BG64957B1 - Process for preparing a polyvinyl alcohol gel and mechanically highly stable gel produced by this process - Google Patents

Abstract

A polyvinyl alcohol gel can be easily and quickly produced by a process having the following steps: (a) use of an aqueous polyvinyl alcohol solution with a degree of hydrolysis (98 % by moles; (b) admixture of an additive that is dissolved in the aqueous polyvinyl alcohol solution and forms a separate, finely distributed and aqueous phase after concentration of the solution; (c) drying of the aqueous solution to a residual water content of maximum 50 wt. % to cause the phases to separate and hence the polyvinyl alcohol to gel; (d) rehydrating the polyvinyl alcohol in an aqueous medium.

Description

Technical field

The present invention relates to a process for the preparation of a polyvinyl alcohol gel. The invention also relates to a mechanically high-strength gel produced by this method.

After standing, the solutions containing polyvinyl alcohol (PVA) solutions show an increase in viscosity. It is also known that PVA solutions can be gelled when the solution is frozen and then melted again (FR 2 107 711 A). The gelatinized bodies thus obtained, however, exhibit relatively low stability.

It is known from EP 0 107 055 B1 that the strength of the freeze-dried gelatinous masses of PVA can be increased, and the process of freezing and melting is not only repeated once but also repeated two to five times. In this case, a PVA solution with a degree of saponification of> 95 mol% was obtained. or, as recommended in the invention, > 98 mol%. The upper limit for freezing the solution is 3 ° C, the cooling rate can be from 0, 1 ° C / min to 50 ° C / min. The PVA used in this case has a degree of polymerization of at least 700. The concentration of PVA in the solution should be greater than 6% by weight, and it is recommended that it be between 6 and 25% by weight. %. The PVA gel obtained by repeated freezing and melting has good mechanical strength and high water content, which is retained even under mechanical loading. The resulting gel is highly elastic, non-toxic and can be used for a variety of medical purposes.

Various substances and materials can be added to this gel that can increase its strength, for example glycol, glycerin, sucrose, glucose, agar, gelatin, methylcellulose, etc. By adding active substances, for example heparin, the use of for medical purposes, in cases where the active substance is intended to be released from the gel gradually and evenly over a long period of time. In addition, the gel can be mixed with microorganisms and enzymes to form a biologically active system.

From US-PS 4 663 358, the addition of organic solvents to an aqueous solution of polyvinyl alcohol is known to reduce the freezing point of the solution. In this way, it is possible to avoid freezing of water at freezing temperatures below -10 ° C, or as recommended at a temperature of -20 ° C, which results in a more homogeneous and hence a more transparent gel. . The low freezing temperature is applied to the formation of fine crystalline gels which are characterized by satisfactory mechanical strength.

The preparation of PVA gelatinized bodies using the freezing technique is laborious and slow.

From DE 43 27 923 C2, a method is known which enables the preparation of PVA gels without a freezing process. Using a PVA solution with a hydrolysis rate> 99 mol% and adding any soluble substance containing non-aqueous OH groups or CH ₂ groups, it is possible to achieve PVA gelation at temperatures higher than 0 ° C. The gelling process in this case, however, requires several hours, in which cases, in some cases, additional hours of residence should be added in order to achieve the necessary hardening to complete stability of the gelatinized body. This, of course, is too disadvantageous when it comes to making larger quantities of gel on an industrial scale.

Therefore, the concept underlying the present invention is to achieve an easy and rapid preparation of a gelatinized body from PVA while enhancing the quality of the gelatinized bodies produced.

Starting from this formulation, the method according to the present invention includes the following technological steps:

(a) use of an aqueous solution of polyvinyl alcohol with a degree of hydrolysis> 98 mol%;

(b) the addition of an additional substance which, when added, dissolves in the aqueous solution of the polyvinyl alcohol and, after increasing the concentration, forms a finely dispersed phase containing water;

c) drying the aqueous solution to a residual water content up to a maximum of 50% by weight to obtain phase separation and the associated gelation of the polyvinyl alcohol;

d) restoration of swelling of polyvinyl alcohol in an aqueous medium.

Unsurprisingly, the method of the present invention allows gelling of polyvinyl alcohol to be achieved within minutes at room temperature or even at higher temperatures. By adding water-soluble additives and increasing the concentration due to the evaporation of the water, a finely dispersed phase separation is achieved, which makes it possible to obtain very rapid gelation within the PVA phase. A prerequisite for this is that the water-soluble additive also forms a water-containing phase so that due to the separation of the PVA phase, a corresponding proportion of water is released very quickly, resulting in the gelation of the polyvinyl alcohol. It is appropriate that the water-soluble additive has an affinity for water that is at least comparable to that of polyvinyl alcohol.

The P / A phase, which is dehydrated upon separation, will absorb water in the subsequent swelling recovery, thereby improving the elasticity and mechanical stability of the polyvinyl alcohol gel without producing a reversible gelation process. When swelling is restored, the presence of a known relative proportion of electrolyte in the aqueous medium results in greater stability of the PVA gel, so it is recommended that swelling be restored in pipeline water or, preferably, in saline solution.

The method according to the present invention has the advantage that the production of gelled PVA bodies can be accomplished more easily and very quickly, especially without the freezing and repeated drying procedures, so that highly economical production is achieved of gelatinized masses of polyvinyl alcohol. The gelatinized bodies of the present invention are also distinguished by their high elasticity and stability, in particular with regard to the tensile strength, in this respect the resulting gelatinous bodies being superior to the gelatinized bodies of PVA produced by known methods so far.

To achieve an even greater increase in the stability and elasticity of polyvinyl alcohol gelatinized bodies, the use of a non-soapy aqueous PVA solution also helps.

As a water-soluble additive, it is recommended to use polyethylene glycol, which is added at a concentration of from 4 to 30% by weight, preferably from 4 to 20% by weight. % or better from 6 to 16 wt. %. Examples of other possible additives include cellulose ester, cellulose ether, starch ester, starch ether, polyalkylene glycol ether, polyalkylene glycol, long chain alcohols (C _n H _{2n + 1} OH, with> η = 8), sugar ester, sugar ether .

A particularly preferred field of application for PVA gelatinized bodies is their preparation as biologically, physically or chemically active masses, i. the incorporation of biologically, physically or chemically active material into the PVA gel. Thus, the PVA gel is particularly suitable for example in the preparation of chemical or biological catalysts.

The drying of the aqueous solution in order to separate the phases and obtain the associated gelling is carried out until a residual water content of a maximum of 50 wt. %. The lower limit of residual water content of about 10 wt. %, on the other hand, is conditioned by the fact that the PVA gel obtained must still be fully capable of restoring swelling, that below that residual water content of about 10 wt. % there is a decrease in the elasticity of the gelatinous mass and that under said residual water content, some of the incorporated biological materials may be damaged. The recommended range for residual water content is the range between 10 and 30 wt. %.

Drying can be accomplished easily for a short time by evaporating the water at exposure to air at ambient temperature if the solution is divided into small portions, and in particular portions in which the solution is in a thin layer. In this case, it is appropriate to apply the droplets of the solution on some solid support such that the droplet diameter is at least twice the height of the droplet. The same effect can be obtained by pouring the solution in a mold and / or as a layer on a material carrier. When a very thin film or film layer is obtained, evaporation to the desired residual water content can be achieved in a few minutes, for example within 15 minutes. Accelerating the drying process - and hence the gelling process - can also be achieved by drying in an oven at a higher temperature.

The recommended saline solution to effect swelling recovery contains multivalent anions.

The method according to the present invention is particularly suitable in cases where the immobilization of biologically active material is required, since it can now be carried out with extreme sparing of the biological material, so that the biological material will have a significantly higher initial activity than at other methods of immobilization.

It may be added here that the aqueous medium in which the re-swelling of the PVA gel takes place may at the same time be some nutrient solution for the biologically active material.

The density of the types of PVA gelatinized bodies obtained according to the invention can be modified by suitable additives. For example, the specific gravity can be increased by the addition of titanium oxide, respectively, and reduced by the addition of fine glass hollow grains.

The gelation effected according to the present invention may be obtained, as mentioned above, at room temperature, but may also wilt at lower or higher temperatures. The biologically active material included in the PVA gel may represent any enzymes, microorganisms, spores and cells.

The process of the present invention may be carried out in a variety of embodiments. For example, this can be done in a columnar gravity feeder, the drying of the phase separation droplet being carried out during the fall itself, so that when the drop falls on the substrate, the gel after phase separation has already occurred . This method is particularly suitable for the preparation of gelatinous masses of PVA as a chromatographic material, which for laboratory purposes may have a diameter of 10 to 100 µm, and for other purposes, from 100 to 800 μπι. It is also possible that any source fluid, resulting in a higher viscosity, may be subjected to drying upon extrusion so as to obtain gelation of PVA.

The gelatinized body obtained by the method proposed by the present invention shows a higher mechanical stability than the previously known gelatinized masses, especially with regard to the tensile strength and tensile strength.

These better mechanical properties allow the gelatinized bodies obtained according to the present invention to be produced in a lenticular form favorable for the reaction kinetics, for which known gelatinous bodies have not shown satisfactory mechanical stability, and in particular stability at stirring. However, the gelatinized body of the present invention remains stable and resistant to erasure for months, even in high-speed mixing processes. The large-diameter, small-height lens forms allow the chemical, physically or biologically active material to remain close to the surface at all times, resulting in a constellation favorable to the reaction kinetics.

The present invention enables the polyvinyl alcohol body to be easily added to any magnetic additive so that, if necessary, the gelatinized bodies can be easily removed from the liquid by means of a magnet.

It turns out that the porous structure of the polyvinyl alcohol gelatinized bodies of the present invention can be adjusted by the molecular weight of the phase-added additives added. By adjusting the molecular weights of the added polyethylene glycols, whose molecular weight is recommended to be between 800 and 1350, the pore sizes of the gelatinized body of polyvinyl alcohol between 1 and 15 pm can be obtained.

For the preparation of the present invention, an aqueous solution of polyvinyl alcohol and any additive have been found to require a higher degree of drying in the use of distilled water to obtain the same mechanical properties. Indicators are instantly improved if plain water with some hardness is used. Therefore, it should be assumed that the presence of a certain content of salts in water favors the implementation of the method proposed by the present invention.

Below, we will elucidate the present invention by means of a few exemplary embodiments.

Example 1.

16.8 g of water were added to 2 g of PVA and 1.2 g of polyethylene glycol (PEG 1000). The solution was heated to 90 ° C until all components were completely dissolved to give a viscous colorless solution. After cooling to 30 ° C, the polymer solution was applied dropwise using a pressure syringe onto a polypropylene plate. The dripping is performed by touching the cannula to the polypropylene plate at a rate of about 1/2 s; the resulting droplets are about 3 mm in diameter and about 1 mm high. Applying a white waxy film to the surface of the droplets. After evaporating 89% by weight of water at room temperature, the gelatinized bodies are allowed to swell again in water or in brine. The resulting gelatinous bodies have a diameter of 3-4 mm and a height of about 200-400 pm.

Example 2.

After cooling the polymer slurry (composition: 2 g PVA, 1.2 g polyethylene glycol (PGA 1000) and 15.8 g water), 1 ml of nitrified mixed culture (Nitrosomonas europea and Nitrobacter Winogradsky) was added to 20 g of the polymer solution. to obtain a dry biomass density (VTM) of 0.06 wt. %. The formation of the gelatinized bodies was done according to Example 1. The resulting gelatinous bodies were placed in a standard mineral salts medium (STMN) for nitrifiers to restore swelling. The immobilized Nitrosomonas thus obtained show an initial activity of about 70% after immobilization for Nitrosomonas spp. and 100% for Nitrosobacter spp., compared to the same amount of free nitrifiers.

When nitrifiers were incorporated into PVA cryogels at -20 ° C, the initial activity for Nitrosomonas spp. is at about 1%, and at -10 ° C at about 25%, with the mechanical stability of the PVA hydrogel reducing.

The incubation of the immobilizates is carried out in the same medium at 30 ° C. After 10 mg of gelatinized bodies were incubated in 30 ml of standard mineral salts (STMN), a maximum ammonia degradation value of 7 to 8 μιοοη NH ₄ * (g _{Ka [} * min) was obtained after 19 days.

Example 3.

1.6 g of polyethylene glycol (PEG 1000) were dissolved in 12.8 g of water, then 1.6 g of PVA was added, and then proceeded according to Example 1. After cooling the polymer solution to 30 ° C in the solution was dispersed 4 ml of a culture of the strictly anaerobic Bakteriums Clostridium butyricum NRRL B-1024, which was converted overnight into an oxygen-free atmosphere, which converted glycerol to 1,3-propanediol (PD) (Saturation with polymer solution cells: 6 x 10 ⁷ per ml). The formation of the gelatinized bodies was carried out as described in Example 1. After 70 wt. % of water, immobilizers return to swell again in mineral salts (20x excess). The incubation of cell-filled gelatinized bodies was carried out in the same medium (40-fold excess) at 30 ° C. For sufficient nutrient content of the immobilized biomass, the medium changes several times during the growth phase.

If 0.25 g of the immobilized biocatalyst thus obtained are placed in 40 ml of mineral salts medium with 24.4 g'L-Ι glycerol, the concentration of 1,3-PD will increase within 3.25 hours by 2.8 g'L-Ι. This corresponds to a catalyst activity of 0.14 g of 1,3-PD every g Kat and hour. After withdrawing the activity of the reduced cells, a catalyst activity of 0.0 8 g of 1,3-PD (g _Kat * h) was obtained.

Example 4, 5

15.8 water was added to 2 g of polyvinyl alcohol and 1.2 g of polyethylene glycol (PEG 1000) and then worked as described in Example 1.

After cooling the polymer slurry to about 20-27 ° C, 1 ml of some defined suspension of spores from Pilzes Aspergillus terreus was added to 20 g of the polymer solution and dispersed in the solution. The spore suspension is selected so that, after increasing for 5 days in the culture medium, a dry biomass density of 0.005 wt. %.

After evaporating at room temperature 70 wt. % of water, immobilizers are placed to restore swelling in mineral salts medium for Aspergillus terreus (20x excess).

The incubation of immobilizations is carried out in a growth medium. For the preparation of itaconic acid, the growth medium is replaced by the production medium.

The resulting immobilizers immediately after immobilization have an initial activity of about 60%, compared to the same amount of free fungal cells. If 0.2 g of gelatinized bodies with 60 g / коglucose are incubated in 100 ml of the production medium, 35 mg of itaconic acid (g _Kat * h) will be obtained after 7 days.

Example 5.

Greater amounts of gelatinized bodies are obtained by dropping the polymer solution (composition according to Example 1) by means of a multi-jet system on a conveyor belt. In principle, a tape dryer is dried by PVA in a drying tunnel to a certain residual moisture content and then collected with a scapula and placed in a container where it swells and grows.

Example 6

In the production of Example 1, the polymer solution is not dripped but poured into pre-prepared semi-open molds with an internal diameter of 1 to 10 mm and of any length.

After re-swelling in the water, the resulting strips show an extension of up to 3-4 times without breaking. The extension is irreversible. The tape obtained in this way can withstand a load of 500 g without breaking.

Example 7.

After standing for 14 days in tap water, the tapes obtained according to Example 6 were subjected to mechanical testing. After this stay, the strips had a width of about 8 mm and a height of about 1 mm. The degree of recovered swelling takes into account the decrease in the weight of the strip after re-swelling and 14 days of standing in water relative to the total mass of polymer solution used before the drying process. The straps retain their elastic characteristics up to 40% tear elongation.

Mechanical properties of the tapes produced at different drying rates for a composition of 10 wt. % polyvinyl alcohol and 6 wt. % polyethylene glycol:

^ .Content of sufficient water; after drying, ί 1 Degree of swelling [%] Extension of bliss E-module [N / ia *] 27 76 455 0.11 1 20 74 420 0.11 | 15 68 410 ^0.18 1 13 65 390 0.24 10 63 380 0.27 1 57 360 0,34 |

Mechanical properties of the strips at a drying rate of 80 wt. % for composition 10 wt. % polyvinyl alcohol and 8 wt. % polyethylene glycol:

Polyethylene grade 1 glycol [Degree of swelling [%] Extension ^- tear [V] E-module (N / mm ² ) | 400 57 410 0.27 600 66 290 0.22 800 82 360 0.19 1000 84 420 0.11 1350 I2 370 0.12

Mechanical properties of PVA hydrogel strips for different concentrations of PVA with the addition of 6 wt. % polyethylene glycol (PEG 1000) at degree of drying (amount of water evaporated during drying) 80 wt. %:

| Polyvinyl alcohol 1 ^l ' ^J · .. Extension of tearing E-module. [N / PP ² ] 1 ⁸ 350 0.09 j 1 · ¹⁰ 420 0.11 1 ¹² 420 0.17 1 ¹⁴ 460 . 1 0.19 1 ¹⁶ 440 0.25 |

Mechanical properties of the strips at a drying rate of 80 wt. % for composition 10 wt. % polyvinyl alcohol and 6 wt. % polyvinyl glycol (PEG 1000) for various swelling recovery media:

Swelling Recovery Environment Break extension E-module ([W / it ² ] early .pa ι 1 network 420 0.11 K ₂ HPO4 (100 jnmoi / 1) 410 0.17 r-JCjSO ^ (120 mmol / l) ' 530 0.15 I ^ CaClj (120 tsh1 / 1) 360 0.10 PKC1 (175 mmol / l) 370 0.15

Example 8.

The gelatinized bodies were prepared according to Example 1 and allowed to swell again in deionized water (5 μ S H ₂ O). The degree of re-swelling of the gelatinized bodies is determined directly after the swelling process for different degrees of drying. With a degree of recovered swelling 100 wt. % by weight of the gelatinized bodies before the drying process and after the re-swelling is the same as can be seen from the accompanying drawing.

Claims (22)

Claims 1. A method for preparing a biocatalyst with a biologically active material incorporated into a gel of polyvinyl alcohol in the form of microorganisms, enzymes, spores and / or cells, characterized by the following technological steps: (a) use of an aqueous solution of polyvinyl alcohol with a degree of hydrolysis> 98 mol%, (b) the addition of an additive which, after the addition, dissolves in the aqueous solution of polyvinyl alcohol and, as the concentration increases, forms a separated, finely dispersed water-containing phase, (c) the addition of the biologically active material, (d) drying the aqueous solution to a residual water content of not more than 50% by weight; % to obtain the phase separation and associated gelation of polyvinyl alcohol, (e) restoration of swelling of polyvinyl alcohol in an aqueous medium. 2. The method of claim 1, wherein the polyvinyl alcohol solution has a concentration of from 4 to 30% by weight. %, preferably from 6 to 16 wt. %. Method according to claim 1 or 2, characterized in that a water-soluble additive whose affinity for water is at least comparable to that of polyvinyl alcohol is used. A method according to claims 1 to 3, characterized in that the water-soluble additive is selected from the group of cellulose ester, cellulose ether, starch ester, starch ether, polyalkylene glycol ether, polyalkylene glycol, long-chain alkanols (n> 8), sugar ester, sugar ether. 5. A method according to claim 4, characterized in that polyethyleneglyl is used as an additive. Method according to claims 1 to 5, characterized in that the water-soluble additive used is at a concentration of from 4 to 20% by weight, preferably from 6 to 10% by weight. %. Method according to any one of claims 1 to 6, characterized in that the drying of the aqueous solution is carried out until a residual water content of at least 10 wt. %. A method according to claim 7, characterized in that the drying of the aqueous solution is carried out until a residual water content of 10 to 30% by weight is reached. %. Method according to claims 1 to 8, characterized in that the drying is carried out after the solution is applied dropwise on a solid support. A method according to claims 1 to 8, characterized in that the drying is carried out after pouring the solution into a mold. A method according to claim 8 or 10, characterized in that the solution is poured or poured in such a way as to obtain a gelatinized body with a diameter of at least twice its height. A method according to claim 11, characterized in that the solution is poured or poured so as to form a gelatinized body with a diameter of> 1 mm, preferably between 2 and 4 mm, and a height between 0.1 and 1 mm , preferably between 0.2 and 0.4 mm. Method according to one of Claims 1 to 8, characterized in that the drying is carried out after pouring the solution in the form of a long strip. Method according to one of Claims 1 to 13, characterized in that the drying of the aqueous solution is carried out after pouring the solution onto a carrier. A method according to any one of claims 1 to 14, characterized in that the swelling restoration is carried out in water from the pipeline network. Method according to one of Claims 1 to 14, characterized in that the swelling restoration is carried out in saline solution. 17. A method according to claim 16, characterized in that a nutrient solution for the biologically active material is used as the saline solution. A method according to claim 16 or 17, characterized in that a saline solution containing multivalent anions is used. Method according to one of Claims 1 to 18, characterized in that the drying takes place entirely during the drop itself formed in the gravity feed column. 20. Mechanically highly stable biocatalyst of polyvinyl alcohol produced by the process according to any one of claims 1 to 18. 21. The biocatalyst according to claim 20, produced in a lens form, the diameter of which is substantially larger than its height. The biocatalyst according to claim 20 or 21, comprising a magnetic additive.