Packaging Material Stress Cracking Testing Methods and Standards | De Varo Packaging

Stress cracking is one of the most common failure risks in packaging materials, especially for plastic closures, containers, and composite packaging. To ensure product safety and long-term performance, standardized stress cracking testing is essential.

In this article, we introduce stress cracking test methods applicable to various types of packaging materials.

1. Purpose

To standardize the testing method for evaluating stress cracking resistance in packaging materials.

2. Scope

This method is applicable to all types of packaging materials, including plastic, heat-sealed, and composite packaging components.

3. Equipment & Instruments

Constant temperature oven (60°C), Torque tester

4. Test Procedure

(1) Sampling

Development stage: Select 10 representative samples for testing.

Incoming inspection stage: Sampling shall follow GB/T 2828-2012 (Normal inspection, single sampling plan for attributes).

(2) Conditioning

Place the products in an environment of 23°C / 50% RH for 24 hours. Clearly mark the test samples.

(3) Application to Stress-Prone Areas

Apply the test product to areas where stress concentration may occur, such as from the thread neck opening down to the base of the threaded area.

For threaded products, tighten the closure according to the torque values specified below.

Thread Diameter (Approx. Major Diameter T, mm)	Applied Torque (N·m)	Thread Diameter (Approx. Major Diameter T, mm)	Applied Torque (N·m)
8	0.8	43	3.1
10	0.8	48	3.4
13	0.9	51	3.7
14	0.9	53	4.1
15	1.0	58	4.5
18	1.2	60	4.6
20	1.4	63	4.9
22	1.5	66	5.2
24	1.7	70	5.6
28	2.0	77	6.2
30	2.1	83	6.7
33	2.4	89	7.2
38	2.8	100	8.0
40	2.8	120	9.7

6. Product Filling & Positioning

Invert all containers and apply the test product to the inner wall of each container.

7. High-Temperature Static Test (Applicable to plastic, heat-sealed, and composite products)--- Record all observations.

• Place 10 capped containers in a 60°C oven: 5 upright 5 inverted

  
  

• Observe samples after 24h, 48h, 72h, and 7 days.

  
  

• Samples should be evaluated immediately after removal from the oven (no need to return to room temperature).

  
  

• Apply manual pressure to the container to assess forced environmental cracking.

  
  

• Resistance during pressure application indicates no micro-cracking.

  
  

⚠️ Note: At 60°C, caps may loosen. After each inspection, manually retighten the caps before returning samples to the oven. After 15 days, remove samples and allow them to equilibrate at room temperature for 24 hours before final evaluation.

8. Accelerated Stress Cracking Test Using Chemical Solution (Applicable to polyolefin products such as plastic stoppers)

Solution Preparation

Prepare a stress cracking solution using TRIDECETH-12 (CAS No. 78330-21-9) at a concentration of 0.5% ± 0.05% (by weight) in distilled or demineralized water.

To accelerate dissolution, the solution may be prepared at 35°C.

Note: TRIDECETH-12 is a mixed C11–C14 iso-alkyl ether. Due to varying molecular melting points, the solution may partially solidify at room temperature. If this occurs, reheat and mix thoroughly before testing.

Test Method

• Fully immerse the test samples in a glass container filled with the cracking solution (both internal and external surfaces must contact the solution).

  
  

• Seal the container to prevent evaporation.

  
  

• Place the container in a 55°C oven for 24 hours.

  
  

• Remove samples, wipe dry with absorbent paper, and inspect stress-concentrated areas for cracks.

  
  

• Record all findings.

⚠️ Safety Notice:

The cracking solution is corrosive. Always wear rubber gloves and protective goggles when handling.

9. Calculation

Not applicable.

10. Defect Classification & Acceptance Criteria

When requirements differ from specific packaging material standards, the packaging material standard shall prevail.

Defect Classification and Acceptance Criteria

Description	Defect
	0 defect	Serious AQL 0.15%	Main AQL 0.65%	Minor AQL 1.5%	Very Minor AQL 4.0%
Bottle crack		√
Minor crack		√
Function defect		√

Note: When requirements differ from the applicable packaging material standards, the packaging material standards shall prevail.

11. Sample Retention

All tested samples and original reference samples must be retained for 6 months after testing.