Vapour Permeability in the Ionomers Industry

Uses and Applications

Ionomers, a class of polymers containing ionic groups, are widely used in industries where moisture control, chemical resistance and mechanical durability are critical. An ionomer is a type of polymer that contains a small proportion of ionised groups (typically carboxylic or sulfonic acid groups) distributed along its backbone. These ionic groups are neutralised with metal cations (e.g., sodium, zinc), forming ionic crosslinks between polymer chains. This structure gives ionomers a unique combination of mechanical strength, flexibility, and toughness.

 Primary Characteristics of Ionomers:

• Thermoplastic behaviour (can be melted and reshaped)
• High impact resistance
• Transparency and clarity (depending on formulation)
• Scratch and abrasion resistance
• Good adhesion to polar surfaces
• Moisture sensitivity due to ionic content
• Moderate barrier properties, including vapour permeability control

The most well-known ionomer is Surlyn® by DuPont, often used in packaging and sporting goods.

Applications of Ionomers

• Packaging and Barrier Films – Used in food packaging, ionomers provide moisture control to extend shelf life and prevent spoilage. Their vapour permeability must be carefully managed to balance protection and breathability.
• Medical and Pharmaceutical Applications – Ionomers are used in drug delivery systems, sterile medical packaging and breathable wound dressings, where controlled vapour transmission is essential for maintaining sterility and product stability.
• Sports Equipment – Golf balls and other sporting goods incorporate ionomers for durability and moisture resistance, ensuring performance consistency in varying environmental conditions.
• Adhesives and Coatings – Ionomers are used in high-performance adhesives and coatings, where vapour permeability impacts bonding strength and long-term durability.
• Fuel Cells and Energy Storage – In proton exchange membranes for fuel cells, vapour permeability affects water transport, efficiency and overall performance.
• Construction Materials – Ionomer-based coatings and films are used in building materials for weather resistance and controlled moisture transmission to prevent condensation and degradation.

Vapour Permeability in Ionomers

Vapour permeability in ionomers is a significant factor, particularly because:

• Their ionic groups attract moisture, increasing water uptake compared to purely non-polar plastics.
• The permeability to water vapour varies based on:
• Degree of neutralisation
• Type of counter-ion (Na⁺, Zn²⁺, etc.)
• Film thickness and crystallinity
• Blending or co-extrusion with other materials
  

Problems with Vapour Permeability in Ionomers

• Excess Moisture Transmission – If permeability is too high, ionomer films and membranes can allow excessive moisture passage, leading to reduced effectiveness in packaging, fuel cells or medical applications.
• Insufficient Vapour Transmission – If too low, trapped moisture can cause degradation, bacterial growth, or compromised structural integrity in various applications.
• Environmental and Regulatory Challenges – Maintaining the right balance of vapour permeability while meeting industry regulations for food safety, pharmaceuticals and energy efficiency can be complex.
• Material Degradation – Improper permeability can lead to hydrolytic degradation, reducing the lifespan and performance of ionomer-based products.

Standards

Vapour permeability is a critical property in assessing how materials, including ionomers, allow moisture transmission. Several standardized test methods are employed to evaluate this characteristic, ensuring consistency and reliability across various applications. Key standards relevant to vapour permeability measurement include:​

• ISO 9932: This international standard specifies a method for determining the water vapour transmission rate of flexible barrier materials using an infrared detection technique. It is commonly used alongside ASTM F1249 for comprehensive analysis.​
• ASTM F1249: This standard outlines a procedure for determining the rate of water vapour transmission through flexible barrier materials. It is applicable to sheets and films up to 3 mm in thickness, including single or multilayer synthetic or natural polymers and foils, as well as coated materials. The method provides measurements for water vapour transmission rate (WVTR), and permeability. ​
• ASTM E96: This test method covers the deterination of water vapour transmission for materials where moisture passage is significant, such as paper, plastic films and other sheet materials. It describes two techniques: the desiccant method and the water method, both assessing the rate of water vapour movement through a sample under controlled conditions.
• DIN 53122: This German standard outlines methods for measuring water vapour permeability in materials. Part 2 of the standard describes the electrolysis method, suitable for detecting low permeation rates, with a detection limit of 0.001 g/m² per day.

These standards provide structured methodologies for assessing vapour permeability, facilitating quality control and material selection in industries utilizing ionomers. Adherence to these standards ensures that materials meet specific performance criteria related to moisture transmission, which is vital for applications such as packaging, medical devices and coatings.

Ionomers vs Other Polymers

Ionomers are exceptionally good at sealing through contamination compared to many other plastics. This is due to their:

• Ionic interactions, which help maintain contact and bonding even with slight interference.
• Soft, tacky nature when heated, allowing them to flow around particles and still form a tight bond.

In contrast, common sealing materials like polyethylene may require cleaner surfaces to form reliable seals.

Comparison of Ionomers to other Barrier Materials

Material	Water Vapour Barrier	Oxygen Barrier	Sealability	Seals Through Contamination	Mechanical Strength	Clarity	Typical Uses
Ionomer (e.g. Surlyn®)	◼◼◼○○	◼◼◼○○	◼◼◼◼◼ (excellent)	◼◼◼◼◼	◼◼◼◼○	◼◼◼◼◼	Food packaging, golf balls, medical films
LDPE (Low-Density Polyethylene)	◼◼◼◼○	◼◼○○○	◼◼◼◼○	◼◼○○○	◼◼◼◼○	◼◼◼◼○	Basic food packaging, film wrap
EVOH (Ethylene Vinyl Alcohol)	◼◼◼◼◼	◼◼◼◼◼ (very high)	◼◼○○○	◼○○○○	◼◼◼○○	◼◼◼◼○	High-barrier multilayer films, medical packaging
PET (Polyester)	◼◼◼◼○	◼◼◼◼○	◼◼◼○○	◼◼○○○	◼◼◼◼◼	◼◼◼◼◼	Bottles, trays, flexible packaging
Aluminium Foil	◼◼◼◼◼ (impermeable)	◼◼◼◼◼	◼◼○○○	◼○○○○	◼◼◼◼◼	○○○○○ (opaque)	Pharmaceuticals, long-life food, military rations
PVDC (Polyvinylidene Chloride)	◼◼◼◼◼	◼◼◼◼◼	◼◼◼◼○	◼◼◼○○	◼◼◼◼○	◼◼◼◼○	Meat packaging, twist wraps, blister packs

Squares imply excelenct water vapour permeability - with 5 being the maximum, circles imply low vapour permeability

Conclusion

Vapour permeability is a critical factor in the performance of ionomer-based products across numerous industries. Achieving the right balance is essential to ensure durability, efficiency and regulatory compliance. Whether in packaging, medical applications, or energy storage, controlling moisture transmission can prevent degradation, improve longevity and enhance overall functionality. Understanding and measuring vapour permeability with precision allows manufacturers to optimize ionomer formulations for specific applications, reducing failures and improving product performance.