Improving the Continuous Microcellular Extrusion Foaming Ability with Supercritical CO2 of Thermoplastic Polyether Ester Elastomer through In-Situ Fibrillation of Polytetrafluoroethylene

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 CO 2 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 × 10 7 -8.6 × 10 7 cells/cm 3 .2 of 16 has many excellent properties including thermal stability, good elasticity, chemical and oil resistance and, especially, rebound resilience at low-temperatures [3,5]. Also, TPEE has higher tear and impact strengths over a broad range of service temperatures when compared with other traditional TPEs [8]. Because of the extraordinary performance of TPEE, it has attracted increasing interest from many fields such as the sports, automotive and military industries.Although TPEE is an attractive engineering material, its application has to overcome the exorbitant price. To overcome this shortcoming, many attempts have been made to further improve the mechanical properties or to lower the weight (i.e., material consumption). Blending the matrix with micro-sized particles is an efficient method to improve the thermal or mechanical properties of TPEE [9][10][11][12][13]. Paszkiewicz et al. [12] added carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) to poly(trimethylene terephthalate) (PTT)-based TPEE to improve the electrical conductivity. They found that CNTs had greater potential to improve electrical conductivity when compared to GNPs due to the higher purity and higher aspect ratio. Qiu et al. [13] controlled the structure of mixed filler particles in TPEE to enhance the mechanical properties. The results showed that a closely packed particle structure can significantly improve the yield strength by about 40% with a decrease of about 20% in the Young's modulus, which is preferred in TPEE used as an elastomer.Foaming is a very effective way to lower the weight and expand the application of polymers. In recent decades, foamed materials have exhibited a balance between price and...

Recent progress in micro‐/nano‐fibrillar reinforced polymeric composite foams

“…Increasing the fiber content in fibrillated blends enhances the storage moduli in the low frequency regime (Figure 7). [ 23, 90 ] This suggests that the fibers are capable of storing deformation energy and also of restricting the long‐range motion of the matrix polymer chains, preventing them from complete relaxation when subjected to dynamic shear. [ 132, 137 ] If the fiber loading is sufficiently high, the fibrillated blend can start to show rheological signatures of a solid where G"(ω) < G'(ω) due to the contribution of the fibrillar network to the elasticity.…”

“…Thus, more and more thermoplastic foams have emerged in the market, such as polystyrene (PS) foams [ 17, 18 ] for thermal insulation, polypropylene (PP) [ 19‐22 ] foams for automotive parts, and thermoplastic elastomer (TPE) foams for sportswear. [ 23 ]…”

Foamability and Special Applications of Microcellular Thermoplastic Polymers: A Review on Recent Advances and Future Direction

“…Studies have been reported on foaming of polymeric materials (neat polymers, blends, and nanocomposites) based on different types of block copolymer TPEs, namely, styrenic block copolymers, [ 33,105,106 ] poly(ethylene‐ co ‐octene) (PEOc), [ 93,107 ] thermoplastic polyurethane (TPUs), [ 108,109 ] poly(ether‐block‐amide) (PEBA), [ 4,110 ] and thermoplastic polyester elastomer (TPEE). [ 111,112 ] Various research groups have conducted foaming of different thermoplastic polyolefins (TPOs) (blends of thermoplastics and elastomers in which there is no vulcanization of rubber) [ 15,113,114 ] and thermoplastic vulcanizate (TPVs) (blends of thermoplastics and elastomers in which the elastomer is dynamically vulcanized). [ 13,115,116 ]…”

Polypropylene/thermoplastic polyester elastomer blend: Crystallization properties, rheological behavior, and foaming performance

“…Thermoplastic elastomers (TPEs), as a kind of polymer material covering rubber and plastic boundary, have attracted much attention. For example, the block copolymer (TPEE) blended from polybutylene terephthalate (PBT) and polytetramethylene ether glycol (PTMG) is one of the TPEs, which has both rubber and plastic properties 20,21 . The crystalline phase formed by PBT can be used as the hard segment of the material to provide strong mechanical properties of the material.…”