Preparation and characterization of poly(ethylene terephthalate) incorporated with secondary-modified montmorillonite

Abstract

Hexadecyl triphenyl phosphonium bromide montmorillonite (PMMT) was first modified via secondary modification method, and then conjugated with toluene-2,4-diisocyanate (TDI). The as-prepared TDI-PMMT sample was used as a blend polymer in poly(ethylene terephthalate)/TDI-PMMT composite (PET/TDI-PMMT). The chemical properties of original PMMT, TDI-PMMT and PET/TDI-PMMT composite were investigated by X-ray diffraction (XRD), infrared spectroscopy (FTIR) and thermogravimetry analysis (TGA). Results showed that chemical bonds which were formed between TDI and montmorillonite surface provided massive active isocyanate groups in in situ polymerization for the montmorillonite and matrix materials. This structure could have improved the compatibility between PMMT and PET effectively, and allow good distribution of the montmorillonite in polymer matrix. The spacing of montmorillonite layer decreased from 3.72 to 3.28 nm owing to the encapsulation of TDI groups. The physical morphology of nanocomposites was observed through scanning electron microscopy (SEM), transmission electron microscopy (TEM) and XRD, and their thermal performance was evaluated by differential scanning calorimetry (DSC). XRD and SEM studies confirmed that compared to PMMT, the secondary-modified montmorillonite exhibited a better dispersion in PET matrix. TGA and DSC results showed that the thermal stability of PET/TDI-PMMT was superior to PET/PMMT. TEM images of PET/TDI-PMMT indicated that the TDI-PMMT exhibited good dispersion and the TDI-PMMT silicate layers were in better exfoliated state. The interface spacing of all samples was enlarged because of the heating reaction of oligomers. In the meanwhile, the mechanical properties such as tensile strength, flexural strength and flexural modulus of PET/TDI-PMMT were higher than those of PET/PMMT.