EP2152482A1

EP2152482A1 - Modified wood and method for producing modified wood

Info

Publication number: EP2152482A1
Application number: EP08753825A
Authority: EP
Inventors: Mats Westin; Stig Lande
Original assignee: Kebony AS
Current assignee: Kebony AS
Priority date: 2007-05-11
Filing date: 2008-05-09
Publication date: 2010-02-17
Also published as: CA2686948A1; JP2010526692A; AP2009005063A0; AU2008251134A1; RU2009145034A; WO2008140323A1

Abstract

A method for modifying a wood specimen, wherein the wood specimen is immersed in an impregnation solution comprising polymerizable, low molecular furan derivatives in a vessel, the vessel is pressurized to between 5 and 29 bar from between 30 to 120 minutes, the wood specimen is subjected to a vacuum in the range of 0.01 to 0.5 bar fro from between 60 to 600 minutes, and the impregnation solution polymerized.

Description

MODIFIED WOOD AND METHOD FOR PRODUCING MODIFIED WOOD

BACKGROUND OF THE INVENTION

It is often desirable to modify wood with an impregnation compound. The degree of retention of the impregnation compound is expressed in terms of "Weight Percent Gain" (WPG), of the parent wood material. It is sometimes desirable for the retention of the impregnation compound to be at reduced levels. There exists a need therefore for an improved method of impregnating wood with a polymerizable fluid wherein the retention level of the fluid can be controllably reduced.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 : Duration of vacuum step versus chemical uptake

Figures 2 and 3: Two blocks cut in half (top and right end-sealed and bottom EN252 stake).

Figure 4: Two pine blocks cut in half. On top the one with 75% HW, bottom 60% HW.

Figure 5. Duration of vacuum step versus chemical uptake - with addition of 10% ethanol

DESCRIPTION OF THE INVENTION

Furan polymer modified wood is produced by first impregnating the wood with a suitable amount of a polymerizable liquid of low molecular furan derivatives, e.g. furfural, furfuryl alcohol, bishydroxymethylfuran or combinations thereof, and optionally catalysts, initiators, low boiling point alcohols such as ethanol or other compounds depending upon the nature of the impregnating solution. After impregnation the wood is heated, whereby the polymerizable compounds are polymerized into a furan polymer in the wood cells.

According to one embodiment of the invention, the polymerizable component is utilized without dilution by a diluent such as water or other solvent. The impregnation is done by first applying the impregnation liquid to the wood under a pressure of at least 5 bar for a time period of at least 30 minutes. According to another aspect of this embodiment, the pressure is at least 10 bar and the impregnation time under this pressure is between 30 and 60 minutes. This overpressure step is followed by a prolonged vacuum step, where the impregnation vessel is evacuated and the pressure maintained at low levels (0.1 bar) for at least 4 hours. According to another aspect of this embodiment the vacuum is maintained from 5 to 6 hours.

According to a second embodiment of the invention, the wood is subjected to an initial air pressure of 2 to 6 bar for a time span of 10 to 30 minutes before the liquid impregnation is started, thus filling up more of the wood cell volume with air prior to impregnation.

According to yet another aspect of the invention, the impregnation solution further comprises a low boiling point alcohol such as ethanol in an amount from 5 to 10%.

After the impregnation step the impregnated wood is heated to a temperature in the range of 80 to 15O⁰C, whereby the polymerizable components are polymerized to a furan polymer in the wood cells. Since water is not used as a diluent, no further drying of the wood is required.

According to another aspect of the invention, products obtainable by the described process can have a range of furan polymer retentions, with dry density increases, expressed as "Weight Percent Gain" (WPG), of the parent wood material ranging from 30 to 100 %. According to yet a further aspect of the invention, the products can exhibit WPG of from 30 to 80%, and according to yet another aspect a WPG of 70% or less.

EXAMPLES

MATERIALS AND METHODS:

WOOD SPECIMENS

I. Pure Scots pine (Pinus sylvestris) sapwood boards, 28 x 125 mm cross-section and 200mm length, from Hallsjo bradgard outside Uppsala, Sweden. II and III. Two groups of Scots pine, 28 x 125 mm cross-section and 200mm length, with approximately 60% and 75% heartwood content (standard quality for production of preservative treated wood), respectively, from Varberg Timber, Varberg, Sweden.

IV and V. Pure Scots pine sapwood EN252-stakes (25x50x500mm) and ENl 13- blocks (15x25x50mm) from Unnared Sawmill, south-east part of Sweden. VI. Beech (Fagus sylvatica) boards of varying cross-section and 200mm length from WPT.

All 200mm long wood blocks were endgrain-sealed with Sicaseal primer followed by Sicaseal building silicone. The field stakes (25x50x500mm) were not endgrain- sealed.

TREATMENT MIXTURES

FA refers to furfuryl alcohol . The "FAlOO" mix is based on undiluted furfuryl alcohol with addition of catalysts. The "FA40" mix is a waterborne furfuryl alcohol solution containing approximately 28% furfuryl alcohol with the addition of catalysts and stabilizing chemicals. The "FA 50" mix is a waterborne furfuryl alcohol solution containing approximately 32 % furfuryl alcohol with the addition of catalysts and stabilizing chemicals. The FAlOO -mix is based on a commercial recipe developed by Wood Polymer Technologies ASA (WPT, now Kebony ASA). A modification to the FAlOO mix was done after the first set of tests by adding 10% ethanol (m/m based on final mix).

IMPREGNATION PROCESS

Example 1 : Control - Standard Lo wry process using FAlOO treatment mix. 12 bar pressure for 90 min followed by 60 min post-vacuum.

Example 2: FAlOO treatment mix. 12 bar pressure for 45 min followed by 6h post- vacuum (divided in 2h periods with intermediate weighting of the specimens). Example 3: FAlOO treatment mix modified by addition of ethanol. 12 bar pressure for 60 min followed by 6h post-vacuum (divided in 2h periods with intermediate weighting of the specimens).

2 and 3 were also run without intermediate weighting of the specimens. During the impregnation all end-sealings seem to fill their function.

CURING

Except for one endgraine-sealed specimen (that were put directly in the oven), the surfaces of all specimens were wiped clean. The specimens were then wrapped in aluminium foil and placed in an oven at 103⁰C over night (approx 12h). In the morning the foil was removed and the specimens put back in the oven. After 2h, the temperature was raised to 12O⁰C for Ih and then turned down to 103⁰C again, after which the specimens were taken out. During the curing blisters appeared in the end- sealing coatings.

EXAMPLES AND RESULTS

Example 1: Control - Standard Lowry process (90 min pressure + 60 min post- vacuum)

Table 1: Treatment data for control - Standard Lowry process

After Pressure step After post-vacuum After curing

Type No Wt before approx approx Weight Uptake Uptake Weight Uptake Uptake Weight WPG retention

(g) density dry-wt (9) (9) (kg/m^J) (g) (g) (kg/m^J) (g) (%) (kg/m^J)

I. 10:7 406,07 627 363,43 835,76 429,69 663 806,02 399,95 617 648,48 78,43 401

I 10:8 404,84 625 362,33 837,09 432,25 667 811 ,13 406,29 627 653,00 80,22 409

10:9 396,74 612 355,08 833,11 436,37 673 804,38 407,64 629 649,12 82,81 413

9:9 360,86 557 322,97 809,71 448,85 693 775,60 414,74 640 598,28 85,24 387

Average 674 628 81,7 403 rv. 181 324,66 519 290,57 761 ,66 437 699 734,14 409,48 655 590,91 103,36 441

183 304,11 487 272,18 717,22 413,11 661 673,01 368,90 590 519,70 90,94 373

Average 680 623 97,2 407

V. 978 10,66 569 9,54 21 ,86 11 ,20 597 18,07 89,38 418

979 8,97 478 8,03 - - - 20,21 11 ,24 599 16,06 100,09 400

980 10,10 539 9,04 - - - 22,66 12,56 670 20,07 122,01 531

981 10,07 537 9,02 - - - 21 ,73 11 ,66 622 17,75 96,82 432

982 10,62 567 9,51 - - - 21 ,85 11 ,23 599 18,08 90,15 417

983 8,89 474 7,95 - - - 20,16 11 ,27 601 15,85 99,21 391

984 10,04 535 8,98 - - - 21 ,82 11 ,78 628 17,68 96,79 427

985 10,01 534 8,96 - - - 21 ,53 11 ,52 614 17,78 98,41 424

986 11 ,13 594 9,96 - - - 22,23 11 ,10 592 18,22 82,86 409

987 8,82 470 7,89 - - - 20,46 11 ,64 621 16,49 108,83 422

988 8,77 468 7,85 - - - 20,30 11 ,53 615 16,56 110,87 427

989 10,79 575 9,66 - - - 21 ,85 11 ,06 590 18,17 88,20 418

990 8,87 473 7,94 22,02 13,15 701 20,25 11 ,38 607 16,33 105,69 415

991 10,59 565 9,48 - - - 22,35 11 ,76 627 18,27 92,70 422

992 10,44 557 9,34 - - - 22,21 11 ,77 628 17,93 91 ,94 417

993 10,24 546 9,16 - - - 21 ,27 11 ,03 588 17,46 90,62 422

994 10,89 581 9,75 - - - 21 ,82 10,93 583 18,07 85,36 423

995 10,39 554 9,30 - - - 21,45 11 ,06 590 17,67 89,98 421

996 10,61 566 9,49 - - - 23,03 12,42 663 18,76 97,65 465

997 10,61 566 9,50 - - - 19,13 8,52 454 15,87 67,00 316

Average 537 701 604 95,2 421

Total Average 676 626 87 404

In Table 1 the data for the first Lowry impregnations is shown. Full penetration was obtained but the reduction in chemical uptake by the post-vacuum step was 10 only 50 kg/m³ out of 676 kg/m³ and the resulting WPG was 87% (the retention was 404 kg/m³ based on final volume). The wood block that was not wrapped in alu-foil had the highest WPG of that group but since it had also higher uptake after impregnation it lost 12% more of the furfuryl alcohol than the other that were wrapped.

15 Since the uptake seemed to be unnecessary high it was decided to shorten the pressure step by half. Furthermore, it was noticed that new liquid kept pouring out of the surface after the post- vacuum step and it was therefore decided to prolong the vacuum step.

Example 2: 45 min pressure + 360 min vacuum

In these impregnations it was obvious that the uptake during the pressure step was reduced by the shorter duration of the pressure - 10% lower for the end-sealed sapwood blocks and 22% lower for the EN252-stakes. Furthermore, the uptake after 6h post- vacuum was reduced by further 12% and 9%, respectively, compared to the 2h in A (total reduction 22 and 31%, respectively).

The chemical uptake as plotted versus post-vacuum time (Fig. 1) and it was obvious that the prolonged vacuum step doubled the amount removed (approx 100 kg/m³ instead of 50).

The resulting WPG was now 70% (315 kg/m³) for the end-sealed pine sapwood blocks and approx. 50-60% (260-300 kg/m³) for non-sealed EN252 stakes. This is almost the same WPG level as was reached with the waterborne FA50 mix used at Wood Polymer Technologies for preparation of the highest WPG-level for the EN252 test started June 2005.

Table 2: Data for example 2 (45 min pressure + 360 min vacuum)

After pressure step After post-vacuum After curing

Type No Wt before Approx Approx Weigth Uptake Uptake Weight Uptake Uptake Weight WPG Retention (9) Density Dry-Wt (g) (g) (kg/rrO (g) (g) (kg/ml (g) (g) (kg/m")

I. 98 352,93 545 315,872 752,42 399,49 616 675,12 322,19 497 539,72 70,87 316

9 10 353,14 545 316,06 745,10 391,96 605 670,92 317,78 490 538,17 70,27 314

10 10 389,87 602 348,934 773,67 383,8 592 702,52 312,65 482 579,02 65,94 325

Average 605 490 70,57 315

II. 13 9 353,59 526 316,463 456,77 103,18 154 439,23 85,64 127 403,75 27,58 128

17 8 324,44 483 290,374 475,29 150,85 224 456,17 131,73 196 402,81 38,72 163

187 319,66 476 286,10 459,29 139,63 208 444,61 124,95 186 399,04 39,48 164

Average 216 191 39,10 163

III. 169 328,85 489 294,321 428,68 99,83 149 409,73 80,88 120 376,41 27,89 121

22 11 333,56 496 298,536 432,43 98,87 147 420,09 86,53 129 384,88 28,92 126

16 12 344,56 513 308,381 436,70 92,14 137 423,40 78,84 117 391,81 27,05 123

Average 144 122 27,96 123

IVa. 182 376,20 581 336,70 718,17 341,97 528 660,28 284,08 438 552,35 64,05 313

184 371,73 574 332,70 701,38 329,65 509 643,52 271,79 419 535,99 61,10 299

Average 518 429 62,58 306

IVb. 6 393,90 608 352,541 692,54 298,64 461 638,69 244,79 378 533,66 51,38 260

7 390,14 602 349,175 692,70 302,56 467 636,15 246,01 380 530,34 51,88 259

Average 464 379 51,63 259

VI. 1 414,80 692 371,246 593,36 178,56 298 543,77 128,97 215 495,23 33,40 190

2 376,64 628 337,093 579,41 202,77 338 523,37 146,73 245 473,78 40,55 218

3 427,36 713 382,487 599,37 172,01 287 548,43 121,07 202 499,89 30,69 179

4 404,97 675 362,448 588,14 183,17 305 540,18 135,21 225 487,19 34,42 194

Average 307 222 34,76 195

When looking at the "cut-in-middle" cross-sections of end-sealed pure sapwood blocks and EN252 stakes there seemed to be a gradient in the end-sealed but not in the EN 252 stakes (see Fig. 2 and 3).

The end-sealed beech blocks reached a WPG of only 35% (195 kg/m³) but there was a clear gradient in the cross-section. However, penetration in the radial and tangential direction is low for beech whereas the longitudinal is extremely high (4m boards would be fully penetrated through the end-grain).

For the pine specimens with 60% and 75% heartwood content there was clearly a slight penetration of the heartwood (similarly to what was found by Vinden & McQuire (1981) and Jermer & Sebring (2006) with waterborne preservatives impregnated with Lowry process) as can be seen in figure 4. This makes it difficult to calculate the WPG in the sapwood zone but the overall WPG was 39% and 28% (163 and 123 kg/m³), respectively. The sample on the top in figure 4 had a knot in the middle which evidently increased the penetration in the zone around the knot.

The effect of the sapwood being more permanently swollen than the heartwood (leading to a slight "I-beam" effect) can also be clearly seen in figure 4. Also after 6h vacuum, the same tendency that was noted after 2h was seen - new liquid kept pouring out of the surface when left alone for 5 min. Therefore, we decided to try to lower the viscosity by addition of 10% ethanol and hoped that this would lead to higher reduction in uptake after the vacuum step.

Example 3: 60 min pressure + 360 min vacuum In these trials 10% ethanol was added to the FAlOO-mix and the pressure time was increased slightly - 60 min instead of 45 min still shorter than the Standard 90 min.

The results show that the initial uptake was slightly higher than in example 2, which may be attributed to the ethanol-addition but may also be an effect of longer pressure time. However, the reduction in the vacuum step was slightly less when comparing with example 2 (compare EN252 stakes in figure 2 with figure 4) and seems to level out after 2h.

The resulting WPG was slightly lower for the end-sealed pure sapwood but higher for the other groups. Especially for the beech and the high HW/SW ratio in pine there was a dramatic increase in uptake (better penetration in beech and into the heartwood zone of pine).

For the EN 252 stakes the final WPG was almost as high as with example 1 , which was very unexpected. One theory is that it is mainly the ethanol which is evaporated during the vacuum step, thereby leaving most of the FA in the wood, contrary to what we hoped for - we had hoped that the ethanol would help removing larger amount of the FA than without ethanol which was obviously not the case. Table 3. Data for example 3 (6 Omin pressure + 360 min vacuum) - with 10% ethanol

After pressure After post-vacuum After curing

Type No Wt before Approx. Approx. Weigth Uptake Uptake Weight Uptake Uptake Weight WPG Reten (9) Density Dry-Wt (g) (g) (kg/m') (g) (g) (kg/πr⁵) (9) (g) (kg/n

I. 8 390,02 602 349,07 776,33 386,31 596 723,46 333,44 515 573,02 64,16 31! g 391 ,32 604 350,23 786,93 395,61 611 733,01 341 ,69 527 578,39 65,15 32'

Average 603 521 64,7 32(

II. 18:9 323,97 482 289,95 476,29 152,32 227 463,57 139,60 208 403,86 39,28 162

13:10 351 ,20 523 314,32 473,19 121 ,99 182 456,84 105,64 157 408,65 30,01 13-!

Average 204 182 34,6 14! m. 21:4 323,09 481 289,17 465,84 142,75 212 459,10 136,01 202 407,34 40,87 16/

21:5 323,32 481 289,37 476,76 153,44 228 468,30 144,98 216 414,76 43,33 17€

Average 220 209 42,1 171

IV. 189 294,23 471 263,34 745,56 451 ,33 722 693,13 398,9 638 550,82 109,17 42'

190 369,82 592 330,99 787,45 417,63 668 759,00 389,18 623 617,24 86,48 41f

191 360,89 577 323,00 771,85 410,96 658 733,84 372,95 597 595,80 84,46 39€

192 346,51 554 310,13 748,75 402,24 644 708,73 362,22 580 567,59 83,02 38J

193 299,94 480 268,45 749,13 449,19 719 694,62 394,68 631 555,21 106,82 41 {

Average 682 614 94,0 4Oi

VI. 5 481,62 705 431,05 740,32 258,7 379 702,98 221 ,36 324 615,61 42,82 23<

6 486,02 696 434,99 756,42 270,4 387 714,22 228,20 327 624,08 43,47 241

7 486,93 707 435,80 831 ,53 344,6 501 777,47 290,54 422 664,34 52,44 29^

8 476,10 705 426,11 707,49 231 ,39 343 672,92 196,82 292 595,02 39,64 22.

Average 402 341 44,6 24<

Claims

1. A method for modifying a wood specimen, comprising: a. Immersing the wood specimen in an impregnation solution comprising polymerizable, low molecular furan derivatives in a vessel, b. Pressurizing the vessel to between 5 and 29 bar from between 30 to 120 minutes, c. Thereafter subjecting the wood specimen to a vacuum in the range of 0.01 to 0.5 bar fro from between 60 to 600 minutes, and d. Polymerizing the impregnation solution.

2. The method of claim 1, wherein the wood specimen is subjected to pressurized air at pressures in the range 2 to 6 bar, applied for 10 to 30 minutes, before the wood is immersed in the impregnation solution.

3. The method according to claim 1 or 2, wherein the polymerizable, low molecular furan derivatives are selected from furfural, furfuryl alcohol, bishydroxymethylfuran or combinations thereof.

4. The method according to claim 3, wherein the vessel is pressurized from 10 to 29 bar from between 30 to 60 minutes.

5. The method according to claim 4, wherein vacuum is 0.1 bar or less, and is applied from 4 to 6 hours.

6. The method according to claim 1 where the specimen is a board.

7. A wood product obtainable by the method of claim 1.

8. A wood product obtainable by the method of claim 2.

9. A wood product obtainable by the method of claim 3.

10. A method for impregnating a wood sample with an impregnating solution, such that the level of retention of the impregnating solution expressed in term of Weight Percentage Gain (WPG) is from 30 to 80%, comprising the use of an impregnating solution that is not diluted by a diluent, wherein the wood sample is impregnated under a pressure between 5 and 29 bar for between 30 to 120 minutes, and thereafter subjected to a vacuum in the range of 0.01 to 0.5 bar fro from between 60 to 600 minutes.

11. The method according to claim 10, wherein the impregnating solution comprises a low molecular furan derivative.