Testing environmental stress crack resistance

The launch of new resins being rare, progress on materials intended for medical applications is by way of formulation, alloys and modifications of existing resins. Thus, new radiation-stable polypropylene grades are available for the manufacture of cups, boxes, baskets, mixers, etc. that are radiation sterilized. And polyesters with better environmental stress cracking resistance are extending their potenti in the area of medical testing. 

PDLCOM William Andrew, Inc., Plastics Design Library test data on the chemical compatibility and the environmental stress crack resistance of plastics... 

MPa (264 psi)J, good electrical properties, good environmental stress-crack resistance (relative to other amorphous plastics), and low flammability based on standard laboratory tests. 

Acknowledgment Authors are grateful to William D. Richards for helpful discussions on conventional test methods of environmental stress cracking resistance. 

An example of the dependence of polymer properties on catalyst activation temperature is shown in Table 5. Polymers of various MW were made with a Cr/silica catalyst activated at various temperatures. The polymers were then tested for environmental stress crack resistance (ESCR), a measure of their ability to resist chemical attack when polymer strips are placed under stress (bent). The test is conducted in the presence of hot surfactant, and the time to failure is monitored. Like most other polyethylene physical properties, ESCR is usually improved when the MW is increased. Therefore, comparisons of catalysts are usually made at similar melt indices (a surrogate for MW). A broader MW distribution... 

Differences between development and production packs need to be recognised, plus any possible special test requirements for such deficiencies as environmental stress crack resistance, surface changes and static charges, panelling/cavitation, etc., which should be established at an early stage. 

Mechanical Properties 1. Plastic properties 2. Tests on the failed material, e.g., tensile and environmental stress crack resistance (ESC)... 

Ram Ramsteiner, R Evaluating environmental stress cracking resistance. In Grellmann, W., Seidler, S. (eds.) Polymer testing. Carl Hanser Verlag, Munich, 2007, chapter 7, 383-428. 

ROLE OF AN ACTIVE ENVIRONMENT OF USE IN AN ENVIRONMENTAL STRESS CRACK RESISTANCE (ESCR) TEST IN STRETCHED POLYETHYLENE A VIBRATIONAL SPECTROSCOPY AND SEM STUDY Lagaron J M Pastor J M Kip B J DSM Research Valladolid,Universidad... 

ASTM D2561-12, Standard Test Method for Environmental Stress-Crack Resistance of Blow-Molded Polyethylene Containers (Philadelphia, 2012)... 

In the usual tests on stress crack resistance (see Sect. 5.3.2), e.g. the pin impression test EN ISO 4600 1998 Plastics - Determination of Environmental Stress Cracking (ESC) - Ball or Pin Impression Method, or in the so-called bend strip test or Bell-test as per ASTM D1693-97a Standard Test Method for Environmental Stress-Cracking of Ethylene Plastics, no failure of HDPE geomembranes is observed under the test conditions required by the standards. These index tests therefore cannot be used for the assessment of stress crack resistance of plastic geomembranes. The requirements are simply too low. 

An important measure of chemical resistance which is often used in household and industrial containers is environmental stress-crack resistance (ESCR). Many variations of the test are known and used, such as ASTM D1693, Conditions A and B. In these tests, the plastic part, a molded bar, a bottle, or a tube, etc, is placed under a standardized stress usually at elevated temperature, and exposed to a surface active agent. For example, one test uses 10% surfactant in aqueous solution at 60° C. The time needed for the sample to break is then recorded. The surfactant is thought to aid in the relaxation and disentanglement of chains. 

Tests using a constant stress (constant load) normally by direct tension have been described in ISO 6252. This test takes the specimen to failure, or a minimum time without failure, and frequently has a flaw (drilled hole or notch) to act as a stress concentrator to target the area of failure. This type of testing, as well as the constant strain techniques, requires careful control of specimen preparation and test conditions to achieve consistent results (246,247). Use of a slow strain rate with a four-point bend specimen configuration and constant load has been suggested as a method for ranking materials for environmental stress-crack resistance (248). 

Environmental Stress Cracking n The formation of internal or external cracks in a plastic caused by tensile stresses well below its short-time strength, and induced by exposure to heat, solvent vapor, or chemically active solutions. ASTM Test F 1248 describes the measurement of the environmental stress-cracking resistance of polyethylene pipe in the presence of a surface-active agent. Other ASTM tests treating this subject are D 1693, D 2561, D 2951, and, in Section 15.03, F 484, F 791, and F 1164. 

Figure 13.31 Environmental stress cracking resistance (ESCR) plotted against strain-hardening modulus for a range of EIDPEs, both catalyst based with broad molecular weight distribution, and bimodal. Points labelled reproducibility are repeated tests on the same sample. (Reproduced from Kurelec, L, Teeuwen, M., Schoffeleers, El. et al. (2005) Strain hardening modulus as a measure of environmental stress crack resistance of high density polyethylene. Polymer, 46, 6369. Copyright (2005) Elsevier Ltd.)...

XLPE exhibits high environmental stress-crack resistance, but available data is limited and tests are recommended for severe conditions or chemicals not listed in this chart. 

Table A. 18 shows results from an environmental stress cracking resistance (ESCR) test as described in Section 2.5.5.2.4.2 for a variety of PMMA materials, at different strains of the outer fiber, three different test media, and 30 min test duration [1047]. Higher values represent higher resistance.

Environmental stress-crack resistance (tested in accordance with 7.8 ASTM F 876) and chemical resistance in specific media (test method ISO 4433 or BS 1973) are significant in such service. 

Environmental stress crack resistance (ESCR) is the ability of the material to resist long-term exposure to stress-cracking agents. Materials with ESCR values in excess of 1000 h are typically considered acceptable based on one of the common test procedures. 

The environmental stress crack resistance (ESCR) of glass fiber-reinforced SPS/nylon blends was characterized by exposing the surface of test bars with 0% and 1 % strains applied to drops of solvent and then observing the damage to the surface. In addition, 7-day and 30-day chemical inunersion resistance were evaluated. The results of this testing for glass fiber-reinforced SPS/nylon blends are shown in Table 16.7. 

Environmental stress crack resistance is covered in chapters Geotextile resins and additives and Mechanical properties, behavior, and testing of geotextiles of this book. 

Environmental Stress Cracking Resistance (ESCR) of PE (D 1693) is the oldest and most conunon test method for SCG. Comj d to the PH test (1) it h poor precision with respect to inter-laboratory reproducibility being about 60%,(2) it takes longer to get a result and uses an Igepal enviroiunent that can contaminate the laboratory, (3) it involves different test conditions depending on the grade of the PE, (4) its stress intensi cannot be defined. It is recommended Aat ASTM conunittees in Table S that are concerned with the resistance to SCG of their PE product remove their ESCR requirement and insert the PENT test. Each committee can then more precisely specify the desired quality of their resin with the assurance that the PENT lifetime will be related to the performance of their... 

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