Effect of urea on solution behavior and heat-induced gelationof chitosan-β-glycerophosphate
Effect of urea on solution behavior and heat-induced gelationof chitosan-β-glycerophosphate
复制标题
DOI：
10.1016/j.carbpol.2005.10.013
复制
发表时间：
2006-03
影响因子：
11.2
通讯作者：
Jaepyoung Cho;M. Heuzey;A. Bégin;P. Carreau
中科院分区：
文献类型：
--
作者：
Jaepyoung Cho;M. Heuzey;A. Bégin;P. Carreau
在本研究中，我们研究了尿素对壳聚糖-β-GP系统的物理化学（pH和电导率）和流变特性的影响，以评估低温和高温下主要的聚合物-聚合物相互作用。由于尿素水解消耗了溶液中的 H+，溶液的 pH 值略有增加。此外，尿素的添加显着降低了电导率，从而降低了溶液的离子强度，并且这种影响在高温下更为重要。这表明尿素通过削弱低温下的氢键强烈影响聚合物-聚合物相互作用，但此外还可以阻碍高温下的疏水作用，因为离子强度的降低导致质子化葡萄糖胺基团之间静电排斥的屏蔽减少。在15°C下，在壳聚糖-β-GP溶液中添加尿素会降低其弹性，缩短弛豫时间，并由于氢键的破坏而简化弛豫过程。在尿素存在下，壳聚糖体系的热诱导凝胶化在非等温测试中表现出更高的凝胶化温度（Tgel），在等温条件下表现出更长的凝胶化时间（tgel）。凝胶化的活化能也随着尿素浓度的增加而增加。我们得出的结论是，尿素对凝胶过程的不利影响主要与聚合物-聚合物疏水效应的降低有关，如电导率的降低所示。
In this study, we have investigated the effect of urea on the physicochemical (pH and conductivity) and rheological properties of the chitosan-β-GP system in order to assess the main polymer–polymer interactions at low and high temperature. The pH of the solutions was slightly increased due to the consumption of H+in solution through the hydrolysis of urea. Furthermore, the addition of urea considerably decreased the conductivity, and therefore the ionic strength of the solutions, and this effect was more important at high temperature. It indicated that urea strongly affects polymer–polymer interactions by weakening hydrogen bonds at low temperature, but in addition can hinder hydrophobic effect at high temperature since the reduction of ionic strength results in less screening of electrostatic repulsion between protonated glucosamine groups. At 15°C, the addition of urea to chitosan-β-GP solutions decreased their elasticity, shortened relaxation times and simplified the relaxation process due to the disruption of hydrogen bonds. Heat-induced gelation of the chitosan system in the presence of urea showed higher gelation temperature (Tgel) in non-isothermal tests and longer gelation time (tgel) in isothermal conditions. The activation energy for gelation also increased with increasing urea concentration. We concluded that the detrimental effect of urea on the gelation process was mainly related to a decrease in polymer-polymer hydrophobic effect, as shown by the decrease in conductivity.