Byrne, G. A,, Gardiner, D., Holmer, F. H., J . Appl. Chem. 16, 81 (1966). Carlson, J., U. S. Patent 3,235,541 (Feb. 15, 1966); C A 64, 16122 (1966). Carvalho, J. da Silva, Prins, W., Schuerch, C., J . A m . Chem. SOC.81,16122 (1966). Chatterjee, P. K., Conrad, C. M., Textile Res. J . 36, 487 (1966). Epshtein Ya. V., Golova, 0. P., Durynina, L. I., Izu. Akad. Nauk, S S S R , Otdel. Khim. Nauk 1959, 1126; C A 54, 1330 (1960). Esterer, A. K., U. S. Patent 3,298,928 (Jan. 17, 1967); C A 66, 56886 (1967a). Esterer, A. K., U. S. Patent 3,309,356 (March 14, 1967); C A 66, 106072 (1967b). 1966 (C), 1473. Gardiner, D., J . Chem. SOC. Golova, 0. P., Pakhamov, A. M., Andrievskaya, E. A., Krylova, R. G., Llokl. Akad. Nauk, S S S R 115, 1122 (1957); C A 52,4165 (1958). Golova, 0. P., Pakhamov, A. M., Nikloaeva, I. I., Izu. Akad. Nauk, SSSA!, Otdel. Khim. Nauk 1957, 519; C A 51, 14258 (1957). Heritage, C. C., Esterer, A. K., U. S. Patent 3,309,355 (March 14, 1967); C A 66, 10607 (1967). Irvin, J. C., Oldham, J. W. H., J . Chem. SOC.119, 1744 (1921). Karrer, P., Helu. Chirn Acta 3, 258 (1920). Kato, K., Agr. Biol. Chem. (Tokyo) 31, 519, 657 (1967). Kilzer, F. J., Broido,, A., Pyrodynamics 2 , 151 (1965). Madorsky, S. L., Hart, V. E., Strauss, S., J . Res. Natl. Bur. Std. 60, 343 (1!358). Pakhamov, A. M., Im. Akad. Nauk, S S S R , Otdel. Khim. Nauk 1957, 1497; C A 52, 5811 (1958).
Parks, W. G., Esteve, R. M., Gollis, M. H., Guercia, R., Petrarca, A., Abstracts, Division of Cellulose Chemistry, 127th meeting, ACS, Cincinnati, Ohio, April 5, 1955. Pictet, A., Helu. Chim. Acta 1, 226 (1918). Pictet, A., Cramers, M., Helu. Chim. Acta 3, 640 (1920). Pictet, A., Sarasin, J., Helu. Chim. Acta 1, 87 (1918). Ruckel, E. R., Schuerch, C., J . Org. Chem. 31, 2233 (1966). Sawardeker, J. S., Sloneker, J. H., Dimler, R. J., J . Chromatog. 20, 260 (1965). Schwenker, R. F., Jr., Beck, L. R., J . Polymer Sci., Part C, No. 2, 331 (1963). Schwenker, R. F., Jr., Pacsu, E., I d . Eng. Chem., Chem. Eng. Data Ser. 2, 83 (1957). Sweeley, C. C., Bentley, R., Mikita, M., Wells, W. W., J. A m . Chem. SOC.85, 2497 (1963). Tishchenko, D. V., Fedorishev, T., Zh. Priklad. Khim. 20, 393 (1953). Ward, R. B., “Methods in Carbohydrate Chemistry,” Vol. 11, R. L. Whistler, M. L. Wolfrom, Eds., p. 394, Academic Press, New York, 1963. Wolff, I. A., Olds, D. W., Hilbert, C. E., Sturke 20, No. 5 , 150 (1968). Zemplh, G., Csuros, Z., Angyal, S., Ber. 70, 1848 (1937). Zemplh, G., Gerecs, A., Ber. 64B, 1545 (1931). RECEIVED for review November 27,1968 ACCEPTED April 29,1969 Project supported by the Agricultural Research Service, U. S. Department of Agriculture, Grant 12-14-100-8043 (71) administered by the Northern Utilization Research and Development Division, Peoria, Ill.
URETHANE PLASTICS BASED ON STARCH AND STARCH-DERIVED GLYCOSlDES F . H . O T E Y , R . P . W E S T H O F F , W . F . K W O L E K , C . 1. M E H L T R E T T E R , A N D C . E . R l S T
Northern Regional Research Laboratory, U. S . Department of Agriculture, Peoria, Ill. 61604
INCORPORATION of low-cost starch and starch derivatives into polymers provides a potential method for expanding the applications and improving the economics of certain plastics. The chem.istry, processing conditions, and increasing importance of polyurethanes make them especially promising for starch modification. Polyurethanes are generally defined as polymers produced by the addition reaction between diisocyanates and polyols:
n OCN-R-NCO
+ n HO-Ri-OH
0
II
(C--MH-R-NH-C
-+
0
II
-O-R1-0-),
The alcoholysis reaction between starch-derived glycol glycosides and castor oil gives a series of polyols with a wide range of equivalent weights suitable for preparing urethane polymers. Furthermore, when isocyanate in excess of that required for the poly01 is added, polymers are produced with terminal -NCO groups. A significant number of these -NCO groups are believed to react with hydroxyls on the surface of starch particles when a mixture of the urethane polymer and starch is subjected to heat and pressure molding. Presumably, starch particles and the urethane interact to form crosslinked structures, causing changes in properties of the plastics. On the one hand, the urethane resin contains the “soft segment” of the plastics and thus contributes to low glass transition temperatures, elasticity, elongation, and tear strength. On VOL. 8 NO. 3 S E P T E M B E R 1 9 6 9
267
Urethane plastics were prepared from a polymeric diisocyanate and a series of mixed polyols-castor oil and the products from alcoholysis of castor oil with glycol glycosides. In formulating the plastics, the equivalent ratio of isocyanate to polyol (NCO/OH) was varied from 1 to 2 and the polyol equivalent weight from 200 to 336. Starch was incorporated into these formulations to determine its effect upon the chemical cost and properties of urethane plastics. The plastics were prepared by uniformly mixing the components and subjecting the mixture to pressure molding at 14OOC. As the amount of starch was increased from 0 to 6O%, the NCO/OH ratio from 1 to 2, and the polyol equivalent weight was decreased from 336 to 200, there was a corresponding increase in tensile strength, hardness, and heat resistance of the plastics. The use of starch and starch-derived glycol glycosides can significantly reduce chemical costs of urethane plastics.
the other hand, starch can improve the “hard segment” required for strength, hardness, and abrasive resistance of the plastics. Moreover, encapsulation of the starch by the resin can reduce attack by moisture, acids, and microorganisms. Starch has been investigated as a filler or reinforcing agent in polyester-based urethanes (Boggs, 1959), in polyether-based urethanes (Otey et al., 1968a), and in rubber (Buchanan et al., 1968). Starch has also been added to rigid urethane foam to reduce its cost and to improve fire resistance (Bennett et al., 1967). Patton and coworkers (1960) prepared and evaluated several urethane elastomers based on castor polyols. The urethane polymers described were prepared by reaction of a polymeric diisocyanate with castor oil and with polyols from the alcoholysis of castor oil with glycol glycosides. Starch in various amounts was mixed with these reactants before they were molded into plastics. The investigation was designed to show the effects of starch concentration, equivalent ratio of isocyanate to poly01 (NCO/OH), and poly01 equivalent weight on properties of the molded plastics. The plastics might have applications in many areas where urethane plastics are now used. They should be particularly suitable for household and industrial floor and wall coverings. I t is impractical to symbolize all chemical reactions involved in the synthesis of urethane polymers described in this paper. However, basic types of chemical structures are shown, to improve clarity. Castor oil is a naturally occurring triglyceride of ricinoleic acid having the idealized structure:
containing 45% glycol a-D-glucoside, 21% glycol p-Dglucoside, and 34% mixed glycosides with two or more glucose units per glycol unit (Otey et al., 1965). The structure of glycol a-D-glucoside is:
CH20H I
H
OH
Alcoholysis of castor oil with glycol glycosides yields a random mixture of ricinoleic esters of glycosides and glycerol which are designated in this paper as polyols. The following structures are intended to represent types of molecules formed during the alcoholysis of 3 moles of pure castor oil with 1 mole of pure glycol a-D-glucoside.
0 OH II H*COC[ CH2]7CH=CH-CH2-iH(CH2]$H3 OH HCOC(CH2]7CH=CH-CH2-l!H(CH2]$H3 OH H2COC[CH2)7CH=CH-CH2-iH(CH2]5CH3
I!
The commerical grade of castor oil used had a hydroxyl equivalent weight of 336 (theoretical for the idealized structure is 311). Glycol glycosides are obtained by reaction of ethylene glycol with starch (Otey et al., 196813). They are a mixture 268
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
The poly01 mixture shown has a calculated hydroxyl equivalent weight of 215. Decreasing the ratio of glycoside to castor oil increases the hydroxyl equivalent weight of the polyols. By varying the amount of glycoside from 14 to 0%, a series of polyols was obtained having analytical hydroxyl equivalent weights ranging from 200 to 336.
Polyurethanes are readily formed by adding a diisocyanate to the above types of polyols. When sufficient diisocyanate is added to react with all of the available hydroxyls, the NCO/OH ratio is 1. When twice the necessary amount of diisocyanate is added, the NCO/OH ratio is 2. Plastics were made a t NCO/OH ratios of 1.1, 1.5, and 2.0. Thus, at each level studied, terminal -NCO groups were available for reacting with starch, which was added as a reactive filler. Experimental
Polyols. The reaction products of castor oil and glycol glycosides were selected as polyols for this study. Castor oil has an equivalent weight (based on hydroxyls) of about 336. Alcoholysis of castor oil with various amounts of glycol glycosides gave a series of polyols with equivalent weights from 200 to near 336. Other polyhydric materials could be used to prepare a similar series of polyols. However, glycol glycosiides made directly from the reaction of starch with ethylene glycol were selected because of their potential economic advantage (Otey et al., 1968b) over other polyhydric materials. In a typical alcoholysis procedure, castor oil (500 grams of AA standard from Baker Castor Oil Co.) and 0.13 gram of LiOH were mixed and heated under Nz to 250" C. in a 1-liter three-necked flask equipped with stirrer, downward condenser, thermometer, and nitrogen inlet. Then 57.5 grams of aqueous glycol glycosides (20% HzO, 46 grams of nonvolatiles; 1 equivalent) was added a t 240" to 250°C. during 1 hour with good stirring a t a reduced pressure of 5 to 10 cm. of Hg. The solution was heated for 10 minutes more and then treated with 8 grams of activated carbon (Darco G-60) and 8 grams of filter aid (Celite). Upon cooling to 170" C., the product was filtered to yield a light amber liquid. Analysis of the liquid for hydroxyl content by the acetic anhydride method showed an equivalent weight of 241 (calculated, 219; based on glycol glycoside and castor oil equivalent weights of 46 and 336, respectively). Since the equivalent weights of all polyols analyzed about 10% higher than the corresponding calculated values, some dehydration may have occurred during alcoholysis. Starch Pretreatment. Pearl cornstarch was reduced in particle size by milling twice in an Alpine Kolloplex pin mill (Model 160Z) operated at 14,000 r.p.m. Particlesize distribution analysis with a Sharples Micromerograph showed that 50% of the milled starch had a particle size of less than 17 microns and 96% had a particle size of less than 30 microns. ,4fter milling, the starch was dried in a vacuum oven a t 100°C. and 5 mm. of Hg for 5 hours and stored in sealed containers. Plastic Preparation. 'The milled and dried starch, poly01 (containing 0.25% dibutyl tin dilaurate catalyst), and polymeric diisocyanate (Mondur MR from Mobay Chemical Co.) were mixed in a 250-cc. resin flask equipped with ground glass stirrer, nitrogen inlet, and vacuum source. The mixture was stirred to a uniform paste at a reduced pressure of 2 to 5 mm. of Hg for 5 minutes. If an exothermic reaction was not evident during this time, heat was applied to initiate the reaction. After the vacuum was broken with nitrogen, the mixture was poured into a heated mold (chrome.plated cavity, 6 x 6 x 0.075 inches) and cured a t 140" C. and 500-p.s.i. pressure for 15 minutes. Physical properties of the plastics were determined after an additional cure of at least 8 days at room conditions.
Test Methods
The plastics and raw materials were tested by the following ASTM procedures: tensile strength and per cent elongation, D 638-64T; effects of chemical reagents, D 543-60T; flexural strength, D 790-66; deflection temperature at 264 p.s.i., D 648-56; specific gravity, D 79266; Shore D hardness, D 1706-61; Izod impact, D 25656; poly01 equivalent weight by the acetic anhydride method, D 1638-61T; and unreacted isocyanate, modified D 1638-61T. For the aging tests (ASTM D 543-60T) (Table I) specimens were cut into the shape used for tensile measurements, suspended on glass rods, and completely immersed for 7 days a t 6 P C . in water or a t 25°C. in either 10% NaOH or 3% HZSOa. Cross-sectional measurements before and after aging were made at the narrowest width of the sample and used to calculate the per cent crosssectional change due to aging. Tensile strengths were determined on the aged specimens after washing and airequilibrating. Solvent-exposure data (Table 11) were accumulated on samples cut to 0.5 x 3.5 x 0.08 inch. The samples were immersed in water, ethanol, xylene, or acetone for 24 hours a t room temperature, and the length and weight changes determined immediately after blotting dry. Unreacted or free isocyanate in the plastic was measured by modifying the ASTM D 1638-611' procedure. Data given in Table I11 were obtained from plastic specimens made with 0 and 50% starch. Each specimen was stored over CaC12 in a desiccator until all analyses were completed. Samples (2 to 4 grams) were cut from the specimens on a milling machine and allowed to stand with an excess of 2N dibutylamine in toluene a t 90°C. for 10 minutes. The excess amine was titrated with 1N HC1 to determine the amount of free isocyanate. Results are reported as per cent free isocyanate based on total isocyanate in the plastic formulation. Analyses of Data
Formulation changes, which significantly affect plastic properties, are per cent starch, NCO/OH ratio, and equivalent weight of the polyols. However, small-scale synthesis and plastics formulating introduce unknown variables which make data analyses difficult. To overcome this problem, the data were analyzed by a multiple regression equation and plotted in Figures 1 to 5. The plastics were made according to various combinations of three factors: NCO/OH ratios of 1.0, 1.1, 1.5, and 2.0; poly01 equivalent weights of 197 to 336 and a t various levels in this range; and per cent starch from 0 to 60% at increments of 10%. Responses to five physical property tests were measured on up to 126 plastic preparations for a single test. The results shown in Figures 1 to 5 were prepared from a general second-degree multiple regression equation
where
Y = physical property
Xi = equivalent weight X p = per cent starch X s = NCO/OH ratio VOL. 8 N O . 3 S E P T E M B E R 1 9 6 9
269
Table 1. Formulations, Properties, and Chemical Costs of Urethane Plastics
After Aging 1 Week Deflection HzO, 10% 3% Temp., H a d - Chemical 60°C. NaOH H2SOa Change Polyol Tensile in Flexural Impact, ElonF. at ness cost, Composition, W t . %E. p, NCOI Strength, Tensil area, Strength, Ft. Lb.1 gation, 264 Specik (Shore Cents/ my. strength,p.s.i. %' P.S.I. In. 76 P . S . I . Gravity D) Starch! MR" Polyol W t . OHb p . s . 1 , Lb. 0
20
30
40
50
60
42.6 49.8 48.6 38.2 45.3 34.1
57.4 50.2 51.4 61.8 54.7 65.9
197 201 211 237 241 282
1.1 1.5 1.5 1.1 1.5 1.1
5517 7018 7112 3827 5486 1827
5593 6959 6867 4044 5437 2126
34.1 39.9 38.9
45.9 40.1 41.1
197 201 211
1.1 1.5 1.5
5585 7346 7216
34.0 28.2 23.9
36.0 41.8 46.1
211 217 282
1.5 1.1 1.1
7296 5314 2211
25.2 29.8 34.1 18.0 23.4 27.7
34.8 30.2 25.9 42.0 36.6 32.3
202 202 202 336 336 336
1.1 1.5 2.0 1.o 1.5 2.0
6706 8418 9228 1495 3640 6909
4538
21.5 21.0 24.9 20.8 25.8 22.7
28.7 29.0 25.1 29.2 24.2 27.3
197 202 202 217 217 241
1.1 1.1 1.5 1.0 1.5 1.5
6591 7997 8254 6929 7003 6263
2683
16.8 22.8 20.7 23.4 13.4 16.3 19.2 12.0 15.7 18.4
23.2 17.2 19.3 16.6 26.6 23.7 20.8 28.0 24.3 21.6
202 202 217 217 289 289 289 336 336 336
1.1 2.0 1.5 2.0 1.1 1.5 2.0 1.0 1.5 2.0
6837 6877 7356 6848 3311 5848 6691 1587 4575 6254
5601 6662 4422 5741 5389 1768 7976 7658 751 829 4216 7099 7173 6668 4909 5540 2864 3100 4574 5345 3344 5038 4947 656 1170 4132
9,900 12,500 12,900 7,500 10,200
0.3
...
2.6
1.2 1.7 4.3
10,700
0.3
13,000
...
1.8 1.7 4.5
12,700 10,500
0.2 -1.3 -1.3 0.0 0.0 0.0
5.1 0.5 1.5 -4.0 13.8 1.3 6.1 3.3 4.4 2.1 1.8 2.5
2.0 3.0 3.3 3.1 4.4 3.6 8.7 7.5 11.0 4.0
... ... ...
... 13,700 ... 6,800 11,700 12,000
... 13,000
... 14,900 13,400
... ... 10,600 ... ... ...
12,800
...
8,600 12,100
12 9 15 33 12 95
130 145 144 108 133
...
1.14 1.15 1.15 1.11 1.13 1.09
81 83 81 78 81 67
25.1 25.9 25.8 24.6 25.4 24.1
10 7 7
130 145 141
1.20 1.21 1.21
82 84 84
21.1 21.8 21.7
4 8 50
142 123
1.24 1.22 1.19
85 83 73
19.6 18.9 18.4
3 3 4 36 5 3
144
83 85
...
1.26 1.27 1.29 1.24
106 136
1.27
17.0 17.6 18.1 16.2 16.8 17.3
0.2 0.3 0.2 0.3 0.3
135 140 154
...
3 4 3 3 2 5
0.2 0.2 0.3 0.3 0.3 0.3 0.3 3.3 0.2 0.2
2 2 2 2 9 5 2 8 3 3
..,
., , ...
3.0
... ...
0.5 2.6 0.2 0.3 0.3
... ...
0.3
... ...
176
...
173 136
... 194 167
... ... ...
140
...
114 129
...
1.30 1.30 1.31 1.29 1.30 1.30 1.33 1.35
...
...
1.31 1.32 1.33 1.30 1.31 1.32
... ... 78 84 85
... ... 85 87 85 86 87 89 89 80 84
... 68 78 81
15.1 15.0 15.5 15.0 15.6 15.2 13.0 13.7 13.5 13.8 12.6 13.0 13.3 12.4 12.9 13.2
a Polymeric isocyanate, Mondur M R . 'Equivalent ratio of isocyanate to polyol (does not include starch hydroxyls). e Per cent change in cross-sectional area after aging 1 week in &O, NaOH, or H2SOa.
fitted to the observations available for each test response. The method of least squares estimates coefficients bo to bs. After the coefficients in the equation were calculated, they were used to predict Y for a series of XI,X2,and X3 values. A predicted Y was calculated for all combinations of X1 from 200 to 340 (increment of 20), X Z from 0 to 60 (increment of lo), and X 3 a t 1.1, 1.5, and 2.0. Figures 1 to 5 were prepared from these data. Zero and 60% starch lines are plotted for each NCO/ OH ratio and lines for intermediate starch levels can be interpolated between these levels. Although a 0% starch line is shown for NCO/OH of 2, the lowest actual per cent starch in the experiment a t NCO/OH of 2 was 40%. Thus, an extrapolation appears in this area of the figures. Results and Discussion
Plastic specimens without starch were amber and transparent, whereas those with starch were light tan and translucent. All specimens were uniform in appearance and could be drilled, sawed, or milled. Colored plastics 270
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
were readily prepared by incorporating a pigment or dye into the formulations. Formulation changes that significantly affect plastic properties include per cent starch, NCO/OH ratio, and equivalent weight of the polyol. Concentration of the dibutyl tin dilaurate catalyst was not critical, but appeared to optimize a t about 0.25% based on polyol. Curing conditions of 15 minutes a t 140" C. were arbitrarily selected. Cure times were studied over a range of 5 to 30 minutes a t temperatures of 100" to 160°C.; however, within these ranges the properties of the plastics were not significantly different. I t was essential that the plastics be further cured for several days a t room conditions to achieve maximum tensile strength. About 20% of the plastics prepared and evaluated are listed in Table I according to increasing order of per cent starch and poly01 equivalent weight. The polyol with equivalent weight of 336 is castor oil, and all other polyols are the products from alcoholysis of castor oil with varying amounts of glycol glycosides. Table I is intended only
~~
~~~~
~
~~
Table II. Solvent Resistance of Urethane Plastics at 25' C. for 24 Hours
Starch, %
Water
xylene
Acetone
Ethanol
NCOIOH"
Polyol Ep. w t .
70 AL'
% AWLb
% AL
% AWt.
70 AL
% AWt.
% AL
1.5 1.5 1.5
201 211 241
0.0 0.0
0.1 0.2 0.7
5.2 6.7 13.5
...
...
F' F
F F
...
0.0
0.1 0.1 0.1
10
1.5
201
0.0
0.2
0.0
3.9
F
20
1.5
211
0.1
0.3
0.1
4.5
30
1.5
211
0.1
0.4
0.1
3.0 1.9 0.4 5.3 19.6 10.9
0
40
50
1.1 1.5 1.5 1.0 1.5
202 202 289 336 336
0.1 0.1 0.1 0.3 0.2
0.7 0.5 0.7 1.4 1.o
0.0 0.0 0.4 8.1 3.5
1.0 1.5 .1.5 2.0
217 241 289 336
0.2 -3.3 0.4 0.2
1.1 0.9 1.8 0.7
0.1
1.1 2.0 1.5 2.0
202 217 289 336
0.3 0.2 0.3 0.2
1.5 1.1 1.6 1.4
60
1.9
% AWt.
... ...
0.1
3.4
F
0.1
2.2
F
F
0.0
2.2
F
F
0.0
1.5
F
F
0.0
6.6
F
...
1.1
0.6
F
6.4 6.5
14.5 15.1
0.1 1.5 0.2
1.4 2.9 2.0
9.5 10.9 12.2 11.6
0.0
1.o
1.3 0.0
2.6 1.0
5.0 1.3 8.2 8.6
0.0 -0.1 0.0 0.0
0.5 0.0 0.8 0.7
...
...
7.0 0.4
18.1 4.1
4.3 4.8 5.2 5.1
0.1 0.0 0.2 0.2
0.9 0.5 2.8 2.3
1.0 0.0 3.8 4.3
...
...
...
...
Equivalent ratio of isocyanate to polyol (does not include starch hydroxyls). ' Change in length and weight, % , Failed. Table 111. Effect of Starch on Percentage of Free Isocyanate
Free Isocyanate by Analysis, %
8000
Starch, Isoc:yanateb Days after Plastic Preparation 7c NCOIOH" Calculated, 70 Initial 1 7 14 21
7000
I
I
rim
0
1.1 1.5 2.0
9.1 33.3 50.0
12 29 46
13 28 44
9 26 41
10 25 40
8 25 38
50
1.1 1.5 2.0
9.1 33.3 i50.0
8 15 22
7 14 23
6 13 22
4 14 22
4 12 20
"Equivalent ratio of isocyanate to polyol (does not include starch hydroxyls). 'Percentage of unreacted isocyanate based on total isocyanate calculated to be present, assuming no reaction with moisture or starch.
-
6000
v,
5000
5
=
M
v,
4000
.W
E 3000
I-
2000 to provide a cross section of formulations and properties of the plastics. Figures 1 to 5 give a more accurate assessment of the effects of varying NCO/OH ratios, poly01 equivalent weights, and per cent starch on strength, elasticity, heat stability, and hardness of the plastics. Data in Table I and Figure 1 show that tensile strengths of plastics are greatly affected by NCO/OH ratios, poly01 equivalent weights, and per cent starch. As the poly01 equivalent weight is increased, the reinforcing effect of starch becomes more pronounced. For example (Figure l),most plastics madle from polyols with low equivalent weights, with or without starch, have tensile strengths that fall within a narrow range of 6000 to 7500 p.s.i. In contrast, as the poly01 equivalent weight is increased to 336, plastics containing starch generally have much higher tensile strengths than those without starch. The data suggest that a t high poly01 equivalent weights the isocyanate-polyol polyiner crosslinks starch to improve the strength of plastics, whereas a t low equivalent weights the poly01 functionality is sufficiently high that further
1000
0 200
220
240 260 280 300 Polyol Equivalent Weight
320
340
Figure 1. Effects of NCO/OH, starch concentration, and polyol equivalent weight on tensile strength of urethane plastics
crosslinking of starch does not greatly increase strength. Specimens cut in the shape for tensile measurements, and aged for 1 week a t 6 P C . in water or a t 25°C. in either 10% alkali or 3% acid, generally decreased in tensile strength as the starch concentration increased (Table I). However, several plastics retained much of their strength after these stringent aging conditions. At 25°C. in either VOL. 8 N O . 3 S E P T E M B E R 1 9 6 9
271
16,000
% i 1.1 I 1.5 I 2.0
14,000 12,000
-
E10,000 a 2
z"
-
Ln
8,000
m
h
-S 3
6,000
Y
4,000 2,000 0 200
220
240 260 280 300 Polyol Equivalent Weight
320
: I
'o90 o:
Figure 2. Effects of NCO/OH, starch concentration, and polyol equivalent weight on flexural strength
80 200
I
220
I
I
I
I
240 260 280 300 Polyol Equivalent Weight
I
320
:
Figure 4. Effects of NCO/OH, starch concentration, and polyol equivalent weight on deflection temperature
go{
Starch
%
I 1.1
NCO/OH 1.5 2.0
/
I
Polyol Equivalent Weight Figure 3. Effects of NCO/OH, starch concentration, and polyol equivalent weight on per cent elongation 272
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
water or ethanol the dimensional and weight change resistance of the plastics was good (Table 11); to xylene, fair, but to acetone, poor. As the starch concentration was increased, however, the plastics became more resistant to both xylene and acetone. I t is significant that all solvent and chemical aging studies were made on specimens cut a t 0.5-inch widths. Larger specimens would undoubtedly exhibit improved resistance, because solvent attack appeared to be a t the cut surfaces. Flexural strengths (Table I and Figure 2) of the plastics depend upon NCO/OH ratios, starch concentration, and poly01 equivalent weights. At low polyol equivalent weights, flexural strength is usually highest when the starch concentration is low; the reverse is observed for plastics made with high equivalent weight polyols. Flexural strength increases with increased NCO/OH ratios a t all levels of starch and poly01 equivalent weights. Impact strength (Table I) and per cent elongation (Table I and Figure 3) decrease with increased starch concentration, reduced poly01 equivalent weigh, and increased NCO/OH ratio. Deflection temperatures (Table I and Figure 4) are highest when the plastics are made with low equivalent weight polyols and high starch concentrations; however, a t high poly01 equivalent weights the starch reduces the heat deflection temperature. At all levels of starch and poly01 equivalent weights the heat deflection temperature increases with increased NCO/OH ratios.
Table IV. Summary Results after Multiple Regression Calculations
85
Measurement
75
s 0 u,
70 v)
s Q)
E
' M e a n of all observations. 'Standard deviation with N - 10 degrees of freedom. Least signibant difference between two observations 'is approximately 3s. Total number of observations.
2 65 60
7 200
Nd
S'
Tensile 89.5 5,188 684 126 strength Flexural strength 75.2 10,890 1127 70 Elongation 85.9 11.06 5.30 123 Deflection temperature 83.5 132.5 7.74 73 Shore D hardness 91.0 80.7 2.04 109 " R measures correlation between observed and predicted Y . 100 RZ is per cent of variation explained by factors XI, Xz,and X3.
80
r
X*
100 R"
220
240 260 280 300 Polyol Equivalent Weight
320
340
Figure 5. Effects of NCO/OH, starch concentration, and polyol equivalent weight on Shore D hardness
Table V. Mean Deviation of Observed from Predicted Tensile Strength by Batch
No. of Observations
Polyol Batch, Eq. Wt.
Mean Deviation in Tensile Strength
7 7 9 3 7 13 7 7 9 7 9 9
197 20 1 202 207 211 217 237 241 253 282 289 300 313 336
-474 -379 353 -63 225 91 -296 -90 876 -366 283 -568 -508 206
9
Because starch has a low specific gravity, its inclusion does not greatly increase the specific gravity of plastics, particularly when com.pared to the use of most inorganic fillers. Specific gravity of the plastics ranged from about 1.1without starch to 1.3 with 60% starch. The plastics became harder as starch concentration and NCO/OH ratios were increased (Table I and Figure 5). As the poly01 equivalent weight was increased, the plastics decreased in hardness if the NCO/OH ratios were below about 1.5; maximum hardness was observed for higher ratios at intermediate equivalent weights. Raw-material costs are lowered by about one half as the starch concentration increases to 60% (Table I ) . Low raw-material costs, coupled with low densities and improvements in most physical properties, make the plastics based on starch attractive for a variety of applications. The costs are based 011 32 cents per pound for the polymeric isocyanate, 5 cents per pound for starch, and 20 cents per pound for both the castor oil and the glycol glycoside-castor oil polyols. Although glycol glycosides are not commercially available, their estimated selling price of 12 cents per pound makes a poly01 price of 20 cents per pound reasonable. Some isocyanate is apparently bound to the starch molecule. Data in Table I11 show that nearly 50% of the excess isocyanate reacted when starch was added to the plastic formulations. Excess or free isocyanate is the amount above that required for the polyol. Additional disappearance of free isocyanate during 21 days in a desiccator was not significant. Exposure of the plastics to atmospheric conditions, however, caused a more rapid and erratic disappearance of the isocyanate within several weeks.
23
Table IV summarizes the multiple regression calculations; 100 R2 is the per cent of variation explained by factors XI, XZ,and X3.Thus, 75 to 91% of the variations in observations, on which Figures 1 to 5 are based, is accounted for by NCO/OH ratios, equivalent weight of polyols, and starch concentrations. Data in Table V show the mean deviation of observed from predicted tensile strengths of plastics within a given poly01 preparation. Significant variations between poly01 preparations is evidence that the standard deviations in Table IV are low when comparisons are made between polyol batches, but high when comparisons are made for plastics based on one poly01 preparation. Establishment of more consistent reaction conditions for polyoi preparations would undoubtedly improve reproducibility of plastic properties. Conclusions
Alcoholysis of castor oil with starch-derived glycosides yields polyols that can be used in preparing urethane plastics. Equivalent weights can be varied from 200 to 336, depending upon the ratio of glycoside and castor oil used. As the poly01 equivalent weight is decreased, the derived plastics become stronger, harder, and more resistant to heat. Incorporation of u p to 60% starch as a reactive filler into the plastic formulations further improves these properties generally; but its effect is even more pronounced when the plastics are made with high VOL. 8 N O . 3 S E P T E M B E R 1 9 6 9
273
equivalent weight polyols. Properties are usually the best when the NCO/OH ratio is 1.5 or greater. A wide range of physical properties were built into the plastics by properly selecting the poly01 and the amounts of isocyanate and starch. The range of properties these relatively inexpensive materials provide suggests that starch and starch-derived polyols have potential for the commercial production of urethane plastics. Acknowledgment
We thank A. J. Ernst, R. G. Fecht, and D. E. Smith for their assistance with physical measurements, and V. F. Pfeifer and L. H. Burbridge for milling the starch and determining its particle size. literature Cited
Bennett, F. L., Otey, F. H., Mehltretter, C. L., J. Cell. Plast. 3, 369 (1967). Boggs, F. W. (to United States Rubber Co.), U. S. Patent 2,908,657 (Oct. 13, 1959).
Buchanan, R. A., Weislogel, 0. E., Russell, C. R., Rist, C. E,, IND. ENG. CHEM.PROD.RES. DEVELOP.7, 155 (1968). Otey, F. H., Bennett, F. L., Mehltretter, C. L., U. S. Patent 3,405,080 (1968a). Otey, F. H., Bennett, F. L., Zagoren, B. L., Mehltretter, C. L., IND. ENG. CHEM.PROD.RES. DEVELOP.4, 228 (1965). Otey, F. H., Mehltretter, C. L., Rist, C. E., Cereal S c i . T o d a y 13 (5), 199 (1968b). Patton, T. C., Ehrlich, A., Smith, M. K., Rubber A g e 86,639 (1960). RECEIVED for review December 16, 1968 ACCEPTED May 19, 1969 Division of Organic Coatings and Plastics Chemistry, 157th Meeting, ACS, Minneapolis, Minn., April 1969. The Northern Laboratory is part of the Northern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture. Mention of firm names or commercial products does not constitute an endorsement by the U. S. Department of Agriculture.
PERFORMANCE OF POROUS CELLULOSE
ACETATE MEMBRANES IN SOME REVERSE OSMOSIS EXPERIMENTS J.
K O P E C E K ' A N D
s.
S O U R I R A J A N
Division of Applied Chemistry, flational Research Council of Canada, Ottawa, Canada
The effects of surface layer-side and backside reverse osmosis operations on the performance of the Loeb-Sourirajan type porous cellulose acetate membranes have been studied at the operating pressures of 100 and 250 p.s.i.g. The mechanism of reverse osmosis transport is the same in both operations. The relative selectivity of the membrane for different solutes changes with operating pressure and membrane pretreatment. Backpressure treatment offers an effective method of improving membrane performance. The results of cyclic experiments at pressures up to 250 p.s.i.g. indicate the possibility of utilizing the backpressure treatment technique for simultaneous brackish water conversion.
THEselectivity of the Loeb-Sourirajan type porous cellulose acetate membranes, and the effects of compaction and backpressure treatment on their performance at operating pressures of 600 p.s.i.g. or higher, have been discussed (Agrawal and Sourirajan, 1969; Kimura and Sourirajan, 1968; KopeEek and Sourirajan, 1969). This paper gives similar results for operating pressures of 100 and 250 p.s.i.g. with membranes initially pressure-treated a t 120 and 300 p.s.i.g., respectively. This work is of interest from the point of view of both the effect of porous structure and backpressure treatment on the performance of reverse osmosis membranes, and the design of low pressure reverse osmosis units for brackish water conversion. Present address, Institute of Macromolecular Chemistry, Prague, Czechoslovakia 274
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
Experimental Details
Reagent grade chemicals and porous cellulose acetate membranes (designated here as CA-NRC-18 type films), made in the laboratory, were used. The films were cast a t -10" C. in accordance with the general method described earlier (Sourirajan and Govindan, 1965), using the following composition (weight per cent) for the film casting solution: acetone 68.0, cellulose acetate (acetyl content = 39.8%) 17.0, water 13.5, and magnesium perchlorate 1.5. Membranes shrunk a t different temperatures were used to give different levels of solute separation a t preset operating conditions. The apparatus and the experimental procedure have been reported (KopeEek and Sourirajan, 1969; Sourirajan, 1964). All experiments were carried out a t the laboratory
