Spin coating of polymer blends from a common solvent often leads to films of intriguing morphologies, either due to the formation of a single homogenous phase or due to separation of the various polymer fractions into phases and leading to variation in film roughness and configuration. Herein, we elucidate on the phase separation behavior of lignin-xylan and lignin-polystyrene blend systems employing dimethylsulfoxide (DMSO) and tetrahydrofurane (THF) as solvents, respectively. Atomic Force Microscopy (AFM) imaging was applied to visualize the film morphologies and to reveal morphologies on the surface of the spin coated films. We attempt to correlate the film’s morphology with the polymer and polymer blend characteristics including the molecular weight, the polydispersity index and the chemical affinity and compatibility of the polymers in the blend. Finally, we aim in developing knowledge on the system that allows predicting the behavior of the bio-based polydisperse polymer blends upon spin coating from common solvents.