Yoo, Young Jin
(Department of Bio-fibers and materials Science, Kyungpook National University)
Um, In Chul
(Department of Bio-fibers and materials Science, Kyungpook National University)
In this study, the thermo-gelation behavior of hydroxypropyl methylcellulose (HPMC) and hydroxyethyl methylcellulose (HEMC) were examined by rheology. Temperature sweep shear viscosity measurements revealed a significant decrease in the shear viscosity of HPMC and HEMC at the aggregation temperature ($T_{agr}$), which depended on the substitution type (HPMC or HEMC) and degree of substitution. In the dynamic test, G' decreased slightly at $T_{agr}$ and increased significantly at the gelation temperature ($T_{gel}$). The shear viscosity and shear storage modulus (G') can be utilized complementarily to examine $T_{agr}$ and $T_{gel}$. $T_{agr}$ could be detected clearly by the shear viscosity measurement but could not be observed in the G' measurement. On the other hand, $T_{gel}$ could not be detected in the shear viscosity measurement although it can be clearly recognized in G' measurement. Conclusively, the two rheological measurements could be utilized complementarily in detection of $T_{agr}$ and $T_{gel}$. In the meanwhile, HPMC with more hydrophobic residues (methoxy and hydroxypropyl residues) showed smaller $T_{agr}$ and $T_{gel}$ than HEMC, which has hydroxyethyl and methoxy groups. $T_{agr}$ and $T_{gel}$ decreased with increasing number of hydrophobic groups. Molecular weight almost did not affect $T_{agr}$ and $T_{gel}$ of HPMC solution.