Efficient preparation method of polyvinyl alcohol with polymerization degree of 20-300

文档序号：744332 发布日期：2021-04-23 浏览：48次中文

阅读说明：本技术 一种聚合度为20~300聚乙烯醇的高效制备方法 (Efficient preparation method of polyvinyl alcohol with polymerization degree of 20-300 ) 是由张军华宋贤妮赵小海于 2020-07-22 设计创作，主要内容包括：本发明提供一种聚合度为20～300聚乙烯醇的高效制备方法,该制备方法是将聚合度至少为500的聚乙烯醇,配制为浓度至少为2.5wt.％、完全溶解的水溶液,然后加入强氧化剂,搅拌反应,得到氧化处理后的溶液A,再将所得溶液A加入至有机试剂中沉淀分离干燥即得聚合度为20～300、黏度不高于4.65mPa·S的聚乙烯醇。本发明制备方法通过中高聚合度PVA与强氧化剂的相互作用来制备超低聚合度PVA,并通过严格控制工艺条件可选择性的制备聚合度不同的超低聚合度聚乙烯醇,最终所得超低聚合度PVA平均产率不低于80wt.％,且具有工艺操作简单、无需使用链转移剂、试剂原料回收分离简单、成本较低的特性。(The invention provides an efficient preparation method of polyvinyl alcohol with a polymerization degree of 20-300, which comprises the steps of preparing the polyvinyl alcohol with the polymerization degree of at least 500 into a completely dissolved aqueous solution with the concentration of at least 2.5 wt.%, then adding a strong oxidant, stirring for reaction to obtain a solution A after oxidation treatment, adding the obtained solution A into an organic reagent, precipitating, separating and drying to obtain the polyvinyl alcohol with the polymerization degree of 20-300 and the viscosity of not higher than 4.65mPa & S. The preparation method of the invention prepares the PVA with ultra-low polymerization degree through the interaction of the PVA with medium and high polymerization degree and the strong oxidant, and can selectively prepare the polyvinyl alcohol with ultra-low polymerization degree with different polymerization degrees through strictly controlling the process conditions, and the average yield of the finally obtained PVA with ultra-low polymerization degree is not lower than 80 wt.%, and the preparation method has the characteristics of simple process operation, no need of using a chain transfer agent, simple recovery and separation of reagent raw materials and lower cost.)

1. The preparation method of polyvinyl alcohol with the polymerization degree of 20-300 is characterized by comprising the following steps:

(1) preparing polyvinyl alcohol with the polymerization degree of at least 500 into a completely dissolved aqueous solution with the concentration of at least 2.5 wt%, adding a strong oxidant, and stirring for reaction to obtain an oxidized solution A; wherein the strong oxidant is sodium hypochlorite, one or a combination of sodium periodate, hypochlorous acid, chlorine dioxide, sodium ferrate and sodium permanganate, and the addition amount of the strong oxidant is (1-4) in molar ratio to polyvinyl alcohol: 1, stirring and reacting for 1-24 h;

(2) adding the solution A obtained in the step (1) into an organic reagent, precipitating, separating and drying to obtain the polyvinyl alcohol with the polymerization degree of 20-300 and the viscosity of not higher than 4.65mPa & S.

2. The method of claim 1, wherein: and (2) selecting one or more polyvinyl alcohols with polymerization degrees of 500-2600 from the polyvinyl alcohols with polymerization degrees of at least 500 in the step (1).

3. The method of claim 1, wherein: the strong oxidant in the step (1) is sodium hypochlorite.

4. The method of claim 1, wherein: the organic reagent in the step (2) is methanol.

5. The method of claim 1, wherein:

the preparation method of the polyvinyl alcohol with the polymerization degree of 20-150 and the viscosity of less than 2.23mPa & S comprises the following steps:

(1) preparing polyvinyl alcohol with the polymerization degree of at least 500 into a completely dissolved aqueous solution with the concentration of at least 10 wt.%, adding a strong oxidant, and stirring and reacting at the speed of 300-1200 rpm for 6-24 hours at the temperature of 35-90 ℃ under the environment condition to obtain an oxidized solution A; wherein the strong oxidant is sodium hypochlorite, one or a combination of sodium periodate, hypochlorous acid, chlorine dioxide, sodium ferrate and sodium permanganate, and the addition amount of the strong oxidant is (2-4) in molar ratio to polyvinyl alcohol: 1, adding;

6. The method according to claim 5, wherein:

the preparation method of polyvinyl alcohol with polymerization degree of 32 and viscosity of 1.62 mPa.S comprises the following steps:

(1) preparing 52g of polyvinyl alcohol with the polymerization degree of 2499 into a polyvinyl alcohol aqueous solution with the concentration of 15 wt.% and complete dissolution, adding 240ml of sodium hypochlorite, and stirring at the speed of 375rpm at the temperature of 50 ℃ for reaction for 10 hours to obtain an oxidized solution A; wherein the addition amount of the strong oxidant is added in a mode that the molar ratio of the strong oxidant to the polyvinyl alcohol is 3: 1;

(2) adding the solution A obtained in the step (1) into 800ml of methanol solution, precipitating, separating and drying to obtain polyvinyl alcohol with the polymerization degree of 32 and the viscosity of 1.62mPa & S;

the preparation method of polyvinyl alcohol with the polymerization degree of 139 and the viscosity of 2.09mPa & S comprises the following steps:

(1) preparing 52g of polyvinyl alcohol with polymerization degree of 1799 into a polyvinyl alcohol aqueous solution with concentration of 20 wt% and complete dissolution, adding 160ml of sodium hypochlorite, and stirring at a speed of 600rpm at 50 ℃ for reaction for 8 hours to obtain an oxidized solution A; wherein the addition amount of the strong oxidant is added in a mode that the molar ratio of the strong oxidant to the polyvinyl alcohol is 2: 1;

the preparation method of the polyvinyl alcohol with the polymerization degree of 118 and the viscosity of 1.88mPa & S comprises the following steps:

(1) preparing 52g of polyvinyl alcohol with the polymerization degree of 599 into a polyvinyl alcohol aqueous solution with the concentration of 20 wt.% and complete dissolution, adding 160ml of sodium hypochlorite, and stirring at the speed of 600rpm at the temperature of 50 ℃ for reaction for 8 hours to obtain an oxidized solution A; wherein the addition amount of the strong oxidant is added in a mode that the molar ratio of the strong oxidant to the polyvinyl alcohol is 2: 1;

(2) adding the solution A obtained in the step (1) into 800ml of methanol solution, precipitating, separating and drying to obtain the polyvinyl alcohol with the polymerization degree of 118 and the viscosity of 1.88mPa & S.

7. The method of claim 1, wherein:

the preparation method of the polyvinyl alcohol with polymerization degree of 150-300 and viscosity of 2.23-4.65 mPa & S comprises the following steps:

(1) preparing polyvinyl alcohol with the polymerization degree of at least 500 into a completely dissolved aqueous solution with the concentration of 2.5-10 wt%, adding a strong oxidant, and stirring and reacting at the speed of 75-1200 rpm for 1-10 hours at the temperature of 25-90 ℃ to obtain an oxidized solution A; wherein the strong oxidant is sodium hypochlorite, one or a combination of sodium periodate, hypochlorous acid, chlorine dioxide, sodium ferrate and sodium permanganate, and the addition amount of the strong oxidant is (1-2) in molar ratio to polyvinyl alcohol: 1, adding;

8. The method according to claim 7, wherein:

the preparation method of polyvinyl alcohol with the polymerization degree of 169 and the viscosity of 2.63mPa & S comprises the following steps:

(1) preparing 52g of polyvinyl alcohol with the polymerization degree of 2499 into a completely dissolved polyvinyl alcohol aqueous solution with the concentration of 5 wt.%, adding 144ml of sodium hypochlorite, and stirring at the speed of 600rpm at the temperature of 25 ℃ for reaction for 8 hours to obtain an oxidized solution A; wherein the addition amount of the strong oxidant is added in a mode that the molar ratio of the strong oxidant to the polyvinyl alcohol is 1.8: 1;

the preparation method of the polyvinyl alcohol with 286 polymerization degree and 4.31 mPa.S viscosity comprises the following steps:

(1) preparing 52g of polyvinyl alcohol with polymerization degree of 1799 into a polyvinyl alcohol aqueous solution with concentration of 2.5 wt% and complete dissolution, adding 80ml of sodium hypochlorite, and stirring at a speed of 300rpm at 25 ℃ for reaction for 4 hours to obtain an oxidized solution A; wherein the addition amount of the strong oxidant is added in a mode that the molar ratio of the strong oxidant to the polyvinyl alcohol is 1: 1;

the preparation method of the polyvinyl alcohol with the polymerization degree of 204 and the viscosity of 3.24mPa & S comprises the following steps:

(1) preparing 104g of polyvinyl alcohol with the polymerization degree of 599 into a completely dissolved polyvinyl alcohol aqueous solution with the concentration of 5 wt.%, adding 255.6ml of sodium hypochlorite, and stirring at the speed of 300rpm at the temperature of 25 ℃ for reaction for 2 hours to obtain an oxidized solution A; wherein the addition amount of the strong oxidant is added in a mode that the molar ratio of the strong oxidant to the polyvinyl alcohol is 1.6: 1;

(2) adding the solution A obtained in the step (1) into 1500ml of methanol solution, precipitating, separating and drying to obtain the polyvinyl alcohol with the polymerization degree of 204 and the viscosity of 3.24mPa & S.

Technical Field

The invention belongs to the technical field of polyvinyl alcohol preparation, particularly relates to an efficient preparation method of polyvinyl alcohol with a polymerization degree of 20-300, and particularly relates to an efficient preparation method of polyvinyl alcohol with an ultralow polymerization degree, with a polymerization degree of 20-150.

Background

PVA (polyvinyl alcohol) is one of important water-soluble polymers, and is widely used in industry, commerce, medical treatment and food because of its non-toxicity, excellent biocompatibility and water solubility. With the continuous development of scientific technology, the classification application of PVA with different Degrees of Polymerization (DP) is gradually subdivided. Generally, the PVA can be classified into four types according to the degree of polymerization of PVA: the polymerization degree is ultrahigh, high, medium and low, and the molecular weight is 25-30 ten thousand, 17-22 ten thousand, 12-15 ten thousand and 2.5-3.5 ten thousand respectively. At present, various kinds of PVA with high and low polymerization degrees have been developed abroad, and the varieties of the PVA exceed 200 kinds. The varieties of domestic PVA products are relatively few, about 60-70 types, and the polymerization degree is 300-2600, and all the PVA products are prepared by adopting a solution polymerization mode. In 2018, the apparent consumption of PVA in china was about 75 million tons, while the consumption structure of PVA was mainly polymeric auxiliary (43%), textile pulp (20%), binder (12%), vinylon fiber (11%), and pulp and paint (8%). It can be seen that the polymerization aid accounts for a large proportion, however, PVA as the polymerization aid is mainly PVA with ultra low degree of polymerization (ULDP, DP <300) [ lynper. For example, in suspension polymerization of vinyl chloride, the dispersing agents used are mainly imported PVA GH-23, KH-20, KH-17, KP-08, KZ-04, LL-02, etc. These are basically imported products from Colorado, Japan, and the chemical industry of Changchun, Taiwan, and about 5000 to 8000 tons are required each year. Therefore, there is a need to develop polyvinyl alcohols with low polymerization degree, especially to prepare PVA with ultra low polymerization degree (DP < 300).

Typically, PVA is formed by polymerization of vinyl acetate (VAc) followed by alcoholysis. Therefore, in order to obtain the ultra-low polymerization degree PVA, it is first necessary to synthesize ultra-low polymerization degree polyvinyl acetate (PVAc). At present, solution polymerization and emulsion polymerization methods are generally used to obtain PVA with ultra-low polymerization degree, and the preparation method mainly depends on a high-efficiency chain transfer agent added in solution reaction. Firstly, synthesizing PVAc with ultra-low polymerization degree under the action of a chain transfer agent, and then carrying out alcoholysis on the obtained PVAc to obtain PVA with ultra-low polymerization degree. For example, patent publication No. CN 101054426A discloses a method for preparing polyvinyl alcohol with low polymerization degree, in which dimercaptoethanol is used as a chain transfer agent to obtain polyvinyl alcohol with polymerization degree of 50-500. Although PVA with low polymerization degree can be obtained by the method, a chain transfer agent used in the method, namely dimercapto ethanol, has high toxicity, and the foul smell of the PVA can influence the sensory quality of products and is not easy to separate and remove. The invention patent with publication number CN 108864345A discloses a synthesis method of ultra-low molecular weight polyvinyl alcohol, which uses carbon tetrachloride as a chain transfer agent and adopts a solution polymerization method to prepare the polyvinyl alcohol with ultra-low molecular weight (5000-25000). The method realizes the controllability of polymerization degree, but has low monomer conversion rate and low economic benefit. The invention patent publication No. CN 102108107A discloses a method for preparing polyvinyl alcohol with low polymerization degree, which uses acetaldehyde as a chain transfer agent to obtain PVA with polymerization degree of 50-500. The method takes acetaldehyde as a chain transfer agent to solve the problem that the chain transfer agent is difficult to separate, but still has the problem of low monomer conversion rate.

Although the method for preparing PVA with low degree of polymerization or ultra-low degree of polymerization is currently known as a synthesis method, it is obvious from the above prior art documents that although PVA with low degree of polymerization can be prepared, the monomer conversion rate is low, the production cost is high, the economic benefit is low, and the operation is complicated, especially in the prior art documents, the yield of polyvinyl alcohol with ultra-low degree of polymerization obtained by the synthesis method is generally considered to be low when the DP is lower than 100; and various defects of the system exist due to the addition of the chain transfer agent, such as toxicity problem of the chain transfer agent, separation problem and the like.

Disclosure of Invention

Aiming at the defects in the background art, the invention provides the efficient preparation method of the polyvinyl alcohol with the polymerization degree of 20-300, the preparation method is used for preparing the PVA with the ultralow polymerization degree through the interaction of the PVA with the medium and high polymerization degree and a strong oxidant, the polyvinyl alcohol with the ultralow polymerization degree with different polymerization degrees can be selectively prepared by strictly controlling the process conditions, the viscosity of the finally obtained PVA with the ultralow polymerization degree is not higher than 4.65mPa & S, the average yield is not lower than 80 wt%, and the preparation method has the characteristics of simple process operation, no need of using a chain transfer agent, simple recovery and separation of reagent raw materials and lower cost.

In order to achieve the purpose, the invention adopts the technical scheme formed by the following technical measures.

A preparation method of polyvinyl alcohol with a polymerization degree of 20-300 comprises the following steps:

In the step (1), the polyvinyl alcohol with a polymerization degree of at least 500 is prepared into a completely dissolved aqueous solution with a concentration of at least 2.5 wt.%, and it is worth to be noted that, at normal pressure, the polyvinyl alcohol solutions with medium and high polymerization degrees are limited by solubility, and the mass concentration of the polyvinyl alcohol solutions has an upper limit under the precondition that the polyvinyl alcohol is completely dissolved, and the specific upper limit can be known from the literature of the prior art according to the polymerization degree of the polyvinyl alcohol in the actual solution, for example, the polyvinyl alcohol solution with a polymerization degree of about 1700 has a maximum dissolution concentration of 15 wt.% to 20 wt.% at normal pressure, and the polyvinyl alcohol solution with a concentration higher than this cannot form a homogeneous solution at normal pressure, so that the optimal oxidation treatment effect cannot be achieved. However, it is known from the common knowledge in the art that the solubility of polyvinyl alcohol under pressure is further improved, for example, the above-mentioned polyvinyl alcohol solution with a degree of polymerization of about 1700 is dissolved at a concentration of up to 33 wt.% under pressure, and is suitable for use as a raw material in the present invention, and the best oxidation treatment effect can be achieved. In addition, the highest solubility of the polyvinyl alcohol solution with a relatively low degree of polymerization (degree of polymerization of about 500) is 30 wt.% at normal pressure, and the highest solubility can reach 45 wt.% under pressure, so that the method is also suitable for the oxidation treatment in the technical scheme of the invention, and the optimal oxidation treatment effect can be achieved.

In summary, under the condition of normal pressure, the polymerization degree of the polyvinyl alcohol is at least 500, and the concentration is 2.5 wt.% to 30 wt.%, and under the condition of satisfying the condition of completely dissolving the polyvinyl alcohol, the method is suitable for the technical scheme of the invention to be used as a raw material for preparing the polyvinyl alcohol with ultralow polymerization degree;

under the pressurization condition, the polymerization degree of the polyvinyl alcohol is at least 500, and the concentration is 2.5 wt.% to 45 wt.%, and under the condition that the polyvinyl alcohol is completely dissolved, the method is suitable for the technical scheme of the invention to be used as a raw material for preparing the polyvinyl alcohol with ultralow polymerization degree.

Preferably, the polyvinyl alcohol is selected from one or more polyvinyl alcohols with the polymerization degree of 500-2600. It is worth to be noted that the technical scheme of the invention is applicable to all polyvinyl alcohol products in the market and has universality.

Wherein, the strong oxidant in the step (1) is one or a combination of more of sodium hypochlorite, sodium periodate, hypochlorous acid, chlorine dioxide, sodium ferrate and sodium permanganate. However, the inventors of the present invention found that the effect obtained by using a combination of strong oxidizing agents is less different from the effect obtained by using a single strong oxidizing agent, and a single strong oxidizing agent is more preferable in view of ease of operation and economic cost. To better illustrate the present invention and to provide a preferred solution, the strong oxidant is sodium hypochlorite.

Wherein, the organic reagent in the step (2) is selected from organic reagents which can be used for the precipitation separation of the polyvinyl alcohol in the common knowledge in the prior art, such as alcohol organic reagents, and methanol is preferred. Further, the precipitation separation and drying of the solution A by adding it to an organic reagent is a conventional precipitation separation operation in the common knowledge of the prior art, and a person skilled in the art can select a precipitation separation operation mode suitable for polyvinyl alcohol according to actual conditions. In order to better illustrate the invention and provide a reference process mode, under laboratory conditions, the precipitation separation drying is specifically to add the solution A into an organic reagent, after the precipitation is completed, the solution A is dried after the vacuum filtration of a Buchner funnel.

It is important to point out that the inventors of the present invention, through a large number of experiments, compare the polymerization degree of the polyvinyl alcohol as the raw material and its initial concentration, the selection and addition of the strong oxidant, and the specific process conditions of the stirring reaction, such as time, temperature and stirring rate, all directly affect the polymerization degree of the finally prepared polyvinyl alcohol. However, as can be seen from experiments, since the influence of each process condition on the final product is not linear, and the influence weight of each process condition is changed according to the required polymerization degree of the polyvinyl alcohol product, the inventor of the present invention has summarized the above preparation method empirically for preparing the polyvinyl alcohol having a polymerization degree of 20 to 300, in view of the limited experimental conditions of the inventor.

The polyvinyl alcohol with the polymerization degree of 20-300 and the viscosity of not higher than 4.65mPa & S can be prepared by the skilled person in the art through any selected combination of the process conditions in the preparation method, and the average yield of the polyvinyl alcohol is not lower than 80 wt.%.

Further, in order to obtain any polymerization degree value or any polymerization degree value range (range less than 20 to 300) within a polymerization degree range of 20 to 300, it is preferable that:

a preparation method of polyvinyl alcohol with polymerization degree of 20-150 and viscosity lower than 2.23mPa & S comprises the following steps:

It is worth noting that the preparation method of the polyvinyl alcohol with the polymerization degree of 20-150 and the viscosity of less than 2.23mPa · S is the best process method summarized by the inventor of the invention through a large number of experiments. If the polymerization degree is within the range of 20-150 or within any polymerization degree range (the range is less than 20-150), the addition amount of the strong oxidant is (2-4): the polymerization degree of the PVA to be obtained may be adjusted within 1, and in general, the higher the amount of the strong oxidizing agent to be added, the lower the polymerization degree of the PVA to be obtained. For a better illustration of the invention and to provide reference to several preparation methods, it is preferred that:

a method for preparing polyvinyl alcohol with polymerization degree of 32 and viscosity of 1.62mPa & S comprises the following steps:

The inventors of the present invention have made experiments on the above method for producing polyvinyl alcohol having a polymerization degree of 32 and a viscosity of 1.62mPa · S, and the yield is 79.87%.

A method for preparing polyvinyl alcohol with a polymerization degree of 139 and a viscosity of 2.09mPa & S comprises the following steps:

The above-mentioned polyvinyl alcohol having a polymerization degree of 139 and a viscosity of 2.09mPa · S was prepared, and the yield was 90.04% by the experiment of the present inventors.

A method for preparing polyvinyl alcohol with polymerization degree of 118 and viscosity of 1.88mPa & S comprises the following steps:

The above-mentioned polyvinyl alcohol having a polymerization degree of 118 and a viscosity of 1.88 mPaS was obtained in a yield of 88.65% as a result of experiments by the inventors of the present invention.

Through the above listed optimal preparation methods, obviously, the polymerization degree of the finally obtained polyvinyl alcohol can be greatly changed within the range of 20-150 by mainly adjusting the addition amount of the strong oxidant; when the selection, the addition concentration and the addition amount of the strong oxidant are consistent, the polymerization degree of the finally obtained polyvinyl alcohol can be slightly changed within the range of 20-150 by selecting the polymerization degree of the raw material polyvinyl alcohol. Secondly, it is known from the common knowledge in the art that the initial concentration of the raw material polyvinyl alcohol, the specific process conditions of the stirring reaction, such as time, temperature and stirring rate, also have a certain influence on the degree of polymerization of the finally obtained polyvinyl alcohol, but the degree of polymerization change caused by the above influence is small. It is generally considered that, when the polyvinyl alcohol having a desired degree of polymerization cannot be produced by adjusting the amount of the strong oxidant and the degree of polymerization of the raw polyvinyl alcohol, those skilled in the art can select and finely adjust the above-mentioned other process conditions.

Further, in order to obtain any polymerization degree value or any polymerization degree value range (range less than 20-300) within a polymerization degree range of 20-300 and further improve the molecular weight dispersion coefficient of the obtained polyvinyl alcohol, it is preferable that:

a preparation method of polyvinyl alcohol with polymerization degree of 150-300 and viscosity of 2.23-4.65 mPa & S comprises the following steps:

It should be noted that the preparation method of the polyvinyl alcohol having a polymerization degree of 150 to 300 and a viscosity of 2.23mPa · S to 4.65mPa · S is an optimal process method summarized by the inventors of the present invention through a large number of experiments. If a person skilled in the art needs to prepare a polyvinyl alcohol with any polymerization degree value or any polymerization degree value range (range less than 150-300) within the polymerization degree range of 150-300, the higher the addition amount of the strong oxidant or the longer the reaction time, the lower the polymerization degree of the obtained polyvinyl alcohol, and when the addition amount of the strong oxidant is higher ((1.5-2): 1), the influence of the reaction time on the polymerization degree is small, and the addition amount of the strong oxidant in the polyvinyl alcohol is only required to be within the range of (1.5-2): 1, adjusting within the range of 1; when the dosage of the strong oxidant is smaller ((1-1.5): 1), the reaction time is a secondary factor influencing the polymerization degree, and the reaction time is required to be adjusted within the range of 6-10 h. For a better illustration of the invention and to provide reference to several preparation methods, it is preferred that:

a method for preparing polyvinyl alcohol with 169 degree of polymerization and 2.63mPa & S viscosity comprises the following steps:

The above-mentioned method for producing polyvinyl alcohol having a polymerization degree of 169 and a viscosity of 2.63 mPaS was carried out by the inventors of the present invention, and the yield was 90.78%.

A preparation method of polyvinyl alcohol with 286 polymerization degree and 4.31mPa & S viscosity comprises the following steps:

The above-mentioned polyvinyl alcohol having a polymerization degree of 286 and a viscosity of 4.31mPa · S was prepared by the present inventors, and the yield was 93.21% through the experiment.

A method for preparing polyvinyl alcohol with a polymerization degree of 204 and viscosity of 3.24mPa & S comprises the following steps:

The above-mentioned method for producing polyvinyl alcohol having a polymerization degree of 204 and a viscosity of 3.24 mPaS was conducted by the inventors of the present invention, and the yield was 91.72%.

Through the above listed optimal preparation methods, obviously, the polymerization degree of the finally obtained polyvinyl alcohol can be greatly changed within the range of 150-300 by mainly adjusting the addition amount of the strong oxidant; when the selection, the addition concentration and the addition amount of the strong oxidant are consistent and the dosage of the strong oxidant is small ((1-1.5): 1), the polymerization degree of the finally obtained polyvinyl alcohol can be greatly changed within the range of 150-300 by adjusting the stirring reaction time. Secondly, it is known from the common knowledge in the art that the polymerization degree and initial concentration of the raw material polyvinyl alcohol, and the specific process conditions of the stirring reaction, such as temperature and stirring rate, also have a certain influence on the polymerization degree of the finally obtained polyvinyl alcohol, but the variation range of the polymerization degree caused by the influence is small. It is generally considered that those skilled in the art can select fine adjustment of the above-mentioned other process conditions to achieve the desired degree of polymerization of polyvinyl alcohol, even if the polyvinyl alcohol cannot be produced after the addition of the strong oxidant and the stirring reaction time are adjusted.

Generally, the polyvinyl alcohol in the technical scheme of the invention is completely dissolved, and when the polyvinyl alcohol is under normal pressure, a mode of heating the polyvinyl alcohol to 90 ℃ through a water bath to completely dissolve the polyvinyl alcohol can be selected in the common knowledge in the field, and then the polyvinyl alcohol is cooled to the temperature environment required by stirring reaction.

The invention has the following beneficial effects:

(1) the preparation method of the invention prepares polyvinyl alcohol with ultra-low polymerization degree by the interaction of polyvinyl alcohol with medium and high polymerization degree and strong oxidant, and can selectively prepare polyvinyl alcohol with ultra-low polymerization degree with different polymerization degrees by strictly controlling process conditions, the viscosity of the finally obtained polyvinyl alcohol with ultra-low polymerization degree is not higher than 4.65 mPa.S, and the average yield is higher than 80 wt.%.

(2) The invention takes the polyvinyl alcohol with medium and high polymerization degrees as the raw material, is produced and prepared by using the principle that the commercially available polyvinyl alcohol with medium and high polymerization degrees is low in cost and sufficient in supply on the market, is suitable for the existing polyvinyl alcohol with all polymerization degrees on the market, has better oxidative degradation effect on the polyvinyl alcohol raw material with high concentration and high polymerization degrees, and improves the additional value of the polyvinyl alcohol. And the structure of the polyvinyl alcohol is not affected in the preparation process.

(3) The preparation method can be carried out at low temperature and normal pressure in the whole process, the requirement on production equipment is simple, and the average yield can reach 85%.

(4) The preparation method has the characteristics of simple process operation, no need of using a chain transfer agent, simple recovery and separation of reagent raw materials and lower cost. Compared with the common method for preparing polyvinyl alcohol with low polymerization degree by a synthesis method, the method has the advantages of simple operation, no need of adjusting the pH value of the solution in the whole oxidation process, mild reaction process, high controllability, capability of obtaining the polyvinyl alcohol product with the required polymerization degree by adjusting the reaction conditions, and contribution to industrial continuous production.

Drawings

FIG. 1 is a photograph showing a comparison between polyvinyl alcohol as a raw material in example 1 of the present invention (FIG. (a)) and polyvinyl alcohol having an ultralow polymerization degree finally obtained (FIG. (b)).

FIG. 2 is an IR spectrum of polyvinyl alcohol used as a raw material and polyvinyl alcohol having an ultralow polymerization degree finally obtained in examples 1 to 3 of the present invention. In which PVA-2499, PVA-1799 and PVA-0599 are used to represent the polyvinyl alcohols used in examples 1-3, and the final polyvinyl alcohols of ultra-low degree of polymerization obtained in examples 1-3 are designated as PVA-H, PVA-M and PVA-L, respectively. It is apparent that the structure of the ultra-low polymerization degree polyvinyl alcohol obtained by the preparation is not damaged.

FIG. 3 is a nuclear magnetic hydrogen spectrum of polyvinyl alcohol as a raw material and polyvinyl alcohol having an ultra-low polymerization degree finally obtained in examples 1 to 3 of the present invention. In which PVA-2499, PVA-1799 and PVA-0599 are used to represent the polyvinyl alcohols used in examples 1-3, and the final polyvinyl alcohols of ultra-low degree of polymerization obtained in examples 1-3 are designated as PVA-H, PVA-M and PVA-L, respectively. It is apparent that the structure of the ultra-low polymerization degree polyvinyl alcohol obtained by the preparation is not damaged.

FIG. 4 is a graph showing the change in the shear viscosity of polyvinyl alcohol as a raw material and polyvinyl alcohol having an ultra-low polymerization degree finally obtained in examples 1 to 3 of the present invention. In which PVA-2499, PVA-1799 and PVA-0599 are used to represent the polyvinyl alcohols used in examples 1-3, and the final polyvinyl alcohols of ultra-low degree of polymerization obtained in examples 1-3 are designated as PVA-H, PVA-M and PVA-L, respectively. As is apparent from the shear viscosity, it is indeed possible to obtain a PVA of low viscosity, i.e.of ultra-low degree of polymerization, rapidly and simply by the process of the invention.

Detailed Description

The invention is further illustrated by the following examples. It should be noted that the examples given are not to be construed as limiting the scope of the invention, and that those skilled in the art, on the basis of the teachings of the present invention, will be able to make numerous insubstantial modifications and adaptations of the invention without departing from its scope.

In the following examples, reference is made to the national standard GB 12010.3-89 and to the method after optimization for the determination of the viscosity number of PVA. That is, PVA was formulated into an aqueous PVA solution at a concentration of 4 wt.%, and the measurement was performed at 25 ℃. The measurement of the test viscosity adopts a Physica MCR301 rheometer to measure the shear viscosity of the polyvinyl alcohol, and the shear rate is 10s^-1。

Example 1

This example is a method for producing a polyvinyl alcohol having a polymerization degree of 68 and a viscosity of 1.82mPa · S, comprising the steps of:

(1) preparing 52g of polyvinyl alcohol with the polymerization degree of 2499 into a polyvinyl alcohol aqueous solution with the concentration of 15 wt.% and complete dissolution, adding 176ml of sodium hypochlorite, and stirring at the speed of 375rpm at the environmental condition of 50 ℃ for reaction for 10 hours to obtain a solution A after oxidation treatment; wherein the addition amount of the strong oxidant is added in a mode that the molar ratio of the strong oxidant to the polyvinyl alcohol is 2.2: 1;

The above-mentioned polyvinyl alcohol having a polymerization degree of 68 and a viscosity of 1.82 mPaS was obtained at a yield of 81.13%.

Example 2

This example is a method for producing a polyvinyl alcohol having a polymerization degree of 125 and a viscosity of 2.03mPa · S, comprising the steps of:

(1) preparing 52g of polyvinyl alcohol with polymerization degree of 1799 into a polyvinyl alcohol aqueous solution with concentration of 15 wt% and complete dissolution, adding 160ml of sodium hypochlorite, and stirring at a speed of 600rpm at 45 ℃ for reaction for 8 hours to obtain an oxidized solution A; wherein the addition amount of the strong oxidant is added in a mode that the molar ratio of the strong oxidant to the polyvinyl alcohol is 2: 1;

The yield of the above-mentioned polyvinyl alcohol having a polymerization degree of 125 and a viscosity of 2.03 mPaS was 89.96%.

Example 3

This example is a method for producing a polyvinyl alcohol having a polymerization degree of 120 and a viscosity of 1.92mPa · S, comprising the steps of:

(1) preparing 52g of polyvinyl alcohol with the polymerization degree of 599 into a polyvinyl alcohol aqueous solution with the concentration of 20 wt.% and complete dissolution, adding 160ml of sodium hypochlorite, and stirring at the speed of 300rpm at the temperature of 40 ℃ for reaction for 6 hours to obtain a solution A after oxidation treatment; wherein the addition amount of the strong oxidant is added in a mode that the molar ratio of the strong oxidant to the polyvinyl alcohol is 2: 1;

The above-mentioned polyvinyl alcohol having a polymerization degree of 120 and a viscosity of 1.92 mPaS was obtained in a yield of 89.72%.

Example 4

This example is a method for producing a polyvinyl alcohol having a polymerization degree of 226 and a viscosity of 3.66mPa · S, comprising the steps of:

(1) preparing 52g of polyvinyl alcohol with polymerization degree of 1799 into a completely dissolved polyvinyl alcohol aqueous solution with concentration of 5 wt%, adding 80ml of sodium hypochlorite, and stirring at a speed of 300rpm at 25 ℃ for reaction for 6 hours to obtain an oxidized solution A; wherein the addition amount of the strong oxidant is added in a mode that the molar ratio of the strong oxidant to the polyvinyl alcohol is 1: 1;

The yield of the above-mentioned polyvinyl alcohol having a polymerization degree of 226 and a viscosity of 3.66 mPaS was 92.32%.

Example 5

This example is a method for producing polyvinyl alcohol having a polymerization degree of 189 and a viscosity of 2.99mPa · S, comprising the steps of:

(1) preparing 52g of polyvinyl alcohol with the polymerization degree of 599 into a 7.5 wt.% completely dissolved polyvinyl alcohol aqueous solution, adding 120ml of sodium hypochlorite, and stirring at a speed of 300rpm at 25 ℃ for reaction for 10 hours to obtain an oxidized solution A; wherein the addition amount of the strong oxidant is added in a mode that the molar ratio of the strong oxidant to the polyvinyl alcohol is 1.5: 1;

The above-mentioned polyvinyl alcohol having a polymerization degree of 189 and a viscosity of 2.99 mPaS was obtained at a yield of 91.08%.

Example 6

This example is a method for producing a polyvinyl alcohol having a polymerization degree of 32 and a viscosity of 1.62mPa · S, comprising the steps of:

The above-mentioned polyvinyl alcohol having a polymerization degree of 32 and a viscosity of 1.62 mPaS was obtained in a yield of 79.87%.

Example 7

This example is a method for producing a polyvinyl alcohol having a polymerization degree of 139 and a viscosity of 2.09mPa · S, comprising the steps of:

The above-mentioned polyvinyl alcohol having a polymerization degree of 139 and a viscosity of 2.09 mPaS was produced at a yield of 90.04%.

Example 8

This example is a method for producing a polyvinyl alcohol having a polymerization degree of 118 and a viscosity of 1.88 mPaS, comprising the steps of:

The above-mentioned polyvinyl alcohol having a polymerization degree of 118 and a viscosity of 1.88 mPaS was produced at a yield of 88.65%.

Example 9

This example is a method for producing a polyvinyl alcohol having a polymerization degree of 169 and a viscosity of 2.63mPa · S, comprising the steps of:

The above-mentioned polyvinyl alcohol having a polymerization degree of 169 and a viscosity of 2.63 mPaS was obtained in a yield of 90.78%.

Example 10

This example is a method for producing a polyvinyl alcohol having a polymerization degree of 286 and a viscosity of 4.31mPa · S, comprising the steps of:

The above-mentioned polyvinyl alcohol having a polymerization degree of 286 and a viscosity of 4.31 mPaS was obtained in 93.21% yield.

Example 11

This example is a method for producing a polyvinyl alcohol having a polymerization degree of 204 and a viscosity of 3.24mPa · S, comprising the steps of:

The above-mentioned polyvinyl alcohol having a polymerization degree of 204 and a viscosity of 3.24 mPaS was obtained at a yield of 91.72%.

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Efficient preparation method of polyvinyl alcohol with polymerization degree of 20-300

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