Lignin, the second most abundant biopolymer on earth, has the potential as a low-cost and renewable precursor for carbon fibers. By creating lignin-based carbon nanofibers for lightweight structural composites for automobiles and functional applications such as electromagnetic shields, the value of lignin will be enhanced. In this chapter, we present the feasibility of producing carbon nanofibers from lignin by electrospinning and heat treatment, as well as reviewing the potential applications. The morphological, mechanical, and electromagnetic properties of the lignin-based carbon nanofibers are presented. The strength of lignin random nanofiber mats was significantly improved after carbonization and alignment. By doping the lignin polymer with carbon nanotubes and functional nanoparticles such as magnetite, it was possible to improve the strength and introduce electromagnetic functionality to the lignin nanofiber assemblies. These encouraging results demonstrate the potential of lignin-based composite carbon nanofibers as a unique engineering material, thus establishing a pathway for adding value to the abundantly available natural polymer, lignin.

This research studied the influence of formulations of wood-plastic composites on dynamic mechanical properties—storage modulus (E′), loss modulus (E′′) and mechanical loss factor (tan δ)—according to dynamic mechanical analysis spectra. The specimens were made with wood flour, high-density polyethylene (HDPE) and maleic anhydride polypropylene as a coupling agent. Generally, the presence of fillers and a coupling agent in polymer affect the relaxation processes and produce a more complex morphology, thereby influencing the mechanical and viscoelastic properties of the composites. In this work, the addition of a higher content of wood flour resulted in higher values of E′, indicating a better stiffness, but tan δ decreased. The bonding agent significantly improved E′, which can be attributed to an enhanced interface between the wood and the HDPE. Coupled products had better E′ retention at elevated temperatures than uncoupled samples. The addition of wood flour and a coupling agent increased the value of E′, but did not significantly change the range of relaxation transition.

With increasing interest in using lignin as an alternative material to petroleum-based chemicals (e.g., in the manufacture of carbon fibers or adhesives), it is becoming important to understand what properties of lignin are required to impart key features in the final product. Commercial lignins are complex, heterogeneous, macromolecular mixtures. To obtain maximum value, lignins will require classification and possibly fractionation or modification to improve properties and enable their utilization in high-value applications. To this end, the physicochemical properties of fractions derived from two industrial softwood Kraft lignins (New Bern Mill, Weyerhaeuser, U.SA, and Backhammar Mill in Kristinehamn, Sweden) have been determined and compared to previously published data on commercially available Indulin AT lignin from MeadWestvaco.(1,2) The fractions were obtained by successive extraction with organic solvents and analyzed using a range of techniques (e.g., DSC, C-13 NMR, P-31 NMR). The results showed that these industrial softwood Kraft lignins varied significantly in both the amounts of the various fractions and in the properties of the analogous fractions. These differences emphasize the issues industry faces in the utilization of industrial lignins for high-value application where minor inconsistencies between lignin sources could pose major technical challenges.

Various noble monometallic and bimetallic nanoparticles, including Pd, Pt, Au, Pd/Pt, Pd/Au, and Pt/Au, deposited lignin nanofiber mats (LFMs), and lignin carbon nanofiber mats (LCFMs) were fabricated using a novel lignin fiber surface PDMAEMA brush-guided strategy. PDMAEMA brushes were immobilized on lignin nanofiber mat surfaces by surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET-ATRP) in an aqueous solution followed by monometallic nanoparticle deposition. For the Pd and Pt nanoparticle-immobilized LFMs, the metallic ions were reduced using citric acid and ascorbic acid, respectively; however, for the Au nanoparticle-immobilized LFMs, in-situ reduction occurred via the reducing potential of the PDMAEMA. The process was repeated to produce the bimetallic, Pd/Pt, Pd/Au, and Pt/Au-immobilized lignin nanofiber mats. The resultant mono and bimetallic nanoparticle-immobilized LFMs were then carbonized to the corresponding metallic-modified carbon nanofibers. XPS, XRD, and SEM were used to confirm the uniformity of nanoparticle deposition and the metallic state on the lignin fiber and carbon nanofiber surfaces.

Softwood kraft lignin (SKL) pH-responsive hydrogels were prepared through controlled aggregation using poly[2-(dimethylamino) ethyl methacrylate] (PDMAEMA) and poly(2-(dimethylamino) ethyl methacrylate)-block-poly(ethylene oxide)-block-poly(2-(dimethylamino) ethyl methacrylate) triblock copolymer (PDMAEMA-co-PEO-co-PDMAEMA). At low SKL concentrations, the SKL/polymer (PDMAEMA and PDMAEMA-co-PEO-co-PDMAEMA) aqueous solutions exhibited pH-dependent aggregation arising from the formation of strong intermolecular hydrogen bonds. Decreasing the SKL/polymer weight ratio resulted in the pH-reversible soluble-insoluble (S-I) transition to become a soluble-insoluble-soluble (S-I-S) transition, which upon increasing the SKL concentration resulted in hydrogel formation. Under neutral conditions relatively strong hydrogels were formed, which upon either increasing or decreasing solution pH resulted in the hydrogels collapsing to liquid solutions, but were readily reformed upon neutralization. The effects of polymer structure, concentration, and intermolecular interactions on solution behavior and gelation are thoroughly discussed.

ABSTRACTA series of cellulose acetate (CA) ternary system solutions consisting of the CA, N,N‐dimethylacetamide, and various nonsolvents, such as 1‐propanol, 1‐hexanol, 1‐octanol, 1‐decanol, 1,3‐propane diol, and glycerol, were prepared, and the effects of the component composition on the solutions characteristics and electrospinning were examined. In particular, the effects of the nonsolvent concentration, structure, and degree of miscibility with other components were studied. In some cases, increasing the nonsolvent content increased the solution viscosity and facilitated the electrospinning process. However, we found that electrospinning was also governed by the structure of the nonsolvents and by the solution viscosity. An increase in the number of hydroxyl groups or an increase in the hydrocarbon chain length of the monohydroxyl alcohol nonsolvent improved the fiber formation. The calculated Hansen sphere [D(S‐p)] values of the CA ternary system solution were then used to explain their electrospinnability. The increases in the hydrophilicity and hydrophobicity of system caused by changes in the nonsolvent structure increased the D(S‐p) values and improved fiber formation in electrospinning process. The calculated D(S‐p) values were also shown to be in good agreement with the obtained microscopy images of the electrospun fiber. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42819.

Inter‐connected carbon sub‐µm fibrous materials are prepared by electrospinning of Kraft lignin solutions in DMF followed by thermal treatment consisting of oxidative thermostabilization at 250 °C and carbonization in the temperature range 600–1000 °C. Inter‐fiber bonding is achieved by taking advantages of the intrinsic differences in thermal mobility between different Kraft lignin fractions. Inter‐fiber bonding is observed to enhance the mechanical properties of both the thermostabilized and carbonized materials and enhances the electrical conductivity of the carbonized materials. The surface area, morphological, and structural characteristics are also characterized by the BET method, scanning electron microscopy, and Raman spectroscopy, respectively.

Surface modification of electrospun lignin nanofibres with poly(N-isopropylacrylamide) (PNIPAM) was conducted through surface-initiated atom transfer radical polymerization (ATRPase) using various biocatalysts under aqueous conditions.

Viscoelastic properties of N,N-dimethylforrnamide (DMF) solutions of softwood kraft lignin (SKL) containing small amounts of poly(ethylene oxide) (PEO) were investigated. Of interest is the relationship between viscoelastic properties of the spinning solutions and their corresponding electrospinning behavior. Although it is well established that fiber diameter is critical in determining the material properties of nanofibers, lignin solutions have been observed to display poor electrospinnability in many instances. Thus, the motivation behind this work was to understand and exert control over the relevant fluid properties that control the fiber diameter of SKL/PEO fibers, The results of dynamic shear and capillary breakup extensional rheometry (CaBER) experiments indicated that SKL solutions were weakly elastic in shear and Newtonian in elongational flow. SKL solutions were not electrospinnable at concentrations of 25-45 wt % but form fibers at 50 wt % concentration. The addition of PEO to SKL solutions led to an increase in shear moduli and pronounced strain hardening in elongational flow. The characteristic time scales of tensile stress growth (lambda) measured with CaBER were dependent on the SKI; concentration, PEO concentration, and PEO molecular weight. In contrast to SKL solutions, SKL/PEO solutions are electrospinnable over the concentration range of 25-45 wt % SKL depending on the combination of SKL concentration, PEO concentration, and PEO molecular weight. Correlation between the fiber diameters obtained during electrospinning and the measured value of lambda are discussed.

The development of value-added wood-derived polymer products is of significant importance. Of particular interest is the synthesis of advanced bioactive cellulosic materials. In the present research, novel cellulosic honeycomb films are reported. Cellulose was reacted with dimethylthexylsilyl chloride to form regioselective 2,6-di-O-thexyldimethylsilyl cellulose followed by substitution of the C3 with functionalized poly(ethylene glycol) (PEG). The free end of the PEG side chains of the regioselective 3-O-poly(ethylene glycol)–2,6-di-O-thexyldimethylsilyl cellulose served as an attachment point for bioactive molecules. As an example, Fmoc–Gly–OH was linked to the free end of PEG to produce 3-O-Fmoc–Gly–poly(ethylene glycol)–2,6-di-O-thexyldimethylsilyl cellulose. Honeycomb films were produced through film casting under a humid airflow. AFM analysis revealed the directed self-assembly of the 3-O-Fmoc–Gly–poly(ethylene glycol)–2,6-di-O-thexyldimethylsilyl cellulose wherein the pendent 3-O-Fmoc–Gly–poly(ethylene glycol) groups allocated preferentially around the edges of the honeycomb pores.

An overview of the production of carbon fibers based on lignin is presented. The structure, isolation, and properties of lignin are first discussed in the context of their effects on carbon fiber production. A general overview of carbon fiber manufacturing is then presented to provide background for a discussion of previous and current research on lignin-based carbon fiber. Current research on fiber spinning, thermostabilization, and carbonization of lignin is reviewed and directions for future research are discussed. Finally, emerging new opportunities for lignin-based carbon fiber in non-structural applications are presented, highlighting recent research from our laboratory on the production of sub-micron and nanometer scale carbon fibers by electrospinning of lignin.

Hydrogen-bonding-based reversible polymer networks are prepared from poly(2-(dimethylamino ethyl)methacrylate)-block-poly(ethylene oxide)-block-poly(2-(dimethylamino ethyl) methacrylate) (PDMAEMA-co-PEO-co-PDMAEMA) triblock copolymer blends with lignin. FTIR and DSC analyses reveal miscible blends. Fitting of the T-g/composition data using the Kwei equation produces significantly large positive q-values: +275 for PDMAEMA and +413 PDMAEMA-co-PEO-co-PDMAEMA. In solution the blends self-assemble into a hydrogen-bonded polymer network with a strong dependence on blend composition and solution pH. H-1 NMR spectra show that there is a clear core/corona transformation by adjust the solution pH.

Phage therapy is a potentially beneficial approach to food preservation and storage. Sustained delivery of bacteriophage can prevent bacterial growth on contaminated food surfaces. Using coaxial electrospinning bacteriophage can be encapsulated in electrospun fibers with high viability. The resulting bio-based electrospun fibers may have potential as a food packaging material. In the present work, T4 bacteriophage (T4 phage) was incorporated into core/shell electrospun fibers made from poly(ethylene oxide) (PEO), cellulose diacetate (CDA), and their blends. Fibers prepared using PEO as the shell polymer showed an immediate burst release of T4 phage upon submersion in buffer. The blending of CDA with PEO significantly decreased the rate of phage release, with no released T4 phage being detected from the solely CDA fibers. Increasing the PEO molecular weight increased the electrospun fiber diameter and viscosity of the releasing medium, which resulted in a relatively slower T4 phage release profile. SEM analyses of the electrospun fiber morphologies were in good agreement with the T4 phage release profiles. Depending on the PEO/CDA ratio, the post-release electrospun fiber morphologies varied from discontinuous fibers to minimally swollen fibers. From these results it is suggested that the T4 phage release mechanism is through solvent activation/polymer dissolution in the case of the PEO fibers and/or by diffusion control from the PEO/CDA blend fibers.

ABSTRACT This study has shown that ultrafiltration allows the selective extraction from industrial black liquors of lignin fraction with specific thermo‐mechanical properties, which can be matched to the intended end uses. Ultrafiltration resulted in the efficient fractionation of kraft lignin according to its molecular weight, with an accumulation of sulfur‐containing compounds in the low‐molecular weight fractions. The obtained lignin samples had a varying quantities of functional groups, which correlated with their molecular weight with decreased molecular size, the lignin fractions had a higher amount of phenolic hydroxyl groups and fewer aliphatic hydroxyl groups. Depending on the molecular weight, glass‐transition temperatures ( T g ) between 70 and 170°C were obtained for lignin samples isolated from the same batch of black liquor, a tendency confirmed by two independent methods, DSC, and dynamic rheology (DMA). The Fox–Flory equation adequately described the relationship between the number average molecular masses ( M n ) and T g 's‐irrespective of the method applied. DMA showed that low‐molecular‐weight lignin exhibits a good flow behavior as well as high‐temperature crosslinking capability. Unfractionated and high molecular weight lignin ( M w >5 kDa), on the other hand, do not soften sufficiently and may require additional modifications for use in thermal processings where melt‐flow is required as the first step. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131 , 40799.

An understanding of lignin chemical structure and properties is required before connections can be drawn between lignin sources and utilisation. Of particular interest, and one cause for the limited use of lignin, is chemical heterogeneity. The principal applications for lignin are power/fuel (short term), macromolecules (medium term) and aromatic chemicals (long term), with the preferred use ultimately directed by the global price of oil and biomass. The intention of this chapter is to compile and evaluate the properties of lignins from various sources and to identify applications that match the unique properties of each lignin.

Preparation of moisture-responsive Kraft lignin-based materials by electrospinning blends of Kraft lignin fractions with different physical properties is presented. The differences in thermal mobility between lignin fractions are shown to influence the degree of interfiber fusion occurring during oxidative thermostabilization of electrospun nonwoven fabrics, resulting in different material morphologies including submicrometer fibers, bonded nonwovens, porous films, and smooth films. The relative amount of different lignin fractions and degree of fiber flow and fiber fusion is shown to influence the tendency for the electrospun materials to be transformed into moisture-responsive materials capable of reversible changes in shape. Material characterization by scanning electron microscopy and atomic force microscopy as well characterization of the chemical and physical properties of Kraft lignin fractions by dynamic rheology, 1H and 13C NMR, and gel permeation chromatography combined with multiangle laser light scattering are presented. A proposed mechanism underlying moisture-responsiveness, shape change, and shape recovery is discussed based on the differences in chemical structure and physical properties of Kraft lignin fractions.

Time–temperature–stress superposition principle (TTSSP) was widely applied in studies of viscoelastic properties of materials. It involves shifting curves at various conditions to construct master curves. To extend the application of this principle, a temperature–stress hybrid shift factor and a modified Williams–Landel–Ferry (WLF) equation that incorporated variables of stress and temperature for the shift factor fitting were studied. A wood–plastic composite (WPC) was selected as the test subject to conduct a series of short-term creep tests. The results indicate that the WPC were rheologically simple materials and merely a horizontal shift was needed for the time–temperature superposition, whereas vertical shifting would be needed for time–stress superposition. The shift factor was independent of the stress for horizontal shifts in time–temperature superposition. In addition, the temperature- and stress-shift factors used to construct master curves were well fitted with the WLF equation. Furthermore, the parameters of the modified WLF equation were also successfully calibrated. The application of this method and equation can be extended to curve shifting that involves the effects of both temperature and stress simultaneously.

Functionalized nanoparticles are promising building blocks for well-defined nanomaterials with unique properties. Site-specific or regio-selective functionalization of those nanoparticles and organization into high-order assemblies is a major challenge in materials research. Here, we demonstrate site-specific immobilization of a model protein at one tip of nanocrystalline cellulose (NCC), single-crystalline rod-like shaped nanoparticles that are isolated by acid hydrolysis of bulk cellulose. Click reaction between reducing end functionalized NCC bearing azide groups and β-casein micelles bearing acetylene groups results in mushroom-like conjugated nanoparticles in different arrangements. The strategy developed here to design hybrid polysaccharide–protein nanoparticles could be useful for building novel functional self-assembled nanobiomaterials and have potential in nanomedicine, immunoassay and drug delivery applications.