Method and Device for Cleaning an Absorptive Polyester

Abstract

In a method for cleaning an absorptive polyester, the polymer is dissolved in a first solvent ( 12 ) and subsequently the polymer solution is brought into tight contact with a second solvent ( 41 ) in a turbulent shear field under the influence of strong shear forces. Here, the second solvent ( 41 ) represents a non-solvent for the absorptive polyester and is mixable with the first solvent ( 12 ) to an unlimited extent. Subsequently, the polymer suspension resulting from the addition of the second solvent ( 41 ) is conveyed onto or into a rotating, cylindrical screen body ( 71 ) of a drum shear screen ( 70 ) and then the moist polymer mass is removed from the screen body ( 71 ) and subsequently dried. The method is suitable for the production of absorptive polyester with a high degree of quality and may be performed in a cost-effective fashion on an industrial scale as well.

1 . A process for purifying a resorbable polyester comprising the steps of:
 (a) dissolving the resorbable polyester in a first solvent ( 12 ) to form a polymer solution, wherein the first solvent ( 12 ) is a genuine solvent;   (b) intimately contacting the polymer solution with a second solvent ( 41 ) under action of high shear forces in a turbulent shear field to form a polymer suspension, wherein the second solvent ( 41 ) is a non-solvent for the resorbable polyester and is unlimitedly miscible with the first solvent ( 12 );   (c) conveying the polymer suspension onto or into a rotating, cylindrical screen body ( 71 ) of a drum shear screen ( 70 ) to form a moist polymer mass;   (d) separating the moist polymer mass from the screen body ( 71 ); and   (e) drying the polymer mass.   
   
   
       2 . The process according to  claim 1 , wherein the first solvent ( 12 ) is acetone, ethyl acetate, 1,4-dioxane, dimethylacetamide, tetrahydrofuran, toluene, dimethylformamide, dimethylsulphoxide, hexafluoroisopropanol or another halogenated hydrocarbon or a mixture of the aforementioned solvents. 
   
   
       3 . The process according to  claim 2 , wherein the first solvent ( 12 ) is acetone, chloroform or dichloromethane. 
   
   
       4 . The process according to any one of  claims 1  to  3 , wherein the second solvent ( 41 ) is ethanol, methanol or water or a mixture of the aforementioned solvents. 
   
   
       5 . The process according to  claim 1 , wherein the resorbable polyester dissolved in the first solvent ( 12 ) is further filtered and subsequently mixed with the second solvent ( 41 ) via a two-fluid nozzle ( 40 ). 
   
   
       6 . The process according to  claim 1 , wherein the moist polymer mass is separated by means of gravity and by means of one or more helically attached conveyor rails and/or guide blades ( 72 ) inside the rotating, cylindrical screen body ( 71 ). 
   
   
       7 . The process according to  claim 1 , wherein the drying step involves passing nitrogen or air through the polymer mass in a dryer ( 90 ). 
   
   
       8 . The process according to  claim 1 , wherein the resorbable polyester is an amorphous or partially crystalline polyester. 
   
   
       9 . The process according to  claim 1 , wherein the resorbable polyester contains one or more units derived from lactide (L-lactide, D-lactide, DL-lactide, meso-lactide), glycolide, trimethylene carbonate, epsilon-caprolactone, gamma-butyrolactone, dioxanone, delta-valerolactone and/or similar polymerisable heterocycles and/or polyethylene glycols. 
   
   
       10 . The process according to  claim 1 , wherein the resorbable polyester is composed of copolymers of lactide and glycolide and/or polyethylene glycols having any desired composition. 
   
   
       11 . The process according to  claim 1 , wherein resorbable polyester has a residual monomer content of less than 1%. 
   
   
       12 . The process according to  claim 1 , wherein the resorbable polyester has a solvent and/or moisture content of less than 2%. 
   
   
       13 . A pharmaceutical formulation or a resorbable implant containing a resorbable polyester made by the process according to  claim 1 . 
   
   
       14 . A purification device for purifying a resorbable polyester that contains as its main components a dissolving vessel ( 10 ) in which the polymer is dissolved in a first solvent ( 12 ), a separation device for separating a moist polymer mass from a polymer suspension and a dryer ( 90 ) for drying the polymer mass, characterised in that the separation device is constructed as a drum shear screen ( 70 ) comprising a rotating, cylindrical screen body ( 71 ). 
   
   
       15 . The purification device according to  claim 14 , characterised in that the cylindrical screen body ( 71 ) has in its interior conveyor rails and/or guide blades ( 72 ). 
   
   
       16 . The purification device according to  claim 14 , characterised in that the drum shear screen ( 70 ) has a suction device ( 74 ), in particular comprising a suction nozzle, above the rotating, cylindrical screen body ( 71 ) in an upper housing cover ( 76 ). 
   
   
       17 . The purification device according to  claim 14 , characterised in that the dryer ( 90 ) is a fluidised bed dryer, a circulating air dryer or a tubular-flow dryer. 
   
   
       18 . The purification device according to  claim 14 , characterised in that the dryer ( 90 ) has a conical portion ( 95 ) and a cylindrical portion ( 96 ). 
   
   
       19 . The purification device according to  claim 14 , characterised in that the dryer ( 90 ) comprises inside the cylindrical portion ( 96 ) at least one screen insert ( 94 ). 
   
   
       20 . The purification device according to  claim 14 , characterised in that the dryer ( 90 ) has a filter bag ( 92 ) for collecting the purified resorbable polyester. 
   
   
       21 . The purification device according to  claim 14 , characterised in that the dryer ( 90 ) is provided with a swivel bearing ( 93 ). 
   
   
       22 . The purification device according to  claim 14 , characterised in that at least the product-guiding parts of the drum shear screen ( 70 ) and of the dryer ( 90 ) are made of stainless steel.