JPH0337487B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for modifying a wood material, which comprises chemically modifying hydroxyl groups in a wood component and then subjecting the wood material to a graft polymerization treatment.

Wood materials have poor thermoplasticity and cannot be easily deformed or densified by applying heat or heat and pressure at the same time, and their moldability is significantly inferior to that of general thermoplastic resins. Furthermore, wood materials have the disadvantage that they become carbonized when molded under severe heating conditions, and their tissue structure is damaged under severe pressurized conditions.

On the other hand, it is possible to improve physical properties such as dimensional stability of wood by acetylating or graft copolymerizing cellulose, which is the main component of wood.
It has been known for a long time.

Additionally, the present inventors have discovered that it is possible to impart thermoplasticity to wood by treating it with an esterifying agent or an etherifying agent, but it is not possible to impart remarkable thermoplasticity with complete thermal melting. It is not easy to do this except when using a higher fatty acid as an esterifying agent, when acetylating with a trifluoroacetic acid-acetic acid system and then aging saponification, or when acetylating using a sulfuric acid catalyst method and then aging saponifying. .

Furthermore, it has been found that higher fatty acids and trifluoroacetic acid are expensive and have practical problems, and in the case of a sulfuric acid catalyst method, it is difficult to wash away the sulfuric acid after the reaction treatment.

As a result of further intensive studies, the present inventors found that after treating wood with a reactant that can react with the hydroxyl group in the wood components, such as an esterifying agent or an etherifying agent,
By subjecting this treated wood to a graft copolymerization treatment, the reactant used is an esterifying agent consisting of a highly practical lower fatty acid anhydride such as acetic anhydride.
Alternatively, it is possible to easily impart excellent thermoplastic properties to wood materials even when using reactants such as etherification agents, which have conventionally been difficult to impart remarkable thermoplastic properties to the extent that they require complete thermal melting. This discovery led to the completion of the present invention. That is, the present invention provides a wood material which is obtained by treating a wood material with a reactant capable of reacting with a hydroxyl group in the wood component, and then subjecting the treated wood material to a graft copolymerization treatment by reacting with a polymerizable substance. The present invention provides a method for modifying.

The method of the present invention is divided into (a) a step of treating wood material with a reactant (first step), and (b) a step of graft copolymerizing the thus treated wood material (second step), as follows. will be explained in detail.

In the first step, the wood material is brought into contact with a reactant by an appropriate means to chemically modify the hydroxyl groups of wood components, particularly cellulose, and to amorphize the crystal structure of cellulose.

The wood material that can be used in the present invention is powdery, fibrous,
It may be sheet-like, plate-like, column-like, etc.
Thick shapes such as plates and columns are often used primarily for the purpose of modifying their surfaces.

As mentioned above, the term "reactant" refers to a substance that chemically reacts with the hydroxyl groups of wood components, particularly cellulose, and typical examples thereof include esterification agents and etherification agents.

Esterifying agents include organic acid anhydrides (for example, acid anhydrides such as acetic acid, propionic acid, and butyric acid), organic acid halides (for example, in addition to the above acids, acid halides such as caproic acid, lauric acid, stearic acid, and methacrylic acid). (in particular acid chlorides), and mixtures of organic acid anhydrides and fatty acids (for example mixtures of trifluoroacetic anhydride or chloroacetic anhydride with acetic acid, propionic acid, caproic acid or lauric acid, etc.). These esterifying agents can be used alone or in combination of two or more. In particular, in the present invention, anhydrides and halides of lower fatty acids such as acetic acid and propionic acid are practically preferred in view of economical efficiency.

A catalyst for promoting the reaction with the wood component and/or a solvent for promoting the penetration of the esterifying agent into the wood cell membrane can be added to the esterifying agent. Examples of such catalysts include perchloric acid, urea-ammonium sulfate, zinc chloride, sulfuric acid, pyridine, etc., and solvents include acetic acid, benzene, toluene, dimethylformamide, dinitrogen tetroxide-dimethylformamide, etc. It may be used as a species or as a mixture of more than one species.

Instead of or in addition to being added to the esterifying agent, these catalysts and/or solvents may be impregnated in advance into the wood material before being treated with the esterifying agent.

Next, as the etherification agent, for example, 1,2- such as ethylene oxide, propylene oxide, etc.
Activated with epoxides, alkyl halides such as methyl chloride and ethyl chloride, aromatic halides such as benzyl chloride, dialkyl sulfates such as dimethyl sulfate, α-halogen acids such as monochloroacetic acid, and negative groups such as vinyl cyanide. Vinyl compounds, aldehydes such as formaldehyde, etc. can be used.

In the case of an etherification agent, as in the case of an esterification agent, a catalyst (for example, an alkaline catalyst such as sodium hydroxide) and a solvent (for example, a solvent similar to that used in the case of an esterification agent) may be appropriately added. It is also possible to pre-impregnate the wood material with the etherification agent before treating it with the etherification agent, but in the case of a catalyst, the latter method is particularly preferred.

In addition to the above-mentioned esterifying agents and etherifying agents, examples of reactants capable of reacting with hydroxyl groups include isocyanates (eg, methyl isocyanate, ethyl isocyanate, etc.).

The reactant may be brought into contact with the wood material by, for example, immersing the wood material in the reactant, or by vaporizing the reactant and exposing the wood material to this. Also,
Such a method can be carried out under reduced pressure, increased pressure, or a reduced pressure method to promote impregnation of the reactant into the wood material.

Chemical treatment with such reactants esterifies the hydroxyl groups of wood components, especially cellulose.
Through chemical modification such as etherification, the crystalline structure of cellulose becomes amorphous, thus producing wood in a swollen state. At this time, the hydroxyl groups of hemicellulose and lignin, which are the main components of wood along with cellulose, may undergo similar chemical changes, and in this case, the bonds between the wood components become weaker, and the degree of swelling of the wood becomes even more significant. Become.

The treated wood material obtained in the first stage is
It is subjected to a step-by-step graft copolymerization treatment.

Graft copolymerization treatment involves immersing the wood material in a polymerizable substance, exposing it to a vaporized polymerizable substance, or applying a polymerizable substance to the wood material, and then graft copolymerizing it by an appropriate method. Consists of things. Graft polymerization is thought to occur mainly between the residual hydroxyl groups of cellulose in the treated wood material that has been chemically treated in the first step as a backbone polymer and the added polymerizable substance.

As the polymerizable substance, monomers, oligomers and prepolymers of vinyl compounds such as methyl methacrylate, styrene, acrylic acid, acrylonitrile, acrylamide and butadiene can be used.

Graft copolymerization can be carried out according to conventional methods. That is, for example, a method of radical polymerization by impregnating a radical polymerization catalyst such as hydrogen peroxide, benzoyl peroxide, azobisisobutyronitrile, ammonium persulfate, potassium persulfate, etc. together with a polymerizable substance into a wood material, and similarly a method of radical polymerization using a cerium salt. There are methods using a redox catalyst such as, and methods of impregnating a wood material with a polymerizable substance and then irradiating it with radiation such as gamma rays or electron beams. Either method may be used.

As mentioned above, since the wood material obtained in the first stage treatment is amorphous and swollen, in this second stage treatment, not only voids such as ducts and tracheids but also intracellular The polymerizable substance is sufficiently and easily impregnated into the graft copolymer, and thus a highly uniform graft copolymer can be obtained. It should be noted that not all of the polymerizable substance impregnated into the wood material participates in the graft copolymerization, and some of it is thought to become a homopolymer and remain in the voids of the wood material, but this does not need to be particularly removed. Rather, the presence of the homopolymer has the advantage of improving compatibility with the graft copolymerized wood component, and can often improve the physical properties of the final product as a composite.

The modified wood material obtained in this way is
The hydroxyl groups in the components are chemically modified by treatment with reactants such as esterification agents and etherification agents, resulting in advanced internal plasticity, as well as being graft copolymerized with polymerizable substances. It has such remarkable thermoplasticity that it can be easily melted by heat.

In particular, when using lower fatty acid anhydrides such as acetic anhydride and propionic anhydride as reactants, and other highly practical substances, it has traditionally been difficult to impart remarkable thermoplasticity to the extent of complete thermal melting. Also, remarkable thermoplasticity can be imparted by graft copolymerization.

Therefore, the wood material obtained by the method of the present invention can be used, for example, in the following manner by taking advantage of its high thermoplasticity.

When the method of the present invention is applied to granular or fibrous wood materials, it is easier to mold the wood material after modification or by applying heat and pressure to the wood material mixed with other synthetic resins. It can be formed into any shape by extrusion molding, injection molding, or other molding processes. Furthermore, when applied to a sheet-like or plate-like wooden material, it can be extremely easily formed into a curved or bent shape. Furthermore, when the method of the present invention is suitable for the surface of thick plate-like or columnar wood materials, the surface can be formed into a dense material with excellent water and abrasion resistance by heat-pressing the material. can. In addition, desired physical properties can be imparted to these molded products by grafting vinyl polymers such as styrene onto wood components, and by changing the type and amount of the homopolymer remaining in the wood voids. By adjusting the heating and pressurizing conditions, it is possible to adjust the heat softening state and heat melting state of the modified wood material, and form a molded product with a desired appearance quality without causing carbonization or damage.

Examples of the present invention are listed below.

Example 1 15 g of wood flour was pretreated by immersing it in 26.3 ml of glacial acetic acid for several hours, followed by 62.2 ml of acetic anhydride and propionic anhydride.
36.5 ml (molar ratio 7:3), 48 ml of glacial acetic acid, perchloric acid
0.19 ml was added thereto, and the mixture was immersed for 6 hours to react, washed and dried to obtain acetyl-propionylated wood flour.

Put 5 g of this acetyl-propionylated wood flour into a reaction container, add 20 ml of pyridine and 20 ml of styrene, replace the inside of the container with nitrogen, and then reduce the dose rate to 0.1 Mrad/hr.
Simultaneous irradiation with Co ⁶⁰ r-rays was performed for 19 hours, and after the reaction was completed, the homopolymer was immersed in methanol to co-precipitate the homopolymer. The obtained graft copolymerized wood flour 1 is
The homopolymer was removed by benzene extraction, and the apparent grafting rate was calculated to be 12% (grafting efficiency was 35%).

Also, under the same conditions as above, the dose rate was 0.1 Mrad/hr.
Co ⁶⁰ r-ray simultaneous irradiation time of 1 hour, 24 hours,
After 34 hours, graft copolymerized wood flours 2, 3, and 4 were obtained.

The apparent graft ratios of the graft copolymerization-treated wood flours 2, 3, and 4 were 2%, 15%, and 18%, respectively.

Next, the graft copolymerization treated wood flours 1, 2, 3, and 4 obtained above and the acetylpropionylated wood flour 5 obtained in the above operation (without graft copolymerization treatment) were subjected to a thermomechanical test. Pressure: 3Kg/cm ² , heating rate:
Thermoplasticity was measured on the basis of 1 Co/min. The results are shown in Figure 1 (thermo-mechanical behavior diagram).

In FIG. 1, the vertical axis shows the amount of depression deformation (Δ) due to thermal softening of the sample due to heating, and the horizontal axis shows the heating temperature (T).

As is clear from FIG. 1, acetyl-propionylated wood flour 5 undergoes thermal softening, but does not completely thermally flow even at temperatures of 300°C or higher, whereas graft copolymerized wood flour 1, 2, It was confirmed that samples 3 and 4 exhibited complete thermal fluidity at approximately 300°C and were endowed with remarkable thermoplasticity accompanied by melting even at a small apparent grafting rate.

In addition, the obtained graft copolymerization treated wood flour 1,
For items 2, 3, and 4, the heating temperature can be lowered by applying strong pressure. For example, hot pressing at 150℃ and 100Kg/cm ² is suitable for molded products such as sheets with molten wood flour. I was able to mold it.

Example 2 15 g of wood flour was pretreated under the same conditions as in Example 1, and then treated with 89.1 ml of acetic anhydride, 48 ml of glacial acetic acid, and perchloric acid.
It was immersed in a 0.19 ml mixture at a temperature of 35°C for 6 hours to react, washed and dried to obtain acetylated wood flour.

5 g of this acetylated wood flour was placed in a reaction vessel, 20 ml of pyridine and 20 ml of styrene were added, and the inside of the vessel was purged with nitrogen, followed by simultaneous Co ⁶⁰ r-ray irradiation at a dose rate of 0.1 Mrad for 10 hours.

The resulting graft copolymerization treated wood flour 6 had an apparent grafting rate of 8% (grafting efficiency 30%).

Example 1 This graft copolymerization treated wood flour 6 and the acetylated wood flour 7 obtained by the above operation (not subjected to graft copolymerization treatment) were tested in the thermomechanical testing machine described in Example 1. Thermoplasticity was measured under the same conditions as . The results are shown in FIG.

As is clear from Figure 2, acetylated wood flour 7 does not have complete thermal fluidity even at a temperature of 300°C, whereas graft copolymerized wood flour 1 exhibits complete thermal fluidity at approximately 300°C, resulting in significant heat generation. It was confirmed that plasticity was imparted.

Example 3 5 g of acetyl-propionylated wood flour obtained in Example 1 was placed in a reaction vessel, and 1×10 ^-3 mol of FeSO ₄ was added.
50 ml of an aqueous solution containing hydrogen peroxide, 50 ml of an aqueous solution containing 1×10 ^-2 mol of hydrogen peroxide, and 80 ml of methyl methacrylate were added, and a reaction was carried out at 50° C. for 4 hours. The apparent grafting rate of the resulting graft copolymerized wood flour was 60% (grafting efficiency 22%). This graft copolymerized wood flour was also endowed with remarkable thermoplasticity that caused perfect thermal flow.

Example 5 A 0.8 mm thick straight-grain birch wood veneer was pretreated by immersing it in a sodium hydroxide solution for 1 hour, then acetic anhydride was injected under reduced pressure and reacted at 130°C for 30 minutes, resulting in a weight increase rate of 18 % acetylated veneer was obtained. Then,
A solution of pyridine:styrene=1:1 was injected, and after replacing the inside of the container with nitrogen, Co60 irradiation was performed for 10 hours at a dose rate of 0.1 Mrad.

The apparent grafting rate of the resulting graft copolymerization treated veneer was 6%. When this treated veneer was heat-pressed in a hot press at a temperature of 130°C, a press pressure of 5 kg/cm ² , and a press time of 20 minutes, the spring wood part had high transparency and the annual ring width was wider than the original veneer. A veneer that can be used as a decorative material with a rough appearance was obtained.

Example 4 5 g of acetylated wood flour obtained in Example 2 was
% ammonium persulfate aqueous solution for 30 minutes, then 50 ml of methyl methacrylate and 50 ml of methanol.
was added, and the reaction was carried out at 60°C for 3 hours.

The apparent grafting rate of the resulting graft copolymerized wood flour was about 120%.

This graft copolymerization-treated wood flour also had significant thermoplasticity that resulted in perfect thermal flow.

[Brief explanation of the drawing]

Figures 1 and 2 show thermomechanical behavior diagrams of acetyl-propionylated wood flour and acetylated wood flour before and after graft copolymerization treatment with styrene, respectively. 1, 2, 3, 4 and 6...apparent grafting rate is 2%, 12%, 15%, 18% and 8% respectively
Graft copolymerization treated wood flour, 5 and 7...
...Wood flour before graft copolymerization treatment.

Claims (1)

[Claims] 1. A wood material comprising treating a wood material with a reactant capable of reacting with a hydroxyl group in the wood component, and then subjecting the treated wood material to a graft polymerization treatment by reacting with a polymerizable substance. Method of modifying materials. 2. The method for modifying wood materials according to claim 1, wherein the reactant is an esterification agent or an etherification agent. 3. The method for modifying wood materials according to claim 1 or 2, wherein the polymerizable substance used in the graft polymerization treatment is a vinyl compound monomer, oligomer, or prepolymer.