JP3165734B2 - New high water absorption shape memory material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shape memory material comprising a dried polymer blend hydrogel and a stretched dried polymer blend hydrogel. More specifically, it relates to a shape memory material comprising a polymer blend hydrogel dried product having an extremely fast water absorption rate and a high water absorption rate and a polymer blend hydrogel stretched dried product having an extremely fast water absorption rate and a high water absorption rate and contracting when absorbing water. is there.

[0002]

2. Description of the Related Art It has been known that a tough high water-containing hydrogel can be produced by repeatedly freezing and thawing a high-concentration aqueous solution of polyvinyl alcohol (Japanese Patent Laid-Open No. 57-130,543). The cause of this tough hydrogel formation is mainly by repeatedly freezing and thawing,
It is also known that water molecules between polyvinyl alcohol molecules are converted into bound water, which serves as a crosslinking point in the hydrogel. This type of tough, highly hydrous hydrogel is being used in a wide range of biomaterial applications.

It is also known that a gel is formed by mixing another water-soluble polymer with an aqueous solution of polyvinyl alcohol at atmospheric pressure and at a temperature of 100 ° C. or lower [Polymer Chemistry Vol. 273-278 (196
0 years)]. However, no attempt has been made to utilize the gel thus produced as a solid material. The reason is considered to be that a gel was formed during the purpose of producing the polymer blend fiber, and it was considered that this gel should not be formed in the fiber spinning solution.

The present inventors have also found that a polyvinyl alcohol-based blend gel having high water content and high elasticity can be obtained by blending polyvinyl alcohol and other water-soluble polymers under heat and pressure. Kaihei 3-
No. 161046), suggesting its use for artificial skin thin films, soft contact lenses or artificial joints.

[0005] However, there has been a demand for the development of a further application method of a heated and pressurized polymer blend hydrogel having useful properties such as tough rubber elasticity, high water content, light permeability and oxygen permeability.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a new method for utilizing a heated and pressurized polymer blend hydrogel having useful properties such as tough rubber elasticity, high water content, light transmittance and oxygen permeability. To provide.

[0007]

SUMMARY OF THE INVENTION
Having a degree of polymerization and 90% or more of the degree of saponification of _{~4,000 - (CH 2 -CH (OH} )) - polyvinyl alcohol having predominantly recurring units of the high concentration mixed aqueous solution of other water-soluble polymers From 1.2 to 1.2 in the presence of steam.
It is composed of a dried product of a tough rubber-like polymer blend hydrogel obtained by maintaining the temperature at 105 to 150 ° C. at a pressure of 5.0 atm, dehydrating the obtained aggregate, and reswelling with water. This is achieved by the present invention. These objects also has a degree of polymerization and 90% or more of the degree of saponification of 500~4,000 - (CH ₂ -CH (O
H)) A high-concentration mixed aqueous solution of a polyvinyl alcohol mainly having a repeating unit of-and another water-soluble polymer is applied in the presence of steam at a pressure of 1.2 to 5.0 atm.
It is made of a shape memory material consisting of a stretched and dried product of a tough rubbery polymer blend hydrogel obtained by maintaining the temperature at 5 to 150 ° C., dewatering the obtained aggregate, and reswelling with water. This is achieved by the present invention.

In the present invention, the mixing ratio of the polyvinyl alcohol to the other water-soluble polymer is 85:15 to 60: 4.
0. It is a shape memory material consisting of a dried or stretched dried polymer blend hydrogel.

The present invention is also a shape memory material comprising a dried or stretched dried polymer blend hydrogel having a weight average molecular weight of 1,000 to 300,000 of the other water-soluble polymer.

[0010] The present invention is also a shape memory material comprising a dried or stretched dried polymer gel in which the other water-soluble polymer is polyethylene glycol or a polyamino acid or a salt thereof.

The polyvinyl alcohol used in the present invention has a polymerization degree of 500 to 4,000, preferably 1,000.
2,000, most preferably 1,300 to 1,700, the degree of saponification is 90% or more, preferably 95% or more, and the repeating unit of-(CH ₂ -CH (OH))- It mainly has.

Other water-soluble polymers to be mixed with the polyvinyl alcohol include, for example, polyethylene glycol, polyacrylic acid or a salt thereof, acrylic acid-acrylamide copolymer or a salt thereof, polyallylamine, polyacrylamide, polyglutamate. And natural or semi-synthetic carboxylate such as alginate, pectic acid, carboxymethylcellulose, etc., and polyvinylpyrrolidone. These water-soluble polymers have a weight average molecular weight of 1,000 to 300,000, preferably 2,000 to 200,000. The weight ratio of the polyvinyl alcohol to the other water-soluble polymer is 85:15
The ratio is 60:40, preferably 80:20 to 70:30. That is, when the weight ratio is out of the range, the yield of the rubbery polymer blend hydrogel becomes low. A mixture of these polyvinyl alcohols and other water-soluble polymers is used as an aqueous solution, and its concentration is 8 to 40% by weight, preferably 10 to 35% by weight.

The reason for increasing the concentration of the aqueous solution of polyvinyl alcohol in the present invention is that the mixing ratio between polyvinyl alcohol and water is such that most of the existing water is bound water, thereby increasing the crosslink density between polymers. It is to make it. As a result, it is expected that amorphous rubberization is promoted.

The production of the high hydrous polymer blend hydrogel is as described in JP-A-3-161046. That is, a mixed aqueous solution of a predetermined concentration of polyvinyl alcohol and another water-soluble polymer is prepared, and then the mixed aqueous solution is placed in an autoclave, and in the presence of steam, 1.2 to 5.0 atm, preferably 1.5 to 3 atm. Heating and pressurization is performed at a pressure of 0.7 atm and a temperature of 105 to 150 ° C, preferably 110 to 140 ° C for 30 to 120 minutes, preferably 45 to 90 minutes.

The reason for using an autoclave in the present invention, that is, heating under pressure in the presence of water vapor, is that a high-concentration aqueous solution of polyvinyl alcohol is dissolved under atmospheric pressure even when heated to around 100 ° C., which is the boiling point of water. The use of an autoclave makes it easy to dissolve it at high temperature and high pressure, and when blending other water-soluble polymers with polyvinyl alcohol, the mutual diffusion between them is difficult. This facilitates the formation of a complex between polymers by strong polymer-polymer interaction, and allows the complex to function as a crosslinking point. It is believed that a synergistic effect of these actions results in the formation of a tough rubbery polymer blend hydrogel.

The dried polymer blend hydrogel of the present invention can be obtained by drying the polymer blend hydrogel prepared as described above by a known drying method, for example, by air drying. Further, the shape memory material comprising the stretched and dried product of the polymer blend hydrogel of the present invention is obtained by stretching the prepared polymer blend hydrogel uniaxially or biaxially by a known method, fixing the stretched state, and fixing the stretched state by a known drying method. And dried by drying. The shape memory material composed of the dried polymer blend hydrogel and the stretched dried product thus obtained can be processed into various shapes.
For example, it can be in the form of a plate, film, thread, hollow fiber, powder, or the like.

In the case of forming a hollow fiber, a mixed aqueous solution of a predetermined concentration of polyvinyl alcohol and another water-soluble polymer is heated and pressurized as described above, and the obtained solution is spun and swollen with water. It can also be used for separation membranes for substance permeation and artificial blood vessels. When the hollow fiber is dried and stretched and fixed, it shrinks when water is absorbed, and returns to its original shape.

Moreover, this hollow fiber membrane has a honeycomb structure on the order of μm, and can remove particles of a considerably large size.

The dried product after stretching and fixing shrinks due to water absorption as described above, and exhibits the original shape, so that it can be used as an actuator. The cause of such shrinkage is derived from the structure of the gel. That is, a very large number of polyvinyl alcohol (PVA) microcrystals and a complex between polyvinyl alcohol (PVA) and polyethylene glycol (PEG) form a crosslinked structure having a large crosslink density. Such a high crosslink density is caused by stretching. Shear deformation between molecules is less likely to occur, and amorphous chains can be effectively oriented, and the orientation is fixed by drying. It is considered that when the dried sample after stretching and fixing absorbs water, the oriented amorphous chains exhibit entropy elasticity and shrink.

The shape memory material of the present invention comprising a dried gel or stretched dried product, particularly a fiber, has a very high water absorption rate and a water absorption rate exceeding about four times its own weight. It is thought that this high water absorption also makes it possible for a three-dimensional honeycomb structure on the order of several μm to rapidly absorb a large amount of water.

Further, since the ultrafine fibers and powders have a large surface area, the above-mentioned high water absorption is further improved, and can be used as a water absorbing agent for diapers, sanitary articles and the like. There is also an advantage that the post-treatment is facilitated by shrinking by water absorption. The same applies to biaxially stretched films and sheets.

[0022]

Next, the present invention will be further described with reference to examples. In the following examples, the water content is defined as follows.

[0023]

(Equation 1)

Example 1 1. Preparation of fiber a) Preparation of spinning solution As polyvinyl alcohol (PVA), PVA-120 (Kuraray Povar) powdered PVA having a saponification degree of 99.85% and a polymerization degree of 1200 was used. Polyethylene glycol (P
EG) used was PEG 4000 manufactured by Wako Pure Chemical Industries, Ltd., having an average molecular weight of 3000.

A simple chemical reaction device (TEM-V1000) manufactured by Pressure Glass Co., Ltd. was used for blending. In this apparatus, the blend aqueous solution was 20 wt%, and the mixing ratio of polyvinyl alcohol and polyethylene glycol was 80:20.
Add each powder and distilled water so that The temperature is increased while stirring until the medium temperature and pressure reach 150 ° C. After reaching the target temperature, the power was turned off and the temperature was lowered to 50 ° C. to obtain a spinning solution.

B) Preparation of hollow fiber by gel spinning a) Spinning conditions Nozzle outer diameter: 2.0 mm Inner diameter: 0.7 mm Coagulation liquid: methanol (containing 99.6%) (-50 ° C)
[Dry ice] Inner solution: Methanol (99.6% content) (-40 to-
30 ° C) [Dry ice] Extrusion pressure +1 kg / mm ² .

B) Spinning method In order to form a hollow portion, the inner liquid is allowed to fall freely in advance, and then the spinning aqueous solution is dropped from the spinning bath at about 1 kg / mm ² at −50.
The mixture was extruded into a coagulation bath at 0 ° C., solidified by rapid cooling, and then gradually thawed and returned to water to form a hollow fiber. Then
The produced hollow fiber was air-dried at room temperature for 24 hours to obtain a dried polymer blend hydrogel.

The stretched hollow fiber was stretched and fixed three times, and then air-dried at room temperature for 24 hours to obtain a shape memory material consisting of a stretched dried polymer blend hydrogel.

The size of the hollow fiber can be changed by changing the outer diameter and inner diameter of the nozzle and the extrusion pressure.

When it is desired to prepare a solid yarn, it can be easily obtained by spinning without flowing the inner liquid. The ultrafine fibers can be easily obtained by jet spinning into methanol at minus several tens of degrees Celsius and drying. An apparatus for obtaining such ultrafine fibers is achieved by flowing air at a high speed through a nozzle during spinning. In the case of jet spinning, the spinneret has a diameter of 2
The fiber is spun into methanol at -50 ° C at 50 µm, nitrogen gas pressure of 11 kg / cm ² , and blowing air flow rate of 9 m ³ / hr for elongation to obtain a fiber having a diameter of 4 µm.

Test Example 1 The water absorption (%) and the elongation (%) of the shape memory material made of the dried polymer blend hydrogel and the stretched dried polymer blend hydrogel prepared in Example 1 were immersed in water. Tables 1 and 2 show the shrinkage (%).

[0032]

[Table 1]

[0033]

[Table 2]

Both the shape memory materials composed of the dried polymer blend hydrogel and the stretched dried polymer blend hydrogel rapidly contained water, and thereafter continuously absorbed water. The dried polymer blend hydrogel swelled by 30 to 40% by absorbing water.

On the other hand, a shape memory material composed of a polymer blend hydrogel stretched and dried product shrinks by about 40% upon absorbing water,
It approaches the original shape.

[Test Example 2] Examination of the scattering angle dependence of the X-ray diffraction intensity in the gel state before drying revealed that, in addition to the halo due to water, diffraction due to PVA microcrystals was slightly observed at around 20 °, and PVA microcrystals were observed. Plays a role of a crosslinking point.

When the dissolution behavior of the gel was examined by DSC,
Dissolution by PVA microcrystals appears around 60 ° C., and a dissolution peak is also observed on the higher temperature side. This higher temperature peak is expected to be due to dissolution of the complex formed between PVA and PEG, which also appears to play a role as a cross-linking point.

The X-ray diffraction photograph of the freeze-dried gel contains P
A diffraction ring of VA microcrystals appears, indicating that no orientation occurs during fiberization. The crystallinity was 48 (%), which was about twice the value of the blend film.

[0039]

As described above, according to the present invention, 500 to
A high-concentration mixed aqueous solution of a polyvinyl alcohol having mainly a repeating unit of-(CH ₂ -CH (OH))-having a polymerization degree of 4,000 and a saponification degree of 90% or more, and another water-soluble polymer. 1.2 in the presence of steam
Since it is a shape memory material consisting of a dried product and a stretch-dried product of a tough rubbery high water-containing polymer blend hydrogel obtained by maintaining a temperature of 105 to 150 ° C. at a pressure of 5.0 atm. Excellent, excellent elasticity because absorbed water is combined with polymer, and excellent in elasticity. In particular, shape-memory material made of stretched and dried material shrinks by absorbing water, so it is a water-absorbing agent for diapers, sanitary products, portable toilets, etc. It is useful as a material, hydrophilic coating material, water retention material, actuator, etc.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C08J 3/00-3/075 C08L 29/04

Claims (1)

(57) [Claims] 1. A mixture comprising a polyvinyl alcohol having a repeating unit of-(CH2-CH (OH))-having a degree of polymerization of 500 to 4,000 and a degree of saponification of 90% or more, and a water-soluble polymer. A shape memory material obtained by keeping an aqueous solution at a temperature of 105 to 150 ° C. at a pressure of 1.2 to 5.0 atm in the presence of steam, drying and stretching.