Effect of high temperatures on the physical and mechanical properties of HDPE geomembranes in air

Abstract

The effect of elevated temperatures, particularly between 95 and 115°C as encountered in some geoenvironmental applications, on the physical and mechanical properties of high-density polyethylene (HDPE) geomembranes (GMBs) is examined. Four commercially available HDPE GMBs were incubated in air at temperatures ≥ 85°C. Investigation of the thermograms by differential scanning calorimetry showed a significant change in the polymer morphology with an increase of the incubation temperature and duration, especially at 105 and 115°C. The morphological changes due to annealing involve thickening of the lamella crystals of the polymer and a change in the tie molecules joining the lamella crystals. The effect of annealing was most evident in the stress crack resistance of the GMB incubated at 105 and 115°C prior to polymer degradation. In particular, an increase in stress crack resistance due to annealing could mask the effects of polymer degradation at temperatures above 95°C. Changes in morphology did not affect melt index whose changes were largely attributed to polymer degradation.

Effect of a post‐annealing process on microstructure and mechanical properties of high‐density polyethylene/silica nanocomposites

“…It is worth noting that L c before annealing was evaluated at 171 Å, which is consistent with results previously found by Tireau on an HDPE matrix. The appearance of a second melting peak is driven by the recrystallization of secondary thinner melted crystals during the cooling step after annealing . Moreover, the rapid increase in X c and %P accompanied with a sharp decrease in %S and T ms for short annealing times suggests that a significant amount of recrystallization by an “annealing effect” occurred as previously evidenced by some authors .…”

“…Post‐annealing was performed at T a = 125°C thus at a temperature that was located in the first part of the HDPE melting peak (see Fig. ) and allowed possible restructuration of the crystalline phase as demonstrated by some authors . It is important to keep in mind that this process was performed under air conditions that could involve potential chemical modification and degradation phenomena.…”

“…Several studies have examined the impact of annealing below or near the melting peak of PE samples and subsequent effects on the morphology . This process is usually accompanied with an increase in crystallinity ( X c ) due to the rearrangement of amorphous chains because of a higher mobility at high temperature and a diffusion of the crystalline defects out of the crystals.…”

Study on the durability of HDPE geomembranes applied to geotechnics and the environment using laboratory aged samples and in situ exhumed samples

“…In HDPE geomembranes, temperatures in the range of 80 °C to 90 °C are suggested as the maximum. Temperatures around 105 °C or higher should be avoided because the melting point of polyethylene is 125 ºC (KOERNER, 2005;ISLAM et al, 2011;KOERNER et al, 2007;ABDELAAL et al, 2015).…”

“…The results of these immersions showed that thermogravimetric analysis did not show changes in thermal stabilities, but an average decrease was noted in the tensile yield strength of 34 % for the vinasse sample and an expressive tear strength loss of 40 % was verified in the sodium hydroxide sample. Four different high-density polyethylene geomembranes, 1.5 mm thick, incubated in air at high temperatures were evaluated by Abdelaal et al (2015). These aging samples were investigated by oxidative-induction time tests (standard and high-pressure), the melt flow index test, the stress cracking test (single point), and the morphological changes due to annealing, using the differential scanning calorimetry (DSC).…”