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Diblock Copolymers and Epoxidized Carthamus Tinctorius Oil as Novel Polyvinyl Chloride Plasticizers |
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Diblock Copolymers and Epoxidized Carthamus Tinctorius Oil as Novel Polyvinyl Chloride Plasticizers |
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This project is a continuation of one completed in 2006. In 2006, we endeavoured to replace the primary plasticizer, di(2-ethylhexylpthalate (DEHP), used in poly(vinyl chloride) (PVC) plastics. Finding a suitable replacement for DEHP is of immense importance, as DEHP is a known toxin and carcinogen, yet up to 40% by weight of commercial PVC is composed of DEHP. PVC plastics are used in a number of sectors, such as for internal automobile parts, medical tubing, water pipes and teething rings. The DEHP forms a very weak bond with PVC, held only by weak Van der Waals forces, and thus is prone to leaching. Leaching of the toxin endangers the humans who produce and use the plastic, as well as the environment and the organisms within it for years after the product?s lifespan has expired. DEHP has been identified to be a reproductive toxicant and endocrine disruptive agent, and it is found in our water supply, aquatic environments and the atmosphere. In 2006, we found that cathamus tincorius oil, safflower oil, was a suitable replacement for DEHP, as when tested for flexural strength, there was no statistical difference between the product made with the safflower alternative and that of the conventional plasticizer.
This year, we furthered our research with two primary goals: to develop new degradable plasticizers of extremely high performance, and to create a degradable PVC polymer. We biochemically altered safflower oil by partial epoxidation by means of an enzymatic reaction. It was found that the safflower oil epoxy plasticizer was of higher overall performance than that of safflower oil. The epoxy was also of dual function, in that it acted as both a plasticizer as well as a very strong heat stabilizer. The two diblock molecules, poly(lactic-co-glycolic) acid methoxpolyethylene (MePEG) and polycaprolactone MPEG, are used in drug delivery systems and were tested as potential PVC plasticizers. Diblock molecules are safe to be used in the body, and have hydrophobic heads but hydrophilic tails, making them water soluble, thereby increasing the biodegradability of the plastic as a whole. High performance liquid chromatography (HPLC) was used to test the leaching rates of the plasticizers, and a thermal mechanical analyser (TMA Q400) was used to carry out plastic performance tests, such as glass transitional temperature and gravimetric stress and strain. These tests showed that both epoxidized safflower oil and certain diblock molecules may very well be suitable replacements for DEHP, with the commercial use of one over the other determinable by desired product function.
The PVC polymer was made degradable by photodegradation. This was done by introduction of a ketone group into the PVC polymer by incorporating a copolymer, co-vinyl acetate. Ketone groups initiate as well as facilitate photodegradation, Photodegradation rates were measured by using mass change, colour degradation, and performance degradation as indicators. It was found that the rate of photodegradation could be controlled by the amount of the copolymer added.