The P C E resins differ from the majority of the standard polyester resins because they contain structurally stable chlorine, leading to a high degree of flame resistance and improved environmental stability. Acknowledgment
Special appreciation is expressed to the Battelle Memorial Institute, Columbus, Ohio, for developing some of the data reported. literature Cited
Boenig, H . V., “Unsaturated Polyesters. Structure and Properties,” pp. 173-83, Elsevier, Amsterdam, New York, 1964. Chae, Y. C., Rinehart, W. M., Shull, C. S., Cass, R . A., Rohrbacker, R . J., 22nd Annual Technical Conference, S P I Reinforced Plastics Division, Washington, D . C., 1967. Davis, P. (to Wyandotte Chemicals Corp.), U. S. Patents 3,251,903 (May 17, 1966), 3,254,057 (May 31, 1966). Michigan Chemical Corp., Brit. Patent 988,304 (April 7, 1965); CA 62, 1646Bh (1965).
Nametz, R. C., Id.Eng. Chem. 59, No. 5, 99 (1967). Nordlander, B., Cass, W. J., J . Am. Chem. Soc. 69, 2679 (1947). Ohse, H., Cherdron, H., Makromol. Chem. 95, 283 (1966). Palm, R.,Ohse, H., Cherdron, H., Angew. Makromol.. Chem. 1, 1 (1967). Pape, P. G., Nulph, R. J., Nametz, R. C., 23rd Annual Technical Conference, S P I Reinforced Plastics/ Composites Division, Washington, D. C., 1968. Robitschek, P., Bean, C. T., Ind. Eng. Chem. 46, 1628 (1954). Robitschek, P., Bean, C. T. (to Hooker Electrochemical Co.), U. S. Patents 2,779,700, 2,779,701 (Jan. 29, 1957). Spatz, S. M., Koral, M. (to Allied Chemical Corp.), Can. Patent 741,390 (Aug. 23, 1966).
RECEIVED for review September 22, 1969 ACCEPTED December 19, 1969 Washington SPI Meeting on Reinforced Plastics, 1969.
ESTERS OF ISOMALIC ACID AS PRIMARY PLASTICIZERS IN POLY(VINYL CHLORIDE) NONTOXIC FORMULATIONS F A U S T O B A R G E L L I N I ’
A N D
LUIGI B E N E D E T T I ’
Research Centers, Montecatini Edison S.p . A., Port0 Marghera, Venice, and Bollate, Milano, Italy
Esters of higher aliphatic alcohols with isomalic acid and their acyl derivatives weire prepared, and some were evaluated in PVC-based formulations. Because of their low toxicity, these esters are expected to find application in nontoxic forrnulations. The best results were obtained with di( 2-ethylhexyl) 0-acetyl isomallate and di( 2-ethylhexyl) 0-propionyl isomalate, the properties of which are comparable to those of tributyl 0-acetyl citrate, but the acyl isomalate esters show better low temperature flexibility.
COMPOUNDED PVC flexible films may be competitive with films such as cellophane and polyethylene as foodpackaging material, because of the present availability of particular low toxcity plasticizers. This paper describes the preparation of sorne esters of isomalic acid and gives a technological evaluation of them in suitable PVC compounds. Isomalic acid [methylhydroxymalonic acid, CHsC(OH)(COOH),] has long been known; in 1876 Schmoger prepared it from methylbromomalonic acid and silver oxide. Only recently could i t be obtained industrially, starting with acetone (via 2-cyano-2-hydroxypropionamide) (Marangoni and Nenz, 1962, 1965; Nenz et al., 1963, 1964, 1965, 1966) or with ketene or acetic anhydride (via 1,ldicyanoethyl acetate) (Brunner, 1892; Marangoni et al., 1967). Present address, Divisione Petrolchimica e Resine ( D I P R ) , Montecatini Edison S.p.A., Brindisi, Italy Present address, Direzione Centrale delle RiCerche ( D I R I ) , Montecatini Edison S.p.A., Largo Donegani 1, Milano, Italy
Because the acid has low toxicity (Cima, 1966), comparable to that of the organic acids normally used in the foodstuff industry, its esters might find acceptance for end uses involving contact with food (Benedetti and Marangoni, 1965). However, very little is known about isomalate and acyl isomalate and their toxicity. Only the ethyl (Eskola and Moutinen, 1947) and n-butyl (Colonge et al., 1947) esters were reported before 1965. Type and Properties of Products Studied
This paper describes results obtained with the acyl derivatives of higher alcohol esters (Bargellini et al., 1966, 1968) having the following chemical structure:
R-COO
\
I
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9,No. 1, Morch 1970
1 13
where
0
R=CH3-C
I1
/O
\
R'=CsHi;-;
CH3-CHZ-C--,.
.. . . . . .
CioH21; C13H27-;
. .. . ... .
;
Because most citric acid esters used in nontoxic PVC plasticizers contain an esterified OH group, the authors have considered as a useful comparison products having the type structure I, in which both the alcohols used to esterify the carboxylic groups and the organic acid for esterifying the hydroxylic group were varied. The properties of the products obtained are reported in Table I. Method of Preparation
The general scheme for preparing acyl isomalates involves the preparation of the ester of isomalic acid, followed by acylation of the ester. The esters of isomalic acid have been prepared by transesterification of the dimethyl isomalate obtained from the acid saponification in methanol of 2-cyano-2hydroxypropionamide (80% yield with respect to the amide) or of 1,l-dicyanoethyl acetate (65% yield with respect to the dicyano derivative). The esters of isomalic acid were acylated with the anhydrides or acyl chlorides of low aliphatic acids. Experimental
Preparation of Esters. The starting materials used for the esters were: Dimethyl isomalate Boiling point Refractive index, :n Density, 20120" C .
59" C. per 0.6 mm. Hg 1.4287 1.201
2-Ethylhexyl alcohol Boiling point Refractive index, Density 20120" C.
184-85" C. 1.4315 0.8342
Isodecyl alcohol Boiling point Refractive index, :n Density 2O/2O0C.
217-23" C 1.4395 0.8395
Isotridecyl alcohol Boiling point Refractive index, n; Density, 20/20" C.
246-57" C . 1.4480 0.8476
The preparation of di(2-ethylhexyl) acetyl isomalate is described as an example. The other esters, listed in Table I, were obtained by the sample procedure. DI(2-ETHYLHEXYL) ISOMALATE. Into a flask equipped with a Vigreux column, 256 grams of dimethyl isomalate, 835 grams of 2-ethylhexyl alcohol, 580 ml. of anhydrous benzene, and 0.2 gram of metallic sodium were introduced. The benzene-methanol azeotrope (boiling point 57.5" C .) was removed slowly by distillation, raising the reaction temperature from 95" to 120"C. The reaction product, washed to neutrality with 5% HC1 solution and a saturated solution of NaC1, was separated from the benzene by evaporation and then distilled; 498 grams of the product with a boiling point of 152°C. per 0.4 mm. of Hg and ng = 1.4434 were obtained. Yield was 88.5% based on dimethyl isomalate used. DI(2-ETHYLHEXYL) ACETYLISOMALATE. TO 100 grams of di(2-ethylhexyl) isomalate and 33 grams of acetic anhydride, 0.1 ml. of concentrated H S 0 4 was added. The temperature rose spontaneously to 45" C. and was maintained a t 60" C. for half an hour. The mixture was poured into 1.500 ml. of HZO; the oil layer separated and was washed repeatedly with water and distilled. The product, 93.5 grams with a boiling point of 160-62°C. per 0.6
Table 1. Properties of Synthesized
Di-n-butyl Isomalate Formula Molecular weight Elementary analysis, 70 C / % H Calculated Found Boiling point, C. per mm. Hg Refractive index, n; Density, 20/10" C. Viscosity, cps. at 20" C. Color APHA max Color APHA max after 2 hr. at 180" C. Free acidity, % in equiv. Free acidity after 2 hr. a t 180" C., % in equiv. Saponification number, mg. KOH per gram Calculated Found Hydroxyl number, mg. KOH per gram Calculated Found % water (K.F.), max. Volatility, % loss after 6 hr. a t 100" C. Flash point (P.M., closed cup), "C. ' Crude product, could not be dutrlled.
1 14
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 1, March 1970
Di-n-butyl 0-Acetyl Isomalate
Di(2-ethylhexyl) Isomalate
Ci2H2205 246.30
CirHzaOs 288.34
CmHx05 358.52
58.5219.0 58.918.7 92/0.5 1.4314 1.0174 7.63 5 Very dark (out of scale) 0.82 1.5
58.31/8.39 58.318.5 11110.7 1.4346
67.0110.68 67.0111 152/0.4 1.4434 0.9587 20.25 10 10
455 455
584 581
228 227 0.01 0.02 136-38
...
... ...
0 0
...
0.9 0.9 313 314 156 161 0.1 1.3 148-50
mm. of Hg and n: == 1.4425, was collected. Yield was 84%, based on the di(i!-ethylhexyl) isomalate. Evaluation. The plasticizer properties of the following acyl isomalates were studied by adding them to a PVC base formulation: 1. Di(2-ethylhexyl) 0-acetyl isomalate
2. 3. 4.
Di(2-ethylhexyl) 0-propionyl isomalate Di(isodecy1) 0-acetyl isomalate Di(isotridNecy1) 0-acetyl isomalate
Base formulation. PVC resins Zn stabilizer Lubricant
100 parts 1.5 parts
As required
The PVC resin used was Sicron 548 (manufactured by Montecatini Edison) . Specific viscosity 0.49, measured in cyclohexanone of 0.42% (w./w.), using Oswald-Fenske viscometers, and calculated by q - v / q o . Dry time 2 minutes (Coaker and Williams, 1955). Apparent density 0.46 (ASTM D 1895/61 T). The Zn stabilizer used was Ferroclere 707, a mixture of zinc and antioxidative and epoxidic compounds, with a specific density of 0.65 and U. S. Food and Drug Administration approval. Various plasticizers were introduced into the recipe in different quantities according to the determinations to be made. The ingredients were mixed using a common blender which operates at a !speed of 66 r.p.m. a t 80”C., long enough to obtain a bllend with a high degree of dryness. This dry blend was subsequently worked on a roll mill a t a temperature of 158-60°C. for a total period of 10 minutes. The sheets obtained were pressed a t 150”C. and 50 atm. for 3 minutes, and conditioned for 7 days at 23°C. and 50% of relative humidity; from these sheets the specimens for the measurements were obtained.
The following determinations were made according to ASTM specifications: TYPICAL PROPERTIES, as “plasticizer efficiency” and “low temperature flexibility” (Figures 1 and 2). PROPERTIES, as tensile strength, per cent MECHANICAL of elongation, and shore hardness (Table 11). PERMANENCE PROPERTIES,such as weight loss on heating, resistance to extraction by water and kerosine, and compatibility after 7 days of bending stress (Table 111). The compatibility was determined by forcing the specimens in a loop test holder such that the folded portion extended ?4 inch from the edge of the holder. A check was made every 2 days to see if the strips had begun the spew that generally occurs inside the loop. For a comparison of two or more plasticizers, the relative amount of spew was determined by taking the strip from the holder and wiping with a cigarette paper. PROCESSABILITY CHARACTERISTICS (Figure 3). The processability of the formulation was determined by a Brabender plastograph. This apparatus has a cell which can be thermostatically regulated between 40” and 200” C. The cell has two gelation rotors which can attain a maximum of 200 r.p.m. T h e processability of a formulation refers to its capacity to achieve the state of a homogeneous melt in a certain period of time under the action of thermal and mechanical stress. It flows according to the laws of rheology. I t is characterized by the following parameters: FUSIONTIME (expressed in minutes) defined as the time required for achieving maximum consistency value of the melt; the shorter the time required, the more readily will the formulation be processed. CONSISTENCY OF MELT AT FUSIONPEAK (expressed in grams per cm.), resistance offered by the formulations at the peak of the fusion curve.
~~
Esters of lsomalic Acid
Dii2-ethylhexyl) 0-Acetyl Isomlate CjiHdoOE 400.56 65.96j10.06 66.91 10.4 159.510.6 1.4445 0.9781 41.5
Ui(2-ethylhexyl) O-PIQpiOTZyl Isomalate C2II-[U06 41437 66.631 10.21 66.’7:10.2
... 1.4439 0.9709
...
Dzzsodecyl D i GsooctJ~l Isomalate
C~dHd(iOi
C26H4~06
C &,Os
414.63
456.63
540.81
67.01 10.68 68110.7 158/0.6 1.4439 0.9398
...
0
...
...
0.22
...
0.44
10
...
69.55111.18 69.8111.4
...
1.4489 0.9637
1.4531 0.9526
...
... ... ...
...
... ... 3.6
...
313 297
271 249
0
0
4-5
0 0.07
156 144
134 155 0.1
0.07
...
... ...
...
71.06; 11.18 7 1.O / 11.1
1.4485 0.9368
406 402
0.02 193
68.37/ 10.50 68.61 10.6
...
420 402
0.02
Dmotridecyl 0-Acetjl Isomalate
358.52
5
...
0-Acet) 1 Isomalate
C>,,HwO;
5
0.72
D i isodecyl@ Isomalate
... ...
...
...
...
...
...
...
...
369 363
311 324
0
0 0
0 0.01 0.03
...
... 0.05
...
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 1, March 1970
1 15
Figure 1. Plasticizing efficiency of esters tested as a function of their concentration in a PVC compound Test method ASTM D 1043-51 Apparent modulus of elasticity. 1800 p s i A Tributyl acetyl citrate 0 Di(2-ethylhexyl)acetyl isomalate 0 Di(2-ethy1hexyl)propionyl isornolate U Dihodecvl)ocetvl ,, , isomalate
I
0'
Di(isotridecy1)acetyI isomalate
I
I
I
30
45
60
p.h.r.
parts of plasticizer Table II. Mechanical Properties of PVC Formulations Containing Plasticizers 45 parts plasticizer in formulation
Plasticizers"
D i(2-ethylhexyl) 0-Acetyl Isomalate
Tensile strength, kg. per sq. m. 5% elongation a t break Shore A hardness a
Diisodecyl 0-Acetyl Isomalate
1.95
1.95
281 78-80
285 87-89
Diisotridecyl 0-Acetyl Isomalate
Di(2-ethylhexyl) 0-Propionyl Isomalate
1B O
230 90
Tributyl 0-Acetyl Citrate
1.75
1.85
295 78-80
280 78-80
Test method A S T M 0-412. Table 111. Permdnence in PVC Formulations of Synthesized lsomalic Esters and Tributyl Acetyl Citrate 45 p.h.r. plasticizer in formulation
Type of Measurement Compatibility" After 48-hr. stress After 168-hr. stress Resistance to extractionb by kerosine, % plastic extracted by water % ' weight loss 'X water absorbed Weight loss',% plasticizer lost after 48-hr. stress
Di(2-ethylhexyl) 0-acetyl Isomalate
Diisodecyl 0-acetyl Isomalate
Diisotridecyl 0-acetyl Isomalate
Di(2-ethylhexyl) 0-prop ionyl Isomalate
Tributyl 0-acetyl Citrate
Complete Complete
Complete Partial
Partial Marked incompatibility
Complete Complete
Complete Complete
15
35
56
16
10
0.16 0.15 16
1.4 0.3
19
5.5 0.2 30
0.5 0.4 18
0.5 0.4
14
a Compatibility measurements taken by submitting specimens to permanent stress; periodically surface examined uisually for exudation and by application of sheet of blotting paper. b A S T M D 570. ' A S T M D 1239-55.
CONSISTENCY OF MELTAT EQUILIBRIUM (grams per cm.), the resistance offered by the melt, under the operatiohal conditions chosen, once viscosity and temperature constancy liave been attained (this being due to both the heat applied and that which develops by friction); it is proportional to the apparent viscosity of the melt. Toxicity. The acute toxicity (in rats via intraperitoneal) or di(2-ethylhexyl) isomalate and of its acetyl derivative was determined. Discussion of Results For comparison of the plasticizing properties of compounds derived from isomalic acid, tributyl 0-acetyl citrate 1 16
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9,No. 1, March 1970
was used. This compound is commonly used in PVC formulations for nontoxic end uses. Typical Properties. Figures 1 and 2 show, as expected, that increase in the size of the alkyl chain in the molecule of the isomalic ester decreases plasticizing efficiency. Practically similar values are obtained instead with tributyl 0-acetyl citrate and the ethylhexyl esters of acetyl and propionylisomalic acid. The increase of one carbon atom of the acylic radical did not affect the plasticizing efficiency. The low temperature flexibility of the 0-acyl isomalates is better than that of the tributyl 0-acetyl citrate. Among the acylisomalic esters the best results were obtained in
30
parts
01
45
60
p.hc
pbsticizer.
Figure 2. Low temperature flexibility of esters tested as a function of their concentrdtion in a PVC compound Test method ASTM D 1043-51 Apparent modulus of elasticity. 135,000 p.s.i.
A Tributyl acetyl citrate 0 Di(2-ethylhe!xyl)acetyl isomalote
0 Di(2-ethylhexyl)propionyl
isomalate
Di(isotridecy1)acetyI isomalate
0 Di(isodecy1)acetyl isomalate
the case of the 2-ethylhexyl esters, the propionyl derivative giving better results than the corresponding acetyl derivative. Mechanical Properties. The data in Table I1 concern formulations containing the plasticizers in 45 phr (parts per hundred parts of resin). Di(2-ethylhexyl) 0-acetyl isomalate has lower hardness, higher tensile strength, and higher flexibility and elongation than diisotridecyl 0-acetyl isomalate. Its mechanical properties are very similar to those of tributyl 0-acetyl citrate. Permanence Propertises (Table 111). The plasticizers and PVC blends were measured for compatibility and for resistance to extraction by kerosine and by water and weight
loss on heating. Compatibility is obtained when the alkyl portion of the ester derived from isomalic acid does not exceed 8 carbon atoms and only one alkyl branch is present. The highly branched diisodecyl 0-acetyl isomalate shows signs of incompatibility with the polymer; the highly branched tridecyl ester is practically incompatible. This incompatibility causes weight loss and lowers the resistance to kerosine extraction. As compared with 2-ethylhexyl esters, the isodecyl and isotridecyl esters have low& resistance to hydrolysis. Di(2ethylhexyl) 0-acetyl and 0-propiohyl isomalates and tributyl 0-acetyl citrate are slightly better in resistance to kerosine and weight loss than di(2-ethylhexyl) 0-acetyl and 0-propionyl isomalate. Ind. Eng. them. Prod. Res. Develop., Vol. 9, No. 1, March 1970
1 17
2
4
6
6
1
0
2
time in minutes
4
6
8
1
0
2
4
-
6
8
1
0
time in minutes
time in m'inutes
Figure 3. Processability data as determined on Brabender piastograph on granules obtained from PVC compounds containing isomalates and tributyl acetyl citrate A.
Di(2-ethylhexyl)propionyl isomalate
E. Tributyl acetyl citrate C. Di-2-ethylhexy1)acetyl isomalate D. Di(isodecy1)acetyl isomalate E. Di(isotridecy1)acetyI isomalate Thermostatically regulated temperature Rotor speed Cell capacity Parts of plasticizer in compound
170" C. 50 r.p.m. 45 grams 45 p.h.r. 2
4
6
8
1
0
\ime in minutes
Processability Characteristics. Figure 3 shows that fusion time increases as the size of the alkyl chain increases in isomalic esters. Replacement of the acetyl group by the propionyl group in di(2-ethylhexyl) 0-acyl isomalate worsens the processability. Tributyl 0-acetyl citrate and di(2-ethylhexyl) 0-acetyl isomalate are similar in processability. The data (maximum and a t equilibrium) show that tributyl 0-acetyl citrate, di(2-ethylhexyl) 0-acetyl isomalate, and di(2-ethylhexyl) 0-propionyl isomalate are almost identical in processability. The 0-acetyl isomalate has much higher consistency peak values. Toxicity. The acute toxicities of the following two compounds were determined in rats via intraperitoneal: Di(2-ethylhexyl) isomalate.
LDw = 3.6 i.0.3 grams per kg.
Di(2-ethylhexyl) 0- acetylisomalate.
LDw = 22
&
1.32 grams per kg.
The toxic symptomatology of the acetyl derivative is characterized only by depression which occurs not less than 4 hours after it is administered to animals which subsequently die. I n the animals that survive no anomaly is noted.
Conclusions
The most convenient method for preparing isomalates is by tratlsesterification of dimethyl isomalate. Except for one case, these esters are suitable primary plasticizers for PVC. Di(2-ethylhexyl) 0-acetyl isomalate and di(2ethylhexyl) 0-propionyl isomalate are the best plasticizers in the series, and they are generally comparable with 1 18
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 1, March 1970
2
4
6
8
4
0
time in minute5
tributyl 0-acetyl citrate, except that the acyl isomalates have better low temperature flexibility. Acknowledgment
The authors thank L. Cima, Pharmacology Institute, University of Padua, for the toxicological evaluation. literature Cited
Bargellini, Fausto, Benedetti, Luigi, Marangoni, Luigi, Ital. Patent 826,082 (1968); Belg. Patent 676,715 (1966). Benedetti, Luigi, Marangoni, Luigi, I d . Conserve (Parma) 40 (l),14-18 (1965). Brunner, J. S., Monatsh. Chem. 13, 835 (1892). Cima, Lorenzo, Toxicol. A p p l . Pharrnacol. 9 (2), 274-8 (1966). Coaker, W. M., Williams, M. W., Modern Plastics 33, 2, 160 (1955). Colonge, Jean, Watteau, Leon, Cumet, Louis, Bull. SOC. Chim. France 1947, 247. Eskola, Salli, Moutinen, Vuokko, Suomen Kemistilehti 20B, 16 (1947). Marangoni, Luigi, Cossi, Giovanni, Caprara, Giuseppe, Benedetti, Luigi, Ital. Patent 765,507 (1967); Belg. Patent 697,988 (1967). Marangoni, Luigi, Nenz, Adriano, U. S. Patent 3,201,468 (1965); Belg. Patent 626,071 (1962). Nenz, Adriano, Marangoni, Luigi, Ital. Patent 686,019 (1965); U. S. Patent 3,238,244 (1966); Belg. Patent 631,288 (1963). Nenz, Adriano, Marangoni, Luigi, Gallinella, Enzo, Iliceto, Antonio, Chim. I n d . (Milano) 46, 509 (1964). Schmoger, K. W., J . Prakt. Chem. 2 (14), 81 (1876). RECEIVED for review November 22, 1968 ACCEPTED July 24, 1969
