Abstract
In-situ fibrillated polytetrafluoroethylene (PTFE) enhanced nanocomposites were successfully prepared by mixing thermoplastic polyether ester elastomer (TPEE) and PTFE using a twin-screw extruder. Well-dispersed, long aspect ratio PTFE nanofibrils with a diameter of less than 200 nm were generated and interwoven into networks. Differential scanning calorimetry and in-situ polarized optical microscopy showed that the PTFE nanofibrils can greatly accelerate and promote crystallization of the TPEE matrix and the crystallization temperature can be increased by 6 °C. Both shearing and elongational rheometry results confirmed that the introduction of PTFE nanofibrils can significantly improve the rheological properties. The remarkable changes in the strain-hardening effect and the melt viscoelastic response, as well as the promoted crystallization, led to substantially improved foaming behavior in the continuous extrusion process using supercritical CO2 as the blowing agent. The existing PTFE nanofibrils dramatically decreased the cell diameter and increased cell density, together with a higher expansion ratio and more uniform cell structure. The sample with 5% PTFE fibrils showed the best foaming ability, with an average diameter of 10.4–14.7 μm, an expansion ratio of 9.5–12.3 and a cell density of 6.6 × 107–8.6 × 107 cells/cm3.
Highlights
Thermoplastic elastomers (TPEs) are copolymers composed of crystalline rigid segments and amorphous soft segments
The long aspect ratio PTFE nanofibrils can significantly promote the of Thermoplastic polyether ester elastomer (TPEE) and refine the crystals
The improvements in the crystallization and rheological properties enhanced the foaming which was tested by a continuous extrusion foaming process
Summary
Thermoplastic elastomers (TPEs) are copolymers composed of crystalline rigid segments and amorphous soft segments. To overcome the low melt strength of linear polymers, chemical modification or electron beam crosslinking can be used as a common strategy to improve foaming ability [21,23,24]. These efficient processes require a radioactive source or reactor which may increase the cost of the product. Rizvi et al using a fiber-spun system [27,28] In these works, the well dispersed polymer fibrils could significantly enhance the extensional rheological properties of the matrix and hinder cell coalescence, resulting in a higher cell density and a higher expansion ratio. With the addition of PTFE fibrils, the TPEE/PTFE blends showed excellent foaming ability with a high expansion ratio and a finer cell structure
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