ESCR Testing: How to Measure Environmental Stress Cracking Resistance of Polyethylene

Environmental stress cracking is the silent killer of polyethylene products. A container, cable jacket or pipe that passes every short-term strength test can still crack in service when modest stress combines with a surface-active liquid — detergent, oil, or wetting agents. Industry data has long attributed a large share of all plastic product failures to this mechanism.

ASTM D 1693 defines the classic bent-strip ESCR test, performed on an E.S.C.R. Apparatus. Here is how it works and how to read the results.

The Bent-Strip Method

Ten rectangular specimens, each with a controlled longitudinal nick, are bent 180° and held in a metal channel — imposing a constant strain. The loaded channel is immersed in a tube of aggressive reagent (typically a 10 % nonylphenoxy surfactant solution such as Igepal) held at 50 °C in a constant-temperature bath. Specimens are inspected on schedule, and the result is reported as F50 — the time at which half the specimens have cracked.

Conditions A, B and C in the standard vary specimen thickness, nick depth and reagent concentration to suit different PE grades — condition B is the common requirement for pipe and container resins.

What Influences ESCR

• Molecular weight — higher MW (lower MFI) polyethylene resists stress cracking dramatically better.
• Comonomer content — copolymer grades with hexene or octene branches outperform homopolymers.
• Density — very high crystallinity reduces tie-molecule density and hurts ESCR.
• Processing — moulded-in stress and poor weld lines create initiation sites; ESCR on finished parts can expose processing faults invisible in resin testing.

Equipment Essentials

A proper ESCR setup needs a precise nicking jig (blade depth controls everything), bending and transfer fixtures, sealed test tubes, and a thermostatic bath holding 50 ± 0.5 °C for weeks at a time. Pair ESCR with MFI and density testing and you have the three-test fingerprint that identifies almost any polyethylene lot problem.

Frequently Asked Questions