Fabrication and characterization of flexible high performance thermoplastic foams derived from rigid polyetherketoneketo
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Fabrication and characterization of flexible high performance thermoplastic foams derived from rigid polyetherketoneketone via a VOC-free foaming method Bin Li • Tian Liu • Zack C. W. Tang Wei-Hong Zhong
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Received: 21 November 2012 / Accepted: 7 January 2013 / Published online: 24 January 2013 Ó Springer Science+Business Media New York 2013
Abstract There is a high demand for a volatile-organiccompound (VOC)-free approach to converting high performance polymers (HPPs), such as polyetherketoneketone (PEKK), to porous structures. This is particularly true for achieving flexible foams from these very rigid HPPs. This current work introduces a facile and environmentally benign approach to fabricating flexible PEKK foams via a hydration-induced foaming and desulfonation treatment. This foaming technique possesses three major advantages: energy efficiency, environment friendliness, and super flexibility. The resultant flexible PEKK foam has a uniform porous structure with a cell diameter of ca. 5 lm, as well as low mass density of ca. 0.42 g/cm3. Thermal analysis revealed that the porous PEKK showed a high thermal stability with a thermal degradation temperature of 520 °C, showing superiority over other reported flexible polymer foams. Compared with solid PEKKs fabricated by compression molding, the porous PEKK has a higher crystallinity and more thermodynamically stable crystal structures. According to nanoindentation analysis, the flexibility of porous PEKK may be a result of the better chain mobility in porous PEKK. The reduced modulus and hardness of porous PEKK are 0.73 ± 0.16 and 0.09 ± 0.03 GPa, respectively. The porous structures also efficiently reduced the dielectric constant from ca. 4.0 to 2.6 in a wide frequency range.
B. Li T. Liu Z. C. W. Tang W.-H. Zhong (&) School of Mechanical and Materials Engineering, Washington State University, Pullman, WA 99164, USA e-mail: [email protected]
Introduction High performance polymers (HPPs), such as polyaryletherketone (PAEK)s, which have superior mechanical properties, thermal and chemical stability, as well as unique physical properties [1–5], are playing an increasingly important role in our daily life, as a result of their chain structures consisting of covalently bonded phenyl groups and strong inter/intra-molecular interactions (hydrogen bond, dipole–dipole force, van der Waals force, etc.). Significant applications of these HPPs include electronics, structural materials for aerospace and automotive, capacitors, batteries, fuel cells, and medical implants [6–11]. However, the same chain structures accounting for the superiority of HPPs over other commodity polymers also make the processing of PAEKs difficult due to their extremely high melt viscosities and strong chemical resistance. Concurrently, the demands for porous polymeric materials are rapidly growing, mainly due to their ultra low mass density, high strength to-weight ratio, and high surface area. According to previous studies, promising applications of porous polymeric materials include chem
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