X-ray texture investigations of bacterial cellulose

Never dried highly swollen bacterial cellulose fleeces produced by the bacteria Acetobacter xylinum were deformed uniaxially and kept under strain during the drying process. The orientation of the crystalline nanofibrils was determined by X-ray pole figure measurements of the (1-10) lattice plane in reflection mode and the (004) interference in transmission mode. Appropriate cuts through the pole figures were used for the determination of planar and axial degrees of orientation. Generally, a uniplanar texture with the (1-10) planes parallel to the fleece surface and an axial component in the draw direction were found. With increasing draw ratio both the axial orientation and the uniplanar orientation in draw direction were improved, whereas transversely the uniplanar texture component broadened slightly. Mechanical strength and modulus were almost doubled and tripled, respectively, for favoured cases. As compared to the wet aqueous samples, a higher coherent deformation of the bacterial cellulose membrane could be achieved by drawing the samples soaked in NaOH solutions with concentrations in the range of 8 to 10 wt.-%. By the presence of the lye significant improvements of the axial chain orientation of up to 100% could be obtained resulting in a maximum strength of 580 MPa. The improved orientability is likely to be explained by a NaOH-induced reduction in the number of inter-fibrillar bridging points formed by H-bonds.