Environmental stress cracking resistance of blends of high‐density polyethylene with other polyethylenes

Abstract

A special modified tensile creep test was used to investigate the stress cracking behabior of various high-density polyethylenes (HDPE). Blends of HDPE with other HDPE:s, with linear low-density polyethylene (LLDPE), and specifically with various slightly long-chain branched linear low-density polyethylenes (HBPE) were tested for their failure times. Whereas HDPE blends, including higher-molecular-weight HDPE components, yield only a minor improvement in stress cracking resistance, a considerable improvement was produced when an LLDPE weight fraction of 0.3 or more was used. Adding HBPE also improves the environmental stress cracking resistance. Environmental stress cracking resistance improves with increasing HBPE content, and, for a constant HBPE concentration, it increases with increasing octene content of the HBPE. Adding HBPE with a low octene content, however, results in reduced failure times of the blend compared with HDPE blends that exhibit relatively good environmental stress cracking behavior. The results are explained in terms of the tie-molecule density. INnlODUCTIONThis paper discusses the environmental stress crackhe influence of chemicals on the environmental

Polyethylene blends: A correlation study between morphology and environmental resistance

“…This means that the effect is more pronounced in the LDPE blends than in the LLDPE ones. The improvement in stress cracking resistance of HDPE with addition of 0.3% weight fraction of LLDPE has been previously observed and was explained in terms of the tie-molecule density [13].…”

“…6 and 7 would predict a higher increase in the resistance to stress cracking of the LDPE based systems compared to those based on LLDPE. Moreover, since the stress cracking resistance is related to the number of tie molecules [3,12,13] which is larger in LDPE than in LLDPE, the former should be more effective in enhancing this property. However, in practice, the results were the opposite: the stress cracking resistance was much greater in the more rigid, more crystalline LLDPE blends (which also showed lower tan d values) than in the corresponding LDPE ones, as shown in Fig.…”

“…Among the controlling factors that have been considered in the literature the most relevant are interlamellar failure in a process highly influenced by the concentration of tie molecules [8], the disentanglement of the macromolecules within the crystalline regions, the number of tie molecules and the strength of the crystals that anchor them [10]. Several authors agree with the assumption that the resistance to ESC is directly related to the density of tie molecules [3,11e13], which in turn is related to the number of short branches [13,14] and the molar mass of the polymer [11]. In general, resistance to ESC goes in a direction opposite to processibility, that is, the more ESC resistant materials are often the more difficult to process.…”

Environmental Stress Cracking

“…[5][6][7][8][9][10][11][12] Polyethylenes ranging in molecular weight from 67,000 to 158,000 exhibited an increase in the rate of crack growth as molecular weight decreased during exposure. Usually, a material and solvent pair are the subject of the investigation with less contribution to generalization.…”

Effect of Metallocene-Catalyzed Polyethylene on the Physicomechanical Properties of Blends with High-Density Polyethylene or Low-Density Polyethylene

“…This is also the case for the flexural and impact properties of HDPE=LLDPE blends and is attributed to the composition of the amorphous phase of the blend [18] . The resistance to SCG of HDPE=LLDPE blends can increase significantly with levels greater than 30-50% (w=w) LLDPE in the blend [19,20] .…”