JPS6210242B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a low viscosity starch-polyvinyl alcohol graft copolymer which allows the preparation of a thick paste with high concentration and low viscosity.

Starch-polyvinyl alcohol graft copolymers have been recognized as useful in a variety of industrial fields, such as adhesives, sizing agents for fibers and paper, coating agents, and molding materials for various water-soluble films, and are currently being used in practical applications. is being considered. However, starch-polyvinyl alcohol graft copolymers usually have the disadvantage of poor workability because they form a paste with a high viscosity at low concentrations.

As a result of various studies to solve the above-mentioned difficulties, the present inventors have developed a low-viscosity starch-polyvinyl alcohol graft copolymer that can be used to prepare a starch-polyvinyl alcohol graft copolymer with high concentration and low viscosity through simple operations and economically. The present invention has been completed by discovering a method for producing .

In other words, the present invention involves treating polyvinyl alcohol graft-modified starch (hereinafter simply referred to as graft-modified starch), which is obtained by grafting polyvinyl alcohol onto various types of starch, with acid, enzymes, or roasting to moderately hydrolyze the graft-modified starch. The present invention provides a method for producing a low-viscosity starch-polyvinyl alcohol graft copolymer, which is characterized by lowering the viscosity by lowering the molecular weight.

Naturally produced starches used in the present invention include potato starch, sweet potato starch, corn starch, waxy corn starch, high amylose corn starch, wheat starch, rice starch, tapioca starch, sago starch, and their decomposition products, as well as amylose and amylopectin components. Examples of starch-containing starches include modified starches such as starch, cross-linked starch, etherified starch, esterified starch, oxidized starch, and acid-treated starch, as well as starch-containing products such as wheat flour, corn flour, dried sweet potato, and dried tapioca.

Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl trifluoroacetate, t-butyl vinyl ether, vinyl trimethylsilyl ether, and vinyl acetate is preferred from the viewpoint of economy and easy availability.

Graft-modified starch produced by any method can be used, but for example, various conventional methods of grafting vinyl acetate or other vinyl esters onto starch, such as ceric salt, potassium persulfate, etc. Graft polymerization can be carried out by using redox systems with persulfates and sulfites such as ammonium persulfate, graft initiators such as Mohr's salt-hydrogen peroxide, Mohr's salt-hydrogen peroxide-ascorbic acid, or by radiation, ultraviolet rays, electron beams, etc. death,
It can be produced by saponifying this with alkali, acid, etc. By controlling the saponification conditions, complete saponification and partial saponification can be performed, and both can be used as the graft-modified starch in the present invention.

Treatment with acids or enzymes or roasting can be carried out in the form of powder, water suspension, heated gelatinization solution, or gelatinization process of the graft-modified starch, depending on the purpose or given conditions. It is something that can be determined.

When treating graft-modified starch with acid, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, etc. are suitable. When treating the graft-modified starch as an aqueous suspension, the graft-modified starch is treated with acid at an acid concentration of about 0.5 to 1N. The product is immersed and stirred in a dilute aqueous solution at a temperature below the gelatinization temperature, then neutralized with an alkali, washed with water, and dried.

Graft modified starch with enzyme (liquefied amylase)
When processing as an aqueous suspension,
Generally, graft-modified starch is treated at a temperature (usually 45 to 60°C) and pH (usually 6 to 8) that does not gelatinize,
In addition, when processing as a heat gelatinization liquid, it is generally processed at a temperature of about 70 to 90℃ and a pH of about 6 to 8, and when further processed during the gelatinization process, it is processed at a heat and gelatinization temperature of about PH6 to 8. That is appropriate. When processing as an aqueous suspension, add acid after the reaction is complete.
Adjust the pH to 3, wash with water, and dry.

When roasting graft-modified starch, suitable acids to use include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, etc., which are added to the graft-modified starch as a dilute solution of water or methanol and heated at 100 to 200°C. To roast.

Conventionally, unprocessed starch used for paper coating, sizing, etc. has often been modified to form a liquid with high concentration and low viscosity, and the means for this modification is usually oxidation, acid, or amylase treatment. It is being done. However, no attempt has yet been made to modify graft-modified starch in order to obtain a thick paste with high concentration and low viscosity.

According to the present invention, the low viscosity of the graft-modified starch;
It becomes possible to adjust high-concentration size liquid, and the rheological properties of the size liquid are also improved.

Next, the present invention will be explained with reference to Examples.

Example 1 2.5 kg of tapioca, 5 water, 2.5 g of Mohr's salt, and 13 ml of 1N sulfuric acid were mixed, and after stirring for 10 minutes, 280 ml of vinyl acetate and 10 ml of hydrogen peroxide were added, and the mixture was heated at 40°C.
After stirring and reacting for a period of time, centrifugal dehydration is performed to reduce the water content.
A graft-modified starch with a graft ratio of 45% and a graft ratio of 6.7% was obtained. This was dispersed in a methanol solution containing 15 g of sodium hydroxide and stirred at room temperature for 6 hours to completely saponify it. The viscosity of a 15% aqueous solution at 50℃ is
It was 50000cps. This graft modified starch is 20
Water and hydrochloric acid are added to give a hydrochloric acid solution with a concentration of 0.8N in weight% water suspension solution, and the mixture is reacted at 50°C for 1 hour. After the reaction is completed, the mixture is neutralized with a 3% by weight sodium hydroxide solution, dehydrated by centrifugation, dried with hot air at a temperature of 40°C, crushed, and sieved. The viscosity of the 15% aqueous solution at 50°C was 900 cps.

Example 2 15% by weight of the graft modified starch used in Example 1
Add water to the concentration of an aqueous suspension solution, and add liquefied amylase (potency 10,000 units/g) to starch.
Add 0.02% by weight and raise the temperature to 85% while stirring for 10 minutes.
℃ and heat at 85℃ or higher for 10 minutes to gelatinize and reduce viscosity. After replenishing the evaporated water and lowering the temperature to 50°C, the viscosity was measured and found to be 67 cps.

Example 3 Graft-modified starch produced in the same manner as in Example 1 (viscosity of 15% aqueous solution at 50°C is 5800 cps)
Add 1 ml of 0.7 wt% hydrochloric acid methanol solution to 50 g (weight on anhydrous basis) and roast at 150°C for 20 minutes while dehydrating in an evaporator. 15% at 50℃
The viscosity of the aqueous solution was 300 cps.

Example 4 30% by weight of the graft modified starch used in Example 3
Add water to obtain an aqueous suspension solution concentration. After addition, 0.5% by weight of liquefied amylase (potency 10,000 units/g) is added to the starch, the pH is adjusted to 6.1 with calcium hydroxide solution, and the mixture is reacted at 55°C for 6 hours. After the reaction is complete, adjust the pH to 3 with 2N hydrochloric acid. After pH adjustment, it is washed with water, centrifugally dehydrated, dried with hot air at a temperature of 40℃, crushed, and sieved. The viscosity of the 15% aqueous solution at 50°C was 1820 cps.

Claims (1)

[Claims] 1. A low-viscosity starch-polyvinyl alcohol graft copolymer, which is obtained by treating polyvinyl alcohol graft-modified starch, which is obtained by grafting polyvinyl alcohol onto various types of starch, with acid, enzymes, or roasting to reduce the viscosity. manufacturing method.