New TP elastomers offer heat resistance and more.

New TP Elastomers Offer Heat Resistance and More

Two new families of thermoplastic-elastomer alloys represent the leading edge of technology for St. Louis-based Advanced Elastomer Systems (AES) L.P., a newly formed joint venture between Monsanto Chemical Co. and Exxon Chemical Co. The venture merges the TPE business lines and associated operations of Exxon and Monsanto, which include Santoprene, Vistaflex, Geolast, Trefsin, Dytron XL, and Vyram (see PT, July '90, p. 99; Feb. '91, p. 95). Two additional product lines, designated TPE 3000 and 4000, were previewed a little over a year ago by Monsanto executives (see PT, Dec. '89, p. 89). Additional details were recently provided to PLASTICS TECHNOLOGY by Barry M. Rosenbaum, AES v.p. of technology.

He says the firm's recently unveiled TPE 3000 series consists of a PP matrix and a dispersed phase of butyl rubber, together with proprietary compatibilization technology. General-purpose grades have a hardness range between 50 and 90 Shore A. Several new grades in the series are still in development. It's believed the TPE 3000 grades will contain a butyl rubber content of up to 30%.

The TPE 3000 series boasts a continuous-use temperature of 257 F, comparable to the firm's Santoprene TPEs, and processing characteristics similar to Santoprene as well. Rosenbaum says TPE 3000 will target medical and automotive applications that require significant barrier properties to gases and water vapor.

While injection molding is anticipated to be its main use, the series also will include grades for extrusion and blow molding.

A representative grade in the new family is TPE 3201-60, with 55A hardness of 55, tensile strength of 650 psi, ultimate elongation of 350%, tear strength of 120 psi, -56 F impact brittleness, and compression set of 25% after 22 hr at 212 F. Recommended melt temperature is about 380 F, with a mold temperature of 85-140 F. Desiccant drying for up to 3 hr at 150-170 F is advised to avoid porosity.

TOWARD HIGHER HEAT

Further out on the development timetable for AES is the TPE 4000 series, which may be introduced by the end of 1992. Rosenbaum says TPE 4000 will address higher-end temperature applications, with molded components performing in a continuous temperature range of 350 F and withstanding intermittent exposure up to 390 F in air or oil environments.

The final composition of TPE 4000 is still in development, with various combinations of engineering thermoplastic matrix resins and rubbers being considered and tested. End-use application targets also will help determine the eventual profile of the material. One possible composition of TPE 4000 is a polyester matrix alloyed with a dispersed phase of acrylate rubber.

TPE 4000 is said to have superior heat-aging characteristics, approaching the performance of materials such as silicone rubber. It's expected that automotive and business machines will be key application targets. Injection molding, blow molding and extrusion grades are planned for TPE 4000.

While more development work remains to be done with TPE 4000, Rosenbaum says there is great interest and market demand for higher temperature TPEs. "As we get into high-temperature applications, the ability to process and recycle elastomers as a thermoplastic material becomes more important." He says a major challenge in coming years will be to convince processors of the inherent benefits of higher temperature TPEs, compared with thermoset rubbers.

Another key research area for AES is the Trefsin line, based on Exxon technology, which involves an unnamed polyolefin-based matrix compatibilized with two or more discrete rubber phases. Robert D. Banning, AES automotive market manager, points out that the Trefsin series has advantages in its ability to be easily coextruded or adhesive bonded with other plastic materials, unlike standard olefinic-based TPEs.