Nano boron nitride/polyurethane adhesives in flexible laminated food packaging: Peeling resistance and permeability properties

Polymeric multilayer films are widely used in food packaging due to their versatility. However, there are still some properties that might be improved, such as gas and vapor barrier behaviors. The incorporation of boron nitride into polymer matrixes is emerging as a potential method for the improvement of barrier properties due to its lamellar structure. In this context, our work investigates the addition of boron nitride into a bicomponent reactive polyurethane (PU), which could be used as an adhesive and improve the barrier layer. This material could be used as an alternative to aluminum foil in food packaging. Different concentrations of two different sizes of boron nitride (BN) particles were added to the PU adhesive: micro-structured boron nitride (BNm) and nano-structured boron nitride (BNn). The aim was to investigate the influence on the barrier properties against moisture and the peeling resistance. Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) were performed to characterize the boron nitride samples. The effect of BNm or BNn addition on the glass transition of the nanocomposites was investigated by differential scanning calorimetry (DSC). Barrier properties were measured by a water vapor permeation test and the practical adhesion of laminates with BN/PU adhesives was characterized using peeling tests. The nanocomposites achieved reduction in water vapor permeance of up to 50% and a 37% increase in mechanical adhesion properties compared to the PU adhesive. The results revealed the high potential of boron nitride/PU adhesives for food packaging applications.