Hydrogen bonding interactions in poly(ethylene-co-vinyl alcohol)/lignin blends.

Blends were prepared from lignin and ethylene-vinyl alcohol (EVOH) copolymers to study the effect of hydrogen bonding interactions on compatibility and structure. The vinyl alcohol (VOH) content of the copolymers changed between 52 and 76 mol%, while the lignin content of the blends varied between 0 and 60 vol%. Low density polyethylene with 0 mol% VOH content was used as reference. The components were homogenized in an internal mixer and they were characterized by various methods including Fourier transform infrared spectroscopy (FTIR), dynamic mechanical analysis, differential scanning calorimetry and scanning electron microscopy. The results of the experiments proved that strong hydrogen bonds form between the two components shown by FTIR spectroscopy, a shift in the relaxation temperatures of the matrix polymer and by the decrease of crystallite size and crystallinity with increasing lignin content. In spite of the strong interactions, heterogeneous structure forms in the studied blends since self-interactions within the neat components are also very strong. The size of dispersed lignin particles is determined by competitive interactions in the blends; stronger EVOH/lignin interactions result in smaller particle size. Although hydrogen bonds are strong, miscible polymer/lignin blends can be prepared only by applying other approaches like plasticization or chemical modification.