PROCESS FOR PREPARING A BONDING RESIN

Abstract

The present invention relates to a process for preparing a bonding resin, wherein a resin prepared from lignin, phenol and formaldehyde and comprising a formaldehyde scavenger, is mixed with a resin prepared from phenol and formaldehyde and comprising a formaldehyde scavenger to achieve a mixture useful as a bonding resin useful in the manufacture of oriented strand board (OSB).

Claims

1. A method for preparing a resin in a form of a mixture comprising the steps of: a) preparing a first resin comprising lignin, phenol, formaldehyde, and a formaldehyde scavenger; b) preparing a second resin comprising phenol, formaldehyde, and a formaldehyde scavenger, wherein the second resin comprises less than 1 wt-% lignin, by weight of the second resin; c) mixing the first resin and the second resin in a weight ratio of from 0.5:10 to 10:0.5 based on weight of a mixture of the first resin and the second resin.

2. The method according to claim 1, wherein the mixing in step c) is carried out by stirring at a speed from 20 to 1000 rpm.

3. The method according to claim 1, wherein a duration of the mixing in step at least one minute.

4. The method according to claim 1, wherein the formaldehyde scavenger is urea.

5. A resin in the form of the mixture obtained by the method of claim 1.

6. The method of claim 1 further comprising: manufacturing an oriented strand board with the mixture of the first resin and the second resin.

7. An oriented strand board manufactured using the resin according to claim 5.

8. A method for selecting an optimized resin mixture for a specific end use, the method comprising the steps of: a) defining one or more desirable properties of a resin; b) preparing a first resin comprising lignin, phenol, formaldehyde, and a formaldehyde scavenger; c) preparing a second resin comprising phenol, formaldehyde, and a formaldehyde scavenger, wherein the second resin comprises less than 1 wt-% lignin, by weight of the second resin; d) mixing the first resin and the second resin in a defined weight ratio of from 0.5:10 to 10:0.5 based on weight of a mixture of the first resin and the second resin; e) in a different vessel, repeating step d) with a different weight ratio; repeating step e) at least five times with additional different weight ratios in step d) in each repetition; g) evaluating properties of each mixture of the first resin and the second resin, said evaluation being carried out based on the properties of the mixture or based on properties of a final product prepared using each mixture of the first resin and the second resin obtained in step f); h) selecting an optimized mixture of the first resin and the second resin obtained in step f), based on the results of the evaluation carried out in step g), said selection step comprising a determination of which mixture of the first resin and second resin obtained in step f) has properties closest to the one or more desired properties of a resin defined in step a).

9. The method according to claim 2, wherein a duration of the mixing in step c) is at least one minute.

10. The method according to claim 8, wherein the mixing in step d) is carried out by stirring at a speed from 20 to 1000 rpm.

11. The method according to claim 10, wherein a duration of the mixing in step d) is at least one minute.

12. The method according to claim 8, wherein a duration of the mixing in step d) is at least one minute.

13. The method according to claim 8, wherein the formaldehyde scavenger is urea.

Description

DETAILED DESCRIPTION

[0031] 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. 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.

[0032] The pH of the mixture of the first resin and the second resin may be adjusted by addition of acid or base, depending on the final use of the mixture of the first resin and the second resin. To the extent alkali is added, it is preferably sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide or a mixture thereof. To the extent acid is added, it is preferably sulphuric acid or paratoluenesulphonic acid.

[0033] The mixture of the first resin and the second resin according to the present invention is useful for example in the manufacture of oriented strand board. The mixture of the first resin and the second resin is then mixed with strands of wood and heated under elevated pressure at a temperature of about 130-220° C.

EXAMPLES

Example 1

[0034] Reference phenol formaldehyde (PF) resin for oriented strandboard (OSB) was prepared in a 5 L glass reactor equipped with pitched blade stirrer. Firstly, 1320 g of molten phenol, 600 g of water and 294 g of NaOH solution (50%) were added to the glass reactor and mixed. Secondly, 1740 g of formaldehyde solution (concentration 52.5%) was added slowly to prevent excessive heat development. The temperature of the reaction mixture was increased to 80° C. and the reaction mixture was continuously stirred for 155 minutes. The reaction mixture was cooled to 60° C. and then 720 g of urea was added to the reaction mixture. The reaction was stopped by cooling to ambient temperature. The reaction was monitored by measuring the viscosity at 25° C. using a Brookfield DV-II+LV viscometer.

[0035] The resin was analyzed and the results of the analysis are given in Table 1.

Example 2

[0036] Lignin-phenol-formaldehyde (LPF) resin was synthesized for oriented strandboard (OSB) with a phenol replacement level of 50% with lignin. In the first step, 761 g of powder lignin (solid content 88.5%) and 1090 g of water were added to a 5 L glass reactor at ambient temperature and were stirred until the lignin was fully and evenly dispersed. Then, 326 g of sodium hydroxide solution (50%) was added to the lignin dispersion. The composition was heated to 80° C. and stirred for 60 minutes to make sure that lignin was completely dissolved in the alkaline media. Then, the temperature of the lignin composition was lowered to 45° C.

[0037] In the second step, 672 g of phenol, 57 g of sodium hydroxide solution (50%), 24 g of water and 1255 g of formalin solution (52.5%) were added into the reaction mixture. The temperature of the reaction mixture was increased to 80° C. and the reaction mixture was continuously stirred for 190 minutes. The reaction mixture was cooled to 60° C. and then 797 g of urea was added to the reaction mixture. The reaction was stopped by cooling to ambient temperature. The reaction was monitored by measuring the viscosity at 25° C. using a Brookfield DV-II+LV viscometer.

[0038] The resin was analyzed and the results of the analysis are given in Table 1.

Example 3

[0039] The resin blend was prepared by mixing PF resin from example 1 and LPF resin from example 2 in a ratio of 1:1 by weight.

[0040] The resin blend was analyzed and the results of the analysis are given in Table 1.

Example 4

[0041] The resin blend was prepared by mixing PF resin from example 1 and LPF resin from example 2 in a ratio of 3:1 by weight.

[0042] The resin blend was analyzed and the results of the analysis are given in Table 1.

Example 5

[0043] The resin blend was prepared by mixing PF resin from example 1 and LPF resin from example 2 in a ratio of 1:3 by weight.

[0044] The resin blend was analyzed and the results of the analysis are given in Table 1.

TABLE-US-00001 TABLE 1 Resin properties Resin Resin Resin Resin Resin from from from from from Example 1 Example 2 Example 3 Example 4 Example 5 Viscosity 177 178 181 172 195 [cP] at 25° C. pH at 23° C. 10.3 10.5 10.4 10.3 10.4 Solid 54 52.9 53.9 54.8 53.1 Content [%] 155° C. Gel Time 26 27 23 22 26 at 100° C.
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 6

[0045] Pine wood strands for use as surface layer strands were resinated with the resin from example 5 (8% solid resin on oven dry wood mass) and 1% wax, producing strands with a moisture content of 11% after resination).
For the core layer, pine strands were resinated with 4% pMDI (Suprasec 1561, percentage on oven dry wood mass) and 1% wax producing strands with a moisture content of 4%.
The layer ratio was 2×30%/40% between the surface/core layers. The board was pressed at 190° C. for 13 s/mm with a target thickness of 11.5 mm. The thickness swell and water uptake was measured according to ASTM 1037 point 23 Method B after 24 h immersion in cold water. The internal bond strength was measured according to ASTM1037 point 11, the modulus of rupture and modulus of elasticity were measured according to ASTM 3043 point 8, all after acclimatization at 20° C., 65% r.h for 1 week.

TABLE-US-00002 TABLE 2 Board properties Board Thickness Density Thickness Water Internal MOR MOE sample [mm] [kg/m.sup.3] swell [%] uptake [%] bond [N/mm.sup.2] [N/mm.sup.2] [N/mm.sup.2] Resin from 11.67 596 21.3 39.5 0.27 23.1 4020 example 5