Photocatalytic degradation of flexible PVC/TiO 2 nanohybrid as an eco-friendly alternative to the current waste landfill and dioxin-emitting incineration of post-use PVC

Abstract

Photo-degradable poly(vinyl chloride) (PVC)/titanium dioxide (TiO 2) nanohybrid has been investigated to be utilized as an eco-friendly alternative strategy to the current waste landfill and toxic byproduct-emitting incineration of PVC wastes. Thus, the present study suggests a novel idea related to preparing the photocatalytically degradable nanohybrid through TiO 2 nanoparticle-integrated hyperbranched poly(ε-caprolactone) (HPCL–TiO 2). The main aim of this study is to find a solution to the unresolved problem in the conventional PVC/TiO 2 composites related to the poor dispersion of the nanoparticles in PVC polymer. First, TiO 2 nanoparticles are prepared by a sol–gel process, and the size of the particle is about 5–10 nm in diameter as measured by using a transmission electron microscopy (TEM) and dynamic light scattering (DLS). The hyperbranched poly(ε-caprolactone) (HPCL) with numerous COOH groups and good miscibility with PVC as a binder for TiO 2 nanoparticles is prepared from moisture-sensitive catalyst-free polymerization of 2,2-bis[ω-hydroxy oligo(ε-caprolactone)methyl]propionic acids followed by modification reaction using pyridinium dichloromate (PDC), then characterized with 1H NMR and 13C NMR analyses. The integration of TiO 2 nanoparticles onto HPCL is carried out by a dip-coating method based on the spontaneous self-assembly between TiO 2 nanoparticles and HPCL, and the loading amount of the nanoparticles in the HPCL–TiO 2 is determined to be ca. 3.3 wt% by X-ray photoelectron spectroscopy (XPS). Then, the HPCL–TiO 2 is blended with PVC by solution blending in THF as solvent, and the resulting dispersibility of TiO 2 nanoparticle in PVC is characterized by field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectrometry (EDS), which exhibits the TiO 2 nanoparticles are well-dispersed in PVC matrix, while some agglomerates are observed in the PVC/TiO 2 sample prepared from TiO 2 nanoparticle itself. The photocatalytic degradation of the samples are examined and verified from the change of surface morphology, chemical structure, molecular weight, and molecular-level structure after UV irradiation through field-emission scanning electron microscopy (FESEM), UV–visible spectroscopy, gel permeation chromatography (GPC), and positron annihilation lifetime spectroscopy (PALS). The remarkable photocatalytic degradation is observed in the PVC/HPCL–TiO 2, and the structural change accompanied by the degradation of the irradiated sample can clearly explained.