Preparation and characterization of enzyme-modified konjac glucomannan/xanthan blend films

Enzyme-modified konjac glucomannan (KGM) and xanthan blend films have been prepared and characterized. Enzymatic hydrolysis of purified KGM by beta-mannanase yielded samples of various weight-average molecular weight (M(w)) that were determined by size-exclusion chromatography coupled with multi-angle laser light scattering (SEC-MALLS) and calculated using the established Mark-Houwink-Sakurada equation [eta] = 4.07 x 10(-4)M(w)(0.733). KGM degradation products were blended with xanthan for preparation of films that were used in orthogonal-designed experiments. These films were characterized in terms of their structures, thermal stability, crystallinities and mechanical properties. The results of Fourier transform infrared spectroscopy indicated that, after blending, there was strong intermolecular interaction caused by hydrogen bonds between xanthan and KGM hydrolysates. This phenomenon was more marked at lower M(w) of KGM. The thermal stability of the blend films determined by differential scanning calorimetry was higher with increasing KGM molecular weight. The degrees of crystallinity characterized by X-ray diffraction (XRD) decreased with the increasing content of non-degraded KGM. Mechanical properties of the polymer blends including the tensile strength and elongation rate were also correlated to M(w) of KGM. The tensile strength achieved a maximum at 10.25 MPa with KGM of M(w) = 4.25 x 10(5) and the elongation rate reached a maximum value of 89.5% with KGM of M(w) = 8.95 x 10(5). These results were directly attributed to intermolecular interactions between xanthan and KGM, and this synergistic behavior led to good physicochemical and mechanical performance of the blended films.