Understanding the self-assembly of lignin-based biomaterials

Developing bio-renewable raw materials for manufacturing and technology has become a focus of research, with special interest in the field of biomaterials. Lignocellulosic biomass can be utilized as a raw material to produce chemicals and it is an important feedstock for renewable fuels in the production of energy. Lignocellulose is composed of mainly three biomacromolecules (cellulose, hemicellulose and lignin). Currently, most of the extracted lignin is either decanted in nearby waters or burned in energy-recovery systems. The reason why lignin is disposed of instead of being further processed is that lignin is immiscible with most polymers and its association behavior is still unknown due to its non-uniform aromatic structure with a number of methoxy, ether and ester groups. To fully utilize lignin, an improved understanding of the interfacial adhesion and interfacial tension is needed. The main motivation for this project is to find new possible ways to make lignin, a lignocellulose component, miscible with most polymers, and to understand how the molecule associates and behaves in the presence of other natural macromolecules. One of the main barriers to utilization of lignin is the absence of significant intermolecular interactions, which cause miscibility problems resulting in phase separation, a generally undesirable characteristic for manufacturing applications, especially in the production of materials. Lignin-based polymeric blends in solution have provided a possible avenue for understanding lignin’s self-assembly behavior in solid and the variations in morphology, physical and thermal properties that come with the addition of secondary and tertiary components, and as well as foreign molecules such reduced graphene oxide (rGO). In the first study, we focused on understanding the association behavior using high and low proportions of cellulose to test how the various functional groups may interact differentially with lignin utilizing ionic liquids as the solvent and water as the coagulation agent. A tertiary component, rGO, was introduced into the lignin-based biocomposite to modify π-π aggregations. The study looks at the effect of rGO as a function material concentration. The biocomposites were investigated using Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR), Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Scanning Electron Microscope (SEM) techniques. Results show that π-π aggregates are driven by the π-π interaction of the aromatic groups in lignin. The π-π aggregates undergo disaggregation by the addition of rGO on the blended biocomposite. The results showed that increasing the cellulose content in the cellulose-lignin biocomposite can increase the molecular interactions, causing an increase in the stability of the blended film and an increase in the crystallinity of the cellulose. Profound changes in the morphology was observed upon the addition of rGO. Results demonstrates that the addition of rGO into the biocomposite prevented the self-assembly of lignin. The second study investigated the material morphological and thermal effects upon the addition of rGO as a function of material composition in a tertiary system comprised of lignin, cellulose, and xylan. The results demonstrated that the regenerated films’ structural, morphological and thermal character changed as a function of lignin-xylan concentration and upon the addition of rGO. We observed how the fibrous/spherical structure changed as results of the addition of rGO into the system. We provided evidence that shows a dramatic change in the glass transition temperature and degradation temperature. The two studies provided evidence to suggest that the addition of rGO prevented the self-assembly of lignin by reducing π-π aggregations and reducing the cellulose percent crystallinity. In addition, it suggested that by increasing interfacial adhesion while mitigating interfacial tension increase the utility of lignin. The increase in the interfacial adhesion between the lignin backbone hydroxyl groups and the matrix with its abundant hydroxyl and ether functional groups which are available for hydrogen bonding, impacts it’s the suitability and, consequently, the its utilization as a value-added biomaterial.M.S.Includes bibliographical referencesby Dalia Al-Shahran