Understanding Breaking Strength and Elongation in Polyester PET Strap

The Two Numbers That Define Performance

When evaluating PET strap (polyester strap), two mechanical properties matter more than any others: breaking strength and elongation. Together, they determine whether a strap will secure your load, maintain tension during transit, and perform reliably in your equipment. According to ASTM D3950, the standard specification for strapping, both breaking strength and elongation must be tested and verified for every production batch.

At Jushuo Packaging, our production data shows that buyers who understand these two properties make better specification decisions. This guide explains what breaking strength and elongation mean, how they interact, and how to use them for selecting the right PET strap.

1. Breaking Strength: The Load Capacity Metric

1.1 What Is Breaking Strength?

Breaking strength (also called break force or tensile strength) is the maximum force a strap can withstand before breaking. According to ASTM D3950, breaking strength is measured by pulling a strap sample until it fails, recording the maximum force achieved.

Breaking strength is typically expressed in:

• Kilograms (kg): Common in European and Asian markets

• Pounds (lbs): Common in North American markets

• Newtons (N): Scientific standard

• Megapascals (MPa): Material property (force per unit area)

1.2 Typical Breaking Strength Range for PET Strap

According to industry specifications, PET strap breaking strength ranges from 160kg to 1,360kg depending on width, thickness, and grade:

1.3 How Breaking Strength Is Tested

According to ASTM D3950, breaking strength testing follows a standardized procedure:

1. Sample preparation: Representative samples from production batch

2. Test speed: Standardized testing speed (typically 50mm/min)

3. Measurement: Maximum force at break recorded

4. Result evaluation: Must meet or exceed specified breaking strength

Jushuo Packaging's quality documentation includes breaking strength test results for every production batch.

2. Elongation: The Stretch Behavior Metric

2.1 What Is Elongation?

Elongation (also called elongation at break) is the amount a strap stretches before breaking, expressed as a percentage of its original length. According to ASTM D3950, elongation is measured during the same tensile test that determines breaking strength.

For PET strap, elongation at break typically ranges from 10% to 18%, significantly lower than PP strap (12–20%) and much lower than nylon (30%+).

2.2 Why Elongation Matters

Elongation affects how a strap behaves under load:

2.3 How Elongation Is Tested

According to ASTM D3950, elongation is measured during tensile testing:

1. Initial length recorded

2. Strap stretched until break

3. Final length at break recorded

4. Elongation calculated as percentage increase

At Jushuo Packaging, our lab data confirms that PET strap consistently delivers elongation values in the 10–18% range, depending on grade and thickness.

3. The Relationship Between Breaking Strength and Elongation

3.1 The Trade-Off

Breaking strength and elongation are related but distinct properties. According to material science principles, there is often a trade-off:

• Higher breaking strength often comes with lower elongation

• Higher elongation often means lower breaking strength

This trade-off exists because molecular orientation—the alignment of polymer chains that increases strength—also reduces the material's ability to stretch.

3.2 Why PET Achieves Both

PET strap achieves an optimal balance of high breaking strength and low elongation through its manufacturing process. According to patent literature on strapping production, controlling draw ratio during manufacturing directly affects both properties:

PET strap is typically manufactured at draw ratios that deliver high breaking strength with low elongation—the ideal combination for load security.

4. Practical Applications

4.1 Load Security

Breaking strength determines the maximum load a strap can secure. According to safety standards, strapping should be rated at least 150% higher than expected working loads to accommodate shock loads and material degradation.

Example calculation:

• Load weight: 500kg

• Required breaking strength: 500kg × 1.5 = 750kg minimum

4.2 Tension Retention

Elongation affects how well a strap maintains tension over time. Low-elongation PET strap maintains tension as loads settle, while higher-elongation straps may relax. For long-distance shipping, low elongation is preferred.

4.3 Equipment Compatibility

Both properties affect equipment performance. According to equipment manufacturers, automatic strapping machines are calibrated for specific breaking strength and elongation ranges. Using strap outside these ranges can cause feeding issues, seal failures, or equipment damage.

5. Selection Guidelines

5.1 Matching Properties to Applications

5.2 Safety Factor Considerations

According to safety standards, always apply a safety factor:

• Static loads: 1.5× minimum

• Dynamic loads: 2× minimum

• Critical applications: 3× recommended

5.3 Sample Testing

According to quality standards, sample testing is recommended before full-scale production. Test both breaking strength and elongation to ensure specifications meet requirements.

Jushuo Packaging provides samples with documented breaking strength and elongation values for verification.

Summary

Breaking strength and elongation are the two most important mechanical properties of PET strap. Breaking strength determines the maximum load a strap can secure, while elongation determines how the strap behaves under load. PET strap achieves an optimal balance of high breaking strength (160–1,360kg) and low elongation (10–18%) through controlled manufacturing processes.

When selecting PET strap, consider both properties together: breaking strength for load capacity and safety factor, elongation for tension retention and application suitability. Apply a minimum 1.5× safety factor for static loads and 2× for dynamic loads. For long-distance shipping or rigid loads, low elongation is preferred. For compressible loads, moderate elongation provides shock absorption.

Jushuo Packaging offers comprehensive PET strap solutions with documented breaking strength and elongation specifications. Our manufacturing capabilities—4 PET production lines with 20,000 tons annual capacity—ensure consistent performance across all specified dimensions. We provide complete test documentation with every shipment and support clients through specification selection.

If you need assistance understanding breaking strength and elongation for your PET strap application, please send an email to sales@jushuopackaging.com, and our professional team will provide one-on-one support.

References

1. ASTM International. “ASTM D3950 – Standard Specification for Strapping, Flat Steel and Seals.” ASTM.org, 2021.

2. European Committee for Standardization. “EN 13394:2001 – Packaging – Strapping – Specifications for Polyester Strapping.” CEN.eu, 2001.

3. Google Patents. “Molecularly oriented plastic strapping and methods and apparatus for manufacturing said strapping.” Google Patents, Patent GB1593012A.

4. International Organization for Standardization. “ISO 9001:2015 – Quality Management Systems – Requirements.” ISO.org, 2015.

5. PAC Strapping Products. “High-Performance Polyester Strapping.” Plant Engineering, 2024.