Recently, relying on richer timber resources, the wood flooring industry in Yunnan Province has developed rapidly. In 1997, the number of wood flooring manufacturers has grown to more than 200, with an annual production capacity of nearly 2 million M2. A certain reputation. Wood flooring materials generally require higher material quality, and the air dry density requirement is greater than 0. 60 g·cm-3, the hardness requirement is greater than 60 MPa, and the moisture absorption deformation property cannot be excessive. A small number of woods such as southwestern birch, teak and rosewood can meet these performance requirements and are therefore popular among wood flooring manufacturers and users. Due to the low recoverability of the latter two types of wood, the current timber flooring in Yunnan Province is mainly dependent on the southwestern birch. In the wooden flooring produced in 1997, the material used for the southwestern birch accounted for 90%, a large number. Harvesting has made the southwestern birch preserved in Yunnan Province close to the edge of the pick. At the same time, a large number of fast-growing and under-utilized hybrid trees such as winter melon and rubber wood have not been fully utilized. In this case, these miscellaneous woods are densified and modified to improve their mechanical properties such as hardness and reduce their water absorption. They are used in the manufacture of wood flooring and other products to improve the utilization efficiency of wood and alleviate the contradiction between supply and demand of wood. And the status quo of the forest resource crisis undoubtedly has important practical and scientific significance.
1 Experimental materials and methods
1.1 Experimental materials
Test materials and samples The four common Yunnan native woods are musk wood, M. fordianna Oliv, code A, air dry density 0. 3 1 8g · cm-3; winter melon wood, A. nepalen-sis D. Don, Code B, air dry density 0. 455g·cm-3; Maple, L. formosana Hance, code F, air dry density 0. 465g· cm-3; smoked ash, English name unknown, code YB, air dry density 0 473 g·cm-3; B. alnoides, Buch. - Ham. ex D. Don, code C, air dry density 0 789 g· cm-3 for comparison. According to GB1 92 9-91 and GB1 93 1 - 91, the sample is sawn and polished from the board. There are two types of samples: 1. Samples prepared by sanding and grinding, the size of which is 3 0 × 2 0 × 2 0 mm (measured mechanical properties) or 2 0 × 2 0 × 15 mm (measured with impregnation rate); 2. Quality controlled at 0.5 to 1.0 g irregular shape sample (water absorption rate) Sample). When selecting the sample, pay attention to: (1) sawing from the same plate; (2) its density should be close to the average density; (3) its appearance should have no obvious defects.
Modifiers used for modifiers are chemically pure or analytical
Pure reagent, modified monomer styrene (ST) and methyl methacrylate (MMA), respectively, washed with alkali and passed through an alumina column to remove the polymerization inhibitor, the initiator is benzoyl peroxide (BPO), The electron beam radiation sensitizer is triallyl cyanurate (TAC).
1.2 Test equipment and equipment
Decompression immersion system (self-made), the vacuum degree controllable range is 0. 0 75 ~ 0 MPa, the constant temperature controllable range is 20 ~ 80 ° C, the temperature control accuracy is 0. 5 ° C. KFG-1 high-frequency high-voltage electron accelerator has an accelerating voltage of 3 Mev, a beam flow rate of 3 0 MA, a carrier speed of 0 to 25 m·min-1, and a radiation dose (KGY) through accelerating voltage, beam current and Adjusted by the speed of the car, the radiation vacuum is 10 - 5Pa.
1. 3 Experimental methods
Under normal pressure and reduced pressure impregnation, the sample is treated under reduced pressure at 50 ° C and a set vacuum (under reduced pressure), and then the modified monomer is impregnated with the sample. After a certain period of time, the sample is taken out with a filter paper. Dry, measure the liquid absorption rate (impregnation rate) of the sample by weighing method:
p = mn - m0 / m0 × 1 0 0 %
In the formula:
P——liquid absorption rate (impregnation rate) of wood samples / %
M0 - the mass of the wood sample before impregnation / g
Mn - the mass of the wood sample after impregnation / g
Pre-radiation heat treatment and electron beam irradiation The impregnated wood samples are placed in an oven, heat-treated according to a certain heating procedure, and then irradiated at a set radiation dose on a KFG-1 high-frequency high-voltage electron accelerator. Sampling in these processes determines the retention and loss rate of the modifier in the wood:
R = pi / p0 × 1 0 0 %
r =1 0 0 % - R
In the formula:
R, r—the retention and loss rate of the modifier in the wood sample during thermal or electron beam irradiation, P0—the impregnation rate of the modifier in the wood sample before thermal or electron beam irradiation, Pi— The impregnation rate of the modifier in the wood sample after heat or electron beam irradiation treatment.
The determination of wood properties refers to the method (1) density of GB1 92 9-91 and GB1 93 1 - 91, the mass of the sample is measured with a balance, the volume of the sample is measured with a vernier caliper and the density of the sample is calculated; (2) Compressive strength and fracture compression ratio, measured and recorded by the MTS81 0 Material Test System (MTS), compression load to displacement curve, compression speed set to 1 mm · min-1, maximum load set to 50 0 0 kg; (3) hardness The sample size is 3 0 × 2 0 × 2 0 mm (non-standard sample), measured by Swiss Amsler wood mechanics tester, the head area is 1 cm2, the maximum load is 40 0 ​​0 kg; (4) water absorption Rate, take 0.5 to 1 g of wood sample, take it out in distilled water at room temperature for a certain period of time, take it out, dry the water droplets on the surface of the sample with filter paper, weigh it and calculate the water absorption rate.
2 Results and discussion
2 . 1 wood immersion treatment process
The densification modification of wood is to introduce a polymerizable polymer monomer or / and some prepolymer modifier into the interior of the wood, and then react the modifier in the wood in situ under the action of heat and other radiation. The curing process, thus immersing the modified liquid into the internal voids of the wood and reaching a certain amount, is the basis for the compaction modification of the wood.
Wood is a porous composite material composed of cellulose, hemicellulose and lignin [1 -3 ]. The impregnation process is a process in which the modifier solution is gradually immersed in the interior of the wood or even through the wood body by wetting and diffusion on the surface of the wood. The density of wood depends mainly on the tree species. It is the comprehensive degree of fiber looseness in the wood, the diameter of the catheter, the thickness of the cell wall and the volume of the cell cavity. The density determines the speed and ability of the wood to absorb the modified liquid to a certain extent. The results in Figure 1 show that under the same impregnation conditions, the A-density A wood has a much higher impregnation rate than the dense C wood when impregnated. Under normal pressure, the impregnation rate and density of wood show an approximate linear relationship with the decrease of density; under decompression, the impregnation rate of wood with low density increases with the decrease of wood density, so that The relationship between the impregnation rate and the density deviates from linearity, and the greater the degree of vacuum, the greater the degree of deviation.
Before the impregnation, the pre-vacuum of the wood under a certain negative pressure condition can pre-empt the air in the inner cavity of the wood, which is to clear the passage of the modified liquid into the interior of the wood, and also reduce the immersion of the modified liquid into the wood. The resistance increases the space in which the modified liquid can remain inside the wood. The results of Figures 2 to 3 show that when the pre-vacuum degree is 0. 0 75 MPa, the wood impregnation effect can be greatly improved regardless of the pre-vacuum time of the wood, and the wood is subsequently immersed for 2 to 4 hours. The absorption of styrene can be increased by 5 to 10 times compared with that under normal pressure.
Fig. 2 Effect of pre-vacuum time on wood impregnation Pre-vacuum degree 0 . 0 75MPa Modified monomer styrene immersion time 2 h / 50 °C
2. 2 The heat treatment of the impregnated wood before electron beam irradiation is immersed, and the wood absorbs the modifier. If it is directly subjected to electron beam irradiation, the liquid modifier will be lost due to volatilization. The results in Figure 4 show that the volatilization loss of the modified monomer in the untreated wood is as high as 60% to 90%. This is because the high-energy electron beam acts on the wood and the monomer in a short period of time, and the temperature thereof is greatly increased. When the polymerization of the monomer is too late, the volatilization to the outside of the wood occurs first. Pre-heating the impregnated wood Figure 3 Effect of impregnation time on wood impregnation Modified monomer styrene impregnation temperature 50 ° C after the situation has changed, at appropriate temperature such as 60 ° C and mixed initiator Under the action, the monomer on the outer surface of the wood first polymerizes and partially solidifies to form a polymer, which blocks the pores in the wood. Under the action of the subsequent high-energy electron beam, the volatilization of the monomer to the outside of the wood is hindered, and only the reaction of polymerization, grafting and crosslinking in the wood [4] is left, so that the loss rate of the modifier in the wood is caused. Drop to about 10%.
Figure 4 Effect of heat treatment on modifier loss during electron beam irradiation Heat treatment temperature 60 ° C (initiator and radiation sensitizer added to the monomer)
The importance of preheating can also be seen from the change in weight of the wood after electron beam irradiation reflected in Fig. 5. The electron beam radiation-modified wood obtained without heat treatment has a significant weight loss during the placement process, which indicates that the initiation of electron beam irradiation alone cannot complete the polymerization reaction, and the combined initiation of heat-electron beam radiation can ensure the polymerization.
2. 3 Mechanical properties of wood and modified wood As shown in Figure 6 and Tables 1-2, the density, hardness and compressive strength of the four local woods used in the experiment are small, much lower than the indicators of the southwestern birch. It is often cut into charcoal by residents in the forest area, and its utilization value is very low. Densified wood is prepared by thermal-chemical or/and thermo-chemical-electron beam irradiation combined modification. The density can be doubled, and the hardness and compressive strength can be increased by 50% to 100%. (Tables 1 to 2), the densification of materials shows a new picture for the value-added use of inferior wood.
Figure 6 Effect of densification modification on wood density
Table 1 Hardness of wood and modified wood*
From the results of Tables 1-2, it can be found that the improvement effect of wood hardness and compressive strength depends on the modified monomer used: A wood styrene, YB wood with methyl methacrylate has better modification effect; benzene The fracture compression ratio of ethylene-modified wood is much lower than that of the original wood, which indicates that the brittleness of the modified wood is increased; while the fracture compression ratio of the methyl methacrylate-modified wood is not significantly changed. The law of attention should be paid attention to in the design of wood compacting modified formula.
2.4 Water absorption of wood and modified wood
Wood has a great absorption of water, and its saturated water absorption rate can reach more than 100%. After the wood absorbs water, it usually undergoes volume expansion to cause warping or cracking of the product, and also creates conditions for the growth of the mold and the decay of the product. The water absorption and hygroscopicity of wood has greatly restricted its application, reducing the water absorption of wood and thus becoming an important aspect of wood modification. After combined modification by thermo-chemical or thermo-chemical-electron beam irradiation, the loose, porous and hydrophilic properties of the wood are fundamentally changed due to the fact that the polymer having a small solubility parameter is charged into the wood, and the water absorption is greatly improved. decline. The results of Fig. 7 and Fig. 8 show that the water absorption of the wood is reduced to 10% to 30% of the original wood by the densification modification. The more polymer that is filled into the wood and the higher the density of the modified wood, the smaller the water absorption of the modified wood. This change in wood properties indicates that wood products made from this type of modified wood have broad prospects for use in contact with water and in humid environments.
Figure 7 Water absorption of wood and modified wood
A wood / room temperature
3 Conclusion
3.1 Four kinds of Yunnan native wood eucalyptus (A), winter melon (B), maple (F) and ash (YB), which have lower density, hardness and compressive strength, higher water absorption and poor quality. Excellent material for wood flooring, southwestern birch.
3.2 The densely modified wood of the above wood is prepared by the combination of thermal-chemical or thermo-chemical-electron beam irradiation, and its density, hardness and compressive strength can be increased to 50%~1 compared with the original wood. 0 0 %, the water absorption rate is reduced to 10% to 30% of the original wood, which has exceeded the excellent material of the wooden floor.
Figure 8 Relationship between water absorption of wood and modified wood and wood density Room temperature, indicated by the arrow as raw wood
3. 3 styrene has better effect on the modification of sapwood (YB) by musk wood (A) and methyl methacrylate. The former monomer will make the modified wood brittle, the latter monomer Less negative impact
1 Experimental materials and methods
1.1 Experimental materials
Test materials and samples The four common Yunnan native woods are musk wood, M. fordianna Oliv, code A, air dry density 0. 3 1 8g · cm-3; winter melon wood, A. nepalen-sis D. Don, Code B, air dry density 0. 455g·cm-3; Maple, L. formosana Hance, code F, air dry density 0. 465g· cm-3; smoked ash, English name unknown, code YB, air dry density 0 473 g·cm-3; B. alnoides, Buch. - Ham. ex D. Don, code C, air dry density 0 789 g· cm-3 for comparison. According to GB1 92 9-91 and GB1 93 1 - 91, the sample is sawn and polished from the board. There are two types of samples: 1. Samples prepared by sanding and grinding, the size of which is 3 0 × 2 0 × 2 0 mm (measured mechanical properties) or 2 0 × 2 0 × 15 mm (measured with impregnation rate); 2. Quality controlled at 0.5 to 1.0 g irregular shape sample (water absorption rate) Sample). When selecting the sample, pay attention to: (1) sawing from the same plate; (2) its density should be close to the average density; (3) its appearance should have no obvious defects.
Modifiers used for modifiers are chemically pure or analytical
Pure reagent, modified monomer styrene (ST) and methyl methacrylate (MMA), respectively, washed with alkali and passed through an alumina column to remove the polymerization inhibitor, the initiator is benzoyl peroxide (BPO), The electron beam radiation sensitizer is triallyl cyanurate (TAC).
1.2 Test equipment and equipment
Decompression immersion system (self-made), the vacuum degree controllable range is 0. 0 75 ~ 0 MPa, the constant temperature controllable range is 20 ~ 80 ° C, the temperature control accuracy is 0. 5 ° C. KFG-1 high-frequency high-voltage electron accelerator has an accelerating voltage of 3 Mev, a beam flow rate of 3 0 MA, a carrier speed of 0 to 25 m·min-1, and a radiation dose (KGY) through accelerating voltage, beam current and Adjusted by the speed of the car, the radiation vacuum is 10 - 5Pa.
1. 3 Experimental methods
Under normal pressure and reduced pressure impregnation, the sample is treated under reduced pressure at 50 ° C and a set vacuum (under reduced pressure), and then the modified monomer is impregnated with the sample. After a certain period of time, the sample is taken out with a filter paper. Dry, measure the liquid absorption rate (impregnation rate) of the sample by weighing method:
p = mn - m0 / m0 × 1 0 0 %
In the formula:
P——liquid absorption rate (impregnation rate) of wood samples / %
M0 - the mass of the wood sample before impregnation / g
Mn - the mass of the wood sample after impregnation / g
Pre-radiation heat treatment and electron beam irradiation The impregnated wood samples are placed in an oven, heat-treated according to a certain heating procedure, and then irradiated at a set radiation dose on a KFG-1 high-frequency high-voltage electron accelerator. Sampling in these processes determines the retention and loss rate of the modifier in the wood:
R = pi / p0 × 1 0 0 %
r =1 0 0 % - R
In the formula:
R, r—the retention and loss rate of the modifier in the wood sample during thermal or electron beam irradiation, P0—the impregnation rate of the modifier in the wood sample before thermal or electron beam irradiation, Pi— The impregnation rate of the modifier in the wood sample after heat or electron beam irradiation treatment.
The determination of wood properties refers to the method (1) density of GB1 92 9-91 and GB1 93 1 - 91, the mass of the sample is measured with a balance, the volume of the sample is measured with a vernier caliper and the density of the sample is calculated; (2) Compressive strength and fracture compression ratio, measured and recorded by the MTS81 0 Material Test System (MTS), compression load to displacement curve, compression speed set to 1 mm · min-1, maximum load set to 50 0 0 kg; (3) hardness The sample size is 3 0 × 2 0 × 2 0 mm (non-standard sample), measured by Swiss Amsler wood mechanics tester, the head area is 1 cm2, the maximum load is 40 0 ​​0 kg; (4) water absorption Rate, take 0.5 to 1 g of wood sample, take it out in distilled water at room temperature for a certain period of time, take it out, dry the water droplets on the surface of the sample with filter paper, weigh it and calculate the water absorption rate.
2 Results and discussion
2 . 1 wood immersion treatment process
The densification modification of wood is to introduce a polymerizable polymer monomer or / and some prepolymer modifier into the interior of the wood, and then react the modifier in the wood in situ under the action of heat and other radiation. The curing process, thus immersing the modified liquid into the internal voids of the wood and reaching a certain amount, is the basis for the compaction modification of the wood.
Wood is a porous composite material composed of cellulose, hemicellulose and lignin [1 -3 ]. The impregnation process is a process in which the modifier solution is gradually immersed in the interior of the wood or even through the wood body by wetting and diffusion on the surface of the wood. The density of wood depends mainly on the tree species. It is the comprehensive degree of fiber looseness in the wood, the diameter of the catheter, the thickness of the cell wall and the volume of the cell cavity. The density determines the speed and ability of the wood to absorb the modified liquid to a certain extent. The results in Figure 1 show that under the same impregnation conditions, the A-density A wood has a much higher impregnation rate than the dense C wood when impregnated. Under normal pressure, the impregnation rate and density of wood show an approximate linear relationship with the decrease of density; under decompression, the impregnation rate of wood with low density increases with the decrease of wood density, so that The relationship between the impregnation rate and the density deviates from linearity, and the greater the degree of vacuum, the greater the degree of deviation.
Before the impregnation, the pre-vacuum of the wood under a certain negative pressure condition can pre-empt the air in the inner cavity of the wood, which is to clear the passage of the modified liquid into the interior of the wood, and also reduce the immersion of the modified liquid into the wood. The resistance increases the space in which the modified liquid can remain inside the wood. The results of Figures 2 to 3 show that when the pre-vacuum degree is 0. 0 75 MPa, the wood impregnation effect can be greatly improved regardless of the pre-vacuum time of the wood, and the wood is subsequently immersed for 2 to 4 hours. The absorption of styrene can be increased by 5 to 10 times compared with that under normal pressure.
Fig. 2 Effect of pre-vacuum time on wood impregnation Pre-vacuum degree 0 . 0 75MPa Modified monomer styrene immersion time 2 h / 50 °C
2. 2 The heat treatment of the impregnated wood before electron beam irradiation is immersed, and the wood absorbs the modifier. If it is directly subjected to electron beam irradiation, the liquid modifier will be lost due to volatilization. The results in Figure 4 show that the volatilization loss of the modified monomer in the untreated wood is as high as 60% to 90%. This is because the high-energy electron beam acts on the wood and the monomer in a short period of time, and the temperature thereof is greatly increased. When the polymerization of the monomer is too late, the volatilization to the outside of the wood occurs first. Pre-heating the impregnated wood Figure 3 Effect of impregnation time on wood impregnation Modified monomer styrene impregnation temperature 50 ° C after the situation has changed, at appropriate temperature such as 60 ° C and mixed initiator Under the action, the monomer on the outer surface of the wood first polymerizes and partially solidifies to form a polymer, which blocks the pores in the wood. Under the action of the subsequent high-energy electron beam, the volatilization of the monomer to the outside of the wood is hindered, and only the reaction of polymerization, grafting and crosslinking in the wood [4] is left, so that the loss rate of the modifier in the wood is caused. Drop to about 10%.
Figure 4 Effect of heat treatment on modifier loss during electron beam irradiation Heat treatment temperature 60 ° C (initiator and radiation sensitizer added to the monomer)
The importance of preheating can also be seen from the change in weight of the wood after electron beam irradiation reflected in Fig. 5. The electron beam radiation-modified wood obtained without heat treatment has a significant weight loss during the placement process, which indicates that the initiation of electron beam irradiation alone cannot complete the polymerization reaction, and the combined initiation of heat-electron beam radiation can ensure the polymerization.
2. 3 Mechanical properties of wood and modified wood As shown in Figure 6 and Tables 1-2, the density, hardness and compressive strength of the four local woods used in the experiment are small, much lower than the indicators of the southwestern birch. It is often cut into charcoal by residents in the forest area, and its utilization value is very low. Densified wood is prepared by thermal-chemical or/and thermo-chemical-electron beam irradiation combined modification. The density can be doubled, and the hardness and compressive strength can be increased by 50% to 100%. (Tables 1 to 2), the densification of materials shows a new picture for the value-added use of inferior wood.
Figure 6 Effect of densification modification on wood density
Table 1 Hardness of wood and modified wood*
From the results of Tables 1-2, it can be found that the improvement effect of wood hardness and compressive strength depends on the modified monomer used: A wood styrene, YB wood with methyl methacrylate has better modification effect; benzene The fracture compression ratio of ethylene-modified wood is much lower than that of the original wood, which indicates that the brittleness of the modified wood is increased; while the fracture compression ratio of the methyl methacrylate-modified wood is not significantly changed. The law of attention should be paid attention to in the design of wood compacting modified formula.
2.4 Water absorption of wood and modified wood
Wood has a great absorption of water, and its saturated water absorption rate can reach more than 100%. After the wood absorbs water, it usually undergoes volume expansion to cause warping or cracking of the product, and also creates conditions for the growth of the mold and the decay of the product. The water absorption and hygroscopicity of wood has greatly restricted its application, reducing the water absorption of wood and thus becoming an important aspect of wood modification. After combined modification by thermo-chemical or thermo-chemical-electron beam irradiation, the loose, porous and hydrophilic properties of the wood are fundamentally changed due to the fact that the polymer having a small solubility parameter is charged into the wood, and the water absorption is greatly improved. decline. The results of Fig. 7 and Fig. 8 show that the water absorption of the wood is reduced to 10% to 30% of the original wood by the densification modification. The more polymer that is filled into the wood and the higher the density of the modified wood, the smaller the water absorption of the modified wood. This change in wood properties indicates that wood products made from this type of modified wood have broad prospects for use in contact with water and in humid environments.
Figure 7 Water absorption of wood and modified wood
A wood / room temperature
3 Conclusion
3.1 Four kinds of Yunnan native wood eucalyptus (A), winter melon (B), maple (F) and ash (YB), which have lower density, hardness and compressive strength, higher water absorption and poor quality. Excellent material for wood flooring, southwestern birch.
3.2 The densely modified wood of the above wood is prepared by the combination of thermal-chemical or thermo-chemical-electron beam irradiation, and its density, hardness and compressive strength can be increased to 50%~1 compared with the original wood. 0 0 %, the water absorption rate is reduced to 10% to 30% of the original wood, which has exceeded the excellent material of the wooden floor.
Figure 8 Relationship between water absorption of wood and modified wood and wood density Room temperature, indicated by the arrow as raw wood
3. 3 styrene has better effect on the modification of sapwood (YB) by musk wood (A) and methyl methacrylate. The former monomer will make the modified wood brittle, the latter monomer Less negative impact
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