JPS5941446B2 - Process for producing starch↓-polyvinyl alcohol graft copolymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing a starch-polyvinyl alcohol graft copolymer, more specifically, a method for producing a starch-polyvinyl alcohol graft copolymer, and more specifically,
The present invention relates to a method for producing a starch-polyvinyl alcohol graft copolymer that is water-insoluble at room temperature and gelatinized by heat.

The starch-polyvinyl alcohol graft copolymer has been recognized to be useful in a variety of fields as a component of adhesives, fiber and paper sizing agents, coating agents, and various water-soluble films, and its practical application is currently being considered. However, there are various difficulties in producing the graft copolymer, and there are still
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Generally, a starch-polyvinyl alcohol graft copolymer is a starch-polyvinyl ester graft copolymer obtained by graft copolymerizing a vinyl ester, typically vinyl acetate, onto starch according to a known grafting method. Typically, it is produced by saponifying a starch-polyvinyl acetate graft copolymer with an alkali.

Usually, the graft polymerization step is carried out in water. on the other hand,
Saponification is considered difficult to carry out in water because it requires a large amount of alkali and the starch gelatinizes.
The resulting starch-polyvinyl ester graft copolymer is separated from water, dried or dehydrated, and then treated separately in methanol. However, the use of different solvents in the graft polymerization process and the saponification process makes the process complicated, and the use of methanol, an organic solvent, is important for preventing fires, preserving the work environment, and recovering methanol. In addition, the starch-polyvinyl ester graft copolymer swells and partially dissolves in methanol, whereas the saponified product is insoluble in methanol. As saponification progresses, large hard lumps of saponified material are generated, and unless strong pulverization is performed, cleaning and drying of the saponified material becomes difficult. This poses problems that require a great deal of labor and equipment.

Moreover, the starch particles of the starch-polyvinyl alcohol graft copolymer obtained by saponification in methanol have collapsed and are soluble in cold water; It also has the disadvantage that it tends to cause As described above, there are various problems and drawbacks in the production of starch-polyvinyl alcohol graft copolymers, and improvements are desired.

In view of these circumstances, the present inventors have conducted extensive research on the production of starch-polyvinyl alcohol graft copolymers, and have found that by selecting the amount of alkali added and temperature conditions in the saponification process, the graft polymerization process and the saponification process can be improved. They discovered that the oxidation process can be carried out in water without causing any disintegration of the starch particles, leading to the completion of the present invention.

That is, the present invention uses a room-temperature insoluble heat-gelatinable particulate starch-polyvinyl ester graft copolymer produced according to a conventional method in water at a concentration of 2.0% based on the weight of the entire saponified system.
% (wt%, same hereinafter) or less in the presence of an alkali, 60
The present invention provides a method for producing a particulate starch-polyvinyl alcohol graft copolymer that is insoluble at room temperature and gelatinized under heat, which is saponified at a temperature of 0.degree. C. or lower.

According to the production method of the present invention, both graft polymerization and saponification can be carried out in water, which eliminates the complexity of the steps mentioned above and the need for equipment to prevent fires and preserve the working environment due to the use of methanol. The starch-polyvinyl alcohol graft copolymer can be produced very easily and economically using existing size liquid preparation equipment without any problems or problems such as formation of saponified product agglomerates. Furthermore, since the viscosity of the saponification system can be kept low, it has the advantage that a highly concentrated slurry can be passed through the entire process. On top of that,
The resulting product is a heat-gelatinable particulate starch-polyvinyl alcohol graft copolymer that is insoluble at room temperature and has no disintegrated starch particles.It has good dispersibility in water at room temperature, and does not have the drawbacks of becoming "mamako" when used. It also has the advantage that when higher water solubility is required, starch can be reduced in molecular weight at the same time as saponification. The term "room-temperature insoluble heat-gelatinable particulate" as used herein refers to
The starch particles used as a raw material substantially remain, and the polymer component is bound to the inside and surface of the particles, and 3
Although the starch particles may swell slightly at a water temperature of 5°C or lower, they do not disintegrate, and the starch particles greatly swell, disintegrate, and dissolve only after heating. To obtain a starch-polyvinyl alcohol graft copolymer according to the production method, starch and vinyl ester are first graft copolymerized in water.

The starches used include natural starches such as potato starch, sweet potato starch, corn starch, waxy corn starch, high amylose corn starch, wheat starch, rice starch, tapioca starch, and sago starch, their decomposition products, amylose, and amylopectin fractions. , cross-linked starch, etherified starch, esterified starch, oxidized starch, acid-treated starch, and other starch-containing products, such as wheat flour, corn flour, dried sweet potato, and dried tapioca, and more water-soluble starch-polyvinyl alcohol. If a graft copolymer is desired, oxidized starch,
It is preferable to use low-molecular-weight starch such as acid-treated starch, dextrin, or enzyme-modified starch.

In addition, vinyl esters include vinyl acetate, vinyl formate, vinyl propionate, vinyl trifluoroacetate, t-
Examples include butyl vinyl ether, vinyl trimethylsilyl ether, etc. Vinyl acetate is preferred from the viewpoint of economy and availability. The graft polymerization can be carried out by a conventional method, for example, a redox system using persulfates and sulfites such as ceric salt, potassium persulfate or ammonium persulfate, Mohr's salt hydrogen monoperoxide, Mohr's salt hydrogen monoperoxide-ascorbic acid, etc. This can be carried out by using a graft initiator, or by using radiation or an electron beam.

If the grafting ratio (the percentage of the weight increase due to graft polymerization relative to the weight of starch used) is too low, the desired product with good physical properties cannot be expected, and if it is too high, a large amount of alkali will be required for saponification, which will increase the saponification time. Since the grafting efficiency may become longer or the grafting efficiency may decrease, it is set at 0.1 to 20%, preferably 0.5 to 10%. Then, the obtained starch-polyvinyl ester graft copolymer is saponified by dispersing it in water either directly in the aqueous solution where the graft polymerization has been completed, or after separating it from the graft polymerization system by, for example, centrifugal dehydration.

The saponification is carried out at a concentration of 20I) or less, preferably 1.5%, based on the total weight of the saponification system, in order to suppress the disintegration of starch particles.
Hereinafter, it is more preferably carried out in the presence of 1.0% or less alkali at a temperature of 60°C or less, preferably 55 to 30°C.

The reaction time can be selected as appropriate depending on the desired degree of saponification, and the degree of saponification can also be selected as appropriate depending on the intended use of the starch-polyvinyl alcohol graft copolymer.
It is preferable that the degree of saponification is 5 to 99 mol% in 1 to 48 hours. In addition, salts such as sodium sulfate, for example,
5-500 based on the total weight of the system! ) is also effective in suppressing the disintegration of starch particles. Examples of the alkali used include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonium hydroxide, and calcium hydroxide, with sodium hydroxide and potassium hydroxide being preferred.

When saponifying directly in the polymerization solution, for example, the concentration is 5%.
Adjust the alkali concentration to a predetermined level by dropping an aqueous alkali solution of about 100 ml. In addition, when dispersing the obtained copolymer in water and saponifying it, an alkali is dissolved in water in advance, and if desired, an aqueous alkali solution is added dropwise to adjust the concentration to a predetermined concentration. In either case, when the liquid volume increases significantly, the saponification system may be concentrated using a nozzle separator, centrifugation, filtering, Oliver filter, etc., thereby preventing a decrease in production efficiency. In addition, when dispersing the starch-polyvinyl ester graft copolymer in water and saponifying it, the graft copolymer is not limited to the one polymerized by the above method, but can be polymerized by other methods, such as an organic solvent. Polymerized materials can also be used. Furthermore, a vinyl ester used in graft polymerization may be further copolymerized with a vinyl monomer before or after graft polymerization. Furthermore, as mentioned above, if a more water-soluble target product is desired, low-molecular starch may be used as a raw material, but hypochlorite, hydrogen peroxide, etc. may be used simultaneously with or after graft copolymerization. Starch chains may be reduced in molecular weight by acid treatment with oxidizing agents such as oxidizing agents such as hydrochloric acid, sulfuric acid, nitric acid, and other mineral acids. It's okay. In particular, it is difficult to reduce the molecular weight using an oxidizing agent in the saponification process using the conventional method of saponification in methanol, but this becomes possible when saponification is performed in water as in the present invention. . The target starch-polyvinyl alcohol graft copolymer thus produced is separated from the saponification system, washed, and dried according to a conventional method.

The obtained graft copolymer usually contains unreacted starch, polyvinyl alcohol homopolymer, etc.
This may be used as is, or may be further purified by washing, if desired. In addition, in order to improve storage stability, the obtained graft copolymer was prepared using a known method.
For example, the treatment may be carried out by esterification using acetic anhydride, vinyl acetate, etc., etherification using ethylene oxide, propylene oxide, monochloroacetic acid, etc., or oxidation using hypochlorous acid, etc. The starch-polyvinyl alcohol graft copolymer obtained by the production method of the present invention suppresses the disintegration of starch particles, is extremely easily dispersed in water at room temperature, and can be dissolved by heating, making it suitable for various uses. Can be used.

For example, starch with relatively low molecular weight and more water-soluble forms a transparent gelatinized product, which can be used as sizing agents, coating agents, rewetting adhesives, various masking agents, various excipients, binders, paints, etc. suitable for use. In addition, starch with higher molecular weight is suitable for applications that involve gelatinization at high temperatures.
Back coating agents for textiles, adhesives, binders, heat sensitive,
It can be used in pressure-sensitive papers, thickeners, glue stabilizers, film-forming agents, etc. Next, the present invention will be explained in more detail with reference to Examples.

Example 1 711 water, 300 ml vinyl acetate, 209 ammonium ceric nitrate, and 0.1 ml nitric acid are added to 3k9 tapioca starch (calculated as anhydrous).

After stirring and reacting at 40° C. for 2 hours, the mixture was centrifugally dehydrated to obtain a starch-polyvinyl acetate graft copolymer with a water content of 45% and a graft ratio of 8.7 (:f).

This was dispersed in an aqueous solution of 400 g of sodium hypochlorite and 409 parts of sodium hydroxide in 10 parts of water (alkali concentration of the initial reaction mixture was approximately 0.3%), and stirred at 55°C for 5 hours to obtain a saponification degree of 48 mol. % starch-polyvinyl alcohol-polyvinyl acetate graft copolymer was obtained. 50℃
The viscosity of a 15% aqueous solution in O was 182 cps.
Example 2 Oxidized starch 3k9 (anhydrous equivalent) to water 711 vinyl acetate 15
0 ml of 49 mole salt and 10 ml of hydrogen peroxide were added, and polymerization was carried out at 30° C. for 2 hours.

Claims (1)

[Scope of Claims] 1. When producing a starch-polyvinyl alcohol graft copolymer, a particulate starch-polyvinyl ester graft copolymer that is insoluble at room temperature and heat-gelatinable is mixed in water based on the weight of the entire saponified system. A method for producing a room temperature-insoluble heat-gelatinable particulate starch-polyvinyl alcohol graft copolymer, which comprises saponifying the copolymer at a temperature of 60°C or lower in the presence of 2.0% by weight or less of alkali. 2. The method of item 1 above, wherein the alkali is sodium hydroxide or potassium hydroxide. 3. Said first method using vinyl acetate as the vinyl ester
The manufacturing method described in Section 1 or Section 2. 4. The method according to any one of Items 1 to 3 above, using a starch-polyvinyl ester graft copolymer having a graft ratio of 0.1 to 20%.