木质素微纳米球的制备与应用研究现状

在植物纤维原料中,木质素是仅次于纤维素的天然可再生资源,但由于结构复杂且不同类型木质素结构性能差异,其通常被认为是一种废料或低价值副产品。微纳米木质素是近年来兴起的新发展方向,可为木质素产品高值化利用提供一种新途径。木质素微纳米球是一种具有规整结构的微纳米木质素,其自组装制备方法主要有溶剂-反溶剂法、气溶胶的流式反应器法和界面细乳液聚合法。利用四氢呋喃、二氧六环和乙醇等溶剂对木质素或化学修饰木质素进行溶解,然后滴加反溶剂去离子水可获得木质素微纳米球,然而溶剂-反溶剂法获得的木质素微纳米球悬浮液在干燥过程中存在微纳米球团聚问题;气溶胶的流式反应器法能将木质素溶液直接雾化自组装成气溶胶;界面细乳液聚合法可使木质素分子在非共价自组装形成微纳米球基础上实现共价键结合。相比实心微纳米球,中空微纳米球拥有较高的比表面积。木质素微纳米球当前主要应用于药物载体、紫外防护和纳米填料等方面。采用木质素包载疏水药物,能提高药物在水溶液中的溶解性能,实现可控释放,延长作用时间,降低毒副作用;将木质素微纳米球用于光敏性农药的包载,能使其具有可控释放和抗光降解功效;将木质素微纳米球对酶进行包载,能使其具有较好的稳定性和催化活性。通过调控木质素自组装过程,可使其微纳米球具有相对亲水或疏水外表面,使微纳米球与相应亲水或疏水高分子聚合物共混时具有较强的分子间作用。此外,木质素微纳米球亦可用于吸附材料、聚集诱导发光纳米材料和锂离子电池电极材料等方面。目前,木质素微纳米球研究还处于起步阶段,其简单可行的可控构筑方法及其高值化应用领域需要进一步探索。界面细乳液聚合法能使木质素分子自组装过程中实现非共价键和共价键协同作用,且通过该方法可获得中空木质素微纳米球,为新型中空结构木质素微纳米球的开发提供了新方向;木质素具有自发荧光特性,且自组装制备微纳米球过程中木质素分子会产生J-聚集增强其荧光强度,为新型木质素基发光材料的开发提供了新思路。

Progress of Preparation and Application of Lignin Micro/Nano-Spheres

Lignin is the second most abundant plant biopolymer on earth after cellulose.However,lignin is not used extensively due to its complex structures.Lignin micro/nano-particles can provide many opportunities for value-added applications of lignin.Self-assembly method of lignin micro/nano-spheres,which possess regular structure,include solvent and anti-solvent method,aerosol flow reactor and interfacial miniemulsion polymerization.When lignin and its derivatives are dissolved in solvent,such as tetrahydrofuran,dioxane and ethanol,and then dropped disionized water,the micro/nano-spheres can be formed.However,the micro/nano-spheres obtained through solvent and anti-solvent method may agglomerate in the drying process.Lignin precursor solution is directly atomized aerosol through aerosol flow reactor.When the micro/nano-spheres are prepared through interfacial microemulsion polymerization,lignin molecules will be linked by covalent and non-covalent bonded.Currently the micro/nano-spheres are mainly used in the fields of ultraviolet protection,drug carriers and nano-filler.When hydrophobic drugs are loaded by the micro/nano-spheres,the solubility of drugs in aqueous solution will be improved.And the loaded drugs exhibit the controlled release,a longer action time and a lower toxic and side effects.When photosensitive pesticides are loaded by the micro/nano-spheres,they display the characteristics of the controlled release and anti-photodegradation.The micro/nano-spheres are used to encapsulate the enzyme,which exhibit good stability and catalytic activity.Hydrophilic or hydrophobic outside surface of the micro/nano-spheres can be controlled through the change of self-assembly.Therefore,strong intermolecular interaction can be formed between the micro/nano-spheres and corresponding hydrophilic or hydrophobic polymer at the time of blending.In addition,the applications of the micro/nano-spheres have also been reported in the fields of adsorption materials,aggregation-induced emission nanomaterials and li-ion battery electrode materials.At present,studies on the micro/nano-spheres have been still in its infancy,there are much more to do.Because the interfacial miniemulsion polymerization can achieve synergies between non-covalent bond and covalent bond in the self-assembly process of lignin molecules,hollow lignin microspheres can be obtained by this method,which provides a new direction for the preparation of hollow lignin micro/nano-spheres.Moreover,light-emitting nanomaterials based on lignin may be as an important development direction due to the fact that lignin molecules have the characteristic of autofluorescence and aggregation-induced emission through J-aggregates.