Their search ended with the recent development of HeatBoss EPDM, a next-generation, high heat-resistant compound that’s prepared by novel formulation design using EPDM monomer with a selected third diene monomer and peroxide cure system, according to George Papazotos, vice president of sales and product development for Rubber Solutions, and Steven Yu, vice president of compound technology for the division.
“We were looking for a formulation that rivals silicone, but is more cost effective,” said Papazotos, who helped kick off the project to develop the new rubber compound. He also will present a paper on the new formulation at the Rubber in Automotive Conference, organized by Rubber & Plastics News, to be held virtually June 1-3.
“Our HeatBoss EPDM, after being aged at 350°F for 672 hours, shows only 53 percent loss in elongation at break, 18 percent in tensile strength, along with seven points increase in hardness,” they stated.
“This means that this performance is comparable to that of a typical silicone rubber used in automotive muffler hanger applications, which shows a loss of 54 percent in elongation, 20 percent in tensile and seven points increase in hardness.”
However, they said the HeatBoss formulation had better initial dynamic and mechanical properties than silicone.
Their study shows that HeatBoss EPDM can match the performance of silicone after aging. “FTIR (Fourier Transform Infrared Spectroscopy) and microscopes were used to investigate the physical and chemical change, if any, of the aged HeatBoss EPDM surface,” according to Yu.
Results showed there was no noticeable crack or craze formation, and a minor change in the chemical structure of the surface was spotted after aging, he said, which demonstrated that HeatBoss EPDM has excellent resistance to ozone and oxygen attack at elevated temperatures.
“Such excellent heat-aging performance has qualified our HeatBoss EPDM for type E applications per J200 or ASTM D2000,” the authors noted. In addition, they said HeatBoss can be formulated to possess similar processability as silicone, but at a 50 to 60 percent lower cost, which makes it an ideal alternative as a replacement for silicone in muffler hanger and potentially other applications that require Grade E elastomers.
AirBoss Rubber Solutions developed the compound, according to Yu, because modern cars keep getting smaller, the space for engine compartments is shrinking for both functional and aesthetic reasons, and reducing the space results in hotter engine components. “That restricts the rubber materials that can be used and there’s a fast growing demand within the rubber industry for durable elastomer compounds to deal with the heat.”
Among elastomers, both silicone and fluoroelastomers proved to be effective resisting heat, Yu said. However, he added, their main drawbacks are the high price of the materials and the high cost of processing them.
“That makes compounding, molding and the final preparation very expensive,” he said.
In their paper, the authors said EPDM, as the lowest density elastomer, is one of fastest growing synthetic rubber elastomers available. It can be found in a wide range of applications within the automobile sector, principally because of its exceptional qualities, including decent thermal stability that can be attributed to its saturated main chain structure.
In terms of sales volume, they said EPDM is the top elastomer of choice among non-tire elastomers.
“Although the mostly saturated backbone provides good resistance to oxidation, ozonation and weathering, the capability of operating for an extended service life without losing functionality at high temperatures is still the most critical unmet need for EPDM systems,” they said.
The authors noted that the progressive change of elastomeric material (such as deterioration under heat aging) can be due to the occurrence of three typical types of reactions: heat-induced crosslinks, chain scission and chemical structure alteration.
When EPDM is vulcanized, two types of chemical bonds are formed: S-S and S-C, Yu said. “However, if the rubber is vulcanized by peroxide, the main chemical bond is C-C, which has a higher bond energy than S-S and S-C,” he said. “This means the C-C bond is stronger than the S-S and S-C bonds and can tolerate higher heat.
“Our high-heat EPDM is vulcanized by peroxide. Therefore it has better heat resistance than normal EPDM rubber cured by sulfur.”
It is well documented that peroxide curing leads to improved performance, service life and high temperature resistance of EPDM as compared to sulfur curing, according to the paper.