Indian scientists invent a way to safe plastics

NEW DELHI, DEC 19: The Government has as last woken up to set standards for plastics but so pervasive is their use that trying to ban the...

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NEW DELHI, DEC 19: The Government has as last woken up to set standards for plastics but so pervasive is their use that trying to ban them may never really work. That’s why the best option, in the long run, could be to ensure that plastics themselves turn benign thus making them both safer and less toxic to humans.

Two Indian researchers have now discovered a simple way to make certain medical grade plastics more friendly to humans.

Why are plastics dangerous? Poly vinyl chloride or PVC, the integral constituent of plastic, is very rigid and to make it flexible, one needs to add a softener. These are normally synthetic compounds called plasticizers which help reduce the rigidity. The more flexible you want the PVC to be, the more plasticizer you need to add, and for most medical applications one obviously needs very flexible tubes and bags.

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The most commonly used plasticizer is a compound called DEHP but unfortunately this has a habit of slowly leaching out of the plastic. That’s why most PVC productsturn brittle with age. DEHP is also a well known carcinogen in rodents and hence worries have been expressed on its large-scale use, though it must be said that conclusive evidence of its toxicity in humans still evades researchers.

Researchers have shown that samples of blood and drugs do get contaminated with this toxic plasticizer when stored in a PVC container. PVC is preferred because it is cheap and very versatile but to make casings as flexible as say blood bags, as much as 40 per cent DEHP has to be added.

It is here that trouble starts. DEHP slowly seeps out contaminating the stored product and in the past, many attempts like photo-irradiation; blending and coating of PVC with other polymers have been made to ensure that DEHP does not seep out but nothing seems to work perfectly.

Now, A Jayakrishnan and S Lakshmi, two polymer chemists from the Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum, describe a novel process for immobilizing this toxic plasticizer withinthe confines of its flexible plastic in the latest issue of the well-known British magazine Nature.

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While trying to make safer and better quality blood bags, they found that in the presence of water and a suitable catalyst, PVC reacts with a salt called sodium sulfide. The substitution of chloride ions by sulfide in the PVC causes the polymer chains to crosslink.

The fine net like mesh that is subsequently formed on the surface of the plastic helps to retard the migration of the plasticizer. They report that when exposed for 6 months to petroleum ether — a potential extractant for DEHP — surface-treated PVC lost virtually no DEHP, whereas unmodified PVC lost almost all its plasticizer in a day. Thus the treated plastic would be potentially safer for humans.

But this treatment of the polymer has its downside as well, for about fifth of the transparency of the plastic was lost — not a particularly desirable thing to happen for medical products — and the final product also lost some of itsflexibility. Still Jayakrishnan, the inventor of this technique, says that the treatment should “benefit” the medical and related applications of flexible PVC and adds that the “the treated polymer material is certainly more compatible to blood and to tissues.”

S Varadarajan a well known organic chemist and president of the Indian National Science Academy, New Delhi calls this a “significant scientific advance having novelty” which if properly applied could go on to make some of the most widely used PVC medical devices still safer for humans.