Tensile Breaking Strength Testing of Packaging Materials: Standards, Methods, and Applications

Tensile breaking strength testing is one of the most critical quality control procedures for evaluating the mechanical performance and durability of packaging materials such as plastic films, paper, paperboard, laminates, tapes, and strapping. This article provides a comprehensive technical overview of packaging material tensile strength testing, covering applicable international standards, sample types, testing items, test methods, calculation principles, and typical industrial applications. By understanding the testing workflow in accordance with ISO, ASTM, EN, GB, and JIS standards, manufacturers and quality engineers can ensure their packaging reliably withstands filling, sealing, transportation, and storage stresses.

Technical Overview

Tensile breaking strength, often referred to simply as tensile strength, is defined as the maximum tensile stress a packaging material can sustain before it ruptures during a controlled uniaxial pulling test. It is expressed in units of force per unit cross-sectional area, typically megapascals (MPa) or newtons per square millimeter (N/mm²), while breaking force itself is reported in newtons (N) for strip-shaped specimens. For packaging materials, this property directly determines whether a bag, film, laminate, tape, or strap can survive the mechanical stresses of filling, sealing, handling, stacking, vibration, and long-distance transportation without failure.

The test is performed on a universal testing machine (UTM), also called a tensile tester or materials testing machine, which pulls a conditioned specimen between two grips at a constant crosshead speed while continuously recording the force-extension curve. From this curve, key parameters such as tensile strength, yield stress, tensile modulus, and elongation at break are derived. Because packaging materials are predominantly anisotropic, specimens are usually tested in both the machine direction (MD) and the transverse direction (TD), and the results are reported separately.

Testing is governed by well-established international and national standards, including ISO 527-1 and ISO 527-3 for plastics and plastic films, ASTM D882 for thin plastic sheeting and films, ASTM D638 for rigid and semi-rigid plastics, ISO 1924-2 and ISO 1924-3 for paper and board, ASTM D828 and TAPPI T 494 for paper tensile properties, ISO 37 and ASTM D412 for elastomeric materials, GB/T 1040 and GB/T 13022 for plastic films in the Chinese national system, GB/T 12914 for paper and board, and JIS Z 0238 and related JIS methods for flexible packaging in the Japanese system. Accredited third-party laboratories routinely perform these tests for supplier qualification, incoming inspection, and regulatory compliance.

Testing Samples

Plastic Films and Sheets

Flexible polymer films such as LDPE, LLDPE, HDPE, CPP, OPP, BOPP, PET, PA, PVC, EVOH, and PE-based shrink films are the most frequently tested packaging materials. Depending on thickness, films below approximately 1 mm are tested as strip specimens or dumbbell specimens according to ASTM D882, ISO 527-3, GB/T 13022, or JIS K 7127, while thicker sheets are generally tested using the dumbbell geometry of ISO 527-2, ASTM D638, or GB/T 1040.

Paper and Paperboard

Kraft paper, sack paper, corrugating medium, linerboard, white top board, and coated board are tested as rectangular strips according to ISO 1924-2, ISO 1924-3, TAPPI T 494, ASTM D828, or GB/T 12914. In addition to tensile strength and elongation, results for paper are often converted into breaking length, expressed in meters or kilometers, which normalizes the strength value with respect to grammage.

Composite Laminates and Multilayer Structures

Multilayer laminates such as PET/AL/PE, PET/PE, PA/PE, OPP/CPP, and paper/foil/polymer structures used for food and pharmaceutical packaging are tested to evaluate the combined mechanical response of the laminate. Testing frequently includes the delamination or peel behavior of the layers as a complementary evaluation, since laminate failure can occur either by film rupture or by interlayer separation.

Packaging Tapes and Adhesive Tapes

Pressure-sensitive tapes, BOPP sealing tapes, paper tapes, and filament-reinforced tapes are tested for breaking strength and elongation at break according to methods aligned with ASTM D638, ASTM D3759, or relevant JIS and GB tape standards. Backing thickness and total tape thickness are measured before calculating tensile strength.

Strapping and Banding Materials

PET strapping, PP strapping, steel strapping, and composite banding used for palletizing and bundling are tested for breaking force and breaking strength using long strip specimens gripped with specialized fixtures. The results define safe working tension limits for load securing in logistics applications.

Woven Bags, Sacks, and Nonwoven Materials

PP woven sacks, FIBC fabric, jute bags, and nonwoven packaging fabrics are tested in strip form, often including woven seam and stitched joint specimens, to verify both fabric strength and the strength of sewn joints in accordance with ISO 13934-1 or equivalent national standards.

Heat Seals and Sealing Areas

Specimens containing heat-sealed joints from pouches, sachets, and bags are tested in tension to determine whether failure occurs in the seal region or in the base film. This evaluation is closely related to seal strength testing under ASTM F88, and it helps distinguish between film breaking strength and seal integrity.

Testing Items

A full tensile evaluation of packaging materials typically includes the following measured and calculated parameters:

• Tensile strength (breaking strength), reported in MPa or N/mm², calculated as the maximum force divided by the original cross-sectional area of the specimen.
• Breaking force, reported in N, representing the peak load sustained by a strip or strap specimen of defined width.
• Elongation at break, expressed as a percentage of the original gauge length at the moment of rupture.
• Tensile stress at yield, the stress at which the material continues to elongate without a proportional increase in load.
• Tensile modulus, also called Young's modulus or elastic modulus, defined as the slope of the initial linear region of the stress-strain curve, or as a secant modulus between two defined strain points.
• Breaking strength of seams, stitches, and heat seals, reported as force per unit width or per stitch.
• Breaking length for paper grades, expressed in meters, calculated from tensile strength and grammage.
• Statistical descriptors of the dataset, including mean value, standard deviation, and coefficient of variation for each direction tested.

Testing Methods

Specimen Preparation

Specimens must be cut cleanly and free of nicks, burrs, wrinkles, and edge damage, because any defect at the edge acts as a stress concentrator and produces artificially low results. Plastic films are typically cut into rectangular strips 10 mm to 25 mm wide with a minimum gauge length of 50 mm to 100 mm, or into ISO 527 dumbbell shapes using a calibrated cutting die. Paper strips are usually 15 mm wide with a test span of 100 mm or 180 mm depending on the standard applied. At least five valid specimens per direction are required, and ten or more are recommended when results show high scatter.

Conditioning

Prior to testing, plastic specimens are conditioned under standard laboratory atmosphere at 23 ± 2 °C and 50 ± 10 % relative humidity for a minimum of 40 hours in accordance with ISO 291 or ASTM D618. Paper and board specimens are conditioned at 23 ± 1 °C and 50 ± 2 % relative humidity according to ISO 187 before testing. The actual conditioning state must be reported together with the results, since temperature and humidity strongly influence the tensile behavior of both polymers and cellulose-based materials.

Instrumentation and Test Setup

Testing is conducted on a calibrated universal testing machine equipped with a suitable load cell selected so that the breaking force falls within 15 % to 85 % of the cell capacity for optimal accuracy. Pneumatic or mechanical grips, often with rubber-faced or serrated inserts, must hold the specimen without slippage or premature jaw breaks. An extensometer or the crosshead displacement, corrected for system compliance, is used to measure strain, and the crosshead speed is selected from the standard, commonly 50 mm/min, 100 mm/min, 200 mm/min, or 300 mm/min depending on the material and the applicable standard.

Test Procedure

Measure and record specimen width and thickness at several points using calibrated instruments, then mount the specimen in the grips with the specified gauge length and apply a slight preload to remove slack. Start the test and record the force-extension curve continuously until specimen rupture. Verify that failure occurred within the gauge region between the grips; specimens that fail at the jaw line are normally rejected and retested. Repeat the procedure for all specimens in both the machine direction and the transverse direction.

Calculation of Results

Tensile strength is calculated as the maximum force recorded during the test divided by the original minimum cross-sectional area of the specimen, that is, sigma equals Fmax divided by the product of width and thickness, and is expressed in MPa. Elongation at break is calculated as the increase in gauge length at rupture divided by the original gauge length, multiplied by 100. Breaking length for paper is obtained by dividing the tensile strength by the grammage and by gravitational acceleration. For each direction, the arithmetic mean, standard deviation, and coefficient of variation of the valid results are computed and reported.

Test Report

A complete test report identifies the material and its structure, the sampling plan, the applicable standard, specimen geometry and number, conditioning atmosphere, grip type and gauge length, crosshead speed, load cell capacity, individual and mean values of all calculated parameters, failure mode and location, and the identification of the testing laboratory and test date.

Applications

Tensile breaking strength testing of packaging materials supports a wide range of industrial and regulatory applications:

• Quality control and incoming inspection of films, papers, laminates, and straps purchased from suppliers.
• Food and beverage packaging validation, including pouches, sachets, bags, and barrier laminates that must survive vacuum, hot filling, retort sterilization, and drop impacts.
• Pharmaceutical packaging qualification for blister foils, laminate sachets, and sterile barrier systems where mechanical integrity is linked to patient safety and regulatory compliance.
• E-commerce and transport packaging development, ensuring mailers, cushioning films, and stretch wrap withstand automated sorting, stacking, and vibration during distribution.
• Palletizing and load securing, where strapping breaking strength defines safe tension limits for cargo restraint.
• Material research and development, including formulation comparison, thickness reduction studies, recycled content evaluation, and shelf-life aging assessment.
• Failure analysis of packaging that ruptured in service, providing objective data for root cause investigation and corrective action.
• Compliance demonstration for customer specifications, purchasing agreements, and certification programs verified by accredited third-party laboratories.

FAQ

What is the difference between tensile strength and breaking strength?

Tensile strength is the maximum stress, in force per unit area, sustained before rupture, while breaking strength is a broader term that may refer either to that same stress value or simply to the maximum breaking force in newtons, depending on the standard and material. For strip specimens of films and straps, many specifications quote breaking force per unit width rather than stress, so the terminology of the applicable standard should always be followed.

Why must specimens be tested in both machine direction and transverse direction?

Manufacturing processes such as film extrusion, orientation, calendering, and papermaking align polymer chains and fibers, producing pronounced anisotropy. Machine direction strength can be substantially higher or lower than transverse direction strength, and packaging performance depends on both, so standards require separate reporting for each direction.

Which standard should be selected for a given packaging material?

Thin plastic films below about 1 mm are best tested to ASTM D882, ISO 527-3, GB/T 13022, or JIS K 7127, while thicker plastic sheets use dumbbell specimens to ISO 527-2, ASTM D638, or GB/T 1040. Paper and paperboard are tested to ISO 1924-2, TAPPI T 494, ASTM D828, or GB/T 12914, elastomeric films to ISO 37 or ASTM D412, and seal areas to ASTM F88. Customer specifications usually nominate the exact method.

How many specimens are required for a valid test?

Most standards require a minimum of five valid specimens per direction, and if any specimen fails at the grips or shows anomalous behavior, additional specimens must be tested. Ten specimens per direction are recommended when the material is heterogeneous or the coefficient of variation is high.

What load cell capacity is appropriate?

The load cell should be selected so the expected breaking force lies between roughly 15 % and 85 % of its full-scale capacity. Common laboratory configurations use interchangeable 50 N, 100 N, 500 N, 1 kN, and 5 kN cells to cover the range from thin films to heavy strapping and woven fabrics.

Why did the specimen break at the grips, and what should be done?

Jaw breaks occur when grip pressure, serration, or edge damage creates local stress concentration. Remedies include using gentler grip faces or pneumatic pressure, lining the grips with a compliant material, slightly loosening clamping force, improving specimen cutting quality, or switching to dumbbell specimens with widened shoulders.

Can test results from different standards be compared directly?

Only with caution. Differences in specimen geometry, gauge length, crosshead speed, conditioning, and strain measurement can shift results measurably, so comparisons should be made within a single standard, or conversion studies should be performed. Reports should always state the exact method used.

How often should tensile testing be performed?

Frequency depends on the quality plan: incoming batches are commonly tested per lot, production lines are monitored on a scheduled basis such as hourly or per shift, and full characterization is performed during supplier qualification, design changes, or when process deviations occur. Universal testing machines must also be verified and calibrated at defined intervals with traceable reference standards.