Competitive Interactions in Aromatic Polymer/lignosulfonate Blends

Polymer/lignosulfonate blends were prepared from three polymers containing an aromatic moiety in their chain: polystyrene (PS), polycarbonate (PC), and a glycol modified poly(ethylene terephthalate) (PETG), in order to study the effect of aromatic, pi electron interactions on miscibility and on the structure and properties of the blends. Polypropylene (PP)/lignin blends were used as a reference. The components were homogenized in an internal mixer and compression molded into plates of I mm thickness. Structure was characterized by scanning electron microscopy (SEM) and image analysis, while mechanical properties were characterized by tensile testing and acoustic emission measurements. Component interactions were estimated from solubility parameters, the composition dependence of glass transition temperature, and mechanical properties. The results indicated that pi electron interactions result in better compatibility than the dispersion forces acting in PP blends. The average size of the dispersed lignin particles was smaller and properties were better in aromatic polymers than in PP. After PP, PS containing only aromatic rings and no other functional groups formed the weakest interaction with lignin, while interactions in PC and especially PETG capable of also forming hydrogen bonds were much stronger, showing that the combined effect of competitive interactions determines the structure and properties of the blends.