Blends of poly(vinylidene fluoride) with polyamide 6: interfacial adhesion, morphology and mechanical properties

Abstract

The poly(vinylidene fluoride) (PVDF)/polyamide 6 (PA6) interfacial adhesion has been measured, and morphology and mechanical properties of the binary blends have been investigated. The lap shear strength of the PVDF/PA6 pair indicates a high interfacial adhesion, which is evidence for specific intermolecular interactions between the two polymers. Immiscibility of PVDF and PA6 has clearly been observed by transmission electron microscopy (TEM). It reflects the high propensity of each polymer to crystallize on its own and the strong hydrogen bonding that prevails in PA6. This interfacial adhesion can account for the fine phase morphology of the binary blends. Dependence of Young's modulus and yield stress on the blend composition shows a slightly negative deviation with respect to the additivity law, in contrast to elongation at break, ultimate tensile strength and impact toughness that display a positive deviation. These experimental observations have been discussed in reference to the interfacial adhesion and the change in crystallinity of the continuous phase. An optimum interfacial adhesion seems to be required for promoting a synergism in the impact resistance of these polyblends.Keywords: interfacial adhesion; phase morphology; synergism INTRODUCTION Poly(vinylidene fluoride) (PVDF) is a very useful thermoplastic that combines an excellent chemical resistance [1] with ferroelectric, piezoelectric and pyroelectric properties [2][3][4] . A high cost is however a limitation for widespread applications. Today, polymer blending is a versatile and widely used method for optimizing the cost-performance balance and increasing the range of potential applications. Miscibility and mechanical properties of PVDF/ poly(methylmethacrylate) (PMMA) blends have been extensively studied [5][6][7][8][9]. These blends are valuable models for miscible semi-crystalline polymer/amorphous polymer blends. Actually, PVDF and PMMA are completely miscible in the melt [5], and phase separation occurs upon cooling as a result of PVDF crystallization in a close relationship with blend composition and cooling conditions [6][7]. These blends are, however, quite brittle, as shown by Mizovic et al. [8] who reported that the impact strength dramatically decreased when the PMMA content was increased. Murff et al. [9] have observed a negative deviation in the ultimate tensile strength composition relationship of the PVDF/PMMA blends. Special attention has also been paid to blends of PVDF with immiscible polymers, and strategies have been devised to improve the detrimental effect of polymer immiscibility on the mechanical properties. A series of blends of PVDF with, e.g. Noryl [10][11] poly(α-methylstyrene) [12] and polyolefins [polyethylene (PE) and polypropylene (pp)][13] have been added with diblock copolymers, i.e. poly(styrene-b-methylmethacrylate) [10][11], poly (α-methy lstyrene-b-methylmethacrylate) [12], and poly(hydrogenated diene-b-methylmethacrylate) [13], respectively, that have proved to be very efficient interfacial agents. ...

Ferroelectric properties of nylon 11 and poly(vinylidene fluoride) blends

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