Long-term yellowing-resistant transparent wood and preparation method thereof

Abstract

The invention discloses long-term yellowing-resistant transparent wood and a preparation method thereof. Comprising the following steps that firstly, delignification veneers are treated through acid-base combination to serve as filling materials; secondly, placing the delignified veneer in an alicyclic epoxy resin impregnation liquid for vacuum impregnation; and finally, curing and forming are conducted, and the yellowing-resistant transparent wood is prepared. The transparent wood has the advantages of high light transmittance, excellent long-term ultraviolet resistance and excellent high-temperature yellowing resistance. The composite material is widely applicable to the fields of building external windows, skylights, photovoltaic panel substrates, automobile window glass, high-end home decoration materials and the like, and has a remarkable application prospect.

Description

Technical Field

[0001] The invention relates to a transparent wood material with long-term yellowing resistance and a preparation method thereof, belonging to the technical field of wood composite materials. Background Art

[0002] Wood is a green, renewable and abundant material. It is widely used in daily life due to its excellent mechanical properties, low thermal conductivity, easy functionalization and anisotropy. In recent years, transparent wood, as an important branch of functional wood composites, has gradually become a research hotspot.

[0003] Transparent wood, with its high light transmittance, high haze and significant anisotropy, shows great application potential compared to traditional glass, especially as an energy-saving material. The thermal conductivity of transparent wood glass windows is significantly lower than that of traditional single-layer glass windows, thus showing good thermal insulation performance in the construction field. At the same time, transparent wood has excellent mechanical properties, which helps to improve safety during transportation and use. Therefore, transparent wood is considered to be a new type of building material that can replace traditional glass, and has broad prospects in the fields of building exterior windows, photovoltaic panel substrates, etc.

[0004] However, most transparent woods currently have the problem that the lignin in the wood skeleton is sensitive to ultraviolet rays (UV). Ultraviolet radiation can cause lignin degradation, leading to yellowing and aging. At the same time, the commonly used bisphenol A epoxy resin is prone to molecular chain breakage, free radical generation and oxidation reaction under ultraviolet irradiation, thereby causing embrittlement, strength loss, yellowing and surface cracks of the epoxy resin. These problems can cause the light transmittance of transparent wood to decrease, color change and appearance deterioration, seriously limiting its long-term performance. Therefore, developing a transparent wood with excellent anti-yellowing properties has become one of the important directions of current research.

[0005] The present invention proposes a method for preparing a transparent wood that is resistant to UV yellowing for a long time. The core idea is to remove lignin from the wood by combining two chemical methods so as to achieve the purpose of transparency by impregnating an epoxy resin with a more matching refractive index, while reducing the sensitivity of the wood itself to UV radiation and reducing the discoloration of the wood. The impregnated alicyclic epoxy resin has no benzene rings and unsaturated double bonds in its molecular structure. Compared with the bisphenol A type epoxy resin system, it has the characteristics of low viscosity, good weather resistance and excellent performance. The influence of ultraviolet rays on the yellowing of the resin itself is reduced, thereby preparing a transparent wood that is resistant to UV yellowing for a long time. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a transparent wood resistant to ultraviolet yellowing and a preparation method thereof, which can maintain a high transmittance and a low color change under ultraviolet radiation, and improve its weather resistance and long-term use stability.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] A long-lasting yellowing-resistant transparent wood and a preparation method thereof, comprising the following steps: selecting delignified balsa wood treated by a combined acid-base treatment method as a wood template, using alicyclic epoxy resin, and performing vacuum impregnation and curing processes to allow the resin to fully penetrate and evenly distribute in the pores of the wood, thereby improving transparency and long-term yellowing resistance.

[0009] The invention is characterized in that: the delignified veneer used is stored in an ethanol solution, the epoxy resin is selected from alicyclic epoxy, the amount of anhydride curing agent added is 110 to 120 parts, the accelerator is preferably N'N-dimethylbenzylamine, and the amount of addition is 1 part; the wood is placed in the epoxy impregnation solution for vacuum impregnation, the impregnation time is 30 minutes each time, the vacuum degree is -0.1Mpa, and the impregnation is repeated for more than 3 times; the curing conditions are curing at 100°C for 2 hours, and curing for 1 hour when the temperature is increased to 150°C.

[0010] Beneficial effects of the present invention: The present invention reduces residual lignin through a combined acid-base delignification treatment, and selects alicyclic epoxy resins to enable the transparent wood to maintain a high light transmittance and a low degree of yellowing under radiation, significantly improving its long-term aging resistance. At the same time, the optimized impregnation and curing process ensures that the resin evenly fills the pores of the wood, so that the material can still maintain optical stability under long-term ultraviolet radiation and high temperature environment, reducing yellowing and light transmittance reduction. In addition, the transparent wood has good thermal stability and is not prone to yellowing, brittleness or performance degradation under high temperature conditions. With its excellent optical and weather resistance, the transparent wood prepared by the present invention can be widely used in the fields of building exterior windows, skylights, photovoltaic panel substrates, automobile window glass, high-end home decoration, and display screen protection materials, and has broad market prospects. DETAILED DESCRIPTION

[0011] The present invention is further described in detail below in conjunction with implementation examples. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and cannot be used to limit the protection scope of the present invention.

[0012] Example 1

[0013] First, 2 mm balsa wood veneer was immersed in an alkaline sodium sulfite solution, wherein the concentration of sodium hydroxide was 2.5 mol / L and the concentration of sodium sulfite was 0.4 mol / L. Vacuum treatment was first performed, the vacuum treatment time was 30 min, the vacuum degree was -0.1 MPa, and then the reactor was boiled, and the mixed solution in the reactor was kept boiling for 2 h to obtain alkali-treated delignified balsa wood. The alkali-treated delignified wood was repeatedly cleaned with deionized water, and then boiled with an acidic sodium chlorite solution, wherein the concentration of sodium chlorite was 1 wt%, and the pH value was adjusted to about 4.6 with glacial acetic acid, and the solution was kept boiled at 80 ° C until the sample color turned white. , the time is about 2h, and then it is repeatedly washed with deionized water, and the freeze-dried sample is obtained to obtain the delignified balsa veneer treated with acid and alkali; secondly, 110-130 parts of 4-methylhexahydrophthalic anhydride are added to 100 parts of alicyclic epoxy resin (such as E73), and then 1 part of N'N-dimethylbenzylamine is added, and the impregnation liquid is prepared, and the delignified balsa veneer is placed in the impregnation liquid, and vacuum impregnation is performed, the vacuum degree is -0.1Mpa, the impregnation time is 30min, and the positive and negative pressures are switched and repeated 3 times, and the impregnated sample is taken out and placed in a mold for curing at 100℃ for 2h, and the temperature is raised to 150℃ for curing for 1h, and a long-lasting yellowing-resistant transparent wood is obtained. UV light (wavelength 365nm) is irradiated for 12h, and compared with the blank sample, the color difference changes by 2.53, and the transmittance is higher than 80%.

[0014] Example 2

[0015] 3mm birch veneer was immersed in an alkaline sodium sulfite solution, wherein the sodium hydroxide concentration was 2.0mol / L and the sodium sulfite concentration was 0.6mol / L, and vacuum treatment was performed. The vacuum treatment time was 45min and the vacuum degree was -0.1Mpa. The reactor was boiled and the mixed solution in the reactor was kept boiling for 3h to obtain alkali-treated delignified birch veneer. The alkali-treated delignified veneer was repeatedly cleaned with deionized water, and then boiled with an acidic sodium chlorite solution, wherein the sodium chlorite concentration was 1wt%, and the pH value was adjusted to about 4.6 with glacial acetic acid. The solution was kept boiled at 80°C until the sample color turned white. The time is about 2 hours, and then after repeated cleaning with deionized water, the freeze-dried sample is obtained to obtain the delignified birch veneer treated with acid and alkali; secondly, 110-130 parts of 4-methylhexahydrophthalic anhydride are added to 100 parts of alicyclic epoxy resin (such as E73), and then 1 part of N'N-dimethylbenzylamine is added, and the mixture is stirred evenly to obtain an impregnation solution, and the delignified balsa veneer is placed in the impregnation solution, vacuum impregnation, vacuum degree -0.1Mpa, impregnation time 30min, switching positive and negative pressures and repeating 3 times, taking out the impregnated sample and putting it into the mold for curing at 100℃ for 2h, and curing at 150℃ for 1h to obtain a long-lasting yellowing-resistant transparent wood. After irradiation with ultraviolet light (wavelength 365nm) for 12h, compared with the blank sample, the color difference changes by 2.36, and the transmittance is higher than 80%.

[0016] Example 3

[0017] 3mm poplar veneer is immersed in alkaline sodium sulfite solution, wherein the concentration of sodium hydroxide is 1.5mol / L, the concentration of sodium sulfite is 0.4mol / L, and vacuum treatment is performed. The vacuum treatment time is 45min, and the vacuum degree is -0.1Mpa. Then, the reactor is boiled, and the mixed solution in the reactor is kept boiling for 3h to obtain alkali-treated delignified birch veneer. The alkali-treated delignified veneer is repeatedly cleaned with deionized water; secondly, it is boiled with acidic sodium chlorite solution, wherein the concentration of sodium chlorite is 2wt%, and the pH value is adjusted to about 5.0 with glacial acetic acid, and the solution is kept boiling at 75℃. Until the color of the sample turns white, the time is about 3 hours, and then it is repeatedly washed with deionized water, and the freeze-dried sample is obtained to obtain the delignified poplar veneer treated with acid and alkali; secondly, 110-130 parts of 4-methylhexahydrophthalic anhydride and 1 part of N'N-dimethylbenzylamine are added to 100 parts of alicyclic epoxy resin (such as E73), and then mixed and stirred to obtain an impregnation solution, and the delignified balsa veneer is placed in the impregnation solution, vacuum impregnation, vacuum degree -0.1Mpa, impregnation time 30min, switching positive and negative pressures and repeating 3 times, taking out the impregnated sample and putting it into the mold for curing at 100℃ for 2h, and curing at 150℃ for 1h to obtain a long-lasting yellowing-resistant transparent wood. Irradiate with ultraviolet light (wavelength 365nm) for 12h, compared with the blank sample, the color difference changes by 2.27, and the transmittance is higher than 80%.

[0018] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A long-lasting yellowing-resistant transparent wood and a preparation method thereof, characterized in that: The following steps are involved: Firstly, the delignified veneer treated with acid and alkali is used as the filling material; secondly, the delignified veneer is placed in an epoxy resin impregnation solution for vacuum impregnation; finally, the veneer is cured and formed to obtain a transparent wood that is resistant to yellowing for a long time.

2. The transparent wood material with long-term yellowing resistance and the preparation method thereof according to claim 1, characterized in that: First, immerse the wood veneer in an alkaline sodium sulfite solution, perform vacuum treatment, and then perform steaming treatment on the reactor to obtain alkali-treated delignified balsa wood. After repeatedly cleaning the alkali-treated delignified wood with deionized water, cook it with an acidic sodium chlorite solution until the sample turns white. After repeatedly cleaning it with deionized water, freeze-dry the sample to obtain a delignified veneer treated with acid and alkali. The wood can be balsa, poplar, birch, white sycamore, etc., with a thickness of 0.5 mm to 3 mm.

3. The transparent wood material with long-term yellowing resistance and the preparation method thereof according to claim 1, characterized in that: The epoxy resin is an alicyclic epoxy resin; 4. The transparent wood material with long-term yellowing resistance and the preparation method thereof according to claim 1, characterized in that: The curing agent is preferably an anhydride curing agent 4-methylhexahydrophthalic anhydride, and the addition amount is 110 to 120 parts; 5. The transparent wood material with long-term yellowing resistance and the preparation method thereof according to claim 1, characterized in that: The accelerator in the anhydride curing agent system is preferably N'N-dimethylbenzylamine, and the addition amount is 1 part; 6. The transparent wood material with long-term yellowing resistance and the preparation method thereof according to claim 1, characterized in that: The vacuum impregnation time is 30 minutes each time, the vacuum degree is -0.1Mpa, and the impregnation is repeated for more than 3 times; 7. The transparent wood material with long-term yellowing resistance and the preparation method thereof according to claim 1, characterized in that: The acid anhydride curing agent is cured at high temperature. The curing conditions are curing at 100°C for 1 to 2 hours, and curing at 150°C for 0.5 to 1 hour.

8. A transparent wood material that is resistant to yellowing for a long time, characterized in that: The wood is prepared by the method for preparing long-lasting yellowing-resistant transparent wood according to any one of claims 1 to 7.