JPH0598023A - Nonporous particle of polyvinyl alcohol, and preparation thereof - Google Patents

Abstract

PURPOSE: To obtain non-crosslinked and non-porous PVA by dropping a soln. of PVA is dimehylsulfoxide into a specific liquid.

CONSTITUTION: PVA with a mol.wt. of 80,000-115,000 is an amount of 1-20 wt.% is dissolved in a solvent consisting of 60-100 wt.% of dimethylsulfoxide and 40-0 wt.% of water or 1-8C liquid aliphatic alcohol to obtain a soln. which is, in turn, dropped into a liquid which is compatible with sulfoxide and non- solvent to PVA at 25°C or lower through a sprayer or a spray nozzle.

COPYRIGHT: (C)1993,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to particulate polyvinyl alcohol. More particularly, the present invention relates to non-crosslinked, substantially non-porous polyvinyl alcohol and processes for making it without freezing using a unique method.

[0002]

PRIOR ART AND PROBLEM TO BE SOLVED BY THE INVENTION Diameter 1
Particulate polyvinyl alcohol hydrogels below 0 mm have been reported in patents and other literature. This polymer is
In order to strengthen the finally obtained particles, they are sometimes cross-linked during the formation of the particles.

Known methods for preparing solid particulate polymers with a diameter of less than 1 mm generally include polymerizing the corresponding monomers by emulsion or suspension, or by solubilizing the polymer in the presence of a polymer nonsolvent. It may precipitate.

Polyvinyl alcohol cannot be obtained by directly polymerizing the corresponding vinyl alcohol monomer because of its unstable nature. Therefore, a suspension of vinyl carboxylate, such as vinyl acetate, is polymerized and the resulting polymer is at least partially hydrolyzed.

Crosslinking has been used to improve the strength and other desirable properties of small diameter particles or beads formed from PVA (polyvinyl alcohol),
Crosslinked PVA hydrogels, unlike non-crosslinked polymers, are not soluble in hot water. For some end uses, especially with controlled release and packing for chromatographic columns, it is desirable for the non-crosslinked PVA particles to dissolve in hot water to facilitate disposal of the particles after use.

We have found that the non-porous, substantially spherical particles or beads of polyvinyl alcohol have many of the physical properties of prior art crosslinked particles and do not sacrifice their solubility in hot water. However, a solution of polyvinyl alcohol in dimethyl sulfoxide, in the form of drops or droplets, is added to a relatively large volume of a liquid such as methanol that is compatible with dimethyl sulfoxide but is a nonsolvent for polymers. It was discovered that it can be prepared by adding.

The size and shape of the particles depends, at least in part, on the viscosity of the polymer solution, the size and shape of the solubilized polymer droplets or droplets, and the rate at which these droplets or droplets impact the surface of the non-solvent. It depends on The non-solvent is preferably kept below 25 ° C.

The non-porous nature of the particles of the present invention renders them optically transparent.

The method of the present invention avoids freezing of the liquid phase both before and during the particle formation process. Freezing adversely affects both the physical structure and properties of the final gel particles. This process changes the morphology of the gel particles because the freezing process divides the initially homogeneous polymer solution into a water-rich phase and a polymer-rich phase.

[0010]

The present invention provides non-porous particles of non-crosslinkable polyvinyl alcohol. The particles are prepared in the following steps:

(1) Polyvinyl alcohol and 60 to 10
0 wt% dimethyl sulfoxide and 0-40 wt%
Forming a solution containing water or a solvent consisting of liquid aliphatic alcohol having 1 to 8 carbon atoms;

(2) Adding the solution in the form of discrete drops or droplets to a liquid that is compatible with dimethyl sulfoxide and is a non-solvent for polyvinyl alcohol. However,
The concentration of polyvinyl alcohol in the solution is 1 to 20% by weight, and the temperature of the liquid is 25 ° C or lower.

The particles of the invention are preferably spherical in contour. The shape of the final particles depends on the shape of the solubilized polymer droplet as it comes into contact with the liquid used to insolubilize the polymer, the ability of the droplet to retain its shape in a liquid medium before solidification and the polymer solution. Is a function of the viscosity of.

The diameter of the particles prepared according to the method of the invention ranges from less than 1 μm to 1 mm or more, depending on the processing conditions and the viscosity of the polymer solution. The particular size range selected will depend on the end use of the particles.

Polyvinyl alcohol is generally prepared by hydrolysis or saponification of an ester of a polymerized alcohol, such as vinyl acetate. The degree of hydrolysis of the resulting polymer depends on the end use of the polymer.
The vinyl alcohol polymers of the present invention are preferably at least 90% hydrolyzed.

It is believed that the degree of branching and the 1,2-glycol linkages within the polymer are of secondary importance with respect to the processability of the solutions in the present invention and their effect on the physical properties of the final particles obtained. The linear shape of the polymer molecule is preferable for maximizing the degree of hydrogen bonding.

The molecular weight of polyvinyl alcohol affects the viscosity of the solution prepared by dissolving the polymer in dimethyl sulfoxide and the nature of the particles formed by coagulating the polymer according to the method of the present invention. Within these limits, any of the commercially available grades of polyvinyl alcohol can be used to prepare the particles according to the method of the present invention. These polymers are high (about 86,000 or more), medium (40,0) depending on their molecular weight.
00-52,000), and low (14,000). A molecular weight range of 80,000 to 115,000 is preferred to achieve the optimum combination of desirable physical properties of the particles.

The polyvinyl alcohol in the particles of the present invention does not crosslink using a reactant forming a covalent bond. It is believed that the hydrogen bonds between the hydroxyl groups on adjacent polymer molecules and the controlled crystallization of the polymer cause the particles of the present invention to develop a desirable combination of physical properties.

The optimum concentration of polyvinyl alcohol in the solution used to prepare the particles of this invention depends on the molecular weight of the polymer and the equipment used to prepare the final particles. To prepare these particles, about 1 to
Concentrations of about 20% by weight are useful, with concentrations of 2 to about 5% being preferred.

According to the invention, 1 to about 20 in dimethyl sulfoxide or a mixture of dimethyl sulfoxide and up to about 40% by weight of water and / or at least one alcohol having 1 to 4 carbon atoms. A solution containing wt.% Polyvinyl alcohol is prepared and added in finely divided form to the non-solvent for the polymer compatible with dimethyl sulfoxide.

Dimethyl sulfoxide dissolves polyvinyl alcohol and when this solution is added to the cooled non-aqueous, non-solvent for the polymer in the form of drops or droplets,
It is unique in its ability to form the small, non-porous, essentially spherical particles or beads of the present invention.

Water and alcohol are non-solvents for polyvinyl alcohol below room temperature, but the inventors have found that when these liquids are combined with dimethyl sulfoxide, the crystal structure of polyvinyl alcohol prepared by the method of the invention. And to improve the physical properties.

It has been found that the presence of more than about 40% by weight of water or alcohol, based on total solvent, in the original polyvinyl alcohol solution increases the porosity of the final particles and adversely affects the particles.

The temperature of the solution of solubilized polyvinyl alcohol that is added to the cooled non-solvent to form the particles of the invention can be from ambient temperature to the boiling point of the solvent.

The optimum temperature range for preparing particles in a given diameter range is a function of several variables. The variables include, but are not necessarily limited to, the viscosity of the polyvinyl alcohol solution and the type of equipment used to prepare the particles.

The viscosity of the polymer solution is, in turn, a function of the molecular weight of the polymer and the concentration of polymer in solution. Solution temperatures within the range of ambient temperature up to about 80 ° C. are preferred for preparing particles with an average diameter of less than 1 mm.

If water or a water-alcohol mixture as the solvent for the polyvinyl alcohol replaces all of the dimethylsulfoxide, then when the polymer solution according to the invention is sprayed into a chilled solvent, it will give rise to more than discrete particles. A solidified and agglomerated polymer is formed.

According to the second step of the method of the invention, the solubilized polyvinyl alcohol is made into drops or droplets by passing it through at least one suitable orifice.
The diameter of the formed drop or droplet is determined by the diameter and shape of the orifice used to form the drop or droplet and the pressure used to push the polymer solution through the orifice.

According to a preferred drop formation method, the solubilized polyvinyl alcohol is extruded through a at least one atomizer or spray nozzle for forming a fine mist toward a cooled, non-solvent vessel. The solution is extruded through a nozzle, generally under pressure, into a mist of finely divided droplets. The maximum pressure that can be used in this droplet formation method is a function of atomizer design. The resulting solid particles are generally less than 1 mm in diameter, preferably 1
It is less than 0 μm.

When particles larger than about 0.5 mm are desired, it is achieved by adding the solubilized polymer drop-wise to the non-solvent using a burette or similar flow control device capable of dispensing liquid drop-wise. , Can be prepared.

Depending on the concentration of the polyvinyl alcohol solution and the desired diameter of the final gel particles, the average diameter of the solubilized polyvinyl alcohol drops or droplets can be less than 1 mm to a few mm.

The ability of a drop or droplet to retain its original spherical shape prior to solidification to form the particles of the present invention depends, at least in part, on the viscosity of the polyvinyl alcohol solution, the surface on which the drop or droplet is nonsolvent. Their velocity before hitting and the distance traveled by the drop or droplet before reaching the surface of the non-solvent.

The solubilized polyvinyl alcohol droplets or droplets solidify on contact with the cooled non-solvent of the polymer. The only requirement for the non-solvent is that it is compatible with polyvinyl alcohol and that it is a liquid at the temperature used to solidify it. 25 for the preparation of non-porous particles
Temperatures below ℃ are required. Temperatures of 0 to -25 ° C are preferred.

As the non-solvent which can be used, there are 1 to 1 carbon atoms.
Non-limiting examples are alcohols of about 8, ketones having 2 to 10 carbon atoms, cyclic ethers such as tetrahydrofuran and amides such as N, N-dimethylacetamide. As previously disclosed in this specification, a small amount of alcohol may be included in dimethyl sulfoxide to prepare the initial solution of polyvinyl alcohol.

Particles of polyvinyl alcohol prepared using the method of the present invention are useful in many applications. Diameter about 1
Particles smaller than 0 μm are useful as a packing material for chromatography columns, in the embolization process for stopping local blood flow in the living body, and as a reinforcing packing material. Larger particles are used as water absorbents, as carriers for controlling the release of various materials including biologically active compounds such as insecticides, herbicides and pharmaceuticals, and as fertilizers, fish foods, flavors and deodorants. It is useful.

[0036]

EXAMPLES In the following examples, unless otherwise specified
All parts and percentages are by weight.

In all examples, the polyvinyl alcohol used had a molecular weight of 86,000 and was at least 99.5.
% Was hydrolyzed.

Example 1 This example describes a preferred method of preparing polyvinyl alcohol particles according to the method of the present invention. While stirring the mixture of the polymer and the solvent shown in Table 1 11
A 3 wt% polyvinyl alcohol solution was prepared by heating at 0 ° C. for 30 minutes. The mixture of dimethyl sulfoxide and water used as the solvent contained 20% by weight of water.

The resulting solution was cooled to 80 ° C and then placed in a nebulizer. The airflow used to draw this solution from the reservoir and force it through the nozzle was 5-10 psig (1
It was under a pressure of 38-173 kPa). This solution is shown in Table 1.
A fine mist was discharged from the nozzle toward the non-solvent container having the composition and temperature shown in (1).

The diameter of the precipitated particles is 0.025 to 0.2.
It was 5 mm. All particles formed in the non-solvent containing water dissolved when left in the non-solvent for about 16 hours. These particles are within the scope of the invention. Because they are useful for some end use.

When the polymer was dissolved in a mixture of dimethyl sulfoxide and water, some of the particles aggregated into larger spheroids.

In Table 1, dimethyl sulfoxide is D
Shown as MSO and isopropanol as IPA.

For comparison, an attempt was made to make particles from a solution of the polymer in water, using methanol and acetone as nonsolvents. These samples are designated as 1C and 2C. The polymer precipitated as agglomerated translucent strands. This type of product would be one that would be expected when the solubilized polymer was added to the non-solvent.

[0044]

[Table 1]

Example 2 This example shows that the particles of the invention have the ability to act as encapsulating material and provide a controlled release of water soluble substances.

A solution prepared by dissolving 7 g of copper nitrate in 17.2 g of water and 6 g of polyvinyl alcohol together with 7 g of polyvinyl alcohol.
Added to 6.8 g of dimethyl sulfoxide (DMSO). The weight ratio of DMSO to water in the final mixture is 4: 1.
Met. The mixture was then heated with stirring at a temperature of 110 ° C. for 30 minutes in a reactor fitted with a mechanically operated stirrer and a water cooled condenser. The resulting solution was cooled to the temperature shown in Table 2 and then added dropwise through a 1.7 mm diameter orifice to a vessel of methanol or isopropanol cooled to about -55 ° C.

The distance between the orifice where the drop is formed and the surface of the non-solvent is shown in Table 2 along with the resulting solid particle shape.
All particles were transparent and had a diameter of 0.5-2 mm.

Particles precipitated. By immersing the particles in the non-solvent in which they are deposited for 2 days,
DMSO and water were extracted from these particles. This non-solvent was replaced with an equal volume of fresh non-solvent after the first day.

0.15 g of the particles were suspended in 93 g of distilled water, and Yellow Springs Instru
ment Co. Type 31 conductivity bridge (condu
The rate at which the entrapped copper nitrate was released from the particles was measured by measuring the conductance of this liquid using a citiness bridge). The measurement was performed for 8 hours.

Before putting the particles in distilled water,
The effect of polymer morphology on the release rate was studied by drying at ambient temperature and a pressure of 4 mm of mercury for 4 hours.

Both samples of particles showed a substantially similar rapid rise in conductance during the first few minutes.
This first rapid conductivity was followed by a period of fairly modest rise. During this period, the conductance of the liquid containing undried particles is much higher than that of the liquid containing pre-dried particles (1.14 μmOh / hr) and 5.3 μmOh / hr. became. This difference in the rate of increase in conductivity is due to the higher crystallinity that occurred during polymer drying.

[0052]

[Table 2]

[0053]

According to the present invention, non-porous, substantially spherical polyvinyl alcohol particles having many of the physical properties of prior art crosslinked particles are obtained without sacrificing their solubility in hot water. Provided.

Claims (3)

[Claims] 1. A method for preparing non-porous particles of non-crosslinked polyvinyl alcohol comprising the steps of: (1) Polyvinyl alcohol and 60-100 wt% dimethyl sulfoxide and 0-40 wt% water or carbon atoms. Forming a solution containing a solvent consisting of a liquid aliphatic alcohol of the number 1 to 8; (2) the solution being compatible with dimethyl sulfoxide in the form of discrete drops or droplets and not compatible with polyvinyl alcohol. Addition to a liquid that is a solvent (provided that the concentration of polyvinyl alcohol in the solution is 1 to 20% by weight,
The temperature of the liquid is 25 ° C. or lower); and (3) collecting the produced solid particles of polyvinyl alcohol. 2. The method of claim 1, wherein said solution comprises up to 25% by weight water and water-soluble additives. 3. Non-porous, optically transparent particles of non-crosslinked polyvinyl alcohol having a diameter of less than 1 mm.