It's Time for a Straight Pitch on Green Polymers

Climate change is a good marketing pitch, but it's often not the whole story.

Case in point: Arkema is now bringing to market a product called Plexiglas Rnew [pron. Rnew], an acrylic resin that targets transparent disposable medical devices. The compound is based on a blend that includes high levels of carbon renewable resources.

The sales pitch is that "the higher bio-based content offers a 'green' alternative to non-renewable resins," according to a press release issued by Arkema. The compound is part of a new family of materials that are designed to reduce carbon footprint.

The story behind the press release is that Arkema scientists have been looking for feedstocks that could produce acrylic as a replacement for methyl methacrylate (MMA), which has been in short supply. Demand for MMA is rising, but supply in the United States has dropped due to plant closings. Major chemical producers, such as Dow, are putting less emphasis on bulk petrochemicals because of weak pricing for many years.

Dow ordinarily supplies a large percentage of the requirements for MMA and surprised the market when it closed its Deer Park, Texas, plant in the spring of 2010. The MMA shortage last year also created headaches for highway contractors because it's a major component of the paint used to make lane stripes.

On May 6, 2010, Dow declared force majeure, a legal term that releases it from contracted supply requirements. "We have experienced a number of unplanned repairs, and unexpected mechanical failures, including, more recently, plugging in our crude MMA production unit," wrote Colin Gouveia, commercial director, Dow Construction Chemicals North America, in a letter to customers that were being placed on allocation. Another important producer, Lucite, had a shutdown last year and also put customers on allocation.

Explaining the Deer Park shutdown, Dow CEO Andrew Liveris said: "We've taken the opportunity to root-cause investigate not only MMA but the entire acrylics production units there so that they run to Dow's standards." Supplies for MMA are better this year, but pricing remains strong because of growing demand.

It made sense for Arkema, a major producer of acrylic trademarked Plexiglas, to protect its feedstock position by seeking alternatives. No details on the substitute chemistry are provided. But it's believed Arkema is augmenting its acrylic with polylactic acid (PLA), possibly in the 20 to 40 percent range. That makes sense because Arkema is a major developer of additives that boost performance (particularly impact resistance) of PLA, which is a thermoplastic aliphatic polyester derived from corn starch, sugar cane, and other crops, even tapioca.

The new compound looks like a winner from a design engineering perspective.

Plexiglas Rnew resin has a light transmittance near 92 percent, allowing better fluids visualization in medical applications. The new resin is also color stable and shows no significant discoloration after exposure to 40K gray Gamma radiation, according to Arkema. In addition, the resin is stable to other sterilization techniques, such as EtO and E-beam.

Another benefit is moldability. Arkema says the compound has excellent shear-thinning properties, making it an option for both thin-wall applications and complex multi-cavity molds. The resin's higher bio-based content results in higher melt flow.