Polyethylene terephthalate/organoclay nanocomposites: Improvement of morphology and viscoelastic properties by using a chain-extender

Abstract

A major challenge in the industrialization of polymer-clay nanocomposites at high processing temperatures is the thermal degradation of the matrix induced by the commercial organoclays. This work investigated the reactive extrusion of polyethylene terephthalate (PET) nanocomposites using a styrene–acrylic multi-functional oligomeric chain extender, Joncryl® ADR 4368 (Joncryl), to address the thermal degradation of the matrix and improve the microstructure of the nanocomposites. The matrix degradation in the nanocomposites induced by the introduction of 2 wt% Cloisite® 30B (C30B) and Nanomer® I28E (Nanomer) was estimated using the high-frequency data and the Maron-Pierce equation. While PET/C30B nanocomposite showed a highly exfoliated morphology, large tactoids were observed for the sample containing Nanomer particles. Therefore, the chain extender at different concentrations (0.5 to 2 wt%) were introduced in the sample containing Nanomer to achieve a highly exfoliated morphology. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses revealed a significantly improved morphology for the nanocomposites containing the chain extender. The effect of the chain extender on the control of the degradation of PET nanocomposites containing Nanomer particles was assessed through small amplitude oscillatory shear (SAOS) rheological experiments. The mechanism of stabilization, through the formation of long chain branched (LCB) molecular structure, was considered by comparing the loss angle plots of the unmodified and chain extended samples. Re-linking the degraded PET chains by the multifunctional epoxy-based chain extender led to increase by more than ten times of the complex viscosity of PET nanocomposites containing Nanomer at low frequencies.