CN108051389B - Method for quantitatively determining content of lignin in wood fiber without separation - Google Patents
Method for quantitatively determining content of lignin in wood fiber without separation Download PDFInfo
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
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Abstract
The invention discloses a method for quantitatively determining the content of lignin in wood fiber, which comprises the following steps: crushing a series of wood fiber samples with different lignin contents, and removing extracts; performing ball milling treatment on the obtained sample; weighing the obtained sample, and placing the sample in a LiCl/DMSO solvent system for dissolving; diluting the solution, and controlling the ultraviolet absorbance value of the diluted solution to be 0.2-0.8; and establishing a standard curve of the ultraviolet absorbance value and the lignin concentration. And (4) measuring the ultraviolet absorbance value of the sample solution to be measured, and calculating the content of lignin according to the standard curve. The invention firstly provides mechanical force action combined with LiCl/DMSO solvent dissolution, and under the condition of not carrying out lignin extraction and chemical treatment, the ultraviolet colorimetric method is used for measuring the lignin content, so that the method can be suitable for directly measuring the lignin content of different raw materials, the result is close to that of the method for measuring the lignin by using a TAPPI method, the structure of the lignin is not changed, the method is simple and convenient, and the accuracy and the sensitivity are high.
Description
Technical Field
The invention relates to component analysis of wood fibers, in particular to a method for quantitatively determining the content of lignin in wood fibers.
Background
Lignin is one of three major components of plant cell walls, and accounts for about 20-30% of the chemical composition of plant cell walls. The lignin is of various types, and can be divided into coniferous wood, broad leaf wood and gramineous lignin according to plant species; the basic structural units can be divided into guaiacyl lignin (G), syringyl lignin (S) and p-hydroxyphenyl lignin (H); according to different separation methods, lignin sulfonate, Kraft lignin (Kraft lignin), Soda lignin (Soda lignin) and the like can be further classified. The lignin has a complex structure, and the natural lignin is rich in aromatic rings, is a three-dimensional net-shaped natural polymer, and is filled between microfibrils formed by cellulose macromolecules together with hemicellulose. The complex chemical structure and special physicochemical properties of lignin determine the detection difficulty of the lignin, and in the aspects of separation, modification and related application of lignocellulose, lignocellulose treated by different methods has different physicochemical properties, so that the development of a new simple, convenient, accurate and high-sensitivity method has very important significance on the basis of fully mastering the existing lignin detection method and mechanism.
The methods commonly used at present for detecting lignin comprise a Klason method, an acetyl bromide-UV method, a high performance liquid chromatography method, a turbidity method, a redox method, an ammonolysis method, a non-aqueous conductive titration method and other methods for calculating characteristic functional group quantification by utilizing infrared spectroscopy, nuclear magnetic resonance spectroscopy and the like. Although many methods for quantitatively detecting lignin are available, the sensitivity and the accuracy range of the method are limited, for example, the Klason method has large error in measuring samples with small lignin content; the acetyl bromide-UV method needs to chemically modify lignin, the acetylation effect is influenced by various factors, and meanwhile, the method is difficult to select a proper standard substance; liquid lignin can be detected by adopting a nuclear magnetic resonance technology, but a solvent capable of fully dissolving the lignin is not found at present. Thus, quantitative determination of lignin still presents various difficulties.
Lignin molecules have aromatic ring structures and conjugated carbonyl groups, and have strong absorption to ultraviolet light under certain wavelength, so that UV method quantitative analysis of lignin has been studied for a long time. However, the UV analysis must be usually carried out in solution, and the lignocellulosic tissue is dense and complex and difficult to dissolve in common solvents without structural changes.
Disclosure of Invention
The purpose of the invention is as follows: in order to solve the problem that the existing lignin content measuring method is inaccurate in lignin content measurement due to the problems of low sensitivity, large error when the lignin content is low, difficulty in dissolving the lignin, easiness in changing the structure in a solvent and the like, the invention provides a method for quantitatively measuring the lignin content in wood fibers by using an ultraviolet colorimetric method under the condition of not extracting the lignin and carrying out chemical treatment by combining the mechanical force action with LiCl/DMSO solvent to dissolve the lignin.
The technical scheme is as follows: the invention discloses a method for quantitatively determining the content of lignin in wood fiber, which comprises the following steps:
(1) pretreating a series of wood fibers with different lignin contents;
(2) ball-milling the sample obtained in the step (1) by using a ball mill, and drying in vacuum;
(3) weighing the sample obtained in the step (2), and placing the sample in a LiCl/DMSO solvent system for dissolving to obtain a completely dissolved material solution;
(4) diluting the sample solution obtained in the step (3) to ensure that the ultraviolet absorbance value of the diluted sample solution under a certain wavelength is 0.2-0.8; fitting a standard curve by using the ultraviolet absorbance value and the lignin concentration according to the Laggelber's law;
(5) and (3) processing the wood fiber to be detected according to the steps (1) to (3) to obtain a completely dissolved sample solution to be detected, diluting the sample solution to be detected to enable the ultraviolet absorbance value to be 0.2-0.8, and substituting the ultraviolet absorbance value into the standard curve in the step (4) to calculate the content of lignin.
The wood fiber in the step (1) is wheat straw fiber, poplar fiber, eucalyptus bark fiber or yew bark fiber, and the wood fiber can be wood fiber raw material which is not chemically treated or material obtained by treating the wood fiber raw material by a chemical method.
The wood fiber with different lignin contents in the step (1) is one of the following four conditions:
i comprises a series of wood fibers with different lignin contents obtained by processing wood fiber raw materials by a chemical method;
II comprises a series of wood fibers with different lignin contents obtained by chemically treating the wood fiber raw material, and wood fiber raw material which is not chemically treated; the lignin content of the wood fiber raw material which is not treated by the chemical method is high, the lignin content is reduced after the wood fiber raw material is treated by the chemical method, and the wood fiber raw material which is not treated by the chemical method can be used for fitting points with high lignin concentration in a standard curve.
III comprises a series of wood fibers with different lignin contents obtained by treating wood fiber raw materials by a chemical method and wood fibers obtained by oxygen delignification treatment after chemical treatment; the lignin content in the wood fiber after oxygen delignification is extremely low, and the method can be used for fitting points with low lignin concentration in a standard curve.
IV includes a series of lignins of different lignin content obtained by chemical treatment of lignocellulosic feedstocks, and lignocellulosic feedstocks that have not been chemically treated, and lignocellulosic feedstocks that have been chemically treated followed by oxygen delignification.
The chemical method is NaOH pulping method, NaOH-anthraquinone pulping method, NaOH-Na2The method comprises the following steps of S pulping, alkaline sulfite pulping and formic acid-acetic acid pulping, wherein the same chemical method is used for treating the wood fiber raw material to obtain wood fibers with different lignin contents by adjusting treatment parameters. NaOH pulping method, NaOH-anthraquinone pulping method, NaOH-Na2S-pulping, alkaline sulfite or formic-acetic acid pulping, oxygen delignification are techniques well known to those skilled in the art.
In the step (1), a series of wood fibers with different lignin contents obtained by treating wood fiber raw materials by a chemical method and wood fibers obtained by oxygen delignification treatment after chemical treatment are pretreated according to the following method: crushing and sieving, wherein the sieving is to sieve through a 40-60-mesh sieve; the non-chemically treated lignocellulosic feedstock is pretreated as follows: crushing, sieving, extracting with benzene alcohol and hot water, and air drying; the conditions for extracting the benzene alcohol are as follows: condensing and refluxing a benzene-alcohol mixed solution with a volume ratio of 2:1 under boiling for extraction for 6-24 hours, wherein the hot water extraction condition is that hot water extraction is carried out for 4 hours at 95 ℃, and the extraction aims to remove lipid impurities in the raw material and avoid interference on absorption of lignin during ultraviolet measurement.
In the step (2), the ball milling condition is that ball milling is carried out for 2-4 h at room temperature and 400-1000 rpm. Wherein, the ball milling equipment is a micro planetary high-energy ball mill (Pulverisette 7, Germany); the vacuum drying is performed at P2O5Vacuum drying for 12 h. Preferably, the ball milling condition is room temperature, 600rpm ball milling for 3h, and the milling period is stopped for 10min every 5min operation, and the purpose of stopping is to prevent the ball mill from overheating.
In the step (3), the mass fraction of LiCl in the LiCl/DMSO solvent system is 6-10%. Preferably, the LiCl is 8% by mass, and the LiCl/DMSO solvent system with the mass fraction of 8% is prepared according to the following steps: drying anhydrous lithium chloride (LiCl) in an oven at 105 ℃ for 3-5 days until the LiCl is completely dried, firing a 4A molecular sieve (sodium-A type) in a muffle furnace at 300 ℃ for 4h, adding dimethyl sulfoxide (DMSO) into the fired molecular sieve, drying for 3-5 days, dissolving 8g of the completely dried LiCl in 92g of DMSO dried by the molecular sieve, stirring until the completely dissolved solution is obtained, and sealing and storing after obtaining a LiCl/DMSO solvent system with the mass fraction of 8%.
When a series of wood fibers with different lignin contents are the condition I or the condition III, stirring for 18-36 h at 600-1000 rpm at room temperature under the dissolving condition in the step (3), and continuously heating to 40-75 ℃ and stirring for 1-3 h.
When a series of wood fibers with different lignin contents are the condition II and the wood fibers are wheat straw fibers, a series of wheat straw fibers with different lignin contents obtained by processing a wheat straw raw material by a chemical method are stirred for 18-36 hours at room temperature and 600-1000 rpm in the dissolving condition in the step (3), and are continuously heated to 40-75 ℃ and stirred for 1-3 hours; the dissolving condition of the wheat straw raw material which is not chemically treated in the step (3) is that the wheat straw raw material is stirred for 18-36 hours at room temperature and 600-1000 rpm;
when a series of wood fibers with different lignin contents are the condition II and the wood fibers are poplar fibers, eucalyptus fibers or taxus chinensis bark fibers, a series of wood fibers with different lignin contents obtained by treating wood fiber raw materials by a chemical method and wood fiber raw materials which are not treated by the chemical method are stirred for 18-36 hours at room temperature and 600-1000 rpm in the dissolving condition in the step (3), and are continuously heated to 40-75 ℃ and stirred for 1-3 hours.
When a series of wood fibers with different lignin contents are the condition IV and the wood fibers are wheat straw fibers, a series of wheat straw fibers with different lignin contents obtained by processing a wheat straw raw material by a chemical method and wheat straw fibers obtained by oxygen delignification treatment after chemical treatment are stirred for 18-36 hours at room temperature and 600-1000 rpm in the dissolving condition in the step (3), and are continuously heated to 40-75 ℃ and stirred for 1-3 hours; the dissolving condition of the wheat straw raw material which is not chemically treated in the step (3) is that the wheat straw raw material is stirred for 18-36 hours at room temperature and 600-1000 rpm;
when a series of wood fibers with different lignin contents are the condition IV and the wood fibers are poplar fibers, eucalyptus bark fibers or taxus chinensis bark fibers, a series of wood fibers with different lignin contents obtained by treating a wood fiber raw material by a chemical method, a wood fiber raw material which is not treated by the chemical method, and wood fibers which are treated by oxygen delignification after the chemical treatment are stirred for 18-36 hours at room temperature and 600-1000 rpm, and are continuously heated to 40-75 ℃ and stirred for 1-3 hours.
The completely dissolved material solution in step (3) is characterized as follows: and (3) taking a LiCl/DMSO solvent system as a control, respectively measuring the turbidity values of the material solution obtained in the step (3) and the control by using a turbidity meter, and determining that the material is completely dissolved when the difference between the turbidity values of the material solution and the control is +/-0.1-0.3. Preferably, 0.1g of the ball-milled material (to the nearest 0.0002g) is accurately weighed out and completely dissolved in 20.0mL of a screw-top glass vial containing 8% LiCl/DMSO by mass fraction, i.e., the ball-milled sample has a concentration of 5g/L (0.5%).
The solvent system used in the dilution in the step (4) is the same as that used in the dissolution of the material in the step (3); the fitting method of the standard curve comprises the following steps: (1) when a standard curve of a series of LiCl/DMSO total-soluble systems of the wood fibers with different lignin contents, which are obtained by processing the wood fiber raw material by a specific chemical method, is fitted, the wood fibers with different lignin contents are obtained by adjusting processing parameters of the wood fiber raw material processed by the same chemical method, the material solutions with different concentrations obtained in the step (3) are further diluted to enable the absorbance value to be 0.2-0.8, and the concentration of the lignin is calculated according to a Langerbil formula; then, a standard curve was fitted with the lignin concentration (g/L) as the abscissa and the absorbance as the ordinate. Preferably, a standard curve can be fitted in combination with using oxygen delignification with low lignin content and/or a chemically untreated lignocellulosic feedstock with high lignin content, with good linear fit characteristics. (2) When a standard curve of a LiCl/DMSO total-soluble system of a wood fiber raw material which is not chemically treated is fitted, a plurality of groups of data fitting can be carried out by combining a series of LiCl/DMSO total-soluble systems of wood fibers with different lignin contents, which are obtained by treating the wood fiber raw material by a plurality of chemical methods; preferably, a standard curve can be fitted in combination with using low lignin content oxygen delignification and/or high lignin content lignocellulosic feedstocks, with good linear fit characteristics.
It should be noted that the content of lignin in the wood fiber is not determined in advance by using a TAPPI method in the process of fitting a standard curve; the content of lignin in the wood fiber is unknown, after the completely dissolved material solution is obtained through the steps (1) to (3), the absorbance value is measured at a certain wavelength, and the concentration and the content of the lignin are calculated according to the formula of the Largel law. The main purpose of using the TAPPI method in the present invention is to compare it with the determination method of the present invention, thereby demonstrating the advantages of the method of the present invention.
Wherein, the formula of the Langerbil law is as follows:
A＝ε·c·l
a-absorbance value
l-thickness of the cuvette, cm, typically 1cm
c-Lignin concentration, g/100mL
Epsilon-absorptivity, L/(g cm), absorptivity of wheat straw raw material is 26; the absorption coefficient of poplar is 21; the absorption coefficient of the eucalyptus bark is 22; the absorption coefficient of the bark of the Chinese yew is 23.8.
When the wood fiber in the step (1) is wheat straw fiber, the wavelength in the step (4) is 282 nm; when the wood fiber in the step (1) is poplar fiber, the wavelength in the step (4) is 276 nm; when the wood fiber in the step (1) is eucalyptus bark fiber, the wavelength in the step (4) is 278 nm; when the wood fiber in the step (1) is the bark fiber of the Chinese yew, the wavelength in the step (4) is 280 nm.
According to the Largebi law, the method establishes a standard curve for quantitatively determining the lignin content by the LiCl/DMSO-UV method, wherein the standard curve is suitable for wheat straw raw materials and wheat straw fibers obtained by processing through different chemical methods.
The method is characterized in that the lignin concentration (g/L) is used as the abscissa, the absorbance at 282nm is used as the ordinate, and a series of regression equations and fitting degrees (R) of wheat straw fibers with different lignin contents in a LiCl/DMSO total-dissolution system are obtained after wheat straw raw materials are subjected to various chemical treatments2) The following were used:
NaOH method: 22.139x-0.1028, R2＝0.9904；
NaOH-anthraquinone Process: y 17.948x +0.0767, R2＝0.9965；
NaOH-Na2S method: 20.456x-0.0061, R2＝0.9983；
Sulfite method: y is 18.135x-0.072, R2＝0.9948；
Formic acid-acetic acid method: y-18.465 x-0.0266, R20.9954; the regression equation can be used for quantitative analysis of lignin content with clear sample sources and high requirement on accuracy, and is also suitable for determining the lignin content in the wood fiber raw material without chemical treatment.
Wheat straw raw material: y is 18.599x +0.0056, R20.9342; the regression equation can be used for rapidly measuring the lignin content of the sample with low requirement on the accuracy of the measurement result or uncertain lignin type.
The method for measuring the lignin content is also suitable for poplar, eucalyptus bark, Chinese redwood bark and the like of broad-leaved wood.
Taking lignin concentration (g/L) as abscissa and absorbance at 276nm as ordinate, and subjecting poplar wood to NaOH-Na treatment2Regression equation and fitting degree (R) of a series of poplar fibers with different lignin contents, oxygen delignification and chemically untreated poplar raw materials obtained after chemical treatment by S method in LiCl/DMSO total-solution system2) The following were used:
y＝13.235x+0.0817，R2＝0.9901；
taking lignin concentration (g/L) as abscissa and absorbance at 278nm as ordinate, processing Eucalyptus bark with NaOH-Na2Regression equation and fitting degree (R) of a series of eucalyptus bark fibers with different lignin contents, oxygen delignification and chemically untreated eucalyptus bark raw materials in LiCl/DMSO total-solution system obtained by S method treatment2) The following were used:
y＝14.049x+0.082，R2＝0.9881；
taking lignin concentration (g/L) as abscissa and absorbance at 280nm as ordinate, and subjecting cortex Taxilli to NaOH-Na2S method for processing a series of woodRegression equation and fitting degree (R) of bark fibers of taxus chinensis with different lignin contents in LiCl/DMSO total-solution system2) The following were used:
y＝34.978x+0.0224，R2＝0.9966。
has the advantages that:
(1) the invention firstly proposes that the total amount of lignin in the wood fiber can be directly measured by using an ultraviolet method under the condition of not carrying out lignin extraction and chemical treatment, and a LiCl/DMSO solvent system is used for completely dissolving the wood fiber, and the structure of the lignin is not changed; the method is close to the method for determining lignin by using a TAPPI method, does not change the structure of the lignin, and is simple and convenient, and high in accuracy and sensitivity;
(2) the invention firstly proposes that the dissolution state of the solution is represented by using a turbidimeter method, and compared with the visual observation, the solution can be quantitatively represented and has higher accuracy;
(3) the method is suitable for measuring the wood fiber raw material with high lignin content and the chemically treated wood fiber with low lignin content, the measurement range of the lignin content is 0.3-30 wt%, and the application range is wider. After oxygen delignification, the concentration of lignin is very low, the lignin is difficult to further extract and separate, and the content of acid-soluble lignin in a solution is difficult to accurately determine by using an ultraviolet method in the national standard; in the invention, even if the lignin content in the slurry after oxygen delignification is calculated by using a standard curve and a formula which are fit by a sample with high lignin content, the calculation is consistent with the actual situation, namely after the lignin is dissolved by using a DMSO/LiCl solvent system, the fit standard curve is suitable for quantitatively determining the sample with high content or low content, and the applicability is wide;
(4) the invention has wide application range, is not only suitable for wheat straw raw materials, wheat straw fibers treated by different chemical methods and different treatment degrees, but also suitable for raw materials such as poplar, eucalyptus bark, red cedar bark and the like, and has the fitting degree R of the regression equation2>0.99, the accuracy of the method is high.
Drawings
FIG. 1 is a UV absorption spectrum of untreated wheat straw feedstock in an 8% LiCl/DMSO solvent system;
FIG. 2 shows the UV absorption spectrum of the wheat straw fiber treated by NaOH method in 8% LiCl/DMSO solvent system, wherein 1# to 7# corresponds to 1# to 7# samples of NaOH method in Table 2, and raw corresponds to wheat straw raw material in Table 2 without chemical treatment;
FIG. 3 shows the UV absorption spectra of wheat straw fiber treated by different chemical methods in a solvent system of 8% LiCl/DMSO, wherein AP-AQ is sodium hydroxide-anthraquinone pulping and cooking, and KP is NaOH-Na2S, pulping and cooking, wherein ASP is alkaline sulfite pulping and cooking, and Formacell is formic acid-acetic acid pulping and cooking;
FIG. 4 is the relationship between the UV absorbance and lignin concentration of a series of wheat straw fibers with different lignin contents obtained after different chemical treatments, wherein AP is sodium hydroxide cooking, AP-AQ is sodium hydroxide and anthraquinone cooking, and KP is NaOH-Na2S-method cooking, ASP is alkaline sulfite cooking, and Formacell is formic acid-acetic acid method cooking;
FIG. 5 is a graph showing the relationship between UV absorbance and lignin concentration for a series of wheat straw fibers with different lignin contents obtained after all chemical treatments;
FIG. 6 is a graph of a solution of NaOH-Na2The relation between the ultraviolet absorbance and the lignin concentration of a series of poplar fibers with different lignin contents is obtained by the S method;
FIG. 7 is a graph of a solution of NaOH-Na2The relation between the ultraviolet absorbance and the lignin concentration of a series of eucalyptus bark fibers with different lignin contents obtained by the S method;
FIG. 8 is a graph of a solution of NaOH-Na2The relation between the ultraviolet absorbance and the lignin concentration of a series of Chinese yew bark fibers with different lignin contents obtained by the S method.
Detailed Description
Example 1
1. Pretreatment of raw wheat straw without chemical treatment
Wheat straw (Triticumaestivum. v.yang No.4), from the area of pure of Nanjing, was manually cleaned of impurities, leaves, ears and sheaths; the sample is peeled, washed, sliced and air-dried, then crushed by a miniature plant crusher, screened by a standard inspection sieve to obtain 40-60 meshes, extracted by using benzyl alcohol (2:1, v/v) for 8 hours, then extracted by using hot water at 95 ℃ for 4 hours, and air-dried for later use to obtain degreased sample powder.
2. Preparation of LiCl/DMSO solvent system
Anhydrous lithium chloride (LiCl) (AR, available from Kyoho chemical Co., Ltd.) was oven-dried at 105 ℃ for 3-5 days until completely dried; 4A molecular sieve (Na-A type, chemical reagent of national drug group, Co., Ltd.) is calcined in a muffle furnace at 300 ℃ for 4 h; dimethyl sulfoxide (DMSO) (AR, Nanjing chemical reagent Co., Ltd.), was added to the calcined molecular sieve, and dried for 3-5 days. 8g of absolute dry LiCl is dissolved in 92g of DMSO dried by a molecular sieve, and the mixture is stirred until the mixture is completely dissolved to obtain a LiCl/DMSO solvent system with the Li mass fraction of 8%, and then the LiCl/DMSO solvent system is sealed and stored.
3. Ball mill
A micro planetary high energy ball mill (pulveresette 7, germany) was used. Get P2O54g of degreased sample powder dried in vacuum for 12 hours is placed in a zirconia pot with the capacity of 45ml, 25 zirconia balls with the inner diameter of 1cm are filled in the pot, and the ball milling is carried out for 3 hours at the room temperature and the speed of 600 rpm. During the period, the operation is stopped for 10min every 5min, so that overheating is avoided.
4. Dissolution
P for ball-milling sample2O5Vacuum drying for 12h, accurately weighing 0.1g (accurate to 0.0002g) in a screw-top glass bottle containing 20.0ml of 8% LiCl/DMSO, sealing, and magnetically stirring at normal temperature (25 ℃) for 24h (800rpm) to obtain an 8% LiCl/DMSO total-solution system of wheat straw raw material.
5. Quantitative comparison of dissolution status
The dissolution conditions of the complete dissolution system are qualitatively and quantitatively compared by a definition method, a microscopy method and a turbidimetric method respectively, and the wheat straw raw material is determined to be ball-milled for 3 hours without any chemical treatment, and can be completely dissolved in an 8% LiCl/DMSO solvent system after being stirred for 24 hours at the rotating speed of 800rmp under the conditions of 0.5% concentration and normal temperature stirring. At this time, no particulate matter was observed by microscopic observation, and the turbidity of the dissolution system (3.68 to 3.77) obtained by the turbidimetric method was very close to the turbidity of the solvent itself (3.64).
6. Direct determination of lignin content in LiCl/DMSO total-soluble system by UV method
The ultraviolet-visible spectrophotometer model for the experiment was UV757CRT (Shanghai precision scientific instruments, Inc.). Scanning conditions are as follows: the wavelength range is 800-200 nm, the scanning interval is 1nm, the scanning speed is medium speed, the slit width is 1nm, and the measurement mode is to measure the absorbance.
Taking deionized water as a blank control, performing spectral scanning on a LiCl/DMSO solvent system with LiCl mass fractions of 4%, 6% and 8%, a DMSO pure solvent and a LiCl aqueous solution with LiCl mass fraction of 8% within a wavelength range of 200-800 nm, determining a reference solution for UV analysis of a full-solution system, and finally selecting a LiCl/DMSO solvent system with LiCl mass fraction of 8% as the reference solution. Diluting the total-solution sample system by 5-25 times (making the light absorption value in the range of 0.2-0.8), and adjusting the transmittance by using the selected reference solution to obtain the absorption spectrum of the total-solution sample in the wavelength range of 200-800 nm, as shown in figure 1. The LiCl/DMSO solvent system had a distinct absorption peak before 260nm and a large reduction after 260nm, thus determining the characteristic absorption wavelength of the dissolved sample, with the characteristic absorption wavelength of wheat straw being chosen at 282 nm.
The ultraviolet absorption of the wheat straw raw material in a LiCl/DMSO full-solution system is quite stable, and after the LiCl/DMSO full-solution system is placed for 36 hours, the peak pattern and the absorbance of an ultraviolet absorption spectrum of the wheat straw raw material are not changed, so that the wheat straw raw material meets the requirements of chemistry and instrument analysis.
Example 2
The measurement method was the same as in example 1, except that:
in the step 1, wheat straw raw materials are subjected to chemical treatment with different degrees by a NaOH pulping method to obtain wheat straw fibers with different lignin contents, which is shown in 1# to 8# of a NaOH method in a table 1; then crushing by a miniature plant crusher respectively, and screening by a standard inspection sieve to obtain 40-60 meshes.
In the step (6), the content of lignin in the LiCl/DMSO full-solution system is directly measured by using a UV method, and an absorption spectrum chart of the 8% LiCl/DMSO full-solution system of the wheat straw fiber obtained after the treatment by the NaOH method in the wavelength range of 200-800 nm is shown in figure 2, wherein 1# to 7# corresponds to 1# to 7# samples in the NaOH method in table 2, and raw corresponds to wheat straw raw materials in table 2. And respectively diluting the complete solution system to ensure that the ultraviolet absorbance of the diluted solution is 0.2-0.8, and establishing a standard curve for quantitatively determining the lignin content by an LiCl/DMSO-UV method of wheat straw fibers treated by an NaOH method based on the ultraviolet absorbance of the 8% LiCl/DMSO complete solution system and the lignin concentration according to the Largery's law, wherein the standard curve is shown in figure 4.
The method is characterized in that the lignin concentration (g/L) is used as the abscissa, the absorbance at 282nm is used as the ordinate, and the regression equation and the fitting degree (R) of a series of wheat straw fibers with different lignin contents in a LiCl/DMSO total-dissolution system are obtained after a wheat straw raw material is treated by a NaOH method2) The following were used: 22.139x-0.1028, R2＝0.9904。
The TAPPI method, the method of the embodiment and the standard curve are respectively used for measuring the lignin content in the wheat straw fiber chemically treated by the NaOH pulping method to different degrees, the measurement results are shown in the table 1, and the measurement results of the two methods have good parallelism.
Example 3
The method is the same as example 2, except that the wheat straw raw material in step (1) is chemically treated by NaOH-anthraquinone pulping method in different degrees, as shown in 1# to 3# in NaOH-AQ method in Table 1. The absorption spectrum of the 8% LiCl/DMSO full-solution system of the wheat straw fiber obtained after the treatment of the NaOH-anthraquinone pulping method in the wavelength range of 200-800 nm is shown in figure 3. Based on the Largebi's law, a standard curve for the LiCl/DMSO-UV method quantitative determination of the lignin content of wheat straw fibers treated by the NaOH-anthraquinone method is established, and the standard curve is shown in figure 4.
The method is characterized in that the lignin concentration (g/L) is used as the abscissa, the absorbance at 282nm is used as the ordinate, and the regression equation and the fitting degree (R) of a series of wheat straw fibers with different lignin contents in a LiCl/DMSO total-solution system are obtained after chemical treatment of a wheat straw raw material by a NaOH-anthraquinone method2) The following were used: y 17.948x +0.0767, R2＝0.9965。
The TAPPI method, the method of the embodiment and the standard curve are respectively used for measuring the lignin content in the wheat straw fiber chemically treated by the NaOH-anthraquinone pulping method to different degrees, the measurement results are shown in the table 1, and the measurement results of the two methods have good parallelism.
Example 4
The method is the same as example 2, except that the wheat straw raw material in the step (1) is processed by NaOH-Na2S pulping process, NaOH-Na in Table 121# to 3# in the S method. NaOH-Na2The absorption spectrum of the 8% LiCl/DMSO total solution system of the wheat straw fiber obtained after the S method treatment in the wavelength range of 200-800 nm is shown in figure 3. Based on the Lagger's law, the method establishes the method suitable for being used by NaOH-Na2A standard curve for the quantitative determination of lignin content by LiCl/DMSO-UV method for S-treated wheat straw fiber is shown in FIG. 4.
Taking lignin concentration (g/L) as abscissa and absorbance at 282nm as ordinate, and treating with NaOH-Na2Regression equation and fitting degree (R) of a series of wheat straw fibers with different lignin contents obtained after chemical treatment by S method in LiCl/DMSO total-solution system2) The following were used: 20.456x-0.0061, R2＝0.9983。
NaOH-Na determination Using the TAPPI method and the method and calibration Curve of this example, respectively2The lignin content in the wheat straw fiber chemically treated by the S pulping method in different degrees is shown in the table 1, and the measurement results of the two methods have good parallelism.
Example 5
The method is the same as example 2, except that the wheat straw raw material in step (1) is chemically treated by alkaline sulfite method in different degrees, which is shown in table 1 as No. 1-No. 3 in the alkaline sulfite method. The absorption spectrum of the wheat straw fiber 8% LiCl/DMSO full-solution system obtained after the treatment by the alkaline sulfite method in the wavelength range of 200-800 nm is shown in figure 3. Based on the Largebi's law, a standard curve for the quantitative determination of lignin by LiCl/DMSO-UV method for wheat straw fiber treated by alkaline sulfite method was established, and is shown in FIG. 4.
The method is characterized in that the lignin concentration (g/L) is used as the abscissa, the absorbance at 282nm is used as the ordinate, and the regression equation and the fitting degree (R) of a series of wheat straw fibers with different lignin contents in a LiCl/DMSO total-solution system are obtained after wheat straw raw materials are chemically treated by an alkaline sulfite method2) The following were used: y is 18.135x-0.072, R2＝0.9948。
The TAPPI method, the method of the example and the standard curve are respectively used for measuring the lignin content in the wheat straw fiber chemically treated by the alkaline sulfite pulping method to different degrees, the measurement results are shown in the table 1, and the measurement results of the two methods have good parallelism.
Example 6
The method is the same as example 2, except that the wheat straw in step (1) is chemically treated by formic acid-acetic acid mixed organic solvent pulping method to different extent, as shown in table 1 in 1# 1-3 # of formic acid-acetic acid mixed organic solvent pulping method. The absorption spectrum of the 8% LiCl/DMSO full-solution system of the wheat straw fiber obtained after the treatment by the formic acid-acetic acid mixed organic solvent method in the wavelength range of 200-800 nm is shown in figure 3. Based on the Largebi's law, a standard curve for the quantitative determination of lignin by LiCl/DMSO-UV method for wheat straw fiber treated by formic acid-acetic acid method was established, and is shown in FIG. 4.
The method is characterized in that the lignin concentration (g/L) is used as the abscissa, the absorbance at 282nm is used as the ordinate, and the regression equation and the fitting degree (R) of a series of wheat straw fibers with different lignin contents in a LiCl/DMSO total-solution system are obtained after chemical treatment of wheat straw raw materials by a formic acid-acetic acid method2) The following were used: y-18.465 x-0.0266, R2＝0.9954。
The TAPPI method, the method of the embodiment and the standard curve are respectively used for measuring the lignin content in the wheat straw fiber chemically treated by the formic acid-acetic acid mixed organic solvent pulping method to different degrees, the measurement results are shown in the table 1, and the measurement results of the two methods have good parallelism.
TABLE 1 wheat straw raw material and wheat straw fiber treated with different chemicals
a, b lignin content is based on the sample; total lignin content ═ Klason lignin content + acid soluble lignin content in TAPPI process
Example 7
The ultraviolet absorbance and the lignin concentration based on the 8% LiCl/DMSO total-soluble system follow the Largebil law, and a standard curve for quantitatively determining the lignin content by the LiCl/DMSO-UV method applicable to wheat straw raw materials is established, and is shown in figure 5.
Regression equation and fitting degree (R) of a series of wheat straw fibers with different lignin contents obtained in examples 2-6 in LiCl/DMSO total-soluble system by taking lignin concentration (g/L) as abscissa and absorbance at 282nm as ordinate2) The following were used: y is 18.599x +0.0056, R2＝0.9342。
The lignin content of the wheat straw raw material was determined by TAPPI method and the standard curve of example 4, and the determination was repeated 6 times, and calculated by LiCl/DMSO-UV method using NaOH-Na2Standard curve of S method (y-20.456 x-0.0061, R)20.9983) and the results are shown in table 2. The measurement result of the LiCl/DMSO-UV method is very similar to that of the TAPPI method, and the measurement results of the two methods have good parallelism. The standard deviation and RSD value of the LiCl/DMSO-UV method are slightly lower than those of the TAPPI method, which shows that the LiCl/DMSO-UV method has the advantages of high accuracy and good repeatability in the determination of the lignin content.
TABLE 2TAPPI method and LiCl/DMSO-UV method
Example 8
The procedure is as in example 4, except that: (1) the raw material is poplar wood which is processed by NaOH-Na2S pulping, performing chemical treatment to different degrees to respectively obtain series poplar fibers with the total lignin contents of 2.67 wt.%, 6.50 wt.%, 9.82 wt.%, 15.67 wt.%, 21.34 wt.%, 26.28 wt.% and 25.24 wt.%; further oxygen delignification treatment resulted in low content poplar fiber with lignin content of 1.18 wt.% and 1.31 wt.%. Based on the Lagger's law, the method establishes the method suitable for being used by NaOH-Na2A standard curve for quantitative determination of lignin content by LiCl/DMSO-UV method of S method treated poplar fiber is shown in figure 6.
The absorbance at 276nm on the abscissa of the concentration (g/L) of ligninAs ordinate, over NaOH-Na2Regression equation and fitting degree (R) of a series of poplar fibers with different lignin contents obtained after chemical treatment by S method in LiCl/DMSO (LiCl/DMSO) total-solution system2) The following were used: 13.235x +0.0817, R2＝0.9901。
Example 9
The procedure is as in example 4, except that: (1) the raw material is eucalyptus bark processed by NaOH-Na2Chemical treatment is carried out to different degrees by an S pulping method, and series eucalyptus bark fibers with the total lignin content of 11.04 wt.%, 5.18 wt.%, 8.20 wt.%, 13.27 wt.%, 17.47 wt.% and 20.65 wt.% are obtained respectively; further oxygen delignification treatment resulted in eucalyptus bark fibers with lignin contents of 1.54 wt.% and 2.44 wt.%, respectively. Based on the Lagger's law, the method establishes the method suitable for being used by NaOH-Na2A standard curve for the quantitative determination of lignin content by LiCl/DMSO-UV method for eucalyptus bark fibers treated by the S method is shown in FIG. 7.
Using lignin concentration (g/L) as abscissa and absorbance at 278nm as ordinate, and passing through NaOH-Na2Regression equation and fitting degree (R) of a series of eucalyptus bark fibers with different lignin contents obtained after chemical treatment by S method in LiCl/DMSO total-solution system2) The following were used: 14.049x +0.082, R2＝0.9881。
Example 10
The procedure is as in example 4, except that: (1) the raw material is North American yew bark processed with NaOH-Na2The S pulping method is used for chemical treatment to different degrees, and series of Chinese redwood bark samples with total lignin contents of 29.11 wt.%, 32.64 wt.%, 41.52 wt.% and 46.75 wt.% are obtained. Based on the Lagger's law, the method establishes the method suitable for being used by NaOH-Na2The standard curve of the lignin content of the S-method treated Chinese yew bark fiber is quantitatively determined by the LiCl/DMSO-UV method, and is shown in figure 8.
Taking lignin concentration (g/L) as abscissa and absorbance at 280nm as ordinate, and treating with NaOH-Na2Regression equation and fitting degree (R) of a series of Chinese yew bark fibers with different lignin contents obtained after chemical treatment by S method in LiCl/DMSO total-soluble system2) The following were used: y 34.978x +0.0224, R2＝0.9966。
Claims (10)
1. A method for quantitatively determining the content of lignin in wood fiber is characterized by comprising the following steps:
(1) pretreating a series of wood fibers with different lignin contents;
(2) performing ball milling treatment on the sample obtained in the step (1) by using a ball mill, and performing vacuum drying;
(3) weighing the sample obtained in the step (2), and putting the sample into a LiCl/DMSO solvent system for dissolving to obtain a completely dissolved sample solution;
(4) diluting the sample solution obtained in the step (3), and controlling the ultraviolet absorbance value of the diluted sample solution at a certain wavelength to be 0.2-0.8; establishing a standard curve of the ultraviolet absorbance value and the lignin concentration according to the Langerbil law;
(5) and (3) processing the wood fiber to be detected according to the steps (1) to (3) to obtain a completely dissolved sample solution to be detected, diluting the sample solution to be detected to enable the ultraviolet absorbance value to be 0.2-0.8, substituting the ultraviolet absorbance value into the standard curve in the step (4), and calculating the content of lignin.
2. The method of claim 1, wherein the wood fiber in step (1) is wheat straw fiber, poplar fiber, eucalyptus fiber or redwood bark, and the series of wood fibers with different lignin contents in step (1) is one of the following four conditions:
i comprises a series of wood fibers with different lignin contents obtained by processing wood fiber raw materials by a chemical method;
II comprises a series of wood fibers with different lignin contents obtained by chemically treating the wood fiber raw material, and wood fiber raw material which is not chemically treated;
III comprises a series of wood fibers with different lignin contents obtained by treating wood fiber raw materials by a chemical method and wood fibers obtained by oxygen delignification treatment after chemical treatment;
IV includes a series of lignins of different lignin content obtained by chemical treatment of lignocellulosic feedstocks, and lignocellulosic feedstocks that have not been chemically treated, and lignocellulosic feedstocks that have been chemically treated followed by oxygen delignification.
3. The method of claim 2, wherein the chemical process is NaOH-pulping, NaOH-anthraquinone-pulping, NaOH-Na2The method comprises the following steps of S pulping, alkaline sulfite pulping and formic acid-acetic acid pulping, wherein the same chemical method is used for treating the wood fiber raw material to obtain wood fibers with different lignin contents by adjusting treatment parameters.
4. The method of claim 1, wherein the ball milling conditions in step (2) are room temperature and ball milling at 400-1000 rpm for 2-4 h.
5. The method according to claim 1, wherein the LiCl/DMSO solvent system in the step (3) has a mass fraction of LiCl of 6-10%.
6. The method as claimed in claim 2, wherein when a series of wood fibers with different lignin contents are case I or case III, the dissolving conditions in step (3) are room temperature, 600-1000 rpm stirring for 18-36 h, and heating to 40-75 ℃ and stirring for 1-3 h.
7. The method of claim 2, wherein when a series of wood fibers with different lignin contents are the case II and the wood fibers are wheat straw fibers, the wheat straw fibers with different lignin contents obtained by chemically processing wheat straw raw materials are stirred for 18-36 h at 600-1000 rpm at room temperature in the dissolving condition of step (3), and are continuously heated to 40-75 ℃ and stirred for 1-3 h; the dissolving condition of the wheat straw raw material which is not chemically treated in the step (3) is that the wheat straw raw material is stirred for 18-36 hours at room temperature and 600-1000 rpm;
when a series of wood fibers with different lignin contents are the condition II and the wood fibers are poplar fibers, eucalyptus fibers or taxus chinensis bark fibers, a series of wood fibers with different lignin contents obtained by treating wood fiber raw materials by a chemical method and wood fiber raw materials which are not treated by the chemical method are stirred for 18-36 hours at room temperature and 600-1000 rpm in the dissolving condition in the step (3), and are continuously heated to 40-75 ℃ and stirred for 1-3 hours.
8. The method according to claim 2, wherein when a series of wood fibers with different lignin contents are the condition IV and the wood fibers are wheat straw fibers, the wheat straw fibers with different lignin contents obtained by chemically treating wheat straw raw materials and the wheat straw fibers obtained by chemically treating the wheat straw raw materials and then performing oxygen delignification treatment are stirred for 18-36 hours at room temperature and 600-1000 rpm in the dissolving condition of the step (3), and the temperature is continuously increased to 40-75 ℃ and the stirring is performed for 1-3 hours; the dissolving condition of the wheat straw raw material which is not chemically treated in the step (3) is that the wheat straw raw material is stirred for 18-36 hours at room temperature and 600-1000 rpm;
when a series of wood fibers with different lignin contents are the condition IV and the wood fibers are poplar fibers, eucalyptus bark fibers or taxus chinensis bark fibers, a series of wood fibers with different lignin contents obtained by treating a wood fiber raw material by a chemical method, a wood fiber raw material which is not treated by the chemical method, and wood fibers which are treated by oxygen delignification after the chemical treatment are stirred for 18-36 hours at room temperature and 600-1000 rpm, and are continuously heated to 40-75 ℃ and stirred for 1-3 hours.
9. The method of claim 1, wherein the completely dissolved material solution in step (3) is characterized as follows: and (3) taking a LiCl/DMSO solvent system as a control, respectively measuring the turbidity values of the material solution obtained in the step (3) and the control by using a turbidity meter, and determining that the material is completely dissolved when the difference between the turbidity values of the material solution and the control is +/-0.1-0.3.
10. The method of claim 2, wherein when the wood fiber in step (1) is wheat straw fiber, the wavelength in step (4) is 282 nm; when the wood fiber in the step (1) is poplar fiber, the wavelength in the step (4) is 276 nm; when the wood fiber in the step (1) is eucalyptus bark fiber, the wavelength in the step (4) is 278 nm; when the wood fiber in the step (1) is the bark fiber of the Chinese yew, the wavelength in the step (4) is 280 nm.
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| CN101957315A (en) * | 2010-09-11 | 2011-01-26 | 大连工业大学 | Method for measuring lignin content in black liquor |
| CN104089912A (en) * | 2014-06-30 | 2014-10-08 | 浙江天能电池(江苏)有限公司 | Method for determining dissolved quantity of lignin |
| CN105622980A (en) * | 2015-11-27 | 2016-06-01 | 南京林业大学 | Method for preparing wood fiber gel material from LiCl/DMSO dissolved lignocelluloses |
| CN106065080A (en) * | 2016-04-06 | 2016-11-02 | 南京林业大学 | A kind of dissolving recycled wood quality extracting method |
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2018
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101957315A (en) * | 2010-09-11 | 2011-01-26 | 大连工业大学 | Method for measuring lignin content in black liquor |
| CN104089912A (en) * | 2014-06-30 | 2014-10-08 | 浙江天能电池(江苏)有限公司 | Method for determining dissolved quantity of lignin |
| CN105622980A (en) * | 2015-11-27 | 2016-06-01 | 南京林业大学 | Method for preparing wood fiber gel material from LiCl/DMSO dissolved lignocelluloses |
| CN106065080A (en) * | 2016-04-06 | 2016-11-02 | 南京林业大学 | A kind of dissolving recycled wood quality extracting method |
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| Dissolution of Beech and Spruce Milled Woods in LiCl/DMSO;ZHIGUO WANG et al;《J. Agric. Food Chem》;20091231;6167-6170 * |
| Quantitative evaluation of milling effects on lignin structure during the isolation process of milled wood lignin;Aya Fujimoto;《J Wood Sci》;20051231;89-91 * |
| 基于 LiCl/DMSO 溶剂体系的非木材木质纤维木质素的分离与结构表征;吴文娟;《中国博士学位论文全文数据库 工程科技Ⅰ辑》;20160331;摘要，第14、17、18、20、51页 * |
| 沉默ＣＣＲ 和ＣＡＤ 基因培育低木质素含量转基因多年生黑麦草;胡可等;《草业学报》;20131031;72-83 * |
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