How to Enhance Glassine's Barrier Properties

Created on 09.16

Enhancing the barrier properties of glassine is a common and important objective in packaging, particularly for industries like food, medical, and specialty consumer goods that require protection from moisture, grease, oxygen, and aromas.

Here is a comprehensive guide on how to enhance glassine's barrier properties, from fundamental principles to advanced technologies.

Understanding the Base Material: Why Glassine is a Good Starting Point

First, it's crucial to understand what standard glassine is:

Manufacture: It is a supercalendered paper. The paper pulp is beaten extensively to fray the fibers, which allows them to bond tightly during a high-pressure, high-temperature calendering process.

Inherent Properties: This process creates a sheet that is dense, smooth, glossy, and has native resistance to air and grease due to its low porosity. However, this native resistance is not a complete barrier.

The goal of enhancement is to build upon this naturally dense structure to create a true functional barrier.

Methods to Enhance Barrier Properties

Enhancement methods can be categorized into three main approaches: Coatings & Laminations, Internal Additives, and Physical Modifications.

1. Coatings and Laminations (Most Common and Effective)

This involves applying a layer of another material to the surface of the glassine.

a) Extrusion Coating/Lamination:

Process: A molten polymer is extruded through a flat die and pressed directly onto the glassine web.
Materials:
Polyethylene (LDPE/LLDPE): The most common choice. Provides an excellent moisture barrier and heat-sealability. Often used for bakery and frozen food packaging.

Ethylene Vinyl Alcohol (EVOH): An outstanding barrier to oxygen and aromas. It is almost always used as a co-extruded layer between PE, as it is hygroscopic (loses barrier properties when wet).
Polypropylene (PP): Offers a good moisture barrier and higher temperature resistance than PE.

Result: Creates a very strong, impermeable barrier. The choice of polymer determines the specific barrier (moisture, oxygen, or both).

b) Dispersion Coating (or Solution Coating):

Process: A water-based or solvent-based polymer emulsion is applied to the surface of the glassine (e.g., via rod, air knife, or blade coater) and then dried.
Materials:
PVdC (Polyvinylidene Chloride): Provides an exceptional barrier to moisture, oxygen, and aromas. A traditional, high-performance coating.

Acrylics: Good barrier to grease and oils, often used in butter and grease-proof wraps.
Fluorochemicals: Provide extremely high oil and grease resistance (e.g., for popcorn bags).
Wax Lamination: While less common now, wax can be applied for moisture resistance and a unique aesthetic, but it can crack and is less recyclable.

Result: A thinner, more paper-like feel than extrusion coating while still significantly improving barrier properties. Often more sustainable-looking.

c) Film Lamination:

Process: A pre-made plastic film (e.g., BOPP, PET, PLA) is adhesively bonded to the glassine sheet.

Result: Provides the specific properties of the chosen film (e.g., clarity, stiffness, high barrier). Offers great design flexibility but can be more expensive and less recyclable.

2. Internal Additives (Mass Addition)

These are chemicals added to the pulp slurry before the paper sheet is formed.

Process: Additives are mixed into the fiber slurry.
Materials:
Sizing Agents (e.g., AKD - Alkyl Ketene Dimer): These are hydrophobizing agents that make the cellulose fibers themselves repel water. They increase the paper's resistance to liquid water and moisture vapor.

Grease Resistance Additives: Similar agents can be used to enhance the native grease resistance of the glassine.

Result: Improves the bulk properties of the sheet rather than just creating a surface barrier. This is often used in conjunction with coatings for a synergistic effect. The effect is generally less absolute than a continuous plastic coating.

3. Physical and Process Modifications

Increased Calendering: Further increasing the pressure and temperature during the supercalendering process can densify the sheet even more, reducing its porosity and improving its native barrier. However, there is a practical limit before the paper becomes too brittle and loses tensile strength.

Grammage (Basis Weight): Using a heavier, thicker glassine paper will naturally provide a better barrier than a very thin one, as the path for vapor transmission is longer and more tortuous.

Choosing the Right Enhancement for Your Needs

Barrier Requirement	Recommended Enhancement Methods	Common Applications
Moisture / Water Vapor	Extrusion Coating with PE, Dispersion Coating with PVdC/Acrylics, Internal Sizing	Frozen food bags, bakery bags, multi-wall sacks
Grease / Oil	Fluorochemical Dispersion Coating, Acrylic Coating, Internal Additives	Fast food packaging, butter wraps, popcorn bags, pet food bags
Oxygen & Aroma	Co-extrusion with EVOH, Dispersion Coating with PVdC	Coffee bags, medical packaging, specialty foods (nuts, spices)
Overall Robustness	Film Lamination (e.g., BOPP), Extrusion Coating	Premium retail bags, gift packaging

The Critical Consideration: Sustainability

Modern enhancements must balance performance with environmental impact.

Recyclability: Traditional plastic coatings and laminations (PE, PP) can complicate recycling in paper streams. Monomaterials (e.g., PE-coated glassine) are often preferred over complex laminates as they are easier to recycle.
Biodegradability/Compostability: There is a growing trend towards using:
Bio-based Polymers: PLA (Polylactic Acid) extrusion coatings can provide a moisture barrier and is compostable in industrial facilities.

Water-based Biopolymer Coatings: Coatings based on proteins (zein), starches, or chitosan are being developed to provide barriers while maintaining compostability.

PFAS-Free: Fluorochemical coatings (which often contain PFAS) are facing regulatory pressure due to environmental and health concerns. The industry is rapidly moving towards PFAS-free alternatives, such as advanced acrylics and other novel chemistries.

Summary: How to Decide

1. Define Your Barrier Needs: Quantify what you need to block (water, oil, oxygen?) and to what degree. Test standards like MVTR (Moisture Vapor Transmission Rate) or OGR (Oil Grease Resistance) are key.

2. Consider the Product: Is it dry, moist, oily, or aromatic? What is the shelf-life requirement?

3. Determine Handling Requirements: Does the package need heat sealability? Does it need to be stiff or flexible?

4. Prioritize Sustainability: What are your end-of-life requirements? Recyclable? Compostable? This will heavily influence your choice of coating.

5. Partner with a Converter: Glassine producers (converters) have extensive expertise. Work with them to test and select the most cost-effective and performant solution for your specific application. They can run trials on pilot coaters to find the perfect fit.

By leveraging these methods—especially advanced dispersion coatings and extrusion laminations—you can transform standard glassine into a high-performance barrier material suitable for the most demanding packaging applications.

Hands holding glassine paper sheet on a wooden table with tea and brush nearby.

Ray

Ferrill

Evelyn