The inconvenient truth about PVC

December 14, 2015

OK, they don't like us. They think we're poisonous, evil. They won't listen to reason (who does, when they feel threatened?). Well, here is my dose of reason, but don't expect anyone to listen.

PVC is an unusual plastic. Compared to the other majors, it's the only one that is not primarily fossil-fuel-based (it's 56% chlorine) and, therefore, is flame-resistant; has good chemical resistance; gives the most rigidity per unit cost; can also be flexible or rigid, as desired; and takes less energy per pound to make and process. And, despite its foes, PVC is one of the most extruded plastics, with products ranging from electrical conduits and building wire to garden hoses and gummy-worm fish baits.

What's the difference between vinyl and PVC? In common usage, none. PVC stands for poly vinyl chloride, and, thus, is one of the vinyl polymers. This is a large family, which even includes polyethylene and polystyrene, but only a few of the materials retain "vinyl" in their names; of these, PVC is by far the most important. As the acronym PVC has received so much negative publicity, some users prefer the term vinyl, but it usually refers to good old PVC. Other vinyls include PVOH (polyvinyl alcohol), PVDC (polyvinylidene chloride) and PVAc (polyvinyl acetate).

All plastics contain additives, even PE, PP and PET, which are usually formulated by their producers. And it's the additives that cause most of the anxiety in the anti-PVC camp, where they may be (incorrectly) considered as part of the PVC itself.

PVC comes in two types: Soft-floppy and hard-rigid. The PVC resin itself is hard and rigid, and its hard-rigid applications have stabilizers to prevent molecule breakdown, lubricants to make extrusion easier (lower viscosity) and other additives such as colorants, as needed. The soft-floppies, on the other hand, have these additives but also need 20 to 50% plasticizers to get the floppiness. There's very little in between: The properties of a lightly plasticized PVC fit very few big applications. Plasticizers are typically high-boiling liquids and may be plant-based, but most of them are manufactured compounds, especially phthalates (esters of phthalic acid). The Greek-based spelling with phth makes them sound "chemical" and contributes to the popular aversion to PVC. Never mind that the rigids don't contain any plasticizer at all, nor that there are many FDA-OK non-phthalate alternatives, nor that the harm attributed to phthalates is still questionable and, in any case, must depend on how much gets into whom and how. The public image is still that PVC, and by extension, all plastic, is bad for you.

There is an important distinction between orthophthalates and terephthalates that matters in any study of toxicity or legal activity, and is well known to chemists, serious environmentalists and even lawyers in this area. All phthalates have two usually identical groups attached to the phthalic acid ring, but the orthos have their two groups next to each other, where they may interact and cause the behavior that has raised concern. The teres have their groups opposite each other, which makes them far

Comments (0)

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