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How do plasticizers change the properties of PVC?

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plastic soft-drink bottles — plastic Plastic soft-drink bottles are commonly made of polyethylene terephthalate (PET).

Plasticizers are additives used to modify the physical properties of polyvinyl chloride (PVC) by lowering its glass transition temperature ( $T_{g}$ ).1

In its pure, unplasticized form, PVC is a rigid, lightweight plastic with a $T_{g}$ of approximately 85 to 90 °C (185 to 195 °F), making it suitable for structural applications like window frames and piping. By mixing PVC with nonvolatile liquids—most commonly phthalates such as di-2-ethylhexyl phthalate (DEHP)—manufacturers can produce a flexible material that retains its pliability even at low temperatures. For example, a mixture of 30 parts plasticizer to 70 parts PVC can lower the $T_{g}$ to about -10 °C (15 °F), allowing the material to be used for products like garden hoses, floor tiles, and upholstery.21

Beyond flexibility, plasticizers can also influence the finished product's cost, flammability, odor, and biodegradability. PVC is uniquely capable of accepting and retaining a wide variety of plasticizers, which has been a key factor in the polymer's commercial success.12