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• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
  • C08L23/06—Polyethylene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
  • C08L23/08—Copolymers of ethene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/10—Homopolymers or copolymers of propene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L29/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal or ketal radical; Compositions of hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Compositions of derivatives of such polymers
  • C08L29/02—Homopolymers or copolymers of unsaturated alcohols
  • C08L29/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L101/00—Compositions of unspecified macromolecular compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2205/00—Polymer mixtures characterised by other features
  • C08L2205/02—Polymer mixtures characterised by other features containing two or more polymers of the same C08L -group
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L91/00—Compositions of oils, fats or waxes; Compositions of derivatives thereof
  • C08L91/06—Waxes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L91/00—Compositions of oils, fats or waxes; Compositions of derivatives thereof
  • C08L91/06—Waxes
  • C08L91/08—Mineral waxes

Definitions

• the present invention relates to polyvinyl alcohol gels, in particular hydrogels, which are produced by means of new processes and recipes and have a property profile which can be set in a wide range, e.g. outstanding mechanical properties.
• Hydrogels based on PVA can be produced with the consistency of biological tissue and cartilage and have an outstanding stability and biocompatibility in the living organism, which is due on the one hand to the high water content of these gels and on the other hand to the macromolecule itself, which the organism as a result of the numerous hydroxyls Groups similar to water, to put it succinctly, "are perceived as polymerized long-chain water”. Therefore PVA gels (PVAG) are predestined for applications in the living organism, especially PVAG which are manufactured without chemical cross-linking, without radiation cross-linking and without the aid of problematic chemicals.
• the mechanical properties are continuously improved, e.g. after 10 cycles.
• the strength sm is in the range of 1 Pa and the modulus of elasticity is in the range of 0.1 MPa.
• the mechanical properties are only slightly improved.
• Such PVAG are widely described in the prior art, e.g. by F. Yokoyama et al in Colloid & Polymer Science (1986), 264, pages 595-601.
• EP 0107055 artificial organs or membrandes for medical use
• dermal gels in EP 0095892 wound-covering materials
• EP 0070986 gel for use as cooling-medium
• Isolation gel for low temperatures in JP 57190072 as a phantom for NMR diagnosis in GB 2209401 (phantoms for NMR diagnosis), or as a golf ball filling in GB 2182571 (golf ball cores).
• the PVA solution is produced by means of mixtures of water and organic solvents, in particular DMSO, and then frozen at -20 ° C.
• the gel obtained is then stored in water in order to largely extract the DMSO, dried in the atmosphere and then dried under vacuum in order to extract the rest of the DMSO.
• PVAG After swelling of the samples in water, PVAG were obtained which showed a transparency of up to 99% and a strength of up to 5.6MPa.
• Such transparent PVAGs have been proposed for biomedical applications and for the food industry.
• Mowiol 66-100 one of the highest molecular commercially available PVAs with a degree of hydrolysis DH of 99.4mol% and a degree of polymerization DP of around 4,500, already has a maximum processable viscosity of 1000 mPas at 80 at a concentration Cp of 10% at room temperature ° C the limiting concentration Cp is around 15%. With higher molecular weight PVA, the limiting concentration is even lower. This is a major disadvantage of the previous methods. Another disadvantage is the long period of time that the previous methods require, a single freeze / thaw cycle, for example. takes at least 24h, dehydration by lyophilization at 10h, removal of organic solvents takes days.
• the present invention describes new possibilities with regard to the type of PVA used and new processes, by means of which these goals can be achieved and polyvinyl alcohol gels with customized properties can be obtained for various applications.
• the invention comprises measures regarding the type of PVA used and the method, both measures being able to be used individually or in combination:
• a first preferably fully hydrolyzed PVA1 with high DP is used, on the other hand, in combination with such PVA1, a preferably fully hydrolyzed PVA2 with medium and in particular low DP in the range of about 1000-50 is used.
• a preferably fully hydrolyzed PVA2 with medium and in particular low DP in the range of about 1000-50 is used.
• thermoplastic processes are used, a PVA melt being produced instead of the PVA solution and having viscosities far above 1000 mPas. This means that even the highest molecular weight PVA can be brought into the amorphous state at concentrations Cp »15%, which enables gel formation. Shaping is then no longer possible using conventional casting technology, but shaped bodies can be obtained analogously to the methods used in the processing of thermoplastics, for example. by pressure and injection molding or extrusion and pressing processes.
• the degree of swelling is essentially determined by the network density set and can also be defined, in particular minimized, by its parameters.
• the temperature of the gel formation and in particular the use of PVA2 play an important role here, which makes the combination of the two measures described here for the production of new polyvinyl alcohol gels particularly important.
• Another advantage of using short-chain PVA2 is that not only the viscosity of solutions at low Cp, but also the viscosity of melts at high Cp can be massively reduced, which means that the temperature during plasticization is controlled when using thermoplastic processes , in particular can be kept low and thus also melts with a very high Cp can be processed.
• the parameters which relate to the regularity of the PVA such as degrees of hydrolysis DH, content G of 1, 2-glycol, tacticity, and proportion of short-chain branches
• the parameters of the molecular weight distribution such as DPn, DPw
• the parameters for the topology of the macromolecules such as degrees of branching of long chains and the length of these long or side chains.
• the degree of hydrolysis DH in mol% is> 95, preferably> 98, more preferably> 99, most preferably> 99.8.
• the content G of 1,2-glycol in mol% is ⁇ 3, preferably ⁇ 1, more preferably ⁇ 0.5, most preferably ⁇ 0.2.
• the number of short chain branches per monomer unit is ⁇ 10 "2 , preferably ⁇ 10 " 3 , more preferably ⁇ 10 "4 , most preferably ⁇ 10 " 6 .
• tacticity In terms of tacticity, an atactic conformation is preferred over an isotactic one; the most preferred is a syndiotactic conformation. the highest possible proportion of syndiotactic diads.
• the tacticity of PVA is determined by the type of monomers, with which the precursor polymer, from which the PVA is obtained, is polymerized, and also by the reaction conditions in this polymerization, the syndiotactic component increasing with decreasing temperature during the polymerization.
• Monomers are therefore preferred for the polymerization of the precursor polymer, such as vinyl acetate, vinyl chloroacetate, vinyl dichloroacetate, vinyl bromoacetate, in particular vinyl trifluoroacetate.
• the precursor polymer is produced from aliphatic vinyl acid esters, high proportions of syndiotatic diads are also obtained, while the resulting PVA also have very low 1,2-glycol contents.
• Examples are vinyl format, vinyl propionate, vinyl butyrate, vinyl pivalate. Very high molecular weights can also be achieved using vinyl pivalate.
• Fully hydrolyzed PVA obtained from polyvinyl acetate are soluble in water even at high degrees of crystallization at 100 ° C, while fully hydrolyzed PVA whose precursor polymer was produced from vinyl acetate derivatives with voluminous group R (e.g. vinyl trifluoroacetate) or from aliphatic vinyl acid esters (e.g. vinyl chromate, vinyl pivalate) due to the low 1 , 2-Glycol content and the high proportion of syndiotactic diads can be obtained even at 100 ° C in insoluble form. This shows the importance of these parameters for the crystallizability and the stability of the crystallites. Such PVA are therefore particularly suitable for the present invention.
• voluminous group R e.g. vinyl trifluoroacetate
• aliphatic vinyl acid esters e.g. vinyl chromate, vinyl pivalate
• the crystallites can slide easily against each other and hardly any strength is obtained.
• this friable consistency increases.
• a prerequisite for effective connections is that at least two segments of a macromolecule are incorporated in at least two crystallites.
• the number of crystallites, in which different segments of a PVA macromolecule are involved increases and mechanically more stable and increasingly elastic networks are obtained, which is why high DPs are advantageous in previous PVAGs.
• the fact that only crumbly and brittle PVAG are obtained at low DP may have been one reason why previously low DP was not considered for PVAG.
• PVA1 and PVA3 PVA with DP> 1000, preferably> 2000, more preferably> 3000, most preferably> 5000 are used for the present invention.
• the upper limit is given by the state of the art for the production of high molecular weight PVA, PVA with DP up to about 180,000 can currently be produced.
• PVA2 PVA with comparatively low DP are used, on the one hand to reduce the viscosity of the solutions and melts, on the other hand to maintain high crystallization rates and degrees of crystallinity, as well as high network densities.
• PVA2 is used for the present invention with DP in the range of about 50-1000, preferably 60-500, more preferably 70-300, most preferably 75-200.
• the lower limit is given by the stability of the crystallites formed by PVA2 (segments of PVA1 and PVA3 being incorporated by heterocrystallization).
• the lamellar thickness of these crystallites is directly proportional to the DP at low DP and the stability towards temperature and solvent (water) increases with the lamellar thickness.
• the optimal DP range in this regard is around 75 -
• PVA2 is preferred, more preferably ⁇ 3, most preferably ⁇ 2.
• PVA3 type PVA are currently not commercially available.
• PVA obtained from polyvinyl benzoate that long chain branches can be obtained under suitable reaction conditions in the polymerization of vinyl benzoate.
• Another possibility for the production of PVA3 can be carried out by grafting PVA of type PVA2 onto PVA of type PVA1, the number and length of the side chains being adjustable.
• the proportion of PVA2 based on PVA in% by weight is in the range 1-95, preferably 2-90, most preferably 3-85.
• a high proportion of PVA2 is particularly advantageous for setting high moduli of elasticity, although surprisingly still very much high strains can be obtained.
• the proportion of PAV3, based on PVA, in% by weight is in the range 1-80, preferably 2-60, most preferably 3-50.
• the proportion of PVA based on PVA and swelling agent in% by weight is in the range 5-90, preferably 7-95, most preferably 10-80.
• thermoplastic processes are used when the viscosity becomes too high for the production of solutions and the pouring of these solutions. Another advantage of thermoplastic processes is that homogeneous mixtures of PVA and swelling agent can be produced much more quickly than by solution processes, which usually also requires the use of autoclaves.
• thermoplastic processes also enable a continuous production of PVA-swelling agent mixtures and can in principle be processed in any large quantities, while the solution processes, which are carried out as a batch process, typically work in the 100 g range.
• gelation can also take place without a freeze / thaw process, for example. by storing the mixture at a temperature above the freezing point of the mixture.
• the optimum storage temperature increases with Cp, but it also depends on the proportion of PVA2 and the structural parameters of the PVA.
• the mechanical properties that can be achieved by the freeze / thaw process or without the freeze / thaw process are roughly comparable. Storage is, however, compared to free ze / thaw procedure much easier. The mechanical properties increase significantly with increasing concentration Cp.
• concentrations Cp> 40% better mechanical properties are obtained by storage compared to freeze / thaw processes, at concentrations> 50%, heat treatments are increasingly advantageous.
• concentration Cp of BSW. 60% can start to gel, especially when using a significant amount of PVA2 at temperatures around 100 ° C.
• the PVA swelling agent mixtures can be slowly dried to an equilibrium water content in atmospheres with adjusted water activity, with a heat treatment optionally then being carried out at temperatures of, for example, 100-180 ° C. after the gel formation has taken place at least partially, the gel can swell and in it Condition to undergo a freeze / thaw process.
• Crosslinking by high-energy radiation is also possible after partial to complete gel formation.
• thermoplastic methods can alternatively or additionally also be used in the concentration range Cp, which could be made accessible through the use of thermoplastic methods, and on PVA swelling agents, mixtures which have a proportion of PVA2 and / or PVA3.
• Previous PVAGs are typically opaque, in order to obtain transparency, organic solvents are used, which then have to be completely removed from the gel.
• thermoplastic processes at Cp greater than about 30%, completely transparent PVAG could also be obtained, this transparency also being able to be obtained after swelling, both in PVAG with and without a proportion of PVA2.
• swelling agents Swelling agents in the narrower sense and solvents are referred to here as swelling agents.
• the most important swelling agent is water and water is used in most cases as the sole swelling agent, or in mixtures with other swelling agents, but in addition the solvents and swelling agents and mixtures thereof described in the prior art are possible, such as, for example. DMSO, dimethylformamide, acetamide or polyols such as, for example.
• Glycerin erythritol, xylitol, sorbitol, mannitol, galactitol, tagatose, lactitol, maltitol, maltulose, isomalt, methylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, pentanediol, hexanetriol.
• the swelling agent can also have a proportion of salt (physiological salt solution).
• the PVAG can contain other polymers for modification of the properties and for specific applications, e.g. synthetic polymers such as Polycarbonates, polyacrylates and polymethacrylates, polyethylene glycols, polyethylene oxides, Polyvinylpyrrolidones, polycaprolactones or polymers of natural origin such as, for example. Hydrocolloids and polysaccharides, especially starch and starch derivatives.
• synthetic polymers such as Polycarbonates, polyacrylates and polymethacrylates, polyethylene glycols, polyethylene oxides, Polyvinylpyrrolidones, polycaprolactones or polymers of natural origin such as, for example. Hydrocolloids and polysaccharides, especially starch and starch derivatives.
• Additives are simple fillers and functional fillers or active ingredients such as, for example.
• Clay minerals for PVAG which are used as cooling medium, or antimicrobial substances for PVAG, which are used as wound dressings, or medicinal substances for PVAG, which are used as delivery systems of these medicinal products, or the like. in the form of dermal gels, pills or tablets.
• additives reference is also made to the state of the art for PVAG.
• PVAGs according to the invention can replace previous PVAGs in all their applications, such a replacement being advantageous on account of the simplified production processes and the improved mechanical properties.
• Typical applications of PVAG are in the field of biomedicine, or in the area of tissue and scaffold engineering and in orthopedics, etc.
• PVAG as artificial organs and membranes, as heart valves, vessels, urethral, tendons, cartilage, meniscus or intervertebral discs, furthermore PVAG can advantageously be used as dermal gels, e.g.
• the PVAG according to the invention was produced using a Brabender kneader, PVA in the form of granules, together with water at speeds of 80-120 rpm and mass temperatures of 95-105 ° C., being plasticized for 3-7 minutes, thus obtaining a thermoplastic melt.
• PVA1 was first at least partially plasticized and only then was the short-chain PVA2 added. If PVA1 and PVA2 were plasticized together with high proportions of PVA2, the PVA2 quickly formed a melt of comparatively low viscosity, which made the application of significant shear forces to the PVA1 impossible and the plasticization of the PVA1 took a very long time or was completely impossible.
• the melt obtained was then pressed in a plate press into films 0.5 mm thick. With water contents W> 50%, the pressing temperature was 120 ° C, with lower water contents 140 ° C. After a 5-minute pressing time, the press was cooled with maximum cooling devices. The films were then wrapped using Saran film to keep the water content constant. These films, protected from the atmosphere, were stored at room temperature and / or subjected to freeze / thaw treatments. In the freeze / thaw process, the films were cooled at a rate of around 0.2 ° C to -20 ° C, stored at this temperature for 12 hours and then thawed again at 0.2 ° C and, if necessary, frozen again. The water content of the films was determined by weighing the drying loss over phosphorus pentoxide for 24 hours.
• the mechanical properties were carried out with an Instron Tensile Tester, the samples were punched out of the films and had a sample length of 13 mm and a width of 2 mm. The stretching rate was 10 cm / min. The measured values obtained are mean values of at least 5 individual tensile tests. As a control, the water content of the samples examined was determined after the tensile test.
• the associated stress-strain curve represents the mechanical properties which, according to the prior art, can be obtained from a solution and subsequent freeze / thaw cycles.
• the tension increases continuously in the tensile test, the slope of the curve also increasing and the second derivative of the curve being positive in the entire range of elongation, ie there is a positive curvature of the curve.
• the highly viscous PVA-water mixture was then subjected to 5 freeze / thaw cycles. An increased modulus of elasticity of 0.5MPa and an increased strength of 5MPa were measured, whereby the curvature of the curve is again positive in the entire stretch range.
• the mechanical properties of PV22-F5 are characteristic of PVAG, which can be obtained from the solution with subsequent freeze / thaw cycles if additional processes are subsequently used, such as. partial freeze drying or drying at low relative humidity.
• PV22-F5 represents the maximum of mechanical properties that is currently feasible according to the prior art by means of a combination of methods.
• such a property profile was obtained solely by using freeze / thaw cycles, in which a high concentration Cp could be processed using a thermoplastic process.
• the water content was further reduced to 41%, whereby again without freeze / thaw cycles, simply by storing at RT, a PVAG with an elastic modulus of 5MPa and a strength of 20MPa with an elongation at break of more than 600% was obtained has been.
• the negative curvature after an initially high slope of the curve has become even clearer with this PVAG, i.e. the PVAG can absorb a high tension even at a comparatively low elongation, which means that, compared to PVAG according to the state of the art, new application possibilities can be realized.
• the PVAG PV25-7 can already absorb a tension of 2MPa with a strain in the range of 50%, while the PVAG PV21-F5 only reaches this tension with a strain of 500%.
• PV17-4d and PV30-6d where a proportion of PVA2 is based on PVA of 20 or 40% was used.
• PVAGs were also produced using a thermoplastic process and without the use of freeze / thaw cycles, with the highly viscous PVA-water mixture being annealed at 70 ° C for PV17-4d and then stored at RT for 4 days, while the annealing was carried out for PV30-6d was carried out at 110 ° C. and the PVAG was then stored at RT for 6 days.
• PVAG PV30-6d can already absorb a high voltage under tensile loads at low strains. With compression, such high tension is achieved with even less deformation. PV30-6d thus fulfills the requirements with regard to the mechanical properties, which are required for use as a spinal disc replacement.
• FIG. 2 shows the course of the moduli of elasticity of PVAG after 3 (F3) and 5 (F5) freeze / thaw cycles as a function of the water content W of the PVA-water mixture for various PVA and PVA mixtures.
• PVAG with 87% water content, which was produced from a solution
• all other PVAGs were produced using thermoplastic processes. Solutions based on the polyvinyl alcohols PVA1-A and PVA1-B, both of which have a degree of polymerization DP of around 4500, reach about 15% at 80 ° C, i.e. at Cp.
• the curve for PVA1-B, F3 is lower compared to PVA1-A, F3 in the entire water content range, which is due to the fact that the degree of hydrolysis of 98.5 mol% is reduced compared to 99.4 mol% of PVA1-A, which makes these macromolecules crystallizable is reduced (irregularities in the polymer chain).
• FIG. 3 shows the strength sm of the PVAG as a function of the water content W for the various PVAG.
• the influence of a share of 15% PVA2 is almost neutral, ie by replacing a share of 15% in PVA1-B, F3 with PVA2, there is hardly any influence on the strength.
• the viscosity of the melt was significantly reduced as a result of the proportion of PVA2, thus making it easier to process, which is particularly important at low water temperatures.
• the strength sm is of subordinate importance, since the PVAG undergo significant irreversible deformations at elongations of around> 50%. Such irreversible deformations are undesirable when PVAG is used in practice and the stress must not exceed the reversible range.
• the moduli of elasticity of PVAG are plotted as a function of the water content W by means of a thermoplastic process.
• the PVAGs were stored at RT for 7 or 6 days after molding, i.e. the PVAG were obtained without the use of freeze / thaw cycles. It becomes clear that especially in the range W ⁇ 60% PVAG can be obtained by simple storage at RT even without the use of freeze / thaw cycles. Based on PVA1-A with the higher degree of hydrolysis, the PVAG have the highest moduli of elasticity.
• PVAG based on PVA1-B containing a share of 15% of short-chain PVA show slightly higher moduli in the range 50% ⁇ W ⁇ 60% than the PVAG based on PVA1-B, whereby with decreasing W the values of PVAG are increasingly based can be achieved on PVA1-A.
• the situation is analogous to the PVAG, which were obtained using the freeze / thaw method (FIG. 2).
• PVAG containing a proportion of PVA2 results in higher moduli of elasticity and that even the moduli of elasticity of PVAG can be achieved which are based on more hydrolysed PVA.
• the elongation at break eb of PVAG with a developed network depends only to a small extent on the recipe, the manufacturing parameters and the storage time or the number of freeze / thaw cycles.
• FIG. 7 shows the degree of swelling Q for various PVAG obtained after 3 freeze / thaw cycles as a function of the water content of the PVAG.
• the influence of the degree of hydrolysis is representative of the other parameters such as 1,2-glycol content and tacticity, which strongly influence the crystallizability.
• the degree of swelling increases with the 1,2-glycol content and the degree of swelling decreases with increasing syndiotactic content. In order to obtain minimal degrees of swelling, these material parameters must therefore be optimized.
• FIG. 8 shows the development of the elastic moduli as a function of the storage time at RT from PVAG with different proportions of PVA2.
• the PVAG were produced using a thermoplastic process with a water content of 31% and annealed at 110 ° C. It is clearly expressed that the moduli of elasticity increase with the proportion of PVA2, which is due to the good crystallizability of the short-chain PVA2. The measured value in particular at 97% PVA2 shows this very clearly.
• the elongations at break eb of the PVAG were surprisingly not significantly dependent on the share of PVA2 even with a share of 60% PVA2 and were almost 600% in all PVAGs with the exception of the PVAG with 97% share in PVA2, where despite the very high share still around 100% was achieved.
• the strengths sm showed up to 40% PVA2 also no clear dependence on the proportion of PVA2 and were slightly more than 20MPa with 6 days storage time, while a reduction to 14MPa was found in 60% proportion of PVA2.
• the degrees of swelling Q after 1d storage time showed a clear dependence on the proportion of PVA2, for the proportions of 0, 30, 40, 60 and 97% they were 1.7, 1.4, 1.3, 1.2 and 1.05.
• thermoplastic melt consisting of PVA1 and PVA2-B and 31% water was found that the gel formation already at temperatures> 100 ° C, so the heat treatment was carried out at 110 C C. Obviously, however, there is also a further networking as a function of time at RT.
• PVA1 and PVA2 with higher degrees of hydrolysis, reduced 1,2-glycol content and a high syndiotactic content, the kinetics of network formation are accelerated and even lower degrees of swelling can be obtained.
• the following example compares the development of the mechanical properties during storage at RT and during freeze / thaw treatment.
• the PVAG was at 70 ° C. heat-treated and then stored at RT, or subjected to freeze / thaw cycles.
• the mechanical properties are listed in Table 2:

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  • 2004-04-15 BR BRPI0408932-4A patent/BRPI0408932A/pt not_active IP Right Cessation
  • 2004-04-15 WO PCT/CH2004/000230 patent/WO2004092280A1/de not_active Ceased

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