Optimal ring-opening polymerization for producing surface-modified cellulose nanofibers-graft-poly(lactic acid)s

Abstract

New cellulose-based Cell-g-HEMA-co-AAc copolymer was prepared through potassium persulfate initiated free radical polymerization of vinyl monomers hydroxyethyl methacrylate (HEMA) and acrylic acid (AAc) onto cellulose for the adsorptive uptake of a toxic Ni(II), Pb(II) and Cu(II) ions from aqueous solution. Maximum Pg (316.0) and GE (147.7%) for the grafting of AAc was obtained at 1.5 M ratios w.r.t. the concentration of the HEMA. Evidence of incorporation of new functional groups on cellulose after grafting was provided by FTIR, TGA/DTA, XRD and FESEM techniques. The maximum percent uptake (Pu) for Ni(II) and Pb(II) metal ions was observed 74.7% and 78.7% at pH 5.0. For Cu(II) ions 60.4% uptake was recorded at optimized pH 6.0. Cell-g-HEMA-co-AAc copolymer showed the preferential sorption of metal ions in order of Pb(II) > Ni(II) > Cu(II) at optimized conditions of 6 h of contact time and 30 °C temperature. From kinetic studies, the sorption of Ni(II) and Pb(II) metal ions was found to occur through chemisorption following pseudo-second-order kinetics model, whereas Cu(II) ions preferred physisorption and pseudo-first-order kinetics. A high determinant coefficient (R2) for the Langmuir model suggested monolayered sorption of metal ions. Negative values of ΔG° confirmed that the sorption of Ni(II) and Pb (II) on Cell-g-HEMA-co-AAc was thermodynamically favorable and highly spontaneous as compared to sorption of Cu(II) ions.