Ultrafine polyactic acid fibers and fiber structure, and process for their production

Abstract

A fiber structure is obtained by spinning of a solution of an L-lactic acid condensate and a D-lactic acid condensate by electrospinning. It is possible to provide a fiber structure comprising fibers with extremely small fiber diameters, as well as excellent heat resistance and biodegradability.

1 . Ultrafine polylactic acid fibers comprising as the main constituent component a polylactic acid component with a melting point of 190° C. or higher, with a mean fiber diameter of no greater than 10 μm and fiber lengths of 20 μm or greater.  
   
   
       2 . Fibers according to  claim 1 , which contain substantially no constituent component with a melting point of below 190° C.  
   
   
       3 . Fibers according to  claim 1 , having depressions with diameters of 0.01-1 μm on the fiber surfaces, the depressions constituting 10-95% of the fiber surfaces.  
   
   
       4 . Fibers according to  claim 1 , wherein the polylactic acid component is a blend of a condensate with at least 80 mol % L-lactic acid based on the total repeating units and a condensate with at least 80 mol % D-lactic acid based on the total repeating units.  
   
   
       5 . Fibers according to  claim 4 , wherein the weight ratio of the L-lactic acid condensate and the D-lactic acid condensate is (6:4)-(4:6).  
   
   
       6 . A fiber structure comprising at least ultrafine polylactic acid fibers according to  claim 1 .  
   
   
       7 . A fiber structure according to  claim 6 , wherein the fibers forming the fiber structure have a mean diameter of no greater than 10 μm and contain substantially no fibers with fiber lengths of less than 20 μm.  
   
   
       8 . A production process for a fiber structure, which includes a stage wherein a condensate with at least 80 mol % L-lactic acid based on the total repeating units and a condensate with at least 80 mol % D-lactic acid based on the total repeating units are combined in a weight ratio of (6:4)-(4:6) and then dissolved in a solvent to produce a solution, a stage wherein said solution is spun by an electrospinning method, and a stage wherein a fiber structure is accumulated on a collecting plate by said spinning.  
   
   
       9 . A production process according to  claim 8 , wherein the solvent is a volatile solvent.  
   
   
       10 . A production process according to  claim 8 , wherein the relative humidity is in the range of 20-80% RH between the nozzle and collecting plate where the filamentous substance is formed in the stage of spinning by electrospinning.  
   
   
       11 . A production process for a fiber structure which includes a stage wherein a condensate with at least 80 mol % L-lactic acid based on the total repeating units is dissolved in a solvent to produce a solution, a stage wherein a condensate with at least 80 mol % D-lactic acid based on the total repeating units is dissolved in a solvent to produce a solution, a stage in which the two solutions are mixed in a weight ratio of (6:4)-(4:6), a stage wherein said mixed solution is spun by an electrospinning method, and a stage wherein a fiber structure is accumulated on a collecting board by said spinning.  
   
   
       12 . A production process according to  claim 11 , wherein the solvent is a volatile solvent.  
   
   
       13 . A production process according to  claim 12 , wherein the volatile solvent is at least one selected from the group consisting of methylene chloride, chloroform, dichloroethane, tetrachloroethane, trichloroethane, dibromomethane, bromoform, tetrahydrofuran and 1,4-dioxane.  
   
   
       14 . A production process according to  claim 11 , wherein the relative humidity is in the range of 20-80% RH between the nozzle and collecting plate where the filamentous substance is formed in the stage of spinning by electrospinning.