Banbury Dispersion of High-Styrene Copolymer Resins with Rubber

factors have marked influence upon dispersion characteris- tics: the heat softening point, the ... In orderto evaluate the dispersion of the resin com...
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Banbury Dispersion of High-Styrene Copolymer Resins with Rubber HAROLD S. SELL

AND

ROBERT J. MCCUTCHEON

CHEMICAL PRODUCTS DEVELOPMENT DIVISION, THE GOODYEAR TIRE AND RUBBER CO., AKRON, OHIO

Reinforcement with high-styrene copolymer resins has become an integral part of rubber compounding. Although these resins impart many unique and desirable properties, their hard, horny characteristics have presented dispersion problems. This study investigated, under controlled Banbury conditions, factors that influence the ease of incorporation of these resins into rubber. The results of this study indicate that the following factors have marked influence upon dispersion characteristics : the heat softening point, the flow characteristics, and the particle size of the resin, the internal structure of the polymer, and the Banbury temperature and cycle under which mixing is done. Desirable ranges for each of the properties are recommended, and the Palidity of the conclusions drawn is confirmed by a comparison of an “ideal polymer” with commercial polymers. The paper presents working data and evaluation procedures useful to the user of high-styrene reinforcing reains. It also presents a set of evaluation standards whereby the processability can be judged from the physical properties of the resin.

D

URISG the past five years, the use of high-styrene copolymer resins as reinforcing resins for rubber has gained widespread acceptance within many segments of the rubber industry. Conipounders now consider them in many applications because of their reinforcing, hardening, and high temperature plasticizing effect (I-?‘). Although these resins impart many unique and desirable properties, their hard and horny characteristics have always presented problems of incorporation into the rubber stock and have created a need for resins with more desirable mixing characteristics. Expanding usage has increased this desire for resins which would incorporate readily in low temperature, rapid Banbury cycles without the nccessity of premasterbatching. Attempts have been made to achieve ease of processing through spray drying, micropulverizing, production of a friable particle, and adjustments in the softening range of the polymer; however, no systematic study has been published showing the influence of each factor upon dispersibility, andsetting forth the general requirements for a so-called “easy processing resin.” It was the purpose of this study t o investigate factors that influence the ease of incorporation of the resins. It was recognized that the factors influencing dispersion would fall within three main classifications-physical form of the resin, which includes particle size and shape; intrinsic properties of the resin, which include its flow characteristics and softening point; and operating conditions under which it is used, such as Banbury temperature, mixing time, discharge temperature, a i d the formulation being mixed. I n order to evaluate the dispersion of the resin completely, both visual examination and the resultant physical properties of the stock had t o be considered.

EVALUATION EQUIPMENT AND PHOCEDUHES

Because a large percentage of resins are mixed in Banbury operations, this study has been confined solely to Banbury incorporation of the resins. I n order t o determine t’he factors influencing the dispcrsion of these resins, it was necessary t o establish uniform processing procedures to be used in the evaluation, and to create a uniform rating system so t’hat samples mixed and rated at different tiines could be direct’ly compared.

A laboratory Banbury mixer (2500 gram-volumes), equipped with a cooling system which automatically maintained the desired temperature of cooling water on the shell and rotors, was used in the mixing studies. The Banbury was also equipped with variable rotor speed adjustment and recording Micromax and wattmeter. Unless otherwise indicat,ed, the Banbury was maintained a t a const’ant rotor speed of 32 r.p.m. and cooled with 100”F. cooling water, as it was felt that these approximated normal operating conditions. At the completion of each batch, the Banbury was allowed t o attain a constant temperature before the next batch was started, thereby assuring equal operational conditions on each batch. Temperature and power chart,s, shown later in this paper, indicate the uniformit’y of mixing conditions. An 8 X 16 inch even-speed laborat’orymill, also equipped with automatic temperature control, was used for sheeting off the stock from the Banbury and preparing the 0.010-inch gage sample for observation. Two basic formulations were used in studying the dispersion characteristics of the resin. One stock, the so-called gum formulation comprised of 100 parts of GR-S and 50 parts of resin, represented the most difficult mixing operation because i t involved the dispersing of a hard resin into a soft rubber. The other batch, comprised of 100 parts of GR-S, 50 parts of resin, and 50 parts of hard clay, was used to observe the effect of pigment in the mixing operation. I n those cases where curing ingredient,s were added in t’he dispersion st’udy, the following formulas xere used:

GR-S 26

High-styrene resin Hard clay Zinc oxide Stearic acid Acceleration componentU Altax Methyl tuads sulfur^

I

G u 111 Formulation 100.00 50.00

...

5.00 1.00 1.50 0.10 2 00 159.60

-___

Loaded Formulation 100 00 50 00 50.00 R

~

,oo

1.00 1 50 0 10 2 00 20.4 60

0 Optional, added only if cured samples were desired. Where information o n physical properties was not desired, only rubber, resin, and loading pigment components were used.

4 uniform method of mixing, comparable to factory operation, was used throughout the study. In a typical batch the resin, rubber, and clay, if any, were charged into the Banbury within 1.5 seconds, the ram was lowered, and the timer was started. Because some batches contained acceleration and sulfur, the Banbury was operated in such a manner that in all cases the :am was raised 2 minutes prior to the discharge time and the acceleration,” if any, was added, the throat swept, and the rani lowered within 5 seconds. The operation of raising the ram and sweeping was repeated 1 minute prior to the discharge time, at 1234

1235

INDUSTRIAL AND ENGINEERING CHEMISTRY

May 1951

I

(0

I

s z 0 v)

W

fi I

-

:

/

+

0

/+

I

400

IPOO

BOO

IS00

PO00

0

LBO0

2400

400

BOO

1200

PARTICLE

SIZE

PARTICLE

I MICRONS1

IS00 SIZE

I

2000

1

2400

I

tW0

(MICRONS)

Figure 1. Particle Size vs. Dispersibility of Fused Particle Resin

Figure 2. Particle Size vs. Dispersibility of Fused Particle

Resin 1, gum formulation

Resin 2, gum formulation

which time the sulfur, if any, was added. are a s follows: Cycle 1. Charge resin, rubber, and loading. Lower ram, pressure on 2. Raise ram sweep, and add acceleration 3. Raise ram: sweep, and add sulfur 4 . Discharge

Typical mixing cycles 4 Min. 0 2 8 4

4.5 5 5.5 Min. Min. Min. 0 0 0 2 5 3.5 4.5

3 4

5

3.5 4.5 5.5

The discharge temperature of each batch was recorded. The batch a s discharged from the Banbury was passed through the mill a t a '/*-inch gage setting to mass the stock together, to remove some of the heat, and to sheet the stock out. The trailing end of the Banbury batch was cut off and sheeted a t 0.010inch gage and the dispersion observed and rated against standard dispersion samples representing ratings from 1 to 10. These ratings could be classified as follows: Rating Excellent dispersion Very ood dispersion Good rfisnersion

1 2 8

Resin

setting up mixing cycles for each of the resins used in this evaluation, a series of preliminary batches was run t o determine that time cycle which would produce a marginal dispersion. I n this manner, it was possible during the run t o achieve both better or poorer dispersions. I n some cases, after running the series on the cycle chosen and observing the dispersion ratings obtained, it was felt advisable t o rerun the series on either a shorter or longer cycle t o define these differences more clearly. EFFECT O F RESIN PARTICLE SIZE

It is logical t h a t one of the first influences t o be considered should be the effect of particle size of the resin upon its ability t o disperse in rubber, inasmuch as considerable attention has been focused upon particle size by the introduction of high-styrene reinforcing resins in both micropulverized and spray-dried form. It can be theorized t h a t because the temperature of the resin must exceed its flow point in order t o be fluxed into the rubber, the size of the resin particle through which the heat must be transferred would be critical. By this theory, resins of small

Very bad dispersion

No mix

10

I t is obvious from the ratings t h a t the first five ratings represent small changes in dispersion, while the latter five represent major changes in the amount of undispersed resin; therefore, in graphic interpretation, a logarithmic scale was used: 1

2

3

4

5

6

7

8

9

10

A marginal dispersion (No. 5 rating) was taken as that point a t which grainy dispersions or small resin particles were recognized in the heavy gage sheets, and probably is that Point a t which resin particles would be evident in normal factory operation. In

Figure 3.

Range of Particle Sizes Used for Dispersion Studies

INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY

1236

Vol. 43, No. 5

greater power and generate greater heat than the large particles. The resin particles in excess of 8 mesh, when mixed into the rubber, apparently just rode in the rubber matrix and drew considerably less po~v-er; and this, in part, may have accounted for the “no nlix” dispersion rating. Although few commercial resins are marketed in this hard, fused state, some we marketed in large friable particles which, under moderate pressure, break down into i~ fine powder. The advant.aye of this type of resin lies in its ease of handling and freedom ol dusting. A t.ypica1 example of such a resin is demPOWER CHART . onstrated in Table 11. This resin in the original form contains many large 8 8 - I2 12- 16 16 20 20-48 particles which, upon rolling in a gallon MESH SIZE OF PARTICLES can witli a %pound steel roller, break Figtire 1. Effect of Particle S i m o n P o w e r arid Temperature down into much smaller narticles. The theoiy behind such a lriable polymer is that thc shearing action in the initial state of the mixing will reduce the resin t o a fine powder for ease of incorporation and at the same time eliminate the dusting and fly loss problems characteristic t o the fine powder resins. The differenccs between the resins can hc more readily seen in Figure 5 . bury charge Cycle, ‘l’einp., - . Dispersion Rating To check the reaction of these friable particle resins to mixing, llic~ronq IIin. r. Descriptiye Siiinerirai two typical friable particle resins, selected a t random, were separated into different fractions on a Rotap sifter in a manner similar to that used for the fused resin, and these fractions were evaluated for dispersibility in the method established previously. These data are icported in Table I11 and shown graphically in Figures 6 and 7. 2380-1680 4.5 190 Very bad 9 1680-1190 4.5 196 Very poor 7 These results tend t o confirm the claims that friable particles 1190-840 4.5 195 Poor 6 are broken in early stages of mixing, as little change in dispersion 840-420 4.5 194 Fair 4 rating or power load occurred even from the largest t o the RESIN2, GUM F O R M U L I T I O K smallest particle size. The dispersion curves, as shown in Figure 2760-2380 8 192 Bad TEMPERATURE

CHART

3

OVER

Sieve fraction, niesli

8--12 12-16 16-20 20-40 6-8 8-12 12-1G 16-20 20-40 40-60 60-80 < 80

6-8 8-12 12-16 16-20 20-40

-

2380-1680 1680-1190 1190-840 840-420 420-260 250-177 >177

2760-2380 2380-1680 1680-1190 1190-840 840-420

4.5 4.5 4.5 4.5 4.5

197 198 198 195 196 197 203

Poor Marginal Marginal Good Fair Fair to marginal Fair to marginal

194 203 209 206 205

Narginal Good Good Very good Excellent

6

5 5

3 4 4.5

IPI‘PARTICLE SIZEOF TABLE 11. REDUCTION

5 3 3 2 1

particle size would disperse much more readily than the same resin of larger particle size. To check this point, two fused styrene-butadiene resins, selected at random, were ground and separated into different fmct’ionson a Rotap sifter. These fractions of resin were evaluated for dispersibility by the procedure outlined above ; the results of the runs are givcn in Table I and a graphic representation of the ratings is shown in Figures 1 and 2. The relative sizcs of thc resin particles used arc pictured in Figure 3. It is apparent that, under comparable mixing condit,ions, th(. particle size of the resin markedly influences its dispersion characteristics, as ratings from “good” to “no mix” were obtained from the same resin in particle sizes ranging from 40- to 8-mesh. The dispersions obtained from the finely divided fract.ions of resiii indicate that no improvement ivas made in dispersion ratings when resins smaller than 20- t o 40-mesh were used. It is interesting t o note the power and mixing charts (Figure 4 ) and discharge temperatures for this series of babches. It is clearly indicated that the resins of finer particle size (under 12mesh) act somewhat like a pigment in mixing, in t h a t t.hey require

A

FRIABLE I’OI,YMER

UKUER I\IODERSTE PRESSURE

4-5

,iginal resin 23.0 >8 40.9 &20 13.0 20-40 11.2 40-80 80-120 3.6 < 120 6.7 Loss 1.0 a Rolled in 1-gallon can with 2-pound roller.

Figure 5.

Resin after moderate pressuren 0.0 6.8 28.4 33.3 10.3 20.2 1.0

Fused us. Friable Resins ITsed for Dispersion Studies

May 1951

INDUSTRIAL AND ENGINEERING CHEMISTRY

123'1

TABLE111. EFFECTOF PARTICLE SIZE ON DISPERSION OF FRIABLE PARTICLE RESIN Particle Si Sieve fraction, mesh Microns

CyCie,

RESIN3, Gubr FORMULATION >8 8-12 12-16 16-20 20-40 40-80

5 5 5 5

Over 2380 2380-1680 1680-1190 1190-840 840-420 420-177

5 5

202 200 206 207 210 209

Very pool Poor

7 6 6 5-6 5 5

Poor llarginal to pool Marginal Marginal

REBIN4, Guhi FORVLILATIOX PLUSCURE >8

8-20 20-40 40-80 80-120 20-40 recheck

4

Over 2380 2380-840 840-420 420-177 177-126 840-420

4 4

4 4 4

195

205 205

193 196 208

Marginal Good Very good Fair Good Very good

5 3 2 4 3 2

SIZEmr DISPERSION OF KESIKTABLEIV. EFFECTOF PARTICLE

CLAYSTOCKS

Particle Size

0

I 400

1

800

I

1200

PARTICLE

I

1800 SlZE

I 2000

I 2400

I

(UICROWSI

Figure 6. Particle Size ws. Dispersibility of Friable Particle Resin Resins 3 and 4, gum formulation

i

M

I

E800

6-8 8-12 12-16 16-20 20-40 40-60 60-80 80-120

RESIN3, 2760-2380 2380-1680 1680-1 190 1190-840 840-420 420-250 250-177 177-1 25

CLAY

4.5 4.5 4.5 4 3.5 3.5 3.5 3.5

FORMULATION 223 Mar inal Goo2 223 Very good 224 220 Good good Very 21 8 227 Excellent Excellent 231 226 Excellent

6, are much flatter than those shown in Figures 1 and 2 for the check this, resin 3 in a range of particle sizes was evaluatrd for fused resin. dispersion in the clay-loaded stock. The results are tabulated in Although both resins showed the same trend with respect t o Table IV and shown graphically in Figure 8. improved dispersion with decreasing particle size, the more rapid The results shown in Table IV and plotted in Figure 8 shorn the mixing of resin 4 compared t o resin 3 suggests t h a t other physical same trend toward better dispersions with the resins of finer parcharacteristics of the resin, more critical than the particle size, are ticle size. The stocks containing the clay discharge a t a higher involved in determining its dispersibility. These factors are temperature than the gum stocks, a factor which favors the disdiscussed in a later section of the paper. persion of the resin. Inclusion of the clay in thc batch retarded The data thus obtained appear t o indicate t h a t as the size of the agglomeration of the fraction of very fine particle size. the particle decreases, the dispersions improve ; however, this Thus far, the dispersion ratings of the stocks have been diEimprovement did not continue indefinitely, but rather t o a point cussed only in terms of visually appearing resin particles. In beyond which there appeared t o be little, if any, improvement. addition t o this, the dispersion should be considered in its relaThis point seemed t o occur in the 20- to 40-mesh fractions, and regardless of the cycle used or whether the resin is a fused or friable particle. The resins of very fine particle size TEMPERATURE CHART seemed t o filter into the areas of close clearancein the Banbury and fuse, withthe result that, when the batch was dumped, the thin pieces of resin would be loosened and appear on the surface of the batch. These were removed before milling and rating the dispersions. I n spite of this, there appeared to be no improvement in dispersibility on particle sizes less than 20 mesh. I n the stocks mixed from the finely powdered resin, the undispersed resin did not appear as the finely divided resin but rather as resin agglomerates, indicating that there was 6 ' CYCLE --f some tendency for the fine resin to fuse POWER CHART together before it was completely nuxed. I J While agglomeration occurred with OVER 8 8 - I2 12- IS 16-LO 2 0 +Q the fine resin in the gum stock, the MESH SIZE OF PARTICLES possibility remained t h a t this tendency Figure 7 . Effect of Particle Size on Power and Temperature would be retarded by the filler pigments normallv used in the rubhrr stock. To Resin 3, friable particle resin

-t

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INDUSTRIAL AND ENGINEERING CHEMISTRY

1238

s4 2 I

1

9

G

400

7

:

: 1000

800

PARTICLE

Figure 8.

7

, 1600

SIZE

1 2000

I

2400

1

170

150

160

I40

BOCTENIN@

.40

-30

2800

Figure 9.

(MICRONS)

AT.

POINT

212.

AND

I20

I30

I10

(*Fl

.BO

.50 FLOW

Vol. 43, No. 5

.eo

.60

.TO

1500 p o i

Softening Point us. Dispersibility

Olsen flow

disporsibility 5.5-minute cycle

DS.

Particle Size os. Dispersibility Resin 3, loaded formulation

tionship t o the physical properties of the stock. It will be noted in Table I11 that the batches mixed with resin 4 included curing ingredients during mixing. These stocks were cured without further milling in order to observe any correlation between the state of dispersion and resultant physical properties (Table V). The important, facts shown by these data are t h a t the state of

dispersion of the resin is reflected in the physical data and that even a t the point where the dispersion appears t o be complete (20 to 40 mesh, Table T), the physical data have not rrached the optimum point. This is ala0 reflected by the fact that remilling the batches on a cold mill iniproved the physical properties. Thus, in considering the state of dispersion, not only visual examination, but also physical property determinations should be considered.

TABLE V.

PHYSIC.4L PROPERTIES O F STOCKS DISPERSION RATINGS

HAVINGVARYING

Resin 4 (Table 111) G u m formulation Particle size, mesh Dispersion rating Mixing cycle (minutes) Ultimate tensile, Ib./sq. inch 30'/305' F 40 50 Elongation, %5 30/305 40 50

Shore A hardners 30/305 40 50 Crescent tear H 30/305 40 :0

>8

8-20 3 4

20-40 2 4

40-80

425 575 600

400 600

750

025 800 850

276 225

220

275 240 270

67 74 74

5

4

143

188 173

Control

4

1 ,5

500 575 650

375 500 675

772 1100 1150

235 230 240

175 100 130

210 160 200

425 415 400

62 70 72

68 75 74

75 78 78

62 72 74

70

131

205 178 183

176 222 208

147 170 185

153

177

169

4 4

80-120 3

74 72 150

17'1

REMILLED O S COLDMILL

5.0'

4.0'

3.0' YIXINB

TIME

(MINUTES)

Figure 10. Influence of Flow on Dispersion Mixing Time us. Dispersibility Resin 10

US.

reGn 11, gum formulation

Ultimate tensilr, Ib./sq. inch 30/305 875 1125 40 1175 50 Elongation, % 480 30/305 480 40 385 60 Shore A liardnms 80 301305 78 40 78 Crescent teal 13 30/305 4. 11 .

50

154 166 171

875 1173 1100

1000 1050 1200

1000 1200 1175

800 1075 1050

1050 1200 1200

475 525

395 385 388

460 BOO

400

440

463 470 405

525 430 426

77

75 74

78

77 78 78

80 77 78

78 78 76

176 167 162

156 161 171

15; 167 176

181 163 161

77 78

150 16!l 164

INDUSTRIAL AND ENGINEERING CHEMISTRY

May 1951

EFFECT O F BANBURY TEMPERATURE'

While the previous runs were made with a constant temperature of 100 F. on the shell and rotors of the Banbury, there is evidence that the temperature of the Banbury could influence the dispersion of the resins. O

-

To check this effect upon mixing, a typical resin was mixed in both a clay and gum formulation in the Banbury with rotor and shell temperatures ranging froin 60" to 150" F. At the start of each run, the automatic cooling system was set a t the desired temperature and the equipment was allowed to reach equilibrium before mixing the batch. TBe Banbury mixed stock was passed through an open mill once to sheet out the stock and then passed through a tight mill, as previously discussed, and the dispersion was rated by comparison with the standards. The results of the run are shown in Table VI.

*

of low average molecular weight would flow more readily than the same copolymer having a high average molecular weight, even though both polymers might have essentially the same softening point. Thus, both influences must be considered in any study of flow characteristics. To check these possibilities, a series of copolymers was prepared by varying the proportions of the monomers in the polymerization. This resulted in a series of copolymers giving a wide range in flow characteristics and a corresponding lowering in softening point; these are identified as resins 5, 6, 7, 8, and 9. At the same time, two copolymers were prepared having the same monomer ratio and heat-softening point but flow characteristics which varied by virtue of the changes made in the internal structure of the polymer, one of high molecular weight and the other of low molecular weight. These polymers were evaluated as resins 10 and e l l . These resins, in a uniform particle size, were evaluated for dispersion characteristics in the gum formulation and followed the procedures outlined above.

The results of the runs are shown in Table VI1 and in Figures 9 TABLE VI. EFFECTO F BANBURY TEMPERATURE O N DISPERSION and 10. O F FRIABLE PARTICLE RESIX These data show much improved dispersions with increased Disflow in the copolymers, regardless of whether the flow improveBanbury Temperature, F BC&,ncb:fY +ig: -Dispersion Rating ment was obtained by adjustment of the monomer ratio, with Shell Rotors Rani Min. F. Descriptive Numerical 60 100 125 60 100 125 150

60 100 126

GUM FoRMnLArroN 66 4 182 100 4 187 125 4 212

Very pool Marginal Excellent

7 5 1

60 100 125 150

CLAYFORMULATION 85 4 185 Poor Fair 100 4 209 125 4 222 Good Verygood 150 4 230

6 4 3 2

TABLE VII. EFFECT OF FLOW CHARACTERISTICS ON D~SPERSION

-.-..

(Gum formulation)

Plnar ot

I"

212' F., 1500 SofLb./Sq. Inch, tening Resin Inches in P$int, No. 2 Min. , F.

A.

The data in Table VI clearly indicate that with both the gum and clay stocks the hotter the Banbury, the better the dispersion of the resin. This is probably due, in part, t o the higher discharge temperatures resulting from the hotter Banbury, a factor which favors the rapid dispersion of the resin. The improvements in dispersion on changing Banbury temperatures from 60' to 125" F. were of the same order as those obtained on changes in particle size as shown in Tables I and 111. Particularly in the clay stocks, 25 O F. increment changes in shell and rotor temperatures do not reflect as corresponding increases in the discharge temperature. This presents the possibility that dispersion of the resins can be aided bv the manufacturer by proper adjustment of the operating temperature of the Banbury, so long as he stays within a safe discharge temperature for the stock being mixed. (.

1239

5 6 7 8 9

0.32 0.40 0.61 0.72 0.88

10

0.60

Banbury Cyple, Min.

Discharge Temp.,

F.

Dispersion Rating Descriptive Numerical

HIQH MOLECULAR WEIGHTRESINSO 160 5.5 214 Very poor Poor 5.5 222 150 131 5.5 218 Fair to good 124 5.5 Good 221 119 Verygood 5.5 218

7 6 3-4 3 2

B.

11

HIGH us. Low MOLECULAR WEIQHTRESINS 131 5 215 Good 4 200 Very bad 4.09 128 4.5 210 Good 4 210 Marginal

3 9 3 5

a Resins 5 through 9 contained gel in sufficient degree t o indicate relatively high average molecular weights. Resin 10 contained 3 8 7 gel, which indicates a high average molecular weight, whereas resin 11 %ad no gel and an intrinsic viscosity of 0.60. Resin 11. therefore, is of much lower molecular veight than resin 10.

EFFECTOF FLOWCHARACTERISTICS ON MIXIKG

TABLEVIII.

CYCLE Flow ra t

*.en

AIL-

EFFECT O F RESIN FLOW PROPERTIES

Resin

Another property which can be of importance in the dispersion Characteristics of the resin is its ability t o soften, flow, and admix with the rubber. I n this respect, it would seem that the point at which the resin first softened, and the fluidity of the resin a t some point during the mixing cycle, would be criteria of its ability t o disperse. This was of no consequence in the previous studies, because in any given series of evaluations, a'single resin was used which necessarily had the same softening point and flow characteristics. However, in a study involving more than a single resin, this definitely must be considered. The flow properties of the high-styrene resins can be altered in two different manners, each achieving the same result. When copolymers of butadiene and styrene are made with increasing amounts of butadiene, the flow properties of the copolymers are improved and the softening point is lowered. If the modification continues far enough, the copolymer eventually assumes rubberlike, rather than resinlike, characteristics. While flow is thus influenced by the ratio of monomers, it can also be changed by the internal structure of the polymer-for instance, a copolymer

12 13

No.

r.,

1500 Lb./ SofBan- Disbury charge Dispersion Rating 9s. Inch, tening Inchesin Point Formu- Cycle, Temp., DescripNu2 Min. F.' lation Min. F. tive merical 1.29 81 Impractical, fuses a t room temperature 1.16 99 Gum 4 182

14

0.88

118

Gum

3.5 4 4.5

190 194 195

Mar inal Goo8 T'ery good

5 3 2

15

0.80

122

Gum

3.5 4 4.5

192 199 202

Poor Marginal Good

6 5 3

16

0.61

131

Gum

4.5 5 5.5 6

202 203 207 210

Poor Good Good Excellent

3 3 1

17

...

146

Gum

5.5

6 6.5

208 213 212

Poor Good Excellent

(5 3

16

0.32

160

Gum

6.5 7 7.5

212 216 218

Verypoor Marginal Fair

?

9

222

Bad

224 222

No mix No mix

19

. ..

184

Gum

20

00

206

Gum

Produced a very nervy sheet.

8.5 10.5

Dispersion very diificult to rate.

I3

1

a 4

8 10 10

INDUSTRIAL AND ENGINEERING CHEMISTRY

1240

Vol. 43, No. 5

ie c

e

e s 3

-

u n 8c-

3

1

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a

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5 UlXlNQ

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e

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IO

I 1

II

IO

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e $1 f

o

I*O

I40 1)EOlM

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(MINUTES)

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I

IO0

Figure 12.

1

1

160

I00

SOFTIMlMO

POINT

eo0

ILC

1.C)

Softening Point z's. Oispersion Tiuir

Figure 11. Influence of Softening Point a i d F l o w RIixing Time US. Dispersibility

Resins 14 to 20, gum formulation

Resins 14 to 20, gum formulation

flow accompanied by a loLTering in the softening point of the resin is a much more important consideration in improving the ease of dispersion than increasing the flow of the resin. To t,his point in t,he discussion, only the effects of these changes on dispersibility have been considered. Equally important is the effect the changes within the copolymer have upon the physical properties of tho stock in n-hich the resins are mixed. Improvements macle in processing characteristics are t o no avail if, in making these changes, the desirable properties imparted by the resins are destroyed. For this reason, the changes in flow should be judged not by processing alone, but in combination with the physical properties imparted t o the rubber stock. The range of polymers 5 through 11 and selected resins were evaluated in both t,he gum formulation and a typical application (shoe sole) formulat,ion. The results shown in Tables IX and S indicate that resins 7 , 8, 9, and 10 compare favorably with each other and with the commercial resins in all respects and t h a t improving the flow and lon-cring the softening point have no adverse effect upon physical properties. However, a comparison of the low molecular weight resin (11) with its control (lo),and resiris 5,8, and 9 s h o w it t,o br low in hardness, tensile strength, and flex in the shoe sole compound. Thus, the improvement in flow achieved in polymer 11 is more than offset by its poorer reinforcing properties. This indicates that improvements in flow are restricted to those not affecting the structure of the polymer.

the corresponding lowering in softening point, or by alteration of the internal structure, with a constant softening point. It has been shown in Table VI1 that in a given mixing cycle the dispersion rating is improved by increased flow. Another important consideration is whether the increased flow contributed t o comparable dispersions in shorter mixing cycles. To approach this problem, another series of copolymer resins was prepared by monomer adjustment, having wider variations in softening points and flow characteristics. These resins were evaluated for dispersion characteristics in the gum formulation previously used, but over a range of mixing times. The results of these runs are given in Table VI11 and shown graphically in Figure I I. From the plot on Figure 11,it is possible t o calculate the mixing cycle required t o give a comparable dispersion on each of the resins. Because only sufficient resin nTas available on resin 19 for one batch, the dispersion curve is assumed, based upon the character of the other curves. If the mixing time t o achieve comparable dispersion for each of the resins, as obtained from Figure 11, is plotted against softening point, a direct relationship results. The relationship, shown in Figure 12, is assumed to be a straight line because the possible variations in determining softening point and dispersion rating are relatively large. The area surrounding the actual point represents the probable range of error, and the line drawn passes through each of the areas. Thus, it appears t h a t the softening point and flow characteristics of the resin greatly influence the ability of the resin t o disperse. Compared to the results obtained with the friable particle discussed earlier, it is clear that the softening point and flow characteristics arc much more important in dispersion than the particle size of the resin. Figure 10 would indicate that a sevenfold increase in flow at B constant softening point (from 0.61 t o 4.09) would reduce the mixing time of the batch by only 0.55 niinute based upon equal dispersion rating. On the other hand, Figure 12 shows that the same savings in mixing time could be accomplished with an 8' F. lowering in softening point of the resin with a relatively minor change in flow. Thus, i t appears that a small improvement in

CHARACTERISTICS O F IDEAL. EASY PROCESSIYG RESIN

The results of this study indicate that the following factors have marked influence upon the dispersion characteristics of the resin and the physical properties of the stock into which the resin is mixrd: Mixing temperature and cycle Softening point of resin Flow characteristics of resin Particle size of resin Internal structure of resin The study has shown that any styrene copolymer resin can be dispersed into rubber if a sufficiently long mixing cycle and a

May 1951 TABLE

PROPER TIE^ Ix. PHYSICAL

O F EXI'ERI1fENTAL

(See Tahle VI11 Commercial Resin __ Experimental Resin A B 5 6 7 8 9 1 0 Ultimate tensile 30'/30R0 F. 40 50 Elongation 30/30R 40 ;n

306q0 niodiiltir 30/305 40 50

--

Hardnebs, Shore .A 30/300 40 50 Hardness, Shoie 13 30/305 40 50

860 11.50 117.5 1075 750 1300

RESIKS

1

1

800 500 1000 700 1060 810

,525 600 600 son 030 RT,0

1075 IO50 1250

1000 900 925

1050 1150 978

400 350 820

500

430 460

465 390 340

560 510 470

375 415 385

900 650 530

.iJO

730 925

700 775 825

700 750 850

575 650 625

730 820 910

440 600 700

480 395 100

490 JOO

800 025 075

650 750

77 78 77

70 77 77

67

68 74 73

77 78 78

77 78 78

77 79 79

75 76 76

68 69 60

56 &mesh 2.0 8-12 17.7 16.4 0 4.7 0 0 i4.(i 17.6 12-20 26.6 29.2 0 23.3 2 4 . 4 1 0 . 0 0 . 3 27.: 20-40 1 5 . 8 1 7 . 3 0 . 7 13.6 2 3 . 3 20.6 0.7 1 9 . i 40-80 1 2 . 6 1 1 . 6 2 0 . 0 1 1 . 2 2 8 . 6 26.7 40.G 1 3 . 4 80-120 3.3 3.8 46.7 3.G 1 0 . 7 11.4 3 6 . 0 3 . 0 %mesh 0 0 0 8-12 12-20 8 4 0 0 20-40 380 116 0 6 40-80 33 6 35 8 20 4 8 7 138 470 80-120 O

1025 1050 1123

G50

73 77 77

71

73 73

74 76

73

76

22

48

73 73

34 d.4

52

.52

52 j3 33

148

142 143 142

I25 111 116

133 118

460

750 875

1100 800 127.5 923 1373 1450 400 415 370 800 900 1075

9.50 900

117;

-.- 345

480

:>Jo

460

370

40.5 840

030 723

430 1100 600 1200 750 , . .

1200

340 275

65 68

65

65 68 71

32 54 56

72 75

$2 .14 34

46

46

37 38

32

154 143 145

112 112 I15

2;

4;

40

129 140 116

$1.5 81) 68

76 53 56

110

117 118

CLAYFORUULATIO-.

Tensile

1100 1350 1350

1025 1175 1175

1275 1450 1250

1100 1225 132s

950 1200 1200

625 650 545

525 535 440

550 500 400

585 620 530

515 555 495

430

io

415 440

660 G55 580

570 385 43.5

io

600 675 750

700 725 900

700 850 1000

625 675 775

626 700 800

700 850 950

450 575 650

600 675 775

io

82 84 84

80 80 80

83 83 84

82 82 82

78 80 80

79 80 80

68 68 70

82 82 83

57

59 59

56 56 58

57 57 58

57 p7

52 54 54

53 55 55

48 48

$77

40

56 66 57

142 150 150

150 170 155

172 146 157

166 166 163

163 156 150

149 153 157

131 118 112

163 153 150

40/305" F.

50 70 Elongation, 40/305 50

56

300% niodulus 40/305 50 Shore A 40/305 50 Shore R 40/305 50 70 Crescent tear B 40/305 50 70

800 975 1050 1400 1173 l37,5

873 800 1100

reaction and evaluated against seven commercially availablc resins for both ease of processing and physical properties. The results of these studies are reported in full in Tables XI, XII, and XIII, and the dispersion ratings are shown in Figures 13 and 14.

covcLusIoYs The results of this study indicate that thc following factors have marked influence upon the dispersion charactcristics of the resin : Particle size of resin Softening point of resin Flow characteristics of resin Banbury temperature and cycle Internal structure of copolymer Based upon this Tvork, the following conditions were determined as dcsirablc for an ideal processing resin :

A softening point as low- as practical. The niinimum appears to be about 115" F.

A particle size under 20 mesh (or friable enough to reduce to 20mesh or finer). An Olsen flom gieater than 0.75 inch in 2 minutes a t 1500 pounds per square inch and 212" F. A polymer of high average molecular weight. Tlic validity of the results was confirmed bv a comparison with c.oiiirnercia1 polymers which shovied superiorities for the experiiiiental resin in both processing and physical properties. TESTS

The following tests w r ' v used: Stress-strain, A.S.T.M. D 412-41.

INDUSTRIAL AND ENGINEERING CHEMISTRY

May 1951

OF EXPERIMENTAL RESINWITH COMMERCIAL RESINS TABLEXIII. COMPARISON

Application formulation (shoe sole) Resin 21

*

e

Tensile 12'/315' F 24 Elon ation, % 127315 24 Shore A 12/315 24 Shore B 12/315 24 Crescent tear B 12 24 Ross flex, aged 24 hours, 212O F oven, 0.250inch sole 12/315 cycles Rating 24/315 cycles Rating Taber abrasion, H-22 wheels, 1000 grams, 500 rev., grams loss 12 min 24 min

Teat Formula A

B

C

D

E

F

G

1500 1675

1450 1525

1525 1400

1750 1600

1750 1475

1475 1425

1625 1700

1500 1375

290 305 90 88

300 275 83 83

390 395 84 84

370 340 85 86

320 360 87 85

250 370 87 86

430 405 72 73

305 315 84 84

70 67

63 63

64 64

65 66

67 65

66

67

52 53

64 64

147 156

173 133

137 143

162 141

175 180

156 172

125 94

169 178

250,046 5 287,587 1 5

65,000 201,643 250,046 10 10 2 160,000 287,587 287,587 10 5 2 5

0 411

0 368

0 275

0 432

0 400

0 321

90,061 250,046 250,046 250,046 10 3 6 4 9 287,587 42,210 196,560 166,000 5 5 10 10 10

0 405 0 399

0.302 0.336

0 386 0 373

0.252 0.303

0 321 0 361

FORMULATION GR-6 26 No. 1 smoked sheet Resin aa shown Ca1oi;rn silicate Zinc oxide Process oil

50.00 50.00 50 00 85.00 5.00 5.00

Cumar M H 21/n

Paraffin

Altax Methyl tuads Sulfur

Crescent tear A.S.T.M. D 62448, Die B Hardness, A.B.T.M. D 676421'. Olsen f l ~ w A.S.T.M. , D 569-48. Heabbftenmg Point* A 0*075 inch is placed over '/le-inch diameter mandrels, placed 2 inches on center and supports a 143-gram weight having a specified presser foot, In a circulation water bath, the temperature of which is raised a t the rate of 1 per minute. The temperatures are taken a t the firat deflection and when the sample is deflected 0.5 inch; the average of these temperatures is considered the heat-softening point.

8.

7.00 1.50 2.00 0.15 3.00 268.65

-

ACKNOWLEDGMENT

The authors wish to acknowledge the assistance of the Production Service Section of the Chemical Products Developnient Division, and the Chemical Engineering Division, for the preparation of the experimental polymers, and are grateful to the Goodyear Tire & Rubber Co. for permission t o publish this paper LITERATURE CITED

R E a s I V E D April

21, 1950.

Presented before the Division of Rubber Chemis-

try at the 117th hfeeting of the AVERICANCHEXICAL SOCIETY Detroit Mioh.

STUDIES OF CATALYST DISTRIBUTION

AND

Intrinsic viscosities, obtained by a conventional method, using 0.2 gram of resin in 100 ml. of benzene. Taber Abrasion. Using Taber machine, the sample was tested after 500 revolutions using an H-22 wheel and 1000-gram weight. Ross Flex. Ross flex, a standard of the shoe industry, was obtained on ,a 1 X 6 X 0.250 inch sample, cut with a l/lo-inch chisel awl perpendicular t o the length a t a distance of 2.5 inches from the attached end, aged for 24 hours in a 212" F. oven, and flexed on the Ross flex machine a t the rate of 100 flexes per minute through an angle of 90". The flex cut growth, measured in 0.1 inch, ia given as the rating after flexing.

(1) Border, Juve, and Hem, IND ENQ CHEM.,38, 955 (1946). ( 2 ) Cunningham, E. N., Rubber Age, 62, 187 (November 1947). (8) Holt, Susie, and Jones, India Rubber World, 121, 416 (January 1950). (4) Jones and Prqtt, Ibid., 117,609 (February 1948). (6) Sell and McCutcheon, Zbid., 119,66 (October 1948). (6) susie and Wald, Rubber 65, 637 (August 1949). (') Thies and Ibid.t 61f 51 1947)*

Coal Hydrogenation Catalysts

SOL WELLER'

1243

EngineeEing

I s:0Panc:r development -

M. G. PELIPETZ

U. S. B U R E A U OF MINES, BRUCETON, PA.

I

N T H E liquid phase hydrogenation of mal on a large scale, an

attempt is usually made to achieve good dietribution of the catalyst in the coal-oil paste. When the tin-ammonium chloride combination is employed, as in the Billingham plant of the Imperial Chemical Industries, Ltd., the tin is added in the form of tin oxalate, which is presumed to decompose under reaction conditions to give tin in a very finely divided state (3). Ferrous sulfate, when it was employed as a catalyst constituent in German plants at Politz, Blechhammer, and Gelsenberg, WN impregnated on the coal from aqueous solution (7). There have been almost no 1

Present address, Houdry Process Corp., Marcus Hook, Pa.

published reports, however, of the significance of catalyst dlstribution for coal hydrogenation, and apparently no systematic study has been made of this subject. Almost all batch autoclave investigations of solid coal hydrogenation catalysts have involved the addition of powered catalyst to the coal or coal-oil mixture (I,$, 443,IO). In the case of one bituminous coal, a comparisoa has been made of powered stannous chloride and stannous chloride impregnated on the coal (IO). Very little difference was observed between the modes of catalyst addition a t a concentration level of 1% tin; however, a t lower concentrations (0.5 and 0.1% tin) superior results were obtained with the impregnated catalyst. It