Title of Invention	"PROCESS FOR PRODUCING A POLYVINYL ALCOH OL GEL AND A MECHANICALLY HIGHLY STABLE GEL PRODUCED ACCORDING TO THE PROCESS"
Abstract	Process for producing a biocatalyst with a biologically active material, introduced into a get of potyvinyl alcohol, in the form of microorganisms, enzymes, spores and/or cells with the process steps. a) use of an aqueous polyvinyl alcohol solution with a degree of hydrolysis of > 98 mol%. b) dissolving an additive such as herein described to an aqueous poty vinyl alcohol solution having a degree of hydrolysis of >98 mol % and forms a separate, finely distributed and aqueous phase after concentration of the solution selected from the group formed by polyethylene glycol, cellulose esters, cellulose ethers, starch esters, starch ethers, polyafkylene gtycol ethers, polyalkylene grycols, long- chain alkanoles (CnH2n+1OH mit N>8), sugar esters and sugar ethers followed by c) addition of the biologically active material, : d) dehydration of the aqueous solution to a maximum residual water- content of 50-wt% In order to cause the phases to separate and hence the poly vinyl alcohol to get and e) rehydration of the polyvinyl alcohol in an aqueous medium.

Title of Invention

"PROCESS FOR PRODUCING A POLYVINYL ALCOH OL GEL AND A MECHANICALLY HIGHLY STABLE GEL PRODUCED ACCORDING TO THE PROCESS"

Abstract

Process for producing a biocatalyst with a biologically active material, introduced into a get of potyvinyl alcohol, in the form of microorganisms, enzymes, spores and/or cells with the process steps. a) use of an aqueous polyvinyl alcohol solution with a degree of hydrolysis of > 98 mol%. b) dissolving an additive such as herein described to an aqueous poty vinyl alcohol solution having a degree of hydrolysis of >98 mol % and forms a separate, finely distributed and aqueous phase after concentration of the solution selected from the group formed by polyethylene glycol, cellulose esters, cellulose ethers, starch esters, starch ethers, polyafkylene gtycol ethers, polyalkylene grycols, long- chain alkanoles (CnH2n+1OH mit N>8), sugar esters and sugar ethers followed by c) addition of the biologically active material, : d) dehydration of the aqueous solution to a maximum residual water- content of 50-wt% In order to cause the phases to separate and hence the poly vinyl alcohol to get and e) rehydration of the polyvinyl alcohol in an aqueous medium.

Full Text	Process for producing a pplyvinyl alcohol gel and a mechanically highly stable gel produced according'to the process The invention refers to aprocess for producing a polyvinyl alcohol gel. The invention also refers to a mechanically highly stable gel produced according to the process. It is well known that solutions containing polyvinyl alcohol (PVA) become more viscous when left to stand. It is also well known that PVA solutions can be converted into a gel if the solution is frozen and subsequently thawed (FR 2 107 711 A). However, gels formed in this manner have a relatively low strength. It is also known through EP 0 107 055 Bl that the strength ofPVAgels produced by freezing is increased by carrying out the freezing and thawing process at least once, but preferably repeating it two to five times. To this end, a PVA solution with a degree of saponification of > 95 mol %, but preferably of 98 mol %, is used. The upper temperature limit for freezing the solution is -3 degrees Celsius, the cooling rate can be between 0.1 to 50 degrees Celsius per minute, the thawing rate between 0.1 to 50 degrees Celsius per minute. The PVA that is used must have a degree of polymerization of at least 700. The concentration of PVA in the solution should be over 6 wt.% and is preferably between 6 and 25 wt.%. The PVA gel produced by repeated freezing and thawing has a good mechanical strength and a high water content, which is maintained even under mechanical stress. The gel produced in this manner is highly elastic, non-toxic, and can be used in many applications, particularly in medicine. Various substances and materials can be added to the gel to increase the strength, for instance glycol, glycerine, saccharose, glucose, agar, gelatine, methyl cellulose, etc. The admixture of agents such as heparin permits medical applications in which the active agent is continuously and evenly released from the gel over a period of time. In addition, microorganisms and enzymes can be mixed with the gel in order to create a biologically active system. 2 It is known from US-PS 4 663 358 that adding organiosolvents to the aqueous polyvinyl solution lowers the freezing point of the solution. This prevents the water from freezing at gelling temperatures below -10 degrees Celsius, preferably approximately -20 degrees Celsius, thus forming a more homogeneous and transparent gel. The low gelling temperature is used for creating compact grained gels with sufficient mechanical strength. Producing PVA gels using the freezing method is complicated and time consuming. DE 43 27 923 C2 disclosed a process by which PVA gels can be produced without using the freezing process. By using a PVA solution with a degree of hydrolysis of > 99-mol % and adding a dissolved additive that has non-aqueous OH or NH2 groups,_a gelling of the PVA can be achieved at temperatures above 0 degrees Celsius. However, the gelling process takes several hours or may even require an additional storage period of many hours in order to ensure that it is cured sufficiently to provide full strength to the gel substance. Due the nature of this method, it is disadvantageous for producing large amounts of the gel substance. Therefore, the purpose of the present invention is to be able to produce the PVA gel substances simply and quickly, as well as improving the quality of the gel substance as much as possible in this process. Based on this objective, the process for producing a polyvinyl alcohol gel includes the following steps: a) Use of an aqueous polyvinyl alcohol solution with a degree of hydrolysis of > 98 mol %. b) The addition 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) Dehydration of the aqueous solution to a maximum residual water content of 50 wt.% in order to cause the phases to separate and hence the polyvinyl alcohol to gel. d) Rehydration of the polyvinyl alcohol in an aqueous medium.. Surprisingly, the process according to the invention permits the gelling of the polyvinyl alcohol within^e^eTaTminuteJ)at room temperature or even higher temperatures. The addition of the water-soluble additive and concentration by evaporation of the water results in a finely distributed phase separation, whereby gelling happens within a very short period of time during the PVA phase. A prerequisite is that the water-soluble additive creates a hydrous phase , so that within a very short period of time a respective proportion of water is removed through the phase separation of the PVA phase, whereby a gelling of the polyvinyl alcohol is achieved. It is advantageous if the water-soluble additive has an affinity to water at least comparable to that of the PVA. The PVA phase, which is under-supplied with water during the gelling process; subsequently absorbs water during rehydration, whereby the elasticity and mechanical strength of the PVA gel is improved without reversing the gelling. It has been shown that a certain amount of electrolytes in the aqueous rehydration medium results in a higher stability of the PVA gel, so that the rehydration is advantageously carried out in tap water or, better yet, in a saline solution, The process according to the invention has the advantage that it permits the production of PVA gel within a very short time without using complicated processes, in particular without a freezing process and without repeated dehydration processes, so that an extremely economical production of PVA gel is possible. The gel substances according to the invention are also characterized by a high elasticity and stability, in particular tensile strength, and in this regard are significantly superior to the PVA gel substances produced in the traditional way. The stability and elasticity of the PVA gel substances are further enhanced by using a resaponified aqueous PVA solution in the production process./ Polyethylene glycol is a preferred water-soluble additive which is added at a concentration of 4 to 30 wt.%, preferably at 4 to 20 wt.%, and more specifically at 6 to 16 wt.%. - Cellulose esters, cellulose ethers, starch esters, starch ethers, polyalkylene glycol ethers, polyalkylene glycols, long-chain alkanoles (CnH2n+1OH where n > 8), sugar esters and sugar ethers are other examples of possible additives. A particularly advantageous area of application of the PVA gel substances is their production as biologically, physically or chemically active substances, i.e. incorporating , biologically, physically or chemically active material in the PVA gel. Thus the PVA gel is superbly suited for the production of chemical or biological catalysts, for instance. The dehydration of the aqueous solution for the purpose of phase separation and the associated gelling is carried out until a maximum residual water content of 50 wt.% is reached. A lower limit for the residual water content is 10 wt.% because the PVA gel produced should be completely rehydrateable, because the elasticity of the gel substance is lower if the residual water content drops below approximately 10 wt.%, and because any incorporated biological materials can be damaged if the aforementioned residual water content is lower. An advantageous range for the residual water content is between 10 and 30 wt.%. Dehydration can conveniently be carried out in a short period of time by evaporating water at ambient air temperature if the aqueous solution is divided into small portions, especially portions tn which there is only a small proportion of starch in the solution. In particular, it is advantageous to drip the solution onto a hard surface in such a way that the diameter of the drop is at least twice that of the height of the drop. This can similarly be achieved by pouring the solution into a form and/or coating a base material. A thin, or even film-like shape permits evaporation to the required residual water content within several minutes, for instance within 15 minutes. An acceleration of the dehydration process (and, therefore, the gelling process) can be achieved by carrying out dehydration in a drying oven at a higher temperature. 5 The saline solution used advantageously for rehydration preferably contains polyvalent anions. The process according to the invention is particularly advantageous for immobilizing biologically active material in that it is extraordinarily gentle on the biological material so that the biological material has a significantly higher initial activity in comparison with other immobilization processes. This can be enhanced if the aqueous medium in which the PVA gel is rehydrated is also a culture solution for the biologically active material. The density of the PVA gel produced according to the invention can be modified by using suitable additives. For instance, the specific gravity can be increased by adding titanium oxide and lowered by adding hollow glass microballs. As already mentioned, gelling according to the invention is possible at room temperature but can also be carried out at lower or higher temperatures. The biologically active material that is incorporated into the PVA gel can be enzymes, microorganisms, spores and cells. The process according to the invention can be implemented in various embodiments. For instance, it is possible to carry out the dehydration of a drop for phase creation during the falling process in a drop tower, so that when the drop impacts the surface, the gelling has already occurred after the phase separation. This production process is particularly suited for producing PVA gel substances as chromatography material whose diameter is 10 to 100 µm for laboratory purposes, and which can otherwise be between 100 and 800 µm. It is also possible to dehydrate an initial liquid that is set to a higher viscosity during extrusion of a strand and to carry out the gelling simultaneously. Compared to previously known gel substances, the gel substance produced by the process 6 according to the invention has superior mechanical stability, in particular with regard to abrasion resistance and tensile strength. These superior mechanical characteristics permit, in particular, to produce the gel substance according to the invention in a lenticular form that is advantageous to the kinetics of the reaction and in which previously known gel substances had insufficient mechanical stability, in particular agitation stability. On the other hand, the gel substance according to the invention is stable and abrasion resistant for many months, even when subject to high-speed agitation. The lenticular form with a large diameter and low height has the effect that the chemically, physically and biologically active material is always arranged near the surface, resulting in a constellation that is advantageous for the kinetics of the reaction. T'he present invention permits the addition of a magnetic additive to the polyvinyl alcohol substance by a very simple method in order to collect the gel substance out of a liquid by means of magnets?) It has been shown that the pore structure of the polyvinyl alcohol gel substance can be controlled by the molecular weight of the additive that effects the phase separation. By varying the molecular weight of the added polyethylene glycol, whose molecular weight is preferably in the range of 800 and 1350, the pore size of the polyvinyl alcohol gel substance can be adjusted to between 1 and 15 µm. Regarding the production of the aqueous solution of polyvinyl alcohol and the additive, it has been shown that the use of distilled water requires a higher degree of dehydration in order to achieve the same mechanical characteristics. The results are immediately better if normal tap water with a certain degree of hardness is used. Therefore, it can be assumed that a certain salt content in the water is advantageous for the process according to the invention. The invention is explained in more detail below by means of examples of embodiments. Example1: 15.8 or16.8 g of Water are added to 2 g of PVA and 1.2 g of polyethylene glycol (PEG 1000). The solution is heated to 90 degrees Celsius until all the components have dissolved completely, so that a viscous, colourless solution is obtained. After cooling to 30 degrees Celsius, the polymer solution is dripped onto a polypropylene plate by means of a syringe and application of pressure. The dripping is carried out by touching the cannula onto the PP plate at a rate of approx. l-2/second; the drop has a diameter ofapprox. 3 mm and a height of approx. 1 mm. After application of the drops, a white, wax-like film forms on the surface of the drops. After 89 wt.% of the water has evaporated at room temperature, the gel substances are rehydrated in water or a saline medium. The gel substances obtained have a diameter of 3-4 mm and a height of approx. 200-400 µm. ¦ Example 2: After the polymer suspension (composition: 2 g PVA, 1.2 g PEG 1000 and 15.8or16.8g water) has cooled, 1 ml of a nitrogen-fixing mixed culture (Nitrosomonas europaea and Nitrobacter winogradsky) is added to 20 g of a polymer solution and dispersed, resulting in a dry biomass load of 0.06 wt.%. The production of the gel substances is carried out according to Example 1. The gel substances obtained are rehydrated in a standard mineral salt medium for nitrogen-fixers. Compared to the same amount of free nitrogen fixers, after immobilization the immobilizates produced in this way have an initial activity of approx. 70% for Nitrosomonas spp. and 100% for Nitrobacter spp. After occlusion of the nitrogen fixers in the PVA kyrogels at -20 degrees Celsius, the initial activity of Nitrosomonas spp. is approx. 1%, at -10 degrees Celsius approx. 25% with decreasing stability of the PVA hydrogels. The incubation of the immobilizates is carried out in the same medium at 30 degrees Celsius. After 19 days a maximum ammonium decomposition rate of between 7 and 8 8 umol NH4+ (gcat x min) is achieved if 10 mg of gel substance is incubated in 30 ml of standard mineral salt medium. Example 3: 1.6 g of polyethylene glycol (PEG 1000) is dissolved in 12.8 g H2O, followed by 1.6 g of PVA. The process is continued according to Example 1. After the polymer solution has cooled to 30 degrees Celsius, 4 ml of a culture of the strictly anaerobic bacteria Clostridium butyricum NRRL B-1024, which converts glycerine into 1.3-propame diol (PD), grown overnight in an oxygen-free atmosphere is dispersed in the solution (cell load of the polymer solution: 6 x 107 per ml). The gel substances are produced according to Example 1. After 70 wt.% of the water has evaporated at .room temperature, the immobilizates are rehydrated in a mineral salt medium (20 times more than required). The incubation of the cell-loaded gel substance is carried out in the same medium (40 times more than required) at 30 degrees Celsius. The medium is changed several times during the growing phase in order to provide the immobilized biomass with an adequate nutrient supply. If 0.25 g of the immobilized bio-catalyst thus obtained are placed in 40 ml of mineral salt medium together with 24.4 g L-l glycerine, within 3.25 h the concentration of 1.3-PD increases by 2.8 g L-l. This corresponds to a catalyst activity of 0.14 g 1 3-PD per g cat per hour. After deducting the activity of fully developed cells, the result is a catalyst activity of 0.08 g 1.3-PD (gcat x h). , Example 4: 15.8 g of water is added to 2g PVAL and 1.2 g polyethylene glycol (PEG 1000) and the process is continued according to Example 1. After cooling the polymer suspension to approx. 30-37 degrees Celsius, 1 ml of a defined spore suspension of the fungus Aspergillus terreus is added to a polymer solution of 20 g and dispersed. The spore suspension is selected so that 5 d of fouling in the growth 9 medium results in a dry biomass load of 0.05 wt.%. After 70 wt.% of the water has evaporated at room temperature, the immobilizates are rehydrated in a mineral salt medium for Aspergilius terreus (20 times more than required). The incubation of the immobilizates is carried out in the growing medium. The growing medium is replaced with production medium for producing the itaconic acid. Co'mpared to the same amount of free fungus cells!, the immobilizates thus produced have an initial activity of approx. 60% directly after immobilization. If 0.2 g of gel substance is incubated in 100 ml of production medium together with 60 g/1 glucose, a productivity of 35 mg of itaconic acid (gcatx h) is achieved after 7 d. Example 5: Larger amounts of gel substances are obtained by dripping the polymer solution (composition according to Example 1) through a system of multiple nozzles onto a conveyer belt. According to the principle of a belt dryer, the PVA drops are dehydrated in a tunnel drier to a defined residual moisture content and subsequently collected in a collection container by means of a scraper, where they are rehydrated and washed. Example 6: In the production process according to Example 1, the polymer solution is not dripped, but poured into prefabricated semi-open forms of optional length with an interior diameter of 1-10 mm. After rehydration in water, the strands can be stretched to 3-4 times their length without breaking. This stretching is irreversible. A strand produced in this way can be loaded with . a weight of 500 g without breaking. Example 7: -10- After a shortage period of 14 days, the strands produced according to Example 6 are mechanically characterized in tap water. At that time, the strands are approximately 8 mm wide and approximately 1 mm high. The degree of rehydration takes into account the strand's loss of weight after rehy drat ion and 14 d storage in water in relation to the total mass of the polymer solution prior to the dehydration process. The strands have an elastic behaviour up to an elongation at tear of 40%. Mechanical characterization of the produced strands with various degrees of dehydration for the composition 10 wt% PVA and 6 wt% PEG 1000. Residual water Degree of Elongation at tear E-modulus content after rehydration % [N/mm2] dehydration [%] Mechanical characterization of the strands at a degree of dehydration of 80 wt% for the composition 10 wt% PVA and 8 wt% PEG for various types of PEG. -11- Type of PEG Degree of Elongation at tear E-modulus Rehydration [%] [N/mm2] Mechanical characteristics of the PVA hydrogel strands for various concentrations of PVA with the add if ion of 6 wt% PEG 1000 at a degree of dehydration (amount of water evaporated during the dehydration process) of 80 wt%. PVAL Elongation at tear E-modulus Mechanical characteristics of the strands at a degree of dehydration of 80 wt% for the composition 10 wt% PVA and 6 wf% PEG 1000 for various rehydration media. -12- Example 8: Gel substances are produced according to Example 1 and rehydrated In de Ionized water (5 µSH2O). The degree If rehydration for various degrees of dehydration of the gel substances is defined directly after the rehydration process. With a degree of rehydration of 100 wt%, the weight of the gel substances prior to the dehydration process and after the rehydration process is the same, as shown in the attached drawing. WE CLAIM: 1. Process for producing a biocatafyst with a biologically active material, introduced into a gel of polyvinyl alcohol, in the form of microorganisms, enzymes, spores and/or cells with the process steps. a) use of an aqueous; polivinyl alcohol solution with a degree of hydrolysis of > 98 mol %. b) dissolving an additive such as herein described to an aqueous poty vinyl alcohol solution having a degree of hydrolysis of >98 mol % and forms a separate, finely distributed and aqueous phase after concentration of the solution selected from the group formed by polyethylene glycot, cellulose esters, cellulose ethers, starch esters, starch ethers, polyalkylene glycol ethers, polyalkylene glycols, long- chain alkanoles (CnH2n+OH mit N>8), sugar esters and sugar ethers followed by c) addition of the biologically active material, d) dehydration of the aqueous solution to a maximum residual water content of 50-wt% in order to cause the phases to separate and hence the poty vinyl alcohol to get and e) rehydrat ion of the poty vinyl alcohol in an aqueous medium. 2. Process as claimed fn claim 1, in which the poly vinyl alcohol solution has a concentration of 4-30 wt%, preferably 6-16 wt%. 3. Process as claimed fn claims 1 and 2, in which a water-soluble additive is used which has an affinity to water at least similar to that of the poty vinyl alcohol. 4. Process as claimed in claims 1 to 3, in which the water-soluble additive is selected from the group cellulose esters, cellulose ethers, starch esters, starch ethers, potyaikylene glycoi ethers, polyafkylene glycofs, long-chain alkanoles (n>8), sugar esters and sugar ethers. 5. Process as claimed in claim 4, in which polyethylene glycol is used as a water-soluble additive. 6. Process as claimed in claims 1 to 5, in which the water-soluble additive Is used in a concentration of 4-20 wt%, preferably 6-10 wt%. 7. Process as claimed in claims 1 to 6, in which the dehydration of the aqueous solution is carried out until a residual water content of at feast 10 wt% is reached. 8. Process as claimed in claim 7, in which the dehydration of the aqueous solution is carried out until a residual waiter content of 10-30 wt% is reached. 9. Process as claimed in claims 1 to 8, in which the dehydration process is carried out after dripping the solution onto a hard surface. 10. Process as claimed in claims 1 to 9, in which the dehydration process is carried out after pouring the solution into a form. 11. Process as claimed in claim 9 and 10 in which the gel substance is formed with a diameter at feast double its height. 12. Process as claimed in claim 11, in which the gel substance is formed 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. 13. Process as claimed In claims 1 to 8, in which the dehydration process is carried out after pouring the solution to form a long strand. 14. Process as claimed in claims 1 to 13, In which the dehydration process is carried out after pouring the solution onto a base material. 15. Process as claimed in claims 1 to 14, In which the rehydration is carried out in tap water. 16. Process as claimed in claims 1 to 15, in which the rehydration is carried out in a saline solution. 17. Process as claimed in claims 1 to 16, with the addition of a biologically, chemically or physically active material. 18. Process as claimed in claims 16 to 17, in which a culture solution for the biologically active material is used as the saiine solution. 19. Process as claimed in claims 16 and 18 using a saline solution containing polyvalent anions. 20. Process as claimed in claims 1 to 19, characterized in that additives which increase or decrease the specific gravity are added to the solution prior to dehydration. 21. Process as claimed in claims 1 to 20, in which the dehydration process is completely carried out during the time the created rip falls In a drop tower. 22. Mechanically highly stable gel substance of poly vinyl alcohol, produced according to the process as claimed in claims 1 to 19. 23. Gel substance as claimed in claim 22, produced in a lenticular form, in which the diameter is significantly greater than the height. 24. Gel substance as claimed in claims 22 and 23 with a magnetic additive. Process for producing a biocatalyst with a biologically active material, introduced into a get of potyvinyl alcohol, in the form of microorganisms, enzymes, spores and/or cells with the process steps. a) use of an aqueous polyvinyl alcohol solution with a degree of hydrolysis of > 98 mol%. b) dissolving an additive such as herein described to an aqueous poty vinyl alcohol solution having a degree of hydrolysis of >98 mol % and forms a separate, finely distributed and aqueous phase after concentration of the solution selected from the group formed by polyethylene glycol, cellulose esters, cellulose ethers, starch esters, starch ethers, polyafkylene gtycol ethers, polyalkylene grycols, long- chain alkanoles (CnH2n+1OH mit N>8), sugar esters and sugar ethers followed by c) addition of the biologically active material, : d) dehydration of the aqueous solution to a maximum residual water- content of 50-wt% In order to cause the phases to separate and hence the poly vinyl alcohol to get and e) rehydration of the polyvinyl alcohol in an aqueous medium.

Full Text

Process for producing a pplyvinyl alcohol gel and a mechanically highly stable gel produced according'to the process
The invention refers to aprocess for producing a polyvinyl alcohol gel. The invention also refers to a mechanically highly stable gel produced according to the process.
It is well known that solutions containing polyvinyl alcohol (PVA) become more viscous when left to stand. It is also well known that PVA solutions can be converted into a gel if the solution is frozen and subsequently thawed (FR 2 107 711 A). However, gels formed in this manner have a relatively low strength.

It is also known through EP 0 107 055 Bl that the strength ofPVAgels produced by freezing is increased by carrying out the freezing and thawing process at least once, but preferably repeating it two to five times. To this end, a PVA solution with a degree of saponification of > 95 mol %, but preferably of 98 mol %, is used. The upper temperature limit for freezing the solution is -3 degrees Celsius, the cooling rate can be between 0.1 to 50 degrees Celsius per minute, the thawing rate between 0.1 to 50 degrees Celsius per minute. The PVA that is used must have a degree of polymerization of at least 700. The concentration of PVA in the solution should be over 6 wt.% and is preferably between 6 and 25 wt.%. The PVA gel produced by repeated freezing and thawing has a good mechanical strength and a high water content, which is maintained even under mechanical stress. The gel produced in this manner is highly elastic, non-toxic, and can be used in many applications, particularly in medicine.
Various substances and materials can be added to the gel to increase the strength, for instance glycol, glycerine, saccharose, glucose, agar, gelatine, methyl cellulose, etc. The admixture of agents such as heparin permits medical applications in which the active agent is continuously and evenly released from the gel over a period of time. In addition, microorganisms and enzymes can be mixed with the gel in order to create a biologically active system.

2
It is known from US-PS 4 663 358 that adding organiosolvents to the aqueous polyvinyl solution lowers the freezing point of the solution. This prevents the water from freezing at gelling temperatures below -10 degrees Celsius, preferably approximately -20 degrees Celsius, thus forming a more homogeneous and transparent gel. The low gelling temperature is used for creating compact grained gels with sufficient mechanical strength.
Producing PVA gels using the freezing method is complicated and time consuming.
DE 43 27 923 C2 disclosed a process by which PVA gels can be produced without using the freezing process. By using a PVA solution with a degree of hydrolysis of > 99-mol % and adding a dissolved additive that has non-aqueous OH or NH2 groups,_a gelling of the PVA can be achieved at temperatures above 0 degrees Celsius. However, the gelling process takes several hours or may even require an additional storage period of many hours in order to ensure that it is cured sufficiently to provide full strength to the gel substance. Due the nature of this method, it is disadvantageous for producing large amounts of the gel substance.
Therefore, the purpose of the present invention is to be able to produce the PVA gel substances simply and quickly, as well as improving the quality of the gel substance as much as possible in this process.
Based on this objective, the process for producing a polyvinyl alcohol gel includes the following steps:
a) Use of an aqueous polyvinyl alcohol solution with a degree of hydrolysis of > 98 mol
%.
b) The addition 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) Dehydration of the aqueous solution to a maximum residual water content of 50
wt.% in order to cause the phases to separate and hence the polyvinyl alcohol to gel.

d) Rehydration of the polyvinyl alcohol in an aqueous medium..
Surprisingly, the process according to the invention permits the gelling of the polyvinyl alcohol within^e^eTaTminuteJ)at room temperature or even higher temperatures. The addition of the water-soluble additive and concentration by evaporation of the water results in a finely distributed phase separation, whereby gelling happens within a very short period of time during the PVA phase. A prerequisite is that the water-soluble additive creates a hydrous phase , so that within a very short period of time a respective proportion of water is removed through the phase separation of the PVA phase, whereby a gelling of the polyvinyl alcohol is achieved. It is advantageous if the water-soluble additive has an affinity to water at least comparable to that of the PVA.
The PVA phase, which is under-supplied with water during the gelling process; subsequently absorbs water during rehydration, whereby the elasticity and mechanical strength of the PVA gel is improved without reversing the gelling. It has been shown that a certain amount of electrolytes in the aqueous rehydration medium results in a higher stability of the PVA gel, so that the rehydration is advantageously carried out in tap water or, better yet, in a saline solution,
The process according to the invention has the advantage that it permits the production of PVA gel within a very short time without using complicated processes, in particular without a freezing process and without repeated dehydration processes, so that an extremely economical production of PVA gel is possible. The gel substances according to the invention are also characterized by a high elasticity and stability, in particular tensile strength, and in this regard are significantly superior to the PVA gel substances produced in the traditional way.
The stability and elasticity of the PVA gel substances are further enhanced by using a resaponified aqueous PVA solution in the production process./

Polyethylene glycol is a preferred water-soluble additive which is added at a concentration of 4 to 30 wt.%, preferably at 4 to 20 wt.%, and more specifically at 6 to 16 wt.%. - Cellulose esters, cellulose ethers, starch esters, starch ethers, polyalkylene glycol ethers, polyalkylene glycols, long-chain alkanoles (CnH2n+1OH where n > 8), sugar esters and sugar ethers are other examples of possible additives.
A particularly advantageous area of application of the PVA gel substances is their
production as biologically, physically or chemically active substances, i.e. incorporating , biologically, physically or chemically active material in the PVA gel. Thus the PVA gel is superbly suited for the production of chemical or biological catalysts, for instance.
The dehydration of the aqueous solution for the purpose of phase separation and the associated gelling is carried out until a maximum residual water content of 50 wt.% is reached. A lower limit for the residual water content is 10 wt.% because the PVA gel produced should be completely rehydrateable, because the elasticity of the gel substance is lower if the residual water content drops below approximately 10 wt.%, and because any incorporated biological materials can be damaged if the aforementioned residual water content is lower. An advantageous range for the residual water content is between 10 and 30 wt.%.
Dehydration can conveniently be carried out in a short period of time by evaporating water at ambient air temperature if the aqueous solution is divided into small portions, especially portions tn which there is only a small proportion of starch in the solution. In particular, it is advantageous to drip the solution onto a hard surface in such a way that the diameter of the drop is at least twice that of the height of the drop. This can similarly be achieved by pouring the solution into a form and/or coating a base material. A thin, or even film-like shape permits evaporation to the required residual water content within several minutes, for instance within 15 minutes. An acceleration of the dehydration process (and, therefore, the gelling process) can be achieved by carrying out dehydration in a drying oven at a higher temperature.

5

The saline solution used advantageously for rehydration preferably contains polyvalent anions.
The process according to the invention is particularly advantageous for immobilizing biologically active material in that it is extraordinarily gentle on the biological material so that the biological material has a significantly higher initial activity in comparison with other immobilization processes.
This can be enhanced if the aqueous medium in which the PVA gel is rehydrated is also a culture solution for the biologically active material.
The density of the PVA gel produced according to the invention can be modified by using suitable additives. For instance, the specific gravity can be increased by adding titanium oxide and lowered by adding hollow glass microballs.
As already mentioned, gelling according to the invention is possible at room temperature but can also be carried out at lower or higher temperatures. The biologically active material that is incorporated into the PVA gel can be enzymes, microorganisms, spores and cells.
The process according to the invention can be implemented in various embodiments. For instance, it is possible to carry out the dehydration of a drop for phase creation during the falling process in a drop tower, so that when the drop impacts the surface, the gelling has already occurred after the phase separation. This production process is particularly suited for producing PVA gel substances as chromatography material whose diameter is 10 to 100 µm for laboratory purposes, and which can otherwise be between 100 and 800 µm. It is also possible to dehydrate an initial liquid that is set to a higher viscosity during extrusion of a strand and to carry out the gelling simultaneously.
Compared to previously known gel substances, the gel substance produced by the process

6
according to the invention has superior mechanical stability, in particular with regard to abrasion resistance and tensile strength.
These superior mechanical characteristics permit, in particular, to produce the gel substance according to the invention in a lenticular form that is advantageous to the kinetics of the reaction and in which previously known gel substances had insufficient mechanical stability, in particular agitation stability. On the other hand, the gel substance according to the invention is stable and abrasion resistant for many months, even when subject to high-speed agitation. The lenticular form with a large diameter and low height has the effect that the chemically, physically and biologically active material is always arranged near the surface, resulting in a constellation that is advantageous for the kinetics of the reaction.
T'he present invention permits the addition of a magnetic additive to the polyvinyl alcohol substance by a very simple method in order to collect the gel substance out of a liquid by means of magnets?)
It has been shown that the pore structure of the polyvinyl alcohol gel substance can be controlled by the molecular weight of the additive that effects the phase separation. By varying the molecular weight of the added polyethylene glycol, whose molecular weight is preferably in the range of 800 and 1350, the pore size of the polyvinyl alcohol gel substance can be adjusted to between 1 and 15 µm.
Regarding the production of the aqueous solution of polyvinyl alcohol and the additive, it
has been shown that the use of distilled water requires a higher degree of dehydration in
order to achieve the same mechanical characteristics. The results are immediately better if
normal tap water with a certain degree of hardness is used. Therefore, it can be assumed
that a certain salt content in the water is advantageous for the process according to the
invention.

The invention is explained in more detail below by means of examples of embodiments.
Example1:
15.8 or16.8 g of Water are added to 2 g of PVA and 1.2 g of polyethylene glycol (PEG 1000).
The solution is heated to 90 degrees Celsius until all the components have dissolved
completely, so that a viscous, colourless solution is obtained. After cooling to 30 degrees
Celsius, the polymer solution is dripped onto a polypropylene plate by means of a syringe
and application of pressure. The dripping is carried out by touching the cannula onto the
PP plate at a rate of approx. l-2/second; the drop has a diameter ofapprox. 3 mm and a
height of approx. 1 mm. After application of the drops, a white, wax-like film forms on
the surface of the drops. After 89 wt.% of the water has evaporated at room temperature,
the gel substances are rehydrated in water or a saline medium. The gel substances obtained
have a diameter of 3-4 mm and a height of approx. 200-400 µm.

¦ Example 2:
After the polymer suspension (composition: 2 g PVA, 1.2 g PEG 1000 and 15.8or16.8g water) has cooled, 1 ml of a nitrogen-fixing mixed culture (Nitrosomonas europaea and Nitrobacter winogradsky) is added to 20 g of a polymer solution and dispersed, resulting in a dry biomass load of 0.06 wt.%. The production of the gel substances is carried out according to Example 1. The gel substances obtained are rehydrated in a standard mineral salt medium for nitrogen-fixers. Compared to the same amount of free nitrogen fixers, after immobilization the immobilizates produced in this way have an initial activity of approx. 70% for Nitrosomonas spp. and 100% for Nitrobacter spp.
After occlusion of the nitrogen fixers in the PVA kyrogels at -20 degrees Celsius, the initial activity of Nitrosomonas spp. is approx. 1%, at -10 degrees Celsius approx. 25% with decreasing stability of the PVA hydrogels.
The incubation of the immobilizates is carried out in the same medium at 30 degrees Celsius. After 19 days a maximum ammonium decomposition rate of between 7 and 8

8
umol NH4+ (gcat x min) is achieved if 10 mg of gel substance is incubated in 30 ml of standard mineral salt medium.
Example 3:
1.6 g of polyethylene glycol (PEG 1000) is dissolved in 12.8 g H2O, followed by 1.6 g of PVA. The process is continued according to Example 1. After the polymer solution has cooled to 30 degrees Celsius, 4 ml of a culture of the strictly anaerobic bacteria Clostridium butyricum NRRL B-1024, which converts glycerine into 1.3-propame diol (PD), grown overnight in an oxygen-free atmosphere is dispersed in the solution (cell load of the polymer solution: 6 x 107 per ml). The gel substances are produced according to Example 1. After 70 wt.% of the water has evaporated at .room temperature, the immobilizates are rehydrated in a mineral salt medium (20 times more than required). The incubation of the cell-loaded gel substance is carried out in the same medium (40 times more than required) at 30 degrees Celsius. The medium is changed several times during the growing phase in order to provide the immobilized biomass with an adequate nutrient supply.
If 0.25 g of the immobilized bio-catalyst thus obtained are placed in 40 ml of mineral salt
medium together with 24.4 g L-l glycerine, within 3.25 h the concentration of 1.3-PD
increases by 2.8 g L-l. This corresponds to a catalyst activity of 0.14 g 1 3-PD per g cat
per hour. After deducting the activity of fully developed cells, the result is a catalyst
activity of 0.08 g 1.3-PD (gcat x h). ,
Example 4:
15.8 g of water is added to 2g PVAL and 1.2 g polyethylene glycol (PEG 1000) and the process is continued according to Example 1.
After cooling the polymer suspension to approx. 30-37 degrees Celsius, 1 ml of a defined spore suspension of the fungus Aspergillus terreus is added to a polymer solution of 20 g and dispersed. The spore suspension is selected so that 5 d of fouling in the growth

9
medium results in a dry biomass load of 0.05 wt.%.
After 70 wt.% of the water has evaporated at room temperature, the immobilizates are rehydrated in a mineral salt medium for Aspergilius terreus (20 times more than required).
The incubation of the immobilizates is carried out in the growing medium. The growing medium is replaced with production medium for producing the itaconic acid.
Co'mpared to the same amount of free fungus cells!, the immobilizates thus produced have an initial activity of approx. 60% directly after immobilization. If 0.2 g of gel substance is incubated in 100 ml of production medium together with 60 g/1 glucose, a productivity of 35 mg of itaconic acid (gcatx h) is achieved after 7 d.
Example 5:
Larger amounts of gel substances are obtained by dripping the polymer solution (composition according to Example 1) through a system of multiple nozzles onto a conveyer belt. According to the principle of a belt dryer, the PVA drops are dehydrated in a tunnel drier to a defined residual moisture content and subsequently collected in a collection container by means of a scraper, where they are rehydrated and washed.
Example 6:
In the production process according to Example 1, the polymer solution is not dripped, but poured into prefabricated semi-open forms of optional length with an interior diameter of 1-10 mm.
After rehydration in water, the strands can be stretched to 3-4 times their length without breaking. This stretching is irreversible. A strand produced in this way can be loaded with . a weight of 500 g without breaking.
Example 7:

-10-
After a shortage period of 14 days, the strands produced according to Example 6 are mechanically characterized in tap water. At that time, the strands are approximately 8 mm wide and approximately 1 mm high. The degree of rehydration takes into account the strand's loss of weight after rehy drat ion and 14 d storage in water in relation to the total mass of the polymer solution prior to the dehydration process. The strands have an elastic behaviour up to an elongation at tear of 40%.
Mechanical characterization of the produced strands with various degrees of dehydration for the composition 10 wt% PVA and 6 wt% PEG 1000.
Residual water Degree of Elongation at tear E-modulus
content after rehydration % [N/mm2]
dehydration [%]

Mechanical characterization of the strands at a degree of dehydration of 80 wt% for the composition 10 wt% PVA and 8 wt% PEG for various types of PEG.

-11-
Type of PEG Degree of Elongation at tear E-modulus
Rehydration [%] [N/mm2]

Mechanical characteristics of the PVA hydrogel strands for various concentrations of PVA with the add if ion of 6 wt% PEG 1000 at a degree of dehydration (amount of water evaporated during the dehydration process) of 80 wt%.
PVAL Elongation at tear E-modulus

Mechanical characteristics of the strands at a degree of dehydration of 80 wt% for the composition 10 wt% PVA and 6 wf% PEG 1000 for various rehydration media.

-12-
Example 8:
Gel substances are produced according to Example 1 and rehydrated In de Ionized water (5 µSH2O). The degree If rehydration for various degrees of dehydration of the gel substances is defined directly after the rehydration process. With a degree of rehydration of 100 wt%, the weight of the gel substances prior to the dehydration process and after the rehydration process is the same, as shown in the attached drawing.

WE CLAIM:
1. Process for producing a biocatafyst with a biologically active material,
introduced into a gel of polyvinyl alcohol, in the form of microorganisms,
enzymes, spores and/or cells with the process steps.
a) use of an aqueous; polivinyl alcohol solution with a degree of
hydrolysis of > 98 mol %.
b) dissolving an additive such as herein described to an aqueous
poty vinyl alcohol solution having a degree of hydrolysis of >98 mol %
and forms a separate, finely distributed and aqueous phase after
concentration of the solution selected from the group formed by
polyethylene glycot, cellulose esters, cellulose ethers, starch esters,
starch ethers, polyalkylene glycol ethers, polyalkylene glycols, long-
chain alkanoles (CnH2n+OH mit N>8), sugar esters and sugar ethers
followed by
c) addition of the biologically active material,
d) dehydration of the aqueous solution to a maximum residual water
content of 50-wt% in order to cause the phases to separate and hence
the poty vinyl alcohol to get and
e) rehydrat ion of the poty vinyl alcohol in an aqueous medium.

2. Process as claimed fn claim 1, in which the poly vinyl alcohol solution has
a concentration of 4-30 wt%, preferably 6-16 wt%.
3. Process as claimed fn claims 1 and 2, in which a water-soluble additive is
used which has an affinity to water at least similar to that of the poty vinyl
alcohol.

4. Process as claimed in claims 1 to 3, in which the water-soluble additive is
selected from the group cellulose esters, cellulose ethers, starch esters,
starch ethers, potyaikylene glycoi ethers, polyafkylene glycofs, long-chain
alkanoles (n>8), sugar esters and sugar ethers.
5. Process as claimed in claim 4, in which polyethylene glycol is used as a
water-soluble additive.
6. Process as claimed in claims 1 to 5, in which the water-soluble additive Is
used in a concentration of 4-20 wt%, preferably 6-10 wt%.
7. Process as claimed in claims 1 to 6, in which the dehydration of the
aqueous solution is carried out until a residual water content of at feast 10
wt% is reached.
8. Process as claimed in claim 7, in which the dehydration of the aqueous
solution is carried out until a residual waiter content of 10-30 wt% is
reached.
9. Process as claimed in claims 1 to 8, in which the dehydration process is
carried out after dripping the solution onto a hard surface.
10. Process as claimed in claims 1 to 9, in which the dehydration process is
carried out after pouring the solution into a form.
11. Process as claimed in claim 9 and 10 in which the gel substance is formed
with a diameter at feast double its height.

12. Process as claimed in claim 11, in which the gel substance is formed 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.
13. Process as claimed In claims 1 to 8, in which the dehydration process is
carried out after pouring the solution to form a long strand.
14. Process as claimed in claims 1 to 13, In which the dehydration process is
carried out after pouring the solution onto a base material.
15. Process as claimed in claims 1 to 14, In which the rehydration is carried
out in tap water.
16. Process as claimed in claims 1 to 15, in which the rehydration is carried
out in a saline solution.
17. Process as claimed in claims 1 to 16, with the addition of a biologically,
chemically or physically active material.
18. Process as claimed in claims 16 to 17, in which a culture solution for the
biologically active material is used as the saiine solution.
19. Process as claimed in claims 16 and 18 using a saline solution containing
polyvalent anions.
20. Process as claimed in claims 1 to 19, characterized in that additives which
increase or decrease the specific gravity are added to the solution prior to
dehydration.

21. Process as claimed in claims 1 to 20, in which the dehydration process is
completely carried out during the time the created rip falls In a drop tower.
22. Mechanically highly stable gel substance of poly vinyl alcohol, produced
according to the process as claimed in claims 1 to 19.
23. Gel substance as claimed in claim 22, produced in a lenticular form, in
which the diameter is significantly greater than the height.
24. Gel substance as claimed in claims 22 and 23 with a magnetic additive.
Process for producing a biocatalyst with a biologically active material, introduced into a get of potyvinyl alcohol, in the form of microorganisms, enzymes, spores and/or cells with the process steps.
a) use of an aqueous polyvinyl alcohol solution with a degree of
hydrolysis of > 98 mol%.
b) dissolving an additive such as herein described to an aqueous
poty vinyl alcohol solution having a degree of hydrolysis of >98 mol %
and forms a separate, finely distributed and aqueous phase after
concentration of the solution selected from the group formed by
polyethylene glycol, cellulose esters, cellulose ethers, starch esters,
starch ethers, polyafkylene gtycol ethers, polyalkylene grycols, long-
chain alkanoles (CnH2n+1OH mit N>8), sugar esters and sugar ethers
followed by
c) addition of the biologically active material, :
d) dehydration of the aqueous solution to a maximum residual water-
content of 50-wt% In order to cause the phases to separate and hence
the poly vinyl alcohol to get and
e) rehydration of the polyvinyl alcohol in an aqueous medium.

Documents:

« Previous Patent

Next Patent »

Patent Number

207364

Indian Patent Application Number

IN/PCT/2000/00634/KOL

PG Journal Number

23/2007

Publication Date

08-Jun-2007

Grant Date

07-Jun-2007

Date of Filing

14-Dec-2000

Name of Patentee

DR. KLAUS-DIETER VORLOP

Applicant Address

HOCHSTRASSE 7 D-38102 BRAUNSCHWEIG

Inventors:

#	Inventor's Name	Inventor's Address
1	DR. KLAUS-DIETER VORLOP	HOCHSTRASSE 7 D-38102 BRAUNSCHWEIG

PCT International Classification Number

CO8T3/075,CO8L29/04,

PCT International Application Number

PCT/DE99/00975

PCT International Filing date

1999-03-30

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	19827552.8	1998-06-20	Germany