Lignin-Assisted Stabilization of an Oriented Liquid Crystalline Cellulosic Mesophase, Part A: Observation of Microstructural and Mechanical Behavior

Abstract

Liquid crystalline polymer blends containing lignin have been scarcely studied in the literature, albeit demonstrating potential for the design of high-performance lignin-based materials. In this study, organosolv lignin is blended in solution with hydroxypropyl cellulose (HPC), a lyotropic cellulose derivative, and its impact on the dynamics of the cellulosic liquid crystalline mesophase is investigated. Rheological measurements and rheo-optical investigations under crossed polarizers reveal that lignin enhances the persistence of the shear-induced orientation of the cellulosic macromolecules. In shear-cast films, the retention of the microstructural organization or band texture entails a drastic increase of the mechanical anisotropy and properties with lignin content. For the origin of the textural stabilization, we propose a specific “jacketing”-like effect of lignin on HPC. This study indicates the possibility of a beneficial impact of lignin on the relaxation behavior of liquid crystalline cellulosic polymers.

Lignin in Bio-Based Liquid Crystalline Network Material with Potential for Direct Ink Writing

“…Because of the ability of a liquid crystalline polymer (LCP) to serve both as processing aid and reinforcement, solution blending rod-like polymers with flexible coil polymers represents an established and potent approach to design strong lightweight molecular composites. − Within the current context of material sustainability, a renewed interest for LCPs blended with bio-based or biogenic polymers has recently emerged. , Concurrently, bio-based lyotropic polymers such as cellulose derivatives are revisited. − Building upon the efforts of Glasser and his co-workers − at adding value to lignin, the second most abundant biopolymer on earth, the potential of organosolv lignin (OSL) dispersed in the lyotropic phase of hydroxypropyl cellulose (HPC) for material design could be evidenced recently. , Interestingly, lignin was found to significantly improve the stability of the shear-induced transient band texture enabling the manufacture of highly oriented films via shear casting . The observed phenomenon was ascribed to enhanced miscibility and secondary intermolecular interactions between low molecular weight, phenolic OH-rich lignin fractions and HPC .…”

“…Revisiting the processing of the HPC/OSL system in this regard, DIW appears particularly suited for the LCP blend as it circumvents drawbacks of melt processing, viz the limited adaptability of the rheological properties and the thermomechanical instability of lignin. , Instead, the solution state is beneficial in many respects: apart from the eased dispersibility of blends, we propose that the adjustable rheological behavior of the lyotropic cellulosic LC phase facilitates the processing via additive manufacturing; acting as an effective shear-thinning processing aid, the emergence of the mesophase also allows a high polymer loading, which contributes to the structural stability of the drying filament. Finally, the cellulosic LC phase appears to stimulate lignin to stabilize the oriented mesophase …”

“…This proposition builds on the idea of unlocking the potential of manufacturing LC network materials with anisotropic properties from blends of OSL and HPC. In this regard, the study is focused on the utilization of lignin as an essential additive for the formation of highly anisotropic cellulose-based materials, which has been investigated in the water-soluble biopolymer blend previously . Based on this, we screen the fixation of the flow-induced organization via esterification with different polycarboxylic acids.…”

3D printing of lignin: Challenges, opportunities and roads onward

“…Lignin stabilizing effect in this blend was further found to stem from its phenolic‐OH groups and low molecular weight fraction, which enhanced lignin miscibility with HPC. [ 52,53 ] The anisotropic swelling imparted by molecular orientation and the resulting band texture formation endowed parts with morphing properties upon exposure to humidity, paving the way to the manufacture of sensing and soft robotic devices from fully bio‐based lignin systems. However, dragging of the outer layers to the center during printing limited dimensional stability and restricted the design space to continuously‐printed structures such as rings.…”

Bringing Material Concepts into Conventional Biorefineries: Considerations of Sources, Preparations, and Applications of Lignin Nanomaterials

“…After delignification, the carbohydrate-rich fraction is substituted for further valorizations, while the lignin-rich fraction needs to be further valorized. Pretreatment by organic solvents or solvolysis, is rarely used in the pulp and paper industry, but has attracted wide attention in the bioenergy field. − Lignin extracted from biomass materials via organic solvents such as alcohols and ketones is collectively called organosolv lignin (OL) . In addition, other biomass pretreatment technologies have been developed, including acid hydrolysis, alkaline hydrolysis, reduction or oxidation catalytic fractionation, etc .…”