Effect of Lignin without Surface Treatment inIn SituMethyl Methacrylate Miniemulsion Polymerization

Lignin has been analyzed as reinforcement in polymers due to its properties as a nontoxic, biorenewable, and inexpensive natural raw material. Nevertheless, the use of lignin in polymers has proved to be very restricted since technical lignin is highly hydrophilic and polymers are usually hydrophobic. Usually, the lignin surface is modified to enable its dispersion; however, this procedure is costly and time-consuming. In situ polymerization generally achieves more efficient dispersion; however, the radical scavenger capacity of lignin poses a major challenge for this technique. In this study, poly(methyl methacrylate) (PMMA)/lignin composites were prepared by in situ miniemulsion polymerization without changing the surface of lignin. Two kinds of technical lignins were used: Kraft lignin and lignosulfonate. Lignin was fed in the reactor in two different ways: before and after the beginning of the polymerization. Synthesis with lignosulfonate presented higher conversions, probably due to its lower radical scavenger capacity. Synthesis carried out feeding lignosulfonate after the beginning of the polymerization presented higher conversions, demonstrating excellent potential to produce PMMA/lignosulfonate composites by in situ polymerization with nonmodified lignosulfonate. Lignosulfonate acted as an antioxidant, improving the polymer thermo-oxidative properties. Cryogenic electron microscopy (Cryo-EM) images showed equidistant, nonagglomerated, and spherical nanoparticles in the latices, revealing good stability.