Fabrication and characterization of bacterial cellulose/κ-carrageenan composite sheets

Bacterial cellulose (BC)/κ-carrageenan composite sheets were prepared from a visible two-layer-structured composite pellicle using two methods: (1) direct drying of the two-layer-structured pellicle and (2) drying of the composite pellicle after κ-carrageenan layer removal. The surface morphology of the sheets was observed using scanning electron microscopy (SEM). Structural analyses of the sheets were performed using Fourier-transform infrared (FTIR) spectroscopy, solid-state ¹³C nuclear magnetic resonance (ssNMR) spectroscopy, and X-ray diffraction (XRD). The SEM and FTIR results showed that κ-carrageenan aggregates were present on the surface from which the κ-carrageenan layer was removed. The ssNMR results revealed that the addition of 0.4 wt% κ-carrageenan was suitable for incorporating κ-carrageenan into pellicles. The XRD results indicated that the removal of the κ-carrageenan layer affected the cellulose fibers near the κ-carrageenan layer boundary, thereby changing the plane orientation. The mechanical properties of the sheets were evaluated by tensile testing. The composite sheet with the κ-carrageenan layer removed became harder in terms of the tensile strength. The fracture stress of the two-layer-structured sheets was lower than that of the BC sheet. After κ-carrageenan layer removal, the 0.4 wt% composite sheet was stronger and harder than the BC sheet, but the brittleness of the two sheets was identical. These findings will facilitate fundamental research on BC/κ-carrageenan composite sheets and help determine their applicability as ecofriendly sheet materials.