Guigo Nathanael, Mija Alice, Vincent Luc, Sbirrazzuoli Nicolas
Thermokinetic Group, Laboratory of Chemistry of Organic and Metallic Materials C.M.O.M., Institute of Chemistry of Nice (CNRS FR3037), University of Nice-Sophia Antipolis, 06108, Nice Cedex 2, France.
Phys Chem Chem Phys. 2009 Feb 28;11(8):1227-36. doi: 10.1039/b812512k. Epub 2009 Jan 7.
The glass transition of lignin has been studied by multifrequency calorimetric measurements in order to highlight the morphological changes and the dynamic aspects associated to this relaxation process. Influences of water sorption and thermal annealing on molecular mobility have been considered. Additional investigations by thermogravimetry, infra-red spectroscopy and rheometry have been performed to corroborate the claims. The relaxation process of annealed lignin shows a different behaviour as the consequence of micro-structural modifications of lignin. These are explained by redistribution of secondary bonds as well as formation of new interunit linkages. Concerning the dynamic aspects, apparent activation energy, E, and sizes of cooperatively rearranging region, V(crr), have been evaluated respectively from the frequency dependence and heat capacity measurements of the glass transition. Compared to dried lignin, both E and V(crr) significantly decrease in a water-sorbed matrix indicating that the three-dimensional structure presents a higher mobility and is less confined.
为了突出与这种松弛过程相关的形态变化和动力学方面，通过多频量热测量研究了木质素的玻璃化转变。考虑了水吸附和热退火对分子流动性的影响。通过热重分析、红外光谱和流变学进行了额外的研究，以证实这些说法。由于木质素的微观结构改性，退火木质素的松弛过程表现出不同的行为。这些可以通过二级键的重新分布以及新的单元间连接的形成来解释。关于动力学方面，分别从玻璃化转变的频率依赖性和热容测量中评估了表观活化能E和协同重排区域的大小V(crr)。与干燥的木质素相比，E和V(crr)在水吸附基质中均显著降低，这表明三维结构具有更高的流动性且限制较少。
