Studies on interaction of hydroxypropylmethyl cellulose and konjac glucomannan mixed systems

Aiming at the synergistic effects between cellulose ethers and other polysaccharides, hydroxypropylmethyl cellulose (HPMC) and konjac glucomannan (KGM) mixed systems in aqueous medium were studied. Dynamic mechanical analysis (DMA) .viscosity and oscillatory measurements were employed to analyze the mechanism of interactions with a molecular structure model proposed. Viscosity measurements revealed the negative synergistic viscosity effects of HPMC-KGM systems, by reason of brokenness of inter-and intra-hydrogen bonds of KGM. DMA tests were carried out from 30°C to 95°C. The results showed when the mass ratio of KGM was no less than 1: 1 , the thermal gelation of HPMC around 76 ∼ 77°C with a sharp drop in G' was replaced by a steady decrease during a broad temperature range, and G' of the mixed solutions stayed at relatively higher values compared with the single ones for the whole available temperatures. The degradation of KGM caused by the break of β-1, 4 glycosidic bonds especially (M-M) glycosidic bonds approaching to 90°C was to a great extent weakened in mixed systems. It was interpreted that in HPMC-KGM systems, the unsubstituted mannan regions of KGM and hydrophobic groups of HPMC formed weak junction zones through hydrophobic interactions, and the structure of HPMC as main network with KGM combined was finally formed, resulting in retardation or partial prevention to the thermal gelation of HPMC and degradation of KGM. Viscoelastic behavior characteristics and loss tangent values obtained from oscillatory measurements combined with thermal hysteresis observed from DMA tests showed that the hydrophobic association effects were more stable than hydrogen bonds, and more pronounced with HPMC/KGM mass ratios from 3: 1 to 1: 1 (W/W).