A phenol-formaldehyde resin for impregnating reconstituted wood and a method for preparing the same

Abstract

The present application relates to the field of C08L23 / 12, especially relates to a kind of phenolic resin for impregnating reconstituted wood and preparation method thereof, preparation raw material includes: aromatic phenolic compound, saturated monoaldehyde, lye, polyethylamine compound and its derivative, the mass content of water in the phenolic resin is 40-50%.The phenolic resin prepared in the present application is suitable for impregnating reconstituted wood, especially bamboo wood and eucalyptus wood, the bonding performance of resin is good, without opening glue or curling and other adverse conditions, improve the mechanical strength of wood after pressing, by changing the amount of lye in prior art, reach better infiltration effect and water-soluble dispersibility.

Description

Technical Field

[0001] This invention relates to the field of C08L23 / 12, and more particularly to a phenolic resin for impregnating reconstituted wood and a method for preparing the same. Background Technology

[0002] With the increasing exploitation of timber resources, the supply of high-quality timber is becoming increasingly scarce, leading to the emergence of more economical and environmentally friendly reconstituted timber. Reconstituted timber is a new type of building material made by impregnating wood chips, such as bamboo strips and eucalyptus, with an adhesive and then curing and pressing them together. It is widely used in furniture, flooring, and decorative items. However, during the impregnation and reconstitution process, due to the inherent properties of the wood chips and their fragmented nature, they have poor luster and extremely low mechanical properties. The adhesive strength after impregnation and pressing is also very low, frequently resulting in cracking and delamination.

[0003] CN106589275A discloses a modified phenolic resin for producing outdoor reconstituted bamboo and its preparation method. The prepared resin has good wettability and viscosity, but it does not improve the mechanical strength of wood chips with poor mechanical properties, which indirectly limits the application fields of the finished product.

[0004] CN110054740A discloses lignin-modified phenolic resin, its preparation method, and reconstituted material. If the amount of lignin added in the formula is too high, it will increase the selective adsorption of wood while adjusting the viscosity, resulting in a decrease in bonding strength.

[0005] There is still a lack of phenolic resins in the current technology that can be specifically applied to reconstituted bamboo and eucalyptus trees and can help improve the mechanical strength of wood. Summary of the Invention

[0006] The first aspect of the present invention provides a phenolic resin for impregnating reconstituted wood, the raw materials for which include: aromatic phenolic compounds, saturated monohydric aldehydes, alkali solutions, polyethylamine compounds and their derivatives, wherein the water content in the phenolic resin is 40-50% by mass.

[0007] The applicant discovered that excessive water content in phenolic resin increases the selective adsorption of moisture by wood, leading to problems such as insufficient adhesive in wood layers and delayed curing. Conversely, insufficient moisture content reduces the resin's wettability, causing premature curing on the wood surface. Only when the water content in the phenolic resin is 40-50% can a balance between curing and bonding effects be achieved.

[0008] In a preferred embodiment, the weight ratio of the aromatic phenolic compound to the alkaline solution is (1.8-2.3):1.

[0009] To improve the solubility and wetting effect of the resin, the weight ratio of the aromatic phenolic compound to the alkaline solution is 2:1.

[0010] In the prior art, the weight of the alkali solution is generally 10-15% of the weight of the aromatic phenolic compound. The applicant found that when the weight ratio of the aromatic phenolic compound to the alkali solution is (1.8-2.3):1, the prepared resin has good solubility in water and significantly improves the wettability of bamboo, wood and eucalyptus, but also leads to a decrease in the bonding strength of the wood.

[0011] In a preferred embodiment, the alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, and barium hydroxide.

[0012] Preferably, the alkaline solution is sodium hydroxide, specifically a sodium hydroxide aqueous solution with a mass concentration of 30%.

[0013] In a preferred embodiment, the weight ratio of the aromatic phenolic compound to the saturated monohydric aldehyde is 1:(2-3).

[0014] To reduce the content of free aldehydes in the resin, the weight ratio of the aromatic phenolic compound to the saturated monohydric aldehyde is 1:2.15.

[0015] In a preferred embodiment, the aromatic phenolic compound includes at least one of phenol, xylenol, resorcinol, polyanthrol, and naphthol.

[0016] Preferably, the aromatic phenolic compound is phenol.

[0017] In a preferred embodiment, the methanol content in the saturated monoaldehyde is no more than 12% by mass.

[0018] The applicant discovered that the methanol content in saturated monoaldehyde has a significant impact on the quality of phenolic resin. When the methanol content is too high, the hydroxymethyl group will be further methoxylated, and the product cannot be further cross-linked, thereby reducing the cross-linking density, adhesive strength, and water resistance.

[0019] In a preferred embodiment, the mass content of iron ions in the saturated monohydric aldehyde is not greater than 0.0005%.

[0020] The applicant discovered that when the iron ion content in the saturated monoaldehyde was greater than 0.0005%, the prepared resin darkened in color after curing, affecting the color of the wood itself and reducing its quality.

[0021] Preferably, the saturated monoaldehyde is formaldehyde, purchased from Thermo Fisher Chemicals, and is a first-grade product.

[0022] Preferably, the formaldehyde is a formaldehyde aqueous solution with a mass concentration of 37%.

[0023] In a preferred embodiment, the solid content of the phenolic resin is 50-52 wt%.

[0024] The applicant discovered that when the solid content of phenolic resin is 50-52 wt%, a balance can be achieved between high wettability to wood and high bonding strength.

[0025] In a preferred embodiment, the polyethylamine compound and its derivatives account for 0.1-0.3% of the total weight of the raw materials used in the preparation.

[0026] In a preferred embodiment, the polyethylamine compound and its derivatives include at least one of diethylamine, triethylamine, tetraethylamine, diethanolamine, triethanolamine, and tetraethanolamine.

[0027] Preferably, the polyethylamine compound and its derivatives are triethylamine.

[0028] The applicant discovered that the addition of triethylamine significantly improved the bonding strength of the resin and enhanced the mechanical strength of cured bamboo and eucalyptus. The presumed reason is that triethylamine synergistically bonds the broken fibers of bamboo and eucalyptus with phenolic resin, filling the hollow spaces within them and encapsulating the dry, brittle trunk, thus increasing the mechanical strength after curing.

[0029] The second aspect of the present invention provides a method for preparing phenolic resin for impregnating reconstituted wood, comprising the following steps: (1) adding aromatic phenolic compounds, alkaline solution, and polyethylamine compounds into a reaction vessel; (2) controlling the temperature of the reaction vessel to 25-45°C, adding saturated monohydric aldehyde, adjusting the temperature to 60-70°C and keeping it warm; (3) heating up, reacting for 180-240 min, and detecting the viscosity; (4) cooling down and discharging the material.

[0030] In a preferred embodiment, the temperature is increased to 72-77°C.

[0031] In a preferred embodiment, the viscosity value in the viscosity test (25°C) is 19-20 s for Forte-4 cup.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The phenolic resin prepared by this invention is suitable for impregnating reconstituted wood, especially bamboo and eucalyptus wood. The resin has good bonding properties, with no defects such as delamination or curling, and improves the mechanical strength of the wood after pressing.

[0034] 2. By changing the amount of alkali solution used in the existing technology, better wetting effect and water solubility and dispersibility were achieved.

[0035] 3. By adding triethylamine, the problem of poor bonding strength caused by excessive alkali solution was solved, and a balance between high wettability and high adhesiveness was finally achieved. Detailed Implementation

[0036] Example 1

[0037] The first aspect of this embodiment provides a phenolic resin for impregnating reconstituted wood, the raw materials for which, by weight, are: 300 parts of aromatic phenolic compounds, 645 parts of saturated monohydric aldehydes, 150 parts of alkali solution, and 2.2 parts of polyethylamine compounds and their derivatives.

[0038] The aromatic phenolic compound is phenol.

[0039] The saturated monohydric aldehyde is a 37% aqueous solution of formaldehyde, with a methanol content of 12% and an iron ion content of no more than 0.0005%. The formaldehyde was purchased from Thermo Fisher Chemicals and is a Grade 1 product.

[0040] The alkaline solution is a 30% sodium hydroxide aqueous solution.

[0041] The polyethylamine compound and its derivatives are triethylamine.

[0042] The second aspect of this embodiment provides a method for preparing phenolic resin for impregnating reconstituted wood, comprising the following steps: (1) adding aromatic phenolic compounds, alkaline solution, and polyethylamine compounds into a reaction vessel; (2) controlling the temperature of the reaction vessel to 30°C, adding saturated monohydric aldehyde, adjusting the temperature to 65°C and keeping it at that temperature for 30 min; (3) raising the temperature to 75°C, reacting for 200 min, and detecting the viscosity (at 25°C) as 19-20 s in a Forte 4 cup; (4) cooling the temperature to 35°C and discharging the material.

[0043] Comparative Example 1

[0044] The first aspect of this comparative example provides a phenolic resin for impregnating reconstituted wood. The specific implementation method is the same as in Example 1, except that, by weight, the raw materials include: 300 parts of aromatic phenolic compound, 645 parts of saturated monohydric aldehyde, 150 parts of alkali solution, 2.2 parts of polyethylamine compound and its derivatives, and 100 parts of water.

[0045] The second aspect of this comparative example provides a method for preparing phenolic resin for impregnating reconstituted wood, comprising the following steps: (1) adding aromatic phenolic compounds, alkaline solution, and polyethylamine compounds into a reaction vessel; (2) controlling the temperature of the reaction vessel to 30°C, adding saturated monohydric aldehyde, adjusting the temperature to 65°C and keeping it at that temperature for 30 min; (3) raising the temperature to 75°C, reacting for 200 min, and detecting the viscosity (at 25°C) as 19-20 s in a Forte 4 cup; (4) cooling the temperature to 35°C, adding water, and discharging the material.

[0046] Comparative Example 2

[0047] The first aspect of this comparative example provides a phenolic resin for impregnating reconstituted wood. The specific implementation method is the same as in Example 1, except that the saturated monohydric aldehyde is a 37% formaldehyde aqueous solution, the formaldehyde contains 16% methanol, the iron ion content is not greater than 0.005%, and the formaldehyde is purchased from Thermo Fisher Chemicals, and is a grade II product.

[0048] The second aspect of this comparative example provides a method for preparing phenolic resin for impregnating reconstituted wood, with the specific implementation method being the same as in Example 1.

[0049] Comparative Example 3

[0050] The first aspect of this comparative example provides a phenolic resin for impregnating reconstituted wood, with the specific implementation method being the same as in Example 1, except that the alkali solution is replaced with 80 parts.

[0051] The second aspect of this comparative example provides a method for preparing phenolic resin for impregnating reconstituted wood, with the specific implementation method being the same as in Example 1.

[0052] Comparative Example 4

[0053] The first aspect of this comparative example provides a phenolic resin for impregnating reconstituted wood, with the specific implementation method being the same as in Example 1, except that the polyethylamine compound and its derivatives are replaced with 0 parts.

[0054] The second aspect of this comparative example provides a method for preparing phenolic resin for impregnating reconstituted wood, with the specific implementation method being the same as in Example 1.

[0055] Performance testing

[0056] The tests were conducted in accordance with GB / T 14732-2017 "Urea-formaldehyde, phenol-formaldehyde and melamine-formaldehyde resins for wood industry adhesives" and GB / T14074-2017 "Test methods for adhesives and resins for wood industry". The quality indicators are shown in Table 1.

[0057] Table 1

[0058]

[0059] Referring to GB / T 17657-2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels", the following tests were conducted: Class I bond strength, Class I impregnation peeling, and water absorption thickness swelling rate.

[0060] Five layers of 40×40×2mm eucalyptus veneer were used, completely impregnated in the phenolic resin of the examples and comparative examples for 30 minutes, then dried at 60°C for 40 minutes, and hot-pressed at 125°C for 15 minutes at a pressure of 17 kg / cm². 2 The test results are shown in Table 2.

[0061] Table 2

[0062]

Claims

1. A phenolic resin for impregnating reconstituted wood, characterized in that, The raw materials for preparation, by weight, include: 300 parts of aromatic phenolic compounds, 645 parts of saturated monohydric aldehydes, 150 parts of alkaline solution, and 2.2 parts of polyethylamine compounds and their derivatives; the water content in the phenolic resin is 48.75% by weight. The aromatic phenolic compound is phenol; The saturated monohydric aldehyde is a 37% formaldehyde aqueous solution, in which the formaldehyde contains 12% methanol and no more than 0.0005% iron ions; the alkaline solution is a 30% sodium hydroxide aqueous solution. The polyethylamine compound and its derivatives are triethylamine.

2. A method for preparing a phenolic resin for impregnating reconstituted wood according to claim 1, characterized in that, The process includes the following steps: (1) Add aromatic phenolic compounds, alkaline solution, and polyethylamine compounds to the reactor; (2) Control the reactor temperature to 25-45℃, add saturated monoaldehyde, adjust the temperature to 60-70℃ and keep it warm; (3) Heat up, react for 180-240 min, and test the viscosity; (4) Cool down and discharge the material.

3. The method for preparing a phenolic resin for impregnating reconstituted wood according to claim 2, characterized in that, The viscosity value in the measured viscosity is 19-20 s for the Forecast-4 cup.

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