Dynamic crosslinking and reactive compatibilisation of nylon/EPDM blends with high rubber content. Blend phase morphology, deformation and recovery behaviour at molecular, nano- and microscale.
Gabriel Groeninckx, Jeroen Oderkerk
KULeuven
Belgium

Keywords: Vulcanisation, thermoplastic elastomer, reactive blending

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This paper deals with the study of high performance engineering thermoplastic vulcanisates based on nylon6/rubber blends. Thermoplastic vulcanisates (TPVs) are blends consisting of a thermoplastic matrix and a high concentration of finely dispersed crosslinked rubber particles. These polymer blend systems exhibit an excellent melt-processing behaviour and a high strain recovery after plastic deformation.

Nylon6/EPDM rubber TPVs with a high amount of dispersed rubber can be prepared by combining both reactive compatibilisation and dynamic vulcanization. Making use of a maleic anhydride grafted EPDM rubber and by slightly crosslinking the rubber phase during melt-mixing, it was possible to finely disperse up to 60-70 wt% of rubber in the nylon matrix. It was found that the viscosity ratio between the rubber and the nylon plays a crucial role in achieving a nylon/rubber TPV with a fine rubber dispersion.

The investigated nylon6/EPDM-g-MA TPVs display an excellent strain recovery, even though the matrix consists of a semicrystalline thermoplastic polymer which deforms plastically upon extension. In order to understand this unusual elastic recovery behaviour, infrared spectroscopy in combination with tensile stress-strain recovery experiments, as well as real-time atomic force microscopy (AFM) and transmission electron microscopy (TEM) measurements were performed. This will provide us with detailed information on the deformation and recovery behaviour at molecular, nano- and microlevel.

It has been observed that during stretching, the nylon matrix of the TPVs deforms plastically in an inhomogeneous way. The plastic deformation is clearly concentrated in those regions where the nylon matrix between the rubber particles is the thinnest. When the applied stress is removed from the sample, the elastic force of the stretched rubber phase is able to pull back the highly plastically deformed thin nylon regions. This is achieved by buckling and/or bending, and is considered to be the key mechanism for the elastic recovery behaviour of the investigated TPVs.