Innovations boost role of SBCs in medical tubing, IV bags

Polypropylene combined with styrenic block copolymers (SBCs) from Kraton are rapidly penetrating medical markets as a replacement for polyvinyl chloride (PVC) in intravenous bags and tubing.

"You're seeing traction in the marketplace for viable alternatives to PVC," John Marx, global industry manager in the Advanced Materials Group at Kraton, told PlasticsToday in an interview. "We're seeing growth year over year." The growth last year was particularly remarkable—about 91% in the IV market alone.

"The trending toward PVC alternatives began six to eight years ago and we were at the forefront of that," said Marx. "You're basically now seeing the market acceptance and the continuing pressures to move away from PVC."

The specific SBCs targeting PVC replacement in medical applications are in the Kraton G family, which are second-generation materials with a hydrogenated midblock of styrene-ethylene/butylene-styrene (SEBS) or styrene-ethylene/propylene-styrene (SEPS). Kraton G ERS (enhanced rubber segment) has played a particularly important role in the bag segment, where it is often used as an inside layer of a multilayer PP film. Kraton ERS allows softer, more flexible compounds with better processing.

"We're really talking about addressing levels of purity and low extractables as well as the promotion of enhanced durability, impact, elasticity, clarity, and also the compatibility characteristics with the materials used in the other layers of the bags."

Cost impact is 3-5% in general
Marx Is not clear on the cost impact of the Kraton materials on the final bag structure because Kraton sells to compounders who then sell to converters who keep cost and application data confidential. In general, however, the impact of blended Kraton on final costs is in the range of 3% to 5%.

Major health systems report they are saving millions of dollars with a conversion to PVC replacements for intravenous bags and tubing even though materials such as Kraton's are more expensive than PVC on a per pound basis.

Asked how that makes sense, Marx said: "It depends on how you ask the question. If you look at pure materials costs, you may get one answer, but you get another if you look at overall systems costs associated with the manufacture of a complete bag structure and you look at the systems costs of the risk inherent in products using phthalate plasticizer, or the costs of disposal of PVC. That kind of thinking is gaining traction as awareness grows and as supply chains begin to make adjustments."

Marx also said that manufacturers are finding ways to make PVC replacements in a more cost-effective manner.

For example the multilayer structures of PP and Kraton used in IV bags typically would have been made in a cast film process. However, expertise is growing in how to make these films with blown film equipment. Blown film typically requires symmetrical layers, whereas cast film can accommodate asymmetrical layers.

"Everyone from the machinery suppliers to the resin companies to the converters are working on creative ways to make these products more cost-competitive," said Marx. He declined to provide specifics due to confidentiality agreements.

Clear, effective tie layer
One area where there have been advances is clarity.

"You can make pretty clear structures with polypropylene/Kraton blends today," said Marc Hein, research and technical service manager for North America. The clarity of the five-layer structures is comparable to the clarity of PVC bags, he said. He also described Kraton G as a very good tie-layer material.

For tubing, Kraton is blended with polypropylene to create a monolayer structure because tubing does not have the same puncture and tear requirements as bags. Loadings vary widely depending on flexibility needs, tubing thickness, and other factors.

The Kraton compounds available today "don't require any concessions in terms of performance," Marx added, indicating another reason why the PVC replacement trend is accelerating.

SBCs are highly engineered synthetic elastomers that compete with other elastomeric compounds in many applications, including medical tubing and bags. Kraton is targeting PVC replacement in a number of markets, including automotive and wire and cable. Growth of Kraton as a replacement for PVC in medical and wire/cable markets combined was 28% for the trailing 12-month period ending March 31, 2012, Gene Shiels, investor relations manager for Kraton, told PlasticsToday.

In 2011, the company generated $1.4 billion in overall sales revenue based on 303.0 kilotons of sales volume. Total capacity at the end of last year was 420 kilotons.

Later this year, Kraton expects to build a $40 million semiworks plant near its manufacturing plant in Belpre, OH to replace its current pilot plant at the Shell Westhollow Technology Center in Houston, TX. In other capacity news, Kraton last year formed a joint venture with Formosa Petrochemical Corp. to build a 30-kiloton hydrogenated styrenic block copolymer ("HSBC") plant in Mailiao, Taiwan. It is hoped the plant will open in the first half of 2014. Kraton also makes HSBC material at a plant in Berre, France that is operated by LyondellBasell.

Significant Asian competition
Kraton's most significant competitors in the SBC industry are: Asahi Chemical, Chi Mei, Dynasol Elastomers, Kuraray Co., Korea Kumho P.C., Lee Chang Yung, LG Chemical, Polimeri Europa, Sinopec, Taiwan Synthetic Rubber Corp. and Zeon Corp.

The roots of Kraton Performance Polymers go back to efforts to develop natural rubber replacements by the U.S. government during World War II. Shell Chemical, which supplied butadiene for the government's styrene butadiene synthetic rubber plants, bought one of the plants in Torrance, CA when the government decided to get out of the business in 1955. That division of Shell Chemical evolved into Kraton Polymers.