FI104285B - Process for Improving Biodegradation Strength and Dimensional Stability of Cellulosic Products - Google Patents

Description

104285

The present invention relates to a method according to the preamble of claim 1 for improving mold and rot resistance and dimensional stability of cellulose based products.

According to such a method, the cellulose-based product is subjected to a heat treatment which is carried out at elevated temperature.

Heat treatment can be known to improve the dimensional stability of wood. In the prior art, reference is made, for example, to FI-15 Patent Publication No. 68122, which describes a method for treating wood at a temperature of 160-240 ° C and a pressure of 3-15 bar, whereby the ability of the wood to absorb water and thereby expand. The effect of heat treatment on the rot resistance of wood has also been studied. Thus, Mailun, N.P. 20 and Arenas, CV, in their article "Effect of Heat on Natural Decay Resistance of Philippine Woods" (Philippinen Lumberman, Vol. 20, no. 10, 1974, pp. 18-19, 22-24) describe dry wood treatment of Asian 90, 110, 130 , 150 and 175 ° C for 240 hours. As a result of the treatment, the color of the trees 25 turned chocolate brown. The extended treatment time at 130, 150 and 175 ° C increased the resistance of the investigated trees to two brown rot fungi, but at the same time the treatment weakened the wood's strength. 1 2 3 4 5 6

Since not all species of wood are suitable for conventional pressure crystallization using 2 agents for inhibiting fungal growth and spreading, heat treatment is an interesting alternative for rot-4 -1 protection. However, prior heat treatment processes, which require the use of pressure and long treatment times, 6 have been too complex to be suitable for industrial use. It has also been found that at high pressures and temperatures, wood becomes brittle and weakens. In addition, the wood easily ignites at high temperatures.

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It is an object of the present invention to overcome the drawbacks of the prior art and to provide a novel solution for improving the dimensional stability and the resistance to rot and mold (i.e., biodegradability) of cellulose-based products.

The invention is based on the idea that the heat treatment of a moist cellulose-based product is carried out in two steps: first, the product is dried to a desired humidity, usually below 10% to 15%. The temperature is then rapidly raised above 150 ° C (typically about 180-250 ° C), at which temperature the treatment is continued until a weight loss of at least 3% has been achieved for the product to be treated.

More specifically, the method according to the invention is essentially characterized in what is stated in the characterizing part of claim 1.

As stated above, the invention proceeds from the use of fresh timber or a similar cellulosic product. The product can be dried under any suitable conditions (even outdoors at ambient temperature) to a desired humidity of less than 15%. However, according to a preferred embodiment of the invention, the product is dried at an elevated temperature. At the same time the color of the wood product is darkened.

During drying, care is taken to ensure that the product does not crack. Advantageously, this object is achieved by continuously determining the temperatures of the inner wood and the outer surface of the wood, respectively, and keeping the temperature difference at a relatively low level. Most preferably, the difference is about 10-30 ° C. This is the case for both raising and lowering heat. It has surprisingly been found that this solution can even completely prevent the formation of (internal) cracks in the wood. When drying larger quantities of wood, there are 35 reasons to equip more specimens with sensors. The industrial scale equation preferably works by determining the appropriate heating program for each timber, taking into account the effect of initial humidity on the process.

In order to protect the wood and accelerate the heat transfer, steam is preferably used in the drying process. According to a preferred embodiment, the drying comprises the steps of: a) first raising the temperature of the drying furnace to at least about 90 ° C, preferably at least 100 ° C, and maintaining this temperature until the wood temperature reaches at least about the same temperature, b) gradually increasing the temperature of the furnace so that the difference between the inside temperature of the wood and the temperature of the furnace does not exceed 30 ° C until the desired humidity of the wood is reached; and c) finally decreasing the temperature of the furnace reach the desired temperature.

If necessary, step C may be omitted so that the heat treatment described in more detail below is carried out directly after step b.

In the first step of the process of the invention, the drying oven temperature is preferably set at about 100-150 ° C, preferably at 100-120 ° C. In the second step (step b), the heating is stopped when the humidity of the wood is less than 15%, e.g. 1-15%. In step B and optionally step c, the difference between the outside and inside temperatures of the cellulose-based product is maintained at 10-30 ° C. Too little temperature difference prolongs the drying process, while a large difference increases the risk of internal cracks. In step c, the furnace heat is reduced until the internal wood temperature has dropped below 100 ° C.

During the steps a, b and c, the furnace is fed with water vapor, which enables the so-called. the wet temperature is maintained at about 80-120 ° C, preferably about 100 ° C. Preferably, saturated water vapor is used.

104285 4

Once the product has dried to below 15% humidity, the treatment is continued at elevated temperature.

In the second step of the process, the temperature is kept higher than the first 5 steps. Preferably, the reaction is carried out at a temperature of about 180 to 250 ° C under a saturated vapor atmosphere. The temperature may also be raised during the second stage, as shown in Example 2. The treatment time and temperature are interdependent as explained in Example 1. Typically, the second 10-step heat treatment takes at least 0.5 hours, preferably 1-20 hours, and particularly preferably about 2 to 10 hours. By adjusting the weight loss of the product through heat treatment, its strength and rot resistance properties can be modified as desired. Thus, the heat treatment is continued until a weight loss of at least 3% (based on dry matter) is achieved. The product's dimensional stability properties already provide clear improvements in this value. Mold and decay resistance properties are also improved, but said durability can be further increased by continued heating after a weight loss of at least about 5%, preferably about 6 or even 8%, has occurred in the product.

The properties achieved by the method of the invention are summarized as follows: • 25 - Improvement of rot resistance (by comparison, trees that are naturally rot resistant) Improvement of mold resistance Improvement of dimensional stability Removal of pitch 30 - Reduction of thermal conductivity 25 - 40%

Improved paint stability

The second stage heat treatment according to the invention is preferably carried out at least under substantially non-pressurized conditions 35, i.e. normal atmospheric pressure.

The process of the invention is applicable to solid wood such as sawn timber, logs and poles. In addition, the method can be used for veneers, plywood, chips, sawdust, fibers and other cellulose-based products such as packaging boxes.

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Example 2 illustrates in more detail the anti-rot effect produced by the process. However, it should be noted in this connection that in order to provide good rot control, dried pine sawn timber is preferably kept at a temperature of 200-250 ° C for about 2 to 8 hours. The same conditions apply for birch and larch, while good rot resistance is achieved at slightly lower temperatures, e.g., about 175 to 210 ° C. The method is also well suited for wound treatment.

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Example 3 describes in greater detail the reduction in thermal conductivity in connection with the treatment according to the invention.

There are considerable advantages to the invention. Thus, it can shorten the drying time of the wood, utilize the color change of the wood during drying, and improve the mold and rot resistance and dimensional stability of the wood. Coniferous wood can be treated to remove harmful resin. Applications include exterior cladding boards, window sills and outdoor furniture and '* 25 sauna benches.

After treatment according to the invention, the moisture life of the wood products is reduced by 50-70%. The products will at best improve their rot resistance to a pressure saturation level or even better than 30 without substantially reducing their strength properties. At the same time, wood becomes a good base for painting.

The manufacturing process is simple and quick (short processing time) and does not require pressure. Process 35 can influence the properties of the product in a controlled manner with respect to its weather resistance, rot and mold resistance and strength properties. The method is suitable for all types of wood. Heat treatment can also improve the durability properties of heartwood, which cannot be achieved by pressure impregnation. The durability of difficult to impregnate wood species can be increased. Increasing the permeability (permeability) of wood may allow the absorption of other dyes into the wood.

The invention will now be further explored by means of the accompanying drawings and a few embodiments.

Fig. 1 is a simplified diagram of the apparatus suitable for the method according to the invention, Fig. 2 shows the effect of temperature and treatment time on weight loss, Fig. 3 shows the effect of weight loss on wood tangential swell 15, and Fig. 4 shows the effect of weight loss on wood radial swelling. Fig. 5 shows the effect of weight loss on decreasing moisture absorbed by wood, Fig. 6 shows the change in bending strength of wood caused by heat treatment, Fig. 7 shows the humidity of bending test pieces after 4 weeks of equilibration, Fig. 8 shows the heat treated and weight loss after decomposition test, Fig. 9 shows drying of fresh spruce according to a preferred embodiment of the invention, Fig. 10 shows weight loss of veneer as a function of heat treatment, Fig. 11 a reduction-processing plywood effect "thickness swelling and ** illustrated in Figure 12 the effect of the heat treatment plywood moisture reduction.

The apparatus utilized in the invention is, for example, the apparatus shown in Fig. 1, comprising an oven 2 surrounded by a sheath 1 in which the test pieces 3 are placed. Connected to the furnace are air inlet and outlet 104285 channels 4 and 5, respectively, through which moist air is passed through the furnace. The outlet duct 5 is then provided with a combined steam supply duct 6 for supplying additional water vapor to the air to be removed from the furnace. To form a closed loop, the inlet and outlet ducts are connected to each end of the fan and heating ducts 7. The air passing through said ductwork is heated by the electrical resistors 8 to the set temperature and is supplied through the fan 9 to the furnace inlet duct 4. The direction of air circulation in the apparatus is indicated by 10 arrows.

With the apparatus shown, it is possible to ensure that the test pieces placed in the furnace can be heated to the desired temperature with humid air. By varying the amount of steam 15 supplied, the moisture content of the air can be varied. Usually the furnace air is saturated with water vapor.

Example 1 .. Heat Treatment of Wood 20 Wet wood is dried in the above apparatus at 120-140 ° C, with or without steam, resulting in a slight darkening of the color but no cracking. When the humidity of the wood is less than 15%, the temperature is raised to at least 175 ° C, preferably to 180-250 ° C. Processing time is 2 to 10 hours. Saturated steam is introduced into the equipment. Temperature and time adjust the desired result. As a result, the color of the wood still darkens.

Figure 2 shows the effect of temperature and time on the weight loss of wood.

Thus, changes in the desired direction can be controlled by weight loss. Figures 3, 4, and 5 show the reduction of tan-35 Gent swelling, radial swelling and the amount of water absorbed by the wood (wood moisture) relative to the comparators. The curves 4 and 5 of Fig. 8 104285 correspond to the modeled curve of Fig. 1.

Heat treatment reduces the bending strength of the wood after a certain weight loss. On the other hand, in our experiments, we found that the bending strengths of the other pieces were even better than those of the reference pieces (Figure 6). This is because the heat-treated bodies absorb significantly less water at a given humidity than the control samples (Fig. 7).

Example 2

The rot resistance test

The demolition test was carried out in accordance with European standard EN 113: four parallel test pieces, 5x20x35 mm test-15 test pieces, the test pieces were not rinsed before the test. The exposure times were 2, 4, 8 and 12 weeks. The cellulose fungus (Coniophora puteana) was used as a rush fungus.

The specimens were sawn from 20 pine, birch, larch and spruce boards treated in accordance with Example 1. The processing conditions are summarized in Table 1.

Table 1. Treatment conditions for the decomposition test specimens

Test specimen Wood species__Heat treatment (time / lpt) _

25 _1__Pine__1.5 h / 200 ° C + 1 h / 220 ° C

_2__Pine__2 h / 220 ° C_ 3 Pine__4 h / 210 ° C_ 4 Birch 1 h / 160 ° C_ _5__Birch__4 h / 210 ° C_ 30 _6__Birth__1 h / 160 ° C + 2 h / 220 ° C_ 7 Birch__1 h / 160 ° C + 4 h / 220 ° C_ 8 Leaf__4 h / 210 ° C_9__Sex__4 h / 210 ° C_ 10 Six 1 h / 180 ° C_ 35 9 104285 After the heat treatment, the dry weights of the pieces of wood were determined. The specimens were sterilized by irradiation (Co-60), the sterilized specimens were placed in collar plates on a fungal culture of malt malt agar. At least one heat-treated sample and one untreated control were placed in each of the mal-5 plates.

At the end of the digestion period, the specimens were dried at 103 ° C and the weight loss of the specimens was calculated according to EN 113. In the case of pine 10, the heat treatment resulted in a wood weight loss of less than 10%, whereas in the case of untreated wood it is greater than 30%. The weight loss of birch, larch and spruce after heat treatment was at least close to zero.

The results of the decomposition tests are shown in Figure 8. As shown in the figure, a mild heat treatment (160 ° C) does not yet significantly improve the decay resistance of the treated timber.

Example 3 «20 Drying of Fresh Spruce

With wet spruce (50 x 100 x 1500 mm), initial humidity of about 40%, according to the preferred drying alternative of the invention, the heating was heated for 24 hours using a control system with 10 to 20 degrees difference between internal and surface temperature; (Figure 9). The final moisture content of the dry specimens was less than 5%.

Example 4 30 Decrease in thermal conductivity

Table 2 shows the thermal conductivity and treatment conditions of heat-treated spruce, pine and aspen pieces.

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Table 2. Thermal conductivity of test specimens

Wood / treatment lamp - Density measurement Thermal conductivity space / time instant, kg / m3__λ10, W / (mK) _ 5 Aspen, comparison__415__0,098_

Aspen, 4h 210 ° C__403__0,077_

Aspen, 10 h 210 ° C 379__0,077_

Six, Comparison__497__0.11

Spruce, fresh 26 h, 375 0,086 10 heat treatment 3 h / 220 ° C ___

Six, 8 h 230 ° C__399__0,080_ Pine, Comparison__583__0,13_ Pine, fresh, heat 520 0.107 15 treatment 3 h 220 ° C ___ Pine, 30 h 230 ° C 476__0,088_ 20 Example 5

Birch veneer, 1.5 mm thick, was heat treated in the furnace of Figure 1. The treatment temperature was 200 ° C and the time was 2 to 7 hours. 1 2 3 4 5 6 7 8 9 10 11

The test pieces were selected so that the veneer was divided into two 2 parts, with half of the veneer remaining as a reference and 3 half heat-treated. Veneers were made of 3 ply plywood 4. Bonding was done with FF adhesive. The adhesive was applied to the surfaces to be glued with a brush 5. The veneers were pressed at 130 ° C for 6 minutes. The compression pressure was 1.7 MPa. Reference plywood 7 and heat-treated veneer 8 were in the same compression.

9 • «10

To determine the thickness swelling, the specimens were dried in an 11 oven at 102 ° C. They were then immersed in 20 ° C water for 2, 6, 26 and 168 hours. For strength tests, test specimens were equilibrated at 65% relative humidity, followed by determination of wood fracture percentage, tensile strength, and flexural strength. 11 104285 duplicate samples were included in the test.

The weight loss from the dry weight of the wood due to the heat treatment is shown in Figure 10. As a result of the treatment, the weight of the 5 wood was reduced by 3.4 to 8.4%.

Table 3 shows the thickness swelling of the plywood.

Table 3. Peat swelling and moisture in water soaking 10 Sample__Thickness swelling Moisture_ 2 h 6 h 27 h 168 h 2 h 6 h 27 h 168 h 2 h heat 2.9 5.5 10.2 11.7 18.0 29.6 50.0 79.1 15 2h ver- 9.1 11.4 12.3 12.5 38.0 49.5 60.8 72.3 tailu_______ 3h heat 2.7 5.2 8.9 11, 0 14.8 27.0 43.2 74.8 3 h ver- 5.5 9.3 10.9 11.1 28.8 43.5 61.4 75.9 tailu_________ 20 4 h heat 1.8 3 , 7 7.4 9.9 13.4 23.6 42.0 74.2 4 h ver- 8.6 11.9 14.5 14.7 28.8 39.3 53.9 66.5 tailu_________ 5 h heat 1.9 4.1 8.0 11.2 16.1 27.4 46.6 79.9 5 h ver- 6.8 12.2 10.9 11.1 34.1 47.3 65, 6 78.7 25 tailu_______ •. 6 h heat 1.8 3.6 6.3 8.6 14.5 25.1 43.0 77.2 6 h ver- 5.4 8.6 10.4 10.6 29.1 43.3 62 , 8 79.0 tailu_________ 7 h heat 1.2 2.8 5.5 7.9 13.2 22.2 38.0 67.5 30 7 h ver- 6.7 9.7 11.1 11.2 31.2 48.8 59.1 73.7 tail____________

Thickness swellings of the reference material differed significantly 35. Therefore, the results are shown in Figure 11, with the swelling reduction calculated relative to the control for each series of experiments. Figure 12 shows a reduction in the amount of water absorbed by the wood compared to the untreated sample.

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For thickness swelling, the best results were obtained with the longest treatment time, that is, 7 hours of heat treatment. In this case, after 2 hours of immersion, the thickness swelling was 80% less than that of the control sample. Almost as good a result was achieved with 4 to 5 hours treatment. Heat treatment at 2 and 3 hours reduced the swelling after 50 hours immersion by 50 or 70%. After 24 hours of immersion, the thickness swelling of the heat-treated plywood for 7 and 4 hours was 50% less than that of the reference plywood.

10 Heat treatment reduces the amount of water absorbed into the wood (= wood moisture). After 24 hours of water immersion, the moisture content of the heat-treated plywood for 7 hours was approximately 38% lower than that of the reference plywood.

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Table 4 shows the strength values of the plywood.

Table 4. Plywood strengths 20 Sample Adhesive joint cut Tensile strength Humidity% Bending strength N / mm2 Tensile strength N / mm2

Wood- Cutting - Fracture% Strength ___ N / mm2 ____ 2h heat__21__1 / 7__65,3__5 / 5__132_ ': 2h Comparison 97__3 / 0__61,7__5 _; _ 3__148_3h Heat__81__2 ^ 4__83,1__4 / 7__155_ 25 3h Comparison 98__3 / 7__4 /.__ 148_ 4h heat__99__2 / 2__55,4__5 / 2__130_ 4h comparison 95__3,0__110,9__5,0__165_ 5h heat__100__1 / 7__50,4__4 ^ 2__95_ 5h comparison 84__3,1__74.5__4.7__128_30 6h7__.5 /, __ 108_ 6 h comparison 77__2 / 1__92,8__4 ^ _9__139_ 7 h heat__97__1 / 3__55,2__4 / 7__101_ 7 h comparison 94__3 / 9__84.5_ 5.4 141 35 13 104235 3-ply plywood requirements: adhesive shear strength, dry, strength = 2.1 N / mm 2. If the strength is less than this, the wood fracture percentage must be greater than 5 or = 50%.

tensile strength 54 N / mm2 flexural strength 72 N / mm2 The shear strength of plywood made from heat-treated veneers was almost all below the required value of 2.1, but since the wood fracture percentage was more than 50%, the shear strength can be found.

Plywood made from heat-treated veneer had a lower tensile strength than reference plywood but still met the requirements. The tensile strength values of the heat-treated plywood were below the requirements at a treatment time of 5 or 6 hours.

Example 6

The field

The test pieces (50 x 25 x 500 mm) were heat treated for 4 h at 220 ° C. The test pieces were placed on the test field for ground contact. After 25 years, the specimens were reviewed and evaluated.

The grading scale is as follows: 1 = tiny onset rot (25%), 2 = 50%, 3 = 75%, 4 = weight break. Averages for results: 30: Pine, comparison = 0.3. Heat treated pine = 0.

Six, comparison = 1. Heat treated six = 0.2.

Birch, comparison = 3.6. Heat treated birch = 2,5.

Claims (10)

104285 A process for improving the mold and la-5 resistance and dimensional stability of cellulose-based products, comprising: - drying the cellulose-based products to less than 15% humidity, then - subjecting them to a heat treatment at elevated temperature, characterized in that - after drying, the articles to be treated are kept under substantially normal atmospheric pressure at a temperature above 150 ° C in a humidified furnace fed with water vapor, 15 and treatment is continued until at least about 5% weight loss has occurred in the product. The process according to claim 1, wherein the cellulose-based products are dried at an elevated temperature, characterized in that, when the wet product is dried, the difference between the internal and external temperatures of the product is maintained at about 10-30 ° C to prevent cracking. Process according to Claim 2, characterized in that the product is dried in the presence of steam. The process according to claim 2 or 3, wherein the cellulose-based product consists of wood, characterized in that the product is dried by a) placing it in a drying oven which is raised to a temperature of at least about 90 ° C, preferably at least 100 ° C. b) then gradually increasing the temperature of the furnace so that the difference between the internal temperature of the wood and the furnace temperature does not exceed 30 ° C until the desired humidity of the wood is reached; and 104285 c) optionally finally lowering the furnace temperature; the temperature gradually so that the difference between the internal wood temperature and the oven temperature does not exceed 30 ° C until the internal wood temperature has reached the desired temperature. 5 A process according to any one of the preceding claims, characterized in that the cellulose-based product dried to less than 15% moisture is treated at 180-250 ° C for 1-20 hours, preferably about 2-10 hours. 10 Method according to one of the preceding claims, characterized in that saturated water vapor is supplied to the furnace. Method according to claim 1, characterized in that wood, poles, logs, sawn timber, veneer, plywood, chips, sawdust or fibers are treated. The method of claim 1 for treating pine lumber, characterized in that the dried lumber is held for 2 to 8 hours at a temperature of 200 to 250 ° C to provide good rot protection. A method according to claim 1 for treating spruce sawn timber, characterized in that the dried sawn timber is kept for 2 to 8 hours at a temperature of 175 to 210 ° C to provide good rot protection. Process according to claim 1 for the treatment of birch wood material, characterized in that the dried wood material is kept at a temperature of 200-250 ° C for 2-8 hours in order to provide good rot protection. A process according to claim 1 for treating hardwood material, characterized in that the dried wood material is kept at a temperature of 200-250 ° C for 2-8 hours in order to provide good rot protection. 16 104285