Compounding Report: Be Prepared – PVC’s vs TPE’s

Perception is reality. Despite the fact that the safety of PVC has been demonstrated in a large number of scientific studies, on-going concerns about PVC by certain segments of consumers have prompted OEMs in a number of markets to specify alternate materials. While types of PVC compounds still account for the largest share of the North American compounding market (See Figure 1), at a minimum many processors want to have a non-PVC substitute material approved and ready to run should a customer require it. Increasingly these processors are relying on compounders to supply them with modified or new grades of TPEs specifically commercialized for flexible PVC-replacement applications.

Kraton Polymers has recently introduced film-grade formulations based on its styrenic block copolymers (SBCs) to the North American market. The materials, which contain no plasticizers, are targeted for stretch-films used in food applications. The materials were first developed in response to regulations in Japan prohibiting the use of PVC in food wrap, says Jim Dieter, Kraton global business director of compounding and polymer systems. Kraton is now selling the product in Japan, as well in several European countries; and it has attracted pre-commercial interest of several North American companies. One of the key benefits of the material is that it can generally be processed on the same equipment as PVC.

“With traditional SBC you usually have a high shear characteristic, so we’ve developed a low-shear product that will allow customers to use their regular equipment without additional capital investments,” says Dieter.

The SBC polymers are blended with polypropylene and the material is typically co-extruded with EVA in a three-layer structure. The film has clarity, elasticity and barrier properties similar to PVC.

“What people want is an option in their pocket,” says Dieter. “This product mimics PVC on a cost-performance basis.”

New options for medical, automotive

Dieter says over the last six months he has noticed a significant increase in customer requests for alternatives to PVC, especially for markets such as automotive, medical and toys.

The Thermoplastic Division at Teknor Apex has developed Monprene MP 1848 as a substitution for flexible PVC in medical tubing and other molded components. The material provides clarity and kink-resistance comparable to PVC; however, unlike vinyl, Monprene MP 1848 is inherently elastic and does not contain plasticizer.

Monprene compounds are styrenic block copolymer TPEs that incorporate hydrogenated isoprene rubber. Many medical-grade Monprene formulations are designed to replace latex rubber rather than vinyl in medical films as well as tubing.

Teknor Apex senior vice president, Bertram M. Lederer, says the company is impartial as to which material customers specify and sees its role as assisting them in selecting the compound that best meets the need of a specific application. However, he believes PVC is well positioned to hold its own.

“In most of the applications now served by flexible PVC, we are not seeing, and do not anticipate seeing, major replacement by TPEs or any other thermoplastic,” says Lederer. “Vinyl provides the most appropriate performance for these uses, costs less, and has a decades-long history of reliability and safety.”

Still, Lederer foresees TPEs growing increasingly more competitive with vinyl in the market for certain low-modulus materials applications such as automotive air bag covers, instrument panel skins, closure liners and appliance wire.

A. Schulman Inc. has introduced Invision soft-touch polyolefin compounds in response to OEM demands for a high quality alternative for PVC in automotive interior applications. The compounds, with durometer values ranging from 60 Shore A to 75 Shore A, have received approval from General Motors and designated “mainstream materials” for upcoming programs by the company. The initial Invision portfolio will focus on injection molding compounds for applications such as armrests, assist handles, shifter knobs and others. Compounds are also available for extrusion and blow molding.

According to A. Schulman Canada senior account manager Frank Grisolia, Invision has the soft touch and feel of PVC, without sacrificing performance properties such as scratch resistance, weatherability, moisture resistance and other critical characteristics.

“Invision is quite new, so we’re just ramping up to some commercial applications,” says Grisolia. “There’s still a lot of preference in the market for PVC because of the price advantage, but now we believe we have a cost effective alternative.”

New technology to push envelope

Phthalate-free technology is another option for processors who want to offer customers the benefits of PVC without the health concerns. Bayer Corporation’s phthalate-free plasticizer Mesamoll is an alternative plasticizer for the production of PVC film. In one application, a Dutch water bed manufacturer, Akva, uses Mesamoll in the PVC film used to make a water bed’s vinyl cover. The film is produced by a calendering process in which the plasticizer’s good galling characteristics facilitates processing the film economically at low temperatures. The additive is also reported to have good migration resistance, which ensures the plasticizer remains fully effective for many years.

Kraton’s Dieter reports that the company is developing a new technology for producing PVC alternative materials. He says the new technology will represent a “step change” in comparison to similar types of materials currently commercial. While Dieter declined to give details about the technology or chemistry of the new materials, he allowed that the breakthrough would make it possible to create materials with very low viscosity.

“We’re attempting to validate it now,” says Dieter. “The advantage of this is that it will allow PVC users to run the new materials on existing equipment, tooling, etc.”

He says Kraton is aiming for a launch of the technology at next year’s NPE in Chicago.

Teknor Apex Company’s Lederer says material selection still largely boils down to a cost-performance issue, noting that modern compounding technology can blur the distinction between grades of PVC and TPEs.

“Putting pressure on specifiers to employ political rather than performance criteria to pacify unfounded fears is not in the best interest of plastics processors or consumers,” Lederer states.

Canadian facilities add services, capacity

While the North American compounding market has seen a slowing of growth over the past few years, business at Canadian compounding operations has remained generally upbeat.

The St. Thomas, ON compounding facility of A. Schulman has recently become the single source for the company’s rotational molding compounds. According to plant manager Kit Brown, the business was moved from the firm’s closed Akron, OH plant, where the compounds were pelletized, then sent to an outside contractor for pulverizing. At St. Thomas, the rotational molding compounds are both pelletized and pulverized at the plant, thus improving efficiency and lowering costs. Brown also reports that the facility will be adding four additional silos, to give the plant a total of 18 silos. The St. Thomas plant is also the single source of A. Schulman’s line of thermoplastic urethane and ionomer compounds.