Improving gas barrier properties with boron nitride nanosheets in polymer-composites

Liquid exfoliated, size selected, hexagonal boron nitride (hBN) nanosheets are dispersed in thermoplastic polyurethane (TPU) via solution processing and their properties such as CO₂ gas barrier and mechanical properties were evaluated. Aspect ratio and filler loading are important parameters for gas permeation of polymer composites. The range of BN volume in the polymer matrix is 0–1.1%. The aspect ratio ∼331 of BN is estimated with transmission electron microscope. With the inclusion of tiny BN, the permeation reduction levels are considerably enhanced for CO₂ in BN-TPU composites. At 0.011 vol% BN, permeability is reduced up to ∼55%, further reducing to 82% (0.054 vol% BN). Further increase of BN concentration (0.5–1.1 vol%) in TPU slightly reduces the gas retention maintaining a permeation level of 76–80% as compared to the base polymer. Theoretical models predict well the experimental results at low BN concentrations with both Neilson and Bhardawaj models which differ for orientation of fillers inside the polymer. The reduction in gas retention at maximum BN loading occurs may be due to the aggregation of filler inside polymer. X-ray diffraction and tensile testing also suggest the aggregation phenomena. The enhancement in CO₂ barrier properties and the mechanical robustness may pave a way for utilization of these composites in applications like coating in CO₂ gas transmission pipelines and food packaging.