Compatibilization of poly(vinylidene fluoride)/Nylon 6 blends by carboxylic acid functionalization and metal salts formation: Part 2. Mechanism and effects on physical properties

doi:10.1016/S0032-3861(97)00270-X

Polymer

Volume 39, Issue 2, 1998, Pages 369-378

https://doi.org/10.1016/S0032-3861(97)00270-X Get rights and content

Abstract

A study was made of the mechanism for the compatibilization of blends of PVDF and Nylon 6, induced first by grafting the chains of the two polymers with methacrylic acid and, subsequently, by the formation of zinc salts. The physical properties and rheological behaviour of the blends were examined in order to elucidate the mechanism. It was found that for blends containing minor amounts of PVDF effective compatibilization was achieved only when either grafted Nylon 6 was blended with pristine PVDF, or zinc acetyl acetonate was added to blends of grafted PVDF and pristine Nylon 6. This second effect was attributed to the interfacial sharing of zinc cations between the carboxylate anions in the PVDF phase and the amide groups of the Nylon component. At high concentrations of grafted PVDF compatibilization was observed even in simple mixtures with Nylon 6, owing to the greater propensity of interfacial amidation reactions during mixing. As in the previous case compatibilization of the blends was enhanced by the addition of zinc acetyl acetonate. The type of improvements in mechanical properties, resulting from compatibilization induced by the addition of ZnAcAc, however, was found to depend on the nature of the component forming the main phase. A large increase in tensile strength was observed in blends with PVDF as the main component, while a higher ductility was achieved when the polyamide formed the main phase. Dynamic mechanical property measurements have revealed that an appreciable level of molecular miscibilization takes place within the amorphous domains of the blend, which is more easily discerned for blends in which the Nylon component forms the main phase. No evidence for the formation of ionomeric clusters for either components or the corresponding blends could be found for acid grafted systems neutralized by the addition of ZnAcAc. © 1997 Elsevier Science Ltd.

Section snippets

INTRODUCTION

Poly(vinylidene fluoride) (PVDF) has the highest strength, wear resistance and creep resistance of all fluoropolymers and exhibits the typical oxidative and UV resistance of highly fluorinated compounds.

The polymorphism of PVDF and the alternation of CH₂ and CF₂ groups along the polymer chains provide a unique polarity which is responsible for its solubility in aprotic solvents.

Polyamides possess a very high melting point and excellent mechanical properties, which are maintained up to high

Materials

1.
(1) Polyvinylidene fluoride. An emulsion polymer, Kynar 461 from Atochem North America inc., having a weight average molecular weight equal to 5.34 × 10⁵ g mole⁻¹, melting point around 156–160°C and particle diameter in the region of 0.2 μm.
2.
(2) Nylon 6. A high viscosity grade in granular form, Sniamid ads 40, obtained from SNIA Ricerche, having a relative viscosity of 4 and a melting point around 220–223°C.
3.
(3) Nylon 6 cast films 20 μm thick, produced from Sniamid ads 40, also obtained from SNIA

RESULTS AND DISCUSSION

The micrograph in Fig. 1 shows that, for blends in which PVDF is the minor component (i.e. 20 wt%, corresponding to 13 vol%), effective compatibilization is not achieved by the grafting of methacrylic acid on the PVDF chains. This suggests that the reaction between the grafted acid groups in the PVDF and the terminal amine groups in the polyamide cannot have taken place to a significant extent. Extensive compatibilization of the two phases is observed, in contrast, when either ZnAcAc is added

CONCLUSIONS

The main conclusions that can be drawn from this study are the following:

1.
(1) PVDF and Nylon 6 form partially miscible blends with a typical two-phase morphology of particles dispersed in a continuous matrix of the major component. The mechanical properties are inferior to those exhibited by the individual polymers in isolation owing to the low interfacial adhesion between the two phases.
2.
(2) Grafting methacrylic acid groups on the PVDF chains is effective in inducing compatibilization of the

Acknowledgements

The authors wish to thank Dr A. Valenza of the University of Palermo for carrying out the rheological measurements and providing the graphs for Fig. 2, Fig. 3, Fig. 5.

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It is well known that water acts as a plasticizer for polyamide based system and is quite difficult to remove by simple vacuum drying before processing and has been extensively reported by Davis et al. [22] in PA6/clay systems. Such plasticization effect has also been reported in PA6/PVDF system with zinc salts [23]. Fedullo et al. reported that injection of water during melt-processing of polyamide 6/clay composites enhanced the polarity and fluidity of the polyamide chains which further led to improved dispersion of clay [24].
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We firstly synthesized and characterized a series of functional carboxylated polyvinylidene fluoride (PVDF-g-AAc). Then the temporal change of the complex viscosity (η*) of the two plates consisting of the graft polymer PVDF-g-AAc and polyamide 6 (PA6) was measured by a rotational rheometer. There were two distinct stages for the change of the complex viscosity (η*) with time: (i) stage I, where η* increased rapidly at short times, a reaction-controlled kinetics was induced; (ii) stage II, where η* increased slowly at a long time, however, a diffusion-controlled kinetics was obtained. Despite whether the kinetics are reaction-controlled or diffusion-controlled, the reaction could be predicted by pseudo-first-order kinetics. Meanwhile, the reaction temperature had an effect on the interfacial width and roughness. The value of the interfacial root-mean-square (rms) roughness obtained from AFM was consistent with that of the interfacial width from ellipsometer at different temperatures.
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Compatibilization of poly(vinylidene fluoride)/Nylon 6 blends by carboxylic acid functionalization and metal salts formation: Part 2. Mechanism and effects on physical properties

Abstract

Section snippets

INTRODUCTION

Materials

RESULTS AND DISCUSSION

CONCLUSIONS

Acknowledgements

Colloid Polym Sci.

Polym. Int.

J. Macromol. Sci. Rev. Macromol. Chem.

Polym. Eng. Sci.

Macromolecules

Macromolecules

Macromolecules

Polym Int.

Polym. Eng. Sci.

Polym. Eng. Sci.

J. Apply. Polym. Sci.

J. Polym. Sci. Part B: Polym. Phys.

Polym. Eng. Sci.