PVOH for Oxygen-Sensitive Food Packaging

PVOH coatings offer plastics professionals a powerful tool for oxygen-sensitive packaging when designed for real conditions.

The plastics industry focuses on sustainable alternatives, and PVOH shows significant promise as a coating for paper-based packaging. PVOH’s strong oxygen barrier, biodegradability, and ease of application make it an attractive substitute for petroleum-based plastics in various food packaging applications. However, a recent study emphasizes the need to evaluate PVOH under real-world conditions to understand and fully optimize its performance.

You can also read: Sustainable Packaging: Adhesives and Coatings.

The study Polymer-coated cardboards as strawberry packaging alternatives: The importance of considering close-to-real testing conditions in a food requirement-driven approach focused on PVOH-coated cardboard trays designed for strawberries. This research highlights the importance of testing polymer performance in configurations that mimic actual use and under environmental stresses, rather than relying solely on tests of flat sheets in controlled laboratory settings.

PVOH: Balancing High Barrier with Environmental Sensitivity

PVOH is notable for its excellent oxygen barrier properties, essential for preserving food quality in packaging. Additionally, PVOH offers oil resistance and has reached a technology readiness level that facilitates its practical application in commercial settings.

Despite these benefits, PVOH is hydrophilic, meaning it absorbs water. This absorption can lead to swelling and alter its barrier properties. The researchers tested two types of PVOH-coated cardboard: CN_8_2L, which has 8 g/m² of PVOH coating applied in two layers on one side, and CN_11_2+1L, which has 11 g/m² of PVOH coating applied in two layers on one side and one layer on the other. To understand how environmental factors influence the materials, they characterized the cardboards under both standard conditions (23°C and 50% relative humidity) and more realistic refrigerated storage conditions (5°C and 100% relative humidity).

• Oxygen permeability of PVOH films increased substantially in humid conditions.
• Water vapor permeability also increased.

These findings emphasize the need to assess PVOH’s performance under conditions that replicate the high humidity of refrigerated food storage.

Enhancing PVOH: Surface Modification Strategies

To address PVOH’s moisture sensitivity, researchers explored modifying coated cardboards with fatty acid chlorides (palmitoyl chloride) through a chromatogeny process. This modification aimed to introduce hydrophobic properties, reducing water absorption and stabilizing barrier performance.

The grafting process did reduce the impact of humidity on the coated cardboards. However, the cardboards still experienced swelling at 100% RH, and their gas barrier properties decreased. While surface modification offers a valuable strategy to improve PVOH’s performance in humid environments, the study indicates that it may not completely eliminate moisture-related challenges. This suggests that considering bulk material properties remains crucial for predicting barrier behavior.

Conversion Processes: An Important Factor in PVOH Performance

The study also examined the impact of converting processes, such as folding, sealing, and shaping, on PVOH-coated materials. These processes introduce mechanical stresses that can alter the polymer layer’s structure and affect its barrier properties.

For instance, researchers successfully sealed the CN_11_2+1L coated cardboard using ultrasonic welding, a process requiring direct contact between PVOH layers. However, even in this case, oxygen ingress increased after sealing, compared to measurements on the flat material. Scanning electron microscopy revealed micro-defects in folded areas, suggesting that mechanical deformation can compromise the coating’s integrity. These defects can create pathways for gas and moisture transfer, reducing the packaging’s effectiveness.

Optimizing PVOH for Real-World Applications

This research emphasizes that data from material data sheets may not fully predict PVOH’s performance in real-world applications. The effectiveness of PVOH depends on several factors:

• Humidity levels, which influence water absorption and swelling.
• Temperature variations, which affect gas diffusion and permeability.
• Converting processes, which can alter the structural integrity of the coating.

The study demonstrated that packaging designed using standard measurements did not provide optimal preservation for strawberries. Accurate predictions of packaging performance and food preservation required simulations that incorporated real environmental conditions and post-conversion properties.

PVOH: A Promising Material with Refined Application

This study confirms PVOH’s potential for food packaging when used with a clear understanding of its properties and limitations. PVOH excels in applications requiring strong oxygen barriers and predictable environmental conditions.

To fully leverage PVOH, the industry should adopt an integrated approach:

• Select polymer coatings based on the specific preservation needs of the food product.
• Evaluate materials under relevant storage conditions.
• Validate performance in converted packaging formats.

This approach is crucial for sustainability-driven innovations, ensuring that alternative materials meet performance requirements while supporting recyclability and food quality.