Stretchable Plastics Continue to Expand

Specialty Elastomers

Not long ago, demand for thermoplastic elastomers (TPEs) grew at double-digit rates because they have the properties of thermoset rubber but can be processed as easily as thermoplastics. TPEs have been available for more than 40 years and have built up a considerable following.

Many of the easy substitutions for thermoset rubber have already been done. Demand growth has slowed to the high single digits, says one industry observer, who places annual world production at about 2.5 million metric tons with a value of almost $12 billion. But as producers tweak their lines to offer a number of new TPE variants, they are finding some large but mostly small opportunities.

In the short term, the recent hurricane activity along the U.S. Gulf Coast is likely to affect both the output and value of TPEs. Hurricane-induced increases in energy, raw material, and transportation costs will likely have an effect, too.

Companies are still having a hard time restoring power and resuming operations at thermoset rubber plants shut down because of Hurricanes Katrina and Rita. Many olefin-based TPEs incorporate fine particles of cured rubber. A number of ethylene, propylene, and derivative plants were also shut down because of the storm and have been slow in coming back on-line. Raw materials from these plants used to produce both cured rubbers and TPEs are still in short supply, making it difficult for some TPE producers to get the materials they need.

Add to the mix the high cost of energy and it's easy to see why elastomer producers, along with the rest of the petrochemical industry, are in a cost bind. Solvay, for instance, recently announced price increases of 10 cents per lb on two categories of TPEs: thermoplastic polyolefins (TPOs) and TPE vulcanizates (TPVs). Frederick W. Young, president of Solvay Engineered Polymers, blames the increase on the rising cost of polypropylene used to make some elastomers as well as gasoline and natural gas, which have driven up both the cost of producing our materials and the cost of distributing them to our customers.

Bruce Denison, applications engineering manager for Solvay Engineered Polymers, thinks the raw material situation is manageable-at least for Solvay. The plant where Solvay makes its TPEs, just outside Dallas, can continue production for six to eight weeks with raw materials on hand. He is optimistic that his customers will get the product they need despite the raw material situation.

Producers have increased prices for a wide variety of materials over the past two years. But the current situation makes it easier for certain low-priced materials to make inroads against more expensive ones, Denison says. For instance, a breakthrough in formulating better appearing and higher impact resistant TPOs has allowed them to displace higher priced acrylonitrile-butadiene-styrene (ABS) and blends of polycarbonate (PC) with ABS.

Solvay's Indure TPOs may be able to replace not only other engineering resins, but also steel and fiberglass parts, Denison says. Unlike other TPOs that have a matte finish, these newly introduced resins can yield a high-gloss, scratch-resistant automotive part, for example. Denison says they can be precolored to match any car color, including metallics. Painting a part often costs twice what the plastic part costs alone, he says.

Michael J. Balow, advanced polyolefins technology manager at Basell, agrees that TPOs are making inroads in substituting for ABS and ABS/PC blends. For instance, automotive instrument panels often have a soft covering of ABS/PVC over a rigid olefin-based plastic. To address concerns about the recyclability of automotive parts once they've reached the end of their useful life, certain manufacturers now specify soft TPOs from Basell for instrument panel skins to complement the polyolefin base. In this way, they would have a complete olefin-based unit to recycle rather than one of mixed plastics.

The auto market is one of the largest users of TPEs. Car manufacturers are focused on a cost-down approach, says David Kyle, Dow Chemical senior marketing manager. And Dow, with a large stable of both plastic and elastomeric materials, can tailor the products it offers automotive customers based on their needs. For instance, the firm's Versify propylene-ethylene copolymer can be combined with Engage TPO and/or Affinity polyolefin plastomer-all products of Dow's Insite catalyst technology-to produce a range of elastomers from very soft to relatively rigid and from less to more expensive.

Dow's elastomer line is not limited to automotive applications. Versify copolymers can be used in roofing membranes and can substitute for chlorinated polymers. The Insite catalyst technology has also allowed Dow to produce a spandexlike polyethylene fiber that put the company into textile fiber markets it has not been in before. Brooks Brothers, for example, has incorporated Dow's XLA fiber into shirts that do not require ironing and that retain their fit and shape.

Other TPEs, such as styrene block copolymers (SBCs), serve markets that are different from those for TPOs. Major markets for SBCs include footwear, adhesives and sealants, and asphalt modification. Growth in those markets prompted Kraton Polymers to announce last month a 10,000-metric-ton-per-year capacity increase for Kraton D polymers at its Belpre, Ohio, plant. The addition should be on-line in April 2006.

George B. Gregory, CEO of Kraton, says growth at his firm, spun off from Shell Chemical in 2001 and now owned by private investors Texas Pacific Group and J.P. Morgan Partners, is also coming from a number of new applications. At a Bank of America investor conference last month, Gregory said new SBC applications include automotive sound-deadening foam, fibers, and surgical gloves in which SBCs displace polyvinyl chloride. New products such as these account for 30% of the firm's revenues, Gregory said.

TPEs that are more expensive and higher performing than TPOs and SBCs are also available. The flagship product of Advanced Polymer Alloys, a division of Ferro, is a melt-processible rubber known as Alcryn. This cross-linked chlorinated olefinic interpolymer alloy mimics natural rubber's hydrocarbon- and wear-resistant properties, according to Jeff Senich, business development manager. Senich says Alcryn is used by manufacturers in applications such as fuel lines, where material failure would be a catastrophe. It is also coextruded with PVC to form a gasket that most major automakers use to hold windshields in place.

The higher performing, higher priced TPEs tend to have niche applications. Jay Hatfield, market development manager for Degussa, says the primary market for Vestamid nylon-12-based TPE is cleated professional athletic shoes. Vestamid films are also used as angioplasty balloons because of their durability and physical properties, Hatfield says. And because of their high-temperature resistance, printed Vestamid films are starting to be used in place of polyester films in auto engine compartments.

Eastman Chemical targets its copolyester TPEs exclusively at the medical market. The largest use is for intravenous bags that contain medications and nutritional supplements, says Doris G. Hobbs, durables and medical business manager. Such bags have high strength and can resist puncturing, endure an autoclave, and withstand -ray sterilization without discoloration, she says.

Many of the easy substitutions of TPEs for plastics and thermoset rubber are past, but chemical companies say a combination of new TPE variants and market development ingenuity should keep the business vibrant for years to come.