JPS62235348A - Polyvinyl alcohol-dimethyl sulfoxide solution having improved thermal stability - Google Patents

Abstract

PURPOSE:The titled solution, obtained by containing specific amounts of a polyvinyl alcohol based polymer and an acid having a specific acid dissociation constant, having improved thermal stability without causing deterioration in viscosity and coloring of the solution even under condition of allowing to stand at high temperatures and capable of solution molding into fibers, etc. CONSTITUTION:A polyvinyl alcohol-dimethyl sulfoxide solution prepared by containing <=50wt%, preferably <=30wt% polyvinyl alcohol based polymer having >=1,500, preferably >=2,000 polymerization degree, adding 1X10<-5>-1X10<-1>mol/l, preferably 1X10<-4>-1X10<-2>mol/l acid having <=2 acid dissociation constant, e.g. sulfuric acid, nitric acid, etc., and adjusting the hydrogen ion concentration to 4-10, preferably 5-9.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a polyvinyl alcohol-dimethyl sulfoxide solution that has excellent thermal stability, especially when it is left at high temperatures of 80°C or higher for a long time, the viscosity of the solution does not decrease. This invention relates to a polyvinyl alcohol-dimethyl sulfoxide solution that has excellent thermal stability and does not cause solution coloration.

[Prior Art] Conventionally, water, dimethyl sulfoxide, ethylene glycol, glycerin, N-methylpyrrolidone, diethylenetriamine, etc. are known as solvents for polyvinyl alcohol (hereinafter abbreviated as PVA). In industrial applications such as film production, water is generally used as a solvent in terms of price and ease of handling.

However, in recent years, highly crystalline PVA such as low-temperature polymerized P■A, PVA rich in syndiotactic structure,
The physical and mechanical properties of high polymerization degree PVA have started to attract attention, and when water is used as a solvent for molding PVA, it may not always be possible to completely dissolve it, or even if it is soluble, it may not be possible to dissolve it completely at 100°C. In addition to requiring the above-mentioned pressurized state, the obtained PVA solution also tends to gel when left at 100° C. or lower, making industrial handling difficult.

Dimethyl sulfoxide (hereinafter abbreviated as DMSO) is a good solvent for such highly crystalline PVA and highly polymerized PVA.
is known, and when DMSO is used as a solvent, it is possible to dissolve not only general PVA but also PVA copolymers, so it is an extremely useful solvent.

However, if a solution of a PVA-based polymer dissolved in DM SO is left at room temperature for a long time, the viscosity of the solution will decrease, and if it is left at a high temperature of 80°C or higher, not only will the viscosity of the solution drop rapidly, but the viscosity of the solution will drop. Currently, DMSO has not been used at all as a solvent for PVA-based polymers industrially due to the problem that it is colored yellow-brown.

Regarding the thermal stability of such a PVA-DMSO solution, there is a report by Naito et al. [Kobunshi Kagaku Vol. 16, No. 168, 2
1? (1959)], the carbonyl group present in the main chain of the PVA polymer is ionically cleaved by DMSO, which is an essentially basic solvent, in a reverse aldol reaction, thereby cleaving the PVA polymer chain. It is presumed that this cleavage of the main chain lowers the molecular weight of PVA and causes a decrease in viscosity, and that the solution is colored yellowish brown by the generated aldehyde.

DMSO OOH This is how rvt So far, there has been no study on how to prevent the decomposition of PVA-based polymers by SO, and the current situation is that DMSO's excellent solubility in PVA-based polymers cannot be effectively utilized. It is.

The inventors of the present invention have discovered the present invention as a result of extensive research into a PVA-DMSO solution with excellent thermal stability that does not cause thermal decomposition or coloring even at high temperatures.

[Problems to be Solved by the Invention] The purpose of the present invention is to provide DMSO which has excellent dissolving power not only for general PVA but also for highly crystalline PVA, high polymerization degree PVA, and PVA copolymers. The present invention solves the problem of thermal decomposition of PVA-based polymers as a solvent, and provides an NPVA-DMSO solution that has great industrial utility.

[Means for Solving the Problems] The above-mentioned object of the present invention is to achieve a polymerization degree of at least 1500.
This is achieved by a PVA-DM, SO solution containing 50% by weight or less of a PVA-based polymer and having excellent thermal stability in which the hydrogen ion concentration (pH) of the solution at 25°C is 4 or more and 1O or less.

Hereinafter, the present invention will be explained in more detail and specifically.

The PVA-based polymer used in the PVA-DMSO solution of the present invention is preferably a PVA-based polymer that is difficult to dissolve in an aqueous solvent. Polymers are good. If the degree of polymerization of the PVA-based polymer does not exceed 1500, the mechanical performance of the PVA molded product obtained from the PVA-DMSO solution will be poor, and it will not be suitable for general industrial use.

Furthermore, the PVA-based polymer of the present invention is not particularly limited as long as it is a PVA-based polymer that is soluble in DMSO, such as completely saponified PVA, partially saponified PVA, syndiotactic PVA, etc.
Examples include VA, low-temperature polymerized PVA, and PVA in which a small amount of olefinic monomers such as ethylene, propylene, and butylene are copolymerized in the main chain, but completely saponified PVA with a saponification degree of 99 mol% or more is preferable. good.

The polymer concentration of the PVA-based polymer of the present invention (DPVA-DMSO solution (7)) should be 50% by weight or less, preferably 30% by weight or less, and the polymer concentration should be 50% by weight or less, preferably 30% by weight or less.
If it exceeds 0% by weight, the solution viscosity becomes extremely high (several tens of blades voice), exhibits no fluidity even at high temperatures, and molding becomes difficult.

The most important point of the present invention is that the PVA-DMSO solution of the present invention has a hydrogen ion concentration (pH) of 4 or more l at 25°C.
0 or less, preferably 5 or more and 9 or less.

As is well known, DMSO is essentially a basic solvent, and its l) H at 25°C is usually 12 to 13 or more, indicating strong basicity. P of the present invention
The VA-DMSO solution is heated to 80°C by adjusting the pi of the solution within a specific range of 4 or more and 1O or less.
or more, preferably 100°C or more, more preferably 12
It has excellent thermal stability without causing thermal decomposition or thermal coloring of PVA even at high temperatures of 0° C. or higher. If the pH exceeds 1O, the thermal stability of the solution deteriorates, and if p)( is less than 4, it is strongly acidic, leading to equipment corrosion problems and the thermal stability of DMSO itself. This is not desirable because of the problem of rapid decomposition.

In order for the pH of the PVA-DMSO solution of the present invention to be 4 or more and 10 or less, the acid dissociation constant (p
1 acid with a Ka) of 2 or less, OX 10-5 mol/
1 or more and less than 1.0 x 10-1 mol/l, preferably 1.
OX 10-'mol/on support 1.0XlO-2mol/l
It is necessary to contain a range of amounts less than or equal to An acid with a pKa of more than 2 in water at 25°C is unlikely to cause dissociation in DMSO, and the pH of the PVA-DIVISO solution should be adjusted to 1.
Since it is necessary to contain an extremely large amount of acid to maintain the level below 0, it may cause problems with acid leakage during molding, and PVA
-The thermal stability of the DMSO solution is adversely affected, resulting in 1, which is not preferable.

Specifically, the acids having a pKa of 2 or less in water at 25°C contained in the PVA-DMSO solution of the present invention include inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, benzenesulfonic acid, toluenesulfonic acid, and phenolsulfonic acid. Acid, sulfosalicylic acid, sulfobenzoic acid, aniline sulfonic acid, methane or ethanesulfonic acid, lauryl sulfonic acid, cetyl sulfonic acid, styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, sulfopropyl acrylate, sulfopropyl methacrylate, 2-acrylamide-2 - Examples include organic acids such as methylpropanesulfonic acid, but sulfuric acid, nitric acid, benzenesulfonic acid, and toluenesulfonic acid are preferred.

The PVA-DMSO solution of the present invention contains the above-mentioned acids alone or in combination of two or more, and the total amount is 1.0 x 1.
0-5 mol/older brother or older 1. OX less than 10-1 mol/l,
Preferably 1.0X10-2 mol/t, oxto
It is necessary to contain an amount in the range of −→mol/K. Outside the above range, the solution pH will not be able to satisfy the range of 4 or more and 1O or less, which is a requirement for the PVA-DMSO solution of the present invention.

The PVA-DMSO solution of the present invention may contain a small amount of a solvent that is compatible with DMSO, such as water, ethylene glycol, or glycerin, in order to improve the viscosity of the solution.

Furthermore, the thermal stability of the PVA-DMSO solution of the present invention is further improved by adding a small amount of an antioxidant such as hydroquinone, a hindered phenol compound, or a hindered amine compound.

The method for producing the PVA-DMSO solution of the present invention described above includes dissolving PVA in DMSO and then adding an appropriate amount of acid, or adding acid in advance to DMSO, and then
Examples include methods such as dissolving PVA, but the method is not limited thereto.

[Effects of the Invention] The PVA-DMSO solution of the present invention solves the conventional problem of thermal decomposition of PVA-based polymers due to DMSO, and is a solution that has been used to solve problems other than general PVA, which have previously been impossible to dissolve in water. Its industrial utility value is extremely high, as it allows PVA-based polymers to be solution-molded into fibers, films, molded objects, etc.

Hereinafter, the present invention will be briefly described in detail based on Examples.

Example 1, Comparative Example 1 Using azobisisobutyronitrile as an initiator, at a temperature of 50
Bulk polymerization of vinyl acetate was carried out at °C, and the obtained polyvinyl acetate was completely saponified to obtain PVA with a degree of polymerization of 3500 (polymerization rate: 25%).

100g of the obtained PVA was added to DMS011 (1)-)/
l,1 ounce/l, fonic acid 0.34g (2,OXlo-
3mat/l) and 1 were dissolved by heating at a temperature of 80°C. The pH of the obtained PVA-DMSO solution at night was 6.
8, and the solution viscosity at 45°C was 450 voids.

As a comparison, a PVA-DMSO solution prepared without adding p-)luenesulfonic acid had a pH of 12.5, and a solution viscosity of 440 boids at 45°C.

After each solution was purged with nitrogen, it was left standing in a silicon bath at 120'C, and changes in solution viscosity over time were examined. The results are shown in Table 1.

From the results in Table 1, the PVA-DMS of the present invention (Example 1)
It is found that the O solution has extremely excellent thermal stability.

Table 1 Examples 2, 3, 4, Comparative Examples 2, 3 PVA with different solution pH by changing the content of sulfuric acid (pKao, 4) in DMSO (degree of polymerization 3500, polymer concentration 10 pffi%) - A DM SO solution was made. Each solution was left standing in a silicone bath at 120'C, and changes in viscosity after 24 hours were examined. The results are shown in Table 2.

From the results in Table 2, it can be seen that solutions whose pH was within the range of the present invention (Examples 2 and 3.4) had excellent thermal stability.

(Hereinafter, blank space) Table 2 (Unit: voice) Example 5 Using various acids with different pK a, add amount of acid and PV
A (degree of polymerization 3500, polymer concentration 10%) -D
I)H of MSO solution was investigated. The results are shown in Table 3. According to the results in Table 3, acids with pKa of 2 or less are DMS.
It can be seen that the pH of the O solution can be made 9 or less by adding a small amount.

(Hereinafter, blank space) Table 3 Example 6, Comparative Example 4 Using dimethylphosphinate pivalate as an initiator, -
Bulk ultraviolet polymerization of vinyl acetate was carried out at 30°C, and the obtained polyvinyl acetate was completely saponified with sodium methylate to obtain PVA with a degree of polymerization of 8700 (polymerization rate: 15
%).

50 g of the obtained PVA was dissolved in DMS O11 together with 0.29 g of sulfuric acid (3,OX 10-3 mol/l) at 80°C. The pH of the obtained DMSO solution was 6.3, and the solution viscosity at 45°C was 260 voids (Example 6). This solution was allowed to stand in a silicone bath at 130° C. under nitrogen for 24 hours, but no coloration occurred and the viscosity was extremely stable at 245 voices.

For comparison, a DMSO solution obtained without adding any sulfuric acid had a pH of 12.7 at night, and after being left at 130°C for 24 hours, the viscosity decreased to 50 boids and the solution was colored reddish brown (comparison). Example 4).

Claims (4)

[Claims] (1) Polyvinyl alcohol-dimethyl sulfoxide with excellent thermal stability, containing 50% by weight or less of a polyvinyl alcohol polymer with a degree of polymerization of at least 1500, and having a hydrogen ion concentration (pH) of 4 or more and 10 or less at 25°C. solution. (2) Acid dissociation constant (pKa) in water at 25°C is 2
Add the following acids to 1.0×10^-^5 mol/l or more 1.0×
A polyvinyl alcohol-dimethyl sulfoxide solution having excellent thermal stability as claimed in claim (1), containing an amount in a range of less than 10^-^1 mol/l. (3) The degree of polymerization of polyvinyl alcohol polymer is 20
00 or more, a polyvinyl alcohol-dimethyl sulfoxide solution having excellent thermal stability according to claims (1) and (2). (4) A polyvinyl alcohol-dimethyl sulfoxide solution with excellent thermal stability as set forth in claims (1) and (2), which has a polymer degree of 30% by weight or less.