The inconvenient truth about PVC: Page 2 of 3

December 14, 2015

less likely to interact. The most important use of terephthalates is in PET polyester (that's what the T stands for), our #1 in the recycle code, used for food and beverages for more than 40 years, and unlikely to receive significant opposition. So much for the phth. Out of sight, out of mind, out of danger.

All extruders of flexible product have to deal with this mess. Do they pay more or sacrifice properties to be able to say "phthalate-free?" That will depend on the market, of course; makers of dam seals and sewer pipe gaskets are less likely to worry than makers of tubing used in food processing plants. The medical area has been the main arena of conflict so far, where users of tubing and blood bags are under pressure to "get rid of the vinyl."

In the rigid world, the stabilizers are the main worry, and there are some bad ones (e.g., those with lead) but it's easy to find stabilizers that are FDA-OK for food contact. The PVC-phobes will say that vinyl siding and pipe somehow contaminate the air or water, no matter what additives are used, and if you can pin them down, they will usually point to chlorine as the villain. No matter that the chlorine is tied up as chloride (like salt = sodium chloride), nor that the resin is very stable in service and not likely to leach chlorine anywhere. As for chlorine-containing dioxin, its evil is well known, but conditions to transform PVC to dioxin are not seen in its manufacture or fabrication, and certainly not in service. The ‘phobes have even brought up the BPA issue in attacking PVC, which is meaningless, as BPA isn't involved in PVC at all, nor does it contain any chlorine.

By the way, if you ever get attacked by someone who says chlorine is bad, ask them what makes plants green, and if they know it's chlorophyll, stop there. They may not know that there is no chlorine in chlorophyll.

A word on additives: They usually cost more than the PVC resin, so we want to use as little as possible, which means good mixing to get uniform compound, and low processing temperatures to reduce the need for stabilizers. This is the real justification for the higher cost of twin-screw extruders, which are common but not necessary to run PVC. If they can mix well at lower temperatures, they use less stabilizer and the savings can pay for the machinery cost differential.

In conclusion, if you're already using PVC or considering its use, maybe this article can help make you less afraid and more able to defend your decision. Know the properties of what you're using, know the ingredients and their alternatives, know how to test for stability and viscosity and whatever else is important in your use, and work safely, make useful product and keep reading PlasticsToday!

Allan Griff is a veteran extrusion engineer, starting out in tech service for a major resin supplier, and working on his own now for many years,

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