A new water-based composite coating made of polyvinyl alcohol (PVA) and polyethyleneimine (PEI) addresses several weaknesses of traditional PVA barriers for food packaging. At the heart of the system is a semi-interpenetrating polymer network structure that improves both adhesion to common polyolefin substrates and barrier performance under high humidity conditions. The results were published in the journal *Progress in Organic Coatings*.
PVA is considered an interesting alternative to PVDC and EVOH due to its excellent oxygen barrier properties, with OTR values below 1 mL/m²·day. In practical applications, however, its limited adhesion to polyolefins, pronounced moisture sensitivity above 60% relative humidity, and weak water vapor barrier limit its use. The approach now presented combines PVA with PEI, whose amino groups form hydrogen bonds with the hydroxyl groups of the PVA. Additionally, they can react with carbonyl and carboxyl groups that form on corona-treated polyolefin surfaces.
Adhesion to BOPP, PET, and BOPE
This dual function both strengthens the coating’s internal network and improves interfacial adhesion to the substrate. With a PEI content of 5%, peel strengths of 1.29 ± 0.14 N/15 mm were achieved on biaxially oriented polypropylene (BOPP), 1.97 ± 0.09 N/15 mm on PET, and 2.53 ± 0.11 N/15 mm on biaxially oriented polyethylene (BOPE). The coating thus meets the requirements for food packaging on various substrates. At the same time, the primer for PVA on polyolefins—which is otherwise often necessary—is no longer required. Isocyanate crosslinkers, which are viewed critically in food-contact applications, are also not required.
Barrier Performance at High Humidity
As the PEI content increased, so did the barrier performance, particularly under humid conditions. For a laminate structure consisting of BOPP-PVA/PEI//CPP, an oxygen transmission rate of 5.80 ± 0.88 mL/m²·day and a water vapor transmission rate of 2.89 ± 0.12 g/m²·day were measured at 85% relative humidity. The authors therefore consider the structure suitable for the preservation of foods with high sugar or fat content. The publication states that the PVA/PEI composite coatings “outperform conventional PVDC-coated counterparts in oxygen barrier at both 0% and 85% RH.”
In addition to functional performance, the packaging structure is also relevant: The approach aims for a single-material design and thus for flexible packaging that is more easily recyclable. This aligns with regulatory developments such as the EU Plastics Strategy and the trend toward replacing complex multilayer structures with simpler barrier concepts. For surface technology, the combination of corona pretreatment, improved adhesion, and water-based coating is particularly interesting.