Special modified starch ether for papermaking as well as preparation method and application thereof

Abstract

The invention discloses special modified starch ether for papermaking as well as a preparation method and application thereof, and belongs to the technical field of preparation of starch ether. The preparation method comprises the following steps: (1) pretreatment: pretreating starch at 60-90 DEG C, and then removing impurities to obtain a pretreated raw material; (2) alkalization: adding 100 parts of the pretreated raw material and 5-10 parts of sodium sulfate into a solvent, carrying out dehydration treatment, cooling to 35 DEG C or below, supplementing the solvent, adding alkali liquor, fully mixing, and carrying out heating reaction to obtain an alkalized product; (3) etherification: vacuumizing after alkalization is finished, adding epoxypropane into an alkalized product, and reacting to obtain an etherified product; and (4) post-treatment: desolventizing, neutralizing and drying the etherified product to obtain the special modified starch ether for papermaking. The modified starch ether obtained 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 in papermaking, and provides good coating uniformity, viscosity stability and water retention so as to improve various properties of paper.

Description

Technical Field

[0001] The present application relates to a modified starch ether for papermaking, a preparation method and an application thereof, belonging to the technical field of starch ether preparation. Background Art

[0002] At present, starch ethers generally modified from potato starch, corn starch, cassava starch, etc. on the market have significantly lower water retention than cellulose ethers, and show different acid-base stabilities due to different degrees of modification. Most products are applicable to gypsum-based mortar and cement-based mortar, and are all medium-viscosity or high-viscosity finished products.

[0003] As is well known, the addition of starch ether in the papermaking industry can improve the dry and wet strength, abrasion resistance, opacity and printability of paper, etc.; due to the relatively large original particles and poor dispersibility, direct use affects the quality of paper. Through modification treatment, these properties can be further improved, such as cross-linking modification, grafting modification, graft copolymerization modification, etc., making the modified starch ether have a significant improvement in performance. Only by stabilizing the viscosity of the paper with starch ether can the paper be made more compact and uniform, improving the strength, stability, surface smoothness and printing adaptability of the paper, and reducing ink consumption.

[0004] Patent No. CN1191222 discloses a preparation method of hydroxypropyl starch ether. The hydroxypropyl starch ether is prepared by using starch, propylene oxide, complex alcohol and sodium hydroxide as raw materials in an aqueous medium through dispersion, etherification, low-temperature reaction, high-temperature reaction, recovery, drying and screening. However, it has medium viscosity and low whiteness. Patent No. CN201810228871.7 discloses a papermaking reinforcing starch and a preparation method thereof, which uses a mixing reactor and automatically controls the reaction temperature with circulating hot water. The preparation method is a segmented semi-dry method reaction. This method increases the reaction activity of the etherifying agent and reduces the dosage of the alkaline activator, but also has the disadvantages 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. After acidifying the starch and then alkalizing and etherifying it, a low-viscosity and high-strength hydroxypropyl starch ether is prepared. However, the viscosity of this hydroxypropyl starch ether is still above 78 mPa·s, and the whiteness is below 83%. A bleaching process and environmental pollution treatment are required in the later stage of the papermaking process.

[0005] In summary, the viscosities of starch ethers currently applied on the market are mainly medium and high viscosities, and the whiteness and light transmittance are relatively low. When used, it needs to be formulated according to different viscosities, which causes unstable factors for the stability of the formulation and the product quality, and is not conducive to the application of modern high-end papers. Therefore, there is an urgent need for a papermaking special starch ether with good leveling property, viscosity stability, strong water retention performance, high whiteness and low viscosity. Summary of the Invention

[0006] To solve the above problems, a preparation method of a modified starch ether for papermaking is provided. The modified starch ether prepared by this method has the advantages of ultra-low viscosity, high light transmittance, high whiteness, and low ash content. When used in papermaking, it can provide excellent solubility, thermal stability, shear resistance, adhesiveness, and film-forming property, thereby increasing the strength of the paper, improving the whiteness and smoothness of the paper, and reducing powdering and fluffing of the paper.

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

[0008] (1) Pretreat the starch at 60 - 90 °C, and then remove impurities to obtain a pretreated raw material. 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 oxidant used in oxidation to starch is (1 - 10):10. In the cases of acidification followed by oxidation and oxidation followed by acidification, the treatment time of acidification is 0.1 - 3 h, the treatment time of oxidation is 40 - 60 min, and the treatment time of simultaneous acidification and oxidation is 70 - 90 min;

[0009] (2) Alkalization: Add 100 parts of the pretreated raw material and 5 - 10 parts of sodium sulfate to a solvent, cool down to below 35 °C after dehydration treatment, supplement the solvent and add an alkali solution until the pH is 12 - 14, fully mix and then heat up to react to obtain an alkalized product;

[0010] (3) Etherification: After the alkalization is completed, evacuate the air, add propylene oxide to the alkalized product, and react to obtain an etherified product;

[0011] (4) Post-treatment: Perform desolvation, neutralization, and drying on the etherified product to obtain the modified starch ether for papermaking.

[0012] In the present application, the pretreatment of acidification and oxidation of starch can reduce the molecular weight of starch and stabilize the molecular weight distribution, laying a foundation for the subsequent synthesis of ultra-low viscosity starch ether. Moreover, the viscosity difference of the prepared starch ether is small, and the dissolution uniformity and dispersibility in paper production are improved, thereby improving the uniformity of various properties while enhancing 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 this application is carried out by adding acidification treatment on the basis of oxidation treatment. The reasons are as follows: Oxidation can reduce the molecular weight of starch. If the oxidation reaction is excessive, the finished product will have low viscosity, poor strength, and it is easy to cause poor bonding of cardboard. If the oxidation is insufficient, the viscosity is too high to be used on the machine, the cardboard dries slowly, and it is easy to form a skin and gel. The oxidation in this application can promote the oxidation of hydroxymethyl in the glucose basic unit within the starch molecule to aldehyde group or carboxyl group. The additional acidification can make the aldehyde group easily form hydrogen bonds between molecules under acidic conditions, enhance the intermolecular force within the starch ether, and improve the tensile force in the paper. If only acidification is carried out, the reduction of the starch molecular weight is insufficient, resulting in poor viscosity reduction effect in the subsequent reaction.

[0014] In the above oxidation treatment, the dosage of the oxidant is related to the viscosity of the final starch ether. If the addition amount of the oxidant is too large, the viscosity of the obtained starch ether is lower than 10 mp.s and it is difficult to play a role in papermaking. If the addition amount of the oxidant is too small, the viscosity of the obtained starch ether increases and the viscosity difference increases, which will cause the adverse consequence of insufficient tensile strength of the paper.

[0015] The above acidification treatment can be carried out before, during, and after the oxidation treatment. Its pH affects the viscosity of the starch ether. If the pH is greater than this range, the acidification treatment is insufficient, resulting in an increase in the molecular weight and molecular weight distribution of the pretreatment raw material, and the viscosity of the starch ether increases and the viscosity difference increases. Since acidification also affects the molecular weight of the pretreatment raw material, if the pH is less than this range, the viscosity of the starch ether is lower than 10 mp.s and it is difficult to play a role in papermaking.

[0016] The temperature of the above pretreatment is 60 - 90 °C. Conducting 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% and a whiteness of more than 90%, reducing or eliminating the usage amount of bleaching agents in the papermaking process. If the pretreatment temperature is too high or too low, the expected effect of this application cannot be achieved.

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

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

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

[0020] The above acidifying agents can all achieve acidification treatment of raw materials. The concentration of the acidifying agent is the mass concentration. At this concentration, it is convenient to accurately control the pH of the acidification treatment, reduce the difficulty of industrial operation, improve production efficiency, and the acidifying agent is more likely to improve the mixing uniformity with the raw materials at this concentration. Furthermore, it is beneficial to obtain a pretreated raw material with a low molecular weight and a narrow molecular weight distribution, thereby obtaining a starch ether with a low viscosity and a small viscosity difference, so as to improve the uniformity of various properties of the 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 achieve oxidative degradation of starch to prepare an ultra-low viscosity starch ether. The concentration of the oxidizing agent is also the mass concentration. At this concentration, it is also beneficial to obtain a pretreated raw material with a low molecular weight and a narrow molecular weight distribution, thereby obtaining a starch ether with a low viscosity and a small viscosity difference. If the concentration exceeds this range, the oxidizing agent and starch are not easily mixed evenly, and through oxidation, the molecular weight of the starch will be low and the molecular weight distribution will be too wide, resulting in the viscosity of the starch ether being lower than 10 mp.s and it being difficult to play a role in papermaking; if the concentration is lower than this range, the viscosity of the obtained starch ether will increase and the viscosity difference will increase, resulting in uneven tensile strength of the paper and large differences in the mechanical properties of the paper.

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

[0025] The above alkali solutions can all achieve alkalization of the pretreated raw material to obtain an ideal starch ether product. By carrying out alkalization with the alkali solution at a pH of 12-14, it can ensure the progress of the material and the alkali solution, reduce the risk of excessive local alkalization, make the temperature rise slowly during the alkalization process, and achieve a uniform alkalization effect. If the pH is higher than this range, the material will be overly alkalized and the pH value of the finished product will be too high, resulting in an increase in conductivity and affecting the quality of the paper product. If the pH is lower than this range, the molecular weight of the alkalized starch will be insufficient, affecting the synthesis of hydroxypropyl groups in the subsequent reaction stage.

[0026] Preferably, the solute in the alkali solution is selected from sodium hydroxide.

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

[0028] This dehydration temperature and time can achieve rapid dehydration of the system, provide a very low humidity environment for the subsequent addition of the alkali solution, and facilitate the smooth progress of alkalization.

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

[0030] This alkalization temperature is slightly higher than that of ordinary starch, which meets the requirements of this pretreated starch to achieve the purpose of alkalization. If the alkalization temperature is too low or the alkalization time is too short, the activity of raw material molecules is insufficient, the decomposition amount is small, which affects the synthesis of hydroxypropyl reaction. If the alkalization temperature is too high or the alkalization time is too long, the material is prone to gelatinization and discoloration, affecting the whiteness and light transmittance of the finished product.

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

[0032] Propylene oxide is used to etherify the alkalized product to obtain a modified starch ether. The addition amount of this propylene oxide can increase the hydroxypropyl content in the modified starch ether to obtain a high-quality modified starch ether. Using this modified starch ether in papermaking can significantly improve the various properties of the paper. If the addition amount of propylene oxide is too small, the synthesis of hydroxypropyl will be reduced due to insufficient etherification agent. If the addition amount of propylene oxide is too large, the material will agglomerate seriously in the later stage of the reaction, making it difficult to discharge the material, and causing waste of the etherifying agent.

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

[0034] The temperature and time of the above etherification reaction can ensure that the etherifying agent and the material are fully and evenly mixed and contacted, slowly etherify at a low temperature in one stage, and carry out long-term mild etherification at a constant temperature in the second stage, preventing the rapid release of the reaction pressure of the etherifying agent and the sudden increase in pressure at high temperature.

[0035] Optionally, the desolvation is to cool the etherification product to 65 - 75 °C and evacuate for 20 - 30 min to obtain the desolvated product.

[0036] This desolvation treatment can remove the residual solvent and take away most of the water in the material at the same time, reduce the caking of the desolvated product, and facilitate the subsequent drying to proceed smoothly, 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 desolvated product, carry out acidification reaction for 60 - 90 min, evacuate for 10 - 20 min, and then cool the material to below 45 °C to obtain the neutralized product.

[0038] The neutralization operation is to neutralize with acid to a pH of 6 - 8. Adding solvent in this neutralization can improve the mixing uniformity of the acid and the desolvated product, thereby improving the neutralization efficiency and effect. Cooling the material to below 45 °C can prevent the neutralized product from oxidizing and turning back to color at high temperature, improving 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 dry until the moisture content of the material ≤ 8.0%.

[0041] This drying can meet the industry's requirements, avoid caking of the modified starch ether during storage, and improve the storage stability of the modified starch ether.

[0042] According to the second aspect of the present application, there is provided a paper-making special modified starch ether prepared by the preparation method of the low paper-making special modified starch ether described in any one of the above.

[0043] Optionally, the viscosity of the paper-making 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 paper-making special modified starch ether is above 87%, preferably above 90%, and more preferably above 92%.

[0045] Optionally, the light transmittance of the paper-making special modified starch ether is above 11%, preferably above 16%.

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

[0047] Optionally, the moisture content of the paper-making special modified starch ether is below 8%, preferably below 7.9%.

[0048] Optionally, the ash content of the paper-making special modified starch ether is below 6%, preferably below 5.9%.

[0049] According to the third aspect of the present application, there is provided the application of the low paper-making special modified starch ether described in any one of the above in papermaking.

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

[0051] 1. According to the preparation method of the paper-making special modified starch ether of the present application, it has the advantages of ultra-low viscosity, high light transmittance, high whiteness, low ash, etc., can be quickly dispersed when added to papermaking, and provides good leveling property, viscosity stability, and water retention property to improve the various properties of the paper.

[0052] 2. According to the preparation method of the paper-making special modified starch ether of the present application, pre-treating the starch can reduce the molecular weight of the raw material and stabilize the molecular weight distribution, facilitate subsequent alkalization and etherification to obtain an ultra-low viscosity starch ether, and this starch ether also has the advantages of small viscosity difference and higher uniformity.

[0053] 3. According to the preparation method of the modified starch ether for papermaking special type of the present application, the pretreatment raw materials can increase the content of hydroxypropyl groups during subsequent vacuum low-temperature dehydration, low-temperature alkalization and etherification, and improve the whiteness and light transmittance of the product, reduce the miscellaneous color spots, and the various indicators are steadily improved.

[0054] 4. According to the preparation method of the modified starch ether for papermaking special type of the present application, the raw material cost is low, the heat consumption is small, and the quality stability is good, which is better than the current requirements of the papermaking industry for the starch ether indicators, and is conducive to promoting the technological innovation and upgrading of the papermaking industry.

[0055] 5. The modified starch ether for papermaking special type according to the present application has a viscosity between 10-45 mp.s, a hydroxypropyl content above 21%, a whiteness above 90% and a light transmittance above 16%, which is completely better than the standard, and the physical and chemical indicators meet the requirements of market users, and has good application prospects in the papermaking industry. Specific embodiments

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

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

[0058] Unless otherwise specified, the methods used in the embodiments and comparative examples of the present application are conventional methods in the prior art. The concentrations of the acidifying agent and the oxidizing agent in the present application refer to mass concentrations. The solvents used in the preparation of the modified starch ether for papermaking special type of the present application can be solvents commonly used in the art, such as methanol, ethanol, etc. The specific selection of the solvent does not constitute a limitation to the present application. The solvent used in the following embodiments and comparative examples is anhydrous ethanol.

[0059] Example 1

[0060] This example relates to a preparation method of a modified starch ether for papermaking special type, including the following steps:

[0061] (1) Pretreat potato starch by first acidifying and then oxidizing at 60 °C, and then remove impurities to obtain the pretreatment raw materials. The pH of acidification is 6.5, the weight ratio of the oxidizing agent used in oxidation to starch is 10:10. The treatment time of acidification in both first acidifying and then oxidizing and first oxidizing and then acidifying is 3 h, and the treatment time of oxidation is 60 min. The acidifying agent is selected from acetic acid, and the concentration of the acidifying agent is 1%. The oxidizing agent is selected from hydrogen peroxide, and the concentration of the oxidizing agent is 10%;

[0062] (2) Alkalization: Add 100 parts of pretreated raw materials and 5 parts of sodium sulfate to the solvent. After dehydration at 65°C for 20 min, cool down to below 35°C, replenish the solvent and add anhydrous sodium carbonate alkali solution until the pH reaches 14. After thorough mixing, heat up to 45°C and react for 60 min to obtain the alkalized product;

[0063] (3) Etherification: After the alkalization is completed, evacuate the air. Add 21 parts of propylene oxide to the alkalized product. First, heat up to 40°C and react for 1 h, then heat up to 65°C and react for 4.5 h to obtain the etherified product;

[0064] (4) Post-treatment: Cool down the etherified product to 75°C and evacuate the air for 20 min to obtain the desolventized product. Add 4 parts of hydrochloric acid and 8 parts of solvent to the desolventized product, carry out acidification reaction for 60 min, evacuate the air for 10 min, and then cool down the material to below 45°C to obtain the neutralized product. Dry the neutralized product until the moisture content of the material ≤ 8.0% to obtain the modified starch ether for papermaking.

[0065] Example 2

[0066] This example relates to a preparation method of a modified starch ether for papermaking, including the following steps:

[0067] (1) Simultaneously carry out oxidation and acidification pretreatment on cassava starch at 90°C, and then remove impurities to obtain the pretreated raw materials. The treatment time is 90 min, the pH of acidification is 5, the weight ratio of the oxidant used in oxidation to starch is 1:10, the acidifying agent is selected from sulfuric acid, the concentration of the acidifying agent is 30%, the oxidant is selected from benzoyl peroxide, and the concentration of the oxidant is 50%;

[0068] (2) Alkalization: Add 100 parts of pretreated raw materials and 10 parts of sodium sulfate to the solvent. After dehydration at 60°C for 30 min, cool down to below 35°C, replenish the solvent and add sodium bicarbonate alkali solution until the pH reaches 12. After thorough mixing, heat up to 52°C and react for 90 min to obtain the alkalized product;

[0069] (3) Etherification: After the alkalization is completed, evacuate the air. Add 27 parts of propylene oxide to the alkalized product. First, heat up to 52°C and react for 1 h, then heat up to 60°C and react for 5 h to obtain the etherified product;

[0070] (4) Post-treatment: Cool down the etherified product to 65°C and evacuate the air for 30 min to obtain the desolventized product. Add 6 parts of oxalic acid and 12 parts of solvent to the desolventized product, carry out acidification reaction for 90 min, evacuate the air for 20 min, and then cool down the material to below 45°C to obtain the neutralized product. Dry the neutralized product until the moisture content of the material ≤ 8.0% to obtain the modified starch ether for papermaking.

[0071] Example 3

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

[0073] (1) Pretreat corn starch by first acidifying and then oxidizing at 80 °C, and then remove impurities to obtain the pretreated raw material. The treatment time for acidification in the case of first oxidizing and then acidifying is 0.1 h, the treatment time for oxidation is 40 min, the pH for acidification is 6, the weight ratio of the oxidant to starch used for oxidation is 3:10, the acidifying agent is selected from hydrochloric acid, the concentration of the acidifying agent is 20%, the oxidant is selected from sodium hypochlorite, and the concentration of the oxidant is 35%;

[0074] (2) Alkalinization: Add 100 parts of the pretreated raw material and 5 parts of sodium sulfate to the solvent, perform dehydration treatment at 65 °C for 20 min, then cool down to below 35 °C, supplement the solvent and add sodium hydroxide alkali solution until the pH reaches 12, fully mix and then heat up to 45 °C and react for 60 min to obtain the alkalized product;

[0075] (3) Etherification: After the alkalinization is completed, evacuate the vacuum, add 24 parts of propylene oxide to the alkalized product, first heat up to 40 °C and react for 1 h, then heat up to 60 °C and react for 5 h to obtain the etherified product;

[0076] (4) Post-treatment: Cool down the etherified product to 75 °C and evacuate the vacuum for 20 min to obtain the desolvated product. Add 4 parts of glacial acetic acid and 10 parts of the solvent to the desolvated product, perform acidification reaction for 60 min, evacuate the vacuum for 20 min, then cool down the material to below 45 °C to obtain the neutralized product. Dry the neutralized product until the moisture content of the material ≤ 8.0% to obtain the special modified starch ether for papermaking.

[0077] Example 4

[0078] The difference between this example and Example 3 is that the concentration of the acidifying agent is 40%, and the rest is the same as in Example 3.

[0079] Example 5

[0080] The difference between this example and Example 3 is that the concentration of the oxidant is 70%, and the rest is the same as in Example 3.

[0081] Example 6

[0082] The difference between this example and Example 3 is that the concentration of the oxidant is 5%, and the rest is the same as in Example 3.

[0083] Example 7

[0084] The difference between this example and Example 3 is that the alkalinization temperature in step (2) is 30 °C, and the rest is the same as in 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 raised to 60 °C and reacted for 5 h, and then the temperature is lowered to 40 °C and reacted for 1 h to obtain an etherification product, and the rest is the same as in Example 3.

[0087] Comparative Example 1

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

[0089] Comparative Example 2

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

[0091] Comparative Example 3

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

[0093] Test Example 1

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

[0095] Table 1 Detection method

[0096] Inspection Items Inspection Instruments Inspection Methods Reference Standards Whiteness Whiteness Meter —— GB / T22427.6-2008 Transmittance Photometer —— GB / T34263-2017 Viscosity Analyzer —— GB / T2242707.2023 Hydroxypropyl Photometer Spectrophotometry GB / T40998-2021 Moisture Oven —— GB / T2242707-2023 Ash Content Muffle Furnace, Crucible —— GB / T22427.8-2024

[0097] Table 2 Detection results

[0098]

[0099]

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

[0101] In Example 4, the concentration of the acidifying agent was adjusted to twice that of Example 3, and the acidification pH remained unchanged. As a result, the whiteness and light transmittance of the product slightly decreased, and the viscosity slightly decreased. This shows that although the concentration of the acidifying agent affects the whiteness, light transmittance, and hydroxypropyl content of the final product to some extent and also affects the viscosity of the product to a certain extent when the pH remains unchanged, and the viscosity difference of the starch ether in Example 4 is larger than that in Example 3. In Examples 5 and 6, compared with Example 3, the concentration ratio of the oxidizing agent was adjusted. The light transmittance decreased, and the higher the oxidizing agent, the lower the viscosity, while the lower the oxidizing agent, the higher the viscosity. This indicates that the oxidizing agent, like the acidifying agent, also has a restrictive effect on the viscosity, and the viscosity difference of the starch ether in Examples 5 and 6 is larger than that in Example 3.

[0102] In Example 7, after reducing the alkalization temperature, the light transmittance and hydroxypropyl content of the product decreased significantly, and the viscosity increased. This shows that on the basis of the raw material pretreatment in this application, the alkalization temperature of the pretreated raw material is also a key point for reducing the viscosity, and the alkalization temperature has a great impact on the subsequent synthesis of hydroxypropyl.

[0103] From the comparison of Comparative Example 1, Comparative Example 2, and Example 3, it can be seen that only by performing single acidification and oxidation treatments on the raw materials, the whiteness and light transmittance of the product are relatively low, similar to those of ordinary formula starch ethers, without achieving an improvement effect. Moreover, the viscosity is relatively high, and the synthesis of hydroxypropyl is also at a medium level. In Comparative Example 3, untreated starch was used, and the whiteness and light transmittance of the product were significantly different from those of the acidified and alkalized tests. The viscosity was too high to meet the papermaking process, and the hydroxypropyl content was also at a low level.

[0104] Thus, it can be seen that the acidification, oxidation pretreatment of the raw materials and the subsequent alkalization treatment in this application have obvious effects on reducing the viscosity and increasing the whiteness of the product, and can better 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 have the advantages of good leveling property, viscosity stability, strong water retention performance, high whiteness, and low viscosity, and can be used to prepare papers with high tensile strength and high tensile strength. Due to the relatively high viscosity of the products of the comparative examples, the leveling property and viscosity stability in papermaking are lower than those of the products of the examples, and the whiteness is insufficient, resulting in a decrease in the appearance texture of the paper. In Examples 4 - 6, compared with Example 6, the concentrations of the acidifying agent and the oxidizing agent were adjusted, and the differences in the properties of the prepared papers were larger than those in Example 3, especially the tensile strength was more uneven. The reason is that the viscosity obtained in Table 2 is the average viscosity of the product, but the viscosity difference of the products in Examples 4 - 6 is larger than that in Example 3, so it will affect the performance uniformity of the paper.

[0106] As described above, the above are only embodiments of the present application. The protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modifications, equivalent replacements, improvements, etc. made within the technical idea and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A preparation method of a modified starch ether special for papermaking, characterized in that, The following steps are involved: (1) pretreating starch at 60-90° C., and then removing impurities to obtain a pretreated raw material, wherein the pretreatment is selected from one of acidification followed by oxidation, simultaneous acidification and oxidation, and 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 treatment time in the acidification followed by oxidation and the oxidation followed by acidification is 0.1-3 h, the oxidation treatment time is 40-60 min, and the simultaneous acidification and oxidation treatment time is 70-90 min; (2) Alkalization: add 100 parts of pre-treated raw materials and 5-10 parts of sodium sulfate to the solvent, cool to below 35° C. after dehydration, add more solvent and add alkali solution until the pH is 12-14, mix thoroughly, and then heat to react to obtain an alkalized product; (3) Etherification: After the alkalization is completed, vacuum is applied, and propylene oxide is added to the alkalization product to obtain an etherification product after reaction; (4) Post-treatment: The etherification product is subjected to desolventizing, neutralization and drying to obtain the modified starch ether for papermaking.

2. The preparation method of the modified starch ether for special use in papermaking according to claim 1, characterized in that, The acidulant is selected from at least one of acetic acid, hydrochloric acid and sulfuric acid; The concentration of the acidulant is 1-30%.

3. The preparation method of the modified starch ether for special use in papermaking according to claim 1, characterized in that, The oxidant is selected from at least one of hydrogen peroxide, sodium hypochlorite and benzoyl peroxide; The concentration of the oxidant is 10-50%.

4. The preparation method of the modified starch ether for special use in papermaking according to claim 1, characterized in that, The solute in the alkali solution is selected from at least one of anhydrous sodium carbonate, sodium bicarbonate, sodium hydroxide and potassium hydroxide.

5. The preparation method of the modified starch ether for special use in papermaking according to claim 1, characterized in that, The dehydration temperature in step (2) is 60-65°C and the dehydration time is 20-30 min; and / or The alkalization reaction temperature in step (2) is 45-52° C., and the reaction time is 60-90 min.

6. The preparation method of the modified starch ether for special use in papermaking according to claim 1, characterized in that, The amount of propylene oxide added in step (3) is 21-27 parts; and / or The reaction of step (3) is first heated to 40-52°C for 1-1.5h, and then heated to 60-65°C for 4.5-5h.

7. The preparation method of the modified starch ether for special use in papermaking according to claim 1, characterized in that, The desolventizing step is to cool the etherification product to 65-75° C. and evacuate the temperature for 20-30 minutes to obtain the desolventizing product.

8. The preparation method of the modified starch ether for special use in papermaking according to claim 1, characterized in that, The neutralization is to add 4-6 parts of acid and 8-12 parts of solvent to the desolvated product, acidify for 60-90 minutes, evacuate for 10-20 minutes, and then cool the material to below 45°C to obtain a neutralized product; and / or The drying is performed until the moisture content of the material is ≤8.0%.

9. The modified starch ether for papermaking prepared by the method for preparing the modified starch ether for papermaking according to any one of claims 1 to 8.

10. Use of the low-density modified starch ether for papermaking according to claim 9 in papermaking.

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