Crystallization Studies of Polymer Blends of Nylon-11/Poly(vinylidene fluoride)

Abstract

ABSTRACT:The crystallization of blends of two semi-crystalline polymers nylon-11 and poly(vinylidene fluoride) (PVF 2 ) was studied. The existence of separate melting and crystallization temperatures over the whole composition range showed that these two polymers did not co-crystallize. However, blending affected the crystallization behavior of each component. Adding nylon-11 decreased the crystallization temperature (T c ) of PVF 2 , but increased its crystallization rate. On the other hand, the T c of nylon-11 decreased, and its crystallization rate decreased as well when blended with PVF 2 . The crystallization mechanism of both nylon-11 and PVF 2 changed in the blends compared to that in the pure states. The Ozawa index, or Avrami exponent, of PVF 2 in the blend decreased from 3 to 1 as the crystallization temperature decreased from 137• C to 131• C, compared with a decrease from 2.5 to 1.3 observed in pure PVF 2 at the temperature range from 145• C to 135• C. The Avrami exponent of nylon-11 in the blend decreased from 2 to 1 as the crystallization temperature decreased from 159• C to 153• C, compared with a decrease from 2.5 to 0.75 observed in pure nylon-11 at the same temperature range. KEY WORDS Nylon-11 / Poly(vinylidene fluoride) / Non-Isothermal / Crystallization / Ozawa's Theory / Intermolecular Interactions / Polymer Blends / Nylon-11 and PVF 2 are both semi-crystalline polymers. Besides their excellent mechanical properties and chemical resistance, when uniaxially drawn, they also exhibit unique electroactive properties: high ferroelectric, piezoelectric and pyroelectric response. 1 In previous studies, we found large enhancements in ferroelectric, 2 and piezoelectric properties 3 produced by powder blending PVF 2 with nylon-11. The drawing behavior of PVF 2 was also significantly improved by blending with nylon-11. All the improvement of properties should be closely related to the structural development, especially the crystalline structure development in the blends. In this paper, we present a study of the crystallization behavior of the undrawn nylon-11/PVF 2 blend compared with that of the pure polymers which provide a base for establishing a structure-property relationship of this new ferroelectric polymer composite system. Nylon-11 is ferroelectric in the undrawn state while PVF 2 is not.It is well known that these two polymers contain strong polar groups: CONH in nylon-11 and CF 2 in PVF 2 , which, depending on their crystal structures, allows them to be ferroelectric and piezoelectric polymers. It is also known that the smaller the dipole moment difference, the more compatible the polymers. The dipole moment of the CONH group in nylon is 6.4 × 10 −30 cm, while that of the CF 2 group in PVF 2 is 6.3 × 10 −30 cm. For the mechanically mixed fine powder blends, the intra-and intermolecular interactions should contribute to the crystallization kinetics, crystallinity and even the polymorphic crystal form, which are all closely related to the processing and properties of these blends.In this work...

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