Recovery of hydrophobicity in high density polyethylene

A study of the recovery of the hydrophobicity in high density polyethylene (HDPE) after immersion in a saline solution at different temperatures is reported. The conductivity of the saline solution was varied from 5 to 10⁵ μS/cm and its temperature from 23±3 to 73±2°C. The contact angle which gives a measure of the hydrophobicity of the surface decreased sharply during immersion. After removal from the saline solution the recovery of the contact angle was determined at 23±3°C in air. The contact angle and hence the hydrophobicity of HDPE initially recovered rapidly and then slowly with time after removal from the solution. The contact angle recovered completely to its original value after immersion in 5 μS/cm at 23±3 and 44±2°C whereas it did not fully recover to its original value for 1, 10 and 100 mS/cm. After immersion at 73±2°C the contact angle did not recover fully for any conductivity level even 3000 h following the removal from the saline solution. The recovery time of the hydrophobicity depended on the temperature and the conductivity of the solution. Immersion of HDPE in the saline solution also increased the surface roughness and the weight of the specimens. Both of these parameters decreased during the recovery of the contact angle. The change in the surface roughness and the water desorption while drying were responsible for the observed partial recovery of the hydrophobicity in HDPE