Teknor Apex has introduced new thermoplastic vulcanizate (TPV) elastomers which it says present better properties and can be suitable for high-performance appliance, automotive and construction applications.
The advantages cited by the company’s Thermoplastic Elastomer Division include greater long-term resistance to heat and solvents than conventional TPV compounds, higher tensile strength, and better long-term elastic recovery.
Teknor Apex said comparative tests it undertook showed that the elastic recovery properties of conventional TPVs (measured by compression set) deteriorated by 20 to 50 per cent after long-term exposure at 125 degrees C, while new Uniprene XL compounds exhibited a change of only five per cent. The new TPVs also exhibited substantially lower weight gain after over 500 hours of immersion in IRM 903 oil at 125 °C. Their tensile strength values were typically 10 to 20 per cent greater.
“Uniprene XL compounds are even more rubber-like than conventional TPVs, enabling processors to meet more stringent requirements for dynamic components that undergo repeated flexure or for applications in aggressive end-use environments,” said Tonya McBride, sales engineer. “Unlike specialty TPVs that cost many dollars per pound more than conventional TPV compounds, the new XL series provides enhanced performance at only a small premium.”
According to details provided by the company, Uniprene XL compounds can be extruded or injection-moulded and are readily coloured. Currently available grades span the Shore A hardness range from 45 to 80. Suggested applications include seals, plugs, grommets, and mechanical components; automotive tubing and bellows; glazing strips, weather seals, and expansion joints; and electrical insulators.
Development of Uniprene XL compounds was described in a paper delivered at Antec 2004 by Teknor Apex scientists Jushik Yun, Raman Patel, and Darnell C. Worley II.
Conventional TPVs, including standard Uniprene grades developed and sold by Teknor Apex, typically consist of EPDM rubber domains dispersed in a polypropylene (PP) matrix, with cross linking of the EPDM providing more rubber-like properties than are available with thermoplastic elastomer blends not subjected to cross linking. In developing Uniprene XL compounds, Teknor Apex replaced EPDM with a modified hydrogenated styrene block copolymer (hSBC).
“As with conventional TPVs, the ‘soft segment’ of Uniprene XL compounds takes the form of spherical, micro-sized [0.5- to 2-micron] domains of cross-linked rubber,” said Dr. Yun. “Within the soft-segment domains of cross-linked hSBC, however, are nano-sized domains consisting of polystyrene hard segments that also act as cross links [see illustration]. It is this dual-network morphology that provides the long-term compression set consistency and solvent resistance that distinguish Uniprene XL TPVs.”
Other high-performance TPVs on the market are based on nylon/polyacrylate, nylon/silicone, and copolyester elastomer formulations. While prices for these engineering TPVs range up to $10 a pound, Teknor Apex expects to offer Uniprene XL compounds at selling prices, which are substantially lower.
The illustration helps throw light on the keys to improved performance of new Uniprene XL compounds, which are: 1) a rubber component different from those in other TPVs; and 2) a unique dual-network morphology, shown in schematic. At left, micro-sized domains of cross-linked rubber are shown in polypropylene matrix. At right, magnification of one rubber domain shows the soft segment crosslinking plus nano-sized polystyrene hard segments, also crosslinked.
The Thermoplastic Elastomer Division of Teknor Apex is a leading manufacturer of custom and standard thermoplastic elastomer (TPE) compounds including Elexar, Monprene, Telcar, Tekbond, Tekron, and Uniprene products.
