Fluoropolymer composition

Abstract

A melt-mixed composition of non-melt flowable polytetrafluoroethylene (PTFE) and melt-fabricable perfluoropolymer is provided that exhibits thixotropy at increasing shear rate in the molten state and high elongation at break even at PTFE concentrations well above 4 wt %, based on the combined weight of the PTFE and the perfluoropolymer, e.g. at least 200% up to at least 30 wt % PTFE, the composition also exhibiting the structure of a dispersion of submicrometer-size particles of the PTFE in a continuous phase of the melt-fabricable perfluoropolymer.

1 . Melt-mixed composition comprising non-melt flowable polytetrafluoroethylene and melt-fabricable perfluoropolymer, said polytetrafluoroethylene constituting at least about 4 wt % of the combined weight of said polytetrafluoroethylene and said melt-fabricable perfluoropolymer, said composition exhibiting thixotropy when being subjected to increasing shear in the molten state.  
   
   
       2 . The melt-mixed composition of  claim 1  wherein said thixotropy is characterized by a reduction in melt viscosity upon increasing the shear rate applied to said composition in the molten state from about 10 s −1  to about 100 s −1  that is at least about 10% greater than the reduction in melt viscosity at the same shear rates for the melt-fabricable perfluoropolymer by itself, as determined by the capillary rheometer method.  
   
   
       3 . The melt-mixed composition of  claim 2  wherein said reduction is at least 100%.  
   
   
       4 . The melt-mixed composition of  claim 1  exhibiting an elongation at break at least as high as that for said melt-fabricable perfluoropolymer by itself.  
   
   
       5 . The melt-mixed composition of  claim 4  wherein said elongation at break exists for said composition wherein said polytetrafluoroethylene constitutes at least up to about 15 wt % of the combined weight of said polytetrafluoroethylene and said melt-fabricable perfluoropolymer.  
   
   
       6 . The melt-mixed composition of  claim 1  exhibiting an elongation at break of at least about 200% at up to about 30 wt % of said polytetrafluoroethylene, based on the combined weight of said polytetrafluoroethylene and said melt-fabricable perfluoropolymer.  
   
   
       7 . The melt-mixed composition of  claim 6  wherein said elongation at break is at least 250%.  
   
   
       8 . The melt-mixed composition of  claim 1  wherein said polytetrafluoroethylene constitutes up to about 75 wt % based on the combined weight of said polytetrafluoroethylene and said melt-fabricable perfluoropolymer.  
   
   
       9 . Melt-mixed composition comprising a dispersion of submicrometer-size particles comprising non-melt flowable polytetrafluoroethylene in a continuous phase comprising melt-fabricable perfluoropolymer, said dispersion exhibiting thixotropy when being subjected to increasing shear in the molten state.  
   
   
       10 . The composition of  claim 9  wherein said thixotropy is characterized by a reduction in melt viscosity upon increasing the shear rate applied to said composition in the molten state from about 10 s −1  to about 100 s −1  that is at least about 10% greater than the reduction in melt viscosity at the same shear rates for the melt-fabricable perfluoropolymer by itself, as determined by the capillary rheometer method.  
   
   
       11 . The melt-mixed composition of  claim 9  exhibiting an elongation at break at least as high as that for said melt-fabricable perfluoropolymer by itself.