Time-temperature equivalence in environmental stress cracking of high-density polyethylene

Abstract

In this work the environmental stress cracking resistance of two high-density polyethylene grades, employed for the manufacturing of bleach bottles, was investigated by using a fracture mechanics approach. Two aqueous solutions similar to common bleach products (with and without sodium hypochlorite) were considered as the active environment, whose effect on both the initiation and propagation phases of fracture was evaluated for the two materials. Tests at different temperatures were performed and a time-temperature superposition scheme was applied both in air and in the active environment. Temperature was shown to influence fracture behaviour only through the material inherent viscoelasticity.

A comparison between $K$ and $G$ approaches for a viscoelastic material: the case of environmental stress cracking of HDPE

“…Since, as already found in (Contino et al, 2018), these two solutions have the same influence on the fracture resistance of the two HDPEs, no distinction between the two active environments will be made in the following.…”

“…During this work, two blow moulding HDPE grades, supplied in pellets form by FATER S.p.A., were compression moulded into 1 mm and 11 mm thick plates, according to the procedure described in (Contino et al, 2018). These two materials have a monomodal and a bimodal molecular weight distribution and in the following will be named HDPE-MONO and HDPE-BI, respectively.…”

“…Characteristic initiation and propagation curves were built by plotting both the crack initiation time and the crack growth rate vs. the stress intensity factor and the energy release rate, respectively. The fracture behaviour of the two materials in terms of the stress intensity factor was already discussed in (Contino et al, 2018) and only the main equations and results will be summarised in the following. The novelty of the current study is the analysis of the fracture behaviour of the two HDPEs in terms of the energy release rate and the comparison of the two fracture approaches via the effective modulus , evaluated as reported in Sections 2.2.1.2 and 3, respectively.…”

“…This approximation, which constitutes the basis of the so-called pseudo-elastic approach, was found to be adequate to describe the behaviour of a variety of polymeric materials, among which were also some nonlinear viscoelastic materials. For instance, and were used for the analysis of the Slow Crack Growth (SCG) and Environmental Stress Cracking (ESC) of several polymers (Williams and Marshall, 1975;Frassine et al, 1996;Kamaludin et al, 2017), including: -toughened polymethyl methacrylate (Mariani et al, 1996;Pini et al, 2018) -high impact polystyrene (Andena et al, 2013(Andena et al, , 2016Kamaludin et al, 2016) -polybutene (Andena et al, 2009) -polyethylene (Chan and Williams, 1983;Brown, 1986, 1987;Chang and Donovan, 1989;Rink et al, 2003;Frank, Pinter and Lang, 2009;Contino et al, 2016Contino et al, , 2018Kamaludin et al, 2016) Assumptions on the validity of these two fracture parameters and of Equation (1) are supported by the accurate description of the fracture behaviour of the polymers considered in these works.…”

“…To further examine the validity of the pseudo-elastic approach, the SCG and ESC of two high-density polyethylenes, already studied in (Contino et al, 2016(Contino et al, , 2018 using the stress intensity factor approach and having a markedly nonlinear mechanical behaviour, were further analysed. Results in terms of were compared with those obtained using the stress intensity factor.…”