A method for identifying white oak wood and red oak wood

Abstract

The application provides a method for identifying white oak wood and red oak wood, which is used for identifying the white oak wood and the red oak wood by detecting whether an S-type Hibbert ketone structure exists in a molecular structure of acidolysis lignin, belongs to an identification method in the field of molecular structures, and has the advantages of improving the efficiency and accuracy of identification of the white oak wood and the red oak wood, and being capable of distinguishing the red oak wood processed or dyed and the white oak wood, and has good universality.

Description

Technical Field

[0001] This invention relates to a classification of wood species, specifically a method for distinguishing between white oak and red oak. Background Technology

[0002] Oak wood is widely used in timber manufacturing. Currently, all commercially harvested oak trees can be divided into two categories: red oak and white oak. White oak has good corrosion resistance and is often used in shipbuilding and exterior construction projects, while red oak is only suitable for interior items such as cabinets, furniture, and flooring. This difference in price leads to a price discrepancy between the two types of wood. Currently, white oak costs between $11.99 and $14.99 per board-foot, while red oak costs between $4.39 and $5.59 per board-foot. This price difference has led some unscrupulous merchants to sell red oak as white oak. Therefore, effectively distinguishing between red and white oak is a problem that urgently needs to be solved.

[0003] Compared to native trees, timber lacks crucial information such as leaves, crowns, and origin, leading to numerous uncertainties in identifying its species origin. Currently, red oak and white oak are mostly distinguished by direct observation of wood color and morphological anatomy. For example, unfinished red oak wood is light brown with a slight reddish tinge, while unfinished white oak wood is light brown with a slight olive tinge. However, some red and white oak pieces exhibit abnormal or blurred colors, potentially affecting the accuracy of these methods, and these methods are not applicable to processed or dyed red and white oak. For the latter, white and red oak are primarily identified by the shape and distribution of pores in the cross-section, the content of tyloses in the pores, the distribution of axial parenchyma, and the morphology of wood rays. However, this method is mainly used to distinguish oak from other hardwood species; white and red oak belong to the same genus, with similar macroscopic and microscopic structures, making accurate identification difficult. Summary of the Invention

[0004] To address the current lack of effective identification methods for distinguishing between white oak and red oak, this invention provides a method for differentiating white oak and red oak. This method identifies white oak and red oak by detecting the presence of an S-type Hibbert ketone structure in the molecular structure of acid-hydrolyzed lignin. This identification method belongs to the field of molecular structure and not only improves the efficiency and accuracy of white oak and red oak identification, but also distinguishes processed or dyed red oak wood from white oak wood, demonstrating good universality.

[0005] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0006] A method for distinguishing between white oak and red oak, characterized by comprising the following steps:

[0007] S1: Take the wood to be tested, remove impurities, crush it, and sieve it to obtain wood powder;

[0008] S2: Wood flour, γ-valerolactone, deionized water and sulfuric acid are mixed in a mass ratio of 1:10:1:0.1, and then added to a hydrothermal reactor for acid hydrolysis reaction for 1 to 5 hours. After cooling, hydrolysate is obtained.

[0009] S3: Extract acid-hydrolyzed lignin from the hydrolysate and dry it to obtain acid-hydrolyzed lignin powder;

[0010] S4: Collect and analyze the 2D HSQC NMR and 2D HMBC NMR spectra of acid-hydrolyzed lignin powder. If a side chain signal of the S-type Hiberbertone structure is detected in the 2D HSQC NMR spectrum and a benzene ring signal of the S-type Hiberbertone structure is detected in the 2D HMBC NMR spectrum, then the wood to be tested is white oak; otherwise, it is red oak.

[0011] Further, in step S1, the impurity removal step is as follows: the wood is refluxed and extracted using a benzene-ethanol mixed solution, followed by ultrasonic dispersion treatment for 1 hour, and the resulting extract is filtered and dried.

[0012] Further, in step S1, the volume ratio of benzene to ethanol in the benzene-ethanol mixed solution is 2:1.

[0013] Furthermore, in step S1, the reflux extraction time is 8 to 12 hours.

[0014] Furthermore, in step S1, the pulverized powder is sieved using a 200-mesh sieve.

[0015] Furthermore, in step S2, the temperature inside the hydrothermal reactor is 80–120°C, and the pressure is 0.01–0.05 MPa.

[0016] Further, in step S3, the specific steps for extracting acid-hydrolyzed lignin are as follows: filter the hydrolysate obtained in step S2, wash the filtrate with γ-valerol solution and dilute it with deionized water, then let it stand to obtain lignin precipitate; centrifuge the obtained lignin precipitate, wash it, and dry it to obtain acid-hydrolyzed lignin powder.

[0017] Furthermore, in step S3, the settling time is not less than 10 hours.

[0018] Furthermore, in step S3, the specific process parameters for centrifugation are: rotation speed: 3500 rpm; centrifugation time: 4 min.

[0019] Furthermore, in step S3, a freeze dryer is used for drying.

[0020] The method for distinguishing between white oak and red oak described in this invention is based on the distinguishing characteristic that the hydroxyl groups on the glycosyl carbon chain of white oak lignin do not break during acid hydrolysis, while the hydroxyl groups on the glycosyl carbon chain of red oak lignin break into hydroxyl radicals during acid hydrolysis. The generated hydroxyl radicals are used to hinder the breaking of the β-O-4 bond in the red oak lignin molecular structure, ultimately causing red oak lignin to form only ester or aldehyde groups during acid hydrolysis. In contrast, the β-O-4 bond in the white oak lignin molecular structure breaks smoothly during acid hydrolysis due to the absence of hydroxyl radicals, ultimately revealing an S-type Hibbbert ketone structure. By detecting the presence of the S-type Hibbbert ketone structure in the acid-hydrolyzed lignin, it can be determined whether the wood is white oak or red oak.

[0021] The S-type Hiberbert ketone structure comprises a benzene ring and a side chain with a ketone structure, and its specific molecular structure is as follows:

[0022]

[0023] The beneficial effects of this invention are as follows:

[0024] 1. This invention determines whether a piece of wood is white oak or red oak by detecting the presence of an S-type Hibbert ketone structure in the molecular structure of lignin after acid hydrolysis. This identification method in the field of molecular structure not only avoids the influence of abnormal oak color on the accuracy of the identification results, effectively improving the efficiency and accuracy of white oak and red oak identification, but also can be applied to processed or dyed red oak and white oak, and has good universality.

[0025] 2. This invention utilizes the organic solvent γ-valerol under acidic conditions to separate and dissolve high-quality lignin in the cell wall matrix of hardwood by retaining more β-ether and aliphatic units. Compared with traditional wood grinding and enzymatic hydrolysis methods, this method shortens the extraction time, simplifies the process, and can extract more complete lignin fragments, ensuring the accuracy of subsequent detection. Attached Figure Description

[0026] Figure 1 The image shows the 2D HSQC NMR spectrum of acid-hydrolyzed white oak lignin collected in an embodiment of the present invention.

[0027] Figure 2 The image shows the 2D HSQC NMR spectrum of acid-hydrolyzed red oak lignin collected in an embodiment of the present invention.

[0028] Figure 3 This is the 2D HMBC NMR spectrum of acid-hydrolyzed white oak lignin collected in an embodiment of the present invention;

[0029] Figure 4This is the 2D HMBC NMR spectrum of acid-hydrolyzed red oak lignin collected in an embodiment of the present invention;

[0030] Figure 5 The above are FTIR comparison spectra of acid-hydrolyzed lignin (white oak and red oak) collected in the embodiments of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0032] The principle of the identification method described in this embodiment is based on the distinguishing characteristic that the hydroxyl groups on the glycosyl carbon chain of white oak lignin do not break during acid hydrolysis, while the hydroxyl groups on the glycosyl carbon chain of red oak lignin break into hydroxyl radicals during acid hydrolysis. The generated hydroxyl radicals are used to hinder the breaking of the β-O-4 bond in the red oak lignin molecule, ultimately causing red oak lignin to form only ester or aldehyde groups during acid hydrolysis, while the β-O-4 bond in the white oak lignin molecule breaks smoothly without the hindrance of hydroxyl radicals, ultimately revealing the S-type Hiberbertone structure. This embodiment uses 2DHSQC NMR spectroscopy to detect the C-type Hiberbertone structure. α -H and C γ The -H side chain signal was detected by using 2DHMBC NMR spectrum to detect the CH signal of the benzene ring in the S-type Hiberbertone structure. The combination of these two methods was used to determine the presence or absence of the S-type Hiberbertone structure and to determine whether the wood was white oak or red oak.

[0033] Based on the above principles, the method for distinguishing between white oak and red oak described in this embodiment includes the following steps:

[0034] S1: A certain amount of white oak wood was taken and refluxed for 12 hours using a benzene-ethanol mixed solution, wherein the volume ratio of benzene to ethanol in the benzene-ethanol mixed solution was 2:1. Then, ultrasonic dispersion was performed for 1 hour to remove unwanted compounds, such as extracts and inorganic impurities. The resulting extract was then filtered, dried, pulverized, and passed through a 200-mesh sieve to obtain white oak wood powder.

[0035] S2: White oak wood powder, γ-valerol, deionized water and sulfuric acid are prepared in a mass ratio of 1:10:1:0.1, and then added to 500ml of hydrothermal reactor for acid hydrolysis reaction for 3h. After cooling, hydrolysate is obtained. The temperature in the hydrothermal reactor is set to 95℃ and the pressure is set to 0.02MPa.

[0036] S3: Filter the hydrolysate obtained in step S2, wash the filtrate with 50 ml of γ-valerol solution, and dilute with deionized water. The volume ratio of the washed filtrate to deionized water is 1:9. Let it stand for 12 hours to obtain a lignin precipitate. Centrifuge the obtained lignin precipitate at 3500 rpm for 4 minutes and wash it three times with deionized water. Finally, dry it in a freeze dryer for a period of time to obtain acid-hydrolyzed white oak lignin powder.

[0037] S4: Collect 2D HSQC NMR and 2D HMBC NMR spectra of acid-hydrolyzed white oak lignin powder.

[0038] The 2D HSQC NMR spectrum was obtained as follows: acid-hydrolyzed white oak lignin powder was transferred to a nuclear magnetic resonance quartz sample tube, and dimethyl sulfoxide (DMSO) NMR solvent was added until the acid-hydrolyzed white oak lignin powder was completely dissolved in the solvent system. The instrument conditions for the 2D HSQC NMR spectroscopy were as follows: all samples were analyzed at 295 K using a Bruker superconducting NMR spectrometer, with the following parameters: data acquisition pulse sequence: hsqcedetgpsisp2.3; spectral width (7142.9 Hz, 30120.5 Hz); number of scans: 96; and scan delay: 1.5 s. The 2D HSQC NMR spectrum of the acid-hydrolyzed white oak lignin powder was then obtained.

[0039] The 2D HMBC NMR spectrum was obtained as follows: acid-hydrolyzed white oak lignin powder was transferred to an NMR quartz sample tube, and dimethyl sulfoxide (DMSO) NMR solvent was added until the acid-hydrolyzed white oak lignin powder was completely dissolved in the solvent system. The instrument conditions for the 2D HMBC NMR spectroscopy were as follows: all samples were analyzed at 295 K using a Bruker superconducting NMR spectrometer, with the following parameters: data acquisition pulse sequence: hmbcgpndqf; spectral width: (7142.9 Hz, 36231.9 Hz); number of scans: 60; scan delay: 1.5 s. The 2D HMBC NMR spectrum of the acid-hydrolyzed white oak lignin powder was then obtained.

[0040] To verify the feasibility of the identification method described in this invention, this embodiment also weighed a certain amount of red oak wood, prepared acid-hydrolyzed red oak lignin powder according to the above steps, and collected the 2D HSQC NMR and 2DHMBC NMR spectra of the acid-hydrolyzed red oak lignin powder.

[0041] Figure 1 The above is the 2D HSQC NMR spectrum of acid-hydrolyzed white oak lignin collected in this embodiment. Figure 1 The qualitative assignments of the positions of the glycosyl carbon chain structure X33 and the S-type lignin-bound Hibbertone unit HK in the lignin structure are listed in Table 1.

[0042] Table 1

[0043]

[0044] like Figure 1 As shown, the molecular structure of acid-hydrolyzed white oak lignin exhibits C0. α -H and C γ -H side chain signal confirms the C-H side chain of the S-type Hibernate structure. α -H and C γ The presence of the -H sidechain.

[0045] Figure 2 This is the 2D HSQC NMR spectrum of acid-hydrolyzed red oak lignin collected in this embodiment. As can be seen from the figure, C20 is not observed in the molecular structure of acid-hydrolyzed red oak lignin. α -H and C γ The -H signal is because the β-O-4 bond in the original red oak lignin molecule structure is not broken, and the S-type Hiberbertone structure is not present in the acid-hydrolyzed red oak lignin molecule structure, so the side chain signal in the S-type Hiberbertone structure cannot be detected.

[0046] Figure 3 The figure shows the 2D HMBC NMR spectrum of acid-hydrolyzed white oak lignin collected in this embodiment. CH signals belonging to the benzene ring in the S-type Hiberbertone structure were detected at positions S1 (δC / δH 128.4 / 3.65), S2 / 6 (δC / δH 106.2 / 7.23 and 7.07), S3 / 5 (δC / δH 139.9 / 3.58), and Sβ (δC / δH 208.6 / 3.67), confirming the presence of the benzene ring in the S-type Hiberbertone structure. This is consistent with the presence of C in the 2D HSQC NMR spectrum. α -H and C γ The -H side chain signal confirmed the existence of the S-type Hibbertone structure in the acid-hydrolyzed white oak lignin molecule.

[0047] Figure 4 The image shows the 2D HMBC NMR spectrum of acid-hydrolyzed red oak lignin collected in this embodiment. No CH signal of the benzene ring in the S-type Hiberbertone structure was detected in the acid-hydrolyzed red oak lignin, further confirming that the S-type Hiberbertone unit does not exist in the molecular structure of acid-hydrolyzed red oak lignin.

[0048] To verify the accuracy of the identification method described in this invention, FTIR comparison spectra of acid-hydrolyzed white oak lignin powder and acid-hydrolyzed red oak lignin powder were also collected. The results are as follows: Figure 5 As shown in the figure, the location of C=O in acid-hydrolyzed white oak lignin is 1724 cm⁻¹. -1This indicates that the peak at this location belongs to the Hiberbert ketone functional group. The C=O of the acid-hydrolyzed red oak lignin appears at 1740 cm⁻¹. -1 and 1765cm -1 The presence of aldehyde or ester groups indicates that the peak values ​​are consistent with both, further demonstrating that the identification method described in this embodiment is reliable in practice.

[0049] In summary, the identification method described in this embodiment belongs to the field of molecular structure identification. It not only improves the efficiency and accuracy of identifying white oak and red oak, but also can be applied to processed or dyed red oak and white oak, and has good universality.

[0050] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for distinguishing between white oak and red oak, characterized in that, Includes the following steps: S1: Take the wood to be tested, remove impurities, crush it, and sieve it to obtain wood powder; S2: Wood flour, γ-valerolactone, deionized water and sulfuric acid are mixed in a mass ratio of 1:10:1:0.1, and then added to a hydrothermal reactor for acid hydrolysis reaction for 1 to 5 hours. After cooling, hydrolysate is obtained. S3: Extract acid-hydrolyzed lignin from the hydrolysate and dry it to obtain acid-hydrolyzed lignin powder; S4: Collect and analyze the 2D HSQC NMR and 2D HMBC NMR spectra of acid-hydrolyzed lignin powder. If a side chain signal of the S-type Hiberbertone structure is detected in the 2D HSQC NMR spectrum and a benzene ring signal of the S-type Hiberbertone structure is detected in the 2D HMBC NMR spectrum, then the wood to be tested is white oak; otherwise, it is red oak.

2. The method according to claim 1, characterized in that, In step S1, the impurity removal step is as follows: the wood is refluxed and extracted using a benzene-ethanol mixed solution, followed by ultrasonic dispersion treatment for 1 hour, and the resulting extract is filtered and dried.

3. The method according to claim 2, characterized in that, In step S1, the volume ratio of benzene to ethanol in the benzene-ethanol mixed solution is 2:

1.

4. The method according to claim 2, characterized in that, In step S1, the reflux extraction time is 8 to 12 hours.

5. The method according to claim 1, characterized in that, In step S1, the pulverized powder is sieved using a 200-mesh sieve.

6. The method according to claim 1, characterized in that, In step S2, the temperature inside the hydrothermal reactor is 80–120°C and the pressure is 0.01–0.05 MPa.

7. The method according to claim 1, characterized in that, In step S3, the specific steps for extracting acid-hydrolyzed lignin are as follows: filter the hydrolysate obtained in step S2, wash the filtrate with γ-valerol solution and dilute it with deionized water, then let it stand to obtain lignin precipitate; centrifuge the obtained lignin precipitate, wash it, and dry it to obtain acid-hydrolyzed lignin powder.

8. The method according to claim 7, characterized in that, In step S3, the settling time shall not be less than 10 hours.

9. The method according to claim 7, characterized in that, In step S3, the specific process parameters for centrifugation are: rotation speed: 3500 rpm; centrifugation time: 4 min.

10. The method according to claim 1, characterized in that, In step S3, a freeze dryer is used for drying.

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