The Microstructures Of Lignin Amphiphilic Polymers Influenced By Molecular Interaction And The Preparation Of Lignin-based Nanosphere

After cellulose, lignin is the most abundant renewable resource in nature. In the industries of paper pulping process, cellulosic ethanol and textile,in which the plant fibre is served as core material, lignin is always obtained as a by-product. Lignin amphiphilic polymers come from the waste liquid of paper pulping. They mainly include the alkali lignin which is obtained from alkaline pulping and the lignosulfonate which is obtained from acid polishing. In addition, they also include some other lignin derivatives which are obtained by the chemical modification of alkali lignin and lignosulfonate. The microstructures of lignin amphiphilic polymers in solutions and on the interfaces have important basic significance for realizing there product function.In this dissertation, the microstructures of lignin amphiphilic polymers in solutions and on the interfaces were centered as the themes, and the molecular interaction related to the lignin amphiphilic polymers was thread in the researches of the regulation of the lignin microstructures. The researches were conducted on both of the theory and application levels. On the one hand, combined with the application background, the interactions between the lignin amphiphilic polymers and the solvent, the interactions between the lignin amphiphilic polymers and the substrates which they are adsorbed to were revealed from the theory aspect; on the other hand, to explore the new way for the application of lignin, the microstructures of lignin amphiphilic polymers in solutions were given a target regulation for the preparation of lignin-based nanosphere.The influence of temperature on the microstructure of lignin amphiphilic polymers in solutions was studied. For the changing of temperature could adjust the interactions between the lignin amphiphilic polymers and water molecule, thus the microstructure of lignin influence by the interactions between the lignin and water molecule could be studied by changing of temperature. The temperature effect on the physicochemical behaviours of alkali lignin, such as aggregation morphology, molecular surface charge, adsorption characteristics and the molecular internal microstructure were investigated at first, and then give a further research about the lignosulfonate. Results show that the increasing of temperature not only reduces the intramolecular and intermolecular electrostatic repulsion of the lignin amphiphilic polymers, but also reduces the hydrogen bond between the lignin amphiphilic polymers and the water molecules. These changes would cause the intramolecular and intermolecularaggregation of lignin amphiphilic polymers. Although lignin amphiphilic polymers is often viewed as a kind of anionic surfactants, the changing regularity of its physicochemical behaviours influenced by temperature is more similar to nonionic surfactant.Hydroxyl group is a main functional group of the lignin amphiphilic polymers, the change of the hydroxyl groupscontent would cause the change of the interactions between lignin and solvent, and then it would influence the microstructures of lignin amphiphilicpolymers. By comparing the difference of the alkali lignin and the acetylated alkali lignin which has nearly no hydroxyl groups, the influences of the hydroxyl groups on the lignin microstructures was studied. Results show that the hydroxyl group would enhance theintramolecular and intermolecular hydrogen bond of alkali lignin. This effect would make alkali lignin more coiled and form more aggregates. The experiments also revealed that alkali lignin should be acetylated firstly before the GPC test when the THF was as the mobile phase, otherwise there would be an experimental artifact for the measuring result.By adjusting the proportion of THF and water, it would change the interactions between the THF,lignin amphiphilic polymers and water. And then the microstructure and the aggregation morphology of lignin amphiphilic polymers in the mixed THF-water solventcould also undergo the conformational changes. Alkali lignin and acetylated alkali lignin can form alkali lignin hollow microspheres and acetylated alkali lignin solid colloidal spheres respectively. It is the first time to obtain the lignin-based nanospheres. And this method opens up a new way to prepare the lignin-base nano materials. For the reasons that the amphipathy of alkali lignin and acetylated alkali lignin is different to each other, the interactions between these two kinds of lignin and THF or water are also different to each other. Comparatively speaking, the interactions between acetylated alkali lignin and THF are stronger than alkali lignin, while the interactions between acetylated alkali lignin and water are weaker than alkali lignin. So, alkali lignin would form the hollow microspheres which has a loosened structure, while, the acetylated alkali ligninwould form the solid colloidal spheres which has a compact structure.By adjusting the proportion of ethanol and water, it would also change the interactions of the ethanol,lignin amphiphilic polymers and water. Similarly, alkali lignin can alsoform alkali lignin hollow nonospheres in the mixed ethanol-water solvent. It is also the first time to obtain the lignin-based nanospheres with an innocuous pathway. The particle size can be controlled by changing the initial concentration or the water dropping speed. The feature and the assemblemechanisms of the alkali lignin hollow nonospheres were studied by a variety of characterization methods. As the solvent environment become worse(the water content increase), alkali lignin would form the lamelleted aggregate first, and then, the lamelleted aggregate would be bend and connected to each other for the assembling of nonospheres. Results show that the p–p interactions between the aromatic nucleusmakes significant contribution for the formation of the hollow nonospheres. The hollow nonospheres made from the ethanol-water mixed solvent have the advantages of biological compatible characteristic, biodegradability, innocuous and environmentally friendly, so it has broad application prospects in the areas of life sciences, medical science, biological and agriculture.The silicon nitride(Si3N4), Alumina(Al2O3) and Au were selected as three typical substrates to study the relationships of the adsorption characteristic of lignosulfonate and the interaction forces between the substrates and lignosulfonate. The quartz crystal microbalance(QCM) was used to study the adsorption process when the lignosulfonate was adsorbed on the three substrates. And the atomic force microscopy was used to study the interaction forces between the substrates and lignosulfonate. The study found that the interaction forcesbetween the substrates and lignosulfonate not only influence the adsorption amount of lignosulfonate, but also influence the adsorption conformation of lignosulfonate. In theadsorption process of lignosulfonate onto Si3N4, the adsorption amount would increase firstly but then decrease a little. The lignosulfonate adsorbed on Si3N4 would also present a more stretchedadsorption comformation.These phenomena are caused by the electrostatic repulsionbetween Si3N4 and lignosulfonate. The stronger interaction forces between the Al2O3 and lignosulfonate make the adsorption comformation of lignosulfonate on Al2O3 present a more applanate feature which would also make the adsorption amount on Al2O3 is less than the adsorption amount on Au. The interaction forces between lignosulfonate and Au is bigger than Si3N4 but smaller than Al2O3. Lignosulfonate adsorbed onto Au is mainly driven by the hydrophobic effect. The adsorption conformation of lignosulfonate on Au is similar to its conformation in solution. In the process of this research, the methods for measuring the intermolecular forces related to the lignin amphiphilic polymers by atomic force microscopy also has been founded, which could lay the foundation for the other related researches about lignin.