Effect of P(MMA-co-MAA) compatibilizer on the miscibility of nylon 6/PVDF blends

doi:10.1016/S0014-3057(02)00366-X

European Polymer Journal

Volume 39, Issue 6, June 2003, Pages 1249-1265

https://doi.org/10.1016/S0014-3057(02)00366-X Get rights and content

Abstract

With the ultimate objective of enhancing the impact strength and weatherability of nylon 6 engineering plastic, blending with poly(vinylidene fluoride) (PVDF) was studied. In the absence of a compatibilizer the two polymers phase separate, resulting in a deterioration of the properties. Since poly(methyl methacrylate) is known to be miscible with PVDF, we evaluated poly(methyl methacrylate-co-methacrylic acid) (P(MMA-co-MAA)) of low methacrylic acid content as the compatibilizer. The carboxylic acid groups in the MAA units were expected to react with the end amino groups of nylon 6 forming block or graft copolymers, P(MMA-co-MAA)–g-nylon 6, in situ, which will function as the actual compatibilizer. The amount of P(MMA-co-MAA) added, the MMA/MAA composition and heat treatment time were varied to study their effects on the miscibility, morphology, and mechanical properties of nylon 6/PVDF blends. The enhancement of the compatibility of nylon 6 and PVDF by addition of P(MMA-co-MAA) and the partial miscibility of nylon 6 and PVDF has been confirmed through DSC, dynamic mechanical testing, SEM of fracture surfaces, and tensile testing. The decrease in the crystallization temperatures on addition of compatibilizer in DSC experiments suggests that the compatibilizer enhances the interaction between the two components and retards the crystallization. The dynamic mechanical thermal analysis experiments suggest that the compatibility in the amorphous regions of nylon 6 and PVDF in particular has been enhanced. The increase in the heat treatment time in the molten state resulted in further enhancement of the miscibility. The enhancement of compatibility by addition of a reactive compatibilizer and heat treatment resulted in a significant increase in the energy of rupture in tensile testing.

Introduction

Nylon 6 is used widely as engineering plastic due to its good processibility, mechanical properties, and abrasion resistance, but its low temperature impact strength and weatherability limit its use.

Generally the flexibility and low temperature impact strength are improved by random incorporation of fine rubber particles into the nylon 6 matrices. Direct blending of ethylene polymers, propylene polymers, ethylene–propylene copolymers, butadiene rubber, or isobutylene rubber is widely used. But due to the poor miscibility of nylon 6 with these polymers, the interfacial strengths are weak and improvement in properties is not sufficient. In the anionic polymerization of ε-caprolactam via the reaction injection molding process, amino-terminated butyronitrile rubber (ATBN), polyethylene glycol–diamine (PEG–diamine) or polypropylene glycol–diamine (PPG–diamine) can be added to enhance the impact strength. The added diamine reacts with nylon 6 to form copolymers, nylon 6–ATBN–nylon 6, nylon 6–PEG–nylon 6, or nylon 6–PPG–nylon 6, which may act as a compatibilizer for the unreacted polymers [1], [2], [3], [4], [5], [6], [7], [8], [9]. However, 1–2% alkali metals such as Na and Mg used as catalyst remain in the plastic and reduce the weatherability and resistance to hydrolysis.

Recently, incorporation of poly(vinylidene fluoride) (PVDF) by melt blending has been proposed for the enhancement of both the weatherability and the low temperature impact resistance [10], [11], [12]. PVDF is a fluoropolymer that has good ductile properties due to its very low glass transition temperature and exhibits good hydrolysis resistance and weatherability [13]. Although polyamide and PVDF exhibit partial miscibility in the non-crystalline region [10], [11], [14], both are semi-crystalline and crystallization induced phase separation occurs during cooling of the molded specimen. In order to minimize the phase separation the compatibility must be enhanced to retard the phase separation and crystallization rates.

A method to enhance the compatibility of nylon 6 and PVDF by the incorporation of a compatibilizer is proposed in this study. Since no known polymer exhibits miscibility with both nylon 6 and PVDF, we took the approach of selecting a polymer miscible with one of the polymers, then using a derivative capable of reacting with the other polymer to form a block or graft copolymer. The block or graft copolymer would then act as a compatibilizer for nylon 6 and PVDF. The compatibilizer capable of forming the actual compatibilizer in situ may be termed as a “reactive” compatibilizer. Poly(methyl methacrylate) (PMMA) is known to be miscible with PVDF over the entire composition range [15], [16], [17], [18]. Since the terminal amino groups of nylon 6 are known to be capable of in situ condensation reactions with polymers containing carboxylic acid or acid anhydride groups to form nylon 6 graft copolymers [11], [19], poly(methyl methacrylate-co-methacrylic acid) (P(MMA-co-MAA)) of low MAA content was selected. On melt blending at high temperatures, the carboxylic acid groups of the MAA residue in P(MMA-co-MAA) is expected to react with the terminal amino groups of nylon 6 to form P(MMA-co-MAA)–g-nylon 6 in situ which will then function as the actual compatibilizer for nylon 6 and PVDF.

The effect of incorporation of P(MMA-co-MAA) as a reactive compatibilizer in nylon 6/PVDF blends was studied. The amount of P(MMA-co-MAA) added as the reactive compatibilizer, the MMA/MAA composition of the reactive compatibilizer, and the heat treatment time were varied to study their effects on the compatibility, morphology, and mechanical properties of nylon 6/PVDF blends.

Section snippets

Polymer samples

The PVDF powder used in this study was Kynar 761 produced by Atochem. The nylon 6 chips, whose number-average molecular weight and weight-average molecular weight are 28,323 and 76,177, respectively, were supplied by Kolon Ltd. The P(MMA-co-MAA) whose composition in weight ratio is 99/1 MMA/MAA (compatibilizer-1) was obtained from Aldrich. Its number-average molecular weight and weight-average molecular weight are 15,000 and 34,000, respectively. The P(MMA-co-MAA) sample whose composition in

Crystallization and melting behavior

The effect of compatibilizer on the DSC crystallization behavior on cooling nylon 6/PVDF blends from the melt was studied.

In nylon 6/PVDF 90/10 blends (Fig. 1), addition of compatibilizer resulted in only a slight decrease in the crystallization temperatures of the nylon 6 component from 184 °C of pure nylon 6 and the blend without compatibilizer. However, the crystallization peak of the PVDF component was barely discernible and decreased drastically to 118.5 °C from that of pure PVDF, 138.9

Conclusions

The enhancement of compatibility of nylon 6 and PVDF by addition of P(MMA-co-MAA) as a reactive compatibilizer and the partial miscibility of nylon 6 and PVDF has been confirmed through DSC, dynamic mechanical testing, morphology studies and tensile testing.

The decrease in the crystallization temperatures in DSC cooling experiments on addition of compatibilizer suggests that it retards the crystallization of the two component polymers and the DMTA experiments suggest that the compatibility in

Acknowledgments

Financial support of the fiscal year 2000 by Kyung Hee University is gratefully acknowledged.

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Effect of P(MMA-co-MAA) compatibilizer on the miscibility of nylon 6/PVDF blends

Abstract

Introduction

Section snippets

Polymer samples

Crystallization and melting behavior

Conclusions

Acknowledgments

J. Korean Fiber Soc.

Polymer

Polymer

Polymer

Eur. Polym. J.

J. Korean Fiber Soc.

J. Appl. Polym. Sci.

Polym. Eng. Sci.

Die Angew Makromol. Chem.