In a recent webinar on cool roofing, a presenter discussed some concerns with the roofing industry’s focus on single-ply roof membranes based on Thermoplastic Polyolefin (TPO). The presenter noted that Hypalon – the trademarked Chlorsulfonated Polyethylene (CSPE) supplied by DuPont – was now out of the U.S. market, a situation that would likely expand the use of TPO-based single-plies.
Back in 1995, I wrote a pair of columns discussing whether the up-and-coming TPO single-ply would displace Hypalon as the white single-ply membrane of choice. There were – and are – a number of advantages to CSPE, including 40 years of roofing experience, inherent fire resistance through the chlorine atoms on the polymer chain, remarkable chemical and oil resistance, the existence of ASTM standards, the availability of colored CSPE coatings, and more. CSPE did not require external plasticizers, as did Polyvinyl Chloride (PVC) and Chlorinated Polyethylene (CPE), nor the external fire retardants required of TPO.
After the publication of my 1995 columns, DuPont, the major U.S. producer of CSPE polymers, acknowledged that it had ceased production of CSPE polymer in Maydown, Northern Ireland, but had made a significant capital investment in its Beaumont, TX, site to improve plant reliability and environmental stewardship. “Hypalon has been a strategic part of DuPont Eastomers for the last 40 years and these actions represent a commitment that it plans to be in the Hypalon business for the next 40 years,” said Marvin T. Huypers, Hypalon Product Manager at the time. Nevertheless, DuPont announced in May 2009 that it would cease production of Hypalon, and the shutdown was completed on April 20, 2010.
An informal poll of Hypalon membrane suppliers confirmed that several, such as JPS and Mule-Hide, no longer offer CSPE membranes. But that’s not the end of the story.
Stephen Roades, vice president of Burke Industries, San Jose, CA, has advised me that “Burke has always had a second source of CSPE. The CSPE resin produced by Tosoh Japan is a virtual mirror image of what was produced by DuPont. Burke is now a strategic partner of Tosoh and we are producing CSPE roofing membrane. The material has been fully accredited by UL, FM, and ICBO.” The ASTM Standard for CSM D5019 was updated in 2007 and Burke’s product meets this standard with the Tosoh polymer.
While noting that the supply of resin remains limited, Roades says that a second reactor being built by Tosoh will add 8 million metric tons of resin to the street this year. “This will allow Burke to continue to produce membranes for roofing, liners and floating covers well into the future. Burke is fully committed to the production of one of the best single-ply membranes available,” Roades says.
The Tremco Company has long used either black or white, vulcanized CSPE as a critical component of its roofing systems, and it too plans to use CSPE for the foreseeable future, taking advantage of the polymer’s compatibility with asphalt, modified bitumen, cold process adhesives and its resistance to extreme temperatures, UV and ozone exposure.
But back to the TPO option. TPO has met its initial goals of being low in cost, available in light, reflective colors, and heat weldable throughout its life. It may also be recyclable. However, there are concerns that when used in very hot exposures – such as beneath photovoltaic panels or where reflective window glass bounces the IR energy back on the roof – more rapid degradation of TPO might occur. Nevertheless, TPO is now the volume leader, and undoubtedly will evolve much as EPDM systems have evolved over the years.
Meanwhile, I would like to remind readers that EPDM, PVC, KEE, BUR, CSPE, metal and MB systems are all respectable alternatives and will continue to share the marketplace with the TPOs. There are also alternatives to the industry’s current infatuation with high albedo (mainly white) membranes, such as ballasted roofs, cross-batten tile roofs, vegetated roofs, and – especially in colder climates – well-insulated roofs.