Preparation and properties of pH-responsive gas permeable CNC/PBAT composite membranes
Films with tunable gas permeation are important for the development of the packaging and preservation field,while designing films with pH-responsive permeation and high mechanical properties remains a challenge.In this paper,a two-step substitution reaction of succinic anhydride esterification and diethylenetriamine amidation was designed to achieve functionalized modification of amine group(A-CNC)and carboxyl group(S-CNC)on the surface of cellulose nanocrystals,which was further composited with poly(butylene adipate-co-terephthalate)(PBAT)to prepare composite films with pH-responsive gas permeation.The results showed that the cellulose nanocrystals and their functionalisation were characterised by scanning electron microscopy(SEM),infrared spectroscopy(FTIR)and nuclear magnetic resonance 13 C spectroscopy(13 C NMR),confirming the success of the modification.Characterisation of the composite film properties:in terms of mechanical properties,the tensile strength of S-CNC/PBAT(3/97)and A-CNC/PBAT(5/95)composite films reached the highest,which was 40.44%and 50.56%higher than PBAT respectively,whereas the elongation at break decreased and the fracture mode shifted from ductile to brittle fracture.In terms of gas permeability,the composite films showed mutual inverse pH response permeability characteristics.The permeability of S-CNC/PBAT(5/95)composite films showed a positive response to the trend of change,with the increase of buffer pH(3-12),CO2 and O2 permeability increased by 67.98%and 48.34%,respectively,and the water vapour permeability varied from 2.467×10-13 to 3.039×10-13 g·cm/(cm2·s·Pa),and A-CNC/PBAT(5/95)composite film permeation appeared pH negative responsive phenomenon,CO2 and O2 permeability decreased by 63.00%and 54.61%,respectively,and the water vapour permeability changed from 2.747×10-13 to 2.043×10-13 g·cm/(cm2·s·Pa).This composite film with pH-responsive permeability has a broad prospect in the field of smart packaging.
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