JPS6044037B2 - Method for recovering modified polyvinyl alcohol from aqueous solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating and recovering modified polyvinyl alcohol from an aqueous solution in which the resin is dissolved.

Recently, various polyvinyl alcohols have been widely used as sizing agents for fibers, and these polyvinyl alcohol sizing agents are inevitably dissolved in wastewater after scouring.

Therefore, if polyvinyl alcohol glue can be recovered from such wastewater, the cost of glue can be reduced and the C of wastewater can be reduced.
The two problems of reducing OD can be solved at once. Conventional techniques for removing polyvinyl alcohol from desizing wastewater by sumo wrestlers include salting-out method, coagulation-sedimentation method using polyvalent metal salts,
Although bubble separation methods, oxidative decomposition methods, adsorption methods, insolubilization methods by formalization, and microbiological treatment methods have been proposed, their removal rates are generally low, and polyvinyl alcohol is either decomposed or recovered. However, there are problems such as additives being mixed in and making it impossible to reuse as a sizing agent, and in some cases, secondary pollution may occur due to the additives used in the treatment.

The present inventors have been researching the use of low saponification degree polyvinyl alcohol as a warp sizing agent for some time, and as a result, we have found that a copolymer of unsaturated sulfonic acid or its salt and vinyl acetate, especially unsaturated sulfonic acid or its salt content is 0.0
Modified polyvinyl alcohol obtained by alkali saponification of 2 to 2 mol% of a copolymer can be used to combine materials made of 100% hydrophobic fibers such as polyester long fiber yarn or hydrophilic fibers such as polyester and cotton, viscose rayon, and linen. Although it has been discovered that the sizing agent exhibits excellent sizing properties for blended yarns, the effective treatment method for desizing wastewater and washing wastewater in which this specific modified polyvinyl alcohol is dissolved has not yet been completely solved. I hadn't done it.

However, as a result of continued research by the present inventors,
1 acid is added to the wastewater in which the specific modified polyvinyl alcohol is dissolved.

2. Keep the temperature of wastewater above 40°C.

It has been found that when these two operations are performed in any order, the polymer immediately precipitates from the wastewater, making it possible to separate and recover it.

Moreover, when such a method is used, the separation efficiency of the aggregated polymer is high; only a small amount of modified polyvinyl alcohol remains in the wastewater; the separated aggregate does not contain any impurities; If it is converted to the original salt-type modified polyvinyl alcohol, it can be reused as a textile glue, which can solve the problems of the past at once.

As the unsaturated sulfonic acid or salt thereof in the copolymer of unsaturated sulfonic acid or its salt and vinyl acetate in the present invention, ethylene sulfonic acid, allylsulfonic acid, metaallylsulfonic acid, or salts thereof are used.

The content of the unsaturated sulfonic acid or its salt in the copolymer is not particularly limited, but a range of 0.02 to 2 mol%, particularly 0.05 to 1 mol%, is suitable for textile glues. If the content is less than 0.02 mol%, the polymer will precipitate under the temperature conditions during gluing, and desizing wastewater,
It becomes difficult to separate and recover the polymer from washing wastewater, and on the other hand, if the content exceeds 2 mol%, the hygroscopicity and stickiness become excessive, resulting in poor glue performance, and wastewater treatment and recovery become difficult. This results in various disadvantages in the process.

The above-mentioned copolymer of unsaturated sulfonic acid or its salt and vinyl acetate is prepared in the presence of an alkali catalyst such as caustic soda, caustic potash, or an alkali metal alkoxide, preferably in methanol,
Saponified in an alcoholic medium such as ethanol.

Saponification methods include kneader saponification and tower saponification, continuous or batch static saponification that does not involve kneading, and dispersion of the copolymer alcohol solution in the form of fine droplets in a non-solvent such as liquid paraffin. A granular saponification method that advances the saponification reaction while Saponification should be carried out until the degree of saponification of the vinyl acetate component in the copolymer is 50 mol% or more and less than 83 mol%, and the degree of saponification should be 50 mol%.
If it is less than 8, the desizing property will be poor when used as a sizing agent;
When the amount is 3 mol% or more, the adhesion to hydrophobic fibers is poor, and it becomes difficult to separate and recover the polymer from desizing wastewater and washing wastewater.

In addition, within the saponification degree range above, 60 mol% or more and 80 mol%
The range below is particularly preferable from the viewpoint of sizing agent performance and wastewater treatment properties. Now, in order to separate the above specific modified polyvinyl alcohol from the wastewater in which the polymer is dissolved, an acid is added to the wastewater.

2. Maintain the temperature of the wastewater at 40°C or higher, preferably at 50°C or higher.

It is necessary to perform both of these two operations.

Although the order of both operations does not matter, it is practical to heat the wastewater in which the modified polyvinyl alcohol has been dissolved to 40° C. or higher, and then add the acid while stirring the mixture. If only one of the operations 1 and 2 is performed, the polymer will not be precipitated, or even if it is precipitated, it will be extremely insufficient, and the purpose of wastewater treatment cannot be achieved.

The acids used in the above operation 1 include various inorganic or organic acids including hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, pyrophosphoric acid, phosphorous acid, acetic acid, oxalic acid, and citric acid.

Among these, hydrochloric acid, sulfuric acid, and acetic acid are preferred. It is desirable that the amount of acid used is approximately equivalent to or more than the amount of the unsaturated sulfonate component in the modified polyvinyl alcohol in the wastewater. use. When an acid is added to wastewater, the pH of the system is often about 7 or less, usually about 6 to 2. Regarding the temperature conditions in the above-mentioned operation 2, it is necessary that the temperature of the waste water is at least 40°C or higher, and 50°C or higher is particularly preferable.

Any method can be used to increase the temperature, such as heating the wastewater externally while placing it in a container or flowing it through a flow path, blowing steam into the wastewater, introducing heated water or a heating element, or using solar heat. Can be adopted. By the operations 1 and 2 above, modified polyvinyl alcohol is immediately precipitated in the form of flocs from the wastewater.

The precipitated polymer can be easily separated from the mother liquor by known means such as filtration, centrifugation, decantation, and skimming with a screen. In particular, when wastewater is stirred under appropriate conditions, polymer flocs aggregate and float to the surface of the wastewater, so by scraping them up with a scraper,
Separation and recovery can be easily achieved. The separation efficiency is generally good, and usually about 70-90% of the modified polyvinyl alcohol in wastewater can be easily removed. Although the separated agglomerates are still hydrated, drying them is often not necessary.

This is because if an alkaline substance such as caustic soda, caustic potash, soda carbonate, or aqueous ammonia is added to this water-containing material, the initially used aqueous solution of salt-type modified polyvinyl alcohol can be regenerated as it is. This aqueous solution can be used again for the same purpose by adjusting its concentration. Such recycling is extremely advantageous industrially, and it becomes possible to reduce costs by treating wastewater and using recovered polymers. This is something that conventional polyvinyl alcohol-containing wastewater treatment technology has not been able to predict. Fiber scouring wastewater contains sizing materials other than modified polyvinyl alcohol (such as starch, various oils, auxiliaries, antifoaming agents, etc.), and wastewater containing these coexisting can also be treated by the method of the present invention. Only modified polyvinyl alcohol can be efficiently recovered.

The above has been explained using as an example the recovery of polymers contained in wastewater when modified polyvinyl alcohol is used as a fiber sizing agent, but modified polyvinyl alcohol is not limited to use as a textile sizing agent, and can be used for films, fibers, etc. It is also used in applications such as adhesives, coatings, binders, laundry starches, cosmetics, and temporary protective films.

Regardless of the purpose used, the method of the present invention can be applied to separating and recovering specific modified polyvinyl alcohol from an aqueous solution containing the modified polyvinyl alcohol. Next, the method of the present invention will be further explained with reference to Examples. The term 1% hereinafter refers to % by weight unless otherwise specified. Example 1 Modified polyvinyl with a saponification degree of 69 mol% of the vinyl acetate component obtained by saponifying a sodium allylsulfonate-vinyl acetate copolymer with a sodium allylsulfonate content of 0.3 mol% in methanol in the presence of a caustic soda catalyst. Using alcohol, we repeated the steps of precipitation, recovery, neutralization, and redissolution in the laboratory.

In this case, as the acid addition condition described above in 1, hydrochloric acid was used in an amount equivalent to 10 times that of the sodium allylsulfonate component, and as the heating condition 2, the temperature was raised to 60°C, and both of these operations were performed. When the mixture was stirred at 600 r'Pm with a propeller-type stirrer to promote foaming with vortex stirring, the precipitated polymer floated to the surface of the liquid soil in a cream-like form, so it was easy to simply scoop it out without letting it stay overnight. It was possible to separate it very easily.

In this case, no polymer was precipitated at all when only one of operations 1 and 2 was performed, and precipitation occurred only when both operations were performed consecutively.

In this example, after heating in step 2, hydrochloric acid was added in step 1.

The polymer concentration in the collected material was 12 to 16% due to operational variations, but it was neutralized with caustic soda so that the pH was 7 using BTB as an indicator.

The amount of caustic soda required for neutralization is 1.5 times the amount of allylsulfonic acid.
The amount was 7 to 2.1 times equivalent, but this was due to the difference in the amount of hydrochloric acid mixed. When the viscosity and degree of saponification of the recovered polymers were measured, the results shown in Table 1 were obtained.

In the table, there are slight changes in the recovery rate and the viscosity of the recovered polymer up to the second recovery, but after the third recovery, both become stable.

Example 2 The following composition liquid 3000f was made using the same sodium allylsulfonate modified polyvinyl alcohol as in Example 1, heated to a temperature of 60°C, and then stirred at 450 rpm with a propeller type stirrer.
4.8 k9 of hydrochloric acid with a concentration of 5% was added to the flask while stirring in a vortex for 100 m, and at the same time creating aeration from an air supply vibrator attached to the bottom of the can.

As a result of this operation, the polymer instantly precipitated and agglomerated.

When stirring and aeration were stopped, the precipitated polymer floated to the top of the liquid, forming a white muddy layer. This was scooped out to obtain paste 78.3k9 with a solid content of 13.8%. The recovery rate will be 72%. To this was added 5% caustic soda 1k9 to adjust the pH to 7 while testing with a BTB indicator to regenerate salt-type modified polyvinyl alcohol.
3 combinations of polymer before recycling, recycled polymer, and commonly used partially saponified polyvinyl alcohol starch
Sizing and weaving tests were conducted to determine the glue composition of seeds.

Sizing Solution Composition New Size Solution Recovered Size Solution Control Example Sizing and Weaving Using the above size solution, sizing was carried out on polyester/cotton = 65135 blended yarn 45S/1 using a Sankyo type sizing machine.

The size tank temperature and size adhesion rate are both 7 for new size liquid and recovered size liquid.
It was 10.0-10.5% at 0°C, and 11-12% at 90°C in the case of the control example.

Next, weaving was performed using this sized yarn under the following conditions.

Target fabric Poplin Total number of warps: 483 pots, 115/inch Weft thread count: 45S/1, 65/inch Loom Automatic loom, 150-160r'Pm Loom room conditions 25
~30℃, 70~80%RH test 60 yards x 2
The results of weaving 5 rolls x 2 machines = 3000 yards are shown in Table 2.

Example 3 An allyl sulfonate-vinyl acetate copolymer having a sodium allyl sulfonate content of 0.6 mol % was saponified in methanol in the presence of a caustic soda catalyst. The degree of saponification of the vinyl acetate component was 70.5 mol %. When desizing wastewater 3000e containing 0.40% modified polyvinyl alcohol was heated to a temperature of 60°C and 2.8k9 of 10% hydrochloric acid was added and stirred, the wastewater instantly became cloudy and the precipitated polymers mutually interacted with each other. They started to stick together and form a white slurry.

A white slurry with a solid content of 30% was separated by filtration, washed with water, a part of it was dried and weighed, and the solid content was calculated, and it was found that 83% of the low saponification substances in the wastewater had been removed. I found out. Next, the solid content of the white slurry is 9.0k9.
When 800 V of a 5% aqueous solution of caustic soda was added to the solution and stirred, the original aqueous solution of polyvinyl alcohol modified with sodium allylsulfonate was regenerated.

This aqueous solution showed almost the same properties and performance as the originally prepared glue solution, and it was found that the recovered polymer could be reused.

The performance of the sizing agent when the initially prepared sizing liquid and the recovered low saponification product aqueous solution were used as a sizing liquid is shown below.

As a control example, the results for a typical polyvinyl alcohol-acrylic combined sizing agent for polyester processed yarns are also shown.

Sizing Solution Composition New Size Solution Recovered Size Solution Control Example Sizing and Weaving Using the above size solution, 75 denier/36 filament processed polyester yarn was sized using a warping sizing machine.

The glue bath temperature was 50° C., and the amount of glue was 9.5 to 10.0%. Next, weaving was performed using this sized yarn under the following conditions.

Target fabric: 5 pieces of satin (suede) Total number of warps: 691 Pot weft and number of stitches: 75 denier/36 filaments
Polyester processed yarn, 125 threads/inch loom Automatic loom 155-160r'. P. m. Loom room conditions 25
℃, 75%RH Test amount 56m, x 40 x 2 units = 44
80rn, the adhesive strength is determined by forming the adhesive film in the same way as in the case of adhesive strength, then putting the adhesive films together, 20°C, 75% RH.
A load of 1rrL/Clt was applied below, and after 24B1, the peel strength was measured using a tensile strength tester.

Examples 4 to 8 Wastewater was treated in the same manner as in Example 3, except that wastewater containing modified polyvinyl alcohol having the following composition was used.

The conditions and results are shown in the table below. Example 4 Metaallylsulfonic acid sodium vinyl acetate copolymer with a sodium metaallylsulfonic acid content of 0.3 mol% was
Saponification degree of vinyl acetate component obtained by saponification in alcohol in the presence of a caustic soda catalyst: 70 mol%
of modified polyvinyl alcohol.

Example 5 Sodium metaallylsulfonate content 0.5
Modified polyvinyl alcohol with a saponification degree of 65 mol% of the vinyl acetate component obtained by saponifying mol% of metaallylsulfonic acid-soda-vinyl acetate copolymer in methanol in the presence of a caustic soda catalyst.

Example 6 Sodium ethylene sulfonate content 0.8 mol%
The degree of saponification of the vinyl acetate component obtained by saponifying the sodium ethylene sulfonate monovinyl acetate copolymer in methanol in the presence of a caustic sorter catalyst is 6.
3 mol% modified polyvinyl alcohol.

Example 7 Ethylene sulfonic acid content 0.5 mol%
The saponification degree of vinyl acetate component obtained by saponifying ethylene sulfonic acid monovinyl acetate copolymer in methanol in the presence of a caustic soda catalyst was changed to 71 mol%.
polyvinyl alcohol.

Claims (1)

[Scope of Claims] 1. An aqueous solution in which modified polyvinyl alcohol having a saponification degree of 50 mol% or more and less than 83 mol% of a vinyl acetate component obtained by alkali saponification of an unsaturated sulfonic acid or its copolymer with vinyl acetate is dissolved. A method for recovering modified polyvinyl alcohol from an aqueous solution, which comprises adding an acid to the aqueous solution and maintaining the temperature of the aqueous solution at 40° C. or higher to precipitate the modified polyvinyl alcohol, and then separating the precipitate. 2. The method according to claim 1, wherein the degree of saponification of the vinyl acetate component is 60 mol% or more and less than 80 mol%. 3 Content of unsaturated sulfonic acid or its salt is 0.02 to 2
The method according to claim 1, characterized in that modified polyvinyl alcohol obtained by alkali saponification of a copolymer of mol% of unsaturated sulfonic acid or its salt and vinyl acetate is used. 4. The method according to claim 1, characterized in that the temperature of the aqueous solution is maintained at 50° C. or higher.