CN114633331A - Preparation method of mildewproof compressed rubber wood with stable size - Google Patents

Abstract

A preparation method of dimensionally stable and mildew-proof compressed rubber wood relates to a preparation method of compressed rubber wood. The present invention solves the problems of low density, poor material properties, easy deformation, mildew and blue stain of rubber wood. Treatment methods: 1. Prepare water-soluble acylated lignin solution; 2. Impregnate rubber wood with water-soluble acylated lignin solution; The invention is used for the preparation of dimensionally stable and mildew-proof compressed rubber wood.

Description

A kind of preparation method of dimensionally stable, mildew-proof compressed rubber wood

technical field

The present invention relates to a preparation method of compressed rubber wood.

Background technique

Rubber tree is one of the important tropical economic crops in my country. It is mainly used for the production of natural latex and is planted in large quantities in Hainan, Yunnan, Guangdong and other regions of my country. When the rubber production capacity of rubber trees declines, a large amount of rubber wood can be obtained by new cutting. The annual output of rubber wood logs in China is about 2 million m ³ . Now rubber wood has become one of the important wood sources in China. Rubber wood is a fast-growing wood with excellent characteristics such as elegant color and easy processing. However, compared with other precious woods, rubber wood has a large number of macroporous structures for the transmission of nutrients, and parenchyma cells contain a large amount of starch, protein and other substances for glue production and degumming. The survival of microorganisms and fungi provides convenience, so rubber wood is very susceptible to mildew and blue. In addition, the distribution of starch in rubber wood is uneven, resulting in uneven density, poor material properties, poor strength and easy deformation and cracking. Therefore, the modification of rubber wood is particularly important.

Wood is a porous material. At present, the modification methods for low-quality wood are mostly single and targeted, such as improving strength, flame retardant, mildew resistance, etc., while the technical methods for composite modification are relatively few. However, compound modification often greatly improves the performance and quality of wood in many ways, which has a very positive effect on broadening the application scope of low-quality wood.

Wood compression and densification is an environmentally friendly, high-efficiency and easy-to-industrial wood physical modification method. The traditional wood compression technology usually softens the wood first, compresses the wood without destroying the wood structure, and reduces the internal structure of the wood. The pores of the wood can be compressed and densified, so that the low-quality wood becomes uniform in texture, and its density, material properties and strength are improved. However, compressed wood is prone to moisture absorption, water absorption and rebound in environments such as high humidity and water soaking, thereby losing the performance of compression and compaction. Therefore, the dimensional stability of compressed wood is a key indicator to maintain the improvement of its wood properties.

In addition to improving the wood quality by reducing the pores in the wood by compaction, in recent years, people have impregnated the pores of the wood with resins, polymer monomers, etc. to improve the wood properties and quality. The above-mentioned polymers can improve the dimensional stability, biological durability, etc. of the wood by being solidified, filled and fixed on the wood cell wall or in the cell cavity. However, most of the impregnating agents used are derived from fossil resources, which are unsustainable; the modified agents contain toxic catalysts or organic solvents that are difficult to separate. and potentially harmful to the environment. The development of biomass-based environmentally friendly impregnation agents is of great significance for wood impregnation modification.

SUMMARY OF THE INVENTION

The invention solves the problems of low density, poor material properties, easy deformation, mildew and blue-staining of rubber wood, and further provides a preparation method of compressed rubber wood with stable dimensions and mildew resistance.

A preparation method of dimensionally stable and mildew-proof compressed rubber wood, which is carried out according to the following steps:

1. Preparation of water-soluble acylated lignin solution:

The water-soluble acylated lignin is added to the water, and the pH of the solution is adjusted to the pH of rubber wood, and then an initiator and a catalyst are added to obtain a water-soluble acylated lignin solution;

The mass percentage of the water-soluble acylated lignin in the water-soluble acylated lignin solution is 5% to 15%; the mass percentage of the initiator in the water-soluble acylated lignin solution is 0.5% to 2%; The mass percentage of the catalyst in the water-soluble acylated lignin solution is 0% to 5%;

2. Water-soluble acylated lignin solution impregnating rubber wood:

Immerse the rubber wood in the water-soluble acylated lignin solution, and then under the conditions of vacuum degree of -0.05MPa～-0.1MPa and pressure of 0.60MPa～1.0MPa, immersion until the water-soluble acylated lignin solution completely penetrates the rubber The wood is then placed in the atmospheric environment to dry naturally until the moisture content is 30% to 50% to obtain the impregnated rubber wood;

3. Hot pressing and densification treatment of impregnated rubber wood:

①. Put the impregnated rubber wood between the two heating plates of the hot press, close the heating plate without applying pressure, and under the condition that the temperature of the double heating plate is 60 ℃ ~ 80 ℃, the impregnated rubber The wood is preheated for 10min-30min, and then the temperature of the double heating plate is raised to 100℃～200℃ within 30min;

②. Under the condition that the temperature of the double heating plate is 100℃～200℃ and the applied pressure is 50kg·cm ^-2 ～300kg·cm ^-2 , compress the impregnated rubber wood vertically and hold the pressure for 20min～40min. The compressibility in the thickness direction of the impregnated rubber wood is 15% to 25%, and then the temperature of the double heating plate is 100 ℃ to 200 ℃ and the applied pressure is 50kg·cm ^-2 to 300kg·cm ^-2 , Continue to carry out The vertical wood texture is compressed and kept under pressure for 20 to 40 minutes, so that the compression rate of the impregnated rubber wood in the thickness direction is 35% to 45%, and the rubber wood after secondary compression is obtained;

③. Under the condition that the temperature of the double heating plate is 100℃～200℃ and the applied pressure is 50kg·cm ^-2 ～300kg·cm ^-2 , the rubber wood after secondary compression is compressed vertically to the maximum extent in the thickness direction. Compress and densify, and keep the pressure for 20-40 minutes to obtain rubber wood after three compressions;

4. Turn off the heating, cool down the temperature of the double heating plate to below 50°C under the condition of maintaining pressure, and take out the rubber wood that has been impregnated with acylated lignin and treated with hot pressing and densification;

4. Drying and curing:

1. Put the rubber wood treated with acylated lignin impregnation combined with hot pressing and densification in the atmospheric environment for 5d-10d to obtain the rubber wood after natural drying;

②. Put the naturally dried rubber wood in a vacuum blast drying oven, and then raise the temperature of the vacuum blast drying oven from room temperature to 40℃ to 120℃～140℃ at a rate of 20℃～40℃ every 4h～6h. ℃, and at a temperature of 120 ℃ to 140 ℃, the temperature is kept for 24h to 48h, that is, the preparation of dimensionally stable and mildew-proof compressed rubber wood is completed.

The beneficial effects of the present invention are:

Using dealkalized lignin as raw material, acylating lignin with maleic anhydride to obtain water-soluble acylated lignin with active double bonds and hydrophilic carboxyl groups, the active double bonds endow the acylated lignin with cross-linking The curing characteristics, the carboxyl group endows the acylated lignin with good water solubility, making the acylated lignin more easily impregnated into the interior of the wood. The acylated lignin is impregnated and filled into the cell cavity of rubber wood, and then combined with hot pressing and densification treatment to make the acylated lignin fully contact with the inner wall of the rubber wood cell cavity, and the synergistic effect of high temperature and initiator and (or) catalyst Under cross-linking and curing, a cross-linked network structure that is insoluble in water is formed, which is fixed on the inner wall of the rubber wood cell cavity or solidified into a block and filled in the cell cavity to obtain high-performance acylated lignin modified compressed rubber wood. Due to the insoluble acylated lignin cross-linked network structure filled in the compressed rubber wood, the density of the modified rubber wood can reach up to 1.28g·cm ^-3 , and the maximum compression ratio (CR) can reach 48 %, the 24h water absorption rate (WU) of compressed rubber wood can be as low as 19.73%, the 24h water absorption thickness expansion rate (TS) is reduced from 100% to 25.59%, and the moisture absorption thickness expansion rate (TS') under the humidity condition of 93%RH It can be as low as 20.93%, and the impact strength can be increased by up to 11% compared with that before modification, and there is no problem of brittleness of compressed wood caused by high temperature hot pressing; not only that, lignin is rich in benzene ring structure and phenol structural unit, This endows the lignin with excellent antibacterial properties, and the acylation modification does not change the main structure of the lignin, so the compressed rubber wood modified by the above method is filled with acylated lignin in the internal cell cavity and thermally compacted. The technical means occupied and squeezed the living space of fungi, cut off the food chain of fungi, and achieved the purpose of inhibiting the growth of mold, thus effectively curbing the mildew and blue change of rubber wood.

To sum up, the acylated lignin-modified compressed rubber wood prepared by the present invention has high density, good dimensional stability and mildew resistance, and the impact strength is also improved, which provides high value utilization for low-quality rubber wood. condition.

Description of drawings

Fig. 1 is a physical map, a is the acylated lignin-modified compressed rubber wood prepared in Example 5, and b is the untreated dry rubber wood prepared in Comparative Example 1;

Fig. 2 is the microscopic topography of untreated absolutely dry rubber wood prepared by Comparative Example 1;

Fig. 3 is the microscopic topography of the acylated lignin-modified compressed rubber wood prepared in Example 4;

Fig. 4 is a comparison diagram before and after the infection of Aspergillus niger for four weeks;

Figure 5 is a comparison diagram before and after four weeks of Cocoa globosa infection.

Detailed ways

Embodiment 1: The present embodiment is a preparation method of dimensionally stable and mildew-proof compressed rubber wood, which is carried out according to the following steps:

1. Preparation of water-soluble acylated lignin solution:

The water-soluble acylated lignin is added to the water, and the pH of the solution is adjusted to the pH of rubber wood, and then an initiator and a catalyst are added to obtain a water-soluble acylated lignin solution;

The mass percentage of the water-soluble acylated lignin in the water-soluble acylated lignin solution is 5% to 15%; the mass percentage of the initiator in the water-soluble acylated lignin solution is 0.5% to 2%; The mass percentage of the catalyst in the water-soluble acylated lignin solution is 0% to 5%;

2. Water-soluble acylated lignin solution impregnating rubber wood:

Immerse the rubber wood in the water-soluble acylated lignin solution, and then under the conditions of vacuum degree of -0.05MPa～-0.1MPa and pressure of 0.60MPa～1.0MPa, immersion until the water-soluble acylated lignin solution completely penetrates the rubber The wood is then placed in the atmospheric environment to dry naturally until the moisture content is 30% to 50% to obtain the impregnated rubber wood;

3. Hot pressing and densification treatment of impregnated rubber wood:

①. Put the impregnated rubber wood between the two heating plates of the hot press, close the heating plate without applying pressure, and under the condition that the temperature of the double heating plate is 60 ℃ ~ 80 ℃, the impregnated rubber The wood is preheated for 10min-30min, and then the temperature of the double heating plate is raised to 100℃～200℃ within 30min;

②. Under the condition that the temperature of the double heating plate is 100℃～200℃ and the applied pressure is 50kg·cm ^-2 ～300kg·cm ^-2 , compress the impregnated rubber wood vertically and hold the pressure for 20min～40min. The compressibility in the thickness direction of the impregnated rubber wood is 15% to 25%, and then the temperature of the double heating plate is 100 ℃ to 200 ℃ and the applied pressure is 50kg·cm ^-2 to 300kg·cm ^-2 , Continue to carry out The vertical wood texture is compressed and kept under pressure for 20 to 40 minutes, so that the compression rate of the impregnated rubber wood in the thickness direction is 35% to 45%, and the rubber wood after secondary compression is obtained;

③. Under the condition that the temperature of the double heating plate is 100℃～200℃ and the applied pressure is 50kg·cm ^-2 ～300kg·cm ^-2 , the rubber wood after secondary compression is compressed vertically to the maximum extent in the thickness direction. Compress and densify, and keep the pressure for 20-40 minutes to obtain rubber wood after three compressions;

4. Turn off the heating, cool down the temperature of the double heating plate to below 50°C under the condition of maintaining pressure, and take out the rubber wood that has been impregnated with acylated lignin and treated with hot pressing and densification;

4. Drying and curing:

1. Put the rubber wood treated with acylated lignin impregnation combined with hot pressing and densification in the atmospheric environment for 5d-10d to obtain the rubber wood after natural drying;

②. Put the naturally dried rubber wood in a vacuum blast drying oven, and then raise the temperature of the vacuum blast drying oven from room temperature to 40℃ to 120℃～140℃ at a rate of 20℃～40℃ every 4h～6h. ℃, and at a temperature of 120 ℃ to 140 ℃, the temperature is kept for 24h to 48h, that is, the preparation of dimensionally stable and mildew-proof compressed rubber wood is completed.

The water-soluble acylated lignin described in step 1 of this embodiment is water-soluble and has cross-linkable double bonds, and the pH of the solution is 4-5, which is close to the pH range of the rubber wood to be treated.

In the second step of the present embodiment, it is placed in the atmospheric environment for natural drying and continuously monitored during the process until the moisture content is 30% to 50%.

In the third step of the present embodiment, the compression ratio is controlled by stainless steel bars of different thicknesses.

In the second step of this embodiment, the moisture content of the impregnated rubber wood needs to be strictly controlled, and if the moisture content is too low or too high, the gain effect brought by the third step will be reduced.

In the hot pressing process of step 3 of this embodiment, the water-soluble acylated lignin will be pre-cured, and the first step will play the role of bonding the adjacent cell walls of rubber wood.

In step 4 of this implementation, cross-linking and curing is carried out under the conditions of 120 ℃ ~ 140 ℃ for 24h ~ 48h, so that the acylated lignin pre-cured in the rubber wood in step 3 is fully cross-linked and cured, and further improves its adhesion to adjacent rubber wood. effect of the cell wall.

Lignin is a natural aromatic polymer with a three-dimensional network structure composed of p-coumarol, coniferyl alcohol and sinapyl alcohol, which is polymerized by lignification. Lignin has a wide range of sources, is renewable, has a large number of reactive groups, and is easy to be chemically modified. In the wood and wood products industry, lignin is often used as an adhesive. Lignin has a large molecular weight. Treating wood with functionalized modified lignin can fill the wood cell cavity, which in turn endows wood with good physical and mechanical properties. There is no report on the method of improving the dimensional stability of compressed wood by impregnating the functionalized lignin and giving it functionalization.

The beneficial effects of this embodiment are:

Using dealkalized lignin as raw material, acylating lignin with maleic anhydride to obtain water-soluble acylated lignin with active double bonds and hydrophilic carboxyl groups, the active double bonds endow the acylated lignin with cross-linking The curing characteristics, the carboxyl group endows the acylated lignin with good water solubility, making the acylated lignin more easily impregnated into the interior of the wood. The acylated lignin is impregnated and filled into the cell cavity of rubber wood, and then combined with hot pressing and densification treatment to make the acylated lignin fully contact with the inner wall of the rubber wood cell cavity, and the synergistic effect of high temperature and initiator and (or) catalyst Under cross-linking and curing, a cross-linked network structure that is insoluble in water is formed, which is fixed on the inner wall of the rubber wood cell cavity or solidified into a block and filled in the cell cavity to obtain high-performance acylated lignin modified compressed rubber wood. Due to the insoluble acylated lignin cross-linked network structure filled in the compressed rubber wood, the density of the modified rubber wood can reach up to 1.28g·cm ^-3 , and the maximum compression ratio (CR) can reach 48 %, the 24h water absorption rate (WU) of compressed rubber wood can be as low as 19.73%, the 24h water absorption thickness expansion rate (TS) is reduced from 100% to 25.59%, and the moisture absorption thickness expansion rate (TS') under the humidity condition of 93%RH It can be as low as 20.93%, and the impact strength can be increased by up to 11% compared with that before modification, and there is no problem of brittleness of compressed wood caused by high temperature hot pressing; not only that, lignin is rich in benzene ring structure and phenol structural unit , which endows the lignin with excellent antibacterial properties, and the acylation modification does not change the main structure of the lignin, so the compressed rubber wood modified by the above method is filled with acylated lignin in the internal cell cavity and densified by hot pressing The technical means of the technology occupy and squeeze the living space of the fungus, cut off the food chain of the fungus, and achieve the purpose of inhibiting the growth of the mold, thereby effectively curbing the mildew and blueness of the rubber wood.

To sum up, the acylated lignin-modified compressed rubber wood prepared in this embodiment has high density, good dimensional stability and mildew resistance, and also has improved impact strength. In order to achieve high-value utilization of low-quality rubber wood. conditions are provided.

Embodiment 2: The difference between this embodiment and Embodiment 1 is that the water-soluble acylated lignin described in Step 1 is prepared according to the following steps:

①. Dissolve the dealkalized lignin in dimethyl sulfoxide, and heat it up to 80 °C, add maleic anhydride and anhydrous pyridine at a temperature of 80 °C, and then heat up to 100 °C, at a temperature of Under the condition of 100 °C, the reaction was carried out for 1 h to obtain a mixed system;

The quality of the dealkalized lignin and the volume ratio of dimethyl sulfoxide are 1g: 5mL; the mass ratio of the dealkalized lignin and maleic anhydride is 1:1.47; the dealkalized lignin The volume ratio of the mass and anhydrous pyridine is 1g: 2.41mL;

2. Disperse the mixed system in a poor solvent, precipitate and centrifuge to remove the supernatant to obtain the bottom product;

3. Dissolving the bottom product in dimethyl sulfoxide to obtain a bottom product solution, repeating the bottom product solution according to step ② for 3 to 7 times, and finally vacuum drying to obtain a water-soluble acylated lignin. Others are the same as the first embodiment.

Embodiment 3: The difference between this embodiment and Embodiment 1 or 2 is that the poor solvent described in step ② is ethyl acetate or ethanol. Others are the same as in the first or second embodiment.

Embodiment 4: The difference between this embodiment and one of Embodiments 1 to 3 is that the volume ratio of the mixed system described in step ② to the poor solvent is 1:(7-10). Others are the same as the specific embodiments one to three.

Embodiment 5: The difference between this embodiment and one of Embodiments 1 to 4 is that the volume ratio of the bottom product described in step ③ to dimethyl sulfoxide is 1:(5～7). Others are the same as those in Embodiments 1 to 4.

Embodiment 6: The difference between this embodiment and one of Embodiments 1 to 5 is that in step 1, the pH of the solution is adjusted to 4 to 5 by using lye with a concentration of 2 mol/L to 4 mol/L. Others are the same as the specific embodiments 1 to 5.

Embodiment 7: The difference between this embodiment and one of Embodiments 1 to 6 is that the lye solution is sodium hydroxide or potassium hydroxide. Others are the same as the specific embodiments 1 to 6.

Embodiment 8: This embodiment is different from one of Embodiments 1 to 7 in that: the initiator described in step 1 is ammonium persulfate or potassium persulfate; the catalyst described in step 1 is sodium hypophosphite. Others are the same as those in Embodiments 1 to 7.

Embodiment 9: The difference between this embodiment and one of Embodiments 1 to 8 is that in step 2, under the conditions of vacuum degree of -0.05MPa to -0.1MPa and pressure of 0.60MPa to 1.0MPa, immersion is carried out for 6h to 18h. . Others are the same as the specific embodiments 1 to 8.

Embodiment 10: The difference between this embodiment and one of Embodiments 1 to 9 is that the cooling of the dual heating plates in step 3 (4) is natural cooling or cooling by flowing water. Others are the same as the specific embodiments 1 to 9.

Adopt the following examples to verify the beneficial effects of the present invention:

Example 1:

A preparation method of dimensionally stable and mildew-proof compressed rubber wood, which is carried out according to the following steps:

1. Preparation of water-soluble acylated lignin solution:

The water-soluble acylated lignin is added to the water, and the pH of the solution is adjusted to the pH of rubber wood, and then an initiator is added to obtain a water-soluble acylated lignin solution;

The mass percentage of the water-soluble acylated lignin in the water-soluble acylated lignin solution is 15%; the mass percentage of the initiator in the water-soluble acylated lignin solution is 1%;

2. Water-soluble acylated lignin solution impregnating rubber wood:

Immerse the rubber wood in the water-soluble acylated lignin solution, then under the condition of vacuum degree of -0.09MPa and pressure of 0.60MPa, immerse until the water-soluble acylated lignin solution completely soaks the rubber wood, and then place it in the atmospheric environment Dry naturally in the middle until the moisture content is 40% to obtain the impregnated rubber wood;

3. Hot pressing and densification treatment of impregnated rubber wood:

①. Put the impregnated rubber wood between the two heating plates of the hot press, close the heating plate without applying pressure, and preheat the impregnated rubber wood under the condition that the temperature of the double heating plate is 80 °C 30min, then the temperature of the double heating plate was raised to 103°C within 30min;

②. Under the condition that the temperature of the double heating plate is 103°C and the applied pressure is 100kg·cm ^-2 , the vertical wood texture compression of the impregnated rubber wood is carried out and the pressure is maintained for 30 minutes, so that the compression rate of the impregnated rubber wood in the thickness direction is 20%, and then under the condition that the temperature of the double heating plate is 103 ℃ and the applied pressure is 200kg·cm ^-2 , the vertical wood texture compression is continued and the pressure is maintained for 30 minutes, so that the compression rate of the impregnated rubber wood in the thickness direction is 40%, Obtain the rubber wood after secondary compression;

③. Under the condition of double heating plate temperature of 103℃ and applied pressure of 300kg·cm ^-2 , the rubber wood after secondary compression was compressed vertically to the maximum extent in the thickness direction, and the pressure was maintained for 30min. Get rubber wood after three compressions;

4. Turn off the heating, cool down the temperature of the double heating plate to below 50°C under the condition of maintaining pressure, and take out the rubber wood that has been impregnated with acylated lignin and treated with hot pressing and densification;

4. Drying and curing:

1. Put the rubber wood impregnated with acylated lignin combined with hot pressing and densification in the atmospheric environment to balance for 5 days to obtain the rubber wood after natural drying;

2. Place the naturally dried rubber wood in a vacuum blast drying oven, and then increase the temperature of the vacuum blast drying oven from 40°C to 120°C at a rate of 40°C per 6h, and under the condition that the temperature is 120°C 24h, to obtain acylated lignin-modified compressed rubber wood.

The water-soluble acylated lignin described in step 1 is prepared according to the following steps:

①. Dissolve 50g of dry dealkalized lignin in 250mL of dimethyl sulfoxide, and heat it up to 80°C. Under the condition that the temperature is 80°C, add 73.5g of maleic anhydride and 120.68mL of anhydrous pyridine, then The temperature was raised to 100 °C, and the reaction was carried out for 1 h at a temperature of 100 °C to obtain a mixed system;

2. Disperse the mixed system in 500 mL of poor solvent, precipitate and centrifuge to remove the supernatant to obtain the bottom product;

Described poor solvent is ethyl acetate; The volume ratio of described mixed system and poor solvent is 1:7;

3. Dissolving the bottom product in dimethyl sulfoxide to obtain a bottom product solution, repeating the bottom product solution 3 times according to step 2, and finally vacuum drying to obtain water-soluble acylated lignin;

The volume ratio of the bottom product to dimethyl sulfoxide is 1:5.

In step 1, the pH of the solution is adjusted to 5 by using a sodium hydroxide solution with a concentration of 2 mol/L.

The initiator described in step 1 is ammonium persulfate.

In step 2, under the conditions of vacuum degree of -0.09MPa and pressure of 0.60MPa, immersion is carried out for 18h.

In step 3 (4), the cooling double heating plate is natural cooling.

The size of the rubber wood described in the second step is 50×50×5mm ³ (length×width×thickness).

The dimethyl sulfoxide, maleic anhydride, ethyl acetate, sodium hydroxide, and ammonium persulfate are all analytically pure, and have not undergone any purification treatment after purchase.

In step 3, the compression rate is controlled by stainless steel bars of different thicknesses. In step 3 ②, the compression rate of the impregnated rubber wood is controlled by 4 mm thick stainless steel bars to 20%. The stainless steel strip with a thickness of 3 mm controls the compression rate of the rubber wood after dipping to 40%; the 3 mm stainless steel strip used in ② is taken out in step 3 ③.

The hot-pressing machine described in step 3 is a small hot-pressing machine of XW-212C purchased from Dongguan Xunwei Testing Instrument Co., Ltd.

Embodiment 2: The difference between this embodiment and Embodiment 1 is that in step 3 ①, the temperature of the double heating plate is raised to 120° C. within 30 minutes. Others are the same as the first embodiment.

Embodiment 3: The difference between this embodiment and Embodiment 1 is that: in step 3 ①, the temperature of the double heating plate is raised to 140° C. within 30 minutes. Others are the same as the first embodiment.

Embodiment 4: The difference between this embodiment and Embodiment 1 is that in step 3 ①, the temperature of the double heating plate is raised to 160° C. within 30 minutes. Others are the same as the first embodiment.

Embodiment 5: The difference between this embodiment and Embodiment 1 is that in step 3 ①, the temperature of the double heating plate is raised to 180° C. within 30 minutes. Others are the same as the first embodiment.

Embodiment 6: The difference between this embodiment and Embodiment 5 is that an initiator and a catalyst are added in step 1; the catalyst described in step 1 is sodium hypophosphite; the water-soluble acylated lignin solution described in step 1 is added The mass percentage of the catalyst is 5%. Others are the same as the fifth embodiment.

Embodiment 7: The difference between this embodiment and Embodiment 5 is that the mass percentage of water-soluble acylated lignin in the water-soluble acylated lignin solution described in step 1 is 5%. Others are the same as the fifth embodiment.

Embodiment 8: The difference between this embodiment and Embodiment 5 is that the mass percentage of water-soluble acylated lignin in the water-soluble acylated lignin solution described in step 1 is 10%. Others are the same as the fifth embodiment.

Comparative Example 1: The rubber wood with a size of 50mm×50mm×5mm was dried in a blast drying oven at 105°C for 6 hours to obtain an untreated absolutely dry rubber wood.

Comparative Example 2: The difference between this comparative example and Example 1 is that the hot-pressing densification treatment in step 3 is cancelled. Others are the same as the first embodiment.

Comparative Example 3: The difference between this comparative example and Example 1 is that step 1 is canceled, and in step 2, rubber wood is immersed in water. Others are the same as the first embodiment.

Comparative Example 4: The difference between this Comparative Example and Comparative Example 3 is that: in step 3 ①, the temperature of the double heating plate was raised to 120° C. within 30 minutes. Others are the same as the control example 3.

Comparative example 5: The difference between this comparative example and the comparative example 3 is: in step 3 ①, the temperature of the double heating plate is raised to 140° C. within 30 minutes. Others are the same as the control example 3.

Comparative example 6: The difference between this comparative example and the comparative example 3 is: in step 3 ①, the temperature of the double heating plate is raised to 160° C. within 30 minutes. Others are the same as the control example 3.

Comparative example 7: The difference between this comparative example and the comparative example 3 is: in step 3 ①, the temperature of the double heating plate is raised to 180° C. within 30 minutes. Others are the same as the control example 3.

Measure the density of the compressed rubber wood prepared in Comparative Examples 1 to 7 and Embodiments 1 to 8, and utilize the formula:

Among them, m is the mass of the test piece, L is the length of the test piece (mm), T is the width of the test piece (mm), and R is the thickness of the test piece (mm). There are 10 samples in each group, 5 replicate points for each sample R, 3 replicate points for L and T each, and the results are averaged. The results of the density of each group are the average of the replicates. Show.

Table 1: Density of untreated and modified materials (g·cm ^-3 )

Density (g·cm^-3) Comparative Example 1 0.62±0.06 Comparative Example 2 0.73±0.01 Comparative example three 1.03±0.08 Comparative Example Four 0.89±0.05 Control Example 5 0.92±0.04 Comparative Example 6 1.00±0.03 Comparative Example Seven 1.09±0.01 Example 1 1.05±0.08 Embodiment 2 1.15±0.04 Embodiment 3 1.16±0.04 Embodiment 4 1.23±0.02 Embodiment 5 1.28±0.01 Embodiment 6 1.26±0.03 Embodiment 7 1.16±0.02 Embodiment 8 1.22±0.01

It can be seen from the table that compared with the control example, the density of rubber wood treated by acylated lignin impregnation combined with hot pressing densification is significantly improved, all can reach more than 1.05g·cm ^-3 , and the highest can reach 1.28g·cm ^-3 . The change of density is related to the hot-pressing temperature and the concentration of acylated lignin solution. The higher the content, the higher the density of the prepared acylated lignin-modified compressed rubberwood. Density is an important factor affecting the performance of wood, and the increase in density will also bring about a significant improvement in various properties of wood, which is of great significance for the high-value utilization of rubber wood.

Carry out the measurement of 24h water absorption rate and water absorption thickness expansion rate to the compressed rubber wood prepared by Comparative Examples 3 to 7 and Embodiments 1 to 8, and the test method is as follows:

1) Saw the compressed rubber wood prepared in Comparative Examples 3 to 7 and Examples 1 to 8 into 20×20×H (length×width×thickness) mm ³ samples, and dry them in a blast drying oven at 103°C for 6h , use the analytical balance to weigh the mass and record it as m ₀ ; use the rapid thickness measuring instrument to measure the thickness and record it as h ₀ (each sample measures 5 points, and the results are averaged);

2) Put the weighed sample into a container filled with distilled water, press the sample to at least 50mm below the water surface with a pad, and keep the water temperature within the range of (20±2℃).

3) 24h after the sample is put into the water, the mass is weighed and recorded as m, and the thickness measurement is recorded as h.

Among them, the 24h water absorption is calculated by the following formula:

In the formula, m is the mass of the sample after 24h of water absorption, and m _o is the absolute dry mass of the sample.

Among them, the 24h water absorption thickness expansion ratio is calculated by the following formula:

In the formula, h is the thickness of the sample after 24h of water absorption, and h ₀ is the thickness of the sample in the dry state.

The average value of the duplicates in each group of the above two data is taken as the final result, and the results are shown in Table 2:

Table 2: 24h water absorption rate (%) and water absorption thickness swelling rate (%) of untreated wood and treated wood

WU TS Comparative example three 111.55±10.56 107.85±3.25 Comparative Example Four 118.76±5.13 95.03±4.44 Control Example 5 107.442±1.37 111.93±5.56 Comparative Example 6 106.31±2.01 120.18±1.21 Comparative Example Seven 97.21±7.825 132.98±12.08 Example 1 38.52±0.82 27.61±0.41 Embodiment 2 36.88±0.63 31.91±3.54 Embodiment 3 39.53±0.08 39.34±0.29 Embodiment 4 31.27±0.35 35.07±0.55 Embodiment 5 24.97±0.26 27.58±1.48 Embodiment 6 19.73±0.81 25.59±0.42 Embodiment 7 27.30±0.48 30.25±0.54 Embodiment 8 22.40±0.31 26.80±0.21

It can be seen from the table that the water absorption rate and water absorption thickness expansion rate of the compressed rubber wood prepared by the method provided in the examples are greatly reduced compared with the control group, and the two parameters of acylated lignin solution concentration and hot pressing temperature will affect the impregnation of acylated lignin. The amount of wood inside and the level of densification, and with the increase of the concentration of acylated lignin solution and the increase of hot-pressing temperature, the water absorption rate and the water absorption thickness expansion rate also gradually decrease. Among them, the water absorption rate can be as low as 19.73%, the water absorption thickness expansion rate is as low as 25.59%, such a low rebound rate is attributed to the curing and filling of the acylated lignin inside the rubber wood and the composite modification of compression and densification, resulting in less wood pores and hindering moisture. It is the channel that enters the wood, so it shows good water stability on the macro level, which can ensure that the performance of compressed rubber wood will not be lost due to water absorption and expansion.

The measurement of the moisture absorption thickness expansion ratio under the condition of 93% RH is carried out to the comparative examples three to seven and the embodiments one to eight, and the test method is as follows:

1) Saw the compressed rubber wood prepared in Comparative Examples 3 to 7 and Examples 1 to 8 into 20×20×H (length×width×thickness) mm ³ samples, and dry them in a blast drying oven at 103°C for 6h , use a quick thickness measuring instrument to measure the thickness and record it as h ₀ ' (5 points are measured for each sample, and the result is averaged);

2) Put the sample after thickness measurement into a constant humidity airtight container filled with saturated potassium nitrate solution (not immersed in the solution), and keep the room temperature within the range of (20±2℃).

3) After the sample is placed in the constant humidity container for 168 hours, the thickness is measured and recorded as h'.

The 93%RH moisture absorption thickness expansion ratio is calculated by the following formula:

In the formula, h' is the thickness of the sample after moisture absorption reaches equilibrium, and h ₀ ' is the thickness of the sample in the dry state.

The average value of the duplicates in each group of the above two data is taken as the final result, and the results are shown in Table 3:

Table 3: The moisture absorption thickness expansion ratio (%) of the sample under the condition of 93%RH

TS’ Comparative example three 47.57±1.16 Comparative Example Four 48.64±0.52 Control Example 5 50.77±2.75 Comparative Example 6 51.39±3.61 Comparative Example Seven 47.68±4.13 Example 1 25.41±1.71 Embodiment 2 26.13±3.06 Embodiment 3 35.34±3.64 Embodiment 4 29.33±1.19 Embodiment 5 20.93±2.02 Embodiment 6 21.97±0.54 Embodiment 7 28.77±1.10 Embodiment 8 25.21±2.02

It can be seen from the table that under the condition of being exposed to high humidity environment for up to 168 hours, the dimensional stability of the compressed rubber wood is greatly improved by the method provided in the embodiment, and the moisture absorption thickness expansion ratio of the compressed rubber wood is affected by the impregnation of the acylated lignin into the wood. The amount of the interior and the effect of hot-pressing temperature, with the large amount of acylated lignin filling and the improvement of the degree of compression and densification, and the degradation of the easily hygroscopic components of wood at high temperature, the hygroscopic thickness expansion rate can be as low as 20.93%. The dimensional stability of compressed rubberwood under high humidity conditions is also attributed to the filling of acylated lignin in the wood, resulting in fewer wood pores, and it is difficult for water vapor to enter the wood interior, and the combination of thermal compaction treatment leads to unimpregnated parts. The pores of the cells are compacted. Not only that, the high temperature will degrade the moisture-absorbing components in the wood, making it difficult for the compressed rubberwood to rebound due to moisture absorption, and losing the performance improvement brought by compression, which makes the application range of compressed rubberwood. further expand.

According to the test method for physical and chemical properties of wood-based panels and veneer wood-based panels (GBT 17657-2013), the impact strength of Comparative Examples 1, 2, 4 to 6 and Examples 2 to 4 was tested by an impact testing machine. The impact strength (Impactstrength) can be Directly reflects the impact resistance of a material, that is, the degree of brittleness and toughness. The average value of 8 replicates in each group is taken as the final result. The environmental conditions such as temperature and humidity are the same. The results are shown in Table 4:

Table 4

Impact strength(MPa) Comparative Example 1 8.65±0.95 Comparative Example 2 8.7242±0.83 Comparative Example Four 7.86±1.65 Control Example 5 6.19±1.06 Comparative Example 6 6.17±1.31 Embodiment 2 9.61±1.60 Embodiment 3 9.55±2.41 Embodiment 4 8.47±2.38

The impact strength of untreated rubber wood, that is, Comparative Example 1, is about 8.65 MPa, and the ordinary compressed wood prepared by compression after water immersion, that is, Comparative Examples 4 to 6, shows a regular decrease compared to Comparative Example 1: that is, with the increase of hot pressing temperature. Gradually increased, the impact strength gradually decreased, mainly because the higher the temperature, the more serious the degradation of wood components, the mechanical properties also decreased; and the control example 2, which only impregnated acylated lignin without compression, was compared with The mechanical properties of Comparative Example 1 were almost unchanged, indicating that the acylated lignin had little effect on the impact properties of rubber wood. Compared with the above-mentioned control examples, Examples 2 and 3 of impregnated acylated lignin combined with compression and densification are improved, up to 9.61MPa, and the impact strength of untreated rubber wood can be increased by about 11% at most. Compared with Examples 2 and 3, Example 4 has a decrease, which is attributed to the partial degradation of wood components caused by hot pressing at 160°C, but it also maintains the same level as Comparative Examples 1 and 2. The above results prove that the amorphous network structure of lignin curing and filling has a positive effect on the enhancement of the impact strength of compressed rubber wood, effectively improving the impact of high temperature on the mechanical properties of compressed wood, and compared with resin, the compression of impregnated acylated lignin Rubber wood does not become brittle due to high temperature hot pressing, which also reflects one of the advantages of this method.

Fig. 1 is a physical map, a is the acylated lignin modified compressed rubber wood prepared in Example 5, and b is the untreated dry rubber wood prepared in Comparative Example 1; Compressed rubber wood is dark brown in appearance. Compared with untreated wood, it is thick and simple in appearance, and its color is closer to the color of precious woods such as mahogany and red sandalwood. It has wide application prospects in surface decoration, flooring and other fields.

Figure 2 is the microscopic topography of the untreated dry rubber wood prepared in Comparative Example 1; it can be seen from the figure that rubber wood, as a typical representative of fast-growing broad-leaved wood, has a unique macroporous structure, which is very suitable for filling and modifying macromolecules. properties, improve the properties of rubber wood, and expand the application range of rubber wood.

Figure 3 is a microscopic topography of the acylated lignin-modified compressed rubber wood prepared in Example 4; it can be seen from the figure that the rubber wood impregnated with acylated lignin and compressed and densified forms a dense structure. The structure determines the properties. The macropores are cured and filled by acylated lignin, and the unimpregnated part is compressed and compacted, which not only greatly increases the density of rubber wood and improves its physical properties, but also forms insoluble due to the curing of acylated lignin. The cross-linked network structure of water makes the acylated lignin-modified compressed rubberwood have the characteristics of water resistance and humidity resistance and dimensional stability. Not only that, the phenolic and benzene ring structure of lignin endows the compressed rubberwood with anti-mildew properties.

According to GB/T18261-2013 "Test method for the control effect of antifungal agent on wood mold and discoloration fungus", the test for the infection of the compressed rubber Trichoderma and cyanobacteria prepared in Comparative Examples 1 to 7 and Examples 1 to 5, wherein, the test Aspergillus niger and Lasiodiplodiatheobromae purchased from China Forestry Microbial Culture Collection and Management Center were used as representatives of mold and cyanobacteria, respectively. After four weeks of inoculation of the test bacteria, the comparison chart of the anti-mold results was observed.

Fig. 4 is a comparison diagram before and after the infection of Aspergillus niger for four weeks; Fig. 5 is a comparison diagram before and after the infection of Cocoa globulus for four weeks; It can be clearly seen from the comparison diagram that the infestation of Aspergillus niger and Cocoa bisporus in four weeks of Comparative Examples 1 to 6 is respectively In the infection experiment, they were all infected to a large extent, and the infection level reached the highest; for Cocoa coccus bisporus, Examples 1 to 5 all showed good resistance to infection, and after four weeks of infection experiments, the The infection level of the specimen is almost 0, because the necessary conditions for the survival of the fungus are suitable temperature, humidity, nutrients and a certain living space. The cyanobacteria mainly use sugars and starches in the wood as nutrients. Examples 1 to 5 Due to the combined treatment of acylated lignin dipping and hot-pressing densification, cyanobacteria cannot enter the wood parenchyma cells where starch and other substances are mainly distributed, so that nutrients cannot be obtained, and the compound modification treatment compresses the fungal cells. growth space, thus showing good resistance to Cocoa globosa; for Aspergillus niger, Comparative Examples 1 to 6, Examples 1 and 2 are still infested by Aspergillus niger, while Examples 3 to 5 show better Anti-Aspergillus niger infestation properties. This is mainly because Aspergillus niger mainly grows on the surface of wood, and the impregnation and compaction of acylated lignin will make the wood difficult to absorb moisture, which to a certain extent oppresses the optimal growth conditions and living space of Aspergillus niger; The three to five surfaces are filled with acylated lignin, and the compression density is higher, with a denser structure, and it is difficult for moisture and mold to enter the interior of the wood from the surface, resulting in better anti-infestation properties. Mildew resistance is particularly important for rubber wood that is prone to mildew and blue staining, and lignin is rich in benzene ring structure and phenol structural units, which endow lignin with excellent antibacterial properties, and acylation modification will not Its main structure is changed. Therefore, the compressed rubber wood prepared by the cell cavity filling of acylated lignin combined with thermal compaction has a compact structure and exhibits excellent anti-mildew properties, which broadens the application of rubber wood. scope.

Claims (10)

1. The preparation method of the compression rubber wood with stable size and mildew resistance is characterized by comprising the following steps:

firstly, preparing a water-soluble acylated lignin solution:

adding water-soluble acylated lignin into water, adjusting the pH of the solution to the pH of the rubber wood, and then adding an initiator and a catalyst to obtain a water-soluble acylated lignin solution;

the mass percentage of the water-soluble acylated lignin in the water-soluble acylated lignin solution is 5-15%; the mass percent of the initiator in the water-soluble acylated lignin solution is 0.5-2%; the mass percent of the catalyst in the water-soluble acylated lignin solution is 0-5%;

secondly, impregnating the rubber wood with a water-soluble acylated lignin solution:

soaking rubber wood in a water-soluble acylated lignin solution, then soaking the rubber wood under the conditions that the vacuum degree is-0.05 MPa to-0.1 MPa and the pressure is 0.60MPa to 1.0MPa until the water-soluble acylated lignin solution completely soaks the rubber wood, and then placing the rubber wood in an atmospheric environment for natural drying until the water content is 30 percent to 50 percent to obtain the soaked rubber wood;

thirdly, hot-pressing densification treatment of impregnated rubber wood:

placing the impregnated rubber wood between two heating plates of a hot press, closing the heating plates under the condition of no pressure, preheating the impregnated rubber wood for 10-30 min under the condition that the temperature of the double heating plates is 60-80 ℃, and then increasing the temperature of the double heating plates to 100-200 ℃ within 30 min;

② the temperature of the double heating plates is 100-200 ℃ and the applied pressure is 50kg cm^-2～300kg·cm^-2Under the conditions of (1), performing vertical wood grain compression on the impregnated rubber wood and maintaining the pressure for 20-40 min to ensure that the compression ratio of the impregnated rubber wood in the thickness direction is 15-25%, and then performing double-heating plate temperature of 100-200 ℃ and applied pressure of 50 kg-cm^-2～300kg·cm^-2Under the condition of (3), continuously performing vertical wood texture compression and maintaining the pressure for 20-40 min to ensure that the compression ratio of the impregnated rubber wood in the thickness direction is 35-45 percent to obtain secondarily compressed rubber wood;

③ at the temperature of 100-200 ℃ and the applied pressure of 50 kg-cm of double heating plates^-2～300kg·cm^-2Under the condition of (1), performing vertical wood grain compression on the rubber wood after the secondary compression to the maximum degree in the thickness direction, and maintaining the pressure for 20-40 min to obtain the rubber wood after the tertiary compression;

closing heating, cooling the double heating plates to below 50 ℃ under the pressure maintaining condition, and taking out to obtain the rubber wood subjected to the acylation lignin impregnation combined hot pressing densification treatment;

fourthly, drying and curing:

firstly, placing the rubber wood subjected to the combination of the acylation lignin impregnation and the hot pressing densification treatment in an atmospheric environment for 5-10 days to balance to obtain the naturally dried rubber wood;

secondly, placing the naturally dried rubber wood in a vacuum air-blast drying oven, heating the vacuum air-blast drying oven from room temperature to 40 ℃ to 120-140 ℃ at the speed of heating 20-40 ℃ every 4-6 h, and preserving heat for 24-48 h at the temperature of 120-140 ℃ to finish the preparation of the compression rubber wood with stable size and mildew resistance.

2. The method of claim 1, wherein the water-soluble acylated lignin is prepared by the steps of:

dissolving dealkalized lignin in dimethyl sulfoxide, heating to 80 ℃, adding maleic anhydride and anhydrous pyridine under the condition of 80 ℃, heating to 100 ℃, and reacting for 1h under the condition of 100 ℃ to obtain a mixed system;

the volume ratio of the mass of the dealkalized lignin to the dimethyl sulfoxide is 1g:5 mL; the mass ratio of the dealkalized lignin to the maleic anhydride is 1: 1.47; the volume ratio of the mass of the dealkalized lignin to the anhydrous pyridine is 1g:2.41 mL;

dispersing the mixed system in a poor solvent, precipitating and centrifuging to remove supernatant to obtain a bottom product;

dissolving the bottom product in dimethyl sulfoxide to obtain a bottom product solution, repeating the bottom product solution for 3-7 times according to the step II, and finally performing vacuum drying to obtain the water-soluble acylated lignin.

3. The method for preparing a dimensionally stable, moldproof compressed rubber wood according to claim 2, wherein said poor solvent in the step (ii) is ethyl acetate or ethanol.

4. The preparation method of the compressed rubber wood with stable dimension and mildew resistance as claimed in claim 2, wherein the volume ratio of the mixed system and the poor solvent in the step (II) is 1 (7-10).

5. The method for preparing the compressed rubber wood with stable dimension and mildew resistance according to the claim 2, characterized in that the volume ratio of the bottom product and the dimethyl sulfoxide in the step (c) is 1 (5-7).

6. The method for preparing a dimensionally stable, moldproof compressed rubber wood according to claim 1, wherein in the first step, the pH of the solution is adjusted to 4 to 5 by using 2 to 4mol/L alkali solution.

7. The method of claim 6, wherein the alkali solution is sodium hydroxide or potassium hydroxide.

8. The method for preparing a dimensionally stable, moldproof compressed rubber wood according to claim 1, wherein the initiator in the first step is ammonium persulfate or potassium persulfate; the catalyst in the first step is sodium hypophosphite.

9. The method for preparing a dimensionally stable, moldproof compressed rubber wood according to claim 1, wherein in the second step, the wood is dipped for 6 to 18 hours under a vacuum degree of-0.05 to-0.1 MPa and a pressure of 0.60 to 1.0 MPa.

10. The method for preparing a dimensionally stable, moldproof compressed rubber-wood according to claim 1, wherein the cooling double heating plate in the third and fourth steps is natural cooling or continuous flowing water cooling.

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