Determination of Tensile Failure Load of Packaging Materials: Principles, Methods, and Standards

The tensile failure load of packaging materials is a critical mechanical property that determines whether films, laminates, paperboard, and seals can withstand the stresses of manufacturing, filling, transport, and storage. Accurate determination of this parameter, in accordance with internationally recognized standards such as ISO 527, ASTM D882, and GB/T 1040, helps manufacturers validate material quality, optimize package design, and prevent costly product loss. This article provides a comprehensive technical guide to the principles, sample requirements, test procedures, and applications of tensile failure load testing for packaging materials.

Technical Overview

Tensile failure load, also referred to as maximum tensile force or breaking force, is the highest force a packaging material can sustain before it ruptures when stretched under controlled conditions. It is one of the most fundamental mechanical indicators used to evaluate the load-bearing capacity, durability, and structural integrity of packaging materials throughout their service life.

During distribution, packaging materials are subjected to repeated tensile stresses from machine conveying, filling operations, stacking, vibration, and handling. If the tensile failure load of a film, laminate, seal, or strap is insufficient, the package may split, delaminate, or burst, resulting in product contamination, spillage, and economic loss. Determining the tensile failure load therefore provides essential data for quality control, incoming material inspection, supplier comparison, and package design validation.

The test is typically performed on a universal testing machine (UTM), in which a specimen of defined dimensions is clamped between two grips and stretched at a constant crosshead speed until failure. The force-displacement curve recorded during the test yields the maximum force (failure load), as well as secondary parameters such as tensile strength, elongation at break, and elastic modulus. Testing must be conducted under standardized temperature and humidity conditions, since polymeric and cellulosic packaging materials are sensitive to environmental conditioning.

Testing Samples

Plastic Films and Sheets

Flexible plastic films made of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyamide (PA), polyvinyl chloride (PVC), and oriented films such as BOPP and BOPET are the most commonly tested packaging materials. Thin films below 1 mm in thickness are tested as strips in accordance with ISO 527-3 or ASTM D882, while thicker sheets are tested as dumbbell-shaped specimens under ISO 527-2 or ASTM D638. Both machine direction (MD) and transverse direction (TD) specimens are required, since oriented films exhibit pronounced anisotropy.

Flexible Laminates and Multilayer Structures

Multilayer laminates combining aluminum foil, metallized films, barrier coatings, and adhesive layers are tested to evaluate overall breaking force as well as interlayer bonding. Composite structures used for food pouches, pharmaceutical blister lidding, and stand-up bags must demonstrate adequate tensile failure load to survive drop impact, top-load compression, and vacuum or gas-flush filling processes.

Paper and Paperboard

Kraft paper, corrugated medium, linerboard, coated paperboard, and paper-based flexible packaging are tested under ISO 1924-2 or ASTM D828. Because paper is highly hygroscopic, specimens must be conditioned at standard atmospheres, typically 23 °C and 50% relative humidity, before testing to ensure reproducible results.

Seals, Seams, and Welded Joints

Heat-sealed and adhesive-bonded joints of flexible packages are tested for seal strength in accordance with ASTM F88 or GB/T 8808-related procedures. The failure load of a seal indicates whether package closure integrity can be maintained under internal pressure and external mechanical stress, and the failure mode (adhesive, cohesive, or material fracture) provides diagnostic information about sealing parameters.

Strapping, Tapes, and Wrapping Materials

Plastic strapping bands (PET, PP), pressure-sensitive adhesive tapes, stretch films, and shrink films are tested to verify their ability to unitize pallet loads and secure heavy products. The tensile failure load and elongation behavior of these materials directly affect load stability during transportation.

Testing Items

Tensile failure load determination typically forms the core of a broader mechanical characterization program for packaging materials. The principal measurands include:

• Tensile failure load (maximum force at rupture, expressed in newtons, N)
• Tensile strength (maximum stress, expressed in megapascals, MPa, calculated from the specimen cross-section)
• Elongation at break (percentage extension at the moment of rupture)
• Tensile elastic modulus (slope of the initial linear region of the stress-strain curve)
• Yield strength and yield elongation for ductile films
• Seal strength of heat seals and peel force of easy-open structures
• Bond or peel strength of laminated layers
• Force at break of strapping and sealing tapes
• Breaking length for paper and paperboard materials

Each parameter complements the failure load value: for example, a film with a high failure load but very low elongation may be strong yet brittle, while a highly extensible film with moderate failure load may absorb impact energy more effectively. A complete interpretation requires reviewing the entire force-displacement curve rather than a single data point.

Testing Methods

Specimen Preparation and Conditioning

Specimens are cut from representative samples of the packaging material free from visible defects, wrinkles, or creases. For film testing, rectangular strips are commonly 10 to 25 mm wide with a gauge length of 50 to 100 mm, or 180 mm as specified in ASTM D882. At least five valid specimens are tested in each principal direction, and more if results show high scatter. Sharp, burr-free cutting dies or blades must be used to avoid stress concentrations that cause premature failure. Unless otherwise specified, specimens are conditioned at 23 ± 2 °C and 50 ± 10% relative humidity for a minimum of 24 hours prior to testing, in line with ISO 291 or ASTM D618.

Instrumentation and Test Setup

Testing is conducted on a calibrated universal testing machine fitted with an appropriate load cell selected so that the anticipated failure force falls within the calibrated range, ideally between 20% and 80% of full scale. Grip selection is critical for packaging films: pneumatic side-action grips with rubber-faced jaws prevent slippage without introducing jaw breaks, while extended travel capabilities are necessary for highly extensible films such as stretch wrap and LDPE.

Test Procedure

The specimen is mounted centrally in the grips with the gauge length verified, preload is applied to remove slack, and the crosshead is driven at the constant speed specified by the governing standard. Typical test speeds range from 5 mm/min for rigid sheets to 200 to 500 mm/min for thin films and strapping. The machine continuously records force and extension until the specimen ruptures, and the software identifies the maximum force as the tensile failure load. Invalid results, such as failures occurring within the grips or at pre-existing flaws, are discarded and retested.

Governing Standards

The most widely applied test standards for tensile failure load determination of packaging materials include:

• ISO 527-1 / ISO 527-3: Determination of tensile properties of plastics, including films and sheets
• ASTM D882: Standard test method for tensile properties of thin plastic sheeting
• ASTM D638: Standard test method for tensile properties of plastics
• ASTM D828: Standard test method for tensile properties of paper and paperboard
• ISO 1924-2: Paper and board — Determination of tensile properties
• ASTM F88 / ISO 11607-related methods: Seal strength of flexible barrier materials
• GB/T 1040.3 and GB/T 12914: Chinese national standards corresponding to ISO 527-3 and ISO 1924-2
• ASTM D3953 or related procedures for strapping and load-securing materials

Data Processing and Reporting

For each specimen direction, the arithmetic mean and standard deviation of the tensile failure load are calculated, along with elongation at break and, where required, tensile strength. The test report should document the material identification, specimen dimensions, number of specimens, conditioning atmosphere, test speed, gauge length, grip type, individual and mean results, failure modes, and the specific standard applied. This level of traceability ensures that results are comparable between laboratories and across production batches.

Applications

Tensile failure load data supports a wide range of engineering and commercial decisions across the packaging industry:

• Incoming material inspection and supplier qualification for films, foils, and laminates
• Quality control during film extrusion, orientation, lamination, and printing processes
• Optimization of heat-sealing parameters such as temperature, dwell time, and pressure
• Verification of downgauging initiatives, where thinner materials must still meet strength targets
• Validation of packaging performance for food, pharmaceutical, medical device, and industrial products
• Compliance demonstration for regulatory submissions and customer specifications
• Failure analysis of package ruptures, splits, and delamination observed in the field
• Comparative evaluation of recycled-content and bio-based materials against conventional materials
• Shelf-life and aging studies, where tensile properties are tracked after exposure to heat, humidity, and sterilization

Accredited third-party laboratories routinely perform these determinations to provide impartial test reports that are accepted by brand owners, retailers, and regulatory authorities worldwide.

FAQ

What is the difference between tensile failure load and tensile strength?

Tensile failure load is the absolute maximum force, in newtons, at which the specimen ruptures. Tensile strength is the maximum stress, in megapascals, obtained by dividing the failure load by the original cross-sectional area of the specimen. Failure load is convenient for direct comparison of specimens with identical geometry, while strength allows comparison between materials of different thicknesses.

Why must films be tested in both machine and transverse directions?

Manufacturing processes such as blown-film extrusion and biaxial orientation align polymer chains, producing directional differences in mechanical properties. A film may be strong in one direction yet weak in the perpendicular direction, so both orientations must be evaluated to guarantee package performance under multi-axial stress.

What causes invalid results such as jaw breaks?

Jaw breaks occur when the specimen fails at or inside the grips rather than within the gauge length, typically due to excessive clamping pressure, jaw slippage, sharp jaw edges, or misalignment. Such results are not representative of the material and must be excluded, with additional specimens tested to obtain the required number of valid measurements.

How does conditioning affect tensile test results?

Paper, paperboard, and many polymers absorb or desorb moisture, which plasticizes the material and alters both strength and ductility. Testing without standardized conditioning produces results that cannot be compared between laboratories, which is why ISO 291, ASTM D618, and the individual test standards specify the atmosphere and conditioning duration.

Which test speed should be selected?

The test speed is dictated by the governing standard and the material behavior. Thin flexible films are commonly tested at 200 to 500 mm/min per ASTM D882, plastics at 1 to 500 mm/min per ISO 527 depending on specimen type, and paper at 20 mm/min per ISO 1924-2. Deviating from the specified speed changes the measured failure load, since polymers exhibit rate-dependent viscoelastic behavior.

How many specimens are required for a valid determination?

Most standards require a minimum of five valid specimens per direction. If the coefficient of variation exceeds the limit stated in the standard, or if invalid failures occur, additional specimens should be tested and the statistical outliers evaluated using the criteria defined in the method before reporting the mean value.