Fluoropolymer composition
View Patent ↗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 a dispersion of submicrometer-size particles comprising non-melt flowable polytetrafluoroethylene having a melt creep viscosity of at least 1×10 6 Pa·s at 380° C. in a continuous phase comprising melt-fabricable perfluoropolymer having a melt flow rate of from about 0.1 to 500 g/10 min as measured in accordance with Table 2 of ASTM D-1238-94a, said non-melt flowable polytetrafluoroethylene constituting at least about 4 wt % of the combined weight of said non-melt flowable 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 − 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 up to 50 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.