Medical Musings: PVC is headed for a much greener future

January 20, 2012

PVC is under heavy fire again - and this time the shots are coming from major corporate customers, not public health researchers. Kaiser Permanente, a huge West Coast health provider, is banning use of PVC in tubing and bags and P&G is replacing PVC packaging in toothbrush containers with PET, which is more easily recyclable.

The irony is that just as widespread conversions out of PVC might really take hold in a few years, PVC could becoming one of the greener materials on the planet.

Will medical components, such as these cartridge covers, someday be made from a fully natural plastic - PVC?

For starters, consider that PVC is the only major volume thermoplastic that is substantially derived (57%) from a non-fossil fuel feedstock. Vinyl chloride monomer is derived from brine, which is industrial-grade salt.

The other feedstock for polyvinyl chloride (PVC) is ethylene, which can now be made from sugar-derived ethanol in very large quantities in Brazil. Braskem has a huge plant while a Dow Mitsui joint venture is building another world-scale plant.

Solvay Indupa, the Brazilian arm of Belgium-based chemical giant Solvay, has announced plans to use Brazilian sugarcane ethanol as a PVC feedstock to replace naphtha, which has been bought from Middle-Eastern sources.  According to Solvay's Erik De Leye, the project remains in the project stage for now, but a plant of 120,000 tonnes a year is envisioned.

That would make PVC a 100% natural material from a polymer point of view.

The typical PVC compound, however, is heavily loaded with chemical additives, most famously plasticizers that impart flexibility.  According to Kaiser Permanente, research suggests that long-term exposure to a commonly used plasticizer called DEHP can affect the body's endocrine system, resulting in a variety of hormonal abnormalities, particularly in infants. The European Union has banned some uses of DEHP, such as children's toys.

There are alternatives, however, including high molecular weight phthalates.

And a single reactor synthesis can be used to produce phthalate-free plasticizers based on vegetable oils. According to researchers at the University of Minnesota,  the plasticizer can be manufactured at the same price with similar performance compared to dioctyl pthalate. One was recently approved for food-contact applications. Many leading companies, including Dow and PolyOne, have either already developed or are working on improved grades of bio-based plasticizers.

In a big move showing the breadth of action under way,  a tech startup called BioAmber and Mitsubishi Chemicals are  building a world-scale biosuccinic acid plant in Sarnia, ON this year using wheat-derived glucose as a feedstock.

BioAmber is teaming with Lanxess to develop a portfolio of bio-succinic-based phthalate-free plasticizers that can exceed the performance of general-purpose plasticizers at competitive prices. Solvay is also doing research in the area.

Getting these materials to function at comparable levels (and at comparable costs) to plasticizers currently used in medical applications is a big job, but the level of work under way implies optimism about the future.

That still leaves some questions surrounding chlorine, the primary polymeric feedstock for PVC. A chlorine backbone is very different that a carbon/hydrogen backbone and provides some of the attributes that make PVC one of the most widely used plastics in the world. These attributes include inherent flame retardance and chemical resistance.

But is it safe?

In its press release, Kasier Permanente made this comment: "When PVC plastic is manufactured or incinerated, dioxin pollution is created. Dioxin is a known carcinogen."

These points are contested by the vinyl industry. Modern incinerators minimize dioxin formation and are equipped with devices to catch dioxins that are produced. The Web site for the International Occupational Safety and Health Information Centre (CIS) lists a lot of hazards of working in a chlorine manufacturing plant, but exposure to dioxins didn't make the list. Industry sources say that vinyl plants have much better safety records than other manufacturing plants.

In an interview, Allen Blakey, chief spokesperson for the Vinyl Institute, said that organizations like Kaiser Permanente get big PR play by bashing PVC, but fail to perform the necessary scientific due diligence to back up their charges. The particular issue is the relative safety of materials such as nitrile that the health provider is using as alternates.

Maybe someday it will be possible that major organizations can get a PR charge by saying they are using PVC - a fully natural polymer.










Comments (0)

Please log in or to post comments.
  • Oldest First
  • Newest First
Loading Comments...