Determination of Barrier Properties of Rigid Pharmaceutical Sheets for Solid Dosage Forms

Determination of the barrier properties of rigid pharmaceutical sheets is essential for verifying that blister packaging materials effectively protect tablets, capsules, and other solid dosage forms from moisture and oxygen throughout their shelf life. This article provides a professional overview of the testing samples, testing items, and standardized methods—such as water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) measurement—used to evaluate the barrier performance of rigid sheets for solid pharmaceutical packaging.

Technical Overview

Rigid sheets, also known as hard films or forming webs, are thermoplastic sheets—typically 0.15 mm to 0.60 mm thick—used to thermoform the cavities of blister packs for solid oral dosage forms such as tablets and capsules. Common materials include unplasticized PVC, polypropylene (PP), polyethylene (PE), and multilayer structures enhanced with high-barrier coatings such as PVDC (polyvinylidene chloride) or barrier laminates such as PCTFE (polychlorotrifluoroethylene).

Because most drug products are sensitive to water vapor and oxygen, permeation can trigger hydrolysis, oxidation, loss of potency, changes in dissolution behavior, and other physicochemical degradation. The barrier capability of the forming web is therefore a critical quality attribute that directly affects product stability and shelf life. Barrier performance is quantified primarily as the water vapor transmission rate (WVTR) and the oxygen transmission rate (OTR), and results are compared against product specifications, pharmacopoeial requirements, and stability data. Testing is typically carried out in accredited third-party laboratories or qualified in-house QC laboratories using permeation analyzers operated in accordance with recognized GB/T, ISO, and ASTM standards.

Testing Samples

Samples should be representative of commercial production, taken from areas free of wrinkles, pinholes, scratches, and visible defects. Prior to testing, specimens are normally conditioned in a standard laboratory atmosphere, for example 23 °C ± 2 °C and 50% ± 5% relative humidity as specified in GB/T 2918, for a sufficient period to reach equilibrium.

PVC Rigid Sheets

Unplasticized PVC is the most widely used forming web for pharmaceutical blisters. It offers excellent thermoformability, high transparency, good stiffness, and reliable heat-sealing behavior with lidding foils. Its moisture and oxygen barrier performance is moderate, which makes it the reference material against which coated and laminated alternatives are compared.

PVDC-Coated PVC Rigid Sheets

PVC sheets coated on one or both sides with PVDC at coating weights commonly ranging from 40 g/m² to 120 g/m² provide substantially improved resistance to both water vapor and oxygen. These sheets are widely selected for moisture- and oxygen-sensitive preparations. Because coating weight and coating uniformity strongly influence the measured transmission rates, careful specimen preparation and leak-tight sealing are essential for accurate results.

Polypropylene and Polyethylene Rigid Sheets

PP-based rigid sheets deliver a significantly better moisture barrier than PVC and are used for moisture-sensitive products. PE layers, whether as coextruded components or laminated structures, improve heat-sealing compatibility and chemical resistance. These materials are often tested to confirm their suitability for products requiring enhanced protection against water vapor.

Multilayer and Laminated Rigid Sheets

Engineered structures such as PVC/PE, PVC/PVDC/PE, and PVC/PCTFE laminates combine thermoformability with high barrier performance for highly sensitive molecules. Since each functional layer contributes to the overall permeation behavior, the laminate is tested as a complete system, in the same configuration in which it will be used on the packaging line.

Testing Items

The barrier evaluation of rigid pharmaceutical sheets centers on the following quantitative indices:

• Water vapor transmission rate (WVTR), expressed in g/(m²·24 h), determined under specified temperature and humidity conditions such as 38 °C/90% RH or 23 °C/85% RH.
• Oxygen transmission rate (OTR), expressed in cm³/(m²·24 h), commonly normalized to a defined oxygen partial pressure (e.g., 0.1 MPa or 1 atm) and determined at 23 °C under dry or humid conditions.
• Where required, gas permeability of other gases (such as nitrogen, carbon dioxide, or air) determined by the differential-pressure method.
• Supporting determinations, including sheet thickness measurement, coating weight verification, and pinhole or appearance inspection, which assist in the interpretation of barrier data.

Testing Methods

Water Vapor Transmission Rate Determination

• Cup (gravimetric) method per GB/T 1037, ASTM E96/E96M, and ISO 2528: the specimen is sealed over a dish containing desiccant or water, and the weight change is tracked gravimetrically until a steady state is reached. This method is simple and widely used for conventional barrier materials.
• Infrared sensor method per GB/T 26253, ASTM F1249, and ISO 15106-2: water vapor permeating through the specimen is carried by a dry gas stream to an infrared detector. The method offers high sensitivity and short test cycles and is particularly suitable for low-transmission materials such as PVDC-coated and PCTFE laminated sheets.
• Electrolytic (coulometric) sensor method per ISO 15106-3 and relative humidity sensor method per ISO 15106-1: alternative sensor-based techniques providing high sensitivity across a broad range of transmission rates.

Testing is commonly performed at 38 °C/90% RH to simulate tropical or accelerated storage conditions, or at 23 °C/85% RH for long-term storage conditions. At least three valid specimens are usually tested, and the arithmetic mean is reported together with the test conditions.

Oxygen Transmission Rate Determination

• Coulometric sensor (equal-pressure) method per GB/T 21529, ASTM D3985, and ISO 15105-2: oxygen permeating through the specimen is transported by a nitrogen carrier gas to a coulometric sensor, where it is reduced and quantified. Humidity conditions (e.g., 0% RH or 90% RH) can be controlled on both sides of the specimen, making the method well suited to humidity-sensitive, high-barrier materials.
• Differential-pressure (manometric) method per GB/T 1038, ASTM D1434, and ISO 15105-1: one side of the specimen is evacuated while the other is exposed to the test gas at a defined pressure, and permeability is calculated from the pressure increase over time. The method requires no carrier gas and can be extended to gases other than oxygen.

In both methods, specimens must be mounted flat and crease-free, sealed leak-tight with vacuum grease or wax, and verified for the absence of pinholes. Reports should state the material, thickness, test temperature and humidity, and the transmission rate with units.

Applications

• Incoming material control by pharmaceutical manufacturers and qualification of blister packaging lines.
• Batch release testing and periodic quality verification for rigid sheet producers.
• Packaging selection and shelf-life studies supporting product development and stability programs.
• Regulatory registration dossiers demonstrating conformity of packaging materials with pharmacopoeial and national packaging standards.
• Research and development benchmarking of new resins, coatings, and coextruded or laminated structures.
• Failure investigation of moisture- or oxygen-related product degradation and complaint analysis.

FAQ

What are typical barrier values for rigid pharmaceutical sheets?

Indicative values for WVTR at 38 °C/90% RH are approximately 2 to 4 g/(m²·24 h) for uncoated PVC, below about 0.9 g/(m²·24 h) for PVC with a 40 g/m² PVDC coating, and below about 0.5 g/(m²·24 h) for a 90 g/m² coating. Indicative OTR values at 23 °C are roughly 10 to 20 cm³/(m²·24 h) for PVC and below 2 cm³/(m²·24 h) for well-coated or laminated structures. Actual values vary with thickness, formulation, and test conditions, and must always be confirmed against the material specification.

Why are WVTR and OTR tested under different conditions?

Condition selection simulates the storage environment relevant to the product. Elevated temperature and humidity, such as 38 °C/90% RH, accelerate permeation and provide a worst-case assessment, while 23 °C conditions reflect long-term storage. Oxygen testing may be performed under dry or humid conditions because the permeability of many polymers changes significantly with humidity.

Which method should be selected for high-barrier sheets?

Sensor-based techniques—the infrared sensor method for WVTR and the coulometric sensor method for OTR—provide the sensitivity and lower detection limits needed for PVDC-coated and PCTFE laminated sheets. The gravimetric cup method and the differential-pressure method remain reliable options for conventional and medium-barrier materials.

Can barrier test results predict product shelf life?

Transmission rate data are a key input, but shelf-life prediction also requires the blister cavity geometry, dose, headspace volume, desiccant use, and the sensitivity of the active ingredient. Permeation modeling based on WVTR and OTR results should be confirmed through formal stability studies on the packaged product.