Biocomponent fibers with an exterior component comprising polypropylene

Abstract

The present invention relates to bicomponent fibers with improved bonding properties. In particular, the present invention relates to bicomponent fibers comprising an exterior component, which in turn comprises a polypropylene that has been degraded from a first melt flow index MFI 1 (measured according to ISO 1133, condition L, 230° C., 2.16 kg) to a second melt flow index MFI 2 (measured according to ISO 1133, condition L, 230° C., 2.16 kg), such that the degradation ratio MFI 1 /MFI 2 is within a well-defined range and such that the second melt flow index MFI 2 is in the range from 50 dg/min to 300 dg/min. Further, the present invention relates to nonwovens, composites and laminates comprising said bicomponent fibers. The present invention also relates to a process for making such bicomponent fibers, nonwovens, composites and laminates.

1 . Bicomponent fiber comprising
 a) an exterior component covering at least 50% of the surface of the bicomponent fiber, and   b) an interior component comprising a thermoplastic polymer,   wherein the exterior component comprises a polypropylene, which has been degraded chemically or thermally from a first melt flow index MFI 1  (measured according to ISO 1133, condition L, 230° C., 2.16 kg) to a second melt flow index MFI 2  (measured according to ISO 1133, condition L, 230° C., 2.16 kg), such that the second melt flow index MFI 2  is in the range from 50 dg/min to 300 dg/min and such that the degradation ratio MFI 1 /MFI 2  is at least 0.10 and at most 0.80.   
     
     
         2 . Bicomponent fiber according to  claim 1 , wherein the exterior component comprises said polypropylene in at least 50 wt % relative to the total weight of the exterior component. 
     
     
         3 . Bicomponent fiber according to  claim 1 , wherein the exterior component comprises a polypropylene, said polypropylene comprising at least 200 ppm, relative to the weight of said polypropylene, of a primary antioxidant. 
     
     
         4 . Bicomponent fiber according to  claim 3 , wherein the exterior component comprises a polypropylene, said polypropylene comprising at least 200 ppm, relative to the total weight of said polypropylene, of a primary antioxidant and at least 500 ppm, relative to the total weight of said polypropylene, of a secondary antioxidant. 
     
     
         5 . Bicomponent fiber according to  claim 1 , wherein the thermoplastic polymer of the interior component is a polypropylene different from the polypropylene of the exterior component. 
     
     
         6 . Nonwoven comprising the bicomponent fiber of  claim 1 . 
     
     
         7 . Composite and laminate comprising the nonwoven of  claim 6 . 
     
     
         8 . Process for the production of bicomponent fibers comprising the steps of
 a) polymerizing propylene and one or more optional comonomers with a polymerization catalyst to produce a polypropylene having a first melt flow index MFI 1  (measured according to ISO 1133, condition L, 230° C., 2.16 kg),   b) thermally or chemically degrading the polypropylene obtained in step (a) to a second melt flow index MFI 2  (measured according to ISO 1133, condition L, 230° C., 2.16 kg),   c) melting a polypropylene composition comprising the polypropylene obtained in step (b) in a first extruder to form a molten polypropylene composition,   d) melting a thermoplastic polymer composition comprising a thermoplastic polymer in a second extruder to form a molten thermoplastic polymer composition,   e) extruding the molten thermoplastic polymer composition from a number of fine, usually circular, capillaries of a spinneret,   f) extruding the molten polypropylene composition of step (c) from a number of fine openings surrounding said capillaries of step (e), and   g) combining the extrudates of steps (e) and (f) to form a single filament of an intermediate diameter, such that the extrudates of step (f) form an exterior component covering at least 50% of the surface of the so-produced filament,   wherein the polypropylene obtained in step (b) has a second melt flow index MFI 2  (measured according to ISO 1133, condition L, 230° C., 2.16 kg) in the range from 50 dg/min to 300 dg/min and wherein the degradation ratio MFI 1 /MFI 2  is at least 0.10 and at most 0.80.   
     
     
         9 . Process according to  claim 8 , wherein the polypropylene in step (a) is produced by a Ziegler-Natta polymerization catalyst. 
     
     
         10 . Process according to  claim 8 , wherein the exterior component and the interior component are further defined according to  claims 2  to  5 . 
     
     
         11 . Process according to  claim 8 , wherein the process further comprises the step of
 (h) rapidly reducing the intermediate diameter of the filaments extruded in the previous step to a final diameter.   
     
     
         12 . Process according to  claim 8 , wherein the process further comprises the step of
 (i) collecting the filaments obtained in step (g) or (h) on a support, and   (k) subsequently bonding the collected filaments to form a bonded nonwoven.   
     
     
         13 . Process according to  claim 8 , further comprising the step of
 (1-1) laminating a film to the bonded nonwoven obtained in step (k) to form a laminate   
     
     
         14 . Process according to  claim 8 , further comprising the step of
 (1-2) applying a spunbond and/or a meltblown nonwoven to the bonded nonwoven obtained in step (k).   
     
     
         15 . Process according to  claim 8 , wherein the bonded nonwoven is a spunbond nonwoven.