Q: Why does the hose harden after being used for a long time?
A: The PVC hose will harden after being used for a long time. Although PVC resin is as hard as conventional PVC rigid pipes, the hose becomes soft when a softener (oil) called "plasticizer" is added in the process of wrapping the hose or cable. The addition here does not refer to a chemical reaction, but refers to the mixing of PVC molecules with each other, like a state of hand in hand.
However, due to external stimuli (UV or temperature, etc.), the plasticizer separates from the fluid and oozes out of the hose surface. This phenomenon is generally called "tacky", but as the phenomenon continues, the plasticizer in the hose will continue to decrease, and over time it will become as hard as a rigid PVC pipe.
