Viscoelastic Behavior of Polyamide 6–COC Blends: Role of Crystallinity and Frequency-Domain Modeling

Abstract

The mechanical performance of semicrystalline thermoplastics like polyamide 6 (PA6) is strongly influenced by crystallinity, which poses challenges for consistent viscoelastic characterization, especially at elevated temperatures. This study addresses this issue by exploring immiscible blends of PA6 and amorphous cyclic olefin copolymer (COC) as a novel approach to systematically tailor crystallinity without relying on thermal annealing, thereby avoiding cold crystallization during mechanical testing. Blends with varying crystallinity were prepared via melt blending and characterized using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) across wide temperature and frequency ranges. To extend the measured data and identify relaxation spectra, time–temperature superposition (TTS) was applied and master curves were constructed. Shift factors were modeled using both the Williams–Landel–Ferry (WLF) equation and a custom polynomial fit, enabling reliable extrapolation across the entire experimental temperature spectrum. The viscoelastic behavior was quantitatively described using a Generalized Maxwell Model (GMM) with parameters fitted via nonlinear optimization. The resulting model accurately captures the viscoelastic behavior of the blends over several frequency decades. This work establishes a comprehensive experimental and modeling framework to describe the thermomechanical performance of PA6 as a function of crystallinity; thereby supporting its application in temperature- and frequency-sensitive environments.