Improving Gas Barrier Properties with Boron Nitride Nanosheets in Polymer Composites

Abstract

Hexagonal boron nitride is promising gas barrier material due to higher aspect ratio, effective corrosion resistant and Hydrophobic nature. Liquid phase exfoliated, size selected, defect free hexagonal boron nitride (hBN) nanosheets are dispersed in thermoplastic polyurethane (TPU) via solution processing. Aspect ratio is an important parameter along with the volume fraction of filler in relation to the gas permeation of polymer composites. The range of hBN volume in polymer matrix is fraction 0-1 vol. %. The aspect ratio of hBN is estimated to be ~331 with the help of transmission electron microscope. With the inclusion of minute level of hBN, the permeation reduction levels are considerably enhanced for Co2 in hBN-TPU composites. By addition of just 0.011 vol% nanosheets, permeability is reduced up to 54%. By addition of 0.054 vol% permeability is fell up to 82%, the maximum attained permeation reduction achieved for current work. Further increase in the hBN concentration (0.5-1 vol. %) in TPU slightly reduces the gas retention but still maintains a permeation level of 76-80% as compared to the base polymer. The reduction in gas retention may be due to the aggregation of filler inside polymer. X-ray diffraction and tensile testing have validated the aggregation phenomena. The maximum ultimate tensile strength and Young’s modulus are also achieved at 0.05 vol. % BN-TPU composites; beyond this loading the mechanical properties are compromised. Theoretical models predict well the experimental results at low BN concentrations with Neilson model being the closest but at higher loadings the results are compromised probably due to restacking of fillers. The enhancement in the barrier properties for CO2 and the mechanical robustness may pave a way for utilization of these composites in application like food packaging, biological membranes and in natural gas transmission pipelines where CO2 causes corrosion due to its acidic nature