I
RUSSELL VAN CLEVE and D. H. MULLINS Research Department, Union Carbide Chemicals Co., Division of Union Carbide Corp., South Charleston, W. Va.
Derivatives of Cyclohexene Oxide as Plasticizers and Stabilizers for Vinyl Chloride Resins New classes of epoxy compounds, now in the research stage, which contain the cyclohexene oxide group will answer, in part, the need for a greater variety of epoxy plasticizers and stabilizers. The cyclohexene oxide segment of these compounds is an effective solvating group for vinyl chloride resins, is particularly effective as a light stabilizer, and contributes markedly to heat stability. T H E ability of certain epoxy-containing compounds to plasticize and stabilize vinyl chloride resins (8, 9, 77, 78) has resulted in an estimated consumption of 25,000,000 pounds for these uses in 1956. Epoxidized natural oils, such as epoxidized soybean oil, accounted for the major part of this total, and alkyl epoxystearates for most of the remainder. Limitations in choice, compatibility, and performance (70) undoubtedly prevented epoxy compounds from taking more of the estimated 331,000,000pound plasticizer market. The new compounds described are based on Carbide's high-purity peracetic acid process, which will be operated in a plant now under construction and described in this issue (76). Use of this versatile peracetic acid as the epoxidizing agent results in greater freedom from undesirable side reactions, such as oxirane-ring opening and resinification, than has been possible heretofore, thus assuring optimum compatibility and stabilizing ability with the final product (3, 4).
Evaluation Methods The epoxy compounds were evaluated in the dual role of plasticizers and heat and light stabilizers in vinyl resin VYNW (Bakelite Co.), a copolymer of high molecular weight containing approximately 97.5% vinyl chloride and 2.5y0 vinyl acetate. Plasticizing ability was determined in conventional laboratory tests, which consisted of fluxing mechanical mixtures of resin and plasticizer at 158' C. on a two-roll mill. Specimens were molded at 158' C. from the plasticized sheet formed in this manner. The "effectiveness" values listed refer to the amount of plasticizer required to impart an arbitrary degree of flexibility to the normally rigid VYNW resin. The point chosen was a tensile modulus of 1000 p.s.i. at 100% elongation as measured on a Scott L-6 tensile tester at 23" C. This degree of flexibility is slightly greater than that of plastic items such as garden
hose and upholstery. Plasticizer ratios are expressed in parts per 100 parts of VYNW (phr). Performance characteristics of the plasticized compositions were determined in tests which showed resistance to low-temperature impact ( TB)(7) ; volatility of the plasticizer at 70' C. [activated carbon test ( 2 ) ] ; and resistance of 6-mil films to extraction of plasticizer by mineral oil and water in 10-day tests at 23' C. Performances as heat and light stabilizers were studied in VYNW compositions plasticized with 54 phr of various blends of di 2 ethylhexyl phthalate (DOP) and epoxy compound. In general, 1.5, 3.0, 7.7, 15.4, and 54 phr, respectively, of epoxy compound were used to replace corresponding amounts of DOP in these blends. Ability of the epoxy compounds to protect VYNW compositions against discoloration by heat was determined on a laboratory two-roll mill operating at a roll temperature of 170" C. Samples of the milling sheet were removed at regular intervals for color measurements. A Photovolt reflection meter, Model 610, equipped with a Wratten C-5 blue filter, was used to obtain a numerical reading of blue light reflectance (% BLR) on a piece of sheet 30 mils thick mounted on a white (100% BLR) background. I n general, the compositions showed a BLR of SOY0, or higher, initially, and the stability is listed herein as the minutes of milling the composition will withstand before reaching the slight discoloration corresponding to a BLR of 75%. Samples of 30-mil film were sent to the South Florida Test Service in Miami, where they were mounted on open racks at a 45' angle facing south. Color changes, exudation, tackiness, stiffening, spotting, and other evidence of undesirable changes were looked for in clippings which were returned at intervals of 100 and 250 sun-hours, and every 250 sun-hours thereafter. (A sun-hour is defined as a cumulative period of 60 minutes during which radiant energy
- -
amounts to as much as 0.823 gram-calorie per sq. cm. per minute.) The general term "failure" refers to any alteration in appearance or film surface that would cause the composition to be withdrawn from service. Performances of the new epoxy compounds as both plasticizers and stabilizers were compared with those of an epoxidized soybean oil and iso-octyl 9,10-epoxystearate, respectively.
Discussion The discussion is limited to three new classes of epoxy compounds prepared with the high-purity peracetic acid and having utility in vinyl chloride resin compositions. Derivatives of 3,4-Epoxycyclohexylmethanol. Esters of 3,4-epoxycyclohexylmethanol can be prepared according to Equation 1. 0
CHz
// I
HC HC
H C '
+ 2
Butadiene
Acrolein 0
T R G 3-C yclohexenecarboxaldehyde
,O-CH~--O-C-R /I 0
CHs-
b-0-OH
(Peracetic acid) 0
(1)
Ester of 3,4-epoxycyclohexylrnethanol VOL. 50, NO. 6
JUNE 1958
873
Table 1.
Evaluation of 3,4-Epoxycyclohexylmethyl Esters as Plasticizers
Esters based on 12- to 14-carbon monobasic acids offer an attractive combination of compatibility, volatility, and law-temperature performance Oxirane Phr % ExtracT B , ~ VOI.,~ tion Oxygen, on Epoxycyclohexylmethyl Ester % VYNW O C . % Oil HzO 2-Ethylhexanoate 51 -20 19.2 11.2 2.1 5.8 Laurate 7.8 60 -36 19.5 0.5 4.3 0.2 31.6 0.2 3.7 71 -26 Palmitate 60 -23 1.2 9,lO-Epoxystearate 6.3 13.0 0.4 0.8 64 -14 14.0 1.0 9,10,12,13-Diepoxystearate 9.1 Epoxyalkanoate [from safllower oil] 61 -14 0.5 7.4 10.0 4.2 67 -12 0.4 Epoxyalkanoate [from tall oil] 7.8 10.8 1.0 71 -3 0.3 Sebacate 6.1 3.9 1.6 Controls Epoxidized soybean oil 6.2 69 -26 0.5 14.3 0.1 Iso-octyl9,lO-epoxystearate 3.5 62 -62 2.9 31.1 0.1 Brittle temperature ( I ) . Volatility at 70° C. ( 2 ) .
*
Crotonaldehyde can be substituted for acrolein to obtain esters of 3,4epoxy-6-methylcyclohexylmethanol,or a mixture of isoprene and piperylene for the butadiene to obtain esters of 2-, 3-, and 4-methyl substituted epoxycyclohexylmethanols. The epoxycyclohexylmethy1 esters of mono- and dibasic acids are compatible with and will stabilize vinyl chloride resins. Table I lists some of the esters prepared in this study and summarizes their evaluation as plasticizers for VYNW resin. The acetic, oxalic, succinic, maleic, and terephthalic esters of 3,4-epoxycyclohexylmethanol were demonstrated to be compatible with VYNW resin. These data show that esters based on 12- to 14-carbon monobasic acids (73) offer an attractive combination of compatibility, volatility, and low-temperature performance. Epoxycyclohexylmethyl esters of 18carbon epoxy acids such as 9,lO-epoxystearic acid (6) (from oleic acid), 9,10,12, 13-diepoxystearic acid (7) (from linoleic acid) or the epoxidized mixed fatty acids from natural oils, such as soybean, safflower, and tall oils, are attractive Table 11.
plasticizers characterized by low volatility. The oxirane rings in the acid portion of the molecule enhance compatibility and oil resistance, but at some sacrifice in low-temperature performance. Epoxycyclohexylmethyl diesters of dibasic acids (72) show good compatibility with VYNW resin, and are characterized by good oil resistance. 3,4-Epoxycyclohexylmethyl9,lO-epoxystearate is generally similar to epoxidized soybean oil in plasticizing ability, and the low-temperature performance of 3,4-epoxycyclohexylmethyl laurate is intermediate between that of epoxidized soybean oil and iso-octyl 9,lOepoxystearate. Ability of the epoxycyclohexylmethyl esters to heat-stabilize VYNW compositions and results of exposure in Florida are shown in Table 11. The epoxycyclohexylmethyl esters are in a general class with epoxidized soybean oil as heat stabilizers for VYNW resins. Stabilizing ability is amply demonstrated in the comparison with an unstabilized 100 to 54, VYNW to DOP, composition which discolored in less than 1 minute on the mill.
Most of the epoxycyclohexylmethyl esters have clear-cut superiority as light stabilizers. I n some instances there are 5- to 10-fold increases in light stability over that of similar compositions containing a comparable amount of epoxidized soybean oil or iso-octyl 9,lO-epoxystearate. The effectiveness of 3,4-epoxycyclohexylmethyl9,10,12,13-diepoxystearate at low concentrations is especially noteworthy. 3,4-Epoxycyclo h e x a n e c a rb o x yli c Acid Esters. 3-Cyclohexenecarboxaldehyde can be oxidized to form 3-cyclohexenecarboxylic acid (Equation 2), another promising raw material for the making of combination plasticizers and stabilizers for vinyl chloride resins.
i:/ V
I V
-1
0
LJ 0
3,4-Epoxycyclohexanecarboxylic acid ester
Cyclohexenecarboxylic acid has been made to react with various alcohols and diols and then epoxidized to form monoxides (75) and dioxides (71) that are compatible with and will flexibilize vinyl chloride resins. Although the epoxycyclohexanecarboxylate system has not been evaluated as completely as the epoxycyclohexylmethyl series, Table I11 illustrates synthesis, performance, and plasticizing possibilities. The diethylene glycol and 2-ethyl-1,3hexanediol bis (3,4-epoxycyclohexanecarboxylate) esters were also prepared and
Evaluation of 3,4-Epoxycyclohexylmethanol Compounds as Light and Heat Stabilizers
Most of the epoxycyclohexylmethyl esters have clear-cut superiority as light stabilizers DOP = 54 phr) (Epoxy cpd. Phr Phr Epoxycyclohexylmethy1 1.5 3.0 7.7 15.4 54.0 1.5 3.0 7.7 15.4 54.0 170' C. milling test, minutes t o 75% BLR Florida exposure, sun-hours t o failure Ester 2-Ethylhexanoate 10 11 13 15 13 500 500 1250 1500 1000 8 9 11 15 15 100 100 750 1500 500 Laurate 8 13 20 100 100 500 1250 250 Palmitate 4 7 15 15 40 250 750 750 1750 500 9,lO-Epoxystearate 15 20 9,10,12,13-Diepoxystearate 13 15 20 20 22 1000 1250 1500 1500 1000 20 14 750 1500 1500 750 Epoxyalkanoate (from samower oil) 12 14 12 500 1500 1500 500 6 750 1000 7 8 12 10 Epoxyalkanoate (from tall oil) 13 10 250 250 Oxalate 1000 1000 1000 16 20 19 500 Succinate 750 750 1250 15 14 13 500 Maleate 1750 750 20 750 Terephthalate 1250 1500 1000 13 12 17 21 26 250 750 Sebacate Controls Epoxidized soybean oil 15 16 18 20 24 100 250 500 500 250 Iso-octyl9,lO-epoxystearate 11 11 14 16 36 100 250 750 750 750 DOP (no stabilizer)
