Institute of Plant and Wood Chemistry, Technische Universitaet Dresden, Dresden, Germany.
ACS Appl Mater Interfaces. 2012 Nov;4(11):5852-62. doi: 10.1021/am3015179. Epub 2012 Nov 1.
Highly swellable lignin derivatives were prepared by cross-linking of oxidatively preactivated spruce organosolv lignin (OSL) with poly(ethylene) glycol diglycidyl ether (PEGDGE). The lignin gels obtained are considered to be an environmentally friendly alternative to synthetic hydrogels and superabsorbents and represent a novel type of lignin based functional materials. For their application, it is not only the absorption of water in terms of hydrogel swelling that plays an important role, but also the adsorption and retention of moisture by the corresponding xerogels. To reveal the mechanisms involved in moistening and reswelling of the lignin gels, the interaction of water vapor with lyophilized xerogels was investigated and compared with sorption characteristics of parent lignin. The chemical structure of PEGDGE-modified lignin was investigated using attenuated total reflectance Fourier-transformed infrared spectroscopy and selective aminolysis and was related to its sorption and swelling characteristics. Bound and free water in hydrogels was determined by differential scanning calorimetry and by measuring the free swelling capacity of the gels. Moisture sorption of OSL and PEGDGE-modified lignin xerogels was determined using dynamic vapor sorption analysis. In order to determine monolayer and multilayer sorption parameters, sorption data were fitted to the Brunauer-Emmett-Teller and the Guggenheim-Anderson-de Boer model. Swelling properties of the hydrogels and moisture sorption of the corresponding xerogels were found to be strongly dependent on the degree of chemical modification with PEGDGE: Total and free water content of hydrogels decrease with increasing cross-linking density; on the other hand, water bound in hydrogels and moisture sorption of xerogels at high levels of water activity strongly increase, presumably because of the hydration of hydrophilic oligo(oxyethylene) and oligo(oxyethylene) glycol substituents, which lead to moisture diffusion into the xerogel matrix, plasticization, and swelling of the gels.
高溶胀木质素衍生物是通过氧化预处理的云杉有机溶剂木质素（OSL）与聚乙二醇二缩水甘油醚（PEGDGE）的交联制备的。所得到的木质素凝胶被认为是合成水凝胶和超级吸收剂的环保替代品，代表了一类新型的基于木质素的功能材料。对于它们的应用，不仅水凝胶溶胀的水吸收起着重要的作用，而且相应的干凝胶对水分的吸附和保持也起着重要的作用。为了揭示木质素凝胶吸湿和再溶胀的机制，研究了水蒸气与冷冻干燥的干凝胶的相互作用，并将其与原始木质素的吸附特性进行了比较。使用衰减全反射傅里叶变换红外光谱和选择性氨解研究了 PEGDGE 改性木质素的化学结构，并将其与吸附和溶胀特性相关联。通过差示扫描量热法和测量凝胶的自由溶胀能力来确定水凝胶中的结合水和自由水。通过动态蒸汽吸附分析测定 OSL 和 PEGDGE 改性木质素干凝胶的水分吸附。为了确定单层和多层吸附参数，将吸附数据拟合到 Brunauer-Emmett-Teller 和 Guggenheim-Anderson-de Boer 模型。水凝胶的溶胀性能和相应干凝胶的水分吸附强烈依赖于与 PEGDGE 的化学改性程度：水凝胶的总含水量和自由含水量随交联密度的增加而降低；另一方面，水凝胶中结合水和高水分活度下干凝胶的水分吸附强烈增加，可能是由于亲水性低聚（氧乙烯）和低聚（氧乙烯）二醇取代基的水合作用，导致水分扩散到干凝胶基质中，增塑和凝胶溶胀。
