Why does the hose harden after being used for a long time?

The PVC hose will harden after a long time. Although PVC resin is as hard as conventional PVC pipes, in the process of wrapping rubber hoses or cables, adding a softener (oil) called "plasticizer" to the hose can become soft. The addition here does not refer to a chemical reaction, but refers to the mixing of PVC molecules with each other, just like holding hands.

However, due to external stimuli (ultraviolet rays or temperature, etc.), the plasticizer separates from the fluid and oozes out of the surface of the hose. This phenomenon is generally called "sticky", but as the phenomenon continues, the plasticizer in the hose will continue to decrease, and over time it will become as hard as a PVC pipe.

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