New non-SARA 313 ether ester plasticizers.

Ether ester plasticizers based on ethylene glycol monobutyl ether and diethylene glycol monobutyl ether are listed in Section 313 of SARA Title Ill by the EPA. Plasticizers such as dibutoxyethyl adipate (DBEA) and dibutoxyethoxyethyl adipate (DBEEA) are examples of ester plasticizers that fall under these regulations. The chemical industry as a whole has a goal to reduce the use of chemicals or compounds listed under this government regulation.

Our purpose in this work was to synthesize new ether ester plasticizers based on propylene glycol n-butyl ether and dipropylene glycol n-butyl ether, which are not regulated. The new "propylene" synthesized plasticizers were compared to their standard "ethylene" counterparts in a standard NBR compound.

Regulatory

Glycol ethers both mono and di-ethers of ethylene glycol, diethylene glycol and triethylene glycol are regulated by the EPA and SARA Title 111, Section 313. Esters synthesized from these glycol ethers must be mentioned on a MSDS if used at 1.0% or higher concentration in a compound. The EPA requires manufacturers to report use levels of 10,000 lbs. and higher of the regulated ether esters. The excerpt from the regulation which affects glycol ether plasticizers is shown in table 1. In this case, the R' is a dibasic carboxylic acid such as adipic or sebacic acid (ref. 1).

Table 1

Glycol ethers - (Category Code N230) Includes mono-and di-ethers of ethylene glycol, diethylene glycol and triethylene glycol.(1.0) R - ([OCH.sub.2.CH.sub.2])[eta]-OR Where [eta]=1, 2 or 3 R = alkyl or argyl groups R' = R, H or groups which, when removed yield glycol ethers with the structure R - ([OCH.sub.2.CH.sub.2])[eta] - OH Polymers are excluded from this category

Toxicity

Although ethylene and propylene based glycol ethers have similarities in chemical structure, there are significant differences in toxicological properties. Also, no two products in either family has the same toxicological properties.

Broadly, toxicity studies have established that there are very significant differences between ethylene and propylene based glycol ethers. The toxicity data on each of the four glycol ethers used in synthesis for this plasticizer study are summarized in tables 2-5 (ref. 2). The intention of this work is to synthesize three new esters and determine their comparative properties with ethylene based esters. Two esters synthesized with dipropylene glycol n-butyl ether and one ester from propylene glycol n-butyl ether. The two dipropylene glycol n-butyl ether esters, dibutoxypropoxypropyl adipate (DBPPA) and dibutoxypropoxypropyl sebacate (DBPPS) have been listed in TOSCA as new chemicals. The TOSCA listing for dibutoxypropyl adipate is being pursued.

Table 2 - ethylene glycol monobutyl ether (EB)

Type of study      Species   Exposure    Effects
                             level
90-day             Rats      77 ppm      Blood effects
subchronic                   25 ppm      NOEL
inhalation study

90-day             Rabbits   150 mg/kg   No treatment
subchronic                    50 mg/kg   related effects
                              10 mg/kg   at any level

Teratology         Rats      300 ppm     Maternal and
                                         embryo lethality

                             200 ppm     Maternal toxicity,
                             100 ppm     embyro
                                         toxicity, fetotoxity

                              50 ppm     NOEL

                   Rabbits   200 ppm     Maternal toxicity,
                                         embryo
                                         toxicity
                             100 ppm     NOEL

  Table 3 - propylene glycol monobutyl ether (PnB)

Type of study  Species   Exposure Level    Effects

13 week        Rabbits     2ml/kg/day of   Skin effects
subchronic                     57% soln.   at all levels;
dermal study                  5.7% soln.   no systemic
                             0.57% soln.   effects at
                                           any level

13-week        Rats          1 ml/kg/day   Minor skin
subchronic               (880 mg/kg/day)   effects at all
dermal study               0.3 ml/kg/day   levels; no
                           0.1 ml/kg/day   systemic
                                           effects at
                                           any level
13-week        Rats          1,000 mg/kg   Increased
subchronic                     350 mg/kg   liver and
                               100 mg/kg   kidney
                                           weights at
                                           1,000
                                           NOEL=350
                                           mg/kg
Dermal         Rats          1 ml/kg/day   No embryo
teratology                 0.3 ml/kg/day   /fetotoxicity
study                                      or teratogenicity at
                                           any level

               Rabbits     100 mg/kg/day   No embryo
                            40 mg/kg/day   /fetotoxicity
                            10 mg/kg/day   or teratogenicity
                                         at any level

      Table 4 - diethylene glycol monobutyl ether

Type of study   Species      Exposure level   Effects

90-day          Rats         200 mg/kg        Slight
subchronic                   666 mg/kg        hermoglobinuria
                             200 mg/kg        NOEL

90-day          Rats         200 mg/kg        No
subchronic                   666 mg/kg        reproductive
reproductive                 200 mg/kg        effects at
study                                         any level

Dermal          Rabbits      100 mg/kg        NOEL for
teratology                                    embryo
study                                         toxicity and

90-day          Rats       2,000 mg/kg        NOEL
subchronic
neurotoxicity
study

[TABULAR DATA OMITTED]

As shown in figure 1, the major metabolite of ethylene based ethers was found to be an alkoxyacetic acid; however, that of propylene based ethers was determined to be propylene glycol, which a multitude of studies indicates is a substance with minimal toxicity. These differences in routes of metabolism and types of metabolites appear to be the basis for the remarkably different toxicological properties of the two major types of glycol ether products.

Experimental

The new plasticizers are listed in table 6. The physical properties of the new plasticizers as compared to the standards are very similar. Table 7 lists the physical properties of each plasticizer.

[TABULAR DATA OMITTED]

The saponification value for a plasticizer is an indication of its polarity. The DBPA, DBPPA and DBPPS are slightly less polar when compared to DBEA, DBEEA and DBEES, respectively. Polarity is one of the many properties of plasticizers that determines compatibility. The compatibility of the propylene ether esters at the level tested was excellent. Further work will be done to determine compatibility at higher levels of concentration.

DBPA, DBPPA and DBPPS have significantly lower specific gravities as compared to ethylene ether esters. The lower specific gravities are an advantage when evaluating pound-volume cost.

Compounding, mixing, molding and testing

Compounds for performance testing were mixed in an internal mixer except for curatives which were added on a two roll, 6 x 12 inch mill. Test specimens for compound performance properties were molded as follows: Press temperature - 1700[degrees]C (338[degrees]F). Press time - 1.25 x t'c (90) minutes and at 833 psi on the sheet surface. Specimens for original properties, low-temperature, immersions and air agings were die cut from molded sheets .075 [+ or -] .005 inch thick. Other information is shown in table 8.

[TABULAR DATA OMITTED]

Results and discussion

The viscosity and curing of each compound is shown in table 9. The NBR compounds plasticized with the propylene and ethylene esters have similar curing characteristics. All three compounds containing propylene and dipropylene based glycol ether esters have slightly longer scorch times and cure rates.

Compound physical properties

All six plasticizers evaluated provide nearly equivalent original physical properties. Glycol ether esters are very efficient plasticizers in lowering the hardness of a nitrile compound. One of our main objectives in this study was to synthesize new plasticizers that provide equivalent or superior performance in elastomers. As shown in table 10, the NBR compounds plasticized with the propylene and dipropylene glycol ether esters provide equivalent as-molded physical properties.

[TABULAR DATA OMITTED]

Glycol ether esters are used primarily for applications needing both good low temperature and heat aging properties. The only difference between the propylene and ethylene versions in low temperature is that NBR compounds with DBPA and DBPPA are 2[degrees]C warmer than DBEA and DBEEA for the T-10 value, (low temperature torsion - Gehman - table 11) which is considered moderately significant. All other low temperature properties show propylene and ethylene esters are equivalent.

Heat aging

Glycol ether esters, as stated earlier, provide good heat aging properties. These plasticizers are higher in molecular weight than most of the common monomeric plasticizers. The data from table 12 indicate that as molecular weight increases, weight loss decreases. Lower weight loss of plasticizer after heat aging is an indication that compound properties are retained to a higher degree (ref. 3). The data indicate that the propylene esters are essentially equivalent to the ethylene esters.

[TABULAR DATA OMITTED]

Water immersion

One of the significant advantages of the propylene and dipropylene glycol ether esters is low sensitivity to water immersion. The data in table 13 wERE expected since ethylene and diethylene glycol ethers are much more soluble in water than propylene and dipropylene glycol ethers. Applications requiring low extraction by water or humidity would be ideally suited for the propylene esters.

[TABULAR DATA OMITTED]

ASTM oil #1 and #3

As expected, the NBR compounds when immersed in ASTM oil #1 show almost complete extraction of the plasticizer. ASTM oil immersion results indicate that the propylene and ethylene esters provide equivalent properties.

Conclusion

The NBR compound physical properties show that the ether esters based on diethylene glycol monobutyl ether and dipropylene glycol n-butyl ether are essentially equal in performance. In many cases the propylene versions are slightly superior. The same can be said for the comparison of the ether ester plasticizers based on ethylene glycol monobutyl ether and propylene glycol n-butyl ether.

These new ether ester plasticizers provide exciting alternatives to compounders who are concerned with reducing or eliminating SARA 313 compounds from their formulas.

References

[1.] Title 111 of Superfund Amendments and Reauthorization Act, Section 313, 1995. [2.] Dowanol Glycol Ethers Handbook, Health and Environmental Data, 1994 [3.] W.H. Whittington, Ester plasticizers for polar elastomers with emphasis on low temperature, The C. P. Hall Co.