CN114295902B - Method for measuring surface charge density of lignin fiber - Google Patents
Method for measuring surface charge density of lignin fiber Download PDFInfo
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- CN114295902B CN114295902B CN202111668124.3A CN202111668124A CN114295902B CN 114295902 B CN114295902 B CN 114295902B CN 202111668124 A CN202111668124 A CN 202111668124A CN 114295902 B CN114295902 B CN 114295902B
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- 239000000835 fiber Substances 0.000 title claims abstract description 90
- 229920005610 lignin Polymers 0.000 title claims abstract description 65
- 238000000034 method Methods 0.000 title claims abstract description 28
- 229920001661 Chitosan Polymers 0.000 claims abstract description 54
- XMBWDFGMSWQBCA-UHFFFAOYSA-N hydrogen iodide Chemical compound I XMBWDFGMSWQBCA-UHFFFAOYSA-N 0.000 claims abstract description 51
- 239000000243 solution Substances 0.000 claims abstract description 51
- 239000000706 filtrate Substances 0.000 claims abstract description 39
- 239000011550 stock solution Substances 0.000 claims abstract description 37
- -1 iodide ions Chemical class 0.000 claims abstract description 34
- 238000001179 sorption measurement Methods 0.000 claims abstract description 33
- 238000002835 absorbance Methods 0.000 claims abstract description 32
- XMBWDFGMSWQBCA-UHFFFAOYSA-M iodide Chemical compound [I-] XMBWDFGMSWQBCA-UHFFFAOYSA-M 0.000 claims abstract description 20
- 238000006243 chemical reaction Methods 0.000 claims abstract description 14
- 238000005342 ion exchange Methods 0.000 claims abstract description 12
- 238000004611 spectroscopical analysis Methods 0.000 claims abstract description 10
- 238000001914 filtration Methods 0.000 claims abstract description 9
- 238000000862 absorption spectrum Methods 0.000 claims description 49
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 claims description 20
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 19
- 229910052740 iodine Inorganic materials 0.000 claims description 18
- 239000011630 iodine Substances 0.000 claims description 18
- 239000008367 deionised water Substances 0.000 claims description 14
- 229910021641 deionized water Inorganic materials 0.000 claims description 14
- WGCNASOHLSPBMP-UHFFFAOYSA-N hydroxyacetaldehyde Natural products OCC=O WGCNASOHLSPBMP-UHFFFAOYSA-N 0.000 claims description 10
- GETQZCLCWQTVFV-UHFFFAOYSA-N trimethylamine Chemical compound CN(C)C GETQZCLCWQTVFV-UHFFFAOYSA-N 0.000 claims description 10
- 229920002678 cellulose Polymers 0.000 claims description 8
- 239000012528 membrane Substances 0.000 claims description 8
- 239000011148 porous material Substances 0.000 claims description 8
- 239000001913 cellulose Substances 0.000 claims description 7
- 238000010586 diagram Methods 0.000 claims description 7
- 150000002632 lipids Chemical class 0.000 claims description 6
- 238000001228 spectrum Methods 0.000 claims description 6
- 229920006395 saturated elastomer Polymers 0.000 claims description 5
- 150000001449 anionic compounds Chemical class 0.000 claims description 4
- 229910001412 inorganic anion Inorganic materials 0.000 claims description 4
- 230000002452 interceptive effect Effects 0.000 claims description 4
- 229940006461 iodide ion Drugs 0.000 claims description 3
- 238000003760 magnetic stirring Methods 0.000 claims description 3
- 238000005259 measurement Methods 0.000 abstract description 10
- NLKNQRATVPKPDG-UHFFFAOYSA-M potassium iodide Substances [K+].[I-] NLKNQRATVPKPDG-UHFFFAOYSA-M 0.000 description 25
- 229920000867 polyelectrolyte Polymers 0.000 description 11
- 125000002091 cationic group Chemical group 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 238000004448 titration Methods 0.000 description 5
- 229920006317 cationic polymer Polymers 0.000 description 4
- 238000004537 pulping Methods 0.000 description 4
- 238000005303 weighing Methods 0.000 description 3
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 239000000654 additive Substances 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 239000010419 fine particle Substances 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 239000012452 mother liquor Substances 0.000 description 2
- 239000012466 permeate Substances 0.000 description 2
- 229920000642 polymer Polymers 0.000 description 2
- 125000001453 quaternary ammonium group Chemical group 0.000 description 2
- 238000002371 ultraviolet--visible spectrum Methods 0.000 description 2
- 238000012369 In process control Methods 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 229920006318 anionic polymer Polymers 0.000 description 1
- 239000012752 auxiliary agent Substances 0.000 description 1
- 238000004061 bleaching Methods 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 230000005591 charge neutralization Effects 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- GQOKIYDTHHZSCJ-UHFFFAOYSA-M dimethyl-bis(prop-2-enyl)azanium;chloride Chemical compound [Cl-].C=CC[N+](C)(C)CC=C GQOKIYDTHHZSCJ-UHFFFAOYSA-M 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 238000010965 in-process control Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 239000012744 reinforcing agent Substances 0.000 description 1
- 238000004513 sizing Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 238000006557 surface reaction Methods 0.000 description 1
- 230000002522 swelling effect Effects 0.000 description 1
- 238000000870 ultraviolet spectroscopy Methods 0.000 description 1
- 238000002211 ultraviolet spectrum Methods 0.000 description 1
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- Investigating Or Analysing Materials By Optical Means (AREA)
Abstract
The invention provides a method for measuring the surface charge density of lignin fibers, which comprises the following steps: respectively adding chitosan iodide solutions with different volumes into a plurality of parts of stock solutions, carrying out ion exchange reaction, and filtering to obtain a plurality of parts of filtrate; wherein the concentrations of chitosan iodide solutions with different volumes are the same, and the stock solution is lignin fiber solution with preset concentration; analyzing the filtrate by utilizing a derivative spectrometry, and drawing a line graph of the change of the absorbance first derivative value at a selected wavelength along with the addition amount of chitosan iodide to determine the iodine ion adsorption saturation point; substituting the first derivative value at the adsorption saturation point of the iodide ions into a KI standard curve to obtain the concentration of the iodide ions during adsorption saturation; combining the volume of the stock solution and the absolute dry mass of the fiber therein to obtain the surface charge density of the fiber; the invention combines derivative spectroscopy to subtract interference; realizes the rapid measurement of the surface charge density of the lignin fiber, and has high accuracy of measurement results.
Description
Technical Field
The invention belongs to the technical field of lignin fiber detection, and particularly relates to a method for measuring the surface charge density of lignin fibers.
Background
The plant fiber itself or the acidic groups generated in the pulping and bleaching processes can negatively charge the fiber in water, so that the fiber is used as the most main adsorption site of cation auxiliary agents (such as filler, retention aid, sizing agent, reinforcing agent and the like), and the content of the fiber plays a decisive role in the fiber exchange capacity; meanwhile, the apparent potential of the fiber is closely related to the hydrophilicity and swelling property of the fiber; therefore, an analytical method that can accurately determine the surface charge density of fibers is of great importance in process control related applications.
Currently, polyelectrolyte titration is a typical method for determining the apparent potential of lignin fibers, based on the ratio of the counter ions released after polyelectrolyte adsorption to the total charge of the polymer adsorbed by the fiber. Although stoichiometric charge neutralization occurs between the cationic polymer and the anionic polymer, it does not provide information on the reactive charge between the fiber and the cationic polymer. This is because the charge density of the cationic polymer is much higher than the charge density of the fiber surface. Thus, the amount of bound cationic polymer has no correlation with the position of the neutralized charge in the fiber. Furthermore, because the molecular weight of the cationic polyelectrolyte (typically Poly-DADMAC) is not high enough, some of the polymer may penetrate into the pores of the fibers and react with negative charges on the fiber pore walls (not the surface charges of the fibers). In summary, this polyelectrolyte titration method has a fundamental problem in the measurement of the surface charge density of the fiber, which leads to a higher result of the charge density of the fiber.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a method for measuring the surface charge density of lignin fibers, which aims to solve the technical problem that the measurement of the surface charge density of the fibers by the conventional polyelectrolyte titration method can lead to higher charge density results of the fibers.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the invention provides a method for measuring the surface charge density of lignin fibers, which comprises the following steps:
step 1, mixing lignin fibers to be measured with known mass with water to obtain lignin fiber solution with preset concentration; equally dividing lignin fiber solution with preset concentration to obtain a plurality of parts of stock solution;
step 2, respectively adding chitosan iodide solutions with different volumes into a plurality of parts of stock solutions, carrying out ion exchange reaction, and filtering to obtain a plurality of parts of filtrate; wherein the concentrations of the chitosan iodide solutions with different volumes are the same;
step 3, respectively analyzing each filtrate in the step 2 by using an ultraviolet spectrophotometer to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance; derivative spectrometry is utilized to derive a spectrogram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance, and a function chart of the ultraviolet absorption spectrum and the wavelength is obtained; then, according to a function chart of the differential coefficient of the ultraviolet absorption spectrum with respect to the wavelength and the wavelength, a line graph of the added chitosan iodide and the first derivative value of the iodine ions in the filtrate is obtained;
step 4, determining an iodine ion adsorption saturation point according to a line graph of the added amount of chitosan iodide and the first derivative value of iodine ions in the filtrate, and obtaining the first derivative value at the iodine ion adsorption saturation point;
step 5, substituting the first derivative value at the iodine ion adsorption saturation point in the step 4 into the KI standard curve to obtain the iodine ion concentration in the stock solution when the adsorption saturation is carried out;
and 6, according to the concentration of iodide ions in the stock solution when adsorption saturation is carried out in the step 5, and combining the volume of the stock solution and the absolute dry mass of lignocellulose in the stock solution, calculating to obtain the surface charge density of the lignin fiber.
Further, in step 1, before mixing the lignin fiber to be measured with water, deionized water is used to clean the lignin fiber to be measured to remove the interfering inorganic anions.
Further, in the step 2, the chitosan iodide solution is prepared by uniformly mixing trimethylammonium glycol chitosan iodide and deionized water; wherein the molecular weight of the trimethylammonium glycol chitosan iodide is more than or equal to 1000kDa.
In step 2, the ion exchange reaction is carried out under magnetic stirring.
Further, in the step 2, a filtering process is carried out by adopting a mixed cellulose lipid filter membrane; wherein the pore diameter of the mixed cellulose lipid filter membrane is less than or equal to 0.1 mu m.
In the step 3, each filtrate in the step 2 is analyzed by an ultraviolet spectrophotometer to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance; derivative spectrometry is utilized to derive a spectrogram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance, and a function chart of the ultraviolet absorption spectrum and the wavelength is obtained; and then, according to a function chart of the differential coefficient of the ultraviolet absorption spectrum with respect to the wavelength and the wavelength, obtaining a line graph of the added chitosan iodide and the first derivative value of the iodine ions in the filtrate, wherein the line graph comprises the following specific steps:
step 31, respectively carrying out UV-VIS scanning on each filtrate in the step 2 by using an ultraviolet spectrophotometer and adopting ultraviolet visible light with a preset wavelength range to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance;
step 32, solving a first derivative of a spectrogram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance to obtain a function chart of a differential coefficient of ultraviolet absorption spectrum relative to wavelength and wavelength;
and 33, selecting a line graph of the first derivative value of the pure lignin fiber filtrate at a wavelength of which the first derivative is close to zero and the corresponding chitosan iodide addition amount from a function graph of the differential coefficient of the ultraviolet absorption spectrum with respect to the wavelength and the wavelength, and obtaining the line graph of the chitosan iodide addition amount and the first derivative value of the iodine ions in the filtrate.
Further, in step 31, before each filtrate in step 2 is scanned by UV-VIS using a UV spectrophotometer and using UV-VIS in a preset wavelength range, the deionized water is scanned by UV-VIS in a preset wavelength range, and absorbance zero point is corrected; wherein the preset wavelength range of the ultraviolet visible light is 200-400nm.
Further, in step 33, the wavelength of the first derivative of the pure lignin fiber filtrate close to zero is selected to be 245nm.
Further, in step 5, the KI standard curve is obtained according to the following steps:
step 51, preparing a plurality of KI solutions with different concentrations;
step 52, respectively carrying out UV-VIS scanning on each part of KI solution by using an ultraviolet spectrophotometer and adopting ultraviolet visible light with a preset wavelength range to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance in the KI solution;
step 53, solving a first derivative of a spectrum diagram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance in the KI solution to obtain a function diagram of a differential coefficient of the ultraviolet absorption spectrum in the KI solution relative to the wavelength and the wavelength;
and 54, selecting a first derivative value at 245nm wavelength and corresponding iodide ion concentration as a line graph in a function graph of a differential coefficient of an ultraviolet absorption spectrum in the KI solution relative to the wavelength and the wavelength, and obtaining a KI standard curve.
Further, in step 6, the surface charge density of the lignin fiber is:
Q＝cV/m
wherein Q is the surface charge density of the lignin fiber; c is the concentration of iodide ions in the stock solution when adsorption is saturated; v is the volume of the stock solution; m is the absolute dry mass of lignocellulose in the stock solution.
Compared with the prior art, the invention has the beneficial effects that:
the invention provides a method for measuring the surface charge density of lignin fibers, which is characterized in that from an effective reaction site, a natural high molecular weight cationic polyelectrolyte, namely chitosan quaternary ammonium iodized salt, is firstly selected to be subjected to ion exchange with the surface reaction site of the lignin fibers to be measured, then the content of iodine ions released in the solution is measured through ultraviolet spectroscopy, and finally the interference of impurities such as lignin, fine particles and the like is deducted through derivative spectroscopy, so that the surface charge density of the fibers is rapidly and accurately determined; specifically, by selecting high molecular weight cationic polyelectrolyte trimethyl ammonium glycol chitosan iodide as an indicator, from a reaction site, iodine ions are released by ion exchange between the chitosan iodide and a negative site on the surface of the fiber, and as the charge density of the chitosan iodide is far higher than that of lignin fiber, the growth rate of released and unbound iodine ions in the solution is obviously different before and after adsorption saturation along with the increase of the addition amount of the chitosan iodide. The content of iodide ions in the solution is determined by means of ultraviolet-visible spectrum, and the adsorption saturation point is accurately found finally by drawing a relation chart of the addition amount of chitosan iodide and the content of iodide ions in the solution, so that the defects that the polyelectrolyte titration is high in difference of charge density between a titrant and an object to be measured and the measurement result is high due to the fact that the titrant possibly permeates into fiber pores and the measurement result is high are overcome, and the method plays a very important guiding role in chemical control of wet parts of pulping and papermaking, such as the addition amount of chemical additives and the like.
Drawings
FIG. 1 is a first derivative spectrum of the filtrate in the examples;
FIG. 2 is a graph showing the change in absorbance first derivative value at 245nm wavelength with the addition amount of chitosan iodide in the example.
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects solved by the invention more clear, the following specific embodiments are used for further describing the invention in detail. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The invention provides a method for measuring the surface charge density of lignin fibers, which comprises the following steps:
step 1, mixing lignin fibers to be measured with known mass with water to obtain lignin fiber solution with preset concentration; equally dividing lignin fiber solution with preset concentration to obtain a plurality of parts of stock solution; before mixing the lignin fiber to be measured with water, deionized water is adopted to clean the lignin fiber to be measured so as to remove interfering inorganic anions.
Step 2, respectively adding chitosan iodide solutions with different volumes into a plurality of parts of stock solutions, carrying out ion exchange reaction under the condition of magnetic stirring, and filtering to obtain a plurality of parts of filtrate; wherein the concentrations of the chitosan iodide solutions with different volumes are the same; wherein, the chitosan iodide solution is prepared by uniformly mixing trimethyl ammonium glycol chitosan iodide with deionized water; wherein the molecular weight of the trimethylammonium glycol chitosan iodide is more than or equal to 1000kDa; a filtering process, wherein a mixed cellulose filter membrane is adopted for filtering; wherein the pore size of the mixed cellulose lipid filter membrane is 0.1 μm or less.
Step 3, respectively analyzing each filtrate in the step 2 by using an ultraviolet spectrophotometer to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance; derivative spectrometry is utilized to derive a spectrogram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance, and a function chart of the ultraviolet absorption spectrum and the wavelength is obtained; then, according to a function chart of the differential coefficient of the ultraviolet absorption spectrum with respect to the wavelength and the wavelength, a line graph of the added chitosan iodide and the first derivative value of the iodine ions in the filtrate is obtained; the specific process is as follows:
step 31, respectively carrying out UV-VIS scanning on each filtrate in the step 2 by using an ultraviolet spectrophotometer and adopting ultraviolet visible light with a preset wavelength range to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance; before each filtrate in the step 2 is scanned by ultraviolet-visible light in a preset wavelength range, the deionized water is scanned by the ultraviolet-visible light in the preset wavelength range, and absorbance zero points are corrected; wherein the preset wavelength range of the ultraviolet visible light is 200-400nm.
And step 32, solving the first derivative of the spectrogram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance to obtain a function chart of the derivative coefficient of the ultraviolet absorption spectrum relative to the wavelength and the wavelength.
And 33, selecting a line graph of the first derivative value of the pure lignin fiber filtrate at a wavelength of which the first derivative is close to zero and the corresponding chitosan iodide addition amount from a function graph of the differential coefficient of the ultraviolet absorption spectrum with respect to the wavelength and the wavelength, and obtaining the line graph of the chitosan iodide addition amount and the first derivative value of the iodine ions in the filtrate.
Step 4, determining an iodine ion adsorption saturation point according to a line graph of the added amount of chitosan iodide and the first derivative value of iodine ions in the filtrate, and obtaining the first derivative value at the iodine ion adsorption saturation point;
step 5, substituting the first derivative value at the iodine ion adsorption saturation point in the step 4 into the KI standard curve to obtain the iodine ion concentration in the stock solution when the adsorption saturation is carried out; the KI standard curve is obtained according to the following steps:
step 51, preparing a plurality of KI solutions with different concentrations;
step 52, respectively carrying out UV-VIS scanning on each part of KI solution by using an ultraviolet spectrophotometer and adopting ultraviolet visible light with a preset wavelength range to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance in the KI solution;
step 53, solving a first derivative of a spectrum diagram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance in the KI solution to obtain a function diagram of a differential coefficient of the ultraviolet absorption spectrum in the KI solution relative to the wavelength and the wavelength;
and 54, selecting a first derivative value at 245nm wavelength and corresponding iodide ion concentration as a line graph in a function graph of a differential coefficient of an ultraviolet absorption spectrum in the KI solution relative to the wavelength and the wavelength, and obtaining a KI standard curve.
Step 6, according to the concentration of iodide ions in the stock solution when adsorption saturation is carried out in the step 5, the volume of the stock solution and the absolute dry mass of lignocellulose in the stock solution are combined, and the surface charge density of the lignin fiber is obtained through calculation; wherein the surface charge density of the lignin fiber is:
Q＝cV/m
wherein Q is the surface charge density of the lignin fiber; c is the concentration of iodide ions in the stock solution when adsorption is saturated; v is the volume of the stock solution; m is the absolute dry mass of lignocellulose in the stock solution.
According to the method for measuring the surface charge density of the lignin fiber, from an effective reaction site, natural high-molecular-weight cationic polyelectrolyte, namely chitosan quaternary ammonium iodized salt, is selected to perform ion exchange with the reaction site on the surface of the lignin fiber to be measured; then determining the content of the released iodide ions in the solution through ultraviolet spectrum; and finally, subtracting the interference of impurities such as lignin, fine particles and the like by adopting a derivative spectrometry method, thereby rapidly and accurately determining the surface charge density of the fiber.
Examples
The embodiment provides a method for measuring the surface charge density of lignin, which specifically comprises the following steps:
step 1, weighing 0.415g of potassium iodide and 500g of deionized water, uniformly mixing, and preparing 0.005mol/L standard KI mother liquor for later use.
Step 2, weighing 12.5mg of trimethylammonium glycol chitosan iodide and 25mg of deionized water, uniformly mixing, and preparing a chitosan iodide aqueous solution with the concentration of 0.5g/L for later use.
Step 3, weighing 45mg of absolute dry lignin fiber to be measured, and cleaning other interfering inorganic anions by using deionized water; then 600mL of deionized water is added to prepare lignin fiber solution with the concentration of 75mg/L, and the lignin fiber solution is placed on a magnetic stirrer for standby.
Step 4, accurately transferring 13 parts of 20mL of lignin fiber solution by using a pipette, respectively placing the solution into 13 different beakers, sequentially adding 0 mu L, 80 mu L, 100 mu L, 120 mu L, 140 mu L, 160 mu L, 180 mu L, 200 mu L, 220 mu L, 240 mu L, 260 mu L, 280 mu L and 300 mu L of chitosan iodide aqueous solution in the step 2 into the 13 beakers, magnetically stirring the solution for 30min for ion exchange reaction, and filtering the solution by using a mixed cellulose ester filter membrane to obtain 13 parts of filtrate; wherein the pore diameter of the mixed cellulose lipid filter membrane is less than or equal to 0.1 mu m.
Step 5, adopting an ultraviolet spectrophotometer to respectively perform UV-VIS scanning on 13 parts of the filtrate obtained in the step 4 to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance; before each filtrate in the step 4 is scanned by ultraviolet-visible light in a preset wavelength range, scanning deionized water by ultraviolet-visible light in the preset wavelength range, and correcting absorbance zero points; wherein the preset wavelength range of the ultraviolet visible light is 200-400nm.
Step 6, solving a first derivative of a spectrogram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance to obtain a function chart of a differential coefficient of ultraviolet absorption spectrum relative to wavelength and wavelength; selecting a first derivative value at 245nm and the corresponding chitosan iodide addition as a line graph to obtain a line graph of the chitosan iodide addition and the first derivative value of iodine ions in the filtrate; determining an iodine ion adsorption saturation point according to a line graph of the added chitosan iodide and the first derivative value of iodine ions in the filtrate to obtain the first derivative value at the iodine ion adsorption saturation point; as shown in fig. 1 and 2, as can be seen from fig. 1, by taking the first derivative of the spectrum of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance, the function diagram of the derivative coefficient of ultraviolet absorption spectrum with respect to wavelength and wavelength can be observed, the pure lignocellulose filtrate with 245nm has the interference of almost 0 mu L of chitosan iodide addition; as can be seen from fig. 2, by plotting the first derivative value of absorbance at 245nm as a function of chitosan addition, a distinct turning point can be observed; thus, measurement based on derivative spectra is effective, whether determining turning points or quantifying fiber surface charge density.
Step 7, the standard KI mother liquor in step 1 is diluted to 100 mu mol/L, 80 mu mol/L, 60 mu mol/L, 40 mu mol/L, 20 mu mol/L and 10 mu mol/L; repeating the operations of the step 5 and the step 6 to obtain a KI standard curve.
Step 8, substituting the first derivative value at the iodine ion adsorption saturation point in the step 6 into a KI standard curve to obtain the iodine ion concentration in the stock solution, namely the number of charge sites on the surface of the lignin fiber to be detected when the adsorption saturation is carried out; and according to the concentration of iodide ions in the stock solution when adsorption is saturated, the volume of the stock solution and the absolute dry mass of lignocellulose in the stock solution are combined, and the surface charge density of the lignin fiber is calculated.
Wherein the surface charge density of the lignin fiber is:
Q＝cV/m
wherein Q is the surface charge density of the lignin fiber; c is the concentration of iodide ions in the stock solution when adsorption is saturated; v is the volume of the stock solution, v=20 mL; m is the absolute dry mass of lignocellulose in the stock solution, m=0.0015 g.
In the invention, the ion exchange between trimethylammonium glycol chitosan iodide with high molecular weight and the negative charge reaction site on the surface of lignin fiber is adopted to release iodide ions, and the interference is deducted by combining a derivative spectrometry; realizes the rapid and accurate measurement of the surface charge density of lignin fibers and provides a method for chemical control of wet end of pulping and papermaking.
According to the method for measuring the surface charge density of the lignin fiber, disclosed by the invention, the cationic polyelectrolyte trimethyl ammonium glycol chitosan iodide with high molecular weight is selected as an indicator, and from a reaction site, the chitosan iodide and a negative electric site on the surface of the fiber are subjected to ion exchange to release iodine ions, so that the charge density of the chitosan iodide is far higher than that of the lignin fiber, and the increase rate of released and unbound iodine ions in a solution is obviously different before and after adsorption saturation along with the increase of the addition amount of the chitosan iodide; the content of iodide ions in the solution is determined by means of ultraviolet-visible spectrum, and the adsorption saturation point is accurately found finally by drawing a relation chart of the addition amount of chitosan iodide and the content of iodide ions in the solution, so that the defects that the polyelectrolyte titration is high in difference of charge density between a titrant and an object to be measured and the measurement result is high due to the fact that the titrant possibly permeates into fiber pores and the measurement result is high are overcome, and the method plays a very important guiding role in chemical control of wet parts of pulping and papermaking, such as the addition amount of chemical additives and the like.
The above embodiment is only one of the implementation manners capable of implementing the technical solution of the present invention, and the scope of the claimed invention is not limited to the embodiment, but also includes any changes, substitutions and other implementation manners easily recognized by those skilled in the art within the technical scope of the present invention.
Claims (8)
1. A method for determining the surface charge density of lignin fibers comprising the steps of:
step 1, mixing lignin fibers to be measured with known mass with water to obtain lignin fiber solution with preset concentration; equally dividing lignin fiber solution with preset concentration to obtain a plurality of parts of stock solution;
step 2, respectively adding chitosan iodide solutions with different volumes into a plurality of parts of stock solutions, carrying out ion exchange reaction, and filtering to obtain a plurality of parts of filtrate; wherein the concentrations of the chitosan iodide solutions with different volumes are the same;
in the step 2, the chitosan iodide solution is prepared by uniformly mixing trimethyl ammonium glycol chitosan iodide with deionized water; wherein the molecular weight of the trimethylammonium glycol chitosan iodide is more than or equal to 1000kDa
Step 3, respectively analyzing each filtrate in the step 2 by using an ultraviolet spectrophotometer to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance; derivative spectrometry is utilized to derive a spectrogram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance, and a function chart of the ultraviolet absorption spectrum and the wavelength is obtained; then, according to a function chart of the differential coefficient of the ultraviolet absorption spectrum with respect to the wavelength and the wavelength, a line graph of the added chitosan iodide and the first derivative value of the iodine ions in the filtrate is obtained;
step 4, determining an iodine ion adsorption saturation point according to a line graph of the added amount of chitosan iodide and the first derivative value of iodine ions in the filtrate, and obtaining the first derivative value at the iodine ion adsorption saturation point;
step 5, substituting the first derivative value at the iodine ion adsorption saturation point in the step 4 into the KI standard curve to obtain the iodine ion concentration in the stock solution when the adsorption saturation is carried out;
in step 5, the KI standard curve is obtained according to the following steps:
step 51, preparing a plurality of KI solutions with different concentrations;
step 52, respectively carrying out UV-VIS scanning on each part of KI solution by using an ultraviolet spectrophotometer and adopting ultraviolet visible light with a preset wavelength range to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance in the KI solution;
step 53, solving a first derivative of a spectrum diagram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance in the KI solution to obtain a function diagram of a differential coefficient of the ultraviolet absorption spectrum in the KI solution relative to the wavelength and the wavelength;
54, selecting a first derivative value at 245nm wavelength and corresponding iodide ion concentration as a line graph in a function graph of a differential coefficient of an ultraviolet absorption spectrum in the KI solution with respect to the wavelength and the wavelength, so as to obtain a KI standard curve;
and 6, according to the concentration of iodide ions in the stock solution when adsorption saturation is carried out in the step 5, and combining the volume of the stock solution and the absolute dry mass of lignocellulose in the stock solution, calculating to obtain the surface charge density of the lignin fiber.
2. The method for measuring the surface charge density of lignin fibers according to claim 1, wherein in step 1, before mixing the lignin fibers to be measured with water, the lignin fibers to be measured with known mass are washed with deionized water to remove interfering inorganic anions.
3. The method for measuring the surface charge density of lignin fibers according to claim 1 wherein in step 2, the ion exchange reaction is performed by performing the reaction under magnetic stirring.
4. The method for determining the surface charge density of lignin fibers according to claim 1 wherein in step 2, the filtration process is performed using a mixed cellulose lipid filter membrane; wherein the pore diameter of the mixed cellulose lipid filter membrane is less than or equal to 0.1 mu m.
5. The method for measuring the surface charge density of lignin fibers according to claim 1, wherein in the step 3, each filtrate in the step 2 is analyzed by an ultraviolet spectrophotometer to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance; derivative spectrometry is utilized to derive a spectrogram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance, and a function chart of the ultraviolet absorption spectrum and the wavelength is obtained; and then, according to a function chart of the differential coefficient of the ultraviolet absorption spectrum with respect to the wavelength and the wavelength, obtaining a line graph of the added chitosan iodide and the first derivative value of the iodine ions in the filtrate, wherein the line graph comprises the following specific steps:
step 31, respectively carrying out UV-VIS scanning on each filtrate in the step 2 by using an ultraviolet spectrophotometer and adopting ultraviolet visible light with a preset wavelength range to obtain a spectrogram of ultraviolet wavelength-ultraviolet absorption spectrum absorbance;
step 32, solving a first derivative of a spectrogram of ultraviolet light wavelength-ultraviolet absorption spectrum absorbance to obtain a function chart of a differential coefficient of ultraviolet absorption spectrum relative to wavelength and wavelength;
and 33, selecting a line graph of the first derivative value of the pure lignin fiber filtrate at a wavelength of which the first derivative is close to zero and the corresponding chitosan iodide addition amount from a function graph of the differential coefficient of the ultraviolet absorption spectrum with respect to the wavelength and the wavelength, and obtaining the line graph of the chitosan iodide addition amount and the first derivative value of the iodine ions in the filtrate.
6. The method according to claim 5, wherein in step 31, before each filtrate in step 2 is scanned by UV-VIS in a predetermined wavelength range using an ultraviolet spectrophotometer, deionized water is scanned by UV-VIS in a predetermined wavelength range, and absorbance zero is corrected; wherein the preset wavelength range of the ultraviolet visible light is 200-400nm.
7. The method according to claim 5, wherein in step 33, the wavelength of the first derivative of the pure lignin fiber filtrate is 245nm, which is close to zero.
8. The method of claim 1, wherein the surface charge density of the lignin fiber in step 6 is:
Q＝cV/m
wherein Q is the surface charge density of the lignin fiber; c is the concentration of iodide ions in the stock solution when adsorption is saturated; v is the volume of the stock solution; m is the absolute dry mass of lignocellulose in the stock solution.
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