Material Characterization of Lignin‐Filled Polypropylene Composites

ABSTRACT

Lignin, an environmentally friendly byproduct from pulping and biorefinery processes, was incorporated into polypropylene (PP) as ground and spray‐dried powders. The effects of lignin morphology, particle size, and loading on the mechanical, rheological, viscoelastic, and thermal properties of PP composites were evaluated. Spray‐dried lignin powders exhibited a smaller average particle size and a more uniform circularity distribution than ground lignin powders. After adding 5 wt% lignin to PP, the mechanical properties of neat PP decreased, with further reductions observed at 10 wt%. The incorporation of lignin powders reduced the complex viscosity of PP, with composites containing spray‐dried lignin exhibiting lower viscosity than those containing ground lignin powders. The storage and loss modulus of PP decreased at a lignin loading of 5 wt% but increased at 10 wt%, with higher values observed in composites containing ground lignin than in those containing spray‐dried lignin. The crystallization onset temperature of PP showed no significant change with lignin addition, whereas the degree of crystallinity decreased. The coefficient of thermal expansion (CTE) decreased at a lignin loading of 5 wt% but increased at 10 wt%, with spray‐dried lignin exhibiting lower CTE values than ground lignin at the same loading.