Environmental Stress Cracking of High-Density Polyethylene Applying Linear Elastic Fracture Mechanics

Abstract

The crack propagation rate of environmental stress cracking was studied on high-density polyethylene compact tension specimens under static loading. Selected environmental liquids are distilled water, 2 wt% aqueous Arkopal N100 solution, and two model liquid mixtures, one based on solvents and one on detergents, representing stress cracking test liquids for commercial crop protection products. The different surface tensions and solubilities, which affect the energetic facilitation of void nucleation and craze development, are studied. Crack growth in surface-active media is strongly accelerated as the solvents induce plasticization, followed by strong blunting significantly retarding both crack initiation and crack propagation. The crack propagation rate for static load as a function of the stress intensity factor within all environments is found to follow the Paris–Erdogan law. Scanning electron micrographs of the fracture surface highlight more pronounced structures with both extensive degrees of plasticization and reduced crack propagation rate, addressing the distinct creep behavior of fibrils. Additionally, the limitations of linear elastic fracture mechanisms for visco-elastic polymers exposed to environmental liquids are discussed.

Understanding environmental stress cracking in the Bell Test at the notch region

“…Reflecting on the tabulated results compared to the plotted data, the onset time identifies the end of the lag stage, the transition time reflects the midway point in the transition, and the acceleration time gives the start time of exclusively accelerated growth; a key difference between the acceleration time versus the other times for notch dilation was that it corresponded to physically detectable changes with micro‐voids forming at the notch tip, fitting the yielding observations of Thuy et al and Yeh et al 39,40 …”

“…At the same time, stresses measured by the load cell increased due to swelling of the amorphous phase. The onset time for the parameter, stress intensity factor K, closely related to the acceleration time for notch dilation. These two overlapping points in time are related to changing molecular structure whereby tie molecules are trying to hold back the expanding amorphous regions caused by plasticization, with the latter being indicative of yielding 39,40 . This state may be called the plasticization threshold .…”

“…These two overlapping points in time are related to changing molecular structure whereby tie molecules are trying to hold back the expanding amorphous regions caused by plasticization, with the latter being indicative of yielding. 39,40 This state may be called the plasticization threshold. As the crystalline structure yields, a period of rapid absorption occurs for the stress cracking agent; at this point in time, the notch and its outer proximate surfaces showed a deep blue coloring.…”

Chemically Recyclable Linear and Branched Polyethylenes Synthesized from Stoichiometrically Self-Balanced Telechelic Polyethylenes

“…It has been reported that the C–O bond is weaker than C–C bond, resulting in lower stress at break under deformation in PPDL . The polar nature of the functional groups, molar mass, and degrees of crystallinity can also affect the materials’ strength. − These multiple competing effects may have influenced the ultimate strength of the materials, and further investigations are necessary to comprehensively understand this behavior.…”

Crazing Initiation and Growth in Polymethyl Methacrylate under Effects of Alcohol and Stress

“…Luo et al investigated the diffusion between PMMA and solvent molecules and discovered that diffusion caused volume expansion and surface distortion in PMMA, leading to stress concentration [ 15 ]. The crack expansion rate of polyethylene under different environmental conditions was studied by Maximilian Thuy et al, who showed that environmental factors played a role in the crack expansion rate [ 16 ]. The effects of natural weathering on the mechanical properties of PMMA, ABS, and ASA were studied by Sánchez-Calderón, I et al, who reported that the natural environment and light considerably reduced the mechanical properties of PMMA [ 17 ].…”