Enhancement of bonding strength of polypyrrole/cellulose fiber (PPy/CF) hybrid through lignosulfonate doping

Lignosulfonate (LS), a byproduct from sulfite pulping process, was used as a dopant during the preparation of polypyrrole/cellulose fiber (PPy/CF) hybrid to enhance the bonding strength. PPy/CF hybrids were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy and differential scanning calorimetry analyses to reveal the related mechanism. The results indicated that the bonding strength of PPy/CF hybrid doped by LS was greatly improved due to formation of more hydrogen bonds and better melting of PPy compared with PPy/CF hybrids doped by ferric chloride and p-toluenesulfonic acid. The LS with larger molecular weight tended to give lower electrical conductivity but higher bonding strength within a reasonable range of LS dosage owing to the difference in the steric effect of macromolecular LS and the amount of acidic groups in LS. The electrical conductivity of LS-doped PPy/CF hybrid decreased, and the bonding strength first increased and then decreased with the increase of LS dosage. This phenomenon might be caused by multiple factors, such as the incorporation of non-conductive LS, the template effect of macromolecular LS and the formation of LS-Fe complex.