Plastic woven fabric breaking strength testing measures the maximum tensile force that polypropylene (PP) and polyethylene (PE) woven fabrics can withstand before rupture in the warp and weft directions. As a fundamental quality control requirement for woven sacks, FIBC jumbo bags, tarpaulins, and geotextile products, the test is performed on constant-rate-of-extension (CRE) tensile testing machines in accordance with recognized methods such as GB/T 3923.1, ISO 13934-1, and ASTM D5035. This article explains the test principle, sample preparation, operating procedures, data evaluation, and typical industrial applications of breaking strength testing for plastic woven fabrics.
Technical Overview
Plastic woven fabric is produced by circular or flat weaving of polypropylene (PP) or high-density polyethylene (HDPE) flat tapes slit from oriented film. The tape linear density, draw ratio, weave construction, and weaving density together determine the mechanical performance of the finished fabric. Among all mechanical properties, breaking strength is the primary indicator of load-bearing capacity and is routinely specified in purchase contracts and product standards.
Breaking strength is defined as the maximum tensile force, expressed in newtons (N) or normalized as N/50 mm, recorded when a conditioned specimen of specified width is extended to rupture on a calibrated constant-rate-of-extension (CRE) tensile testing machine. Because the weaving process orients the load-bearing tapes in two perpendicular directions, strength must be evaluated separately in the warp (machine/lengthwise) direction and the weft (crosswise) direction.
The test is essential for verifying conformity with product standards such as GB/T 8946 for plastic woven sacks and GB/T 10454 for flexible intermediate bulk containers (FIBC), and it underpins safety-factor calculations for bulk packaging used in chemicals, food, and construction materials. Testing may be performed in-house or by accredited third-party laboratories operating to ISO/IEC 17025.
Testing Samples
Polypropylene (PP) Woven Fabric
PP fabric is the most widely tested category, covering light sack fabric (approximately 50–100 g/m²), medium-weight tarpaulin fabric, and heavy FIBC base fabric (approximately 140–220 g/m²). Specimens are cut from full-width rolls at positions spaced across the width to represent the whole fabric, avoiding the first meter of a roll and any visibly defective area.
Polyethylene (PE/HDPE) Woven Fabric
HDPE woven fabric, commonly used for tarpaulins, covers, and laminated packaging, is sampled in the same manner. Because PE tapes show somewhat different elongation behavior, the rate of extension is selected according to the elongation class defined by the test standard.
Coated or Laminated Woven Fabric
Fabric with an extrusion-laminated PP/PE film layer is tested with the coating in place, since the film contributes to strip rigidity and can influence jaw slippage. If the specification requires evaluation of the woven substrate alone, the coating may be removed mechanically before specimens are cut.
Samples Taken from Finished Products
When testing is part of product certification or failure analysis, specimens are cut from finished woven sacks, FIBC body panels, sewn seams, and lift-loop attachments. Fabric cut near seams is oriented so that seam strength can be compared directly with base fabric strength.
Testing Items
Depending on the specification and end use, the following items are determined during a breaking-strength test program:
- Warp-direction breaking strength (N or N/50 mm)
- Weft-direction breaking strength (N or N/50 mm)
- Elongation at break and elongation at maximum force (%)
- Breaking strength of sewn seams, joints, and lift loops (N)
- Grab breaking strength for coated or heavily constructed fabric (N)
- Tape breaking tenacity (cN/dtex) for raw woven tape quality control
- Strength retention after artificial weathering or UV exposure (%)
For general-purpose woven sack fabric, breaking strength commonly falls in the range of 500–1500 N per 50 mm in each direction, while heavy FIBC base fabric is typically specified above 1500 N per 50 mm. Exact limits are defined by the applicable product standard or by customer specification.
Testing Methods
Applicable Standards
- GB/T 3923.1 / ISO 13934-1 — Strip method for determination of maximum force and elongation
- GB/T 3923.2 / ISO 13934-2 — Grab method
- ASTM D5035 — Breaking force and elongation of textile fabrics (strip method)
- ASTM D5034 — Breaking force and elongation of textile fabrics (grab method)
- GB/T 8946 — Plastic woven sacks (product standard referencing tensile requirements)
- GB/T 10454 — Flexible intermediate bulk containers (product standard)
- GB/T 6529 / ISO 139 — Standard atmospheres for conditioning and testing
Specimen Preparation
For the strip method, at least five specimens are cut parallel to the warp and five parallel to the weft. Each specimen has an effective width of 50 mm (cut or raveled) and a length sufficient to provide a 200 mm gauge length plus clamping allowance, typically no less than 350 mm. Specimens are taken well apart from one another and must not contain the same set of warp or weft tapes. For the grab method, wider specimens are gripped through a defined central width so that only a limited zone of the fabric is stressed.
Conditioning
Specimens are conditioned in the standard textile atmosphere of 20 ± 2 °C and 65 ± 4 % relative humidity, normally for at least 24 hours before testing, and the test is carried out in the same atmosphere. Conditioning is important because the oriented crystalline structure of PP and HDPE tapes makes their strength moderately sensitive to temperature.
Test Procedure
- Verify the calibration status of the CRE machine, load cell, and elongation measurement system; select grips with serrated or rubber-faced inserts appropriate for woven tapes.
- Set the gauge length to 200 mm for the strip method and apply the specified pre-tension (2 N, 5 N, or 10 N according to fabric mass per unit area).
- Select the rate of extension based on expected elongation: 20 mm/min for elongation up to 8 %, 100 mm/min for 8–75 %, and 200 mm/min above 75 %.
- Clamp the specimen centrally without slack or twist, start the machine, and extend the specimen until rupture.
- Record the maximum force, elongation at maximum force, and break type (normal break, jaw break, or slippage).
- Discard and replace specimens that break within 5 mm of the jaw line or slip in the grips, documenting all retained and discarded data.
Calculation and Expression of Results
The breaking strength of each direction is the arithmetic mean of the valid specimens, reported in newtons or converted to N/50 mm, N/mm, or kN/m as required (1 kN/m equals 1 N/mm equals 50 N/50 mm). Elongation is calculated from the extension at maximum force relative to the original gauge length, and the coefficient of variation is reported together with the number of specimens. A complete test report identifies the standard used, machine and grip details, conditioning atmosphere, specimen dimensions, individual and mean results, and any deviations or discarded specimens.
Precautions and Common Issues
Common sources of error include incorrect specimen width after raveling, misaligned clamping causing oblique tape breaks, worn grip faces causing slippage, and testing immediately after weaving while tapes still retain heat. For coated fabric, excessive clamping pressure can cut the film layer and trigger premature jaw breaks. Each of these factors must be controlled to obtain representative strength values.
Applications
Breaking strength data for plastic woven fabric directly support safety, compliance, and engineering decisions across multiple industries:
- FIBC and jumbo bag manufacturing, where base fabric and seam strength underpin the 5:1 or 6:1 design safety factor
- Woven sacks for fertilizer, flour, rice, cement, sand, and other granular products under GB/T 8946 or customer specifications
- Tarpaulins, truck covers, and greenhouse covering fabric requiring balanced warp and weft strength
- Geotextiles and construction separation fabric subjected to soil loads
- Lamination base fabric for flexible packaging and paper-plastic composite products
- Incoming inspection by bag makers, outgoing quality control by weavers, and third-party conformity assessment before shipment
Manufacturers exporting woven products frequently submit fabric samples to accredited third-party laboratories to obtain standards-based test reports recognized by overseas buyers and certification bodies.
FAQ
What is a typical breaking strength requirement for plastic woven fabric?
Requirements depend on grammage and application. Light sack fabric is commonly specified in the range of 500–1000 N per 50 mm, medium fabric around 1000–1500 N per 50 mm, and heavy FIBC fabric above 1500 N per 50 mm. The governing values are always those stated in the applicable product standard or contract.
Should the strip method or the grab method be used?
The strip method measures the strength of the full 50 mm width and is the reference procedure for plastic woven fabric in GB/T and ISO systems. The grab method is faster and suits coated or dense fabrics where raveling is impractical, but results from the two methods are not interchangeable, and the method used must be clearly stated on the report.
How many specimens are tested?
A minimum of five valid specimens per direction is standard, so ten specimens (five warp, five weft) constitute a complete routine determination. Additional specimens are tested if jaw breaks or high variability cause individual results to be discarded.
What equipment is required?
A constant-rate-of-extension universal testing machine with a suitable load cell (for example 5 kN or 10 kN capacity), pneumatic or mechanical grips designed for woven tapes, an extensometer or crosshead-based elongation measurement, and a conditioned laboratory atmosphere are required.
Why do specimens sometimes fail at the jaws, and how is this handled?
Jaw breaks occur when stress concentrates at the grip edge or when grip faces damage the tapes. Standards permit such results to be discarded and replacement specimens to be tested, with all raw data documented so the final report reflects only valid breaks.
Where can breaking strength testing be performed?
Testing can be conducted in a manufacturer's own physical testing laboratory or outsourced to accredited third-party laboratories with the relevant GB/T, ISO, or ASTM methods within their accredited scope, which is common practice for export certification and buyer verification.