title: A gel network constituted by rigid schizophyllan chains and nonpermanent cross-links.
abstract: This work reports a gel network formed by rigid schizophyllan (SPG) chains with Borax as a cross-linking agent. The formed cross-links are non-permanent and somewhat dynamic in nature because the cross-linking reaction is governed by a complexation equilibrium. Gelation processes are traced by dynamic viscoelastic measurements to examine the effects of Borax content, SPG concentration, temperature, salt concentration, salt type, and strain. The first-order kinetic model containing three parameters, t(0) (induction time), 1/tau(c) (gelation rate), and (saturated storage modulus), is successfully applied to describe the gelation of the SPG-Borax system. Gelation occurs faster at higher Borax content, higher SPG concentration, higher salt concentration, or lower temperature. Moreover the gelation is cation-type-specific. Storage modulus is a linear function of both Borax content and SPG concentration. The linear relationship between storage modulus and Borax content can be explained by a modified ideal rubber elasticity theory with a front factor alpha to take into account the presence of ineffective cross-links and the effect of SPG chain rigidity. On the other hand, the linear dependence of storage modulus on SPG concentration could be explained on the basis of chain-chain contacting behavior of extended SPG chains. Apparent activation energy and cross-linking enthalpy are calculated to be -74.5 and -32.4 kJ/mol for the present system. Strain sweep measurements manifest that the elasticity behavior of this gel starts to deviate from Gaussian-chain network at a small strain of 10%.
authors.affiliation: Department of Food and Human Health Sciences, Graduate School of Human Life Science, Osaka City University, Sumiyoshi, 558-8585, Japan.
authors.forename: Yapeng
authors.initials: Y
authors.lastname: Fang
authors.forename: Rheo
authors.initials: R
authors.lastname: Takahashi
authors.forename: Katsuyoshi
authors.initials: K
authors.lastname: Nishinari
mesh_terms: D001881:Borates; D003432:Cross-Linking Reagents; D005782:Gels / Q000737:chemistry*; D012566:Sizofiran / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D001881:Borates; D003432:Cross-Linking Reagents; D005782:Gels; C018851:borax; D012566:Sizofiran