Thermogravimetric/Mass spectrometric (TG/MS) characterization of toner particles from photocopied wastepaper and the impact of these features on flotation deinking

Flotation deinking of photocopies from office waste is known to be much more difficult than the flotation deinking of newsprint. In this regard, research has been undertaken to better understand the phenomena which account for the poor efficiency in the flotation deinking of such office waste. During the photocopying process, toner particles, mainly consisting of styrene-acrylate copolymer (>85%), are photoelectrically attached to the cellulose fiber and heated to bond the toner particles to the paper. Even with the short time of exposure to heat, light, and oxygen, it is expected that surface styrene groups undergo oxidation and polymerization with the subsequent formation of peroxide bonds. Thermogravimetry/mass spectrometry (TG/MS) results show that the decomposition temperatures of monomer, dimer and trimer styrenes and styrene-acrylate present in the toner particles have been increased by about 10 to 30 °C after photocopying, and that their decomposition activation energies have been increased by about 7 to 20 kcal/mol. Correspondingly, it was found that volatile release was diminished, that thermal stability of toner residue increased slightly, and that the phase change (softening) around 72 °C, which is below the printing temperature, disappeared. On the other hand, the acrylate component of the toner which contains the oxygen-functional groups (-OH and -O-), was found to be relatively more stable during the photocopying process and this component of the toner was not affected. It appears that the strong bond of the toner particles with the cellulose fibers, the polymerization (fusion), and the oxidation of the styrene, which creates a greater polarity at the toner particle surface, accounts for the difficulty in making more efficient flotation deinking separations in the recycle of office waste containing photocopies.