A special modified starch ether for papermaking and a preparation method and application thereof

Abstract

The application discloses a special modified starch ether for papermaking and a preparation method and application thereof, and belongs to the technical field of starch ether preparation. The preparation method comprises the following steps: (1) pretreatment: pretreating starch at 60-90 DEG C, and then removing impurities to obtain pretreated raw materials; (2) alkalization: adding 100 parts of the pretreated raw materials and 5-10 parts of sodium sulfate into a solvent, carrying out dehydration treatment, cooling to below 35 DEG C, supplementing the solvent, adding alkali liquor, fully mixing, and then carrying out temperature rising reaction to obtain an alkalized product; (3) etherification: carrying out vacuum extraction after the alkalization is completed, adding propylene oxide into the alkalized product, and then carrying out reaction to obtain an etherified product; and (4) post-treatment: carrying out desolventization, neutralization and drying on the etherified product to obtain the special modified starch ether for papermaking. The modified starch ether prepared by the preparation method has the advantages of ultralow viscosity, high light transmittance, high whiteness, low ash and the like, can be quickly dispersed when being added into papermaking, and can provide good uniform coating, viscosity stability and water retention, so that the performance of paper can be improved.

Description

TECHNICAL FIELD

[0001] The application relates to a modified starch ether special for papermaking, a preparation method and application, and belongs to the technical field of starch ether preparation. BACKGROUND

[0002] At present, starch ethers on the market are generally modified from potato starch, corn starch, cassava starch and the like, and have obvious lower water retention than cellulose ethers, and different acid and alkali stabilities due to different modification degrees, and most products are suitable for gypsum-based mortar and cement-based mortar, and are medium or high viscosity finished products.

[0003] It is known that the addition of starch ethers in the papermaking industry can improve the dry and wet strength, wear resistance, opacity and printability of paper; due to large original particles and poor dispersibility, direct use affects the quality of paper. Modification treatment can further improve these properties, such as crosslinking modification, graft modification and graft copolymerization modification, so that the modified starch ether has a significant improvement in performance. Only by stabilizing the viscosity of the paper with the starch ether, the paper can be more compact and uniform, the strength, stability, surface smoothness and printability of the paper can be improved, and the ink consumption can be reduced.

[0004] Patent No. CN1191222 discloses a preparation method of a hydroxypropyl starch ether, which is prepared from starch, propylene oxide, complex alcohol and sodium hydroxide in water medium through dispersion, etherification, low-temperature reaction, high-temperature reaction, recovery, drying and screening, but the hydroxypropyl starch ether has medium viscosity and low whiteness. Patent No. CN201810228871.7 discloses a papermaking reinforcing starch and a preparation method thereof, adopts a mixed reaction machine, and automatically controls the reaction temperature through circulating hot water, and the preparation method is a segmented semi-dry method. The method increases the reactivity of the etherifying agent and reduces the amount of the alkaline activator, and also has the defects of high viscosity, low whiteness and low light transmittance. Patent No. 201611063122.0 discloses a one-pot method for preparing low-viscosity and high-strength hydroxypropyl starch ether, which is prepared by acidizing the starch and then alkalizing and etherifying the starch, and the hydroxypropyl starch ether has low viscosity and high strength, but the viscosity of the hydroxypropyl starch ether is still above 78 mPa.s, and the whiteness is below 83%, and a bleaching process is needed in the late stage of the papermaking process, and environmental pollution treatment is also needed.

[0005] In summary, the viscosity of the starch ethers applied on the market at present is mainly medium and high, and the whiteness and light transmittance are low, and the starch ethers need to be used according to different viscosities during use, which causes unstable factors for the stability of the formula and the quality of the product, and is not conducive to the application of modern high-end paper, and therefore, there is an urgent need for a papermaking special starch ether with good uniformity, viscosity stability, strong water retention, high whiteness and low viscosity. SUMMARY

[0006] In order to solve the above problems, a preparation method of a modified starch ether for papermaking is provided, and the modified starch ether prepared by the method has the advantages of ultra-low viscosity, high light transmittance, high whiteness, low ash and the like, and can provide excellent solubility, thermal stability, shear resistance, adhesion and film-forming property in papermaking, thereby increasing paper strength, improving paper whiteness and smoothness, and reducing paper powder and hair drop.

[0007] According to a first aspect of the present application, a preparation method of a modified starch ether for papermaking is provided, comprising the following steps:

[0008] (1) The starch is pretreated at 60-90°C, and then impurities are removed to obtain a pretreated raw material, and the pretreatment is selected from one of acidification followed by oxidation, simultaneous acidification and oxidation, and oxidation followed by acidification, the pH of acidification is 5-6.5, the weight ratio of the oxidizing agent to the starch used for oxidation is (1-10):10, the treatment time of acidification in acidification followed by oxidation and oxidation followed by acidification is 0.1-3h, the treatment time of oxidation is 40-60min, and the treatment time of simultaneous acidification and oxidation is 70-90min;

[0009] (2) Alkalization: 100 parts of the pretreated raw material and 5-10 parts of sodium sulfate are added to a solvent, after dehydration treatment, the temperature is lowered to below 35°C, solvent is supplemented, and alkali is added to a pH of 12-14, and then the mixture is fully mixed and heated to obtain an alkalized product;

[0010] (3) Etherification: After the alkalization is completed, vacuum is extracted, and propylene oxide is added to the alkalized product, and then the reaction is completed to obtain an etherified product;

[0011] (4) Post-treatment: The etherified product is subjected to desolventization, neutralization and drying to obtain the modified starch ether for papermaking.

[0012] The pretreatment of acidification and oxidation of the starch in the present application can reduce the molecular weight of the starch and stabilize the molecular weight distribution, which lays a foundation for subsequent synthesis of ultra-low viscosity starch ether, and the viscosity difference of the prepared starch ether is small, the solubility and dispersibility in paper production are improved, thereby the uniformity of various properties can be improved on the basis of improving the various properties of the paper. The starch in the present application is selected from at least one of corn starch, cassava starch and potato starch.

[0013] The pretreatment of the present application is based on the oxidation treatment supplemented with acidification treatment, the reason is that: oxidation can reduce the molecular weight of starch, excessive oxidation reaction will appear in the finished product with low viscosity, poor strength, easy to cause the poor adhesion of paperboard; insufficient oxidation, high viscosity, unable to use on the machine, paperboard drying slow, easy to skin and gelatinization. The oxidation of the present application can promote the oxidation of the intramolecular glucose basic unit of starch to aldehyde group or carboxyl group, and the additional acidification can make the aldehyde group in the acidification conditions form hydrogen bond between molecules, so that the interaction between the molecules in the starch ether is enhanced, and the tension in the paper is improved. If only acidification is performed, the molecular weight of starch will be insufficient, resulting in poor reaction viscosity reduction effect.

[0014] The amount of oxidizing agent in the above oxidation treatment is related to the viscosity of the final starch ether, if the amount of oxidizing agent is too large, the viscosity of the obtained starch ether is less than 10mp.s, which is difficult to play a role in papermaking, if the amount of oxidizing agent is too small, the viscosity of the obtained starch ether is increased and the viscosity difference is increased, which will cause the disadvantageous consequences of insufficient tensile strength of paper.

[0015] The above acidification treatment can be carried out before, during and after the oxidation treatment, the pH will affect the viscosity of the starch ether, if the pH is greater than the range, the acidification treatment is insufficient, resulting in the increase of the molecular weight and the molecular weight distribution of the pretreatment raw material, so that the viscosity of the starch ether is increased and the viscosity difference is increased, since the acidification will also affect the molecular weight of the pretreatment raw material, if the pH is less than the range, the viscosity of the starch ether is less than 10mp.s, which is difficult to play a role in papermaking.

[0016] The temperature of the above pretreatment is 60-90℃, the starch pretreatment at this temperature can shorten the process processing time, adapt to the preparation of ultra-low viscosity and high strength starch ether, and the obtained finished product can have a hydroxypropyl content of more than 21%, a whiteness of more than 90%, and the amount of bleaching agent used in the papermaking process can be reduced or eliminated. If the pretreatment temperature is too high or too low, the expected effect of the present application cannot be achieved.

[0017] Preferably, the pretreatment is a process of oxidation first and then acidification.

[0018] Optionally, the acidifying agent is selected from at least one of acetic acid, hydrochloric acid, sulfuric acid;

[0019] The concentration of the acidifying agent is 1-30%.

[0020] The acidifying agent can realize acidification of the raw material, the concentration of the acidifying agent is mass concentration, at which the pH of the acidification process can be accurately controlled, the industrial operation difficulty is reduced, the life efficiency is improved, and the acidifying agent is more easily mixed uniformly with the raw material at the concentration, thereby being conducive to obtaining pretreated raw material with low molecular weight and narrow molecular weight distribution, and thereby obtaining starch ether with low viscosity and small viscosity difference, so as to improve the uniformity of various performances of paper.

[0021] Optionally, the oxidizing agent is selected from at least one of hydrogen peroxide, sodium hypochlorite, and benzoyl peroxide.

[0022] The concentration of the oxidizing agent is 10-50%.

[0023] The oxidizing agent can realize oxidative degradation of the starch to prepare starch ether with ultra-low viscosity, and the concentration of the oxidizing agent is also mass concentration, at which it is also conducive to obtaining pretreated raw material with low molecular weight and narrow molecular weight distribution, and thereby obtaining starch ether with low viscosity and small viscosity difference. If the concentration exceeds the range, the oxidizing agent is not easily mixed uniformly with the starch, and the molecular weight of the starch is low and the molecular weight distribution is too wide through oxidation, resulting in the viscosity of the starch ether being less than 10 mp.s, which is difficult to play a role in papermaking; if the concentration is lower than the range, the viscosity of the obtained starch ether is increased and the viscosity difference is increased, which can cause uneven tensile strength of the paper, resulting in large difference in mechanical properties of the paper.

[0024] Optionally, the solute in the lye is selected from at least one of anhydrous sodium carbonate, sodium bicarbonate, sodium hydroxide, and potassium hydroxide.

[0025] The lye can realize alkalization of the pretreated raw material to obtain ideal starch ether product, and alkalization of the lye at pH 12-14 can ensure that the material is warm with the lye, reduce the risk of excessive local alkalization, slow down the temperature rise during the alkalization process, and achieve uniform alkalization effect. If the pH is higher than the range, the material is alkalized excessively, the pH of the finished product is too high, the conductivity is increased, and the paper quality is affected. If the pH is lower than the range, the molecular weight of the alkalized starch is insufficient, which affects the synthesis of hydroxypropyl in the subsequent reaction stage.

[0026] Preferably, the solute in the lye is sodium hydroxide.

[0027] Optionally, the dehydration temperature in step (2) is 60-65°C, and the dehydration time is 20-30 min.

[0028] The dehydration temperature and time can realize rapid dehydration of the system, provide a very low humidity environment for subsequent addition of lye, and facilitate smooth alkalization.

[0029] Optionally, the reaction temperature in step (2) is 45-52℃, and the reaction time is 60-90 min.

[0030] The alkali temperature is slightly higher than the alkali temperature of common starch, which is suitable for the needs of the pretreated starch and achieves the purpose of alkali; if the alkali temperature is too low or the alkali time is too short, the molecular activity of the raw material is insufficient, the decomposition amount is small, and the hydroxypropyl reaction synthesis is affected; if the alkali temperature is too high or the alkali time is too long, the material is easy to be gelatinized and discolored, which affects the whiteness and light transmission of the finished product.

[0031] Optionally, the addition amount of propylene oxide in step (3) is 21-27 parts.

[0032] The propylene oxide is used for etherification of the alkali product to obtain modified starch ether, and the addition amount of the propylene oxide can increase the hydroxypropyl content in the modified starch ether to obtain high-quality modified starch ether, and the use of the modified starch ether in papermaking can significantly improve the performance of the paper; if the addition amount of the propylene oxide is too small, the synthesis of hydroxypropyl is reduced due to insufficient etherifying agent, and if the addition amount of the propylene oxide is too much, the material is severely agglomerated after the reaction, the discharge is difficult, and the etherifying agent is wasted.

[0033] Optionally, the reaction in step (3) is first heated to 40-52℃ for 1-1.5h, and then heated to 60-65℃ for 4.5-5h.

[0034] The temperature and time of the above etherification reaction can ensure that the etherifying agent and the material are fully and uniformly mixed and contacted, and the etherification is slowly carried out at a low temperature in the first stage and is long-acting and gentle at a constant temperature in the second stage, which prevents the rapid release of reaction pressure of the etherifying agent at high temperature.

[0035] Optionally, the desolventization is to cool the etherification product to 65-75℃ and vacuumize for 20-30 min to obtain the desolventized product.

[0036] The desolventization treatment can remove the residual solvent while removing most of the water in the material, reduce the caking of the desolventized product, and facilitate the smooth progress of subsequent drying, thereby improving the production efficiency of the modified starch ether.

[0037] Optionally, the neutralization is to add 4-6 parts of acid and 8-12 parts of solvent to the desolventized product, acidify for 60-90 min, vacuumize for 10-20 min, and then cool the material to below 45℃ to obtain the neutralized product.

[0038] The neutralization operation uses acid to neutralize to pH 6-8, and the addition of solvent in the neutralization can improve the mixing uniformity of the acid and the desolventized product, thereby improving the neutralization efficiency and effect; cooling the material to below 45℃ can prevent the high-temperature oxidation of the neutralized product and improve the whiteness of the modified starch ether.

[0039] Optionally, the acid used for neutralization is selected from at least one of hydrochloric acid, oxalic acid or glacial acetic acid.

[0040] Optionally, the drying is to a moisture content of the material of ≤8.0%.

[0041] The drying can meet the needs of the industry, avoid the caking of modified starch ethers during storage, and improve the storage stability of the modified starch ethers.

[0042] According to a second aspect of the present application, there is provided a papermaking special modified starch ether prepared by the preparation method of the papermaking special modified starch ether according to any one of the above.

[0043] Optionally, the viscosity of the papermaking special modified starch ether is 10-45 mp.s, preferably 10-30 mp.s, and more preferably 20-30 mp.s.

[0044] Optionally, the whiteness of the papermaking special modified starch ether is 87% or more, preferably 90% or more, and more preferably 92% or more.

[0045] Optionally, the light transmittance of the papermaking special modified starch ether is 11% or more, preferably 16% or more.

[0046] Optionally, the hydroxypropyl content of the papermaking special modified starch ether is 21% or more, preferably 21%-25%, and more preferably 23%-25%.

[0047] Optionally, the moisture content of the papermaking special modified starch ether is 8% or less, preferably 7.9% or less.

[0048] Optionally, the ash content of the papermaking special modified starch ether is 6% or less, preferably 5.9% or less.

[0049] According to a third aspect of the present application, there is provided the use of the papermaking special modified starch ether according to any one of the above in papermaking.

[0050] The beneficial effects of the present application include but are not limited to:

[0051] 1. The preparation method of the papermaking special modified starch ether according to the present application has the advantages of ultra-low viscosity, high light transmittance, high whiteness, low ash content, etc., can quickly disperse when added in papermaking, and provides good uniformity, viscosity stability, water retention, to improve the performance of paper.

[0052] 2. The preparation method of the papermaking special modified starch ether according to the present application can reduce the molecular weight of the raw material and stabilize the molecular weight distribution by pretreating the starch, which is beneficial for subsequent alkalization and etherification to obtain a starch ether with ultra-low viscosity, and the starch ether also has the advantages of small viscosity difference and higher uniformity.

[0053] 3. The method for preparing the papermaking special modified starch ether according to the application, the pretreatment of the raw material can increase the content of hydroxypropyl group in the subsequent vacuum low-temperature dehydration, low-temperature alkalization and etherification, and improve the whiteness and light transmittance of the product, and reduce the color spots, and the various indexes are stably improved.

[0054] 4. The method for preparing the papermaking special modified starch ether according to the application, the raw material cost is low, the heat consumption is small, and the quality stability is good, which is superior to the current requirements of the papermaking industry for the indexes of starch ether, and is beneficial to promote the technological innovation and upgrading of the papermaking industry.

[0055] 5. The papermaking special modified starch ether according to the application, the viscosity is between 10-45mp.s, the content of hydroxypropyl group is more than 21%, the whiteness is more than 90%, and the light transmittance is more than 16%, which is completely superior to the standard, the physical and chemical indexes meet the market user demand, and has a good use prospect in the papermaking industry. DETAILED DESCRIPTION

[0056] The application will be described in detail below in combination with examples, but the application is not limited to these examples.

[0057] Unless otherwise specified, the raw materials in the examples and comparative examples of the application are purchased through commercial channels.

[0058] Unless otherwise specified, the method used in the examples and comparative examples of the application is a conventional method in the prior art. The concentration of the acidifying agent and the oxidizing agent in the application refers to the mass concentration, and the solvent used in the preparation of the papermaking special modified starch ether of the application can be a solvent commonly used in the art, such as methanol, ethanol, etc. The specific selection of the solvent does not constitute a limitation on the application, and the solvent used in the following examples and comparative examples is anhydrous ethanol.

[0059] Example 1

[0060] This example relates to a method for preparing a papermaking special modified starch ether, which comprises the following steps:

[0061] (1) The potato starch is pretreated by acidification and then oxidation at 60℃, and then impurities are removed to obtain a pretreated raw material, the pH of acidification is 6.5, the weight ratio of the oxidizing agent to the starch used in oxidation is 10:10, the treatment time of acidification in the acidification and then oxidation and the acidification and then oxidation is 3h, the treatment time of oxidation is 60min, the acidifying agent is selected from acetic acid, the concentration of the acidifying agent is 1%, and the oxidizing agent is selected from hydrogen peroxide, and the concentration of the oxidizing agent is 10%;

[0062] (2) Alkalization: 100 parts of pretreated raw material, 5 parts of sodium sulfate were added into solvent, and after dehydration treatment at 65 °C for 20 min, the temperature was lowered to below 35 °C, solvent was supplemented, and sodium carbonate alkali was added to pH 14, and after mixing, the temperature was raised to 45 °C for reaction for 60 min to obtain an alkalized product;

[0063] (3) Etherification: After the alkalization was completed, vacuum was extracted, 21 parts of propylene oxide was added to the alkalized product, and the temperature was raised to 40 °C for reaction for 1 h, and then the temperature was raised to 65 °C for reaction for 4.5 h to obtain an etherified product;

[0064] (4) Post-treatment: The etherified product was cooled to 75 °C and vacuum-extracted for 20 min to obtain a desolventized product, 4 parts of hydrochloric acid and 8 parts of solvent were added to the desolventized product, and acidification reaction was performed for 60 min, vacuum-extraction was performed for 10 min, and then the material was cooled to below 45 °C to obtain a neutralized product, and the neutralized product was dried until the moisture content of the material was ≤8.0% to obtain a papermaking special modified starch ether.

[0065] Example 2

[0066] The present embodiment relates to a preparation method of a papermaking special modified starch ether, comprising the following steps:

[0067] (1) The cassava starch was simultaneously oxidized and acidified pretreated at 90 °C, and then impurities were removed to obtain a pretreated raw material, the treatment time was 90 min, the pH of acidification was 5, the weight ratio of oxidizing agent to starch was 1:10, the acidifying agent was selected from sulfuric acid, the concentration of acidifying agent was 30%, and the oxidizing agent was selected from benzoyl peroxide, and the concentration of oxidizing agent was 50%;

[0068] (2) Alkalization: 100 parts of pretreated raw material, 5 parts of sodium sulfate were added into solvent, and after dehydration treatment at 65 °C for 20 min, the temperature was lowered to below 35 °C, solvent was supplemented, and sodium carbonate alkali was added to pH 14, and after mixing, the temperature was raised to 45 °C for reaction for 60 min to obtain an alkalized product;

[0069] (3) Etherification: After the alkalization was completed, vacuum was extracted, 21 parts of propylene oxide was added to the alkalized product, and the temperature was raised to 40 °C for reaction for 1 h, and then the temperature was raised to 65 °C for reaction for 4.5 h to obtain an etherified product;

[0070] (4) Post-treatment: The etherified product was cooled to 75 °C and vacuum-extracted for 20 min to obtain a desolventized product, 4 parts of hydrochloric acid and 8 parts of solvent were added to the desolventized product, and acidification reaction was performed for 60 min, vacuum-extraction was performed for 10 min, and then the material was cooled to below 45 °C to obtain a neutralized product, and the neutralized product was dried until the moisture content of the material was ≤8.0% to obtain a papermaking special modified starch ether.

[0071] Example 3

[0072] The embodiment relates to a preparation method of a special modified starch ether for papermaking, and comprises the following steps:

[0073] (1) the corn starch is pretreated by acidification and oxidation at 80 DEG C, and then impurities are removed to obtain pretreated raw materials, the acidification time of the acidification after oxidation is 0.1 h, the oxidation time is 40 min, the pH of the acidification is 6, the weight ratio of the oxidizing agent to the starch is 3:10, the acidifying agent is selected from hydrochloric acid, the concentration of the acidifying agent is 20%, and the oxidizing agent is selected from sodium hypochlorite, and the concentration of the oxidizing agent is 35%;

[0074] (2) alkali treatment: 100 parts of the pretreated raw materials and 5 parts of sodium sulfate are added into a solvent, dehydration treatment is carried out at 65 DEG C for 20 min, then the temperature is lowered to below 35 DEG C, the solvent is supplemented, and sodium hydroxide lye is added until the pH is 12, the mixture is fully mixed, then the temperature is raised to 45 DEG C, and reaction is carried out for 60 min to obtain alkali-treated products;

[0075] (3) etherification: after the alkali treatment is completed, vacuum is extracted, 24 parts of propylene oxide are added into the alkali-treated products, the temperature is raised to 40 DEG C first, and reaction is carried out for 1 h, then the temperature is raised to 60 DEG C, and reaction is carried out for 5 h to obtain etherification products;

[0076] (4) post-treatment: the etherification products are cooled to 75 DEG C, vacuum is extracted for 20 min, and the desolventized products are obtained, 4 parts of glacial acetic acid and 10 parts of the solvent are added into the desolventized products, acidification reaction is carried out for 60 min, vacuum is extracted for 20 min, then the material is cooled to below 45 DEG C to obtain neutralized products, the neutralized products are dried until the moisture content of the material is less than or equal to 8.0%, and the special modified starch ether for papermaking is obtained.

[0077] Example 4

[0078] The embodiment is different from the example 3 in that the concentration of the acidifying agent is 40%, and the rest is the same as the example 3.

[0079] Example 5

[0080] The embodiment is different from the example 3 in that the concentration of the oxidizing agent is 70%, and the rest is the same as the example 3.

[0081] Example 6

[0082] The embodiment is different from the example 3 in that the concentration of the oxidizing agent is 5%, and the rest is the same as the example 3.

[0083] Example 7

[0084] The embodiment is different from the example 3 in that the alkali treatment temperature of the step (2) is 30 DEG C, and the rest is the same as the example 3.

[0085] Example 8

[0086] The difference between this example and Example 3 is that after adding propylene oxide in step (3), the temperature is first increased to 60°C for 5h, and then decreased to 40°C for 1h to obtain the etherification product, and the rest is the same as Example 3.

[0087] Comparative Example 1

[0088] The difference between this comparative example and Example 3 is that only acidification treatment is performed in step (1), and no oxidation treatment is performed, and the specific acidification treatment conditions and the rest of the conditions are the same as Example 3.

[0089] Comparative Example 2

[0090] The difference between this comparative example and Example 3 is that only oxidation treatment is performed in step (1), and no acidification treatment is performed, and the specific oxidation treatment conditions and the rest of the conditions are the same as Example 3.

[0091] Comparative Example 3

[0092] The difference between this comparative example and Example 3 is that step (1) is not performed, and step (2) is directly performed on corn starch, and the rest of the conditions are the same as Example 3.

[0093] Test Example 1

[0094] The modified starch ethers prepared in the above examples and comparative examples were tested according to the test methods in Table 1, and the test results are shown in Table 2.

[0095] Table 1 Test Methods

[0096] Test item Test instrument Test method Reference standard Whiteness Whiteness meter —— GB / T 22427.6-2008 Transmittance Luminometer —— GB / T 34263-2017 Viscosity Analyzer —— GB / T 22427.7-2023 Hydroxypropyl Luminometer Spectrophotometry GB / T 40998-2021 Moisture Oven —— GB / T 22427.7-2023 Ash content Muffle furnace, crucible —— GB / T 22427.8-2024

[0097] Table 2 Test Results

[0098]

[0099]

[0100] According to the above test results, it can be seen that the whiteness of the finished product obtained by Example 1, which first acidifies and then oxidizes the raw material, Example 2, which first oxidizes and then acidifies the raw material, and Example 3, which simultaneously acidifies and oxidizes, are all greater than 90%, indicating that the pretreatment of the raw material is the key to whitening. In Examples 1-3, the light transmittance and hydroxypropyl content are correspondingly increased, and the viscosity is effectively reduced. In Example 3, the raw material is first oxidized and then acidified, and the acidification pH value is 6 (between 5-6.5), which can well adjust the molecular chain, and the viscosity of the finished product is more in line with the requirements of papermaking process.

[0101] The whiteness and transparency of the product slightly decreased and the viscosity slightly decreased, which indicated that although the concentration of the acidifying agent affected the whiteness, transparency and hydroxypropyl content of the final product and to some extent affected the viscosity of the product, the viscosity difference of the starch ether of Example 4 increased compared with Example 3 when the concentration of the acidifying agent was doubled and the pH of the acidification was unchanged. The transparency decreased and the viscosity decreased as the oxidizing agent increased and the viscosity increased as the oxidizing agent decreased in Example 5 and Example 6 compared with Example 3, which indicated that the oxidizing agent also affected the viscosity and the viscosity difference of the starch ether of Example 5 and Example 6 increased compared with Example 3.

[0102] The transparency and hydroxypropyl content of the product greatly decreased and the viscosity increased when the alkalization temperature decreased in Example 7, which indicated that the alkalization temperature of the pretreated raw material was also a key point for reducing the viscosity on the basis of the pretreatment of the raw material and the alkalization temperature greatly affected the synthesis of hydroxypropyl.

[0103] It can be seen from the comparison of Comparative Example 1 and Comparative Example 2 and Example 3 that the whiteness and transparency of the product were low and the viscosity was high and the synthesis of hydroxypropyl was moderate when only the raw material was subjected to single acidification and oxidation treatment, which did not improve the starch ether of the ordinary formula. The whiteness and transparency of the product using untreated starch in Comparative Example 3 were obviously different from the test after acidification and alkalization, the viscosity was too high to meet the papermaking process and the hydroxypropyl content was also low.

[0104] It can be seen that the acidification, oxidation pretreatment and subsequent alkalization treatment of the raw material in the application had obvious effects on the viscosity reduction and whiteness improvement of the product and could promote the synthesis of hydroxypropyl.

[0105] The modified starch ethers in the above examples and comparative examples were used for papermaking according to the same ratio and process, the products of the examples had the advantages of good uniform coating, stable viscosity, strong water retention, high whiteness and low viscosity, and high-tension and high-tensile-strength paper could be prepared. The uniform coating and viscosity stability of the products of the comparative examples decreased compared with the products of the examples due to the high viscosity, and the whiteness was insufficient and the appearance and texture of the paper decreased. The performance difference of the paper prepared by adjusting the concentrations of the acidifying agent and the oxidizing agent in Example 4-6 compared with Example 3 increased, especially the tensile strength was more uneven, which was because the viscosity obtained in Table 2 was the average viscosity of the product, but the viscosity difference of the products in Example 4-6 was larger than that in Example 3, which affected the uniformity of the performance of the paper.

[0106] The above merely illustrates the embodiments of the present application, and the protection scope of the present application is not limited to these specific embodiments, but determined by the claims of the present application. The present application can have various changes and modifications for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the technical thought and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a paper-making-specific modified starch ether, characterized in that, Includes the following steps: (1) The starch is pretreated at 60-90℃ and then impurities are removed to obtain the pretreated raw material. The pretreatment is selected from oxidation followed by acidification. The pH of the acidification is 5-6.

5. The weight ratio of the oxidant used in the oxidation to the starch is (1-10):

10. The acidification time in the oxidation followed by acidification is 0.1-3h and the oxidation time is 40-60min. The acidifying agent used in the acidification is selected from at least one of acetic acid, hydrochloric acid, and sulfuric acid. The concentration of the acidifying agent is 1-30%. The oxidizing agent is selected from at least one of hydrogen peroxide, sodium hypochlorite, and benzoyl peroxide. The concentration of the oxidizing agent is 10-50%. (2) Alkalization: Add 100 parts of pretreatment raw material and 5-10 parts of sodium sulfate to the solvent. After dehydration, cool down to below 35°C, add solvent and alkali solution to make the pH 12-14. After thorough mixing, heat up to react and obtain alkalization product. The reaction temperature of alkalization is 45-52°C and the reaction time is 60-90 min. (3) Etherification: After the alkalization is completed, vacuum is drawn, propylene oxide is added to the alkalization product, the temperature is first raised to 40-52℃ and reacted for 1-1.5h, and then the temperature is raised to 60-65℃ and reacted for 4.5-5h to obtain the etherified product; (4) Post-processing: The etherified product is desolventized, neutralized and dried to obtain the paper-making-specific modified starch ether.

2. The preparation method of the papermaking-specific modified starch ether according to claim 1, characterized in that, The solute in the alkaline solution is selected from at least one of anhydrous sodium carbonate, sodium bicarbonate, sodium hydroxide, and potassium hydroxide.

3. The preparation method of the papermaking-specific modified starch ether according to claim 1, characterized in that, In step (2), the dehydration temperature is 60-65℃ and the dehydration time is 20-30min.

4. The preparation method of the papermaking-specific modified starch ether according to claim 1, characterized in that, In step (3), the amount of propylene oxide added is 21-27 parts.

5. The preparation method of the papermaking-specific modified starch ether according to claim 1, characterized in that, The desolventization process involves cooling the etherified product to 65-75°C and then applying a vacuum for 20-30 minutes to obtain the desolventized product.

6. The preparation method of the papermaking-specific modified starch ether according to claim 1, characterized in that, The neutralization process involves adding 4-6 parts of acid and 8-12 parts of solvent to the desolventized product, acidifying for 60-90 minutes, applying vacuum for 10-20 minutes, and then cooling the material to below 45°C to obtain the neutralized product; and / or The drying process involves drying the material until the moisture content is ≤8.0%.

7. The paper-making-specific modified starch ether prepared by the preparation method of any one of claims 1-6.

8. The application of the paper-specific modified starch ether as described in claim 7 in papermaking.

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