New TPEs push performance envelope.

A range of new thermoplastic elastomers were highlighted at an SPE RETEC devoted to the subject last month in Akron, Ohio. Among them were soft PVC-based TPEs that combine low compression set with oil resistance, new olefinic TPVs with enhanced colorability and uv resistance, breathable TPUs with very high moisture permeability, and a new acrylate modifier that improves heat-aging and uv resistance of TPEs.

OIL RESISTANCE

A new series of PVC-based TPEs from Teknor Apex Co., Pawtucket, R.I., is said to have very low compression set and good oil resistance - an unusual combination for very soft compounds. Ten grades of Flexalloy OR (oil-resistant) TPEs for injection molding, extrusion, blow molding, and calendaring range in Shore A hardness from 40 to 60. Priced at $1.80/lb tl, they are said to have oil resistance equivalent to PP/nitrile-rubber blends and chlorinated polyolefin blends costing 25-50% more. Injection grades have original elongations over 315360% and retain 73-97% of these values after aging for three days in ASTM #3 oil at 125 C. Compression sets for all grades range from 32% to 42% when tested at 70 C for 22 hr - nearly equivalent to a more costly TPV, Teknor says. Dimensional change after seven days in #3 oil at 125 C is from -4.3% to +1.3%, reportedly much less than for TPVs or styrenic TPEs. Another benefit is low brittle points, from -41 to -54 C, suiting them to transportation and building construction uses.

MORE UV-STABLE TPVs

New data on the Santoprene 8000 series of non-hygroscopic, fully cured TPVs reveal superior resistance to color change after exposure to uv light. When these PP-based products were introduced about a year ago (see PT, Nov. '96, p. 13) by Advanced Elastomer Systems, Akron, they were said to be notable for their unusually high whiteness and color uniformity and ability to be processed without predrying. Now, AES reports that extrusion grades of the 8000 series easily pass auto, interior tests for color stability. Gray and white samples remain below 3.0 [delta]E until after 2000 kj exposure. TPV 8000 also reportedly resists die build-up, provides much higher surface smoothness in extrusion than competitive grades, and is produced with a new process that minimizes oxidation and generation of black specks.

YOU CAN WEAR THESE TPUs

Two polyether-based TPU compounds discussed at the meeting by BFGoodrich Co., Cleveland, are advantageous for use in textile laminates because they have five to six times the moisture-vapor transmission rates of standard TPUs, the company says. The two products are now commercially available after having been first announced in late 1995. Estane 58237 has a 90 Shore A hardness, tensile strength of 7300 psi, ultimate elongation of 500%, and tear strength of 480 psi. Its moisture-transmission rate is 9000 g/[m.sup.2]/day at 38 C and 90% RH. Estane 58245 is somewhat softer and even more breathable. It has an 80 Shore A hardness, tensile strength of 4000 psi, 800% elongation, tear strength of 390 psi, and moisture transmission rate of 14,000 g/[m.sup.2]/day.

DURABLE TPE MODIFIER

A new acrylate-terpolymer elastomeric modifier for TPEs comes from Goodyear Chemical Div. in Akron. It can be used with a variety of matrix resins. For example, PVC is said to show better heat-aging and uv resistance than with acrylonitrile butadiene (NBR) rubber as the modifier. PVC wire and cable modified with acrylate shows improved insulation properties, Goodyear says.

Meanwhile, polyester and polyester/polyether TPUs blended with up to 30% acrylate modifier reportedly show no significant drop in physical properties. The acrylate also reduces the overall viscosity of the material, cutting cycle times for injection molding. In extrusion, samples containing acrylate polymer have reduced torque requirements.

This acrylate polymer can also be used with various plasticizers to flexibilize ASA resins and obtain Shore D hardnesses from 60 to less than 10.