RHEOLOGICALLY DEFINED LIGNIN COMPOSITIONS

Abstract

Anthropogenic derivatives of native lignin are disclosed, having specific viscoelastic metrics which selectively facilitate the processing of these lignin derivatives into particular finished products. Such lignin derivatives are characterized by rheological metrics that include minimum storage modulus (G′.sub.min), onset of softening temperature (T.sub.1), and/or cross-over temperature (T.sub.2) from predominately viscous to predominately elastic behaviour.

Claims

1. An anthropogenic lignin derivative having a minimum storage modulus (G′.sub.min) of less than or equal to 10,000 Pa, an onset of softening temperature (T.sub.1) greater than or equal to 125° C., a cross-over temperature (T.sub.2) from predominately viscous to predominately elastic behaviour of greater than or equal to 175° C., and an extent of crosslinking (ΔG′.sub.2=G′.sub.250/G′.sub.min) such that an increase in storage modulus (ΔG′.sub.2) from G′.sub.min to that measured at 250° C. (G′.sub.250) is less than about 4 or more than about 7.

2. The anthropogenic lignin derivative of claim 1, characterized as having a G′.sub.min of about 8,000 Pa or less, about 5,000 Pa or less, or about 1,000 Pa or less, or about 100 Pa or less.

3. The anthropogenic lignin derivative of claim 1, characterized as having a T.sub.1 about 130° C. or greater, about 150° C. or greater, about 170° C. or greater.

4. The anthropogenic lignin derivative of claim 1, characterized as having a T.sub.2 of about 180° C. or greater, about 200° C. or greater, or about 220° C. or greater.

5. The anthropogenic lignin derivative of claim 1, wherein the lignin derivative has an extent of crosslinking (ΔG′.sub.2=G′.sub.250/G′.sub.min) such that an increase in storage modulus (ΔG′.sub.2) from G′.sub.min to that measured at 250° C. (G′.sub.250) is about 7 or greater, about 8 or greater, about 10 or greater, or about 100 or greater.

6. The anthropogenic lignin derivative of claim 1, wherein the lignin is derived in whole or in part from hardwood biomass, softwood biomass, annual fibre biomass or a combination thereof.

7. The anthropogenic lignin derivative of claim 1, wherein the lignin derivative is produced by a process comprising: solvent extraction of finely ground wood; acidic dioxane extraction of wood; biomass pre-treatment using steam explosion, dilute acid hydrolysis, ammonia fibre expansion, or autohydrolysis; pulping of lignocellulosics by Kraft pulping, soda pulping, sulphite pulping, ethanol/solvent pulping, alkaline sulphite anthraquinone methanol pulping, methanol pulping followed by methanol NaOH and anthraquinone pulping, acetic acid/hydrochloric acid or formic acid pulping, or high-boiling solvent pulping.

8. The anthropogenic lignin derivative of claim 1, wherein the lignin derivative is a composite lignin composition, comprising a blend of two or more distinct lignin derivatives, wherein the distinct lignin derivatives differ in one or more of: minimum storage modulus (G′.sub.min); onset of softening temperature (T.sub.1); and cross-over temperature (T.sub.2) from predominately viscous to predominately elastic behaviour.

9. A method of forming a molded or extruded thermoplastic form having a shape, comprising: heating the lignin derivative of claim 1 above T.sub.1, to form a heated thermoplastic material that is in a predominantly viscous state and has a storage modulus of less than or equal to 10,000 Pa; forming the heated thermoplastic material into the shape of the thermoplastic form; and cooling the heated thermoplastic material below T.sub.1 to provide the thermoplastic form.

10. The method of claim 9, wherein the lignin derivative is mixed with one or more thermoplastic polymer.

11. The method of claim 10, wherein the lignin derivative and the thermoplastic polymer are coextruded to form a freestanding, self-supporting composite form.

12. The method of claim 10, wherein the thermoplastic polymer comprises a condensation polymer, an alkyd, a polymer resin, a modified polymer alloy and/or a filled polymer blend.

13. A method of thermo-forming a composite material comprising binding a plurality of parts composed of solid material into a solid composite form, wherein the parts are joined by heating and compression in an admixture with an adhesive comprising the lignin derivative of claim 1, wherein the heating and compression raise the admixture to a temperature above T.sub.1.

14. A method of forming a molded or extruded thermoset form having a shape, comprising: heating the lignin derivative of claim 1 above T.sub.1, to form a heated material, so that the heated material is in a predominantly viscous state and has a storage modulus of less than or equal to 10,000 Pa; forming the heated material into the shape of the thermoset form, to form a shaped thermoset form; heating the shaped thermoset form beyond T.sub.2; holding the shaped thermoset form at T.sub.2 for more than 1 minute; and cooling the shaped thermoset form below T.sub.1 to provide the molded or extruded thermoset form.

15. The method of claim 14, wherein the lignin derivative is mixed with one or more thermoplastic polymers.

16. The method of claim 15, wherein the lignin derivative and the thermoplastic polymer are coextruded to form a freestanding, self-supporting composite form.

17. The method of claim 15, wherein the thermoplastic polymer comprises a thermoset polymer and/or an elastomer.

18. A method of solution forming a composite material comprising a plurality of parts composed of solid material into a solid composite form, wherein the parts are consolidated by a heating and/or compression as an admixture comprising the lignin derivative of claim 1, wherein the heating and/or compression raise the admixture to a temperature above T.sub.2, or to a temperature above temperature at G′.sub.min.

19. The method of claim 18, wherein the lignin derivative is mixed with one or more thermoplastic polymers.

20. The method of claim 19, wherein the thermoplastic polymer comprises polyacrylonitrile and/or associated copolymers.

21. The method of claim 19, wherein the thermoplastic polymer comprises a condensation polymer, an alkyd, a polymer resin, a modified polymer alloy and/or a filled polymer blend.

22. The method of claim 18, wherein the lignin derivative is mixed with one or more thermosetting polymers and/or one or more thermosetting resins.

23. The method of claim 22, wherein the one or more thermosetting polymers and/or the one or more thermosetting resins comprise a polyester resin, a polyurethane, a phenol-formaldehyde, a urea-formaldehyde, a melamine resin, an epoxy resin, an elastomer or a combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1: Temperature ramp of a derivative of native lignin showing the changes in viscoelastic moduli, G′ and G″, and their ratio (G″/G′=tan(δ)) as a function of temperature while a small amplitude sinusoidal strain is applied to the sample. Also included are magnified views of points <T.sub.1>, <T.sub.2>, <G′.sub.min>, <ΔG′.sub.2> shown in the corresponding black boxes.

[0028] FIG. 2: Weight loss as a function of temperature for a derivative of native lignin.

[0029] FIG. 3: Storage modulus vs temperature for derivatives of native lignin Illustrating the impact of the specific rheological metrics on processability into carbon fibres.

[0030] FIG. 4: Effect of blending different lignins on the resulting blend viscoelastic metrics.

DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention provides derivatives of native lignin having certain viscoelastic metrics. Lignin derivatives having specific combinations of onset of softening (T.sub.1), minimum storage modulus (G′.sub.min), cross-over temperature from predominately viscous to predominately elastic behaviour (T.sub.2) and extent of crosslinking (ΔG′.sub.2) have been found to process more effective in industrially relevant applications. Thus, selecting for derivatives of native lignin having specific viscoelastic metrics results in a product having a higher and more predictable processing and materials performance.

[0032] It has been found that derivatives of native lignin having a minimum storage modulus (G′.sub.min) of less than or equal to 10,000 Pa, along with an onset of softening temperature (T.sub.1) greater than or equal to 125° C. and a cross-over temperature (T.sub.2) from predominately viscous to predominately elastic behaviour of greater than or equal to 175° C. result in good thermosoftening materials. For example, a G′.sub.min about 8,000 Pa or less, about 5,000 Pa or less, or about 1,000 Pa or less, or about 100 Pa or less, a T.sub.1 about 130° C. or greater, about 150° C. or greater, about 170° C. or greater, and a T.sub.2 of about 180° C. or greater, about 200° C. or greater, or about 220° C. or greater.

[0033] Furthermore, said derivatives of native lignin also having a high extent of crosslinking (ΔG′.sub.2=G′.sub.250/G′.sub.min), i.e. an increase in storage modulus (ΔG′.sub.2) from G′.sub.min to that measured at 250° C. (G′.sub.250) is more than 600% (ΔG′.sub.2>7) results in plastic materials with a good combination of thermosoftening and thermosetting properties (e.g. melt/fusion fibre spinning, thermosetting resins, etc.). For example, a ΔG′.sub.2 about 7 or greater, about 8 or greater, about 9 or greater, about 10 or greater, or about 100 or greater. In other embodiments, a ΔG′.sub.2 of about 4 or less, about 3 or less, about 2 or less, or about 1 or less also results in plastic materials with a good combination of thermosoftening and thermosetting properties.

[0034] Similarly, derivatives of native lignin having a minimum storage modulus (G′.sub.min) of greater than or equal to 100,000 Pa, along with an onset of softening temperature (T.sub.1) greater than or equal to 170° C. and a cross-over temperature (T.sub.2) from predominately viscous to predominately elastic of greater than or equal to 250° C. result in good fibre forming materials (e.g. carbon fibres) via solution spinning (e.g. wet-, dry-, gel-, electrospinning, and the like). For example, a G′.sub.min about 200,000 Pa or greater, about 500,000 Pa or greater, or about 1,000,000 Pa or greater, a T.sub.1 about 175° C. or greater, about 200° C. or greater, about 225° C. or greater, or about 245° C. or greater, and a T.sub.2 of about 260° C. or greater, about 280° C. or greater, or about 300° C. or greater.

[0035] The present invention provides derivatives of native lignin recovered during or after pulping of lignocellulosic feedstocks. The pulp and/or lignin and/or derivative thereof may be from any suitable lignocellulosic feedstock including hardwoods, softwoods, annual fibres, and combinations thereof.

[0036] It has been found that derivatives of native lignin, for example from hardwood, softwood or annual fibre feedstocks, having G′.sub.min of less than or equal to 10,000 Pa, T.sub.1 greater than or equal to 125° C. and ΔG′.sub.2 of more than 7 have good fibre melt/fusion spinning and thermal processing (e.g. stabilization kinetics) into carbon materials. For example, G′.sub.min about 5,000 Pa or less, 1,000 Pa or less, about 100 Pa or less, T.sub.1 about 130° C. or greater, about 150° C. or greater, about 170° C. or greater, a ΔG′.sub.2 about 7 or greater, about 8 or greater, about 10 or greater, or about 100 or greater. In other embodiments, a ΔG′.sub.2 of about 4 or less, about 3 or less, about 2 or less, or about 1 or less also results in lignin deriavatives with good fibre met/fusion spinning and thermal processing into carbon materials.

[0037] It has been found that derivatives of native lignin, for example from hardwood, softwood or annual fibre feedstocks, having a G′.sub.min of greater than or equal to 200,000 Pa, T.sub.1 greater than or equal to 170° C. and T.sub.2 greater than or equal to 250° C. have good fibre solution spinning and thermal processing into carbon materials. For example, G′.sub.min about 250,000 Pa or greater, 500,000 Pa or greater, about 1,000,000 Pa or greater, T.sub.1 about 175° C. or greater, about 180° C. or greater, about 200° C. or greater, a T.sub.2 about 260° C. or greater, about 280° C. or greater, or about 300° C. or greater.

[0038] In the present invention, “onset of softening”, “minimum storage modulus”, “cross-over temperature [from predominately viscous to predominately elastic behaviour]” and “extent of crosslinking” refer to the viscoelastic behaviour or “metrics” of the lignin derivatives. These viscoelastic metrics can be measured by small amplitude oscillatory shear (SAOS) rheometry (also known as dynamic mechanical thermal analysis or DTMA) using, for example, a TA Instruments DHR rheometer. Various sample forms can be utilized including powders, pressed disks, sheets, fibres and other woven/nonwovens and analyzed under oxidative and/or inert atmospheres. In a typical experiment a lignin derivative is placed between two parallel circular plates, a sinusoidally varying strain, γ(t)=γ.sub.0 sin(ωt) is applied and the sample is heated through a specific temperature range while the mechanical response is measured.

[0039] In select embodiments, the signal quality and consistency of the measurements may be better at low temperatures (prior to any thermal softening that may occur) when compressed samples are used. Compressed samples are typically less affected by frictional dissipative losses, but are known to also possess dissipative losses, and thus moduli reported therefrom are reported as apparent values.

[0040] In some embodiments, a consistent low temperature modulus measurement may be helpful to facilitate the proper execution of the temperature ramp program by the rheometer, where the sample is typically held under a small positive axial compressive force to prevent slipping at low temperature. The program may also be designed to reduce the axial compression at a set modulus value prior to the occurrence of significant thermal softening, to prevent the more fluid-like sample from being squeezed out from between the plates.

[0041] The modulus corresponding to the stress component that is in phase with the strain wave is commonly referred to as the storage modulus, is equal to τ.sub.0′/γ.sub.0, and is typically denoted G′. The modulus corresponding to the stress component that is 90° out of phase with the strain wave (in phase with the rate of strain wave) is commonly referred to as the loss modulus, is equal to τ.sub.0″/γ.sub.0, and is typically denoted G″. In the present examples, the frequency to is held constant at 1 Hz (6.2 rad/s) and γ.sub.0 held within a limit so as to ensure that the measurements are made within the limits of the linear viscoelastic region of the material. As illustrated herein (FIG. 1), the small strain viscoelastic moduli G′ and G″ provide valuable information about the viscoelastic behaviour of lignin as a function of temperature and time. In addition, in some embodiments, it is useful to define the ratio G″/G′=tan(δ) to describe the relative magnitude of the viscous and elastic contributions to the measured shear stress. While the sinusoidal strain is being applied to the lignin sample, it can be heated at controlled rates up to 5° C./min (a practical upper limit to avoid lag between actual temperature of the sample and set temperature) and the value of G′ and G″ can be measured as a function of temperature at different heating rates. While the present viscoelastic metrics relate to samples heated at a rate of 3° C./min, slower or faster heating rates can be used to reveal the relative thermoplasticity and reactivity, i.e. softening and crosslinking behaviour, of lignins and derivatives of lignin.

[0042] Anthropogenic derivatives of native lignin can, for example, be obtained by (1) solvent extraction of finely ground wood (milled wood lignin, MWL) or by (2) acidic dioxane extraction (acidolysis) of wood. Derivatives of native lignin can be also isolated from biomass pre-treated using (3) steam explosion, (4) dilute acid hydrolysis, (5) ammonia fibre expansion, (6) autohydrolysis methods. Derivatives of native lignin can be recovered after pulping of lignocellulosics including industrially operated (3) Kraft and (4) soda pulping (and their modifications) and (5) sulphite pulping. In addition, a number of various pulping methods have been developed but not industrially introduced, among them are (1) ethanol/solvent pulping (aka the Alcell® process), (2) alkaline sulphite anthraquinone methanol pulping (aka the “ASAM” process), (3) methanol pulping followed by methanol, NaOH, and anthraquinone pulping (aka the “Organocell” process), (4) acetic acid/hydrochloric acid or formic acid pulping (aka the “Acetosolv” process) and (5) high-boiling solvent pulping (aka “HBS” pulping).

[0043] Prior to or following extraction, isolation and/or pulping, the anthropogenic derivatives of native lignin may be separated into discrete fractions by one or more than one refining techniques. These refining techniques include, for example, filtration (such as, for example, nano-, micro- or ultra-filtration), extraction (such as, for example, liquid-liquid extraction or liquid-solid extraction), thermal treatment (such as, for example, atmospheric or under reduced pressure) and the like. In various embodiments, prior to or following extraction, isolation and/or pulping, the anthropogenic derivatives of native lignin are separated into discrete fractions by extraction and/or thermal treatment. In other embodiments, the anthropogenic derivatives of native lignin are not separated into discrete fractions by refining techniques prior to or following extraction, isolation or pulping.

[0044] The derivatives of native lignin herein may be utilized alone or may be incorporated into polymer compositions. The compositions disclosed herein may comprise a derivative of native lignin according to the present invention and a polymer-forming component. As used herein, the term ‘polymer-forming component’ means a component that is capable of being polymerized into a polymer as well as a polymer that has already been formed. For example, in certain embodiments the polymer-forming component may comprise monomer units which are capable of being polymerized. In certain embodiments, the polymer component may comprise oligomer units that are capable of being polymerized. In certain embodiments, the polymer component may comprise a polymer that is already substantially polymerized.

[0045] Polymer forming components for use herein may result in thermoplastic or thermoset polymers and copolymers such as epoxy resins, urea-formaldehyde resins, phenol-formaldehyde resins, polyimides, polyacrylates, polynitriles, isocyanate resins, and the like. For example, polyolefins such as polyethylene or polypropylene and polynitriles like polyacrylonitrile copolymers.

[0046] Typically, the derivative of native lignin will comprise from about 0.1%, by weight, or greater, about 0.5%, by weight, or greater, about 1%, by weight, or greater, of the composition. Typically, the lignin derivative will comprise from about 99.9%, by weight, or less, about 80%, by weight, or less, about 60%, by weight, or less, about 40%, by weight, or less, about 20%, by weight, or less, about 10%, by weight, or less of the composition.

[0047] The compositions comprise a derivative of native lignin and polymer-forming component, but may comprise a variety of other optional ingredients such as adhesion promoters; biocides (antibacterials, fungicides, and moldicides), anti-fogging agents; anti-static agents; bonding, blowing and foaming agents; dispersants; fillers and extenders; fire and flame retardants and smoke suppressants; impact modifiers; initiators; lubricants; micas; pigments, colorants and dyes; plasticizers; processing aids; release agents; silanes, titanates and zirconates; slip and anti-blocking agents; stabilizers; stearates; ultraviolet light absorbers; foaming agents; defoamers; hardeners; odorants; deodorants; antifouling agents; viscosity regulators; waxes; and combinations thereof.

[0048] The present invention provides the use of the present derivatives of native lignin as a functional component in thermoplastics, thermosets, and fibre forming polymers, alone or in combination with traditional or evolving polymers. For example, the present use may be to impart enhanced thermal stability and mechanical performance with thermoplastic polymers such as polyethylenes, polypropylenes, polyamides, polynitriles, styrene-butadiene, and combinations thereof. Other examples include: increased curing of butyl rubbers, improved abrasion index in synthetic (polybutadiene, nitrile, neoprene, styrene-butadiene) and natural rubbers; improved yield and thermal processing of polyacrylonitrile copolymer into carbon fibres; enhanced mechanical properties, gluability, and reduced emissions (e.g. formaldehyde) in adhesive sealants, epoxy resins and phenolic-formaldehyde resins.

EXAMPLES

Example 1: The Temperature Ramp Curve of a Lignin Sample

[0049] A typical curve for a lignin sample heated at 3° C./min under nitrogen gas flow (in the absence of oxygen) is shown in FIG. 1. The general shape of the curves in FIG. 1 are indicative of a significant degree of softening occurring roughly between 125-225° C. At low temperature, the storage modulus (G′) is roughly 1 order of magnitude larger than the loss modulus (G″), indicating that the lignin pellet displays predominantly elastic or solid-like mechanical behaviour (as expected, since the analysis temperature is far below T.sub.g). Just prior to softening, both moduli show an increase up to a peak value, which can be attributed to compaction/densification of the sample as it is heated above its glass transition temperature, leading to increased overall resistance to deformation. After reaching their peak values, both G′ and G″ decrease by roughly 4 orders of magnitude as temperature is raised from 125 to 225° C., this decrease in moduli corresponds to thermal softening.

[0050] An aspect of this example involves the definition and determination of select points along a temperature ramp curve in a rheological characterization of lignin. In one aspect of the invention, there are three alternative points of rheological characteristics that may be used to classify lignin, which are indicated with black boxes in FIG. 1, and further illustrated in the associated magnified images.

[0051] The point <T.sub.1> represents the temperature (T=T.sub.1) at the first point of cross-over where G′=G″ and beyond which G′<G″. In this Example, the apparent viscoelastic moduli G′ and G″ are around 10.sup.6 Pa. Beyond this point the material still displays significant resistance to deformation, but this resistance drops off rapidly as temperature is increased and the viscous contribution to the shear stress is larger than the elastic contribution. The value of temperature at the point T.sub.1 will be referred to as the softening onset temperature. Likewise, the second cross-over is denoted T.sub.2 and represents the temperature where G′=G″ again and beyond which G″<G′ once more. This point indicates a transition from predominantly viscous liquid behaviour back to predominantly elastic behaviour, and is represented by the cross-over temperature T.sub.2. Beyond this point as temperature is increased further both moduli continue to decrease until point G′.sub.min, where a local minimum is reached. At this point we have reached the softest state that this lignin sample will enter, and define the minimum storage modulus G′.sub.min. It should be noted here that not all lignin samples display a local minimum in storage modulus below the onset of thermal decomposition, so in these cases the extent of softening would be determined based on the change in storage modulus between the onset of softening at T.sub.1 and the modulus at a temperature of thermal degradation onset, which for most lignin's is approximately around 250° C. A graph of % weight loss as a function of temperature at a heating rate of 10° C./min is shown in the FIG. 2 for this typical Kraft lignin.

[0052] For the lignin sample shown in FIG. 1 it can be seen that G′ starts to increase between G′.sub.min and 250° C., indicating the onset of thermally induced crosslinking; another phenomenon that is of interest for the production of lignin-based materials through thermal processing routes. This temperature may also be a convenient endpoint for evaluation of thermal softening and low temperature cross-linking, as 250° C. is a typical temperature to conduct oxidative thermostabilization of lignin fibres to prepare them for production of carbon fibres, and can be considered a practical upper limit for processing of some commodity thermoplastics. Therefore, we define the extent of crosslinking (ΔG′.sub.2) as the change in modulus occurring between G′.sub.min and that at 250° C. (ΔG′.sub.2=G′.sub.250/G′.sub.min).

Example 2: Rheological Comparison of Different Lignins and Corresponding Thermal Processability

[0053] FIG. 3 shows the rheological fingerprint of three lignins measured in an air atmosphere using 25 mm lignin pellets. Lignin 1 (bottom curve) exhibits a high degree of thermal softening with a small G′.sub.min (<100 Pa) and a relatively low extent of crosslinking, ΔG′.sub.2=3.6. Lignin 2 (top curve) exhibits a low degree of thermal softening (G′.sub.min>10,000 Pa) and a moderate extent of crosslinking, ΔG′.sub.2=6.3. Lignin 3 (middle curve) exhibits a moderate degree of thermal softening (G′.sub.min>1,000 Pa) and a high extent of crosslinking, ΔG′.sub.2=19.4. Lignin 1 and 3 are readily processed thermally, e.g. thermo-formed or melt-spun into a variety of forms, including fibres, while Lignin 2 does not sufficiently soften to enable thermal spinning into a fibre form. By the same token, Lignin 1 cannot be converted into carbon fibre at commercially relevant processing rates, requiring very slow thermostabilization heating rates of <1° C./min. Lignin 3 on the other hand can be readily spun into fibres and thermostabilizes at heating rates well in excess of 5-10° C./min.

[0054] Table 1 illustrates the effect of lignin viscoelastic metrics on solution forming and subsequent thermal processing. Lignin 4 exhibits a low degree of thermal softening with a G′.sub.min<100,000 Pa and is a moderately viscous material with a tan(δ)>1. Lignin 5 exhibits very little softening with G′.sub.min>100,000 Pa and tan(δ)<1, indicative of predominately elastic behaviour. Lignin 4 requires significantly lower thermal processing rates than that of Lignin 5, which can be thermally processed at heating rates greater than 20° C./min.

TABLE-US-00001 TABLE 1 Effect of lignin viscoelastic metrics on solution forming and subsequent thermal processing G′.sub.min Heating Rate Sample Tan(δ) (Pa) (° C./min) Lignin 4 3.9 12,831 <3 Lignin 5 0.65 257,798 >>20

Example 3: Effect of Lignin Blending to Manipulate Viscoelastic Metrics

[0055] FIG. 4 shows the effect of blending lignin 1 and 2 from example 3 on the resulting blend viscoelastic metrics as measured under air using 25 mm lignin pellet. It can be seen that the dilution of lignin 2 with increasing amounts of lignin 1 has the effect of decreasing all of its viscoelastic metrics. Any decrease in softening temperature (T.sub.1) is met with a corresponding decrease in extent of crosslinking, ΔG′.sub.2.

Example 4: Effect of Lignin Viscoelastic Metrics on Phenol-Formaldehyde Resin Shear Strength

[0056] Table 2 illustrates the effect of lignin viscoelastic metrics on resulting thermoset resin performance in a typical engineered wood product application. Lignin 1 and lignin 3 from example 2 were used to replace 25% of a standard phenol-formaldehyde (PF) resin and the impact on shear strength was determined using an automated bond evaluation system (ABES). Approximately 1.8 g of resin was applied to a conditioned (25° C./50% RH) set of hardwood veneers and the bond strength determined after curing for 15 seconds at 190° C. It can be seen that lignin 3 with the higher potential for cross-linking (larger ΔG′.sub.2) produced a bond strength superior to the lignin 1.

TABLE-US-00002 TABLE 2 Effect of lignin substitution for phenol-formaldehyde resin on resulting lap shear bond strength T.sub.2 Shear Strength Resin (° C.) ΔG′.sub.2 (MPa) PF (100) 5.3 PF/lignin 1 (75/25) 166 3.6 4.8 PF/lignin 3 (75/25) 232 19.4 5.6

REFERENCES

[0057] Baker, D. A. and T. G. Rials (2013). “Recent advances in low-cost carbon fiber manufacture from lignin.” Journal of Applied Polymer Science 130(2): 713-728. [0058] Baker, D. A., F. S. Baker and N. C. Gallego (2009). Thermal Engineering of Lignin for Low-cost Production of Carbon Fiber. The Fiber Society 2009 Fall Conference. Athens Ga. [0059] Baker, D. A., N. C. Gallego and F. S. Baker (2012). “On the characterization and spinning of an organic-purified lignin toward the manufacture of low-cost carbon fiber.” Journal of Applied Polymer Science 124(1): 227-234. [0060] Hu, T. Q. (2002). Chemical Modification, Properties, and Usage of Lignin, Springer US. [0061] Macfarlane, A. L., M. Mai and J. F. Kadla (2014). 20—Bio-based chemicals from biorefining: lignin conversion and utilisation. Advances in Biorefineries. K. Waldron, Woodhead Publishing: 659-692. [0062] Mainka, H., O. Täger, E. Körner, L. Hilfert, S. Busse, F. T. Edelmann and A. S. Herrmann (2015). “Lignin—an alternative precursor for sustainable and cost-effective automotive carbon fiber.” Journal of Materials Research and Technology 4(3): 283-296. [0063] Norberg, I., Y. Nordstrom, R. Drougge, G. Gellerstedt and E. Sjoholm (2013). “A new method for stabilizing softwood kraft lignin fibers for carbon fiber production.” Journal of Applied Polymer Science 128(6): 3824-3830. [0064] Paul, D. R. and C. B. Bucknall (2000). Polymer Blends: Formulation, Wiley.