A new strategy for functionalization of char derived from pyrolysis of textile waste and its application as hybrid fillers (CNTs/char and graphene/char) in cement industry

Char derived from pyrolysis of textile waste (CTW) represents about 18 wt% of pyrolysis products with smaller economic value. In order to maximize the economic performance of CTW, this research aims to develop a sustainable strategy for reprocessing CTW into fine spherical carbon black (CB) particles that can be used as single or hybrid fillers (Carbon nanotubes (CNTs)/CB and graphene (GO)/CB) in cement composite applications. The implementation of the suggested strategy was started by producing of CTW using a pyrolysis reactor, followed by refining of CTW using milling and chemical treatments to synthesize CB of 10–20 μm. The synthesized CB (0.05 wt%) was used as a single filler and hybrid fillers (CNTs/CB and graphene/CB: 50/50) to enhance the properties of cement paste. Also, two other samples CNTs/cement and GO/cement were prepared for comparison. In case of all the prepared cement matrixes, colloidal silica was used as a pre-dispersion medium to disperse the selected fillers uniformly in the aqueous solutions. Besides, silica fume (25 wt %) was added during the mixing process to facilitate dispersion and to increase the interfacial strength between fillers in cement paste. The morphology, chemical structure, and composition of the treated char were observed using Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and inductively coupled plasma mass spectrometry (ICP). Meanwhile, the compressive and flexural strengths of the prepared cement pastes were tested according to standard EN 196-1 for 28 and 56 days. Also, the basic chemical and physical properties (X-ray diffraction analysis (XRD), pore size distribution, etc.) and thermal behaviour (using Thermogravimetric) of cement pastes were studied. The results showed that the treated char can be a strong competitor for both CNTs and graphene, especially at longer curing time (56 day) with compressive and flexural strengths estimated at 82 and 12 MPa, respectively. Also, the hybrid paste (CNTs-CB) proved results almost similar to CNTs and GO, which means that the treated char can be a sustainable alternative and a cheap filler, when compared to CNTs and GO.