Stable Lignin-Phenol Blend for Use in Lignin Modified Phenol-Formaldehyde Resins

Abstract

Provided is a stable lignin-phenol blend for use in lignin modified phenol-formaldehyde resins comprising lignin in an amount between 10-80 wt %, phenol in an amount between 15-90 wt %, and a solubilizer in an amount between 0%-25 wt %.

Claims

1-11. (canceled)

12. A stable lignin-phenol blend free of formaldehyde as a precursor blend for use in lignin modified phenol-formaldehyde resins comprising lignin in an amount between 15-70 wt %, preferably 30-60 wt %, preferably 40-55 wt %, wherein the lignin is a homogenous soluble lignin with a weight average molecular weight Mw between 3000 and 8000, preferably between 3500 and 6000, more preferably between 3800 and 5000 and a polydispersity between 2 and 5, preferably between 2.5 and 4.7, more preferably between 3.0 and 4.6, phenol in an amount between 20-85 wt %, preferably 30 and 70 wt %, preferably 40% and 55 wt %; and a solubilizer in an amount between 1-15 wt %, preferably 4-10 wt %, wherein the solubilizer is one of water, an aqueous alkaline solution or an alkaline compound, wherein the sum of all ingredients adds up to 100%.

13. The lignin-phenol blend according to claim 12, wherein when using an aqueous alkaline solution or an alkaline compound as solubilizer the pH range of the lignin-phenol blend is between 11 and 14, preferably between 12 and 13.

14. The lignin-phenol blend according to claim 12, having a viscosity between 20 and 1500 mPas, preferably between 50 and 1500 mPas, and more preferably between 80 and 1200 mPas measured at 25° C. in oscillation mode.

15. The lignin-phenol blend according to claim 12, having a stability of more than 3 weeks.

16. A method for preparing a stable lignin-phenol blend according to claim 12 comprising the steps of: providing a fraction of lignin in an amount between 15-70 wt %, preferably 30-60 wt %, preferably 40-55 wt %, wherein the lignin is a homogenous soluble lignin obtained by chemical extraction with a weight average molecular weight Mw between 3000 and 8000, preferably between 3500 and 6000, more preferably between 3800 and 5000 and a polydispersity between 2 and 5, preferably between 2.5 and 4.7, more preferably between 3.0 and 4.6, providing a fraction of liquefied phenol in an amount between 20-85 wt %, preferably 30 and 70 wt %, preferably 40% and 55 wt %; providing a solubilizer, wherein the solubilizer is one of water, an aqueous alkaline solution or an alkaline compound, and mixing the fraction of the soluble lignin with the fraction of liquefied phenol and the solubilizer with an amount between 1-15 wt %, preferably 4-10 wt %, wherein the sum of all ingredients adds up to 100%.

17. The method according to claim 16, wherein the phenol is molten or liquefied at 50° C., lignin is dosed to the molten or liquefied phenol and the mixture is stirred at 50° C. for a certain time.

18. The method according to claim 16, wherein the soluble homogenous lignin is obtained by mixing a suitable lignin source with an organic solvent, preferably an aqueous organic solvent at room temperature to obtain a dispersion; separating soluble and insoluble fraction of lignin, and evaporating the organic solvent, in particular the aqueous organic solvent, from the soluble lignin fraction to obtain solid soluble

19. The method according to claim 18, wherein the soluble lignin fraction is separated from the insoluble lignin fraction by centrifuging, decantation, siphonication, sedimentation, or filtration.

20. A method for preparing lignin modified phenol-formaldehyde resins using the lignin-phenol blend according to claim 12.

21. A lignin modified phenol-formaldehyde resins obtainable by reacting a stable lignin-phenol blend according to claim 12 and an aldehyde, in particular formaldehyde.

22. A wood composite board comprising at least one lignin modified phenol-formaldehyde resin according to claim 21.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] The present solution is explained in more detail by means of the following examples with reference to the Figures.

[0082] FIG. 1 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 solution:

[0083] FIG. 2 shows a diagram illustrating the condensation time and viscosity of lignin modified phenol-formaldehyde resin according to the solution and comparative examples (excluding the time for dissolution of lignin in adhesive mixture).

DESCRIPTION OF THE INVENTION

[0084] I) Lignin Raw Materials

[0085] 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 lignins 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 Mn 1196 1095 1105 Mw 5534 4695 4755 DP 4.6 4.3 4.3

[0086] II) Soluble Lignin

[0087] Extraction of Soluble Lignin

[0088] The lignin was first pre-treated by a simple milling process for homogeneity reasons. Then, 15 g of the lignin was dosed portionally into 150 ml water/acetone solvent mixture. That mixture is stirred for 1 hour at room temperature and subsequently centrifugated for 20 min at 8500 rpm (16 g-force). The organic solvent/water is then removed by an evaporation step, usually done at reduced pressure conditions and finally dried in an oven at 60° C.

[0089] The following table 2 illustrates the different extraction examples:

TABLE-US-00002 TABLE 2 extraction of Lignin with different water acetone ratios (RT = room temperature; S = Soxhlet-extraction process) Acetone Water Yield Poly- PL# Supplier Pretreatment [%] [%] [%] Mw Mn dispersity 1 Lignin 1 None 5534 1196 4.63 2 Lignin 1 Milled 5534 1196 4.63 3 Lignin 1 Frac 60% Ac S 60 40 74 n.a. n.a. n.a. 4 Lignin 1 Frac 100% Ac S 100 0 77 n.a. n.a. n.a. 5 Lignin 1 Frac 40% Ac S 40 60 64 n.a. n.a. n.a. 6 Lignin 1 Frac 40% Ac RT 40 60 76 2340 596 3.92 7 Lignin 1 Frac 60% Ac RT 60 40 85 5063 1068 4.75 8 Lignin 1 Frac 90% Ac RT 90 10 82 6741 1328 5.07 9 Lignin 1 Frac 100% Ac RT 100 0 78 3086 1092 2.83 10 Lignin 1 Milled 5534 1196 4.63 11 Lignin 1 Milled 5534 1196 4.63 12 Lignin 1 Frac 100% Ac RT 100 0 78 3086 1092 2.83 13 Lignin 2 None 5155 1264 4.18 14 Lignin 2 Milled 5155 1264 4.18 15 Lignin 2 Frac 100% Ac RT 100 0 85 4072 1192 3.32 16 Lignin 2 Milled 5155 1264 4.18 17 Lignin 2 Frac 100% Ac RT 100 0 85 4072 1192 3.32 18 Lignin 3 None 4755 1105 4.3 19 Lignin 3 Milled 4755 1105 4.3 20 Lignin 3 Frac 100% Ac RT 100 0 86 3677 1152 3.19 21 Lignin 3 Milled 4755 1105 4.3 22 Lignin 3 Frac 100% Ac RT 100 0 86 3677 1152 3.19

[0090] The molar mass distributions of solutions of the lignin samples in NaOH are performed by size exclusion chromatography on a Thermo Fisher Dionex ICS 5000+. The chromatographic system consists of a pre-column PSS MCX Guard 50×8 mm and three analytical (PSS Analytical 100A, 300×8 mm; PSS Analytical 1000A, 300×8 mm; PSS Analytical 100000A, 300×8 mm) columns. The UV detector used is a VWD detector with 280 nm as standard wavelength. Molar mass calibrations are carried out using Polystyrene standards.

[0091] III) Soluble Lignin—Phenol—Blend

[0092] First Blend According to the Solution (Blend A1)

[0093] 146 g phenol is heated up to 60° C., 4.3 g water is added and continuously stirred at 800 rpm in a bottom-round flask using a magnetic stirrer. When phenol is completely liquified, 50 g sieved lignin powder is added stepwise to ensure no agglomeration, which takes 30 min. The final blend with a phenol:lignin (calc. on dry matter) of 75:25 is cooled down and stored at room temperature.

[0094] Second Blend According to the Solution (Blend B1)

[0095] In a round bottom flask, 120 g powdered softwood kraft lignin is dissolved in 1.2 L 99.9% acetone and stirred at 800 rpm with a magnetic stirrer. After mixing for one hour, the acetone with the dissolved lignin is decanted from the insoluble lignin. The resulting solution is concentrated by evaporation of the acetone followed by drying at 60° C. for 48 h.

[0096] For the blend production with 50% phenol substitution, 70.0 g phenol is melted at 60° C., 4.2 g water is added and continuously stirred at 800 rpm in a bottom-round flask using a magnetic stirrer. When phenol is completely molten, 70.0 g of the acetone soluble, dried lignin is added stepwise to ensure no agglomeration, which takes 2.5 h. The final blend is cooled down and stored at room temperature. The blend is stable for more than 3 weeks at room temperature.

[0097] A general preparation for obtaining the lignin-phenol-blends comprises: [0098] 220 g of 25%-lignin containing PL Blend ( ) [0099] 160.2 g of Phenol, 53.4 g of Lignin, 6.4 g of distilled water [0100] Phenol melting (60° C.), Stirring with 900 rpm [0101] Dosage of Lignin (25 min, 60° C.), Stirring with 1140 rpm [0102] Stirring (25 min, 60° C.), Stirring at 1140 rpm

[0103] In the following Table 3 the synthesis of further lignin-phenol-blends according to the solution are provided.

TABLE-US-00003 TABLE 3 Phenol Water NaOH Lignin Storage PL# Supplier Pretreatment [%] [%] [%] [%] [days] 1 Lignin 1 None 86 4 10 >21 2 Lignin 1 Milled 81 4 15 >21 3 Lignin 1 Frac 60% Ac S 71 4 25 >21 4 Lignin 1 Frac 100% Ac S 71 4 25 >21 5 Lignin 1 Frac 40% Ac S 71 4 25 >21 6 Lignin 1 Frac 40% Ac RT 71 4 25 >21 7 Lignin 1 Frac 60% Ac RT 71 4 25 >21 8 Lignin 1 Frac 90% Ac RT 71 4 25 >21 9 Lignin 1 Frac 100% Ac RT 46 4 50 >21 10 Lignin 1 Milled 46 3 1 50 >21 11 Lignin 1 Milled 60 10 30 >21 12 Lignin 1 Frac 100% Ac RT 36 3 1 60 >21 13 Lignin 2 None 76 4 20 >21 14 Lignin 2 Milled 76 4 20 >21 15 Lignin 2 Frac 100% Ac RT 36 4 60 >21 16 Lignin 2 Milled 46 3 1 50 >21 17 Lignin 2 Frac 100% Ac RT 26 3 1 70 >21 18 Lignin 3 None 76 4 20 >21 19 Lignin 3 Milled 76 4 20 >21 20 Lignin 3 Frac 100% Ac RT 36 4 60 >21 21 Lignin 3 Milled 46 3 1 50 >21 22 Lignin 3 Frac 100% Ac RT 26 3 1 70 >21

[0104] IV) Lignin Modified Phenol Formaldehyde Resin

[0105] The stable lignin-phenol blends were used for producing a lignin-phenol-formaldehyde resin. The general target values for such a resin are summarized in the following scheme:

TABLE-US-00004 Lignin amount 25% (L/(P + L)) (P.-substitution) F/P 2   mol/mol Step-wise NaOH addition F/L 0.2 mol/mol Step 1 Step 2 NaOH/P 0.8 mol/mol 33.3% 66.7% Solid content (cal.) 60% Water amount (cal.) 40%

[0106] First Lignin Modified Phenol Formaldehyde Resin According to the Solution (Resin A2, LP-Blend F)

[0107] To 177.4 g of blend A1, 37 g of 40% aqueous NaOH-solution, was added and stirred at 65° C. A 226.7 g of formaldehyde solution (37%) and then 58.6 g a 50% NaOH solution were constantly added over 30 minutes for each. The adhesive was further condensed at an elevated temperature of 80° C. until the viscosity increased to 500 mPa*s and then immediately cooled down.

[0108] Second Lignin Modified Phenol Formaldehyde Resin According to the Solution (Resin B2)

[0109] Blend B1 was condensed with concentrated formalin at a formaldehyde to phenol molar ratio of 2.35 at a temperature of at least 80° C. Aqueous NaOH was used as catalyst and added in multiple portions until a NaOH to phenol molar ratio of 1.1 was reached. The reaction was stopped by cooling upon reaching the desired viscosity of 500 mPas.

Comparative Example A (LPF)

[0110] For the reference sample, 36.7 g crystalline phenol was melted at 65° C. and 12.2 g powdered kraft lignin and after a short time 13.7 g 42% NaOH solution was added. At a constant temperature, the mixture is stirred and over a period of 30 min 64.5 g of formaldehyde (37%) solution and then 22.9 g 50% NaOH solution are added. The mixture is heated up to 85° C. and condensed to a final viscosity of approx. 500 mPa*s. After reaching the target viscosity, the mixture is immediately cooled down to room temperature.

Comparative Example B (LPF)

[0111] Phenol and lignin in a 1:1 mass ratio were condensed with concentrated formalin at a formaldehyde to phenol molar ratio of 2.35 at a temperature of at least 80° C. Aqueous NaOH was used as catalyst and added in multiple portions until a NaOH to phenol molar ratio of 1.1 was reached. The reaction was stopped by cooling upon reaching the desired viscosity of 500 mPas.

[0112] When comparing lignin-phenol-formaldehyde resin A2 (LP-Blend F) with a standard blend a (LPF) it is apparent that the properties of both resins are essential the same (see Table 4 below). Thus, the lignin-phenol-formaldehyde resin A2 according to the solution can be used in the same manner and for the same purposes as the standard resin.

TABLE-US-00005 TABLE 4 LP-Blend F LPF Lignin:Phenol 25:75 25:75 Solid content [%] 49   49   Viscosity [mPa*s] 400-600 400-600 pH (50% in water) [—] 11-12 11-12 Free Formaldehyde [%] 0.1 0.1

[0113] In Table 5 the synthesis of further lignin modified-phenol-formaldehyde resins are provided.

TABLE-US-00006 TABLE 5 Lignin Lignin Lignin Lignin Lignin Lignin Info A A-blend B B-blend C C-blend Molecular MW g/mol 5534 4695 4755 Weight av. Polydispersity PDI 4.6 4.3 4.3 index Solid Content 1 g, 140° C., 3 h % 49.5% 49.4% 49.1% 49.0% 49.1% 47.1% Viscosity 24 h 100 1/s, days 1, mPa*s 642 430 576 320 453 365 after 20° C. condensation pH (50% water) 11.2 11.2 11.7 11.2 11.7 11.3 Free Titration in % 0.1 0.1 0.1 0.1 0.1 0.1 Formaldehyde water B-Time 120° C. s 91 99 72 76 85 112

[0114] IV) Wood Composite Board Comprising Lignin Modified Phenol-Formaldehyde Resin

[0115] The following method is used to test the adhesive strength, which explains the effect of the solution:

[0116] The adhesive mixtures produced according to examples A2 and B2 were tested according to EN 314-1 and evaluated according to EN 314-2. For this purpose, 9-ply plywood boards with a glue application of 155 g/m.sup.2 were produced and pressed at 130° C. for 20 min in a hydraulic press. The hardened compound was air-conditioned after cutting to samples for 7 days at standard climate (20° C./65% r.h.). Half of the sample was stored for 24 hours in 20° C. warm water and the other half was immersed in boiling water for 6 hours and then cooled down in water at 20° C. for 1 hour. For Example B and B2, also criteria 3 (immersion for 4 h boiling water followed by 16-20 h of drying, 4 h in boiling water and 1 h cooling in water) of the standard were tested. The determined average tensile shear strengths (N/mm.sup.2) of the examples given are summarized in the following table 6.

TABLE-US-00007 TABLE 6 Treatment of Comparative Comp. plywoods example A Example A2 Example B2 Example B immersion for 1.6 N/mm.sup.2 1.6 N/mm.sup.2 Not tested Not tested 24 h in water (20° C.) immersion for 1.2 N/mm.sup.2 1.2 N/mm.sup.2 1.7 N/mm.sup.2 decomposed 6 h boiling water followed by 1 h cooling in water immersion for Not tested Not tested 1.3 N/mm.sup.2 Decomposed 4 h boiling water followed by 16-20 h of drying, 4 h in boiling water and 1 h cooling in water

[0117] The diagram of FIG. 1 shows the tensile strength of a plywood board obtained with the lignin modified phenol-formaldehyde resin A2 (LP-Blend F) and a standard resin (LPF). As clearly deducible, the tensile strength is essentially the same in both cases.

[0118] The diagram of FIG. 2 illustrates the condensation time and viscosity of lignin modified phenol-formaldehyde resin according to the solution and comparative example B and a further comparative example.

[0119] As can be seen when using the lignin modified phenol formaldehyde resin according to the solution (Example B2) a viscosity of 500 mPas (as target criteria for the resin manufacturing) is reached after about 90 min condensation time. The longer condensation time allows for achieving the required parameters in the final wood composite boards.

[0120] In contrast, when using comparative lignin sources (Example B) the viscosity of the resin is too high right from the beginning of the condensation reaction. This causes a reduction of the resin synthesis time and finally the performance of the wood composite boards when such adhesive is used (see results in the experimental section).