ASTM D1693 Test for Environmental Stress-Cracking of Ethylene Plastics

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ASTM D1693 Standard Test Method for Environmental Stress-Cracking of Ethylene Plastics

ASTM D1693 determination of the susceptibility of ethylene plastics, to environmental stress-cracking when subjected to the conditions herein specified. Under certain conditions of stress and in the presence of environments such as soaps, wetting agents, oils, or detergents, ethylene plastics may exhibit mechanical failure by cracking.

Test Principle

Environmental stress-cracking (ESC) is a material failure mechanism where relatively low tensile stress combines with chemical/environmental agents to cause premature cracking, often at stress levels far below the material's ultimate tensile strength.

ASTM D1693 operates on these core principles:

1), Stress Concentration: The standardized notch creates a local stress riser, simulating real-world defects or material inhomogeneities;

2), Chemical Acceleration: Igepal CO-630 (nonylphenoxypolyethoxyethanol) surfactant solution acts as a potent stress-cracking agent, accelerating failure compared to service environments;

3), Thermal Acceleration: Elevated temperature (50°C standard) increases molecular mobility, further accelerating crack propagation;

4), Controlled Stress: Bent specimen holders apply consistent, uniaxial tensile stress to the outer surface of the bend;

ASTM D1693 Test for Environmental Stress-Cracking of Ethylene Plastics

The cracking obtained with Igepal CO-630 is indicative of behavior expected from a wide variety of surface-active agents, soaps, and organic substances that are not significantly absorbed by the polymer.

Test methods:

ASTM D1693 employs a notched, bent strip method (Bell Test configuration) to accelerate environmental stress-cracking in a controlled laboratory setting. It creates high local multiaxial stresses through a standardized pre-formed imperfection (notch) while specimens are immersed in a surface-active agent solution at elevated temperature. The method is qualitative/quantitative, providing either pass/fail results at a specified time or time-to-failure data.

Using the classic scheme of 'notched specimens + reagent immersion + failure statistics,' the core steps are as follows:

Choose group A/B/C (corresponding to different thicknesses, notch depths, and bath temperatures) according to ASTM D1693 standard test conditions (for example specimen thickness 3.00mm, notch depths 0.50mm, and temperature 50°C. )

Mold/cut specimens with controlled notches; Bend and fix the specimens, introducing multiaxial stress; Immerse in reagent, accelerate reactions in a constant temperature bath;

Failure evaluation: Observe at regular intervals, recording the proportion of cracked specimens or failure time.

Test device, equipment for ASTM D1693 Environmental Stress-Cracking Test of Ethylene Plastics:

UnitedTest ESC-95 series Environmental Stress Cracking Resistance (ESCR) Apparatus determines the susceptibility of ethylene plastics to stress-cracking when exposed to different environments such as soaps, wetting agents, oils and detergents.

Equipment Component	Specifications	Purpose
Blanking Die	Rectangular, cuts specimens to 38±2.5 mm × 13±0.8 mm	Standardize specimen geometry
Notching Jig	Precision fixture with sharp blade.	Create controlled notch (depth 0.3±0.05 mm) for stress concentration
Specimen Holders	Brass channel (Inner width 11.75±0.05mm).	Maintain specimens in fixed bent position to apply consistent stress
Test Tubes	Hard glass, ~200 mm long × 32 mm OD	Contain test solution and specimens.
Constant-Temperature Bath	Capable of maintaining 50°C ± 0.5°C (or 100°C) or other specified temperatures.	Control thermal environment.
Bending clamp	Closing time 30-35 seconds (using a vise/press), ensure the stress is applied evenly.	Used to clamp the test specimen uniformly.
Timer	Accurate to 1 minute	Record exposure time and time-to-failure.

Test Specimen Information

Material: Ethylene plastics (polyethylene homopolymers and copolymers) as defined in ASTM D883.

Size: Rectangular strips, 38±2.5 mm (length) × 13±0.8 mm (width) × specimen thickness (typically 1.5-3 mm)

Notch Requirements: Single notch, parallel to long edges, centered on one broad face

Depth: 0.3±0.05 mm (critical dimension for stress concentration)

Sharp, clean cut using the specified jig and blade

Sample Preparation:

Cut with square edges (beveled ends avoided)

No surface scratches or defects (other than the intentional notch)

Minimum of 10 specimens recommended for statistical validity.

Environmental Stress Cracking (ESC) Background: Polymers can undergo brittle cracking under stresses lower than their short-term tensile strength when exposed to reactive media (such as detergents and oils). This is one of the main causes of failure in polyethylene pipes and packaging materials.

Reagent Selection: Igepal CO-630 (nonylphenol ethoxylate) is preferred, non-hygroscopic, stable in a 10% aqueous solution, but other surfactants can also be used.

Test procedure of ASTM D1693 Environmental Stress-Cracking Test

Sample Preparation	Cut specimens to specified dimensions using the blanking die. Prepare notch using the notching jig, verifying depth with depth micrometer. (check the blade every 30 uses, up to 100 times) Clean specimens with alcohol to remove surface contaminants.
Solution Preparation	Prepare 10% volume/volume aqueous solution of Igepal CO-630 (standard reagent); For referee purposes, concentration shall be consistent with material specifications (if none given, use 10%).
Specimen Loading:	Place 10 specimens (notch facing up) into the bending fixture, close for 30-35 seconds; Use a transfer tool (Figure 4) to move to the brass rack, ensuring the bottom of the specimens contacts the bottom of the rack;
Reagent Immersion:	Insert into test tubes within 10 minutes, add fresh reagent at 23±1°C (liquid level 13 mm above specimen top); After sealing, place in a thermostatic water bath 50°C ± 0.5°C (or other specified temperature), ensuring the notch does not touch the tube wall;
Failure Observation:	Check at regular intervals (recommended intervals: 0.1, 0.25, 0.5, 1, 2, 4, 8, 16, 24, 48 h) visible cracks to the naked eye (including cases where surface depressions develop into cracks);
Data Processing:	Failure ratio: record the proportion of cracked specimens at the specified times; Failure time: estimated by observation (fp, e.g., f50 = time when the 5th specimen fails) or calculated from graphs (Fp, using log-probability paper to fit a straight line); F50: Time at which 50% of specimens have failed (commonly used indicator reflecting the average crack resistance of the material).

Test Applications

ASTM D1693 is applied across multiple stages of material/product lifecycle:

Material Development: Compare ESCR of different resin formulations and grades

Quality Control: Routine inspection of incoming materials or finished products

Product Qualification: Evaluate suitability for specific applications (e.g., pipes, containers, household goods)

Failure Analysis: Investigate field failures suspected to involve environmental stress-cracking

Research: Study fundamental mechanisms of ESC in polyethylene materials

Key Industry Applications:

Packaging: Food containers, detergent bottles, and other household plastics exposed to cleaning agents

Piping Systems: PE pipes for water, gas, and chemical transport

Consumer Products: Components in dishwashers, washing machines, and other appliances exposed to soaps/detergents

Automotive: Plastic parts in contact with oils, fuels, and cleaning fluids

Wire & Cable: Insulation and jacketing materials exposed to various environmental chemicals

ESC-95 Environmental Stress Cracking Resistance (ESCR) Apparatus determines the susceptibility of ethylene plastics to stress-cracking when exposed to different environments such as soaps, wetting agents, oils and detergents.

Q1. What is the primary purpose of ASTM D1693-08?

A: ASTM D1693-08 is a standard test method designed to determine the susceptibility of ethylene plastics (e.g., polyethylene) to environmental stress-cracking (ESC). It evaluates how these materials fail mechanically (via cracking) when subjected to tensile stresses belowtheir short-time strength, in the presence of environments like soaps, wetting agents, oils, or detergents.

Q2. Why is ASTM D1693-08 important for ethylene plastics?

A: This test is critical for quality control, material selection, and failure prevention in applications where ethylene plastics (e.g., pipes, packaging, wire coatings) encounter stress and chemical exposure. ESC is a leading cause of premature failure in polyethylene products—this test simulates real-world conditions to predict material performance. Based on my pretrained knowledge, ESC accounts for ~30% of polyethylene pipe failures globally, making this standard a cornerstone for reliability assessment.

Q3. What is the core principle of the ASTM D1693 test?

The test relies on controlled stress concentration + environmental exposure:

A sharp notch (controlled imperfection) is machined into a bent plastic specimen to create localized stress.

The specimen is immersed in a surface-active reagent (e.g., Igepal CO-630) at a constant temperature.

The proportion of specimens that crack (or the time to 50% failure, F₅₀) is measured.

Essentially, it quantifies how well a material resists crack initiation/propagation under "low stress + chemical attack."

Q4. How are test specimens prepared?

A: Specimens must meet strict dimensional and processing rules:

Molding: Follow Procedure C of ASTM D 4703 (no release agents; use inert liners like polyester film).

Cutting: Use a die to cut 38±2.5mm × 13±0.8mm pieces from smooth sheets (within 24h of sheet preparation).

Dimensions: Match Table 1 (e.g., Condition A for low-density PE: 3.00–3.30mm thick, 0.50–0.65mm notch depth).

Q5. What defines a "failure" in ASTM D1693?

A: Per Section 3.1.2: A visible crack to the naked eye constitutes failure. Key notes:

Multiple cracks in one specimen count as onefailure.

Surface depressions (dimpling) that later become cracks are timed at the dimpling moment.

Extension of the original notch is nota failure.

Q6. What factors most affect test precision?

A: Per Appendix X1.2, the top variables are:

Specimen thickness: Thicker samples crack faster (but have smaller standard deviations).

Notch depth: Must be tightly controlled (0.030–0.040mm range; hardware-dependent).

Thermal history: Low crystallinity increases failure time.

Reagent concentration: Igepal CO-630 (10% aqueous) is preferred; moisture affects results.

Q7. Why is Igepal CO-630 the preferred reagent?

A: Igepal CO-630 (a nonylphenoxy poly(ethyleneoxy)ethanol) is chosen because:

It is non-absorbable by most ethylene plastics.

A 10% aqueous solution is stable for 1000h at 50°C (Note 8).

It mimics a wide range of surface-active agents (soaps, detergents) (Section 5.1).

Q8: What is the difference between ESCR and impact resistance?

A: ESCR (measured by D1693) is resistance to slow crack growth under long-term low stress + chemical attack. Impact resistance (e.g., ASTM D256) is resistance to sudden high-speed force. They measure different failure mechanisms.

Q9: What is the standard test temperature?

A: The referee temperature is 50°C ± 0.5°C. Other temperatures may be used by agreement, but 50°C is the default for comparison.

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