Method for evaluating performance of polymeric liners for environmental applications
Description
Polymeric liners are widely used in rehabilitation of sewer and potable water lines and containment of solid waste and water (polymeric membranes). Studies conducted to date on the performance of polymeric liners considered the effect of mechanical stress, chemicals, moisture, and temperature. However, no study provided a measure of and tools for a practical method to determine the combined effects of in-situ stresses and exposure to chemicals on the long-term performance of liners. This research work aims at quantifying the simultaneous effects of chemical exposure and stress on material properties of polyethylene typically used in liners for pipeline rehabilitation and waste/water containment. An experimental method with a custom designed soaking apparatus was developed for exposing polymeric specimens to water treatment residuals and other abrasive chemicals under an applied stress. High and low density polyethylene specimens (63.5 x 12.7 x 3.2 mm) were mounted on the apparatuses and tested under different levels of deformation, temperature, and time while being exposed to chlorine and trichloroethylene solutions. Following the soaking under each of the foregoing conditions, the specimens were tested for their flexural strength in accordance with ASTM D 790. A computational analysis using the finite element method was performed to verify the results of the flexure tests and determine the stress and strain distribution over a bent specimen during exposure. The results did not indicate a significant effect of chlorine or TCE on degradation of HDPE and LDPE. The developed method with the chosen variables and their levels allows for an analytical interpretation for the effect of moisture and deformation on the long-term flexural modulus of elasticity, which is indicated by the degradation coefficient zeta. The effect of temperature on the degradation of the two tested materials was evident by the observed early failure in addition to the decreased flexural modulus of elasticity noted in the HDPE specimens. The equation proposed for zeta accounts for the effects of temperature and molecular weight distribution. However, analytical interpretation of the effects of these parameters is subject to a future study