Method for Preparing a Stable Lignin-Phenol Blend and a Stable Lignin-Phenol Blend Obtained by Said Method

Abstract

A method for preparing a stable lignin-phenol blend includes a) mixing a lignin source with a dispersion system comprising a solvent to at least partially disperse the lignin and obtain a first mixture comprising a dispersed lignin fraction, a precipitated lignin fraction and the dispersion system, b) separating the precipitated lignin fraction from the dispersion system, and c) mixing phenol with the second mixture to provide a third mixture comprising dispersed lignin, phenol and the dispersion system; wherein the second mixture comprising dispersed lignin and dispersion system is used without any further treatment before mixing with phenol; d) optionally removing at least part of the dispersion system from the third mixture comprising dispersed lignin, phenol and dispersion system, e) obtaining a stable lignin-phenol blend with content of solvent of lower than 20 wt %.

Claims

1. A method for preparing a stable lignin-phenol blend comprising the steps of: a) mixing a lignin source with a dispersion system comprising a solvent to at least partially disperse the lignin and to obtain a first mixture comprising a dispersed lignin fraction, a precipitated lignin fraction and the dispersion system, b) separating the precipitated lignin fraction from the dispersed lignin fraction to provide a second mixture comprising dispersed lignin and the dispersion system, c) mixing phenol with the second mixture comprising dispersed lignin and dispersion system to provide a third mixture comprising dispersed lignin, phenol and the dispersion system; wherein the second mixture comprising dispersed lignin and dispersion system is used without any further treatment before mixing with phenol; and d) optionally removing at least part of the dispersion system from the third mixture comprising dispersed lignin, phenol and dispersion system, e) obtaining a stable lignin-phenol blend withcontent of solvent.

2. The method according to claim 1, wherein steps b) and c) are applied in reverse order.

3. The method according to claim 1, wherein the dispersion system comprises water, low molecular alcohol(s); low molecular ketone(s), glycol(s), phenol, and/or mixtures thereof with water.

4. The method according to claim 1, wherein the dispersion system comprises a) acetone, ethanol, methanol, and/or iso-propanol, or b) an acetone/water, ethanol/water, phenol/water, phenol/acetone/water or phenol/acetone mixture.

5. The method according to claim 1, wherein 100-800 g lignin source/L solvent are mixed with the dispersion system in step a).

6. The method according to claim 1, wherein the dispersed lignin fraction is separated from the precipitated fraction in step b) by centrifugation, decantation, siphoning, sedimentation, or filtration.

7. The method according to claim 1, wherein the amount of phenol added to the mixture of dispersed lignin and dispersion system in step c) is 20 wt % to 80 wt % in respect to the combined sum of lignin and phenol.

8. The method according to claim 1, wherein the dispersion system is removed from (third) mixture comprising dispersed lignin, phenol and the dispersion system in step d) until the mixture has a phenol/lignin/organic solvent composition of 50/50/0 to 40/40/20.

9. The method according to claim 1, wherein the dispersion system is removed from the (third) mixture comprising dispersed lignin, phenol and the dispersion system in step d) until the mixture has a phenol/lignin/water/organic solvent composition of 50/50/0/0 to 40/40/10/10.

10. The method according to claim 1, wherein in a further step at least one stabilizer is added to the lignin phenol blend obtained.

11. A stable lignin-phenol blend for use in lignin modified phenol-formaldehyde resins obtained in a method according to claim 1, comprising lignin in an amount of 10-90 wt %; phenol in an amount pf 15-90 wt %; and optionally a stabilizer in an amount of 0-25 wt %, and having a residual solvent content of less than 20 wt %.

12. The lignin-phenol blend according to claim 11, wherein the lignin-phenol blend has a residual content of organic solvent lower than 15 wt %.

13. The lignin-phenol phenol blend according to claim 11, wherein the lignin-phenol blend has a viscosity of at most 25 000 mPa*s (measured at 25 C. according to ASTM D7042-04).

14. A lignin modified phenol-formaldehyde resin obtainable by reacting a stable lignin-phenol blend according to claim 11 and an aldehyde.

15. A wood composite board comprising at least one lignin modified phenol-formaldehyde resin according to claim 14.

16. The method according to claim 1, wherein the solvent comprises water and/or organic solvent.

17. The method according to claim 4, wherein the dispersion system comprises c) acetone, ethanol, or d) acetone/water or ethanol/water.

18. The method according to claim 7, wherein the amount of phenol added to the mixture of dispersed lignin and dispersion system in step c) is 25 wt % to 70 wt %.

19. The lignin-phenol blend according to claim 11, wherein the lignin-phenol blend has a residual content of organic solvent lower than 10 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0087] The present disclosure is explained in more detail by means of the following examples with reference to the Figures.

[0088] FIG. 1 shows a scheme illustrating the process according to non-limiting embodiments of the disclosure;

[0089] FIG. 2 shows a diagram illustrating the viscosity profile of the lignin-phenol blend obtained by the method according to the disclosure;

[0090] FIG. 3 shows a diagram illustrating the condensation time and viscosity of lignin modified phenol-formaldehyde resin according to the disclosure; and

[0091] FIG. 4 shows a diagram illustrating the tensile strength development according to ASTM D7998-15 measured on beech veneers obtained with the lignin modified phenol-formaldehyde resin according to the disclosure.

DETAILED DESCRIPTION

Lignin Raw Materials

[0092] Softwood Kraft Lignin from different supplier is used as starting material. The molecular mass of soluble lignin is determined by Size Exclusion Chromatography equipped with an ultraviolet detector using 0.1 M sodium hydroxide solution as solvent. Concerning the quantification, polystyrene standards are used for the calibration. The reactivity of lignin for blend and adhesive preparation depends on the concentration of hydroxyl groups and methoxyl groups in the polymer backbone. In laboratory, hydroxyl and methoxyl groups are determined as sum parameters. The ratio of the sum parameters and the molecular mass determination show a basic characterization of the reactivity of the lignin. Analytical results of used lignins are shown in table 1.

TABLE-US-00001 TABLE 1 Data sheet of used soluble lignin Lignin 1 Lignin 2 Lignin 3 Dry matter/% 97.0 68.0 67.3 Ash/% 2.7 0.6 0.8 Acid Soluble Lignin/% 0.5 0.3 2.1 Acid Insoluble Lignin/% 92.0 93.0 96 Total carbohydrates/% 2.2 5.8 2.4 Phenolic OH/mmol/g 3.5 4.0 3.0 Methoxy Group/mmol/g 5.7 5.3 5.3 M.sub.n 1196 1095 1105 M.sub.W 5534 4695 4755 Polydispersity (DP) 4.6 4.3 4.3

Lignin-Phenol Blend

Example 1

[0093] FIG. 1 shows simplified process scheme of non-limiting embodiments of the present method (wet blending).

[0094] Softwood Kraft Lignin from a supplier was used as starting material. In the next step of lignin extraction, the supplied lignin was dissolved in acetone or acetone/water mixture with intensive stirrer configuration, and the undissolved lignin part (<5%) is separated via filtration, centrifugation, decantation etc. Subsequently, the acetone/(water)-lignin mixture was blended with phenol (blending of extracts). In the following step, the solvent (acetone/water) was removed until a mixture of phenol/lignin/water/acetone starting from 50/50/0/0 to 44/44/6/6 and variants thereof was obtained. The recovered acetone may have been recycled to the lignin extraction step. Phenolic water underwent a work up. It would have also been possible to add caustic soda or other base during the blending and/or extraction step or for the purpose of removing deposits during operational periods of cleaning and regeneration of the equipment.

[0095] The steps of lignin extraction and blending the extract with phenol could have also be applied in a reverse order.

[0096] The viscosity of the lignin-phenol blend may have been adjusted by the acetone content of the blend.

[0097] FIG. 2 shows a typical viscosity profile of a 1:1 phenol-lignin blend. The viscosity of the blend decreases with the addition of a suitable viscosity adjusting additive, such as acetone.

Viscosity Measurement

[0098] The dynamic viscosity was determined by the Stabinger viscosimeter SVM 3000 (Anton Paar, Austria) at 25 C. following the ASTM D7042 standard test method. Ambient conditions were 21 C. and 50-60% r.h.

[0099] Principle of the measurement was as follows: a rotating magnet produced an eddy current field with an exact speed-dependent brake torque. The torque resolution was an unmatched 50 pNm. A measuring cell containing a tube filled with 2.5 ml of the sample was rotating at a constant speed, which was determined by the equilibrium between the effect of the eddy current brake and the shear forces at work in the sample. The dynamic viscosity was calculated from the rotor speed.

Example 2

[0100] In non-limiting embodiments, the PLB is synthesized in the following three steps: [0101] 1. Lignin extraction in acetone [0102] 2. Extract centrifugation [0103] 3. Solvent (i.e., acetone+water) distillation

[0104] In the first step, wet (containing 35 wt % of water) or dry (with no water) lignin was extracted in acetone. In particular, 1200 ml of acetone was added into 2 L RC1 reactor (Mettler Toledo) equipped with anchor stirrer. Afterwards, either 600 g of wet lignin or ca. 400 g of dry lignin was added slowly (300 g of wet lignin/min) into the acetone stirred at 300 rpm. For the dry lignin, acetone containing 12 wt % of water was used. For the wet lignin, no additional water was added into the mixture. Next, the mixture was heated up to 30 C. and stirred at 600 rpm for 10 min to allow full homogenization.

[0105] In the second step, homogenized lignin-acetone-water (LAW) extract was centrifuged for 10 min at relative centrifugal force (RCF) of 3200. For the centrifugation, centrifuge Rotanta 460R (Hettich) was used.

[0106] Subsequently, the lignin content in the centrifuged lignin-acetone-water (LAW) extract was measured after drying the LAW at 105 C. In particular, 2 g of LAW was added onto a Petri dish, the exact weight was noted and the dried LAW was weighted afterwards to calculate the lignin solid content in wt %. Based on this value, phenol amount in g was calculated and added into the centrifuged LAW (lignin: phenol mass ratio is of 1:1). As the result, phenol-lignin-acetone-water (PLAW) solution was ready for solvent (i.e., acetone+water) distillation in the third step. In the third step, solvent distillation was performed either in the rotavapor (Bchi) at 120 C. under atmospheric pressure or at 35 C. under vacuum. The target residual solvent content was approx. 12%, therefore the final condensate weight was calculated upfront and serves, together with the vapour temperature, as the stop criterium for the distillation (once reached, the distillation was stopped).

[0107] In the following

[0108] Table the preparation of further PL-blends according to the disclosure are shown.

TABLE-US-00002 TABLE 2 Phenol Water Acetone Lignin PL# Supplier (%) (%) (%) (%) 1 Lignin 1 centrifuged 41.00 13.53 0.64 44.83 2 Lignin 1 centrifuged 38.33 12.65 7.14 41.88 3 Lignin 1 not centrifuged 41.14 14.81 7.36 36.69 4 Lignin 1 centrifuged 43.30 3.10 3.10 50.50 5 Lignin 2 centrifuged 43.30 3.20 3.20 50.30

Lignin Modified Phenol-Formaldehyde Resin (LPF)

[0109] The PL-blends were used for the preparation of lignin-phenol-formaldehyde (LPF) resins.

Example 3: First Lignin Modified Phenol Formaldehyde (LPF) Resin According to the Disclosure (LPF Resin A2)

[0110] 152.83 g of PL blend 1 was added in a round flask equipped with a magnetic stirrer and heated up to 65 C. Water (11.04 g) was added followed by 19.77 g of 50% aqueous NaOH-solution, which was constantly added over 20 minutes. The mixture was further stirred at 65 C. for 15 minutes. A 126.83 g of a laboratory formaldehyde solution (concentration of 37%) was then added over 30 minutes followed by another 20 minutes of stirring at 65 C. The second part of the 50% NaOH solution (39.54) was then constantly added over 20 minutes, while temperature could increase due to the exothermal reaction up to 85 C. The LPF resin was further condensed at this elevated temperature until the viscosity increased to 500 mPa*s (measured at 25 C.) and then cooled down to room temperature in a cold water bath.

Example 4: Second Lignin Modified Phenol Formaldehyde (LPF) Resin According to the Disclosure (LPF Resin B2)

[0111] In total 47.24 g of PL blend 2 was added in a round flask, stirred with a magnetic stirrer and heated up to 45 C. The first part of a 50% aqueous NaOH solution (4.62 g) was then added slowly to the blend over 20 minutes, while temperature could increase to 65 C. followed by 35.42 g of a laboratory formaldehyde solution (concentration of 37%), which was constantly added over 30 minutes to the mixture. The resin was then condensed at 85 C. until viscosity reached 400 mPa*s (measured at 25 C.) and cooled down to 70 C. by adding the recalculated amount of water (5.73 g). The second part of the NaOH solution (5.98 g) was then added continuously over 20 minutes. A second condensation step was then performed, where the LPF resin was condensed at 85 C. until viscosity reached 500 mPa*s (measured at 25 C.) followed by cooling down to room temperature.

[0112] Table provides the main resin properties of the LPF resins A2 and B2, while FIG. 4 shows the bonding strength development of the two resins measured with ABES (Automated Bonding Evaluation System). For the measurements two beech veneers with an overlapping area of 5 mm by 20 mm were bonded together using a LPF resin application amount of 200 g/m.sup.2 and a press temperature of 120 C. at varying press times. Both examples of LPF resins performed similarly in their bonding properties.

TABLE-US-00003 TABLE 3 LPF resin A2 LPF resin B2 Lignin:Phenol 52.2:47.8 52.2:47.8 Solid content (%) 54.1 53.6 Viscosity (mPa*s) at 25 C. 616 567 pH (50% in water) () 10.8 9.7 Free formaldehyde (%) 0.16 1.07

[0113] In Table 4 the preparation of further LPF resins are provided.

TABLE-US-00004 TABLE 4 Formaldehyde Phenol Lignin LPF solution substitution F/P NaOH/P PL# from LPF# supplier recipe (%) (%) (mol/mol) (mol/mol) Table 1 Lignin 1 Recipe 1 37 52.2 2.35 1.1 1 2 Lignin 1 Recipe 1 54 52.2 2.35 1.1 1 3 Lignin 1 Recipe 1 37 52.2 2.35 1.1 2 4 Lignin 1 Recipe 1 54 52.2 2.35 1.1 2 5 Lignin 1 Recipe 2 37 52.2 2.30 0.722 1 6 Lignin 1 Recipe 2 37 52.2 2.30 0.722 2 7 Lignin 1 Recipe 1 37 47.1 2.35 1.1 3 8 Lignin 1 Recipe 1 37 53.8 2.35 1.1 4 9 Lignin 2 Recipe 1 37 53.7 2.35 1.1 5 10 Lignin 1 Recipe 1 37 51.9 2.35 1.1 6

Wood Composite Board Comprising Lignin Modified Phenol Formaldehyde Resin (LPF)

[0114] The following method was used to test the adhesive strength of plywood boards. The LPF resin synthesised according to example A2 was tested according to the plywood standard EN 314-1 and evaluated according to EN 314-2. Plywood was prepared using 9 layers of birch veneers. Before resin application, 35 g of water and 35 g of dry wheat flour (10% calculated on wet LPF resin) were added to the LPF resin (350 g) in order to increase the viscosity of the adhesive mixture.

[0115] On each veneer 155 g/m.sup.2 of resin was applied before the plywood board was cold pressed for 10 minutes in a hydraulic press at a specific pressure of 1 MPa. After a lay-up time of 1 hour, the plywood board was hot pressed at 135 C. for 11 minutes using a specific pressure of 1.6 MPa. Lap-joint specimens were cut out of the plywood board after 7 days of storage in standard climate (20 C./65% r.h.). The specimens were further stored before being tested. Half of the specimens were immersed in 20 C. warm water for 24 hours, while the second half was immersed in boiling water for 6 hours followed by cooling down in water at 20 C. for 1 hour. The tensile shear strength was measured in wet conditions and the determined arithmetic mean values are summarized in Table 5.

TABLE-US-00005 TABLE 5 LPF resin A2 immersion for 24 hours in water (20 C.) 1.07 N/mm.sup.2 immersion for 6 hours in boiling water 0.92 N/mm.sup.2 followed by 1 hour of cooling in water at 20 C.