Lignin-based phenolic resin

Abstract

The present invention relates to a lignin-based phenolic resin, particularly useful in the manufacture of oriented strand boards (OSB).

Claims

1. An aqueous bonding resin having 35-75% solid content, the aqueous bonding resin being a product of a reaction among phenol and formaldehyde, the aqueous bonding resin comprising a group 1 alkaline metal hydroxide and lignin, wherein the phenol and formaldehyde is 40 to 80% of the weight of the solids provided to the reaction; the group 1 alkaline metal hydroxide is 5 to 20% of the weight of the solids provided to the reaction; and the lignin is 21.0 to 35% of the weight of the solids provided to the reaction.

2. An aqueous bonding resin according to claim 1, wherein the lignin is 25 to 35% of the weight of the solids provided to the reaction.

3. An aqueous bonding resin according to claim 2, wherein the lignin is 25 to 30% of the weight of the solids provided to the reaction.

4. An aqueous bonding resin according to claim 1, wherein the lignin has been generated in the Kraft process.

5. An engineered wood product manufactured using the aqueous bonding resin of claim 1.

6. An engineered wood product according to claim 5, wherein said product is an oriented strand board.

7. A method for manufacturing an oriented strand board product wherein the surface layers of an oriented strand board panel or article are treated by coating particles or strands with a wax and mixing the particles or strands with the resin of claim 1, so that the particles or strands will be adhered together; followed by curing under heat and pressure to form the product.

8. An aqueous bonding resin according to claim 1, further comprising urea, wherein the urea is no more than 30% of the weight of the solids provided to the reaction.

9. An aqueous bonding resin according to claim 8, wherein the amount of urea is 5 to 25% of the weight of the solids provided to the reaction.

10. An aqueous bonding resin according to claim 9, wherein the amount of urea is 5 to 15% of the weight of the solids provided to the reaction.

11. An aqueous bonding resin according to claim 1, further comprising urea, wherein the lignin is 25 to 35% of the weight of the solids provided to the reaction, and wherein the urea is 5 to 25% of the weight of the solids provided to the reaction.

12. An aqueous bonding resin according to claim 1, further comprising urea, wherein the lignin is 25 to 30% of the weight of the solids provided to the reaction, and wherein the urea is 5 to 15% of the weight of the solids provided to the reaction.

Description

DETAILED DESCRIPTION

(1) One embodiment of the present invention is thus directed to an aqueous bonding resin having 35-75% solid content, the aqueous bonding resin being a product of a reaction among phenol and formaldehyde, a group 1 alkaline metal hydroxide, lignin and optionally urea, wherein the phenol and formaldehyde is 40 to 80% of the weight of the solids provided to the reaction; the group 1 alkaline metal hydroxide being 5 to 20% of the weight of the solids provided to the reaction; the lignin being 21.0 to 35% of the weight of the solids provided to the reaction; and the urea being 0 to 30% of the weight of the solids provided to the reaction.

(2) In one embodiment, the lignin is 21.0 to 30% of the weight of the solids provided to the reaction. In one embodiment, the lignin is 25 to 35% of the weight of the solids provided to the reaction such as 30 to 35% of the weight of the solids provided to the reaction. In one embodiment, the lignin is 25 to 30% of the weight of the solids provided to the reaction.

(3) The amount of urea is preferably 0.1 to 30% of the weight of the solids provided to the reaction, such as 1 to 30% of the weight of the solids provided to the reaction, preferably 5 to 25% of the weight of the solids provided to the reaction, more preferably 5 to 15% of the weight of the solids provided to the reaction.

(4) It is intended throughout the present description that the expression “lignin” embraces any kind of lignin, e.g. lignin originated from hardwood, softwood or annular plants. In one embodiment, the lignin is a kraft liquor degraded lignin. Preferably the lignin is an alkaline lignin generated in e.g. the Kraft process. The lignin may then be separated from the black liquor by using the process disclosed in WO2006031175.

(5) The resin is made by reacting formaldehyde and phenol at a molar ratio of 1.5-3.5 moles of formaldehyde to one mole of phenol in the presence of lignin, water and a group 1 alkaline metal hydroxide at a temperature of 60-100° C. for a period of time sufficient to achieve a viscosity of 200-5,000 cps. The formaldehyde, water, group 1 alkaline metal hydroxide, phenol and lignin may be combined in a number of ways. They may all be added together in a single charge or several discrete charges. The formaldehyde, water and group 1 alkaline metal hydroxide may be added to a reactor along with the phenol and lignin prior to initiating the reaction during the first stage of this process, or the formaldehyde, water and group 1 alkaline metal hydroxide might be added in multiple discreet aliquots to the phenol and lignin during this first stage. This first stage of resin synthesis is the polymerization stage, when the phenol and formaldehyde are reacted together to form a polymeric material.

(6) In a second stage of the synthesis process the mixture is cooled to a temperature of less than 60° C., and optionally urea, and optionally water and a group 1 alkaline metal hydroxide, are added with stirring to form the final resin binder composition. The viscosity of the composition is 50-1000 cps.

(7) Phenolic resin made using lignin has advantages over existing OSB binder technologies. These advantages include reduced ammonia emissions, improved shelf life and lower cost without loss of board properties, including internal bond strength.

(8) Phenol/formaldehyde adducts associated with this invention are formed by the reaction of phenol and formaldehyde in the presence of lignin and a group 1 alkaline metal hydroxide in an essentially aqueous medium. In one embodiment the formaldehyde/phenol molar ratio is 2.0-3.0 moles of formaldehyde to one mole of phenol. The formaldehyde reactant can exist as either a formalin solution or decomposable formaldehyde products such as paraformaldehyde or trioxane. In the event that formalin is used the solution concentration can generally be as high as about 50%.

(9) Levels of the different components are selected to achieve a composition in the final resin corresponding to phenol/formaldehyde adduct and an alkaline metal salt or alkaline metal salts of the phenol-formaldehyde adduct (40-85% of the total weight of the solids in the resin), urea (0-35% of the total weight of the solids in the resin), and lignin and an alkaline metal salt or alkaline metal salts of the lignin (5-25% of the total weight of the solids in the resin). The term ‘phenol/formaldehyde adduct’ simply means reaction product of phenol and formaldehyde. Adducts of phenol and formaldehyde could include relatively small compounds such as methylolated phenol or larger molecules that are products of the condensation of methylolated phenol. The urea and, optionally, some portion of the caustic and water are added subsequent to polymerization of the phenol and formaldehyde reaction mixture.

(10) Examples of group 1 alkaline metal hydroxides suitable for this invention include sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, cesium hydroxide, and francium hydroxide. Other alkaline materials such as sodium carbonate and potassium carbonate can also be used in place of or in addition to the group 1 alkaline metal hydroxide for the purpose of this invention. There would be residuals of the carbonates in the resin. These could include bicarbonates.

(11) The lignin can be obtained from the substance commonly known as ‘black liquor’. The black liquor can be derived from wood chips, including those based on softwood or hardwoods. Softwoods can include pines (loblolly, lodge pole, slash, pitch, ponderosa, shortleaf, yellow, white, jack and red), fir (Douglas, Frazier, white, balsam, Pacific silver, sub alpine), cedar (Alaskan, Northern white, Eastern red, Western red, incense, Port Orford), spruce (red, white, black, englemann, Sitka), hemlock (Eastern, Western, Mountain, larch) and others. Hardwoods can include oak (white, red, bur, live), poplar (yellow, balsam, quaking aspen, big tooth), maple (sugar, silver, red), basswood, birch, alder, beech, gum, cherry, cypress, elm, hack berry, hickory, sassafras, sycamore, cucumber, walnut, locust and others.

(12) The black liquor is formed by steeping wood chips in solutions of sodium sulfide and sodium hydroxide at elevated temperatures for a period of time and subsequent removal of the cellulosic fibers. The residual liquor is dark in color due to the presence of degraded lignin. The term ‘black liquor’ is a consequence of this dark color. The process used to generate the black liquor is generally known as the kraft pulping process. The lignin may then be separated from the black liquor by using the process disclosed in WO2006031175. In one embodiment, the lignin is produced using the “LignoBoost” process.

(13) The resins are used to manufacture the surface layers of an oriented strand board panel or article. The method is to coat the particles or strands with a wax and mix the particles or strands with the resin so that the particles or strands will be adhered together in the final article. The particles or strands are then laid up into the article and cured under heat and pressure to form the article.

(14) A typical oriented strand board has surface layers and core layers. The wood strands are typically 25-45 mm thick, 10-60 cm wide, and 0.1-2 m long. The strands are sprayed or otherwise treated with a slack wax and a resin, either a core layer resin for the core layer strands or a surface layer resin such as the present resin for the surface layer strands. The core and surface layer strands are then laid up on a caul plate and screen into a mat having outer surface layers and inner core layers. The strands in the surface layers are usually aligned along one major axis and the strands in the core layers are aligned along the other major axis.

(15) The mat, caul plate and screen are placed in a hot press and heated and pressed to form a composite OSB panel. The surface temperature of the press platens usually is between 200 and 220° C.; the initial pressure on the mat is about 500-2200 psi; and the time in the press is around 2-5 minutes depending on the thickness of the panel. There is a first phase in which the mat is compressed to its target thickness, a second phase in which the mat is maintained at its target thickness, and a third phase in which the press is opened and all external pressure on the consolidated mat is relieved. A mat is typically compressed from around 7-15 cm thickness to a desired thickness such as 1.5-2.5 cm.

(16) Commercial OSB panels are usually hot at the time that they are stacked into bundles. In this configuration the elevated temperature of the OSB can persist for several days and it is common for this prolonged heat-treatment to affect some of the properties of the OSB. During this process the resin will change. The water will be removed from the resin and phenol-formaldehyde adducts will condense into larger molecules. It is possible, but not known, that some of the lignin might react with phenol-formaldehyde adducts. The pH of the wood/resin mixture is about 5.5 to 7 and at this pH level most of the phenol-formaldehyde adducts and lignin material are insoluble. During the hot-pressing process a portion of the phenol-formaldehyde adducts are converted into load-bearing solids, which effectively transfer stress between adjacent strands.

EXAMPLES

Example 1

(17) Lignin-phenol-formaldehyde resin for OSB panel was cooked in a 5 L glass reactor and mixed with pitched blade stirrer. Firstly, 633.4 g of lignin (95% lignin), 950.1 g of molten phenol, 824 g of water and 1.71 litres of 37% formaldehyde solution were added to the glass reactor and mixed.

(18) Secondly, 250 ml of NaOH solution (45%) was added slowly to prevent excessive heat development and giving a pH of 10.2-10.5. The temperature was kept constant at 60° C. for 60 minutes and was then increased to 85° C. The viscosity was measured at 25° C. using a Höppler viscometer. When the viscosity had increased to app. 350-400 mPas the jacket temperature was set to 60° C. When the reaction temperature had decreased to ≤75° C., 250 ml of 45% w/w sodium hydroxide was slowly added keeping the reaction temperature below 75° C. The jacket temperature was then adjusted to 74° C. and the increase in viscosity followed as before. When the desired viscosity was obtained, the reaction was stopped by cooling to ambient temperature as fast as possible. The lignin content in the final resin was 24% by weight of the solids used.

Example 2

(19) Reference phenol formaldehyde (PF) resin for OSB panel was cooked in a 5 L glass reactor and mixed with pitched blade stirrer. Firstly, 956 g of molten phenol, 915 ml of water and 1.46 litre of 37% formaldehyde solution were added to the glass reactor and mixed.

(20) Secondly, 196 ml of NaOH solution (45%) was added slowly to prevent excessive heat development and giving a pH of 10.2-10.5. The temperature was kept constant at 60° C. for 30 minutes and was then increased to 85° C. The viscosity was measured at 25° C. using a Höppler viscometer. When the viscosity had increased to app. 350-400 mPas the jacket temperature was set to 60° C. and water (64 ml) was added. When the reaction temperature had decreased to ≤75° C., 131 ml of 45% w/w sodium hydroxide was slowly added keeping the reaction temperature below 75° C. The jacket temperature was then adjusted to 75° C. and the reaction followed as before. When the desired viscosity was obtained, the reaction was stopped by cooling to ambient temperature as fast as possible.

Example 3

(21) Spruce boards were cut into 190 mm long pieces and strands were manufactured in a disk flaker and sieved. The impregnation of the wood strands was performed in a rotating drum batch using the resin from Example 1 or 2 which was diluted with water to reach a specific viscosity. The impregnated OSB strands were spread and hot-pressed at 160° C. for a total pressing time of 10 min to achieve boards measuring 540×540 mm.sup.2. After hot-pressing, the boards were cooled between two aluminium plates at room temperature. Prior to evaluation all samples were conditioned at 20° C. and 65% RH. Internal bonding was evaluated before and after cyclic test conditions specified in V313 standard. Average data from 3 boards is presented in Table 1.

(22) TABLE-US-00001 TABLE 1 OSB board densities, internal bond and residual strength after conditioning and aging according to V313 standard. After After aging conditioning according to V313 (20° C., 65% RH) standard Density Internal Bond Internal Bond OSB (Kg/m3) (MPa) (MPa) Panel Average Average AVERAGE Board based on resin from Example 1 LPF resin 621 0.62 0.43 based OSB Board based on resin from Example 2 Ref. PF 627 0.51 0.51 resin based OSB

(23) In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.

Example 4

(24) Lignin based phenolic resin was synthesized for OSB applications. In the first step, lignin solution was prepared by mixing of 433 g of kraft lignin (solid content 95%), 635 g of water and 204 g of 50% sodium hydroxide solution in a 5 liter glass reactor equipped with overhead stirrer, condenser and temperature control unit. Lignin solution was continuously stirred for 90 minutes.

(25) In the second step, 320 g of phenol and 835 g of formalin (concentration 52.5%) were added to the lignin solution. The temperature was increased to 80° C. The reaction was monitored by measuring the viscosity using the Brookfield DV-II+LV viscometer. The reaction mixture was continuously heated at the temperature at 80° C. and 36 g of 50% sodium hydroxide solution was added after 45 minutes of reaction, followed by addition of 100 g of phenol and 15 g of water after 95 minutes. The reaction was cooled down to 45° C. after minutes, then 380 g of urea was added and the reaction was cooled down to room temperature.

(26) The resin was analyzed and the results of the analysis are given in Table 2.

(27) TABLE-US-00002 TABLE 2 Resin Properties S.C (%) 59.8 pH 10.5 Gel time (min) @100° C. 25

Example 5

(28) Spruce boards were cut into 190 mm long pieces and strands were manufactured in a disk flaker and sieved. The impregnation of the wood strands was performed in a rotating drum batch using the resin from Example 4 (which was diluted with water to reach a specific viscosity) for surface layer and pMDI for the core layer. The strands had a moisture content of 4%. The ratio between surface layer and core layer was 3:2, and 8% resin was used for the surface layer and 4% for the core layer.

(29) The impregnated OSB strands were spread and hot-pressed at 215° C. for a total pressing time of 3 minutes and 40 seconds to achieve boards measuring 540×540 mm.sup.2.

(30) After hot-pressing, the boards were cooled between two aluminium plates at room temperature. Prior to evaluation all samples were conditioned at 20° C. and 65% RH. Internal bonding was evaluated after cyclic test conditions specified in V313 standard. Average data from 2 boards is presented in Table 3.

(31) TABLE-US-00003 TABLE 3 OSB board densities, internal bond and residual strength after aging according to V313 standard. After aging according to V313 Density standard (Kg/m3) Internal Bond (MPa) OSB Panel Average AVERAGE LPF resin 640 0.24 based OSB