Starch-Elastomer Masterbatches Preparation, Properties, and Process Design Howard 1. Stephens, Robert W. Roberts, Thomas F. Reed, and Richard J. Murphy Institute of Polymer Science, University of A k r o n , A k r o n , Ohio 44304
Masterbatches containing up to 100 phr of zinc starch xanthate or starch xanthide, and resorcinol-formaldehyde modified zinc starch xanthate or starch xanthide were prepared from styrene-butadiene and nitrile latices. The degree of dispersion of the modified starches was a function of the amount of loading, the coagulant system, drying method, and the elastomer used. In vulcanizates, the physical properties obtained were a function of the amount of starch derivative incorporated, the degree of dispersion, the coagulation, and drying processes. Tensile strengths of 2000 psi with SBR, and 2500 psi with NBR masterbatches were typical for certain starch-elastomer combinations. In commercial-type recipes, the masterbatches show potentialities for use in general purpose and automotive goods. A process design was prepared for commercial-scale production of starch xanthide masterbatches. The design and economic profile were based on pilot-scale r u n s using conventional coagulation and drying equipment.
Previous papers by Buchanan et al. (1968a,b), and Stephens et al. (1969) have described the use of gelatinized or modified starch as reinforcing fillers for natural, SBR, and nitrile rubbers. This effect was only obtained when masterbatches were prepared by coprecipitation of starch solutions and latex mixtures. Some of the effects of coagulation, drying, and dispersion on vulcanizate properties of SBR and NBR masterbatches reinforced with modified starch are given in this paper. A process for the production of these masterbatches is described and cost estimates are included. Masterbatch Preparation
Four types of masterbatches were prepared, they are classified as follows: Zinc Starch Xanthate Masterbatches. Mixtures of SBR or NBR latex (ca. 20% solids, p H 10) with starch xanthate (ea. 10% solutions) and antioxidant dispersion (1.25 phr of phenyl-beta-naphthylamine) were coprecipitated by the addition of a 50/50 mixture of 1M sulfuric acid and 1M zinc sulfate to a p H of 7 . Coagulation was completed by the addition of a slight excess of 1M zinc sulfate. With adequate stirring during the process, small crumbs were produced. The coagulum was separated from the serum by filtration through a 16-mesh stainless steel screen or No. 90 straining cloth. These masterbatches are referred to as SBR/ Zinc Starch Xanthate (SBR/SX) or NBRiZinc Starch Xanthate (NBR:SX). The starch is present as zinc starch xanthate of' D.S. varying from 0.07 to 0.09. Starch Xanthide Masterbatches. The masterbatches were prepared by mixing the latex, starch xanthate, and sodium 84
Ind. Eng. Chern. Prod. Res. Develop., Vol. 10, No. 1, 1971
nitrite solutions (1 mole of nitrite per mole of xanthate group). The pH was lowered to 4 by the addition of 1M sulfuric acid, and adequate stirring was necessary to produce a suitable crumb. An adequate exhaust system and scrubber is necessary to remove any nitrogen oxides which may be formed if excess sodium nitrite is present. The p H was maintained a t this level by the addition of sulfuric acid until complete coagulation had occurred. Antioxidants were not used as reactions with nitrous acid would occur. The filtered crumbs were washed thoroughly to remove all traces of the oxidizing agent. The starch xanthate in these masterbatches is crosslinked by the action of sodium nitrite to form starch xanthide. The masterbatches are referred to as SBRiStarch Xanthide (SBR/SX/SN) or NBRiStarch Xanthide (NBRISXiSN). Zinc Starch Xanthate/Resorcinol-Formaldehyde Masterbatches. The latex, starch xanthate solution, and antioxidant dispersion were mixed. Sufficient resorcinol and formaldehyde (mole ratio of forma1dehyde:resorcinol of 3-to-1) solution was added to give a combined weight of 8% based on the total weight of the starch. A 30-min reaction period a t room temperature (with stirring) was allowed before the mixture was coagulated using the same procedure given for the zinc starch xanthate masterbatches. These masterbatches containing resorcinolformaldehyde (RF) are identified as SBR/Zinc Starch XanthateiRF (SBR/SX/RF) or NBRiZinc Starch Xanthate/ R F (NBRISX / R F ) . Starch Xanthide/Resorcinol-FormaldehydeMasterbatches. As above, the reaction with the latex, starch xanthate, and the same ratio and amount of resorcinol-formaldehyde was completed before the mixture was coagulated using
67T (ASTM, 1968b), and rated using the method developed by Medalia (1965).
Table I. ASTM D 15-66T (1968f) Recipes Used for Masterbatch Evaluations ingredients
Styrene-butadiene masterbatches Nitrile rubber masterbatches Zinc oxide Sulfur Stearic acid Benzothiazyl disulfide Phenyl-beta-naphthylamine Vulcanization temperature, C
SBR, 28"
NBR, l F G
loob
...
5.0 2.0 1.5 3.0 1.25 145
5.0 1.5 1.o 1.0 1.25 150
...
loob
ASTM reference no. 'All recipes were corrected to give 100 parts of rubber in each masterbatch. Table II. Effect of Drying Method on Dispersion and Tensile Strength of SBR/SX/SN, 5 0 phr" Drying Method
Air oven, 70 C Hot mill. 110 C Vacuum. 50' C Extruder, ca lt50"C Commercial extruder. ca 210" C
Tensile Strength, PSI
Dispersion Rating
1330 1070 1320 2090 1980
3-E 2-E 6-H 1-A 1-A
All dried masterbatches contained approximately 3 5 volatile matter SBR SX SN = starch xanthide-SBR masterbatch 15 min cure at 145. C
Vulcanizate Preparation
The elastomer-starch masterbatches were compounded, mixed, and vulcanized using the procedures given in ASTM D 15-661' (ASTM, 1968f). For the initial studies, ASTM recipes were used (Table I) to evaluate the effects of drying, dispersion, and loading on the tensile properties of the various masterbatches. Later studies utilized commercial-type recipes. The Monsanto Rheometer determined the cure time for each compound. A 1-min warm-up time was used, the rotor speed was 3 cycles per minute a t 13O oscillation. The times required for 50, 90, and 100% cure times were used for the preparation of the samples for physical testing. The cure rate index was determined from the slope of the cure rate curve in the steepest region between the scorch time (t.) and 90% cure time. All physical tests were made using ASTM methods D 2632-67, D 224064T, D 395-67, D 2230-63T, D 624-54, D 1646-67, and D 412-66 (ASTM, 1968a,c,d,e,g,h,i) where applicable. Results and Discussion
The effect of drying, mastication, and dispersion of the modified starch masterbatches had to be determined before any extensive testing was started. Drying Studies. A large variation in tensile strength of the SBR masterbatches was obtained when different
sodium nitrite and sulfuric acid. For identification purposes, the masterbatches were classified as SBR/Starch Xanthidei R F (SBR / S X / R F /SN) or N B R / Starch Xanthidei R F ( N B R / S X /R F / SN) . All SBR masterbatches were prepared using a SBR 1500 latex that did not contain antioxidant. The NBR masterbatches were prepared using a nitrile latex containing 39% acrylonitrile (FRN 400). The amount of starch reinforcing filler in a masterbatch is reported as the calculated amount of the starch moiety in any of its modified forms.
0
SBR 1500 SSR 1606
0
SBR/SX ( 5 0 p h r )
A V
SBR/SX/RF (50phr)
SBR/SX/SN ( 5 0 p h r )
Drying Procedures
Air Oven. Small batches were dried directly in a forced air oven at 70°C, this process required more than 4 hr because of the ability of starch to retain water. A modification of this method involving a hot mill proved suitable. The crumbs were passed through a tight nip on a laboratory mill, and the loose sheet was dried for 1 hr in the forced air oven a t 70°C. The milling and drying process was repeated until the masterbatch was dry (3 to 4 hr drying time). Mill temperatures of 45OC were suitable for this process. Vacuum Drying. For comparison purposes, and for drying larger preparations (over 10 pounds), vacuum drying a t 50'C for a minimum of 36 hr at 75 mm Hg was used. Extruder Drying. A 20 to 1 L / D extrusion attachment on a Brabender Plasticorder was used with a screw having a compression ratio of 1-to-1. Partially dewatered strips of masterbatch could be dried after several passes through the extruder at approximately 150" C. Dispersion Studies
To examine the degree of dispersion obtained with the modified starches, samples were prepared using a modification of Method B of ASTM standard D 2663-
I
I
IO
I
20
I
30
I
40
MILLING TIME ( M I N I Figure 1. Effect of milling on SBR masterbatches SBR/SX SBR/SX/SN SBR/SX/RF
= = =
zinc starch xanthate-SBR masterbatches starch xanthide-SBR masterbatches zinc starch xanthate plus resorcinol-formaldehydeSBR mosterbatches
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 1, 1971
85
III
'
\
I
(\I
*
c
\ \
\
W
?( 1-61
0
5
(I-E)
50
0 FRN 503 A NBR/SX (25phr)
A NBR/SX/SN 10
NBR/SX/RF (50phr) NBR/SX/RF/SN (25phr:
v NBR/SX/RF/SN
(25phr)
20
(Wphr:
40
30
MILLING TIME (MIN) Figure 2. Effect of milling on NBR masterbatches NBR/SX NBR/SX/SN NBR/SX/RF NBR/SX/RF/SN
= =
= =
zinc starch xanthate-nitrile rubber masterbatches starch xanthide-nitrile rubber masterbatches zinc starch xanthate plus resarcinol-farmaldehydenitrile rubber masterbatches starch xanthide plus resorcinol-formaldehyde-nitrile rubber masterbatches
batches were prepared and used. Since the masterbatches were prepared under conditions giving good dispersion (rated 1-A), of the starch in rubber, masterbatches prepared under identical conditions were dried by several methods and the dispersion ratings and tensile strengths were determined. The results of the effect of the drying procedures are given in Table 11. Obviously, during the drying some type of agglomeration
of the modified starches has occurred or perhaps chemical reactions have modified the starch structure. Agglomeration is possible as starch is plasticized by water, and large amounts are present in the coagulum after the filtration process. From the results in Table 11, only the two extruder drying processes were suitable for use with SBR-starch masterbatches. The NBR masterbatches gave reasonable tensile properties by either the air or vacuum drying techniques when the dispersion rating was 1-A. Apparently the presence of nitrile groups in the polymer produced masterbatches which were more compatible with the starch. Milling Studies. Attempts were made to improve the dispersion of the modified starches in the SBR and NBR masterbatches by cold milling. The results are given in Figures 1 and 2. Under the conditions used, no improvement in dispersion was found for any of the masterbatches. After the initial milling period, only slight changes in Mooney Viscosity occurred with the SBR masterbatches; however, there was considerable change in the viscosity of the NBR masterbatches. Curing Studies. Most of the modified starch masterbatches affected the cure rate so standard ASTM cure times could not be used for preparing vulcanizates. Cure times were based on the time to reach 50, 90, and 100% maximum torque. In some instances, the 100% cure time was taken as 120 min as the maximum in the cure curve was not obtained before this point. The cure characteristics of the SBR and NBR stocks are given in Tables I11 and IV. Based on the 90% torque values, all of the SBR masterbatches except S B R / S X / R F cured much faster than the SBR 1500 used as the control. The stocks containing zinc starch xanthate or starch xanthide gave increased cure rates as the amount of filler increased. The amount of modified starch/RF did not appear to change the cure rates. All of the NBR-starch stocks cured somewhat faster than the control (FRN 503). Only the NBR/starch xanthide stock containing 50 phr of starch appeared to cure a t a much faster rate. Physical Properties. Some of the tensile properties of the air oven-mill dried masterbatches are shown in Table V, the data given are for 90% Rheometer cures. Two extruder dried compounds are included for comparison. The extruder drying gave the best tensile properties (slight recipechanges) for both the SBR and NBR compounds.
Table 111. Rheometer Data for SBR Masterbatches, 145OC Coagulant
Sodium Nitrite
Zinc Sulfate
Stock
SBR/SX
0
PHR Storch
25
50
25
50
Initial vis, in.-lb 3 3 4 5 8 4 4 7 2.5 3 Minimum vis, in.-lb 57 41 57.5 57.5 40 Maximum vis, in.-lb 110 25 115 120 40 Time to 100% cure, min 3 T,, min 5 20 3 3 51 90% Max vis, in.-lb 51 36 52 37 23 Time to 90% cure, min 89 23 8 14 25 28.5 50"; Max vis, in.-lb 20 20.5 29 7 7 4 68 8 Time to 50% cure, min 5.0 5.0 11.1 20 1.45 Cure rate index, in.-lbimin SBR/SX = zinc starch xanthateSBR masterbatches SBR/SX: R F = zinc starch xanthate plus resorcinol-formaldehyde-SBR masterbatches ~~
86
~~
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 1, 1971
SBR/SX/SN
SBR/SX/RF
75
12 10 148 50 5 133 22 74 10 5.9
25
5 3 76 44 11 68.5 32 38 22 5
50
12 9 130 26 6 117 14 65 9 12.5
Table IV. Rheometer Data for Nitrile Rubber Masterbatches, 150' C Zinc Sulfate
Coagulant
Sodium Nitrite
PHR Starch
Initial vis, in.-lb Minimum vis, in.-lb Maximum vis, in.-lb Time to 100% cure, min T,, min goL>Max vis, in.-lb Time to 90% cure, min 5 0 6 Max vis, in.-lb Time to 50% cure, min Cure rate index, in.-lbimin
NBR/SX/SN
NBR/SX/RF
NBR/SX
Stock
NBR/SX/RF/SN
0
25
50
25
50
25
50
25
50
4 3.0 51 120 6.5 46 63 26 15 1.8
10 8 74 120 5 66.5 52 37 10 2.1
15 11 100 120 5 90 52 50 10 2.1
11
15 12 121.5 120 4 109.5 47 60.5 9 1.0
11 8.5 74 120 8 67 50 37 15 5.2
17 13.5 92.5 90 5 83.5 28 46 9 7.2
11 9 61 120 8 55 57 30.5 18 3.0
17 13 106 120 5 95 50 54 14 5.0
9 76 120 7 67.5 52 38 16 1.7
NBRiSX = zinc starch xanthate-nitrile rubber masterbatches N B R / S X i R F = zinc starch xanthate plus resorcinol-formaldehyde-nitrile rubber masterbatches N B R i S X i S N = starch xanthide-nitrile rubber masterbatches N B R / S X / R F i S N = starch xanthide plus resorcinol-formaldehyde-nitrile rubber masterbatches Table V. Physical Properties of Starch-Elastomer Masterbatches, 90% Cure Mosterbatch, PHR
Tensile Strength, PSI
Modulus at 300%, PSI
Elongation, 9'0
Bashore Rebound %
Shore A Hardness
Air Oven-Mill Dried SBRiSX 25 50 SBRISXISN 25 50 SBR /SX/R F 25 50 75 SBR 1500, control NBR F R N 503, control NBRiSX 25 50 NBRi SXI R F 25 50 NBRi S X i SN 25 50 NBRISXIRFISN 25 50
500 735
90 600
570 380
51 44
52 65
1450 1750
980 1750
450 300
50 42
62 83
1460 1550 1220 230 490
1140 130 280
400 250 120 450 420
42 36 31 53 14
61 80 87 40 52
600 700
430 550
400 400
8 8
61 71
2410 930
1780
410 280
8 8
67 76
1280 1730
1170 1000
380 570
10 13
63 79
2300 1910
1300 1880
510 330
11 12
67 80
... ...
Extruder Dried" SBRISXISN 50 NBRiSX/RF/SN 50
2150 3090
...
370 170
.
I
.
...
57 85
"Recipe for SBR masterbatch contained 3.0 parts of DOTG as the accelerator; the NBR recipe contained 0.6 parts of DOTG, and 1.0 benzothiazyl disulfide.
However, the other properties shown vary depending on loading and type of modified starch present in the masterbatch. The best method for masterbatch preparation appears to be the procedure utilizing sodium nitrite, as the properties obtained are consistently higher with starch xanthide rather than with zinc starch xanthate. The resorcinol-formaldehyde modified compounds gave the best tensile strengths and higher modulus values. Commercial Utilization. Compounds were made from commercial SBR and NBR using representative recipes from the trade literature. These standard compounds were compared with compounds developed from extrusion dried
masterbatches of SBR and N B R xanthide and of SBR and NBR xanthide plus resorcinol-formaldehyde. Processing characteristics and vulcanizate properties are compared in Tables VI and VII. The recipes containing the starch derivatives were developed to give, where possible, results equivalent to the standard recipes. T o compare the physical properties of the vulcanizates, the 90% Rheometer cure time and double this cure time were used. From the data obtained, the SBR and NBR masterbatches appear suitable for use in general purpose and oil-resistant compounds, respectively. Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 1, 1971
87
Table VI. SBR Rubber Compounds General Purpose Molding Compd.
Shoe Sole Standard
Plioflex 1502 Pliolite S6 SBR/SX i S S SBR 1500 SBR/SX/RF!SN Silene E F FEF black Hard clay Picco N 100 Light process oil Parafin wax Stearic acid Zinc oxide Benzothiazyl disulfide
... ...
50 50
...
...
5 5 1.5 1.0 5.0 2.0 0.2 3.0
20
... 2.0 3.0
1.0 5.0 1.5
...
...
0.4 2.5 1.o 1.5
... ...
...
...
150
...
...
5 5 1.5 1.0 5.0 2.0 0.2 3.0
2.0
... ...
...
2.0 0.1 1.0
... ...
...
... ... -
-
247.7 157
247.7 157
230.4 153
162.6 153
8.0 5.5 49.5 16.0 27.0 1.8
1.4 5.5 45.0 6.0 9.0 10.5
5.0 4.3 84.0 7.0 9.0 15.7
6.7 5.4 86.0 6.5 33.0 2.3
... ...
...
4 4 4 4
4 4 3 4
44
60
67
...
... 45
1300 1500 380 93 37 29 85
...
... 25
... ...
27 1130 1550 430 91 35 265 27 55 17.1
... 100
...
Cure temp. O C Processing properties Monsanto rheometer data Initial vis, in -Ib Min vis, in -1b Max vis, in -Ib Time to 50Lccure, min Time t o 90'"~ cure, min Cure rate index, in -lb/min Garvey extrusion rating Swelling and porositv Sharpness, 30° edge Smoothness Corners Compounded viscosity ML-4. 100°C Physical properties Cure time, min Modulus a t 3OOLc, psi Tensile strength, psi Elongation, L; Hardness, shore A Hardness, shore D Tear strength. ppi Bashore rebound Set, c c Compression set, %" Aged 70 hours at 70° C Modulus at 3007, psi Tensile strength, psi Elongation c r Hardness, shore A Hardness, shore D Bashore rebound Set c c
SBR/SX /RF/SN
...
50 150
75
S
Standard
...
... ... ...
TMTD Sulfur Wingstay S Santocure Bondogen Cumate Agerite Staylight
SBR/SX/SN
100 50
54 1200 1500 380 92 34 220 15 80 20.5
... ... ... ...
... ... ...
9 2100 290 91 37 230 29 80 18.9 2400 210 94 40 36 55
18 2250 280 90 35 209 35 82 16.5
... ...
... ... ... ...
9 1830 2500 410 71
18 2070 2420 340 72
...
...
220 29 25 4.9
205 29 20 5.8
2300 290 77
...
31 20
...
... ... ... ... ...
33
66
...
...
2250 230 68
2250 290 69
...
...
164 47 10 3.5
173 46 18 3.4
...
...
2300 200 70
...
45 8
... ...
... ... ...
...
SBR SX R F SN = starch xanthide plus resorcinol-formaldehyde-SBR masterbatch " 22 hours at 70' C.
Process Development
Starch Xanthide-SBR Masterbatch: Continuous Process. The material balance and flow rates for the continuous production of starch xanthide-SBR masterbatch are given in Table VI11 based on results from a 20-gal scale-up experiment which gave a product yield of 92.3%. (Subsequent trials have given yields of nearly loo%.) The schematic diagram of the process is given in Figure 3. 88
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 1, 1971
A 10% solution of starch xanthate in refrigerated storage a t 50"F, styrene-butadiene latex, a 40% solution of sodium nitrite, and 9.3% sulfuric acid are metered to the continuous coagulator (Linger and Goldstein, 1966) which also receives serum recycle. Injection of the sodium nitrite solution into the serum recycle provides the necessary time lag for dispersion prior to contact with sulfuric acid which is injected below the feed well near the lower impeller. Instrumentation, in a feed forward control
Table VII. Nitrile Rubber Compounds Oil Resistant Shoe Sole
Oil Resistant Fuel Hose NBR/SX/RF/SN
Standard
...
NBRISXIRFISN NBR/ SX ISN SBR I S X /SN SBR 1502 FEF hlack S R F hlack Zinc oxide Stearic acid Trihutoxyethylphosphate Flexricin P4 DLC TMTM Sulfur Pliolite S6 Hi-Si1 Medium process oil Dibutyl phthalate Picco S l 0 0 Benzothiazvl disulfide
... ...
...
...
...
30
30 40 5 1 7 11.10 0.6 1.0
30
...
...
... ...
...
5 1 15 13.9 0.7 1.0
...
...
...
...
...
...
... ... ...
J
5
1
1
... ...
... ...
0.2 1.5 20 60 8 3 5 1.75
0.2 1.5 20 10 8 3 5 1.75
... 206.6
205.45
205.45
154
154
157
157
11.0 10.0 69.0 7.0 9.0 10.4
14.5 14.0 91.0 4.5 10.0 9.1
16.0 16.0 62.0 8.5 15.0 3.0
9.0 8.0 67.7 7.0 9.0 12.0
3 4 4 4
4 4 4 4
... ... ... ...
... ...
...
64 (MS)
36 (MS)
83 (ML) 9 1920 2560 460 63
...
237 19 8 10.1
18 2000 2650 440 64
...
247 18 5 7.7
80 (ML) 10 2670 2700 310 70
...
20 .
.
I
2660 280 70
...
200 23 13 10.2
178 24 11 10.7
...
2350 2400 310 67
...
...
...
2000 230 15
... ...
...
...
12 2
22 10
...
...
105 45
... 195.7
Cure temp. C Processing properties Monsanto rheometer data Initial vis. in.-It) Min vis, in.-lh Max vis. in.-It) Time to SOL, cure, min Time to 90'; cure. min Cure rate index. in.-lhimin Garvey extrusion rating Swelling and porosity Sharpness. 30' edge Smoothness Corners Compounded viscosity ML-4 or MS-4 a t 100" C Physical properties Cure time. min Modulus a t 300'C. psi Tensile strength, psi Elongation. Hardness. shore A Hardness. shore D Tear strength, ppi Bashore rebound Set. '; Compression set. ";" Aged 70 hours a t 70; C Modulus a t 30OCr,psi Tensile strength. psi Elongation. L c Hardness. shore A Hardness. shore D Bashore rehound Set.
70
20 120
100
NBR, F R S 503
NBR/SX/SN
Standard
... ...
...
...
...
... ...
15 1750 2400 440 93 42 329 17 45 14.1 2080 2600 400 93 40 24 65
30 1820 2400 430 92 37 325 23 70 11.4
... ...
...
... ... ... ...
9 1720 1560 360 91 36 251 17 73 16.6 1900 250 89 34 19 30
18 1830 2050 380 84 30 230 18 58 11.5
...
... ... ... ... ...
" 2 2 hr a t 10O0C.
configuration, by ratio control is indicated and is based upon the analysis of the available reactive starch in the stored starch-xanthate solution. The buoyancy and the continuous upward fluid velocity permits overflow of the slurry to a system of vibrating dewatering screens which separates most of the serum from the wet crumb. The wet crumb, containing about 2.6 pounds of water per pound of dry crumb, is fed t o an extruder dryer which further reduces the water content t o about 1 0 7 . The crumb is further dried by a fluidized bed dryer and
conveying system and then drops into a baler hopper for compression into 60-pound bales. Starch Xanthide Resorcinol-Formaldehyde-NBR Masterbatch: Batch Process. The material balance for batch production of starch xanthide resorcinol-formaldehyde-NBR masterbatch is given in Table IX, and is based on results from a 20-gal scale-up experiment which gave a product yield of 90.35. (Subsequent trials have given near 100L; yields.) The schematic diagram of this process is included in Figure 3. Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 1, 1971
89
WaNOz From Bag
9 6 % HzSO4
Formaldehyde
1000 Gal
50 GPM
NBR Reactor 800 Gal
14000 Cat m
Dewatering
r
I
Steam
e H-Baler
Extruder Dryer IO" Dryer
l!L
Apron Dryer
Figure 3. Process for production of starch-elastomer masterbatches
Table IX. Starch Xanthide Resorcinol-Formaldehyde Resin-NBR Masterbatch. Process Material Balance
Table Vlll. Starch Xanthide-SBR Masterbatch. Process Material Balance
Basis: 36 Batches Per Day Lb/Hr
NaNO (dry) from bag storage 9gLr H.SO, from storage Water to NaNOI solution tank Water to H 3 0 , dilution tank YaXO. solution to coagulator 9 3CrH.SO, to coagulator Starch xanthate 10% solution to coagulator SBR latex to coagulator Serum recycle to coagulator rota1 feed to coagulator vol coagulator at 45-min hold-up time \Vet crumb from screens, each Serum from screens, each Serum recycle pump Discharge dewatering extruder, each, at loL; moisture Water removed by extruder, each Water removed by dryer. each Feed to baler, each
GPM
...
129.0 764.0 335.9 7,290.4 464.9 8,039.4 40,456.0
0.83 0.67 14.59 0.67 15.07 85.8
36,192.0 38,333.3
73.5 76.7
123,485.6 11,778 gal 18,958.3 44.936.0
...
...
Est
Resorcinol (dry) from storage Water from resorcinol tank 37% Formaldehyde NaN02 (dry) from storage Water from N a N 0 2 tank 98% HSO, from storage Water from sulfuric acid tank Starch xanthate, 10% solution NBR latex Serum recycle Total vol to batch tank Wet crumb from screens Serum from screens Serum recycle pump
89.9 180
5,720.0 13,238.3 520.0 5,200.0
90 Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 1, 1971
Lb/Batch
Gal/Batch
GPM
8.72 43.23 18.87 5.96 23.49 38.54 379.51 1870.6 795.4 2222.2
...
...
... 2350.0 3027.5
...
Lb/Hr
Discharge 'French' oil press at 207c moisture Water removed by press Water removed by apron dryer Feed to baler
1000 2540 167 833
5.19 2.39
...
2.82 2.52 45.56 261.0 91.53 266.67 675.16 363.4 266.67
1 1
... 1
... 5 50 20
., . ... 50
Table X. Raw Materials Cost
Basis: 1000 Lb, Dry Crumb Starch Xanthide Resorcinol-Formaldehyde Resin-NBR
Storch Xonthide-SBR
Starch xanthate, starch basis Latex, total solids basis NaNO?
HLSOi Formalin. 37", solution Resorcinol
Lb
Cents/Lb
Dollars
Lb
Cents/Lb
Dollars
367 734 12.4 72
6.87 19.59 10.4 1.7
25.21 143.79 1.29 1.22
348.9 697.1 10.7 68.0 34.0 15.7
6.87 53.0 10.4 1.7 3.5 57.0
23.97 369.46 1.12 1.16 1.19 8.95
171.51
1174.4
...
...
...
...
1185.4
Cost. cents Ib
~~
~~
405.85 40.585
17.151 ~~
~~
Table XI. Production Costs of Starch-Elastomer Masterbatches, Cents/Lb
Production rate Fixed investment Raw materials Labor, direct Labor, overhead Supervision Plant overhead Utilities Maintenance Insurance Taxes Depreciation
75,000,000 lbiyr $1,367,000 $1,549,000 17.151 17.151 0.294 0.294 0.044 0.044 0.027 0.027 0.294 0.294 0.245 0.270 0.110 0.131 0.045 0.054 0.018 0.022 0.182 0.218 18.410
Manufacturing costs
Starch Xanthide Resorcinol-Formaldehyde Resin-NBR
Starch Xanthide-SBR
Product
18.505 18.5 centsilb
The starch xanthate solution, nitrile latex and its own serum recycle, are charged to one of three batch coagulation tanks (Brennan, 1962). The ratio of the latex and recycle to starch xanthate solution is controlled by assay of starch. The resorcinol and formaldehyde are added subsequently and the mixture is continuously agitated for about 30 min. Coagulation is accomplished by addition of 40% sodium nitrite solution and subsequent slow addition of 9.3% sulfuric acid over a 20-min period. The small amount of nitrogen oxides formed from excess sodium nitrite could be removed by a scrubber. The three coagulation vessels provide a continuous stream for further processing. The serum and wet crumb pass to dewatering screens where the wet crumb is separated from the serum. A French oil press further dries the crumb to about 20% water. The crumb is then conveyed to a conventional apron dryer which reduces the moisture content to about 1%. A baler is provided to compress the dry crumb in 60-pound blocks. Production Cost Estimates
Preliminary cost calculations were made for a single facility capable of producing 75,000,000 pounds per year of starch xanthide-SBR masterbatch and 6,000,000 pounds per year of starch xanthide resorcinol-formaldehyde-NBR masterbatch. This is about one-third of the annual U.S. production of nonblack SBR and NBR masterbatches. Starch required is 29,600,000 pounds dry basis. At this volume and with starch costing about 5 cents per pound, the total unit cost for starch xanthate is 6.87 cents per pound, starch basis.
6,000,000 Ib;yr $319,000 40.585 1.000 0.150 0.030 0.350 0.300 0.310 0.134 0.053 0.531
$389,000 40.585 1.000 0.150 0.030 0.350 0.300 0.310 0.162 0.065 0.G49
42.443
42.601 42.5 cents/lb
Costs of other ingredients were taken from the regularly published price lists with the exception of SBR-1500 latex. For this latex, the estimated-on-site cost was 19.59 cents per pound, total solids basis, not including addition of antioxidant. Raw materials costs are given in Table X. They are the preponderant factor in these masterbatch costs. For the starch xanthide-SBR, a single coagulator of 14,000 gal is adequate but two parallel screening, drying, and baling lines are required, each being capable of handling 5500 pounds of crumb per hour. The starch xanthide resorcinol-formaldehyde-NBR requires three 800-gal batch coagulators with a single line of dewatering, drying, and baling operations. The combined facilities would be housed in a 60 x 80 x 30 steel frame building with corrugated Transite siding. Storage of starch xanthate, latices, and concentrated sulfuric acid would be outside. The baling and warehousing would be performed in a 60 x 100 x 15 steel frame building with similar siding and contiguous with the processing building. For capital distribution purposes, 808 of the structures would be assignable t o the SBR product. The makeup of the manufacturing costs for the SBR and NBR masterbatches is shown in Table XI, and they are estimated to be about 18.5 and 42.5 cents per pound, or about 1.3 and 1.9 cents per pound above raw materials costs, respectively. The recipes containing the starch derivatives were developed to give, where possible, results equivalent to the standard recipes. T o compare the physical properties of the vulcanizates, the 90% Rheometer cure time and double this cure time were used. From the data obtained, the SBR and NBR masterbatches appear to be suitable Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 1, 1971
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for use in general purpose and oil-resistant compounds, respectively. Conclusions
Elastomer masterbatches prepared with SBR and NBR latices, and starch xanthate derivatives by selective coagulants yielded vulcanizates with physical properties suitable for many commercial products. The masterbatching methods used are believed to be compatible with presentday manufacturing techniques. literature Cited
American Society for Testing and Materials, Philadelphia, ASTM Method D 395-67. “Compression Set of Vulcanized Rubber,” Method B, Book of ASTM Standards. Part 28: p 198,1968a. American Society for Testing and Materials, Philadelphia, ASTM Method D 2663-67T. “Determining the Dispersion of Carbon Black in Rubber Compounds,” Method B, Book of ASTM Standards, Part 28, p 1103, 1968b. American Society for Testing and Materials, Philadelphia, ASTM Method D 2230-631‘. “Extrudability of Unvulcanized Elastomeric Compounds,” Book of ASTM Standards, Part 28, p 1008, 1 9 6 8 ~ . American Society for Testing and Materials, Philadelphia, ASTM Method D 2632-67. “Impact Resilience of Rubber by Vertical Rebound,” Book of ASTM Standards, Part 28, p 1077, 1968d. American Society for Testing and Materials, Philadelphia, ASTM Method D 2240-64T. “Indentation Hardness of Rubber and Plastics by Means of a Durometer,” Book of ASTM Standards, Part 28, p 1019, 1968e. American Society for Testing and Materials, Philadelphia, ASTM Method D 15-661’. “Sample Preparation for Physical Testing of Rubber Products,” Book of ASTM Standards, Part 28, p 1, 1968f. American Society for Testing and Materials, Philadelphia, ASTM Method D 624-54. “Tear Resistance of Vulcanized Rubber,” Die C used, Book of ASTM Standards, Part 28, p 341, 19688.
American Society for Testing and Materials, Philadelphia, ASTM Method D 412-66. “Tension Testing of Vulcanized Rubber (Tensile Stress, Tensile Strength, Set at Break, and Ultimate Elongation) ,” Die C used, Book of ASTM Standards, Part 28, p 206, 1968h. American Society for Testing and Materials, Philadelphia, ASTM Method D 1646-67. “Viscosity and Curing Characteristics of Rubber by the Shearing Disk Viscometer,” Book of ASTM Standards, Part 28, p 815, 19681. Brennan, P. J., Chem. Eng. 69, 125-9 (1962). Buchanan, R. A., Russell, C. R., Rist, C. E., “Starch in Rubber. Reinforcement of Rubber by StarchResorcinol-Formaldehyde Resin.” Paper presented a t 93rd meeting of the Division of Rubber Chemistry, ACS, Cleveland, Ohio, April 23-6, 1968a. Abstract in Rubber Chem. Technol. 41, 1380-1 (1968). Buchanan, R . A., Weislogel, 0. E., Russell, C. R., Ris C. E., IND.ENG. CHEM.PROD.RES. DEVELOP.7. 155 (1968b). Linger, P. N., Goldstein, H. J., Chem. Eng. 73, 11214 (1966). Medalia, A. I., Rubber Age 97 (l), 82-93 (1965). Stephens, H. L., Murphy R. J., Reed, T. F., Rubber World 161, 77-81 (1969).
RECEIVED for review February 18, 1970 ACCEPTED August 14, 1970
Presented at 96th meeting, ACS. Division of Rubber Chemistry, Buffalo. K.Y., October 14-17, 1969. This research was conducted by the Institute of Polymer Science, University of Akron. Akron. Ohio, under contract with the USDA and authorized by the Research and Marketing Act of 1946. The contract was supervised by the Northern Regional Research Laboratory. which is headquarters for the Northern Utilization Research and Development Division. Agricultural Research Service, USDA, Peoria, Ill. Mention of firm names or commercial products does not constitute an endorsement by the USDA over similar firms or products not mentioned.
New Coupling Concepts for Glass Reinforced Thermoplastics Robert C. Hartlein DOLLCorning Corp., Midland, Mich. 48640 u s i n g glass cloth laminates. Plueddemann (1966) demonstrated the feasibility of using organofunctional silanes to improve the bond between glass fibers and thermoplastic polymers. His study involved the screening of several organofunctional silanes as coupling agents between glass fibers and both polystyrene and SAN (styrene acrylonitrile copolymer). The structures of these organofunctional silanes are shown in Table I. As a result of this study, organofunctional silanes were supplied t o several major glass fiber producers for their evaluation in glass fiber-size formulations. Incorporation of these treated glass fibers by Engelhardt et al. (1967) into molten thermoplastic polymers with a compounding extruder failed t o give the same strength increase as had occurred with laminates. The failure of thermoplastic laminate data to correctly 92
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 1, 1971
predict the optimum organofunctional silane for use with each polymer prompted an additional study. The objective of this study was to further investigate the reinforcement of thermoplastics with glass fibers and t o identify the proper interfacial chemistry needed to produce high strength composites. Three thermoplastic polymers (polystyrene, polypropylene, and nylon) were evaluated. Watersized glass roving was used throughout this study. Raw materials used in this study are listed in Table 11. Polystyrene
Initial work with injection molded, chopped glassthermoplastic composites was done to substantiate reported results, t o measure interferences caused by the glass fiber coating, and t o determine molding procedures.
