Structure, properties and interactions in ionomer/lignin blends

Blends were prepared from lignin and ionomers, i.e. ethylene-methacrylic acid copolymers partially neutralized with inorganic salts for the first time in order to check the possible effect of ionic bonds on the structure and properties of the blends. A low density polyethylene and an ethylene-acrylic acid copolymer without any neutralization were used as references. The lignin content of the blends varied between 0 and 60 vol%. The components were homogenized in an internal mixer and the blends were characterized by various methods including dynamic mechanical analysis, differential scanning calorimetry and tensile testing. The size of dispersed lignin particles was determined from scanning electron micrographs, and component interactions were estimated quantitatively. The properties of ionomer/lignin blends indicated the development of strong interactions between the components. The simultaneous action of hydrogen bonds of non-neutralized methacrylic acid moieties and ionic bonds resulted in the formation of small, dispersed lignin particles of the size of several tenth of a micron. Surprisingly, hydrogen bridges improve interactions and compatibility more than ionic bonds. Contrary to most blends prepared from other polymers, ionomer/lignin blends can be produced with a reasonable combination of properties at moderate lignin contents. (c) 2018 Elsevier Ltd. All rights reserved.