Impact Resistance Testing of Rigid Pharmaceutical Sheets for Solid Drug Packaging

Rigid pharmaceutical sheets—PVC, PVDC-coated, and multilayer composite materials used to form blister packs for tablets and capsules—must withstand mechanical shocks during thermoforming, filling, sealing, and distribution. Impact resistance (impact strength) testing quantifies the dynamic energy a sheet can absorb before cracking, puncturing, or breaking, and is a core quality-control requirement under standards such as ASTM D1709, ISO 7765-1, GB/T 9639, and the YBB monographs for pharmaceutical packaging materials. This article explains the test principle, applicable sample types, testing items, methods, acceptance criteria, and typical applications in pharmaceutical packaging quality control.

Technical Overview

Rigid pharmaceutical sheets are calendared or extruded polymer sheets, generally between 0.20 mm and 0.60 mm thick, that serve as the forming web of blister and strip packages for solid dosage forms such as tablets, capsules, and pills. Typical materials include unplasticized rigid PVC, PVC coated or co-extruded with PVDC for enhanced moisture barrier, PVC/LDPE laminates, polypropylene (PP), and PA/Al/PVC multilayer composites used for high-barrier "tropical" blister packaging.

Impact resistance describes the ability of a sheet to absorb a dynamic, concentrated load without cracking, splitting, or puncturing. Throughout the packaging life cycle, the sheet is exposed to shocks from web transport, thermoforming, heat sealing, die-cutting, cartoning, and vibration or drops during logistics. Even a small crack or pinhole compromises the moisture, oxygen, and contamination barrier, potentially degrading the drug product and causing dose loss or leakage. Impact strength testing therefore provides a direct, quantitative measure of package robustness and patient safety.

The basic test principle is straightforward: a circular specimen is clamped over a defined aperture, and a dart or hardened steel ball is allowed to fall freely from a controlled height onto the center of the specimen. Whether the specimen fails or survives each impact is recorded. Statistical procedures then determine the mass or energy at which 50% of specimens fail, or a simple pass/fail verdict is issued according to the requirements of the applicable pharmacopoeial monograph.

Governing references include ASTM D1709 (free-falling dart method, Methods A and B), ISO 7765-1 (staircase method), ISO 7765-2 (instrumented falling dart), GB/T 9639 (the corresponding Chinese national standard), ASTM D3763 and ISO 6603-2 (instrumented high-speed puncture impact), and the YBB monographs for pharmaceutical packaging materials, which specify ball-drop impact requirements for rigid sheets such as PVC sheets for solid pharmaceutical use.

Testing Samples

Rigid PVC Sheets for Solid Pharmaceutical Packaging

Unplasticized PVC rigid sheet is the most widely used forming material for standard blister packs. It offers good thermoformability, transparency, and stiffness, but its impact behavior is sensitive to thickness, residual stress from calendaring, and storage temperature, making routine impact verification essential.

PVDC-Coated and PVC/PVDC Composite Sheets

These structures add a polyvinylidene chloride layer to improve water-vapor and oxygen barrier performance. Because the coating is thin and brittle relative to the PVC substrate, impact testing verifies that coating cracks or delamination do not occur under handling shocks, which would otherwise destroy the barrier function.

PA/Al/PVC Composite Sheets for High-Barrier Blisters

Nylon/aluminum/PVC laminates used for tropical or moisture-sensitive products combine a ductile polymer with a foil layer. Impact testing evaluates whether the laminate punctures, the foil cracks, or the layers separate when struck, and helps confirm that forming and handling do not create micro-fractures in the barrier layers.

PVC/LDPE and Other Multilayer Laminates

Laminates designed for enhanced cold-forming behavior or sealing performance are tested to confirm that the additional interfaces do not introduce weak planes. Failure mode analysis distinguishes cohesive fracture within a layer from adhesive delamination between layers.

Polypropylene (PP) and Other Polymer Rigid Sheets

PP sheets and other specialty polymers used for high-temperature sterilization or specific drug compatibility are evaluated with the same impact principles, with acceptance levels adjusted to the material's ductility and the intended application.

Testing Items

Impact-related testing of rigid pharmaceutical sheets typically includes the following items, tailored to the applicable standard and the customer's specification:

• Free-falling dart impact failure mass (F50) determined by the staircase method, reported in grams.
• Ball-drop pass/fail impact resistance according to YBB monograph requirements.
• Impact failure energy in joules, calculated from the falling mass, drop height, and gravitational acceleration.
• Instrumented puncture impact data: peak force, force at yield, energy to peak, and total failure energy.
• Failure mode classification: brittle fracture, ductile puncture, tearing, or interlayer delamination.
• Directional comparison of impact performance in machine direction (MD) versus transverse direction (TD).
• Testing of as-received specimens versus conditioned or aged specimens to assess long-term durability.

Testing Methods

Free-Falling Dart Method (ASTM D1709 / ISO 7765-1 / GB/T 9639)

The specimen is clamped in an annular holder with a 127 mm circular opening. In Method A, a dart with a 38.1 mm diameter hemispherical head falls from a height of 660 mm; in Method B, a larger 50.8 mm dart head falls from 1520 mm, which is suitable for tougher sheet structures. Using the staircase (Bruceton) procedure, the dart mass is increased after each failure and decreased after each non-failure. After a statistically valid number of impacts, typically at least twenty following the first failure, the 50% failure mass F50 is calculated and reported in grams, and may be converted into impact energy using the drop height.

Falling Ball Impact Test per YBB Monographs

Pharmacopoeial monographs for rigid pharmaceutical sheets, such as the monograph for PVC rigid sheets for solid pharmaceutical packaging, prescribe a pass/fail ball-drop procedure. Specimens are clamped over a circular aperture, and a hardened steel ball of the specified mass is released from the specified height so that it strikes the center of the specimen. The designated number of specimens is tested, and the sheet conforms only if none of them exhibits a crack, hole, or breakage. Specimens are inspected under good lighting, since fine cracks at the impact point or on the reverse side constitute failure.

Instrumented High-Speed Puncture Impact (ASTM D3763 / ISO 6603-2)

Instrumented testing uses a force sensor behind the striker to record the complete force-displacement curve during a single high-speed impact. This yields peak force, energy to peak, and total absorbed energy, and clearly distinguishes brittle from ductile behavior. It is particularly valuable during packaging development for comparing candidate laminate structures, thickness reduction options, or changes in raw material grades.

Specimen Preparation and Conditioning

Specimens must be flat, free of creases, wrinkles, pinholes, and visible defects, and cut larger than the clamping aperture. Unless otherwise specified, specimens are conditioned at 23 ± 2 °C and 50 ± 5% relative humidity for at least 40 hours in accordance with ISO 291 or ASTM D618, and testing is performed in the same environment. Machine direction and coating orientation are marked before cutting so that results can be traced to material direction.

Result Interpretation and Acceptance Criteria

For pharmacopoeial ball-drop testing, acceptance is binary: the specified number of specimens must all survive without cracking. For dart methods, acceptance is based on the F50 value meeting or exceeding the agreed specification between supplier and pharmaceutical customer. The coefficient of variation across replicates is reviewed to confirm test validity, and retesting rules follow the governing standard or monograph.

Applications

• Incoming material inspection and supplier qualification by pharmaceutical manufacturers before releasing sheet stock to blister packaging lines.
• Batch-release quality control by sheet extruders and converters to demonstrate conformity with monograph and customer specifications.
• Packaging development programs comparing laminate designs, barrier coatings, and down-gauging scenarios without sacrificing impact safety.
• Regulatory registration dossiers and drug master file submissions, where impact data support the suitability of the primary packaging material.
• Failure analysis of cracked or punctured blisters from production deviations, transport incidents, or market complaints.
• Supporting stability studies and distribution simulation, linking material impact performance with whole-package transport robustness.
• Validation of thermoforming process windows, ensuring that forming conditions do not embrittle or over-stress the sheet.

FAQ

Why is impact resistance so important for pharmaceutical rigid sheets?

The blister cavity is the primary barrier protecting the dose. A crack or pinhole in the forming sheet allows moisture, oxygen, and contaminants to reach the drug, which can reduce shelf life and compromise patient safety. Impact testing predicts whether the sheet will survive the shocks of production, filling, and distribution.

Which standards govern impact testing of rigid pharmaceutical sheets?

The principal methods are ASTM D1709, ISO 7765-1, and GB/T 9639 for free-falling dart testing; ASTM D3763 and ISO 6603-2 for instrumented puncture impact; and the YBB pharmacopoeial monographs, which define ball-drop impact requirements for rigid pharmaceutical sheets in the Chinese market.

How is failure defined during the test?

Failure is any through-thickness crack, hole, or tear at or around the impact point, or visible delamination that breaches the structure. Slight surface whitening or indentation without loss of integrity is generally not considered failure, but monograph wording takes precedence.

How many specimens are tested?

Staircase dart methods require a statistically sufficient series, typically at least twenty impacts after the first failure, to calculate F50. Pharmacopoeial ball-drop methods specify a fixed number of specimens, commonly ten, all of which must pass for the sheet to conform.

Do temperature and humidity affect the results?

Yes. Rigid PVC and many laminates become measurably more brittle at low temperature, and moisture can plasticize certain layers. Standard conditioning at 23 °C and 50% relative humidity ensures reproducible, comparable data; testing at additional conditions may be specified for products distributed in extreme climates.

Can finished blister packs be tested for impact resistance?

Sheet-level impact tests address the raw material. Finished packs are more commonly evaluated through whole-package drop and transport simulation protocols, and the two approaches complement each other: material impact data qualify the sheet, while package-level testing verifies the complete design in distribution-like conditions. Accredited third-party laboratories routinely perform both types of evaluation.