Discussion
Flexible PVC tubes are used for watering. If some organic solvents are passed through this tube, it becomes stiff. This is due to the fact that the organic solvents
Answer: B
The solvents remove plasticizer and raise \(T_{g}\).
Rigid PVC has a glass transition temperature around 80 °C. Flexible PVC tubing contains a large amount of plasticizer (typically a phthalate), whose small molecules sit between the chains, add free volume and lower \(T_{g}\) below room temperature. Organic solvents dissolve and leach out this plasticizer, so \(T_{g}\) rises back towards that of unplasticized PVC and the tube turns stiff.
Plasticizing PVC would lower \(T_{g}\) and make the tube softer, not stiffer. Removing plasticizer cannot lower \(T_{g}\), and the solvent does not chemically react with PVC.
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