AU2008251134A1 - Modified wood and method for producing modified wood - Google Patents

Description

WO 2008/140323 PCT/N02008/000164 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 5 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. 10 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 15 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 20 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 25 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 30 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.

WO 2008/140323 PCT/N02008/000164 2 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. 5 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. 10 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 15 range of 80 to 150"C, 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 20 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. 25 EXAMPLES MATERIALS AND METHODS: WOOD SPECIMENS 30 I. Pure Scots pine (Pinus sylvestris) sapwood boards, 28 x 125 mm cross-section and 200mm length, from Hallsj6 bridgird outside Uppsala, Sweden.

WO 2008/140323 PCT/N02008/000164 3 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. 5 IV and V. Pure Scots pine sapwood EN252-stakes (25x50x500mm) and ENI 13 blocks (1 5x25x50mm) from Unnared Sawmill, south-east part of Sweden. VI. Beech (Fagus sylvatica) boards of varying cross-section and 200mm length from WPT. 10 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 15 FA refers to furfuryl alcohol . The "FA100" 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 20 of catalysts and stabilizing chemicals. The FA100 -mix is based on a commercial recipe developed by Wood Polymer Technologies ASA (WPT, now Kebony ASA). A modification to the FA100 mix was done after the first set of tests by adding 10% ethanol (m/m based on final mix). IMPREGNATION PROCESS 25 Example1: Control - Standard Lowry process using FA100 treatment mix. 12 bar pressure for 90 min followed by 60 min post-vacuum. Example 2: FA1O treatment mix. 12 bar pressure for 45 min followed by 6h post vacuum (divided in 2h periods with intermediate weighting of the specimens). 30 WO 2008/140323 PCT/N02008/000164 4 Example 3: FA100 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). 5 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 10 aluminium foil and placed in an oven at 103*C 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 120"C for 1h and then turned down to 103"C again, after which the specimens were taken out. During the curing blisters appeared in the end sealing coatings. 15 20 25 30 WO 2008/140323 PCT/N02008/000164 5 EXAMPLES AND RESULTS Example 1: Control - Standard Lowry process (90 min pressure + 60 min post vacuum) 5 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 (g) (g) (kg/rn) (g) (g) (kg/m 3 ) (g) (%) (kg/m) 1. 10:7 406,07 627 363,43 835,76 429,69 663 806,02 399,95 617 648,48 78,43 401 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 1 674 628 81,7 403 IV. 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 1 537 701 604 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/m 3 out of 676 kg/m 3 and the resulting WPG was 87% (the retention was 404 kg/m 3 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 WO 2008/140323 PCT/N02008/000164 6 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 5 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). 10 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/m 3 instead of 50). The resulting WPG was now 70% (315 kg/m 3 ) for the end-sealed pine sapwood blocks and approx. 50-60% (260-300 kg/m 3 ) for non-sealed EN252 stakes. This is 15 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. 20 25 WO 2008/140323 PCT/N02008/000164 7 Table 2: Data for example 2 (45min 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 (g) Density Dry-Wt (g) (g) (kg/m') (g) (g) (kgIm) (g) (g) (kg/m") I. 9:8 352,93 545 315,872 752,42 399,49 616 675,12 322,19 497 539,72 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 H. 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 18:7 319,66 476 286,10 459,29 139,63 208 444,61 124,95 186 399,04 39,48 164 Average 216 191 39,10 163 IH. 16:9 328,85 489 294,321 428,68 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 5 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/M 3 ) 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 10 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 15 to calculate the WPG in the sapwood zone but the overall WPG was 39% and 28% (163 and 123 kg/m 3 ), respectively.

WO 2008/140323 PCT/N02008/000164 8 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. 5 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 10 In these trials 10% ethanol was added to the FA100-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 15 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 20 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 25 amount of the FA than without ethanol which was obviously not the case. 30 WO 2008/140323 PCT/N02008/000164 9 Table 3. Data for example 3 (60min 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 (g) Density Dry-Wt (g) (g) (kg/md) (g) (g) (kg/md) (g) (g) (kg/n I. 8 390,02 602 349,07 776,33 386,31 596 723,46 333,44 515 573,02 64,16 315 9 391,32 604 350,23 786,93 395,61 611 733,01 341,69 527 578,39 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 16, 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 III. 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 17E 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 39E 192 346,51 554 310,13 748,75 402,24 644 708,73 362,22 580 567,59 83,02 38! 193 299,94 480 268,45 749,13 449,19 719 694,62 394,68 631 555,21 106,82 41E Average 682 614 94,0 40j 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 29z 8 476,10 705 426,11 707,49 231,39 343 672,92 196,82 292 595,02 39,64 22e Average 402 341 44,6 2M 5

Claims (11)

1. A method for modifying a wood specimen, comprising: a. Immersing the wood specimen in an impregnation solution 5 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 10 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 15 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, 20 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. 25

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. 30

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. 35

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 40 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. WO 2008/140323 PCT/N02008/000164 11

11. The method according to claim 10, wherein the impregnating solution comprises a low molecular furan derivative. 5 10 15 20