Method for verifying content of effective components of wet strength agent

Abstract

The invention discloses a method for verifying the content of effective components of a wet strength agent, which is used for judging whether the content of the effective components of the wet strength agent meets the requirements of papermaking application or not by taking appearance identification, solid content, viscosity, pH value, charge demand, total nitrogen content and ash content as detection indexes. The method provided by the invention solves the industrial problems that the real content of the effective components in the polyamide epichlorohydrin wet strength agent is difficult to accurately and quickly identify and the polyamide epichlorohydrin wet strength agent is easily interfered by adulterated components such as inorganic salts or other nitrogen-containing organic matters in the prior art, and prevents inferior or adulterated products from flowing into a production link. According to the method, accurate verification of the real content of the effective components in the polyamide epichlorohydrin wet strength agent can be realized only by using common instruments and equipment such as a charge tester, a spectrophotometer and a muffle furnace, the operation is simple, the reliability is high, and the method is suitable for daily rapid warehousing inspection and daily quality monitoring of the wet strength agent by enterprises.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wet strength agent detection, and particularly relates to a method for verifying whether the effective component content of a wet strength agent meets the requirements of papermaking application. BACKGROUND

[0002] A wet strength agent, which is mainly used to improve the mechanical strength and structural stability of paper in a wet state. It is suitable for various paper types such as toilet paper, packaging paper, food packaging paper and special industrial paper, and can significantly improve the wet tensile strength, burst resistance and tear resistance of paper, and improve the water resistance and dimensional stability of paper, ensuring good performance in a humid environment.

[0003] Polyamide epichlorohydrin resin (PAE) is one of the most widely used wet strength agents in the papermaking industry. Its stability, especially its effective content, is directly related to the efficiency of process control and the qualification rate of the final product. However, PAE wet strength agent products provided by different manufacturers differ in raw materials, synthesis process and quality control, which may lead to uneven application results.

[0004] Currently, the quality control of PAE wet strength agent in the industry is mainly based on the group standard "T / CPA 006-2024 Wet Strength Agent for Papermaking Polyamide Epichlorohydrin PAE" released in 2024. The standard provides corresponding detection methods and index ranges for the physicochemical properties of PAE wet strength agent, including appearance, solid content, pH value, viscosity, and the content of epichlorohydrin and chloropropanol. Among them, chloropropanol is a byproduct produced by the hydrolysis or incomplete reaction of epichlorohydrin, both of which have certain toxicity. Therefore, the significance of detecting these two indicators lies in ensuring the safety of the final paper product. However, the standard only reflects the detection of the effective content of PAE wet strength agent in terms of basic indicators such as appearance, solid content, pH value and viscosity. Detecting only these basic indicators cannot effectively identify the distortion of the detection results caused by adulterated ingredients. For example, aluminum sulfate, a commonly used additive in the papermaking industry, may be added to PAE wet strength agent, which may increase the measured value of solid content, leading to distorted detection results and failing to truly reflect the effective component content of PAE.

[0005] Nuclear magnetic resonance (NMR) can provide high detection accuracy by detecting the characteristic peaks of the characteristic functional groups in the hydrogen spectrum of the PAE molecular structure and calculating the concentration or content of PAE using the integral area of the characteristic peaks. However, NMR equipment is expensive, complex to operate, and requires highly skilled operators, making it unsuitable for enterprises to conduct routine rapid warehouse inspection.

[0006] Chinese patent CN 118883773 B discloses a method for detecting the effective ingredient content of a polyamide epoxy chloropropane wet strength agent, which measures the effective ingredient content of PAE by fully hydrolyzing PAE to adipic acid and then esterifying adipic acid diethyl to quantitatively analyze the effective ingredient content of PAE. Although this method can quantitatively detect the effective content of PAE and avoid the problem of distorted test results caused by adulterated ingredients, it involves the control of many factors such as acid-water ratio, reaction temperature, esterification reaction temperature, and the detection method is complex and the detection period is long, which cannot meet the timeliness requirements of batch material inspection in the papermaking production process.

[0007] Therefore, in order to ensure the stability of the papermaking production process and the product quality, it is urgent to establish a stable and reliable, fast and efficient method for verifying the effective content of the wet strength agent, so as to realize the rapid and accurate verification of the real content of the effective ingredient in the wet strength agent provided by different manufacturers, and avoid the inflow of inferior or adulterated products into the production link. SUMMARY

[0008] To solve the above technical problems, the present application provides a method for verifying the effective ingredient content of a wet strength agent, to determine whether the effective ingredient content of the wet strength agent meets the requirements of papermaking application, and realizes the daily rapid warehouse inspection and daily quality monitoring of the wet strength agent by enterprises.

[0009] The technical solution of the present application is:

[0010] A method for verifying the effective ingredient content of a wet strength agent, characterized in that appearance identification, solid content, viscosity, pH value, charge demand, total nitrogen content and ash content are collectively used as detection indexes to determine whether the effective ingredient content of the wet strength agent meets the requirements of papermaking application;

[0011] The charge demand is detected according to the following method:

[0012] S5: Take an appropriate amount of wet strength agent to be tested and dilute it with water, the dilution ratio is A, stir uniformly to prepare a charge demand sample solution; take an appropriate amount of charge demand sample solution into a charge detector to test the charge demand q;

[0013] The total nitrogen content is detected according to the following method:

[0014] S6: Take an appropriate amount of wet strength agent to be tested and dilute it with water, the dilution ratio is B, stir uniformly to prepare a total nitrogen test sample; after digestion and distillation of the total nitrogen test sample, the total nitrogen is determined by colorimetry;

[0015] The ash content is detected according to the following method:

[0016] S7: Take an appropriate amount of wet strength agent to be tested into a crucible, first dry in an oven to obtain an absolutely dry sample, weigh and record the mass of the absolutely dry sample, then calcine the crucible in a high-temperature furnace at high temperature for 1-4 h until the absolutely dry sample is ashed; weigh and calculate the ash content.

[0017] Preferably, the ash content is weighed and calculated after calcining at high temperature for 4 h until the absolutely dry sample is completely ashed.

[0018] The wet strength agent described in the application has polyamide epichlorohydrin (PAE) as an effective component, and the synthesis process mainly includes two core reactions: first, through diethylene triamine and adipic acid , a polyamide polyamine prepolymer is generated through polycondensation reaction.

[0019] Then, the nucleophilic ring-opening reaction occurs between the secondary amino group (-NH-) on the molecular chain of the polyamide polyamine and the epoxy group of epichlorohydrin , generating a linear side chain with chloromethyl and hydroxyl groups. Further, the intramolecular nucleophilic substitution reaction occurs between the chloromethyl group in the linear side chain and the adjacent secondary amino nitrogen atom (i.e. the main chain nitrogen atom to which the side chain is connected), and a stable four-membered ring structure, azetidinium ion, is formed by cyclization. The azetidinium ion is the key active body of PAE in the wet strengthening of papermaking. Its strengthening mechanism is as follows: when PAE is used as a papermaking additive, the nucleophilic groups (carboxyl or alcohol hydroxyl ) on the surface of cellulose fibers attack the ring carbon atom of azetidinium ion, leading to ring opening of the four-membered ring and forming a covalent ether bond. This covalent bond has excellent hydrolysis resistance, thereby building a stable cross-linking network between fibers and giving the paper permanent wet strength.

[0020] Among them, the appearance detection requires that the product color be uniform and consistent, and the color range be light yellow, light red or colorless transparent liquid. Generally, if the purity of the raw material is low, the side reactions increase during synthesis, or the impurity content in the PAE product is high, the product color may deepen or even be abnormal. Therefore, limiting the appearance color to the above range can initially exclude defective products.

[0021] In the prior art, the solid content is usually used as one of the key indicators for evaluating the content of the effective component of the wet strength agent. For example, the solid content control range of the wet strength agent commonly used in the household paper industry is 12.5±0.5%. If the measured solid content is lower than the value, it indicates that the content of the effective component of the wet strength agent may be insufficient.

[0022] Viscosity is another important quality control indicator of wet strength agent. The viscosity of wet strength agent is directly related to the molecular weight and branching degree of its active ingredient. At the same concentration, the higher the molecular weight and branching degree, the higher the viscosity. Under normal process conditions, the viscosity range of wet strength agent corresponds to a specific molecular weight distribution, ensuring that the molecular chain length is sufficient to form a "bridge" between fibers, while avoiding diffusion obstruction due to excessive molecular weight. High viscosity can lead to poor flowability of the wet strength agent, which is prone to deposition and wall-hanging on the inner wall of the pipeline, and even block the delivery pump or filter screen, causing the addition process to be interrupted. In addition, high viscosity can also affect the accuracy of the metering pump, leading to deviations between the actual addition amount and the set value, thereby affecting process stability. If the viscosity abnormally increases, it may be due to excessive self-crosslinking between molecules, which consumes active azetidinium ions, leading to a decrease in the actual crosslinking capacity of the wet strength agent, even if the addition amount is normal, the wet strength effect will be significantly reduced. Conversely, if the viscosity abnormally drops, it may be due to molecular chain breakage, resulting in insufficient molecular weight to form an effective crosslinking network, thereby completely or partially losing the strengthening function.

[0023] In addition, pH is crucial to ensuring the chemical activity, storage stability, and compatibility with other additives in the fiber or papermaking process of PAE wet strength agent. The core function of PAE wet strength agent relies on the covalent crosslinking reaction between the azetidinium ion active group in its molecule and the hydroxyl or carboxyl group on the fiber surface. The reactivity and stability of these active groups are extremely sensitive to the pH environment. If the system is too acidic, the azetidinium ion will lose stability due to excessive protonation, and even hydrolyze and lose its ability to crosslink with fibers. At the same time, the hydroxyl groups on the fiber surface are protonated under acidic conditions, reducing their nucleophilicity and making it difficult to dissociate into more nucleophilic , resulting in a significant decrease in crosslinking reaction efficiency. If the system is too alkaline, azetidinium ions are prone to ring-opening hydrolysis to form hydroxyl compounds with no crosslinking activity. In addition, a strong alkaline environment can accelerate the self-polymerization and reaction between PAE wet strength agent molecules, forming a precipitate that prevents uniform adsorption on the fiber surface.

[0024] In the prior art, the above-mentioned appearance identification, solid content, viscosity, and pH value are usually used as the basis for evaluating the effective content of wet strength agent. However, in actual production practice, only relying on the above four indicators to monitor the effective ingredient of wet strength agent cannot fully ensure the stability of the production process, the root cause of which is that the above indicators are not directly related to the content of azetidinium ion, the active ingredient of PAE.

[0025] For example, aluminum sulfate, a commonly used additive in the paper industry, may increase the measured value of solid content when added to PAE wet strength agent, leading to distorted test results and failing to truly reflect the content of PAE active ingredient.

[0026] The content and stability of the effective component azetidinium ion of PAE mainly depend on the use amount of the key raw material diethylene triamine and the control accuracy of the synthesis process. As shown in the cost structure analysis of PAE in Table 1, the diethylene triamine accounts for as high as 58.76% in the total cost. In order to reduce the cost, some manufacturers will reduce the use amount of diethylene triamine or use inferior raw materials, which will directly affect the content of azetidinium ion in the final product and cannot meet the standard. In addition, in the intramolecular ring reaction process of forming azetidinium ion, pH value and temperature are the two most important process conditions, and if not properly controlled, the production efficiency and stability of the azetidine structure will be significantly affected.

[0027] Table 1 Cost structure of PAE for papermaking

[0028] Therefore, in order to overcome the above-mentioned defects of the prior art, the present application creatively introduces three indexes of charge demand, total nitrogen content and ash content on the basis of the original four detection indexes, and through the synergistic effect of the three indexes, a method for directly and effectively verifying the content of the effective component in the PAE wet strength agent is constructed.

[0029] As for the charge demand test: the feasibility of monitoring lies in the fact that the prior art shows that the charge demand is highly related to the content of the active component azetidinium ion in PAE. Figure 1 The relationship between the charge demand of the PAE sample and the azetidinium ion ratio thereof determined by quantitative 13C nuclear magnetic resonance (NMR) (this is the prior art). It can be seen from the figure that Figure 1 The two present a significant linear positive correlation. This shows that it is feasible to indirectly represent the effective content stability of azetidinium ion by monitoring the charge demand.

[0030] The total nitrogen content test: the monitoring purpose is to ensure the stability of the active nitrogen source. The nitrogen element in PAE exists in the form of azetidine and secondary amino group (-NH-), and all of which are derived from the key raw material diethylene triamine. Therefore, monitoring the stability of the total nitrogen content is essentially a verification of the stability of the diethylene triamine feeding amount in the production process. The introduction of this index can effectively prevent the problem that manufacturers will adulterate inorganic salts (such as aluminum sulfate) containing no nitrogen in order to meet the charge demand index.

[0031] For ash content test: its monitoring purpose is to identify the doping of nitrogen-containing organic impurities. Some nitrogen-containing substances, such as urea, have a melting point of 132.7℃, which will not decompose at the solid content test temperature (105±2)℃, but will artificially increase the solid content measurement value and at the same time increase the total nitrogen content. Then, under the high temperature condition (575±25)℃ of the ash test, such organic matter will completely decompose and burn. Therefore, by adding the ash content index, the problem of artificially increasing the solid content and total nitrogen content by doping low-cost nitrogen-containing organic matter such as urea and ammonium salt can be effectively excluded, and the total nitrogen content result can truly reflect the characteristics of the PAE active ingredient.

[0032] Further, in S5, 0.1-1.0g of the wet strength agent to be tested is taken, and the dilution multiple A is 100-1000 times.

[0033] Further, in S5, an appropriate amount of sample liquid is taken in a charge measuring instrument, and an anionic standard polymer titrant is used. When titrated to a streaming potential of 0mV, the charge demand q is tested.

[0034] The anionic standard polymer is polyvinyl sulfonic acid sodium (PES-Na).

[0035] Further, in S6, 0.1-1.0g of the wet strength agent to be tested is taken and diluted with water, and the dilution multiple B is 20-200 times to prepare a total nitrogen test sample.

[0036] Further, in S6, the total nitrogen test sample is put into a nitrogen fixation bottle, an appropriate amount of sodium hydroxide solution and nitrogen fixation alloy are added, and it is left to stand for 1-2h; then heated and distilled, and the distilled liquid is received by a colorimetric tube containing sulfuric acid solution. After adding sodium hydroxide solution and Nash reagent and dilution, the solution is shaken well, and the color of the solution is compared with that of a standard colorimetric solution.

[0037] Further, in S7, an appropriate amount of the wet strength agent to be tested is taken and placed in a crucible, and the crucible is dried in an oven at a temperature of 100℃-120℃ for 4h to prepare the absolute dry sample.

[0038] Further, the crucible and the absolute dry sample are placed in a high-temperature furnace, first at a temperature of 180-120℃ for 15min, and then at a high-temperature temperature of 575±25℃ for 1-4h until the absolute dry sample is completely ashed.

[0039] Further, it also includes chloropropanol content detection.

[0040] Further, the wet strength agent is a polyamide epoxy chloropropane resin (PAE) wet strength agent.

[0041] Further, the wet strength agent effective component is polyamide epoxy chloropropane resin (PAE), the wet strength agent effective component is polyamide epoxy chloropropane resin (PAE), and when the solid content is 12.5±0.5% and the following index ranges are met simultaneously, it is determined that the wet strength agent effective component content is stable and effective:

[0042] The charge demand q=charge demand measured value×(A / 1000), and the charge demand q is qualified in the range of 300-450 μeq / L;

[0043] The total nitrogen content=total nitrogen measured value×(B / 200); and the total nitrogen content is qualified in the range of 13000-17000 mg / L;

[0044] The ash content is ≤0.5%;

[0045] A is the actual dilution multiple when testing the charge demand, and is 100-1000; and B is the actual dilution multiple when testing the total nitrogen, and is 20-200.

[0046] Further, the wet strength agent effective component is polyamide epoxy chloropropane resin (PAE), and when the solid content is greater than 12.5±0.5% and the following index ranges are met simultaneously, it is determined that the wet strength agent effective component content is stable and effective:

[0047] The charge demand q=charge demand measured value×e1, and the charge demand q is qualified in the range of 300-450 μeq / L;

[0048] The total nitrogen content=total nitrogen measured value×e2, and the total nitrogen content is qualified in the range of 13000-17000 mg / L;

[0049] The ash content=ash measured value×e3, and the ash content is qualified in the range of ≤0.5%;

[0050] Wherein, the e1=(12.5% / C)×(A / 1000);

[0051] The e2=(12.5% / C)×(B / 200);

[0052] The e3=12.5% / C;

[0053] Wherein, C is the solid content of the wet strength agent, and the unit is %.

[0054] The beneficial technical effects of the present application are:

[0055] Compared with the prior art, the application uses appearance identification, solid content, viscosity, pH value, charge demand, total nitrogen content and ash content as detection indexes to evaluate and verify the effective content of the wet strength agent, effectively overcomes the industry problems that it is difficult to accurately and quickly identify the stability of the effective ingredient content in the polyamide epichlorohydrin (PAE) wet strength agent and the interference of adulterated ingredients such as inorganic salts (such as aluminum sulfate) or other nitrogen-containing organic matters (such as urea), and avoids the inflow of inferior or adulterated products into the production link. In addition, the application further limits the PAE wet strength agent with a solid content of ≥12.5±0.5%, which needs to meet the qualified range values of charge demand q, total nitrogen content and ash content at the same time, so as to realize the quick and accurate verification and evaluation of the effective content of PAE wet strength agents of different batches and different sources, and to determine whether the effective ingredient content of the wet strength agent meets the demand of papermaking application.

[0056] The PAE wet strength agent verified as qualified in the application can produce paper products with stable and up-to-standard wet tensile strength in actual papermaking application, thereby significantly improving the production efficiency and product qualification rate and reducing the economic loss caused by the use of unqualified wet strength agent.

[0057] In addition, compared with the prior art, the application only uses common instruments and equipment such as charge determinator, spectrophotometer and muffle furnace to realize the accurate and quick verification of the effective ingredient content in the PAE wet strength agent, which is simple to operate and has high reliability, realizes the daily quick warehouse inspection and daily quality monitoring of the wet strength agent by enterprises. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 is a relationship diagram between the charge demand of the PAE sample and the proportion of azetidinium ion determined by quantitative 13C nuclear magnetic resonance (NMR). DETAILED DESCRIPTION

[0059] In order to more clearly understand the technical means of the application and can be implemented according to the content of the specification, the specific embodiments of the application are further described in detail below in combination with the drawings and examples, the following examples are used to illustrate the application, but not to limit the scope of the application.

[0060] The wet strength agent commonly used in the tissue paper industry is mostly polyamide epichlorohydrin (PAE) series products, i.e. PAE wet strength agent, and the effective ingredient thereof is polyamide epichlorohydrin. Therefore, the method for verifying the effective ingredient content of the wet strength agent according to the application is suitable for PAE wet strength agent.

[0061] The application provides a method for verifying the effective component content of a wet strength agent, which is characterized by appearance identification, solid content, viscosity, pH value, charge requirement, total nitrogen content and ash content as detection indexes to determine whether the effective component content of the wet strength agent meets the demand of papermaking application.

[0062] S1. Appearance detection

[0063] Firstly, the appearance of the PAE wet strength agent is visually observed, and the indexes for judging the qualified appearance include: uniform color, which is light yellow, light red or colorless transparent liquid.

[0064] S2. Solid content determination

[0065] The application adopts the drying method to determine the solid content of the PAE wet strength agent. 1.0 g of the PAE wet strength agent is heated to constant weight at a certain temperature, so that the water and volatile components are evaporated, and the solid content C of the sample is determined by calculating the ratio of the mass of the residual after heating to the mass of the initial sample. The specific method refers to the method specified in GB / T 2677.2-2011, the test temperature is 105±2℃, and the drying time is 4h.

[0066] Based on the method, the solid content C of the polyamide epoxy chloropropane (PAE) wet strength agent determined by the application is qualified in the range of ≥12.5±0.5%.

[0067] S3. Viscosity determination

[0068] The viscosity is determined by a viscometer, and the test conditions include: at 25±0.1℃, the viscosity value of the PAE wet strength agent stock solution is measured at a rotation speed of 60 rpm by selecting a #1 rotor.

[0069] Based on the method, when the solid content of the PAE wet strength agent is =12.5±0.5%, the application limits the qualified range of the viscosity of the PAE wet strength agent to 30-100 mPa.s;

[0070] When the solid content C of the PAE wet strength agent is 13%< solid content C≤20.0±0.5%, the application limits the qualified range of the viscosity of the PAE wet strength agent to 30-150 mPa.s;

[0071] S4. pH value determination

[0072] The pH value of the PAE wet strength agent stock solution is directly measured by a pH meter, and the measurement temperature is 25±0.1℃.

[0073] When the solid content of the PAE wet strength agent is 12.5±0.5%≤ solid content C≤20.0±0.5%, the application limits the qualified range of the pH value of the PAE wet strength agent to 2.0-6.0.

[0074] Under the condition that the above four detection indexes are qualified, the following detection items are continued to be carried out;

[0075] S5. Charge demand amount detection

[0076] The charge demand amount test refers to the method of GB / T 24994-2010 Papermaking Wet Part Dissolved Charge Amount Determination, and the specific steps include:

[0077] Sample dilution:

[0078] 1.0 g of PAE wet strength agent stock solution is accurately measured and diluted with deionized water, the dilution multiple A is 1000, and the charge demand sample solution is prepared after being fully mixed and uniform;

[0079] Instrument titration:

[0080] 10 ml of the charge demand sample solution is injected into the measuring chamber of the particle charge measuring instrument (equipment model: Mütek PCD-06 Premium of BTG), the automatic titrator is started, the anionic standard polymer titrant sodium polyvinyl sulfonate (PES-Na) is used for titration, and when the streaming potential is 0 mV, it is the titration end point.

[0081] Result calculation:

[0082] The measured value (q0) of the charge demand of the PAE wet strength agent is calculated according to the following formula:

[0083] q0=(V1×N) / V

[0084] Wherein:

[0085] q0: measured value of charge demand, unit: μeq / L;

[0086] V1: volume of standard polymer titrant consumed in titration (unit: L);

[0087] N: concentration of standard titrant (unit: eq / L);

[0088] V: volume of the charge demand sample solution injected into the measuring chamber (unit: L);

[0089] The result of the charge demand q is taken as the final determination value, q=q0×e1, and the qualified index range is 300≤ q≤ 450 μeq / L.

[0090] Wherein, e1=(12.5% / C)×(A / 1000);

[0091] C is the solid content of the wet strength agent, unit: %, and C≥12.5%;

[0092] A is the actual dilution multiple when testing the charge demand amount, and is 100-1000;

[0093] That is, when the dilution multiple A=1000 and the solid content of the PAE wet strength agent is 12.5%, e1=1.

[0094] If the charge demand amount result of the PAE wet strength agent to be tested is within the above qualified range, it is determined that the index is qualified, and subsequent total nitrogen content determination is continued. The purpose is to exclude the false qualification of the charge demand amount of the PAE due to the doping of inorganic salts (such as aluminum sulfate) in the PAE. For example, aluminum sulfate is a commonly used additive in papermaking. The hydrolysis product of aluminum sulfate, aluminum hydroxide Al(OH)3 colloid, is positively charged due to the adsorption of Al 3+ ions on the surface, thereby causing the apparent charge demand amount to be falsely increased. In addition, aluminum sulfate does not decompose at high temperatures, and also falsely increases the ash content test value. Therefore, the total nitrogen and ash content indexes need to be combined for comprehensive control, so as to truly, accurately and stably reflect the effective content of the azetidinium ion in the PAE wet strength agent.

[0095] S6. Total nitrogen content determination

[0096] The total nitrogen content determination refers to the national standard GB / T 609-2018 General Method for Determination of Total Nitrogen Content of Chemical Reagents, and the total nitrogen content of the PAE wet strength agent is determined by the Nash reagent colorimetric method. The specific steps include:

[0097] 1g of the PAE wet strength agent stock solution is diluted by a dilution multiple B of 200, and then the diluted test solution is placed in a Kjeldahl nitrogen determination flask, 5ml of sodium hydroxide solution (320g / L) and 1.0g of nitrogen determination alloy (Devarda alloy) are added, and the mixture is allowed to stand for 1h. About 75ml of water is distilled off, and 5ml of sulfuric acid solution (0.5%) is received in a 100ml colorimetric tube. 3ml of sodium hydroxide solution (320g / L) and 2ml of Nash reagent are added, and the mixture is diluted to 100ml and shaken well. The yellow color of the solution is compared with the standard colorimetric solution, and the total nitrogen mass concentration, i.e. the total nitrogen content measured value, is read.

[0098] Preparation of the standard colorimetric solution: a nitrogen standard solution with a specified mass is diluted by 200 times, and then treated in the same way as the sample solution.

[0099] The total nitrogen content result is the final determination value, the total nitrogen content measured value is multiplied by e2, and the total nitrogen content qualified range is 13000-17000mg / L;

[0100] Wherein, e2=(12.5% / C)×(B / 200);

[0101] C is the solid content of the wet strength agent, and the unit is %, and C≥12.5%;

[0102] B is the actual dilution factor when testing total nitrogen, which is 20-200.

[0103] That is, when the dilution factor B = 200 and the solid content of the PAE wet strength agent is 12.5%, e2 = 1.

[0104] If the total nitrogen mass concentration of the PAE wet strength agent to be measured is within the above-mentioned qualified index range, it is determined that the index is qualified, and subsequent ash content determination is continued. The purpose is to exclude the false standard of the total nitrogen mass concentration of the PAE wet strength agent caused by the adulteration of other nitrogen-containing substances, so as to ensure that the measured total nitrogen mass concentration data truly reflects the characteristics of the PAE effective component.

[0105] S7. Ash determination

[0106] The empty crucible is dried in an oven at a temperature of 105℃ for 4h, then cooled to room temperature in a desiccator and weighed to obtain the mass m0 of the empty crucible.

[0107] 10±0.5g of the PAE wet strength agent is weighed and placed in the above-mentioned crucible, and the crucible is dried in an oven at a temperature of 105℃ for 4h to obtain an absolutely dry sample, and the mass m1 (g) of the absolutely dry sample is weighed and recorded;

[0108] Then the absolutely dry sample and the crucible are placed in a muffle furnace and dried at a temperature of 100℃ for 5min, then the muffle furnace is heated to 200℃ and kept for 15min for carbonization of the absolutely dry sample; then the muffle furnace is heated to 575±25℃, and after being kept at this temperature for 4h until the sample is completely ashed, the mass m2 (g) of the residue after burning and the crucible is weighed and recorded after cooling to room temperature;

[0109] The result of the measured value of the ash content is calculated:

[0110] The measured value X (%) of the ash content is calculated according to the following formula: X (%) = m2-m0 / m1

[0111] Wherein, m0 is the mass of the empty crucible (g).

[0112] The result of the ash content is the final determination value, the ash content = the measured value of the ash content × e3, and the qualified range of the ash content is ≤0.5%;

[0113] Wherein, e3 = 12.5% / C;

[0114] C is the solid content of the wet strength agent, in %, and C≥12.5%;

[0115] That is, when the solid content of the PAE wet strength agent is 12.5%, e3 = 1.

[0116] As preferred, the present application further comprises: detection of chloropropanol content.

[0117] Chloropropanols are by-products of the hydrolysis or incomplete reaction of epichlorohydrin, both of which are toxic, so the significance of detecting this indicator is to ensure the safety of the final paper product.

[0118] The content of chloropropanols (total of 3-dichloro-2-propanol and 3-chloro-1,2-propanediol) in the PAE wet strength agent is detected by the gas chromatography-mass spectrometry method specified in T / CNFIA 206-2024 "Determination of chloropropanols content in papermaking chemicals - gas chromatography-mass spectrometry method". Specifically, the first method-direct dilution-gas chromatography / mass spectrometry method in the above standard is used for testing. The sample is dissolved or dispersed with acetonitrile and then ultrasonically extracted, and 2,3-dichloro-1-propanol (2,3-DCP) is used as an internal standard for quantitative determination. This is prior art and will not be described here.

[0119] When the solid content of the PAE wet strength agent is ≥12.5±0.5%, the present application limits the qualified indicator range of the chloropropanol content of the PAE wet strength agent to ≤7000ppm.

[0120] In addition, in order to verify the stability and effectiveness of the synergistic monitoring method of the present application, the following comparative examples are designed for comparative testing:

[0121] Comparative Example 1: The conventional monitoring indicator combination in the prior art is used, i.e. appearance identification, solid content, viscosity, pH value, and chloropropanol content detection;

[0122] Comparative Example 2: The charge demand amount indicator is added to the existing monitoring technology, i.e. appearance identification, solid content, viscosity, charge demand amount, and chloropropanol content detection;

[0123] Comparative Example 3: Compared with Example 1 of the present application, the ash content detection is missing, i.e. appearance identification, solid content, viscosity, charge demand amount, total nitrogen content, and chloropropanol content detection;

[0124] Comparative Example 4: Compared with Example 1 of the present application, the total nitrogen content detection is missing, i.e. appearance identification, solid content, viscosity, charge demand amount, ash content, and chloropropanol content detection;

[0125] The specific detection methods (such as test temperature, dilution ratio, reagents and instruments used) of each indicator involved in Comparative Examples 1-4 and the qualified ranges of each indicator are the same as the methods and ranges used in the present application.

[0126] The present application selects a variety of commercially available PAE wet strength agents from different manufacturers as detection objects, and respectively uses the detection methods of the present application (Example 1) and the detection methods of Comparative Examples 1-3 for detection and determination. The model numbers of the polyamide epichlorohydrin (PAE) wet strength agents from different manufacturers are shown in Table 2.

[0127] Table 2.

[0128] In Table 2, "12.5%" in Sample 1-12 means that the solid content of the wet strength agent product is labeled by the manufacturer as 12.5%, "18%" means that the solid content of the wet strength agent product is labeled by the manufacturer as 18%, and "20%" means that the solid content of the wet strength agent product is labeled by the manufacturer as 20%.

[0129] The verification test results of the effective ingredient content of the PAE wet strength agent of each manufacturer in Example 1 are shown in Table 3.

[0130] Table 3. Test results of Example 1

[0131] In Table 3, the PAE (%) value is the mass concentration of PAE in each wet strength agent sample measured by nuclear magnetic resonance (NMR) detection, which is used to verify the accuracy of the detection method of the present application, and is a prior art, which will not be described here.

[0132] For convenience of comparison, the charge demand q, total nitrogen content and ash content in Table 3 are all converted from the measured values of charge demand, total nitrogen and ash content and the corresponding conversion formulas described above. As shown in Table 3, the verification results of Example 1 on Samples 1-12 are as follows: for Sample 10, Example 1 verifies that the solid content is 10.9%, which is much lower than the factory-labeled solid content of 12.5%, and determines that the effective ingredient content of the wet strength agent is unqualified, which cannot meet the needs of papermaking applications; for Sample 9, the appearance index is unqualified, and it is also determined that the effective ingredient content of the wet strength agent is unqualified, which cannot meet the needs of papermaking applications. These two products have no practical application value in actual production, so their subsequent index detection is not performed.

[0133] For Samples 1-3, the solid content measured by Example 1 is comparable to the factory-labeled solid content, and the corresponding PAE (%) value of each sample also indicates that the effective ingredient content of the wet strength agent in each sample is about 12%, and the other detection index values of Samples 1-3 are also within the range defined by the present application, so Example 1 determines that the effective ingredient content of the wet strength agent is qualified, which can meet the needs of papermaking applications. Similarly, Example 1 verifies and determines that the effective ingredient content of the wet strength agent of Samples 11-12 is qualified, which can meet the needs of papermaking applications.

[0134] Corresponding to samples 4-8, although the corresponding solid content, pH, viscosity indicators are all within the qualified range, but its or charge demand, or total nitrogen content, or ash content is not within the scope of the application defined qualified, therefore, example 1 verification, determination of sample 4-8 wet strength agent effective ingredient content is unqualified, it can't meet the needs of papermaking application.

[0135] According to the verification method described in Comparative Example 1, because the appearance identification, solid content, viscosity, pH value, chloropropanol content of samples 1-8 and samples 11-12 are all within the qualified range, only samples 9-10 wet strength agent effective ingredient content is unqualified, which cannot meet the needs of papermaking application. Compared with Example 1: it cannot effectively verify that the effective ingredient content of samples 4-8 wet strength agent is unqualified.

[0136] According to the verification method described in Comparative Example 2, because the appearance identification, solid content, viscosity, pH value, chloropropanol content and charge demand of samples 1-3, samples 7-8 and samples 11-12 are all within the qualified range, which can meet the needs of papermaking application, so only samples 9-10, samples 4-6 wet strength agent effective ingredient content is unqualified, which cannot meet the needs of papermaking application. Compared with Example 1: it cannot effectively verify that the effective ingredient content of samples 7-8 wet strength agent is unqualified.

[0137] Similarly, compared with Example 1, Comparative Example 3 cannot effectively verify that the effective ingredient content of sample 8 wet strength agent is unqualified, which cannot meet the needs of papermaking application; compared with Example 1, Comparative Example 4 cannot effectively verify that the effective ingredient content of sample 7 wet strength agent is unqualified, which cannot meet the needs of papermaking application;

[0138] In order to further verify the accuracy of the determination results of Example 1 and Comparative Examples 1-4, samples 1-8 and samples 11-12 are applied to the same papermaking process, and the final paper products are tested for wet tensile strength under the same process.

[0139] The wet tensile strength test method refers to the national standard "GB / T 465.2-2008 Paper and paperboard Determination of tensile strength after immersion in water". Specifically: cut the single-layer raw paper product into 15 mm wide, take it out after soaking in deionized water for 15 minutes, and measure its wet tensile strength by using a tensile strength tester (initial clamp distance 180 mm, tensile speed 20 mm / min), the results are recorded in Table 4. Among them, the wet tensile strength in the range of 700-1000 gf / inch is the qualified paper product.

[0140] Table 4. Wet tensile strength test results of paper products corresponding to samples 1-8 and samples 11-12

[0141] From the data in Table 4, it can be seen that only samples 1-3 and 11-12, corresponding to the produced paper, maintain a high and stable level of wet tensile strength, with a wet tensile strength in the range of 700-1000 gf / inch, which is consistent with the results of the verification and determination of Example 1. The wet tensile strength of samples 4-8, corresponding to the produced paper, is significantly lower, all below 670 gf / inch.

[0142] The above results show that the detection method of Comparative Examples 1-4 cannot effectively and reliably verify the true content of the effective component of the wet strength agent from different sources and different batches, as provided by the verification method of the present application, thereby leading to the use of wet strength agents with quality risks in production. This not only causes the performance of the final product to be substandard, but also causes significant economic losses to the enterprise due to process fluctuations and rising product failure rates.

[0143] The above is only a preferred embodiment of the present application and is not intended to limit the present application. It should be noted that, for those skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, and these improvements and modifications should also be considered within the scope of protection of the present application.

Claims

1. A method for verifying the content of active ingredients in wet strength agents, characterized in that, It uses appearance identification, solid content, viscosity, pH value, charge requirement, total nitrogen content and ash content as test indicators to determine whether the effective component content of the wet strength agent meets the requirements of papermaking applications. The charge requirement is detected using the following method: S5: Take an appropriate amount of the wet strength agent to be tested and dilute it with water. The dilution factor is A. Stir evenly to prepare the charge demand sample solution. Take an appropriate amount of the charge demand sample solution in the charge tester and test the charge demand q. The total nitrogen content was detected using the following method: S6: Take an appropriate amount of the wet strength agent to be tested and dilute it with water at a dilution factor of B. Stir well to prepare a total nitrogen test sample. After digestion and distillation, the total nitrogen content of the total nitrogen test sample is determined by colorimetric method. The ash content was detected using the following method: S7: Take an appropriate amount of wet strength agent to be tested and put it into a crucible. First, dry it in an oven to obtain an oven-dried sample. Weigh and record the mass of the oven-dried sample. Then, place the crucible in a high-temperature furnace and ignite it at high temperature for 1-4 hours until the oven-dried sample is completely ashed. Weigh and calculate the ash content.

2. The method for verifying the content of effective components in wet strength agents according to claim 1, characterized in that, In step S5: take 0.1 to 1.0 g of the wet strength agent to be tested, and the dilution factor A is 100 to 1000 times.

3. The method for verifying the content of effective components in wet-strength agents according to claim 1, characterized in that, In S5: Take an appropriate amount of sample liquid into the charge analyzer, use an anionic standard polymer titrant, and when the flow potential is 0mV, test the charge requirement q. The anionic standard polymer is sodium polyvinyl sulfonate (PES-Na).

4. The method for verifying the content of effective components in wet-strength agents according to claim 1, characterized in that, In step S6, 0.1–1.0 g of the wet strength agent to be tested is taken and diluted with water. The dilution factor B is 20–200 times to prepare a total nitrogen test sample.

5. The method for verifying the content of the effective component of a wet strength agent according to claim 4, characterized in that, In step S6, the total nitrogen test sample is placed in a nitrogen determination flask, and an appropriate amount of sodium hydroxide solution and nitrogen determination alloy are added. The mixture is allowed to stand for 1-2 hours. Then, it is heated and distilled, and the distillate is collected using a colorimetric tube containing sulfuric acid solution. Sodium hydroxide solution and Nessler's reagent are added, diluted, and shaken well. The color of the solution is compared with that of the standard colorimetric solution.

6. The method for verifying the content of effective components in a wet-strength agent according to claim 1, characterized in that, In step S7, an appropriate amount of wet strength agent to be tested is placed in a crucible, and the crucible is dried in an oven at a temperature of 100℃~120℃ for 4 hours to obtain the oven-dried sample.

7. The method for verifying the content of the effective component of a wet strength agent according to claim 6, characterized in that, The crucible and the oven-dry sample were placed in a high-temperature furnace and kept at 180–120°C for 15 minutes. Then, they were burned at a high temperature of 575±25°C for 1–4 hours until the oven-dry sample was completely ashed.

8. The method for verifying the content of the effective component of a wet strength agent according to claim 1, characterized in that, It also includes the detection of chloropropanol content.

9. The method for verifying the content of the effective component of a wet strength agent according to claim 1, characterized in that, The wet strength agent is deemed to have a stable and effective content of polyamide epichlorohydrin resin (PAE) with a solid content of 12.5 ± 0.5%, provided that the following indicators are met simultaneously: Charge requirement q = measured charge requirement × (A / 1000), and the acceptable range for charge requirement q is 300~450μeq / L; Total nitrogen content = measured total nitrogen value × (B / 200); the acceptable range for total nitrogen content is 13000~17000 mg / L; The ash content ranges from ≤0.5%; A represents the actual dilution factor when testing the charge requirement, which ranges from 100 to 1000. B represents the actual dilution factor when testing the total nitrogen, which ranges from 20 to 200.

10. A method for verifying the content of the effective component of a wet strength agent according to claim 9, characterized in that, When the active ingredient of the wet strength agent is polyamide epichlorohydrin resin (PAE), and the solid content is greater than 12.5 ± 0.5%, and the following index ranges are simultaneously met, the content of the active ingredient of the wet strength agent is determined to be stable and effective: Charge requirement q = measured charge requirement × e1, and the acceptable range for charge requirement q is 300~450μeq / L; Total nitrogen content = measured total nitrogen value × e2, and the acceptable range for total nitrogen content is 13000~17000 mg / L; Ash content = measured ash content × e3, and the acceptable range for ash content is ≤0.5%; Wherein, e1 = (12.5% / C) × (A / 1000); The value of e2 is (12.5% / C) × (B / 200). The value of e3 is 12.5% / C. Wherein, C represents the solid content of the wet strength agent, in units of %.

Images