Polyamide 6 grades are claimed to meet new gas-permeation rules: manufacturers of gas-powered vehicles and power tools are under pressure to develop fuel-delivery systems and even portable fuel containers that meet stringent federal and state hydrocarbon-emission standards

Plastics Engineering, May, 2008 by Patrick A. Toensmeier

Nonlinear Structure

One feature Kachin notes is that the products' molecular structure is nonlinear. This is a relatively common technique in some barrier designs, since it basically creates overlapping pathways that impede the release--or penetration--of harmful gases.

The molecular structure also improves the performance of the impact modifier Rhodia uses in the PA 6, and allows for a 40%-50% lower loading, another potential money-saver. According to Kachin, the impact modifier is a commercially available product whose efficiency increases as a result of the molecular modification of the polyamide. If an impact modifier is used at loadings of 10% in a conventional PA 6, the modifier loadings in the Rhodia polyamides would typically be 5%-6%. (Kachin declines to reveal which additive is in use, saying formulations are confidential.)

Rhodia has a total of three grades for monolayer tanks, two of which are in production. Based on Kachin's remarks, they are formulated with a "good-better-best" properties package, which primarily applies to impact resistance. He says the differences in permeation levels among the three are "minor".

The grade specified for the motorcycle, moped, and ATV, Technyl C 536XT, is the lowest-performing of the three, Kachin says. The second grade is not yet in production, but he says it will provide greater barrier and impact resistance than the first version. The third grade, he notes, has "significantly greater" impact properties than the other two.

All three materials provide effective permeation barriers to whatever fuel is used in vehicles, Kachin says. Rhodia has tested the PA 6 grades with primary (toluene) and binary (toluene and ethanol) fuel mixtures, as well as fuels that are almost 100% ethanol.

Enormous Opportunity

Should the PA 6 grades gain wide use in multilayer fuel tanks for automotive and other vehicles, the market opportunity would be enormous. Even in a down year (as is the prediction for 2008) the U.S. auto industry produces around 15 million vehicles. And OEMs worldwide manufacture 50 million or so more. A portion of this market would create huge demand for the PA 6 materials.

Rhodia also sees major opportunities in the monolayer fuel-tank market, which is the one most affected by evolving emissions regulations. Kachin says that in North America alone, 6 million lawn mowers are produced every year, and the number of blowers, trimmers, and chain saws manufactured is about 10 million. Each of these products--and many others covered by the regulations--have monolayer fuel tanks that could generate annual demand for at least 20-30 million lbs of resin.

Kachin also believes that the monolayer grades will help blow molders increase business and reduce capital investment while adapting operations for the new regulatory climate. He notes that most blow molders doing this type of work run monolayer machines. Acquiring an option that permits high permeation barriers to be achieved without the use of multilayer structures or machines would be a major cost savings.