Graft Polymerization of Acrylic Monomers onto Lignin with CaCl2–H2O2 as Initiator: Preparation, Mechanism, Characterization, and Application in Poly(lactic acid)

Effective utilization of abundant industrial lignin has growingly attracted much attention besides potential environmental issues. Although chemical graft polymerization modification is one facile strategy for extending its applications, it remains an intractable challenge to select a highly efficient initiation system. We herein have attempt to understand the CaCl2–H2O2 system in initiating the graft polymerization of acrylic monomers onto acetic acid lignin (AAL) and biobutanol lignin (BBL). The initiation system is found to be highly efficient and selective, as proved by the successful graft of polyacrylates onto them, and a possible mechanism is also proposed. Thermal analysis shows that the graft modification results in a higher glass transition temperature and higher thermal stability of lignin. The graft modification make both AAL and BBL become more hydrophobic than before modification. Moreover, adding a small amount of lignin-graft-polyacrylate can considerably improve the UV blocking capability in addition to the reinforcing effect on polylactic acid. This work offers a novel, highly effective, and selective free radical initiation system for functionalizing lignin.