Suppression of dioxin emission in incineration of poly(vinyl chloride) (PVC) as hybridized with titanium dioxide (TiO2) nanoparticles

The present paper has demonstrated suppression of dioxin emission from poly(vinyl chloride) (PVC)/titanium dioxide (TiO2) nanohybrids. In our previous paper, we suggested a novel idea for the preparation of PVC/TiO2 nanohybrid through TiO2 nanoparticle-integrated hyperbranched poly(ɛ-caprolactone) (HPCL-TiO2), aiming at a breakthrough to solve the unresolved problem in the conventional PVC/TiO2 composites related to the poor dispersion of TiO2 nanoparticles in PVC polymer. The integration of TiO2 nanoparticles onto the HPCL could be successfully carried out by a dip-coating method based on the spontaneous self-assembly between TiO2 and HPCL. In this study, three kinds of hyperbranched poly(ɛ-caprolactone)s (HnPCLs) were prepared by varying the number, n, of monomeric units on the branched backbone chains. Thereby, it was possible to control the numbers of functional ends and the contents of TiO2 in the HnPCL-TiO2. The loadings of TiO2 in the HnPCL-TiO2s were found to be 4.37, 3.26, and 2.93wt% for n of 5, 10, and 20, respectively. The preparation of PVC/HnPCL-TiO2 (60/40) blends was performed through solution blending of HnPCL-TiO2 with PVC in tetrahydrofurane (THF) as solvent, and the dispersities of TiO2 in the resulting nanohybrids were investigated by field-emission scanning electron microscope (FE-SEM) equipped with energy dispersive spectroscopy (EDS). The FE-SEM/EDS results showed that TiO2 nanoparticles were dispersed well in PVC matrix, while some agglomerates of TiO2 was observed in the PVC+TiO2 sample prepared from the solution blending of PVC with the same amount of TiO2. The incineration experiments were performed by using a temperature-controllable electric furnace at 350°C under the flow of ambient air, and the exhaust gases resulting from the incineration process were collected. Prior to the identification of the components emitted in the incineration process, the GC experiments for calibration were performed on several commercial standards of dioxin and organic compounds known to be dioxin precursors. The GC results on the exhaust gases from the incineration of samples showed that the emissions of dioxin and precursors were largely suppressed with the increasing content of TiO2 in PVC/HnPCL-TiO2, i.e., the order of PVC/H5PCL-TiO2>PVC/H10PCL-TiO2>PVC/H20PCL-TiO2, as compared with those in the neat PVC/HnPCL without TiO2. Especially, the PVC/H5PCL-TiO2 with a maximum TiO2 loading of 1.6wt% showed removal efficiencies of ca. 60% up to 70% ove