CN114249903A

CN114249903A - Cold-soluble polymer and preparation method and application thereof

Info

Publication number: CN114249903A
Application number: CN202111511107.9A
Authority: CN
Inventors: 李蕴熙; 张泽天; 刘昊; 李道喜; 李丹; 陈玉姣; 张水木
Original assignee: Spic Hydrogen Energy Technology Development Co Ltd
Current assignee: Spic Hydrogen Energy Technology Development Co Ltd
Priority date: 2021-12-10
Filing date: 2021-12-10
Publication date: 2022-03-29

Abstract

The invention provides a cold-soluble polymer and a preparation method and application thereof. The preparation method comprises the following steps: step S1, dispersing the saponified polymer in a good solvent to obtain a polymer dispersion liquid, wherein the polymer is polyvinyl alcohol or an ethylene-vinyl alcohol copolymer, and the saponification degree of the polymer is 94-100 mol%; step S2, precipitating the polymer dispersion liquid by using a precipitating agent to obtain a first polymer wet solid, wherein the first polymer wet solid comprises liquid molecules carried in the polymer, and the liquid molecules comprise a good solvent and the precipitating agent; step S3, extracting liquid molecules in the first polymer wet solid by using an extracting agent to obtain an extracted wet solid, wherein the extracting agent is selected from a precipitating agent and has a volatilization speed higher than that of the precipitating agent used in the step S2, and more than 90% of the extracting agent left in the extracted wet solid is lower alkane; and step S4, drying the extracted wet solid to obtain the cold-soluble polymer. The preparation method has high efficiency and low cost.

Description

Cold-soluble polymer and preparation method and application thereof

Technical Field

The invention relates to the technical field of cold-soluble polymers, and particularly relates to a cold-soluble polymer and a preparation method and application thereof.

Background

Polyvinyl alcohol (hereinafter, may be abbreviated as "PVA") is a crystalline polymer excellent in water solubility, film-forming property and printability. Ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as "EVOH") is a synthetic material having the highest gas barrier ability at present, and is used as a gas barrier material for a gas container such as hydrogen gas or oxygen gas together with PVA. Commercial EVOH is generally not water soluble and is generally melt-processed for use, which has the disadvantage of narrow processing temperature due to the close crystallization and decomposition temperatures. EVOH melts polymers mainly at high temperature, and the finished products are prepared by extrusion molding, injection molding, compression molding or calendaring molding.

In general, polyvinyl acetate is industrially obtained by homopolymerization of vinyl acetate, ethylene-vinyl acetate copolymer is prepared by copolymerization of ethylene and vinyl acetate, and polyvinyl acetate and ethylene-vinyl acetate copolymer are saponified to obtain PVA and EVOH. The hydrogen barrier properties of PVA and EVOH are influenced by many factors such as molecular weight and saponification degree, and the influence of the factors on the hydrogen barrier properties of PVA and EVOH films is the difference of crystallinity. For these two polymers, the higher the degree of saponification, the higher the upper limit of the crystallinity, the higher the hydrogen barrier property, and the greater the difficulty of melt processing. In addition to melt processing difficulties, dissolution difficulties can increase for polymers of high crystallinity.

PVA and EVOH with high saponification degree (> 94 mol%) usually exceed 40 ℃ due to the drying temperature in the production process, and the obtained dried PVA and EVOH products have higher crystallinity. PVA and EVOH with high crystallinity can be dissolved completely only by heating for a long time, and are limited in applications requiring cold dissolution and instant dissolution. The PVA powder with partially low saponification degree shows the characteristics of cold dissolution and instant dissolution, but the physical and chemical properties of the PVA with low saponification degree and the PVA with high saponification degree are obviously different, and the PVA with high saponification degree cannot be replaced. The dispersion of PVA with high saponification degree can be prepared into a solid product with low crystallinity or no crystallinity by adopting a freeze drying method, but the method has high cost and low efficiency.

Disclosure of Invention

The invention mainly aims to provide a cold-soluble polymer, and a preparation method and application thereof, so as to solve the problems of high cost and low efficiency of the method for preparing cold-soluble PVA and EVOH in the prior art.

In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing a cold-melt polymer, the method comprising: step S1, dispersing the saponified polymer in a good solvent to obtain a polymer dispersion liquid, wherein the polymer is polyvinyl alcohol or an ethylene-vinyl alcohol copolymer, and the saponification degree of the polymer is 94-100 mol%; step S2, precipitating the polymer dispersion liquid by using a precipitating agent to obtain a first polymer wet solid, wherein the first polymer wet solid comprises liquid molecules carried in the polymer, and the liquid molecules comprise a good solvent and the precipitating agent; step S3, extracting liquid molecules in the first polymer wet solid by using an extracting agent to obtain an extracted wet solid, wherein the extracting agent is selected from a precipitating agent and has a volatilization speed higher than that of the precipitating agent used in the step S2, and more than 90% of the extracting agent left in the extracted wet solid is lower alkane; and step S4, drying the extracted wet solid to obtain the cold-soluble polymer.

Further, the good solvent is selected from any one or more of first good solvents, a first mixed solvent consisting of any one of the first good solvents and any one of second good solvents, or a second mixed solvent consisting of two of the second good solvents, wherein the mass content of the second good solvent in the first mixed solvent is 25-75%, the first good solvent comprises any one or more of polyhydric alcohols, lower fatty acids, phenolic solvents, lower fatty acids and other solvents, the second good solvent comprises water and lower aliphatic monohydric alcohols, and the mass content of water or lower aliphatic monohydric alcohols in the second mixed solvent is 25-75%, wherein the polyhydric alcohols are selected from any one or more of ethylene glycol, propylene glycol and glycerol; the phenolic solvent is selected from any one or more of phenol, cresol, m-cresol, o-cresol and p-cresol; the lower aliphatic monohydric alcohol is selected from one or more of methanol, ethanol, n-propanol and isopropanol; the lower fatty acid is selected from any one or more of formic acid, acetic acid and propionic acid; the other solvent is one or more selected from N, N-dimethylformamide, N-dimethylacetamide and dimethyl sulfoxide.

Further, the polarity of the above-mentioned precipitant is lower than that of the good solvent, preferably, the precipitant is selected from any one or more of lower aliphatic alcohol, lipid solvent, chlorinated hydrocarbon, lower alkane, low polarity water-soluble solvent, and water, the lower aliphatic alcohol used for the precipitant includes methanol, ethanol, isopropanol, and n-propanol, preferably, the lipid solvent includes ethyl acetate, ethyl formate, methyl formate, propyl formate, methyl acetate, and methyl propionate, the chlorinated hydrocarbon includes dichloromethane and trichloromethane, the lower alkane includes carbon pentaalkane, carbon hexaalkane, and petroleum ether, and the low polarity water-soluble solvent is selected from tetrahydrofuran, acetone, and butanone; preferably, when the precipitator is lower aliphatic alcohol, the mass ratio of the precipitator to the good solvent is 4-8: 1; preferably, when the precipitant is a low-polarity water-soluble solvent, the mass ratio of the precipitant to the good solvent is 2-8: 1; preferably, when the precipitator is a lipid solvent or chlorinated hydrocarbon, the mass ratio of the precipitator to the good solvent is 2-8: 1; preferably, when the precipitator is lower alkane, the mass ratio of the precipitator to the good solvent is 2-8: 1; preferably, when the precipitator is water, the mass ratio of the precipitator to the good solvent is 5-10: 1; preferably, when the good solvent is the second mixed solvent and the mass contents of water and the lower aliphatic monohydric alcohol in the second mixed solvent are respectively and independently 25 to 75 percent, the precipitant is water.

Further, the step S3 includes: performing first extraction on the first polymer wet solid by using a first extraction agent to obtain a first extracted wet solid, preferably, the first extraction is multi-stage extraction, and further preferably, 1-4-stage extraction; performing second extraction on the wet solid after the first extraction by using a second extraction agent to obtain a wet solid after the second extraction, wherein the second extraction is preferably multi-stage extraction, and further preferably 1-4-stage extraction; performing third extraction on the wet solid after the second extraction by using a third extraction agent to obtain a wet solid after the second extraction, wherein the third extraction is preferably multi-stage extraction, and further preferably 1-4-stage extraction; the first extractant is mutually soluble with a good solvent, the second extractant is mutually soluble with lower alkane, the first extractant, the second extractant and the third extractant are preferably mutually soluble, the volatilization speed is gradually increased, the mass ratio of the first extractant to the polymer is preferably 5-100: 1, the mass ratio of the first extractant to the second extractant is preferably 5-1: 1, the mass ratio of the second extractant to the third extractant is preferably 5-1: 1, and the third extractant is preferably selected from any one or more of the lower alkane.

Further, the good solvent is a phenolic solvent, the precipitator does not contain water or methanol, and the carbon pentaalkane, the carbon hexaalkane and the petroleum ether are used as extractants for extraction for 2-4 times in the step S3.

Further, the polymer is polyvinyl alcohol, the mass content of water in the good solvent is less than 5%, the precipitator is a mixed precipitator consisting of lower aliphatic alcohol, a lipid solvent, chlorohydrocarbon, lower alkane and a low-polarity water-soluble solvent, the mass content of the lower alkane is less than 80%, and in step S3, the first extractant does not contain water, and the second extractant does not contain water and methanol.

Further, the polymer is polyvinyl alcohol, and the mass content of water in the good solvent is not lower than 5%; the precipitator is a mixed precipitator consisting of lower aliphatic alcohol, a lipid solvent, chlorohydrocarbon, lower alkane and a low-polarity water-soluble solvent, wherein the mass content of the lower aliphatic alcohol and the lipid solvent is not less than 20 percent, and the mass content of the lower alkane is less than 80 percent; in step S3, the first extractant contains no water, and the second extractant contains no water or methanol.

Further, the polymer is an ethylene-vinyl alcohol copolymer, the good solvent comprises polyhydric alcohol, lower fatty acid, N-dimethylformamide, N-dimethylacetamide or dimethyl sulfoxide, and the first extracting agent is water, lower fatty alcohol, a low-polarity water-soluble solvent, chlorohydrocarbon or a lipid solvent; the second extractant does not contain water or methanol, and the content of ethanol, n-propanol, isopropanol or low-polarity water-soluble solvent in the second extractant is not less than 30%.

Further, the polymer is an ethylene-vinyl alcohol copolymer, the good solvent is a mixed solvent of water and lower aliphatic monohydric alcohol, and the mass content of ethanol, isopropanol, n-propanol or low-polarity water-soluble solvent in the first extracting agent is not less than 30%.

Further, in the step S1, the dispersing temperature is 60-220 ℃, and the dissolving time is 1-72 hours.

Further, in the step S4, the drying is performed by drying under normal pressure or vacuum at 0-30 ℃ for 0.5-200 h.

Further, the ethylene-vinyl alcohol copolymer is an ethylene-vinyl alcohol binary copolymer or an ethylene-vinyl alcohol-vinyl acetate ternary copolymer; the content of basic impurities in the polymer is preferably 0.1% by mass or less, preferably 0.08% by mass or less, more preferably 0.04% by mass or less, and particularly preferably 0.02% by mass or less.

According to another aspect of the present invention, there is provided a cold-soluble polymer prepared according to any one of the above-mentioned preparation methods; preferably, the cold-soluble polymer is cold-soluble polyvinyl alcohol or cold-soluble ethylene-vinyl alcohol copolymer, and preferably, the cold-soluble ethylene-vinyl alcohol copolymer is ethylene-vinyl alcohol binary copolymer or ethylene-vinyl alcohol-vinyl acetate ternary copolymer.

Further, the cold-soluble polyvinyl alcohol and the cold-soluble EVOH have a degree of saponification of 94 to 100 mol%, and preferably the cold-soluble polyvinyl alcohol and the cold-soluble EVOH have a degree of saponification of 94.5 to 99.99 mol%.

Further, the melt index of the cold-soluble polyvinyl alcohol is 2.2-15.2 g/10min, preferably the melt index of the cold-soluble polyvinyl alcohol is 2.7-14.7 g/10min, and more preferably the melt index of the cold-soluble polyvinyl alcohol is 2.9-13.9 g/10 min; the melt index of the cold-soluble ethylene-vinyl alcohol copolymer is 2.2-15.2 g/10min, preferably the melt index of the cold-soluble ethylene-vinyl alcohol copolymer is 2.7-14.7 g/10min, and more preferably the melt index of the cold-soluble ethylene-vinyl alcohol copolymer is 2.9-13.9 g/10 min.

Further, the molar content of vinyl alcohol in the cold-soluble ethylene-vinyl alcohol copolymer is 28 to 94%, preferably 36 to 92%, and more preferably 42 to 84%; .

Further, the cold-melt ethylene-vinyl alcohol copolymer has an ethylene molar content of 6 to 72%, preferably an ethylene molar content of 8 to 64%, and more preferably an ethylene molar content of 16 to 58%.

Further, the cold-soluble ethylene-vinyl alcohol copolymer has a vinyl acetate molar content of 0% to 6%, preferably a vinyl acetate molar content of 0.01% to 6%, and more preferably a vinyl acetate molar content of 0.01% to 5.5%.

The cold-soluble polymer preferably has a yellowness index of 40 or less, more preferably 30 or less, even more preferably 20 or less, and even more preferably 10 or less.

According to another aspect of the present invention, there is provided a use of a cold-soluble polymer, the cold-soluble polymer being any one of the cold-soluble polymers described above, the use comprising applying the cold-soluble polymer to putty powder, concrete, specialty mortar, gap filler, cold-soluble adhesive, interfacial fusion agent, or release agent.

By applying the technical scheme of the invention, the cold-soluble polymer is prepared by a solvent replacement method, the process is simple, and the cost is low; meanwhile, the cold-soluble polymer can be purified in the solvent replacement process, so that the content of transition metal impurities and the content of alkaline impurities in the polymer are effectively reduced, the color phase of the polymer is improved, the optical performance of the polymer is improved, and the polymer is favorably applied to the fields of optical devices such as polaroids or the like, foods, biological packaging materials and the like. Compared with the cold-soluble polymer in the prior art, compared with the raw material with high crystallinity before treatment, the cold-soluble polymer prepared by the preparation method has lower crystallinity, the polymer dispersion obtained by dissolving the cold-soluble polymer in a solvent has better fluidity and is difficult to form gel, and the upper limit of the solid content of the polymer is higher, so that the polymer dispersion is easier to process and has wider processing window; the prepared cold-soluble polymer not only has the characteristics of cold solubility and instant dissolution, but also maintains high saponification degree, even if the polymer with low crystallinity is subjected to heat treatment forming, the crystallinity is improved, the solvent resistance is stronger, the mechanical property is better, and the barrier property is higher.

In the preparation method, a good solvent with good solubility to the polymer is adopted to dissolve the polymer to form a polymer dispersion liquid; then, carrying out precipitation treatment on the polymer dispersion liquid by using a precipitator to obtain a first polymer solid, wherein the polymer is precipitated to form a solid by changing a stable system formed by the polymer dispersion liquid by using the dispersion performance difference of the polymer in different solvents and by using the precipitator, and part of good solvent and/or the precipitator is/are wrapped and precipitated at the same time in the precipitation process; extracting the first polymer wet solid by using an extracting agent, and replacing liquid molecules in the first polymer wet solid by using the extracting agent by using the diffusion and concentration difference of the liquid molecules, such as a good solvent and a precipitating agent which are added previously; and finally, drying the extracted wet solid, controlling the type of the extracting agent to be the same as that of the precipitating agent, controlling the volatilization speed to be higher than that of the precipitating agent used in the step S2, and enabling more than 90% of the extracting agent remaining in the extracted wet solid to be lower alkane, so that liquid molecules in the wet solid are replaced by the lower alkane with low boiling point, high volatilization speed and poor polymer adsorbability according to the intersolubility characteristics of different precipitating agents. Therefore, the temperature required for drying is lower than the dissolution temperature of step S1, the low-temperature drying process is lower than the glass transition temperature of the polymer, the molecular chain is difficult to move and form crystals in the glassy state of the polymer, and the cold-soluble polymer is obtained. The dissolution process destroys the crystallization of the polymer, and the polymer is not crystallized substantially due to the low temperature during the final drying process, and the crystallinity is kept low, i.e. the characteristics of the cold-soluble polymer are kept.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 shows the DSC curve of cold-melt form F171B of example 4 of the present invention;

FIG. 2 shows the DSC curve of hot melt form F171B of comparative example 4 of the present invention.

Detailed Description

It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

As analyzed by the background technology of the application, PVA and EVOH with high saponification degree in the prior art are difficult to cold-dissolve, and in order to solve the problem, the application provides a cold-soluble polymer and a preparation method and application thereof.

In one exemplary embodiment of the present application, there is provided a method of preparing a cold-melt polymer, the method comprising: step S1, dissolving the saponified polymer in a good solvent to obtain a polymer dispersion, wherein the polymer is polyvinyl alcohol or an ethylene-vinyl alcohol copolymer, and the saponification degree of the polymer is 94-100 mol%; step S2, precipitating the polymer dispersion liquid by using a precipitating agent to obtain a first polymer wet solid; step S3, extracting liquid molecules in the first polymer wet solid by using an extracting agent to obtain an extracted wet solid, wherein the extracting agent comprises a first component and a second component; and step S4, drying the extracted wet solid to obtain the cold-soluble polymer.

The cold-soluble polymer is prepared by a solvent replacement method, so that the process is simple and the cost is low; meanwhile, the cold-soluble polymer can be purified in the solvent replacement process, so that the content of transition metal impurities and the content of alkaline impurities in the polymer are effectively reduced, the color phase of the polymer is improved, the optical performance of the polymer is improved, and the polymer is favorably applied to the fields of optical devices such as polaroids or the like, foods, biological packaging materials and the like. Compared with the cold-soluble polymer in the prior art, compared with the raw material with high crystallinity before treatment, the cold-soluble polymer prepared by the preparation method has lower crystallinity, the polymer dispersion obtained by dissolving the cold-soluble polymer in a solvent has better fluidity and is difficult to form gel, and the upper limit of the solid content of the polymer is higher, so that the polymer dispersion is easier to process and has wider processing window; the prepared cold-soluble polymer not only has the characteristics of cold solubility and instant dissolution, but also maintains high saponification degree, even if the polymer with low crystallinity is subjected to heat treatment forming, the crystallinity is improved, the solvent resistance is stronger, the mechanical property is better, and the barrier property is higher.

The good solvent of the present application can be selected by referring to the solvent commonly used in the polymer dissolution in the prior art, combining the properties of the polyvinyl alcohol and the ethylene-vinyl alcohol copolymer, in some embodiments, the good solvent is selected from any one or more of the first good solvents, a first mixed solvent composed of any one of the first good solvents and any one of the second good solvents, or a second mixed solvent composed of two of the second good solvents, the mass content of the second good solvent in the first mixed solvent is 25% to 75%, the first good solvent includes any one or more of polyhydric alcohol, lower fatty acid, phenolic solvent, lower fatty acid and other solvents, the second good solvent includes water and lower aliphatic monohydric alcohol, and the mass content of water or lower aliphatic monohydric alcohol in the second mixed solvent is 25% to 75%, wherein the polyhydric alcohol is selected from ethylene glycol, propylene glycol, ethylene-vinyl alcohol copolymer, and the second good solvent includes any one or more of polyhydric alcohol and other solvents Any one or more of glycerol; the phenolic solvent is selected from any one or more of phenol, cresol, m-cresol, o-cresol and p-cresol; the lower aliphatic monohydric alcohol is selected from one or more of methanol, ethanol, n-propanol and isopropanol; the lower fatty acid is selected from any one or more of formic acid, acetic acid and propionic acid; the other solvent is one or more selected from N, N-dimethylformamide, N-dimethylacetamide and dimethyl sulfoxide. Wherein the lower aliphatic monohydric alcohol is not soluble in polyvinyl alcohol and the ethylene-vinyl alcohol copolymer, but the dissolution of the polymer can be accelerated by a mixed solvent formed by mixing the lower aliphatic monohydric alcohol with a solvent other than the lower monohydric alcohol in the good solvent. Preferably, the polymer is polyvinyl alcohol, and is dissolved by using a good solvent containing lower aliphatic monohydric alcohol, wherein the mass content of the lower aliphatic monohydric alcohol in the good solvent is less than 75%; preferably, the polymer is an ethylene-vinyl alcohol copolymer, and is dissolved by using a good solvent containing water or lower aliphatic monohydric alcohol, wherein the lower aliphatic monohydric alcohol is selected from n-propanol and isopropanol, and the mass content of the lower aliphatic monohydric alcohol or the water in the good solvent is 25-75%.

The good solvent other than water and the lower aliphatic alcohol, either a single solvent or a mixed solvent, can dissolve the polyvinyl alcohol and the ethylene-vinyl alcohol copolymer at a certain temperature. According to the dissolving properties of the polymer in different solvents, the mass ratio of the solvent to the polymer is controlled to be 5-50: 1, so that the polymer can be fully dissolved. For example, EVOH may be dissolved by using a good solvent consisting of 25% water and 75% isopropanol/n-propanol, or by using a good solvent consisting of 75% water and 25% isopropanol/n-propanol. EVOH was also dissolved by 25% water and 75% DMSO. Solvent systems that dissolve EVOH are generally all capable of dissolving PVA.

In order to dissolve the polymer in the good solvent as quickly as possible, in some embodiments, in the step S1, the dissolution temperature is controlled to be 60 ℃ to 220 ℃ and the dissolution time is 1 to 72 hours.

Based on the determination of good solvent, the precipitant is selected based on the control of polarity and solubility parameters. Polyvinyl alcohol polymers are soluble in the most polar water of common solvents, so low polarity solvents are suitable precipitating agents. The lower aliphatic monohydric alcohol is mixed with a solvent such as water, the polarity and solubility parameters of the solvent are adjusted in a proper content to facilitate the dissolution of the polymer, but the excessive lower aliphatic monohydric alcohol can cause the polarity of the solvent to be too low, so that the polymer is separated out and precipitated. In some embodiments, the precipitant of the polymer dispersion is selected from the group consisting of any one or more of lower aliphatic alcohols, lipid solvents, chlorinated hydrocarbons, lower alkanes, low polarity water soluble solvents, and water. Mutual solubility of the precipitant and the good solvent can change the polarity and solubility parameters of the solvent, so that the polymer is precipitated.

The precipitation agent can be divided into five precipitation agents according to the intersolubility of the precipitation agent and the good solvent, wherein the first precipitation agent is lower aliphatic alcohol and is intersoluble with any good solvent. The first precipitator is selected from methanol, ethanol, isopropanol and n-propanol, and the mass ratio of the first precipitator to the good solvent is 4-8. With the increase of the content of the lower aliphatic alcohol, the polarity of the solvent system is continuously reduced, the solubility parameter is changed, and the polyvinyl alcohol polymer and the ethylene-vinyl alcohol copolymer begin to separate out precipitates.

The second precipitator is a low-polarity water-soluble solvent and a precipitator which is mutually soluble with any good solvent. The low-polarity water-soluble solvent is selected from tetrahydrofuran, acetone or butanone, and the mass ratio of the precipitator to the good solvent is 2-8. The second precipitator has lower polarity and large difference with the solubility parameter of the polymer, can be mutually soluble with all the good solvents, and the polarity of the solvent system is reduced along with the addition of the second precipitator, the solubility parameter is changed, and the polyvinyl alcohol polymer and the ethylene-vinyl alcohol copolymer are precipitated.

The third precipitator is a precipitator which is not miscible with water and comprises chlorohydrocarbon and lipid solvent, the preferred chlorohydrocarbon precipitator is dichloromethane and trichloromethane in consideration of drying efficiency and cost of precipitation, and the preferred lipid precipitator is ethyl acetate, ethyl formate, methyl formate, propyl formate, methyl acetate and methyl propionate. Other C1-C5 chlorinated hydrocarbon and lipid solvents can also be used as a precipitator, but the higher boiling point can result in slow volatilization rate, long volatilization time and lower drying efficiency. The third precipitator is immiscible with water and can precipitate polymer dispersion liquid dissolved by a good solvent except water, and the mass ratio of the third precipitator to the good solvent is 2-8. With the addition of the third precipitant, the polarity of the solvent is reduced, the solubility parameter is changed, and the polymer is separated out.

The fourth precipitator is a lowest polarity lower alkane precipitator, and the lower alkane is selected from the group consisting of carbon pentaalkane, carbon hexaalkane and petroleum ether. The alkane with longer carbon chain can also be used as a precipitator, but the higher boiling point can cause slow volatilization speed, long volatilization time and lower drying efficiency. Since the polarity of the fourth precipitant is very low, the fourth precipitant is miscible with the phenolic solvent, ethanol, isopropanol, n-propanol, the second precipitant, and the third precipitant, and immiscible with the good solvent and the precipitant. Therefore, the fourth precipitant acts solely as a precipitant, and the good solvent is a phenolic solvent.

The fifth precipitating agent is the most polar water of common solvents and can be used for the precipitation of the ethylene-vinyl alcohol copolymer in the embodiment of the present invention. In contrast to polyvinyl alcohol, the ethylene segment in an ethylene-vinyl alcohol copolymer is a hydrophobic segment and is a water insoluble polymer. The mixed solvent of water and isopropanol or n-propanol can dissolve the ethylene-vinyl alcohol copolymer, but the content of water and alcohol is limited to 25-75%. The ethylene-vinyl alcohol copolymer is separated out due to excessive water content and high solvent polarity, so that water can be used as a precipitator of the ethylene-vinyl alcohol copolymer. The mass ratio of the water to the good solvent is 5-10, the system temperature is not more than 40 ℃, and the ethylene-vinyl alcohol copolymer precipitates. If the temperature of the system is too high, the vinyl alcohol section and the ethylene section form a core-shell structure, so that emulsion is easily formed, and the polymer cannot be precipitated.

The mixed system of different precipitants also has a good precipitation effect, the mixed precipitant composed of the first precipitant, the second precipitant, the third precipitant and the fourth precipitant, when the mass content of the first precipitant and the second precipitant in the mixed precipitant exceeds 25%, the mixed precipitant has no limit to the composition of the good solvent; when the content of the fourth precipitator in the mixed precipitator is 30-80%, the mass of water in the good solvent is below 1/2 of the mass of the first precipitator and the second precipitator, and other good solvents are not limited. Or the good solvent and the precipitant are mutually soluble, the liquid phase only has one phase after mixing, and when the mass of the second precipitant, the third precipitant and the fourth precipitant in the dispersion is more than 2 times of the molecular mass of other liquids, the polymer is precipitated.

In some embodiments of the present application, in order to displace the liquid molecules in the wet solid of the first polymer as much as possible, the step S3 preferably includes: performing first extraction on the first polymer wet solid by using a first extraction agent to obtain a first extracted wet solid, preferably, the first extraction is multi-stage extraction, and further preferably, 1-4-stage extraction; and performing second extraction on the wet solid after the first extraction by using a second extraction agent to obtain a second extracted wet solid, preferably performing multistage extraction on the second extracted wet solid, further preferably performing 1-4-stage extraction, and performing third extraction on the second extracted wet solid by using a third extraction agent to obtain an extracted wet solid, preferably performing multistage extraction on the third extraction, and further preferably performing 1-4-stage extraction. The first extractant is miscible with the good solvent, the second extractant is miscible with the lower alkane, and in some embodiments, the first extractant, the second extractant, and the second extractant are miscible with each other and have gradually increasing volatilization speeds. Of course, lower alkanes can also be directly used for direct extraction. By adopting three extraction steps, liquid molecules in the wet solid of the first polymer can be removed as far as possible, and simultaneously, the content of liquid except the lower alkane can be gradually reduced, the temperature of subsequent drying is further reduced, and the volatilization rate is increased.

Preferably, the mass ratio of the first extractant to the second extractant is 5-1: 1, the mass ratio of the second extractant to the third extractant is 5-1: 1 or more, liquid molecules contained in the wet solid are continuously reduced along with the increase of the extraction times, the swelling of the wet solid is reduced, the volume is reduced, and the dosage of the extractants can also be continuously reduced.

The dosage of the extracting agent can be referred to the dosage of the polymer, liquid molecules in the first polymer wet solid obtained by the polymer with different dosages are different, and tests prove that the mass ratio of the extracting agent to the polymer is preferably 5: 1-100: 1 so as to completely remove the liquid molecules as far as possible.

The purpose of extraction is to replace the solvent with high boiling point, strong adsorptivity and difficult volatilization with the lower alkane with low boiling point, weak adsorptivity and easy volatilization, so that the first extractant is miscible with the good solvent and the second extractant is miscible with the lower alkane. The extractant is selected from a precipitator, the extractant except water and methanol is mutually soluble with lower alkane, and has proper boiling point and volatilization speed, and on the basis, the third extractant is preferably selected from any one of the lower alkane.

In some embodiments, when the good solvent is a phenol solvent, the precipitant does not contain water or methanol, and in order to simplify the process and reduce the cost, carbon pentaalkane, carbon hexaalkane and petroleum ether are used as the extractant to perform extraction for 2-4 times, and then low-temperature drying can be performed to obtain the cold-soluble polymer. The same effect can be achieved by extraction with a precipitating agent other than water and methanol, followed by extraction with lower alkanes, but with unnecessary losses.

In some embodiments, when the polymer is polyvinyl alcohol, and the mass content of water in the good solvent is less than 5%. The first extractant is free of water (by non-water we mean any extractant other than water), and the mass content of the fourth precipitant is less than 80%, the second extractant is free of water and methanol (by non-water we mean any extractant other than water and methanol), and the mass content of the fourth precipitant is less than 80%.

In some embodiments, when the polymer is polyvinyl alcohol, and the good solvent contains water in an amount of not less than 5% by mass. The first extractant contains no water, the mass content of the first precipitator and the second precipitator is not less than 20%, the second extractant contains no water and methanol, and the mass content of the fourth precipitator is less than 80%.

In some embodiments, when the polymer is an ethylene-vinyl alcohol copolymer and the good solvent comprises a high-boiling point, strong hygroscopic solvent such as a polyol, a lower fatty acid, N-dimethylformamide, N-dimethylacetamide, or dimethylsulfoxide, water is used as the first extractant to remove the high-boiling point organic solvent in order to reduce costs; the second extractant does not contain water or methanol, and the content of ethanol, n-propanol, isopropanol or second precipitator is not less than 30%. The first extractant can also effectively remove the high-boiling organic solvent by adopting the first precipitator, the second precipitator and the third precipitator, but the cost is higher.

In some embodiments, when the polymer is an ethylene-vinyl alcohol copolymer and the good solvent is a mixed solvent of water and lower aliphatic alcohol, in order to simplify the process and reduce the cost, the mass content of ethanol, isopropanol, n-propanol or a second precipitator in the first extractant is not less than 30%, and the second extractant is not used, and a third extractant is directly used for subsequent extraction operation, so that the cold-soluble polymer can be obtained by low-temperature drying.

In order to accelerate the formation efficiency of the cold-melt polymer, in some embodiments, in the step S4, the drying is performed by drying under normal pressure or vacuum, the drying temperature is controlled to be 0 to 30 ℃, and the drying time is controlled to be 0.5 to 200 hours, so as to remove the solvent in the polymer as completely as possible.

In another exemplary embodiment of the present application, a cold-melt polymer is provided, which is prepared according to the above-described preparation method. The cold-soluble polymer in the application has the characteristics of cold solubility and instant dissolution, and also keeps high saponification degree, high crystallinity, stronger solvent resistance, better mechanical property and higher barrier property after heat treatment forming. The cold-soluble polymer can be cold-soluble polyvinyl alcohol or cold-soluble ethylene-vinyl alcohol copolymer, and preferably the cold-soluble ethylene-vinyl alcohol copolymer is ethylene-vinyl alcohol binary copolymer or ethylene-vinyl alcohol-vinyl acetate ternary copolymer.

Referring to the prior art, the higher the saponification degree of the polymer, the stronger the hydrogen barrier property, and the greater the melt processing difficulty, and the cold-soluble polymer of the present application reduces the melt processing difficulty under the condition of keeping high saponification degree. In some examples, when the cold-soluble polyvinyl alcohol and the cold-soluble EVOH have a degree of saponification of 94 to 100 mol%, preferably 94.5 to 99.99 mol%, and less than 94 mol%, the crystallinity of the polyvinyl alcohol and the EVOH significantly decreases, and the physical properties such as mechanical strength and barrier property of the molded article decrease. The saponification degree is preferably 94 mol% or more, more preferably 94.5 mol% or more; when the saponification degree exceeds 99.99 mol%, the production of polyvinyl alcohol tends to be difficult and the moldability tends to be poor. The melt index of the cold-soluble polyvinyl alcohol is preferably 2.2-15.2 g/10min, the melt index of the cold-soluble polyvinyl alcohol is preferably 2.7-14.7 g/10min, and the melt index of the cold-soluble polyvinyl alcohol is more preferably 2.9-13.9 g/10 min.

When the cold-soluble polymer is a cold-soluble ethylene-vinyl alcohol copolymer, the melt index is preferably 2.2 to 15.2g/10min, more preferably 2.7 to 14.7g/10min, and still more preferably 2.9 to 13.9g/10 min.

In some embodiments, the molar content of vinyl alcohol in the cold-soluble ethylene-vinyl alcohol copolymer is 28% to 94%, preferably 36% to 92%, and more preferably 42% to 84%; and/or the molar content of ethylene in the cold-soluble ethylene-vinyl alcohol copolymer is 6 to 72 percent, preferably the molar content of ethylene is 8 to 64 percent, and more preferably the molar content of ethylene is 16 to 58 percent; and/or the molar content of vinyl acetate in the cold-soluble ethylene-vinyl alcohol copolymer is 0 to 6 percent, preferably the molar content of vinyl acetate is 0.01 to 6 percent, and more preferably the molar content of vinyl acetate is 0.01 to 5.5 percent. So as to meet the requirements of the current industrialized application.

The content of transition metal impurities and the content of alkaline impurities in the polymer are reduced through multiple extractions, the hue of the polymer is improved, and the yellowness index of the cold-soluble polymer is less than 40, preferably less than 30, more preferably less than 20, and even more preferably less than 10. The content of basic impurities in the polymer is preferably 0.1% by mass or less, preferably 0.08% by mass or less, more preferably 0.04% by mass or less, and particularly preferably 0.02% by mass or less.

In yet another exemplary embodiment of the present application, there is provided a use of a cold-soluble polymer, the cold-soluble polymer being as described above, the use comprising applying the cold-soluble polymer to putty powder, concrete, specialty mortar, gap fillers, cold-soluble adhesives, interfacial fusion agents, or debonding agents. The cold-soluble polymer can be dissolved below 30 ℃, and can be applied to scenes sensitive to dispersion temperature. The cold-soluble PVA prepared by the method can be applied to emulsifying agents, suspending agents, surfactants, fiber processing agents, various adhesives, paper processing agents, adhesives and films as well as untreated commercial PVA, and the processing is easier.

The present application is described in further detail below with reference to specific examples, which should not be construed as limiting the scope of the invention as claimed.

PVA and EVOH solid yellowness index test: the yellowness index was characterized using an UltraScan VIS type spectrocolorimeter from HunterLab. The polymer solid hue was evaluated by yellowness index.

Optical properties: the optical performance of the polymer film is measured by adopting a Shanghai apparatus electronic light transmittance haze measuring instrument WGT-S, and the test is carried out according to the GB/T2410-2008 standard. The higher the transmission, the lower the haze the better the optical properties.

Determination of transition metal elements: the contents of transition metal elements of iron, cobalt and nickel in the polymer were measured using an inductively coupled plasma mass spectrometer (ICP-MS) of seemefly.

DSC: the thermal properties of the polymers were characterized using a differential scanning calorimeter (DSC3) from Mettler-Torido, the specific test method being shown in the test chart.

In the examples, all PVA was purchased from national drug agents; all EVOH was purchased from korea corporation; other medicines are analytically pure.

In order to prevent metal ion impurity pollution, the high-temperature and high-pressure dissolving process is carried out in a corrosion-resistant high-pressure reaction kettle independently designed by national electric hydrogen energy technology development limited.

Example 1: preparation of cold-soluble PVA1795

5 parts by mass of PVA1795 (degree of polymerization 1700, degree of saponification 95 mol%) was dissolved in 30 parts by mass of dimethyl sulfoxide dispersion with stirring at 180 ℃ for 1 hour to form a PVA dispersion, and 100 parts by mass of methanol was added to the PVA dispersion to precipitate and obtain a wet polymer solid.

And (3) using 500 parts by mass of ethanol as a first extractant to extract the wet solid, stirring for 1 hour, and filtering to separate the solid.

The wet solid was extracted using a mixture of 40 parts by mass of isopropyl alcohol and 60 parts by mass of industrial hexane as a second extractant, stirred for 1 hour, and filtered to separate a solid.

And (3) extracting the wet solid by using 20 parts by mass of cyclopentane as a third extracting agent, stirring for 1 hour, and filtering to obtain a solid. Repeat 4 times. The resulting wet solid was dried under vacuum at 30 ℃ for 72h to give dry cold-soluble PVA1795 solid.

Adding 1 part by mass of cold-soluble PVA1795 into 9 parts by mass of water for dissolving, wherein the dissolving temperature is 30 ℃, the stirring speed is 300r/min, and the polymer solid is completely dissolved within 2 min.

Adding 1 part by mass of cold-soluble PVA1795 into 2 parts by mass of dimethyl sulfoxide for dissolution, wherein the dissolution temperature is 25 ℃, the stirring speed is 300r/min, and the polymer solid is completely dissolved within 5 min.

Example 2: preparation of cold-soluble PVA1799

5 parts by mass of PVA1799 (degree of polymerization 1700, degree of saponification: more than 99 mol%) was dissolved in 30 parts by mass of N, N-dimethylacetamide dispersion with stirring at 90 ℃ for 24 hours, and precipitated by adding a mixed solvent of 100 parts by mass of industrial hexane and 50 parts by mass of ethanol.

And (3) extracting the wet solid by using 100 parts by mass of ethyl acetate as a first extracting agent, stirring for 1 hour, and filtering to obtain a solid.

The wet solid was extracted using a mixture of 20 parts by mass of tetrahydrofuran and 30 parts by mass of industrial hexane as a second extractant, stirred for 1 hour, and filtered to separate a solid. Repeat 2 times.

The wet solid was extracted with 50 parts by mass of industrial hexane, stirred for 1 hour, filtered to separate the solid, and repeated 1 time. The obtained wet solid was dried in vacuum at 30 ℃ for 12 hours to obtain a dry cold-soluble PVA1799 solid.

Adding 1 part by mass of cold-soluble PVA1799 into 9 parts by mass of water for dissolving, wherein the dissolving temperature is 30 ℃, the stirring speed is 300r/min, and the polymer solid is completely dissolved within 5 min. And casting and molding the cold-soluble PVA1799 dispersion liquid at 90 ℃ to obtain a film X-1 with the thickness of 100 +/-3 mu m. The film X-1 had a yellowness index of 2.74, a transmittance of 99.54%, a haze of 0.31%, and contents of iron, cobalt, and nickel of 1.2ppm, 0ppm, and 2.1ppm, respectively.

Adding 1 part by mass of cold-soluble PVA1799 into 4 parts by mass of dimethyl sulfoxide for dissolution, wherein the dissolution temperature is 25 ℃, the stirring speed is 300r/min, and the polymer solid is completely dissolved within 6 min.

Example 3: preparation of cold-soluble PVA2699

5 parts by mass of PVA2699 (degree of polymerization 1700, degree of saponification > 99 mol%) were dissolved in 150 parts by mass of water and 100 parts by mass of an aqueous dispersion of isopropanol under a pressure of 20MPa and stirred at 220 ℃ for 2 hours, and precipitated by adding 1500 parts by mass of acetone.

The wet solid was extracted with 24 parts by mass of industrial hexane and 1 part by mass of dichloromethane as the first extractant, stirred for 1 hour, filtered to separate the solid, and repeated 4 times.

The wet solid was extracted using 24.9 parts by mass of industrial hexane and 0.1 part by mass of methylene chloride as a second extractant, stirred for 1 hour, and filtered to separate the solid, which was repeated 4 times.

Using 25 parts by mass of n-pentane as a third extractant to extract the wet solid, stirring for 1 hour, filtering and separating to obtain the solid, and repeating for 4 times. The obtained wet solid was dried under vacuum at 30 ℃ for 0.5 hour to obtain a dry cold-soluble PVA2699 solid.

Adding 1 part by mass of cold-soluble PVA2699 into 9 parts by mass of water for dissolving, wherein the dissolving temperature is 30 ℃, the stirring speed is 300r/min, and the polymer solid is completely dissolved within 8 min.

Adding 1 part by mass of cold-soluble PVA2699 into 4 parts by mass of dimethyl sulfoxide for dissolving, wherein the dissolving temperature is 25 ℃, the stirring speed is 300r/min, and the polymer solid is completely dissolved within 9 min.

Example 4: preparation of cold-soluble completely saponified PVA

The thermal-soluble completely saponified PVA is obtained after saponification or alcoholysis reaction of polyvinyl acetate in methanol under the catalysis of sodium hydroxide, and the saponification degree of the completely saponified PVA is not less than 99.99 mol%, which is named as PVA-H. 1 part by mass of PVA-H solid was dissolved in 19 parts by mass of a dimethyl sulfoxide dispersion solution with stirring at 80 ℃ for 72 hours, and precipitated in 100 parts by mass of methylene chloride to obtain a wet solid.

The wet solid was extracted using 10 parts by mass of methylene chloride as a first extractant, stirred for 1 hour, and filtered to separate a solid.

Wet solids were extracted using 4.9 parts by mass of n-hexane and 0.1 part by mass of methanol as the second extractant, stirred for 1 hour, and filtered to separate solids.

And 5 parts by mass of isopentane is used as a third extractant to extract the wet solid, the wet solid is stirred for 1 hour, and the solid is obtained by filtration and separation.

Vacuum drying at 20 deg.c for 72 hr to obtain cold soluble PVA-H solid named PVA-H-L.

And (3) adding 1 part by mass of PVA-H-L solid into 9 parts by mass of water for dissolving, wherein the dissolving temperature is 30 ℃, the stirring speed is 300r/min, and the polymer solid is completely dissolved within 30 min.

And (3) adding 1 part by mass of PVA-H-L solid into 4 parts by mass of dimethyl sulfoxide for dissolving, wherein the dissolving temperature is 25 ℃, the stirring speed is 300r/min, and the polymer solid is completely dissolved within 20 min.

Example 5: preparation of cold-soluble E105B, F171B and L171B

E105B, F171B and L171B were all Krolly produced EVOH having a degree of saponification of not less than 99.9% and ethylene contents of 44 mol%, 32 mol% and 27 mol%, respectively.

1 part by mass of F171B was dissolved in 9 parts by mass of an N, N-dimethylacetamide dispersion at 150 ℃ with stirring for 4 hours, and 60 parts by mass of ethanol was added to precipitate to obtain a wet polymer solid.

And (3) extracting the wet solid by using 95 parts by mass of normal hexane and 5 parts by mass of ethanol as first extracting agents, stirring for 1 hour, and filtering and separating to obtain a solid.

Using 19 parts by mass of n-hexane and 1 part by mass of acetone as second extracting agents to extract the wet solid, stirring for 1 hour, and filtering and separating to obtain a solid.

And (3) using 6 parts by mass of isopentane as a third extractant to extract the wet solid, stirring for 1 hour, filtering and separating to obtain the solid, and repeating for 3 times.

Vacuum drying at 10 ℃ for 144h gave F171B as a solid in the cold soluble form.

The cold-soluble forms E105B and L171B were prepared as F171B.

1 part by mass of cold-soluble EVOH solid is added into 4 parts by mass of N, N-dimethylacetamide to be dissolved, the dissolving temperature is 25 ℃, the stirring speed is 300r/min, and the cold-soluble E105B, the cold-soluble F171B and the cold-soluble L171B are completely dissolved within 60 seconds.

1 part by mass of a cold-soluble F171B solid was added to 9 parts by mass of N, N-dimethylacetamide and dissolved, and the resulting dispersion was cast to obtain a film Y-1 having a thickness of 100. + -.3. mu.m. The yellowness index of the film Y-1 was 0.89, the transmittance was 99.32%, the haze was 0.42%, and the contents of iron, cobalt, and nickel were 0.2ppm, 1.6ppm, and 1.1ppm, respectively.

Example 5: preparation of cold-soluble completely saponified EVOH

The obtained copolymer was saponified or alcoholyzed in a methanol dispersion of an ethylene-vinyl acetate copolymer under the catalysis of sodium hydroxide to give a hot-melt completely saponified ethylene-vinyl alcohol copolymer (having an ethylene content of 38 mol% and a saponification degree of not less than 99.99 mol%), which was designated EVOH-H.

1 part by mass of an EVOH-H solid was dissolved in 7 parts by mass of n-propanol and 3 parts by mass of an aqueous dispersion at 70 ℃ and precipitated in 60 parts by mass of ethanol to obtain a wet solid.

The wet solid was extracted using 10 parts by mass of dichloromethane and 30 parts by mass of n-hexane as the first extractant, stirred for 1 hour, filtered to separate the solid, and repeated 2 times.

Using 2 parts by mass of dichloromethane and 8 parts by mass of n-hexane as a second extractant to extract the wet solid, stirring for 1 hour, and filtering to obtain a solid.

Extracting the wet solid by using 10 parts by mass of industrial hexane as a third extractant, stirring for 1h, filtering and separating to obtain a solid, and repeating for 3 times. Vacuum drying at 0 deg.C for 200H to obtain cold-soluble EVOH-H solid, which is named EVOH-H-L.

And (2) adding 1 part by mass of EVOH-H-L solid into 4 parts by mass of dimethyl sulfoxide for dissolving, wherein the dissolving temperature is 25 ℃, the stirring speed is 300r/min, and the polymer solid is completely dissolved within 2 min.

Comparative example 1: dissolution of Hot-melt PVA

The hot melt PVA was dissolved in different solvents at a stirring rate of 300r/min, as shown in Table 1, and the stirring time of the PVA in the dispersion was 48 hours at 30 ℃ and 60 ℃.

Comparative example 2: dissolution of Hot-melt EVOH

Different solvents were used to dissolve hot melt EVOH at a stirring rate of 300 r/min. The hot-melt EVOH was hardly dissolved by stirring at 30 ℃ for 48 hours, and the hot-melt EVOH was partially dissolved by stirring at 60 ℃ for 48 hours. The dissolution at 100 ℃ is shown in Table 2.

Comparative example 3: hot-melt PVA1799 film preparation

1 part by mass of hot-melt PVA1799 is added into 9 parts by mass of water to be heated and dissolved, and the obtained dispersion is cast and molded at 90 ℃ to obtain a film X-2 with the thickness of 100 +/-3 mu m. The film X-2 had a yellowness index of 22.74, a transmittance of 95.38%, a haze of 2.11%, and contents of iron, cobalt, and nickel of 15.2ppm, 0.1ppm, and 9.7ppm, respectively.

Comparative example 4: film preparation by hot melt type F171B

1 part by mass of hot melt type F171B was added to 9 parts by mass of N, N-dimethylformamide and dissolved by heating, and the resulting dispersion was cast at 90 ℃ to obtain a film Y-2 having a thickness of 100. + -.3. mu.m. The yellowness index of the film Y-2 was 3.62, the transmittance was 98.67%, the haze was 0.61%, and the contents of iron, cobalt, and nickel were 1.2ppm, 8.9ppm, and 3.5ppm, respectively.

Compared with the hot-melt PVA1795 in the comparative example 1, the cold-melt PVA1795 can be dissolved at low temperature, the dissolving time is greatly shortened, and the cold-melt and instant-melt characteristics are achieved.

Compared with the hot-melt PVA1799 and the hot-melt PVA2699 in the comparative example 1, the cold-melt PVA1799 and the cold-melt PVA2699 can be dissolved at low temperature, the dissolving time is greatly shortened, and the cold-melt and instant PVA has the characteristics of cold-melt and instant dissolution. Compared with the untreated hot-melt PVA1799 film in the comparative example 3, the films prepared from the cold-melt PVA1799 have the advantages of lower content of metal impurities, higher purity, lower yellowness index, good hue and obviously improved optical performance.

Example 4 compared with the hot-melt EVOH of comparative example 2, the cold-melt EVOH was soluble at a low temperature, and the dissolution time was significantly shortened, and the cold-melt and instant dissolution properties were exhibited.

Compared with the film prepared by untreated hot-melt type F171B in comparative example 4, the film prepared by cold-melt type F171B has the advantages of lower content of metal impurities, improved purity, low yellowness index, good hue and obviously improved optical performance.

The DSC curve of cold melt F171B is shown in fig. 1, and the DSC curve of hot melt F171B is shown in fig. 2, and the crystallinity of cold melt F171B is lower than that of hot melt F171B, and the glass transition phenomenon is observed in fig. 1, and the melting temperature is slightly lower than that of hot melt F171B. In contrast, the hot melt type F171B had a high crystallinity, and only a melting peak was observed.

TABLE 1

TABLE 2

From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects:

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a cold-soluble polymer, comprising:

step S1, dispersing the saponified polymer in a good solvent to obtain a polymer dispersion liquid, wherein the polymer is polyvinyl alcohol or an ethylene-vinyl alcohol copolymer, and the saponification degree of the polymer is 94-100 mol%;

step S2, precipitating the polymer dispersion with a precipitant to obtain a first polymer wet solid, where the first polymer wet solid includes liquid molecules entrained in the polymer, and the liquid molecules include the good solvent and the precipitant;

step S3, extracting the liquid molecules in the first polymer wet solid by using an extracting agent to obtain an extracted wet solid, wherein the extracting agent is selected from the precipitating agent and has a higher volatilization speed than that of the precipitating agent used in the step S2, and more than 90% of the extracting agent left in the extracted wet solid is lower alkane;

and step S4, drying the extracted wet solid to obtain the cold-soluble polymer.

2. The preparation method according to claim 1, wherein the good solvent is selected from any one or more of first good solvents, a first mixed solvent composed of any one of the first good solvents and any one of second good solvents, or a second mixed solvent composed of two of the second good solvents, wherein the mass content of the second good solvent in the first mixed solvent is 25% to 75%, the first good solvent comprises any one or more of polyhydric alcohols, lower fatty acids, phenolic solvents, lower fatty acids, and other solvents, the second good solvent comprises water and lower aliphatic monohydric alcohols, the mass content of the water or the lower aliphatic monohydric alcohols in the second mixed solvent is 25% to 75%, and the polyhydric alcohols are selected from any one or more of ethylene glycol, propylene glycol, and glycerol; the phenolic solvent is selected from any one or more of phenol, cresol, m-cresol, o-cresol and p-cresol; the lower aliphatic monohydric alcohol is selected from any one or more of methanol, ethanol, n-propanol and isopropanol; the lower fatty acid is selected from any one or more of formic acid, acetic acid and propionic acid; the other solvent is one or more selected from N, N-dimethylformamide, N-dimethylacetamide and dimethyl sulfoxide.

3. The production method according to claim 2, wherein the polarity of the precipitant is lower than that of the good solvent,

preferably, the precipitating agent is selected from any one or more of the group consisting of lower aliphatic alcohols, lipid solvents, chlorinated hydrocarbons, lower alkanes, low polarity water soluble solvents, and water, the lower aliphatic alcohols used in the precipitating agent include methanol, ethanol, isopropanol, and n-propanol, preferably the lipid solvents include ethyl acetate, ethyl formate, methyl formate, propyl formate, methyl acetate, and methyl propionate, the chlorinated hydrocarbons include dichloromethane and chloroform, the lower alkanes include carbon pentaalkanes, carbon hexaalkanes, and petroleum ether, and the low polarity water soluble solvents are selected from tetrahydrofuran, acetone, and butanone;

preferably, when the precipitant is the lower aliphatic alcohol, the mass ratio of the precipitant to the good solvent is 4-8: 1;

preferably, when the precipitant is the low-polarity water-soluble solvent, the mass ratio of the precipitant to the good solvent is 2-8: 1;

preferably, when the precipitant is the lipid solvent or the chlorinated hydrocarbon, the mass ratio of the precipitant to the good solvent is 2-8: 1;

preferably, when the precipitant is the lower alkane, the mass ratio of the precipitant to the good solvent is 2-8: 1;

preferably, when the precipitating agent is the water, the mass ratio of the precipitating agent to the good solvent is 5-10: 1;

preferably, when the good solvent is the second mixed solvent and the mass contents of the water and the lower aliphatic monohydric alcohol in the second mixed solvent are each independently 25% to 75%, the precipitant is water.

4. The method for preparing a composite material according to claim 2, wherein the step S3 includes:

performing first extraction on the first polymer wet solid by using a first extraction agent to obtain a first extracted wet solid, preferably, the first extraction is multi-stage extraction, and further preferably, 1-4-stage extraction;

performing second extraction on the wet solid after the first extraction by using a second extraction agent to obtain a wet solid after the second extraction, wherein the second extraction is preferably multi-stage extraction, and further preferably 1-4-stage extraction;

performing third extraction on the wet solid after the second extraction by using a third extraction agent to obtain a wet solid after the second extraction, wherein the third extraction is preferably multi-stage extraction, and further preferably 1-4-stage extraction;

the first extractant is mutually soluble with the good solvent, the second extractant is mutually soluble with the lower alkane, the first extractant, the second extractant and the third extractant are preferably mutually soluble and have gradually increased volatilization speed, the mass ratio of the first extractant to the polymer is preferably 5-100: 1, the mass ratio of the first extractant to the second extractant is preferably 5-1: 1, the mass ratio of the second extractant to the third extractant is preferably 5-1: 1, and the third extractant is preferably selected from any one or more of the lower alkanes.

5. The production method according to claim 3,

the good solvent is a phenol solvent, the precipitator does not contain water or methanol, and in the step S3, carbon pentaalkane, carbon hexaalkane and petroleum ether are used as extracting agents to perform extraction for 2-4 times.

6. The method of claim 4, wherein the polymer is polyvinyl alcohol, the good solvent contains water in an amount of less than 5% by mass, the precipitant is a mixed precipitant comprising a lower aliphatic alcohol, a lipid solvent, a chlorinated hydrocarbon, a lower alkane, and a low-polarity water-soluble solvent, and the lower alkane contains water in an amount of less than 80% by mass, and the first extractant contains no water and the second extractant contains no water and methanol in step S3.

7. The preparation method according to claim 4, wherein the polymer is polyvinyl alcohol, and the mass content of water in the good solvent is not less than 5%; the precipitator is a mixed precipitator consisting of lower aliphatic alcohol, a lipid solvent, chlorohydrocarbon, lower alkane and a low-polarity water-soluble solvent, wherein the mass content of the lower aliphatic alcohol and the lipid solvent in the mixed precipitator is not less than 20%, and the mass content of the lower alkane is less than 80%; in step S3, the first extracting agent contains no water, and the second extracting agent contains no water and methanol.

8. The method according to claim 4, wherein the polymer is an ethylene-vinyl alcohol copolymer, the good solvent comprises a polyhydric alcohol, a lower fatty acid, N-dimethylformamide, N-dimethylacetamide, or dimethylsulfoxide, and the first extractant is water, a lower aliphatic alcohol, a low-polarity water-soluble solvent, a chlorinated hydrocarbon, or a lipid solvent; the second extractant does not contain water or methanol, and the content of ethanol, n-propanol, isopropanol or low-polarity water-soluble solvent in the second extractant is not less than 30%.

9. The preparation method according to claim 4, wherein the polymer is an ethylene-vinyl alcohol copolymer, the good solvent is a mixed solvent of water and lower aliphatic monohydric alcohol, and the mass content of ethanol, isopropanol, n-propanol or a low-polarity water-soluble solvent in the first extractant is not less than 30%.

10. The method according to any one of claims 1 to 9, wherein in step S1, the temperature of dispersion is 60 ℃ to 220 ℃ and the time of dissolution is 1 to 72 hours.

11. The preparation method according to any one of claims 1 to 10, wherein in the step S4, the drying is performed by atmospheric drying or vacuum drying at a temperature of 0 to 30 ℃ for a time of 0.5 to 200 hours.

12. The production method according to claim 1, wherein the ethylene-vinyl alcohol copolymer is an ethylene-vinyl alcohol copolymer or an ethylene-vinyl alcohol-vinyl acetate terpolymer; the content of basic impurities in the polymer is preferably 0.1% by mass or less, preferably 0.08% by mass or less, more preferably 0.04% by mass or less, and particularly preferably 0.02% by mass or less.

13. A cold-soluble polymer, which is produced by the production method according to any one of claims 1 to 12; preferably, the cold-soluble polymer is cold-soluble polyvinyl alcohol or cold-soluble ethylene-vinyl alcohol copolymer, and preferably, the cold-soluble ethylene-vinyl alcohol copolymer is ethylene-vinyl alcohol binary copolymer or ethylene-vinyl alcohol-vinyl acetate ternary copolymer.

14. A cold-soluble polymer according to claim 13, wherein the cold-soluble polyvinyl alcohol and the cold-soluble EVOH have a degree of saponification of 94 to 100 mol%, preferably 94.5 to 99.99 mol%.

15. A cold-soluble polymer according to claim 13, wherein the melt index of the cold-soluble polyvinyl alcohol is 2.2 to 15.2g/10min, preferably the melt index of the cold-soluble polyvinyl alcohol is 2.7 to 14.7g/10min, more preferably the melt index of the cold-soluble polyvinyl alcohol is 2.9 to 13.9g/10 min;

the melt index of the cold-soluble ethylene-vinyl alcohol copolymer is 2.2-15.2 g/10min, preferably the melt index of the cold-soluble ethylene-vinyl alcohol copolymer is 2.7-14.7 g/10min, and more preferably the melt index of the cold-soluble ethylene-vinyl alcohol copolymer is 2.9-13.9 g/10 min; and/or

The molar content of vinyl alcohol in the cold-soluble ethylene-vinyl alcohol copolymer is 28-94%, preferably 36-92%, and more preferably 42-84%; and/or

The mol content of ethylene in the cold-soluble ethylene-vinyl alcohol copolymer is 6-72%, preferably 8-64%, and more preferably 16-58%; and/or

The molar content of vinyl acetate in the cold-soluble ethylene-vinyl alcohol copolymer is 0-6%, preferably the molar content of vinyl acetate is 0.01-6%, and more preferably the molar content of vinyl acetate is 0.01-5.5%.

16. A cold-soluble polymer according to claim 13, wherein the cold-soluble polymer has a yellowness index of 40 or less, preferably 30 or less, more preferably 20 or less, and even more preferably 10 or less.

17. Use of a cold-soluble polymer according to any one of claims 12 to 16, wherein the cold-soluble polymer is applied to putty powder, concrete, specialty mortar, gap filler, cold-soluble adhesive, interfacial fusion agent or release agent.