

S-AN-DBPF Resin

Charged

Polymer

1 2 3 4 5

63-10-27 73-10.5-16.5 55-20-25 55-20-25 55-20-25

64-10-26 74-10-16 60-20-20 57-19-24 62-20-18

a

Convert %

Parts Mixed tert-Mercaptans

98 98 95 98 91

0.70 0.76 1.10 1.32 1.44

0.25 0.22 0.25 0.25 0.25

"Weight ratios based on nitrogen and bromine analyses; styrene by difference. Deciliters/gram in dimethylformamide at 30.00°C. Estimated from terminal % solids. 6 c

Table II.

Butadiene-Acrylonitrile-DBPF Terpolymers

Butadiene-Acrylonitrile-DBFΨ Weight Ratio Charged

In Poly mer

66-34-0 70-25-5 65-25-10 60-25-15

68-32-0 70-24-6 64-24-12 61-23-16

a

a

Hours to 76% Conversion 24.5 21.5 20.0 17.0

Weight ratios based on nitrogen and bromine analyses; butadiene by difference.

Flammability Tests. ASTM D-635. The specimen, 0.25 X 0.5 X 5 inches, was clamped horizontally with its transverse axis inclined at a 45° angle to the horizontal. A 1-inch blue, Bunsen burner flame was held to the end of the specimen for 30 sec. and then removed. If the specimen failed to burn, ignition was attempted again. If it did not burn after the second ignition, or if the flame extinguished before 4 inches of the specimen burned, the specimen was considered self-extinguishing. For the material being tested to be considered self-extinguishing and pass the test, 10 specimens were tested, and all had to pass. U L S U B J E C T 94. The same size sample was used as in ASTM D-635. The specimen was held vertically and ignited with a 1-inch blue, Bunsen


35.

C U M M I N G S

A N D STARK

539

Flame-Resistant Polymer

burner flame for 10 sec. To be classified self-extinguishing, and pass the test, there could be no glow or flame remaining 30 sec. after removing the flame. Also the sample could not drip burning particles capable of igniting a horizontal layer of cotton fibers placed 1 ft. below the specimen. Three specimens were tested, and all had to pass for the material to pass and be considered self-extinguishing.


Discussion Conventional ABS polymers are blends of poly(styrene-coacrylonitrile) with either poly(butadiene-coacrylonitrile) or a graft of poly( styrene-coacrylonitrile ) onto a rubbery spine. To confer flame-resistance on either ABS system using DBPF as a fourth monomer, the major com ponent should be a styrene-acrylonitrile-DBPF terpolymer since the resinous component is the major one. The composition of such a ter polymer is restricted by two considerations: (1) it should contain suffi cient acrylonitrile to impart the resistance to solvent attack which is characteristic of ABS polymers, and (2) the amount of DBPF should be sufficient to give a useful level of flame resistance. Blends with Nitrile Rubbers. The data in Table III show the impor tance of using a terpolymer rubber to obtain good impact strength in a blend with styrene-acrylonitrile-DBPF terpolymer resin. Blend No. 1 gives the properties of a conventional nitrile rubber blend type ABS. Blends 2-4, involving terpolymer resins with the same amount of the rubber used in Blend 1, have a much lower impact strength. If, however, terpolymer resin is blended with terpolymer rubber (Blends 5-7), the impact strength approaches that of the conventional Table III.

Blends of Styrene—Acrylonitrile—DBPF Resins with Nitrile Rubbers 0

S-ANBlend No. DBPF " 1 2 3 4 5 6 7

1 2 3 4 4 4

73-27-0 64-10-26 71-10-19 60-20-20 57-19-24 57-19-24 57-1&-24

Rubber, BDE-ANDBPF a

68-32-0 68-32-0 68-32-0 68-32-0 70-24-6 64-24-12 61-23-16

Impact Hard Strength ness (ft.-lbs./ Rock Rubber, in. of well Br, notch) R % % 7-8 1.5 1.3 2.3 5.8 7.1 4.7

25 25 25 25 25 25 25

98 89 86 95 87 93 95

0 12.1 8.8 9.3 12.1 13.0 13.6

Flame Resist ance b

— Pass Fail Pass Pass Pass Pass

Terpolymer composition by analysis for N and Br ( styrene and butadiene by difference ). Underwriter's Laboratories Subject 94 test. "Abbreviations: S = styrene, AN = acrylonitrile, DBPF = 2,3-dibromopropyl fumarate, BDE = butadiene. α

2

2

b


540

ADDITION

A N D CONDENSATION

P O L Y M E R I Z A T I O N

PROCESSES

ABS (Blend 1). It seems likely that better impact strength is obtained when both phases contain DBPF because of better interphase compatibility. Graft Blends. The properties of ABS-type polymers involving mix tures of terpolymer resins and graft rubbers are shown in Table IV. As with the nitrile rubber types, there is a pronounced gain in impact strength at a given rubber level when DBPF is present in both phases ( Blends 1 vs. 3 and 2 vs. 4). Table IV.

Blends of Styrene—Aerylonitrile—DBPF Resins with Graft Rubbers


0

Resin S-ANBlend No. DBPF

Graft Polymer BDE-S-AN- ΒΌΕ, DBPF % a

Impact Hard Strength ness (ft.-lbs./ Rock well Br, in. of % R notch)

Flame Resistance b

1

4

57-19-24

50-34-16-0

15

1.5

112

10.4

Fail

2

4

57-19-24

50-34-16-0

25

3.7

98

7.4

Fail

3

5

62-20-18

50-32-11-7

13

3.0

106

9.6

Fail (Drip)

4

5

62-20-18

50-32-11-7

25

7.0

94

7.6

Fail (Drip)

"Terpolymer composition by analysis for N2 and Br (styrene and butadiene by difference ). Underwriter's Laboratories Subject 94 test. "Abbreviations: S = styrene, AN = acrylonitrile, DBPF = 2,3-dibromopropyl fumarate, BDE = butadiene. 2

6

Improved interphase compatibility, owing to the greater similarity in constitution of the two phases, again seems a reasonable explanation of the effect. Flame Resistance. Blends with nitrile rubbers ( Table III ) containing at least 10% bromine passed the comparatively stringent Underwriters Subject 94 test. Graft blends having 7-10% bromine failed the Under writer's test only because of dripping. They passed the ASTM D-635 test, as did all the nitrile rubber blend types. Nitrile rubber Blend No. 3 (Table III) which contains 8.8% bromine and which failed the Underwriter's test, was mixed with 6 and 12 parts of tricresyl phosphate. As Table V shows, the plasticizer improved flame resistance and made the compositions softer. Six parts of tricresyl phosphate increased the impact strength notably with little decrease in hardness. With 12 parts of this plasticizer present, the impact strength was intermediate, but the loss in hardness was serious.


35.

C U M M I N G S

Table V .

Parts TCP

b

A N D STARK

Effect of Tricresyl Phosphate on the Properties of a Nitrile Rubber Blend DBPF-Containing ABS Impact Strength (ft.-lbs./in. of notch) Rockwell R, Hardness Flame Resistance

0 6 12 a


6

541

Flame-Resistant Polymer

0

1.3 4.4 2.7

86 84 79

Fail Borderline Pass

Underwriter's Laboratories Subject 94 test. Added to Blend 3 of Table III.

Thermal Stability. The ABS-type polymers containing sufficient DBPF to pass the Underwriter's test were notably less prone to discolora tion during processing than unstabilized PVC. On the other hand, they discolored when subjected to processing conditions normally used for conventional ABS polymers. Tribasic lead silicate was as effective as any of the common PVC stabilizers in preventing this discoloration during milling. Summary Use of bis(2,3-dibromopropyl) fumarate as a fourth monomer in either nitrile rubber- or graft-type ABS materials gives flame-resistant polymers. With either type, better impact strength is obtained when the fourth monomer is present in both the rubber and resin phases. The compositions are more thermally stable than poly (vinyl chloride) and can be stabilized by typical PVC stabilizers. Literature Cited (1) (2) (3) (4)

Amidon, R. W., Bill, J. C., U. S. Patent 3,151,183 (Sept. 29, 1964). Basdekis, C. H., "ABS Plastics," Reinhold, New York, 1964. Cummings, W., U. S. Patent 3,260,772 (July 22, 1966). Lamon, D. Α., Hoskins, E. J., "Physics of Plastics," P. D. Ritchie, Ed., Van Nostrand, Princeton, N. J.

RECEIVED

April 1, 1968.


A Flame Resistant ABS-Type Polymer from Terpolymerization with a

Recommend Documents