CN108858574B - Enhanced laminated veneer lumber and preparation method thereof - Google Patents

Abstract

The invention relates to a poplar reinforced laminated veneer lumber, which researches the influence of the change of the compression density of wood on the mechanical property, the water resistance, the wettability and the roughness of the poplar reinforced laminated veneer lumber. The change rule of the properties of the poplar reinforced laminated veneer lumber in the aspects of mechanical property, water resistance, wettability, roughness and the like is found along with the increase of the density. The invention also provides a better adhesive solution, and particularly adopts diethyl malonate modified phenolic resin and nonyl-containing phenolic resin to combine according to a certain proportion, and the solution ensures that the poplar reinforced laminated veneer lumber keeps better mechanical property and water resistance under the condition of proper or lower density.

Description

Enhanced laminated veneer lumber and preparation method thereof

Technical Field

The invention relates to the field of materials, in particular to the field of wood processing, and particularly relates to a poplar reinforced laminated veneer lumber and a preparation method thereof.

Background

China has long been dedicated to the cultivation of fast-growing forests, and the area of the existing forests is the first in the world. In China, poplar is a fast-growing tree species which is widely planted, and the data of the national forestry administration shows that the planting area and the storage capacity respectively reach 997 hectares and 6 hundred million 2400 cubic meters. Poplar is commonly used to produce wood-based composites such as plywood, particle board, fiberboard, compressed wood and fiber reinforced polymer composites. In China, the yield of poplar is increased to 4700000m³And the capacity of a plurality of poplar board enterprises reaches 150000 cubic meters. However, the low density and dimensional instability of poplar limited its utility. Many studies have shown that densification of poplar can significantly improve the density and mechanical strength of poplar products.

Densification allows low density wood to replace high density wood species, modifies the low density wood into high performance and high value products, and gains commercial interest. Some low-density woods such as spruce, radiata pine, oil palm and poplar, etc. have been widely used to produce compressed wood by appropriate manufacturing processes, and these compressed wood have promising industrial applications. However, the dimensional stability of compressed poplar still remains a challenging task, which limits its industrial application, in particular as outdoor material. The reinforced laminated veneer lumber is a treated compressed wood which is obtained by treating solid wood or veneer with a water-soluble phenolic resin and compressing the wood or veneer into a desired density and thickness. The phenolic resin (PF) resin-impregnated modified poplar is an economic and effective method for improving the dimensional stability and reducing the moisture absorption of poplar so as to improve the bioerodibility of poplar.

However, reinforced laminated veneer lumber is susceptible to deformation and cracking when used in humid environments, particularly outdoor environments. The high-density enhanced laminated veneer lumber has better dimensional stability and physical and mechanical properties. Therefore, there is a need for a complete theoretical study on the dimensional stability of poplar density. In addition, high density manufacturing processes can also affect other properties such as microstructure and porosity. There have been few reports of the effect of density on moisture absorption and surface properties of reinforced laminated veneer lumber. It is necessary to study and understand the mechanism of influence of the change in the compression density of wood on the change in dimensional stability.

Disclosure of Invention

The invention researches the influence of the change of the wood compression density on the mechanical property, the water resistance, the wettability and the roughness of the poplar reinforced laminated veneer lumber. At the same time, the inventor of the application also realizes that the balance between the density of the poplar reinforced laminated veneer lumber and the mechanical property, the water resistance, the wettability and the roughness of the poplar reinforced laminated veneer lumber is also very important to adjust. The application value of the method in the industry is embodied as follows: 1) in order to enable the poplar reinforced laminated veneer lumber to have higher board density, higher requirements are placed on a board pressing device and a board pressing process, and higher energy consumption, more raw material consumption and higher cost are achieved; 2) in industrial applications, or in the selection of materials for various indoor and outdoor applications, in some cases the weight of the finished product or material needs to be controlled, and therefore lower densities are also needed in some cases. The invention aims to find the balance between the density of the poplar reinforced laminated veneer lumber and the mechanical property, the water resistance and the like of the poplar reinforced laminated veneer lumber. And the balance is realized through the improvement of the adhesive, and the industrial application value is obtained.

On one hand, the influence of the change of the wood compression density on the mechanical property, the water resistance, the wettability and the roughness of the poplar reinforced laminated veneer lumber is discovered. According to the results of the experimental examples 1-2, the tested poplar reinforced laminated veneer lumber has certain gains in the mechanical properties, the water resistance, the wettability, the roughness and the like along with the increase of the density. The method provides reference for the selection of process conditions for the industrial preparation of the poplar reinforced laminated veneer lumber.

The preparation method comprises the following steps of adding molten phenol, 3/5 formaldehyde, catalysts (sodium hydroxide and potassium hydroxide) and 3/4 diethyl malonate into a three-neck flask provided with a stirrer and a thermometer according to a ratio of n (phenol) to n (formaldehyde) to n (catalyst) of 1: 2.1: 0.3, uniformly stirring, heating to 85-90 ℃, reacting for 20min, cooling to below 75 ℃, adding the rest of formaldehyde and diethyl malonate, keeping the temperature at 85-90 ℃ for reacting for 20min to reach the required viscosity, finishing the reaction, cooling and discharging, wherein the phenolic resin B is a nonylphenol-containing phenolic resin, the preparation method comprises the following steps of adding nonylphenol/phenol (molar ratio of 1:5) to 1.33mol, adding 1.55% of nonylphenol into a 500m L four-neck flask provided with the stirrer, a reflux condenser and the thermometer, stirring for 20min until the temperature is below 75 ℃, stirring until the temperature reaches 0.60-60-0.09 mol%, heating, stirring until the temperature reaches 0.60-60-0.09 mol%, stirring, heating, stirring again, stirring until the water is removed, and reacting again, and finally heating to obtain a phenolic resin after the product.

The invention also provides the types of the adhesive suitable for the poplar reinforced laminated veneer lumber. The phenolic resin composition comprises one or more of phenolic resin, diethyl malonate modified phenolic resin and nonyl phenol-containing phenolic resin, wherein the combination of diethyl malonate modified phenolic resin and nonyl phenol-containing phenolic resin is preferably adopted, and the proportion of the diethyl malonate modified phenolic resin to the nonyl phenol-containing phenolic resin can be 1:10-10:1, preferably 1: 1.

The invention also provides a preparation method of the peach wood laminated wood. The method comprises the following specific steps:

1. preparation of test materials

Preparing a thin poplar veneer and an adhesive.

2. Preparation of poplar laminated wood

1) Impregnation of materials

The method comprises the following steps of (1) impregnating the poplar veneer by using a vacuum pressurization impregnation tank and a pressurization impregnation method, wherein the impregnation process comprises the following steps: preparing glue solution with solid content of 8-15%, vacuumizing the selected material, keeping for 2-10min, pressurizing to 0.30-0.60MPa, keeping for 2-6min, and measuring the gum dipping amount of the material after glue pouring for 2-10min, wherein the gum dipping amount is 10-20%.

2) Drying process of impregnated veneer

The gum dipping material is dried naturally until the water content is 6-10%.

3) Plate pressing process

The density of the pressing plate is set to be 0.60-1.20g/cm³The final thickness of the plate is controlled to be 3-10 mm. The hot-pressing temperature is 120-.

Wherein, the glue solution with 10 percent of solid content is preferably prepared, the vacuumizing time is preferably kept for 5min, the pressurizing pressure is preferably 0.45MPa and kept for 4min, the glue pouring time is preferably 5min, and the gum dipping amount is preferably 15.0 percent; drying until the water content is preferably 8%; the density of the pressing plate is preferably 1.00-1.20g/cm³The final thickness of the plate is preferably controlled at 6.0 mm; the hot pressing temperature is preferably 140 ℃ and the time is 1 min/mm.

For the adhesive, an adhesive comprising one or more of a phenol resin, a diethyl malonate modified phenol resin, and a nonylphenol-containing phenol resin is preferably used, wherein a combination of a diethyl malonate modified phenol resin and a nonylphenol-containing phenol resin is preferably used, and the ratio of the two may be 1:10 to 10:1, preferably 1:1, by weight.

Detailed Description

Example 1 preparation of phenolic resin A (diethyl malonate modified phenolic resin)

In a three-necked flask equipped with a stirrer and a thermometer, the reaction was carried out in the following manner as n (phenol): n (formaldehyde): n (catalyst) ═ 1: 2.1: adding molten phenol, 3/5 formaldehyde, catalyst (sodium hydroxide and potassium hydroxide) and 3/4 diethyl malonate in a ratio of 0.3, and uniformly stirring; then heating to 85-90 ℃ and reacting for 20 min; cooling to below 75 ℃, adding the rest formaldehyde and diethyl malonate, keeping the temperature at 85-90 ℃, reacting for 20min to reach the required viscosity, finishing the reaction, cooling and discharging.

Example 2 preparation of phenolic resin B (Nonoxyphenol-containing phenolic resin)

Adding 1.33mol of nonyl phenol/phenol (the molar ratio is 1:5), 1.55mol of formaldehyde (37%) and 0.09mol of ammonia water (25%) into a 500m L four-necked bottle provided with a stirrer, a reflux condenser and a thermometer, stirring and heating to 60 ℃, starting boiling the solution when the reaction temperature rises to 96-98 ℃, monitoring the reaction degree by a cloud point method after the reaction is carried out for 60min at constant temperature, stopping heating after the cloud point reaches 80-82 ℃, adding distilled water into the four-necked bottle, heating, stirring and washing, stopping stirring after 10min, standing, sucking out the upper-layer water after the resin is layered, washing once again, and finally removing the water and oligomers at 60 ℃ and 0.09MPa to obtain the phenolic resin B.

Example 3 preparation of poplar-reinforced laminated veneer lumber

1. Test materials

The poplar thin veneer has the size of 2 +/-0.2 mm × 0.71.71 0.71 × 1.27.27 m, the water content of 4.50 +/-1 percent and no flaws, decay and smoothness on the surface, and is provided by Shandong enterprises, wherein the veneer is cut into the size of 300 × 9 × 9 × 2mm and used for manufacturing the reinforced laminated veneer lumber, and the adhesive, namely the phenolic resin A and the phenolic resin B are mixed according to the weight ratio of 1: 1.

2. Preparation of poplar reinforced laminated veneer lumber

1) Impregnation of materials

The method comprises the following steps of (1) impregnating the poplar veneer by using a vacuum pressurization impregnation tank and a pressurization impregnation method, wherein the impregnation process comprises the following steps: and preparing glue solution with solid content of 10%, vacuumizing the selected material, keeping the vacuum for 5min, pressurizing to 0.45MPa, keeping the pressure for 4min, and measuring the gum dipping amount of the material after glue pouring for 5min, wherein the gum dipping amount is about 15.0%.

2) Drying process of impregnated veneer

The gum dipping material is dried naturally until the water content is 8%.

3) Plate pressing process

The density of the press plate is set to be about 0.60, 0.70, 0.80, 0.90, 1.00, 1.10, 1.20g/cm³The final thickness of the plate is controlled to be about 6.0mm, the size is 30 × 88 × 6mm, 3 plates are pressed under each condition, the hot pressing temperature is 140 ℃, the time is 1min/mm, and a hot-in and cold-out process is adopted.

Comparative example 1 preparation of poplar-reinforced laminated veneer lumber from common phenol resin

1. Test materials

The poplar thin veneer has the size of 2 +/-0.2 mm × 0.71.71 0.71 × 1.27.27 m, the water content of 4.50 +/-1 percent and no flaw, rot and smoothness on the surface, and is provided by Shandong enterprises to be cut into the size of 300 × 9 × 9 × 2mm for manufacturing the laminated wood.

PF resins were purchased from Beijing Taier chemical Co., Ltd.

2. Test protocol

1) Impregnation of materials

The method comprises the following steps of (1) impregnating the poplar veneer by using a vacuum pressurization impregnation tank and a pressurization impregnation method, wherein the impregnation process comprises the following steps: and preparing glue solution with solid content of 10%, vacuumizing the selected material, keeping the vacuum for 5min, pressurizing to 0.45MPa, keeping the pressure for 4min, and measuring the gum dipping amount of the material after glue pouring for 5min, wherein the gum dipping amount is about 15.0%.

2) Drying process of impregnated veneer

The gum dipping material is dried naturally until the water content is 8%.

3) Plate pressing process

The density of the press plate is set to be about 0.60, 0.70, 0.80, 0.90, 1.00, 1.10, 1.20g/cm³The final thickness of the plate is controlled to be about 6.0mm, the size is 30 × 88 × 6mm, 3 plates are pressed under each condition, the hot pressing temperature is 140 ℃, the time is 1min/mm, and a hot-in and cold-out process is adopted.

Comparative example 2 preparation of poplar laminated wood from phenolic resin A

The same preparation as in example 3 was used, except that the adhesive was phenol-formaldehyde resin A.

Comparative example 3 preparation of poplar laminated veneer using phenol resin B

The same preparation as in example 3 was used, except that the adhesive was selected to be phenolic resin B.

Test example 1

Comparative example 1 enhanced mechanical properties of laminated veneer lumber

With the increase of the density, the horizontal shear strength of the poplar reinforced laminated veneer lumber tends to increase. The density was 0.60g/cm³The enhanced laminated veneer lumber has the horizontal shear strength of 12.34MPa and the density of 1.22g/cm³The horizontal shear strength of the reinforced laminated veneer lumber reaches 28.68 MPa.

The static bending strength and the elastic modulus of the reinforced laminated veneer lumber also show a positive correlation trend along with the increase of the density. The density was 0.60g/cm³The static bending strength and the elastic modulus of the laminated wood are 112.02Mpa and 8656Mpa respectively; the density was 1.22g/cm³The static bending strength and the elastic modulus of the laminated wood are 241.56MPa and 16170MPa respectively.

Comparative example 1 enhanced laminated veneer lumber Water resistance

After being soaked in water at the temperature of 20 ℃, the water absorption width expansion rate (WSR) of the poplar reinforced laminated veneer lumber is in a decreasing trend along with the increase of the density, the water absorption thickness expansion rate (TSR) of the composite material is in a trend of increasing firstly and then decreasing, and the inflection point is 1.0g/cm³. After being soaked in water at 63 ℃, the WSR of the poplar reinforced laminated veneer lumber has an S-shaped trend, namely the WSR is basically balanced after increasing and then decreasing, and the TSR of the composite material has an increasing trend. After the 63 ℃ water soaking treatment, the TSR, WSR and WAR of the test piece are all higher than those of the test piece treated by the 20 ℃ water soaking treatment.

The Water Absorption (WAR) shows a decreasing trend with increasing density, whether after 20 ℃ or 63 ℃ soaking. The greater the density, the lower the water absorption. The density was 1.22g/cm³Has a water absorption of 13.24% and 30.97% at 20 ℃ and 63 ℃ respectively, and a density of 1.22g/cm³4.5 times and 2.9 times the water absorption of (1).

Third, comparative example 1 enhanced surface wettability of laminated veneer lumber

After the poplar veneer is compressed and recombined, the permeability is reduced, and meanwhile, the wettability of the enhanced veneer laminated timber is reduced along with the increase of the density. The greater the density, the greater the contact angle. At 20s, the density was 1.2g/cm³The surface contact angle of the enhanced laminated veneer lumber is 43.41 degrees to 0.6g/cm³The surface contact angle (33.54 ℃) of the enhanced laminated veneer lumber is increased by 29.4 percent.

Fourth, comparative example 1 enhanced surface free energy of laminated veneer lumber

Dispersion force component of surface with increasing density of enhanced veneer laminateGradually decreasing, polar force componentGradually increase to 1.20g/cm respectively³A minimum value of 23.71 and a maximum value of 2.56 are reached. Total surface free energy of uncompressed poplar veneersIs 35.90mJ.m^-2The surface free energy of the veneer gradually decreases with the increase of the density of the veneer, and the density is 1.20g/cm³The surface free energy was 26.27mJ.m^-2And a minimum value is reached.

Fifth, the surface roughness of the comparative example enhanced laminated veneer lumber

The enhanced laminated veneer lumber has a lower Ra (surface roughness) than poplar wood, and as the density increases, the roughness of the enhanced laminated veneer lumber surface decreases. The density was 1.20g/cm³The reinforced laminated veneer lumber of (1) has the smoothest surface and has an Ra value of 1.02 μm. The density was 1.20g/cm³The surface roughness specific density of the enhanced laminated veneer lumber is 0.60g/cm³g is 43.3% lower.

Sixthly, change of structure of enhanced laminated veneer lumber in comparative example 1

In the process of wood compression and densification, after the veneer is compressed, the cells and the pipe holes are extruded to generate larger deformation, and the cells are firstly compressed into the parenchyma cells, secondly compressed into the conduit cells, and finally compressed into the wood fiber cells.

The greater the density, the more degenerated the cells and the more compact the structure.

Seventh, comparative example 1 enhanced laminated veneer lumber pore structure

The total porosity and average pore size of the laminated wood with the density of 0.60g/cm are more than 0.90 and 1.22g/cm³. The higher the density and the lower the porosity, the more the cell lumen volume is compressed and the more compact the cells become.

Test example 2

Example 3 mechanical Properties of poplar-reinforced laminated veneer lumber

It can be seen that, when compared in the transverse direction under the same density condition, the poplar reinforced laminated veneer lumber prepared by using the composite phenolic resin in example 3 has better effects on the horizontal shear strength, static bending strength and elastic modulus than the poplar reinforced laminated veneer lumber prepared by using a single unmodified phenolic resin.

Example 3 Populus Wood Water resistance

It can be seen that, when the transverse comparison is performed under the same density condition, the poplar reinforced laminated veneer lumber prepared by using the composite phenolic resin in example 3 has better water resistance than the poplar reinforced laminated veneer lumber prepared by using a single unmodified phenolic resin.

Test example 3

The density was 1.02 (g/cm)³) Comparison of mechanical Properties of example 3 with comparative examples 1 to 3 under the conditions

It can be seen that the poplar reinforced laminated veneer lumber prepared by using the composite phenolic resin in example 3 has better mechanical properties than the single unmodified phenolic resin and the single phenolic resin A or B.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention in any way, and all simple modifications and equivalent variations of the above embodiments according to the technical spirit of the present invention are included in the scope of the present invention.

Claims (2)

1. The poplar reinforced laminated veneer lumber is characterized by being prepared according to the following preparation method:

(1) preparing a poplar thin veneer and an adhesive;

(2) preparation of poplar reinforced laminated veneer lumber

1) Impregnation of materials

The method comprises the following steps of (1) impregnating the poplar veneer by using a vacuum pressurization impregnation tank and a pressurization impregnation method, wherein the impregnation process comprises the following steps: preparing glue solution with solid content of 8-15%, vacuumizing and maintaining for 2-10min, pressurizing to 0.30-0.60MPa and maintaining for 2-6min, and pouring glue for 2-10min, wherein the gum dipping amount is 10-20%;

2) drying process of impregnated veneer

Drying the gum dipping material by adopting a conventional kiln until the water content is 6-10%;

3) plate pressing process

The density of the pressing plate is set to be 0.60-1.20g/cm³Controlling the final thickness of the plate to be 3-10mm, controlling the hot pressing temperature to be 120-;

the solid content of the glue solution is 10%, the vacuumizing time is kept for 5min, the pressurizing pressure is 0.45MPa and kept for 4min, the glue pouring time is 5min, and the gum dipping amount is 15.0%;

the drying is carried out until the water content is 8%; the density of the pressing plate is 1.00-1.20g/cm³The final thickness of the plate is controlled to be 6.0 mm; the hot pressing temperature is 140 ℃, and the time is 1 min/mm;

the adhesive is a combination of diethyl malonate modified phenolic resin and nonyl phenol-containing phenolic resin, and the ratio of the diethyl malonate modified phenolic resin to the nonyl phenol-containing phenolic resin is 1: 1;

the preparation method of the diethyl malonate modified phenolic resin adhesive comprises the following steps: in a three-necked flask equipped with a stirrer and a thermometer, the molar ratio n (phenol): n (formaldehyde): n (catalyst) = 1: 2.1: adding molten phenol, 3/5 formaldehyde, catalyst sodium hydroxide and potassium hydroxide and 3/4 diethyl malonate in the ratio of 0.3, and stirring uniformly; then heating to 85-90 ℃ and reacting for 20 min; cooling to below 75 ℃, adding the rest formaldehyde and diethyl malonate, keeping the temperature at 85-90 ℃ for reaction for 20min, finishing the reaction, cooling and discharging;

the preparation method of the nonylphenol-containing phenolic resin adhesive comprises the steps of adding 1.33mol of nonylphenol/phenol, 1.55mol of formaldehyde and 0.09mol of ammonia water into a 500m L four-necked bottle provided with a stirrer, a reflux condenser and a thermometer according to the molar ratio of 1:5, stirring and heating to 60 ℃, starting boiling the solution when the reaction temperature rises to 96-98 ℃, carrying out a constant temperature reaction for 60min, monitoring the reaction degree by using a cloud point method, stopping heating after the cloud point reaches 80-82 ℃, adding distilled water into the four-necked bottle, heating, stirring and washing, stopping stirring after 10min, standing, sucking out the upper-layer water after the resin is layered, repeatedly washing once, and finally removing the water and oligomers at 60 ℃ and 0.09MPa to obtain the nonylphenol-containing phenolic resin adhesive.

2. The preparation method of the poplar reinforced laminated veneer lumber is characterized by comprising the following steps:

(1) preparing a poplar thin veneer and an adhesive, wherein the adhesive is a combination of diethyl malonate modified phenolic resin and nonyl-containing phenolic resin, and the weight ratio of the diethyl malonate modified phenolic resin to the nonyl-containing phenolic resin is 1: 1;

(2) preparation of poplar reinforced laminated veneer lumber

1) Impregnation of materials

The method comprises the following steps of (1) impregnating the poplar veneer by using a vacuum pressurization impregnation tank and a pressurization impregnation method, wherein the impregnation process comprises the following steps: preparing glue solution with solid content of 10%, vacuumizing the selected material, keeping for 5min, pressurizing to 0.45MPa, keeping for 4min, pouring glue for 5min, and controlling the gum dipping amount to 15.0%;

2) drying process of impregnated veneer

Drying the gum dipping material by natural airing until the water content is 8%;

3) plate pressing process

The density of the pressing plate is set to be 0.90-1.20g/cm³Controlling the final thickness of the plate to be 6.0mm, controlling the size to be 30 × 88 × 6mm, controlling the hot-pressing temperature to be 140 ℃ and the time to be 1min/mm, and adopting a hot-in and cold-out process;

the preparation method of the diethyl malonate modified phenolic resin adhesive comprises the following steps: in a three-necked flask equipped with a stirrer and a thermometer, the molar ratio n (phenol): n (formaldehyde): n (catalyst) = 1: 2.1: adding molten phenol, 3/5 formaldehyde, catalyst sodium hydroxide and potassium hydroxide and 3/4 diethyl malonate in the ratio of 0.3, and stirring uniformly; then heating to 85-90 ℃ and reacting for 20 min; cooling to below 75 ℃, adding the rest formaldehyde and diethyl malonate, keeping the temperature at 85-90 ℃ for reaction for 20min, finishing the reaction, cooling and discharging;

the preparation method of the nonylphenol-containing phenolic resin adhesive comprises the steps of adding 1.33mol of nonylphenol/phenol, 1.55mol of formaldehyde and 0.09mol of ammonia water into a 500m L four-necked bottle provided with a stirrer, a reflux condenser and a thermometer according to the molar ratio of 1:5, stirring and heating to 60 ℃, starting boiling the solution when the reaction temperature rises to 96-98 ℃, carrying out a constant temperature reaction for 60min, monitoring the reaction degree by using a cloud point method, stopping heating after the cloud point reaches 80-82 ℃, adding distilled water into the four-necked bottle, heating, stirring and washing, stopping stirring after 10min, standing, sucking out the upper-layer water after the resin is layered, repeatedly washing once, and finally removing the water and oligomers at 60 ℃ and 0.09MPa to obtain the nonylphenol-containing phenolic resin adhesive.